Design, modeling and fabrication of thermal actuated micromirror for fine-tracking mechanism of high-density optical data storage

Abstract

In this thesis, a novel micromirror actuated by four thermal bi-layer cantilevers is proposed as a fine-tracking device for high-density optical disk drives (ODD). Each of the bi-layer cantilevers comprising two material layers with different thermal expansion coefficients can bend vertically and drive an integrated micromirror in the out-of-plane motion. In the meanwhile, the movement of micromirror can be detected by the embedded high-sensitivity piezoresistive sensors on the cantilevers. On the bi-layer cantilever design and modeling, theoretical models are built for thermal-mechanical analysis. Furthermore, finite-element analysis is performed to evaluate the transient responses and thermal deformations under the electrical field. The proposed devices have been fabricated successfully by MEMS technology compatible with standard IC process. The experimental and simulation results show that a micromirror of 225A?m ?? 225A?m can be vertically moved up 1A?m, which is equivalent to 1.4A?m displacement in the track direction of the spinning optical disk, by a lower driving voltage at 3V with 3mW power consumption. The embedded piezoresistive sensor is able to detect the micromirror motion by measuring the resistance change of the cantilever piezoresistive layers. The resistance change of 0.8a?| is characterized when the micromirror is forced down 1A?m by one probe tip. The measured resonance frequency of 7 kHz for the micromirror device is high enough to support high bandwidth servo control in high-density ODD.