High resistivity and high TCR vanadium oxide thin films for infrared imaging prepared by bias target ion beam deposition

Vanadium oxide (VOx) thin films have been intensively studied as an imaging material for uncooled microbolometers due to their low resistivity, high temperature coefficient of resistivity (TCR), and low 1/f noise. Our group has studied pulsed DC reactive sputtered VOx thin films while reactive ion beam sputtering has been exclusively used to fabricate the VOx thin films for commercial thermal imaging cameras. The typical resistivity of imaging-grade VOx thin films is in the range of 0.1 to 10 ohm-cm with a TCR from -2%/K to -3%/K. In this work, we report for the first time the use of a new biased target ion beam deposition tool to prepare vanadium oxide thin films. In this BTIBD system, ions with energy lower than 25ev are generated remotely and vanadium targets are negatively biased independently for sputtering. High TCR (>-4.5%/K) VOx thin films have been reproducibly prepared in the resistivity range of 103-104 ohm-cm by controlling the oxygen partial pressure using real-time control with a residual gas analyzer. These high resistivity films may be useful in next generation uncooled focal plane arrays for through film rather than lateral thermal resistors. This will improve the sensitivity through the higher TCR without increasing noise accompanied by higher resistance. We report on the processing parameters necessary to produce these films as well as details on how this novel deposition tool operates. We also report on controlled addition of alloy materials and their effects on VOx thin films' electrical properties.