Sputtering Growth And Photoelectric Properties Of Vanadium Dioxide Composite Films

Vanadium dioxide?VO₂?will change reversibly from monoclinic structure?M?to rutile structure?R?near the phase transition temperature?68 ??,accompanied with sudden changes in electrical and optical properties,so it has great commercial value in the fields of photoelectric switches,smart windows,microbolometers and sensors and so on.In different application fields,VO₂ films should meet different requirements.In the field of smart windows,VO₂ films need to meet the following requirements: lower phase transition temperature,narrower thermal hysteresis loop width,high visible light transmittance and high solar modulation efficiency.When application in the field of microbolometers,VO₂ films need to meet the following requirements: high temperature coefficient of resistance and high response rate.The preparation temperature of VO₂?M?is higher??500 ??than that of metastable VO₂?B?,which is lower??450 ??.Therefore,this thsics mainly focuses on the metastable B-phase VO₂,and a series of high-quality VO₂?B?films are prepared on silicon and quartz substrates by RF magnetron sputtering.By inserting buffer layers with different properties,the specific structure transformation of VO₂ was realized,the crystallinity and purity of the films were improved,and the photoelectric properties of VO₂ films were optimized.The microstructure and phase structure of the samples were characterized by scanning electron microscopy?FESEM?and X-ray diffraction?XRD?.The relationship between sheet resistance and temperature,transmittance and temperature of the samples were measured by four probe resistance tester and visible-near-infrared-infrared spectrophotometer.The paper mainly includes the following aspects:?1?The phase transformation characteristics and structural changes of VO₂ thin films are analyzed,and several methods of preparing VO₂ thin films are introduced.The VO₂?B?thin films were successfully prepared at a substrate temperature of 400 ? and oxygen argon ratio of 5 sccm: 105 sccm by RF magnetron sputtering,and grown along?001?crystal type.The films have uniform grain size and high repeatability.?2?In order to apply in the field of smart windows,the composite structure of VO₂/Ti O₂/glass was prepared on VO₂?B?by inserting Ti O₂ as buffer layer.With the increase of buffer thickness,VO₂?B?changes to VO₂?M?,and the films quality are the best when the buffer thickness is 50 nm.Before and after the phase transition,the resistance changes rate up to 2.5 orders of magnitude,the phase transition temperature is 66.7 ?and the thermal hysteresis loop width is 7.1 ?,the visible light transmittance reaches 55.5 %,and the solar modulation efficiency is up to 8.6 %,which has far-reaching significance for the application in smart windows.?3?It is further found that V₂O₃ has the same corundum structure as sapphire,which can realize the epitaxial growth of VO₂ thin films.V₂O₃ thin films were successfully prepared at the oxygen argon ratio of 5 sccm:110 sccm and substrate temperature of 400 ?.The films have uniform grain size and high repeatability.?4?The composite structure of VO₂/V₂O₃/substrate was designed to be used in microbolometer.The resistance value is controlled in a lower range?20.7 K?-40.0 K??,and the temperature coefficient of resistance value is from?-2.33 %/K?up to?-3.24 %/K?,which meets the requirements of microbolometer.So V₂O₃ can be used as buffer layer to improve the performance of VO₂?B?film.The experimental basis is provided for the application of the microbolometer.