JP2009157157A - Pixel circuit, display device, and method of manufacturing display device - Google Patents

Pixel circuit, display device, and method of manufacturing display device Download PDF

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JP2009157157A
JP2009157157A JP2007336106A JP2007336106A JP2009157157A JP 2009157157 A JP2009157157 A JP 2009157157A JP 2007336106 A JP2007336106 A JP 2007336106A JP 2007336106 A JP2007336106 A JP 2007336106A JP 2009157157 A JP2009157157 A JP 2009157157A
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wiring
layer
light emitting
emitting element
gate
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Japanese (ja)
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Yukito Iida
Katsuhide Uchino
Tetsuo Yamamoto
勝秀 内野
哲郎 山本
幸人 飯田
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Sony Corp
ソニー株式会社
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<P>PROBLEM TO BE SOLVED: To provide a pixel circuit and a display device preventing a gate pulse from being delayed and preventing the occurrence of shading and uneven stripe and to provide a method of manufacturing the display device. <P>SOLUTION: This pixel circuit has a driving wire WSL, a light emitting element 113 changing luminance depending on flowing current, a driving transistor 111, at least one switching transistor 112 connected between a signal wire SGL and a gate of the driving transistor 111 and connecting a gate with the driving wire WSL, and a capacitor C111 connected between the gate and a source of the driving transistor 111. The driving transistor 111 and the light emitting element 113 are connected in series between a power supply line PSL and a reference potential. A wiring layer for power supply is connected with a wire in the other layer to form multilayered wiring. A cathode wiring layer in the light emitting element is formed into multilayered wiring composed of a wiring layer same as the wiring layer for power supply for multilayered wiring. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a pixel circuit including a light emitting element such as an organic EL (Electroluminescence), an active matrix display device, and a method for manufacturing the display device.

In an image display device, such as a liquid crystal display, an image is displayed by arranging a large number of pixels in a matrix and controlling the light intensity for each pixel in accordance with image information to be displayed.
This is the same for an organic EL display or the like, but the organic EL display is a so-called self-luminous display having a light emitting element in each pixel circuit, and has a higher image visibility than a liquid crystal display. There are advantages such as unnecessary and high response speed.
The luminance of each light emitting element is greatly different from a liquid crystal display or the like in that a color gradation is obtained by controlling the luminance of the light emitting element according to the current value flowing therethrough, that is, the light emitting element is a current control type.

  In the organic EL display, as with the liquid crystal display, a simple matrix method and an active matrix method can be used. However, although the former has a simple structure, it is difficult to realize a large and high-definition display. Due to the problems, active matrix systems have been actively developed to control the current flowing through the light-emitting elements inside each pixel circuit by means of active elements provided inside the pixel circuit, generally TFTs (Thin Film Transistors). ing.

FIG. 1 is a block diagram showing a configuration of a general organic EL display device.
As shown in FIG. 1, the display device 1 includes a pixel array unit 2 in which pixel circuits (PXLC) 2 a are arranged in an m × n matrix, a horizontal selector (HSEL) 3, a light scanner (WSCN) 4, a horizontal Signal line (data line) signals SGL1 to SGLn selected by the selector 3 and supplied with data signals according to luminance information, and scanning lines WSL1 to WSLm selectively driven by the write scanner 4 are provided.
The horizontal selector 3 and the light scanner 4 may be formed on the polycrystalline silicon or may be formed around the pixel by MOSIC or the like.

FIG. 2 is a circuit diagram showing a configuration example of the pixel circuit 2a of FIG. 1 (see, for example, Patent Documents 1 and 2).
The pixel circuit in FIG. 2 has the simplest circuit configuration among many proposed circuits, and is a so-called two-transistor driving circuit.

2 includes a p-channel thin film field effect transistor (hereinafter referred to as TFT) 11 and TFT 12, a capacitor C11, and an organic EL light emitting element (OLED) 13 which is a light emitting element. In FIG. 2, SGL represents a signal line, and WSL represents a scanning line.
Since organic EL light-emitting elements are often rectifying, they are sometimes referred to as OLEDs (Organic Light Emitting Diodes). In FIG. 2 and other figures, diode symbols are used as light-emitting elements. It does not necessarily require rectification.
In FIG. 2, the source of the TFT 11 is connected to the power supply potential VCC, and the cathode (cathode) of the light emitting element 13 is connected to the ground potential GND. The operation of the pixel circuit 2a in FIG. 2 is as follows.

Step ST1 :
When the scanning line WSL is in a selected state (here, at a low level) and the writing potential Vdata is applied to the signal line SGL, the TFT 12 becomes conductive and the capacitor C11 is charged or discharged, and the gate potential of the TFT 11 becomes Vdata.

Step ST2 :
When the scanning line WSL is in a non-selected state (here, high level), the signal line SGL and the TFT 11 are electrically disconnected, but the gate potential of the TFT 11 is stably held by the capacitor C11.

Step ST3 :
The current flowing through the TFT 11 and the light emitting element 13 has a value corresponding to the gate-source voltage Vgs of the TFT 11, and the light emitting element 13 continues to emit light with a luminance corresponding to the current value.
The operation of selecting the scanning line WSL and transmitting the luminance information given to the data line to the inside of the pixel as in step ST1 is hereinafter referred to as “writing”.
As described above, in the pixel circuit 2a of FIG. 2, once Vdata is written, the light emitting element 13 continues to emit light with a constant luminance until it is rewritten next time.

As described above, in the pixel circuit 2a, the value of the current flowing through the EL light emitting element 13 is controlled by changing the gate application voltage of the TFT 11 which is a drive transistor.
At this time, the source of the p-channel drive transistor is connected to the power supply potential VCC, and the TFT 11 always operates in the saturation region. Therefore, the constant current source has a value represented by the following formula 1.

(Equation 1)
Ids = 1/2 · μ (W / L) Cox (Vgs− | Vth |) 2 (1)

  Here, μ is the carrier mobility, Cox is the gate capacity per unit area, W is the gate width, L is the gate length, Vgs is the gate-source voltage of the TFT 11, Vth indicates the threshold value of the TFT 11.

  In the simple matrix type image display device, each light emitting element emits light only at the selected moment, whereas in the active matrix, as described above, the light emitting element continues to emit light even after the writing is completed. In comparison, the peak luminance and peak current of the light emitting element can be lowered, and this is particularly advantageous in a large-sized and high-definition display.

  FIG. 3 is a diagram showing a change with time of current-voltage (IV) characteristics of the organic EL light emitting device. In FIG. 3, the curve indicated by the solid line indicates the characteristic in the initial state, and the curve indicated by the broken line indicates the characteristic after change with time.

In general, the IV characteristics of an organic EL light emitting element deteriorate as time passes, as shown in FIG.
However, since the two-transistor drive in FIG. 2 is driven at a constant current, the constant current continues to flow through the organic EL light emitting element as described above, and even if the IV characteristic of the organic EL light emitting element deteriorates, the light emission luminance is aged There is no deterioration.

  The pixel circuit 2a shown in FIG. 2 is composed of a p-channel TFT. However, if it can be composed of an n-channel TFT, a conventional amorphous silicon (a-Si) process can be used in TFT fabrication. It becomes like this. Thereby, the cost of the TFT substrate can be reduced.

  Next, a basic pixel circuit in which transistors are replaced with n-channel TFTs will be described.

  FIG. 4 is a circuit diagram showing a pixel circuit in which the p-channel TFT in the circuit of FIG. 2 is replaced with an n-channel TFT.

  The pixel circuit 2b in FIG. 4 includes n-channel TFTs 21 and 22, a capacitor C21, and an organic EL light emitting element (OLED) 23 that is a light emitting element. In FIG. 4, SGL represents a data line, and WSL represents a scanning line.

  In the pixel circuit 2b, the drain side of the TFT 21 as a drive transistor is connected to the power supply potential VCC, and the source is connected to the anode of the EL light emitting element 23, thereby forming a source follower circuit.

  FIG. 5 is a diagram showing operating points of the TFT 21 as the drive transistor and the EL light emitting element 23 in the initial state. In FIG. 5, the horizontal axis represents the drain-source voltage Vds of the TFT 21, and the vertical axis represents the drain-source current Ids.

As shown in FIG. 5, the source voltage is determined by the operating point of the TFT 21 as a drive transistor and the EL light emitting element 23, and the voltage has a different value depending on the gate voltage.
Since the TFT 21 is driven in a saturation region, a current Ids having a current value of the equation shown in the above equation 1 is supplied with respect to Vgs with respect to the source voltage at the operating point.

