Broadband mid-infrared carbon black and single-wall carbon nanotube absorbers for thermally isolated LiTaO3-based pyroelectric detectors

Pyroelectric infrared (IR) detectors constitute a critical component in optical-based gas sensing systems, enabling selective detection of gas species through their characteristic mid-IR absorption signatures. We present the detailed comparison of the carbon black (CB) and single-wall carbon nanotubes (SWNTs) as broadband mid-IR absorbers along with their application in fabricating the pyroelectric IR detector utilizing single-crystal lithium tantalate (LiTaO3) as the active sensing material. The LiTaO3 crystal is integrated onto an anisotropically etched silicon (Si) carrier using tetramethylammonium hydroxide (TMAH), which minimizes heat dissipation to the surrounding environment through convection. To enhance IR absorption, two distinct absorber layers, CB and SWNTs, are investigated. CB films exhibit an absorption efficiency exceeding 98% at a 2.5 μm wavelength and maintain an absorption above 92% across the mid-IR spectrum (2.5 to 25 μm). By contrast, SWNTs display a decrease in absorption from 64% at 2.5 μm to 32% at 5 μm, followed by a gradual decrease to 20% at 25 μm. Performance evaluation is carried out using a 1-Hz pulsed IR signal, with the detector’s output response being recorded. The pyroelectric detector incorporating CB absorber demonstrates a peak-to-peak (Vpp) output voltage of 2.2 V, significantly higher than the 0.17 V observed with the SWNT-based detector. These results highlight the superior absorption characteristics of CB, making it suitable for low-frequency applications, where high responsivity is needed, whereas SWNTs are more appropriate for high-frequency detection in mid-IR pyroelectric sensing applications.