Abstract-We have micromachined a mechanical sensor that uses interferometry to detect the differential and absolute deflections of two adjacent cantilevers. The overall geometry of the device allows simple fluidic delivery to each cantilever to immobilize molecules for biological and chemical detection. We show that differential sensing is 50 times less affected by ambient temperature changes than the absolute, thus enabling a more reliable differentiation between specific cantilever bending and background effects. We describe the fabrication process and show results related to the dynamic characterization of the device as a differential sensor. The root-mean-squared (rms) sensor noise in water and air is 1 nm over the frequency range of 0.4-40 Hz. We also find that in air, the deflection resolution is limited only by the cantilever's thermomechanical noise level of 0.008 A Hz 1 2 over the frequency range of 40-1000 Hz.[781]
The Deep Reactive Ion Etching process (DRIE) has made it possible for an increasing number of MEMS devices to be made with flexures as their main components. However, the DRIE creates slightly tapered cross sections in addition to other fabrication variance or even failure, which affect the predicted stiffness. The flexures typically move in the plane of the wafer and it is often desirable to measure the force-displacement characteristics of such flexures after fabrication to close the design feedback loop. However, to our knowledge there is no commercially available instrument to perform this task. This paper introduces an instrument specifically designed to quickly record the force-displacement curve of MEMS flexures. The first prototype features a resolution of 10 nm for the displacement, and 100 µN for the force. It has been successfully used in practice [1].
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