Fabrication and Characterization of a Polymeric Microcantilever With an Encapsulated Hotwire CVD Polysilicon Piezoresistor

Abstract

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.

Polymer MEMS Sensors

“…Piezoresistive SU-8 microcantilevers with diff erent with integrated gold (Au) [10] and polysilicon strain sensitive layers have been reported earlier [20,24]. Gold being a metal strain gauge material that has got very low gauge factor, low temperature deposited polysilicon [24] was a better substitute for gold for improving the sensitivity.…”

“…Gold being a metal strain gauge material that has got very low gauge factor, low temperature deposited polysilicon [24] was a better substitute for gold for improving the sensitivity. However the design constraint was that the polysilicon fi lm should be thin enough such that it does not add to the stiff ness of the structure while ensuring that the thin polysilicon does not lead to a decreased signal to noise ratio.…”

“…Th e performance of SU-8 based polymer nanomechanical sensors could be enhanced by incorporating ultra-sensitive electrical transduction schemes that are compatible with SU-8 processing [23][24][25][26][27][28][29][30][31][32]. Design and development of SU-8 microcantilever sensors with four novel electrical transduction schemes namely (1) polymer nanocomposite piezoresistive microcantilever sensors [25][26][27] (2) Organic CantiFET [28] (3) AZO CantiFET [29] and (4) polymer nanocomposite piezoelectric microcantilever sensors [30][31][32] are discussed here.…”

A Novel SU8 Polymer Anchored Low Temperature HWCVD Nitride Polysilicon Piezoresitive Cantilever

“…The key factors to evaluate the performance of nano mechanical cantilever sensors are spring constant, minimum detectable surface stress and resonant frequency. The stiffness of the cantilever used for bio sensing needs to be designed in such a way that it can withstand the wet chemistry involved in functionalization of the surface and at the same time be sensitive enough to the surface stresses generated by the target molecules [15]. Resonant frequency of a cantilever sensor should be higher than 5 KHz so that they are immune to surrounding noise.…”

“…The spring constant of the nitridepolysilicon-nitride cantilever can be measured by beambending technique. This experiment can be performed by AFM [15] or by a nanoindenter [2]. We have performed the experiments using nanoindenter because of its high load and displacement measurement sensitivity.…”