JP4650726B2 - Display device - Google Patents

Description

  The present invention relates to a display device, and more particularly to a display device that expresses gradation of an image by laminating a plurality of light emitting layers such as an electroluminescence display.

  A display using organic electroluminescence or an organic light emitting diode has attracted attention as a display having an ultra-thin shape, high contrast, high-speed response, and a high viewing angle (hereinafter, electroluminescence is also referred to as EL). An organic EL display uses a phenomenon called electroluminescence in which an organic compound changes electricity into light. Further, by applying the active matrix driving method, the organic EL display can be used with better energy efficiency, so that energy consumption can be reduced. Due to these merits and reasons, organic EL displays are regarded as promising next-generation displays.

FIG. 26 is a schematic diagram of a conventional organic EL display. The organic EL display generally uses the layer structure shown in FIGS. 26 (a) and 26 (b). FIG. 26A shows the basic layer structure of the organic EL display. Here, the number of layers formed between the anode and the cathode is defined as the number of layers. Therefore, the organic EL display of FIG. 26A is a single layer.
An anode 41 is formed on the glass substrate 40. As the anode 41, a transparent ITO (Indium Tin Oxide) electrode is used to transmit light. The ITO electrode is an oxide of indium and tin and is widely used in liquid crystal display devices.

  On the anode 41, a light emitting layer 42 which is a phosphor made of an organic compound is formed. Organic materials include low molecular weight materials and high molecular weight materials, which are appropriately selected according to the characteristics, application, and manufacturing method of the material. A cathode 43 is formed on the light emitting layer 42. In the conventional example shown in FIG. 26A, the light output from the light emitting layer 42 is extracted from the direction of the glass substrate 40, so the cathode 43 is an electrode made of a metal such as aluminum.

  By applying a DC voltage from the power source 44 between the anode 41 and the cathode 43, holes are injected from the anode 41 into the light emitting layer 42, while electrons are injected from the cathode 43 into the light emitting layer 42. The injected holes and electrons recombine in the light emitting layer 42 to be in an unstable excited state, which is a high energy state, and then immediately return to the original stable, low energy state, ground state. The layer 42 emits energy and emits light.

FIG. 26B shows a five-layer organic EL display. As shown in FIG. 26B, this five-layer organic EL display has an anode 46, a hole injection layer 47, a hole transport layer 48, a light emitting layer 49, an electron transport layer 50, an electron on a glass substrate 45. The injection layer 51 and the cathode 52 are sequentially stacked, and a five-layer structure is formed in which five layers are formed between the anode 46 and the cathode 52.
In this conventional example, a hole injection layer 47 and a hole transport layer 48 for transporting the holes to the light emitting layer 49 are provided so that holes can be easily taken out from the anode 46. On the other hand, an electron injection layer 51 and an electron transport layer 50 for efficiently transporting the electrons to the light emitting layer 49 are provided so that electrons can be easily taken out from the cathode 52.

By applying a DC voltage from the power source 53 between the anode 46 and the cathode 52, holes are injected from the anode 46 into the light emitting layer 49 through the hole injection layer 47 and the hole transport layer 48, respectively. On the other hand, electrons pass through the electron injection layer 51 and the electron transport layer 50 from the cathode 52 and are injected into the light emitting layer 49. The injected holes and electrons recombine in the light emitting layer 49 to be in an unstable excited state, which is a high energy state, and then immediately return to the ground state, which is the original stable low energy state. The layer 49 emits energy and emits light.
As described above, the organic EL display emits light more efficiently by using the structure in which the roles are shared.

The layer structure is not limited to those shown in FIGS. 26 (a) and 26 (b), but also has a two-layer to four-layer structure. A hole transport layer, an electron injection layer, and an electron transport layer can be freely combined. Furthermore, there are materials having both functions of a hole injection layer and a hole transport layer, and various organic materials can be selected.
As shown in the figure, the organic EL display has a structure in which light emitting layers 42 and 49, which are phosphors of organic compounds, are sandwiched between anodes 41 and 46 and cathodes 43 and 52. Emits light.

  FIG. 27 is a diagram specifically showing a conventional organic EL display. A silicon oxide film 55 and a thin film transistor (TFT) 59 are formed on the glass substrate 54. The silicon oxide film 55 has a function of preventing metal ions from moving from the glass substrate 54 to the anode 56, and the TFT 59 has a function of turning on / off the light emission of the pixel. An anode 56 is formed on the silicon oxide film 55, and an organic film light emitting layer 57 is formed thereon. The organic film light emitting layer 57 includes a combination of a light emitting layer, a hole injection layer, a hole transport layer, an electron injection layer, and an electron transport layer.

A cathode 58 is formed on the organic film light emitting layer 57. The cathode 58 uses a metal such as aluminum. The conventional example shown here is a bottom light extraction structure in which light output from the organic film light emitting layer 57 is extracted from the glass substrate 54 side including the TFT 59.
Note that transparent ITO is used for the cathode 58 when light is extracted from the cathode 58 side in order to increase luminous efficiency. This is called a top light extraction structure.

Many pixel driving methods have been developed for actually displaying images on a display. The most common method is a method in which an analog memory and a voltage-current conversion circuit are mounted in a pixel to realize gradation driving, and the driving current of the organic EL element is controlled in accordance with the voltage of the analog memory. . An example of a display panel by this gradation driving method is shown in FIG.
FIG. 28 shows a configuration diagram of an example of a display panel driver for driving a pixel 67 composed of an organic EL and an active element to be described later. A plurality of pixels 67 are arranged in a two-dimensional matrix on the display panel.

  The display panel is provided with a horizontal driver 68 for driving the pixels in the horizontal direction. The power supply circuit 69 supplies a power supply voltage to all the pixels 67. A vertical driver 70 is provided to drive the pixels 67 arranged in the vertical direction. For example, when the uppermost display line is to be scanned, the gate driver 65 provided in the vertical driver 70 supplies a voltage to be supplied to the uppermost display line among the horizontal display lines connected to the vertical driver 70. Each pixel 67 is turned on by (shown in FIG. 29). At the same time, the vertical driver 70 outputs a voltage at which the gate driver 65 of each pixel 67 on the display line other than the uppermost display line is turned off to the display lines other than the uppermost display line. To do.

  At this time, a voltage corresponding to the video signal of one scanning line (display line) is output from the horizontal driver 68, and a data voltage is applied to the capacitor 62 of each pixel 67 of the uppermost display line. By doing so, a power supply voltage and a data voltage are applied to both ends of the capacitor 62, and a sufficient charge is stored to hold this potential difference. That is, display data is written and stored in the capacitor 62. Thereafter, when the vertical driver 70 is turned off, the organic EL emits light based on the data stored in the capacitor 62 of each pixel 67 of the uppermost display line, and an image of one scanning line is displayed. Similarly, the vertical driver 70 is driven in units of display lines in order from the top to the bottom, and the video data is output for each line from the horizontal driver 68 in synchronization with the vertical driver 70. All the pixels 67 can be scanned.

  FIG. 29 shows a circuit diagram of each pixel 67. The organic EL 60 corresponds to the organic film light emitting layer 57 of FIG. Data for determining the light emission luminance of the organic EL 60 is input from the data input terminal 64. Here, when a voltage is applied to the gate of the TFT 61 so that the TFT 61 is turned on to the gate driver 65, the data input to the terminal 64 is applied to the capacitor 62 and the gate of the TFT 63 through the source and drain of the TFT 61, respectively. Based on this potential, the current supplied to the organic EL 60 through the source and drain of the TFT 63 is controlled.

  Thereafter, when the TFT 61 is turned off, the potential difference between the power supply 66 and the data input terminal 64 is stored in the capacitor 62. Since the organic EL 60 is a current light emitting device, the organic EL 60 emits light with brightness proportional to the applied current. Therefore, the brightness emitted by the organic EL 60 depends on the potential of data input via the terminal 64, and the gradation of the video output to the display device can be expressed from this data.

  FIG. 27 shows a pixel structure of a conventional display device, and FIG. 29 shows a circuit for driving this pixel by a gradation driving method. Various other driving methods are conceivable. For example, there is a clamped inverter method in which a light emission period in one frame is analog-modulated by a pulse width modulation (PWM) signal. This method can compensate for variations in threshold values, which are element characteristics of TFTs that are active elements, and has a simple circuit configuration because the number of TFTs is small. In addition, since there is a non-light emitting period, a crisp video display is possible (for example, see Non-Patent Document 1 and Patent Document 1).

  In the digital display driving method, the organic EL element is controlled to be in a lighting or non-lighting state by a switch transistor of the pixel. As one of these methods, there is a method in which an image is divided into a plurality of subframes in the time axis direction, and gradation is represented by the sum of luminance weights of the subframes (see, for example, Patent Document 2).

In addition, there is an area division method in which a pixel is divided into a plurality of sub-pixels within a display surface of a display device, and gradation is expressed by the number of light emission of the pixel (see, for example, Patent Document 3). Further, as a method using a similar sub-pixel, the first sub-pixel is controlled by analog drive so as to display multi-tones including halftones, and the second sub-pixel is a binary signal for bright display or dark display. A method of controlling driving so as to perform display is known (for example, see Patent Document 4).
There has also been proposed a display device in which light emitting units having a plurality of light emission colors are stacked in the vertical direction (see, for example, Patent Document 5 or 6).

An Innovative Pixel-Driving Scheme for 64-Level Gray Scale Full-Color Active Matrix OLED Displays, SID2002, 32.2 JP 2003-122301 A Japanese Patent Application Laid-Open No. 10-2114060 Japanese Patent Laid-Open No. 11-073159 JP 2003-280593 A JP 2000-133449 A JP 2002-31571 A

  The conventional display device that drives each pixel 67 by the gradation driving method using the circuit diagram shown in FIG. 29 includes an analog memory and a voltage-current conversion circuit in the pixel 67 in order to realize gradation driving. The drive current of the organic EL element is controlled corresponding to the voltage of the analog memory. However, since the element characteristics of the TFT 59, which is an active element, vary greatly from pixel to pixel, the amount of current flowing through the organic light emitting layer varies. For this reason, the variation in light emission luminance from pixel to pixel becomes large, resulting in non-uniform display luminance of the display device, making it difficult to improve image quality.

  A conventional display device based on the clamped inverter method described in Non-Patent Document 1 improved on this is a device that operates by adopting a drive method effective for eliminating variations in TFTs. Since the TFT is controlled only by on / off, and the light emission period is controlled by the analog pulse width (PWM), the operation is performed by the analog light emission period modulation system that expresses the gradation, so that the influence of TFT variation can be reduced. However, the conventional display device according to this driving method is disadvantageous in that it has a large burden because the amount of current corresponding to the light emission luminance flows through one light emitting layer, which increases the life. In addition, since there are light emission and non-light emission periods for each gradation, it can be predicted that problems such as flicker will occur.

  Further, in the conventional display device based on the digital driving method using the subframe method described in Patent Document 2, the organic EL element of the pixel is binary driven on / off in order to eliminate variations in display luminance. In addition, in order to obtain gradation drive, one frame time is divided into a plurality of subframe periods, all pixels are scanned in each subframe period, and binary display data having a bit structure of each gradation is written to the pixels for display. It is lit for a predetermined time at a predetermined luminance for each gradation during the period. However, the conventional display device using the digital driving method using the subframe method has an effect of eliminating variations in TFTs, but at the same time, there is a problem that interference such as a moving image pseudo contour occurs.

Furthermore, in the conventional display device based on the area division method described in Patent Document 3, a plurality of subpixels are required to form one pixel, which is not suitable for the trend of higher panel resolution expected in the future. .
In addition, in the display device having a structure in which a plurality of light emitting units described in Patent Document 4 and Patent Document 5 are stacked, when each color is analog-driven, the problem due to variation in the amount of current flowing in the organic light emitting layer is as described above. It occurs in the same way.

  The present invention has been made in view of the above points, greatly reducing the variation in luminance for each pixel in the display surface of the display device, enabling high-precision gradation display, reducing power loss, and An object of the present invention is to provide a display device capable of long-life color display.

In order to solve the above-described problems, the present invention provides the following display devices (a) to (c).
(A) One pixel is composed of a plurality of sub-pixels (400d to 400f), and each sub-pixel includes an anode (421, 424, 427) and a light-emitting portion (438-440) having a multi-photon structure having an organic film light-emitting layer. ) And cathodes (423, 426, 429) are stacked in order, and the organic film light emitting layer is formed using a different material for each subpixel, and is a layer of the organic film light emitting layer. The number is different for each sub-pixel, and light emission or non-light emission of the unit element is controlled for each unit element.
(B) The display device according to (a), further comprising a digital drive unit that drives the unit elements to emit light or not.
(C) The display device according to (a) or (b), wherein gradation expression is performed by setting luminance weighting for a plurality of unit elements in a sub-pixel.

