Millimeter-scale actuator with fiber-optic roller bearings

A technique combining semiconductor processing and fiber-optic technology has been developed to micromachine a 1-cm² silicon die that rolls on two wheels above a flat substrate. Each wheel consists of a glass capillary surrounding a fixed solid glass fiber axle. A 100-silicon die is anisotropically etched to create two variable width v-grooves. Each v-groove has a wide center section and two narrow ends, which is schematically illustrated as -==-. The capillary is free to rotate about the axle in the wide v-groove section while the axle is anodically bonded into the narrow v-groove ends. The gap between the die and the substrate is determined by the narrow v-groove width, fiber diameter, and capillary wall thickness. Several rolling die have been fabricated with 210-120 μm gaps. The coefficient of static friction (μ_S) has been investigated on several substrates as a function of the load on the die. Values for μ_S are compared to an unetched die with a silicon nitride coating. With loads ranging from 0-10 grams, the wheels reduce μ_S by more than 50% on borosilicate glass