In-depth Analysis of the Hafnia Ferroelectrics as a Key Enabler for Low Voltage & QLC 3D VNAND Beyond 1K Layers: Experimental Demonstration and Modeling

In this work, we experimentally demonstrate a remarkable performance improvement, boosted by the interaction of charge trapping & ferroelectric (FE) switching effects in metal-band engineered gate interlayer (BE-G.IL)- FE-channel interlayer (Ch.IL)-Si (MIFIS) FeFET. The MIFIS with BE-G.IL (BE-MIFIS) facilitates the maximized ‘positive feedback’ (Posi. FB.) of dual effects, leading to low operation voltage (VPGM/VERS: +17/-15 V), a wide memory window (MW: 10.5 V) and negligible disturb at a biased voltage of 9 V. Furthermore, our proposed model verifies that the performance enhancement of the BE-MIFIS FeFET is attributed to the intensified posi. FB. This work proves that the hafnia FE can play as a key enabler in extending the technology development of 3D VNAND, which is currently approaching a state of stagnation.

Introduction

In order to increase the number of stacks at the same height, 3D VNAND flash has been evolved by scaling WL and space [1]. However, current 3D VNAND is approaching the limits of density enhancement due to issues including (BV) of space between (btw.) word lines, caused by its high operation voltage +20/-25 V) [2] (Fig. 1). Therefore, to achieve 3D VNAND beyond 1K layers, it is urgent to develop low- & large-MW 3D VNAND cells. Accordingly, Yoon et al. reported MIFS FeFET with a wide MW of 10.54 V [3], while Lim et al. presented MIFIS FeFET with analytic model of MW (Fig. 2(a)) [4]. However, previous studies didn't satisfy both large-MW and negligible READ/P ASS disturb. In addition, there is no report regarding the hidden positive interaction btw. charge trapping & FE switching. Fig. 1.

The current issue of 3D V-NAND: space breakdown due to high , restricting further vertical stacking.

Fig. 2.

(a) MW model and (b) operation mechanism for BE-MIFIS FeFET. (c) Wide MW & low are achieved by (d-e) positive feedback.