Infrared detectors based on thin film thermistor of ternary Mn–Ni–Co–O on micro-machined thermal isolation structure

Abstract

Experimental studies on preparation of thin films of ternary compositions of Mn 3O 4, NiO and CoO using ion beam sputtering technique and electrical properties characterization have been carried out. The compatibility of thin films deposited on thermally grown silicon oxide on Si wafer of <1 0 0> orientation to produce thin film thermistors on a thermal isolation structure (TIS) by wet chemical micro-machining process has also been investigated. It is observed from energy dispersive X-ray (EDAX) analysis that the chemical compositions of thin films have close proximity to the target composition, with minor deviations in the individual oxide contents. While the films whose manganese oxide content is higher and nickel oxide lower, have higher thermistor constant 3600 K, and sheet resistance 4×10 7 Ω/sq, the films which have lower manganese oxide and higher nickel oxide are found to have medium thermistor constant 2186 K, and lower sheet resistance 5×10 5 Ω/sq. The micro-machined TIS, analyzed by scanning electron microscope, is observed to have an isolated bridge structure. The voltage–current relationship of the sensor element deposited on the TIS is linear up to an applied bias of 10 V, and the thermal conductivity and the thermal mass of the entire bridge structure are respectively 2.6×10 −6 W K −1 and 1.3 × 10 −9 J K −1. The responsivity, and detectivity of the infrared detector fabricated, using thin film thermistor sensor deposited on a micro-machined TIS together with a suitable infrared absorber coating, are respectively equal to 3000 V W −1 and 4.4×10 8 cm Hz 1/2 W −1 at 10 Hz operating frequency, and the time constant is 0.53 ms.