Light Emitting Device, Driving Method of Light Emitting Device and Electronic Device

• US 20060220581A1
• Filed: 06/13/2006
• Published: 10/05/2006
• Est. Priority Date: 09/21/2001
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Yamazaki, Shunpei, Akiba, Mai, Koyama, Jun
• Granted Patent: US 7,795,618 B2
• Time in Patent Office: Days
• US Class Current: 315/169.300
• CPC Class Codes: G09G 2300/04 Structural and physical details of display devices
• CPC Class Codes: G09G 2300/0426 Layout of electrodes and connections
• CPC Class Codes: G09G 2300/0814 used for selection purposes, e.g. logical AND for partial update
• 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 2300/0866 by means of changes in the pixel supply voltage
• CPC Class Codes: G09G 2310/0256 with the purpose of reversing the voltage across a light emitting or modulating element within a pixel
• CPC Class Codes: G09G 2310/0262 The addressing of the pixel, in a display other than an active matrix LCD, involving the control of two or more scan electrodes or two or more data electrodes, e.g. pixel voltage dependent on signals of two data electrodes
• CPC Class Codes: G09G 2310/027 Details of drivers for data electrodes, the drivers handling digital grey scale data, e.g. use of D/A converters
• CPC Class Codes: G09G 2310/0286 Details of a shift registers arranged for use in a driving circuit
• CPC Class Codes: G09G 2310/0291 Details of output amplifiers or buffers arranged for use in a driving circuit
• CPC Class Codes: G09G 2310/08 Details of timing specific for flat panels, other than clock recovery
• 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 2320/045 Compensation of drifts in the characteristics of light emitting or modulating elements
• CPC Class Codes: G09G 2330/028 Generation of voltages supplied to electrode drivers in a matrix display other than LCD
• CPC Class Codes: G09G 2330/04 Display protection
• CPC Class Codes: G09G 2330/045 Protection against panel overheating
• CPC Class Codes: G09G 3/2018 by time modulation using two or more time intervals
• CPC Class Codes: G09G 3/2022 using sub-frames
• CPC Class Codes: G09G 3/22 : using controlled light sources
• CPC Class Codes: G09G 3/3225 : using an active matrix
• CPC Class Codes: G09G 3/3233 : with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3241 : the current through the light-emitting element being set using a data current provided by the data driver, e.g. by using a two-transistor current mirror
• CPC Class Codes: G09G 3/325 : the data current flowing through the driving transistor during a setting phase, e.g. by using a switch for connecting the driving transistor to the data driver
• CPC Class Codes: G09G 3/3258 : with pixel circuitry controlling the voltage across the light-emitting element
• CPC Class Codes: G09G 3/3283 : in which the data driver supplies a variable data current for setting the current through, or the voltage across, the light-emitting elements
• CPC Class Codes: H01L 27/12 : the substrate being other than a semiconductor body, e.g. an insulating body
• CPC Class Codes: H01L 27/124 : with a particular composition, shape or layout of the wiring layers specially adapted to the circuit arrangement, e.g. scanning lines in LCD pixel circuits wiring structures per se H01L23/52
• CPC Class Codes: H01L 27/1255 : integrated with passive devices, e.g. auxiliary capacitors
• CPC Class Codes: H01L 27/1285 : using control of the annealing or irradiation parameters, e.g. using different scanning direction or intensity for different transistors
• CPC Class Codes: H01L 27/13 : combined with thin-film or thick-film passive components
• CPC Class Codes: H01L 27/15 : including semiconductor components having potential barriers, specially adapted for light emission
• CPC Class Codes: H01L 29/4908 : for thin film semiconductor, e.g. gate of TFT
• CPC Class Codes: H01L 29/66757 : Lateral single gate single channel transistors with non-inverted structure, i.e. the channel layer is formed before the gate
• CPC Class Codes: H01L 33/20 : with a particular shape, e.g. curved or truncated substrate
• CPC Class Codes: H01L 33/32 : containing nitrogen
• CPC Class Codes: H10K 2102/103 : comprising indium oxides, e.g. ITO
• CPC Class Codes: H10K 50/846 : comprising getter material or desiccants
• CPC Class Codes: H10K 59/12 : Active-matrix OLED [AMOLED] displays
• CPC Class Codes: H10K 59/1201 : Manufacture or treatment
• 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 59/123 : Connection of the pixel electrodes to the thin film transistors [TFT]
• CPC Class Codes: H10K 59/124 : Insulating layers formed between TFT elements and OLED elements
• CPC Class Codes: H10K 59/131 : Interconnections, e.g. wiring lines or terminals
• CPC Class Codes: H10K 59/1315 : comprising structures specially adapted for lowering the resistance
• CPC Class Codes: H10K 59/874 : including getter material or desiccant
• CPC Class Codes: H10K 85/113 : Heteroaromatic compounds comprising sulfur or selene, e.g. polythiophene
• CPC Class Codes: H10K 85/114 : Poly-phenylenevinylene; Derivatives thereof
• CPC Class Codes: H10K 85/115 : Polyfluorene; Derivatives thereof
• CPC Class Codes: H10K 85/324 : comprising aluminium, e.g. Alq3
• CPC Class Codes: H10K 85/342 : comprising iridium
• CPC Class Codes: H10K 85/346 : comprising platinum
• CPC Class Codes: H10K 85/631 : Amine compounds having at least two aryl rest on at least one amine-nitrogen atom, e.g. triphenylamine
• CPC Class Codes: H10K 85/6574 : comprising only oxygen in the heteroaromatic polycondensed ring system, e.g. cumarine dyes

Abstract

By controlling the luminance of light emitting element not by means of a voltage to be impressed to the TFT but by means of controlling a current that flows to the TFT in a signal line drive circuit, the current that flows to the light emitting element is held to a desired value without depending on the characteristics of the TFT. Further, a voltage of inverted bias is impressed to the light emitting element every predetermined period. Since a multiplier effect is given by the two configurations described above, it is possible to prevent the luminance from deteriorating due to a deterioration of the organic luminescent layer, and further, it is possible to maintain the current that flows to the light emitting element to a desired value without depending on the characteristics of the TFT.

