An electro-thermal bimorph-based microactuator for precise track-positioning of optical disk drives

Abstract

Electro-thermal actuations are very attractive since they can generate large deflections and forces with low actuating voltages and their fabrication process is compatible with the general integrated circuit (IC) fabrication process. In this paper, we present a novel electro-thermal bimorph-based microactuator as a precise-tracking positioner for high-density optical disk drives (ODD). In the proposed microactuator, four thermal bimorph cantilevers suspend a mirror plate by linkage hinges at the free ends of the cantilever, whose opposing ends are rigidly attached to the substrate. Each bimorph cantilever comprises two material layers with different thermal expansions. Due to the bimorph effect, the mirror can be displaced upwards in the out-of-plane parallel to the substrate by passing electric current through the cantilevers. Thermal-mechanical analysis, transient responses and mechanical vibrations are investigated by analytical modeling and finite element simulation. The overall device, with an area of 700 µm × 700 µm, is fabricated successfully by MEMS technology compatible with the standard IC process. The experimental and simulation results show that the mirror can be vertically moved up 1 µm, which is equivalent to 1.4 µm displacement in the track direction of the spinning optical disk, by a lower driving voltage at 3 V with 3 mW power consumption. Its mechanical frequency of 7 kHz is high enough to support high bandwidth servo control in high-density ODD.