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Schematic figure of the mass sensor consists of two cantilevers for mass detection and reference. The cantilever has two opposite electrodes for capacitive readout and electrostatic actuation, which were fabricated on a Pyrex glass substrate.
Magnified scanning electron microscopy image of the fabricated sensor. Starting material is silicon on insulator with a (100)-oriented -type 340-nm-thick top layer, -thick intermediate layer, and -thick handling layer. The sensing electrode patterned on Pyrex glass substrate opposite to the cantilever with a gap distance was in size, and its calculated capacitance is .
Measurement system of the sensor. As a LC oscillation circuit, the Clapp oscillator was adopted. FM demodulation was performed by Foster-Seeley discriminator.
Detectable minimum mass of the piezoelectrically self-oscillated cantilever measured through both optical detection and capacitive detection using a frequency counter as a function of the signal integrating time.
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