ALD Oxidant as A Tuning Knob for Memory Window Expansion in Ferroelectric FETs for Vertical NAND Applications

TL;DR

This study shows that the choice of ALD oxidant, H2O or O3, significantly influences the memory window size and retention in ferroelectric FETs, providing a process-level tuning method for vertical NAND applications.

Contribution

It introduces oxidant selection as a novel process parameter to optimize memory window expansion and retention in ferroelectric FETs for NAND technology.

Findings

H2O-grown Al2O3 yields larger MW (7-8 V) than O3 (4 V).

H2O increases interlayer leakage, affecting retention.

Tunnel dielectric stacks maintain retention despite larger MW.

Abstract

Dielectric inserts are widely used to expand the memory window (MW) in ferroelectric FETs (FeFETs) for vertical NAND applications, with prior efforts focused primarily on material selection and stack positioning. Here, we demonstrate that the ALD oxidant used for the Al2O3 interlayer serves as a process-level tuning knob for MW engineering. H2O-grown Al2O3 yields a significantly larger MW (7-8 V) compared to O3 (4 V) for both gate-injection (12/3) and tunnel dielectric (8/3/8) configurations. While the tunnel dielectric (8/3/8) stack maintains robust retention up to 1e4s at 125C despite the larger MW, the gate-injection (12/3) configuration exhibits pronounced retention degradation for the H2O case. The enhanced MW is attributed to higher interlayer leakage associated with H2O-based ALD. These results establish oxidant choice as a key process parameter for co-optimizing MW and retention in ferroelectric NAND technologies.