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Abstract-We demonstrate a novel photoplastic nanoelectromechanical device that includes an encapsulated polysilicon piezoresistor. The temperature limitation that typically prevents deposition of polysilicon films on polymers was overcome by employing a hotwire CVD process. In this paper, we report the use of this process to fabricate and characterize a novel polymeric cantilever with an embedded piezoresistor. This device exploits the low Young's modulus of organic polymers and the high gauge factor of polysilicon. The fabricated device fits into the cantilever holder of an atomic force microscope (AFM) and can be used in conjunction with the AFM's liquid cell for detecting the adsorption of biochemicals. It enables differential measurement while preventing biochemicals from interfering with measurements using the piezoresistor. The mechanical and electromechanical characterization of the device is also reported in this paper. [2008-0108]Index Terms-Affinity cantilevers, bio-microelectromechanical system (bio-MEMS), hotwire CVD (HWCVD), piezoresistive sensing, polymeric cantilevers, surface stress.

In this study, the authors demonstrate the fabrication, calibration, and testing of a piezoresistive microcantileverbased sensor for biomedical microelectromechanical system (BioMEMS) application. To use any sensor in BioMEMS application requires surface modification to capture the targeted biomolecules. The surface alteration comprises self-assembled monolayer (SAM) formation on gold (Au)/chromium (Cr) thin films. So, the Au/Cr coating is essential for most of the BioMEMS applications. The fabricated sensor uses the piezoresistive technique to capture the targeted biomolecules with the SAM/Au/Cr layer on top of the silicon dioxide layer. The stiffness (k) of the cantilever-based biosensor is a crucial design parameter for the low-pressure range and also influence the sensitivity of the microelectromechanical system-based sensor. Based on the calibration data, the average stiffness of the fabricated microcantilever with and without Au/Cr thin film is 141.39 and 70.53 mN/m, respectively, which is well below the maximum preferred range of stiffness for BioMEMS applications. The fabricated sensor is ultra-sensitive and selective towards Hg 2+ ions in the presence of other heavy metal ions (HMIs) and good enough to achieve a lower limit of detection 0.75 ng/ml (3.73 pM/ml).

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