Power MOSFET's for medium-wave and short-wave transmitters

This paper describes design and performance of a high-frequency power MOST used for switching-mode power amplifiers in the medium-wave (500 kHz to 1.5 MHz) or short-wave (1.5 MHz to 30 MHz) transmitters whose output power is in the vicinity of 1 kW. To obtain the drain-source voltages greater than 200 V with on-resistance remaining approximately 1 Ω, the offset gate length and field plate length of the high-frequency power MOST are optimized as well as offset gate layer concentration. Employing the molybdenum gate fabricated by RF diode sputter, the MOST operates at high speed with turn-on and turn-off times of 22 and 25 ns, respectively. A high-temperature operation test was performed to assure the stability and reliability of the device. The test results indicate that phosphosilicate glass polarization affects the device reliability only when offset gate layer concentration is much lower than the optimized value.