DE112013006164T5 - High resolution pixel architecture - Google Patents

Abstract

A pixel structure comprises a substantially transparent substrate, a drive transistor formed on the substrate, an organic light device formed on the opposite side of the drive transistor to the substrate, a reflective layer disposed between the light device and the drive transistor, and a light emitting device having reflective surface, which faces the lighting device. The reflective layer forms an opening that is offset from the drive transistor to pass light emitted by the light device to the substrate. At least a portion of the reflective layer preferably has a concave shape to direct reflected light from the light device back onto the light emitting device.

Description

FIELD OF THE INVENTION

The present invention generally relates to displays with organic active matrix light emitting devices (AMOLED), and more particularly to a pixel structure in such displays having a larger aperture content.

BACKGROUND

Currently, organic active matrix (AMOLED) displays are being introduced. The benefits of such a display include lower power consumption, manufacturing flexibility and a faster refresh rate over conventional liquid crystal displays. Unlike conventional liquid crystal displays, there is no backlight for an AMOLED display because each pixel consists of different colored organic light emitting diodes (eg, red, green, and blue) that emit light independently. The organic light emitting diodes (OLEDs) emit light based on a current supplied by a driving transistor. The drive transistor is typically a thin film transistor (TFT) made of either amorphous silicon or polysilicon. The power consumed in each OLED has a direct relationship with the amount of light generated in that OLED.

The drive current of the drive transistor determines the luminance of the pixel and the surface (aperture) of the actual OLED device determines the OLED life of the pixel. AMOLED displays are typically fabricated from the OLED, the drive transistor, any other support circuits such as enable or select transistors, as well as various other drive and program lines. Such other components reduce the aperture of the pixel because they do not emit light, but are necessary for proper operation of the OLED.

In general, color displays have three OLEDs, each in a "stripe" for each pixel 10 are arranged as in 1A shown. The pixel 10 in 1A is a lower emission type OLED in which the OLEDs are fabricated on the integrated circuit substrate where there are no other components such as transistors and metal lines. The pixel 10 includes OLED 12 . 14 and 16 and corresponding drive transistors 22 . 24 and 26 , which are arranged in parallel and create a "strip" arrangement. Parallel power lines 32 . 34 and 36 are necessary to supply voltage to the OLED 12 . 14 and 16 and drive transistors 22 . 24 and 26 to deliver. The OLED 12 . 14 and 16 emit red, green or blue light and different luminance levels can be used for the OLED 12 . 14 respectively. 16 be programmed to produce colors in the spectrum by means of programming voltages coming from a series of parallel data lines 42 . 44 and 46 be fed. As in 1A shown must have additional area for a select line 50 and the data lines 42 . 44 and 46 as well as the power lines 32 . 34 and 36 for the OLED 12 . 14 and 16 and the drive transistors 22 . 24 and 26 reserved. In this known arrangement, the aperture of the integrated circuit of the pixel 10 due to the area required for the drive transistor and the power and data lines, much less than the total area of the integrated circuit. When creating a shadow mask to fabricate such an integrated circuit for the pixel 10 For example, is the distance between two adjacent OLEDs, such as the OLED 12 and 14 and the OLED size significantly (greater than 20 microns). As a result, the aperture percentage for a high resolution display (e.g., 253 pixels per inch with 33.5 μm subpixel width) will be very low.

1B shows a circuit diagram of the electronic components, ie the OLED 12 , the drive transistor 22 , the current input for the drive voltage line 32 and the programming voltage input 42 for each of the colored OLEDs that make up the pixel 10 form. The programming voltage input 42 provides a variable voltage to the drive transistor 22 which in turn regulates the current to the OLED 12 regulates the luminance of the OLED 12 to determine.

1C shows the cross section for the conventional lower emission structure such as the pixel 10 in 1A , As shown, the OLED 12 made in an open area next to the other components on the substrate. Thus, the OLED light emitting area is limited by the other components in the pixel. A common electrode layer 70 provides the electrical connection for the OLED 12 ready. In this case, the current density is high because of the limited area for light emission. The OLED voltage is also high due to the higher current density. As a result, the power consumption is higher and the OLED life is reduced.

Another type of integrated circuit arrangement for each of the OLEDs forming the pixel includes fabricating the OLED over the background components (such as transistors and metal lines) and is referred to as the upper emission array. The top emission assembly allows for a larger surface area for the OLED, and thus a higher aperture fraction, but requires a thinner common electrode for the OLED because such an electrode must be transparent to allow light from the OLED is emitted. The thin electrode results in a higher resistance and causes a significant voltage drop across this electrode. This can be a problem for larger displays that inherently require a common electrode with a larger area.

Therefore, the apertures of the pixels for OLED displays are limited due to the need for drive transistors and other circuits. Furthermore, the aperture portions of the OLED are limited in OLED displays because of the need to keep a minimal amount of space between OLEDs due to design rules. Therefore, there is a need to increase the aperture fraction of pixels with OLED based integrated circuits for higher resolution displays.

