This review describes the testing,analyzing,and evaluating methods for the mechanical reliability of MEMS materials,which has much more importance on the commercialization of MEMS devices that has tiny mechanical structures. The reliability of silicon,the most often used materials as structure in MEMS,is also summarized.

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This paper describes elevated temperatures tensile strength and inelastic constitutive relationship of electroplated nickel (Ni) thin films used in high-density micro connectors. The compact tensile tester operated in Scanning Probe Microscope (SPM) evaluated mechanical properties of electroplated Ni specimens, with nominal dimensions of 15 μm in thickness, 50 μm in width and 600 μm in length, at elevated temperatures. All specimens have line patterns on their specimen gauge section to measure axial elongation under tensile loading with an SPM cantilever. Strain rates faster than 5 %/sec were employed to obtain the time-independent Young's modulus and yield stress of the Ni specimens. Averaged Young's modulus was closed to that of a bulk of Ni, however ultimate tensile strength showed a larger value. Yield stress and breaking elongation were also quite different from previous reported values of the bulk. Inelastic constitutive equations were proposed as a function of temperature in order to reveal inelastic deformation behavior of the Ni micro connector at elevated temperatures in finite element analyses.

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Reliability is one of the most critical issues for designing practical MEMS devices. In particular, the fracture toughness of micro-sized elements for MEMS is important, as micro/nano-sized flaw proved a crack initiation site and cause the final failure of such devices. By the way, MEMS components were often used Si. In this investigation, fracture toughness tests have been carried out using single crystal silicon to micro-sized specimens. Cantilever beam type specimens with notch were prepared by focused ion beam machining. Two specimens types with different notch orientations were prepared. The notch plane and direction were (100) and [010], and (110) and [110] respectively. Fracture toughness tests were carried out using a mechanical testing machine for micro-sized specimens. Fracture occurs in a brittle manner with both orientations. The provisional fracture toughness values (K_Q) are 1.05MPam^1/2 and 0.96MPam^1/2, respectively. These values are valid plane strain fracture toughness values (K_IC). These values are also equivalent to those obtained on bulk-sized specimens. This suggests that the size effect on fracture toughness is not significant for this specimen size in single crystal silicon. The results obtained in this investigation indicate that the fracture toughness measurement method used is applicable for micro-sized components of this material in MEMS devices.

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This paper presents the dependence of fracture toughness, fracture strength, and fracture behavior, such as crack propagation, on the crystal orientation of single-crystal silicon. We conducted on-chip tensile testing to measure fracture strength and fracture toughness of single-crystal silicon films with (100) and (110) surface in the <100> and <110> loading direction. The loading direction had a significant effect on fracture toughness, which was 2.17MPa√m in the <100> direction and 1.27MPa√m in <110>. However, the fracture strength varies with both loading direction and surface orientation. We observed a fracture specimen on which a (111) cleavage plane eventually appeared on any crystal types of the specimen.

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The effect of sputtering gas (Ar gas) pressure on the mechanical properties of free-standing Ti thin film membranes of 300-400 nm thickness, microfabricated by magnetron sputtering, has been studied by using a novel tensile testing machine. These free-standing thin film membranes are extremely difficult to handle because they are fragile. Therefore, the thin film test specimens were fabricated in Si frames to protect them. Sputtering gas pressure was varied from 1.5 to 15 mT. The stress and strain of the thin films was measured continuously from elastic deformation to fracture. Both the tensile strength and the strain at fracture of the thin films were affected by the sputtering gas pressure. The tensile strength of thin films increased with decreasing gas pressure. However, there was no obvious trend between the sputtering gas pressure and Young's modulus of the thin films. The experimental results confirmed that the Ti thin film membranes are more reliable with decreasing the gas pressure.

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A micro-optical distance sensor by a combination of LIGA technology and Si micromachining is proposed. The function of the distance sensor is based on the triangulation principle. This sensor consists of optical components made by the LIGA process, i.e. a free space micro-optical system and micro-cylindrical lenses, and an electrical base with opto-electrical devices.
In this paper, two prototype sensors are described, which have measurement ranges of 1 mm (Type1) and 10mm (Type2). The dimensions of the pure sensor chip are 7 mm (W) × 7 mm (L) × 3 mm (H). The repeatability error of Type1 and Type2 are ±3 μm and ±80 μm, respectively.

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