JP2009109853A - Active matrix type display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an active matrix type display device capable of improving an aperture ratio, suppressing voltage drop due to wiring resistance and capable of improving display quality. <P>SOLUTION: The display device includes: a plurality of display sections including a display element and a pixel circuit for supplying a drive current to the display element and arranged in a matrix on a substrate; a plurality of video signal lines X connected for each line of pixel parts and used to supply video signals; and a power source lines Vdd connected for each line of pixel parts. The pixel circuit includes: a drive transistor connected between the display element and the power source line; and a holding capacity Cs for holding the control potential of the drive transistor. The video signal line is formed in a layer higher than a layer in which the electrode of the holding capacity is formed. The power source line is formed in a layer positioned between the layer in which the electrodes 30 and 32 of the holding capacity are formed and the layer in which the video signal line is formed, so as to overlap the corresponding video signal line. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an active matrix display device in which a display screen is configured by arranging display pixels including organic electroluminescence (hereinafter referred to as EL) elements in a matrix.

  2. Description of the Related Art Planar active matrix display devices are widely used as display devices for personal computers, portable information terminals, and televisions. In recent years, as such a flat-type active matrix display device, an organic EL display device using a self-luminous element such as an organic EL element has attracted attention and has been actively researched and developed. This organic EL display device does not require a backlight that obstructs the reduction in thickness and weight, and is characterized by being suitable for moving image reproduction because of its high-speed response.

  In general, an organic EL display device includes a plurality of display pixels arranged in a plurality of rows and a plurality of columns and constituting a display screen, a plurality of scanning lines extending along each row of display pixels, and a column of display pixels. A plurality of extended signal lines, a scanning line driving circuit for driving each scanning line, a signal line driving circuit for driving each signal line, and the like are provided. Each display pixel includes an organic EL element that is a self-light-emitting element and a pixel circuit that supplies a drive current to the organic EL element (for example, Patent Document 1).

  As the pixel circuit, a current driving method that can cancel the threshold voltage and mobility of the driving transistor and suppress display unevenness is often used. In a current copy type pixel circuit which is one of current drive methods, each pixel circuit is connected in series with an organic EL element between a pixel switch and a pair of power supply lines arranged in the vicinity of the intersection of a scanning line and a signal line. The driving transistor includes a thin film transistor and a storage capacitor that holds a gate control voltage of the driving transistor. The pixel switch is turned on in response to a scanning signal supplied from the corresponding scanning line, and a current is supplied to the corresponding signal line through the driving transistor to perform a writing operation. Next, the gate-source potential of the driving transistor corresponding to this current is written as a gate control voltage in the storage capacitor and held for a predetermined period. Then, the driving transistor supplies a current amount corresponding to the gate control voltage written in the storage capacitor to the organic EL element to perform a light emitting operation.

A thin film transistor is formed of a semiconductor thin film such as low-temperature polysilicon or amorphous silicon. However, since variations in characteristics of individual transistors occur, various circuits have been developed to cancel the variations in characteristics.
JP 2000-208252 A

  However, in the organic EL display device including such a pixel circuit, the number of transistors increases, so that the area of the transistors in the pixels increases and the aperture ratio decreases. In order to increase the aperture ratio, it is possible to reduce the wiring area by narrowing the power supply wiring width. However, in this case, the resistance value of the wiring increases to cause a voltage drop, and a desired voltage cannot be applied. Therefore, the display quality is lowered.

  The present invention has been made in view of the above points, and an object of the present invention is to provide an active matrix capable of improving the aperture ratio, suppressing voltage drop due to wiring resistance, and improving display quality. Is to provide a type display device

In order to achieve the above object, an active matrix display device according to an aspect of the present invention includes a display element and a plurality of pixel circuits arranged in a matrix on a substrate, the pixel circuit supplying a driving current to the display element. A plurality of video signal lines connected to each column of the pixel units and supplying a video signal, and a power supply line connected to each column of the pixel units,
The pixel circuit includes a drive transistor connected between the display element and a power supply line, and a storage capacitor that holds a control potential of the drive transistor, and the signal line is formed by an electrode of the storage capacitor The power supply line is a layer located between the layer in which the electrode of the storage capacitor is formed and the layer in which the signal line is formed, and is in a position overlapping the signal line. Is formed.

