A high sensitivity silicon microcantilever based mass sensor

Abstract

A silicon microcantilever based mass sensor with picogram resolution has been fabricated. In order to improve its sensitivity value, resonator dimensions were reduced. Working in dynamic mode, the cantileverpsilas resonance frequency depends on the stiffness of the spring and the attached mass. Therefore, maintaining constant stiffness and monitoring resonance frequency shift of the cantilever, the change in the cantilever mass can be accurately quantified. The cantilever resonance was driven by a piezoactuator and the frequency sense by four piezoresistors in a Wheatstone bridge. Two resonators with different dimensions were fabricated; the first cantilever is about 400 mum long, 300 mum wide, 15 mum thick and the second 200 mum long, 150 mum wide, 15 mum thick. The first cantilever operates at 100 kHz with a quality factor of 830 and the second at 400 kHz with a quality factor of 900 both in air. An added mass of 400 pg could be resolved, and the measured level of detection was found to be 0,07 and 1,3 Hz/picogram respectively. The sensor characterization was fulfilled by depositing polystyrene microspheres with a glass microcapillary pipette and measuring resonance frequency changes. The results reported in this paper represent an improvement from previous and similar silicon sensor in terms of sensitivity and integration.