SEMICONDUCTOR DEVICE AND DRIVING METHOD THEREOF

• US 20110198483A1
• Filed: 02/04/2011
• Published: 08/18/2011
• Est. Priority Date: 02/12/2010
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: KUROKAWA, Yoshiyuki
• Granted Patent: US 8,586,905 B2
• Time in Patent Office: Days
• US Class Current: 250/214.R
• CPC Class Codes: G01J 1/44 Electric circuits for command of an exposure part G03B7/02
• CPC Class Codes: G01J 2001/4446 Type of detector
• CPC Class Codes: H01L 27/1225 with semiconductor materials not belonging to the group IV of the periodic table, e.g. InGaZnO
• CPC Class Codes: H01L 27/14609 Pixel-elements with integrated switching, control, storage or amplification elements scanning details of imagers (circuitry of solid-state image sensors H04N25/00); circuitry of imagers H04N25/70
• CPC Class Codes: H01L 27/14614 having a special gate structure
• CPC Class Codes: H01L 27/14616 characterised by the channel of the transistor, e.g. channel having a doping gradient
• CPC Class Codes: H01L 29/7869 having a semiconductor body comprising an oxide semiconductor material, e.g. zinc oxide, copper aluminium oxide, cadmium stannate
• CPC Class Codes: H01L 31/032 including, apart from doping materials or other impurities, only compounds not provided for in groups H01L31/0272 - H01L31/0312
• CPC Class Codes: H04N 23/68 for stable pick-up of the scene, e.g. compensating for camera body vibrations
• CPC Class Codes: H04N 25/00 Circuitry of solid-state image sensors [SSIS]; Control thereof
• CPC Class Codes: H04N 25/76 Addressed sensors, e.g. MOS or CMOS sensors

Abstract

A semiconductor device including photosensor capable of imaging with high resolution is disclosed. The semiconductor device includes the photosensor having a photodiode, a first transistor, and a second transistor. The photodiode generates an electric signal in accordance with the intensity of light. The first transistor stores charge in a gate thereof and converts the stored charge into an output signal. The second transistor transfers the electric signal generated by the photodiode to the gate of the first transistor and holds the charge stored in the gate of the first transistor. The first transistor has a back gate and the threshold voltage thereof is changed by changing the potential of the back gate.

Claims

1. A semiconductor device comprising:

a photodiode;

a first transistor having a stacked structure including a gate, a gate insulating layer, a semiconductor layer, an insulating film, and a back gate; and

a second transistor comprising a gate, a first terminal, and a second terminal,

wherein the photodiode is electrically connected to the first terminal of the second transistor,

wherein the second terminal of the second transistor is electrically connected to the gate of the first transistor, and

wherein the second transistor comprises a channel formation region comprising an oxide semiconductor.

2. The semiconductor device according to claim 1, further comprising a display element,

wherein the display element comprises a liquid crystal element.

3. The semiconductor device according to claim 1, further comprising a display element,

wherein the display element comprises a light emitting element.

4. The semiconductor device according to claim 1,

wherein the semiconductor layer of the first transistor comprises an oxide semiconductor.

5. The semiconductor device according to claim 1,

wherein the oxide semiconductor comprises indium, gallium, and zinc.

6. An electronic appliance comprising the semiconductor device according to claim 1.

7. A semiconductor device comprising:

a photodiode comprising a pair of electrodes with a semiconductor interposed between the pair of electrodes;

a first transistor having a stacked structure including a gate, a gate insulating layer, a semiconductor layer, an insulating film, and a back gate, wherein the gate insulating layer and the semiconductor layer are interposed between the gate and the back gate; and

a second transistor comprising;

a gate;

a gate insulating layer over the second gate;

an oxide semiconductor layer over the gate insulating layer;

a first terminal and a second terminal over the oxide semiconductor layer; and

an oxide insulating layer over and in contact with the first terminal, the second terminal, and the oxide semiconductor layer;

wherein one of the pair of electrodes is electrically connected to one of the first terminal and the second terminal, and

wherein the other of the first terminal and the second terminal is electrically connected to the gate of the first transistor.

8. The semiconductor device according to claim 7, further comprising a display element,

wherein the display element comprises a liquid crystal element.

9. The semiconductor device according to claim 7, further comprising a display element,

wherein the display element comprises a light emitting element.

10. The semiconductor device according to claim 7,

wherein the oxide semiconductor layer comprises indium, gallium, and zinc.

11. The semiconductor device according to claim 7,

wherein the semiconductor layer of the first transistor comprises an oxide semiconductor included in the oxide semiconductor layer of the second transistor.

12. An electronic appliance comprising the semiconductor device according to claim 7.

13. A driving method of a semiconductor device comprising a photodiode, the driving method comprising the steps of:

transferring an electric signal generated by the photodiode to a gate of a first transistor through a second transistor which is in a conduction state, keeping a back gate of the first transistor at a first potential, wherein the back gate is provided over the gate with a semiconductor layer therebetween;

holding charge stored in the gate by turning the second transistor to a non-conduction state;

converting the charge stored in the gate of the first transistor to a first output signal;

providing a second potential to the back gate, wherein the second potential is different from the first potential; and

converting the charge stored in the gate to a second output signal, while keeping potential of the back gate at the second potential,

wherein the second transistor comprises a channel formation region comprising an oxide semiconductor.

14. The driving method according to claim 13,

wherein the first transistor comprises a channel formation region comprising the oxide semiconductor.

15. The driving method according to claim 13,

wherein the semiconductor device comprises a display element comprising a liquid crystal element.

16. The driving method according to claim 13,

wherein the semiconductor device comprises a display element comprising a light emitting element.

17. The driving method according to claim 13,

wherein the oxide semiconductor comprises indium, gallium, and zinc.