TABLE OF CONTENTS Translational motions can be generated by a comb drive actuator, as is depicted in Figure 12. The structure is generally patterned in conductive material, like metal or doped silicon (crystalline or poly-crystalline silicon). One of the electrodes is fixed, the other one is free to move, mechanically linked to the substrate by supporting springs but electrically isolated from it.
The development of Equation 4 has indicated that when a voltage difference is applied between the electrodes, the resulting electrostatic forces act to increase the value of the actuator capacitance. According to Equation 4, the force along an x-axis is expressed as:
For a given actuator thickness, the comb structure permits enlargement of the effective surface of the electrodes in interaction and consequently to increase the capacitance and the generated electrostatic forces. Depending on the electrodes topology and the support spring geometry, the mobile electrodes can basically move in the three directions, as it is shown in Figure 13.
Figure 13 details basic comb drive configurations that have already been implemented in operational microsystems (inertial sensor, accelerometers, resonator, positioning devices ).
From the one dimensional force expression, Equation 14, the generated electrostatic force for each of the elementary structures in Figure 13 can be easily derived.