  According to the aspect of the present invention, it is possible to provide an active matrix display device capable of improving the aperture ratio, suppressing the voltage drop due to the wiring resistance, and improving the display quality.

Hereinafter, an organic EL display device according to an embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 schematically shows the entire organic EL device. As shown in FIG. 1, the organic EL display device is configured as, for example, a large active matrix display device of 10 type or more, and includes an organic EL panel 10 and a controller 12 that controls the organic EL panel 10.

  The organic EL panel 10 is arranged in the form of a matrix on an insulating substrate 8 such as a glass plate, and is connected to each row of the display pixels, each of which is connected to each row of the display pixels 11 and independently. The first scanning line Sga (1 to m), the second scanning line Sgb (1 to m), and the n video signal lines X (1 to 1) connected to each column of the display pixels PX, respectively. n), a scanning line driving circuit 14 for sequentially driving the first and second scanning lines Sga (1 to m) and Sgb (1 to m) for each row of display pixels, and a plurality of video signal lines X (1 to n). ) Is provided. The scanning line driving circuit 14 and the signal line driving circuit 15 are integrally formed on the insulating substrate 8 outside the display area 11.

  Each display pixel PX that functions as a pixel portion includes a display element having a photoactive layer between opposing electrodes, and a pixel circuit 18 that supplies a drive current to the display element. The display element is, for example, a self-luminous element. In this embodiment, the organic EL element 16 including at least an organic light-emitting layer is used as a photoactive layer.

  FIG. 2 shows an equivalent circuit of the display pixel PX. The pixel circuit 18 is a current-driven pixel circuit that controls light emission of the organic EL element 16 in accordance with a video signal including a current signal. The pixel circuit 18 includes a pixel switch 20, a drive transistor 22, a first switch 24, an output switch 26, and a holding circuit. The capacitor Cs is provided. Here, the pixel switch 20, the drive transistor 22, the first switch 24, and the output switch (second switch) 26 are formed of thin film transistors of the same conductivity type, for example, a P-channel type. In this embodiment, all the thin film transistors constituting the pixel circuit 18 are formed in the same process and the same layer structure, and are top gate thin film transistors using polysilicon as a semiconductor layer.

  The drive transistor 22, the output switch 26, and the organic EL element 16 are connected in series in this order between the first voltage power supply line Vss and the second voltage power supply line Vdd. The first voltage power line Vss and the second power line Vdd are set to potentials of −9 V and +6 V, for example. The drive transistor 22 has a first terminal, here a source, connected to the second voltage power supply line Vdd. The organic EL element 16 has one electrode, here the cathode, connected to the first voltage power supply line Vss. The output switch 26 functioning as a transistor in the present invention has its source connected to the second terminal of the driving transistor 22, here the drain. The output switch 26 has a drain connected to the anode of the organic EL element 16 and a gate connected to the second scanning line Sgb.

  The drive transistor 22 outputs a light emission current having a current amount corresponding to the video signal to the organic EL element 16. The output switch 26 is controlled to be on (conductive state) and off (non-conductive state) by a control signal Sb (1 to m) from the second scanning line Sgb, and the connection between the driving transistor 22 and the organic EL element 16 is not connected. Control the connection.

  The holding capacitor Cs is connected between the first terminal and the control terminal of the driving transistor 22, here, between the source and the gate, and holds the gate control potential of the driving transistor 22 determined by the video signal. The pixel switch 20 is connected between the corresponding video signal line X (1 to n) and the drain of the driving transistor 22, and its gate is connected to the first scanning line Sga. The pixel switch 20 takes in a signal current as a gradation current from the corresponding video signal line X (1 to n) in response to the control signal Sa (1 to m) supplied from the first scanning line Sga.

