JP2005157264A - Pixel circuit and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a bad influence of threshold fluctuation of a driving TFT. <P>SOLUTION: A selection TFT 20 and a correction TFT 22 (22-1, 22-2) are on, and data voltage of a data line is held at a holding capacity 28 as a gate voltage of a driving TFT 24. After the selection TFT 20 is off, the voltage of a holding capacity line SC is brought down, the driving TFT 24 is on, and the driving current flows to an organic EL element 26. The correction TFT 22 is on before the holding capacity line SC is brought down, and it is off in the course of the bringing down. The capacity value of the correction TFT 22 changes while the gate voltage is bringing down, the inclination of the bringing down of the gate voltage of the driving TFT 24 changes, and the gate voltage after the holding capacity line SC is brought down is set corresponding to the threshold change of the driving TFT24. A multi-gate correction TFT 22-1 and -2 are provided between the gate of the selection TFT 20 and the driving TFT 24, and the leak current of the correction TFT 20 is prevented in the course of the change of the gate voltage of the driving TFT. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a pixel circuit including a light emitting element such as an organic EL element and a display device in which the pixel circuit is arranged in a matrix form.

  Conventionally, an organic EL panel using an organic EL element as a light emitting element is known, and its development is progressing. In this organic EL panel, organic EL elements are arranged in a matrix and display is performed by individually controlling the light emission of the organic EL elements. In particular, an active matrix type organic EL panel has a display control TFT for each pixel, and the light emission for each pixel can be controlled by the operation control of the TFT. Therefore, display with very high accuracy can be performed.

  FIG. 13 shows an example of a pixel circuit in an active matrix type organic EL panel. A data line to which a data voltage indicating the luminance of the pixel is supplied is connected to the gate of the driving TFT 12 via an n-channel selection TFT 10 whose gate is connected to the gate line. The gate of the driving TFT 12 is connected to one end of the storage capacitor 14 whose other end is connected to the storage capacitor line SC, and holds the gate voltage of the driving TFT 12.

  The source of the driving TFT 12 is connected to the EL power supply line, the drain is connected to the anode of the organic EL element 16, and the cathode of the organic EL element 16 is connected to the cathode power supply.

  Such pixel circuits are arranged in a matrix. At a predetermined timing, the gate line provided for each horizontal line becomes H level, and the selection TFT 10 in that row is turned on. In this state, since the data voltage is sequentially supplied to the data line, the data voltage is supplied and held in the holding capacitor 14, and the voltage at that time is held even if the gate line becomes L level.

  Then, according to the voltage held in the holding capacitor 14, the driving TFT 12 operates and a corresponding driving current flows to the cathode power source through the organic EL element 16 from the EL power source, and the organic EL element 16 becomes the data voltage. It emits light in response.

  Then, the gate lines are sequentially set to the H level, and the input video signals are sequentially supplied as data voltages to the corresponding pixels, so that the organic EL elements 16 arranged in a matrix emit light according to the data voltages, Display about the video signal is performed.

Special table 2002-514320 gazette

  However, in such a pixel circuit, if the threshold voltage of the driving TFTs of the pixel circuits arranged in a matrix varies, there is a problem that the luminance varies and the display quality deteriorates. It is difficult to make the characteristics of the TFTs constituting the pixel circuit of the entire display panel the same, and it is difficult to prevent the on / off threshold value from varying.

  Therefore, it is desirable to prevent the influence on the display of the variation in threshold value in the driving TFT.

  Here, various proposals have conventionally been made on a circuit for preventing the influence on the fluctuation of the threshold value of the TFT (for example, Patent Document 1).

  However, this proposal requires a circuit for compensating for threshold fluctuation. Therefore, when such a circuit is used, there is a problem that the number of elements of the pixel circuit increases and the aperture ratio becomes small. In addition, when a circuit for compensation is added, there is a problem that a peripheral circuit for driving the pixel circuit needs to be changed.

  The present invention provides a pixel circuit capable of effectively compensating for fluctuations in the threshold voltage of a driving transistor with a simple change.

  The present invention is a pixel circuit, wherein a first conductive region is connected to a data line, a selection transistor to which a selection signal is inputted to a control terminal, and a first conductive region is connected to a second conductive region of the selection transistor. The control terminal is connected to the first power source having a predetermined voltage, the control terminal is connected to the second conductive region of the correction transistor, and the first conductive region is connected to the second power source as a current supply source. A drive transistor; a storage capacitor having a first electrode connected to a control terminal of the drive transistor; and a second electrode connected to a pulse voltage line; and a driven element that is operated by a current flowing through the drive transistor.

  In the present invention, the display device includes a plurality of pixels arranged in a matrix. Each pixel has a display element that operates according to a supply current, and a first conductive region connected to the data line. A selection transistor to which a selection signal is input, a control transistor having a control terminal connected to a first power source having a predetermined voltage, a first conductive region connected to a second conductive region of the selection transistor, and a first conductive region Is connected to the second power source, the control terminal is connected to the second conductive region of the correction transistor, the driving transistor supplies power to the display element, and the first electrode includes the control terminal of the driving transistor and the correction transistor And a storage capacitor having a second electrode connected to the pulse voltage line.

  In the pixel circuit or the display device, the correction transistor changes the control terminal voltage of the drive transistor in accordance with a change in the voltage of the pulse voltage line, and the drive transistor is turned on in response to the change. The control terminal voltage is controlled based on the operation threshold value and the gate capacitance of the correction transistor, and the correction transistor has a plurality of gates connected to the same first power supply, and the selection transistor And a control terminal of the driving transistor is a multi-gate transistor in which a plurality of transistors are electrically connected in series.

  In another aspect of the present invention, the first power supply and the second power supply are supplied with power from a power supply line arranged to extend in the vertical scanning direction at the same power supply voltage, and the data line Extends in the vertical scanning direction together with the power supply line, is supplied by one power supply line extending in the vertical direction, and the data line also extends in the vertical direction, and the correction transistor is connected to the data line and the power supply line. Located in the area between.

  In another aspect of the invention, the channel length direction of at least one transistor constituting the multi-gate transistor of the correction transistor may be arranged along the vertical scanning direction in which the power supply line extends.

  In another aspect of the present invention, the drive transistor is disposed so as to be close to the power supply line and along a channel length direction in an extending direction of the power supply line, and the correction transistor includes the data line and the data line. The channel length direction of at least one transistor forming the multi-gate transistor is arranged along the vertical scanning direction in which the power supply line extends.

  In another aspect of the present invention, it is preferable that the driving transistor and the correction transistor are arranged close to each other with the power supply line interposed therebetween.

  In another aspect of the present invention, in the pixel circuit or the display device, the active layer of the correction transistor extends in the horizontal scanning direction from the power supply line toward the data line and is bent in the middle to extend the power supply line. It has a pattern extending in the vertical scanning direction along the existing direction. In other words, it is a substantially T-shaped pattern. The gate electrode of the correction transistor extends in the vertical scanning direction from the connection position with the power supply line along the extending direction of the power supply line, and has an insulating layer between the active layer and the active layer of the correction transistor. The channel regions of the multi-gate transistors may be formed in the intersecting regions.

  In the present invention, the selection transistor further includes a plurality of gates to which the same selection signal is input, and the plurality of transistors are electrically connected in series between the data line and the correction transistor. It is also possible to provide a multi-gate transistor.

  As described above, according to the present invention, in the process of turning on the driving transistor by changing the voltage value of the pulse voltage line, the on / off state of the correction transistor is changed, thereby the control terminal when the driving transistor is on. Control the voltage. Therefore, a different voltage can be set at the control terminal of the corresponding drive transistor in accordance with the threshold voltage of the correction transistor. In addition, by making the correction transistor have appropriate characteristics, variations in the threshold voltage of the driving transistor can be compensated, and the amount of current flowing through the driven element such as a light emitting element can be made uniform. Furthermore, in the present invention, the correction transistor provided between the selection transistor and the control end of the drive transistor is a multi-gate, so that an off-leakage current from the control end of the drive transistor toward the data line can be prevented. It is possible to prevent the voltage from fluctuating due to this leakage current.