USP 5,684,365 JP-A-8-234683

The pixel circuit described above is the simplest circuit having the TFT 21 as a drive transistor, the TFT 22 as a switching transistor, and the OLED 23. However, the pixel circuit is switched between two signals as a power signal applied to the power supply line. In some cases, the video signal supplied to the video signal may be switched between two signals to correct the threshold value and mobility.
Alternatively, in some cases, a configuration in which a TFT for mobility or threshold cancellation is provided in addition to a drive transistor or a switching transistor connected in series with the OLED may be employed.

These switching transistor TFTs, or separately provided threshold and mobility TFTs, generate gate pulses by a vertical scanner such as a light scanner disposed on both sides or one side of an active matrix organic EL display panel. The pulse signal is applied to the gate of a desired TFT of the pixel circuit arranged in a matrix through the wiring.
When there are two or more TFTs to which this pulse signal is applied, the timing for applying each pulse signal is important.

However, for example, as shown in FIG. 6, due to the influence of the wiring resistance r and wiring capacitance of the wiring 41 that applies a pulse signal to the gate of the transistor (TFT) in the pixel circuit through the buffer 40 at the final stage of the write scanner. , Pulse delay, transient changes occur. For this reason, a timing shift occurs, and shading and unevenness occur.
The wiring resistance to the gate of the transistor in each pixel circuit 2a increases as the distance from the scanner increases.
Therefore, as will be described later, when both ends of the panel are compared, a difference occurs in the timing of operation in a short period such as a mobility correction period, resulting in a difference in luminance.
In addition, since there is a deviation from the optimum mobility correction period, there is a disadvantage that pixels cannot be sufficiently written and variations in mobility cannot be corrected and are visually recognized as streaks.

  In addition, unevenness such as shading may occur due to a voltage drop in the power supply line, and may occur as unevenness or roughness in an image.

  These problems have a greater effect as the panel size and the definition become higher.

  An object of the present invention is to provide a pixel circuit, a display device, and a method for manufacturing the display device that can suppress the occurrence of shading, uneven stripes, and the like and can obtain a high-quality image.

  A pixel circuit according to a first aspect of the present invention includes a power supply line, a reference potential, a drive wiring through which a drive signal is propagated, a light emitting element whose luminance is changed by a flowing current, a drive transistor, a signal line, and the drive At least one switching transistor connected between the gate of the transistor, the gate being connected to the drive wiring, the conduction state of which is controlled by the drive signal, and a capacitor connected between the gate and the source of the drive transistor; The drive transistor and the light emitting element are connected in series between the power supply line and the reference potential, and the power supply wiring layer is connected to a wiring of another layer to form a multilayer wiring, and the light emission The cathode wiring layer of the element is formed into a multilayer wiring with a wiring layer in the same layer as the power supply wiring layer for the multilayer wiring.

  A display device according to a second aspect of the present invention includes pixel circuits arranged in a matrix, at least one scanner that outputs a drive signal to a control terminal of a transistor forming the pixel circuit, and a plurality of pixel circuits. The transistor control terminal is connected in common, and has at least one drive wiring through which a drive signal from the scanner is propagated. The pixel circuit has a power supply line, a reference potential, and a drive signal propagated through the pixel circuit. The driving wiring, the light emitting element whose luminance is changed by the flowing current, the driving transistor, the signal line and the gate of the driving transistor are connected, the gate is connected to the driving wiring, and the conduction state is set by the driving signal. At least one switching transistor to be controlled; a capacitor connected between the gate and source of the driving transistor; The driving transistor and the light emitting element are connected in series between the power supply line and the reference potential, and the power supply wiring layer is connected to a wiring of another layer to form a multilayer wiring. The cathode wiring layer is formed into a multilayer wiring with a wiring layer in the same layer as the power supply wiring layer for the multilayer wiring.

  Preferably, the anode layer of the light emitting element is formed into a multilayer wiring with the same wiring layer as the power supply wiring layer for the multilayer wiring, and the light emitting element is a light emitting material layer formed on the anode layer. And a cathode layer formed on the light emitting material layer, wherein the cathode layer is connected to a cathode pad formed at a position different from the light emitting region of the light emitting element, and the cathode pad is multilayered. Connected to the wiring layer.

  A third aspect of the present invention is a plurality of pixel circuits arranged in a matrix and including at least a light emitting element, a driving transistor, and at least one transistor whose conduction state is controlled by receiving a driving signal to a control terminal. And at least one scanner that outputs a drive signal to a control terminal of a transistor that forms the pixel circuit, wherein a drive wiring through which the drive signal from the scanner is propagated is wired A step of forming a power supply line; a step of connecting the power supply wiring layer to a wiring of another layer to form a multilayer wiring; and a cathode wiring layer of the light emitting element as a power supply for the multilayer wiring. And a wiring layer having the same layer as the wiring layer.

  According to the present invention, it is possible to suppress the occurrence of shading, stripe unevenness, and the like, and a high-quality image can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 7 is a block diagram showing a configuration of an organic EL display device employing the pixel circuit according to the first embodiment of the present invention.
FIG. 8 is a circuit diagram showing a specific configuration of the pixel circuit according to the first embodiment.

  7 and 8, the display device 100 includes a pixel array unit 102 in which pixel circuits 101 are arranged in an m × n matrix, a horizontal selector (HSEL) 103, a write scanner (WSCN) 104, a power Drive scanner (PDSCN) 105, signal lines SGL101 to SGL10n to which data signal Vsig selected by horizontal selector 103 and input signal SIN of offset signal Vofs corresponding to luminance information are supplied, and gate pulse (scanning pulse) GP by write scanner 104 The power lines PSL101 to WSL10m as drive wirings that are selectively driven by the above and the power drive scanner 105 are applied and driven by the power signal PSG set to selective VCC (for example, power supply voltage) or VSS (for example, negative side voltage). Drive wiring Having a power drive line PSL101~PSL10m of and.

In the pixel array unit 102, the pixel circuits 101 are arranged in an m × n matrix. However, in FIG. 7, for simplification of the drawing, the pixel circuits 101 are arranged in a matrix of 2 (= m) × 3 (= n). An example of arrangement is shown.
Also in FIG. 8, a specific configuration of one pixel circuit is shown in the drawing for simplification.

  As shown in FIG. 8, the pixel circuit 101 according to the present embodiment emits light including an n-channel TFT 111 as a driving transistor, an n-channel TFT 112 as a switching transistor, a capacitor C111, and an organic EL light emitting element (OLED: electro-optical element). It has an element 113, a first node ND111, and a second node ND112.

In the pixel circuit 101, a TFT 111 as a drive transistor, a node ND111, and a light emitting element (OLED) 113 are provided between a power drive line (power supply line) PSL (101 to 10 m) and a predetermined reference potential Vcat (for example, ground potential). Connected in series.
Specifically, the cathode of the light emitting element 113 is connected to the reference potential Vcat, the anode is connected to the first node ND111, the source of the TFT 111 is connected to the first node ND111, and the drain of the TFT 111 is the power drive line PSL. It is connected to the.
The gate of the TFT 111 is connected to the second node ND112.
The first electrode of the capacitor C111 is connected to the first node ND111, and the second electrode of the capacitor C111 is connected to the second node ND112.
The source / drain of the TFT 112 is connected between the signal line SGL and the second node ND112. The gate of the TFT 112 is connected to the scanning line WSL.

  As described above, in the pixel circuit 101 according to the present embodiment, the capacitor C111 as the pixel capacitance is connected between the gate and the source of the TFT 111 as the drive transistor.

9A to 9C are timing charts showing the basic operation of the pixel circuit of FIG.
9A shows a gate pulse (scanning pulse) GP applied to the scanning line WSL, FIG. 9B shows a power signal PSG applied to the power driving line PSL, and FIG. 9C shows a signal line SGL. The input signal SIN applied to each is shown.

In order to cause the light emitting element 113 of the pixel circuit 101 to emit light, as shown in FIGS. 9A to 9C, a power signal VSS (for example, a negative voltage) is applied to the power drive line PSL during the non-light emitting period. The offset signal Vofs is propagated to the line SGL and input to the second node ND112 through the TFT 112, and then the power signal VCC (corresponding to the power supply voltage) is applied to the power driving line PSL to correct the threshold value of the TFT 111.
Thereafter, the data signal Vsig corresponding to the luminance information is applied to the signal line SGL, and the signal is written to the second node ND112 through the TFT 112. At this time, writing is performed while a current is supplied to the TFT 111, and thus mobility correction is performed in parallel.
Then, the TFT 112 is turned off, and the light emitting element 113 emits light according to the luminance information.

