Status of power transistors - Bipolar and field effect

Applications for bipolar transistors (BPT) at the high-frequency end of their range (a few GHz) in power amplification, and advantages and limitations of GaAs MESFETs are emphasized; life testing of transistor devices, gains through improved package design, and BPT improvements are discussed. High-power S-band 200 W radar modules and 5 GHz kW communication amplifiers using BPT are reported on the way. The ruggedness and uniformity of BPT have improved and prices remain low. Higher power densities at the transistor junction, improved heat sinks, and metallization techniques are noted. Minimized package parasitics, intra-package input/output impedance matching, and transistor cell combining are highlighted. The frequency range of MESFETs runs higher (to 15 GHz), but reproducibility is limited, and low breakdown voltages are a problem. Class-A and Class-B amplification with MESFETs is discussed.