For the popular systems with carriers up to 2 GHz (cellular radio, satellite communication, digital audio broadcasting), we are not close to the fundamental limits for the bipolar silicon RF power devices for the high-output power parts. As the volume applications move into higher frequency bands in the 2 to 3 GHz range, the devices will continue to evolve by utilizing the continuing advancements in process technology, careful optimization of layouts and parasitics.

By adding some germanium into the base of the silicon bipolar transistor, the high-frequency characteristics can be improved. The technique is being introduced for commercial HF-ICs [6], and recently, results for pulsed high-voltage RF-Power devices with SiGe bases have been reported [7].

The most promising near-future device is the LDMOS [8], a lateral DMOS structure, which has great expectations with regards to increased gain, improved linearity and even better price/performance because of simpler packaging and less need for internal matching.

Gallium arsenide (GaAs) FETs and HBTs are not so common for high-voltage, high-power applications because of the GaAs material s poor thermal conductivity. There are commercial GaAs FETs on the market for these applications at lower voltages, but they cannot compete with the price/performance and are not widely used in volume applications.

Silicon carbide (SiC) for high-voltage RF Power is currently under investigation, with some promising results [9]. The unique properties of SiC are high electric breakdown field (4E6 V/cm), high saturated electron drift velocity (2E7 cm/s) and high thermal conductivity (4.9 W/cmK). At high voltages,...