Thermal Excitation and Piezoresistive Detection of Cantilever In-Plane Resonance Modes for Sensing Applications

Liquid-Phase Chemical Sensing Using Lateral Mode Resonant Cantilevers

“…In fact, for in-plane mode cantilevers, quality factors as high as 67 have been measured in liquid. 20 As will be shown in the present study, lower damping directly relates to an improved limit of detection for cantilever-based chemical sensors.…”

“…21,22 Advantageously, the drop in resonant frequency upon immersion into liquid and, thus, the drop in device sensitivity due to the surrounding fluid are greatly reduced when the in-plane flexural mode is used, as the effective mass of the accelerated fluid is much smaller during inplane flexural vibrations. It was shown that immersion of such devices into liquid typically yields only a 5−10% shift in resonant frequency, 20 while for cantilevers operated in out-of-plane flexural modes, 50% frequency shifts are typically observed. 18 In addition, the decreased damping associated with the in-plane flexural modes results in quality factors that are up to 5 times larger than those reported for devices operated in out-of-plane modes in liquid.…”

Geometrical considerations for the design of liquid-phase biochemical sensors using a cantilever's fundamental in-plane mode

“…The devices were packaged using acrylic manifolds as presented in [23]. It was determined that the pressure from the top manifold used for fluid injection could slightly alter the beam's resonant frequency.…”

“…Cantilever mechanical characterization was performed in deionized water. For testing in liquid a drop of water was placed inside the acrylic ring (which was glued to the surface of the die for testing) [23] and allowed to percolate through the bulk-micromachined opening. Subsequently, the amplitude and phase response from the piezoresistive Wheatstone bridge [13] was captured using an Agilent 4395A network/spectrum analyzer.…”

“…A single heating resistor was driven with an approx. 2.2 Vpp AC excitation voltage superimposed on a 3 V bias voltage [23]. In some cases, slightly higher voltages (DC and AC) were needed to produce a discernible output signal.…”