hw7.ee245.f09.v5

hw7.ee245.f09.v5 - EE C245 ME C218 INTRODUCTION TO MEMS...

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EE C245 / ME C218 INTRODUCTION TO MEMS DESIGN FALL 2009 PROBLEM SET #7 Issued: Thursday, Nov. 24, 2009 Due (at 7 p.m.): Thursday, Dec. 10, 2009 , in the EE C245 HW box in 240 Cory. 1. Gyroscopes are inertial sensors that measure rotation rate, which is an extremely important variable to know when navigating. In particular, one must know rotation rate (as well as other parameters, e.g., time, linear acceleration, …) in order to determine position accurately (without the aid of GPS). Among the applications that use gyroscopes are airplanes (for na- vigation), boats (again, for navigation), automobiles (for skid control, among other applica- tions), GPS receivers (to allow position determination during periods when the GPS signal cannot be received), and game controllers (e.g., the Wii). Of these applications, the last three already use MEMS-based gyroscopes, and the first two are presently targeted by MEMS realizations. Gyroscopes operate by taking of advantage of the conservation of momentum, where an object moving in a given direction with a certain momentum will tend to continue moving in that direction even if its frame of reference is rotated about an axis. This is perhaps best further explained via example. This problem involves the MEMS-based micro-gyroscope [by Acar & Shkel] pictured in the scanning electron micrograph (SEM) of Fig. 1 and summarized in the figures that follow. This device is fabricated using a bulk-micromachining process, where the 100 μ m-thick sil- icon layer on a silicon-on-insulator (SOI) wafer is patterned and etched to the needed di- mensions with perforations (i.e., etch holes), then a final HF wet release is used to remove oxide under the perforated structures, but not under the contiguous anchors (since this takes
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hw7.ee245.f09.v5 - EE C245 ME C218 INTRODUCTION TO MEMS...

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