By digitally driving the light emitting element and expressing the gradation of one dot with the luminance weighted sum, the light emitting element can be driven without being affected by the variation in the threshold value of the first driving unit. Therefore, luminance unevenness in the display device can be eliminated and power loss can be reduced.
In addition, since the amount of current corresponding to the light emission luminance does not flow through one light emitting layer, the burden on each light emitting layer can be distributed, and a display device having a longer life than that of the related art can be realized.
Furthermore, even if the light emission brightness of each light emitting layer is different due to the problem of material characteristics, the burden on the light emitting layer can be reduced by setting the number of layers of each light emitting layer so that the light emission brightness of each light emitting layer is equal. And the lifetime of the device can be extended.

≪First embodiment≫
FIG. 1 is a schematic diagram of a pixel in the display device according to the first embodiment of the present invention. The display device is, for example, an organic EL display. In the first embodiment, a specific configuration of pixels when performing color display on a display device will be described in detail. The glass substrate 1 is a display surface of the display device. Although the glass substrate 1 is used here, a plastic substrate may be used as long as an organic film layer can be formed.
The light emitting layer groups 36 </ b> B, 36 </ b> G, and 36 </ b> R are respectively stacked on the glass substrate 1 to constitute the pixel 36. The light emitting layer group 36B is a light emitting layer group having a blue light emitting color, the light emitting layer group 36G is a light emitting layer group having a green light emitting color, and the light emitting layer group 36R is a light emitting layer group having a red light emitting color. .
Here, the light emitting layer group 36B will be described. Since the light emitting layer groups 36B, 36G, and 36R have the same layer configuration, the illustration and description of the specific configuration of the light emitting layer groups 36R and 36G are omitted.

An anode 2 is formed on the glass substrate 1. As the anode 2, for example, ITO which is a transparent electrode is used.
An organic film light emitting layer 3 is formed on the anode 2. The organic film light emitting layer 3 is composed of a combination of a hole injection layer, a hole transport layer, an electron injection layer, an electron transport layer, and a light emitting layer which is a phosphor made of an organic compound. This combination is appropriately selected depending on the characteristics of the organic EL.
A cathode 4 is formed on the organic light emitting layer 3. When ITO, which is a transparent electrode, is used as the cathode 4, it does not operate as a cathode as it is, so it is necessary to insert lithium for the cathode thinly between the ITO and the organic film light emitting layer 3.
A power source 13 is connected to apply a DC voltage between the anode 2 and the cathode 4. The light emission principle of the organic film light emitting layer 3 sandwiched between the anode 2 and the cathode 4 is the same as the conventional example.

A silicon oxide film 11 and an anode 5 are sequentially stacked on the cathode 4. The silicon oxide film 11 has an effect of insulating the anode 5 and the cathode 4.
On the anode 5, an organic film light emitting layer 6, a cathode 7, a silicon oxide film 12, an anode 8, an organic film light emitting layer 9, and a cathode 10 are sequentially laminated in the same manner as described above.

Power supplies 14 and 15 are connected to apply a DC voltage between the anode 5 and the cathode 7 and between the anode 8 and the cathode 10, respectively. As a result, a current corresponding to the DC voltage applied by the power supplies 14 and 15 is supplied to the organic film light emitting layers 6 and 9.
Each of the organic film light emitting layers 3, 6, 9 emits light with a luminance proportional to the current value flowing therethrough, and light is extracted from the glass substrate 1 side. This structure can be realized not only by organic EL but also by inorganic EL, and can also be realized by not only active drive but also passive drive display devices.

  The organic film light emitting layers 3, 6, and 9 are switched between lighting and extinguishing (light emission or non-light emission) by digital driving, that is, binary power ON / OFF. The organic film light emitting layers 3, 6, and 9 are formed by selecting materials that emit light with a predetermined luminance.

FIG. 2 shows a specific structure of the pixel in this embodiment. 2, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted. In FIG. 2, the light emitting layer group 36 </ b> B having a blue emission color that is one of the colors (for example, red, green, blue, etc.) constituting one pixel is shown.
Here, thin film transistors (TFT) 16a, 16b, 16c, which are active elements, are formed on the glass substrate 1 and connected to the anodes 2, 5, 8 respectively. The TFTs 16a to 16c can be made of any active element such as p-Si (low temperature polysilicon) or a-Si (amorphous silicon) as long as the organic film light emitting layers 3, 6, and 9 can be driven and controlled. It may be.

  The TFTs 16a to 16c have a circuit function to turn on / off the power applied to the organic film light emitting layers 3, 6, 9, and as described above by turning the power on / off, the organic film light emitting layers 3, 6, 9 is driven to emit light or not emit light. A silicon oxide film 17 formed between the glass substrate 1 and the anode 2 is a film that prevents metal ions from moving from the glass substrate 1 to the anode 2. The cathode 4, the cathode 7, and the cathode 10 are common electrodes.

  In the present embodiment, the glass substrate 1 is provided with the TFTs 16a to 16c and has a bottom light extraction structure for extracting light from the glass substrate 1 side. However, a top surface light extraction structure for extracting light from the cathode 10 side may be employed.

Here, a plurality of TFTs may be connected to one organic film light emitting layer as described later with reference to FIG. Here, for convenience, the TFTs 16a to 16c are shown as one. In the present embodiment, the TFTs 16a to 16c are referred to as element driving units (first driving units).
The anode 2, the organic film light emitting layer 3, the cathode 4 and the element driving unit 16c form a unit element. Similarly, the anode 5, the organic film light emitting layer 6, the cathode 7, and the element driving unit 16b are unit elements, and the anode 8, the organic film light emitting layer 9, the cathode 10, and the element driving unit 16a are unit elements. The organic EL display shown in FIG. 2 is a light-emitting element having a light-emitting layer group having a three-layer structure in which three light-emitting layers are stacked in a direction perpendicular to the display surface of the display device. This light emitting element emits light of one color.

FIG. 3A shows luminance weighting when the light emitting layer group 36 </ b> B shown in FIGS. 1 and 2 has a three-layer structure having the organic film light emitting layers 3, 6, and 9. Luminance weighting is the relative quantification of the light emission luminance of each organic film light emitting layer on the basis of a certain value. Here, when the organic film light emitting layer 3 is the first layer, the organic film light emitting layer 6 is the second layer, the organic film light emitting layer 9 is the third layer, and the luminance of the first layer is “1”, the second layer is The material and configuration of the organic light emitting layers 3, 6, and 9 are selected so that the luminance is "2" and the third layer is "4".
Here, the luminance of each organic film light emitting layer 3, 6, 9 represents the light emission luminance when the power supply voltage is turned on, and each organic film light emitting layer 3, 6, 9 is digitally driven by turning on / off the power supply voltage. The

In FIG. 3B, the unit layer is further divided into two layers by providing one unit element for each of the second layer and the third layer of the light emitting layer group described above, and the organic film light emitting layer has a five-layer structure. In this case, an example in which the same number of gradations as in FIG. The five organic film light emitting layers are designated as a first layer, a second layer, a third layer, a fourth layer, and a fifth layer in order from the side closer to the light extraction side, and the luminance of the first layer is “1”. In this case, the second layer has luminance “1”, the third layer has luminance “1”, the fourth layer has luminance “2”, and the fifth layer has luminance “2”.
FIG. 3C shows that when the organic light emitting layer has a five-layer structure as described above, the luminance of the first layer is “1”, the second layer is “2”, and the third layer is “4”. ”, The fourth layer is“ 8 ”, and the fifth layer is“ 16 ”.
In the present embodiment, the light emitting layer groups 36R, 36G, and 36B are all described as having the same configuration, but the light emitting layer groups 36R, 36G, and 36B may be configured with different numbers of stacked organic film light emitting layers. When the luminance of the light emitting layer of a predetermined color is lower than other colors due to the material properties of the organic film light emitting layer, the number of layers of the organic film light emitting layer is adjusted for each color as shown in FIGS. 3 (a) and 3 (b) In other words, the same number of gradations may be realized.

  Further, the luminance weighting may be different for each light emitting layer group. As shown in FIGS. 3A to 3C, the luminance weighting of the organic film light emitting layer is preferably set to 2 n power weighting because the organic film light emitting layer can be formed in a small number, but is not limited thereto. . Further, the luminance weighting for each layer does not need to be in ascending order from the layer near the side from which light is extracted as shown in FIGS. 3A to 3C, and is arbitrarily rearranged in descending order. May be. This luminance weighting method can be realized not only for organic EL but also for inorganic EL, and can be realized not only for active driving but also for passive driving display devices.

  FIG. 4 shows an example of pixel gradation expression in the display device according to the first embodiment of the present invention. This example is a gradation representation of luminance weighting in the case where the organic film light emitting layer shown in FIG. 3A has a three-layer structure. Since the organic film light emitting layer has three layers, it is the cube of 2; Eight gradations can be expressed. In FIG. 4, the horizontal axis indicates the number of organic film light emitting layers, and the vertical axis indicates the gradation displayed on the display device. A black circle means that the selected layer is lit, and a layer without the black circle does not emit light.

  For example, at the gradation “0”, the first layer, the second layer, and the third layer do not emit light. For this reason, it becomes black. At the gradation “1”, only the first layer is turned on, and the luminance weight is “1”, so the gradation “1” is represented. At the gradation “2”, only the second layer is lit, and the luminance weight is “2”, so the gradation “2” is represented. At the gradation “3”, both the first layer and the second layer are lit, the luminance weights are “1” and “2”, respectively, and the total “3” is the gradation. At the gradation “4”, only the third layer is lit, and the luminance weight is “4”, which represents the gradation “4”.

  At the gradation “5”, both the first layer and the third layer emit light, and the respective luminance weights are “1” and “4”, so this sum “5” is the gradation. At the gradation “6”, both the second layer and the third layer emit light, and the respective luminance weights are “2” and “4”, so this total “6” is the gradation. At the gradation “7”, all of the first layer, the second layer, and the third layer are turned on, and the total “7” of the luminance weights “1”, “2”, and “4” is the gradation.

FIG. 5 shows a driver configuration diagram of the display panel of the display device according to the first embodiment of the present invention. In FIG. 5, one pixel 36 is composed of light emitting layer groups 36R, 36G, and 36B each having three organic film light emitting layers, and each light emitting layer group corresponds to a pixel circuit described later with reference to FIG.
The display panel includes a horizontal driver 37 for sending data to a plurality of pixels 36 arranged in a two-dimensional matrix, a power supply circuit 38 for driving the pixels, and a vertical driver 39 for selecting a vertical line. It has been. Here, the horizontal driver 37 and the vertical driver 39 are used as the second drive unit.
The plurality of pixels 36 are arranged in a two-dimensional matrix composed of rows Y arranged in the vertical direction and columns X arranged in the horizontal direction. In FIG. 5, as an example, a display panel with six columns of X1 to X6 and four rows of Y1 to Y4 is shown. The actual display panel has a larger number of matrices than that shown in FIG. 5, but this is shown here for convenience.
In the first embodiment, the horizontal driver 37 includes data drivers 371 to 376, the power supply circuit 38 includes power supply units 381 to 386, and the vertical driver 39 includes gate drivers 391 to 394.

  For example, when it is desired to scan the display line of the Y1 row which is the uppermost stage of the display panel shown in FIG. 5, the gate driver 391 of the vertical driver 39 turns on each pixel 36 of the Y1 row. The gate drivers 392 to 394 are turned off for the other display lines Y2 to Y4. At this time, one line of video data is output from the horizontal driver 37 and supplied to each pixel 36.

  Next, when the gate driver 391 turns off each pixel 36 in the Y1 row, an image of one line in the Y1 row is displayed. Similarly, the vertical driver 39 is sequentially driven from the Y2 row gate driver 392 to the Y4 row gate driver 394, and video data is output line by line from the horizontal driver 37. The pixel 36 can be scanned.

  FIG. 6 is a circuit diagram for driving the light emitting layer groups 36R, 36G, and 36B constituting the pixel 36 of the first embodiment. Although the light emitting layer group 36B is shown here, since the same circuit is used for the light emitting layer groups 36R and 36G, the illustration and description of the specific configuration are omitted. In FIG. 6, the organic EL light emitting layers 18, 19, and 20 correspond to the organic film light emitting layers 3, 6, and 9 shown in FIGS.

