理解纳米电容器中固有死层效应的起源
Understanding the origins of the intrinsic dead-layer effect in nanocapacitors
摘要：
高介电常数纳米电容器的薄膜被认为是实现用于下一代能量存储和纳米电子应用的高电荷密度纳米电容器的理想候选物。然而，实验观察到的这种薄膜纳米电容器的电容比预期的低一个数量级。电容的这种急剧下降归因于所谓的死层-金属-电介质界面处的低介电常数层与高介电常数电介质串联。死亡层的确切性质及其起源的原因仍然有些不清楚。基于最近发表的SrRuO3/SrTiO3/SrRuO3从头算工作和我们的第一原理模拟Au/MgO/Au和Pt/MgO/Pt纳米电容器的见解，我们构建了一个分析模型，隔离各种物理机制的贡献的内在死层。特别是我们认为，应变梯度自动出现在非常薄膜，即使在没有外部应变诱导剂，由于flexoelectric耦合，是占主导地位的贡献者的死层效应。我们的理论结果比较以及与现有的，以及我们自己的从头计算，并建议列入flexoelectricity是必要的原子结果的定性和解。我们的研究结果还暗示了一些新的补救措施，以减轻死层效应。
英文摘要：
Thin films of high-permittivity dielectrics are considered ideal candidates for realizing high charge density nanosized capacitors for use in next generation energy storage and nanoelectronic applications. The experimentally observed capacitance of such film nanocapacitors is, however, an order of magnitude lower than expected. This dramatic drop in capacitance is attributed to the so called dead layer - a low-permittivity layer at the metal-dielectric interface in series with the high-permittivity dielectric. The exact nature of the dead layer and the reasons for its origin still remain somewhat unclear. Based on insights gained from recently published ab initio work on SrRuO3/SrTiO3/SrRuO3 and our first principle simulations on Au/MgO/Au and Pt/MgO/Pt nanocapacitors, we construct an analytical model that isolates the contributions of various physical mechanisms to the intrinsic dead layer. In particular we argue that strain-gradients automatically arise in very thin films even in absence of external strain inducers and, due to flexoelectric coupling, are dominant contributors to the dead layer effect. Our theoretical results compare well with existing as well as our own ab initio calculations and suggest that inclusion of flexoelectricity is necessary for qualitative reconciliation of atomistic results. Our results also hint at some novel remedies for mitigating the dead layer effect.
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