Opto-Mechanical Characterization of a MEMS Sensor for Real-Time Infrared Imaging

Abstract

MEMS technology has led to the development of new uncooled infrared imaging detectors. These MEMS detectors consist of arrays of bi-metallic cantilevered beams that deflect linearly as a function of temperature associated with infrared radiation from the scene. The main advantage of these detectors is the optical readout system that measures the tilt of the beams based on the intensity reflected light. This removes the need for electronic readout at each of the sensing elements and reduces the fabrication cost and complexity of sensor design, as well as eliminating the electronic noise at the detector. The optical readout accuracy is sensitive to the uniformity of individual pixels on the array. The hypothesis of the present research is that direct measurements of the change in deflection will reduce the need for high pixel uniformity. Measurements of deflection change for a vacuum packaged detector with responsivity of 2.4 nm/K are made with a Linnik interferometer employing the four phase step technique. The interferometer can measure real-time, full-field height variations across the array. In double-exposure mode, the current height map is subtracted from a reference image so that the change in deflection is measured. A software algorithm locates each mirror on the array, extracts the measured deflection at the tip of a mirror, and uses that measurement to form a pixel of a thermogram in real-time. A blackbody target projector with temperature controllable to 0.001 K is used to test the thermal resolution of the imaging system. The minimum temperature resolution is below 250 mK.