A Wafer Level Vibration Test System for MEMS Accelerometer Sensitivity Measurement and Calibration

Sensitivities of microelctromechanical system (MEMS) accelerometers are typically measured and calibrated at final production test of packaged devices. This process typically requires expensive special automated test equipment (ATE) that can generate vibration stimulus. A single-axis vibration test system has been developed on an existing commercial wafer probe/trim system to calibrate sensitivities of MEMS accelerometers during wafer probe/trim process to minimize the need for such vibration test equipment. To increase signal to noise ratio but avoid damage of probe pad/pin during the test, the vibration exciter must be able to generate high frequency but small displacement vibration stimulus. The vibration exciter also needs to be small enough to fit into the existing commercial probe/trim system and requires minimum changes to the system. A high resolution but small size in-situ noncontact vibration measurement technique is needed to ensure calibration accuracy. This paper presents a unique solution to meet all these challenges. The success of this system has been validated by final product test data of a test device, a 3-axis low-g MEMS accelerometer.