TiNb thin films as absorbers for LWIR microbolometers

Abstract

Uncooled microbolometers use ultra-thin metal or dielectric layer to absorb the incoming longwave infrared (LWIR) radiation. This is due to the fact that thermometer layers in microbolometers are typically of very low LWIR absorption coefficients. In this paper, a novel ultra-thin film alloy of Titanium–Niobium (TiNb) is synthesized using sputter deposition, and further morphologically, compositionally and optically characterized. Simultaneous DC and RF sputtering from Ti and Nb targets is used to deposit a 10 nm thin film of TiNb. The surface morphology of the thin film is studied showing surface roughness of 0.23 nm. Compositional analysis was performed using X-ray photoelectron spectroscopy (XPS) and Electron dispersive X-ray spectroscopy (EDX). LWIR ellipsometry was used to measure the optical constants of the TiNb thin film. Finally, a Fabry-Perot cavity microbolometer configuration is numerically simulated and analyzed to assess the effectiveness of the developed TiNb thin film as an absorber for LWIR microbolometers. The TiNb thin film has shown higher absorptance % in the LWIR band at a wider range of cavity air gap thicknesses, when compared to typically used absorbers, NiCr and Ti. This work shows that TiNb thin films, never considered before as IR absorbers, can be effective IR absorbers for LWIR microbolometers.