Understanding the origins of the intrinsic dead layer effect in nanocapacitors
Understanding the origins of the intrinsic dead layer effect in nanocapacitors
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DOI：
10.1103/physrevb.79.115412
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发表时间：
2008-12
影响因子：
3.7
通讯作者：
M. Majdoub;R. Maranganti;P. Sharma
中科院分区：
文献类型：
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作者：
M. Majdoub;R. Maranganti;P. Sharma
高介电常数电介质薄膜被认为是实现用于下一代储能和纳米电子应用的高电荷密度纳米电容器的理想候选者。然而，实验观察到的此类薄膜纳米电容器的电容比预期低一个数量级。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不清楚。基于最近发表的 SrRuO3/SrTiO3/SrRuO3 的从头计算工作以及我们对 Au/MgO/Au 和 Pt/MgO/Pt 纳米电容器的第一原理模拟获得的见解，我们构建了一个分析模型，该模型隔离了各种物理机制对固有死层的贡献。特别是，我们认为即使没有外部应变诱导器，应变梯度也会在非常薄的薄膜中自动出现，并且由于挠曲电耦合，应变梯度是死层效应的主要贡献者。我们的理论结果与现有的以及我们自己的从头计算相比较，表明包含挠曲电对于原子结果的定性协调是必要的。我们的结果还暗示了一些减轻死层效应的新疗法。
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.