【作者】 黄章立；

【导师】 陈四海； 陈长虹；

【作者基本信息】 华中科技大学 ， 光电信息工程， 2013， 博士

【摘要】 由于VO₂在68oC时会发生金属-绝缘体相变而为人所知，在发生金属-绝缘体相变的过程中，VO₂的晶体结构也会随之发生变化，由低温时的单斜结构转变为高温时的四方金红石结构。同时相变也会引起VO₂薄膜光学和电学性能的突变。本论文在分析VO₂薄膜的相变机理基础上，详细讨论和分析了基底类型、基底温度、氧分压以及退火条件等工艺参数对VO₂薄膜相变性能的影响；同时比较了目前几种常用的制备VO₂薄膜的方法。本课题的主要工作是采用磁控溅射法和离子束溅射法制备具有较低相变温度的VO₂薄膜的工艺、相变特性、及智能窗和激光防护等应用研究。详细的理论分析、工艺与实验测试、以及成果如下：在VO₂薄膜相变理论方面，首先介绍了VO₂晶体结构，分析了VO₂晶体相变前后能带的变化。其次介绍了VO₂薄膜相变温度的影响因素，如制备参数、内应力、表面结构以及元素的掺杂等，深入分析了以上因素对VO₂薄膜相变温度的影响机理，用以指导后续的低相变温度薄膜沉积工艺实验。通过对理论知识的运用，实验中采用LD-3型离子束溅射和后退火工艺两步法在Si3N4/玻璃基底上制备了相变温度非常接近室温的VOx薄膜，研究了基底温度、氧分压以及退火温度对VOx薄膜性能的影响。结果表明，在其它工艺参数保持一致的情况下，如Ar、O2流量比为：60:30SCCM（标况毫升每分），退火温度为430oC时，随着基底温度的升高（250～310oC），薄膜的相变温度也随之升高（29～35oC）。其次，Ar、O2流量比不仅对薄膜的相变温度有具大影响，而且对薄膜的光调制深度也有较大影响。在其它工艺参数保持一致的情况下，如基底温度为280oC，退火温度为430oC时， Ar、O2流量比为60:20、60:30以及60:40SCCM获得的薄膜的相变温度分别为36、30和32oC。最后，退火温度也对薄膜的性能有重大影响，当基底温度为280oC，Ar、O2流量比为60:30SCCM时，退火温度为400、430和460oC的薄膜的相变温度分别为35、30和34oC。最终，总结得出采用该种方法制备VO₂薄膜的最优工艺参数为基底温度280oC，氧分压为60:30SCCM以及退火温度430oC，其获得的VO₂薄膜相变温度为30oC，最大光调制深度为85%。其次，采用MSP-3200E型磁控溅射和后退火工艺两步法在蓝宝石基底上制备了相变温度为45oC的VO₂薄膜。制备的工艺参数为基底温度300oC，Ar气流量为40SCCM，氧气流量为5SCCM，退火温度为460oC以及退火时间60分钟。原子力显微测试结果表明，所获得的VO₂薄膜颗粒大小约为100nm，电学和光学测试表明该VO₂薄膜具有良好的相变性能以及较高的红外光调制深度，可以很好的应用于太阳能智能窗以及激光防护。再次，采用丹顿真空科技有限公司生产的HDG双离子源沉积设备室温条件下在不同类型的基底上制备出相变温度接近68oC的VOx薄膜，红外光调制深度高达94%。在此基础在，通过掺入2%（原子浓度比）的W元素，在玻璃基底上获得了相变温度为34±1oC的W-VO₂薄膜，X射线光电子能谱以及拉曼光谱分析结果显示W元素以+6价的离子形式存在于薄膜中。电学与光学测试结果表明，所获得的W-VO₂薄膜相变温度非常接近室温，但是相变幅度不大，并且红外光调制深度仅为60%，与前两者有较大的差距。不过室温沉积以及容易控制的退火工艺为其工业生产打下了良好的基础，另外，较短的退火时间不仅可以节约成本，而且可以加快生产进程。在VO₂薄膜的应用方面，将MSP-3200E磁控溅射设备制得的VO₂薄膜样品进行太阳能智能窗和激光防护等应用研究。太阳能智能窗模拟实验表明，该VO₂薄膜具有很好的智能调节温度能力，高温下可以使室内温度维持在47oC左右。激光防护实验结果表明，该VO₂薄膜具有较强的激光抗损的能力，其能承受功率密度高达1.46×103W/mm2的激光的照射。在论文的最后，对本工作取得的成果以及存在的一些问题作了总结，对未来的工作进行了展望。更多还原