  In the display device 100 of the present embodiment, it depends on the wiring resistance or wiring capacitance of the scanning line WSL that is a wiring to which a driving pulse (gate pulse) applied to the gate of the TFT (transistor) in the pixel circuit 101 is applied. Improve shading and unevenness due to pulse delay and / or unevenness such as shading due to voltage drop in power supply line, improve unevenness and roughness in image, that is, improve image quality In order to do this, the following measures are taken.

  FIG. 10 is a diagram for explaining a first countermeasure example for improving the image quality and the like, and is a simplified plan view and a cross-sectional view of the main part of the pixel circuit.

In the first countermeasure example, the scanning line (gate line) WSL to which the gate GT of the TFT 112 serving as the switching transistor of each pixel circuit 101 is connected is formed of a low resistance metal such as aluminum (Al). The signal line SGL is formed as a wiring of the same material and in the same layer as the line (power signal line) PSL, and the signal line SGL formed of a low resistance metal, for example, aluminum (Al), is lower than the scanning line WSL and the power supply line PSL (illustrated). Layer on the substrate side not to be formed).
Then, the contact formed by forming the scanning line WSL in the upper layer and the low resistance wiring layer 114 of the same material and the same layer as the signal line SGL in the lower layer of the scanning line WSL on the interlayer insulating film 115 such as SIN or SiO 2. 116 is connected to form a two-stage wiring structure.
Furthermore, in the first countermeasure example, the capacitor C111 is arranged so as not to overlap in the stacking direction of the scanning line WSL and the layer.

Note that the TFT 112 of each pixel circuit is a so-called bottom gate type, and its gate electrode (control terminal) is pulled up through a contact formed on an insulating film (not shown) and connected to the scanning line WSL.
In general, a gate electrode of a TFT is formed by depositing a metal or an alloy such as molybdenum (Mo) or tantalum (Ta) or the like by a method such as sputtering.

  As described above, the first countermeasure example is characterized in that the scanning line (gate line) WSL is laid out in a two-stage wiring of the same layer 114 as the low-resistance power supply wiring and the same layer 114 as the signal line. .

According to the first countermeasure example having such a feature, the resistance and capacitance of the scanning line (gate line) WSL can be reduced. That is, the wiring layer that forms the power supply line is formed of a low-resistance metal, and the wiring layer that forms the signal line SGL is also formed of a low-resistance metal. It can be reduced to about half. For this reason, the transient of the gate line of the TFT 112 as the switching transistor can be accelerated.
In addition, the difference between the pulse width of the gate pulse (control signal) GP of the write scanner 104 to the scanning line WSL and the width of the gate pulse GP at a position away from the output terminal can be reduced. It is possible to obtain uniform image quality without unevenness and shading. Further, it is possible to speed up the transient of the gate line, and there is an advantage that high definition can be realized.

  FIG. 11 is a diagram showing a configuration in which a capacitor (capacitor) is arranged at a position overlapping with the scanning line (gate line) and the layer stacking direction as a comparative example of FIG.

As shown in FIG. 11, by adopting a configuration in which capacitors (capacitors) and signal lines are arranged at positions overlapping the stacking direction of the layers of the scanning lines (gate lines) WSL, the parasitic capacitance of the scanning lines WSL tends to increase. is there.
On the other hand, as in the first countermeasure example, the capacitor C111 is arranged so as not to overlap in the stacking direction of the scanning line WSL and the layer, and only the signal line SGL is below the scanning line WSL. It becomes an overlapping state, an increase in parasitic capacitance can be prevented, and a further increase in the propagation speed of the gate pulse can be realized.

Next, the scanning line (gate line) WSL is formed as a wiring of the same material in the same layer as the power supply line (power signal line) PSL formed of a low resistance metal such as aluminum (Al). About the reason why the signal line SGL below the WSL and the low resistance wiring layer 114 of the same material and the same layer are connected through the contact 116 formed on the interlayer insulating film 115 such as SIN or SiO 2 to form a two-stage wiring structure. State.

  FIG. 12 is a plan view of the main part of the pixel when the scanning line (gate line) is formed of a high resistance wiring of the same material and in the same layer as the TFT gate electrode without applying the measures according to the present embodiment. .

Consider writing in the pixel circuit having the configuration of FIG.
As described in relation to FIG. 9, in this pixel circuit, writing and mobility correction are performed at the rising edge of the input signal SIN (Vofs to Vsig) of the signal line SGL and the falling edge of the gate pulse GP applied to the scanning line WSL. Has been decided.
In this method, the pulse is lost at the output end of the gate pulse GP to the scanning line WSL of the light scanner 104 and at a position away from the GP output end (shown as the reverse side of the GP output in FIG. 13). As shown in A) to (D), the writing time differs between the GP output end side and the GP output reverse side. Specifically, since the writing time is longer on the input opposite side of the panel, the image appears as shading.

As a countermeasure, it is possible to perform writing at a timing as shown in FIGS.
In this method, writing and mobility correction are not determined by the rising edge of the signal line SGL and the falling edge of the gate pulse GP but by the rising edge of the gate pulse GP and the falling edge of the gate pulse GP.
However, even in this type of writing, as shown in FIGS. 15A to 15D, the writing time depends on the gradation of the signal between the output end side of the gate pulse GP of the write scanner 105 and the reverse side of the GP output end. It may be different and cause shading.

14A to 14C, it is necessary to determine writing only by the gate pulse GP. If the writing time is too long, the source of the driving transistor continues to rise, so the writing time must be set short in order to obtain luminance.
However, as the size increases, the load on the scanning line (gate line) WSL increases. As shown in FIGS. 16A to 16D, even if a pulse having a short width is output at the output end of the gate pulse GP. On the reverse side of the GP output end, it becomes difficult to perform writing due to rounding (deterioration) of pulses.

As described above, since the gate wiring is generally wired with a high resistance metal (Mo or the like), the load becomes large.
Therefore, in the present embodiment, the scanning line (gate line) WSL is formed as a wiring of the same material in the same layer as the power line (power signal line) PSL formed of a low-resistance metal such as aluminum (Al). is doing.
Further, when considering larger size and higher definition, further lowering of resistance and lowering of capacity are desired. Therefore, the low resistance wiring layer 114 made of the same material and in the same layer as the signal line SGL below the scanning line WSL. Are connected through a contact 116 formed on an interlayer insulating film 115 such as SIN or SiO 2 to form a two-stage wiring structure and / or a position where the capacitor C111 does not overlap with the scanning line WSL in the layer stacking direction. It is arranged to shift to.

  FIG. 17 is a diagram for explaining a second countermeasure example for improving the image quality and the like, and is a simplified plan view and a cross-sectional view of the main part of the pixel circuit.

  The second countermeasure example of FIG. 17 is different from the first countermeasure example of FIG. 10 in that the second countermeasure example is formed of a high resistance metal in a lower layer of the wiring layer 114 formed of the same material and in the same layer as the signal line SGL. A wiring layer 117 of the same material as the gate electrode of the TFT is connected by a contact 119 formed on the gate insulating film 118, and a scanning line (gate line) WSL which is a low resistance wiring layer and a wiring which is a low resistance wiring. The layer 114 and the wiring layer 117, which is a high resistance wiring, are connected in multiple layers to form a three-stage wiring structure.

Thereby, the resistance of the scanning line WSL can be further reduced.
By applying the second countermeasure example, the load on the gate wiring can be reduced, and the speed of the transient can be increased. Thereby, high definition can be achieved.

  FIG. 18 is a diagram for explaining a third countermeasure example for improving the image quality and the like, and is a simplified plan view and a cross-sectional view of the main part of the pixel circuit.

  The third countermeasure example of FIG. 18 is different from the second countermeasure example of FIG. 17 in that the signal line SGL is in the same layer and does not pass through the wiring layer 114 formed of the same material, and further in the lower layer. A wiring layer 117 of the same material and in the same layer as the gate electrode of the TFT formed of a resistance metal is connected by a contact 120 formed on the interlayer insulating film 115 and the gate insulating film 118, and a scanning line (gate) which is a low resistance wiring layer. Line) WSL and a wiring layer 117, which is a high resistance wiring, are connected in multiple layers to form a two-stage wiring structure.

Even in this configuration, the resistance of the scanning line WSL can be reduced.
Also by applying the third countermeasure example, the load on the gate wiring can be reduced and the speed of the transient can be increased. Thereby, high definition can be achieved.

  FIG. 19 is a diagram for explaining a fourth countermeasure example for improving the image quality and the like, and is a simplified cross-sectional view of the main part of the pixel circuit.

  In the fourth countermeasure example, in order to improve the occurrence of unevenness such as shading due to a voltage drop in the power supply line and unevenness or roughness in the image, the power supply line (power drive line) PSL is multilayered. It has become.

