JP4749439B2 - Method for manufacturing display device - Google Patents

Description

  The present invention relates to an EL (electroluminescence) display device formed by forming a semiconductor element (an element using a semiconductor thin film) on a substrate and an electronic device (electronic device) having the EL display device as a display display.

  In recent years, a technology for forming a TFT on a substrate has greatly advanced, and application development to an active matrix display device has been advanced. In particular, a TFT using a polysilicon film has higher field effect mobility (also referred to as mobility) than a conventional TFT using an amorphous silicon film, and thus can operate at high speed. For this reason, it is possible to control a pixel, which has been conventionally performed by a drive circuit outside the substrate, with a drive circuit formed on the same substrate as the pixel.

  Such an active matrix display device has various advantages such as a reduction in manufacturing cost, a reduction in size of the display device, an increase in yield, and a reduction in throughput by forming various circuits and elements on the same substrate. It is attracting attention as.

  Conventionally, the pixel structure of an active matrix EL display device is generally as shown in FIG. In FIG. 3, reference numeral 301 denotes a TFT functioning as a switching element (hereinafter referred to as a switching TFT), and 302 denotes a TFT functioning as an element (current control element) for controlling the current supplied to the EL element 303 (hereinafter referred to as current control). 304 is a capacitor (holding capacity). The switching TFT 301 is connected to a gate wiring 305 and a source wiring (data wiring) 306. The drain of the current control TFT 302 is connected to the EL element 303, and the source is connected to the power supply line 307.

  When the gate wiring 305 is selected, the gate of the switching TFT 301 is opened, the data signal of the source wiring 306 is accumulated in the capacitor 304, and the gate of the current control TFT 302 is opened. After the gate of the switching TFT 301 is closed, the gate of the current control TFT 302 is kept open by the electric charge accumulated in the capacitor 304, and the EL element 303 emits light during that time. The amount of light emitted from the EL element 303 varies depending on the amount of current flowing.

  At this time, the amount of current supplied to the EL element 303 is controlled by the gate voltage of the current control TFT 302. This is shown in FIG.

  FIG. 4A is a graph showing transistor characteristics of a current control TFT, and 401 is called an Id-Vg characteristic (or Id-Vg curve). Here, Id is a drain current, and Vg is a gate voltage. From this graph, the amount of current flowing for an arbitrary gate voltage can be known.

  Usually, in driving the EL element, the region indicated by the dotted line 402 of the Id-Vg characteristic is used. An enlarged view of the area surrounded by 402 is shown in FIG.

  In FIG. 4B, the shaded area is called a subthreshold area. Actually, it indicates a region having a gate voltage near or below the threshold voltage (Vth), and in this region, the drain current changes exponentially with respect to the change of the gate voltage. This region is used for current control by gate voltage.

  The data signal input to the pixel after the switching TFT 301 is opened is first stored in the capacitor 304, and the data signal directly becomes the gate voltage of the current control TFT 302. At this time, the drain current is determined one-to-one with respect to the gate voltage in accordance with the Id-Vg characteristics shown in FIG. That is, a predetermined current flows through the EL element 303 corresponding to the data signal, and the EL element 303 emits light with a light emission amount corresponding to the current amount.

  As described above, the light emission amount of the EL element is controlled by the data signal, and gradation display is performed by controlling the light emission amount. This method is a so-called analog gradation method, and gradation display is performed by changing the amplitude of a signal.

  However, the analog gray scale method has a drawback that it is very weak in TFT characteristic variation. For example, it is assumed that the switching TFT has an Id-Vg characteristic that is different from that of a switching TFT of an adjacent pixel that displays the same gradation (when the switching TFT is shifted to the plus or minus side as a whole).

  In this case, the drain current of each switching TFT differs depending on the degree of variation, and a different gate voltage is applied to the current control TFT of each pixel. That is, different currents flow for each EL element, resulting in different light emission amounts, and the same gradation display cannot be performed.

  Even if an equal gate voltage is applied to the current control TFT of each pixel, the same drain current cannot be output if the Id-Vg characteristics of the current control TFT vary. Further, as apparent from FIG. 4A, since a region in which the drain current changes exponentially with respect to the change in the gate voltage is used, it is equal if the Id-Vg characteristic is slightly shifted. Even when the gate voltage is applied, the amount of output current may vary greatly. In this case, the light emission amount of the EL element is greatly different between adjacent pixels.

  In practice, the switching TFT and the current control TFT have a synergistic effect of the variation between the two, so that the conditions are more severe. As described above, the analog gray scale method is extremely sensitive to variations in TFT characteristics, and this point has been an obstacle to the multicolor colorization of the conventional active matrix EL display device.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an active matrix EL display device capable of clear multi-tone color display. It is another object of the present invention to provide a high-performance electronic device (electronic device) including such an active matrix EL display device as a display for display.

  The present applicant has found that the problem of the analog gradation method is caused by variation in characteristics of the current control TFT flowing through the EL element, in particular, variation in on-resistance of the current control TFT. The on-resistance is a value obtained by dividing the drain voltage of the TFT by the drain current flowing at that time.

  That is, since the on-resistance of the current control TFT varies between TFTs, different currents (drain currents) flow even under the same conditions, and as a result, a problem that a desired gradation cannot be obtained occurs.

  Therefore, in the present invention, a resistor (R) is connected in series between the drain of the current control TFT and the EL element, and the amount of current supplied from the current control TFT to the EL element is controlled by the resistor. With the goal. For this purpose, it is necessary to provide a resistor having a resistance sufficiently higher than the on-resistance of the current control TFT. The resistance value may be selected from the range of 1 kΩ to 50 MΩ (preferably 10 kΩ to 10 MΩ, more preferably 50 kΩ to 1 MΩ).

  When the present invention is implemented, the amount of current flowing through the EL element is determined by the resistance value of the resistor (R), and the supplied current is always constant. That is, the conventional analog gray scale method for performing gray scale display by controlling the current value cannot be used. Therefore, the present invention is characterized by using a time-division gradation display (hereinafter referred to as a time-division gradation) in which the current control TFT is simply used as a switching element for supplying current.

  Specifically, time-division gradation display is performed as follows. Here, a case will be described in which full-color display of 256 gradations (16.77 million colors) is performed by the 8-bit digital driving method.

  First, one image frame is divided into eight subframes. One cycle in which data is input to all the pixels in the display area is called one frame. In a normal EL display, the oscillation frequency is 60 Hz, that is, 60 frames are formed per second. When the number of frames per second becomes less than this, flickering of images such as flicker starts to stand out visually. A frame obtained by dividing one frame into a plurality of frames is called a subframe.

  One subframe is divided into an address period (Ta) and a sustain period (Ts). The address period is the entire time required to input data to all the pixels in one subframe period, and the sustain period (also referred to as a lighting period) indicates a period during which the EL element emits light. ing. (Fig. 10)

  Here, the first subframe is referred to as SF1, and the second to eighth subframes are hereinafter referred to as SF2 to SF8. The address period (Ta) is constant from SF1 to SF8. On the other hand, the sustain periods (Ts) of SF1 to SF8 are Ts1 to Ts8, respectively.

  At this time, Ts1: Ts2: Ts3: Ts4: Ts5: Ts6: Ts7: Ts8 = 1: 1/2: 1/4: 1/8: 1/16: 1/32: 1/64: 1/128 Set the sustain period as follows. However, the order in which SF1 to SF8 appear may be any way. A desired gradation display among 256 gradations can be performed by combining the sustain periods.

  First, a voltage is not applied (not selected) to the counter electrode (the electrode on the side not connected to the TFT, which is normally connected to the TFT) of the EL element of the pixel, and the EL element does not emit light. Data signals are input to each pixel. This period is an address period. Then, when data is input to all the pixels and the address period ends, a voltage is applied (selected) to the counter electrode to cause the EL elements to emit light all at once. This period is the sustain period. In addition, the period during which light is emitted (pixels are lit) is any period from Ts1 to Ts8. Here, it is assumed that a predetermined pixel is lit for a period of Ts8.

Next, the address period starts again, and when a data signal is input to all pixels, the sustain period starts. At this time, any period from Ts1 to Ts7 is a sustain period.
Here, it is assumed that a predetermined pixel is lit during the period of Ts7.

  Hereinafter, it is assumed that the same operation is repeated for the remaining six subframes, Ts6, Ts5... Ts1 and the sustain period are sequentially set, and predetermined pixels are lit in each subframe.

  When eight subframes appear, one frame is finished. At this time, the gradation of the pixel is controlled by integrating the sustain period. For example, when Ts1 and Ts2 are selected, it is possible to express 75% of the luminance when all lamps are 100%, and when Ts3, Ts5, and Ts8 are selected, 16% of luminance can be expressed.

  In the above, the case of 256 gradations has been described, but other gradation display can be performed.

When displaying n-bit (n is an integer of 2 or more) gradation (2 ⁿ gradation), first, n subframes (SF1, SF2,. SF3... SF (n-1), SF (n)). As the number of gradations increases, the number of divisions per frame increases, and the drive circuit must be driven at a high frequency.

  Further, each of these n subframes is separated into an address period (Ta) and a sustain period (Ts). That is, the address period and the sustain period are selected by selecting whether to apply a voltage to the counter electrode common to all EL elements.

The sustain periods of the n subframes (where SF1, SF2, SF3... SF (n-1), SF (n) are the sustain periods corresponding to Ts1, Ts2, Ts3,... Ts (n-1), respectively. , Ts (n)) is expressed as Ts1: Ts2: Ts3: ...: Ts (n-1): Ts (n) = 2 ⁰ : 2 ^-1 : 2 ^-2 : ...: 2- ^(n-2) : Processing is performed so that 2- ^(n-1) is obtained.

  In this state, pixels are sequentially selected in any one subframe (strictly, the switching TFT of each pixel is selected), and a predetermined gate voltage (corresponding to the data signal) is applied to the gate electrode of the current control TFT. Join. At this time, the EL element of the pixel to which the data signal that causes the current control TFT to be turned on emits light only during the sustain period assigned to the subframe after the address period ends, that is, the predetermined pixel is turned on. To do.

  This operation is repeated in all n subframes, and the gradation of each pixel is controlled by integration of the sustain period. Accordingly, when attention is paid to an arbitrary pixel, the gradation of the pixel is controlled depending on how long the pixel is lit in each subframe (how much the sustain period has passed).

  As described above, in the active matrix EL display device, the resistor (R) is provided between the drain of the current control TFT and the EL element so that the current flowing through the EL element is always constant, The feature of the present invention is that the key is displayed. With this configuration, it is possible to prevent gradation failure due to variation in TFT characteristics.

  By implementing the present invention, an active matrix EL display device capable of clear multi-tone color display that is not affected by variation in TFT characteristics can be obtained. Specifically, a resistor is provided between the current control TFT provided in the pixel portion and the EL element, and the current value is determined by the resistance value of the resistor. Then, time-division gradation display is performed using a digital signal, and a high-definition image with good color reproducibility without gradation defects due to characteristic variations of the current control TFT is obtained.

  In addition, the TFT itself formed on the substrate is provided with a TFT having an optimum structure in accordance with the performance required for each circuit or element, thereby realizing a highly reliable active matrix EL display device.

  By providing such an active matrix EL display device as a display display, it is possible to produce a high-performance electronic device with high image quality and high reliability.

