Fabrication of High-Gain CMOS Inverter Based on Ambipolar WSe₂ Negative-Capacitance FETs With Ferroelectric HfZrAlO as Gate Dielectric

A back-gated negative-capacitance FET (NCFET) inverter is fabricated by using the new type of ferroelectric hafnium zirconium aluminum oxide (HZAO) as gate-stack and ambipolar tungsten selenide (WSe2) as a channel material. As a contact engineering of source/drain (S/D) electrodes, different metal electrodes are investigated to fabricate p- and n-type NCFETs, respectively. The measurements of electrical properties show that the most suitable S/D electrode metals are Pt for p-NCFET and Ti for n-NCFET. The WSe2 p- or n-NCFETs prepared using the ferroelectric HZAO thin film combined with Pt or Ti as S/D electrodes exhibit excellent electrical performance: subthreshold swing (SS) of p- or n-NCFET is 20–25 mV/dec or 25–30 mV/dec over three orders of drain current magnitude and on/off current ratio is (2.0–4.6) <tex-math notation="LaTeX">× 10⁶ </tex-math> or (1.1–2.6) <tex-math notation="LaTeX">× 10⁶ </tex-math> . Moreover, the inverter composed of n-NCFET and p-NCFET exhibits a quite high-voltage gain with a maximum gain over 50 at an operating voltage of 5 V. The main mechanisms are attributed to a faster switching speed of NCFETs than conventional FETs and the ambipolar conduction characteristic of WSe2 when contacting with different work-function metals. Because of the WSe2's ambipolar behavior, the process of fabricating inverter becomes much simpler than other 2-D materials.