Improved Performance of MoS2 Negative-Capacitance Transistors by Using Hf1-xAlxOy as Gate Dielectric Plus NH3-Plasma Treatment

A back-gate molybdenum disulfide (MoS2) negative-capacitance field-effect transistor (NCFET) based on a single-layer gate dielectric of Hf
$_{{1} -{x}}$
AlxOy is fabricated to simplify the gate-dielectric process and simultaneously increase its ferroelectricity, as well as facilitate scaling down of the device. The Al content and anneal temperature of the Hf
$_{{1} -{x}}$
AlxOy thin film are optimized to obtain excellent performance of devices. It is found that when the Al content is 10% (Hf0.9Al0.1Oy) and the anneal temperature is 700 °C, good electrical properties can be achieved: a subthreshold swing (SS) of 43.8 mV/dec ade, a switching ratio of
$2.50\times 10^{{7}}$
, and a hysteresis of 51.1 mV. Furthermore, a NH3 plasma is used to treat the surface of the Hf0.9Al0.1Oy thin film to reduce oxygen vacancies in it and thus enhance its ferroelectricity and simultaneously improve interfacial quality through smoothing the surface of the thin film, resulting in excellent device performance: a low SS of 32.5 mV/dec ade, a high switching ratio of
$3.79\times 10^{{7}}$
, and a small hysteresis of 28.7 mV.