Polysilicon pixel electrode

• US 5,471,330 A
• Filed: 07/29/1993
• Issued: 11/28/1995
• Est. Priority Date: 07/29/1993
• Status: Expired due to Term

• Current Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Original Assignee: Honeywell Incorporated (Honeywell International Inc.)
• Inventors: Sarma, Kalluri R.
• Primary Examiner(s): Gross, Anita Pellman
• Assistant Examiner(s): Malinowski, Walter J.
• Application Number:
  US08/099,961
• Time in Patent Office: 852 Days
• Field of Search: 257/59, 257/72, 359/59, 359/87, 437/233, 437/173
• US Class Current: 349/43
• CPC Class Codes: G02F 1/13439 characterised by their electrical, optical, physical properties; materials therefor; method of making
• CPC Class Codes: G02F 1/1368 in which the switching element is a three-electrode device G02F1/136277 takes precedence
• CPC Class Codes: G02F 2202/104 poly-Si

Abstract

A liquid crystal display wherein each pixel has a thin film transistor with a silicon pixel electrode. A doping and recrystallization of the silicon is effected to increase the electrical conductivity and light transmittance of the silicon adequately for the pixel electrode.

Claims

1. A liquid crystal display pixel comprising:

a glass substrate;

a metal gate layer formed on a first portion of said glass substrate;

a gate dielectric layer formed on said metal gate layer and on a second portion of said glass substrate;

an amorphous silicon channel layer formed on a first portion of said gate dielectric layer and located proximate to said metal gate layer;

a polysilicon source layer formed adjacent to said amorphous silicon channel layer;

a polysilicon drain layer formed adjacent to said amorphous silicon channel layer; and

a polysilicon pixel electrode layer formed on a second portion of said gate dielectric layer.

2. A method for fabricating a silicon pixel electrode for a liquid crystal display, comprising:

forming a gate metal layer on a first portion of a glass substrate;

forming a gate dielectric layer on the gate metal layer and on a second portion of the glass substrate;

forming an amorphous silicon channel layer on a first portion of the gate dielectric layer and located proximate to the gate metal layer;

forming a polysilicon source layer adjacent to said amorphous silicon channel layer;

forming a polysilicon drain layer adjacent to said amorphous silicon channel layer; and

forming a polysilicon pixel electrode layer on a second portion of the gate dielectric layer.

3. A method for fabricating a silicon pixel electrode for a liquid crystal display, comprising:

depositing and etching a gate metal layer on a display glass substrate;

depositing a gate dielectric layer on the gate metal layer and glass substrate;

depositing an undoped a-Si layer for the silicon pixel electrode and a TFT, on the gate dielectric layer;

depositing and etching a dielectric masking layer on the undoped a-Si layer;

depositing a doped a-Si layer on the undoped a-Si layer and the dielectric masking layer;

etching the doped and undoped a-Si layers to define the TFT region and the pixel region;

depositing a reflective metal layer on the doped a-Si layer;

etching the reflective metal layer for coverage over the dielectric masking layer;

recrystallizing a portion of the doped and undoped a-Si layers into a doped polysilicon layer;

depositing a source metal layer on a portion of the doped polysilicon layer;

etching a portion of the metal reflective layer;

depositing a dark polyimide layer over the source metal layer, the dielectric masking layer and the doped polysilicon layer; and

etching the dark polyimide layer from the polysilicon layer in the pixel region.

4. The method of claim 3 wherein:

the gate metal layer is a material selected from a group consisting of chromium, nichrome, aluminum, titanium, tantalum and tantalum alloys;

the gate dielectric layer is a material selected from a group consisting of silicon nitride, tantalum pentoxide and silicon dioxide; and

the dielectric masking layer is a material selected from a group consisting of silicon dioxide and silicon nitride.

5. The method of claim 4 wherein the recrystallization of the doped and undoped a-Si layers into the doped polysilicon layer is accomplished by melting the a-Si layers with a laser.

6. The method of claim 4 wherein the recrystallization of the doped and undoped layers into a doped polysilicon layer is accomplished by heating the a-Si layers with radiant heating lamps.

7. The method of claim 4 wherein the glass substrate is a low temperature glass.

8. The method of claim 7 wherein:

the gate metal layer has a thickness between 1000 and 2000 Angstroms;

the gate dielectric layer has a thickness between 1500 and 3000 Angstroms;

the undoped a-Si layer has a thickness between 500 and 2500 Angstroms;

the dielectric masking layer has a thickness between 4000 and 6000 Angstroms;

the doped a-Si layer has a thickness between 150 and 500 Angstroms;

the reflective metal layer has a thickness between 1500 and 3000 Angstroms; and

the source metal layer has a thickness between 4000 and 8000 Angstroms.

