微型机电系统（MEMS）是面向21世纪的关键技术，微型机械的设计与制造在很大程度上取决于材料问题的解决。影响微型机械装置功能和可靠性的薄膜材料力学性能需要精确的评价。利用电磁力驱动，设计了一种微拉伸装置，从而精确地测定了长度为100-660μm，宽度为20-200μm，厚度为2.4μm的多晶硅薄膜的力学性能。结果表明，测得的平均弹性模量为164 GPa±1.2 GPa，与理论计算值相当。平均拉伸强度为1.36 GPa±0.14 GPa，其威布尔分布参量为10.4-11.7。统计分析表明，由于微结构和尺寸的约束使得多晶硅薄膜的拉伸强度表现出对微构件长度、表面积和体积的尺寸效应。拉伸强度随表面积与体积之比值增加而增加，这一比值可作为尺寸效应的控制参量。测试数据解释了微构件力学性能参量的离散性，并可用于多晶硅微机械的可靠性设计。最后，提出了应变设计准则，允许应变为0.0057。

Mechanical stability and sticking are troublesome problems in microfabrication and operation processes when the separations of components in microelectromechanical systems are in the sub-micrometre regime. Some hitherto neglected mechanical effects, including the quantum mechanical effect, should be taken into account for solving the problems. The magnitude of the Casimir force is significant when the membranes work in vacuum without the effect of capillary forces. In this paper, an analysis is presented of the influence of the Casimir effect with surface roughness, conductivity and temperature corrected on the deformation of a membrane strip structure. With nothing other than the Casimir force loading the strip, a stable static equilibrium state and an unstable static equilibrium state exist, depending on the value of a dimensionless constant K. The membrane strip will collapse if the value of K is larger than the critical value of KC. The critical value of KC varies with the value of wo. This provides a way to check if a system with given dimensions and material properties will be in a stable equilibrium. This also provides a way of designing a membrane strip with high resistance to collapse.

In the present study, high-Tc superconducting thin YBa2Cu3O7 films and polysilicon films were prepared to investigate the initial sliding friction properties using a ball-on-flat tribometer when samples were moved against a sapphire ball or a steel ball in ambient environment. The surface topography was measured with atomic force microscope (AFM). After five times testing, the experimental results indicate that the friction coefficient of YBa2Cu3O7 films is lower than that of polysilicon films when sliding against a sapphire ball and almost the same when sliding against a steel ball. In particular, the initial friction of YBa2Cu3O7 films is more stable when sliding against a sapphire ball. However, the initial friction of polysilicon films fluctuates during a cycle period when sliding against a sapphire ball. They are both stable when sliding against a steel ball. Although, the surface profile of the YBa2Cu3O7 film is rough and can be seen to be rougher than the polysilicon film, but the friction coefficient of the YBa2Cu3O7 film is lower than that of polysilicon film. Also, although the topography of YBa2Cu3O7 films changes during friction, the friction coefficients are stable. This clearly shows that the initial sliding friction of YBa2Cu3O7 films under microfriction is stable. The observation signifies YBCO film is a good film to prevent stick-slip motion in ambient environment. The wear properties of YBa2Cu3O7 films suggest that the superconducting outgrowths (CuO) are loose and they can be easily removed.

A molecular dynamics simulation is used to investigate the effect of surface roughness on the nano-rheology of ultra-thin films confined between two solid walls. The results show that friction is sensitive to the confining surface morphology and the fluid molecules near the two confining surfaces are in a layering solid-like structure. At a high shear rate, the interfacial layers of the film stick to the walls, resulting in partial slip inside the film and the development of shear stress in the viscous molecular fluid. The frictional resisting force is due to the shear in the viscous molecular fluid but not dependent on the critical yield stress of the solid-like structure as in the case of smooth boundaries.

Mechanical stability and sticking are the troublesome problems in microfabrication and operation processes when separations of components in MEMS are in the sub-micrometer regime. Some mechanical effect, including quantum mechanical effect should be taken into account for solving the problems. The influence of capillary forces on sticking of a surface micromachined microcantilever in ambient environment or the rinse liquid and the influence of quantum mechanical effect such as the Casimir effect on sticking and stability of a micro membrane strip cavity structure in vacuum were investigated. A factual rough model theory about sticking problem under the Casimir effect was suggested for the first time. The study on the design of anti-sticking structures under different forces shows that sticking and stability of microcantilevers and micro membrane strip cavities has something to do with Young's modulus of materials, surface properties, length of structures, thickness of structures and separation between the fixed surface and the deflecting component. But, it is independent of width of structures. The map of the size design of anti-sticking structures was put forward for the first time. This also provides a way to design a MEMS structure with high resistance to collapse.