SUMMARY

According to one embodiment, a pixel structure comprises a substantially transparent substrate, a drive transistor formed on the substrate, an organic light device formed on the opposite side of the drive transistor to the substrate, a reflective layer disposed between the light device and the drive transistor and having a reflective surface facing the light emitting device, the reflective layer forming an opening offset from the drive transistor to transmit light emitted from the light emitting device to the substrate. At least a portion of the reflective layer preferably has a concave shape to direct reflected light from the light device back onto the light emitting device.

In one implementation, the pixel structure comprises a substrate; a first photoresist layer having a first opening above the substrate; a reflective layer having a second opening, the reflective layer covering the first photoresist layer; a second photoresist layer in the second opening and over the reflective layer; and an organic light emitting device formed over the second photoresist layer. The second opening overlaps with the first opening and at least a portion of the reflective layer has a concave shape. A drive transistor is disposed between the substrate and the first photoresist layer to control the luminance of the organic light emitting diode. The organic light-emitting device preferably comprises an anode layer over the second photoresist layer, an organic electroluminescent layer over the anode layer, and a cathode layer over the organic electroluminescent layer. The reflective layer has a reflective surface that faces the organic light device and conducts light from the organic light device to the second aperture.

According to another embodiment, a method of forming a pixel structure comprises: providing a substrate; Forming a first photoresist layer having a first opening over the substrate; Forming a reflective layer having a second opening, the reflective layer covering the first photoresist layer; Forming a second photoresist layer in the second opening and over the reflective layer; and forming an organic light emitting device over the second photoresist layer. The second opening overlaps with the first opening and at least a portion of the reflective layer has a concave shape. In one implementation, the step of forming the first photoresist layer includes: depositing the first photoresist layer on the substrate; Forming a first mask layer on the first photoresist layer; Depositing a third photoresist layer on the first mask layer; Forming a second mask layer on the third photoresist layer; Applying ultraviolet radiation to the second mask layer, thereby separating the third photoresist layer; Removing the second mask layer; Etching the first mask layer with the third photoresist layer, thereby separating the first mask layer; Removing the third photoresist layer; Etching the first photoresist layer with the first mask layer, thereby forming the first opening; and removing the first mask layer.

The step of forming the reflective layer preferably comprises: depositing the reflective layer on the first photoresist layer and the substrate; Depositing a third photoresist layer on the reflective layer; Applying ultraviolet radiation to the third photoresist layer; Developing the third photoresist layer; Etching the reflective layer with the third photoresist layer, thereby forming the second opening; and removing the third photoresist layer.

The step of forming an organic light emitting device on the second photoresist layer preferably comprises: forming an anode layer over the second photoresist layer; Forming an organic electroluminescent layer over the anode layer; and forming a cathode layer over the organic electroluminescent layer.

The step of forming an organic electroluminescent layer over the anode layer preferably comprises: forming a hole injection layer over the anode layer; Forming a hole transport layer over the hole injection layer; Forming an emission layer over the hole transport layer; Forming an electron transport layer over the emission layer; and forming an electron injection layer over the electron transport layer.

Another example is an integrated circuit for a pixel. The integrated circuit includes a common electrode layer and an organic light emitting device disposed on the common electrode layer. The organic light emitting device comprises an emission surface. A drive transistor is disposed on a part of the emission surface. A reflector layer is disposed between the drive transistor and the organic light device. The reflector layer includes an aperture over the emission surface and a reflective surface facing the emission surface. The reflective surface reflects light emitted from the light emitting surface through the aperture.

The foregoing and additional aspects and embodiments of the present invention will become apparent to those skilled in the art in light of the detailed description of the various embodiments and / or aspects made with reference to the drawings, of which a brief description will next be given.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings.

1A Figure 3 is a prior art integrated circuit design for an OLED pixel;

1B is a circuit diagram of one of the OLED and a corresponding drive transistor for the OLED pixel in 1A ;

1C is a side view of the integrated circuit of the OLED pixel in FIG 1A ;

2 Figure 12 is a block diagram of an AMOLED display with reference pixels for correcting data for parameter compensation control;

3 Fig. 10 is an RGB type pixel integrated circuit arrangement having offset aperture OLED for an extended aperture;

4 Fig. 10 is an arrangement of an RGBW-type pixel integrated circuit having offset aperture OLED for an extended aperture;

5 is an arrangement of an integrated circuit for a top emitting RGB OLED pixel;

6 Figure 4 is an alternative arrangement for an integrated circuit for a top-emitting OLED RGB pixel;

7 Figure 12 is a cross-sectional view of an OLED pixel with a reflector to increase a luminous power of the pixel;

8A FIG. 12 is a graph of the aperture portion of a prior art array of OLEDs in a pixel as compared to the staggered arrangement in FIG 3 ;

8B FIG. 12 is a graph of the aperture fraction of prior art stripe arrangements of OLEDs in a pixel compared to an upwardly emitting staggered array as in FIG 7 ; and

9A - 9M FIG. 15 are cross-sectional views illustrating the formation of a pixel structure having a high effective aperture percentage according to an embodiment of the invention. FIG.

