Study On The Preparation Of VO₂ Film By High Power Impulse Magnetron Supttering And Its Infrared Emissivity Properties

The thermal control system is one of the important guarantee systems for maintaining the normal operation of the spacecraft.The traditional thermal control system can no longer meet the needs of spacecraft adaptive temperature control.VO₂ is a phase change material whose emissivity can be adaptively changed with the ambient temperature to dynamically adjust the temperature of the spacecraft.In this paper,VO₂ thin films were prepared by high energy pulsed magnetron sputtering（HiPIMS）and their emissivity properties were studied.Firstly,the effects of pulse width,sputtering power,oxygen-argon ratio and pressure on the target current were studied during the preparation process,and the variation of the target current was obtained:the increase of the pulse width caused the target current to gradually decrease;The increased of the oxygen-argon ratio,the sputtering power and the pressure will cause the rise of the target current.Through the above research,the preparation parameters were adjusted.The film prepared at a pulse width of 50μs and an oxygen flow rate of 1.4 sccm had certain phase transition characteristics,indicating that the film contained M phase VO ₂.Subsequently,the sputtering power and preparation temperature of VO₂ were optimized.The film with flat surface,small roughness,high transmittance,good crystallinity were prepared when the sputtering power is 260W and 270W.The film’s transmittance change at 2500 nm exceeds 45%,and the V element in the film is mainly V⁴⁺.When the preparation temperature is 540℃,the sputtering power of VO₂ can be adjusted widely.The transmittance of the optimal VO₂ film at 2500nm is close to 60%,and the surface of the film is flat and dense,and obvious crystal grains appear.The V element on the surface of the film is mainly V⁴⁺.When the preparation temperature is lowered to 480℃,the film crystallinity becomes weak,the degree of phase transition is not obvious,and the transmittance is relatively low.The phase transition temperature of VO₂ film at different preparation temperatures was tested.The results show that the phase transition temperature of the prepared VO₂ film is at least 49℃,and the hysteresis loop width is 6℃.This is mainly due to the small size and uniform size distribution of the VO₂ film prepared by high-energy pulsed magnetron sputtering.Based on a single polished aluminum sheet,the sputtering time was controlled to obtain VO₂ films of different thicknesses,and the thermal radiation characteristics of the films at different thicknesses were investigated.The results show that the film exhibiting a phase change of 40 min after sputtering has a temperature of 15.3℃ higher than that of the aluminum film.The emissivity of this sample is also the largest,which can reach 0.117.This is mainly because the increase in the thickness of the VO₂ film leads to an increase in infrared absorption,so that the film with the longest sputtering time has a large change in emissivity.