Mechanisms of instability retention for ferroelectric field effect transistors with HfZrO2gate stack scaling down

Abstract

Instability threshold voltage (VT) with retention loss of read-after-write is a critical issue with fundamental physics for ferroelectric field effect transistors (FeFETs) scaling down under high-speed operation. The mechanisms including charge trapping and depolarization field (Edep) are discovered and related to surface potential and coercive field (EC). The trapped charge can be effectively detrapped by opposite polarity stimulation and validated by technology computer-aided design modeling. In addition, the Edep is revealed to be serious with ferroelectric HfZrO2 (FE-HZO) thin-down due to the unstable low-VT state at a gate voltage (VG) of 0 V. The tunable base voltage (Vbase) compensates the Edep-based polarization degradation. A stable low-VT read-after-write for a 5-nm-thick HZO FeFET is experimentally demonstrated by the opposite polarity detrapping scheme hybrid with a Vbase optimization simultaneously for a wide range of delay times from 10-7 to 102 s. This result provides the feasibility for scaling down FeFETs for nonvolatile memory applications in the future.