As described above, the original power supply line PSL is formed at a predetermined position of the gate insulating film 118 by the low resistance wiring (Al or the like) made of the same material and in the same layer as the scanning line (gate line) WSL.
A contact 121 is formed on the interlayer insulating film 115 formed on the power supply line PSL, and a low resistance wiring layer 122 such as Al formed on the interlayer insulating film 115 is connected to the power supply line PSL via the contact 121 to form a multilayer. In order to reduce the resistance, the power supply line has a two-stage wiring structure, and unevenness such as shading occurs due to a voltage drop, thereby improving unevenness and roughness in the image.
In FIG. 19, a planarizing film 123 is formed on the upper power supply wiring layer 122, and an anode electrode 125 is formed on the planarizing film 123.

  According to the fourth countermeasure example, it is possible to suppress the occurrence of unevenness such as shading due to the voltage drop of the power supply line, and the occurrence of unevenness or roughness in the image.

  FIG. 20 is a diagram for explaining a fifth countermeasure example for improving the image quality and the like, and is a simplified cross-sectional view of the main part of the pixel circuit.

In the fifth countermeasure example, for example, even when the power supply line PSL is formed as a multilayer wiring as described above, the power supply line PSL is formed on the TFT 111 as the driving transistor, that is, on the upper layer side in the layer stacking direction. They are not arranged (formed).
In other words, in the fifth countermeasure example, the power supply line PSL is not overlapped with the upper layer of the TFT 111 arrangement region, and is not affected by the electric field from the power supply line PSL.

A specific configuration will be described.
As shown in FIG. 20, the bottom gate TFT 111 has a gate electrode 133 covered with a gate insulating film 132 on a transparent insulating substrate (for example, a glass substrate) 131. Gate electrode 133 is connected to second node ND112.
As described above, the gate electrode is formed by depositing a metal or alloy such as molybdenum (Mo) or tantalum (Ta) by a method such as sputtering.
In the TFT 111, a semiconductor film (channel formation region) 134 and a pair of n + diffusion layers 135 and 136 are formed on the gate insulating film 132 with the semiconductor film 134 interposed therebetween. After the STO 137 is formed on the semiconductor film 134, an interlayer insulating film 138 is formed.
Although not shown, an n diffusion layer (LDD) is formed between the semiconductor film 134 and each of the n + diffusion layers 135 and 136.
The source electrode 140 is connected to one n + diffusion layer 135 through a contact hole 139a formed in the interlayer insulating film 138, and the contact formed in the interlayer insulating film 138 is connected to the other n + diffusion layer 136. The drain electrode 141 is connected through the hole 139b.
The source electrode 140 and the drain electrode 141 are formed by patterning, for example, aluminum (Al). For example, the anode of the light emitting element 113 is connected to the source electrode 140, and the drain electrode 141 is connected to the power supply line PSL via a connection electrode (not shown in FIG. 20).
An insulating film 142 is stacked on the TFT 111 so as to cover the interlayer insulating film 138, the source electrode 140, and the drain electrode 141.

  Here, the reason why the power supply line PSL is not overlapped with the upper layer of the TFT 111 arrangement region as shown in FIG. 20 and is not affected by the electric field from the power supply line PSL will be described.

FIG. 21 is a cross-sectional view showing a configuration in which a power supply line is arranged on the TFT 111 as a comparative example of FIG.
FIG. 22 is a diagram showing an equivalent circuit of FIG.

  In FIG. 21, the drain electrode 141 of the TFT 111 is connected to the power supply line wiring layer 122 formed on the interlayer insulating film 142 via the contact 143 formed on the interlayer insulating film 142.

Here, the amorphous silicon TFT is considered.
When a power supply potential is present in the upper layer of the TFT 111 as the driving transistor, as indicated by an arrow in FIG. 21, electrons in the amorphous silicon are attracted to the power supply during black display, and a channel is formed on the side opposite to the gate. The back gate effect will appear.
As a result, the leakage current of the driving transistor increases. If this leakage current is large, it appears as a bright spot in black when black is displayed.

  Therefore, in the present embodiment, as shown in FIG. 20, a configuration is adopted in which the power supply line PSL does not overlap the upper layer of the TFT 111 arrangement region and is not affected by the electric field from the power supply line PSL. ing.

  According to the fifth countermeasure example, by not laying out the power supply wiring on the TFT 111, electrons are not attracted to the opposite side of the gate when displaying black or when the transistor is turned off, thereby preventing the back gate effect from occurring. It is possible to eliminate defects such as bright spots, unevenness, and roughness when displaying black.

  FIG. 23 is a diagram for explaining a sixth countermeasure example for improving the image quality and the like, and is a simplified cross-sectional view of the main part of the pixel circuit.

In the sixth countermeasure example, similarly to the fifth countermeasure example, even when the power supply line PSL is formed in a multilayer wiring as described above, for example, on the TFT 112 as a switching transistor (write transistor), That is, the power supply line PSL is not arranged (formed) on the upper layer side in the layer stacking direction.
In other words, the sixth countermeasure example is configured so that the power supply line PSL does not overlap with the upper layer of the TFT 112 arrangement region and is not affected by the electric field from the power supply line PSL.

  FIG. 23 shows a specific configuration of the sixth countermeasure example. Since the basic configuration is the same as that of the fifth countermeasure example, the same constituent elements have the same reference numerals as those in FIG. Represents. A specific description thereof is omitted.

  Here, the reason why the configuration in which the power supply line PSL does not overlap with the upper layer of the TFT 112 placement region as shown in FIG. 23 and is not affected by the electric field from the power supply line PSL will be described.

FIG. 24 is a cross-sectional view showing a configuration in which a power supply line is arranged on the TFT 112 as a comparative example of FIG.
FIG. 25 is a diagram showing an equivalent circuit of FIG.

  In FIG. 21, the drain electrode 141 of the TFT 111 (not shown) is connected to the power supply line wiring layer 122 formed on the interlayer insulating film 142 via the contact 143 formed on the interlayer insulating film 142.

Similarly to the TFT 111 as the driving transistor described above, the TFT 112 as the writing transistor also has a power source potential on the transistor as shown in FIG. Drawn to the side.
As a result, the back gate effect appears, a channel is formed on the opposite side of the gate, and the leakage current increases, so that the holding potential of the driving transistor changes, and the image appears uneven and rough.

  Therefore, in the present embodiment, as shown in FIG. 23, a configuration is adopted in which the power supply line PSL does not overlap the upper layer of the TFT 112 arrangement region and is not affected by the electric field from the power supply line PSL. ing.

  According to the sixth countermeasure example, by not laying out the power supply wiring on the TFT 112, electrons are not attracted to the opposite side of the gate when displaying black or when the transistor is turned off, thereby preventing the back gate effect from occurring. It is possible to eliminate defects such as bright spots, unevenness, and roughness when displaying black.

  FIG. 26 is a diagram for explaining a seventh countermeasure example for improving the image quality and the like, and is a simplified cross-sectional view of the main part of the pixel circuit.

  The seventh countermeasure example is different from the fifth countermeasure example described above in that the power line PSL does not overlap the upper layer of the region where the TFT 111 as the driving transistor is disposed and the influence of the electric field from the power line PSL is reduced. The cathode wiring layer 143 is disposed (formed) on the upper layer of the TFT 111 instead of adopting a configuration that does not receive.

Thus, in the seventh countermeasure example, the cathode wiring 143 is laid out on the TFT 111 instead of the power supply wiring.
The reason is that the back gate effect does not occur because the cathode voltage is lower than the gate voltage and signal voltage of the TFT 111 which is a driving transistor during black display, and the source voltage of the TFT 111 which is a driving transistor.

  According to the seventh countermeasure example, by laying out the cathode wiring 143 on the TFT 111, electrons are not attracted to the opposite side of the gate when displaying black or when the transistor is off, and the back gate effect occurs. , And defects such as bright spots, unevenness, and roughness when displaying black can be eliminated.

  FIG. 27 is a diagram for explaining an eighth countermeasure example for improving the image quality and the like, and is a simplified cross-sectional view of a main part of the pixel circuit.

  The difference between the eighth countermeasure example and the sixth countermeasure example described above is that, similarly to the seventh countermeasure example, the power supply line PSL does not overlap the upper layer of the region where the TFT 112 serving as the write transistor is disposed. Instead of adopting a configuration that is not affected by the electric field from the power supply line PSL, the cathode wiring layer 143 is disposed (formed) above the TFT 112.

As described above, in the eighth countermeasure example, the cathode wiring 143 is laid out on the TFT 112 instead of the power supply wiring.
The reason is that the back gate effect does not occur because the cathode voltage is lower than the source / drain voltage of the TFT 112 which is a writing transistor during black display.