  That is, in the present invention, the selection transistor and the correction transistor are turned on, the data voltage is applied from the data line to the control terminal of the driving transistor, and after the selection transistor is turned off, the voltage of the pulse voltage line is changed, In response to this voltage change, the control terminal voltage of the drive transistor shifts through the storage capacitor, so that the correction transistor is turned off, and the change speed of the control terminal voltage of the drive transistor is changed. The on / off state change voltage depends on the threshold value of the correction transistor, and the change rate of the control terminal voltage is controlled by the capacitance value of the correction transistor. Therefore, when the voltage at the control terminal of the driving transistor changes in accordance with the change of the pulse voltage line, the voltage changes from the voltage first written to the control terminal voltage from the data line. Then, after the correction transistor is turned off, the control terminal voltage changes according to the capacitance value of the correction transistor and the like until the drive transistor is turned on. Here, when a leak current is generated in the OFF correction transistor, the final voltage of the control terminal voltage that should originally be set in accordance with the variation in the threshold value of the drive transistor will fluctuate and flow to the driven element. This will adversely affect the uniformity of the amount of current. According to the present invention, by making the correction transistor multi-gate, such a leakage current can be suppressed, and the threshold compensation of the driving transistor can be performed with high accuracy.

Note that it is possible to further reliably prevent off-leakage current by making the selection transistor multi-gate.
Even if the correction transistor is made multi-gate, if this transistor is arranged between the power supply line and the data line, even if the number of transistors increases, the area increase is minimized. Therefore, it is possible to prevent variations in the operation of the driven element for each pixel without reducing the area of the driven element such as a light emitting element, that is, without reducing the aperture ratio.

  In addition, by arranging the correction transistor and the driving transistor close to each other with a power supply line extending in the vertical scanning direction, for example, an efficient arrangement capable of increasing the aperture ratio as much as possible can be realized. Further, since the transistor arrangement positions are close, the manufacturing conditions can be approximated, and the characteristics of the drive transistor and the correction transistor can be made uniform. As described above, the correction transistor is arranged for the purpose of correcting according to the variation in the characteristics of the drive transistor. Therefore, the characteristic is the same as that of the drive transistor or a similar characteristic having a certain relationship (for example, proportional relationship) In this way, it is possible to facilitate the control for compensating the variation of the driving transistor and the element design.

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

  FIG. 1 is a diagram illustrating a configuration of a pixel circuit of one pixel according to the embodiment. A first conductive region (drain) of the n-channel selection TFT 20 is connected to the data line DL extending in the vertical (scanning) direction. The gate (control end) of the selection TFT 20 is connected to the gate line GL extending in the horizontal (scanning) direction, and the second conductive region (source) is connected to the first conductive region (source) of the p-channel correction TFT 22. Yes. The selection TFT 20 may be a p-channel. In the case of the p-channel, the polarity (H level or L level) of the selection signal (gate signal) output to the gate line GL may be driven in reverse.

  The control end (gate) of the correction TFT 22 is connected to the power supply line PL (voltage Pvdd), and the second conductive region (drain) is connected to the control end (gate) of the p-channel drive TFT 24. Further, one end (first electrode) of the storage capacitor 28 is connected to the gate of the driving TFT 24, and the other end (second electrode) of the storage capacitor 28 functions as a pulse voltage line driven by a pulse voltage. It is connected to a storage capacitor line (hereinafter referred to as a capacitor line) SC. The capacitor line SC is a line extending in the horizontal direction like the gate line GL. If another power supply line is provided and the gate of the correction TFT 22 is connected to the other power supply line, the timing at which the correction TFT 22 is switched from on to off can be arbitrarily adjusted.

  The first conductive region (source) of the driving TFT 24 is connected to the power supply line PL extending in the vertical direction, and the second conductive region (drain) is connected to the anode of the organic EL element 26. The cathode of the organic EL element 26 is connected to a predetermined low voltage cathode power source CV. Here, in the normal case, the cathode of the organic EL element 26 is common to all pixels, and this cathode is connected to the cathode power source CV.

  In the organic EL panel, such pixel circuits are arranged in a matrix, and at the timing when the video signal of the corresponding horizontal line is input, the gate line of the horizontal line becomes H level, and the selection TFT 20 of that row is displayed. Turns on. As a result, the source of the correction TFT 22 becomes the potential of the data line DL.

  Here, a data voltage is supplied to the data line DL. This data voltage Vdata corresponds to a video signal for displaying the corresponding pixel, and expresses, for example, a white level to a black level at about 3 to 5V. On the other hand, the voltage Pvdd of the power supply line PL is set to about 0V. Accordingly, when the selection TFT 20 is turned on and the data voltage Vdata of the data line DL is applied to the correction TFT 22 (here, the source), the correction TFT 22 is turned on, and the data voltage Vdata is turned on to the gate (node Tg24) of the driving TFT 24. ) Is set. That is, a voltage of about 3 to 5 V is set at the gate of the driving TFT 24 during the writing period of the data voltage Vdata to each pixel. At this time, the capacity line SC at the other end of the storage capacitor 28 is set to about + 8V.

  After the writing of the data voltage Vdata is completed, the voltage of the capacitor line SC is lowered to, for example, −4V. In response to this, the gate of the driving TFT 24 is lowered by about 12 V, the driving TFT 24 is turned on, and a current corresponding to the data voltage is supplied from the power supply line PL to the organic EL element 26 via the driving TFT 24 to emit light.

  Here, the correction TFT 22 has a negative voltage of about −9 V to −7 V from 3 to 5 V on the drain (node Tg24) when the capacitance line SC drops from +8 V to about −4 V. (This voltage is slightly different as will be described later), and changes from the on state to the off state. Since the gate capacitance of the correction TFT 22 changes according to the change of the correction TFT 22 from on to off, the change timing of the capacitance, that is, the threshold value Vth22 of the correction TFT 22 affects the final gate potential of the driving TFT 24. . Therefore, the correction TFT 22 can compensate for variations in the threshold voltage Vth24 of the driving TFT 24.

  Here, the drive TFT 24 is turned on according to the difference between the power supply voltage Pvdd and the gate voltage Vg24, that is, Vgs24, and causes a corresponding drive current to flow. When this Vgs24 becomes larger than the threshold voltage Vth24 determined by the characteristics of the TFT, the drive TFT 24 starts to flow current, and the drive current amount is determined by the difference between the gate voltage Vg24 and the threshold voltage Vth24. Is done. On the other hand, it is difficult to make the threshold voltages Vth24 of the driving TFTs 24 of a large number of pixels arranged in a matrix on the substrate completely the same, and it is avoided that the threshold voltage Vth24 varies somewhat depending on the pixel position. I can't. Since the organic EL element 26 emits light with a luminance corresponding to the amount of drive current supplied, the light emission luminance of each pixel varies according to the variation in the threshold voltage Vth24 of the drive TFT 24. In the configuration according to the present embodiment, the variation in light emission luminance is compensated for by the capacitance change of the correction TFT 22.

  Hereinafter, the principle of variation compensation of emission luminance will be described with reference to FIGS. FIG. 3 is an enlarged view showing a state when the capacitance line SC indicated by the long circle in FIG. 2 falls. First, as shown in FIG. 2, the gate line GL becomes active (H) level when the row (horizontal line) is selected. In this example, the selection TFT 20 is an n-channel, and the gate line GL is set to L level = about −4V and H level = about 8V, and is set to 8V at the time of selection (active).

  On the other hand, the voltage Vsc of the capacitor line SC is at the H level for a period slightly longer than the period during which the gate line GL is selected (at the H level). That is, it becomes H level before the gate line GL becomes H level, and becomes L level after the gate line GL becomes L level.

While the gate line GL is at the H level, the selection TFT 20 and the correction TFT 22 corresponding to the gate line GL are turned on, and the data voltage Vdata output to the data line DL at that time passes through the selection TFT 20 and the correction TFT 22. Applied to node Tg24. That is, the gate voltage V _g24 of the driving TFT 24 is set to the data voltage Vdata.

After the gate line GL becomes L level and the data voltage Vdata is written, the voltage of the capacitor line SC falls, and the potential of the node Tg24 decreases accordingly, and the correction TFT 22 is eventually turned off. The gate voltage V _g24 of the drive TFT 24 becomes a voltage lower than the data voltage Vdata by a predetermined voltage according to the decrease of the capacitance line SC (in this example, 12V from 8V to −4V), and the drive current corresponding to this voltage Shed.