Although the invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. It is to be understood, however, that the invention is not limited to the specific forms disclosed. Rather, the invention is intended to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

PRECISE DESCRIPTION

2 is an electronic display system 200 with an active matrix field or a pixel field 202 in which a field of active pixels 204a -D is arranged in a row and column configuration. Each of the active pixels 204 includes a red, a green and a blue organic light emitting diode (OLED) to emit different color components that are combined to produce different colors for emission from the pixel. To simplify the illustration, only two rows and columns of pixels are shown. Outside the active matrix area 202 is a border area 206 in which a peripheral circuit for driving and controlling the pixel fields 202 is arranged. The Peripheral circuitry includes a gate or address drive circuit 208 , a source or a data drive circuit 210 , a controller 212 and an optional drive for a supply voltage (for example Vdd) 214 , The controller 212 controls the gate, source and supply voltage drives 208 . 210 . 214 , The gate drive circuit 208 that from the controller 212 is controlled, works with address or select lines SEL [i], SEL [i + 1], and so on, one for each row of pixels 204 in the pixel field 202 , In pixel sharing configurations described below, the gate or address drive circuitry may be used 208 optional global selector lines GSEL [j] and optional / GSEL [j] operate using multiple lines of pixels 204a -D in the pixel field 202 operate, such as every two pixel lines 204 , The source drive circuit 210 that from the controller 212 is controlled, serves voltage data lines Vdata [k], Vdata [k + 1], and so on, one for each column of pixels 204 in the pixel field 202 , The voltage data lines carry voltage programming information to each pixel 204 which is a brightness of each of the color components of the light emitting devices in the pixel 204 specify. A storage element such as a capacitor stores the voltage programming information in each of the light emitting devices of the pixels 204 until an emission or drive cycle turns on each of the light devices. The optional supply voltage control 214 that from the controller 212 controls a supply voltage line (VDD line), one for each row of pixels 204 in the pixel field 202 ,

The display system 200 may also include a current source circuit that provides a fixed current on bias lines. In some configurations, a reference current may be supplied to the current source circuit. In such configurations, a current source circuit controls the timing of the application of a bias current to the bias lines. In configurations in which the reference current is not supplied to the current source circuit, a current source address driver controls the timing of the application of a bias current to the bias current lines.

As is known, every pixel needs 204 in the display system 200 are programmed with data representing the brightness of each of the light emitting devices in the pixel 204 specify to produce the desired color from the pixel 204 should be emitted. A frame defines the period of time, which includes a program cycle or a program phase, during which each individual pixel 204 in the display system 200 is programmed with programming voltages that emit a brightness and a drive or emission cycle, or a phase in which each light device in each pixel is turned on to emit light having a brightness in accordance with the programming voltage stored in a memory element. A frame is thus one of many still images that make up a complete moving image on the display system 200 is displayed. There are at least two schemes for programming and driving the pixels: line-by-line or frame-by-frame. In line-by-line programming, one line of pixels is programmed and then driven before the next line of pixels is programmed and driven. In frame-by-frame programming, all lines of pixels in the display system become 200 programmed first and all pixels are driven line by line. Both schemes can use a short vertical blanking time at the beginning or end of each frame in which the pixels are neither programmed nor driven.

The components of the pixel field 202 that are arranged outside of it, can be in a border area 206 around the pixel field 202 be arranged on the same physical substrate on which the pixel field 202 is arranged. These components include the gate driver 208 , the source driver 210 and the optional supply voltage control 214 , Alternatively, some of the components in the edge region may be on the same substrate as the pixel array 202 may be arranged while other components are disposed on another substrate or all components in the edge region may be disposed on a different substrate than on the substrate on which the pixel array 202 is arranged. Together they form the gate driver 208 , the source driver 210 and the supply voltage control 214 a display drive circuit. The display drive circuit may, in some configurations, be the gate driver 208 and the source driver 210 but not the supply voltage control 214 include.

The display system 200 further includes a power supply and readout circuit 220 on, the output data from data output lines VD [k], VD [k + 1] and so on, one for each column of pixels 204a . 204c in the pixel field 202 reads. The drive transistors for the OLED in the pixels 204 are in this example thin film transistors made of amorphous silicon. Alternatively, the drive transistors may be made of polysilicon.

In the configurations for the OLED described below, the aperture ratio is improved by minimizing the occluded area of the OLED emission area by changing the arrangement of the drive transistors and the OLED. Another configuration for an upper emission allows the light from the area covered by the Control transistor and metallic layers such as power and programming lines is blocked, is led to a window on the emission surface of the OLED. As a result, the aperture percentage is much larger than the actual aperture.

The arrangement of the OLED and drive transistors, described below, makes the pixel opening more independent of manufacturing design rules that require certain distances between OLEDs and certain widths of the power and data lines. This technique enables the production of high resolution displays while providing a reasonable aperture fraction without the need for a high resolution manufacturing process. Consequently, the use of shadow masks to subdivide the pixel for high pixel densities becomes possible or even easier.

