Small Subthreshold Swing Diamond Field Effect Transistors With SnO₂ Gate Dielectric

A small subthreshold swing (SS) hydrogen-terminated diamond field-effect transistor is realized by using a wide bandgap material (SnO ₂ ). Results showed an SS of 106.4 mV/dec, which should be ascribed to the low interface state density (1.05 $\times10$ ¹² cm $^{-2}\cdot $ eV ⁻¹ ) between SnO ₂ and diamond. The fixed charge density and trapped charge density are $1.1\times10$ ¹² cm ⁻² and $8.6\times10$ ¹¹ cm ⁻² , respectively. Leakage current between source and gate is less than $2.1\times10$ ⁻⁸ A at gate voltages from −5.0 to 1.0 V and the breakdown voltage is measured to be −180 V. In addition, the devices exhibit normally- OFF characteristics, whose threshold voltage and maximum drain current density are −0.12 V and −21.6 mA/mm with 4- $\mu \text{m}$ gate at ${V}_{GS} = -3$ V. The ON/OFF ratio is around 10 ⁷ and the maximum effective mobility is extracted to be 165 cm ² /(Vs). This work indicates that SnO ₂ dielectric could form low interface state density with hydrogen-terminated diamond surface and it also provides a simple method to realize normally- OFF devices.