  One end (the anode in the figure) of the organic EL light emitting layers 18 to 20 is connected to the power sources 30 to 32 constituting the power source unit 381 through the sources and drains of the driving TFTs 24 to 26. The gates of the TFTs 24 to 26 are connected to the sources of the TFTs 27 to 29 as gate transistors, and are connected to the power sources 30 to 32 via the capacitors 21 to 23.

The power supplies 30, 31, and 32 of the power supply unit 381 correspond to the power supplies 13, 14, and 15 shown in FIG. The power sources 30 to 32 may be individual power sources or a common power source, and are set so that the organic EL light emitting layers 18 to 20 emit light with a predetermined luminance with predetermined luminance weighting. Further, the drains of the TFTs 27 to 29 are connected to data holding units 350 to 352 in the data driver 371, and the gates are commonly connected to the gate driver 391.
Here, the data driver 371, the power supply unit 381, and the gate driver 391 are shown. However, as shown in FIG. 6, the data drivers 372 to 376, the power supply units 382 to 386, and the gate drivers 392 to 394 have the same configuration. The data drivers 371 to 376, the power supply units 381 to 386, and the gate drivers 391 to 394 drive the pixels 36 in each row Y and each column X of the display panel.

Next, the operation of this drive circuit will be described. In FIG. 6, data 33 (3 bits) having a predetermined gradation to be displayed on the light emitting layer group 36 </ b> B is first input to the data driver 371. The data 33 is preferably digital serial data or parallel data.
As described above, the pixel 36 includes the light emitting layer groups 36R, 36G, and 36B. Accordingly, since 3-bit data 33 is sent to each of the light emitting layer groups 36R, 36G, and 36B, the data 33 sent to the pixel 36 is 9 bits as shown in FIG.
The data 33 input to the data driver 371 is used to cause the organic EL light emitting layer 18, 19, 20 to emit light corresponding to the gradation displayed on the display device.

  Each bit (1 or 0) of the data 33 is held in the data holding units 350 to 352, and the gate driver 391 applies a predetermined first potential to the gates of the gate transistors 27 to 29 to turn them on. . Data output from the data driver 371 is sent to the capacitors 21 to 23 through the drains and sources of the gate transistors 27 to 29. As a result, the power supply and the data voltage are applied to both ends of the capacitors 21 to 23, and charges sufficient to hold the potential difference are stored in the capacitors 21 to 23. That is, the display data output from the data driver 371 is written and stored in the capacitors 21 to 23 for holding data. Subsequently, the gate driver 391 applies a predetermined second potential to the gates of the gate transistors 27 to 29 to turn them off. When the gate transistors 27 to 29 are turned off, the charges stored in the capacitors 21 to 23 are held. The electric charge held in the capacitors 21 to 23 is a potential difference between the power supplies 30 to 32 and the output voltage of the data driver 371.

In the pixel 36 of the first embodiment, the luminance weighting of the organic EL light emitting layers 18, 19, and 20 (organic film light emitting layers 3, 6, and 9) constituting the light emitting layer groups 36R, 36G, and 36B is shown in FIG. ).
For example, a case where an image having a gradation “5” is displayed on the display device will be described. From FIG. 4, it is necessary to light the organic EL light emitting layers 18 and 20 of the first layer and the third layer at the gradation “5”. The input data 33 is converted into a data string connected to the signal line of the corresponding organic EL light emitting layer by the data driver 371. In this case, the organic EL light emitting layers 18 and 20 emit light to the data holding units 350 and 352. Data to be retained.

  At this time, since the voltage for turning on the TFT 24 is applied to the capacitor 21 and the voltage for turning on the TFT 26 is also applied to the capacitor 23, the TFTs 24 and 26 are respectively turned on. On the other hand, since the voltage for driving the TFT 25 is not applied to the capacitor 22, the TFT 25 is in an off state.

  Accordingly, since the TFTs 24 and 26 are in the ON state, current is supplied from the power sources 30 and 32 to the organic EL light emitting layers 18 and 20 through the drains and sources of the TFTs 24 and 26, and the organic EL light emitting layers 18 and 20 emit light. At this time, since the weights of the luminance of the organic EL light emitting layers 18 and 20 are “1” and “4”, the total gradation “5” is displayed on the display device.

The luminance weighting described above may be realized by forming the respective organic EL light emitting layers 18, 19, and 20 with materials having different light emission luminances, and making the current flowing through the organic EL light emitting layer and the flow time thereof the same. However, it may be realized by using a material having the same light emission luminance and changing a flowing current and a flowing time thereof.
Here, a method of realizing light emission with a predetermined luminance by forming each organic film light emitting layer with the same material and changing a current value and a time for supplying current to each organic film light emitting layer will be described. Luminance weighting follows FIG. In addition, what multiplied the electric current value i which flows into the organic electroluminescent light emitting layers 18-20 and the time length t which flows an electric current becomes the luminance weight of each layer. The set current value i is supplied by the power supply unit 381 in the power supply circuit 38. Further, time length data indicating each time length t is set in the horizontal driver 371.
For example, in order to set three types of luminance weighting “1”, “2”, and “4” shown in FIG. There are methods to set multiple types of combinations.

In addition, a method of equalizing the current value and the light emission time length between the respective light emitting layers when the current value i and the time length t are set to be different for each light emitting layer and averaged within a predetermined time will be described.
FIGS. 7A, 7B, and 7C show tables for explaining the gradation expression method for each frame (for each field during interlace driving). In each of the organic EL light emitting layers (light emitting layers) 18 to 20 which are the first layer to the third layer in FIGS. 7A to 7C, the current value i and the time length set so as to change from frame to frame. The relationship of t is shown. In addition, the total luminance is the same when all the light emitting layers emit light within one frame.

  FIG. 7A shows a table in which currents are set to flow through the respective organic EL light emitting layers at different current values i, and luminance is weighted by switching every frame. The current value i is switched based on the table of FIG. By switching the current value i of the current supplied to each organic EL light emitting layer for each frame, the luminance weighting for each organic EL light emitting layer is switched for each frame. In the fourth and subsequent frames, the set current values i of the respective layers from the first frame to the third frame are sequentially repeated.

That is, the current value of each layer is set to make a round in 3 frames. Therefore, three types of luminance weighting were set.
Furthermore, when all the organic EL light emitting layers emit light in all frames, the total luminance in each organic EL light emitting layer is the same value in units of three frames. By setting in this way, the total amount of the current value flowing through each organic EL light emitting layer is averaged, and there is an effect that the lifetime of each organic EL light emitting layer is made uniform.

  FIG. 7B is a table for setting the current of the same current value i to flow through the light emitting layers (the first layer to the third layer) at different time lengths t and switching the luminance for each frame to weight the luminance. Indicates. Based on the table in FIG. 7B, the time length t is switched. By switching the time length t for supplying current to each light emitting layer for each frame, the weighting of luminance for each light emitting layer is switched for each frame. After the fourth frame, the set time length t of each layer from the first frame to the third frame is sequentially repeated.

That is, the time length t of the current flowing to each light emitting layer is set so as to make a round in three frames. Here, three types of luminance weighting are set.
By setting in this way, the total time amount of the current value flowing through each light emitting layer is averaged, and there is an effect that the life of each light emitting layer is made uniform. Each light emitting layer emits light in a time division (PWM) manner, and finer gradation expression can be achieved.

FIG. 7C shows a table in which currents having different current values i and different time lengths t are set to flow to the respective light emitting layers, and luminance is weighted by switching every frame. As shown in FIG. 7C, in each light emitting layer, the combination of the current value i and the time length t at which the luminance weight is “1”, “2”, and “4” between the first frame and the third frame is completed. The total luminance of each frame is always set to “7”. The fourth and subsequent frames are set in the same manner, but the order of the combination that makes a round may be changed every three frames as shown in FIG. 7C, or may be the same.
Here, three types of combinations of time length t and current value i are set, and three types of luminance weighting are set.

  By setting in this way, the total amount of the current value i and the time length t flowing in each light emitting layer is averaged, and there is an effect that the life of each light emitting layer is made uniform. Each light emitting layer emits light in a time division (PWM) manner, and finer gradation expression can be achieved.

  FIGS. 7A to 7C show an example of luminance weighting in the case where the organic film light emitting layer has three layers. However, the present invention is not limited to this, and can be applied even in the case of further multilayering. is there. In that case, when the number of light emitting layers is n, the luminance weighting for each layer is switched for each frame, and m types (m is a natural number equal to or less than n) of current values i and time lengths t are combined. Is set so as to go around in n frames. Further, as described above, the total luminance when all the light emitting layers emit light in each frame is set to have the same value. When all the light emitting layers emit light in all frames, the total luminance in each light emitting layer is set to be the same value in n frames.

  In FIGS. 7A to 7C, different current values i and time lengths t are set for each organic light emitting layer, but the present invention is not limited to this. For example, the current value i and time length t of the first to third layers may be set to the same current value i and time length t as “1”, “1”, “1”, or “1”, “1”, The current value i and the time length t may be partially the same as 2 ”and“ 2 ”.

  In the present embodiment, the organic film light emitting layers from the first layer to the third layer or from the first layer to the fifth layer are made of the same material. However, the present invention is not limited to this. Even if the material of the organic film light emitting layer is different, the total luminance is shown in FIG. 3 by changing the current value i and the time length t during which the current flows for each organic film light emitting layer as described above. In the case of a), the first layer is “1”, the second layer is “2”, and the third layer is “4”. In FIG. 3C, the first layer is “1”. The second layer is “2”, the third layer is “4”, the fourth layer is “8”, and the fifth layer is “16”.

  In the driving of the pixel 36 of the first embodiment, the driving TFTs 24 to 26 operate only on / off. Therefore, as shown in FIG. 6, the circuit configuration may be a very simple circuit configuration including capacitors 21 to 23 for storing data for turning on / off the driving TFTs 24 to 26 and gate transistors 27 to 29 for holding the capacitors. .

  Further, since the driving TFTs 24 to 26 are only turned on / off, they operate in a saturation region that is not affected by threshold variation due to element characteristics of TFTs that are active elements, which is a problem in conventional organic EL display devices. Can be made. For this reason, problems such as display luminance unevenness and gradation shift in the display panel can be reduced as much as possible. Further, since the operation in the saturation region has less power loss due to the TFT, the power consumption is lower than that of the conventional example.

  Furthermore, the current supplied to the organic EL in the first embodiment is dispersed in a plurality of light emitting layers. It is said that the lifetime of the organic EL is inversely proportional to the square of the current value. Since the amount of current per layer can be reduced by distributing the current to a plurality of layers, the lifetime is longer than that of a conventional circuit configuration.

<< Second Embodiment >>
Next, the pixel 236 in the display device according to the second embodiment of the present invention will be described in detail. FIG. 8 is a diagram showing a configuration of the pixel 236 for realizing color display in the display device of the present embodiment. The display device is, for example, an organic EL display. The pixel 236 includes sub-pixels 236a to 236c.

Each of the sub-pixels 236a to 236c emits light formed of a white organic film light-emitting layer (W) with respect to each light-emitting part formed of red (R) green (G) blue (B) color organic film light-emitting layers. It is the structure which laminated | stacked the part. The white organic film light emitting layer may be driven by analog drive or digital drive. In this embodiment, as a preferred example, the color organic film light emitting layer is digitally driven by a digital drive unit Ddig (shown in FIG. 12), and the white organic film light emitting layer is driven. Will be described in analog drive by an analog drive unit Dana (shown in FIG. 12). Here, the digital driver Ddig is a data driver 271, gate transistors 252 to 254, capacitors 256 to 258, TFTs 244 to 246, and a gate driver 291. The analog driver Dana is TFT 247, a gate transistor 255, a capacitor 259, and a gate. Driver 291. When the white organic film light emitting layer is digitally driven, it is performed in the same manner as the digital driving of the color organic film light emitting layer described in detail below.
In FIG. 8, a power source, an anode, a cathode, and the like are omitted in order to briefly explain the colorization structure and method. Moreover, although the thickness of the organic film light emitting layer of each color is shown to be different according to the weighting of luminance, the weighting method is not limited to changing the thickness of the organic film light emitting layer. Luminance weighting may be realized by changing the laminated structure of the organic film light emitting layer, changing the material forming the organic film light emitting layer, or changing the amount of current flowing through the organic film light emitting layer.