  First, FIG. 1A shows a circuit configuration of an active matrix EL display device of the present invention. In the active matrix EL display device of FIG. 1A, a pixel portion 101, a data signal side driver circuit 102 and a gate signal side driver circuit 103 which are arranged around the pixel portion are formed by TFTs formed on a substrate. The Note that both the data side signal side driver circuit and the gate signal side driver circuit may be provided in pairs with the pixel portion interposed therebetween.

  The data signal side driving circuit 102 basically includes a shift register 102a, a latch (A) 102b, and a latch (B) 102c. In addition, a clock pulse (CK) and a start pulse (SP) are input to the shift register 102a, a digital data signal (Digital Data Signals) is input to the latch (A) 102b, and a latch signal is input to the latch (B) 102c. (Latch Signals) is input.

  In the present invention, the data signal input to the pixel portion is a digital signal, and unlike the liquid crystal display device, it is not a voltage gradation display. Therefore, the digital data signal having information “0” or “1” is directly input to the pixel portion. Is entered.

  A plurality of pixels 104 are arranged in a matrix in the pixel portion 101. An enlarged view of the pixel 104 is shown in FIG. In FIG. 1B, reference numeral 105 denotes a switching TFT, which is connected to a gate wiring 106 for inputting a gate signal and a data wiring (also referred to as a source wiring) 107 for inputting a data signal.

  Reference numeral 108 denotes a current control TFT whose gate is connected to the drain of the switching TFT 105. The drain of the current control TFT 108 is connected to the EL element 110 via the resistor 109, and the source is connected to the power supply line 111. The EL element 110 includes an anode (pixel electrode) connected to the current control TFT 108 and a cathode (counter electrode) provided opposite to the anode across the EL layer. The cathode is connected to a predetermined power source 112. ing.

  Note that the resistor 109 may be any element that has a resistance value sufficiently larger than the on-resistance of the current control TFT 108, and thus the structure and the like are not limited. The use of a semiconductor layer having a high resistance value is preferable because it can be easily formed.

  Further, when the switching TFT 105 is in a non-selected state (off state), a capacitor 113 is provided to hold the gate voltage of the current control TFT 108. The capacitor 113 is connected to the drain of the switching TFT 105 and the power supply line 111.

  The digital data signal input to the pixel portion as described above is formed by the time division gradation data signal generation circuit 114. In this circuit, a video signal (a signal including image information) composed of an analog signal or a digital signal is converted into a digital data signal for performing time-division gradation, and a timing pulse necessary for performing time-division gradation display. And the like.

Typically, the time division gradation data signal generation circuit 114 includes means for dividing one frame into a plurality of subframes corresponding to gradations of n bits (n is an integer of 2 or more), and the plurality of subframes. Means for selecting an address period and a sustain period in a frame, and the sustain period are set to Ts1: Ts2: Ts3:...: Ts (n-1): Ts (n) = 2 ⁰ : 2 ⁻¹ : 2 ^−2:. 2 ^{− (n−2)} : means for setting to be 2 ^{− (n−1)} .

  The time-division gradation data signal generation circuit 114 may be provided outside the EL display device of the present invention. In that case, the digital data signal formed there is input to the EL display device of the present invention. In this case, an electronic device having the EL display device of the present invention as a display includes the EL display device of the present invention and a time-division gradation data signal generation circuit as separate components.

  Further, the time division gradation data signal generation circuit 114 may be mounted on the EL display device of the present invention in the form of an IC chip or the like. In that case, a digital data signal formed by the IC chip is input to the EL display device of the present invention. In this case, an electronic device having the EL display device of the present invention as a display includes the EL display device of the present invention on which an IC chip including a time division gradation data signal generation circuit is mounted as a component.

  Finally, the time division gradation data signal generation circuit 114 can be formed with TFTs on the same substrate as the pixel portion 104, the data signal side drive circuit 102, and the gate signal side drive circuit. In this case, if a video signal including image information is input to the EL display device, all can be processed on the substrate. Of course, it is desirable that the time-division gradation data signal generation circuit in this case is formed of a TFT having a polysilicon film used in the present invention as an active layer. In this case, in the electronic device having the EL display device of the present invention as a display, the time-division gradation data signal generation circuit is built in the EL display device itself, and the electronic device can be miniaturized. .

  Next, an outline of a cross-sectional structure of the active matrix EL display device of the present invention is shown in FIG.

In FIG. 2, 11 is a substrate, 12 is a base insulating film (hereinafter referred to as a base film).
It is. As the substrate 11, a light-transmitting substrate, typically a glass substrate, a quartz substrate, a glass ceramic substrate, or a crystallized glass substrate can be used. However, it must withstand the maximum processing temperature during the fabrication process.

  The base film 12 is particularly effective when a substrate containing mobile ions or a conductive substrate is used, but it need not be provided on the quartz substrate. As the base film 12, an insulating film containing silicon may be used. Note that in this specification, an “insulating film containing silicon” specifically refers to silicon such as a silicon oxide film, a silicon nitride film, or a silicon nitride oxide film (SiOxNy: x and y are each represented by an arbitrary integer). On the other hand, it refers to an insulating film containing oxygen or nitrogen at a predetermined ratio.

  Reference numeral 201 denotes a switching TFT, and 202 denotes a current control TFT, both of which are formed by n-channel TFTs. Since the field effect mobility of the n-channel TFT is larger than that of the p-channel TFT, the operation speed is high and a large current is likely to flow. Even when the same amount of current flows, the n-channel TFT can be made smaller in TFT size. For this reason, it is preferable to use an n-channel TFT as a current control TFT because the effective light emitting area of the image display portion is widened.

  However, in the present invention, it is not necessary to limit the switching TFT and the current control TFT to n-channel TFTs, and it is also possible to use p-channel TFTs for both or one of them.

  The switching TFT 201 includes an active layer including a source region 13, a drain region 14, LDD regions 15a to 15d, an isolation region 16 and channel forming regions 17a and 17b, a gate insulating film 18, gate electrodes 19a and 19b, and a first interlayer insulating film. 20, a source wiring 21 and a drain wiring 22 are formed. Note that the gate insulating film 18 or the first interlayer insulating film 20 may be common to all TFTs on the substrate, or may be different depending on a circuit or an element.

  Further, the switching TFT 201 shown in FIG. 2 has a so-called double gate structure in which the gate electrodes 19a and 19b are electrically connected. Needless to say, not only a double gate structure but also a so-called multi-gate structure (a structure including an active layer having two or more channel formation regions connected in series) such as a triple gate structure may be used.

  The multi-gate structure is extremely effective in reducing off-state current. If the off-state current of the switching TFT is made sufficiently low, the capacitance necessary for the capacitor 112 shown in FIG. 1B can be reduced accordingly. That is, since the area occupied by the capacitor 112 can be reduced, the multi-gate structure is also effective in increasing the effective light emitting area of the EL element 109.

  Further, in the switching TFT 201, the LDD regions 15a to 15d are provided so as not to overlap the gate electrodes 17a and 17b with the gate insulating film 18 interposed therebetween. Such a structure is very effective in reducing off current. The length (width) of the LDD regions 15a to 15d may be 0.5 to 3.5 μm, typically 2.0 to 2.5 μm.

  Note that it is more preferable to provide an offset region (a region including a semiconductor layer having the same composition as the channel formation region and to which no gate voltage is applied) between the channel formation region and the LDD region in order to reduce off-state current. In the case of a multi-gate structure having two or more gate electrodes, an isolation region 16 (a region to which the same impurity element is added at the same concentration as the source region or the drain region) provided between the channel formation regions is provided. It is effective for reducing the off current.

  Next, the current control TFT 202 includes an active layer including a source region 26, a drain region 27, an LDD region 28, and a channel formation region 29, a gate insulating film 18, a gate electrode 30, a first interlayer insulating film 20, a source wiring 31, and The drain wiring 32 is formed. However, in the case of FIG. 2, a resistor 33 and a connection region 34 are provided between the drain region 27 and the drain wiring 32.

  The resistor 33 corresponds to the resistor 109 of FIG. 1B, and the connection region 34 is a high-concentration impurity region (impurity having the same composition as the drain region 27) for electrically connecting the resistor 33 and the drain wiring 32. Area). Here, the active layer of the current control TFT 202 is extended and the TFT and the resistor 33 are electrically connected, but the electrical connection method is not necessarily limited to this structure.

  A thin film indicated by 55 is a thin film used as a doping mask (hereinafter referred to as a mask film) when the resistor 33 is formed, and is formed simultaneously with the gate electrode 30 here. In the case of FIG. 2, the mask film 55 is a conductive film made of the same material as the gate electrode 30 but may be electrically isolated.

  In the case of the structure of FIG. 2, the resistor 33 is formed of an impurity region having the same composition as the LDD region 28. The resistance value is determined by the length and cross-sectional area of the resistor. Although it is possible to form an intrinsic semiconductor layer to which no impurities are added, it is difficult to control the resistance value, so it is preferable to control by adding impurities.

  When the resistor 33 is formed of a semiconductor layer as described above, the resistance value may change when light emitted from the EL element hits the resistor. Therefore, providing a mask film having a light shielding property as shown in FIG. 2 and using it as a light shielding film is effective in preventing a change in resistance value.

Further, as shown in FIG. 1B, the drain of the switching TFT is connected to the gate of the current control TFT. Specifically, the gate electrode 30 of the current control TFT 202 is electrically connected to the drain region 14 of the switching TFT 201 via the drain wiring (also referred to as connection wiring) 22. The gate electrode 30 has a single gate structure, but may have a multi-gate structure.
Further, the source wiring 31 is connected to the power supply line 110 in FIG.

  The current control TFT 202 is an element for controlling the amount of current injected into the EL element, and a relatively large amount of current flows. Therefore, it is preferable to design the channel width (W) to be larger than the channel width of the switching TFT. Further, it is preferable to design the channel length (L) to be long so that an excessive current does not flow through the current control TFT 202. Desirably, it is set to 0.5 to 2 μA (preferably 1 to 1.5 μA) per pixel.

  Based on the above, as shown in FIG. 9, the channel length of the switching TFT is L1 (where L1 = L1a + L1b), the channel width is W1, the channel length of the current control TFT is L2, and the channel width is W2. At this time, W1 is preferably 0.1 to 5 μm (typically 1 to 3 μm), and W2 is preferably 0.5 to 30 μm (typically 2 to 10 μm). L1 is preferably 0.2 to 18 μm (typically 2 to 15 μm), and L2 is preferably 0.1 to 50 μm (typically 1 to 20 μm). However, it is not necessary to limit to the above numerical values. In FIG. 9, L3 is the length of the resistor, and W3 is the width of the resistor.

  In the EL display device shown in FIG. 2, in the current control TFT 202, an LDD region 28 is provided between the drain region 27 and the channel formation region 29, and the LDD region 28 is interposed via the gate insulating film 18. It is also characterized in that it has a region that overlaps with the gate electrode 30 and a region that does not overlap.

  Since the current control TFT 202 allows a relatively large amount of current to flow to cause the EL element 203 to emit light, it is desirable to take measures against deterioration due to hot carrier injection. In addition, when displaying black, the current control TFT 202 is turned off. If the off-current is high at that time, a clear black display cannot be performed, and the contrast is lowered. Therefore, it is necessary to suppress the off current.

  Regarding deterioration due to hot carrier injection, it is known that a structure in which an LDD region overlaps a gate electrode is very effective. However, since the off-current increases when the entire LDD region is overlapped, the applicant of the present invention has a new structure in which an LDD region that does not overlap with the gate electrode is provided in series in addition to the above-described structure. Solves current countermeasures at the same time.

