Unstable Retention Behavior in MIFIS FEFET: Accurate Analysis of the Origin by Absolute Polarization Measurement

TL;DR

This paper investigates the unstable retention behavior in MIFIS FEFET devices, identifying the fundamental causes through polarization measurements and proposing engineering solutions for improved stability.

Contribution

It provides the first detailed analysis of retention instability in MIFIS FEFET, revealing its origin and suggesting methods to enhance retention stability.

Findings

Unstable retention observed especially after erase.

Absolute polarization measurement confirms the retention instability origin.

Proposed charge compensation model for improved stability.

Abstract

Ferroelectric field-effect-transistor (FEFET) has emerged as a scalable solution for 3D NAND and embedded flash (eFlash), with recent progress in achieving large memory window (MW) using metal-insulator-ferroelectric-insulator-semiconductor (MIFIS) gate stacks. Although the physical origin of the large MW in the MIFIS stack has already been discussed, its retention characteristics have not been explored yet. Here, we demonstrate MIFIS FEFET with a maximum MW of 9.7 V, and show that MIFIS FEFET has unstable retention characteristics, especially after erase. We discover the origin of the unstable retention characteristics and prove our hypothesis with absolute polarization measurement and different operation modes, showing that the unstable retention characteristics is a fundamental issue. Based on the understanding, we discuss a novel charge compensation model and promising engineering methodologies to achieve stable retention in MIFIS FEFET.