Movable microstructures made by a sub-micron LIGA process

Abstract

Movable microstructures with high aspect ratios were made with lateral dimensions down to the sub-micron domain by the LIGA process and a sacrificial layer technique. Compared to microstructures usually made by LIGA, all dimensions were reduced approximately by a factor of 10, while the aspect ratio was kept constant. The smaller resist thickness in the range of some ten micrometers allowed much lower X-ray doses and energies to be used for exposure and the absorbers with a thickness of only 3 μm to be employed. As the lateral dimensions are smaller, a much larger number of devices can be fabricated in one batch. Therefore, the production costs of deep etch X-ray lithography are reduced dramatically. Electrostatic linear actuators with lateral dimensions as small as 500 nm were manufactured to demonstrate the advantages of LIGA in sub-micron dimensions. An X-ray mask with absorbers 2.8 μm high was produced by a three-level technique. The linear actuators consisted of several arrays of capacitor plates combined into an electrostatic driving unit with an active area, typically, 0.3 mm2 and less. The driving unit was supported by folded beam flexures to avoid frictional forces. They also guaranteed parallel movement of the capacitor plates. The functionality of these devices was demonstrated by measuring displacement as a function of the voltage applied.