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The dynamic mechanical behavior of sensor elements should be tested and verified before MEMS inertial sensors, including both gyros and accelerometers, are packaged and assembled. Many manufacturers, however, only test for leakage behavior and static capacitance before packaging and assembling sensors. Not testing a MEMS inertial sensor's mechanical behavior before packaging can result in costly mistakes. An excellent test methodology is based on Drive Sense Technology (DST), which verifies an inertial sensor's mechanical behavior and performance at wafer level. DST uses three signals: conditioned output, tuned AC source, and analog drive. The wafer-level test measures resonant frequency, frequency response, Q-factor, quadrature error, damping ratio, spring constant, and hysteresis. The STI3000 wafer-level test system, which is made by Solidus Technologies, interfaces a device-specific element probe card to a mixed-signal tester. The STI3000E probe card conditions the output and analyzes the element response. The STI9000 automated test unit then processes and digitizes the signal. Although DST is good at testing MEMS accelerometers, it excels at measuring the sensor elements of MEMS gyros. Passive wafer-level testing methods do not provide the stimulus and response required by MEMS gyros, but DST-based methods do.
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