Sensitivity improvement of a microcantilever based mass sensor

This article describes two approaches for sensitivity improvement of a micromachined silicon T-shaped cantilever resonator for mass sensing applications. In order to increase sensitivity values, higher order resonance mode was used and device dimensions were reduced. The cantilevers proposed are piezoelectrically actuated and the movement detection is done by four piezoresistors in a Wheatstone bridge configuration. Two types of cantilevers were fabricated: for the first cantilever of 400 μm long, 300 μm wide and 15 μm thick, the fundamental and second resonance frequency in air were 100 kHz ± 0.4 and 690 kHz ± 15, respectively, both with a quality factor of ∼800. And for the second cantilever of 200 μm long, 150 μm wide, 15 μm thick, the fundamental resonance frequency in air was 400 kHz ± 5 with a quality factor of ∼900. The devices were characterized attaching microspheres of polystyrene to the cantilever’s surface tip and measuring resonance frequency changes. For the first cantilever sensitivity values of 0.07 and 0.3 Hz/pg for the fundamental and second mode, respectively were achieved and 1.3 Hz/pg for the second cantilever. These results show the great potential for high sensitive mass sensor of this simple device.