Light emitting device

• US 20030214245A1
• Filed: 02/27/2003
• Published: 11/20/2003
• Est. Priority Date: 02/28/2002
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Seo, Satoshi, Kimura, Hajime, Fukumoto, Ryota, Yamazaki, Shunpei, Yamazaki, Yu
• Granted Patent: US 7,042,162 B2
• Time in Patent Office: Days
• US Class Current: 315/169.3
• CPC Class Codes: G06F 3/147 using display panels
• CPC Class Codes: G09G 2300/0426 Layout of electrodes and connections
• CPC Class Codes: G09G 2300/0809 Several active elements per pixel in active matrix panels
• CPC Class Codes: G09G 2300/0823 used to establish symmetry in driving, e.g. with polarity inversion
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2300/0852 being a dynamic memory with more than 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 2300/0895 having more than one selection line for a two-terminal active matrix LCD, e.g. Lechner and D2R circuits
• CPC Class Codes: G09G 2310/0251 Precharge or discharge of pixel before applying new pixel 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 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2330/028 Generation of voltages supplied to electrode drivers in a matrix display other than LCD
• CPC Class Codes: G09G 3/2011 by amplitude modulation
• CPC Class Codes: G09G 3/2022 using sub-frames
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3275 Details of drivers for data electrodes
• CPC Class Codes: G09G 5/395 Arrangements specially adapted for transferring the contents of the bit-mapped memory to the screen G09G5/399 takes precedence

Abstract

The light-emitting element has a problem that reliability, heat-resisting stability and durability are low because of the deterioration in an organic compound layer. The TFT for driving the light-emitting element has a problem that variation readily occurs in its electrical characteristic due to the defects existing in grain boundaries. The present invention provides a light-emitting device by using the fact that, by applying to the light-emitting element a drive voltage having a polarity reverse to that in light emission during each constant period, the light-emitting element is improved in current-voltage characteristic. Furthermore, the present invention provides a light-emitting device made not dependent upon transistor characteristic, by controlling the amount of a current flowing through the light-emitting element.

Claims

1. A light-emitting device comprising:

a light-emitting element having first and second electrodes;

a current source including at least one transistor and a capacitance element;

drive means for supplying a signal current supplied from the current source to the light-emitting element according to an inputted video signal; and

setting means for applying a reverse bias to the light-emitting element while maintaining potentials on the first and second electrodes.

2. A light-emitting device according to claim 1, wherein the drive means and the setting means are transistors or diodes.

9. A light emitting device according to claim 1, wherein the light emitting device is incorporated into an electronic appliance selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a notebook personal computer, a game machine, a mobile information terminal and an image reproducing device.

3. A light-emitting device comprising:

a light-emitting element having first and second electrodes;

a current source including at least one transistor and a capacitance element;

first setting means for setting a plurality of sub-frame periods within a unit frame period corresponding to a synchronization timing of an inputted video signal;

capacitance means for holding the video signal;

drive means for supplying a signal current supplied from the current source to the light-emitting element;

erasing means for placing potentials on both electrodes of the capacitance means to a same potential thereby ceasing light emission of the light-emitting element; and

second setting means for applying a reverse bias to the light-emitting element while maintaining potentials on the first and second electrodes.

4. A light-emitting device according to claim 3, wherein the first setting means, the drive means, the erasing means and the second setting means are transistors or diodes.

10. A light emitting device according to claim 3, wherein the light emitting device is incorporated into an electronic appliance selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a notebook personal computer, a game machine, a mobile information terminal and an image reproducing device.

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

supplying a signal current supplied from a current source to a light-emitting element which has first and second electrode according to an inputted video signal; and

applying a reverse bias to the light-emitting element while maintaining potentials on the first and second electrodes.

11. A method according to claim 5, wherein the light emitting device is incorporated into an electronic appliance selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a notebook personal computer, a game machine, a mobile information terminal and an image reproducing device.

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

setting a plurality of sub-frame periods within a unit frame period corresponding to a synchronization timing of an inputted video signal;

supplying a signal current supplied from a current source to a light-emitting element which has first and second electrodes; and

applying a reverse bias to the light-emitting element while maintaining potentials on the first and second electrodes.

12. A method according to claim 6, wherein the light emitting device is incorporated into an electronic appliance selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a notebook personal computer, a game machine, a mobile information terminal and an image reproducing device.

7. A light-emitting device comprising:

a light-emitting element having first and second electrodes;

a current source including at least one transistor and a capacitance element;

means for supplying a signal current supplied from the current source to the light-emitting element according to an inputted video signal; and

means for applying a reverse bias to the light-emitting element while maintaining potentials on the first and second electrodes.

13. A light emitting device according to claim 7, wherein the light emitting device is incorporated into an electronic appliance selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a notebook personal computer, a game machine, a mobile information terminal and an image reproducing device.

8. A light-emitting device comprising:

a light-emitting element having first and second electrodes;

a current source including at least one transistor and a capacitance element;

means for setting a plurality of sub-frame periods within a unit frame period corresponding to a synchronization timing of an inputted video signal;

capacitance means for holding the video signal;

means for supplying a signal current supplied from the current source to the light-emitting element;

means for placing potentials on both electrodes of the capacitance means to a same potential thereby ceasing light emission of the light-emitting element; and

means for applying a reverse bias to the light-emitting element while maintaining potentials on the first and second electrodes.

14. A light emitting device according to claim 8, wherein the light emitting device is incorporated into an electronic appliance selected from the group consisting of a video camera, a digital camera, a goggle type display, a navigation system, an audio reproducing device, a notebook personal computer, a game machine, a mobile information terminal and an image reproducing device.