DEVELOPMENT OF SILICON CARBIDE MOSFETS FOR HIGH TEMPERATURE SMALL SIGNAL AMPLIFIERS

A STRONG NEED EXISTS FOR AMPLIFICATION OF SMALL ELECTRICAL SIGNALS AT HIGH TEMPERATURES FOR USE WITH SENSORS. SILICON CARBIDE POSSESSES A UNIQUE COMBINATION OF PROPERTIES THAT ALLOWS HIGH TEMPERATURE OPERATION OF ELECTRONIC DEVICES MADEFROM THIS MATERIAL. THE CUBIC FORM OF SIC (BETA) HAS A WIDEBANDGAP (2.2 EV @27 DEGREES CENTIGRADE) WHICH THEORETICALLY GIVES A MAXIMUM OPERABLE TEMPERATURE OF 925 DEGREES CENTIGRADE. ALPHA-SIC (6H) HAS AN EVEN WIDER BANDGAP (2.86 EV @ 27 DEGREES CENTIGRADE), GIVING A MAXIMUM OPERABLE TEMPERATURE OF 1240 DEGREES CENTIGRADE. BOTH FORMS ALSO HAVE A HIGH BREAKDOWN ELECTRIC FIELD OF 4 X 10 6 V/CM (10 TIMES THAT OF SI AND GAAS), WHICH ALLOWS HIGH POWER OPERATION. RECENT RESEARCH ON SIC HAS RESULTED IN THE FABRICATION OF DEPLETION-MODE METAL-OXIDE-SEMICONDUCTOR FIELD-EFFECT TRANSISTORS (MOSFETS) IN BETA-SIC WITH VERY GOOD CURRENT-VOLTAGE CHARACTERISTICS AT TEMPERATURES AS HIGH AS 650 DEGREES CENTIGRADE; THE HIGHEST TEMPERATURE EVERREPORTED FOR A SOLID-STATE TRANSISTOR. THESE DEVICES FAILEDAT 700 DEGREES CENTIGRADE; HOWEVER, THE MODE OF FAILURE WAS DIELECTRIC BREAKDOWN OF THE VERY THIN GATE INSULATOR, NOT BREAKDOWN OF THE SEMICONDUCTOR. RECENT RESEARCH HAS ALSO YIELDED A PROCESS FOR GROWING 6H-SIC THIN FILMS THAT HAVE A MUCH LOWER DEFECT DENSITY THAN THE BETA-SIC MENTIONED PREVIOUSLY. IT IS HEREIN PROPOSED TO FABRICATE MOSFETS, IN BOTH DEPLETION AND INVERSION-MODE, IN THE HIGHER QUALITY 6H-SIC THIN FILM, AS WELL AS INVESTIGATE INVERSION-MODE MOSFETS IN THE BETA-SIC, FOR USE IN SMALL SIGNAL AMPLIFICATION.