A self-sensing thermal actuator incorporating micromirror for tracking mechanism of optical drive

A novel self-sensing thermal actuator incorporating a micromirror is proposed as a fine positioning actuator for the precise-tracking mechanism of a high-density optical drive. Due to the bimorph effect, a bilayer cantilever, consisting of two materials with different thermal expansion, can provide force or displacement with change in temperature. In the proposed thermal actuator, an integrated micromirror suspended by four identical thermal bilayer cantilevers is vertically driven to move upwards by a driving voltage. Meanwhile, the mirror position can be detected by an embedded high-sensitivity piezoresistive sensor. The process flow of the self-sensing actuator is presented with the prototypes. The experimental results show that the micromirror can be driven up to an equivalent 1.4 μm displacement in the tracking direction by the driving voltage of 3 V. The device also has a measured resonant frequency of 7 kHz and displacement sensitivity of 0.04 ppm/Å to support high bandwidth servo feedback control in an optical drive.