【作者】 董云开；

【导师】 温诗铸；

【作者基本信息】 清华大学 ， 机械工程， 2007， 博士

【摘要】 在微机电系统(MEMS)中,由于尺寸效应和表面效应,微构件间的摩擦成为影响MEMS性能和可靠性的关键。通过微观表面形貌修饰来揭示与控制微构件的摩擦行为成为MEMS摩擦学设计的研究方向之一。本文在硅材料表面进行了微观形貌修饰,并在纳米到微米尺度下对其摩擦行为进行了实验研究和理论分析。由于现有的摩擦测试手段与MEMS实际工况相差甚远,作者研制了一台分辨率为8μN的微摩擦测试实验装置,可以控制不同的相对湿度,测量法向载荷为0.6-5mN范围内的球-面接触和面-面接触黏着力和摩擦力,论文利用该仪器研究了微形貌修饰硅表面的一系列摩擦特性。本文将构件微观形貌对摩擦行为的影响划分为两类,分别为接触区域内影响和接触区域外影响。通过不同形貌修饰表面在针-面、球-面和面-面接触下的干摩擦实验发现,在接触区域内影响摩擦力大小的形貌参数主要为粗糙度、平均峰顶曲率半径、相关长度和条纹方向,并且存在形貌修饰最优化可能。接触区域外的形貌主要影响摩擦的稳定性。本文建立了接触区域外形貌对摩擦影响的弹性棘轮模型,认为摩擦力不仅受斜率影响,而且与表面曲率半径有关。在纳米尺度研究中斜率对摩擦力的影响较大,在微米尺度研究中表面曲率半径的影响较大,并通过实验进行了验证。结合弹性棘轮模型建立了粘滑模型,认为在“粘”的过程中,测头是一边振动一边向前滑行,只是运动的速度很慢,这很好地解释了“爬滑现象(creep-slip)”。并通过AFM、UMT和自制仪器,研究了形貌修饰表面的摩擦不稳定性。结果表明,粘滑距离与表面微观形貌参数相关。建立了湿度环境下的面-面接触摩擦模型,认为存在相对湿度临界值。当相对湿度大于临界值时,摩擦力会突然大幅增加。通过自制仪器对规则凹坑修饰表面做了黏着和摩擦实验,结果发现随表面凹坑面积比增加,黏着力和摩擦系数均增加。更多还原

【Abstract】 Friction between micro components is the key factor that affects the performance and reliability of MEMS (microelectromechanical system) because of scale effect and surface effect. One of the research directions of tribological design in MEMS is exploring and controlling the friction behaviors of micro components by micro surface texturing. In this paper, the micro surface texturing was made on silicon wafer surface, and experiments and theoretical analysis of its friction behaviors were carried out from nano to micro scale.Because there are not satisfied commercial tribology test instruments, a new micro-tribotester was made to measure the pull-off and friction forces in situations of ball-flat and flat-flat contacts, with 0.6-5mN load in varied relative humidity conditions. The resolution of the tester is 8μN. A series of friction experiments of micro textured surfaces were carried out by the micro-tribotester.This paper classified the effects of micro surface topography of components on frcition behavior into two categories, which are effect of interior and exterior contact area. Dry frcition experiments of varied textured surfaces in pin-flat, ball-flat and flat-flat contacts were carried out. The results show that the topography parameters which affect friction force are roughness, radius of curvature of asperity, correlation length and direction of texture. There is the possibility of optimization of surface texturing.The topography of exterior contact area mainly affects the stability of friction. The effects are studied by a new elastic ratchet model presented by this paper. The model indicates that the friction force is affected not only by slope but also radius of curvature of surface topography. In the model, the friction is dominated by slope at nano scale, and by radius of curvature at micro scale. It was validated by experiments. Stick-slip model was developed based on the above elastic ratchet model. The model indicates that the upper head is sliding with high frequency vibrancy in“stick”process, which well explaines the "creep-slip" phenomena. The friction instability of textured surfaces was studied by AFM, UMT and micro-tribotester. The results show that the slip distance is affected by topography parameters.Friction model of flat-flat contact in relative humidity conditions was developed. The model indicates there is a critical relative humidity, upon which the friction force will greatly increase. Adhesion and friction experiments of textured surfaces were carried out. The results show that the pull-off and friction forces increases with dimple area ratio.更多还原