Claims

1. A method of driving a light emitting device comprising:

keeping a first drain current of a first transistor provided in a pixel to be a magnitude corresponding to a voltage of a video signal;

keeping a second drain current of a second transistor provided in the pixel to be proportional to the first drain current with a second gate voltage of the second transistor equal to a first gate voltage of the first transistor;

keeping the second gate voltage of the second transistor to emit a light by supplying a light emitting element with the second drain current; and

impressing a voltage having an inversed bias to the light emitting element.

2. A method of driving a light emitting device according to claim 1 wherein a signal current is supplied from a signal line drive circuit to a signal line based on the video signal and wherein the first drain current is kept to be a magnitude of the signal current.

3. A method of driving a light emitting device according to claim 1 wherein a first gate of the first transistor is connected with a second gate of the second transistor and wherein a first source of the first transistor is connected with a second source of the second transistor.

4. A method of driving a light emitting device according to claim 1 wherein the first gate voltage of the first transistor is a voltage between a gate and a source of the first transistor.

5. A method of driving a light emitting device according to claim 1 wherein the second gate voltage of the second transistor is a voltage between a gate and a source of the second transistor.

6. A method of driving a light emitting device comprising:

keeping a first drain current of a first transistor provided in a pixel to be a magnitude corresponding to a voltage of a video signal during a write period;

keeping a second drain current of a second transistor provided in the pixel to be proportional to the first drain current with a second gate voltage of the second transistor equal to a first gate voltage of the first transistor during the write period;

keeping the second gate voltage of the second transistor during the write period and a display period subsequent to the write period to emit a light by supplying a light emitting element with the second drain current; and

impressing a voltage having an inversed bias to the light emitting element.

7. A method of driving a light emitting device according to claim 6 wherein a first gate of the first transistor is connected with a second gate of the second transistor and wherein a first source of the first transistor is connected with a second source of the second transistor during the write period.

8. A method of driving a light emitting device according to claim 6 wherein a signal current is supplied from a signal line drive circuit to a signal line based on the video signal and wherein the first drain current is kept to be a magnitude of the signal current during the write period.

9. A method of driving a light emitting device according to claim 6 wherein the first gate voltage of the first transistor is a voltage between a gate and a source of the first transistor.

10. A method of driving a light emitting device according to claim 6 wherein the second gate voltage of the second transistor is a voltage between a gate and a source of the second transistor.

11. A method of driving a light emitting device comprising:

feeding a current from a constant-current supply source to a select circuit as a signal current wherein a magnitude of the signal current corresponds to a voltage of a video signal;

keeping a first drain current of a first transistor provided in a pixel to be the magnitude of the signal current;

keeping a second drain current of a second transistor provided in the pixel to be proportional to the first drain current with a second gate voltage of the second transistor equal to a first gate voltage of the first transistor;

keeping the second gate voltage of the second transistor to emit a light by supplying a light emitting element with the second drain current; and

impressing a voltage having an inversed bias to the light emitting element.

12. A method of driving a light emitting device according to claim 11 wherein a first gate of the first transistor is connected with a second gate of the second transistor and wherein a first source of the first transistor is connected with a second source of the second transistor.

13. A method of driving a light emitting device according to claim 11 wherein the first gate voltage of the first transistor is a voltage between a gate and a source of the first transistor.

14. A method of driving a light emitting device according to claim 11 wherein the second gate voltage of the second transistor is a voltage between a gate and a source of the second transistor.

15. A method of driving a light emitting device according to claim 11 wherein the constant-current supply source and the select circuit are provided in a signal-line drive circuit.

16. A method of driving a light emitting device comprising:

feeding a current from a constant-current supply source to a select circuit as a signal current wherein a magnitude of the signal current corresponds to a voltage of a video signal;

keeping a first drain current of a first transistor provided in a pixel to be the magnitude of the signal current during a write period;

keeping a second drain current of a second transistor provided in the pixel to be proportional to the first drain current with a second gate voltage of the second transistor equal to a first gate voltage of the first transistor during the write period;

keeping the second gate voltage of the second transistor during the write period and a display period subsequent to the write period to emit a light by supplying a light emitting element with the second drain current; and

impressing a voltage having an inversed bias to the light emitting element.

17. A method of driving a light emitting device according to claim 16 wherein a first gate of the first transistor is connected with a second gate of the second transistor and wherein a first source of the first transistor is connected with a second source of the second transistor during the write period.

18. A method of driving a light emitting device according to claim 16 wherein the first gate voltage of the first transistor is a voltage between a gate and a source of the first transistor.

19. A method of driving a light emitting device according to claim 16 wherein the second gate voltage of the second transistor is a voltage between a gate and a source of the second transistor.

20. A method of driving a light emitting device according to claim 16 wherein the constant-current supply source and the select circuit are provided in a signal line drive circuit.