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A single-wafer-processed high-g piezoresistive accelerometer is reported. The microsensor has an in-plane self-caging cantilever configuration, in which an electrostatic self-testing function is integrated on-chip. Both the sensing piezoresistors and the self-test actuating electrodes are integrated on vertical sidewalls of the laterally deflecting cantilever. For single-wafer-based fabrication of the self-testable piezoresistive accelerometer, a trench-sidewall micromachining technology is developed, which is capable of integration of both boron-diffused piezoresistive sensors and electrostatic actuators on deep trench sidewalls. In addition, the technology can realize electrical continuity from the vertical trench-sidewall to the wafer surface. After design and fabrication of the accelerometers for a 200 000 g measure-range, characterization was performed to evaluate the developed trench-sidewall integration technology and to test the self-testable high-g accelerometers. A linear I-V relationship for the sidewall-diffused piezoresistor is measured with satisfactory sidewall-to-surface electric-transfer properties. The electrical isolation between adjacent elements on the sidewall shows a breakthrough voltage of about 55 V. Moreover, with the single-chip integrated lateral-actuating structure, both static and dynamic self-testing functions are realized. The measurement of the accelerometer results in a sensitivity of about 1 muV/g/3.3 V, noise-limited vibration resolution of about 1 g and zero-point temperature drift of lower than 100 ppm/degC.
Date of Publication: Dec. 2008