Diamond RF Transistor Technology with ft=41GHz and fmax=44GHz
Initial results for diamond RF transistor technology are presented. Field Effect Transistors (FETs) were fabricated with gate lengths (Lg) ranging from 4µm to 50nm. The FETs have total gate width (Wg) of 40 or 120µm. Lg=100 nm devices show DC drain current ID=600 mA/mm (VGS=-3V, VDS=-10V) with transconductance gm=140mS/mm (VGS=-0.3V, VDS=-4V). Small signal S-parameters were measured to evaluate the high-frequency performance of the diamond FETs. Extrinsic ft and fmax were measured to be 41GHz and 44GHz, respectively. Load pull measurements were used to characterize the devices under large signal excitation. The Lg=200nm, Wg=40µm device, tested at 2GHz, shows peak efficiency of 30.5% at VDS=-5V. Both peak gain of 19.5dB and peak output power density of 0.66W/mm were achieved at VDS=-30V. Biasing the device at VDS=-15V provides a trade off point for the large signal parameters — gain of ~15dB, efficiency of ~20%, and output power of ~0.5W/mm.