3 shows a plan view of an integrated circuit for a pixel 300 , which is a staggered architecture for a bottom-emitting RGB pixel. The integrated circuitry of the pixel 300 has an upper part line 302 and a lower subline 304 each comprising a series of OLEDs. Each of the OLEDs forms a subpixel in each pixel, such as the pixel 300 , The sub-pixels (eg green, red and blue) alternate between the sub-lines. In this example, the upper subline comprises 302 a green OLED 310 , a drive transistor 312 , a red OLED 314 and a drive transistor 316 , The lower subline 304 includes a drive transistor 320 , a blue OLED 322 , a drive transistor 324 and a green OLED 326 , A selection line 330 is on the top of the upper subline 302 manufactured and a selection line 332 is on the bottom of the lower subline 304 manufactured. The drive transistor 316 and the green OLED 326 belong to a next pixel 350 in the field and share the selection lines 330 and 332 with the pixel 300 , The OLED 310 . 314 and 322 in the pixel 300 are therefore in a staggered arrangement, so that they may be arranged closer to each other side by side. It is understood that the term sub-line is simply used for simplicity. From another perspective, the different OLEDs may be offset in adjacent columns. The various OLEDs are arranged so that certain OLEDs are juxtaposed and other OLEDs above or below the OLEDs that are adjacent to each other are to allow the increase in the width of the OLED.

A power line 340 adjoins both the green OLED 310 as well as to the drive transistor 320 at. A data line 342 is between the green OLED 310 and the drive transistor 312 the upper part line 302 made and sits between the drive transistor 320 and the blue OLED 322 the lower part line 304 continued. A power line 344 is between the drive transistor 312 and the red OLED 314 the upper part line 302 made and sits between the blue OLED 322 and the drive transistor 324 the lower part line 304 continued. The structure of the pixel 300 also includes a data line 346 between the red OLED 314 and the drive transistor 314 the upper part line 302 is made and located between the transistor 324 and the green OLED 326 the lower part line 304 continues. Another power line 348 Adjacent to the drive transistor 316 the upper part line 302 and the green OLED 326 of the lower subline 304 , The drive transistor 316 and the green OLED 326 are part of the next pixel 350 next to the pixel 300 but share the data line 346 ,

In 3 becomes the display circuit of the pixel 300 into the two sublines 302 and 304 divided. The OLED 310 . 322 and 314 are alternatively arranged at the top and bottom of the pixel area. As a result, the distance between two adjacent OLEDs will be greater than the minimum distance required. Likewise, the data lines such as the data lines 342 and 346 between two neighboring pixels like the pixel 300 and the neighboring pixel 350 to be shared. This results in a large aperture fraction, as the distance between the OLEDs such as the OLED 310 and the OLED 322 due to the staggered configuration, which leads to larger emission areas of the OLED can be reduced. Because the OLED is in the pixel 300 Sharing power lines reduces the surface area required for such lines, allowing the area to be open to the emitting surfaces of the OLED, thus further increasing the aperture fraction.

4 shows an exemplary offset architecture for a bottom emitting RGBW display pixel circuit 400 , The integrated circuitry for the pixel 400 includes an upper subline 402 and a lower subline 404 , In this example, the upper subline comprises 402 a green OLED 410 , a drive transistor 412 , a red OLED 414 and a drive transistor 416 , The lower subline 404 includes a drive transistor 420 , a blue OLED 422 , a drive transistor 424 and a white OLED 426 , 4 shows the entire pixel that the four OLEDs 410 . 414 . 422 and 426 includes.

A selection line 430 is on top of the upper subline 402 manufactured and a selection line 432 is on the bottom of the lower subline 404 manufactured. A power line 440 is adjacent to the green OLED 410 and the drive transistor 420 , A data line 442 is between the green OLED 410 and the drive transistor 412 the upper part line 402 made and sits between the drive transistor 420 and the blue OLED 422 of the lower subline 404 continued. A power line 444 is between the drive transistor 412 and the red OLED 414 the upper part line 402 made and sits between the blue OLED 422 and the drive transistor 424 the lower part line 404 continued. The circuit 400 also includes a data line 446 between the red OLED 414 and the drive transistor 416 the upper part line 402 is made and located between the drive transistor 424 and the white OLED 426 the lower part line 404 continues. Another power line 448 Adjacent to the drive transistor 416 the upper part line 402 and the white OLED 426 the lower part line 404 , The power lines 440 and 448 are shared by neighboring pixels (not shown).

As with the configuration in 3 indicates the pixel circuit 400 in 4 an increased aperture because of the distance between parallel OLEDs due to the staggered relationship between the OLEDs 410 . 414 . 422 and 426 can be reduced. The white OLED 426 is added as the bulk of the ad, which is the pixel circuit 400 used, typically emitted white color and the white OLED 426 continuous emissions from the blue OLED 422 which is mainly used to white color in RGB type pixels such as the pixel 300 in 3 to emit. As with the configuration in 3 For example, the gaps between the OLEDs can be reduced, which leads to a greater exposure of the emission surfaces. Further, the sharing of data and power supply lines also reduces the area required for such leads, resulting in exposing additional surface emission area for the OLED.

The same staggered arrangement as in 3 and 4 can be used for the above-emitting integrated OLED circuit. 5 shows a staggered color pattern for a top-emitting RGB display structure 500 , The structure 500 includes an upper subline 502 and a lower subline 504 , The upper part line 502 includes a green OLED 512 and a red OLED 514 , The drive transistors for driving the OLED 512 and 514 are on a lower circuit layer 516 under the OLED 512 and 514 assembled. The lower subline 504 includes a blue OLED 522 and a green OLED 524 , The drive transistors that the OLEDs 522 and 524 are on a circuit layer 526 under the OLED 522 and 524 manufactured. In the display structure 500 form the OLED 512 . 514 and 522 a pixel while the green OLED 524 Is part of another pixel. Thus, the structure leads 500 to a display with interleaved pixels sharing different data lines. Such pixels require any interpolation of image data because the data lines are shared among the OLEDs of the pixels.

