RF performance of high transconductance and high-channel-mobility surface-channel polychristalline diamond metal-insulator-semiconductor field-effect transistors

The RF device potential of surface-channel polycrystalline diamond metal-insulator-semiconductor field-effect transistors (MISFETs) is demonstrated for the first time. Utilizing a self-aligned gate field-effect transistor (FET) fabrication process, effective transconductance of 70 mS/mm is realized at 0.7 µm gate length. This FET also shows high fT and fmax of 2.7 and 3.8 GHz, respectively. However, the breakdown voltage and fmax/fT ratio are lower than those for the homoepitaxial layer because of the parasitic capacitance at the grain boundaries in the drain region. Because of the fluctuation of channel mobility, the fluctuation of gm and fT is observed. In order to realize high-power operation at high frequency, the fabrication of the FET on a single grain to reduce the parasitic capacitance is required.