  The first switch 24 is connected between the drain and gate of the drive transistor 22, and the gate thereof is connected to the first scanning line Sga. The first switch 24 is on / off controlled in accordance with a control signal Sa (1 to m) from the first scanning line Sga, controls connection / disconnection between the gate and drain of the drive transistor 22, and holds capacitance. Regulates current leakage from Cs.

  The operation of the pixel circuit 18 is divided into a video signal writing operation and a light emission operation. As shown in FIG. 2, in the video signal writing operation, the control signals Sa and Sb such that the pixel switch 20 and the first switch 24 are turned on (conductive state) and the output switch 26 is turned off (non-conductive state), here The control signal Sa is output as a low level and the control signal Sb is output as a high level. Thereby, the pixel switch 20 and the first switch 24 are turned on (conductive state), the output switch 26 is turned off (non-conductive state), and the video signal writing operation is started.

  In the video signal writing period, the video signal current Idata supplied from the signal line driving circuit 15 to the corresponding video signal line X (1 to n) is supplied to the selected display pixel PX via the pixel switch 20. In the display pixel PX, the pixel switch 20 and the first switch 24 are in an on state, and the captured video signal current Idata is supplied to the drive transistor 22 to put the drive transistor 22 in a writing state. As a result, a write current flows from the second voltage power supply line Vdd to the video signal line X1 through the drive transistor 22, and the gate-source potential of the drive transistor 22 corresponding to the current amount of the video signal current Idata is written to the storage capacitor Cs. .

  Next, the control signal Sa1 becomes a high level (off potential), and the pixel switch 20 and the first switch 24 are turned off. Thereby, the video signal writing operation is completed. Subsequently, the control signal Sb1 becomes low level, and the output switch 26 is turned on. Thereby, the light emission operation starts. During the light emission period, the drive transistor 22 is maintained in a conductive state by the gate control voltage written in the storage capacitor Cs, and the light emission current having a current amount corresponding to the video signal current Idata is supplied from the second voltage power supply line Vdd to the output switch 26 side. To supply. This light emission current is supplied to the organic EL element 16 after passing through the output switch 26. Thereby, the organic EL element 16 emits light, and the light emission operation is started. The organic EL element 16 maintains the light emission state until the control signal Sc1 becomes the off potential again after one frame period.

  FIG. 3 shows a planar configuration of the display pixel PX, and FIG. 4 is a cross-sectional view showing a part of FIG. As shown in FIGS. 3 and 4, on the transparent insulating substrate 8, a polysilicon layer constituting a semiconductor layer of the drive transistor 22, the first switch 20, the first switch 24, and the output switch 26, and the storage capacitor Cs. A conductive layer constituting one of the electrodes 30 is formed. A gate insulating layer 34 is formed over the polysilicon layer and the conductive layer.

  On the gate insulating layer 34, conductive layers such as Al, Ti, and titanium oxide forming the first and second scanning lines Sga and Sgb, the gate of the driving transistor 22 and the other electrode 32 of the storage capacitor Cs are formed. ing. An interlayer insulating film 36 is formed over the conductive layer. Further, a conductive layer for forming a second voltage power supply line Vdd, a transistor source electrode, a drain electrode, and a plurality of wiring groups is formed on the interlayer insulating film 36. An interlayer insulating film 38 is formed over the conductive layer.

  On the interlayer insulating film 38, a conductive layer for forming the video signal lines X (1 to n) and a conductive layer for forming the anode 16a of the organic EL element 16 are formed. A protective layer 40 is formed on these conductive layers.

