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

Abstract
A single-crystalsiliconresonant bulk acoustic mass sensor with a measured resolution of 125 pg ∕ cm 2 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 2.182 MHz , with a quality factor exceeding 10 6 . The mass sensor has a measured mass to frequency shift sensitivity of 132 Hz cm 2 ∕ μ g . 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 7 ppb at an operating pressure of 3.8 mTorr .