A selection line 530 is on the top of the upper subline 502 manufactured and a selection line 532 is on the bottom of the lower subline 504 manufactured. A power line 540 adjoins both the green OLED 510 as well as the blue OLED 520 , A data line 542 is under the green OLED 510 the upper part line 502 made and sits under the blue OLED 522 the lower part line 504 continued. The data line 542 is used to green the OLED 512 and the blue OLED 522 to program. A power line 544 is between the green OLED 512 and the red OLED 514 the upper part line 502 made and sits between the blue OLED 522 and the green OLED 524 the lower part line 504 continued. A data line 546 is over the red OLED 514 the upper part line 502 made and sits above the green OLED 524 the lower part line 404 continued. The data line 546 is used to red OLED 514 and the green OLED 524 to program. Another power line 548 adjoins the red OLED 514 the upper part line 502 and the green OLED 524 the lower part line 504 , The power lines 540 and 548 are shared by the transistors and OLEDs of adjacent pixels.

In this case, the sharing of data programming leads 542 and 546 (VDATA) in the above-emitting structure 500 to more area for the drive transistors under the OLED. As a result, the drive transistors in the emission structure 500 have larger source, drain and gate regions, and the aging of the drive transistors will be slower, requiring lower current densities for the transistors.

The emission structure 500 allows a reduction in the distance between the OLEDs 512 and 522 due to the staggered arrangement. The OLED 512 . 514 . 522 and 524 can be made wider than a known OLED, but with a shorter length compared to. The wider OLED surface leads to an increased aperture percentage. The emission structure 500 requires an image data signal processed from a raw RGB signal because the OLEDs to OLEDs are offset from the neighboring pixels. The transparent common electrode (not shown) over the OLED 512 . 514 . 522 and 524 indicates because of the wider area of the OLED 512 . 514 . 522 and 524 a comparatively lower resistance.

6 shows an alternative pixel arrangement 600 for a top-emitting structure. The pixel arrangement 600 improves the aperture percentage and relaxes the OLED manufacturing requirements. The pixel arrangement 600 includes different pixels 602 . 604 . 606 and 608 , Each of the pixels includes three OLEDs, such as OLEDs 610 . 612 and 614 on one circuit layer 616 which are the driving transistors for driving each of the OLEDs 610 . 612 and 614 includes. In this case, the OLED emits 610 green light and is in a row with the OLED 612 that emits red light. The OLED 614 emits blue light and has a larger emission area than the OLED 610 and 612 , Selection lines such as selection lines 620 . 622 and 624 run on the top and bottom of the pixels 602 . 604 . 606 and 608 , Power lines 630 . 632 and 634 run along the sides of the pixels 602 . 604 . 606 and 608 to voltages for the OLED 610 . 612 and 614 and to provide their respective drive transistors. data lines 640 . 642 . 644 and 646 run under the OLED of the pixels 602 . 604 . 606 and 608 , For example, the data line becomes 640 used to the OLED 610 to program, becomes the data line 642 used to the OLED 612 to program and either the data line 640 or 644 is used to the OLED 614 in the pixel 602 to program.

In the structure 600 is every single stream within a subline. As a result, the lines appear in a display consisting of pixels representing the arrangement 600 use, straighter, and thus provide better quality for a text application. The OLED 614 that emits blue light is larger than the OLED 610 and 612 and covers substantially the entire width of the pixel 602 because of the increased surface area for the blue-colored OLED 614 aging is delayed, which is a result of the faster aging inherent in the blue-colored OLED. The increased surface area requires less current density to produce the same performance as a smaller area OLED, thus aging more slowly. The structure 600 in 6 has an improved appearance compared to the structure 500 in 5 because the red, green and blue OLED elements are in a straight line and are not offset between the pixels. As with the structure 500 in 5 has the transparent common electrode (not shown) over the OLED 610 . 612 and 614 due to the wider areas of the OLED 610 . 612 and 614 a comparatively lower resistance, as in 9E is shown.

7 shows the cross section of a pixel structure 700 , which is a modified down-emissive pixel that increases the aperture fraction by having a reflector, the light that emanates from the areas of the emitting surface of an OLED 702 that are covered by other circuit components emitted, focused. The OLED 702 includes a cathode layer 704 and an anode layer 706 , A common electrode layer 708 provides an electrical bias to the other side of the OLED 702 , The common electrode 708 can be shaped as a concave mirror to bring more light to the reflective surface 740 to reflect. A drive transistor 710 is over part of the emission area of the OLED 702 manufactured. The drive transistor 710 includes a gate 712 , a drain area 714 and a source area 716 , The drive transistor 710 is on a transparent substrate layer 720 made the OLED 702 superimposed. A metallization layer 730 overlays the transparent substrate 720 to electrodes 732 and 734 form each of the drain area 714 and the source area 716 of the drive transistor 710 and provide electrical connections to the other components of the circuit, such as data and power supply lines. An electrode (not shown) is also to the gate of the transistor 710 shaped. The metallization layer 730 has an opening 736 up, through the light from the OLED 702 through the transparent substrate 720 can be emitted.

