Development of Ultrasonic Image Sensor for Micomachine

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This research was aimed at developing the two-dimensional ultrasonic transducer array employing the composite diaphragm structure for the use of image sensors fo micro-machines. First, fabrication process for the structure were investigated. The "sacrificial layr" technique was employed so as to fabricate a large number of the miniature diaphragms with high density in the same wafer. It was shown that yield for the fabrication of composite structure can considerably be improved by adding very thin Si layr to the structure. This is due to the fact that the internal stress caused during the fabrication is diffused throughout the structure by the compliance of the Si film, which reduces the strain (bending) of the diaphragm dramatically. In addition, etching of sacrificial layr was moved to the final step of the device fabrication. This technique enables to construct very thin composite diaphragms with large area. By using these techniques, composite piezoelectric resonator operating in 7 … More 77MHz was constructed. Its resonant Q attained to 303, comparable to the value obtained by using the bulky anisotropic etching technique instead of the sacrificial layr technique.As a next step of the work, the authors has been trying to apply these fabrication process to the construction of the ultrasonic transducer. However, good results have not been achieved due to remaining stress in the diaphragm, which causes considereble increase in the insertion loss.Through this work, the authors found that considerable amount of liquid stream can be generated by the ultrasonic wave radiated by this kind of high-frequency ultrasonic transducers with high efficiency. This is because very high acoustic power density is realized by the transducer and it is essential so as to cause non-linear phenomena effciently. It was experimentally shown that, by applying acoustic power of only 40mW,liquid surface was lifted about 5mm which mostly coincides with the theoretical prediction. Then the authors proposed ultrasonic micropump and actuators which employ the high frequency ultrasonic transducer arrays for the electrical control of liquid streaming. Less