Size Effect In Microstructure Adhesion And Theoretical Study Of Pull-off Test

In the last three decades, the rapid progress of microfabrication techniques in the microelectronics industry has led to the development of various micro-/nano-electromechanical systems (MEMS/NEMS). The sizes of most MEMSstructures typically range from 0.1μm to several micrometers in thickness, 10-500μm in lateral dimensions. And the lateral and vertical gaps to other structuresor to the substrate are around 1μm. The large surface-to-volume ratio and thehigh-aspect ratio make these microstructures adhere to the adjacent surfaces vulnerably, which will lead to the malfunction of micro-devices eventually.At the same time, the applications of adhesion are very common in our life, for example the wafer bonding. Recently, some scientists have found that the interaction between the gecko's foot-hair and the wall is no other than the Van der Waals adhesion. This discovery tells us that there is a new direction to the design of the climbing robots. In order to apply or control the adhesion effects between the microstructures, we should understand the mechanism of adhesion firstly. The adhesion work is a thermodynamic parameter to characterize the surface interaction. There are many methods for measuring the adhesion work. But it is difficult to measure the adhesion work of the film, especially the membrane. The pull-off test is one of the common methods for measuring the adhesion work of membrane. Certainly, the science of surface adhesion is the interdisciplinary field of physics, chemistry, biology and mechanics. The thesis focuses on the theoretical study of the size effect in micro-scale adhesion and the pull-off test for measuring the adhesion work of membrane by mechanical analysis. The main contents of the thesis are two parts as following. Part one:The JKR model, DMT model and Maugis model have been compared in the second chapter. In the third chapter, we have studied the size effect in the fibril adhesion and the virus adhesion in endocytosis. The results may help us to improve the designs of the adhesion feet of climbing robot and the drug carrier. Part two:Firstly, we have deduced the governing equation of the membrane deflection using the von Karman plate theory. And then we have established the theoretical model for measuring adhesion work of membrane in two cases (rectangular punch and circular punch).Secondly, we have studied the effects of the residual stress and the sliding boundary and obtained the modified expressions of the adhesion work. We find that the two effects are related to some experimental factors through the numerical calculation. The study may help us to improve the test method for measuring the adhesion work. The rationality of the assumption that the bending rigidity of the membrane is negligible has also been discussed.At last, we have studied the effect of residual stress on adhesion-induced instability in MEMS. We have found that such instability is mitigated by the presence of tensile residual stress and the effect is significant only when the tensile residual stress is under a proper magnitude. It should be taken account of in the design and fabrication of MEMS.