  Each video signal line X (1-n) extends along each column of display pixels. Similarly, each second voltage power supply line Vdd extends along each column of display pixels and is disposed so as to overlap the video signal line X. The video signal line X and the second voltage power supply line Vdd extend between the storage capacitors Cs adjacent in the row direction.

  The video signal lines X (1 to n) are formed in an upper layer than the layer in which the electrodes 30 and 32 of the storage capacitor Cs are formed, and the second voltage power supply line Vdd is a layer in which the electrode of the storage capacitor Cs is formed. It is formed in a layer located between the layers where the video signal lines X (1 to n) are formed, and is further formed in a position overlapping the video signal lines. The line width W2 of the second voltage power supply line is formed larger than the line width W1 of the video signal line X. The video signal line X is provided so as to overlap within the range of the line width W2 of the second voltage power supply line Vdd.

  According to the organic EL display device configured as described above, the video signal lines X (1 to n) and the second voltage power supply lines are arranged so as to overlap each other to form a two-layer structure, thereby occupying the wiring in the pixel plane. It is possible to reduce the area and increase the aperture ratio. At this time, it is not necessary to make the second voltage power supply line Vdd thinner, and a voltage drop due to wiring resistance can be prevented.

  Further, by providing the second voltage power supply line Vdd in a layer located between the electrode of the storage capacitor Cs and the video signal line X, the second voltage power supply line shields between the storage capacitor and the video signal line. It is possible to suppress the formation of parasitic capacitance between the storage capacitor and the video signal line. If the parasitic capacitance between the video signal line and the storage capacitor increases, the potential of the storage capacitor fluctuates due to fluctuations in the potential of the video signal line, making it impossible to flow a desired current to the organic EL element, resulting in display defects. Will be invited. According to the present embodiment, by reducing the parasitic capacitance, the potential fluctuation of the electrode of the storage capacitor Cs caused by the potential fluctuation of the video signal line X can be reduced, and a desired current can be supplied to the organic EL element 16. It becomes. Thereby, display quality can be improved.

  In addition, according to the present embodiment, the second voltage power supply line Vdd has a wiring width wider than that of the video signal line X. Therefore, the shielding effect by the second voltage power supply line is increased, and the storage capacitor The parasitic capacitance formed between the Cs electrode 32 and the video signal line X can be further reduced.

  Next explained is an organic EL display device according to the second embodiment of the invention. FIG. 5 shows a planar configuration of the display pixel PX, and FIG. 6 is a cross-sectional view showing a part of FIG. As shown in FIGS. 5 and 6, each video signal line X (1-n) extends along each column of display pixels. Similarly, each second voltage power supply line Vdd extends along each column of display pixels and is disposed so as to overlap the video signal line X. The video signal line X and the second voltage power supply line Vdd extend between the storage capacitors Cs adjacent in the row direction.

  The video signal lines X (1 to n) are formed in an upper layer than the layer in which the electrodes 30 and 32 of the storage capacitor Cs are formed, and the second voltage power supply line Vdd is a layer in which the electrode of the storage capacitor Cs is formed. It is formed in a layer located between the layers where the video signal lines X (1 to n) are formed, and is further formed in a position overlapping the video signal lines. The line width W2 of the second voltage power supply line is formed larger than the line width W1 of the video signal line X. The video signal line X is provided so as to overlap within the range of the line width W2 of the second voltage power supply line Vdd.

  Each second voltage power supply line Vdd extends in a direction intersecting with the video signal line X, in this case, a direction orthogonal thereto, in addition to the vertical extension Vdd-v extending along the column of display pixels. A horizontal extension Vdd-h is integrally provided. The horizontal extension Vdd-h extends in both directions from the vertical extension Vdd-v and extends across adjacent vertical extensions. Each horizontal extension Vdd-h is formed to have a sufficiently thick width compared to the vertical extension Vdd-v. In the present embodiment, each horizontal extension portion Vdd-h is disposed at a position overlapping the storage capacitor Cs.

