Image display device having a drive transistor with a channel length longer than a channel length of individual switching transistors

• US 10,229,638 B2
• Filed: 11/21/2017
• Issued: 03/12/2019
• Est. Priority Date: 08/18/2006
• Status: Active Grant

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Yamashita, Junichi, Mitomi, Yutaka, Minami, Tetsuo, Tanikame, Takao
• Primary Examiner(s): Eisen, Alexander
• Assistant Examiner(s): Lam, Nelson
• Application Number:
  US15/820,185
• Publication Number:
  US 20180096651A1
• Time in Patent Office: 476 Days
• Field of Search: 345 76- 83, 3151693
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2300/0861 with additional control of the display period without amending the charge stored in a pixel memory, e.g. by means of additional select electrodes
• CPC Class Codes: G09G 2320/0233 Improving the luminance or brightness uniformity across the screen
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2320/0626 for control of overall brightness
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: H01L 29/78678 with inverted-type structure, e.g. with bottom gate
• CPC Class Codes: H01L 29/78696 characterised by the structure of the channel, e.g. multichannel, transverse or longitudinal shape, length or width, doping structure, or the overlap or alignment between the channel and the gate, the source or the drain, or the contacting structure of the channel H01L29/78612 takes precedence; transistors having a drain offset region or a lightly doped drain [LDD] H01L29/78621
• CPC Class Codes: H10K 59/1213 the pixel elements being TFTs
• CPC Class Codes: H10K 59/1216 the pixel elements being capacitors
• CPC Class Codes: H10K 59/131 Interconnections, e.g. wiring lines or terminals

Abstract

An image display device includes: a pixel array part formed of first to fourth scanning lines arranged in rows, signal lines arranged in columns, pixel circuits in a matrix connected to the scanning lines and signal lines, and a plurality of power source lines which supplies first to third potentials necessary for the operations of pixel circuit; a signal part which supplies a video signal to the signal lines; and a scanner part which supplies a control signal to the first to fourth scanning lines, and in turn scans the pixel circuit for every row, wherein the pixel circuits include a sampling transistor, a drive transistor, first to third switching transistors, a pixel capacitance, and a light emitting device, and a channel length of the drive transistor is made longer than a channel length of the switching transistors to suppress fluctuations in threshold voltage.

Claims

1. An image display device comprising:

a first scanning line extending along a row direction;

a second scanning line extending along the row direction;

a third scanning line extending along the row direction;

a signal line extending along a column direction and configured to supply a video signal;

a first voltage line;

a second voltage line; and

a pixel circuit connected to the first scanning line, the second scanning line, the third scanning line, the signal line, the first voltage line, and the second voltage line, wherein

the pixel circuit includes a sampling transistor, a drive transistor, a pixel capacitor including a first electrode and a second electrode, a light emitting device, a first switching transistor connected between the first voltage line and the light emitting device, and a second switching transistor connected between the second voltage line and the drive transistor,

the first scanning line is connected to a control terminal of the first switching transistor,

the second scanning line is connected to a control terminal of the second switching transistor,

the third scanning line is connected to a control terminal of the sampling transistor,

the sampling transistor is connected to the pixel capacitor,

the pixel capacitor is connected between an anode electrode of the light emitting device and a control terminal of the drive transistor, and

a channel length of the drive transistor is longer than a channel length of the first switching transistor and is longer than a channel length of the second switching transistor.

2. The image display device according to claim 1, wherein the drive transistor includes a polycrystalline silicon film.

3. The image display device according to claim 1, wherein the channel length of the drive transistor is 10 μ

m or greater.

4. The image display device according to claim 1, wherein the channel length of the drive transistor is from 15 μ

m to 20 μ

m.

5. The image display device according to claim 1, wherein the sampling transistor is configured to supply a signal potential from the signal line to the pixel capacitor.

6. The image display device according to claim 1, further comprising a third switching transistor directly connected between a third voltage line and the pixel capacitor.

7. The image display device according to claim 1 wherein

in the pixel circuit, the channel length of the drive transistor is set such that during a light emission period, a gate potential of the drive transistor and a source potential of the drive transistor rise together so that a voltage difference between the gate potential and the source potential remains constant throughout the light emission period.

8. The image display device according to claim 1, further comprising a scanner part configured to supply a first control signal to the first scanning line, a second control signal to the second scanning line, and a third control signal to the third scanning line.

9. The image display device according to claim 8, wherein the pixel circuit and the scanner part are disposed on a substrate.

10. The image display device according to claim 8, wherein the channel length of the drive transistor is longer than a channel length of a particular one of a plurality of transistors in the scanner part.

11. The image display device according to claim 8, wherein the channel length of the drive transistor is longer than respective channel lengths of a plurality of transistors in the scanner part.

12. An image display device comprising:

a first scanning line extending along a row direction;

a second scanning line extending along the row direction;

a third scanning line extending along the row direction;

a signal line extending along a column direction and configured to supply a video signal;

a first voltage line;

a second voltage line; and

a pixel circuit connected to the first scanning line, the second scanning line, the third scanning line, the signal line, the first voltage line, and the second voltage line, wherein

the pixel circuit includes a sampling transistor, a drive transistor, a pixel capacitor including a first electrode and a second electrode, a light emitting device, a first switching transistor connected between the first voltage line and the light emitting device, and a second switching transistor connected between the second voltage line and the drive transistor,

at a time at which the second switching transistor is turned on to begin a light emission period, a gate potential of the drive transistor increases in response to an increase of a source potential of the drive transistor,

the first scanning line is connected to a control terminal of the first switching transistor,

the second scanning line is connected to a control terminal of the second switching transistor,

the third scanning line is connected to a control terminal of the sampling transistor,

the sampling transistor is connected to the pixel capacitor,

the pixel capacitor is connected between an anode electrode of the light emitting device and a control terminal of the drive transistor, and

a channel length of the drive transistor is longer than a channel length of the first switching transistor and is longer than a channel length of the second switching transistor.

13. The image display device according to claim 12, wherein the drive transistor includes a polycrystalline silicon film.

14. The image display device according to claim 12, wherein the channel length of the drive transistor is 10 μ

m or greater.

15. The image display device according to claim 12, wherein the channel length of the drive transistor is from 15 μ

m to 20 μ

m.

16. The image display device according to claim 12, wherein the sampling transistor is configured to supply a signal potential from the signal line to the pixel capacitor.

17. The image display device according to claim 12, further comprising a third switching transistor directly connected between a third voltage line and the pixel capacitor.

18. The image display device according to claim 12, wherein the first switching transistor is turned on at a timing prior to the light emission period so as to apply a bias to the light emitting device.

19. The image display device according to claim 12, wherein the increase of the source potential of the driving transistor is caused by a current through the driving transistor from the second voltage line to a source terminal of the driving transistor.

20. The image display device according to claim 12, wherein the gate potential of the drive transistor increases in response to the increase of the source potential of the driving transistor so that a voltage difference between the gate potential and the source potential remains constant throughout the light emission period.

21. The image display device according to claim 12, further comprising a scanner part configured to supply a first control signal to the first scanning line, a second control signal to the second scanning line, and a third control signal to the third scanning line.

22. The image display device according to claim 21, wherein the pixel circuit and the scanner part are disposed on a substrate.

23. The image display device according to claim 21 wherein the channel length of the drive transistor is longer than a channel length of a particular one of a plurality of transistors in the scanner part.

24. The image display device according to claim 21, wherein the channel length of the drive transistor is longer than respective channel lengths of a plurality of transistors in the scanner part.