High Resolution Position Monitoring of Suspended MEMS towards Biological and Chemical Sensors
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High Resolution Position Monitoring of Suspended MEMS towards Biological and Chemical Sensors G. Putrino1, M. Martyniuk1, A. Keating2, J.M. Dell1, and L. Faraone1 1
School of Electrical, Electronic and Computer Engineering, The University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia
2 School of Mechanical and Chemical Engineering, The University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia
ABSTRACT We present an integrated readout technique for interrogating the suspension height of micro-electro-mechanical systems (MEMS) structures. This readout technique is envisaged to be useful in applications such as MEMS-based biological and chemical sensing, where it is necessary to obtain the accurate position of a MEMS beam. The approach is based on the suspended MEMS structure modulating light transmission in an underlying optical waveguide via Fabry-Perrot phenomena. The performance of the technique is predicted via finite difference time domain (FDTD) simulations the results of which are confirmed by experimental measurements.
INTRODUCTION Microcantilever sensors are readily integrated into an array using low-cost, massproduction fabrication techniques developed for micro-electro-mechanical systems (MEMS), and can facilitate simultaneous multi-analyte chemical sensing [1-3]. MEMS-based microstructures are extremely sensitive elements, demonstrating mass detection limits as low as 10-21 g in controlled, laboratory conditions [4, 5]. If the top surface of the micro-cantilever is functionalized to preferentially adsorb specific molecules, an extremely sensitive and selective sensor can be fabricated. Readout technologies for MEMS sensors include the use of light reflected from the cantilever tip to a distant quadrant detector [1], electrical sensing (piezoresistive, piezoelectric, capacitive, Lorentz force/emf sensing and tunneling current techniques), and optical sensing based on optical interference either in an interferometer or the use of diffraction from an optical grating formed by a line of cantilevers. This latter configuration is often described as an array in the literature, but is still effectively a sensor for a single analyte [4, 6, 7]. The typical deflection noise density (DND) for micro-cantilever sensor systems that use quadrant detectors such as those found in atomic force microscopes (AFMs) is in the range of 100-IP¥+]DOWKRXJKODERUDWRU\YDOXHVRIIP¥+]KDYHEHHQDFKLHYHG> @7KH ORZHVWVKRWQRLVHOLPLWHG'1'SUHYLRXVO\UHSRUWHGZDVIP¥+z for a readout using an optical resonance approach [10]. A significant drawback of these AFM-based readout approaches is that none of them is compatible with the passive, non-electrical readout of compact, large arrays of individually and uniquely functionalized MEMS sensors. Future techniques will need to have the sensitivity of the above techniques, plus the ability to address large arrays of MEMS structures. Recently developed techniques to address large arrays include using cantilevers as optical waveg
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