Design, Fabrication and Testing of Laterally Driven Electrostatic Motors Employing Walking Motion and Mechanical Leverage

Abstract

This paper describes the design, fabrication and testing of laterally driven linear electrostatic micromotors. The motors employ mechanical leverage with the aim to increase the force from the order of 1 μN up to the order of 0.1 mN, in combination with walking motion to increase the stroke to virtually unlimited. Three designs have been made and tested. Although walking motion has been shown to be feasible in MEMS technology, improvement of the clamping is needed to benefit from the use of levers to increase the generated force.

Design, fabrication and testing of laterally driven electrostatic motors employing walking motion and mechanical leverage

“…Calculations with an elastic contact model [9] show that this can already be caused by a single asperity contact, assuming that the stiction is caused by absorbed water layers (capillary forces or hydrogen bonds). In this case a typical value for the work of adhesion is γ = 0.1 J m −2 [8]. The adhesion force of a single asperity with radius R contacting in elastic contact with a smooth surface equals 2π • R • γ [9].…”

“…For proper operation of the motor, the drive beams should be pulled towards the shuttle (lateral pull-in) and not downwards to the substrate (pull-down) by the electrostatic forces. We have therefore developed energy models to calculate the lateral pullin voltage as well as the pull-down voltage [8]. The lateral pull-in voltage has also been determined experimentally.…”

“…Using accurately measured actuator dimensions, the measured voltages squared have been transformed into forces by applying equation (8). The experiment has been carried out using a clamp actuator with 30 plates, and a pull actuator with 15 plates, each plate having an active area of 100 × 5 µm 8), and the effective pull force is given by F pull = α pull • V 2 pull with α pull = (3.8 ± 0.8) × 10 −9 N V −2 .…”

“…This way, the clamp potential U c is only applied to the clamp shoe. A doping mask width of 30 µm was enough to prevent the Boron from diffusing fully underneath the masked region [8]. The size of the clamp shoe (the area of the contacting sidewalls) was designed at 5 × 50 µm 2 .…”

“…The intended step size is 50 nm. Several concepts for the implementation of a lever have been investigated [8]. The implemented concept is a gap-closing actuator in combination with a lever having a constant transformation ratio (figure 15).…”