Suppression of Short Channel Effects in Hydrogen- Terminated Diamond MISFETs Using an Al2 O3 / HfO2 Stacked Passivation Layer

The short channel effects (SCEs) are mainly caused by the generated insufficient depletion region under the gate, which can severely reduce the reliability of devices. In this paper, the effects are analyzed by the proposed metal-insulator-semiconductor (MIS) capacitance model and can be suppressed by the applied high-k upper passivation layer (UPL). To verify the proposed model, the hydrogen-terminated diamond MIS field-effect transistors (C-H diamond MISFETs) with a 40-/100-$\mathrm{nm} \,\mathrm{Al}_{2} \mathrm{O}_{3} / \mathrm{HfO}_{2}$ stacked passivation layer were fabricated. Benefiting from the 100 -nm-thick HfO 2 UPL, the SCEs are suppressed and a high on/off ratio of $\sim 1 \times 10^{9}$ is achieved in the C-H diamond MISFET even a low aspect ratio of 7.5 for the first time. A cut-off frequency (${f}_{\mathrm{T}})$ of 6.1GHz and maximum oscillation frequency $\left(f_{\max }\right.$) of 11.1GHz were also obtained. The above results indicate that C-H diamond MISFETs with a high-k UPL in this work are promising in the high reliability and high frequency applications.