  At this time, the length of the LDD region overlapping with the gate electrode may be 0.1 to 3 μm (preferably 0.3 to 1.5 μm). If it is too long, the parasitic capacitance is increased, and if it is too short, the effect of preventing hot carriers is weakened. The length of the LDD region that does not overlap with the gate electrode may be 1.0 to 3.5 μm (preferably 1.5 to 2.0 μm). If it is too long, it will not be possible to pass a sufficient current, and if it is too short, the effect of reducing off current will be weak.

  Further, in the above structure, a parasitic capacitance is formed in a region where the gate electrode and the LDD region overlap with each other. Therefore, it is preferable not to provide between the source region 26 and the channel formation region 29. Since the current control TFT always has the same direction of carrier (electrons) flow, it is sufficient to provide an LDD region only on the drain region side.

  Further, from the viewpoint of increasing the amount of current that can be passed, the thickness of the active layer (especially the channel formation region) of the current control TFT 202 may be increased (preferably 50 to 100 nm, more preferably 60 to 80 nm). It is valid. On the contrary, in the case of the switching TFT 201, from the viewpoint of reducing the off-state current, the thickness of the active layer (especially the channel formation region) may be reduced (preferably 20 to 50 nm, more preferably 25 to 40 nm). It is valid.

  Although the above has described the structure of the TFT provided in the pixel, a driving circuit is also formed at this time. FIG. 2 shows a CMOS circuit as a basic unit for forming a driving circuit.

  In FIG. 2, a TFT having a structure for reducing hot carrier injection while reducing the operating speed as much as possible is used as the n-channel TFT 204 of the CMOS circuit. Note that the driving circuit here refers to the data signal driving circuit 102 and the gate signal driving circuit 103 shown in FIG. Of course, other logic circuits (level shifter, A / D converter, signal dividing circuit, etc.) can be formed.

  The active layer of the n-channel type 205 includes a source region 35, a drain region 36, an LDD region 37, and a channel formation region 38, and the LDD region 37 overlaps the gate electrode 39 with the gate insulating film 18 interposed therebetween.

  The reason why the LDD region is formed only on the drain region side is to prevent the operation speed from being lowered. In addition, the n-channel TFT 205 does not need to care about the off-current value, and it is better to focus on the operation speed than that. Therefore, it is desirable that the LDD region 37 is completely overlapped with the gate electrode and the resistance component is reduced as much as possible. That is, it is better to eliminate the so-called offset.

  In addition, since the p-channel TFT 205 of the CMOS circuit is hardly concerned with deterioration due to hot carrier injection, it is not particularly necessary to provide an LDD region. Therefore, the active layer includes a source region 40, a drain region 41, and a channel formation region 42, on which the gate insulating film 18 and the gate electrode 43 are provided. Of course, it is also possible to provide an LDD region in the same manner as the n-channel TFT 204 and take measures against hot carriers.

  Further, the n-channel TFT 204 and the p-channel TFT 205 are covered with the first interlayer insulating film 20, respectively, and source wirings 44 and 45 are formed. Further, the two are electrically connected by the drain wiring 46.

  Next, 47 is a first passivation film, and the film thickness may be 10 nm to 1 μm (preferably 200 to 500 nm). As a material, an insulating film containing silicon (in particular, a silicon nitride oxide film or a silicon nitride film is preferable) can be used. The passivation film 47 has a role of protecting the formed TFT from alkali metal and moisture. The EL layer finally provided above the TFT contains an alkali metal such as sodium. That is, the first passivation film 47 also functions as a protective layer that prevents these alkali metals (movable ions) from entering the TFT side.

Reference numeral 48 denotes a second interlayer insulating film having a function as a flattening film for flattening a step formed by the TFT. The second interlayer insulating film 48 is preferably an organic resin film, such as polyimide, polyamide, acrylic, BCB (benzocyclobutene).
Etc. may be used. These organic resin films have an advantage that they can easily form a good flat surface and have a low relative dielectric constant. Since the EL layer is very sensitive to unevenness, it is desirable that the step due to the TFT is almost absorbed by the second interlayer insulating film. Further, in order to reduce the parasitic capacitance formed between the gate wiring or the data wiring and the cathode of the EL element, it is desirable to provide a thick material having a low relative dielectric constant. Therefore, the film thickness is preferably 0.5 to 5 μm (preferably 1.5 to 2.5 μm).

  Reference numeral 49 denotes a pixel electrode (EL element anode) made of a transparent conductive film, which is formed after a contact hole (opening) is formed in the second interlayer insulating film 48 and the first passivation film 47. Are formed so as to be connected to the drain wiring 32 of the current control TFT 202. If the pixel electrode 49 and the drain region 27 are not directly connected as shown in FIG. 2, it is possible to prevent the alkali metal of the EL layer from entering the active layer via the pixel electrode.

  A third interlayer insulating film 50 made of a silicon oxide film, a silicon nitride oxide film, or an organic resin film is provided on the pixel electrode 49 to a thickness of 0.3 to 1 μm. The third interlayer insulating film 50 is etched so that an opening is formed on the pixel electrode 49 by etching, and the edge of the opening is tapered. The taper angle may be 10 to 60 ° (preferably 30 to 50 °).

  An EL layer 51 is provided on the third interlayer insulating film 50. The EL layer 51 is used in a single layer or a laminated structure, but the light emission efficiency is better when it is used in a laminated structure. In general, the hole injection layer / hole transport layer / light emitting layer / electron transport layer are formed on the pixel electrode in this order, but the hole transport layer / light emitting layer / electron transport layer, or hole injection layer / positive layer are formed. A structure such as a hole transport layer / a light emitting layer / an electron transport layer / an electron injection layer may be used. In the present invention, any known structure may be used, and the EL layer may be doped with a fluorescent dye or the like.

  As the organic EL material, for example, materials disclosed in the following US patents or publications can be used. U.S. Patent No. 4,356,429, U.S. Patent No. 4,539,507, U.S. Patent No. 4,720,432, U.S. Patent No. 4,769,292, U.S. Patent No. 4,885,211, U.S. Patent No. 4,950,950, U.S. Patent No. 5,059,861, U.S. Patent No. 5,047,687, U.S. Patent No. 5,073,446, U.S. Patent No. 5,059,862, US Pat. No. 5,061,617, US Pat. No. 5,151,629, US Pat. No. 5,294,869, US Pat. No. 5,294,870, JP-A-10-189525, JP-A-10-189525 JP-A-8-241048, JP-A-8-78159.

The EL display device can be roughly divided into four color display methods, a method of forming three types of EL elements corresponding to R (red), G (green), and B (blue), a white light emitting EL element, and A combination of color filters, a combination of blue or blue-green light emitting elements and phosphors (fluorescent color conversion layer: CCM), cathode (counter electrode)
There is a method in which EL elements corresponding to RGB are stacked using transparent electrodes.

  The structure of FIG. 2 is an example in the case of using a method of forming three types of EL elements corresponding to RGB. Although only one pixel is shown in FIG. 2, pixels having the same structure are formed corresponding to the respective colors of red, green, and blue, so that color display can be performed.

  The present invention can be implemented regardless of the light emission method, and all the above four methods can be used in the present invention. However, since phosphors have a slower response speed than EL and afterglow can be a problem, a method that does not use phosphors is desirable. In addition, it can be said that it is desirable not to use a color filter which causes a decrease in the emission luminance as much as possible.

  On the EL layer 51, a cathode 52 of an EL element is provided. As the cathode 52, a material containing magnesium (Mg), lithium (Li), or calcium (Ca) having a small work function is used. An electrode made of MgAg (a material in which Mg and Ag are mixed at Mg: Ag = 10: 1) is preferably used. Other examples include MgAgAl electrodes, LiAl electrodes, and LiFAl electrodes.

  The cathode 52 is desirably formed continuously after the EL layer 51 is formed without being released to the atmosphere. This is because the interface state between the cathode 52 and the EL layer 51 greatly affects the luminous efficiency of the EL element. Note that in this specification, a light-emitting element formed using a pixel electrode (anode), an EL layer, and a cathode is referred to as an EL element.

  A laminate including the EL layer 51 and the cathode 52 needs to be formed individually for each pixel. However, since the EL layer 51 is extremely sensitive to moisture, a normal photolithography technique cannot be used. Accordingly, it is preferable to use a physical mask material such as a metal mask and selectively form the film by a vapor phase method such as a vacuum deposition method, a sputtering method, or a plasma CVD method.

  In addition, as a method for selectively forming the EL layer, an ink jet method, a screen printing method, a spin coating method, or the like can be used. Can be said to be preferable.

  Reference numeral 53 denotes a protective electrode, which protects the cathode 52 from external moisture and the like, and at the same time connects the cathode 52 of each pixel. As the protective electrode 53, it is preferable to use a low-resistance material containing aluminum (Al), copper (Cu), or silver (Ag). The protective electrode 53 can also be expected to have a heat dissipation effect that alleviates the heat generation of the EL layer. It is also effective to form the protective layer 53 continuously after the EL layer 51 and the cathode 52 are formed without being released to the atmosphere.

  Reference numeral 54 denotes a second passivation film, and the film thickness may be 10 nm to 1 μm (preferably 200 to 500 nm). The purpose of providing the second passivation film 54 is mainly to protect the EL layer 51 from moisture, but it is also effective to have a heat dissipation effect. However, since the EL layer is vulnerable to heat as described above, it is desirable to form the film at as low a temperature as possible (preferably in a temperature range from room temperature to 120 ° C.). Therefore, the plasma CVD method, the sputtering method, the vacuum deposition method, the ion plating method, or the solution coating method (spin coating method) can be said to be a preferable film forming method.

  Needless to say, all the TFTs shown in FIG. 2 have the polysilicon film used in the present invention as an active layer.

  The gist of the present invention is that a TFT having a high operation speed is formed by using a polysilicon film having a high crystal grain boundary continuity and a unique crystal structure with a uniform crystal orientation as an active layer of the TFT. It is possible to perform time-division gray scale display of an active matrix EL display device integrated with a drive circuit. Therefore, it is not limited to the structure of the EL display device of FIG. 2, and the structure of FIG. 2 is only one preferred form for carrying out the present invention.

  Since the TFT using the polysilicon film exhibits a high operation speed, deterioration such as hot carrier injection is likely to occur. Therefore, as shown in FIG. 2, it is highly reliable to form TFTs having different structures (a switching TFT having a sufficiently low off-current and a current control TFT resistant to hot carrier injection) having different structures depending on functions in the pixel. And an EL display device capable of displaying a good image (high operation performance) is very effective.

  An embodiment of the present invention will be described with reference to FIGS. Here, a method for simultaneously manufacturing a TFT of a pixel portion and a driver circuit portion provided around the pixel portion will be described. However, in order to simplify the explanation, a CMOS circuit which is a basic unit with respect to the drive circuit is illustrated.

  First, as shown in FIG. 5A, a substrate 501 having a base film (not shown) provided on the surface is prepared. In this embodiment, a silicon nitride oxide film having a thickness of 100 nm and a silicon nitride oxide film having a thickness of 200 nm are stacked on the crystallized glass as a base film. At this time, the nitrogen concentration in contact with the crystallized glass substrate is preferably 10 to 25 wt%. Of course, the element may be formed directly on the quartz substrate without providing a base film.

  Next, an amorphous silicon film 502 having a thickness of 45 nm is formed on the substrate 501 by a known film formation method. Note that the semiconductor film is not limited to an amorphous silicon film, and any semiconductor film including an amorphous structure (including a microcrystalline semiconductor film) may be used. Further, a compound semiconductor film including an amorphous structure such as an amorphous silicon germanium film may be used.

