Silicon carbide for microwave power applications

Microwave power emission has entered into the citizen's daily life, pushing towards ever increasing availability and decreasing prices for both personal terminal and base station equipment. By lifting threshold limits in operating temperatures, power density and impedance matching capabilities, SIC is expected to bring a technological breakthrough in the RF and microwave high power amplification area. Competitors to SiC could be diamond or III-N materials. However, diamond or BN technologies are far from maturity. III-N materials deposited on sapphire have shown promising small signal results but a thermally conductive substrate will be needed for high power devices and the most obvious candidate is SiC. Preferred device structures on SIC will probably be MOSFET and HBT. Presently, the MOS interface still suffers from very poor channel mobility and HBT is only emerging. Therefore, the only published results today refer to Static Induction Transistors (SIT), JFETs or MESFETs. Westinghouse SIT microwave amplification results in the UHF (more than 1 kW at 600 MHz) and in the S-band (36 W pulse at 3 GHz) are impressive. On the MESFET side, encouraging power results in the (2-4 W) range have been obtained at Westinghouse, Cree/Motorola, and Thomson, although only Westinghouse has been successful yet in using semi-insulating substrates. (C) 1997 Elsevier Science S.A.