  According to the eighth countermeasure example, the layout of the cathode wiring 143 on the TFT 112 can prevent the back gate effect from occurring during black display or when the transistor is turned off. Defects such as unevenness and roughness can be eliminated.

  FIG. 28 is a diagram for explaining a ninth countermeasure example for improving the image quality and the like, and is a simplified cross-sectional view of a main part of the pixel circuit.

  The ninth countermeasure example differs from the sixth countermeasure example described above in that the power line PSL does not overlap the upper layer of the region where the TFT 112 serving as the write transistor is disposed, and the influence of the electric field from the power line PSL is reduced. Instead of adopting a configuration that does not receive, a scanning line (gate line) WSL 144 is disposed (formed) on the upper layer of the TFT 112.

Thus, in the ninth countermeasure example, the upper layer of the TFT 112 and the scanning line WSL which is the gate line of the TFT 112 are laid out.
The reason is that the back gate effect does not occur because the gate voltage of the TFT 112 is also lower than the gate voltage and signal voltage of the TFT 111 which is a driving transistor.
Further, the TFT 112 is turned on not only on the gate side but also on the opposite side to the gate when the TFT 112 is on.
As a result, the on-resistance of the TFT 112 is lower than normal (when not laid out), and high-speed writing can be realized.

According to the ninth countermeasure example, by laying out the scanning line WSL on the TFT 112, electrons are not attracted to the opposite side of the gate when displaying black or when the transistor is off, and the back gate effect occurs. It is possible to prevent defects such as bright spots, unevenness, and roughness during black display.
Further, by laying out the scanning line WSL which is the gate line of the TFT 112 on the TFT 112, when the TFT 112 is on, its on-resistance can be lowered than usual, and high-speed writing can be realized.
High-definition is possible because high-speed writing can be realized.

  FIG. 29 is a diagram for explaining a tenth countermeasure example for improving the image quality and the like, and is a simplified cross-sectional view of a main part of the pixel circuit.

  The tenth countermeasure example is different from the fifth countermeasure example described above, as in the ninth countermeasure example, so that the power supply line PSL does not overlap the upper layer of the region where the TFT 111 as the drive transistor is arranged. In addition, instead of adopting a configuration that is not affected by the electric field from the power supply line PSL, the scanning line (gate line) WSL 144 to which the gate of the TFT 112 is connected is formed (formed) on the upper layer of the TFT 111.

As described above, in the tenth countermeasure example, the scanning line WSL which is the gate line of the TFT 112 is laid out above the TFT 111.
The reason is that the gate voltage of the TFT 112 is also lower than the source voltage of the TFT 111 which is a driving transistor, and therefore the back gate effect does not occur.

  According to the tenth countermeasure example, by laying out the scanning line WSL on the TFT 111, electrons are not attracted to the opposite side of the gate when displaying black or when the transistor is turned off, and the back gate effect occurs. It is possible to prevent defects such as bright spots, unevenness, and roughness during black display.

  FIG. 30 is a diagram for explaining an eleventh countermeasure example for improving the image quality and the like, and is a simplified cross-sectional view of a main part of the pixel circuit.

In the above fourth countermeasure example, in order to improve the occurrence of unevenness such as shading due to the voltage drop of the power supply line and the occurrence of unevenness or roughness in the image, the power supply line (power drive line) PSL is formed in multiple layers. Explained that wiring.
In the eleventh countermeasure example, the cathode wiring, which is normally formed of the metal of the anode, is formed in the same layer as the power supply line layer of the power supply line (power drive line) PSL and multi-layered with the low resistance wiring of the same material. ing.

As described with reference to FIG. 19, the original power supply line PSL is formed at a predetermined position of the gate insulating film 118 by a low resistance wiring (Al or the like) of the same material and in the same layer as the scanning line (gate line) WSL. .
A contact 121 is formed on the interlayer insulating film 115 formed on the power supply line PSL, and a low resistance wiring layer 122 such as Al formed on the interlayer insulating film 115 is connected to the power supply line PSL via the contact 121 to form a multilayer. In order to reduce the resistance, the power supply line has a two-stage wiring structure, and unevenness such as shading occurs due to a voltage drop, thereby improving unevenness and roughness in the image.
On the insulating film 115, a cathode low resistance wiring layer 145 is formed in parallel with the low resistance wiring layer 122 for the power supply line PSL.
For example, the planarization film 123 is formed on the upper power supply wiring layer 122 and the cathode wiring layer 145, the contact 146 is formed on the planarization film 123, and the cathode wiring layer 145 is planarized via the contact 146. A small area cathode pad 147 formed on the film 123 is connected.
An EL light emitting element material layer 148 is formed on the anode electrode 125, and an insulating film 149 is formed between the cathode pad 147, the anode electrode 125, and the EL light emitting element material layer 148, etc., and the EL light emitting element 148, the insulating film 149, A cathode electrode is formed on the cathode pad 147.

Thus, in the eleventh countermeasure example, the cathode line is laid out in the same layer as the power supply wiring having a multilayered structure.
By multilayering the cathode wiring, it is possible to suppress a rise in the voltage of the cathode farthest from the cathode input end and to obtain uniform image quality.
In addition, the cathode line is laid out with the power supply wiring layer to prevent a voltage rise in the center of the panel, and as shown in FIGS. 30 and 31, a large light emitting region (opening) of the EL light emitting element 113 (148) is secured. It becomes possible to do.

  FIG. 32 is a cross-sectional view of a main part of a pixel when a cathode line is formed without applying the countermeasure according to the present embodiment, and FIG. 33 is a plan view thereof.

Here, the light emitting region (aperture ratio) of the panel is considered.
As a method for increasing the light emitting region (aperture ratio), there is a top emission method. In general, the top emission method is characterized in that the cathode is formed by the anode wiring layer 125 of the EL light emitting device 148 as shown in FIGS.
However, as the size and resolution of panels increase, the cathode line must be thicker to prevent uneven image quality due to voltage rise at the center of the panel (the farthest part from the cathode) during light emission. The rate will also drop. As the aperture ratio decreases, the density of current flowing through the EL light emitting element 148 increases, resulting in a problem that the lifetime is shortened.

On the other hand, in the eleventh countermeasure example, as described above, the cathode line is laid out in the same layer as the multilayered power supply wiring, and the cathode line is laid out in the power supply layer. It is possible to prevent an increase in voltage at the center and to secure a large opening.
As a result, the current density flowing in the EL light emitting element 148 during light emission can be reduced. As a result, a long life can be realized.
By multilayering the cathode wiring, it is possible to suppress a rise in the voltage of the cathode farthest from the cathode input end and to obtain uniform image quality.

Next, a more specific operation of the above configuration will be described with reference to FIGS. 34A to 34E and FIGS. 35 to 42, focusing on the operation of the pixel circuit.
34A shows a gate pulse (scanning pulse) GP applied to the scanning line WSL, FIG. 34B shows a power signal PSG applied to the power drive line PSL, and FIG. 34C shows a signal. 34D shows the input signal SIN applied to the line SGL, FIG. 34D shows the potential VND112 of the second node ND112, and FIG. 34E shows the potential VND111 of the first node ND111.

First, when the EL light emitting element 113 is in the light emitting state, as shown in FIGS. 34B and 35, the power drive line PSL is at the power supply voltage VCC and the TFT 112 is turned off.
At this time, since the TFT 111 as the driving transistor is set to operate in the saturation region, the current Ids flowing through the EL light emitting element 113 takes a value represented by Equation 1 according to the gate-source voltage Vgs of the TFT 111. .

  Next, in the non-light emitting period, as shown in FIGS. 34B and 36, the power drive line PSL which is a power supply line is set to Vss. At this time, when the voltage Vss is smaller than the sum of the threshold value Vthel and the cathode voltage Vcat of the EL light emitting element 113, that is, if Vss <Vthel + Vcat, the EL light emitting element 113 is extinguished, and the power drive line PSL which is a power supply line is It becomes the source of the TFT 111 as a driving transistor. At this time, the anode (node ND111) of the EL light emitting element 113 is charged to Vss as shown in FIG.

Further, as shown in FIGS. 34 (A), (C), (D), (E) and FIG. 37, when the potential of the signal line SGL becomes the offset voltage Vofs, the gate pulse GP is set to the high level. The TFT 112 is turned on by setting, and the gate potential of the TFT 111 is set to Vofs.
At this time, the gate-source voltage of the TFT 111 takes a value of (Vofs−Vss). If the gate-source voltage (Vofs−Vss) of the TFT 111 is not larger (lower) than the threshold voltage Vth of the TFT 111, the threshold value correction operation cannot be performed. Therefore, the gate-source voltage (Vofs) of the TFT 111 cannot be performed. −Vss) needs to be larger than the threshold voltage Vth of the TFT 111, that is, Vofs−Vss> Vth.