  The process from here to FIG. 5 (C) can be completely referred to Japanese Patent Laid-Open No. 10-247735 by the present applicant. This publication discloses a technique related to a method for crystallizing a semiconductor film using an element such as Ni as a catalyst.

  First, a protective film 504 having openings 503a and 503b is formed. In this embodiment, a 150 nm thick silicon oxide film is used. Then, a layer (Ni-containing layer) 505 containing nickel (Ni) is formed on the protective film 504 by spin coating. Regarding the formation of this Ni-containing layer, the above publication may be referred to.

  Next, as shown in FIG. 5B, a heat treatment is performed at 570 ° C. for 14 hours in an inert atmosphere to crystallize the amorphous silicon film 502. At this time, with the Ni contact regions (hereinafter referred to as Ni-added regions) 506a and 506b as the starting point, the crystallization proceeds substantially parallel to the substrate, and the polysilicon film 507 having a crystal structure in which rod-like crystals are gathered and arranged is formed. It is formed. At this time, it is known that diffraction spots corresponding to the {110} orientation as shown in FIG. 12A are observed in the electron diffraction photograph.

Next, as shown in FIG. 5C, an element belonging to Group 15 (preferably phosphorus) is added to the Ni-added regions 506a and 506b using the protective film 505 as a mask as it is.
Thus, regions to which phosphorus is added at a high concentration (hereinafter referred to as phosphorus added regions) 508a and 508b are formed.

  Next, as shown in FIG. 5C, heat treatment is performed in an inert atmosphere at 600 ° C. for 12 hours. By this heat treatment, Ni existing in the polysilicon film 507 moves, and finally, almost all of the Ni is captured in the phosphorus-added regions 508a and 508b as indicated by arrows. This is considered to be a phenomenon due to the gettering effect of the metal element (Ni in this embodiment) by phosphorus.

By this step, the concentration of Ni remaining in the polysilicon film 509 is reduced to at least 2 × 10 ¹⁷ atoms / cm ³ as measured by SIMS (mass secondary ion analysis). Ni is a lifetime killer for semiconductors, but if it is reduced to this level, TFT characteristics are not adversely affected. Further, since this concentration is almost the limit of measurement of the current SIMS analysis, it is considered that the concentration is actually lower (2 × 10 ¹⁷ atoms / cm ³ or less).

  Thus, a polysilicon film 509 crystallized using a catalyst and reduced to a level at which the catalyst does not hinder the operation of the TFT is obtained. Thereafter, active layers 510 to 513 using only the polysilicon film 509 are formed by a patterning process. Note that a part of the active layer 513 includes a semiconductor layer to be a resistor later. At this time, a marker for performing mask alignment in later patterning may be formed using the polysilicon film. (Fig. 5 (D))

  Next, as shown in FIG. 5E, a silicon nitride oxide film having a thickness of 50 nm is formed by a plasma CVD method, and then a heat treatment is performed in an oxidizing atmosphere at 950 ° C. for 1 hour to perform a thermal oxidation step. . Note that the oxidizing atmosphere may be an oxygen atmosphere or an oxygen atmosphere to which a halogen element is added.

  In this thermal oxidation process, oxidation proceeds at the interface between the active layer and the silicon nitride oxide film, and the polysilicon film having a thickness of about 15 nm is oxidized to form a silicon oxide film having a thickness of about 30 nm. That is, an 80 nm-thick gate insulating film 514 formed by stacking a 30 nm-thick silicon oxide film and a 50 nm-thick silicon nitride oxide film is formed. The film thickness of the active layers 510 to 513 is 30 nm by this thermal oxidation process.

  Next, as shown in FIG. 6A, a resist mask 515 is formed, and an impurity element imparting p-type (hereinafter referred to as a p-type impurity element) is added through the gate insulating film 514. As the p-type impurity element, typically, an element belonging to Group 13, typically boron or gallium can be used. This step (referred to as channel doping step) is a step for controlling the threshold voltage of the TFT.

In this embodiment, boron is added by an ion doping method in which diborane (B ₂ H ₆ ) is plasma-excited without mass separation. Of course, an ion implantation method for performing mass separation may be used. By this step, impurity regions 516 to 518 containing boron at a concentration of 1 × 10 ¹⁵ to 1 × 10 ¹⁸ atoms / cm ³ (typically 5 × 10 ^{16 to} 5 × 10 ¹⁷ atoms / cm ³ ) are formed. .

Next, as illustrated in FIG. 6B, resist masks 519 a and 519 b are formed, and an impurity element imparting n-type (hereinafter referred to as an n-type impurity element) is added through the gate insulating film 514. Note that as the n-type impurity element, an element typically belonging to Group 15, typically phosphorus or arsenic can be used. In this embodiment, phosphorus is added at a concentration of 1 × 10 ¹⁸ atoms / cm ³ using a plasma doping method in which phosphine (PH ₃ ) is plasma-excited without mass separation. Of course, an ion implantation method for performing mass separation may be used.

In the n-type impurity regions 520 and 521 formed by this step, an n-type impurity element contains 2 × 10 ^{16 to} 5 × 10 ¹⁹ atoms / cm ³ (typically 5 × 10 ^{17 to} 5 × 10 ¹⁸ atoms / cm Adjust the dose so that it is contained at a concentration of cm ³ ).

  Next, as shown in FIG. 6C, an activation process of the added n-type impurity element and p-type impurity element is performed. Although there is no need to limit the activation means, since the gate insulating film 514 is provided, furnace annealing using an electric furnace is preferable. In addition, since there is a possibility that the active layer / gate insulating film interface in the portion to be a channel formation region is damaged in the step of FIG. 6A, it is preferable to perform the heat treatment at as high a temperature as possible.

  In this embodiment, crystallized glass with high heat resistance is used, so the activation process is performed by furnace annealing at 800 ° C. for 1 hour. Note that thermal oxidation may be performed with the treatment atmosphere being an oxidizing atmosphere, or heat treatment may be performed in an inert atmosphere.

By this step, the end portions of the n-type impurity regions 520 and 521, that is, the regions where the n-type impurity element existing around the n-type impurity regions 520 and 521 is not added (formed in the step of FIG. 6A). The boundary (junction) with the p-type impurity region becomes clear.
This means that when the TFT is later completed, the LDD region and the channel formation region can form a very good junction.

  Next, a conductive film having a thickness of 200 to 400 nm is formed and patterned to form a mask film 526 for forming gate electrodes 522 to 525 and a resistor. The channel length of each TFT is determined by the line width of the gate electrodes 522 to 525. Further, the resistance value of the resistor is determined by the line width of the mask film 526.

  Note that although the gate electrode may be formed of a single-layer conductive film, it is preferably a stacked film of two layers or three layers as necessary. A known conductive film can be used as the material of the gate electrode. Specifically, a film made of an element selected from tantalum (Ta), titanium (Ti), molybdenum (Mo), tungsten (W), chromium (Cr), and silicon (Si), or a nitride of the element. A film (typically a tantalum nitride film, a tungsten nitride film, a titanium nitride film), an alloy film (typically a Mo—W alloy or a Mo—Ta alloy), or a silicide film of the element. (Typically, a tungsten silicide film or a titanium silicide film) can be used. Of course, it may be used as a single layer or may be laminated.

  In this embodiment, a stacked film including a tungsten nitride (WN) film having a thickness of 50 nm and a tungsten (W) film having a thickness of 350 nm is used. This may be formed by sputtering. Further, when an inert gas such as xenon (Xe) or neon (Ne) is added as a sputtering gas, peeling of the film due to stress can be prevented.

  At this time, the gate electrodes 523 and 525 are formed so as to overlap part of the n-type impurity regions 520 and 521 with the gate insulating film 514 interposed therebetween. This overlapped portion later becomes an LDD region overlapping with the gate electrode. The gate electrodes 524a and 524b appear to be two in the cross section, but are actually electrically connected.

Next, as shown in FIG. 7A, an n-type impurity element (phosphorus in this embodiment) is added in a self-aligning manner using the gate electrodes 522 to 525 and the mask film 526 as a mask. The impurity regions 527 to 533 thus formed are adjusted so that phosphorus is added at a concentration of 1/2 to 1/10 (typically 1/3 to 1/4) of the n-type impurity regions 520 and 521. To do. Specifically, a concentration of 1 × 10 ^{16 to} 5 × 10 ¹⁸ atoms / cm ³ (typically 3 × 10 ^{17 to} 3 × 10 ¹⁸ atoms / cm ³ ) is preferable.

Next, as shown in FIG. 7B, resist masks 534a to 534d are formed so as to cover the gate electrodes and the like, and an n-type impurity element (phosphorus in this embodiment) is added to contain phosphorus at a high concentration. Impurity regions 535 to 542 are formed. Here again, ion doping using phosphine (PH ₃ ) is performed, and the concentration of phosphorus in this region is 1 × 10 ²⁰ to 1 × 10 ²¹ atoms / cm ³ (typically 2 × 10 ^{20 to} 5 × 10 ^21. atoms / cm ³ ).

  Although the source region or the drain region of the n-channel TFT is formed by this process, the switching TFT leaves a part of the n-type impurity regions 530 to 532 formed in the process of FIG. This remaining region corresponds to the LDD regions 15a to 15d of the switching TFT in FIG.

Next, as illustrated in FIG. 7C, the resist masks 534a to 534c are removed, and a resist mask 543 is newly formed. Then, a p-type impurity element (boron in this embodiment) is added to form impurity regions 544 and 545 containing boron at a high concentration. Here, the concentration is 3 × 10 ^{20 to} 3 × 10 ²¹ atoms / cm ³ (typically 5 × 10 ²⁰ to 1 × 10 ²¹ atoms / cm ³ ) by ion doping using diborane (B ₂ H ₆ ). Boron is added so that

Note that phosphorus is already added to the impurity regions 544 and 545 at a concentration of 1 × 10 ²⁰ to 1 × 10 ²¹ atoms / cm ³ , but the boron added here is added at a concentration of at least three times that of that. Is done. Therefore, the n-type impurity region formed in advance is completely inverted to the P-type and functions as a P-type impurity region.

  Next, as shown in FIG. 7D, after the resist mask 543 is removed, a first interlayer insulating film 546 is formed. As the first interlayer insulating film 546, an insulating film containing silicon may be used as a single layer, or a laminated film combined therewith may be used. The film thickness may be 400 nm to 1.5 μm. In this embodiment, a structure is formed in which a silicon oxide film having a thickness of 800 nm is stacked on a silicon nitride oxide film having a thickness of 200 nm.

  Thereafter, the n-type or p-type impurity element added at each concentration is activated. As the activation means, a furnace annealing method is preferable. In this embodiment, heat treatment is performed in an electric furnace in a nitrogen atmosphere at 550 ° C. for 4 hours.

  Further, a hydrogenation treatment is performed by performing a heat treatment at 300 to 450 ° C. for 1 to 12 hours in an atmosphere containing 3 to 100% hydrogen. This step is a step in which the dangling bonds of the semiconductor film are terminated with hydrogen by thermally excited hydrogen. As another means of hydrogenation, plasma hydrogenation (using hydrogen excited by plasma) may be performed.

  Note that the hydrogenation treatment may be performed while the first interlayer insulating film 546 is formed. That is, after the 200 nm-thick silicon nitride oxide film is formed, the hydrogenation treatment may be performed as described above, and then the remaining 800 nm-thick silicon oxide film may be formed.

