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

摘要

There is an emerging need for low cost and miniature accelerometer and gyroscope for inertial navigation. The inertial navigation system uses gyroscopes and accelerometers to measure the state of motion of a target or a missile by sensing the changes in that state caused by accelerations. The required 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. traditional MEMS principle. MEMS-IDT based microsensors possess typical advantages of MEMS sensors including the additional benefits of robustness, excellent sensitivity, surface conformability and durability. Compared to conventional ones, these new sensors have less number of moving mechanical parts ultimately giving rise to inherent robustness and durability. Consequently, there is no electronics to balance or measure the movement of moving structures, which leads to even smaller micro devices. in this paper, the fabrication, characterization and testing of a MEMS-IDT based accelerometer suitable for inertial navigation system are presented. The accelerometer consists of a suspended silicon micromechanical structure (Seismic mass) that is bonded to a SAW device with an air gap of around 400-2000 A. The seismic mass is sensitive to acceleration and modulates the SAW that propagates on the piezoelectric film. Programmable accelerometers can be achieved with 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.