Then, the power signal PSG applied to the power drive line PSL in the threshold value correcting operation is set to the power supply voltage Vcc again.
By setting the power drive line PSL to the power supply voltage Vcc, the anode (node ND111) of the EL light emitting element 113 functions as the source of the TFT 111, and a current flows as shown in FIG.
The equivalent circuit of the EL light emitting element 113 is represented by a diode and a capacitor as shown in FIG. 38, and therefore satisfies the relationship Vel ≦ Vcat + Vthel (the leakage current of the EL light emitting element 113 is considerably smaller than the current flowing through the TFT 111). As long as this is done, the current in the TFT 111 is used to charge the capacitors C111 and Cel.
At this time, the voltage Vel of the node ND111 increases with time as shown in FIG. After a certain period of time, the gate-source voltage of the TFT 111 takes a value of Vth. At this time, Vel = Vofs−Vth ≦ Vcat + Vthel.

After the threshold cancel operation is completed, as shown in FIGS. 34A, 34C, and 40, the potential of the signal line SGL is set to Vsig with the TFT 112 turned on. The data signal Vsig is a voltage corresponding to the gradation. At this time, since the TFT 112 is turned on, the gate potential of the TFT 111 becomes Vsig as shown in FIG. 34D. However, since the current Ids flows from the power drive line PSL which is a power supply line, the source potential is time. It rises with it.
At this time, if the source voltage of the TFT 111 does not exceed the sum of the threshold voltage Vthel and the cathode voltage Vcat of the EL light emitting element 113 (if the leakage current of the EL light emitting element 113 is considerably smaller than the current flowing through the TFT 111), the TFT 111 The flowing current is used to charge capacitors C111 and Cel.
At this time, since the threshold value correcting operation of the TFT 111 is completed, the current flowing through the TFT 111 reflects the mobility μ.
More specifically, as shown in FIG. 41, those having a high mobility μ have a large amount of current at this time, and the source voltage rises quickly. On the contrary, when the mobility μ is small, the amount of current is small, and the increase of the source voltage is slow. As a result, the gate-source voltage of the TFT 111 is reduced to reflect the mobility μ, and becomes Vgs for completely correcting the mobility after a predetermined time has elapsed.

Finally, as shown in FIGS. 34A to 34C and FIG. 42, the gate pulse GP is switched to a low level to turn off the TFT 112 to finish writing, and the EL light emitting element 113 emits light.
Since the gate-source voltage of the TFT 111 is constant, the TFT 111 passes a constant current Ids ′ to the EL light emitting element 113, and Vel rises to a voltage Vx at which a current of Ids ′ flows to the EL light emitting element 113. Emits light.
In this pixel circuit 101 as well, the EL characteristic of the EL light emitting element 113 changes as the light emission time becomes longer. Therefore, the potential at point B (node ND111) in the figure also changes. However, since the gate-source voltage of the TFT 111 is maintained at a constant value, the current flowing through the EL light emitting element 113 does not change. Therefore, even if the IV characteristic of the EL light emitting element 113 deteriorates, the constant current Ids always flows and the luminance of the EL light emitting element 113 does not change.

Since the pixel circuit driven in this way has the configuration according to the first to eleventh countermeasure examples as described above, it is possible to obtain a high-quality image in which the occurrence of shading, stripe unevenness, and the like is suppressed. .
Note that all of the first to eleventh measures described above may be taken, and various selections such as combining any one or a plurality of measures are possible.

As described above, in the first embodiment, as a countermeasure for effective image quality improvement for the display device 100 having the circuit of FIG. 8, that is, the 2Tr + 1C pixel circuit of two transistors and one capacitor, the first. The eleventh countermeasure example has been described.
However, although the first to eleventh countermeasure examples are effective for the display device 100 having the 2Tr + 1C pixel circuit, these countermeasures can be applied to a drive transistor or a switching transistor connected in series with the OLED. In addition, the present invention can be applied to a display device including a pixel circuit having a structure in which a TFT for canceling mobility, threshold value, or the like is separately provided.
A configuration example of a display device having a 5Tr + 1C pixel circuit including five transistors and one capacitor among these display devices will be described below as a second embodiment.

FIG. 43 is a block diagram showing a configuration of an organic EL display device employing a pixel circuit according to the second embodiment of the present invention.
FIG. 44 is a circuit diagram showing a specific configuration of the pixel circuit according to the present embodiment.

  43 and 44, the display device 200 includes a pixel array unit 202 in which pixel circuits 201 are arranged in an m × n matrix, a horizontal selector (HSEL) 203, a write scanner (WSCN) 204, a drive A scanner (DSCN) 205, a first auto-zero circuit (AZRD1) 206, a second auto-zero circuit (AZRD2) 207, a signal line SGL selected by the horizontal selector 203 and supplied with a data signal corresponding to luminance information, a write scanner 204 The scanning line WSL as the second drive wiring selectively driven by the drive, the drive line DSL as the first drive wiring selectively driven by the drive scanner 205, and the fourth drive selectively driven by the first auto-zero circuit 206. First auto zero line AZL1 as wiring and second auto zero times The 207 has a second auto-zero line AZL2 as the third driving wiring to be selectively driven.

43 and 44, the pixel circuit 201 according to the present embodiment includes a p-channel TFT 211, n-channel TFTs 212 to TFT 215, a capacitor C211, a light-emitting element 216 including an organic EL light-emitting element (OLED: electro-optical element), It has a first node ND211 and a second ND212.
A first switch transistor is formed by the TFT 211, a second switch transistor is formed by the TFT 213, a third switch transistor is formed by the TFT 215, and a fourth switch transistor is formed by the TFT 214.
The supply line (power supply potential) of the power supply voltage Vcc corresponds to the first reference potential, and the ground potential GND corresponds to the second reference potential. VSS1 corresponds to the fourth reference potential, and VSS2 corresponds to the third reference potential.

In the pixel circuit 201, a TFT 211, a TFT 212 as a drive transistor, a first transistor between a first reference potential (power supply potential Vcc in the present embodiment) and a second reference potential (ground potential GND in the present embodiment). A node ND211 and a light emitting element (OLED) 216 are connected in series. Specifically, the cathode of the light emitting element 216 is connected to the ground potential GND, the anode is connected to the first node ND211, the source of the TFT 212 is connected to the first node ND211, and the drain of the TFT 211 is connected to the drain of the TFT 212. The source of the TFT 211 is connected to the power supply potential Vcc.
The gate of the TFT 212 is connected to the second node ND212, and the gate of the TFT 211 is connected to the drive line DSL.
The drain of the TFT 213 is connected to the first node ND211 and the first electrode of the capacitor C211, the source is connected to the fixed potential VSS2, and the gate of the TFT 213 is connected to the second auto zero line AZL2. The second electrode of the capacitor C211 is connected to the second node ND212.
The source / drain of the TFT 214 is connected between the signal line SGL and the second node ND212. The gate of the TFT 214 is connected to the scanning line WSL.
Further, the source and drain of the TFT 215 are connected between the second node ND212 and the predetermined potential Vss1, respectively. The gate of the TFT 215 is connected to the first auto zero line AZL1.

  As described above, in the pixel circuit 201 according to this embodiment, the capacitor C211 as the pixel capacitor is connected between the gate and the source of the TFT 212 as the drive transistor, and the source potential of the TFT 212 is set as the switch transistor during the non-light emission period. The threshold value Vth is corrected by connecting to a fixed potential via the TFT 211 and connecting the source and drain of the TFT 211.

In the second embodiment, the first to eleventh measures for improving the image quality described as the first embodiment are at least one of the scanning line WSL, the drive line DSL, and the auto zero lines AZL1 and AZL2. This is applied to one, two or more or all of the scanning lines WSL and the driving lines DSL.
By taking desired measures, measures such as shading and streaks due to delays due to wiring resistance and wiring capacity of the drive signal (pulse) are performed on the entire panel, and generation of shading and streaks is suppressed, resulting in good image quality An image can be obtained.

Next, the operation of the above configuration will be described with reference to FIGS. 45A to 45F, focusing on the operation of the pixel circuit.
45A shows a drive signal DS applied to the drive line DSL, and FIG. 45B shows a drive signal WS applied to the scanning line WSL (corresponding to the gate pulse GP in the first embodiment). 45C shows the drive signal AZ1 applied to the first auto-zero line AZL1, FIG. 45D shows the drive signal auto-zero signal AZ2 applied to the second auto-zero line AZL2, and FIG. FIG. 45F shows the potential of the second node ND212, and FIG. 45F shows the potential of the first node ND211.