  Next, as shown in FIG. 8A, contact holes are formed in the first interlayer insulating film 546, and source wirings 547 to 550 and drain wirings 551 to 553 are formed. In this embodiment, this electrode is a laminated film having a three-layer structure in which a Ti film is 100 nm, an aluminum film containing Ti is 300 nm, and a Ti film 150 nm is continuously formed by sputtering. Of course, other conductive films may be used.

  Next, a first passivation film 554 is formed with a thickness of 50 to 500 nm (typically 200 to 300 nm). In this embodiment, a silicon nitride oxide film having a thickness of 300 nm is used as the first passivation film 554. This may be replaced by a silicon nitride film.

At this time, it is effective to perform plasma treatment using a gas containing hydrogen such as H ₂ or NH ₃ prior to the formation of the silicon nitride oxide film. Hydrogen excited by this pretreatment is supplied to the first interlayer insulating film 546 and heat treatment is performed, whereby the film quality of the first passivation film 554 is improved. At the same time, since hydrogen added to the first interlayer insulating film 546 diffuses to the lower layer side, the active layer can be effectively hydrogenated.

  Next, as shown in FIG. 8B, a second interlayer insulating film 555 made of an organic resin is formed. As the organic resin, polyimide, acrylic, BCB (benzocyclobutene), or the like can be used. In particular, since the second interlayer insulating film 555 needs to flatten a step formed by the TFT, an acrylic film having excellent flatness is preferable. In this embodiment, an acrylic film is formed with a thickness of 2.5 μm.

  Next, a contact hole reaching the drain wiring 553 is formed in the second interlayer insulating film 555 and the first passivation film 554, and a pixel electrode (anode) 556 is formed. In this embodiment, an indium tin oxide (ITO) film having a thickness of 110 nm is formed and patterned to form a pixel electrode. Alternatively, a transparent conductive film in which 2 to 20% zinc oxide (ZnO) is mixed with indium oxide may be used. This pixel electrode becomes the anode of the EL element.

  Next, an insulating film containing silicon (silicon oxide film in this embodiment) is formed to a thickness of 500 nm, an opening is formed at a position corresponding to the pixel electrode 556, and a third interlayer insulating film 557 is formed. When the opening is formed, a tapered sidewall can be easily formed by using a wet etching method. If the side wall of the opening is not sufficiently gentle, the deterioration of the EL layer due to the step becomes a significant problem.

  Next, an EL layer 558 and a cathode (MgAg electrode) 559 are continuously formed using a vacuum deposition method without being released to the atmosphere. Note that the EL layer 558 may have a thickness of 800 to 200 nm (typically 100 to 120 nm), and the cathode 559 may have a thickness of 180 to 300 nm (typically 200 to 250 nm).

  In this step, an EL layer and a cathode are sequentially formed for a pixel corresponding to red, a pixel corresponding to green, and a pixel corresponding to blue. However, since the EL layer has poor resistance to the solution, it has to be formed individually for each color without using a photolithography technique. Therefore, it is preferable to hide other than the desired pixels using a metal mask, and selectively form the EL layer and the cathode only at necessary portions.

  That is, first, a mask that hides all pixels other than those corresponding to red is set, and an EL layer and a cathode emitting red light are selectively formed using the mask. Next, a mask for hiding all but the pixels corresponding to green is set, and the EL layer and the cathode emitting green light are selectively formed using the mask. Next, similarly, a mask for hiding all but the pixels corresponding to blue is set, and an EL layer and a cathode emitting blue light are selectively formed using the mask. Note that although all the different masks are described here, the same mask may be used. Further, it is preferable to perform processing without breaking the vacuum until the EL layer and the cathode are formed on all the pixels.

Note that a known material can be used for the EL layer 558. As the known material, it is preferable to use an organic material in consideration of the driving voltage. For example, a four-layer structure including a hole injection layer, a hole transport layer, a light emitting layer, and an electron injection layer may be used as the EL layer.
In this embodiment, an example in which an MgAg electrode is used as the cathode of the EL element is shown, but other known materials may be used.

  As the protective electrode 560, a conductive film containing aluminum as its main component may be used. The protective electrode 560 may be formed by a vacuum evaporation method using a mask different from that used when the EL layer and the cathode are formed. In addition, it is preferable that the EL layer and the cathode are formed continuously without being released to the atmosphere after forming the EL layer and the cathode.

  Finally, a second passivation film 561 made of a silicon nitride film is formed to a thickness of 300 nm. Actually, the protective electrode 560 plays a role of protecting the EL layer from moisture or the like. However, by further forming the second passivation film 561, the reliability of the EL element can be further improved.

  Thus, an active matrix EL display device having a structure as shown in FIG. 8C is completed. Actually, when completed up to FIG. 8C, packaging with a housing material such as a highly airtight protective film (laminate film, UV curable resin film, etc.) or ceramic sealing can so as not to be exposed to the outside air. (Encapsulation) is preferable. At that time, the reliability (life) of the EL layer is improved by making the inside of the housing material an inert atmosphere or disposing a hygroscopic material (for example, barium oxide) inside.

  In addition, when the airtightness is improved by processing such as packaging, a connector (flexible printed circuit: FPC) for connecting the terminal routed from the element or circuit formed on the substrate and the external signal terminal is attached. Completed as a product. In this specification, an EL display device that can be shipped is referred to as an EL module.

  Here, the configuration of the active matrix EL display device of this embodiment will be described with reference to the perspective view of FIG. The active matrix EL display device of this embodiment includes a pixel portion 602, a gate side driver circuit 603, and a source side driver circuit 604 formed on a glass substrate 601. The switching TFT 605 in the pixel portion is an n-channel TFT, and is arranged at the intersection of the gate wiring 606 connected to the gate side driving circuit 603 and the source wiring 607 connected to the source side driving circuit 604. The drain of the switching TFT 605 is connected to the gate of the current control TFT 608.

  Further, the source side of the current control TFT 606 is connected to the power supply line 609. In the structure as in this embodiment, a ground potential (ground potential) is applied to the power supply line 609. Further, an EL element 611 is connected to the drain of the current control TFT 608 through a resistor 610. A predetermined voltage (10 to 12 V in this embodiment) is applied to the cathode of the EL element 611.

  The FPC 612 serving as an external input / output terminal is provided with input / output wirings (connection wirings) 613 and 614 for transmitting signals to the driving circuit, and input / output wirings 615 connected to the power supply line 609.

  Further, the EL module of this embodiment including the housing material will be described with reference to FIGS. Note that the reference numerals used in FIG. 11 are cited as necessary.

  On the substrate 1200, a pixel portion 1201, a data signal side driver circuit 1202, and a gate signal side driver circuit 1203 are formed. Various wirings from the respective drive circuits reach the FPC 612 via input / output wirings 613 to 615 and are connected to an external device.

  At this time, a housing material 1204 is provided so as to surround at least the pixel portion, preferably the driver circuit and the pixel portion. Note that the housing member 1204 has a recess or sheet shape whose inner dimension is larger than the outer dimension of the EL element, and is fixed to the substrate 1200 by an adhesive 1205 so as to form a sealed space in cooperation with the substrate 1200. Is done. At this time, the EL element is completely enclosed in the sealed space and is completely shielded from the outside air. A plurality of housing materials 1204 may be provided.

  The material of the housing material 1204 is preferably an insulating material such as glass or polymer. For example, amorphous glass (borosilicate glass, quartz, etc.), crystallized glass, ceramic glass, organic resin (acrylic resin, styrene resin, polycarbonate resin, epoxy resin, etc.), silicone resin Can be mentioned. Ceramics may also be used. Further, if the adhesive 1205 is an insulating substance, a metal material such as a stainless alloy can be used.

  The material of the adhesive 1205 can be an adhesive such as an epoxy resin or an acrylate resin. Furthermore, a thermosetting resin or a photocurable resin can also be used as an adhesive. However, it is necessary that the material does not transmit oxygen and moisture as much as possible.

  Furthermore, it is preferable that the gap 1206 between the housing material and the substrate 1200 is filled with an inert gas (argon, helium, nitrogen, or the like). Moreover, it is also possible to use not only gas but inert liquid (liquid fluorinated carbon represented by perfluoroalkane etc.). As for the inert liquid, a material as used in JP-A-8-78519 may be used.

  It is also effective to provide a desiccant in the gap 1206. As the desiccant, materials described in JP-A-9-148066 can be used. Typically, barium oxide may be used.

  As shown in FIG. 12B, a plurality of pixels each having an isolated EL element are provided in the pixel portion, and all of them have a protective electrode 1207 as a common electrode. In this embodiment, the EL layer, the cathode (MgAg electrode) and the protective electrode are preferably formed continuously without being released to the atmosphere. However, the EL layer and the cathode are formed using the same mask material, and only the protective electrode is separated. If the mask material is used, the structure shown in FIG. 12B can be realized.

  At this time, the EL layer and the cathode need only be provided in the pixel portion, and need not be provided over the driver circuit. Of course, there is no problem even if it is provided on the driver circuit, but it is preferable not to provide it in consideration of the fact that the EL layer contains an alkali metal.

  Note that the protective electrode 1207 is connected to the input / output wiring 1210 via a connection wiring 1209 made of the same material as the pixel electrode in a region indicated by 1208. The input / output wiring 1210 is a power supply line for applying a predetermined voltage (ground potential, specifically 0 V in this embodiment) to the protective electrode 1207, and is connected to the FPC 611 through the conductive paste material 1211.

  Here, a manufacturing process for realizing a contact structure in the region 1208 is described with reference to FIGS.

First, the state of FIG. 8A is obtained according to the steps of this embodiment. At this time, the first interlayer insulating film 544 and the gate insulating film 514 are removed from the substrate edge (region indicated by 1208 in FIG. 12B), and the input / output wiring 1210 is formed thereon.
Of course, it is formed simultaneously with the source wiring and drain wiring of FIG. (FIG. 13 (A))

  Next, in FIG. 8B, when the second interlayer insulating film 553 and the first passivation film 552 are etched, a region indicated by 1301 is removed and an opening 1802 is formed. Then, the connection wiring 1209 is formed so as to cover the opening portion 1302. Of course, the connection wiring 1209 is formed at the same time as the pixel electrode 554 in FIG. (Fig. 13B)

  In this state, an EL element forming step (third interlayer insulating film, EL layer and cathode forming step) is performed in the pixel portion. At this time, in the region shown in FIG. 13, a mask or the like is used so that the third interlayer insulating film and the EL element are not formed. Then, after forming the cathode 557, the protective electrode 558 is formed using another mask. Accordingly, the protective electrode 558 and the input / output wiring 1210 are electrically connected via the connection wiring 1209. Further, a second passivation film 559 is provided to obtain the state of FIG.

  Through the above steps, a contact structure in a region indicated by 1208 in FIG. 12B is realized. The input / output wiring 1210 has a gap between the housing member 1204 and the substrate 1200 (but is filled with an adhesive 1205. That is, the adhesive 1205 needs to have a thickness that can sufficiently flatten the steps of the input / output wiring. And is connected to the FPC 611. Although the input / output wiring 1210 has been described here, the other output wirings 612 to 614 are similarly connected to the FPC 611 under the housing material 1204.

  In this embodiment, an example in which the pixel configuration is different from the configuration shown in FIG. 1B is shown in FIG.

  In this embodiment, the two pixels shown in FIG. 1B are arranged symmetrically with respect to the power supply line 111 for applying the ground potential. That is, as shown in FIG. 14, the number of wirings required is reduced by sharing the power supply line 111 between two adjacent pixels. Note that the TFT structure and the like disposed in the pixel can be left as they are.

