Microwave performance of diamond surface-channel FETs

S-parameters measurements were carried out on diamond-based FET devices with a p-type channel induced by hydrogen surface termination extracting f
_T
and f
_max
for devices with gate lengths ranging from 5 μm to 0.2 μm. For the 0.2 μm gate length FET f
_T
=11.55 GHz and f
_max
(MAG)=33.3 GHz values were obtained. High f
_max
(MAG)/f
_T
ratios of above 2.5 were obtained for all devices. Further downscaling may result in an f
_T
above 20 GHz and in addition, an f
_max
(MAG) above 50 GHz.