Abstract
A microelectromechanical system (MEMS) accelerometerhas been manufactured for wireless vibrationmeasurements on AC motors for condition monitoring.The vibration sensor element has been encapsulated withglass using wafer scale adhesive bonding withBenzycyclobutene (BCB). Cavities in the glass allow themoving mass on the silicon sensor to vibrate freely. Thewafer scale packaging greatly simplifies the subsequentpackaging which includes mounting on a ceramicssubstrate. The ceramic board with the sensor element isdensely packed inside a sensor node together with othercomponents. The battery driven sensor node solution isoptimized with regard to small scale and low powerconsumption to reduce price and extend life time. Thesensor element has a linear response up to 30 g with asensitivity of 0.3 mV/Vg and a resonance frequency of 7.7kHz. Measurements were performed on a bare,unpackaged die and after glass encapsulation. The onlyrecognizable effect of the glass encapsulation on thefrequency response is a moderate damping.