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Ever since Bell Lab physicists Shockley, Bardeen and Brattain invented the transistor, this little solid state device has been constantly evolving; leveraging the advantages of different semiconductor and process technologies and addressing an increasing number of applications once reserved for tubes. Sixty-plus years later — driven by a number of promising commercial and defense-related markets — transistors (and MMICs) specifically targeting high power applications in the RF and microwave frequency range continue to be the focus of sizable research and development.

Among the changing landscape of RF/microwave semiconductor developments, devices with material properties that can sustain high electric breakdown are of particular interest. To understand the state of the high power transistor market, we spoke to a number of leading vendors. Our discussion was mostly concerned with devices that could produce in excess of 30 W at UHF/VHF frequencies and above (up to X-band). These are the high-power transistors required for avionics, radar, EW and wireless infrastructure applications. Although these devices are also found in medical equipment, those applications will not be part of our focus in this article. The following is a summary of our correspondence.

High Power Transistor Technologies and Applications

Within the last six months alone, the Journal has published over a dozen papers on Laterally Diffused MOS (LDMOS), Gallium Nitride (GaN), Silicon Carbide (SiC) and High-Voltage Vertical FETs (HVVFET). The principle market segments for high-power, high-frequency transistors are wireless infrastructure (3G, 3G+, WiMAX/LTE base stations and backhaul), defense and military applications (radar, jamming, counter-measures, guided weapons, etc.) and broadcast and communication satellites (SatCom). The factors that will decide whether a technology dominates a given application include performance (linearity, efficiency), reliability (ruggedness and thermal considerations), size, cost and legacy.

Figure 1 maps the various high-power semiconductor technologies relative to their operating frequencies and available output power. With an understanding of the power and frequency requirements for a given application, this graph provides a rough guide to the leading technologies today. Implicit in this representation are regions where one technology overlaps another due to its cost advantage. This cost can be related to higher production costs (complexity, less mature processes or lower volume production all drive up costs) as well as replacement costs (a technology missed the critical time-to-market). As process technology advances and new standards (i.e. 4G) provide new opportunities to enter a market, technology dominance in any particular region is subject to change. These factors will be discussed later in this article.