Investigation On The Interface Adhesion Properties Of Micro- Machine Under External Electric Field

The interface properties have become the basic key problem of micro-machine because of scale effect and surface effect. The interfacial adhesion failure is one of the most common failure models of micro-machine. This thesis investigates the interfacial adhesion properties under external electric field (EEF) from two points of view: solid-solid interface and solid-liquid interface, which focuses on the two kinds of classical model of adhesion failure: stiction and stick.For investigating the solid-solid adhesion properties under EEF, a micro-adhesion tester is made to measure the pull-off force during different humidity and EEF, with resolution of 10μN in the range of 0.1-7mN. The adhesion properties of solid-solid interface and the effect of liquid on solid-solid's properties under EEF have been investigated by this tester.The adhesion and its'change rule of solid-solid interface under EEF are experimentally researched. The diffuse charging model of roughness surface for ball-plat contacted is constructed. The effect on solid-solid interface adhesion of charging time, EEF strength, material properties has been analyzed by this model. Then the physics model about the relation of EEF strength, material properties and the max charging density, constant charing time is constructed. And the research of different materials on the solid-solid interface adhesion has been completed based on the physics model.The physics model discussed above is applied in the design of RF MEMS switches. The mechanism of three kinds of failure model of RF MEMS swithes have been explained from the C-V curve which considered the roughness. The life-time model of switches has bean constructed with charging effect, and the new design for improving the switches'performance is given. From the analysis of the adhesion mechanism of solid-solid interface under EEF, the liquid has been introduced to change and control the adhesion of solid-solid interface, which has been validated experimentally by the micro-adhesion tester use the classical polar liquid (glycerin) and non-polar liquid (n-hexadecane).This thesis extends the response function of quartz crystal microbalance (QCM) in liquid to two layers model. And then it analyzes the viscoelasticity and phase transition of the near-interface layer of 5CB liquid crystal under EEF based on this model. The investigation indicated that EEF can decrease the complex shear viscocity of near-interface layer of 5CB, which is opposite with the bulk properties. At the same time, the coupling effect of EEF and surface effect will increase the phase transition temperature of 5CB and the increasing level is higher than the theory prediction got by the nematic phase model. This thesis gives the explain of these experiments by molecular model of liquid crystal, and it is found that the ordering of near-interface layer caused by EEF can result in low coefficient of friction in boundary lubrication, which can be used to control the stiction during startup of micro-machine.