Display device

• US 20090050896A1
• Filed: 07/30/2008
• Published: 02/26/2009
• Est. Priority Date: 08/21/2007
• Status: Active Grant

• Current Assignee: Panasonic Intellectual Property Corporation of America (Panasonic Holdings Corporation)
• Original Assignee: Hitachi Displays Limited (Japan Display Incorporated)
• Inventors: Sakai, Takeshi, Miyake, Hidekazu, Kaitoh, Takuo, Saitou, Terunori
• Granted Patent: US 8,624,256 B2
• Time in Patent Office: Days
• US Class Current: 257/72
• CPC Class Codes: H01L 27/1229 with different crystal properties within a device or between different devices
• CPC Class Codes: H01L 27/1251 comprising TFTs having a different architecture, e.g. top- and bottom gate TFTs

Abstract

The present invention provides a display device which forms a drive circuit using a bottom-gate-type TFT made of poly-Si which generates a small leak current in a periphery of a display region. A gate electrode is made of Mo having a high melting point, and a gate insulation film is formed on the gate electrode. A channel layer constituted of a poly-Si layer is formed on the gate insulation film, and the poly-Si layer is covered with an a-Si layer. An n+ Si layer is formed on the a-Si layer, and an SD electrode is formed on the n+ Si layer. Although holes are induced in the poly-Si layer when a negative voltage (inverse bias) is applied to the gate electrode, the holes cannot pass through the a-Si layer and hence, no drain current flows. Accordingly, it is possible to realize a bottom-gate-type TFT using poly-silicon which generates a small leak current.

Claims

1. A display device comprising:

a display region in which pixel electrodes and TFTs for pixel are formed in a matrix array; and

a drive circuit which is formed in a periphery of the display region and includes a TFT for drive circuit, wherein

the TFT for pixel is a bottom-gate-type TFT having a channel portion which is formed of an a-Si layer, and

the TFT for drive circuit is a bottom-gate-type TFT, the TFT for drive circuit is constituted by forming a channel portion using a poly-Si layer, by forming an a-Si layer which covers the poly-Si layer, by forming an n+ Si layer on the a-Si layer, and by forming an SD electrode on the n+ Si layer, and

the poly-Si layer is not brought into contact with the SD electrode.

2. A display device according to claim 1, wherein the poly-Si layer is formed by applying laser annealing to the a-Si layer.

3. A display device according to claim 1, wherein a gate electrode of the bottom-gate-type TFT for the pixel and a gate electrode of the bottom-gate-type TFT for the drive circuit are made of Mo or Mo alloy.

4. A display device according to claim 1, wherein the SD electrode is constituted of a barrier metal layer, an Al layer and a cap metal layer, and the barrier metal layer and the cap metal layer are made of Mo or Mo alloy.

5. A display device according to claim 1, wherein a portion of the poly-Si layer is not covered with the a-Si layer.

6. A display device comprising:

a display region in which pixel electrodes and TFTs for pixel are formed in a matrix array; and

a drive circuit which is formed in a periphery of the display region and includes a TFT for drive circuit, wherein

the TFT for pixel is a bottom-gate-type TFT having a channel portion which is formed of an a-Si layer, and

the TFT for drive circuit is a bottom-gate-type TFT, the TFT for drive circuit is constituted by forming a channel portion -using a poly-Si layer, by forming an a-Si layer which covers the poly-Si layer, by forming an n+ Si layer on an upper portion and a side portion of the a-Si layer, and by forming an SD electrode on the n+ Si layer, and

the poly-Si layer is not brought into contact with the n+ Si layer.

7. A display device according to claim 6, wherein the poly-Si layer is formed by applying laser annealing to the a-Si layer.

8. A display device according to claim 6, wherein a gate electrode of the bottom-gate-type TFT for the pixel and a gate electrode of the bottom-gate-type TFT for the drive circuit are made of Mo or Mo alloy.

9. A display device according to claim 6, wherein the SD electrode is constituted of a barrier metal layer, an Al layer and a cap metal layer, and the barrier metal and the cap metal are made of Mo or Mo alloy.

10. A display device according to claim 6, wherein a portion of the poly-Si layer is not covered with the a-Si layer.

11. A liquid crystal display device comprising:

a TFT substrate which forms a display region in which pixel electrodes and TFTs for pixel are formed in a matrix array and a drive circuit which includes a TFT for drive circuit in a periphery of the display region thereon;

a color filter substrate which faces the TFT substrate in an opposed manner and forms color filters on portions thereof corresponding to the pixel electrodes; and

liquid crystal which is sandwiched between the TFT substrate and the color filter substrate;

wherein

the TFT for pixel is a bottom-gate-type TFT having a channel portion which is formed of an a-Si layer, and

the TFT for drive circuit is a bottom-gate-type TFT, the TFT for drive circuit is constituted by forming a channel portion using a poly-Si layer, by forming an a-Si layer which covers the poly-Si layer, by forming an n+ Si layer on the a-Si layer, and by forming an SD electrode on the n+ Si layer, and

the poly-Si layer is not brought into contact with the SD electrode.

12. A liquid crystal display device according to claim 11, wherein a side portion of the a-Si layer is also covered with the n+ Si layer.

13. A liquid crystal display device according to claim 11, wherein a portion of the poly-Si layer is not covered with the a-Si layer.

14. An organic EL display device including a TFT substrate which forms a display region in which organic EL layers and TFTs for pixel are formed in a matrix array and a drive circuit which includes a TFT for drive circuit in a periphery of the display region thereon, wherein

the TFT for pixel is a bottom-gate-type TFT having a channel portion which is formed of an a-Si layer, and

the TFT for drive circuit is a bottom-gate-type TFT, the TFT for drive circuit is constituted by forming a channel portion using a poly-Si layer, by forming an a-Si layer which covers the poly-Si layer, by forming an n+ Si layer on the a-Si layer, and by forming an SD electrode on the n+ Si layer, and

the poly-Si layer is not brought into contact with the SD electrode.

15. An organic EL display device according to claim 14, wherein a side portion of the a-Si layer is also covered with the n+ Si layer.

16. An organic EL display device according to claim 14, wherein a portion of the poly-Si layer is not covered with the a-Si layer.

17. A display device comprising:

a display region in which pixel electrodes and TFTs for pixel are formed in a matrix array; and

a drive circuit which is formed in a periphery of the display region and includes a TFT for drive circuit, wherein

the TFT for pixel is a bottom-gate-type TFT having a channel portion which is formed of an a-Si layer, and

the TFT for drive circuit is a bottom-gate-type TFT, the TFT for drive circuit is constituted by forming a channel portion using a strip-shaped crystal silicon layer, by forming an a-Si layer which covers the strip-shaped crystal silicon layer, by forming an n+ Si layer on the a-Si layer, and by forming an SD electrode on the n+ Si layer, and

the strip-shaped crystal silicon layer is not brought into contact with the SD electrode.