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.