AVS 56th International Symposium & Exhibition
    Thin Film Monday Sessions
       Session TF1-MoM

Paper TF1-MoM9
Process Control of Vanadium Oxide Thin Films Grown by Pulsed-dc Reactive Sputtering for Microbolometer Applications

Monday, November 9, 2009, 11:00 am, Room B3

Session: Thin Films: Growth and Characterization I
Presenter: C. Venkatasubramanian, The Pennsylvania State University
Authors: C. Venkatasubramanian, The Pennsylvania State University
W.R. Drawl, The Pennsylvania State University
S.S.N. Bharadwaja, The Pennsylvania State University
M.W. Horn, The Pennsylvania State University
S. Ashok, The Pennsylvania State University
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Low resistivity thin films of vanadium oxide with high temperature coefficient of resistance (TCR) are currently used as the imaging layer in uncooled infrared imaging. However, process control remains an issue because the films are formed under oxygen-starved conditions. In this paper, the influence of cathode current (target current) hysteresis on the properties of pulsed-dc reactive sputtered vanadium oxide thin films is investigated. VOx thin films were sputter deposited from a vanadium metal target under different Ar/O ratios. The gas flow rates and oxygen partial pressures were varied systematically, and the corresponding changes in the cathode current were monitored. Increasing the gas flow rate from 10 sccm to 100 sccm caused the cathode current to decrease by ~25%, but on reversing the flow rate, the cathode current did not go back up along the same curve, instead exhibiting a hysteretic behavior. A similar trend was observed for the change in oxygen partial pressure between 0 and 20% as well. The width and position of the hysteresis curve depends on the relative values of the gas flow rates and the oxygen partial pressures. VOx thin films deposited at various points along the hysteresis curve were evaluated using four-probe resistivity measurements over a wide temperature range. The room temperature resistivity of the films varied by more than six orders of magnitude and was found to have a progressive dependence on the cathode current. Structural characterizations such as X-ray diffraction and transmission electron microscopy studies indicated that the microstructure changes gradually from nano-crystallite to amorphous nature with the increase in total gas flow rate and/or oxygen partial pressure.