Native Oxynitride Layer-Assisted Leakage Current Suppression and Coercive Field Reduction in Nitride Ferroelectrics

A detailed understanding and control of the native oxynitride layer, that rapidly forms on the scandium aluminum nitride (ScAlN) surface upon air exposure, is critical for achieving high-performance, reliable nitride ferroelectric memristors. However, this layer is highly susceptible to damage in alkaline environments, such as those encountered during standard photolithography with developer solutions, which often leads to performance degradation. In this work, we propose and further demonstrate a poly(methyl methacrylate) (PMMA)-based surface protection strategy to preserve the native oxynitride layer throughout the fabrication process, highlighting its positive impact on nitride ferroelectricity. Material characterizations, including X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM), validate the effectiveness of this strategy in protecting the oxynitride layer. Electrical measurements reveal noticeable performance improvements, including a 6% reduction in coercive field (from 4.9 to 4.6 MV cm^–1) and a 68% decrease in leakage current, attributed to the preserved oxynitride layer. Additionally, the surface-protected devices achieve a record-high breakdown voltage to switching voltage (V_BD/V_SW) ratio of 1.92 among molecular beam epitaxy (MBE)-grown ScAlN memristors. These findings underscore the vital role of oxynitride protection in maintaining ferroelectric functionality and pave the way for integrating III-nitride-based ferroelectrics into scalable, high-performance memories and in-memory computing platforms.