In the non-light emitting operation, the drive signal DS of the drive line DSL by the drive scanner 205 is held at a high level, the drive signal WS to the scan line WSL by the write scanner 204 is held at a low level, and the drive signal to the auto zero line AZL1 by the auto zero circuit 206 AZ1 is held at the low level, and the drive signal AZ2 to the auto zero line AZL2 by the auto zero circuit 207 is held at the high level.
As a result, the TFT 213 is turned on. At this time, a current flows through the TFT 213, and the source potential Vs of the TFT 212 (the potential of the node ND211) drops to VSS2. Therefore, the voltage applied to the EL light emitting element 216 is also Vss2, and if Vss2 <Vcathode + VthEL, the EL light emitting element 216 does not emit light.
In this case, even if the TFT 213 is turned on, the voltage held in the capacitor C 211, that is, the gate-source voltage of the TFT 212 does not change.

Next, during the non-emission period of the EL light emitting element 216, as shown in FIGS. 45C and 45D, the drive signal AZ2 to the auto zero line AZL2 is held at a high level, and the auto cell line AZL1 is applied. The drive signal AZ1 is set to a high level. As a result, the potential of the second node ND212 becomes VSS1.
Then, after the drive signal AZ2 to the auto zero line AZL2 is switched to the low level, the drive signal DS of the drive line DSL by the drive scanner 205 is switched to the low level only for a predetermined period.
Accordingly, the TFT 213 is turned off and the TFT 215 and the TFT 211 are turned on, whereby a current flows through the path of the TFT 212 and the TFT 211, and the potential of the first node is increased.
Then, the drive signal DS of the drive line DSL by the drive scanner 205 is switched to the high level, and the drive signal AZ1 is switched to the low level.
As a result, the threshold value Vth of the drive transistor TFT 212 is corrected, and the potential difference between the second node ND212 and the first node ND211 becomes Vth.
In this state, after the elapse of a predetermined period, the drive signal WS to the scanning line WSL by the write scanner 204 is held at a high level for a predetermined period, data is written from the data line to the node ND212, and the drive scanner 205 is in a period when the drive signal WS is at a high level. The drive signal DS of the drive line DSL is switched to the low level.
At this time, the mobility is corrected by turning on the TFT 211 while the TFT 214 is turned on. Eventually, the drive signal WS is switched to the low level, and the TFT 214 is turned off.
In this case, since the TFT 214 is off and the gate-source voltage of the TFT 212 is constant, the TFT 212 passes a constant current Ids to the EL light emitting element 216. As a result, the potential of the first node ND211 rises to the voltage Vx through which the current Ids flows through the EL light emitting element 216, and the EL light emitting element 216 emits light.
Here, also in this circuit, the EL-light emitting element changes its current-voltage (IV) characteristic when the light emission time becomes long. Therefore, the potential of the first node ND211 also changes. However, since the gate-source voltage Vgs of the TFT 212 is maintained at a constant value, the current flowing through the EL light emitting element 216 does not change. Therefore, even if the IV characteristic of the EL light emitting element 216 deteriorates, the constant current Ids always flows, and the luminance of the EL light emitting element 216 does not change.

  In the pixel circuit driven in this way, since shading and streak countermeasures due to the delay due to the wiring resistance of the drive signal (pulse) are taken in the entire panel, the image quality in which the occurrence of shading, streak etc. is suppressed A good image can be obtained.

It is a block diagram which shows the structure of a common organic electroluminescent display apparatus. FIG. 2 is a circuit diagram illustrating a configuration example of a pixel circuit in FIG. 1. It is a figure which shows the time-dependent change of the electric current-voltage (IV) characteristic of an organic electroluminescent light emitting element. FIG. 3 is a circuit diagram illustrating a pixel circuit in which a p-channel TFT in the circuit of FIG. 2 is replaced with an n-channel TFT. It is a figure which shows the operating point of TFT and EL light emitting element as a drive transistor in an initial state. It is a figure for demonstrating the disadvantage by wiring resistance. 1 is a block diagram illustrating a configuration of an organic EL display device that employs a pixel circuit according to a first embodiment of the present invention. FIG. 3 is a circuit diagram illustrating a specific configuration of a pixel circuit according to the first embodiment. 9 is a timing chart showing the basic operation of the pixel circuit of FIG. It is a figure for demonstrating the 1st example of a countermeasure for improving an image quality etc., Comprising: It is the simple top view and sectional drawing of the principal part of a pixel circuit. FIG. 11 is a diagram showing a configuration in which a capacitor (capacitor) is arranged at a position overlapping a scanning line (gate line) and a layer stacking direction as a comparative example of FIG. 10. It is a top view of the principal part of a pixel at the time of forming the scanning line (gate line) with the high resistance wiring of the same material and the same layer as the gate electrode of TFT, without applying the countermeasure which concerns on this embodiment. FIG. 10 is a diagram illustrating pulse deterioration when the operation is performed at the timing of FIG. 9 without taking any countermeasure. 10 is another timing chart different from FIG. It is a figure which shows about pulse deterioration at the time of making it operate | move at the timing of FIG. 14 without taking a countermeasure. It is a figure which shows about the further pulse deterioration at the time of making it operate | move at the timing of FIG. 14 without taking a countermeasure. It is a figure for demonstrating the 2nd example of a countermeasure for improving an image quality etc., Comprising: It is the simple top view and sectional drawing of the principal part of a pixel circuit. It is a figure for demonstrating the 3rd example of a countermeasure for improving image quality etc., Comprising: It is the simple top view and sectional drawing of the principal part of a pixel circuit. It is a figure for demonstrating the 4th example of a countermeasure for improving an image quality etc., Comprising: It is simplified sectional drawing of the principal part of a pixel circuit. It is a figure for demonstrating the 5th example of a countermeasure for improving image quality etc., Comprising: It is simplified sectional drawing of the principal part of a pixel circuit. FIG. 21 is a cross-sectional view showing a configuration in which a power supply line is arranged on a TFT 111 (drive transistor) as a comparative example of FIG. 20. It is a figure which shows the equivalent circuit of FIG. It is a figure for demonstrating the 6th example of a countermeasure for improving an image quality etc., Comprising: It is a simplified sectional drawing of the principal part of a pixel circuit. FIG. 24 is a cross-sectional view showing a configuration in which a power supply line is arranged on a TFT 112 (switching transistor) as a comparative example of FIG. It is a figure which shows the equivalent circuit of FIG. It is a figure for demonstrating the 7th example of a countermeasure for improving an image quality etc., Comprising: It is simplified sectional drawing of the principal part of a pixel circuit. It is a figure for demonstrating the 8th countermeasure example for improving image quality etc., Comprising: It is a simplified sectional view of the principal part of a pixel circuit. It is a figure for demonstrating the 9th example of a countermeasure for improving an image quality etc., Comprising: It is a simplified sectional view of the principal part of a pixel circuit. It is a figure for demonstrating the 10th countermeasure example for improving image quality etc., Comprising: It is a simplified sectional view of the principal part of a pixel circuit. It is a figure for demonstrating the 11th countermeasure example for improving image quality etc., Comprising: It is a simplified sectional view of the principal part of a pixel circuit. It is a figure which shows that the light emission area | region (opening) of EL light emitting element can also be ensured largely by the 11th countermeasure. It is sectional drawing of the principal part of the pixel at the time of forming a cathode line, without applying the countermeasure which concerns on this embodiment. It is a top view of the principal part of a pixel at the time of forming a cathode line, without applying the measure concerning this embodiment. 9 is a timing chart showing a specific operation of the pixel circuit of FIG. 8. It is a figure for demonstrating operation | movement of the pixel circuit of FIG. 8, Comprising: It is a figure which shows the state of a light emission period. It is a figure for demonstrating operation | movement of the pixel circuit of FIG. 8, Comprising: It is a figure which shows the state which made the voltage Vss in the non-light-emission period. It is a figure for demonstrating operation | movement of the pixel circuit of FIG. 8, Comprising: It is a figure which shows the state which input the offset signal. It is a figure for demonstrating operation | movement of the pixel circuit of FIG. 8, Comprising: It is a figure which shows the state which made the voltage Vcc. FIG. 9 is a diagram for explaining the operation of the pixel circuit of FIG. 8, and shows the transition of the source voltage of the drive transistor when the voltage is Vcc. It is a figure for demonstrating operation | movement of the pixel circuit of FIG. 8, Comprising: It is a figure which shows the state when writing the data signal Vsig. FIG. 9 is a diagram for explaining the operation of the pixel circuit in FIG. 8, and shows the transition of the source voltage of the drive transistor according to the mobility. It is a figure for demonstrating operation | movement of the pixel circuit of FIG. 8, Comprising: It is a figure which shows a light emission state. It is a block diagram which shows the structure of the organic electroluminescence display which employ | adopted the pixel circuit which concerns on the 2nd Embodiment of this invention. FIG. 6 is a circuit diagram illustrating a specific configuration of a pixel circuit according to a second embodiment. 45 is a timing chart showing the basic operation of the pixel circuit of FIG. 44.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Display apparatus, 101 ... Pixel circuit, 102 ... Pixel array part, 103 ... Horizontal selector (HSEL), 104 ... Light scanner (WSCN), 105 ... Power drive scanner (PDSCN) , SGL ... signal line, WSL ... scanning line, PSL ... power drive line, 111 ... n-channel TFT as drive transistor, 112 ... n-channel TFT as switch, ND111 ... first node, ND112 ... second node, 114 ... low-resistance wiring layer in the same layer as the signal line, 115 ... interlayer insulating film, 116 ... contact, 117 ... Wiring layer in the same layer as the gate electrode of the TFT, 118... Gate insulating film, 119 to 121... Contact, 122. 123: planarizing film, 124: contact, 125 ... anode electrode, 131 ... transparent insulating substrate, 132 ... gate insulating film, 133 ... gate electrode, 134 ... semiconductor film 135, 136... N + diffusion layer, 138... Interlayer insulating film, 139a, 139b... Contact, 140... Source electrode, 141. 143 ... cathode wiring, 144 ... scanning line (WSL), 145 ... cathode wiring layer, 146 ... contact, 147 ... cathode pad, 148 ... EL light emitting element material layer, 149 ... Insulating film, 150 ... Cathode, 200 ... Display device, 201 ... Pixel circuit, 202 ... Pixel array section, 203 ... Horizontal selector (HSEL), 204 ..Write scanner (WSCN), 205... Drive scanner (DSCN), 206... First autodrive circuit (AZRD1), 207... Second autozero circuit (AZRD2), SGL. Line, WSL ... scanning line, DSL ... drive line, AZL1, AZL2 ... auto-zero line, 211 ... p-channel TFT as a switch, 212 ... n-channel TFT as a drive (drive) transistor, 213 to 215... N-channel TFT as a switch, ND211... First node, ND112.