  If the wiring width of the vertical extension portion Vdd-v of the second voltage power supply line Vdd is too wide for the purpose of reducing the wiring resistance, the area of the wiring becomes large, and the aperture ratio is reduced accordingly. On the other hand, if the vertical extension portion Vdd-v is thin, the resistance value of the wiring increases and a voltage drop occurs. Therefore, as in the second embodiment, the second voltage power supply line Vdd is arranged not only in the direction overlapping the video signal line X but also in the intersecting direction. As a result, even if the line width of the vertical extension Vdd-v extending in the same direction as the video signal line X is narrowed, a desired potential is supplied without increasing the voltage drop of the second voltage power supply line Vdd. It becomes possible to do. Accordingly, it is possible to prevent display quality from being deteriorated.

  In the second embodiment, other configurations of the organic EL display device are the same as those of the first embodiment described above, and the same reference numerals are given to the same portions, and the detailed description thereof is omitted. In the second embodiment, the same operational effects as those of the first embodiment described above can be obtained.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

  For example, the line width of the voltage power line is thicker than the line width of the video signal line. However, the present invention is not limited to this. Obtainable. In the above-described embodiment, the semiconductor layer of the thin film transistor is not limited to polysilicon but can be composed of amorphous silicon. The self-luminous elements constituting the display pixels are not limited to organic EL elements, and various display elements capable of self-luminance are applicable.

FIG. 1 is a plan view schematically showing an organic EL display device according to an embodiment of the present invention. FIG. 2 is a plan view showing an equivalent circuit of display pixels in the organic EL display device. FIG. 3 is a plan view showing a planar configuration of a display pixel PX in the organic EL display device. 4 is a cross-sectional view taken along line AA in FIG. FIG. 5 is a plan view showing a planar configuration of a display pixel PX in an organic EL display device according to a second embodiment of the present invention. 6 is a cross-sectional view taken along line BB in FIG.

Explanation of symbols

8 ... Insulating substrate, 10 ... Organic EL panel, 12 ... Controller,
14 ... scanning line driving circuit, 15 ... signal line driving circuit, 16 ... organic EL element,
18 ... Pixel circuit, 20 ... Pixel switch, 22 ... Drive transistor,
24 ... 1st switch, 26 ... Output switch, Cs ... Holding capacity,
30, 32 ... electrodes, Vdd ... second voltage power supply line, Vdd-v ... vertical extension part,
Vdd-h: Horizontal extension

Claims (6)

A plurality of pixel portions including a display element and a pixel circuit for supplying a driving current to the display element, the pixel parts being arranged in a matrix on the substrate;
A plurality of video signal lines connected to each column of the pixel portion and supplying a video signal;
A power line connected to each column of the pixel portion,
The pixel circuit includes a drive transistor connected between the display element and a power supply line, and a storage capacitor that holds a control potential of the drive transistor,
The video signal line is formed in an upper layer than the layer in which the electrode of the storage capacitor is formed,
The power supply line is a layer located between the layer in which the electrode of the storage capacitor is formed and the layer in which the video signal line is formed, and an active matrix display formed at a position overlapping the video signal line apparatus.   2. The active matrix display device according to claim 1, wherein a width of the power supply line is larger than a width of the video signal line, and the video signal line is provided so as to overlap with a range of the width of the power supply line.   3. The active matrix display device according to claim 1, wherein the power supply line extends in both the same direction and the intersecting direction with the video signal line.   4. The active matrix display device according to claim 3, wherein a portion of the power supply line extending in a direction intersecting with the video signal line is provided at a position overlapping the electrode of the storage capacitor.   4. The active matrix display device according to claim 3, wherein a portion of the power supply line extending in a direction intersecting with the video signal line is formed to be wider than a portion extending in the same direction as the video signal line. .   2. The active matrix display device according to claim 1, wherein the display element includes first and second electrodes opposed to each other and an organic light emitting layer disposed between the first and second electrodes.

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