Numerical Investigation of Laterally Downscaled Hydrogen-Terminated Diamond FETs

Hydrogen-terminated diamond (H-diamond) field-effect transistors (FETs) have been the mainstream structure of diamond microwave devices. In this article, the direct current performance and cutoff frequency (fT) of H-diamond FETs with the gate length (LG) downscal-ing from 2 mu m to 50 nm are investigated by 2-D device simulation. For our central-gated device with a 6-nm-thick Al2O3 gate dielectric, the transition point of LG from the long-channel behavior to the short-channel one is found to be about 200 nm. Though notable short-channel effects appear for LG <= 200 nm such as the negative shift of the threshold voltage and the increase of the drain-induced barrier lowering, the knee voltage at a given gate voltage stays almost constant for all the considered gate length range, which is unfavorable for a small-size device with lower operating voltage. It is found the effective velocity in the channel of short-channel H-diamond FETs at the drain voltage of 7 V is less than half of the saturation velocity. The fT versus VGS relation is quite different in the short channel case and long channel case, and it is analyzed in comparison with the gm versus VGS relation. lent their saturation and [2], activation the two-dimensional est (H-diamond) tors microwave achieved a tance [8], at