Light emitting device, driving method of light emitting device and electronic device

• US 7,795,618 B2
• Filed: 06/13/2006
• Issued: 09/14/2010
• Est. Priority Date: 09/21/2001
• Status: Expired due to Fees

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Akiba, Mai, Koyama, Jun, Yamazaki, Shunpei
• Primary Examiner(s): Nguyen; Thinh T
• Application Number:
  US11/423,757
• Publication Number:
  US 20060220581A1
• Time in Patent Office: 1,554 Days
• Field of Search: 257/59, 257/72, 257/79, 315/169, 315/169.3, 438/48, 438/128.149
• US Class Current: 257/59
• 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 that flows from a first source to a first drain of a first transistor provided in a pixel to be a magnitude corresponding to a voltage of a video signal via a fourth transistor connected with the first drain of the first transistor in series during a write period;

keeping a second drain current that flows from a second source to a second drain 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 via a third transistor connected with the second drain of the second transistor in series; and

impressing an inversed bias voltage of a power supply line to the light emitting element via the second transistor and the third transistor.

2. 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 the first source of the first transistor is connected with the second source of the second transistor during the write period.

3. 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.

4. A method of driving a light emitting device according to claim 1 wherein the light emitting device is one selected from the group consisting of a camera, a computer, a goggle-type display, and a phone.

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

keeping a first drain current that flows from a first source to a first drain of a first transistor provided in a pixel to be a magnitude corresponding to a voltage of a video signal via a fourth transistor connected with the first drain of the first transistor in series during a write period;

keeping a second drain current that flows from a second source to a second drain 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 via a third transistor connected with the second drain of the second transistor in series; and

impressing an inversed bias voltage of a power supply line to the light emitting element just after the display period via the second transistor and the third transistor.

6. A method of driving a light emitting device according to claim 5 wherein a first gate of the first transistor is connected with a second gate of the second transistor and wherein the first source of the first transistor is connected with the second source of the second transistor during the write period.

7. A method of driving a light emitting device according to claim 5 wherein a signal current is supplied from a signal line drive circuit to a signal line based on the video signal.

8. A method of driving a light emitting device according to claim 5 wherein the light emitting device is one selected from the group consisting of a camera, a computer, a goggle-type display, and a phone.

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

keeping a first drain current that flows from a first source to a first drain of a first transistor provided in a pixel to be a magnitude corresponding to a voltage of a video signal via a fourth transistor connected with the first drain of the first transistor in series during a write period;

keeping a second drain current that flows from a second source to a second drain 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 via a third transistor connected with the second drain of the second transistor in series; and

impressing an inversed bias voltage of a power supply line to the light emitting element just after the display period via the second transistor and the third transistor, wherein a period to impress the inversed bias voltage depends on a duration of the display period.

10. A method of driving a light emitting device according to claim 9 wherein a first gate of the first transistor is connected with a second gate of the second transistor and wherein the first source of the first transistor is connected with the second source of the second transistor during the write period.

11. A method of driving a light emitting device according to claim 9 wherein a signal current is supplied from a signal line drive circuit to a signal line based on the video signal.

12. A method of driving a light emitting device according to claim 9 wherein the light emitting device is one selected from the group consisting of a camera, a computer, a goggle-type display, and a phone.

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

keeping a first drain current that flows from a first source to a first drain of a first transistor provided in a pixel to be a magnitude corresponding to a voltage of a video signal via a fourth transistor connected with the first drain of the first transistor in series during a write period;

keeping a second drain current that flows from a second source to a second drain 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 via a third transistor connected with the second drain of the second transistor in series; and

impressing an inversed bias voltage of a power supply line to the light emitting element just after the display period via the second transistor and the third transistor, wherein an absolute value of the inversed bias voltage depends on a duration of the display period.

14. A method of driving a light emitting device according to claim 13 wherein a first gate of the first transistor is connected with a second gate of the second transistor and wherein the first source of the first transistor is connected with the second source of the second transistor during the write period.

15. A method of driving a light emitting device according to claim 13 wherein a signal current is supplied from a signal line drive circuit to a signal line based on the video signal.

16. A method of driving a light emitting device according to claim 13 wherein the light emitting device is one selected from the group consisting of a camera, a computer, a goggle-type display, and a phone.