Low temperature charge transport in vanadium oxide (VOx) thin films processed using pulsed dc sputtering is investigated to understand the correlation between the processing conditions and electrical properties. It is identified that the temperature dependent resistivity ρ(T) of the VOx thin films is dominated by a Efros–Shklovskii variable range hopping mechanism [Efros and Shklovskii, J. Phys. C 8, L49 (1975)]. A detailed analysis in terms of charge hopping parameters in the low temperature regime is used to correlate film properties with the pulsed dc sputtering conditions.
Articles you may be interested inProcess-structure-property correlations in pulsed dc reactive magnetron sputtered vanadium oxide thin films J. Vac. Sci. Technol. A 29, 061504 (2011); 10.1116/1.3636372Compositional study of vacuum annealed Al doped ZnO thin films obtained by RF magnetron sputtering Influence of film thickness on texture and electrical and optical properties of room temperature deposited nanocrystalline V 2 O 5 thin films J. Appl. Phys. 103, 043507 (2008); 10.1063/1.2844438 V O 2 films with strong semiconductor to metal phase transition prepared by the precursor oxidation processThe effects of thermal annealing on vanadium oxide ͑VO x ͒ thin films prepared by pulsed-dc magnetron sputtering were studied to explore methods of improving the efficiency of uncooled IR imaging microbolometers, particularly with respect to maximizing the temperature coefficients of resistance ͑TCR͒ ͑typically ϳ2%͒ while minimizing resistivity values ͑typically 0.05-5 ⍀ cm͒. Since high TCR values are usually associated with high resistivities, the experiments were designed to find processing conditions that provide an optimal balance in these properties and to then determine the underlying structural correlations which would enable rational design of thin films for this specific application. VO x films of different compositions were deposited by pulsed-dc reactive sputtering from a vanadium target at different oxygen flow rates. The deposited films were further modified by annealing in inert ͑nitrogen͒ and oxidizing ͑oxygen͒ atmospheres at four different temperatures for 10, 20, or 30 min at a time. The resistivities of the as-deposited films ranged from 0.2 to 13 ⍀ cm and the TCR values varied from −1.6% to −2.2%. Depending on the exact annealing conditions, several orders of magnitude change in resistance and significant variations in TCR were observed. Optimal results were obtained with annealing in a nitrogen atmosphere. Structural characterization by x-ray diffraction, field emission scanning electron microscopy, atomic force microscopy, and Raman spectroscopy indicated changes in the film crystallinity and phase for annealing conditions over 300°C with the onset and extent of the changes dependent on which annealing atmosphere was used.
Articles you may be interested inPotential for reactive pulsed-dc magnetron sputtering of nanocomposite VOx microbolometer thin films J. Vac. Sci. Technol. A 32, 061501 (2014); 10.1116/1.4894268 Microstructural evolution of thin film vanadium oxide prepared by pulsed-direct current magnetron sputtering J. Appl. Phys. 112, 093504 (2012); 10.1063/1.4759255Enhanced electrical and noise properties of nanocomposite vanadium oxide thin films by reactive pulsed-dc magnetron sputtering Electrical and optical properties of sputtered amorphous vanadium oxide thin filmsCathode hysteresis in the reactive pulsed dc sputtering of a vanadium metal target was investigated to correlate the structural and electrical properties of the resultant vanadium oxide thin films within the framework of Berg's model [Berg et al., J. Vac. Sci. Technol. A 5, 202 (1987)]. The process hysteresis during reactive pulsed dc sputtering of a vanadium metal target was monitored by measuring the cathode (target) current under different total gas flow rates and oxygen-to-argon ratios for a power density of $6.6.W/cm 2 . Approximately 20%-25% hysteretic change in the cathode current was noticed between the metallic and oxidized states of the V-metal target. The extent of the hysteresis varied with changes in the mass flow of oxygen as predicted by Berg's model. The corresponding microstructure of the films changed from columnar to equiaxed grain structure with increased oxygen flow rates. Micro-Raman spectroscopy indicates subtle changes in the film structure as a function of processing conditions. The resistivity, temperature coefficient of resistance, and charge transport mechanism, obeying the Meyer-Neldel relation [Meyer and Neldel, Z. Tech. Phys. (Leipzig) 12, 588 (1937)], were correlated with the cathode current hysteric behavior.
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