The pixel structure includes a reflector 740 that is between the OLED 702 and the drive transistor 710 is arranged. The reflector 740 has a reflective surface 742 on that of the emitting surface of the OLED 702 is facing and light coming from the OLED 702 is emitted and normally by the drive transistor 710 would be blocked, reflected. The reflected light (with arrows in 7 shown) turns off a window 744 in the reflector 740 emitted so as to be actually from the OLED 702 increase emitted light.

Thus, the OLED emission area is not limited to the window opening provided by the drive transistor and the supporting components on the OLED 702 is defined. As a result, the OLED current density is lower for a given luminance than for a conventional bottom emitting array. This arrangement, which is the reflector 740 includes, requires a lower OLED voltage and thus a lower power consumption to achieve the same brightness as a conventional OLED without the reflector. In addition, the life of the OLED 702 be longer due to the lower current density. This structure 700 can also be used with other techniques to further improve the aperture content.

The aperture percentage for different display resolutions is shown in a diagram 800 in 8A demonstrated. The graph 800 compares the aperture portions of the different configurations to display resolutions. A set of data points 802 FIG. 12 shows the aperture portions of a standard amorphous silicon red-green-blue pixel stripe structure as in FIG 1A shown. A second set of data points 804 Figure 12 shows the aperture portions of a standard polysilicon red-green-blue pixel stripe structure. As in 8A As shown, the polysilicon-based pixel has somewhat better aperture ratios than that on the amorphous Silicon based pixels on. A third set of data points 806 shows the aperture portions of a staggered down-emitting structure such as the structure of FIG 3 shown pixels 300 , As in the data points 802 in 8A While the aperture percentage for a higher resolution (eg, 250 pixels per inch) using a standard RGB stripe configuration is zero, the aperture percentage of the offset pixel architecture is shown in FIG 3 in data points 806 higher than 20% at up to 260 PIXEL PER ZOLL.

8B is a graph 850 showing the behavior of the aperture portions at different display resolutions for different OLED pixel structures. A set of data points 852 FIG. 12 shows the aperture portions of a standard amorphous silicon red-green-blue pixel stripe structure as in FIG 1A shown, which is made with a shadow mask. A second set of data points 854 shows the aperture portions of a staggered downwardly emitting structure of amorphous silicon such as the structure of FIG 3 shown pixels 300 which is made with a shadow mask. Another set of data points 856 Figure 12 shows the aperture portions of a top-emitting structure in a red-green-blue pixel stripe structure fabricated by laser-induced thermal imaging (LITI). A last group of data points 858 shows the aperture portions of a top emitting structure corresponding to those in FIG 7 shown staggered arrangement used and manufactured by LITI.

The aperture fraction is used for two types of OLED patterning (shadow mask with a 20 μm gap and LITI with a 10 μm gap), as in the data points 852 and 856 shown for a strip-like arrangement, as in 1A shown, extracted. In the case of shadowmask fabrication, the aperture fraction for an RGB stripe is constrained by OLED design rules, while an RGB stripe using LITI fabrication is constrained by the TFT design rules. However, for both shadow masking and LITI manufacturing, a staggered color pattern can provide a high resolution (eg, 300 pixels per inch) with a large aperture fraction, such as through the data points 854 and 858 shown. This resolution is delivered without providing stricter design rules compared to conventional OLED layouts.

A preferred method of fabricating the pixel structure described above comprises: (1) forming a first photoresist layer having the first opening 736 on the substrate 720 , Forming the reflective layer 740 with the second opening 744 over the first photoresist layer, forming a second photoresist layer in the opening 744 and over the reflective layer; and forming the organic light emitting device 702 over the second photoresist layer. The second opening 744 overlaps with the first opening 736 and at least a portion of the reflective layer 740 has a concave shape. The transistor elements 710 . 712 . 714 . 716 . 732 and 734 are on the surface of the substrate 720 below the reflective layer offset to the openings 736 and 744 educated.

9A to 9M 12 are cross-sectional views showing sequential steps of an exemplary pixel structure manufacturing method having a high effective aperture ratio according to an embodiment of the invention. These steps can be used to create a pixel structure as shown. The pixel structure is a modified up-emitting pixel that increases the effective aperture portion such that the effective aperture fraction is greater than the actual aperture portion of the device. For ease of description, the transistor circuits that support the pixel structure are omitted. However, it is contemplated that the pixel structure of 9A - 9M one or more supporting transistors (eg TFT), such as drive transistor 710 and its associated components may include, as in 7 are shown positioned.

A substrate 910 will be provided. The substrate 910 may be, for example, a glass wafer. The substrate 910 is cleaned with an RCA solution; especially with a 1: 1: 5 solution of NH ₄ OH (ammonium hydroxide), H ₂ O ₂ (hydrogen peroxide) and H ₂ O (water). The substrate 910 is cleaned with the solution at 80 ° C for 20 minutes.