The red organic film light-emitting layer 301, the red organic film light-emitting layer 302, the red organic film light-emitting layer 303, and the white organic film light-emitting layer 304 are sequentially stacked on the substrate 300 to form the first sub-pixel 236a (1 dot in the display device surface). ).
The luminance when the red organic film light emitting layer 301 was caused to emit light by digital driving (on) was set to 1R with a relative reference value. The red organic film light emitting layer 302 emits light with twice the luminance of the red organic film light emitting layer 301 and is represented by 2R. Similarly, the red organic film light emitting layer 303 emits light with a luminance four times that of the red organic film light emitting layer 301 and is represented by 4R. Let the red organic film light emitting layers 301-303 be red light emission parts.
The white organic film light emitting layer 304 is a light emitting unit driven in an analog manner. The total luminance of the four layers is output from the substrate 300 and reproduced at the ratio of the luminance of the digitally driven organic film light emitting layer (digital layer) and the analog driven organic film light emitting layer (analog layer). The color is determined.

The green organic film light emitting layer 305, the green organic film light emitting layer 306, the green organic film light emitting layer 307, and the white organic film light emitting layer 308 are sequentially stacked on the substrate 300 to form the second subpixel 236b in the display device surface. .
The luminance when the green organic film light emitting layer 305 was caused to emit light by digital driving was set to 1 G as a relative reference value. The green organic film light emitting layer 306 emits light with twice the luminance of the green organic film light emitting layer 305 and is represented by 2G. Similarly, the green organic film light emitting layer 307 emits light with a luminance four times that of the green organic film light emitting layer 305 and is represented by 4G. Let the green organic film light emitting layers 305-307 be green light emission parts.
The white organic light emitting layer 308 is an analog driven light emitting unit. The total luminance of these four layers is output from the substrate 300, and the color to be reproduced is determined by the luminance ratio of the digital layer and the analog layer.

The blue organic film light emitting layer 309, the blue organic film light emitting layer 310, the blue organic film light emitting layer 311, and the white organic film light emitting layer 312 are sequentially stacked on the substrate 300 to form the third subpixel 236 c in the display device surface. .
The luminance when the blue organic film light emitting layer 309 is caused to emit light by digital driving is set as a relative reference value, which is 1B. The blue organic film light emitting layer 310 emits light with twice the luminance of the blue organic film light emitting layer 309 and is represented by 2B. Similarly, the blue organic film light emitting layer 311 emits light with a luminance four times that of the blue organic film light emitting layer 309 and is represented by 4B. The blue organic film light emitting layers 309 to 311 are referred to as blue light emitting portions.
The white organic film light emitting layer 312 is a light emitting unit driven in an analog manner. The total luminance of these four layers is output from the substrate 300, and the color to be reproduced is determined by the luminance ratio of the digital layer and the analog layer.
In the present embodiment, the white light emitting units 304, 308, and 312 are stacked on the red light emitting unit, the green light emitting unit, and the blue light emitting unit, respectively, but may be stacked on any one of the red to blue light emitting units. In addition, one white light emitting part may be laminated so as to straddle the red to blue light emitting part.

  FIG. 9 shows a layer configuration of the first sub-pixel 236a that constitutes the pixel 236 in the display device of the second embodiment. Note that the sub-pixels 236a to 236c have the same configuration, and thus illustration and description of the sub-pixels 236b and 236c are omitted. In FIG. 9, a glass substrate 201 is a display surface of the display device and corresponds to the substrate 300 of FIG. Although the glass substrate 201 is used here, a plastic substrate may be used as long as an organic film layer can be formed. An anode 202 is formed on the glass substrate 201. As the anode 202, for example, ITO which is a transparent electrode is used.

An organic light emitting layer 203 is formed on the anode 202. The organic film light emitting layer 203 is composed of a combination of a hole injection layer, a hole transport layer, an electron injection layer, an electron transport layer, and a light emitting layer which is a phosphor made of an organic compound. This combination is appropriately selected depending on the characteristics of the organic EL.
A cathode 204 is formed on the organic film light emitting layer 203. When ITO, which is a transparent electrode, is used as the cathode 204, it does not operate as a cathode as it is, so it is necessary to insert lithium for the cathode thinly between the ITO and the organic film light emitting layer 203.
A power source 214 is connected to apply a DC voltage between the anode 202 and the cathode 204. The light emission principle of the organic film light emitting layer 203 sandwiched between the anode 202 and the cathode 204 is the same as the conventional example.

A silicon oxide film 215 and an anode 205 are sequentially stacked on the cathode 204. The silicon oxide film 215 has an effect of insulating the anode 205 and the cathode 204.
On the anode 205, similarly to the above, the organic film light emitting layer 206, the cathode 207, the silicon oxide film 217, the anode 208, the organic film light emitting layer 209, the cathode 210, the silicon oxide film 219, the anode 211, the organic film light emitting layer 212, and The cathode 213 is sequentially stacked. In the lower surface light extraction structure that does not extract light from the cathode 213 side used in this embodiment, the cathode 213 is made of a metal such as aluminum.

Power supplies 216, 218, 220 are connected to apply a DC voltage between anode 205 and cathode 207, between anode 208 and cathode 210, and between anode 211 and cathode 213, respectively. As a result, a current corresponding to the DC voltage applied by the power sources 216, 218, and 220 is supplied to the organic film light emitting layers 206, 209, and 212.
Each of the organic film light emitting layers 203, 206, 209, and 212 emits light with a luminance proportional to the value of the current flowing therethrough, and the light is extracted from the glass substrate 201 side. Of course, this structure can be realized not only by organic EL but also by inorganic EL, and can be realized not only by active drive but also by a passive drive display device.

  Here, the organic film light emitting layers 203, 206, and 209 are digital drive layers that are switched between light emission and non-light emission (lighting and extinguishing) by the binary value of power on / off. The organic film light emitting layers 203, 206, and 209 are formed by selecting one material that emits red (R), green (G), and blue (B) in each of the sub-pixels 236a to 236c.

On the other hand, the organic film light emitting layer 212 selects a material whose luminance changes in proportion to the amount of current supplied from the power source 220 and emits light with a predetermined luminance. That is, the organic film light-emitting layer 212 is an analog drive layer whose luminance is changed by an operation of changing the magnitude of current, and can emit light at a halftone level. In the present embodiment, a material that emits light in a color different from that of the digital driving layer, for example, W (white) is selected.
Therefore, the element of the second embodiment has a structure in which the digital driving layer is three layers and the analog driving layer is one layer. By combining the digital drive layer and the analog drive layer in this manner, the color reproduction range can be expanded, and a large peak luminance can be secured.

FIG. 10 shows a specific pixel structure of the second embodiment. 10, the same components as those in FIG. 9 are denoted by the same reference numerals, and the description thereof is omitted. FIG. 10 shows one dot (first sub-pixel 236a) of each color (for example, red, green, blue, etc.) constituting one pixel.
On the glass substrate 201, thin film transistors (TFTs) 222a, 222b, 222c, and 222d, which are active elements, are formed and connected to anodes 202, 205, 208, and 211, respectively. The TFTs 222a to 222d can be any active element such as p-Si (low temperature polysilicon) or a-Si (amorphous silicon) as long as the organic film light emitting layers 203, 206, 209, and 212 can be driven and controlled. It may be created.

  The TFTs 222 a to 222 d have a circuit function for turning on / off the power supplied to the organic film light emitting layers 203, 206, 209, and 212. The silicon oxide film 221 formed between the glass substrate 201 and the anode 202 is a film that prevents metal ions from moving from the glass substrate 201 to the anode 202. The cathode 204, the cathode 207, the cathode 210, and the cathode 213 are common electrodes.

  When light is extracted from the glass substrate 201 side, which is the lower side of the subpixel 236a shown in FIG. 10, the cathode 213 is made of a metal such as aluminum so that light does not leak from the cathode 213 side, which is the upper side of the subpixel 236a. It is formed. As a result, the light emitted from the organic film light emitting layers 203, 206, 209, and 212 is emitted upward and downward, but the light emitted to the cathode 213 side is reflected by the cathode 213 and travels downward. It is taken out only from the substrate 201 side.

  In the second embodiment, the glass substrate 201 is provided with TFTs 222a to 222d and has a bottom light extraction structure for extracting light from the glass substrate 201 side. However, the cathode 213 is formed of a transparent electrode, and the anode 202 is a metal such as aluminum. The upper surface light extraction structure for extracting light from the cathode 213 side may be used.

  Here, a plurality of TFTs may be connected to one organic film light emitting layer as described later with reference to FIG. Here, for the sake of convenience, one TFT TFT 222a to 222d is shown. In the present embodiment, the TFTs 222a to 222d are referred to as element driving units (first driving units). The anode, the organic film light emitting layer, the cathode, and the element driving unit form a unit element.

The luminance weighting method of the organic film light emitting layers 203, 206, and 209 in the sub-pixel 236a constituting the pixel 236 of the second embodiment shown in FIGS. 9 and 10 is the same as that already described in FIG. Good. The organic light emitting layer 203 is the first layer, the organic film light emitting layer 206 is the second layer, and the organic film light emitting layer 209 is the third layer.
3B and 3C show an example in which the digitally driven organic film light emitting layer has a five-layer structure, and therefore two unit elements are further provided in the structure shown in FIGS. Consider a five-layer structure. Among the five organic film light emitting layers, a first layer, a second layer, a third layer, a fourth layer, and a fifth layer are sequentially arranged from the side closer to the light extraction side.

  An example of the gradation expression of the first sub-pixel 236a in the display device of the second embodiment is shown in FIG. 4 and has already been described.

FIG. 11 is a driver configuration diagram of the display panel of the display device according to the second embodiment of the present invention. In FIG. 11, each pixel 236 is composed of sub-pixels 236a to 236c each having four organic film light-emitting layers, and each sub-pixel corresponds to a pixel circuit in FIG. The display panel of the second embodiment includes a horizontal driver 237 for sending analog data and 9-bit digital data to a plurality of pixels 236 arranged in a two-dimensional matrix, and a power supply circuit 238 for driving the pixels. And a vertical driver 239 for selecting a vertical line.
The plurality of pixels 236 are arranged in a two-dimensional matrix composed of rows Y arranged in the vertical direction and columns X arranged in the horizontal direction. In FIG. 11, as an example, a display panel of six columns X1 to X6 is shown with four rows Y1 to Y4. The actual display panel has a larger number of matrices than that shown in FIG. 11, but this is shown here for convenience. In this embodiment, data drivers 271 to 276 are incorporated in the horizontal driver 237, power supply units 281 to 286 are incorporated in the power supply circuit 238, and gate drivers 291 to 294 are incorporated in the vertical driver 239, respectively. Here, the horizontal driver 237 and the vertical driver 239 are used as the second drive unit.

  For example, when it is desired to scan the display line of the Y1 row which is the uppermost stage of the display panel shown in FIG. 11, the gate driver 291 (gate TFT) of the vertical driver 239 turns on each pixel 236 of the Y1 row. The gate drivers 292 to 294 are turned off for the other display lines Y2 to Y4. At this time, data for one line of video data (consisting of digital data and analog data) is output from the horizontal driver 237 and supplied to each pixel 236.

  Next, when the gate driver 291 turns off each pixel 236 in the Y1 row, an image of one line in the Y1 row is displayed. Similarly, the vertical driver 239 is sequentially driven from the Y2 row gate driver 292 to the Y4 row gate driver 294, and video data is output line by line from the horizontal driver 237, so that all the display panels in The pixel 236 can be scanned.

  FIG. 12 is a circuit diagram of a drive circuit for driving the first sub-pixel 236a constituting the pixel 236 according to the second embodiment of the present invention. Although the first sub-pixel 236a is shown here, the same circuit is used for the sub-pixels 236b and 236c, and thus a specific configuration is not shown or described. In FIG. 12, organic EL light emitting layers 240, 241, 242, and 243 correspond to the organic film light emitting layers 203, 206, 209, and 212 shown in FIGS. The first sub-pixel 236a has a total of four-layer structure with three digital layers and one analog layer, and the luminance weighting of each organic film light-emitting layer constituting the digital layer is the same as in FIG. “1”, “2”, and “4”.

  One ends (anodes in the figure) of the organic EL light emitting layers 240 to 243 are connected to power sources 248 to 251 constituting the power source unit 281 through the sources and drains of the driving TFTs 244 to 247. The gates of the TFTs 244 to 247 are connected to the sources of the TFTs 252 to 255, and are connected to the power sources 248 to 251 through the capacitors 256 to 259.

