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A miniature tactile sensor has been fabricated by connecting stress-sensitive part with an amplifier of integrated circuit through through-silicon-via (TSV) electrically. The sensitive part consists of three warped cantilevers with piezoresistive NiCr thin film which are prepared on a silicon-on-insulator wafer by the surface micromachining technique. The TSV connection can reduce noise of detected change of the piezoresistive output induced by wire between the sensitive part and the amplifier. Fabricated tactile sensor of 5×5 mm2 size has linear dependence of the output on both normal and shear forces. The output noise has been successfully decreased by 14 and 34% in the sensor using the TSVs compared with that using wires of 3 and 6 mm lengths, respectively.

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We have developed the tactile sensor using the microcantilevers with strain gauge film which can detect normal and shear forces simultaneously. In this work, the tactile sensor and the IC amplifier have been integrated heterogeneously to shorten the wire length by chip-on-chip stacking and reduce the noise in the output voltage. Standard deviation of the noise can be reduced from 27.6 mV to 3.3 mV by heterogeneous integration of the tactile sensor and the IC amplifier using Au wire bonding. By this heterogeneous integration, the device size and wiring numbers can be reduced, and installation of more sensors is allowed on fingertips of the robot. Moreover, through-silicon-via (TSV) holes were fabricated to mount an IC amplifier on the backside of the sensor chip, instead of using Au wires. Although TSV can be fabricated successfully, resistance to sacrificial etching process is problem. As a result, Si3N4 used instead of SiO2 has improved insulation between TSVs.