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 m icroscopy has been described in detail. ANSYS software has been used as a t ool to design and model the mechanical properties of the silicon based cant ilevers. The incorporation of stress concentration regions (SCRs) with a th ickness smaller than the cantilever thickness, to localize stresses, has be en explored in detail to enhance the piezoresistive displacement, force, an d torque sensitivity. In addition, SCRs of widths less than the cantilever width have also been explored. Two basic designs were studied, i.e. a recta ngular cantilever and a U-shaped cantilever. The placement of the SCR was f ound to be critical, and optimal placement and thickness of the SCR can res ult in a 2x and 5x improvement in piezoresistive displacement and force sen sitivity, respectively, for the rectangular cantilever. For the U-shaped ca ntilever, the torsional piezoresistive sensitivity was found to increase by 5x, depending on the SCR thickness. Process flows and associated fabricati on challenges for the proposed cantilever structures are also presented.