Ultrasensitive mass balance based on a bulk acoustic mode single-crystal silicon resonator

Abstract

A single-crystal silicon resonant bulk acoustic mass sensor with a measured resolution of 125pg∕cm2 is presented. The mass sensor comprises a micromachined silicon plate that is excited in the square-extensional bulk acoustic resonant mode at a frequency of 2.182MHz, with a quality factor exceeding 106. The mass sensor has a measured mass to frequency shift sensitivity of 132Hzcm2∕μg. The resonator element is embedded in a feedback loop of an electronic amplifier to implement an oscillator with a short term frequency stability of better than 7ppb at an operating pressure of 3.8mTorr.