Image Display Device and Manufacturing Method for the Same

• US 20100012940A1
• Filed: 07/14/2009
• Published: 01/21/2010
• Est. Priority Date: 07/18/2008
• Status: Active Grant

• Current Assignee: Panasonic Intellectual Property Corporation of America (Panasonic Holdings Corporation)
• Original Assignee: Hitachi Displays Limited (Japan Display Incorporated)
• Inventors: SATO, Takeshi
• Granted Patent: US 7,804,095 B2
• Time in Patent Office: Days
• US Class Current: 257/59
• CPC Class Codes: H01L 27/1214 comprising a plurality of TFTs formed on a non-semiconducting substrate, e.g. driving circuits for AMLCDs
• CPC Class Codes: H01L 27/1233 with different thicknesses of the active layer in different devices
• CPC Class Codes: H01L 27/1251 comprising TFTs having a different architecture, e.g. top- and bottom gate TFTs
• CPC Class Codes: H01L 29/78648 arranged on opposing sides of the channel

Abstract

Provided is an image display device comprising, on a TFT substrate: a plurality of gate lines and a plurality of drain lines which intersect with each other; a pixel TFT provided within a pixel which is enclosed by a pair of adjacent gate lines and a pair of adjacent drain lines; a gate driver TFT which is connected to one of the plurality of gate lines to drive the one of the plurality of gate lines, wherein the pixel TFT and the gate driver TFT each include an amorphous semiconductor film as a channel, wherein the pixel TFT has a bottom gate structure, wherein the gate driver TFT has a dual gate structure, and wherein a mobility on a top surface side of the semiconductor film of the gate driver TFT is higher than a mobility on a top surface side of the semiconductor film of the pixel TFT.

Claims

1. An image display device, comprising, on a TFT substrate:

a plurality of gate lines and a plurality of drain lines which intersect with each other;

a pixel TFT provided within a pixel which is enclosed by a pair of adjacent gate lines and a pair of adjacent drain lines;

a gate driver TFT which is connected to one of the plurality of gate lines to drive the one of the plurality of gate lines; and

a shift register for selecting one of the plurality of gate lines through the gate driver TFT,

wherein the pixel TFT and the gate driver TFT each include an amorphous semiconductor film as a channel,

wherein the pixel TFT has a bottom gate structure in which a gate of the pixel TFT is formed below the amorphous semiconductor film,

wherein the gate driver TFT has a dual gate structure in which a gate of the gate driver TFT is formed below the amorphous semiconductor film and another gate of the gate driver TFT is formed above the amorphous semiconductor film, and

wherein a mobility on a top surface side of the amorphous semiconductor film of the gate driver TFT is higher than a mobility on a top surface side of the amorphous semiconductor film of the pixel TFT.

2. An image display device according to claim 1, wherein the pixel TFT and the gate driver TFT each include a contact layer which is interposed between a source thereof and the amorphous semiconductor film, and between a drain thereof and the amorphous semiconductor film.

3. An image display device according to claim 1, wherein a thickness of the amorphous semiconductor film formed in a region that is not covered with the source and drain of the pixel TFT is larger than a thickness of the amorphous semiconductor film formed in a region that is not covered with the source and drain of the gate driver TFT.

4. An image display device according to claim 1, wherein the TFT substrate faces a counter substrate across a liquid crystal.

5. A method of manufacturing an image display device that comprises, on the same substrate, a bottom gate type pixel TFT, which includes a gate thereof below a semiconductor film, and a dual gate type gate driver TFT, which includes a gate thereof below a semiconductor film and another gate thereof above the semiconductor film, the method comprising:

forming a semiconductor layer and a contact layer sequentially to form a sequentially layered structure for each of the bottom gate type pixel TFT and the dual gate type gate driver TFT;

forming a source and a drain on the sequentially layered structure of the bottom gate type pixel TFT, and then etching an exposed part of the contact layer which is not covered with the source and drain of the bottom gate type pixel TFT until the semiconductor film formed below the contact layer is exposed;

forming a source and a drain on the sequentially layered structure of the dual gate type gate driver TFT, and then etching an exposed part of the contact layer which is not covered with the source and drain of the dual gate type gate driver TFT until the semiconductor film formed below the contact layer is exposed; and

forming, while covering at least a region for forming the dual gate type gate driver TFT with a mask, a low mobility layer on an exposed semiconductor film surface which is not covered with the source and drain of the bottom gate type pixel TFT.

7. A method of manufacturing the image display device according to claim 5, comprising:

forming, while covering a region for forming the dual gate type gate driver TFT with a first mask, a source and a drain on the sequentially layered structure in a region for forming the bottom gate type pixel TFT, and then etching an exposed part of the contact layer which is not covered with the source and drain of the bottom gate type pixel TFT until the semiconductor film formed below the contact layer is exposed, to form a low mobility layer on an exposed semiconductor film surface which is not covered with the source and drain of the bottom gate type pixel TFT; and

forming, while covering the region for forming the bottom gate type pixel TFT with a second mask, a source and a drain on the sequentially layered structure in the region for forming the dual gate type gate driver TFT, and then etching an exposed part of the contact layer which is not covered with the source and drain of the dual gate type gate driver TFT until the semiconductor film formed below the contact layer is exposed.

8. A method of manufacturing the image display device according to claim 5, comprising:

forming, while covering a region for forming the bottom gate type pixel TFT with a first mask, a source and a drain on the sequentially layered structure in a region for forming the dual gate type gate driver TFT, and then etching an exposed part of the contact layer which is not covered with the source and drain of the dual gate type gate driver TFT until the semiconductor film formed below the contact layer is exposed; and

forming, while covering the region for forming the dual gate type gate driver TFT with a second mask, a source and a drain on the sequentially layered structure in the region for forming the bottom gate type pixel TFT, and then etching an exposed part of the contact layer which is not covered with the source and drain of the bottom gate type pixel TFT until the semiconductor film formed below the contact layer is exposed, to form a low mobility layer on an exposed semiconductor film surface which is not covered with the source and drain of the bottom gate type pixel TFT.

6. A method of manufacturing an image display device that comprises, on the same substrate, a bottom gate type pixel TFT, which includes a gate thereof below a semiconductor film, and a dual gate type gate driver TFT, which has a gate thereof below a semiconductor film and another gate thereof above the semiconductor film, the method comprising:

forming a semiconductor layer and a contact layer sequentially to form a sequentially layered structure for each of the bottom gate type pixel TFT and the dual gate type gate driver TFT;

forming, in each of the bottom gate type pixel TFT and the dual gate type gate driver TFT, a source and a drain on the sequentially layered structure, and then etching an exposed part of the contact layer which is not covered with the source and the drain until the semiconductor film formed below the contact layer is exposed;

forming a low mobility layer on an exposed semiconductor film surface that is not covered with the source and drain of the bottom gate type pixel TFT and on an exposed semiconductor film surface that is not covered with the source and drain of the dual gate type gate driver TFT; and

removing, while covering at least a region for forming the bottom gate type pixel TFT with a mask, the low mobility layer that has been formed on the semiconductor film surface of the dual gate type gate driver TFT.