The correction TFT 22 is provided for each pixel and is formed adjacent to the drive TFT 24 of the pixel, and is created through the same process as the drive TFT 24. In particular, as will be described later, for example, when the polycrystalline silicon obtained by polycrystallizing amorphous silicon by laser annealing is used as the active layer of the driving TFT 24 and the correction transistor 22 including the selection TFT 20, the driving TFT 24 and the correction TFT 22 are used. By simultaneously irradiating the active layer region with the same laser pulse for polycrystallization, the TFT characteristics can be made uniform. Also, the impurity concentration implanted into the active layer can be made substantially the same. Accordingly, the drive TFT 24 and the correction TFT 22 have substantially the same threshold voltage. Further, since the gate of the correction TFT 22 is connected to the power supply line PL (here, Pvdd = 0V), it changes from on to off as the voltage V _g24 of the node Tg24 decreases.

Thus, when the capacitance line SC falls, the correction TFT 22 which is a p-channel TFT changes its state from on to off, while the driving TFT 24 changes its state from off to on. The gate capacitance value Cg of the TFT changes depending on the on or off state. Therefore, the change in the gate voltage V _g24 of the driving TFT 24 is affected by the change in the on / off state of the two _{TFTs 22 and} 24. That is, specifically, the TFT has a large Cg in the TFT on state and small in the off state. Since the capacitance is larger when it is on than when it is off, the voltage change state is affected by the capacitance change.

That is, when the correction TFT 22 is turned off from on and the gate capacitance value C _g22 is reduced, the slope α of the decrease in the voltage V _g24 is increased.

Therefore, when the switching voltage at which the correction TFT 22 of a certain pixel is switched from the on state to the off state is the “switching voltage A” in FIG. 3, the voltage at the node Tg24 (gate voltage V _g24 ) is a solid line in the figure. It changes as shown. That is, until the switching voltage A is reached, the gate voltage V _g24 changes (decreases) from the set data voltage Vdata with the first slope α ₁ , and after reaching the switching voltage A, the second slope α _2. Change (decrease). When a driving TFT24 is turned on, the change in the third inclination alpha ₃ and (reduced), after a predetermined period of time the voltage of the capacitor line SC becomes the L level, the voltage V _g24 is set in the correction voltage VcA .

Here, the switching voltage at which the correction TFT 22 changes from on to off is determined by the power supply voltage Pvdd = 0, which is the gate voltage of the correction TFT 22, and the source voltage difference V _gs22 as described above. Therefore, the switching voltages A and B are equal to a voltage (Pvdd + | V _th22 |) _obtained by adding the absolute value of the threshold voltage V _th22 of the correction TFT 22 to the power supply voltage Pvdd.

On the other hand, when the threshold voltage V _th22 of the correction TFT 22 is the “switching voltage B” lower than the “switching voltage A”, the gate voltage V _g24 changes as indicated by a broken line in FIG. That is, the gate voltage Vg24 from once set the data voltage Vdata, until it reaches the switching voltage B varies (decreases) along first gradient alpha _1, a later arrival changed second inclination alpha ₂ ( It decreased), and then the drive TFT24 is on changes in third inclination alpha ₃ (reduction), from when the voltage of the capacitor line SC is the L level after a predetermined period, voltage V _g24 is set in the correction voltage VcB The

Thus, even if the same data voltage Vdata is initially supplied to the node Tg24, the final gate voltage _Vg24 of the driving TFT 24 is set to a higher correction voltage Vc as the threshold voltage is lower. become.

As described above, the threshold voltage V _TH24 of the driving TFT24 corresponds to the threshold voltage V _th22 of the correction TFT 22. Therefore, if the threshold voltage V _th24 of the driving TFT 24 is “V _th24 A”, the gate voltage V _g24 becomes the correction voltage VcA corresponding to the threshold voltage V _th24 A, and is “V _th24 B”. If so, the gate voltage V _g24 is set to the correction voltage VcB corresponding to the threshold voltage V _th24 B. In this example, the difference between the threshold voltage Vth24 and the corrected gate voltage _Vg24 is the same _whether the threshold voltage is V _th24 A or V _th24 B. That is, if the data voltage Vdata is the same by setting the size of the correction TFT 22, the power supply voltage value Pvdd, the size of the drive TFT 24, the capacitance value Cs of the storage capacitor 28, the threshold voltage V _th24 of the drive TFT 24 is set for each pixel. Even if they are different from each _other , the difference between the threshold voltage V _th24 and the gate voltage V _g24 can be made constant, and the influence of the variation in the threshold voltage V _th24 of the drive TFT 24 can be eliminated.

Here, in order to perform the compensation as described above, it is preferable to set the conditions so that the second inclination α ₂ is twice the first inclination α ₁ . This condition setting will be described with reference to FIG. As shown in FIG. 3, when the correction TFT 22 is in the ON state, the capacitance value C _g22 is larger than that in the OFF state, so that the change in the gate voltage V _g24 is suppressed from being affected by the change in the pulse drive voltage. Thus, the inclination α ₁ becomes small. On the other hand, when the correction TFT 22 is in the off state, the capacitance value C _g22 is small, and the influence of the change in the pulse drive voltage is large, so the slope α ₂ is large. Furthermore, since the inclination α ₂ is set to be twice as large as the inclination α ₁ , the correction TFT 22 is turned off for the decrease in the gate voltage V _g24 when the pulse drive voltage becomes L level. The state is double that of the on state.

That is, two threshold voltage difference [Delta] V _TH24 of the driving TFT 24, constitute two correction TFT22 TFT so that the difference [Delta] V _th22 of the threshold voltage is equal to, when changed from ON to OFF of correction TFT22 By doubling the slope of ΔV _th22 = ΔV _th24 , the difference ΔVc between the two correction voltages (VcA, VcB) satisfies ΔVc = ΔV _th24 .

That is, in FIG.
(I) the difference (ΔV _th22 ) between the switching voltages A and B of the two correction _{TFTs 22} ;
(Ii) When the switching voltage B (the slower switching timing: the lower voltage here) and the node Tg24B of the pixel reaches the switching voltage B, the node Tg24B of the pixel having the correction TFT 22 of the switching voltage A Difference from voltage V _g24 A (ΔV _th22 ′),
(Iii) Difference in switching voltage (ΔV _th24 ) between the two drive _TFTs 24,
(Iv) Difference from correction voltages VcA and VcB (ΔVc)
Are all equal.

Even when the sampling voltage, which is the voltage written as the data voltage Vdata, changes, the slope does not change. Therefore, the switching voltage difference ΔV _th22 is equal to the correction voltage difference ΔVc, and the threshold is always maintained. Voltage fluctuations can be compensated.

  Further, according to experiments, the potential difference between the data voltages is amplified by a factor of 2 in the correction voltage after the compensation operation. Therefore, it is possible to reduce the range of the data voltage, hold a sufficient gate voltage difference of the driving TFT 24, and obtain an effect that the load of the circuit for supplying the data voltage is small and can be easily created.

As described above, the gate voltage change of the driving TFT 24 when lowers the voltage of the capacitor line SC is particularly the gate capacitance C _g22 of the correction TFT 22, the gate capacitance C _g24 of the driving TFT 24, the capacitance of the storage capacitor 28 It is affected by the value Cs and the parasitic capacitance Cw of the wiring.

The mechanism of change of V _g24 described above will be described based on the amount of charge transfer. Here, the capacitance value of the storage capacitor 28 is Cs, the gate capacitance of the correction TFT 22 is C _g22 , the gate capacitance of the drive TFT 24 is C _g24 , the threshold voltage of the correction TFT 22 is V _th22 , and the threshold voltage of the drive TFT 24 is V _{In addition to th24} , the capacitance value Cs of the storage capacitor 28 is set to the gate capacitance _Cg22 of the correction TFT 22.
(I) First, from the state of the gate voltage V _g24 = Vdata of the driving TFT 24, lowering 12V capacity line SC, voltage V _g24 of the node Tg24 should also be decreased 12V. If V _g24 considering only this change is expressed as V _g24 ′,
V _g24 '= Vdata-12
It becomes.
(Ii) If the gate capacitance of the correction TFT 22 is C _g22 , the amount of charge Q _f22 flowing out of the correction TFT 22 and flowing into the storage capacitor 28 is
Q _f22 = C _g22 × (Vdata− | V _th22 |)
It is.

