Bolometric properties of reactively sputtered TiO2-x films for thermal infrared image sensors

Abstract

A heat-sensitive layer (TiO2-x) was successfully deposited by RF reactive magnetron sputtering for infrared (IR) image sensors at different relative mass flow of oxygen gas (R-O2) levels. The deposition rate was decreased with an increase in the percentage of R-O2 from 3.4% to 3.7%. TiO2-x samples deposited at room temperature exhibited amorphous characteristics. Oxygen deficiency causes a change in the oxidation state and is assumed to decrease the Ti4+ component on the surfaces of TiO2-x films. The oxygen stoichiometry (x) in TiO2-x films decreased from 0.35 to 0.05 with increasing the RO2 level from 3.4% to 3.7%, respectively. In TiO2-x-test-patterned samples, the resistivity decreased with the temperature, confirming the typical semiconducting property. The bolometric properties of the resistivity, temperature coefficient of resistance (TCR), and the flicker (1/f) noise parameter were determined at different x values in TiO2-x samples. The rate of TCR dependency with regard to the 1/f noise parameter is a universal bolometric parameter (beta), acting as the dynamic element in a bolometer. It is high when a sample has a relatively low resistivity (0.82 Omega.cm) and a lower 1/f noise parameter (3.16 x 10(-12)). The results of this study indicate that reactively sputtered TiO2-x is a viable bolometric material for uncooled IR image sensor devices.