RF performance of surface channel diamond FETs with sub-micron gate length

Abstract

Diamond hydrogen-induced surface channel field effect transistors (FETs) were fabricated with gate lengths down to 0.2 μm in part using electron beam lithography. Down-scaling of the gate-length resulted in both improved DC- and RF characteristics, especially for a 0.2-μm gate length in a maximum output current of IDmax=360 mA/mm with a peak transconductance of 148 mS/mm. The optimum cut-off frequencies were fT=11.5 GHz, fmax(MAG)=31.7 GHz and fmax(U)=40.2 GHz. A maximum drain voltage of 68 V was obtained before pattern-related destructive breakdown occurred. This allows estimation of the RF power handling capability to above 3.0 W/mm. The data are the highest reported for diamond FETs. Scaling of the device parameters with gate length allows to estimate a velocity-limited maximum output current to 750 mA/mm and an fT above 20 GHz at 0.1-μm gate length. At high drive, current drift and current compression is observed in the quasi-DC output characteristics as well as in first microwave large signal measurements. These instabilities seem at present to be the main hurdle of hydrogen-induced surface channel FETs in high power microwave applications.