An Electrothermal Micromirror Array Integrated with Thermal Convection-Based Mirror Position Sensors

A novel electrothermal micromirror array integrated with thermal convection-based mirror position sensors is proposed, in which a heater is integrated on the mirror plate to generate a temperature distribution that will be changed by the movement of the mirror plate. The temperature change is then picked up by the thermistors integrated on the substrate. Both the displacement and the tip-tilt angle can be detected. A 3×3 micromirror array has been successfully fabricated. Experiments show an average sensitivity value of 8.6 mV/μm in the displacement range of 50 μm to 150 μm, and an average sensitivity of 95.5 mV/° in the angular scan range of 2° to 10°.

INTRODUCTION

MEMS micromirror arrays (MMAs) can be widely applied in displays [1], adaptive optics systems [2], optical phased arrays (OPAs) [3], and optical cross-connects (OXCs) [4]. Electrothermal actuation has been used to make micromirror arrays [5] - [7], among which electrothermal bimorph actuation has lower power consumption than thermopneumatic actuation [7]. Electrothermal bimorph actuation also has much larger actuation range and lower driving voltage than electrostatic actuation. For electrothermal micromirror arrays with electrothermal bimorph actuators, the variations of film thicknesses and widths in the bimorph structure can cause the response errors and the inconsistency among the bimorph actuators of each micromirror and among the micromirrors in the array as well. Therefore, it is important to accurately control the mirror plate position (vertical displacement and tip-tilt angle) of every micromirror, while considering the complexity, volume, fabrication process compatibility and cost of the position sensing and control system. The closed-loop control of the mirror plate position requires an integrated mirror plate position sensor.