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MEMS Mechanical Sensors - Stephen Beeby Part 2

Tham khảo tài liệu 'mems mechanical sensors - stephen beeby part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 10 Materials and Fabrication Techniques hydrogen ions is then executed through the oxide layer by a standard high-current ion implanter to form the Smart Cut layer. The implanted hydrogen ions alter the crystallinity of the silicon creating a plane of weakness in the wafer. After the wafers are bonded together the implanted wafer can be cleaved along this plane to leave a thin layer of silicon on top of the oxide layer. The wafer is then annealed at 1 100 C to strengthen the bond and the surface of the silicon is polished to reduce the defect level to a level approaching that of bulk silicon. The buried oxide layer is pinhole free. SOI layers in the range from 0.1 to 1.5 um and BOX layers from 200 nm to 3 um can be fabricated by this method. Other substrates however should not be ignored. Among those that have been used in micromachining are glasses quartz ceramics plastics polymers and metals. Quartz and glass are often used in MEMS mechanical sensors therefore a short description of these materials is given here. 2.2.1.2 Quartz and Glasses Quartz is mined naturally but is more commonly produced synthetically in large long faceted crystals. It has a trigonal trapezohedral crystal structure and is similar to silicon in that it can be etched anisotropically by selectively etching some of the crystal planes in etchants such as ammonium bifluoride or hydrofluoric acid. Unlike silicon however this has not been extensively used as an advantage but has been identified more as a disadvantage due to the development of unwanted facets and poor edge definition after etching. Since the fastest etch rate is along the z-axis 1 most crystalline quartz is cut with the z-axis perpendicular to the plane of the wafer. The property of quartz that makes it useful in MEMS mechanical sensors is that it is piezoelectrical. Quartz has been used to fabricate resonators gyroscopes and accelerometers. Another form of quartz is fused quartz but be careful not to confuse this material with .