Stanley Electric Co., Ltd. has developed a mirror device having an actuator with an innovative structure which is for use in an ultracompact projector system, and exhibited it at the MEMS 2007 event. The ultracompact projector is a device targeting mobile phones, which can project images on the wall or the like by scanning full-color laser light by micromirrors.
Stanley developed a micromirror actuator able to scan laser light along two axes in vertical and horizontal directions with the use of piezoelectric elements. In spite of its large driving force, a piezoelectric-driven actuator can only produce a small deflection. The company succeeded in increasing the deflection by the adoption of a new proprietary structure.
Generally, in biaxial scanning performed by a single chip, it is difficult to perform driving along two axes based on the resonant frequency because the driving frequency in the horizontal direction is very much higher than that in the vertical direction. For this reason, Stanley decided to use the non-resonant frequency for the vertical driving. The company employed a piezoelectric driving method with the use of PZT. Although piezoelectric driving involves a problem of small deflection, it was solved by the adoption of the new structure.
An actuator section in a meandering form including multiple actuators is provided in the new structure. The deflection produced by these actuators is accumulated to result in a larger deflection in total.
The company has already developed a technique called "arc discharged reactive ion plating (ADRIP)," a process to form a PZT film with uniform crystals which is necessary for piezoelectric driving. The technique allows the formation of film at a rate of 3 μm/h in an environment at a comparatively low temperature of 500°C.