Design of a sensitive uncooled thermal imager based on a liquid crystal Fabry-Perot interferometer.

Abstract

Microbolometers are the dominant technology for uncooled thermal imaging; however, devices based on a direct retardation measurement of a liquid crystal (LC) transducer pixel have been shown to have comparable sensitivity. In this paper, an approach for increasing LC transducer sensitivity utilizing an etalon structure is considered. A detailed design for an LC resonant cavity between dielectric mirrors is proposed and the performance is evaluated numerically. The measured quantity is the transmission of a visible wavelength through the etalon, which requires no thermal contact with the IR sensor. Numerical and analytical calculations that consider a 470 nm thick LC pixel demonstrate that the change in transmitted intensity with temperature is 26 times greater in the device based on a resonant structure than in a device based on a direct retardation measurement. Finally, the paper discusses how the dielectric mirror materials, dimensions of the resonant cavity structure, and expected process tolerances affect the sensitivity of the device.