In this embodiment, as described above, C _g22 = Cs, and the voltage V _{g24 at the} node Tg24 increases by (Vdata− | V _th22 |). Therefore, the voltage V _g24 ″ considering this increase is
V _g24 ″ = 2Vdata-12− | V _th22 |
It becomes.
(Iii) Further, charge flows into the storage capacitor 28 also from the gate of the driving TFT 24. This charge amount Q _f24 is obtained by _setting the final gate voltage of the driving TFT 24 to V _g24 .
Q _f24 = −C _g24 '× (V _g24 + | V _th24 |)
It becomes. Here, C _g24 ′ is a capacitance difference between the off time and the on time in the driving TFT 24, and a value of C _g24 ′ = C _g24 × _2/3 calculated using the SPICE (Spice Simulator) MEYER formula is used. It was.
(Iv) The gate voltage V _g24 of the driving TFT 24 may be shifted by an amount _{corresponding} to the charge Q _f24 flowing into the storage capacitor 28. Therefore,
V _g24 = V _g24 ”+ Q _f24 / C _g22
= V _g24 ″ −C _g24 ′ (V _g24 + | V _th24 |) / C _g22
Rewriting this, the final V _g24 is
(1 + C _g24 '/ C _g22 ) V _g24
= 2Vdata-12- | _Vth22 |-( _Cg24 '/ _Cg22 ) | _Vth24 |
It becomes.

If V _th22 = V _th24 = V _th
V _g24 = − | V _th | + (2 Vdata−12) / (1 + C _g24 ′ / C _g22 )
It becomes.

Second term on the right side in this equation, since fixed value by the layout dimensions, V _g24 will be shifted V _th minute, that can be compensated for even if shifted to the threshold voltage V _th of the driving TFT24 Become.

  Strictly speaking, it is necessary to take into account the parasitic capacitance with respect to the wiring. If the power supply voltage Pvdd is not 0V, the value may be taken into consideration.

Further, the threshold voltage V _th22 of the correction TFT 22, when the threshold V _TH24 of the driving TFT 24 is different also, by the threshold V _TH24 of the driving TFT 24, the the gate voltage V _g24 deviates desirable. For this purpose, C _g24 ′ / C _g22 in the above equation may be adjusted. However, too large adjustment is difficult, and it is preferable to form the TFT so that V _th22 = V _{th24 as} much as possible.

Next, the relationship between various capacitors in the pixel circuit according to the embodiment of the present invention will be further described with reference to FIG. The pixel circuit according to the present embodiment, another storage capacitor Cs, the gate capacitance C _g22 of the above-mentioned correction TFT 22, parasitic capacitance of the gate capacitance C _g24 and various drive TFT24 are connected. For example, as shown in FIG. 4, the parasitic capacitance C _w1 between the connection point (node) Tg24 between the drain of the correction TFT 22 and the gate of the driving transistor 24 and the power supply line PL, the source of the correction TFT 22 and the source of the selection TFT 20 There is a parasitic capacitance C _w2 between the connection portion and the power supply line PL. When the relationship between these parasitic capacitances and the slope α of the decrease in the voltage V _g24 at the node Tg24 in FIG. 3 is shown, the slope α ₁ until the voltage (A or B) is reached from the data voltage Vdata in FIG. ,
α ₁ = Cs / (C _w1 + C _w2 + Cs + C _g22 )
Can be shown. Since the charge flows into the storage capacitor Cs from a state where constant charges are charged in all of these parasitic capacitances (C _w1 , C _w2 , C _g22 ), the slope α _{1 at which} the gate voltage V _g24 decreases is It is expressed by the following formula.

Next, in FIG. 3, the slope α ₂ of the decrease in the voltage V _g24 at the node Tg24 during the period from when the switching voltage is reached until the drive TFT 24 is turned on is
α ₂ = Cs / (Cs + C _w1 )
It is represented by This is because, after the switching voltage is reached, the correction TFT 22 is turned off, and the gate capacitance C _g22 and the parasitic capacitance C _w2 between the source and the power supply line PL are electrically reduced from the holding capacitance 28 (capacitance value Cs). Because it will be cut off.
Here, as described above, α ₂ = 2 × α ₁ is set.
Therefore, by setting the capacitance Cs of the storage capacitor 28 so as to satisfy Cs = C _g22 −C _w1 + C _w2 , when the voltage of the capacitance line SC is lowered, the correction TFT 22 is switched from on to off. The inclination α ₂ of the drop of the gate voltage Vg24 of the TFT 24 can be set to twice α ₁ , and appropriate compensation for the threshold voltage fluctuation of the driving TFT 24 can be performed.

Further, as shown in FIG. 3, the inclination α ₃ after the driving TFT 24 is turned on is
α ₃ = Cs / (Cs + C _w1 + C _g24 )
It is represented by

C _g24 is the gate capacitance of the driving TFT 24 as described above. When the driving TFT 24 is turned on, the capacitance C _g24 is connected to the holding capacitor 28, and the slope of voltage drop α ₃ is influenced by the capacitance C _g24 . Will also receive. The timing t _{on24 at} which the drive TFT 24 is turned on is the same for each pixel regardless of the switching voltage of the drive TFT 24, that is, the threshold voltage V _th24 as described above. Specifically, each correction TFT 22 is turned off at a timing corresponding to the variation of the threshold value V _th22 , so that in each pixel circuit, the gate voltage Vg24 is divided from the power supply voltage Pvdd according to each V _th24. This is the timing when a low voltage is reached simultaneously.

  Next, a layout of a pixel including such a pixel circuit will be described with reference to FIGS. FIG. 5 shows a schematic planar structure in one pixel, and FIGS. 6A and 6B show schematic cross-sectional structures taken along lines AA and BB in FIG. 5, respectively.

  A buffer layer 102 is formed on a transparent insulating substrate 100 such as glass, and an active layer of each TFT made of polycrystalline silicon and a semiconductor layer (120, 120) constituting a capacitor electrode. 124 and 28e) are indicated by broken lines in FIG. In FIG. 5, the gate line GL, the capacitor line SC, the gate electrode 22g of the correction TFT 22 and the gate electrode 24g of the driving TFT 24, which are formed above the semiconductor layer and made of a refractory metal material such as Cr, Shown with a dashed line. Further, a data line DL, a power supply line PL, and a metal wiring 24w in the same layer formed by using a low-resistance metal material such as Al formed above the semiconductor layer and the GL and SC are shown by solid lines. .

  In the layout shown in FIG. 5, each pixel has a data line DL formed between the rows of the gate lines GL formed along the horizontal (H) direction of the display device and generally along the vertical (V) direction of the display device. It is configured at the position between the lines. In addition, the power supply line PL is formed in a vertical direction (matrix column direction) substantially in line with the data line DL. In each pixel region, the organic EL of the pixel connected to the data line DL and the data line DL is formed. It passes between the elements 26. As will be described later, the selection TFT 20, the correction TFT 22 and the storage capacitor 28 are between the data line DL and the power line PL, and the driving TFT and the organic EL element 26 are between the power line PL and the adjacent data line DL. Is arranged.

  The selection TFT 20 is formed near the intersection of the gate line GL and the data line DL. A protruding portion is formed from the gate line GL toward the pixel region, and covers a part of the semiconductor layer 120 extending along the gate line GL with the gate insulating film 104 interposed therebetween. The protruding portion from the gate line GL becomes a gate electrode 20g of the TFT 20, and a region covered with the gate electrode 20g of the semiconductor layer 120 is a channel region.

  The correction TFT 22 connected to the selection TFT 20 is arranged in a region sandwiched between the data line DL and the power supply line PL so that the channel length direction is along the extending direction (vertical direction) of the data line DL. The active layer of the correction TFT 22 is formed below the data line DL so as to partially overlap the data line DL. A storage capacitor 28 is arranged between the correction TFT 22 and the capacitor line SC arranged close to the gate line GL of the next row, more specifically along the capacitor line SC. The driving TFT 24 is disposed in a region opposite to the region where the correction TFT 22 is formed (on the organic EL element region 26 side) across the power supply line PL, and at least the channel region 24c of the semiconductor layer 124 constituting the active layer is provided. The layout is so arranged as to be as close as possible to the channel region 22 c of the correction TFT 22.

