Optomechanical uncooled infrared imaging system

Infrared (IR) imaging is a key technology in a variety of military and civilian applications, especially in night vision and remote sensing.; This dissertation presents the design and development of an optomechanical uncooled infrared imaging system. A focal plane array (FPA) composed of two-level bi-material microcantilever pixels absorbs incident IR flux, resulting in a temperature increase at each pixel. Each cantilever beam deflects proportionally to the temperature rise due to bi-material effect. An optical readout system remotely detects thermomechanical deformations of the pixels, and projects the readout signal onto a visible-spectrum charge-coupled device (CCD), yielding a thermal image.; The design of the two-level bi-material microcantilever structure must consider its thermal, thermomechanical, infrared and visible optical performances individually as well as interdependently. Leg structures made of silicon nitride (SiNx) with low thermal conductivity provide thermal isolation approaching the radiative conductance limit of the pixels. Thermomechanical analysis indicates that a silicon nitride/aluminum microcantilever has the optimum performance. The two-level structure and pixel staggering ensure a microcantilever with adequate bi-material segment length, which is critical to maximizing the thermomechanical performance of the microcantilever. An IR absorption structure is designed to maximize temperature sensitivity of the pixels. The metalized surface of the microcantilever serves as an optical reflector in the visible spectrum for optical readout. The FPA is surface micromachined through the deposition and patterning of thin films including phosphorous silicate glass (PSG), low stress SiNx, and undoped poly crystal silicon (PolySi). Wet etching of the sacrificial layers and critical point drying (CPD) release the microcantilevers. A final step thermally evaporates aluminum (Al), forming the bi-material beam and the reflector for optical readout. Two optical readout schemes are developed, (1) using interdigitated fingers for 100 μm x 100 μm pixels; and (2) using local interferometry for smaller 65 μm x 65 μm pixels.; Analysis of system performance indicates that for a system with a pixel size of 65 μm x 65 μm, the theoretical noise equivalent temperature difference (NETD) reaches 10 mK. Characterization of the current system using a temperature controlled uniform heat source yields NETD ∼200 mK at 10 Hz frame rate with f/1 IR optics. Thermal images of room temperature objects (human hand and face) are also demonstrated. A post-processing scheme to correct the non-uniformity in microcantilever initial deflections shows significant improvement in thermal image quality. (Abstract shortened by UMI.)...