Claims (5)

  1. A power line,
    A reference potential;
    Drive wiring through which the drive signal is propagated;
    A light-emitting element whose luminance changes according to a flowing current;
    A driving transistor;
    At least one switching transistor connected between the signal line and the gate of the driving transistor, the gate is connected to the driving wiring, and the conduction state is controlled by the driving signal;
    A capacitor connected between the gate and the source of the driving transistor,
    The drive transistor and the light emitting element are connected in series between the power line and the reference potential,
    The power wiring layer is
    Connected to the wiring of other layers to make a multilayer wiring,
    The cathode wiring layer of the light emitting element is formed into a multilayer wiring with a wiring layer in the same layer as the power wiring layer for the multilayer wiring.
  2. The anode layer of the light emitting element is formed into a multi-layer wiring in the same wiring layer as the power wiring layer for the multi-layer wiring,
    The light emitting element is
    A light emitting material layer formed on the anode layer;
    A cathode layer formed on the light emitting material layer,
    The cathode layer is connected to a cathode pad formed at a position different from the light emitting region of the light emitting element,
    The pixel circuit according to claim 1, wherein the cathode pad is connected to the multilayer wiring layer.
  3. Pixel circuits arranged in a matrix,
    At least one scanner for outputting a drive signal to a control terminal of a transistor forming the pixel circuit;
    The control terminals of the transistors of a plurality of pixel circuits are connected in common and have at least one drive wiring through which a drive signal from the scanner is propagated;
    The pixel circuit is
    A power line,
    A reference potential;
    Drive wiring through which the drive signal is propagated;
    A light-emitting element whose luminance changes according to a flowing current;
    A driving transistor;
    At least one switching transistor connected between the signal line and the gate of the driving transistor, the gate is connected to the driving wiring, and the conduction state is controlled by the driving signal;
    A capacitor connected between the gate and the source of the driving transistor,
    The drive transistor and the light emitting element are connected in series between the power line and the reference potential,
    The power wiring layer is
    Connected to the wiring of other layers to make a multilayer wiring,
    The cathode wiring layer of the light emitting element is formed into a multilayer wiring with a wiring layer in the same layer as the power wiring layer for the multilayer wiring.
  4. The anode layer of the light emitting element is formed into a multi-layer wiring in the same wiring layer as the power wiring layer for the multi-layer wiring,
    The light emitting element is
    A light emitting material layer formed on the anode layer;
    A cathode layer formed on the light emitting material layer,
    The cathode layer is connected to a cathode pad formed at a position different from the light emitting region of the light emitting element,
    The display device according to claim 3, wherein the cathode pad is connected to the multilayer wiring layer.
  5. A plurality of pixel circuits arranged in a matrix and including at least a light-emitting element, a drive transistor, and at least one transistor whose conduction state is controlled by receiving a drive signal to a control terminal;
    A display device comprising: at least one scanner that outputs a drive signal to a control terminal of a transistor that forms the pixel circuit,
    Wiring drive wiring through which the drive signal from the scanner is propagated;
    Forming a power line;
    Connecting the power wiring layer to a wiring of another layer to form a multilayer wiring;
    Forming a cathode wiring layer of the light emitting element into a multilayer wiring with a wiring layer in the same layer as the power supply wiring layer for the multilayer wiring.
JP2007336106A 2007-12-27 2007-12-27 Pixel circuit, display device, and method of manufacturing display device Pending JP2009157157A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
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Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP2007336106A JP2009157157A (en) 2007-12-27 2007-12-27 Pixel circuit, display device, and method of manufacturing display device

Publications (1)

Publication Number Publication Date
JP2009157157A true JP2009157157A (en) 2009-07-16

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CN102024421A (en) * 2009-09-17 2011-04-20 乐金显示有限公司 Organic light emitting display device
JP2013077814A (en) * 2011-09-16 2013-04-25 Semiconductor Energy Lab Co Ltd Semiconductor device, light-emitting device, and electronic apparatus
WO2016056211A1 (en) * 2014-10-06 2016-04-14 株式会社Joled Display device and display device control method

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JP2004006313A (en) * 2002-04-18 2004-01-08 Seiko Epson Corp Manufacturing method of electro-optical device, electro-optical device, and electronic apparatus
JP2005227788A (en) * 2004-02-14 2005-08-25 Samsung Sdi Co Ltd Organic electroluminescence display device and method of manufacturing the same
JP2006113597A (en) * 2002-09-25 2006-04-27 Seiko Epson Corp Light emitting apparatus

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JP2004006313A (en) * 2002-04-18 2004-01-08 Seiko Epson Corp Manufacturing method of electro-optical device, electro-optical device, and electronic apparatus
JP2006113597A (en) * 2002-09-25 2006-04-27 Seiko Epson Corp Light emitting apparatus
JP2005227788A (en) * 2004-02-14 2005-08-25 Samsung Sdi Co Ltd Organic electroluminescence display device and method of manufacturing the same

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102024421A (en) * 2009-09-17 2011-04-20 乐金显示有限公司 Organic light emitting display device
US8344616B2 (en) 2009-09-17 2013-01-01 Lg Display Co., Ltd. Organic light emitting display device
CN102024421B (en) 2009-09-17 2013-04-10 乐金显示有限公司 Organic light emitting display device
JP2013077814A (en) * 2011-09-16 2013-04-25 Semiconductor Energy Lab Co Ltd Semiconductor device, light-emitting device, and electronic apparatus
US9508709B2 (en) 2011-09-16 2016-11-29 Semiconductor Energy Laboratory Co., Ltd. Semiconductor device, light-emitting device, and electronic device
JP6221006B1 (en) * 2011-09-16 2017-10-25 株式会社半導体エネルギー研究所 Light emitting device
JP2018013803A (en) * 2011-09-16 2018-01-25 株式会社半導体エネルギー研究所 Light-emitting device
US10032798B2 (en) 2011-09-16 2018-07-24 Semiconductor Energy Laboratory Co., Ltd. Semiconductor device, light-emitting device, and electronic device
WO2016056211A1 (en) * 2014-10-06 2016-04-14 株式会社Joled Display device and display device control method
JPWO2016056211A1 (en) * 2014-10-06 2017-07-06 株式会社Joled Display device and control method of display device
US10074310B2 (en) 2014-10-06 2018-09-11 Joled Inc. Display device and display device control method

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