  Here, in this embodiment, the active layer of the selection TFT 20, the active layer of the correction TFT 22, and the capacitor electrode 28 e of the storage capacitor 28 are integrally formed by a single semiconductor layer 120 (of course, each is an independent layer). And each may be electrically connected by a predetermined wiring).

  In the region where the selection TFT 20 is formed, the data line DL and the semiconductor layer 120 are connected to each other through a contact hole formed through the gate insulating film 104 and the interlayer insulating film 106. The semiconductor layer 120 extends from the lower layer region of the data line DL (contact region with the data line DL) to the position overlapping the power supply line PL along the gate line GL, and the lower layer of the power supply line PL is powered from the overlapping position. It extends in the vertical direction along the extending direction of the line PL. Further, the semiconductor layer 120 bends in the direction parallel to the extending direction of the gate line GL from the lower layer position of the power line PL just before the contact between the gate electrode 22g of the correction TFT 22 and the power line PL, and the data line DL Extending towards.

  In the region where the selection TFT 20 is formed, the semiconductor layer 120 has an impurity implanted region connected to the data line DL as a first conductive region (for example, the drain region 20d), and an intrinsic region which is overlapped with the gate electrode 20g and is not implanted with impurities. A second conductive region (for example, a source region 20s) in which an impurity having the same conductivity type as that of the first conductive region is implanted is formed on the opposite side across the channel region 20c.

  The semiconductor layer 120 extending from the lower layer of the power line PL toward the data line DL bends in the extending direction of the data line DL in the vicinity where it intersects the data line DL again (near the first conductive region 20d of the selection TFT 20). While a part of the region overlaps the formation region of the power supply line PL (in this example, partly overlaps the data line DL), the region between the data line DL and the power supply line PL extends vertically to the formation region of the capacitor line SC. It is extended.

  The region where the semiconductor layer 120 is disposed along the data line DL constitutes an active layer of the correction TFT 22, and the gate electrode 22 g of the correction TFT 22 is located above the gate insulating film 104 of the active layer. The gate electrode 22g is connected to the power supply line PL through a contact hole formed in the interlayer insulating film 106. The gate electrode 22g extends from the contact position with the power supply line PL toward the data line DL, bends at a position overlapping with the semiconductor layer 120 (active layer of the correction TFT 22), extends in the extending direction of the data line DL, and The upper layer 120 is formed so as to cover the data line DL and the power supply line PL and to partially overlap the data line DL and the power supply line PL.

  The region covered with the gate electrode 22g of the semiconductor layer 120 becomes a channel region 22c in which the impurity of the correction TFT 22 is not doped. Impurities of a conductivity type different from that of the selection TFT 20 are present on the selection TFT 20 side across the channel region 22c. An implanted first conductive region (here, for example, a source region 22s) is formed, and a second conductive region (here, a drain region 22d) into which the same impurities as the first conductive region 22s are implanted is formed on the capacitor line SC side. Is formed. Note that the correction TFT 22 is formed between the data line DL and the power supply line PL by forming the data line DL and the power supply line PL and at least the channel region 22c of the correction TFT 22 partially overlapping with these lines. It is possible to arrange efficiently in a narrow area. Further, the gate electrode 22g is disposed between the channel region 22c, the data line DL, and the power supply line PL, so that the channel region 22c is electrically shielded from the data line DL, and the operation of the correction TFT 22 is controlled by the data line DL. It is prevented from being influenced by the data signal applied to. Since at least the gate electrode 22g of the correction TFT 22 is connected to the power supply line PL, even if the active layer of the correction TFT 22, particularly the channel region 22c, is arranged so as to overlap the power supply line PL, The applied voltage is not substantially different from that covered with the gate electrode 22g. Therefore, it is possible to form most of the active layer of the correction TFT 22 below the power supply line PL. With such an arrangement, an aperture ratio within one pixel, that is, an organic EL element that contributes to light emission. The formation area of 26 can be maximized.

  The semiconductor layer 120 extends from the formation region of the second conductive region of the correction TFT 22 toward the capacitor line SC, bends at a position intersecting the capacitor line SC, and in the horizontal direction that is the extending direction of the capacitor line SC. Patterning is performed so as to overlap the line SC with the gate insulating film 104 interposed therebetween, and a region overlapping the capacitor line SC of the semiconductor layer 120 functions as a capacitor electrode (first electrode) 28e, and the capacitor line SC (second electrode) The storage capacitor 28 is a region where the capacitor electrode 28e is opposed to the capacitor electrode 28e with the gate insulating film 104 interposed therebetween.

  A metal wiring 24 w is connected between the second conductive region 22 d of the correction TFT 22 and the capacitor electrode 28 e of the storage capacitor 28 through a contact hole formed in the interlayer insulating film 106 and the gate insulating film 104. The metal wiring 24w is formed along the extending direction of the capacitor line SC, and is connected to the gate electrode 24g of the driving TFT 24 through a contact hole formed in the interlayer insulating film 106.

  The gate electrode 24g of the driving TFT 24 extends from the contact region with the metal wiring 24w in the direction in which the gate line GL is formed (upward in the figure), crosses the lower layer of the power line PL on the way, and the organic of the power line PL It is formed on the EL element 26 side along the extending direction of the power supply line PL.

  Here, the power supply line PL is bent so as to approach the data line DL from the vicinity of the contact region with the gate electrode 22g of the correction TFT 22, and close to the metal wiring 24w on the organic EL element 26 side so as to bypass the formation region. It bends and extends in the vertical direction from the vicinity of the contact with the semiconductor layer 124 constituting the active layer of the driving TFT 24 toward the pixel in the next row. The drive TFT 24 is formed in a space formed between the organic EL element 26 and the power supply line PL approaching the data line DL side.

  In the semiconductor layer 124 constituting the active layer of the driving TFT 24, a channel region 24c is formed in a region where the upper side is covered with the gate electrode 24g, and a first conductive region (here, a source region) is connected to the power supply line PL. 24s), and a second conductive region (here, drain region 24d) is formed on the connection side with the organic EL element 26. The channel region 24c is an intrinsic region which is not doped with impurities, and the first and second conductive regions (24s and 24d) formed on both sides thereof are doped with impurities of the same conductivity type as the correction TFT 22. Note that the first conductive region 24 s of the driving TFT 24 is connected to the power supply line PL in a contact hole formed in the interlayer insulating film 106 and the gate insulating film 104. The second conductive region 24d of the driving TFT 24 is connected to a connection electrode 24e made of the same material as the power supply line PL, for example, in a contact hole formed in the interlayer insulating film 106 and the gate insulating film 104.

  Further, as shown in FIGS. 6A and 6B, the entire surface of the substrate covering the data line DL, the power line PL, the metal wiring 24w, and the connection electrode 24e is made of an organic resin for flattening the upper surface. A planarization insulating layer 108 is formed. In the planarization insulating layer 108, a contact hole is formed in the formation region of the connection electrode 24e connected to the driving TFT 24. The contact hole is formed on the planarization insulating layer 108 through the contact hole. The first electrode 262 (in this case, the anode) of the organic EL element 26 and the connection electrode 24e are connected. When the connection electrode 24e is not provided, a contact hole that penetrates the planarization insulating layer 108, the interlayer insulating film 106, and the gate insulating film 104 is formed in the formation region of the second conductive region 24d of the driving TFT 24, and the organic EL The first electrode 262 of the element 26 and the second conductive region 24d are directly connected.

  As shown in FIG. 6B, the organic EL element 26 is formed on the substrate side, and emits light between the first electrode 262 and the second electrode 264 having an individual pattern for each pixel connected to the driving TFT 24. An element layer 270 is provided. The first electrode 262 can be formed using a transparent conductive metal oxide such as ITO (Indium Tin Oxide), for example, and functions as an anode (hole injection electrode) here. The second electrode 264 can be constituted by a metal material having a small work function such as Al or Ag, or a laminated structure of such a metal material and the ITO, and functions as a cathode (electron injection electrode) here. Note that the edge portion of the first electrode 262 formed in an individual pattern for each pixel is covered with the second planarization insulating layer 110 formed further above the planarization insulating layer 108, and the light emitting element is formed very thin. The second electrode 264 formed on the layer 270 and the first electrode 262 are prevented from being short-circuited.

