Heterogeneous Integration of LSI Amplifier and the Tactile Sensor Using Stacking and Through-Si-Via Techniques
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Heterogeneous Integration of LSI Amplifier and the Tactile Sensor Using Stacking and Through-Si-Via Techniques Masayuki Sohgawa1, Hokuto Yokoyama1, Takeshi Kanashima1, Masanori Okuyama1, and Haruo Noma2 1 Osaka University, 1-3 Machikaneyamacho, Toyonaka, Osaka 560-8531, Japan. 2 Advanced Telecommunications Research Institute International, 2-2-2 Hikaridai, Seika, Soraku, Kyoto 619-0288, Japan. ABSTRACT 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. INTRODUCTION In recent years, there have appeared serious problems concerning the relative increase in the aged population and the reduction in the working population in many countries. Therefore, care of the aged and automation in manufacturing have become very important in solving these problems, and human-support robots with skillful performance have attracted much attention. In order to produce the skillful and dexterous robot, excellent sensors are required to detect condition of the object and especially tactile sensor is much valuable for holding the object in the nurse care and the automation. We have developed the tactile sensor using the microcantilevers with strain gauge film, fabricated by MEMS technologies and embedded in the elastomer. The sensor can detect normal and shear forces simultaneously [1-4]. However, there appear some problems. One is the signal noise in the sensor output generated in the long wire from the sensor elements to the signal amplifier. The other is a number of wires for collecting many signals of distributed sensor arrays. These problems can be solved by heterogeneous integration of the sensor and the signal amplifier, and moreover, it is considered that stacking of these chips can reduce the device size and allows installation of more sensors on fingertips of the robot. In this work, the tactile sensor chip and the IC amplifier chip have been stacked and integrated heterogeneously to shorten the wire length and reduce the noise in the output voltage. Firstly, IC amplifier chip was mounted on the surface of the tactile sensor chip (chip stacking). Moreover, through-silicon-via (TSV) holes were fabricated to mount an IC ampl
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