ZrO₂ Ferroelectric Field-Effect Transistors Enabled by the Switchable Oxygen Vacancy Dipoles

This paper investigates the impacts of post-rapid thermal anneal (RTA) and thickness of ZrO₂ on the polarization P and electrical characteristics of TaN/ZrO₂/Ge capacitors and FeFETs, respectively. After the RTA ranging from 350 to 500 °C, TaN/ZrO₂/Ge capacitors with 2.5 and 4 nm-thick amorphous ZrO₂ film exhibit the stable P. It is proposed that the ferroelectric behavior originates from the migration of the voltage-driven dipoles formed by the oxygen vacancies and negative charges. FeFETs with 2.5 nm, 4 nm, and 9 nm ZrO₂ demonstrate the decent memory window (MW) with 100 ns program/erase pulses. A 4-nm-thick ZrO₂ FeFET has significantly improved fatigue and retention characteristics compared to devices with 2.5 nm and 9 nm ZrO₂. The retention performance of the ZrO₂ FeFET can be improved with the increase of the RTA temperature. An MW of ~ 0.46 V is extrapolated to be maintained over 10 years for the device with 4 nm ZrO₂.