9. A method for fabricating a silicon pixel electrode having a pixel area for a liquid crystal display, comprising:

depositing and etching a gate metal layer on a display glass substrate;

depositing a gate dielectric layer on the gate metal layer and the glass substrate;

depositing an undoped a-Si layer for the silicon pixel electrode and a TFT, on the gate dielectric layer;

depositing and etching a dielectric masking layer on the undoped a-Si layer covering a channel area of the TFT;

depositing and etching a reflective metal layer on the dielectric masking layer to protect the channel area of the TFT;

doping and recrystallizing, approximately simultaneously, a portion of the undoped a-Si layer into a doped polysilicon layer;

depositing a source metal layer on a portion of the doped polysilicon layer;

etching away a portion of the reflective metal layer;

depositing a dark polyimide on the source metal layer, dielectric masking layer and doped polysilicon layer; and

etching the dark polyimide layer from the polysilicon layer in the pixel area.

10. The method for fabricating a silicon pixel electrode of claim 9, wherein the doping and recrystallizing comprises:

heating the portion of the undoped a-Si layer into molten silicon, with a pulse of laser light; and

exposing the molten silicon to a dopant gas to dope the molten silicon.

11. The method for fabricating a silicon pixel electrode of claim 10, wherein:

the laser light is from an excimer laser; and

the dopant gas is PH₃ or AsH₃ for doping the silicon with phosphorus or arsenic.

12. The method for fabricating a silicon pixel electrode of claim 9, wherein the doping of the undoped a-Si layer is effected by ion implantation of a phosphorus or arsenic dopant species into the a-Si layer with a concentration between 10¹⁹ and 3×

10²⁰ atoms per cubic centimeter.

13. A liquid crystal display comprising a plurality of pixels on a glass substrate, wherein each pixel comprises:

a gate metal layer formed on a first portion of the glass substrate;

a gate dielectric layer formed on the gate metal layer and on a second portion of the glass substrate;

an a-Si layer formed on a first portion of the gate dielectric layer and proximate to the gate metal layer;

a doped polysilicon pixel electrode layer formed on a second portion of the gate dielectric layer;

a dielectric masking layer formed on the a-Si layer;

a polysilicon non-pixel electrode layer formed on a third portion of the gate dielectric layer;

a source metal layer formed on the polysilicon non-pixel electrode; and

a dark polyimide layer formed on the dielectric masking layer and on the source metal layer.

14. The liquid crystal display of claim 13 wherein:

the glass substrate is a low temperature glass;

the gate metal layer has a thickness between 1000 and 2000 Angstroms;

the gate dielectric layer has a thickness between 1500 and 3000 Angstroms;

the a-Si layer has a thickness between 500 and 2500 Angstroms;

the polysilicon pixel electrode layer has a thickness between 650 and 3000 Angstroms;

the dielectric masking layer has a thickness between 4000 and 6000 Angstroms;

the polysilicon non-pixel electrode layer has a thickness between 650 and 3000 Angstroms; and

the source metal layer has a thickness between 4000 and 8000 Angstroms.

15. A liquid crystal display pixel comprising:

a glass substrate;

a metal gate layer formed on a first portion of said glass substrate;

a gate dielectric layer formed on said metal gate layer and on a second portion of said glass substrate;

an amorphous silicon channel layer formed on a first portion of said gate dielectric layer and located proximate to said metal gate layer;

a polysilicon source layer formed adjacent to said amorphous silicon channel layer;

a polysilicon drain layer formed adjacent to said amorphous silicon channel layer; and

a doped polysilicon pixel electrode layer formed on a second portion of said gate dielectric layer.

16. A method for fabricating a silicon pixel electrode for a liquid crystal display, comprising:

forming a gate metal layer on a first portion of a glass substrate;

forming a gate dielectric layer on the gate metal layer and on a second portion of the glass substrate;

forming an amorphous silicon channel layer on a first portion of the gate dielectric layer and located proximate to the gate metal layer;

forming a polysilicon source layer adjacent to Said amorphous silicon channel layer;

forming a polysilicon drain layer adjacent to said amorphous silicon channel layer; and

forming a doped polysilicon pixel electrode layer on a second portion of the gate dielectric layer.