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 (SnO₂). Results showed an SS of 106.4 mV/dec, which should be ascribed to the low interface state density (1.05 × 10¹² cm⁻²·eV⁻¹) between SnO₂ and diamond. The fixed charge density and trapped charge density are 1.1 × 10¹² cm⁻² and 8.6 × 10¹¹ cm⁻², respectively. Leakage current between source and gate is less than 2.1 × 10⁻⁸ 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-μm gate at V_GS = −3 V. The ON/OFF ratio is around 10⁷ and the maximum effective mobility is extracted to be 165 cm²/(Vs). This work indicates that SnO₂ dielectric could form low interface state density with hydrogen-terminated diamond surface and it also provides a simple method to realize normally-OFF devices.