A first photoresist layer 915 is 11.6 μm thick on the substrate 910 formed as in 9A shown. In this embodiment, the first photoresist layer 915 on the substrate 910 applied by spin coating at 800 rpm for 10 seconds and then at 4000 rpm for 60 seconds. The first photoresist layer 915 may be any suitable transparent photoresist material, such as SU-8 photoresist. In a further embodiment, the first photoresist layer comprises 915 a black or dark polymer. The first photoresist layer 915 is then soft baked at 95 ° C for 3 minutes, exposed for 16 seconds and baked hard at 95 ° C for 4 minutes.

Next, as in 9B shown a mask layer 920 with a thickness of 100 μm on the first photoresist layer 915 educated. The mask layer 920 is used as a hard mask for the subsequent etching of the first photoresist layer 915 used and may be, for example, an aluminum foil. In this embodiment, the mask layer becomes 920 using WLOS sputtering with 50 sccm Ar, 9 mTorr pressure, 300 W DC power and deposited for 700 seconds deposition time.

A second photoresist layer 925 gets on the mask layer 920 formed for photolithography, as in 9C shown. In this embodiment, the second photoresist layer becomes 925 on the mask layer 920 by spin-coating at 500 rpm for 10 seconds and then at 4000 rpm for 60 seconds. The second photoresist layer 925 may include any suitable photoresist material such as AZ3312 photoresist. The second photoresist layer 925 is then soft baked at 90 ° C for 1 minute.

A photomask 930a -C is then applied to the second photoresist layer 925 An ultraviolet (UV) exposure is applied from the top (ie on the side of the photomask 930a -C) as in 9D shown applied. In this embodiment, the UV exposure is maintained for 4 seconds with an intensity of 10 mW / cm 2. An AZ-300 MIF developer is then applied and developed for 16 seconds, and the sample is baked after exposure at 120 ° C for 60 seconds resulting in separate second photoresist layers 925a and 925b leads.

As in 9F the mask layer is shown 920 in separate mask layers 920a and 920b etched. In this embodiment, the mask layer becomes 920 etched using a polyacrylonitrile solution (PAN solution); In particular, a 16: 2: 1: 1 solution of each of H ₃ PO ₄ (phosphoric acid), H ₂ O (deionized water), HAc (acetic acid) and HNO ₃ (nitric acid) is used. The mask layer 920 is etched at 40 ° C for 3-4 minutes. Then the second photoresist layers become 925a and 925b away. In this embodiment, the second photoresist layers become 925a and 925b removed using acetone or AZ-300 remover.

A first photoresist layer 915 is then placed in the separate first photoresist layers 915a . 915b etched, as in 9G shown, and forms a concave shape. In this embodiment, the first inductively coupled plasma (ICP) photoresist layer is dry etched isotropically. The ICP dry etching recipe is 20 O ₂ , 2 CF ₄ , 180 ICP power, 50 pressure, and 700 seconds etch time. As in 9H the separate mask layers are shown 920a and 920b away. In this embodiment, the separate mask layers become 920a and 920b with a polyacrylonitrile solution (PAN solution).

The reflective layer 940 is then deposited, as in 9I shown. In this embodiment, the reflective layer becomes 940 using WLOS sputtering with 50 sccm Ar, 9 mTorr pressure, 300 W DC power, and 700 seconds deposition time. As in 9J The emission windows are then shown opened by means of photolithography. A third photoresist layer (not shown) is spin-coated at 3000 rpm for 30 seconds, soft baked at 100 ° C for 6 minutes, and then rehydrated for 30 minutes. The third photoresist layer may comprise any suitable photoresist layer and in this embodiment comprises an AZ-P4330 photoresist. The third photoresist layer is then exposed to UV radiation at 365 nm for 35 seconds and then developed in a 1: 4 solution of each AZ400K developer and deionized water for 6 minutes. The section of a mirror layer 940 on the substrate 910 is then etched with polyacrylonitrile for 4 minutes, resulting in separate mirror layers 940a and 940b results, and the remainder of the third photoresist layer is removed with remover.

As in 9K a fourth photoresist layer is shown 945 in the opening of the mirror layers 940a and 940b and over the reflective layers 940a and 940b applied. In this embodiment, the fourth photoresist layer becomes 945 applied by rotating at 800 rpm for 10 seconds and then at 4000 rpm for 60 seconds. The fourth photoresist layer 945 may be any suitable transparent photoresist material such as SU-8 photoresist. The fourth photoresist layer 945 is then soft baked at 95 ° C for 3 minutes, exposed for 16 seconds and baked hard at 95 ° C for 4 minutes.

An anode 950 is then over the fourth photoresist layer 945 applied, as in 9L shown. In this embodiment, the anode 950 an indium tin oxide film (ITO film). The anode 950 is deposited using an AJA sputtering system having a ratio of Ar: O ₂ of 16: 0.5, a temperature of 150 ° C, an RF power of 100 W and a deposition time of 50 minutes. Afterglow is then carried out at 150 ° C for 30 minutes. The anode 950 can then be patterned using a different photolithography process.