The validity of a novel, direct and convenient method for micromechanical property measurements by beam bending using a nanoindenter has been demonstrated. In the deflection of microbeams, the influence of the indenter tip pushing into the top of the microbeams and the curvature across its width must be considered. The elastic deflection of a polysilicon microcantilever beam will vary linearly with the force. Thus, Young's modulus of the beam determined from the slope of this linear relation is 156 Gpa 92.9-6.3%. The size effects of the manufactured component on Young's modulus and strength of polysilicon microcantilever beams were measured. This result shows that the rupture strengths of polysilicon beams show size effect on the effective volume and surface area of the specimens. The rupture strength of each sample decreased with increasing the specimen effective volume and surface area, but increased with increasing the surface-to-volume ratio. The defect that initiates fracture is often on the surface of the specimen. In such cases the size effect can be traced back to a surface-to-volume ratio as the governing parameter.

A new microtensile test device using a magnetic-solenoid force actuator was developed to evaluate the mechanical properties of microfabricated polysilicon thin films that were 100-660mm long, 20-200mm wide, and 2.4-mm thick. It was found that the measured average value of Young's modulus, 164 GPa

The nanoindentation fracture of multilayer hard coatings of TiNrTi C,N.rTiC, Al2O3rTiCrTi C,N.rTiC, TiNrTi C,N.rTiCrTi C,N.rTiC and TiNrTi C,N.rTiCrTi C,N.rTiCrTi C,N.rTiC, deposited on cemented carbide using a CVD technique was studied. Based on an analysis of the energy released in cracking, the calculated fracture toughness values of these coatings were 2.18, 1.74, 3.40 and 3.90 MPa m1r2, respectively. Both load-penetration depth and loadl penetration depth squared plots have been demonstrated to be necessary if a more complete understanding of the coating system behaviour is to be gained. The interfacial failure and the critical load of interfacial failure of these coatings were also discussed. A step was found in the forcel displacement curves at the onset of coating fracture. A straight line segment in the oad-penetration depth squared curves was discussed. The hardness, fracture toughness and anti-wearability of these coatings were compared. The results show that the fracture toughness and anti-wearability are getting higher with the layers increasing.

The increasing use of small micromechanical devices and advanced sensors has led to concern about the failure modes and reliability of these structures. The enormous promise will not materialize without substantial progress in overcoming the stiction, friction and wear associated with such devices and understanding the mechanical behavior of MEMS materials and structures. Self-assembled monolayers (SAMs) are release and anti-stiction coatings for MEMS. In this paper, the anti-stiction properties of octadecyltrichlorosilane (OTS) SAM were calculated. The microtribological properties of OTS SAM were investigated with a ball-on-flat microtribometer. The influence of OTS SAM on the mechanical properties of micromachined polysilicon films for MEMS was investigated with an accurate evaluation using the microtensile test device. It was concluded that the OTS SAM has good anti-stiction properties and low friction coefficients. The hydrophobic property of OTS is the main factor leading to an increase in the average fracture strength of micromachined polysilicon up to 32.46%. Thus, the operational stability and lifetime of MEMS can be raised when coated with self-assembled monolayers.

For the purposes of pressure measurement at high temperature in oil drilling industry as well as in other industrial measurement and control systems, the strain gauge chip of piezoresistive pressure sensor is designed based on separation by implanted oxygen (SIMOX) SOI (silicon on insulator) technology, and then fabricated in the micro-machining work bay. Some kinds of sensor mechanical structures are designed for different customers and conditions. The thermal coefficients of expansion (TCE) mismatches between different materials within the highpressure sensor system are investigated. The sensor is fabricated successfully by using high temperature packaging process. The temperature coefficient of sensitivity (TCS) and temperature coefficient of offset (TCO) compensation circuitry is demonstrated. Based on experimental data, the sensor is tested with high accuracy and good stability.