RITE-OMIYA　LABORATORY in MITSUBISHI MATERIALS CORPORATION

Silicon carbide field-effect transistors were developed for use in high temperature environments. These transistors are, for example,installed in an engine room of cars to attain more precise control of fuel combustions ,resulting in a lesser emission level of harmful substances such as CO and NOx in the exhausted gas from cars.

A cubic type silicon carbide(3C-SiC) was grown heteroepitaxially by MOCVD using C3H8 and SiH4 gases with H2 gas as a carrier. At first,single crystal n-type layer of 2μm thick, and then 3μm thick Al-doped p-type layer was grown on 2 inch Si single crystal wafers. The carrier densities of SiC layers were 5〜10E16cm-3 for n-type and 5E16cm-3 for p-type layer. The mobility of n-type layer was 300cm2/Vs at room temperature. A cylindrical,inversion type field-effect transistors were constructed on the p-type SiC layer,which had 3μm gate length and 377μm gate width.

The gate oxide was 50nm thick and grown thermally in wet oxygen ambient using pyrogenetic oxidation furnace. Source and drain regions were built in the p-type layer,by three times multiple ion implantations of nitrogen with holding the substrate at 650℃ and successive thermal annealing at 1,400℃. Thermally resistive electrode,insulation and interconnection techniques were used to construct transistor chips and they were assembled in ceramics packages.

The characteristics of the developed transistors were as follows:

　Maximum source-to-drain voltage = 25V

　Maximum drain current = 55mA

　Mutual conductance = 2.5mS(typical)

　　　　　　　　 = 4.5mS max. at room temperature

　　　　　　　　 = 4.0mS max. at 400℃

The transistors are active up to 400℃ and as good as to assemble small signalamplifiers working at,as high temperature as 400℃ environments.