Development of a Microcantilever Based MEMS Device for Biosensor Application

Abstract

In this project a microcantilever based MEMS device for biosensing application had been developed. The geometrical aspects of the cantilever beam structure had been studied for increasing the sensitivity of the sensor devices. Finite Element Analyses of different geometrical shapes were performed to compare the mass sensitivity of different shapes of microcantilever beam structures. Microcantilever beam structures of the promising geometries were fabricated, and their resonant frequencies were measured optically for comparison. Both the FEA results and the optical measurement results agreed that the trends of triangular and the modified shape geometries compared to the regular rectangular shape geometry, in terms of frequency shift performances of those geometries. The triangular shaped geometry showed, approximately, an order of magnitude, and the modified shaped geometry showed more than three times the performance of the regular rectangular shape. Damping effects on these geometries were investigated by testing them in air at different pressure levels, ranging from the atmospheric pressure of 105 Pa to 10-2 Pa. The resulting responses of these geometries followed the same trend as the analytical plot for the rectangular shape structure. As the relative resonant frequency of the structure is proportional to the intrinsic resonant frequency, measured at the lowest pressure levels achieved by the AFM system, different shapes showed different amount of responses as a function of pressure. As the intrinsic resonant frequency of the triangular shape was the highest, its relative resonant frequency was the highest; the modified geometry showed intermediate responses among the three geometries. MEMS devices based on piezoresistive sensing element were designed and fabricated that included regular rectangular, triangular, and the modified geometrical shapes, based on their performances in terms of the mass sensitivities. Piezoresistive measurements of these MEMS devices were performed to characterize the devices, which matched the optical measurement data of those structures. Thus, this project showed the performances of the microcantilever MEMS devices can be improved in terms of sensitivity, by modifying the geometrical shapes of the regular rectangular shaped geometries. Also, the modified shaped geometry showed lesser effect on their resonant frequency response due to damping effect than the triangular shaped geometry. Thus, by using these geometries, part of the reduction in performances of the microcantilever MEMS devices can be recovered.