双轴预应力和元素掺杂对ZnO压电电子学效应的调控及其联合作用

Piezotronics is a kind of electromechanical coupling effect that the conductivity of semiconductor can be modulated by piezoelectric charges. It has an attractive prospect in the applications on the force-electron modulating and strain sensing. The further enhancement of the strain sensitivity and the electronic process compatibility are the key problems to the practice application of piezotronics. In this research proposal, we plan to solve these problems via an integrated strategy. The 2D textured ZnO film is to be used instead of 1D ZnO nanowires in order to improve the electronic process compatibility and the flexibility of the stress loading. Then, the biaxial interface pre-stress and elements doping are considered for enhancing the pizeotronics effect of the ZnO film. Biaxial pre-stress can be used to modulate the initial state of the strain at Schottky interface, thus to change the strain sensitivity. By the study on the strain transfer mechanism along the interface and thickness of the ZnO film and the study on the force-electron modulating mechanism, an optimized method of pre-stressing will be obtained for improving the piezotronics effect. Meanwhile, for the ZnO material itself, elements doping is going to be used for modulating the conductivity and piezoelectricity. The influence mechanism on the property of force-electron modulation by doping will be studied intensively. The study results will be helpful to us for searching an optimized method to enhance the piezotronics effect by modified the property of the material itself. At last, the biaxial pre-stressing and doping will be combined for further improving the piezotronics of the devices, and the integral effect will be evaluated finally. These research will be helpful for further understanding the modulation mechanism of piezotronics and will also offer a series of solutions for improving the modulation effect of piezotronics.

在同时具有压电和半导体特性的材料中，利用压电电荷来调节半导体结区载流子输运的力电耦合效应(压电电子学效应)，在电子器件性能的力调控优化及力电传感方面有着诱人的应用前景。本项目拟从材料内部和界面两方面考虑，研究ZnO薄膜压电性、导电性和界面应力形式对压电半导体耦合效应的作用机理。以织构膜替代纳米线，提升微电子工艺兼容性和应力加载灵活性。在肖特基界面预置双轴应力来调节ZnO的初始状态，对比研究单、双轴应力作用下的空间应变传递机制及力电调控机理。通过元素掺杂来调节ZnO的导电性和压电性，研究导电性和压电性对力电耦合效应的作用本质与调控机理。最后研究双轴应力和掺杂的联合调控，研制出具有高灵敏度和空间分辨率的面内应变传感阵列器件。该项目研究将有助于更深入的理解压电电荷对半导体导电性的调控本质，为提升压电半导体耦合调控效果提供综合的优化方案。

为提升压电电子学效应，本项目通过锂离子掺杂ZnO的方式，降低了半导体的载流子浓度，从而降低其对压电势的屏蔽效应。研究以ZnO 材料为研究载体，使用二维织构薄膜替代一维纳米线；织构薄膜在界面应力作用下的变形机制、压电极化特点，及其对压电电子学效应的调制；研究元素掺杂对ZnO 薄膜的压电性和导电性的调节，和掺杂薄膜的压电电子学效应。研究掺杂和应力对压电电子学效应的联合调控作用和基于联合调控作用的面内微应变分布成像传感。针对微区应变测量问题，采用接触式的测量形式，基于新型应变传感机理——压电电子学效应，和优化的压电半导体传感材料——掺杂氧化锌，借助微加工技术在国际上首次研制出了体积更小的微应变传感单元，并在此基础之上制作了具有高空间分辨率的传感阵列器件。同时建立了相应的应变电信号采集方法与分析系统。在12×12mm2的面积上，总共布置了40×40个单元点，其空间分辨率为0.3mm（76 dpi），是目前国际上用于接触式的面内应变传感器中空间分辨率最高的器件。研究评估并证明了薄膜单元的压电电子学效应，分析结果表明当应变量达到0.5%以上时，器件的灵敏度（gauge factor）可以达到199以上。这个数值为商用应变片灵敏度的50倍。压电电子学效应将高灵敏度与微纳尺寸集成于同一个器件之中，这种优势使得高分辨率的应变成像称为可能。此外，薄膜结构比纳米线具有更好的微电子工艺兼容性，其电阻的各向异性还可以尽可能的避免串扰，从而可以使传感单元共享同一连续薄膜。这大大简化了甚至省略光刻步骤，使得磁控溅射ZnO半导体薄膜可以被制备的更厚以利于利用面内应变来调节顶底电极的肖特基势垒，达到提升灵敏度的目的。