Back-End-of-Line-Compatible Fin-Gate ZnO Ferroelectric Field-Effect Transistors

We report the back-end-of-line (BEOL)-compatible 3-D oxide semiconductor (OS) fin-gate ferroelectric field-effect transistors (Fe-FETs) featuring atomic layer deposition (ALD)-grown zinc oxide (ZnO) channel and Zr-doped HfO _{\text{2}} (HZO) ferroelectric dielectric. Both ZnO and HZO are able to conformally cover the fin-shaped tungsten (W) metal gate with uniform thickness on all surfaces. With the optimization of ALD for the growth of the ZnO channel film and extensive gate-stack engineering, our ZnO Fe-FETs show excellent electrical characteristics, including memory windows (MWs) of 1.9 and 1.5 V with the channel length ( \textit{L}_{\text{ch}} ) of 1 \mu m and 50 nm, respectively, the high endurance of 10 ^{\text{8}} cycles, long-term retention of more than ten years at room temperature, robust ON/OFF ratio of more than six orders, and good linearity of the multistate conductance characteristics. Together with the capability to suppress the device-to-device threshold voltage ( \textit{V}_{\text{th}} ) variation due to the unique fin-gate structure, our devices demonstrate tremendous potential for future ultrahigh-density 3-D integrated computing applications.