Thin film transistor for supplying power to element to be driven

• US 20020074580A1
• Filed: 09/28/2001
• Published: 06/20/2002
• Est. Priority Date: 09/29/2000
• Status: Active Grant

• Current Assignee: Sanyo Electric Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Sanyo Electric Company Limited (Panasonic Holdings Corporation)
• Inventors: Anzai, Katsuya, Komiya, Naoaki
• Granted Patent: US 6,876,346 B2
• Time in Patent Office: Days
• US Class Current: 257/290
• CPC Class Codes: G02F 1/13624 having more than one switching element per pixel
• CPC Class Codes: G09G 2300/0417 Special arrangements specific to the use of low carrier mobility technology
• CPC Class Codes: G09G 2300/0426 Layout of electrodes and connections
• CPC Class Codes: G09G 2300/0465 Improved aperture ratio, e.g. by size reduction of the pixel circuit, e.g. for improving the pixel density or the maximum displayable luminance or brightness
• CPC Class Codes: G09G 2300/0809 Several active elements per pixel in active matrix panels
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2300/0885 Pixel comprising a non-linear two-terminal element alone in series with each display pixel element
• CPC Class Codes: G09G 2320/0204 Compensation of DC component across the pixels in flat panels
• 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 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: H10K 59/12 Active-matrix OLED [AMOLED] displays
• CPC Class Codes: H10K 59/1213 the pixel elements being TFTs
• CPC Class Codes: H10K 59/123 Connection of the pixel electrodes to the thin film transistors [TFT]

Abstract

An EL element (50) having an organic emissive layer or the like between the anode and cathode is used as an element to be driven, and an element driving TFT (20) for controlling the current supplied to the EL element (50) and a compensation thin film transistor (30) having an opposite conductive characteristic as the element driving TFT (20) are provided between the EL element (50) and the power supply line VL. With this structure, variation in the current supplied to each EL element (50) is reduced.

Claims

1. A semiconductor device comprising:

a switching thin film transistor which operates by receiving a gate signal at its gate and for reading a data signal; and

an element driving thin film transistor provided between a driving power supply and an element to be driven, for controlling the power supplied from said driving power supply to said element to be driven based on a data signal supplied from said switching thin film transistor;

characterized in that

a compensation thin film transistor having an opposite conductive characteristic with respect to said element driving thin film transistor is provided between said driving power supply and said element driving thin film transistor.

2. A semiconductor device according to claim 1, wherein a gate and either a source or a drain of said compensation thin film transistor are connected, and said compensation thin film transistor is connected between said driving power supply and said element driving thin film transistor.

3. A semiconductor device according to claim 1, wherein said element driving thin film transistor comprises a plurality of thin film transistors connected to each other in parallel.

4. A semiconductor device according to claim 3, wherein said compensation thin film transistor is a diode connected transistor connected between said driving power supply and said element driving thin film transistor.

5. A semiconductor device according to claim 1, wherein

said element driving thin film transistor comprises a plurality of thin film transistors connected between said driving power supply and said element to be driven and in parallel to each other;

and

said compensation thin film transistor is respectively provided between said plurality of thin film transistors connected in parallel and said driving power supply.

6. A semiconductor device according to claim 5, wherein said compensation thin film transistor is a diode connected transistor connected between said driving power supply and said element driving thin film transistor.

7. A semiconductor device according to claim 1, wherein said element to be driven is an electroluminescence element which includes an emissive layer between a first electrode and a second electrode.

8. A semiconductor device according to claim 6, wherein said electroluminescence element is an organic electroluminescence element which employs an organic compound in an emissive layer.

9. A semiconductor device according to claim 1, wherein said semiconductor device is used for an active matrix type display device wherein each of the pixels arranged in a matrix form comprises said switching thin film transistor, said element driving thin film transistor, said compensation thin film transistor, and said element to be driven as a display element.

10. A semiconductor device according to claim 1, wherein said element driving thin film transistor and said compensation thin film transistor are placed so that the channel length direction of said thin film transistors is along the extension direction of the data line for supplying said data signal to said switching thin film transistor.

11. A semiconductor device according to claim 1, wherein the channel length direction of said element driving thin film transistor does not coincide with the channel length direction of said switching thin film transistor.

12. A semiconductor device according to claim 1, wherein said element driving thin film transistor is formed so that its channel length direction is along the scan direction of a line pulse laser for annealing the channel region of the transistor.

13. A semiconductor device according to claim 12, wherein a gate and either a source or a drain of said compensation thin film transistor are connected, and said compensation thin film transistor is connected between said driving power supply and said element driving thin film transistor.