Effects of duty cycle and oxygen flow rate on the formation and properties of vanadium oxide films deposited by pulsed reactive sputtering

• VOx films were prepared by using pulsed DC reactive magnetron sputtering techniques.
• Decreasing the duty cycle or increasing the oxygen flow leaded to a smoother surface.
• Oxidation of vanadium can be enhanced significantly with the decrease of duty cycle.
• Deposition rate decrease with the duty cycle more evidently at higher oxygen flow.
• Duty cycle was found can be used to tune the electrical properties of the VOx films.

Vanadium oxide (VOx) thin films were deposited on glass substrates at room temperature by pulsed DC reactive magnetron sputtering. The effects of the duty cycle of the pulsed power and oxygen flow on the surface morphology, deposition rate, composition and electrical properties of VOx films were systematically investigated. Experimental results revealed that decreasing the duty cycle or increasing the oxygen flow leaded to the decrease of the root mean square (RMS) roughness of VOx films. Moreover, the deposition rate decreased with the reduction of the duty cycle, and it also became more sensitive to the duty cycle at higher oxygen flow. Electrical measurements indicated that if the oxygen flow was increased from 3.1 sccm to 3.5 sccm, the resistivity and the temperature coefficient of resistivity (TCR) value of VOx films varied from 0.005 Ω cm to 0.409 Ω cm and from −0.209%/K to −1.485%/K, respectively. Particularly, by adjusting the duty cycle, the maximum value of the resistivity and TCR of VOx films can be achieved as 604.2 Ω cm and −2.864%/K, respectively. X-ray photoemission spectroscopy (XPS) analyses revealed that decrease of the duty cycle or increase of the oxygen flow enhanced the oxidation of vanadium. Therefore, with adjustment of the duty cycle in combination with regulation of the oxygen flow, the thermistor properties of VOx films can be well controlled.