体制造旋转MEMS侧壁面的高速纳米磨损研究

Nanoscale wear is a key factor preventing practicability and marketization of rotating MEMS. The existing theories of nanoscale wear do not apply to the rotating MEMS. One of the reasons lies on that the sliding velocity of rotating MEMS is 5-6 orders of magnitude larger than that of atomic force microscope and friction force microscope which are the main measuring instrument of nanoscale wear at present. The other reason is that the wear occurs on the sidewall, which has the special microtopography and damage induced by the fabrication process rather than on the polished surface. The present project is focused on the nanoscale wear on the sidewall of the bulk-fabricated rotating MEMS at high speed. To reflect the wear condition of rotating MEMS, a new off-chip test plan for the “high-speed” nanoscale wear on the sidewall and an atomic model of the sidewall considering the special microtopography and damage are proposed. Based on the research of wear forms and wear rule of the rotating MEMS, the micromechanism of nanoscale wear is investigated, and the related wear model is built. Then, the effects of velocity and load on the nanoscale wear properties and wear mechanism are investigated, and the wear map of nanoscale wear in a wide-range of sliding velocity is plotted. The quantitative relationship of wear properties to the microtopography and damage of the sidewall and the fabrication process are investigated, and the DRIE process is optimized. At last, some improve measures of wear properties of rotating MEMS are put forward. This research is beneficial to improving the capacity of design and manufacture the rotating MEMS, and to forming core competence of our country in this field.

纳米磨损是限制旋转MEMS实用化、市场化的关键因素之一。由于旋转MEMS的滑动速度比纳米磨损研究的主要仪器—原子力显微镜和摩擦力显微镜的典型速度高出5-6个数量级，加之磨损发生在具有特殊微观形貌和损伤的侧壁面，已有的纳米磨损理论不能完全适用于旋转MEMS。申请项目针对旋转MEMS的磨损工况，提出一种侧壁面“高速”纳米磨损的片外测试方案；建立考虑多尺度微观形貌和损伤的侧壁面分子动力学模型，融合实验和模拟，开展高速条件下典型体制造技术—DRIE（反应离子深刻蚀）加工的硅侧壁面的纳米磨损研究。在分析旋转MEMS磨损特性和磨损规律的基础上，查明纳米磨损的微观机理，建立磨损模型。进一步研究滑动速度、载荷对磨损性能和磨损机理的影响规律及转变机制，绘制大速度跨度内硅纳米磨损的磨损图；建立DRIE工艺参数—侧壁面形貌和损伤—磨损性能之间的定量关系，优化DRIE工艺，提出改善旋转MEMS纳米磨损性能的措施。

纳米磨损是限制旋转MEMS实用化、市场化的关键因素之一。由于旋转MEMS的滑动速度比纳米磨损研究的主要仪器—原子力显微镜和摩擦力显微镜的典型速度高出5-6个数量级，加之磨损发生在具有特殊微观形貌和损伤的侧壁面，已有的纳米磨损理论不能完全适用于旋转MEMS。本项目采用分子动力学模拟和实验研究相结合的方法，开展了高速条件下硅侧面的磨损和硅的基础纳米力学行为研究。研究工作首先研究了纳米尺寸下单晶硅的力学行为和塑性变形机制；分析了单晶硅纳米力学行为的各向异性；从原子尺度上揭示了单晶硅高压相变和位错驱动的塑性变形机制和发生条件；阐明了压头尺寸依赖的弹塑性转变及其机理。揭示了纳米硅纳米压痕中多个pop-in行为的高压相变和挤出机理。进而研究了硅纳米尺寸下的摩擦磨损行为；揭示了粗糙的硅侧壁面摩擦行为和摩擦法则以及硅侧壁面的磨损机制；发现了侧壁面粗糙所致非线性到线性摩擦法的转变；分析了单晶硅纳米磨损所致单晶硅的塑性变形和损伤机制；阐明了磨料尺寸依赖的塑性变形和损伤机制转变，即小尺寸磨料促进高压相变的发生，大尺寸磨料导致位错缺陷的形成。当磨料的尺寸小于某一临界值，将会发生无缺陷的磨损，磨损过程将会由高压相变主导。