Design of a piezoresistive triaxial force sensor probe using the sidewall doping method

In this study, we propose a triaxial force measurement sensor probe with piezoresistors fabricated via sidewall doping using rapid thermal diffusion. The device was developed as a tool for measuring micronewton-level forces as vector quantities. The device consists of a 15 μm thick cantilever, two sensing beams and four wiring beams. The length and width of the cantilever are 1240 μm and 140 μm, respectively, with a beam span of 1200 μm and a width of 10-15 μm. The piezoresistors are formed at the root of the cantilever and the sidewalls of the two sensing beams. The sensor spring constants for each axis were measured at k_x = 1.5 N m^-1, k_y= 3.5 N m^-1 and k_z = 0.64 N m^-1. We confirmed that our device was capable of measuring triaxial forces with a minimum detectable force at the submicronewton level.