In the past 20 years, microelectromechanical systems (MEMS) have become an increasingly substantial and visible part of the sensor industry. Since the early 1990s, MEMS inertial sensors in particular have rapidly improved in performance, reliability, and price. As prices have dropped, MEMS accelerometers have begun to replace piezofilm vibration sensors, liquid switches/tilt sensors, strain-gauge pendulum accelerometers, and other "low-end" motion sensors in many automotive, industrial, and consumer applications. However, as MEMS inertial sensor technology matures, the greatest obstacle to cutting prices further has become the cost of hermetic packaging. Currently, half the cost of low-priced MEMS accelerometers comes from the use of hermetic ceramic packaging. In this article, we will review the state of the art in MEMS inertial sensor packaging and introduce a new wafer-level thin-film capping technology that will soon allow such sensors to be packaged in low-cost plastic packages, halving the price.
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