The power supplies 248 to 251 correspond to the power supplies 214, 216, 218, and 220 shown in FIG. The power sources 248 to 251 may be individual power sources or common power sources, and are set so that the organic EL light emitting layers 240 to 243 emit light with a predetermined luminance by weighting with a predetermined luminance. Further, the drains of the TFTs 252 to 254 are connected to data holding units 2710 to 2712 in the data driver 271, and the gates are commonly connected to the gate driver 291. The analog data 231 is applied to the gate of the TFT 247 via the source and drain of the TFT 255.
Here, the data driver 271, the power supply unit 281, and the gate driver 291 are shown. However, as shown in FIG. 11, the data drivers 272 to 276, the power supply units 282 to 286, and the gate drivers 292 to 294 have the same configuration. The data drivers 271 to 276, the power supply units 281 to 286, and the gate drivers 291 to 294 drive the pixels 236 in each row Y and each column X of the display panel.
In FIG. 12, for convenience, the gate drivers 291 (-294) connected to the gate transistors 252 to 254 and the gate transistor 255 are illustrated separately.

Next, the operation of this drive circuit will be described. First, the case where the organic EL light emitting layers 240, 241, and 242 that are digital layers are digitally driven so as to emit light / not emit light by binary on / off will be described.
First, data 233 (3 bits) having a predetermined gradation displayed on the sub-pixel 236 a is input to the data driver 271. The data 233 is preferably digital serial data or parallel data. As described above, the pixel 236 includes sub-pixels 236a to 236c. Therefore, since 3-bit data 233 is sent to each of the sub-pixels 236a to 236c, the data 233 sent to the pixel 236 is 9 bits as shown in FIG.
Data 233 input to the data driver 271 is used to emit light from the organic EL light emitting layers 240 to 242 corresponding to the gradation displayed on the display device.

Each bit (1 or 0) of the data 233 is held in the data holding units 2710 to 2712, and the gate driver 291 applies a predetermined first potential to the gates of the gate transistors 252 to 254 to turn them on. . Display data output from the data driver 271 is written and stored in capacitors 256 to 258 for holding data through the drains and sources of the gate transistors 252 to 254.
Subsequently, the gate driver 291 applies a predetermined second potential to the gates of the gate transistors 252 to 254 to turn them off. When the gate transistors 252 to 254 are turned off, the data stored in the capacitors 256 to 258 are held. Charges held in the capacitors 256 to 258 are a potential difference between the power supplies 248 to 250 and the output voltage of the data driver 271.

In the pixel 236 of the second embodiment, the weighting of the luminance of the organic EL light emitting layers 240 to 242 (organic film light emitting layers 203, 206, and 209) which are digital driving layers constituting the sub pixels 236a to 236c is shown in FIG. ). As described above, the weighting may be realized by forming the respective organic EL light emitting layers 240 to 242 with materials having different light emission luminances, and making the current flowing through the organic EL light emitting layer and the flowing time thereof the same, They may be formed of materials having the same emission luminance, and may be realized by varying the flowing current and the flowing time.
A method for realizing light emission with a predetermined luminance by changing the current value and the time for applying the current to each organic film light emitting layer may be the method already described in the first embodiment.

For example, a case where an image of gradation “5” is displayed on the display device will be described as an example. As shown in FIG. 4, at the gradation “5”, the first and third organic EL light emitting layers 240 and 242 need to be lit. Here, the organic EL light emitting layer 240 is the first layer, the organic EL light emitting layer 241 is the second layer, and the organic EL light emitting layer 242 is the third layer.
The input data 233 is converted into a data string connected to the signal lines of the corresponding light emitting layers 240 to 242 by the data driver 271. In this case, the organic EL light emitting layers 240 and 242 emit light to the data holding units 2710 and 2712. Data to be retained.

  At this time, since the voltage for turning on the TFT 244 is applied to the capacitor 256 and the voltage for turning on the TFT 246 is also applied to the capacitor 258, the TFTs 244 and 246 are turned on. On the other hand, since a voltage for driving the TFT 245 is not applied to the capacitor 257, the TFT 245 is in an off state.

  Accordingly, since the TFTs 244 and 246 are in the on state, current is supplied from the power sources 248 and 250 to the organic EL light emitting layers 240 and 242 through the respective drains and sources of the TFTs 244 and 246, and the organic EL light emitting layers 240 and 242 emit light. At this time, since the weights of the luminance of the organic EL light emitting layers 240 and 242 are “1” and “4”, the total gradation “5” is displayed on the display device.

  Next, a case where analog driving is performed so as to emit light at a halftone level using the organic EL light emitting layer 243 will be described. First, analog data 231 of gradation to be displayed is input to the pixel 236 or the sub-pixels 236a to 236c. As the analog data 231, gradation data corresponding to light emission luminance of a level smaller than the minimum light emission luminance that can be expressed by the digital data 233 is used.

  Here, a case where the gradation “0.3” is displayed on the display device is considered as an example. When the analog data 231 is input, the TFT 255 is turned on by the gate driver 291, so that the analog data 231 is stored in the capacitor 259 for holding data via the drain and source of the TFT 255. Subsequently, since the TFT 255 is controlled to be turned off by the gate driver 291, the analog data 231 is held in the capacitor 259.

  At this time, the electric charge held in the capacitor 259 is a potential difference between the power supply 251 and the analog data 231, which is a value such that a current amount corresponding to the gradation data “0.3” flows to the driving TFT 247. . The driving TFT 247 operates by the electric charge held in the capacitor 259, current is supplied from the power source 251 to the organic EL light emitting layer 243 through the drain and source of the TFT 247, and the organic EL light emitting layer 243 emits light. At this time, the gradation “0.3” is displayed on the display device.

  13 to 16 are diagrams for explaining a method of reproducing a color signal using the pixel 236 of FIG. This is called an xy chromaticity diagram, with x on the horizontal axis and y on the vertical axis. An arbitrary color F including Y as a luminance signal is represented by F (x, y, Y). In general, when an arbitrary color F is represented, the luminance Y is often omitted and represented by F (x, y). All colors in the natural world can be expressed by coordinates in a horseshoe-shaped curve CRU as shown in FIGS.

  Here, the chromaticity coordinate of red (R) is assumed to be R (xr, yr, Yr). Similarly, let chromaticity coordinates of green (G) be G (xg, yg, Yg) and chromaticity coordinates of blue (B) be B (xb, yb, Yb). For example, in the NTSC signal which is a standard of a television signal, the luminance Y is omitted and the chromaticity coordinates are R (0.67, 0.33), G (0.21, 0.71), B (0.14). 0.08).

When R, G, and B are selected as the three primary colors of the display device, colors F that can be reproduced by the display device are R (xr, yr), G (xg, yg) and B (xb, yb) are colors within a range of a triangle TR1 surrounded by a one-dot chain line.

  Let chromaticity coordinates of white be W (xw, yw, Yw). The chromaticity coordinates when using a white light source of D65 are W (0.3127, 0.3291). The chromaticity coordinates when a white light source of C is used are W (0.31, 0.316). When R, G, and B having the above NTSC chromaticity points are used as materials for the organic film light emitting layer, a white color of D65 is obtained by mixing colors with a luminous flux ratio of 2.9: 6.1: 1.0 . Similarly, when R, G, and B having the above NTSC chromaticity points are used as organic film materials and mixed at a luminous flux ratio of 3.0: 5.9: 1.1, C white is obtained.

  In the chromaticity diagrams of FIGS. 13 to 16, R (red) indicates the chromaticity points of the red organic film light emitting layers 301 to 303 of FIG. 8. G (green) indicates the chromaticity point of the green organic film light emitting layers 305 to 307 in FIG. B (blue) indicates the chromaticity point of the blue organic film light emitting layers 309 to 311 in FIG. 8. W (white) indicates the chromaticity point of the white organic film light-emitting layers 304, 308, and 312 in FIG.

  The chromaticity point Rw (xrw, yrw, Yrw) on the chromaticity diagram is obtained by mixing R and W. Similarly, chromaticity point Gw (xgw, ygw, Ygw) on the chromaticity diagram is obtained by mixing G and W, and chromaticity point Bw (xbw, ybw, Ybw) is obtained by mixing B and W. Obtained.

In order to obtain the color of the chromaticity point Rw, R and W may be mixed based on the light quantity ratio of R and W based on the chromaticity points of R and W. Further, the luminance Yrw of the chromaticity point Rw is represented by the sum of the luminances Yr and Yw of R and W. In order to express the color gradation, it is possible to change the amount of light in proportion while maintaining the ratio between the luminances Yr and Yw.
Here, the predetermined luminance Yr is expressed by digitally driving the red organic film light emitting layers 301 to 303 in FIG. On the other hand, the white organic film light emitting layer 304 expresses a predetermined luminance Yw by analog driving.

Similarly to the above, in order to obtain the color of the chromaticity point Gw, G and W may be mixed based on the light quantity ratio of G and W based on the chromaticity points of G and W. Is represented by the sum of the luminances Yg and Yw of G and W. The color gradation can be expressed by changing the amount of light proportionally while maintaining the ratio between the luminances Yg and Yw.
A predetermined luminance Yg is expressed by digitally driving the green organic film light emitting layers 305 to 307 in FIG. On the other hand, the white organic film light emitting layer 308 expresses a predetermined luminance Yw by analog driving.

Similarly to the above, in order to obtain the color of the chromaticity point Bw, B and W may be mixed based on the light quantity ratio of B and W based on the chromaticity points of B and W, and the chromaticity point Bw Is represented by the sum of the luminances Yb and Yw of B and W. The color gradation can be expressed by changing the amount of light proportionally while maintaining the ratio between the luminances Yb and Yw.
A predetermined luminance Yb is expressed by digitally driving the blue organic film light emitting layers 309 to 311 in FIG. On the other hand, the white organic film light emitting layer 312 expresses a predetermined luminance Yw by analog driving.

Further, color display by the pixels 236 will be described in detail with reference to the chromaticity diagrams of FIGS.
In the chromaticity diagram shown in FIG. 13, the color reproduction range that can be displayed on the display device is within the range surrounded by a triangle TR2 indicated by a solid line with Rw, Gw, and Bw as vertices. For Rw, Gw, and Bw, arbitrary coordinate values on the line segments RW, GW, and BW indicated by chain lines can be selected by changing the digital / analog light quantity ratio in each of the sub-pixels 236a to 236c. For this reason, the triangle TR2 representing the color reproduction range can be adjusted to an arbitrary width. Line segments RW, GW, and BW connect R, G, and B chromaticity coordinates to W chromaticity coordinates.
When displaying white W, it can be represented in a triangle TR2 representing the color reproduction range as shown in FIG. 13, so the role of the R, G, B organic film light emitting layer in each of the sub-pixels 236a to 236c is white organic. The light emitting layers 304, 308, and 312 can be shared. Therefore, conventionally, the R, G, and B organic film light emitting layers emit light at peak luminance according to the light quantity ratio, and W is displayed. However, W can be displayed without lighting the R, G, and B organic film light emitting layers. Accordingly, it is possible to solve the problem that the R, G, B organic film light emitting layer emits light with peak luminance and the device life is shortened. Furthermore, it is possible to simultaneously solve the image burn-in problem that occurs in white characters on the display device.

When displaying an arbitrary color F, since it can be represented in a triangle TR2 representing a color reproduction range as shown in FIG. 14, the role of the R, G, B organic film light emitting layer in each of the sub-pixels 236a to 236c, The white organic film light emitting layers 304, 308, and 312 can be shared.
Therefore, it is possible to solve the problem that only the specific organic film light emitting layer is deteriorated and the device life is shortened. For this reason, the problem of burn-in is solved at the same time. This is particularly effective when an arbitrary color to be displayed is close to W.