  In this example, the light-emitting element layer 270 has a three-layer structure including a hole transport layer 272, a light-emitting layer 274, and an electron transport layer 276. It is not limited to a three-layer structure, and may be a single layer having a light emitting function, a two-layer structure, or a laminated structure of four or more layers depending on an organic material used. When a multilayer structure is adopted as the light emitting element layer 270, all the layers may be formed in common for each pixel, or a part or all of the multilayers, for example, as shown in FIG. Only the light emitting layer 274 may be an individual pattern for each pixel similar to the first electrode 262.

  In the organic EL element 26 having such a configuration, in this embodiment, the current supplied from the power supply line PL to the first electrode 262 via the driving TFT 24 flows between the second electrode 264 and the amount of current is increased. Light emission occurs in the light emitting element layer with a corresponding luminance. Note that light emission occurs when holes injected from the first electrode 262 and electrons injected from the second electrode 264 recombine in the light-emitting element layer, and thus excited light-emitting molecules return to the ground state. Here, the light passes through the transparent first electrode 262 and the substrate 100 and is emitted from the substrate to the outside and visually recognized.

  In the present embodiment, as described above, the correction TFT 22 and the drive TFT 24 are laid out as close as possible with the power supply line PL interposed therebetween. In particular, the channel region 22c of the correction TFT 22 and the channel region 24c of the driving TFT 24 are formed such that at least a part of the channel region is aligned with each other in the vertical direction.

In this embodiment, the active layer of each TFT formed in the pixel is a pulse laser (see FIG. 5) shaped in a line shape with respect to an amorphous silicon layer formed by plasma CVD or the like in the longitudinal direction. Is set to coincide with the horizontal direction, and a low-temperature polycrystalline silicon (LTPS) layer obtained by polycrystallization annealing by sequentially illuminating while shifting by a predetermined pitch in the width direction is used. The scanning direction of the laser beam is the width direction of the laser beam and coincides with the vertical direction that is the extending direction of the data line DL and the like. As shown in FIG. 5, the channel regions 22c and 24c of the correction TFT 22 and the driving TFT 24 are arranged so that the channel length direction thereof coincides with the extending direction of the data line DL or the like, that is, the scanning direction of the laser beam. . Therefore, by making the scanning pitch of the laser beam smaller than the channel lengths of the correction TFT 22 and the driving TFT 24, the channel length direction of any channel region 22c, 24c crosses the channel (in the channel width direction). ) The laser beam is always irradiated multiple times. As a result, even if variations in the energy of each laser beam occur, a plurality of laser beams are irradiated on any channel region 22c, 24c, so that the variation in the total amount of energy received in all channel length directions can be determined by which pixel. Can also be reduced.
Further, when a polycrystalline silicon layer formed by so-called laser annealing is used as an active layer of a TFT, the same pulse laser beam is simultaneously irradiated to the regions to be the channel regions 22c and 24c of the correction TFT 22 and the driving TFT 24. By arranging the channel regions 22c and 24c close to each other, it is easy to make the polycrystallized state having a great influence on the TFT characteristics (particularly the threshold value) equal in both TFTs.

  Here, one irradiation area of the pulse laser shaped in a line shape has a length in the longitudinal direction of 10 cm to 30 cm, for example, and its pulse width is about 300 μm. The scanning pitch of such a pulse laser is, for example, about 25 μm, that is, amorphous silicon is polycrystallized while shifting the irradiation position of the pulse laser by 25 μm. In addition, the channel region 22c of the correction TFT 22 and the channel region 24c of the driving TFT 24 are not only arranged close to each other but also arranged so that at least a part thereof is arranged on the same straight line drawn in the direction intersecting the vertical direction. Thus, it becomes possible to irradiate the channel regions 22c and 24c with the same pulse laser. Further, the channel length of both the correction TFT 22 and the driving TFT 24 is set to at least 30 μm or more, more preferably 40 μm or more, so that the pulse laser having the above size is applied to the channel formation region as described above. By scanning along the vertical direction of the pixel at a pitch, it is possible to reliably irradiate the channel regions 22c and 24c of the two TFTs with at least one or more identical pulse lasers.

  Further, impurities of the same conductivity type are simultaneously implanted into the semiconductor layers 120 and 124 using the gate electrodes 22g and 24g as masks. However, since the formation positions are very close, the impurity implantation conditions (implantation concentration, implantation energy, etc.) are changed. From this point of view, the characteristics of the correction TFT 22 and the driving TFT 24 can be made equal.

  By adopting the layout as described above in the pixel area, the horizontal one side area of the pixel area (in the pixel of FIG. 5, the data line DL and the power supply line, and circuit elements such as TFTs 20, 22, and 24 are arranged on the left side. The organic EL elements 26 are arranged on the remaining one side (right side in the pixel of Fig. 5), and can be efficiently arranged as a whole. Thus, the organic EL element 26 can be formed as large as possible, contributing to an improvement in the aperture ratio as a display device, and by changing the pixel area for each emission color in consideration of the light emission efficiency and the required luminance. Even when the lifetimes are made uniform, it is easy to change only the area of the organic EL element 26 without changing the area and layout of the TFTs 20, 22, 24, the storage capacitor 28, etc. Above is Hakare.

  In the layout shown in FIG. 5, the pixels arranged in a matrix employ a so-called delta arrangement in which the positions of the same color pixels are shifted in the horizontal direction by a predetermined pitch for each row, and one data line DL is When the data signal Vdata is supplied to the same color pixel, as shown in FIG. 5, the data line DL extends while meandering in the column direction of the matrix and is connected to the selection TFT 20 of the same color pixel arranged alternately on the left and right of the line. Will be. By adopting such a layout, in the pixel in the next row of the pixel shown in FIG. 5, the organic EL element 26 is on the left side of the pixel as opposed to FIG. 5, and the TFTs 20, 22, 24, etc. are pixels. It is arranged on the right side. Of course, the layout described above can be applied not only to the delta arrangement but also to the stripe arrangement. In this case, the positional relationship between the organic EL element and the TFT for controlling this is reversed horizontally. do not do.

  Here, in the correction TFT 22 of this embodiment, as shown in FIG. 5, the width (channel width) of the channel region 22c formed of the semiconductor layer changes in the channel length direction. Specifically, in FIG. 5, the width is wider on the side closer to the selection TFT 20 (upper side in the figure), and the width is narrower on the connection side (lower side in the figure) with the storage capacitor 28 and the driving TFT 24. Thus, by providing a portion where the channel width of the correction TFT 22 is at least different from the others in the channel length direction, the degree of freedom of arrangement of the correction TFT 22 can be increased. Note that the characteristics of the correction TFT 22 can be considered based on the narrowest channel width. Thus, the layout flexibility of the correction TFT 22 is increased, so that the layout of the gate electrode 24g of the driving TFT 24 which is another circuit element can be effectively performed. In order to increase the degree of freedom of arrangement, it is preferable to change the width (channel width direction) of the semiconductor layer forming the channel region, and change the channel widths of the other selection TFT 20, drive TFT 24, etc. It is also possible to increase the degree of freedom of arrangement.

  Further, as described above, the pixel circuits according to the embodiment are arranged in a matrix form, and a display device is configured. In many cases, a pixel region including an organic EL element and a peripheral driver circuit for driving each pixel are formed on a glass substrate on the glass substrate. As a procedure, the organic region in the pixel region is first formed on the substrate. By forming circuit elements other than EL elements and peripheral driver circuits, and then forming organic EL elements above those circuit elements, and further covering and adhering the sealing substrate to the glass substrate 100 from the element side. An organic EL panel is obtained. Note that the pixel circuit of the embodiment is not limited to such an organic EL panel, and can be applied to other various display devices. In particular, the same effect can be obtained by applying to each pixel when a current-driven display element and a circuit (TFT) for controlling the element are formed.

  Next, in this embodiment, it is more preferable that the selection TFT 20 and the correction TFT 22 are multi-gate. This is because it is particularly effective for reducing a leak current that is often applied to a TFT using a polycrystalline silicon layer as an active layer. In the present embodiment, the leakage current is a current that flows toward the data line DL through the TFT when the correction TFT 22 and the selection TFT 20 are turned off, and the leakage current is suppressed by making these TFTs multi-gate. Can do. As shown in FIG. 7, only the correction TFT 22 may be multi-gated, or only the selection TFT 20 may be multi-gated. Of course, both may be multi-gate as shown in FIG.

