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Mesoscopic models for the mechanically modulated electrical conductivity of piezoelectric semiconductors

压电半导体机械调制电导率的介观模型

基本信息

批准号：
317661385
负责人：
Privatdozent Dr. Erion Gjonaj
金额：
--
依托单位：
Institut für Teilchenbeschleunigung und Elektromagnetische Felder
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2016
资助国家：
德国
起止时间：
2015-12-31 至 2020-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/317661385?language=en
关键词：
Mesoscopic models mechanically modulated electrical

项目摘要

The piezoelectric polarisation induced by internal or applied mechanical stresses in oxide ceramic semiconductors is known to modify the potential barriers at grain boundaries and therefore the electrical conductivity across these boundaries. Besides this modification in the microscopic scale, the effective electrical conductivity of polycrystalline bulk material depends also on the microstructural disorder associated with stochastic variations in grain size, grain boundary properties, crystallographic orientation and the related stress field distribution. The effect of microstructural disorder is manifested in the current flow properties, in particular, in the current filamentation phenomenon consisting in the concentration of current density along a few low resistivity paths within the material. Thus, the effective conductivity of polycrystalline materials depends not only on the piezoelectric grain boundary modification but also on the mesoscopic scale current distribution within the material for different applied voltages and mechanical stress conditions. Both, microscopic and mesoscopic effects are closely connected and should be investigated as coupled phenomena within a common research platform.The project is dedicated to the numerical modeling and simulation of the mechanically modulated electrical conductivity of ZnO. Microscopic-scale charge transport models for bicrystals and multigrain arrangements taking into account drift-diffusion, thermionic emission at grain boundaries as well as the direct and inverse piezoelectric effects will be developed. These models will be incorporated into 3D mechanically informed mesoscopic current flow simulations for polycrystalline ZnO using accurate mechanical stress distributions and taking into account stochastic microstructural variations. The microscopic-scale approach will provide insight into the range of validity of mesoscopic current simulations based on equivalent network and finite element models. The proposed models will be employed in the simulation based electromechanical characterization of ZnO varistors. Furthermore, textured ZnO films with intentionally oriented polarity will be investigated. All proposed investigations will be performed in close cooperation with our project partners.

已知氧化物陶瓷半导体中由内部或施加的机械应力引起的压电极化可以改变晶界的势垒，从而改变这些边界上的电导率。除了微观尺度上的这种改变外，多晶块状材料的有效导电性还取决于与晶粒尺寸、晶界性能、晶体取向和相关应力场分布的随机变化相关的微观结构紊乱。微观结构紊乱的影响表现在电流的流动特性上，特别是在材料内部沿少数低电阻率路径的电流密度集中形成的电流丝化现象上。因此，在不同的外加电压和机械应力条件下，多晶材料的有效电导率不仅取决于压电晶界改性，还取决于材料内部的介观尺度电流分布。微观和介观效应密切相关，应在一个共同的研究平台内作为耦合现象进行研究。该项目致力于ZnO机械调制电导率的数值模拟和仿真。将建立考虑漂移扩散、晶界热离子发射以及压电效应的双晶和多晶排列的微观尺度电荷输运模型。利用精确的机械应力分布并考虑随机微观结构变化，这些模型将被纳入多晶ZnO的三维力学介观电流模拟中。微观尺度的方法将深入了解基于等效网络和有限元模型的介观电流模拟的有效性范围。所提出的模型将用于基于仿真的ZnO压敏电阻机电特性。此外，还将研究具有定向极性的ZnO织构膜。所有拟议的调查都将与我们的项目合作伙伴密切合作。