The chromaticity diagram shown in FIG. 15 shows a case where the blue organic film light emitting layers (B) 309 to 311 in the third subpixel 236c are not caused to emit light (OFF). The color reproduction range that can be displayed on the display device is surrounded by a triangle TR3 indicated by a solid line with W (xw, yw, Yx), Gw (xgw, ygw, Ygw), and Rw (xrw, yrw, Yrw) as vertices. Within range. For Gw and Rw, arbitrary coordinate values on the line segments GW and RW can be selected by changing the digital / analog light quantity ratio in the pixel. For this reason, the triangle TR3 representing the color reproduction range can be adjusted to an arbitrary size.
For example, as shown in FIG. 15, when an arbitrary color F to be displayed is within the triangle TR3 with W, Gw, and Rw as vertices on the symmetrical side of B with W as the center, the blue color in the third sub-pixel 236c Even when the organic film light emitting layers (B) 309 to 311 are off, the white organic film light emitting layer (W) 312 can bear an arbitrary color F. Therefore, it is not necessary to cause the blue organic film light emitting layers 309 to 311 to emit light, and the element lifetime of the blue organic film light emitting layers 309 to 311 can be maintained.
As described above, when an arbitrary color F to be displayed is in a triangle having two chromaticity coordinates of Rw, Gw, and Bw and W as a vertex on the xy chromaticity diagram, the chromaticity that does not become a vertex An arbitrary color F can be displayed without causing the organic film light emitting layers of the color components R, G, and B constituting the coordinates to emit light, and the element lifetime of the organic film light emitting layer can be maintained.

In the chromaticity diagram shown in FIG. 16, the white organic film light emitting layer 304 in the first subpixel 236a, the white organic film light emitting layer 308 in the second subpixel 236b, and the blue organic film light emitting layer 309 in the third subpixel 236c. The case where ˜311 is not caused to emit light (off) is shown. The color reproduction range that can be displayed by the display device is surrounded by a triangle TR4 indicated by a solid line with W (xw, yw, Yx), G (xg, yg, Yg), and R (xr, yr, Yr) as vertices. Within range.
For example, as shown in FIG. 16, when an arbitrary color F to be displayed is close to the line segment GR, even if the blue organic film light emitting layers (B) 309 to 311 in the sub-pixel 236c are off, the white organic film light emitting layer (W) An arbitrary color F can be displayed by 312. Therefore, it is not necessary to cause the blue organic film light emitting layers 309 to 311 to emit light, and the element lifetime of the blue organic film light emitting layers 309 to 311 can be maintained. Further, when reproducing colors close to the primary colors of R, G, and B, the white organic film light emitting layer 304 and the white organic film light emitting layer 308 can be turned off for display without deteriorating color purity.
As described above, when an arbitrary color F to be displayed is in a triangle having any two colors of R, G, and B and W as vertices on the xy chromaticity diagram, an organic film having a color that does not become a vertex An arbitrary color F can be displayed without causing the light emitting layer to emit light, and the element lifetime of the organic film light emitting layer can be maintained.

  As a digital driving method and an analog driving method, the analog data 231 has been described so that gradation data corresponding to light emission luminance of a level smaller than the minimum light emission luminance that can be expressed by the digital data 233 is used. It is not limited to. The analog data 231 may be configured such that gradation data corresponding to a light emission luminance of a level larger than the maximum light emission luminance that can be expressed by the digital data 233 is used.

  As described above, according to the present embodiment, reproduction is performed within one subpixel as compared with the case where the organic film light emitting layers of all unit elements constituting one subpixel are digitally driven to emit light of the same color. The color range that can be increased. Furthermore, by providing an organic film light emitting layer that is digitally driven and an organic film light emitting layer that is analog driven, the luminance component in one subpixel can be shared between the digital layer and the analog layer.

  In addition, according to the present embodiment, since the sub-pixel color expression and gradation expression are performed by the total of the light emission luminances of the organic film light emitting layers having a plurality of light emission luminances stacked, one organic film light emission layer is provided. Compared with a conventional display device configured to flow all current amounts according to light emission luminance, a display device with a long life can be configured.

  Further, according to this embodiment, any display device having a structure in which a plurality of organic film light emitting layers can be stacked can be applied to electroluminescence and other display devices, and can be applied to small to large display devices. It is.

≪Third embodiment≫
FIG. 17 shows the layer structure of the pixel in the display device of the third embodiment of the present invention using multiphotons. The display device is, for example, an organic EL display. In FIG. 17, a glass substrate 110 is a display surface of the display device. Although the glass substrate 110 is used here, a plastic substrate may be used as long as an organic film layer can be formed. An anode 112 is formed on the glass substrate 110. As the anode 112, for example, ITO which is a transparent electrode is used.
An organic light emitting layer 113 is formed on the anode 112. The organic film light-emitting layer 113 is composed of a combination of a hole injection layer, a hole transport layer, an electron injection layer, an electron transport layer, and a light-emitting layer that is a phosphor of an organic compound (organic film light-emitting layers 115 and 117 described later). The same applies to 119). This combination is appropriately selected depending on the characteristics of the organic EL.
A charge generation layer 114 is formed on the organic light emitting layer 113. The charge generation layer 114 operates as an electron and hole injection layer. For the charge generation layer 114, ITO, V ₂ O _5, or the like can be used. An organic film light-emitting layer 115 is formed on the charge generation layer 114, and a charge generation layer 116, an organic film light-emitting layer 117, a charge generation layer 118, and an organic film light-emitting layer 119 are sequentially stacked thereon. A cathode 120 is formed on the organic film light emitting layer 119, and a power source 111 is connected between the cathode 120 and the anode 112.

The display device described here has a structure in which a plurality of organic light emitting layers and charge generation layers are alternately stacked horizontally between the anode 112 and the cathode 120 with respect to the light emitting surface. Is called multiphoton. A light-emitting portion having a multiphoton structure is sandwiched between the anode 112 and the cathode 120.
When light is extracted from the glass substrate 110, the cathode 120 is formed of a metal that reflects light such as aluminum. The light emission principle of each organic film light emitting layer 113, 115, 117, 119 sandwiched between the anode 112 and the cathode 120 is the same as that of the conventional example.

FIG. 18 shows the operation principle of multiphoton. In FIG. 18, the same components as those in FIG. 17 are denoted by the same reference numerals. The charge generation layers 114, 116 and 118 have a function of injecting electrons and holes into the adjacent organic film light emitting layers 113, 115, 117 and 119. In the organic film light emitting layers 113, 115, 117, and 119, electrons and holes are recombined to emit light. The brightness output from the pixel (organic EL) is the sum of the luminances from the respective organic film light emitting layers 113, 115, 117, and 119.
In this embodiment, the multiphoton includes four organic film light emitting layers 113, 115, 117, and 119, and each organic film light emitting layer is formed using a light emitting material having the same characteristics. When the same voltage as the conventional optical recording medium having one organic film light emitting layer is applied to each organic film light emitting layer of the multi-photon having a four-layer structure, the luminance is four times that of the conventional optical recording medium. can get. Therefore, in order to obtain the same brightness as the conventional configuration with the multiphoton of this embodiment, the current flowing through each organic film light emitting layer can be reduced to a quarter, so that the life of the organic film light emitting layer can be extended. . In the present embodiment, the same light emitting material is used for each layer of multiphotons, but this is not the case when the same light emission characteristics can be obtained.

FIG. 19 shows a layer structure of an organic EL display for performing color display according to the present embodiment. FIG. 19 shows a configuration in which three light emitting elements (sub-pixels) 400 a to 400 c that independently emit light form one pixel 400.
First, an anode 412 is formed on a glass substrate 401, and an organic film light emitting layer 413 and a cathode 414 are laminated thereon. This is the first sub-pixel 400a, and the green organic film light emitting layer (G) is used in this embodiment. The organic film light emitting layer 413 has the same configuration as the conventional example. A voltage is applied from the power source 415 to the anode 412 and the cathode 414.
Next to the first subpixel 400a, an anode 407 is formed on a glass substrate 401, and an organic film light emitting layer 408a, a charge generation layer 409, an organic film light emitting layer 408b, and a cathode 410 are sequentially stacked thereon. Yes. A structure between the anode 407 and the cathode 410 is a multi-photon having a two-layer structure including organic light emitting layers 408 a and 408 b and a charge generation layer 409. This is the second sub-pixel 400b, and the red organic film light emitting layer (R) is used in this embodiment. The organic film light emitting layers 408a and 408b are made of the same material, and emit light with the same characteristics when the same voltage is applied to the respective layers. A power source 411 is connected between the anode 407 and the cathode 410 to apply a voltage.
Further, next to the second sub-pixel 400b, an anode 402 is formed on a glass substrate 401, on which an organic film light-emitting layer 403a, a charge generation layer 404a, an organic film light-emitting layer 403b, a charge generation layer 404b, an organic film The film light emitting layer 403c, the charge generation layer 404c, the organic film light emitting layer 403d, and the cathode 405 are stacked in this order. The structure between the anode 402 and the cathode 405 is a multi-photon having a four-layer structure in which organic film light emitting layers 403a to 403d and charge generation layers 404a to 404c are alternately stacked. This is the third subpixel 400c, and in this embodiment, the blue organic film light emitting layer (B) is used. The organic light emitting layers 403a to 403d are made of the same material for all four layers, and emit light with the same characteristics when the same voltage is applied to the respective layers. A power source 406 is connected between the anode 402 and the cathode 405 to apply a voltage.

The organic film light emitting layers 403a to 403d, 408a to 408b, and 413 emit light with luminance proportional to the applied current, and light is extracted from the lower side of the glass substrate 401. The luminous efficiencies of the light emitting materials used for the organic film light emitting layers 403a to 403d, 408a to 408b, and 413 are greatly different. Here, the luminous efficiency indicates how much luminous efficiency level (luminance) can be obtained when a predetermined voltage is applied to the luminescent material. In the present embodiment, when the maximum luminous efficiency when a voltage of the same magnitude is applied to each of the organic film light emitting layers 403a to 403d, 408a to 408b, and 413 is expressed as light emission efficiency level 1, the organic film light emitting layer 413 is level 1, organic film light emitting layers 408a to 408b are level 0.5, and organic film light emitting layers 403a to 403d are level 0.25. That is, the level ratio of the luminous efficiency of the organic light emitting layers 403a to 403d, 408a to 408b, and 413 is (0.25) :( 0.5): 1.
As described above, when the power supply voltage is applied to the power supplies 406, 411, and 415 at a ratio of 4: 2: 1, the same voltage is applied to each of the organic film light emitting layers 403a to 403d, 408a to 408b, and 413, so Flowing. That is, the organic film light emitting layers 403a to 403d have a luminous efficiency of 0.25 × 4 layers = 1 level, and the organic film light emitting layers 408a to 408b have a luminance efficiency of 0.5 × 2 layers = 1 level. From the light emitting layer 413, the luminances output from the three sub-pixels 400a to 400c are all the same, such as luminous efficiency 1 × 1 layer = 1 level of luminance.

Here, the case where the level ratio of the luminous efficiency of the organic film light emitting layers 403a to 403d, 408a to 408b, and 413 is (0.25) :( 0.5): 1, that is, 1: 2: 4 is described. This may be set arbitrarily. For example, if the level ratio of the luminous efficiency of the organic film light emitting layers 403a to 403d, 408a to 408b, and 413 is 1: 1: 3, the second subpixel 400b and the third subpixel 400c have a multi-photon structure having a three-layer structure. The first sub-pixel 400a has a single layer structure. A power supply voltage of 3: 3: 1 is applied to the power supplies 406, 411, and 415.
As described above, when the light emission efficiency of the organic film light-emitting layers forming the sub-pixels 400a to 400c is different, a plurality of organic film light-emitting layers with low light emission efficiency are stacked to form a multi-photon structure sub-pixel having a multilayer structure. The voltage values applied to the sub-pixels may be determined so that the luminances formed and the luminances output from the sub-pixels 400a to 400 are all the same. That is, the voltage value to be applied to each sub-pixel may be determined so that the same voltage is applied to each organic film light emitting layer.
In the present embodiment, each organic film light emitting layer emits light with a predetermined luminance by changing the magnitude of the power supply voltage applied in accordance with the gradation level of the video output to the display device in an analog manner.

FIG. 20 shows current-luminance characteristics according to the third embodiment. In FIG. 20A, a first sub-pixel 400a, a second sub-pixel 400b, and a third sub-pixel 400c schematically show the organic EL layer of FIG. The luminous efficiency levels of the light emitting materials used in the organic film light emitting layers 413, 408a to 408b, and 403a to 403d of the sub pixel 400b and the third sub pixel 400c are “1”, “0.5”, and “0.25”, respectively. It is.
The graph shown in FIG. 20B represents the relationship between the current flowing through the organic film light emitting layer in each of the sub-pixels 400a to 400c and the luminance of light output from the organic film light emitting layer to the lower side of the glass substrate 401. is there. The relationship between the current flowing through each of the sub-pixels 400a to 400c and the light emission luminance is shown by solid lines Lsa to Lsc, and the relationship between the current flowing through each of the organic film light emitting layers 408a to 408b and 403a to 403d and the light emission luminance is shown by broken lines Ldb and Ldc1 to Ldc3. Expressed in A broken line Ldb represents luminance when current is passed through only one layer of the second sub-pixel 400b. Similarly, the broken line Ldc1 indicates the luminance when the current flows through only one layer of the third sub-pixel 400c, the broken line Ldc2 when the current flows through any two layers, and the broken line Ldc3 indicates the luminance when the current flows through any three layers. Indicates.

