Microactuators Composed of Silicon Microstructures with a Tunneling-current-Displacement Sensor

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The purpose of this research is to fabricate a micro miniature moving mechanism together with a displacement sensor on a silicon wafer and to obtain micro motion devices integrated with the displacement sensor of nm-order accuracy. Especially, this study focussed on the IC-based micromachining of a tunneling current unit which is built of many components now. Following results are obtained :(1) A silicon diaphragm with thicknesses of around 10 mum was bent electrostatically. The displacement at the center of the diaphragm was utilized as a Z-direction actuator. The silicon wafer was etched an-isotropically with KOH. The displacement was measured by the electrostatic displacement sensor and controlled through the feedback loop. The rise time was 1 ms and the accuracy was 100 nm.(2) An approximate formula to calculate the deformation of the diaphragm was deduced based on the energy principle. Experimental values fit the theoretical curve. It is possible to design a diaphraghm actuator with the formula.(3) A sharp tungsten needle was fixed at the center of the diaphragm. The diaphragm was electrosatically driven to sustain the gap between the needle and a target. The gap was in the order of 1 nm and the tunneling current from 1 to 100 nA was detected.(4) Electrostatic actuators made of a poly-silicon thin film were fabricated. The actuators will be used to drive the target in a X-Y plane parallel to the substrate surface. One actuator had comb-like structures with overlapped teeth as an electrostatic drive. The other had parallel-plate actuators attached at two opposing end of a parallelogram flexture. These actuators were electorstatically driven. AX-Y stage with 4 of second type actuators were fabricated.