DESIGN AND OPTIMIZATION OF MICROCANTILEVERS
Mo Yang and Cengiz S. Ozkan
GRADUATE STUDENT, US
Keywords: MEMS, Microcantilevers, Biochemical Sensing, FEM Modeling
We discuss the mechanical design and optimization of piezoresistive microcantilevers for use in detecting changes in surface stress upon analyte-receptor binding. Conventional microcantilevers are used along with an optical detection system in many commercially available scaning probe systems, which require a rigorous alignment of the detecting laser beam to the cantilever beam. In a liquid cell environment, turbulence effects could result in additional deflections of the cantilever beam which could render the detection measurements useless. Piezoresistive cantilevers can be utilized to avoid these problems. The fractional change in resistance ( ) for a piezoresistive cantilever is described by the following expression,
where is the piezoresistive coefficient of Sillicon along the <110> axis, is the longitudinal stress, is the transverse stress, t is the thickness of the cantilever, is the Poisson’s ratio, and is a factor that adjusts for the thickness of the piezoresistor. The ( ) ratio is proportional to the stress difference ( ), whose distribution depends on the geometric factors of the layers and the chemo-mechanical forces between the biomolecules and the capture or hybridization layers. The deflection signal can be increased by maximizing the stress difference. In addition, stress concentration regions such as trenches can be employed to increase this stress difference. The use of a double cantilever arrangement can further increase the large stress difference area. Modeling and simulations for piezoresistive cantilevers were conducted using the CFDRCTM.
NSTI Nanotech 2003 Conference Technical Program Abstract