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5.2. Thick SOI MEMS realizations
When compared to early MEMS realizations using poly-silicon layers, the key physical parameters that make thick film SOI an attractive technology for the development of MEMS applications can be classified in two categories : design flexibility and wafers quality. Thick film SOI technology has been used for the development of optical MEMS thanks to the smooth surface of the silicon single-crystalline layer [Lee2004]. HF resonators with good performances can be realized. Accelerometers can also benefit from SOI since high masses are required to get good sensibility to acceleration, what can be easily achieved using thick ( > 5µm) SOI films [Matsumoto99].
One of the leader companies in thick SOI MEMS is Tronic’s, Grenoble, France. In [Renard2002], their surface micromachining process based on Epi-SOI substrates with precise Si overlayer thickness from 5 to 40 µm, developed out of the Smart Cut SOI wafer production technique, has been presented and validated by two prototypes of interest here: a capacitive pressure sensor (65-145 kPa range, 1pF/100kPa sensitivity, linearity and precision < 1% F.S., and 10Pa resolution, over a temperature range from –40 to 125°C) and a capacitive accelerometer (full scale of +/- 2 G, mG resolution and 200fF/G resolution). Other similar SOI pressure MEMS sensors are also produced by LUNA, Honeywell, Thales Avionics, Kulite…
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