LIQUID CRYSTAL DISPLAY DEVICE

• US 20120062811A1
• Filed: 08/18/2011
• Published: 03/15/2012
• Est. Priority Date: 09/15/2010
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: MIYAKE, Hiroyuki
• Granted Patent: US 9,230,994 B2
• Time in Patent Office: Days
• US Class Current: 349/39
• CPC Class Codes: G02F 1/136213 Storage capacitors associated with the pixel electrode
• 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 27/1255 integrated with passive devices, e.g. auxiliary capacitors

Abstract

An object of the present invention is to provide a liquid crystal display device which allows a desirable storage capacitor to be ensured in a pixel without decreasing the aperture ratio in response to changes in frame frequency. In a liquid crystal display device including a pixel transistor and two capacitive elements using an oxide semiconductor material in each pixel, one of the capacitive elements comprises a light-transmitting material to improve the aperture ratio of the pixel. Furthermore, through the use of characteristics of the light-transmitting capacitive element, the size of the storage capacitor in the pixel is varied by adjusting the voltage value of a capacitance value in response to the frame frequency varied depending on images displayed.

Claims

1. A semiconductor device comprising:

a transistor including a gate electrode electrically connected to a scan line, a first electrode electrically connected to a signal line, and a second electrode electrically connected to a pixel electrode;

a first capacitive element including one electrode electrically connected to the second electrode, and the other electrode electrically connected to a capacitance line; and

a second capacitive element including one electrode electrically connected to the second electrode, and the other electrode electrically connected to the capacitance line,

wherein the second capacitive element has a capacitance value variable in response to a time interval of a gate pulse by adjusting an electric potential of the capacitance line.

2. The liquid crystal display device according to claim 1, wherein the pixel electrode and the semiconductor layer have a light-transmitting property.

3. The liquid crystal display device according to claim 1, wherein the semiconductor layer comprises an oxide semiconductor.

4. The liquid crystal display device according to claim 1, wherein the second capacitive element has a MOS capacitor structure with a dielectric layer interposed between the one electrode and the other electrode.

5. The liquid crystal display device according to claim 1,

wherein the one electrode of the second capacitive element is formed from the same layer as the pixel electrode, and

wherein the other electrode of the second capacitive element is formed from the same semiconductor material as the semiconductor layer of the transistor.

6. The liquid crystal display device according to claim 1, wherein a dielectric layer of the first capacitive element or the second capacitive element has a multilayer structure.

7. A method for driving a display device comprising:

a transistor including a gate electrode electrically connected to a scan line, a first electrode electrically connected to a signal line, and a second electrode electrically connected to a pixel electrode;

a first capacitive element including one electrode electrically connected to the second electrode, and the other electrode electrically connected to a capacitance line; and

a second capacitive element including one electrode electrically connected to the second electrode, and the other electrode electrically connected to the capacitance line,

the method comprising a step of;

adjusting an electric potential of the capacitance line, and

varying a capacitance value of the second capacitive element in response to a time interval of a gate pulse.

8. A semiconductor device comprising:

a first transistor including a gate electrode electrically connected to a scan line, a first electrode electrically connected to a signal line, and a second electrode electrically connected to a pixel electrode;

a first capacitive element including one electrode electrically connected to the second electrode, and the other electrode electrically connected to a wiring for shielding;

a second capacitive element including one electrode electrically connected to the second electrode, and the other electrode electrically connected to a capacitance line; and

a second transistor including a gate electrode electrically connected to the wiring for shielding, a first electrode electrically connected to the one electrode of the first capacitive element, and a second electrode electrically connected to the capacitance line,

wherein the second capacitive element has a capacitance value variable in response to a time interval of a gate pulse by adjusting an electric potential of the capacitance line and supplying, to the wiring for shielding, an electric potential that turns off the second transistor at least during image display.

9. The liquid crystal display device according to claim 8, wherein the pixel electrode and the semiconductor layer have a light-transmitting property.

10. The liquid crystal display device according to claim 8, wherein the semiconductor layer comprises an oxide semiconductor.

11. The liquid crystal display device according to claim 8, wherein the second capacitive element has a MOS capacitor structure with a dielectric layer interposed between the one electrode and the other electrode.

12. The liquid crystal display device according to claim 8,

wherein the one electrode of the second capacitive element is formed from the same layer as the pixel electrode, and

wherein the other electrode of the second capacitive element is formed from the same semiconductor material as the semiconductor layer of the first transistor.

13. The liquid crystal display device according to claim 8, wherein a dielectric layer of the first capacitive element or the second capacitive element has a multilayer structure.

14. A method for driving a display device comprising:

a first transistor including a gate electrode electrically connected to a scan line, a first electrode electrically connected to a signal line, and a second electrode electrically connected to a pixel electrode;

a first capacitive element including one electrode electrically connected to the second electrode, and the other electrode electrically connected to a wiring for shielding;

a second capacitive element including one electrode electrically connected to the second electrode, and the other electrode electrically connected to a capacitance line; and

a second transistor including a gate electrode electrically connected to the wiring for shielding, a first electrode electrically connected to the one electrode of the first capacitive element, and a second electrode electrically connected to the capacitance line,

the method comprising a step of;

adjusting an electric potential of the capacitance line,

supplying, to the wiring for shielding, an electric potential that turns off the second transistor at least during image display, and

varying a capacitance value of the second capacitive element in response to a time interval of a gate pulse.