Micro focusing deformable mirror fabricated by combination with silicon based and nonsilicon based micromachining

Abstract

In this work, a micro focusing deformable mirror is designed for fabricated by combination with silicon and nonsilicon based micromachining. The upper electrode and mirror is designed and made by traditional silicon based micromachining in silicon substrate. And lower electrode is fabricated at aluminum substrate. However, the lower electrode is fabricated by nonsislicon based micromachining. From results of numerical analysis, the mirror shape under electrostatic force is parabolic like. Therefore, it would have good focusing performance. And the relationship between structure and metal layers thicknesses of mirror and applying voltages is investigated. The effect of some sizes of mirror on pull-in voltage is also discussed. And then the deformable focusing mirror is fabricated. Due to wafer bonding methods often used in semiconductor like anodic bonding being not suitable used between silicon and aluminum substrates, photo resist SU8 is used to bonding the tow substrates for its good adhere property. And the two substrates are boned tightly and have good isolation between upper and lower electrodes. Some experiments are done to investigate performance of micro deformable focusing mirror. The results show that the mirror needing large applying voltages to deform for large thickness of SU8 photo resist. And the SU8 adhered to silicon and aluminum would be burned to core for too large applying voltage. Therefore, for practical use, other photo resists with thinner thickness should be used instead of SU8. However, the results show photo resist can be used as wafer bonding method for substrates of different materials. And micro focusing mirror designed in this work would have useful focusing ability.