Capacitive resonant mass sensor with LC resonant circuit for use in atmosphere

The paper reports a mass sensor using a very thin single crystal silicon cantilever with capabilities of capacitive readout and electrostatic actuation. A capacitive electrode is formed at the opposite side of the cantilever. The sensing principle employs the frequency modulation of an electrical LC oscillator, in which the capacitance of the sensor serves as the component of the LC oscillator. The vibration of the cantilever is detected by demodulation of the output signal of the LC oscillator. The displacement noise of the sensor is 0.05 nm/(Hz)/sup 0.5/, which is equivalent to a capacitance change of 2.9/spl times/10/sup -21/ F. With a 67-/spl mu/m-long and 250-nm-thick cantilever, the detectable minimum mass of 1/spl times/10/sup -14/ g is achieved using this capacitive detection method in the atmosphere.