A robust lateral shift free (LSF) electrothermal micromirror with flexible multimorph beams

Electrothermal bimorph-based scanning micromirrors typically employ standard silicon dioxide (SiO2) as the electrothermal isolation material. However, due to the brittle nature of SiO2, such micromirrors may be incapable to survive even slight collisions, which greatly limits their application range. To improve the robustness of electrothermal micromirrors, a polymer material is incorporated and partially replaces SiO2 as the electrothermal isolation and anchor material. In particular, photosensitive polyimide (PSPI) is used, which also simplifies the fabrication process. Here, PSPI-based electrothermal micromirrors have been designed, fabricated, and tested. The PSPI-type micromirrors achieved an optical scan angle of +/- 19.6 degrees and a vertical displacement of 370 mu m at only 4 Vdc. With a mirror aperture size of 1 mm x 1 mm, the PSPI-type micromirrors survived over 200 g accelerations from either vertical or lateral directions in impact experiments. In the drop test, the PSPI-type micromirrors survived falls to a hard floor from heights up to 21 cm. In the standard frequency sweeping vibration test, the PSPI-type micromirrors survived 21 g and 29 g acceleration in the vertical and lateral vibrations, respectively. In all these tests, the PSPI-type micromirrors demonstrated at least 4 times better robustness than SiO2-type micromirrors fabricated in the same batch.