Active matrix display with pixel memory

• US 6,765,549 B1
• Filed: 11/06/2000
• Issued: 07/20/2004
• Est. Priority Date: 11/08/1999
• Status: Expired due to Term

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Koyama, Jun, Yamazaki, Shunpei
• Primary Examiner(s): Shalwala, Bipin
• Assistant Examiner(s): SHENG, TOM V
• Application Number:
  US09/707,054
• Time in Patent Office: 1,352 Days
• Field of Search: 345/76-81, 315/169.3
• US Class Current: 345/80
• CPC Class Codes: G09G 2300/0408 Integration of the drivers onto the display substrate
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2300/0857 Static memory circuit, e.g. flip-flop
• CPC Class Codes: G09G 2320/0233 Improving the luminance or brightness uniformity across the screen
• 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 3/3266 Details of drivers for scan electrodes
• CPC Class Codes: G09G 3/3291 in which the data driver supplies a variable data voltage for setting the current through, or the voltage across, the light-emitting elements
• CPC Class Codes: H01L 27/1214 comprising a plurality of TFTs formed on a non-semiconducting substrate, e.g. driving circuits for AMLCDs

Abstract

A display device capable of preventing a reduction of an electric charge stored in a gate electrode of an EL driver TFT, reduction due to a leak current of a switching TFT, and capable of preventing a reduction of the brightness of light emitted by an EL element is provided. One region of a source region and a drain region of a switching TFT is connected to an input side of an SRAM, and an output side of the SRAM and a gate electrode of the EL driver TFT are connected. The SRAM stores an input digital data signal until the next digital data signal is input.

Claims

1. A display device comprising:

a first pixel comprising a first switching TFT, a first SRAM, a first EL driver TFT, and a first EL element wherein the first switching TFT is electrically connected to the first EL driver TFT through the first SRAM;

a second pixel adjacent to said first pixel, said second pixel comprising a second switching TFT, a second SRAM, a second EL driver TFT and a second EL element wherein the second switching TFT is electrically connected to the second EL driver TFT through the second SRAM;

a gate signal line electrically connected to a gate electrode of the first switching TFT and a gate electrode of the second TFT;

a first source signal line and a second source signal line, each extending across said gate signal line wherein one of a source region or a drain region of the first switching TFT is connected to the first source signal line and one of a source region or a drain region of the second switching TFT is connected to the second source signal line;

an electric power supply line extending across said gate signal line wherein said electric power supply line is located between said first signal line and said second signal line and is commonly connected to said first and second EL driver TFTs,

wherein the first SRAM stores a digital data signal input to the first SRAM from the first source signal line through the first switching TFT, until the next digital data signal is input to the first SRAM,

wherein at least one of said first and second SRAM comprises two p-channel TFTs, an n-channel TFT, and a resistor, source regions of the two p-channel TFTs are each connected to the high voltage side electric power supply, a drain region of one p-channel TFT is connected to a drain region of the n-channel TFT, and a drain region of the other p-channel TFT is connected to the low voltage side electric power supply through the resistor, and a source region of the n-channel TFT is connected to the low voltage side electric power supply.

4. A display device according to any one of claims 1 to 3, wherein:

each of the first and second EL elements comprises an EL layer between the anode and the cathode; and

the EL layer comprises a material selected from the group consisting of a low molecular weight organic material and an organic polymer material.

5. A display device according to claim 4, wherein the low molecular weight material is selected from the group consisting of Alq3 (tris-8-quinolinolate aluminum) and TPD (triphenylamine dielectric).

6. A display device according to claim 4, wherein the organic polymer material is selected from the group consisting of PPV (polyvinyl carbazole), and polycarbonate.

8. A computer having the display device according to any one of claims 1 to 3.

9. A video camera having the display device according to any one of claims 1 to 3.

10. A DVD player having the display device according to any one of claims 1 to 3.

2. A display device comprising:

a first pixel comprising a first switching TFT, a first SRAM, a first EL driver TFT, and a first EL element wherein the first switching TFT is electrically connected to the first EL driver TFT through the first SRAM;

a second pixel comprising a second switching TFT, a second SRAM, a second EL driver TFT and a second EL element wherein the second switching TFT is electrically connected to the second EL driver TFT through the second SRAM;

a gate signal line electrically connected to a gate electrode of the first switching TFT and a gate electrode of the second TFT;

a first source signal line and a second source signal line, each extending across said gate signal line wherein one of a source region or a drain region of the first switching TFT is connected to the first source signal line and one of a source region or a drain region of the second switching TFT is connected to the second source signal line;

an electric power supply line extending across said gate signal line wherein said electric power supply line is located between said first signal line and said second signal line and is commonly connected to said first and second EL driver TFTs,

wherein a period within one frame period during which at least the first and second EL elements emits light is controlled by using a digital data signal wherein the first SRAM stores the digital data signal input to the first SRAM from the first source signal line, through the first switching TFT, until the next digital data signal is input to the first SRAM, and

wherein at least one of said first and second SRAM comprises two p-channel TFTs, an n-channel TFT and a resistor, source regions of the two p-channel TFTs are each connected to the high voltage side electric power supply, a drain region of one p-channel TFT is connected to a drain region of the n-channel TFT, and a drain region of the other p-channel TFT is connected to the low voltage side electric power supply through the resistor, and a source region of the n-channel TFT is connected to the low voltage side electric power supply.