Then, OLEDs are on top of the patterned anode 950 isolated, as in 9M shown. In this embodiment, the OLEDs are deposited with a InteVoc thermal evaporation system at a pressure below 5 × 10 ^-6 Torr. The OLEDs comprise the anode 950 , an organic electroluminescent layer 955 and a cathode 960 , However, a common electrode layer (not shown) may be the cathode 960 be formed.

As will be apparent to those skilled in the art, the organic electroluminescent layer 955 include multiple layers, including (from the anode 950 to the cathode 960 ) a hole injection layer, a hole transport layer, an emission layer, an electron transport layer, and an electron injection layer. In one embodiment, the hole injection layer comprises MoO ₃ ; the hole transport layer comprises NPB; the electron transport layer comprises Alq ₃ ; the electron injection layer comprises LiF; and the cathode 960 includes Al.

The pixel structure has reflective layers 940a . 940b on that between the OLED (which is the anode 950 , the organic electroluminescent layer 955 and the cathode 960 and the one or more drive transistors (not shown but between the substrate and the first photoresist layers) 915a and 915b arranged). The reflective layers 940a . 940b include a reflective surface that faces the emission surface of the OLED and reflects light emitted from the OLED that would normally be blocked by the one or more drive transistors. The reflected light becomes an opening between the mirror layers 940a and 940b emitted so as to increase the light that is actually emitted by the OLED. Due to the concave shape of the reflective layers 940a and 940b the reflected light (as well as ambient light) is directed towards the opening between the reflective layers 940a and 940b guided.

Thus, the OLED emission area is not limited to the window opening defined by the drive transistor and the supporting components on the OLED. As a result, the OLED current density for a given luminance is lower than that of a conventional bottom emitting device. This arrangement containing the reflective layers 940a . 940b requires a lower OLED voltage and thus a lower power consumption to achieve the same luminance as a conventional OLED without the mirror layers. In addition, the lifetime of the OLED is extended due to the lower current density. This structure can also be used with other techniques to further enhance the effective aperture fraction.

Although certain embodiments and applications of the present invention have been illustrated and described, it is to be understood that the invention is not limited to the exact construction and exact compositions disclosed herein and that various modifications, changes, and variations will be apparent from the foregoing descriptions without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (13)

Pixel structure comprising: a substantially transparent substrate, a drive transistor formed on the substrate an organic lighting device, which is formed on the opposite side of the substrate of the drive transistor, a reflective layer disposed between the light emitting device and the drive transistor and having a reflective surface facing the light emitting device, the reflective layer forming an opening offset from the drive transistor to receive light emitted by the light emitting device; to pass to the substrate. The pixel structure of claim 1, wherein at least a portion of the reflective layer has a concave shape to direct reflected light from the light device back to the light emitting device. Pixel structure comprising: a substrate; a first photoresist layer having a first opening over the substrate; a reflective layer having a second opening, the reflective layer covering the first photoresist layer; a second photoresist layer in the second opening and over the reflective layer; and an organic lighting device formed over the second photoresist layer, wherein the second opening overlaps the first opening and at least a portion of the reflective layer has a concave shape. The pixel structure of claim 3, further comprising: a drive transistor between the substrate and the first photoresist layer, the drive transistor controlling the luminance of the organic light device. The pixel structure of claim 3, wherein the reflective layer comprises aluminum. The pixel structure of claim 3, wherein the organic light emitting device comprises: an anode layer over the second photoresist layer, an organic electroluminescent layer over the anode layer; and a cathode layer over the organic electroluminescent layer. The pixel structure of claim 3, further comprising a common electrode layer over the cathode layer. The pixel structure of claim 3, wherein the reflective layer has a reflective surface that faces the organic light device and directs light from the organic light device to the second aperture. A method of forming a pixel structure, the method comprising: Providing a substrate; Forming a first photoresist layer having a first opening over the substrate; Forming a reflective layer having a second opening, the reflective layer covering the first photoresist layer; Forming a second photoresist layer in the second opening and over the reflective layer; and Forming an organic light emitting device over the second photoresist layer, wherein the second opening overlaps with the first opening and wherein at least a portion of the reflective layer has a concave shape. The method of claim 9, wherein the step of forming the first photoresist layer comprises: Depositing the first photoresist layer on the substrate; Forming a first mask layer on the first photoresist layer; Depositing a third photoresist layer on the first mask layer; Forming a second mask layer on the third photoresist layer; Applying ultraviolet radiation to the second mask layer, thereby separating the third photoresist layer; Removing the second mask layer; Etching the first mask layer with the third photoresist layer, thereby separating the first mask layer; Removing the third photoresist layer; Etching the first photoresist layer with the first mask layer, thereby forming the first opening; and Removing the first mask layer. The method of claim 9, wherein the step of forming the reflective layer comprises: Depositing the reflective layer on the first photoresist layer and the substrate; Depositing a third photoresist layer on the reflective layer; Applying ultraviolet radiation to the third photoresist layer; Developing the third photoresist layer; Etching the reflective layer with the third photoresist layer, thereby forming the second opening; and Removing the third photoresist layer. The method of claim 9, further comprising: Forming a drive transistor over the substrate, wherein the drive transistor controls the luminance of the organic light device. The method of claim 9, wherein the reflective layer has a reflective surface that faces the organic light device and directs light from the organic light device toward the second opening.

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