Infrared vision using uncooled optomechanical camera

An uncooled infrared (IR) imaging system that is based on thermomechanical sensing of IR radiation in conjunction with a visible optical readout has been developed. The system contains a focal plane array (FPA) consisting of bimaterial cantilever beams made of silicon nitride (SiN_x) and gold (Au) in each pixel. Absorption of incident IR radiation in the 8-14 μm wavelength range by SiN_x in each cantilever beam raises its temperature, resulting in proportional deflection due to mismatch in thermal expansion of the two cantilever materials. The FPA design involved maximizing the thermal resistance between the pixel and its surroundings, maximizing the thermomechanical response within the constraints of the pixel size, optimizing the pixel time response, and maximizing the IR absorption using thin film optics. Microfabrication of stress-balanced bimaterial cantilevers was achieved by varying the silicon concentration along the thickness of the SiN_x films in order to balance the residual tensile stress in the Au film and the Cr adhesion layer between Au and SiN_x. The optical readout utilized Fourier diffractive optics to simultaneously detect deflections of all cantilevers using a single light source. The results suggest that objects at temperatures as low as 30 °C can be imaged with the best noise-equivalent temperature difference (NETD) in the range of 2-5 K. It is estimated that further improvements that are currently being pursued can improve NETD below 5 mK.