Fabrication, characterization and testing of wireless MEMS-IDT based microaccelerometers

There is an emerging need for low cost and miniature accelerometer and gyro scope for inertial navigation. The inertial navigation system uses gyroscop es and accelerometers to measure the state of motion of a target or a missi le by sensing the changes in that state caused by accelerations. The requir ed features in many of these applications are high precision, wide dynamic range and wide frequency range. Wireless MEMS-IDT devices make use of both surface acoustic wave (SAW) employing inter digital transducer (IDT) and tr aditional MEMS principles. MEMS-IDT based microsensors possess typical adva ntages of MEMS sensors including the additional benefits of robustness, exc ellent sensitivity, surface conformability and durability. Compared to conv entional ones, these new sensors have less number of moving mechanical part s ultimately giving rise to inherent robustness and durability. Consequentl y, there is no electronics to balance or measure the movement of moving str uctures, which leads to even smaller micro devices. In this paper, the fabr ication, characterization and testing of a MEMS-IDT based accelerometer sui table fbr inertial navigation system are presented. The accelerometer consi sts of a suspended silicon micromechanical structure (seismic mass) that is bonded to a SAW device with an air gap of around 400-2000 Angstrom. The se ismic mass is sensitive to acceleration and modulates the SAW that propagat es on the piezoelectric film. Programmable accelerometers can be achieved w ith split finger IDTs as reflecting structures. If IDTs are short circuited or capacitively loaded, the wave propagates without any reflection whereas in an open circuit configuration, the IDTs reflect the incoming SAW signal , (C) 2001 Elsevier Science B.V. All rights reserved.