By forming a highly stable Al2O3 gate oxide on a C-H bonded channel of diamond, high-temperature, and high-voltage metal-oxide-semiconductor field-effect transistor (MOSFET) has been realized. From room temperature to 400°C (673K), the variation of maximum drain-current is within 30% at a given gate bias. The maximum breakdown voltage (VB) of the MOSFET without a field plate is 600V at a gate-drain distance (LGD) of 7. We fabricated some MOSFETs for which VB/LGD>100V/These values are comparable to those of lateral SiC or GaN FETs. The Al2O3 was deposited on the C-H surface by atomic layer deposition (ALD) at 450°C using H2O as an oxidant. The ALD at relatively high temperature results in stable p-type conduction and FET operation at 400°C in vacuum. The drain current density and transconductance normalized by the gate width are almost constant from room temperature to 400°C in vacuum and are about 10 times higher than those of boron-doped diamond FETs.
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