As described above, when the light emission efficiency level 1 of the light emitting material used for the organic film light emitting layer 413 of the first subpixel 400a is used as a reference, the organic film light emitting layers 408a and 408b of the second subpixel 400b are used. Although the light emission efficiency level of the light emitting material is 0.5, the second sub-pixel 400b has a multi-photon structure with a two-layer structure. Therefore, even when the same current amount as that of the first sub-pixel 400a is applied, FIG. As shown in the graph, the luminance dynamic range is equivalent to that of the first sub-pixel 400a.
Similarly, in the third sub-pixel 400c, the light emission efficiency level of the light emitting material used in the organic film light emitting layers 403a to 403d is 0.25. However, the third sub pixel 400c has a four-layer multiphoton structure. Even when the same amount of current as that of one sub-pixel 400a is passed, the dynamic range of luminance is equivalent.
Therefore, even if the number of gradations is increased, the amount of current flowing through the organic light emitting layer 413 of the first subpixel 400a does not need to be wide, and the organic film light emitting layer 408a of the second subpixel 400b and the third subpixel 400c. 408b, 403a to 403d, it is not necessary to make the amount of current flowing high. That is, it is relatively easy for the pixel circuit and the driver to control the drive current, and the circuit configuration is simplified.

FIG. 21 shows a layer structure when the display device according to the present embodiment is digitally driven. 19 and 20, the description was made when each organic film light emitting layer was caused to emit light by analog driving. However, FIGS. 21 to 25 are those where the organic film light emitting layer was made to emit light by digital driving.
In FIG. 21, a first sub-pixel 400d, a second sub-pixel 400e, and a third sub-pixel 400f schematically show an organic EL layer. The first sub-pixel 400d, the second sub-pixel 400e, the third sub-pixel 400f, and the third sub-pixel 400f The luminous efficiency levels of the light emitting materials used for the organic film light emitting layer of the sub-pixel 400f are “1”, “0.5”, and “0.25”, respectively.
Here, in the first sub-pixel 400d, three layers of unit elements each including a power source unit composed of a pair of anode and cathode and a light emitting unit in which a plurality of light emitting layers are sandwiched between the power source units are stacked. The first unit element in contact with the substrate has a structure having a single organic film light emitting layer (single layer structure), and the second layer unit element formed thereon has a light emitting part having a two layer multiphoton structure. The third layer unit element formed thereon has a four-layer light emitting portion with a multi-photon structure. The first sub-pixel 400d uses a green organic film light emitting layer (G).

The second sub-pixel 400e has three layers of unit elements, and the first layer unit element in contact with the substrate is a two-layer multi-photon light emitting part, and the second layer unit element formed thereon. Is a four-layer multi-photon structure light-emitting portion, and the third-layer unit element formed thereon has an eight-layer multi-photon structure light-emitting portion. The second sub-pixel 400e uses a red organic film light emitting layer (R).
The third sub-pixel 400f has three layers of unit elements. The first layer unit element in contact with the substrate is a four-layer multi-photon light emitting part, and the second layer unit element formed thereon. Is an eight-layer multi-photon structure light-emitting portion, and the third-layer unit element formed thereon has a sixteen-layer multi-photon structure light-emitting portion. The third sub-pixel 400f uses a blue organic film light emitting layer (B).
As described above, in the three subpixels 400d to 400f, the luminance weighting relationship from the first layer to the third layer on the basis of the light emission efficiency level of each unit element of the first layer is 1 for all the subpixels 400d to 400f. : 2: 4 ratio. The sub-pixels 400d to 400f are digitally driven to emit / do not emit light independently from each other in the three layers of unit elements in accordance with the value of a signal to be displayed, and the light emission luminance of each light emitting unit constituting the three layers of unit elements In total, pixel gradation expression is performed.

FIG. 22 is a diagram schematically showing the layer configuration of the organic EL display during digital driving according to the present embodiment. The first subpixel 400d will be described as a representative of the subpixels 400d to 400f illustrated in FIG.
An anode 421 is formed on a glass substrate 420, and an organic film light emitting layer 422 (green organic film light emitting layer) is formed thereon. The organic film light emitting layer 422 has the same configuration as that of the conventional example, and is a first light emitting unit (light emitting unit). A cathode 423 is formed on the organic film light emitting layer 422, and a voltage is applied from the power source 434 to the anode 421 and the cathode 423.
Subsequently, a silicon oxide film 430 is formed. The silicon oxide film 430 has an effect of electrically insulating the anode 424 formed on the silicon oxide film 430 and the cathode 423 formed below. On the anode 424, an organic film light emitting layer 425a, a charge generation layer 432, an organic film light emitting layer 425b, and a cathode 426 are sequentially stacked. The structure between the anode 424 and the cathode 426 is a two-layer multiphoton including an organic film light emitting layer 425a, a charge generation layer 432, and an organic film light emitting layer 425b. This is the light emitting part of the second layer.
The organic film light emitting layers 425a and 425b are made of the same material as the organic film light emitting layer 422, and emit light with the same characteristics when the same voltage is applied to each layer. A power source 435 is connected between the anode 424 and the cathode 426 to apply a voltage.

A silicon oxide film 431 is formed on the cathode 426. The silicon oxide film 431 has an effect of electrically insulating the anode 427 formed on the silicon oxide film 431 and the cathode 426 formed below. An organic film light emitting layer 428a, a charge generation layer 433a, an organic film light emission layer 428b, a charge generation layer 433b, an organic film light emission layer 428c, a charge generation layer 433c, an organic film light emission layer 428d, and a cathode 429 are sequentially stacked on the anode 427. In addition, a light emitting portion having a four-layer multiphoton structure is formed. This is the light emitting part of the third layer.
The organic film light emitting layers 428a to 428d are made of the same material as the organic film light emitting layer 422, and emit light with the same characteristics when the same voltage is applied to each layer. A power source 436 is connected between the anode 427 and the cathode 429 to apply a voltage.
In the present embodiment, the lower surface light extraction structure extracts light from the substrate 420 side. However, in the case of the upper surface light extraction structure that extracts light from the cathode 429 side, the cathode 429 is formed of a transparent electrode.

  Each of the organic film light emitting layers 422, 425a, 425b, and 428a to 428d emits light with a luminance proportional to the flowing current, and light is extracted from the glass substrate 420 side. Here, the same voltage is applied to each organic film light emitting layer 422, 425a, 425b, 428a to 428d in order to make the luminance output from each organic film light emitting layer 422, 425a, 425b, 428a to 428d the same. Thus, the power supply values of the power supplies 434, 435, and 436 are determined. As described above, the luminance weighting of the first to third light-emitting portions of each sub-pixel has a 1: 2: 4 relationship, and here, the power supply voltage applied to the power supplies 434, 435, and 436 is determined. The ratio is 1: 2: 4.

  Each light emitting unit (multiphoton layer) emits light with a predetermined luminance by switching between light emission and non-light emission (lighting and extinguishing) according to the binary value of power on / off. That is, the organic film light emitting layers 422, 425a, 425b, and 428a to 428d are digitally driven by power ON / OFF operations.

  Here, the display device (first sub-pixel 400d) of FIG. 22 is used by using a light emitting portion having a multi-photon structure including an organic film light emitting layer and a charge generation layer sandwiched between one anode and one cathode. If it represents, it will become a pixel structure shown in FIG. In FIG. 23, the same components as those in FIG. 22 are denoted by the same reference numerals.

In FIG. 23, a silicon oxide film 437, an anode 421, a light emitting portion 438, and a cathode 423 are sequentially stacked on a glass substrate 420, and a silicon oxide film 430, an anode 424, a light emitting portion 439, and a cathode 426 are further formed thereon. Laminated sequentially. Further thereon, a silicon oxide film 431, an anode 427, a light emitting portion 440, and a cathode 429 are sequentially laminated.
The light emitting unit 438 corresponds to the organic film light emitting layer 422, and the light emitting unit 439 includes an organic film light emitting layer 425a, a charge generation layer 432, and an organic film light emitting layer 425b, and has a two-layer multiphoton structure. The light emitting unit 440 includes an organic film light emitting layer 428a, a charge generation layer 433a, an organic film light emission layer 428b, a charge generation layer 433b, an organic film light emission layer 428c, a charge generation layer 433c, and an organic film light emission layer 428d. It is a photon structure.

In the third embodiment, if one light emitting part and an anode and a cathode (power supply part) sandwiching the light emitting part are collectively referred to as a unit element, the anode 421, the light emitting part 438, and the cathode 423 constitute one unit element. ing. Similarly, the anode 424, the light emitting portion 439, and the cathode 426 constitute one unit element, and the anode 427, the light emitting portion 440, and the cathode 429 constitute one unit element. Therefore, the organic EL display shown in FIGS. 22 and 23 has a light emitting element having a three-layer structure in which three unit elements are stacked in a direction perpendicular to the display surface of the display device.
On the glass substrate 420, as shown in FIG. 23, thin film transistors (TFTs) 444 to 446 which are active elements are formed and connected to anodes 421, 424 and 427, respectively. The TFTs 444 to 446 can be made of any active element such as p-Si (low temperature polysilicon), a-Si (amorphous silicon), or an organic transistor as long as the organic light emitting layer can be driven and controlled. It may be.

The TFTs 444 to 446 have a circuit function for turning on / off the power applied to the light emitting units 438 to 440. By turning on / off the power supply, the TFTs 444 to 446 are digitally driven so that the light emitting units 438 to 440 emit light or do not emit light as described above.
The silicon oxide film 437 is a film that prevents metal ions from moving from the glass substrate 420 to the anode 421. Although not shown, the cathode 423, the cathode 426, and the cathode 429 are common electrodes.

When light is extracted from the glass substrate 420 side, which is the lower side of the pixel, the cathode 429 is formed of a metal such as aluminum so that light does not leak from the cathode 429 side, which is the upper side of the pixel. As a result, the light emitted from the light emitting units 438 to 440 is radiated up and down, but the light emitted to the cathode 429 side is reflected by the cathode 429 and travels downward, so that it is extracted only from the glass substrate 420 side. Become.
Here, TFTs 444 to 446 are provided on the glass substrate 420, a bottom surface light extraction structure for extracting light from the glass substrate 420 side, a cathode 429 is formed of a transparent electrode, an anode 421 is formed of a metal such as aluminum, and the cathode Although there is an upper surface light extraction structure for extracting light from the 429 side, either structure may be used in this embodiment. Here, a plurality of TFTs may be connected to one organic film light emitting layer as will be described later with reference to FIG. Here, for convenience, one TFT 444 to 446 is shown. In the present embodiment, the TFTs 444 to 446 are referred to as element driving units (first driving units).

As shown in FIG. 23, when the light-emitting element has a three-layer structure, luminance weighting of each layer follows FIG. Luminance weighting is a numerical value relative to the emission luminance of each light emitting layer relative to a certain value.
Here, the light emitting unit 438 shown in FIG. 23 is the first layer, the light emitting unit 439 is the second layer, the light emitting unit 440 is the third layer, the luminance of the first layer is “1”, and the luminance of the second layer is “2”. ”, The third layer is set to luminance“ 4 ”. This is because, when the voltage applied to each organic film light emitting layer of the multi-photon structure is the same, the luminance output from each light emitting unit 438 to 440 is an integral multiple of the number of organic film light emitting layers that each light emitting unit has. By becoming. Here, the luminance of each light emitting unit represents the light emitting luminance when the power supply voltage is turned on, and each light emitting unit is digitally driven by turning on / off the power supply voltage.

  FIG. 3C shows an example of a luminance weighting method when the light emitting element has a five-layer structure. In the case of a five-layer structure, two unit elements are further stacked on the structure shown in FIG. 23, and the total number of light emitting portions is five. When the first layer, the second layer, the third layer, the fourth layer, and the fifth layer are sequentially arranged from the side closer to the light extraction side among the five light emitting units, as shown in FIG. When the luminance of the first layer is “1”, the second layer has the luminance “2”, the third layer has the luminance “4”, the fourth layer has the luminance “8”, and the fifth layer has the luminance “16”. Become.

