High sensitivity thermal diode infrared sensors using a thin metal film absorber

Abstract

We demonstrate an improvement in the thermal sensitivity of the MelDIR thermal diode infrared sensor which was launched by Mitsubishi Electric Corporation in 2019. To improve the thermal sensitivity of a MelDIR sensor while suppressing any increase in its thermal time constant, we proposed a high thermal absorption pixel structure using an IR absorber composed of a thin metal film. The thin metal film is deposited on the upper layer of the layer of p-n junction diodes. We used a flat structure which has almost the same layer structure as the original MelDIR temperature sensor to confirm the effect of the thin metal film. The measured results showed that the average IR absorbance of the sample at wavelengths from 8 to 14 μm was improved by up to approximately 160%. This value agrees approximately with the calculated results using a Fresnel equation model. Based on these initial results, we numerically estimated the performance of the temperature sensor used in MelDIR using the high thermal absorption pixel structure and verified that the thermal sensitivity of that used in MelDIR had been improved while also suppressing any increase in the thermal time constant.