HZO thickness-dependent charge loss mechanisms in HfO2-based MIFIS FeFETs

Abstract

Hafnium-based ferroelectric field-effect transistors (FeFETs) with metal/gate interlayer/ferroelectric/channel interlayer/silicon (MIFIS) gate stacks are a promising candidate for high-density 3D NAND. However, the severe retention degradation hinders their application, and the dominant mechanism remains unclear. In this work, we investigated the retention characteristics of MFIS and MIFIS FeFETs with the same HZO thicknesses at 25, 55, and 85 °C to distinguish the retention degradation behaviors introduced specifically by the MIFIS gate stack. The two devices show distinct degradation: MFIS has stable retention characteristics dominated by program-state depolarization, whereas MIFIS suffers severe degradation driven by erase-state threshold voltage decay and exhibits strong thermal activation. For MIFIS, activation energy analysis further reveals that HZO thickness rules the degradation mechanism: thin HZO devices are consistent with thermally activated charge detrapping and charge loss toward both the gate side and channel side, while thick HZO devices are consistent with a trap-assisted-tunneling mechanism and charge loss toward the gate side. This work clarifies the retention degradation physics and offers HZO thickness design guidelines for future 3D Fe-NAND designs.