A triaxial tactile sensor without crosstalk using pairs of piezoresistive beams with sidewall doping

This paper reports on a triaxial tactile sensor using piezoresistive beams. The sensor chip is composed of two pairs of sidewall-doped Si beams for shear stress sensing and one pair of surface-doped Si beams for normal stress sensing. The sizes of the shear- and pressure-sensing beams are 180 μm × 15 μm × 20 μm and 250 μm × 50 μm × 20 μm (length × width × thickness), respectively. The sensor chip is embedded in a PDMS sheet 10 mm × 10 mm × 2 mm in size. Because the simple beam structure can be fabricated easily, the proposed sensor is compatible with semiconductor device fabrication. The fabricated sensor was evaluated for normal and shear stress (0-400 kPa and 0-100 kPa, respectively). The responses of the corresponding beam pairs were found to be proportional to the magnitude of the applied stresses without the influence of the other stresses. The relationship between the angle of shear stress and the responses of each beam pair was also evaluated. Each beam pair detects only one axis's shear stress and showed little reaction to the other axes' shear stress. As a result, the proposed sensor can measure the three axial components of normal and shear stress independently.