Study On Adhesive Contact Behaviors Of MEMS

The rapid development of Micro Electro-Mechanical System (MEMS) leads us to a research field, in which the surface effect plays an important role in many physical phenomena. Influenced by the surface effect in MEMS, the adhesion energy and force become the key factors to dominate the adhesion, contact, deformation, et al of solids. The adhesion between solids not only influences the performances of MEMS seriously, but also leads to low eligible products ratio of MEMS. Based on the solid physics, elastic theory, molecular dynamics and adhesion theory, the variations with the distance of adhesion force, elastic deformation, contact area, surface contour, distributing adhesion force between elastic solids are lucubrated with the aid of computer simulation to establish the adhesive contact model in micro/nano meters. The work done in this dissertation not only has an important academic significance in promoting such studies as the adhesive contact from nano to micro meters, the theories of AFM in tapping mode, but also has an instructive significance in the research on the adhesive failure in MEMS.On the basis of the Hamaker hypotheses, Lennard-Jones potential and elastic theory, a elastic model, named adhesion model based on the Hamaker hypotheses, is established of the adhesive contact between a sphere and a plane. The results from the model are consistent not only with those from adhesion model based on Derjaguin approximation, JKR theorem, DMT theorem, MD theorem but also with the experimental results.Based on the computational model of adhesion force of unit area between two parallel planes, the relation is deduced between the equilibrium distance of two planes and the crystal constant. In the meanwhile, the method is given to determine the equilibrium distance between different materials.The gap and modulus of Bradley theorem are ameliorated respectively based on JKR theorem, DMT theorem and MD theorem. Three combined adhesion theorems are deduced by combining ameliorated Bradley theorem with JKR theorem, DMT theorem, MD theorem respectively, which can approximately give the continuous variation of the adhesion force with the distance.Based on the Hamaker hypotheses and Morse potential, a adhesion model between a single atom and a sphere is founded. With the model, the blended simulation model of molecular dynamics(MD) is established between a sphere and a plane. In virtue of the MD model, the adhesion force between a sphere and a plane is analyzed during the loading and unloading process. The results indicate that part of the atoms in the plane transits abruptly and leads to the adhesion hysteresis and energy dissipation in the process of loading and unloading.The cause of 'jumping-on and off', adhesion hysteresis and energy dissipation in AFM are studied by the adhesion model between a sphere and a plane. Based on the law of conservation of energy, the relation is given between the dissipated energy, oscillation amplitude and phase of AFM. The dynamic model of AFM in tapping mode is established and solved based on the adhesion model between a sphere and a plane, with which the oscillation amplitude, phase, and dissipated power of AFM versus distance are researched.Based on the Hamaker hypotheses and the interaction between atoms, the adhesion force of unit area between two lubricous parallel planes is obtained. Based on the G-W model of rough surfaces and the adhesion model between a sphere and a plane, a adhesive contact model between two rough surfaces is established, with which the variations of the adhesion force with the parameters of rough surfaces are analyzed.Based on the adhesive contact model between a rough sphere and a rough plane, the stability of balanceable positions of micro-cantilever beams are researched and the structural sizes are given to prevent the adhesive failure of micro-cantilever beams.