  With such a configuration, a higher-definition pixel portion can be manufactured, and the image quality is improved.

  Further, by sharing the power supply line 111, the margin of the line width of the power supply line 111 is widened, and the line width of the power supply line 111 can be increased without reducing the brightness of the image. Accordingly, the influence of the voltage drop of the power supply line 111 can be reduced, and it is possible to prevent the voltage supplied from the power supply line 111 from being different depending on the position of the pixel.

  Note that the configuration of this embodiment can be easily realized in accordance with the manufacturing steps of Embodiment 1.

  In this embodiment, the case where a pixel portion having a structure different from that in FIG. 1 is formed will be described with reference to FIGS. The first embodiment may be followed up to the step of forming the second interlayer insulating film 48. Further, the switching TFT 201 and the current control TFT 202 covered with the second interlayer insulating film 48 have the same structure as that shown in FIG.

  In the case of the present embodiment, when contact holes are formed in the second interlayer insulating film 48 and the first passivation film 47, the pixel electrode 61 is formed. In this embodiment, an aluminum alloy film (aluminum film containing 1 wt% titanium) having a thickness of 200 nm is provided as the pixel electrode 61. The material for the pixel electrode may be any material as long as it is a metal material, but is preferably a material having high reflectivity.

  Then, a third interlayer insulating film 62 made of a silicon oxide film is formed thereon with a thickness of 300 nm, a 230 nm thick MgAg electrode as the cathode 63, and an EL layer 64 from the bottom as an electron transport layer 20 nm, a light emitting layer 40 nm, a positive layer A hole transport layer of 30 nm is formed. However, the EL layer 64 needs to be formed so as to have a slightly larger pattern than the cathode 63. By doing so, it is possible to prevent the cathode 63 from being short-circuited with the anode 65 to be formed later.

  At this time, the cathode 63 and the EL layer 64 are continuously formed by using a multi-chamber method (also referred to as a cluster tool method) without being exposed to the atmosphere, but first, the cathode 63 is formed on all pixels with the first mask. Next, an EL layer emitting red light is formed using a second mask. Then, the second mask is shifted while being precisely controlled to sequentially form a green light emitting EL layer and a blue light emitting EL layer.

  Note that when the pixels corresponding to RGB are arranged in stripes, it is only necessary to shift the second mask by the above-described method. However, in order to realize a so-called delta arrangement, a green light emitting EL layer is used. For this purpose, a third mask may be used separately, and a fourth mask may be used separately for the blue light emitting EL layer.

  When the EL layer 65 is thus formed, an anode 65 made of a transparent conductive film (in this embodiment, a thin film containing 10 wt% zinc oxide in the ITO film) is formed to a thickness of 110 nm. Thus, the EL element 206 is formed, and if the second passivation film 66 is formed with the material shown in Embodiment 1, a pixel having a structure as shown in FIG. 15 is completed. In this case, since the positions of the cathode and the anode are opposite to those in FIG. 1, a voltage of 10 to 12 V is applied to the power supply line connected to the source wiring of the current control TFT 202 and is connected to the anode 65. 0V (ground potential) is applied to the power source.

  In the case of the structure of this embodiment, red, green, or blue light generated in each pixel is emitted to the opposite side of the substrate on which the TFT is formed. Therefore, almost the entire region in the pixel, that is, the region where the TFT is formed can be used as an effective light emitting region. As a result, the effective light emission area of the pixel is greatly improved, and the brightness and contrast ratio (brightness / darkness ratio) of the image are improved.

  The configuration of this embodiment can be freely combined with any of the configurations of Embodiments 1 and 2.

  In this embodiment, an example of a pixel structure of an active matrix EL display device manufactured according to Embodiment 1 will be described. FIG. 16 is used for the description. In FIG. 16, the reference numerals in FIG. 1 or FIG.

  In FIG. 16, reference numeral 201 denotes a switching TFT, which includes a source region 13, a drain region 14, and a gate wiring (also serving as a gate wiring) 106. Reference numeral 202 denotes a current control TFT, which includes a source region 26, a drain region 27, and a gate electrode 30. Further, the drain of the current control TFT 202 is electrically connected to the pixel electrode 49 through the resistor 33 (referring to a semiconductor layer existing under the mask film 55 in FIG. 16), the connection region 34 and the drain wiring 32. Is done. The dotted lines 51 and 52 indicate the positions where the EL layer 51 and the cathode 52 are formed, and the EL element 203 is formed by the pixel electrode 49, the EL layer 51, and the cathode 52.

  At this time, the drain wiring 22 of the switching TFT 201 is electrically connected to the gate electrode 30 of the current control TFT 202 through the contact portion 1601. The gate electrode 30 forms a storage capacitor 113 in a portion overlapping the source wiring 31 of the current control TFT 202. The source wiring 31 is electrically connected to a power supply line 111 that applies a ground potential.

In this embodiment, the pixel structure shown in FIG. 16 does not limit the present invention in any way, but is only a preferable example. The position of the switching TFT, the current control TFT, or the storage capacitor may be appropriately designed by the practitioner.
This embodiment can be implemented by freely combining with any configuration of Embodiments 1 to 3.

  In this embodiment, an example in which the pixel structure of the active matrix EL display device is different from that of Embodiment 4 will be described. Specifically, FIG. 17 shows an example in which the gate wiring material is different in the pixel structure shown in FIG. Note that FIG. 17 is the same except for the configuration of the gate wiring of FIG.

  In FIG. 17, reference numerals 71a and 71b denote gate electrodes formed of a laminated film of a tungsten nitride film and a tungsten film as in the gate electrode of the first embodiment. These may be isolated patterns as shown in FIG. 17 or electrically connected patterns, respectively, but are electrically floating at the time of formation.

  As the gate electrodes 71a and 71b, another conductive film such as a laminated film of a tantalum nitride film and a tantalum film or an alloy film of molybdenum and tungsten may be used. However, it is desirable that the film has excellent processability and can form a fine line width of 3 μm or less (preferably 2 μm or less). Further, it is desirable that the gate insulating film is not a film containing an element that diffuses into the active layer.

  On the other hand, as the gate wiring 72, a conductive film having a lower resistance than the gate electrodes 71a and 71b, typically an alloy film mainly containing aluminum or an alloy film mainly containing copper is used. The gate wiring 72 is not required to have particularly fine workability. Further, since it does not overlap with the active layer, it does not matter if it contains aluminum or copper that easily diffuses in the insulating film.

  In the case of the structure of this embodiment, an activation process may be performed before the first interlayer insulating film 544 is formed in the process of FIG. In this case, the heat treatment is performed in a state where the gate electrodes 71a and 71b are exposed. However, the gate electrode 71a may be used for the heat treatment in a sufficiently inert atmosphere, preferably in an inert atmosphere having an oxygen concentration of 1 ppm or less. 71b is not oxidized. That is, the resistance value does not increase due to oxidation, and the removal is not covered with an insulating film (oxide film).

  When the activation step is completed, a conductive film containing aluminum or copper as a main component is formed, and the gate wiring 72 may be formed by patterning. At this time, a good ohmic contact is secured at the portion where the gate electrodes 71a and 71b and the gate wiring 72 are in contact, and a predetermined gate voltage can be applied to the gate electrodes 71a and 71b.

  The structure of the present embodiment is particularly effective when the area of the image display area is increased. The reason will be described below.

  Since the EL display device of the present invention is driven by dividing one frame into a plurality of sub-frames, the burden on the driving circuit for driving the pixel portion is large. In order to reduce this, it is preferable to reduce as much as possible the load (wiring resistance, parasitic capacitance, TFT write capacitance, etc.) of the pixel portion.

  The writing capacity of the TFT is not a problem because a TFT having very high operation performance can be realized by the polysilicon film used in the present invention. Further, most of the parasitic capacitance added to the data wiring and the gate wiring is formed between the cathode (or protective electrode) of the EL element formed on the wiring. Since an organic resin film having a low relative dielectric constant is formed as an insulating film with a thickness of 1.5 to 2.5 μm, parasitic capacitance is almost negligible.

  For this reason, the most difficult obstacle to implementing the present invention in an EL display device having a large pixel area is the wiring resistance of data wiring and gate wiring. Of course, the data signal side drive circuit is divided into a plurality of parts for parallel processing, or the data signal side drive circuit and the gate signal side drive circuit are provided across the pixel portion to send signals from both directions, and the drive circuit is substantially It is also possible to reduce the operating frequency. However, in this case, another problem such as an increase in the area occupied by the drive circuit occurs.

  Therefore, reducing the wiring resistance of the gate wiring as much as possible by the structure as in this embodiment is very effective in implementing the present invention. In this embodiment, the pixel structure shown in FIG. 17 does not limit the present invention at all, but is only a preferable example. In addition, this embodiment can be implemented by freely combining with any configuration of Embodiments 1 to 3.

  As in the present invention, a data signal side driving circuit that drives at a very high speed is required to perform time-division gradation that divides one frame into a plurality of subframes. That is, it is preferable to use a TFT having a very high operation speed (response speed). In this embodiment, an example is shown in which a silicon film that is extremely suitable for manufacturing a TFT that can be driven at a very high speed is used as an active layer.

  When the process up to the step of FIG. 5E is performed according to the first embodiment, a silicon film having a unique crystal structure (polysilicon film in the first embodiment) is obtained. This silicon film has high crystal grain boundary continuity and uniform crystal orientation, and a TFT exhibiting a very high operating speed can be obtained by using the TFT active layer. In this specification, the silicon film described in this embodiment is called a continuous grain boundary crystalline silicon film. Hereinafter, the results of the trial production and observation of the continuous grain boundary crystalline silicon film will be described.

  When viewed microscopically, the continuous grain boundary crystalline silicon film has a crystal structure in which a plurality of needle-like or rod-like crystals (hereinafter referred to as rod-like crystals) are gathered and arranged. This was easily confirmed by observation with TEM (transmission electron microscopy).

  Moreover, as a result of observing the electron diffraction pattern having a spot diameter of 1.35 μm in detail with respect to the continuous grain boundary crystalline silicon film, diffraction spots corresponding to the {110} plane appear neatly although there are slight fluctuations. Although some deviation was included, it was confirmed that the main orientation plane had {110} plane.

  FIG. 19A is an electron beam diffraction image obtained by irradiating a continuous grain boundary crystalline silicon film with an electron beam having a spot diameter of 1.35 μm. On the other hand, FIG. 19B is an electron beam diffraction image obtained by irradiating a conventional polysilicon film with an electron beam under the same conditions. In both cases, the center of the photograph is the position irradiated with the electron beam (electron beam irradiation point).

  In FIG. 19A, the diffraction spots corresponding to the {110} plane appear relatively fine, whereas in FIG. 19B, it is almost irregular, and the orientation plane is scattered. It is obvious. Thus, the continuous grain boundary crystalline silicon film can be immediately distinguished from the conventional semiconductor film by looking at the electron diffraction pattern.

  Note that the appearance of diffraction spots corresponding to the {110} plane in the electron diffraction image of FIG. 19A is apparent when compared with the electron diffraction image of a {110} oriented single crystal silicon wafer. . In addition, the diffraction spots of the single crystal silicon wafer appear as sharp points, whereas the diffraction spots of the continuous grain boundary crystal silicon film have a concentric circle centered on the electron beam irradiation point.

