On the design of piezoresistive silicon cantilevers with stress concentration regions for scanning probe microscopy applications

In this paper, the design of silicon based cantilevers for scanning probe microscopy has been described in detail. ANSYS software has been used as a tool to design and model the mechanical properties of the silicon based cantilevers. The incorporation of stress concentration regions (SCRs) with a thickness smaller than the cantilever thickness, to localize stresses, has been explored in detail to enhance the piezoresistive displacement, force, and torque sensitivity. In addition, SCRs of widths less than the cantilever width have also been explored. Two basic designs were studied, i.e. a rectangular cantilever and a U-shaped cantilever. The placement of the SCR was found to be critical, and optimal placement and thickness of the SCR can result in a 2x and 5x improvement in piezoresistive displacement and force sensitivity, respectively, for the rectangular cantilever. For the U-shaped cantilever, the torsional piezoresistive sensitivity was found to increase by 5x, depending on the SCR thickness. Process flows and associated fabrication challenges for the proposed cantilever structures are also presented.