Diamond devices for RF applications

Diamond possesses a combination of ecepctional physical properties such as high breakdown field and carrier mobility, and therefore is expected to be high-efficient high-power devices. We solved a carrier doping by using nitrogen dioxide (NO₂). In addition, we greatly improved stability by using aluminum oxide (Al₂O₃) layer. These two break-through technologies enable us to thermal-stability high-performance diamond field-effect transistors (FETs). The diamond FET showed high maximum I_DS of -1.35 A/mm, cut-off frequencies, f_T of 35 GHz and f_MAX of 70 GHz and RF output power density of 2 W/mm at 1 GHz. The prospects and challenges of diamond RF power transistors will be also discussed.