  This is also a feature of the continuous grain boundary crystalline silicon film. Since each crystal grain has an {110} plane as an orientation plane individually, it is expected that a diffraction spot similar to that of single crystal silicon can be obtained with respect to one crystal grain. However, since it is actually an aggregate of a plurality of crystal grains, each crystal grain has a {110} plane as an orientation plane, but each includes a slight rotation around the crystal axis and corresponds to each crystal grain. Multiple diffraction points appear on a concentric circle. They overlap and show a spread.

  However, since individual crystal grains form crystal grain boundaries with extremely good consistency as will be described later, slight rotation around the crystal axis does not impair crystallinity. Therefore, it can be said that the electron diffraction image of the continuous grain boundary crystalline silicon film is substantially not different from the electron diffraction image of the {110} oriented single crystal silicon wafer.

  From the above, it can be said that the silicon film used as the active layer of the TFT in this embodiment is a silicon film showing an electron diffraction image corresponding to {110} orientation.

Next, the crystal grain boundaries of the continuous grain boundary crystalline silicon film will be described. For convenience of explanation, it is called a crystal grain boundary, but it is derived from a certain crystal grain (branched).
It can be considered as an interface with another crystal grain. In any case, in this specification, the term “crystal grain boundary” includes the above-described interface.

  The present applicant observed the grain boundaries formed by the contact of individual rod-like crystals by HR-TEM (high resolution transmission electron microscopy), and confirmed that the crystal lattice has continuity at the grain boundaries. This was easily confirmed because the observed lattice fringes were continuously connected at the grain boundaries.

  Note that the continuity of the crystal lattice at the crystal grain boundary results from the fact that the crystal grain boundary is a grain boundary called a “planar grain boundary”. The definition of the planar grain boundary in this specification is “Characterization of High-Efficiency Cast-Si Solar Cell Wafers by MBIC Measurement; Ryuichi Shimokawa and Yutaka Hayashi, Japanese Journal of Applied Physics vol.27, No.5, pp.751”. -758, 1988 ”is the“ Planar boundary ”.

  According to the above paper, planar grain boundaries include twin grain boundaries, special stacking faults, and special twist grain boundaries. This planar grain boundary is characterized by being electrically inactive. That is, although it is a crystal grain boundary, it does not function as a trap that inhibits the movement of carriers, and thus can be regarded as substantially nonexistent.

  In particular, when the crystal axis (axis perpendicular to the crystal plane) is the <110> axis, the {211} twin grain boundary and the {111} twin grain boundary are also called the corresponding grain boundary of Σ3. The Σ value is a parameter that serves as a guideline indicating the degree of consistency of the corresponding grain boundary. It is known that the smaller the Σ value, the better the grain boundary.

  As a result of TEM observation of the continuous grain boundary crystalline silicon film, it was found that most of the crystal grain boundaries were Σ3 corresponding grain boundaries. This is because, in a crystal grain boundary formed between two crystal grains, when the plane orientation of both crystal grains is {110}, if the angle formed by lattice fringes corresponding to the {111} plane is θ, Judging from the fact that the grain boundary corresponds to Σ3 when = 70.5 °.

  In addition, when θ = 38.9 °, a corresponding grain boundary of Σ9 is obtained, but such other crystal grain boundaries also existed.

  Such a corresponding grain boundary is formed only between crystal grains having the same plane orientation. That is, it can be said that such a corresponding grain boundary can be formed over a wide range because the continuous grain boundary crystalline silicon film has a plane orientation of approximately {110}.

  Such a crystal structure (exactly, the structure of the crystal grain boundary) indicates that two different crystal grains are joined with extremely good consistency at the crystal grain boundary. That is, the crystal lattice is continuously connected at the crystal grain boundary, and the trap level caused by crystal defects or the like is very difficult to create. Therefore, the semiconductor thin film having such a crystal structure can be regarded as having substantially no grain boundary.

Furthermore, when a continuous grain boundary crystalline silicon film is formed, a heat treatment at 700 to 1150 ° C. is performed in the middle of the process, so that defects existing in the crystal grains (stacking defects and the like) exist.
It is confirmed by TEM observation that almost disappears. This is also clear from the fact that the number of defects is greatly reduced before and after this heat treatment step.

This difference in the number of defects is determined by electron spin resonance analysis (ESR).
Appears as a difference in spin density. At present, it has been found that the spin density of the continuous grain boundary crystalline silicon film is at least 5 × 10 ¹⁷ spins / cm ³ or less (preferably 3 × 10 ¹⁷ spins / cm ³ or less). However, since this measured value is close to the detection limit of existing measuring devices, the actual spin density is expected to be even lower.

  Further details of the continuous grain boundary crystalline silicon film are described in Japanese Patent Application No. 10-044659, Japanese Patent Application No. 10-152316, Japanese Patent Application No. 10-152308, filed by the present applicant. Reference may be made to the specification or the specification of Japanese Patent Application No. 10-152305.

  Further, a TFT fabricated using a continuous grain boundary crystalline silicon film as an active layer exhibited electrical characteristics comparable to a MOSFET. The following data is obtained from the TFT manufactured by the present applicant (however, the thickness of the active layer is 30 nm and the thickness of the gate insulating film is 100 nm).

(1) Sub-threshold coefficient, which is an indicator of switching performance (agility of switching on / off operation), is 60-100 mV / decade for both N-channel TFT and P-channel TFT (typically 60-85 mV / decade) And small.
(2) The field effect mobility (μ _FE ), which is an indicator of TFT operating speed, is 200 to 650 cm ² / Vs (typically 300 to 500 cm ² / Vs) for N-channel TFTs, and P-channel TFTs 100 to 300 cm ² / Vs (typically 150 to ²⁰⁰ cm ² / Vs).
(3) The threshold voltage (V _th ), which serves as an index of TFT driving voltage, is as low as −0.5 to 1.5 V for N-channel TFTs and −1.5 to 0.5 V for P-channel TFTs.

As described above, it has been confirmed that extremely excellent switching characteristics and high-speed operation characteristics can be realized. Furthermore, the ring oscillator prototyped using the TFT described above was able to obtain an oscillation frequency of about 1 GHz at the maximum. The configuration of the prototype ring oscillator is as follows.
Number of stages: 9 stages Film thickness of gate insulating film of TFT: 30 nm and 50 nm TFT gate length (channel length): 0.6 μm
In addition, we actually manufactured a shift register and confirmed the operating frequency. As a result, an output pulse with an operating frequency of 100 MHz was obtained in a shift register having a gate insulating film thickness of 30 nm, a gate length of 0.6 μm, a power supply voltage of 5 V, and a number of stages of 50.

  The amazing data of the ring oscillator and shift register as described above suggests that TFTs with a continuous grain boundary crystalline silicon film as an active layer have an operating performance comparable to or surpassing that of MOSFETs using single crystalline silicon. To do.

  As described above, a TFT having an extremely high operation speed is formed by using a continuous grain boundary crystal silicon film, and a drive circuit capable of high-speed operation can be realized by forming a drive circuit using the TFT. In other words, it is extremely effective to use the TFT as described above in carrying out the present invention.

In addition, a TFT using a continuous grain boundary crystal silicon film is not limited to a driving circuit, and it is also effective to use it for a switching TFT or a current control TFT arranged in a pixel portion.
By increasing the operation speed, the writing time to the storage capacitor is shortened, and the response speed for causing the EL element to emit light is also increased, so that a brighter and clearer image can be provided.

  In the sixth embodiment, an example in which a driver circuit is formed using TFTs that can be driven at a very high speed has been described. In this embodiment, a method for driving a pixel portion that is effective in implementing the present invention will be described. FIG. 20 is used for the description.

  In this embodiment, the pixel unit 80 is divided into two pixel units 80a and 80b, the pixel unit 80a is driven by the data signal side driving circuit 81a and the gate signal side driving circuit 82a, and the pixel unit 80b is driven by the data signal side driving circuit 81b. And it drives with the gate signal side drive circuit 82b.

  In this case, if the pixel portions 80a and 80b are simultaneously driven at the same frequency, the operating frequencies of the data signal side drive circuits 81a and 81b and the gate signal side drive circuits 82a and 82b can be reduced to half. Therefore, an EL display device with a wide operation margin, high reliability, and low power consumption can be obtained.

  Furthermore, since the address period can be halved if the operating frequency is not changed, the sustain period can be made longer accordingly. That is, since the light emission time can be secured longer, the brightness of the image can be improved.

  Further, the pixel portions 80a and 80b can be combined to display one image, or the pixel portions 80a and 80b can display different images. For example, either one may be a still image and the other a moving image. That is, there may be a case where a moving image and a still image are mixed in the pixel unit 80.

  Although the pixel portion is divided into two in this embodiment, it can be further divided into a plurality of pixel portions. In addition, the configuration of this embodiment can be implemented by freely combining with any of the configurations of Embodiments 1 to 6.

  In this embodiment, the pixel portion driving method effective for carrying out the present invention is shown as a driving method different from that of the seventh embodiment. FIG. 21 is used for the description.

  In this embodiment, the pixel portion 83 is divided into four pixel portions 83a to 83d, and the pixel portions 83a to 83d are driven by data signal side drive circuits 84a to 84d and gate signal side drive circuits 85a to 85d, respectively.

  In this case, the operating frequencies of the data signal side drive circuits 84a to 84d and the gate signal side drive circuits 85a to 85d can be lowered to ¼ by simultaneously driving the pixel portions 83a to 83d at the same frequency. Therefore, an EL display device with a wider operation margin, higher reliability, and lower power consumption than in the case of Embodiment 7 can be obtained.

  Furthermore, since the address period can be reduced to ¼ if the operating frequency is not changed, the sustain period can be made longer accordingly. That is, since the light emission time can be secured longer, the brightness of the image can be improved.

  Further, all the pixel portions 83a to 83d can be combined to display one image. Furthermore, it is also possible to display one image on the pixel portions 83a and 83b, display one image on the pixel portions 83c and 83d, and consequently display two different images simultaneously. Furthermore, an image formed by the pixel portions 83a and 83b can be a still image, and an image formed by the pixel portions 83c and 83d can be a moving image. That is, there may be a case where a moving image and a still image are mixed in the pixel unit 83.

  Although the pixel portion is divided into four in this embodiment, it can be further divided into a plurality of pixel portions. In addition, the configuration of this embodiment can be implemented by freely combining with any of the configurations of Embodiments 1 to 6.

  In this embodiment, a case where the driving method of the pixel portion effective for carrying out the present invention is different from that of the eighth embodiment is shown. FIG. 22 is used for the description.

  In this embodiment, the pixel portion 86 is divided into four pixel portions 86a to 86d, the pixel portion 86a is driven by the data signal side drive circuit 87a and the gate signal side drive circuit 88a, and the pixel portion 86b is driven by the data signal side drive circuit 87b. And it drives with the gate signal side drive circuit 88a. Similarly, the pixel portion 86c is driven by the data signal side drive circuit 87c and the gate signal side drive circuit 88b, and the pixel portion 86d is driven by the data signal side drive circuit 87d and the gate signal side drive circuit 88b.

  In this case, by simultaneously driving the pixel portions 86a to 86d at the same frequency, the operating frequency of the data signal side driving circuits 87a to 87d can be lowered to 1/4, and the operating frequency of the gate signal side driving circuits 88a and 88b. Can be reduced to ½ each. Therefore, an EL display device with a wider operation margin, higher reliability, and lower power consumption than in the case of Embodiment 7 can be obtained.

  Furthermore, since the address period can be reduced to ¼ if the operating frequency is not changed, the sustain period can be made longer accordingly. That is, since the light emission time can be secured longer, the brightness of the image can be improved.

