Oxide Channel Ferroelectric NAND Device with Source-Tied Covering Metal Structure: Wide Memory Window (14.3 V), Reliable Retention (> 10 Years) and Disturbance Immunity $(\Delta \mathrm{V}_{\text{th}}\leq 0.1\mathrm{V})$ for QLC Operation

We show an oxide-channel (Ox. Ch.) based gate-injection type ferroelectric NAND (FeNAND) device with source-tied covering metal (SCM) and control dielectric (C.DE). The SCM and C.DE play crucial roles in the performance enhancement of FeNAND cells. (i) The proposed structure addresses the channel depletion issue of Ox.Ch. by utilizing accumulated holes in the grounded SCM during ERS. This increases the electric field across the gate interlayer and FE layer, thereby boosting ERS efficiency. (ii) The read operation of erase states distributes a significant portion of the read voltage to C.DE, intensifying the $\mathrm{V}_{\text{th},\text{ERS}}$. These effects result in a wide memory window (MW~14.3V). Furthermore, the introduction of a $\text{Si}_{3}\mathrm{N}_{4}$ deep trap-level layer and careful gate stack design led to superior retention (MW:11.5V after 10 years) and disturbance immunity ($\Delta \mathrm{V}_{\text{th}} < 0.1\mathrm{V}$ after $10^{5}$ disturb cycles). We also verify the roles of SCM and C.DE through analytical modeling. Lastly, the proposed structure is compatible with current 3D-NAND fabrication, offering equivalent channel hole pitch and density.

I. Introduction

Today, to develop 3D NAND beyond 1K layers, extensive research has focused on materials, structures, and fabrications for various cell components. Among these, the gate-injection type FeNAND cell featuring a metal-gate interlayer (G.IL)-FE-channel interlayer (Ch.IL)-Si (MIFIS) structure has attracted massive attention as a viable future NAND cell candidate [1] (Figs. 1(a) and 1(b)). It exhibits wide MW (>10V) and low PGM voltage (<17V) [2]. However, gate-injected interface trap charges between G.IL and FE are located at shallow trap levels, causing critical retention loss [3]. Also, applying a high- FE lowers but increases disturbance vulnerability [4].