Diamond RF power transistors: Present status and challenges

Using the nitrogen dioxide (NO
₂
) adsorption and aluminum oxide (Al
₂
O
₃
) passivation technique, we have solved the thermal instability problem of hydrogen-terminated (H-terminated) 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.