A novel three-axis AIM vibration sensor for high accuracy condition monitoring

We present a novel micromachining approach for on chip three-axis capacitive high aspect ratio acceleration sensors made from standard silicon wafers. The patented AIM (air gap insulated microstructures) technology with their excellent device properties regarding temperature behavior, capacitive sensitivity and reliability was modified for enabling out-of-plane differential measurements. Therefore electrodes with different heights have been patterned by using one additional masking layer. Using the presented AIM technology, high performance vibration sensors with low temperature sensitivity of typically 40 to 110 ppm/K sensitivity change and ± 0.9 mg/K offset failure at a sensitivity of 10 fF/g (25 fF/g for in-plane sensors), a measurement range of ± 50 g and a bandwidth from DC to 1 kHz were fabricated. The sensors have been packaged hermetically by seal glass bonding.