A Micromachined and Integrated Tunneling Control Unit and Its Application

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We developed a micro fabricated tunneling unit, a device which can control the magnitude of a tunneling current that passes through a vacuum gap by adjusting the gap diostance with a microactuator. Since the unit has a tunneling tip in the direction lateral to the substrate, we call it a lateral tunneling unit(LTU). The LTU was fabricated by IC-compatible surface micromaching process ; it occupies only 0.5mm*0.5mm in area. Because of its layout and fabrication process, the LUT is suitable for intergrating with each other or with other microstructures on a single substrate. This paper describes the design, the fabrication, and an experimental result which shows LTU's ability to control tunneling current.The LTU was successfully applied to mimute displacement detection. An LTU has a tunneling tip protruding from the chip edge and can be moved back and forth by a microactuator. The tip end was positionea crose to a pranar electrode attached to a PZT actuator. When the PZT actuator moved, the gap between the tip and the opposing electrode was kept constant by moving the tip so that the tunneling current flows through the gap should be constant. The displacement of the planar electrode was determined from the change in the microactuator's driving voltage. Possible applications of displacement detection based on LUT include detection of displacement of the prof-mass of an accelerometer or an AFM cantilever. Arrays of LUT could be used in date-storage devices based on SPM(scanning probe microscopes).