  FIG. 4 shows a gradation expression method in the case of luminance weighting in FIG. 3A, as already described.

FIG. 24 is a driver configuration diagram of a display panel using pixels in the display device of the third embodiment. In FIG. 24, each pixel 456 includes sub-pixels 400d to 400f each having three layers of light emitting portions, and each sub-pixel corresponds to a pixel circuit described later with reference to FIG. The display panel selects a horizontal driver 457 for sending 9-bit digital data to a plurality of pixels 456 arranged in a two-dimensional matrix, a power supply circuit 458 for driving the pixels, and a vertical line And a vertical driver 459.
The plurality of pixels 456 are arranged in a two-dimensional matrix composed of rows Y arranged in the vertical direction and columns X arranged in the horizontal direction. In FIG. 24, as an example, a display panel of 6 columns of X1 to X6 is shown with 4 rows of Y1 to Y4. Although an actual display panel has more matrices than those shown in the figure, it is shown in this manner for convenience.
In the third embodiment, data drivers 471 to 476 are incorporated in the horizontal driver 457, power supply units 481 to 486 are incorporated in the power supply circuit 458, and gate drivers 491 to 494 are incorporated in the vertical driver 459, respectively. Here, the horizontal driver 457 and the vertical driver 459 are used as the second drive unit.

For example, when it is desired to scan the display line of the Y1 row which is the uppermost stage of the display panel shown in FIG. 24, the gate driver 491 of the vertical driver 459 turns on each pixel 456 of the Y1 row. The gate drivers 492 to 494 are turned off for the other display lines Y2 to Y4. At this time, one line of video data is output from the horizontal driver 457 and supplied to each pixel 456.
Next, when the gate driver 491 turns off each pixel 456 in the Y1 row, an image of one line in the Y1 row is displayed. Similarly, the vertical driver 459 is sequentially driven from the gate driver 492 in the Y2 row to the gate driver 494 in the Y4 row, and video data is output for each line from the horizontal driver 457. The pixel 456 can be scanned.

FIG. 25 shows a circuit diagram for driving the sub-pixels 400d to 400f constituting the pixel 456 of the third embodiment. In FIG. 25, 438, 439, and 440 indicated by the light emitting diode symbols correspond to the light emitting portions 438, 439, and 440 shown in FIG. In the third embodiment, a structure having three digital layers is shown, and luminance weighting of each organic film light emitting layer constituting the digital layer is “1”, “2”, “4” as in FIG. It is.
In addition, each one end (anode in the drawing) of the light emitting units 438 to 440 is connected to power sources 450 to 452 constituting the power source unit 481 through the respective sources and drains of the driving TFTs 444 to 446. The gates of the TFTs 444 to 446 are connected to the sources of the TFTs 441 to 443, and are connected to the power sources 450 to 452 via the capacitors 447 to 449.

The power sources 450 to 452 may be individual power sources or common power sources, and are set so that the light emitting units 438 to 440 emit light at a predetermined luminance with a predetermined weight. Further, the drains of the TFTs 441 to 443 are connected to data holding units 460 to 462 in the data driver 471, and the gates are commonly connected to the gate driver 491.
Here, the data driver 471, the power supply unit 481, and the gate driver 491 are shown. However, as shown in FIG. 24, the data drivers 472 to 476, the power supply units 482 to 486, and the gate drivers 492 to 494 have the same configuration. The data drivers 471 to 476, the power supply units 481 to 486, and the gate drivers 491 to 494 drive the pixels 456 in each row Y and each column X of the display panel.

Next, the operation of this drive circuit will be described. First, data 453 (3 bits) having a predetermined gradation to be displayed on the sub-pixel 400d is input to the data driver 471. The data 453 is preferably digital serial data or parallel data. As described above, the pixel 456 includes sub-pixels 400d to 400f. Therefore, since 3-bit data 453 is sent to each of the sub-pixels 400d to 400f, the data 453 sent to the pixel 456 is 9 bits as shown in FIG.
The data 453 input to the data driver 471 is used to cause the light emitting unit corresponding to the gray scale displayed on the display device among the light emitting units 438, 439, and 440 to emit light.

Each bit (1 or 0) of the data 453 is held in the data holding units 460 to 462, and the gate driver 491 applies a predetermined first potential to the gates of the gate transistors 441 to 443 to turn them on. . Display data output from the data driver 471 is written and stored in capacitors 447 to 449 for holding data through the drains and sources of the gate transistors 441 to 443.
Subsequently, the gate driver 491 applies a predetermined second potential to the gates of the gate transistors 441 to 443 to turn them off. When the gate transistors 441 to 443 are turned off, charges stored in the capacitors 447 to 449 are held. Charges held in the capacitors 447 to 449 are a potential difference between the power sources 450 to 452 and the output voltage of the data driver 471.

  Now, a case where an image of gradation “5” is displayed on the display device will be described as an example. As shown in FIG. 4, at the gradation “5”, it is necessary to turn on the light emitting portions 438 and 440 of the first layer and the third layer. The input data 453 is converted by the data driver 471 into a data string connected to the signal line of the corresponding light emitting layer. In this case, the data holding units 460 and 462 hold data for causing the light emitting units 438 and 440 to emit light.

  At this time, since the voltage for turning on the TFT 444 is applied to the capacitor 447 and the voltage for turning on the TFT 446 is also applied to the capacitor 449, the TFTs 447 and 449 are turned on. On the other hand, since the voltage for driving the TFT 445 is not applied to the capacitor 448, the TFT 445 is in an OFF state.

  Accordingly, since the TFTs 444 and 446 are on, current is supplied from the power sources 450 and 452 to the light emitting units 438 and 440 through the drains and sources of the TFTs 444 and 446, and the light emitting units 438 and 440 emit light. At this time, since the weights of the light emission luminances of the light emitting units 438 and 440 are “1” and “4”, the total gradation “5” is displayed on the display device.

In the digital driving method of the display panel according to the third embodiment, the driving TFTs 444 to 446 operate only on / off. Therefore, the circuit configuration is composed of capacitors 447 to 449 for storing data for turning on / off the driving TFTs 444 to 446 and gate TFTs 441 to 443 for holding the above data in these capacitors 447 to 449. A simple circuit configuration is sufficient.
In addition, since the driving TFTs 444 to 446 have an on / off switching operation, the driving TFTs 444 to 446 are saturated in a region where there is no influence of threshold variation due to element characteristics of TFTs that are active elements, which is a problem in a conventional organic EL display device. It can be operated. For this reason, problems such as display luminance unevenness and gradation shift in the display device surface can be reduced as much as possible.

  Furthermore, it can be operated in a saturation region where power loss due to TFT is small. For this reason, power consumption can be reduced as compared with a conventional display device.

  In the light emitting device of the third embodiment, since a multi-photon structure is employed for the light emitting portions 438 to 440, brightness higher than that of the conventional one can be obtained while reducing the current flowing through each organic film light emitting layer. Since the lifetime of the organic EL is inversely proportional to the square of the current value, the lifetime is longer than that of the conventional circuit configuration.

In addition, according to the present embodiment, in a display device in which one pixel is formed by a plurality of sub-pixels, the current-luminance characteristics are determined for the plurality of sub-pixels even when the light emission efficiency of the organic film light-emitting layer is greatly different for each sub-pixel. As a result, the drive current control of the pixel circuit and the driver can be facilitated by making them equal.
Furthermore, luminance unevenness in the display device can be eliminated, power loss can be reduced, and the lifetime is longer than that of a conventional display device in which a current amount corresponding to the light emission luminance is made to flow through one light emitting layer. A display device can be configured, and gradation can be easily obtained by digital driving.

  In addition, this embodiment is the same material as the first and second embodiments even if the organic film light emitting layers from the first layer to the third layer or from the first layer to the fifth layer are made of different materials. It may be configured with. For example, even if the material of the organic film light emitting layer is different, the total luminance can be obtained by changing the current value and the time length during which the current flows for each organic film light emitting layer as described above. ) To FIG. 3C may be set.

  Further, the luminance weighting of the organic film light emitting layer and the light emitting unit is desirably 2 n power weighting that can form a small number of light emitting layers, but is not limited thereto. Further, the luminance weighting for each layer does not need to be in ascending order from the layer near the side from which light is extracted as shown in FIGS. 3A to 3C, and is arbitrarily rearranged in descending order. May be.

Further, for example, in FIG. 4, the luminance weighting is different for each light emitting layer, but the present invention is not limited to this, and the luminance weighting of the first layer, the second layer, and the third layer is “1”, The same luminance weighting may be used such as “1” and “1”, and the luminance of the first layer, the second layer, and the third layer may be partially the same as “1”, “2”, and “2”. Luminance weighting may be used.
In addition, this embodiment can be realized not only by organic EL but also by inorganic EL, and can be realized not only by active drive but also by passive drive display devices.

It is a schematic diagram of the pixel in the display apparatus of 1st embodiment. It is a figure which shows the specific pixel structure of 1st embodiment. It is a figure which shows an example of the brightness | luminance weighting of each layer in each case of an organic film light emitting layer of 3 layer structure and 5 layer structure. It is a figure which shows an example of the gradation expression method in this invention display apparatus. It is a driver block diagram of the display panel in the display device of the first embodiment. It is a circuit diagram for driving the light emitting layer group which comprises the pixel of 1st embodiment. It is a figure which shows the table for demonstrating the gradation expression method in the display apparatus of 1st embodiment. It is a schematic diagram for carrying out a color display in the display apparatus of 2nd embodiment. It is a schematic diagram of the pixel in the display apparatus of 2nd embodiment. It is a figure which shows the specific pixel structure of 2nd embodiment. It is a driver block diagram of the display panel in the display apparatus of 2nd embodiment. It is a circuit diagram for driving the light emitting layer group which comprises the pixel of 2nd embodiment. It is a chromaticity diagram explaining the white display by the pixel of 2nd embodiment. It is a chromaticity diagram explaining the display of the arbitrary color F by the pixel of 2nd embodiment. It is a chromaticity diagram explaining the display of the arbitrary color F by the pixel of 2nd embodiment. It is a chromaticity diagram explaining the display of the arbitrary color F by the pixel of 2nd embodiment. It is a figure which shows the pixel of the multiphoton structure in the display apparatus of 3rd embodiment. It is a figure which shows the operation | movement principle of multiphoton. It is a schematic diagram for carrying out a color display in the display apparatus of 3rd embodiment. It is a figure which shows the electric current-luminance characteristic of the pixel in the display apparatus of 3rd embodiment. It is a figure which shows the layer structure at the time of driving the display apparatus of 3rd embodiment digitally. It is a figure which shows the pixel structure of 3rd embodiment. It is a figure which shows the pixel structure of 3rd embodiment by the light emission unit. It is a driver block diagram of the display panel in the display apparatus of 3rd embodiment. It is a circuit diagram for driving the light emitting layer group which comprises the pixel of 3rd embodiment. It is a conventional organic EL display schematic diagram. It is the figure which showed the conventional organic EL display concretely. It is a figure which shows an example of the driver structure in the conventional display apparatus. It is a circuit diagram of the conventional pixel.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass substrate 2, 5, 8 Anode 3, 6, 9 Organic film light emitting layer 4, 7, 10 Cathode 11, 12, 17 Silicon oxide film 13, 14, 15 DC power supply 16a, 16b, 16c Thin film transistor (TFT) (first 1 drive unit)
18, 19, 20 Organic EL light emitting layer 21, 22, 23 Capacitor 24, 25, 26 Driving TFT
27, 28, 29 Gate TFT
36 pixels 36R, 36G, 36B Light-emitting elements 37 Horizontal driver (second drive unit)
38 Power supply circuit 39 Vertical driver (second drive unit)

Claims (3)

One pixel is composed of a plurality of sub-pixels,
The sub-pixel is formed by laminating a plurality of unit elements in which an anode, a light-emitting portion having a multiphoton structure having an organic film light-emitting layer, and a cathode are sequentially laminated,
The organic film light-emitting layer is formed using a different material for each sub-pixel, and the number of layers of the organic film light-emitting layer is different for each sub-pixel,
The display device characterized in that light emission or non-light emission of the unit element is controlled for each unit element. The display device according to claim 1, further comprising a digital driving unit that drives the unit element to emit light or not. The display device according to claim 1, wherein gradation expression is performed by setting a weight of luminance for the plurality of unit elements in the sub-pixel.

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