An approach to maintain vacuum in microelectromechanical systems (MEMS) by integrating the MEMS fabrication process with getter material preparation is presented in this paper. The coating process for a thick film of getter material on silicon and glass wafers, the two commonly used substrates in MEMS fabrication and package, was investigated in detail. The getter material consists of a powder mixture of zirconium, vanadium and iron, which features high sorption capacity to active gases such as H2, O2, N2, CO and H2O vapour. Various kinds of patterned non-evaporable getter (NEG) thick films with thickness from 50 µm to 400 µm were fabricated to investigate the solutions for different MEMS applications. The activation temperature of the thick NEG films was investigated. Fundamental properties of the NEG films were examined, such as the adhesive strength, higher than 119 N cm−2, of the NEG film to Si substrate and the sorption capacity, 4.68 × 106 Pa l m−2, of the coated getter material. The coating of NEG thick film on the inner surface of MEMS pressure sensor illustrates the applicability of the technique in vacuum maintenance of MEMS devices.
Stereolithography (SLA)-manufactured parts behave with anisotropic properties due to the varying interface orientations generated by the layer-based manufacturing process. Part build orientation is a very important factor of anisotropic mechanical properties. In this paper, the build orientation experiment was designed to study the anisotropic behaviour of the mechanical properties of the SLA parts based on the orientation relationship between the force and the layer. The results show that there are obvious brittle characteristics on the fracture surface of the specimens and microcracks perpendicular to the direction of the layer distributed on the side of the fracture. The mechanical properties under brittle fracture have different degrees of sensitivity to the build orientation. Among all the build orientations, whether a specimen is built flat or on an edge shows obvious difference in tensile strength, and the relative range distribution reaches 35%. The changes in elastic modulus and the elongation at break are the most obvious in different angles relative to the XY plane, and the relative range distribution reaches 62% and 56% respectively. In all the build orientations designed, the tensile strength is the largest when it is placed on the edge at 0° with Y-axis in the XY plane, the elastic modulus is the largest when it was placed vertically, and the elongation at break is the largest when it is placed flat at 45° with Y-axis in the XY plane.
Anti-reflection effect of three different surfaces including blank, wet acidic etched and RIE etched are compared on the basis of reflectance measurements. RIE has been to be found as the most effective method to reduce reflection of multicrystalline silicon surface, and as a result, can afford high efficiency of solar cells. We also optimized the RIE parameters. For SF6/O2 flow ratio of 2:1, crowded and dense crater-like structures on silicon surface were observed. Reflectance measurement results show that such a figure exhibits good anti-reflectance behavior. The lowest reflectance we got has been reached about 15.7%. Further increase SF6/O2 flow ratio, the reflectance increased instead of decreased. That means SF6/O2 flow ratio of 2:1 is the most appropriate flow ratio. Another important parameter is etching time. We maintained plasma conditions as earlier and keep SF6/O2 flow ratio of 2:1, then varied the etching time. At etching time of 15min, we got a perfect reflecting result on the surface of multicrystalline silicon.
On account of enhancing surface light trapping by reducing reflectance, front surface texturiing is always a key to improve the solar cells performance. As a maskless plasma texturing technique, reactive ion etching using SF 6 /O 2 plasma brings down reflectance distinctly by fluorine ions etching the surface of mc-silicon solar cells with the assisting of O 2 . The textured surface with bowl-like nanostructure exhibits fine anti-reflectance effect. Optimal reflectance of mc-silicon solar cells could be obtained by adjusting gases flow ratios, plasma power and etching time.
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