Performance of normally-off hydrogen-terminated diamond MISFETs with high-κ Zr-Si-N/Al₂O₃ bilayer dielectrics

Normally-off hydrogen-terminated diamond metal–insulator-semiconductor field-effect transistors (MISFETs) using Zr-Si-N/Al₂O₃ bilayer dielectrics have been investigated. Zr-Si-N and Al₂O₃ are deposited by radio frequency sputtering and atomic layer deposition techniques respectively with gate leakage current density of MISFET lower than 1.12 × 10⁻⁶ A⋅cm⁻², where the gate voltage sweeps from 10 to −9 V. Based on the capacitance–voltage characteristics, the fixed charge density is low which was calculated to be 2 × 10¹¹ cm⁻². The MISFET shows normally-off characteristics which could be attributed to the positive fixed charge in Zr-Si-N/Al₂O₃, the work function difference between Al and H-diamond, and electron compensation by ionized nitrogen impurities in diamond. The maximum drain-source current, threshold voltage, and maximum transconductance of the MISFET are −29.3 mA⋅mm⁻¹, −0.96 V, and 3.12 mS⋅mm⁻¹, respectively.