The equation that describes the relationship between the applied voltage and the resulting electrostatic force within comb drives is often used to assist in choosing the dimensions for their design. This paper re-examines how some of these dimensions—particularly the cross-sectional dimensions of the comb teeth—affect this relationship in vertical comb drives. The electrostatic forces in several vertical comb drives fabricated for this study were measured and compared to predictions made with four different mathematical models in order to explore the amount of complexity required within a model to accurately predict the electrostatic forces in the comb drives.

Twenty-three fabrication processes for vertical comb drives are summarized and compared in terms of:(1) how they produce the vertical offset between their combs, (2) how they electrically isolate their combs from each other, (3) what materials they fabricate their combs and springs out of, (4) how they achieve horizontal alignment between their opposing teeth, (5) whether they can produce comb drives with both actuation and sensing capabilities and additional directions of actuation, and (6) whether they trim the thickness of their springs separately from that of their comb teeth and whether they are able to produce an initial vertical overlap between their opposing teeth. These comparisons, along with brief descriptions of the processes themselves, are intended to assist in choosing fabrication processes for vertical comb drive designs (or parts of processes from which new ones can be created) that are compatible with whichever micromachining facilities are most easily accessible.

This article describes a preliminary step taken in investigating the potential of vertical comb drives to be used as force-compensation mechanisms in interfacial force microscopes, by exploring the lower limit of the stiffness of the springs the comb drives can be fabricated with. The stiffness of their springs will affect the sensitivity of the microscope. Six vertical comb drives were fabricated for this study; the dimensions of their spring beams were chosen with the intention of giving them stiffnesses of three different orders of magnitude. During fabrication it was found that etching the tops of some of the teeth down to create the vertical offset between the combs can be done using only photoresist to mask the rest of the teeth. The stiffnesses of the fabricated springs were estimated by applying loads to them and measuring their resulting deflections. Weights were applied to the two comb drives with the stiffest springs. Voltages were also applied to them so as to determine the force-voltage relationship for their comb design. Since the other four comb drives had the same comb design, the stiffnesses of their springs could be estimated from the displacements of their movable combs when voltages were applied to them.

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