SU-8 Piezoresistive Microcantilever For Chemical Sensing Application

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Date
2011-05
Authors
Lee, Kok Siong
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Publisher
Universiti Sains Malaysia
Abstract
In this research, the ultraviolet (UV) patternable polymer material, SU-8 with very low Young’s modulus compared to conventional silicon based material, is utilized as structural material for microcantilever to enhance the piezoresistive strain. In addition to that, a thorough Finite Element Analysis (FEA) has been carried out for SU-8 piezoresistive microcantilever under the surface stress loading to help in improving the piezoresistive strain when designing the cantilever sensor. The analysis result concluded that the SU-8 cantilevers for chemical sensing should have lower length to width (L/W) ratio for higher piezoresistive strain. There are two cantilever designs that have been fabricated and characterized in this research: single pair cantilever and array of cantilever. For these designs, the SU-8/Silver (Ag) composite has been embedded into the cantilever as piezoresistor. Besides, the cantilever sensors were fabricated using the adhesive bonding method, instead of the conventional flip-chip approach. The results from Scanning Electron Microscope (SEM), Atomic Force Microscopy (AFM), and tensile tests proved that the fabrication works were very well carried out. Furthermore, from current-voltage (I-V) test, the fabricated piezoresistors exhibit the linear resistance characteristic with good conductivity. After deflection test, the calculated gauge factor is as high as 26.3, which induced the surface stress sensitivity of 1.28 x 10-3 [N/m]-1 for nominal 800 μm x 800 μm microcantilever. Microcantilever array with three different L/W cantilever pairs have been used for H2 gas detection to examine the functionality of fabricated cantilever in chemical sensing application. From the result, the cantilever pair with the lowest L/W (0.79) exhibits the highest voltage output, which agrees with the FEA result.
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Keywords
Su-8 piezoresistive microcantilever for , chemical sensing application
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