Three-axis force sensor miniaturized by 3D microstructuring using high-temperature punch creep-forming process

This study developed a small, three-axis force sensor with a 3D microstructure for installation into a robot gripper. The sensor was manufactured by high-temperature punch creep-forming of 5 μm thick single-crystal silicon (Si) cantilevers during an impurity diffusion process for piezoresistors. The punch creep-forming could achieve a large out-of-plane deformation of the Si cantilevers within a small area. The punch creep-forming simulations were conducted for designing the 3D formed force sensor based on the creep constitutive equation for a 5 μm thick Si film at 1050 °C. Consequently, this study succeeded in fabricating a 3D formed force sensor with a 320 μm diameter hemispheric structure by punch creep-forming without breaking the structure. The force sensor was set on a printed circuit board and packaged using urethane resin. The viscoelastic response of the resin-packaged sensor was evaluated by conducting stress-relaxation (SR) tests and dynamic mechanical analysis, and characterized by a five-element generalized Maxwell model (GMM). In the SR tests, the sensor output signal in the vertical direction showed a strong correlation with the displacement applied to the test, whereas that in the lateral direction was closely related to the load acting on the sensor. Numerical analyses based on the GMM could estimate the load and displacement acting on the sensor from its output signal.