High sensitive magnetically actuated micromirrors for magnetic field measurement

Magnetically actuated micromirrors have been developed for high sensitivity magnetic field measurement. Computer modelling was carried out to determine the micromirror structure at low field actuation. A novel SOI wafer process was established for micromirror fabrication. The process offers stress-free micromechanical structures without the stiction problem encountered in conventional surface micromachining process. By using two-step etching, the thickness of suspension beams of a micromirror can be independently defined. The new process also made it possible to electroplate a permalloy layer on one side of a micromirror and to maintain a mirror like reflection surface on the other side. The magnetically actuated micromirrors have been characterised using a simple laser beam reflection and CCD camera recording system. The measurement results have confirmed the computer modelling. Magnetic field detection sensitivity of about 1° of mirror deflection per 10−4 T of field intensity has been achieved.