LIQUID CRYSTAL DISPLAY DEVICE

• US 20120319107A1
• Filed: 08/30/2012
• Published: 12/20/2012
• 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 8,953,112 B2
• Time in Patent Office: Days
• US Class Current: 257/43
• 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 display device comprising:

a transistor comprising a first oxide semiconductor layer, the first oxide layer including a channel;

a pixel electrode comprising a transparent conductive film, the pixel electrode electrically connected to one of a source and a drain of the transistor;

a storage capacitor electrically connected to the transistor, the storage capacitor comprising a second oxide semiconductor layer as a first electrode, a part of the transparent conductive film as a second electrode, and an insulating film between the first electrode and the second electrode.

2. The display device according to claim 1, wherein the first oxide semiconductor layer and the second oxide semiconductor layer are formed by a method comprising:

forming an oxide semiconductor film on an insulating surface;

etching the oxide semiconductor film to form the first oxide semiconductor layer and the second oxide semiconductor layer.

3. The display device according to claim 1, wherein the first oxide semiconductor layer and the second oxide semiconductor layer are formed on a same insulating surface.

4. The display device according to claim 1, wherein each of the first oxide semiconductor layer and the second oxide semiconductor layer comprises indium, zinc and oxygen.

5. A display device comprising:

a gate electrode;

a first insulating film over the gate electrode;

a first oxide semiconductor layer over the gate electrode with the first insulating film interposed therebetween, the first oxide semiconductor layer including a channel;

a source electrode in electrical contact with the first oxide semiconductor layer;

a drain electrode in electrical contact with the first oxide semiconductor layer;

a second oxide semiconductor layer over the first insulating film;

a second insulating film over the first oxide semiconductor layer, the source electrode, the drain electrode and the second oxide semiconductor layer;

a pixel electrode comprising a transparent conductive film over the second insulating film, the pixel electrode being electrically connected to one of the source electrode and the drain electrode through an opening of the second insulating film,

wherein the pixel electrode overlaps the second oxide semiconductor layer to form a storage capacitor between the pixel electrode and the second oxide semiconductor layer with the second insulating film therebetween.

6. The display device according to claim 5, wherein each of the first oxide semiconductor layer and the second oxide semiconductor layer is in direct contact with the first insulating film.

7. The display device according to claim 5, wherein the first oxide semiconductor layer and the second oxide semiconductor layer are formed by a method comprising:

forming an oxide semiconductor film on an insulating surface;

etching the oxide semiconductor film to form the first oxide semiconductor layer and the second oxide semiconductor layer.

8. The display device according to claim 5, wherein each of the first oxide semiconductor layer and the second oxide semiconductor layer comprises indium, zinc and oxygen.

9. A display device comprising:

a gate electrode on an insulating surface;

a first wiring on the insulating surface;

a first insulating film over the gate electrode and the first wiring;

a first oxide semiconductor layer for a channel over the gate electrode with the first insulating film interposed therebetween;

a source electrode in electrical contact with the first oxide semiconductor layer;

a drain electrode in electrical contact with the first oxide semiconductor layer;

a second oxide semiconductor layer over the first insulating film;

a second wiring in electrical contact with the second oxide semiconductor layer, wherein the second wiring is formed over the first insulating film and is electrically connected to the first wiring through an opening of the first insulating film;

a second insulating film over the first oxide semiconductor layer, the source electrode, the drain electrode, the second oxide semiconductor layer and the second wiring;

a pixel electrode comprising a transparent conductive film over the second insulating film, the pixel electrode being electrically connected to one of the source electrode and the drain electrode through an opening of the second insulating film,

wherein the pixel electrode overlaps the second oxide semiconductor layer to form a storage capacitor between the pixel electrode and the second oxide semiconductor layer with the second insulating film therebetween.

10. The display device according to claim 9, wherein the first oxide semiconductor layer and the second oxide semiconductor layer are formed by a method comprising:

forming an oxide semiconductor film on an insulating surface;

etching the oxide semiconductor film to form the first oxide semiconductor layer and the second oxide semiconductor layer.

11. The display device according to claim 9, wherein each of the first oxide semiconductor layer and the second oxide semiconductor layer comprises indium, zinc and oxygen.

12. The display device according to claim 9, wherein each of the first oxide semiconductor layer and the second oxide semiconductor layer is in direct contact with the first insulating film.

13. The display device according to claim 9, wherein a potential supplied to the first wiring is variable in response to a frame frequency of the display device.