APPLICATION OF INTERFEROMETRIC ENHANCEMENT TO SELF-ABSORBING THIN-FILM THERMAL IR DETECTORS

Uncooled thermal IR detectors require a suitable absorbing mechanism in order to achieve efficient radiation capture. For bulk detector materials such as ferroelectric ceramics this mechanism may be a broad-band absorber in the form of a metallic black layer, or a thin-film optical interference filter tuned for maximum absorption at the desired wavelength, deposited onto the surface of the detector. A thin metal film having a sheet resistance of 189 OMEGA per square can absorb 50% of incident radiation, and is employed in the metal film resistance bolometer detector and Golay cell. In this paper an interferometric technique for thin film thermal detectors is described, whereby a thermally sensitive material in the form of a semiconductor or dielectric layer becomes an integral component of a 3-layer absorber stack. The theory of this absorber structure is reviewed and compared with experimental data. It is shown that an effective absorption of 90% can be achieved over the waveband 8-13 mum for a blackbody radiation source at 300 K temperature.