Design rules and test of electrostatic micromotors made by the LIGA process

Abstract

Electrostatic stepping micromotors have been designed with regard to low rotor friction on the axle. The design rules are determined using two-dimensional FEM calculations and taking into consideration the particular rotor position during motion. The motors are fabricated by a fully integrated LIGA process. The minimum driving voltages needed are measured to be about 60 V. Determination of the coefficients of friction in operation completes the rules for future designs.

High-speed microfabricated silicon turbomachinery and fluid film bearings

“…Results presented herein suggest a ratio of mechanical power to turbomachinery volume of over 4 , which is more than twice that achieved by modern aircraft engine technology. Based on microturbine aerodynamic calculations using the MISES CFD code validated herein, silicon microturbines could be designed with an order of magnitude higher power density.…”

“…Previous microfabricated rotating machines have mostly been designed for low force actuation instead of power conversion, hence typically operated at less than 1 m/s of peripheral (tangential) speed, which is two orders of magnitudes less than that required for practical energy conversion applications. Examples include surface micromachined electrostatic micromotors [1], [2], high aspect ratio magnetic and electrostatic micromotors based on LIGA or other electrodeposition techniques [3], [4], and surface micromachined gear trains actuated by electrostatic linear comb drives [5]. Rotors are typically supported by solid contact on a central post, and therefore stiction and wear have been important considerations [6], although lessened by the low-peripheral speed that these devices have operated.…”

Electrostatic micromotor and its reliability

“…There are three micromotor parameters that affect the final operational device characteristics: the motor air-gap size, bearing radius and bearing clearance [52]. Holding all other MEMS parameters constant, reducing the air-gap size increases the motive torque.…”

“…In general, both salient-pole and wobble micromotor performance is enhanced by minimizing the bearing clearance [52,53]. For the salient-pole micromotors, smaller bearing clearances result in reduced bearing friction.…”

MEMS Based on Thin Ferroelectric Layers

“…The parameters of the capacitance electromechanical devices such as driving force, power, reaction time with respect to voltage pulse can be improved by the increase in the field strength in the gaps, as they are proportional to the energy density of the field εε 0 Е 2 /2, where ε and ε 0 are the dielectric permeabilities of the medium and the vacuum. Use of the micromachining for the manufacturing of the electrostatic micromotors allows one to reach significantly smaller gaps (on the order of several micrometers), and to get higher values of electric field strength and energy density (Harness& Syms, 2000;Wallrabe et al,1994;Zappe et al, 1997;Kim & Chun, 2001). The estimates of specific energy output based on the energy density of electric and magnetic fields can be used to determine the gap width necessary for the electric field energy density to be comparable to or higher than magnetic field energy density (~4-5·10 5 J/m 3 with 1 T induction and very high quality of magnetic material).…”