Terahertz absorption characteristics of nickel-chromium film in a microbolometer focal plane array

Nickel-chromium (NiCr) thin film acted as a terahertz (THz) absorption layer in uncooled infrared (IR) microbolometers operated in the THz spectral range. Nanoscale NiCr thin films with different thicknesses were deposited on the diaphragms of 320 × 240 IR focal plane arrays (IRFPAs). The experiments suggested that the THz absorption of NiCr film increased with the increased frequency. Absorption for a lower frequency decreased whereas that for a higher frequency increased with the decreased film thickness. Optimised absorption for different spectral ranges was achieved by adjusting the NiCr film thickness. A 30 nm NiCr film provided the largest absorption in 0.5-1.5 THz whereas an 8 nm NiCr film showed the greatest contribution in 2-2.5 THz. The THz absorption characteristics of the pixel membrane structure in the IRFPAs coupled with a thin metallic film were modelled and analysed. A good agreement was obtained between the calculations and the measurements.