Further, all the pixel portions 86a to 86d can be combined to display one image, or different images can be displayed in the pixel portions 86a to 86d. Of course, it is also possible to display one image with 86a to 86c and make only the pixel portion 86d different.
Further, there may be a case where a moving image and a still image are mixed in the pixel portion 86.

  In addition, the structure of a present Example can be implemented in combination freely with any structure of Examples 1-6.

  In the structure shown in FIG. 2 of the first embodiment, it is effective to use a material having a high heat dissipation effect as the base film 12 provided between the active layer and the substrate 11. In particular, the current control TFT flows a relatively large amount of current over a long period of time, so it tends to generate heat, and deterioration due to self-heating can be a problem. In such a case, the thermal deterioration of the TFT can be suppressed because the base film has a heat dissipation effect as in this embodiment.

Translucent materials with a heat dissipation effect include B (boron), C (carbon), and N (nitrogen).
And an insulating film containing at least one element selected from Al and at least one element selected from Al (aluminum), Si (silicon), and P (phosphorus).

For example, aluminum nitride represented by aluminum nitride (AlxNy), silicon carbide represented by silicon carbide (SixCy), silicon nitride (SixNy)
It is possible to use silicon nitride typified by boron, boron nitride typified by boron nitride (BxNy), and boron phosphide typified by boron phosphide (BxPy). An aluminum oxide typified by aluminum oxide (AlxOy) is excellent in light-transmitting property and has a thermal conductivity of 20 Wm ⁻¹ K ⁻¹ and can be said to be one of preferable materials. In the translucent material, x and y are arbitrary integers.

  In addition, other elements can be combined with the above compound. For example, it is possible to use aluminum nitride oxide represented by AlNxOy by adding nitrogen to aluminum oxide. This material has not only a heat dissipation effect but also an effect of preventing moisture, alkali metal and the like from entering. In the aluminum nitride oxide, x and y are arbitrary integers.

  Moreover, the material described in Unexamined-Japanese-Patent No. 62-90260 can be used. That is, an insulating film containing Si, Al, N, O, and M (where M is at least one rare earth element, preferably Ce (cerium), Yb (ytterbium), Sm (samarium), Er (erbium), Y ( Yttrium), La (lanthanum), Gd (gadolinium), Dy (dysprosium), and Nd (neodymium). These materials have not only a heat dissipation effect but also an effect of preventing intrusion of moisture, alkali metals, and the like.

  In addition, a carbon film including at least a diamond thin film or an amorphous carbon film (in particular, a material having characteristics close to diamond, called diamond-like carbon) can be used. These have very high thermal conductivity and are extremely effective as a heat dissipation layer. However, as the film thickness increases, the film becomes brownish and the transmittance decreases. Therefore, it is preferable to use the film as thin as possible (preferably 5 to 100 nm).

  Moreover, although the thin film which consists of a material with the said heat dissipation effect can also be used alone, you may laminate | stack and use these thin films and the insulating film containing silicon.

  In addition, the structure of a present Example can be implemented in combination with any structure of Examples 1-9 freely.

  In Example 1, it was preferable to use an organic EL material as the EL layer, but the present invention can also be implemented using an inorganic EL material. However, since the current inorganic EL material has a very high driving voltage, a TFT having a withstand voltage characteristic that can withstand such a driving voltage must be used.

  Alternatively, if an inorganic EL material with a lower driving voltage is developed in the future, it can be applied to the present invention.

  Moreover, the structure of a present Example can be freely combined with any structure of Examples 1-10.

  An active matrix EL display device (EL module) formed by carrying out the present invention is a self-luminous type, and therefore has better visibility in a bright place than a liquid crystal display device. Therefore, the present invention can be implemented for a direct-view type EL display (referring to a display display incorporating an EL module). Examples of the EL display include a personal computer monitor, a TV broadcast reception monitor, and an advertisement display monitor.

  In addition, the present invention can be implemented for any electronic device including a display display as a component, including the above-described EL display.

Such electronic devices include EL displays, video cameras, digital cameras, head mounted displays (head mounted displays, etc.), car navigation systems, personal computers, personal digital assistants (mobile computers, mobile phones, electronic books, etc.), Image reproducing apparatus provided with a recording medium (specifically, a display capable of reproducing a recording medium such as a compact disc (CD), a laser disc (registered trademark) (LD), or a digital video disc (DVD) and displaying the image) And the like). Examples of these electronic devices are shown in FIG.

  FIG. 18A illustrates a personal computer, which includes a main body 2001, a housing 2002, a display device 2003, a keyboard 2004, and the like. The present invention can be used for the display device 2003.

  FIG. 18B shows a video camera, which includes a main body 2101, a display device 2102, an audio input portion 2103, operation switches 2104, a battery 2105, an image receiving portion 2106, and the like. The present invention can be used for the display device 2102.

  FIG. 18C shows a part (right side) of a head-mounted EL display, which includes a main body 2301, a signal cable 2302, a head fixing band 2303, a display monitor 2304, an optical system 2305, a display device 2306, and the like. . The present invention can be used for the display device 2306.

FIG. 18D shows an image playback device (specifically a DVD playback device) provided with a recording medium.
A main body 2401, a recording medium (CD, LD, DVD or the like) 2402, an operation switch 2403, a display device (a) 2404, a display device (b) 2405, and the like. The display device (a) mainly displays image information, and the display device (b) mainly displays character information. The present invention can be used for these display devices (a) and (b). Note that the present invention can be used for a CD playback device, a game machine, or the like as an image playback device provided with a recording medium.

  FIG. 18E illustrates a portable (mobile) computer, which includes a main body 2501, a camera portion 2502, an image receiving portion 2503, operation switches 2504, a display device 2505, and the like. The present invention can be used for the display device 2505.

  Further, if the emission luminance of the EL material is increased in the future, it can be used for a front type or rear type projector.

  As described above, the application range of the present invention is extremely wide and can be applied to electronic devices in various fields. Moreover, the electronic device of a present Example is realizable even if it uses the structure which consists of what combination of Examples 1-11.

  In this embodiment, an example is shown in which the resistance value of a resistor provided between a current control TFT and an EL element is determined in accordance with the specifications of an actual EL display device (monochrome display).

First, an EL material used for the EL layer is determined. In this example, an EL element having a structure in which a 50 nm thick TPD as a hole transport layer and an 50 nm thick Alq as an EL layer were formed on an anode made of ITO and a cathode made of MgAg was formed thereon. .
However, an EL layer was vapor-deposited on the entire surface of the striped ITO pattern (2 mm width) to form a striped MgAg electrode (2 mm width) so as to be orthogonal to the ITO pattern.

FIG. 23A shows the relationship between the drive voltage (Voltage) and current density (Current Density) of the EL element manufactured at this time. Also, current density and luminance of light emission (Luminance)
The relationship is shown in FIG. The EL device of this example had a light emission peak at a wavelength near 524 nm, and the chromaticity coordinates were x = 0.30 and y = 0.57.

According to FIG. 23B, a current density of about 100 mA / cm ² is required to obtain a luminance of 5000 cd / m ² . Therefore, when considering an EL display device having a pixel portion of 5 inches diagonally provided with a matrix of square pixels of about 156 μm on a side, the current required per pixel is about 24 μA.

As shown in FIG. 23A, since the EL material used in this example flows at a current density of 100 mA / cm ² when 10 V is applied, in order to flow a current of about 24 μA stably when 10 V is applied. Requires a resistance of about 420 kΩ.

Therefore, if a resistor of 420 kΩ is provided as the resistor 109 shown in FIG. 1B, a constant current of about 24 μA can always be stably supplied to the EL element 110. As a result, a bright image can be displayed with a light emission luminance of about 5000 cd / m ² .

Of course, in order to extend the life of the EL layer, the resistance value of the resistor may be further increased to suppress the current flowing through the EL element. Instead, the emission luminance is slightly reduced. For example, if the luminance of about 1000 cd / m ² is sufficient, the required current density is about 30 mA / cm ² and the driving voltage of the EL element is about 6 V. Therefore, it is sufficient that a current of 7.3 μA flows per pixel. Therefore, a resistor of about 820 kΩ is required.

As described above, if each parameter of the EL display device is used, the resistance value of the resistor necessary for the present invention can be easily derived.

FIG. 11 illustrates a structure of an EL display device. FIG. 11 illustrates a cross-sectional structure of an EL display device. FIG. 10 shows a structure of a pixel portion in a conventional EL display device. 10A and 10B illustrate TFT characteristics used in an analog gradation method. 10A and 10B illustrate a manufacturing process of an EL display device. 10A and 10B illustrate a manufacturing process of an EL display device. 10A and 10B illustrate a manufacturing process of an EL display device. 10A and 10B illustrate a manufacturing process of an EL display device. The figure which expanded the pixel part of EL display apparatus. The figure explaining the operation mode of a time division gradation system. The figure which shows the external appearance of EL module. The figure which shows the external appearance of EL module. The figure which shows the preparation process of contact structure. FIG. 11 illustrates a structure of a pixel portion of an EL display device. FIG. 11 illustrates a cross-sectional structure of an EL display device. FIG. 14 illustrates a top structure of a pixel portion of an EL display device. FIG. 14 illustrates a top structure of a pixel portion of an EL display device. FIG. 11 is a diagram illustrating a specific example of an electronic device. The drawing substitute photograph which shows the electron beam diffraction image of a polysilicon film. FIG. 11 illustrates a circuit configuration of an EL display device. FIG. 11 illustrates a circuit configuration of an EL display device. FIG. 11 illustrates a circuit configuration of an EL display device. The figure which shows the electrical property of EL element.

Claims (1)

A pixel portion in which a semiconductor layer having a first region, a second region, a third region, a fourth region, a fifth region, a sixth region, and a seventh region is disposed;
The first region is a connection region;
The second region is a resistor;
The third region is a drain region of the transistor;
The fourth region is a first LDD region of the transistor;
The fifth region is a second LDD region of the transistor;
The sixth region is a channel formation region of the transistor;
The seventh region is a source region of the transistor;
The second region is disposed between the first region and the third region;
The third region is disposed between the second region and the fourth region;
The fourth region is disposed between the third region and the fifth region;
The fifth region is disposed between the fourth region and the sixth region;
The sixth region is disposed between the fifth region and the seventh region;
Time division gradation display is performed in the pixel portion,
The resistor is a method for manufacturing a display device having a resistance value higher than an on-resistance of the transistor,
Forming the semiconductor layer on a substrate;
Forming a gate insulating layer on the semiconductor layer;
Forming a first mask on the gate insulating layer at a position overlapping the sixth region and the seventh region;
Adding a first impurity element to the semiconductor layer using the first mask;
Removing the first mask;
On the gate insulating layer, a gate electrode that overlaps the fifth region and the sixth region and a light-shielding thin film that overlaps the second region are formed simultaneously,
Adding a second impurity element to the semiconductor layer using the gate electrode and the thin film as a mask;
Forming a second mask on the gate insulating layer and on the gate electrode at a position overlapping the fourth region;
Adding a third impurity element to the semiconductor layer using the gate electrode and the thin film as a mask and using the second mask;
Removing the second mask;
Forming a first insulating layer on the gate electrode and the thin film;
Forming a first wiring electrically connected to the first region and a second wiring electrically connected to the seventh region on the first insulating layer;
Forming a second insulating layer on the first wiring and the second wiring;
A method for manufacturing a display device, wherein an EL element electrically connected to the first wiring is formed over the second insulating layer.

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