A MEMS shield structure for controlling pull-in forces and obtaining increased pull-in voltages

By interposing a conductive shield with an opening between the movable microelectromechanical systems (MEMS) component and the substrate, it is possible to control pull-in forces and to increase pull-in voltages. Modeling results for different opening diameters are presented for a planar structure and one that contains a field emitter tip. Pull-in voltages can be increased from about 2 V (with no shield) to about 12 V with a 7 mum diameter shield hole and to 25 V with a 2 mum shield hole. This shield technology will be demonstrated on a MEMS-activated field emitter amplifier in which the gate plate of a field emitter array is thermally activated and moves with respect to the stationary tips. For a 6.7 mum diameter shield hole, the pull-in voltage is 30 V. This higher voltage, as compared to the modeling results, is caused by built-in stresses that curve the gate cantilever away from the substrate. In order for this concept to work, the field emitter operating voltage has to be smaller than the gate pull-in voltage.