FIG. 7 shows an equivalent circuit when the correction TFT 22 is multi-gated, and FIG. 8 is a plan view showing an example of a layout for realizing the equivalent circuit. In the example of FIG. 7, a so-called double gate structure is adopted as the correction TFT 22. Specifically, a first correction TFT 22-1 having a drain connected to the node Tg24 between the node Tg24 and the selection TFT 20 and a second correction TFT provided between the first correction TFT 22-1 and the selection TFT 20 are provided. Two correction TFTs 22-2 are provided. The gates of the first and second correction TFTs 22-1 and 22-2 are both connected to the power supply line PL, and the source and drain of the first and second correction TFTs 22-1 and 22-2 are connected to the selection TFT 20 and the node Tg24. They are electrically connected in series. With such a connection relationship, the off-leakage resistance between the driving TFT 24 and the selection TFT 20 is increased, and the gate voltage V _{g24 of the} driving TFT 24 held in the holding capacitor 28 leaks to the data line DL from an appropriate value. It is possible to effectively prevent the fluctuation.

More specifically, by dividing the correction TFT 22, a voltage V _s20 (source voltage of the correction TFT 22-2) on the source side of the selection TFT 20 is connected to a connection point between the first and second correction TFTs 22-1 and 22-2. V _d22-2 ) and the voltage V _{g24 of the} node Tg24 are _divided, and the voltage Vm having a value therebetween becomes the source voltage of the first correction TFT 22-1. The TFT off-leakage current is reduced by about one digit when the drain-source voltage Vds of the TFT is lowered by 1V. Therefore, by dividing the correction TFT 22, the drain-source voltage Vds of the first correction TFT 22-1 whose drain is connected to the node Tg24 can be reduced, and the off-leak current is reduced.

  As shown in FIG. 7, when the correction TFT 22 is multi-gate, the size of the channel region of the first correction TFT 22-1 whose conductive region (here, drain) is connected to the gate of the driving TFT 24 is the other size. For example, it is not necessary to make it the same as the size of the channel region of the second correction TFT 22-2.

  For example, the gate capacitance Cg22-1 of the first correction TFT 22-1 can be reduced by making the size of the channel region of the first correction TFT 22-1 smaller than the size of the channel region of the second correction TFT 22-2. If the amount of charge flowing from the gate capacitor Cg22 to the storage capacitor 28 is large when the correction TFT 22 is turned off, the potential of the node Tg24 is maintained high for a long time, and the voltage drop speed following the falling of the capacitor line SC is slowed. Therefore, by reducing the channel size of the first correction TFT 22, the amount of charge from the gate capacitance Cg22-1 of the first correction TFT 22-1 flowing into the storage capacitor 28 at the time of OFF is reduced, and the voltage at the node Tg24 is increased. Can be reduced. In this case, assuming that the channel length of the channel region of the first correction TFT 22-1 is L1, the channel width is W1, the channel length of the channel region of the second correction TFT 22-2 is L2, and the channel width is W2, W1 × L1 <W2 It is preferable to satisfy xL2.

  The channel length L1 of the first correction TFT 22-1 is made as short as possible to meet the minimum requirement for off-leakage reduction, and the channel width W1 is made as large as possible within the range allowed by layout constraints. The longer the channel length L2 of the second correction TFT 22-2, the slower the flow of charges from the gate capacitance Cg22-2 of the second correction TFT 22-2 to the node Tg24. Becomes larger and the data writing time becomes longer. Therefore, it is preferable to increase the width W2 so that the value of L2 / W2 decreases, that is, the length L2 is increased. Therefore, also from this viewpoint, it is preferable that the above W1 × L1 <W2 × L2 is satisfied.

  FIG. 8 is a plan configuration showing an example of a layout in the case where the correction TFT 22 is made multi-gate as described above. Also in the example of FIG. 8, the active layer of the selection TFT 20 and the active layer of the correction TFT 22 are integrally formed of the same semiconductor layer, but for the sake of explanation, the active layers of the first correction TFTs 22-1 and 22-2 are formed. Reference numeral 122 in the drawing is attached to the semiconductor layer that constitutes. The semiconductor layer 122 extends in the adjacent row direction (downward in the drawing) along the data line DL, similarly to the layout of FIG. 5 described above.

  The gate electrodes 22g (22g1, 22g2) of the correction TFTs 22-1 and 22-2 are commonly connected to the power supply line PL in the lower layer region of the power supply line PL. The gate electrode 22g extends in the horizontal direction from the contact position with the power supply line PL toward the data line DL, and a region crossing over the active layer 122 becomes the gate electrode 22g2 of the second correction TFT 22-2. Furthermore, it extends to the formation area of the data line DL, and is folded immediately after crossing the data line DL and passes under the data line PL. In the vicinity of the data line DL, the gate electrode 22g extends in the pixel direction of the next row along the extending direction of the data line DL so as to cover the upper side of the active layer 122 again, and overlaps the active layer 122 here. Becomes the gate electrode 22g1 of the first correction TFT 22-1. The gate electrode 22g1 of the first correction TFT 22-1 is formed between the power supply line PL and the active layer 122, and the active layer 122 is electrically connected to the power supply line PL and the data line DL formed thereabove. Shielded.

  In this way, the gate electrode 22g is formed in a U-shaped pattern so that the upper portion of the semiconductor layer 122 extending in the vertical direction along the data line DL is covered at, for example, two locations, thereby being covered by the gate electrode 22g. Channel regions 22c2 and 22c1 can be formed respectively. The semiconductor layer 122 includes a source region 22s2, a channel region 22c2 (a lower layer region of the gate electrode 22g2), and a drain region 22d2 of the second correction TFT 22-2 in order from the connection side of the second correction TFT 22-2 with the source region 20s of the selection TFT 20. The source region 22s1 of the first correction TFT 22-1, the channel region 22c1 (under the gate electrode 22g1), and the drain region 22d1 of the first correction TFT 22-1 are formed. The drain region 22d1 of the first correction TFT 22-1 is connected to the capacitor electrode 28e of the storage capacitor 28 (same semiconductor layer), and is connected to the gate electrode 24g of the drive TFT 24 via the metal wiring 24e.

  If the layout as shown in FIG. 8 is adopted, even if the correction TFT 22 is made multi-gate (here double-gate), an increase in the installation area can be suppressed as much as possible.

  FIG. 9 shows a circuit configuration example in the case where not only the correction TFT 22 but also the above-described selection TFT 20 is made multi-gate. FIG. 10 is a plan view showing an example of an actual layout when the circuit configuration as shown in FIG. 9 is adopted. In the example of FIG. 9, the selection TFT is composed of two selection TFTs 20-1 and 20-2 connected in series to the data line DL. Note that the gates of the two selection TFTs 20-1 and 20-2 are both connected to the gate line GL.

  In order to make the selection TFT 20 multi-gate, a simple change can be made to the layout in which the selection TFT 20 is constituted by a single gate as shown in FIG. For example, as shown in FIG. 10, the semiconductor layer 120 constituting the active layer of the selection TFT 20 has a U-shape (a U-shape) that is folded from the data line DL to the power line PL in the vicinity of the formation region of the selection TFT 20. It is the shape of. Therefore, the pattern of the gate electrode 20g that protrudes from the gate line GL may be further extended as shown by a dotted line in FIG. 10 so as to overlap the upper layer of the semiconductor layer 120 folded from the power line PL. In this way, the gate electrode 20g is extended, and the gate electrodes 20g1 and 20g2 are formed at two locations on the side close to the gate line GL of the semiconductor layer 120 folded back into a U-shape and on the folded side. By forming 20c2, it is possible to easily form a double gate type selection TFT 20 in which the active layer is electrically connected in series to the data line DL. In addition, as further shown in FIG. 10, a further protruding portion is provided in the horizontal direction from the middle of the gate electrode 20g, and this protruding portion covers the upper layer of the U-shaped bottom portion of the active layer, thereby further adding three active layers. Can be obtained as a triple gate type select TFT 20 connected in series to the data line DL.

