Fabrication of micromotors using LIGA process

An electrostatic wobble micromotor and a comb drive microactuator were fabricated by the LIGA process. The following design rules for the micromotors were decided: a height of 100 μm, a maximum width for movable parts of 10 μm, a minimum width for fixed parts of 40 μm, a driving voltage of about 100 V, and a minimum gap of 2 μm between movable parts and fixed parts. Calculated torque outputs for the wobble motor and the comb drive actuator were 3.19×10^-8 Nm and 11.33×10^-8 Nm respectively under a driving voltage of 100 V. The basic structure of the micromotors was composed of movable and fixed electrodes of Ni and a sacrificial layer of SiO₂ on a Si substrate. These micromotors were fabricated by a single mask process using LIGA. In this process, the difficult phase is removing the PMMA molds before the sacrificial layer etching of SiO₂. The residual PMMA was removed by the GG developer after a second X-ray exposure without a mask. When the residual PMMA was left between the micropatterns, it was removed completely by using an organic solvent and so on. Therefore, the sacrifice layer etching and drive of the micromotors were successful. Actuation of the micromotors was confirmed. The applied voltage to the wobble motor and the comb drive actuator were 125 V and 65 V respectively. The maximum oscillation of the comb drive actuator was 4.54 μm under a frequency of 2.0×10³ Hz