Thin‐film infrared absorber structures for advanced thermal detectors

Imaging thermal detector technology is a rapidly advancing field in which the current emphasis is towards the development of very large arrays of very small pyroelectric detector elements. For maximum responsivity, each of the thin pyroelectric elements (typically ≤25 μm thick) in an array must be provided with a thermal absorber to convert incoming infrared radiation into heat. This absorber must have a low thermal mass compared to the element and a high absorption efficiency to give the maximum responsivity. This paper describes one such absorber structure, comprising a thin metal film, impedance matched to free space, and a quarter‐wave polymer film which offers an acceptably low thermal mass. The structure and properties of this thin‐film absorber are compared with those of an electroplated platinum black absorber commonly used in thermal detectors. The theory of the absorber is presented and good agreement is shown between calculated and experimentally derived absorption spectra. Processing methods a...