# US 4,398,340 A · Method for making thin film field effect transistors

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- Number: US 4,398,340 A
- Document ID: US4398340A
- Status: Granted
- Kind: A
- Application number: 06/371,639
- Filed: 1982-04-26
- Granted: 1983-08-16
- Earliest claimed: 1982-04-26
- Assignees: The United States of America as represented by the Secretary of the Army
- Inventors: Robert L. Brown
- Web page: https://patentgrep.com/patent/US4398340A

## CPC

- H10D 99/00: Subject matter not provided for in other groups of this subclass
- H10D 30/675: {Group III-V materials, Group II-VI materials, Group IV-VI materials, selenium or tellurium}
- H10D: INORGANIC ELECTRIC SEMICONDUCTOR DEVICES

## Abstract

A method for making thin film field effect transistors that utilize a semnductor material that is altered by acid etching and providing steps for producing the transistors such that the semiconductor material is protected from the acid solutions and therefore preventing the semiconductor material from being altered in the process of making the transistors.

## Claims

### Claim 1

A method for making thin film field effect transistors comprising providing a substrate that has a substantially flat surface thereon, mounting a thin metal film on said surface of said substrate, photolithographic and acid etching first and second connections from said thin metal film to define a predetermined gap between said first and second connections, depositing a layer of semiconductor material in said gap and overlapping portions of said first and second connections, depositing an impervious insulation layer that overlaps all sides of said semiconductor layer over said semiconductor and a portion of said first and second connections, depositing a metal layer as a gate over said insulation layer and photolithographic and acid etching said metal gate to a size that is substantially identical in width to the gap between said first and second connections to provide a thin film field effect transistor that has high frequency characteristics due to the materials of the transistor and the precision by which the transistor can be made.

### Claim 2 (depends on 1)

The method of making a thin film field effect transistor as set forth in claim 1, wherein said semiconductor material is selected from polycrystalline cadmium selenide and polycrystalline cadmium sulfide and wherein said semiconductor material is protected from acid etching of said first and second connections by being deposited after said first and second connections are acid etched and being protected by said impervious insulation layer from acid etching of said gate metal layer.

### Claim 3 (depends on 1)

A method of making a thin film field effect transistor as set forth in claim 1, wherein said first and second connections and said gate have metal contacts deposited over a portion thereof to form connections adapting the first and second connections and the gate for ready connection to elements external to the transistor.