  FIG. 11 shows another layout example in which the selection TFT 22 is made multi-gate (double gate). In the layout of FIG. 11, two gate electrodes 20-1g are extended from the gate line GL extending in the horizontal direction from the contact region with the data line DL toward the semiconductor layer 120 disposed in the horizontal direction along the gate line GL. , 20-2g are juxtaposed and formed. In this example, the channel regions 20c1 and 20c2 of the multi-gate selection TFT 20 are arranged side by side in the horizontal direction, which is the extending direction of the gate line GL.

  As described above, as shown in FIGS. 9, 10, or 11, not only the correction TFT 22 but also the selection TFT 20 is multi-gated so that the off-leak current can be more effectively suppressed.

  FIG. 12 shows still another circuit configuration example. In the equivalent circuit configuration per pixel shown in FIG. 12, the other end (second conductive region: for example source) of the selection TFT 20 having one end (first conductive region: for example drain) connected to the data line DL, and the correction TFT 22 A leakage current suppression TFT 30 having a gate connected to the capacitor line SC is further provided between the first conductive region (for example, the source). The leakage current suppression TFT 30 is an n-channel type and has a polarity opposite to that of the correction TFT 22.

  The leakage current suppression TFT 30 is turned on when the capacitance line SC is at the H level and turned off when the capacitance line SC is at the L level. Accordingly, the period during which the gate line GL is at the H level is on, and writing the data voltage Vdata of the data line DL to the gate of the driving TFT 24 causes no problem. On the other hand, after the data writing is completed, the capacitor line SC is turned off because it falls to the L level. That is, when the capacitance line SC falls and the gate potential of the driving TFT 24 becomes a low voltage, the leakage current suppression TFT 30 maintains an off state, and flows from the data line DL toward the gate of the driving TFT 24 at this time. Leakage current can be effectively suppressed. Therefore, it is possible to further improve the uniformity of each light emission luminance in a plurality of pixels in the display device. In the configuration shown in FIG. 12, the correction TFT 22 may be further multi-gated to further reduce the off-leakage current, but an increase in circuit elements causes a decrease in aperture ratio. Therefore, it is preferable to determine whether the correction TFT is to be multi-gate as long as the aperture ratio can be maximized and the emission luminance can be made uniform in each pixel.

It is a figure which shows the structure of the pixel circuit which concerns on embodiment of this invention. It is a figure which shows the timing of the signal applied to the gate line GL and the capacitance line SC which concern on embodiment of this invention. It is a figure which shows the change state of the gate voltage _{Vg24 which concerns} on embodiment of this invention. It is a figure for demonstrating the capacity | capacitance which exists in the pixel circuit which concerns on embodiment of this invention. It is a figure which shows an example of the plane structure of the pixel which concerns on embodiment of this invention. FIG. 6 is a schematic cross-sectional configuration diagram along line AA and line BB in FIG. 5. It is a figure which shows the equivalent circuit per pixel at the time of making correction TFT which concerns on embodiment of this invention multi-gate. FIG. 8 is a schematic plan view showing an example of a layout for realizing the equivalent circuit shown in FIG. 7. It is a figure which shows the equivalent circuit at the time of making both the selection TFT and correction TFT which concern on embodiment of this invention multi-gate. It is a figure which shows an example of the layout which implement | achieves the equivalent circuit shown in FIG. It is a figure which shows the other example of the layout shown in FIG. It is a figure which shows another circuit structural example which concerns on embodiment of this invention. It is a figure which shows the structure of the conventional pixel circuit.

Explanation of symbols

  20 selection TFT, 20g (20g1, 20g2) gate electrode, 22 correction TFT, 22-1 first correction TFT, 22-2 second correction TFT, 22g (22g1, 22g2) gate electrode, 24 drive TFT, 20c, 22c, 24c channel region, 20d, 22d, 24d drain region, 20s, 22s, 24s source region, 24w metal wiring, 26 organic EL element, 28 storage capacitor, 28e capacitance electrode (first electrode), 30 leakage current suppression TFT, 100 transparent Substrate, 102 buffer layer, 104 gate insulating layer, 106 interlayer insulating layer, 108 planarizing insulating layer, 110 second planarizing insulating layer, 262 first electrode (anode), 264 second electrode (cathode), 270 light emitting element layer .

Claims (8)

A selection transistor having a first conductive region connected to the data line and a selection signal input to the control end;
A correction transistor having a first conductive region connected to a second conductive region of the selection transistor and a control terminal connected to a first power source having a predetermined voltage;
A drive transistor having a control end connected to the second conductive region of the correction transistor and a first conductive region connected to a second power source as a current supply source;
A holding capacitor in which a first electrode is connected to a control terminal of the driving transistor and a second electrode is connected to a pulse voltage line;
A driven element operated by a current flowing in the driving transistor;
Have
The correction transistor is
The control terminal voltage of the driving transistor changes according to the fluctuation of the voltage of the pulse voltage line, and the control terminal voltage when the driving transistor is turned on in accordance with this changes the operation threshold voltage of the correction transistor. And control based on gate capacity,
The correction transistor has a plurality of gates connected to the same first power supply, and a plurality of transistors are electrically connected in series between the selection transistor and a control terminal of the driving transistor. A pixel circuit which is a multi-gate transistor. A display device in which a plurality of pixels are arranged in a matrix,
Each pixel is
A display element that operates according to a supply current;
A selection transistor having a first conductive region connected to the data line and a selection signal input to the control end;
A correction transistor having a control terminal connected to a first power source having a predetermined voltage and a first conductive region connected to a second conductive region of the selection transistor;
A drive transistor having a first conductive region connected to a second power source, a control end connected to a second conductive region of the correction transistor, and supplying power to the display element;
A first electrode connected to a control end of the drive transistor and a second conductive region of the correction transistor, and a second capacitor connected to a pulse voltage line;
Have
The correction transistor is
A transistor of the same conductivity type as the drive transistor, and
The control terminal voltage of the driving transistor changes according to the fluctuation of the voltage of the pulse voltage line, and the control terminal voltage when the driving transistor is turned on in accordance with this changes the operation threshold voltage of the correction transistor. And control based on gate capacity,
The correction transistor has a plurality of gates connected to the same first power supply, and a plurality of transistors are electrically connected in series between the selection transistor and a control terminal of the driving transistor. A display device comprising a multi-gate transistor. The pixel circuit or display device according to claim 1 or 2,
The first power source and the second power source have the same power source voltage, and both receive power supply from a power line arranged to extend in the vertical scanning direction,
The data line extends in the vertical scanning direction together with the power line, is supplied by a power line extending in one vertical direction, and the data line also extends in the vertical direction.
The pixel circuit or the display device, wherein the correction transistor is disposed in an interline region of the data line and the power supply line. The pixel circuit or display device according to claim 3,
A pixel circuit or a display device, wherein a channel length direction of at least one transistor constituting the multi-gate transistor of the correction transistor is arranged along the vertical scanning direction in which the power supply line extends. The pixel circuit or display device according to claim 3,
The drive transistor is disposed so as to be close to the power supply line and along a channel length direction in an extending direction of the power supply line,
The correction transistor is formed in an interline region between the data line and the power supply line, and a channel length direction of at least one transistor constituting the multi-gate transistor is along the vertical scanning direction in which the power supply line extends. A pixel circuit or a display device. In the pixel circuit or the display device according to any one of claims 3 to 5,
The pixel circuit or the display device, wherein the driving transistor and the correction transistor are arranged close to each other with the power supply line interposed therebetween. In the pixel circuit or the display device according to any one of claims 3 to 6,
The active layer of the correction transistor extends in the horizontal scanning direction from the power supply line toward the data line, bends in the middle and extends in the vertical scanning direction along the extending direction of the power supply line, and the gate of the correction transistor The electrode extends in the vertical scanning direction from the connection position with the power supply line along the extending direction of the power supply line, and intersects the active layer of the correction transistor at a plurality of positions with an insulating layer interposed therebetween. A pixel circuit or a display device, wherein each channel region of a multi-gate transistor is formed. In the pixel circuit or the display device according to any one of claims 1 to 7,
The selection transistor is a multi-gate transistor having a plurality of gates to which the same selection signal is input, and a plurality of transistors electrically connected in series between the data line and the correction transistor. A pixel circuit or a display device.

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