Tuning Breakdown-to-Coercive Field Ratio in Ultra-Thin Al1-xScxN Films via Reactive Nitrogen Atmosphere

TL;DR

This study demonstrates how adjusting nitrogen gas flow during sputtering can optimize the breakdown and coercive fields in ultra-thin Al1-xScxN films, enhancing their suitability for ferroelectric memory devices.

Contribution

It introduces a method to control defect density and improve the breakdown-to-coercive field ratio in ultra-thin AlScN films through nitrogen flow adjustment during deposition.

Findings

Optimal breakdown field of 12.47 MV/cm achieved.

Maximum EBD/EC ratio of 2.25 at 27.5 sccm nitrogen flow.

Device performance correlates with defect concentration control.

Abstract

Al1-xScxN has attracted significant interest due to its large remnant polarization and low processing temperature when compared to other ferroelectric material systems. However, device dielectric failure before ferroelectric switching remains a critical limitation for AlScN-based memory devices. With the continuing trend toward device miniaturization, expanding the operating window is essential for next-generation memory development. In this work, we optimized the breakdown field (EBD) and coercive field (EC) in ultra-thin Al1-xScxN films by controlling defect density via adjustment of nitrogen gas flow during sputter deposition. The characteristic breakdown field, EBD, was evaluated using Weibull statistics, yielding optimal characteristic breakdown fields of 12.47 MV/cm (EBD+) and -12.63 MV/cm (EBD-) for samples deposited under 27.5 sccm N2 flow. The minimum EC was achieved at a nitrogen flow of 25 sccm and increased for higher gas flows, a trend that is opposite to previous reports in much thicker films. The highest EBD over EC ratio of 2.25 occurred at 27.5 sccm, effectively expanding the operational window. Using a combination of X-ray diffraction and photoluminescence spectroscopy to study changes in crystal orientation and defects, device performance can be tuned by controlling the point defect concentration in the ultra-thin film via adjusting the sputtering N2 process gas flow rate.