Photo-transistor in MOS thin-film technology and method for production and operation thereof

• US 4,823,180 A
• Filed: 10/28/1982
• Issued: 04/18/1989
• Est. Priority Date: 11/26/1981
• Status: Expired due to Fees

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Wieder, Armin, Risch, Lothar
• Primary Examiner(s): James, Andrew J.
• Assistant Examiner(s): JACKSON JR, JEROME
• Application Number:
  US06/437,302
• Time in Patent Office: 2,364 Days
• Field of Search: 357/23 TF, 357/4, 357/59, 357/30, 250/211 J
• US Class Current: 257/290
• CPC Class Codes: H01L 29/04 characterised by their crystalline structure, e.g. polycrystalline, cubic or particular orientation of crystalline planes characterised by physical imperfections H01L29/30
• CPC Class Codes: H01L 31/1136 the device being a metal-insulator-semiconductor field-effect transistor

Abstract

A photo-transistor in MOS thin-film technology operable with alternating voltages is comprised of a semiconductor body (3) composed of polycrystalline silicon having source (4) and drain (5) zones therein spaced apart by an undoped channel region (13) and having a gate electrode (1, 10) separated from the semiconductor body (3) by a SiO₂ layer (2) produced by thermal oxidation. These phototransistors are easily and reproducably produced and are characterized by low threshold voltages and a good transistor characteristic curve. Thus, these photo-transistors are well suited for use as sensor elements, opto-couplers, time-delay elements and as photo-transistors in VLSI circuits.

Claims

1. A method of operating a photo-transistor in MOS thin film technology, comprising steps of:

(a) providing the MOS photo-transistor as

(1) a semiconductor body comprising polycrystalline silicon having a source zone and drain zone located therein and spaced from one another by an undoped channel region,

(2) a gate electrode formed of polycrystalline silicone positioned at and separated from said semiconductor body by an SiO₂ layer generated on the silicon semiconductor body by thermal oxidation, and

(3) a high defect density boundary region between the semiconductor body and the SiO₂ layer;

(b) applying an alternating voltage to the gate and applying an operating voltage between the source and drain zones;

(c) exposing the photo-transistor to varying light amplitudes to cause variations in drain current; and

(d) the photo-transistor being operable with the gate voltage lying anywhere in a range from 100 Hz to 1 Mhz.

2. A method according to claim 1 wherein the photo-transistor is operable with a gate voltage in a range from greater than 0 to 10 volts.

3. A method of operating a photo-transistor in MOS thin film technology, comprising steps of:

(a) providing the MOS photo-transistor as

(1) a semiconductor body comprising polycrystalline silicon having a source zone and drain zone located therein and spaced from one another by an undoped channel region,

(2) a gate electrode formed of polycrystalline silicon positioned at and separated from said semiconductor body by an SiO₂ layer generated on the silicon semiconductor body by thermal oxidation, and

(3) a high defect density boundary region between the semiconductor body and the SiO₂ layer;

(b) applying an alternating voltage to the gate and applying an operating voltage between the source and drain zones;

(c) with no light exposure on the photo-transistor, substantially no drain current flows; and

(d) with increasing light exposure on the photo-transistor, more and more defects in the boundary region are filled and a surface potential associated with the boundary region follows the alternating gate voltage faster and faster.

4. A method according to claim 3 including the step of providing the source and drain zones with a concentration of more than 10¹⁸ arsenic ions per cubic centimeter.

5. A method according to claim 4 including the step of providing the SiO₂ layer with a thickness of between 30 to 50 nm and the semiconductor body with a thickness of 500 to 1000 nm.

6. A method of operating a photo-transistor in MOS thin film technology, comprising steps of:

(a) providing the MOS photo-transistor as

(1) a semiconductor body comprising polycrystalline silicon having a source zone and drain zone located therein and spaced from one another by an undoped channel region,

(2) a gate electrode formed of polycrystalline silicon positioned at and separated from said semiconductor body by an SiO₂ layer generated on the silicon semiconductor body by thermal oxidation, and

(3) a high defect density boundary region between the semiconductor body and the SiO₂ layer;

(b) applying an alternating voltage to the gate and applying an operating voltage between the source and drain zones; and

(c) with light exposure on the photo-transistor, operating the photo-transistor at frequencies greater than 10 kHz.

7. A method according to claim 6 including the step of providing the operating voltage in a range between 5 and 10 volts.

8. A method of operating a photo-transistor in MOS thin film technology, comprising steps of:

(a) providing the MOS photo-transistor as

(1) a semiconductor body comprising polycrystalline silicon having a source zone and drain zone located therein and spaced from one another by an undoped channel region,

(2) a gate electrode formed of polycrystalline silicon positioned at and separated from said semiconductor body by an SiO₂ layer generated on the silicon semiconductor body by thermal oxidation, and

(3) a high defect density boundary region between the semiconductor body and the SiO₂ layer;

(b) applying an alternating voltage to the gate and applying an operating voltage between the source and drain zones; and

(c) the alternating voltage applied to the gate being at least 10 kHz and having a potential between 0 to 10 volts.