Ranjan Alok, O'Shea Sean J, Bosman Michel, Raghavan Nagarajan, Pey Kin Leong
Engineering Product Development, Singapore University of Technology and Design, 8 Somapah Road, Singapore, 487 372.
Agency for Science Technology and Research, Institute of Materials Research and Engineering, 2 Fusionopolis Way, Singapore, 138 634.
ACS Appl Mater Interfaces. 2020 Dec 9;12(49):55000-55010. doi: 10.1021/acsami.0c17107. Epub 2020 Dec 1.
Hexagonal boron nitride (h-BN) has emerged as a promising 2D/layered dielectric owing to its successful integration with graphene and other 2D materials, although a coherent picture of the overall dielectric breakdown mechanism in h-BN is yet to emerge. Here, we have carried out a systematic study using conduction atomic force microscopy to provide insights into the process of defect generation and dielectric degradation in the progressive breakdown (PBD) and hard breakdown (HBD) stages in 2-5 nm thick chemical vapor deposition (CVD)-grown multilayer h-BN films. The PBD and HBD regimes show different behaviors. Under electrical stress in the PBD stage, defects are generated progressively in the h-BN, leading to a gradual reduction of the effective barrier resistance and continuous soft breakdowns (SBDs) of the dielectric material. Random telegraph noise nano-spectroscopy shows that low frequency noise becomes dominant after an SBD event due to the creation of additional defects around the percolation path. We also observe a wide variation in the current-voltage (-) breakdown plots in the PBD stage, giving rise to non-Weibull statistical distribution of the breakdown voltage. We attribute this observation to the significant thickness inhomogeneity in the CVD films. At HBD, h-BN materials are always physically removed from the film, leading to the formation of pits at the breakdown location. Interestingly, pit formation is also occasionally observed in the PBD stage under very low current compliances, suggesting that breakdown may proceed by a mixture of defect generation and material removal in h-BN CVD films.
六方氮化硼（h-BN）已成为一种很有前景的二维/层状电介质，这得益于它与石墨烯及其他二维材料的成功整合，尽管h-BN中整体介电击穿机制的连贯图景尚未形成。在此，我们使用传导原子力显微镜进行了一项系统研究，以深入了解2 - 5纳米厚的化学气相沉积（CVD）生长的多层h-BN薄膜在渐进击穿（PBD）和硬击穿（HBD）阶段的缺陷产生过程和介电降解情况。PBD和HBD状态表现出不同的行为。在PBD阶段的电应力作用下，h-BN中逐渐产生缺陷，导致有效势垒电阻逐渐降低，介电材料持续发生软击穿（SBD）。随机电报噪声纳米光谱表明，由于在渗流路径周围产生了额外缺陷，SBD事件后低频噪声占主导。我们还观察到PBD阶段电流-电压（I-V）击穿曲线存在很大差异，导致击穿电压呈现非威布尔统计分布。我们将这一观察结果归因于CVD薄膜中显著的厚度不均匀性。在HBD时，h-BN材料总是从薄膜上物理去除，导致在击穿位置形成凹坑。有趣的是，在非常低的电流依从性下，PBD阶段偶尔也会观察到凹坑形成，这表明h-BN CVD薄膜中的击穿可能是由缺陷产生和材料去除的混合过程导致的。