【Abstract】 Vanadium dioxide （VO₂） is well-known for its sharp metal-insulator transition （MIT）at68oC which is accompanied by a structural transition from monoclinic （low temperature）to tetragonal （high temperature） phase. This transition also brings with it abrupt changes inthe optical and electrical properties. Based on the phase transition theory, the dissertationpresents a detail discussion of fabricating-condition influence on the transition performanceof VO₂thin films, such as type ofsubstrate, substrate’s temperature, Ar and O2gas mixtureratio, and thermal annealing process. Additionally, several kinds of deposition methods areintroduced, such as Sol-Gel, magnetron sputtering, ion beam sputtering, plused laserdeposition, chemical vapor deposition, and so on. The main purpose of this work is tofabricate VO₂thin films with low phase transition temperature by appling magnetron andion beam sputterings. The main contents including theory analysis, experiments, and resultsare summarized as follows:First, the changes in VO₂lattice and band structures during the phase transition areintroduced. Furthermore, impact factors for Ttvalues of VO₂thin films are discussed, suchas the deposition condition, lattice strains, surface structure and doping, and the mechanismof the above factors to determine the VO₂film Ttis analysed to guide the followingexperiments.Second, nanostructural vanadium oxides （VOx） thin films with low MIT temperaturewere fabricated through reactive ion beam sputtering （LD-3） followed by a thermalannealing process. The VOxfilms were grown on borosilicate glass substrate with a Si3N4buffer layer at varying substrate temperature, Ar and O2gas mixture ratio and the annealingtemperature. The electrical resistance tests indicate that the films’ Ttrises （from29to35oC）as the growth temperature increases （from250to310oC）. Besides, change of Ar and O2gasmixture ratio has significant impact on the films’ transition temperature and switchingefficiency. VOxthin films fabricated with Ar and O2gas mixture ratio of60:20,60:30and60:40SCCM （standard-state cubic centimeter per minute） exhibit a phase transitionfeature at the temperature of36,30and32oC, respectively. Additionally, the VOxthin filmsshow a phase transition character at temperature of35,30and34oC, as the samplesannealed at400,430and460oC, respectively. It can be concluded from the above resultsthat the optimum conditions for fabricating VO₂thin films are: substrate temperature280oC, Ar and O2mixture ratio60:30SCCM and annealing temperature430oC.Third, VO₂films with a low MIT temperature of45oC were fabricated through directcurrent magnetron sputtering （MSP-3200E） followed by a post-annealing. The process parameters are: substrate temperature300oC, Ar flow40SCCM, O2flow5SCCM,annealing temperature460oC and annealing time60min. Atomic force microscopymeasurements show that the VO₂grain size is about one hundred of nanometers. Theresults of electrical and optical tests reveal that the VO₂film not only exhibits outstandingchange in resistace, but also behaves excellent IR switching property, which make the VO₂thin film a proming material for smart window and laser protection application.Fourth, VOxfilms with MIT temperature around68oC on different types of substrateshave been prepared by HDG dual ion source vacuum equipment at room temperature （RT）and a short time thermal process. The IR transmittance measured below/above Tt illustratesthe VOxpossess excellent switching efficiency. Furthermore, tungsten-doped VO₂（V0.98W0.02O2） thin films with low MIT Ttof34±1oC were grown on borosilicate glasssubstrates with varying annealing temperature. X-ray photoelectron spectroscope andRaman measurements demonstrate that the tungsten atoms have been successfully dopedinto VO₂films and exist as the form of W6+in the films. Although the tungsten-doped VO₂films show a MIT near RT, i.e.34±1oC, the amplitude of the transition and the switchingefficiency confirmed by the electrical and optical measurements are not good enoughcompared with the previous studies. Nevertheless, the RT deposition and easy control ofannealing process have laid a good foundation for its industrial production. In addition, theshort annealing time, i.e.30min, will not only save the costs, but also speed up there-production process.The VO₂thin film prepared by MSP-3200E magnetron sputtering and a post annealingprocess is selected for application investigation. The smart window experiment shows thatthe VO₂thin film has an amazing ability to self-adjust the device temperature intelligently,and keeps the indoor temperature at a stable value of47oC under a continuous solarradiation. Moreover, laser radiation test indicates that VO₂thin film exhibits excellent highpower resist property, and threshold power density is up to1.46×103W/mm2. From theabove results we can conclude that the obtained VO₂thin film can be effectively used forsmart window and laser protection application.At the end of the dessertation, the achievements obtained in this work as well as someexisting problems have been summarized, and the prospect of future work has beensuggested.更多还原