Preparation and characterisation of transition metal oxide micro-thermistors and their application to immersed thermistor bolometer infrared detectors

Abstract

Transition metal oxide thermistors consisting of manganese oxide (Mn3O4), nickel oxide (NiO) and cobalt oxide (CoO) in the ratio of 52:16:32 parts by weight are prepared by tape casting technique followed by high temperature calcination and sintering. The resultant thermistors whose linear dimensions, length (l), width (w) and thickness (t) are 650, 150 and 15 μm, respectively show evidence of phase formation of nickel manganese oxide (NiMn2O4) and manganese cobalt oxide (MnCo2O4) which takes place in the temperature range of 550–700 °C. The surface morphology of thermistors sintered at 1000 °C exhibits a well-sintered growth and better particle-to-particle connectivity and crystalline facet formation and the thermistors have packing density in the range of 87–90%. Optically immersed thermistor bolometer infrared (IR) detectors packaged using these thermistors, with an aspect ratio l/w≈1, are found to have noise voltage in the range of 0.3–4 μV/√Hz, responsivity in the range of 600–1000 V/W and field of view (FoV) of ±20°. The observed peak-bias voltage (Vp) of the thermistors and the time constant (τ) of the detectors obey square-root-law, i.e. Vp is proportional to (τ)−1/2 and the detectors whose thermistors have higher peak bias voltage and lower noise voltage show better environmental durability.