Columnar shaped microresonators for mass detection and gas analysis

In this paper miniaturized silicon columns mounted perpendicular to a surface are presented as microresonators for the detection of an exceedingly small mass. In a first sensor design the column resides on a rigid silicon substrate and is forced to oscillate in the first flexural eigenmode. Mass sensitivity was investigated loading a single latex sphere on the top surface of the column and detecting the frequency shift of the resonant frequency. Oscillation was monitored using the optical beam deflection method, focusing a laser beam at the same surface. However, optical readout was substantially hampered by scattering of the laser beam at the loaded particles and diffraction at the column surface. In a second optimized design a silicon column was mounted on a flexible silicon nitride membrane. In this way the optical readout was applied from the flip side of the membrane completely separating the load area and the optical beam path. A proof of principal is given for the optimized sensor design investigating the influence of pure gases on the extrinsic damping behavior of the membrane columnar oscillator. (C) 2009 Elsevier B.V. All rights reserved.