A dual-side fabrication method for silicon plate springs with high out-of-plane stiffness

Abstract

Guiding mechanisms guide the motion of a rigid body along a precisely defined path. For small motions flexible elements are well suited to act as joints of a guiding mechanism. Such joints must have high compliance in one, or more, direction(s), while simultaneously having high stiffness in the other directions. Plate springs meet this requirement, but the support stiffness varies per direction. For micro systems such as gyroscopes, microactuators for hard disk drives, and sample stages for high resolution microscopy, it is desirable to have the highest stiffness perpendicular to the direction, or plane, of motion. This increases the accuracy of the motion and makes the device more robust. In this work we present a fabrication method for such high out-of-plane stiffness plate springs. These high aspect ratio springs are designed and fabricated in silicon using a combination of two technologies: dual-side wafer stepper alignment and deep reactive ion etching. The plate springs are characterized by resonance frequency measurements. A model of the plate spring is fitted to the measurement data to discriminate tolerances of the two technologies used in the fabrication process.