7. A display device according to claim 2 or 3, wherein the first frame period is equal to or less than {fraction (1/60)} second.

3. A display device comprising:

a first pixel comprising a first switching TFT, a first SRAM, a first EL driver TFT, and a first EL element wherein the first switching TFT is electrically connected to the first EL driver TFT through the first SRAM;

a second pixel adjacent to said first pixel, said second pixel comprising a second switching TFT, a second SRAM, a second EL driver TFT and a second EL element wherein the second switching TFT is electrically connected to the second EL driver TFT through the second SRAM;

a gate signal line electrically connected to a gate electrode of the first switching TFT and a gate electrode of the second TFT;

a first source signal line and a second source signal line, each extending across said gate signal line wherein one of a source region or a drain region of the first switching TFT is connected to the first source signal line and one of a source region or a drain region of the second switching TFT is connected to the second source signal line;

an electric power supply line extending across said gate signal line wherein said electric power supply line is located between said first signal line and said second signal line and is commonly connected to said first and second EL driver TFTs,

wherein one frame period is divided into n sub-frame periods SF1, SF2, . . . , SFn;

the n sub-frame periods SF1, SF, . . . , SFn have write-in periods Ta1, Ta2, . . . , Tan, and display periods Ts1, Ts2, . . . , Tsn, respectively;

a digital data signal is input to at least one of first and second pixels during the write-in periods Ta1, Ta2, . . . , Tan;

whether one of the first and second EL elements emits light or does not emit light during the display periods Ts1, Ts2, . . . , Tsn is selected in accordance with the digital data signal;

a ratio of the length of the display periods Ts1, Ts2, . . . , Tsn is expressed by 2⁰;

2<sup>−

1</sup>;

. . . ;

2<sup>−

(n-1)</sup>; and

the first SRAM stores a digital data signal input to the first SRAM from one of the first source signal lines, through the first switching TFT, until the next digital data signal is input to the first SRAM,

wherein at least one of said first and second SRAM comprises two n-channel TFTs a p-channel TFT, and a resistor source regions of the two n-channel TFTs are each connected to the low voltage side electric power supply, a drain region of one n-channel TFT is connected to a drain region of the p-channel TFT, and a drain region of the other n-channel TFT is connected to the high voltage side electric power supply through the resistor, and a source region of the p-channel TFT is connected to the high voltage side electric power supply.

11. An electronic device having a display device, said display device comprising:

at least first and second source signal lines formed over a substrate;

at least one gate signal line extending in an orthogonal direction to said source signal lines over said substrate;

at least a first switching thin film transistor disposed at an intersection of said first source signal line and said gate signal line, wherein a gate electrode of said first switching thin film transistor is electrically connected to said gate signal line and one of source or drain of said first switching thin film transistor is electrically connected to said first source signal line;

a second switching thin film transistor disposed at an intersection of said second source signal line and said gate signal line, wherein a gate electrode of said second switching thin film transistor is electrically connected to said gate signal line and one of source or drain of said second switching thin film transistor is electrically connected to said second source signal line;

at least one power supply line formed over said substrate;

at least first and second EL driver thin film transistors formed over said substrate wherein said first and second EL driver thin film transistors are electrically connected to said power supply line;

an electroluminescence element electrically connected to a drain region of said first EL driver thin film transistor,

wherein said display device further comprises a first SRAM electrically connected to said first switching thin film transistor and a second SRAM electrically connected to said second switching thin film transistor,

wherein at least one of said first and second SRAM comprises two n-channel TFTs, a p-channel TFT, and a resistor, source regions of the two n-channel TFTs are each connected to the low voltage side electric power supply, a drain region of one n-channel TFT is connected to a drain region of the p-channel TFT, and a drain region of the other n-channel TFT is connected to the high voltage side electric power supply through the resistor, and a source region of the p-channel TFT is connected to the high voltage side electric power supply.

12. The electronic device according to claim 11 wherein the other one of the source or drain of the first switching thin film transistor is electrically connected to an input terminal of said first SRAM and a gate of said first EL driver thin film transistor is electrically connected to an output terminal if said first SRAM.

13. The electronic device according to claim 11 wherein said electric device is a personal computer.

14. The electronic device according to claim 11 wherein said electric device is a video camera.

15. The electronic device according to claim 11 wherein said electric device is a head mount display.

16. The electronic device according to claim 11 wherein said electric device is a picture reproducer.

17. The electronic device according to claim 11 wherein said electronic device is a portable information terminal.