【作者】 魏雄邦；

【导师】 吴志明；

【作者基本信息】 电子科技大学 ， 光学工程， 2008， 博士

【摘要】 氧化钒一般以混合价态形式存在,常见的钒氧化物都具有金属—半导体相变的转化特性。氧化钒薄膜具有良好的热敏特性,在红外探测和热成像应用领域有广阔的发展潜力。本论文以氧化钒薄膜为研究对象,采用直流磁控溅射法制备氧化钒热敏薄膜,对氧化钒薄膜的制备、微结构、及其特性进行相关研究。实验过程中,除了充分利用X射线光电子能谱（XPS）、X射线衍射（XRD）、扫描电镜（SEM）、原子力显微镜（AFM）等技术对薄膜的微观结构和化学特征表征外,重点研究了氧化钒薄膜的方阻以及方阻随温度的变化特性,即薄膜的热敏性能。此外对氧化钒薄膜的折射率、消光系数也进行了探讨。论文主要包括以下六方面内容:（1）氧化钒薄膜的微观结构是影响薄膜性能的重要因素。论文首先运用XPS、XRD、SEM、AFM等多种分析手段,对薄膜的成份、价态以及薄膜的晶态与形貌结构进行比较详细的分析,以期对实验采用的直流反应磁控溅射法制备的氧化钒薄膜的微观特征有所了解,从而有助于确定氧化钒薄膜生长工艺的优化。（2）在氧化钒薄膜生长工艺的优化中,论文首先系统研究了直流反应磁控溅射氧化钒薄膜过程中不同工作气体（Ar）流量、不同反应气体（O₂）流量、以及不同比例的Ar/O₂混合气体条件下薄膜沉积速率和溅射电压的变化,从而提出了一种新的监控氧化钒薄膜生长、控制氧化钒薄膜性能的方法——溅射电压控制法。采用溅射电压控制法,通过监控溅射电压的变化,适时调整溅射过程中的气体流量,可以有效提高薄膜制备工艺的重复性和可控性,对提高薄膜性能的稳定性和可重复性有重要的作用。采用此法在不同的溅射电压下制备了氧化钒薄膜,对这些薄膜的性能做了分析和比较。当溅射电压选择在（304～318）V时,薄膜方阻值可控制在（30～150）KΩ/□,薄膜的方阻温度系数在-4%/℃～-5%/℃,生长的氧化钒薄膜相应的O/V比在1.91～2.13。（3）对氧化钒薄膜在Si基片、玻璃基片、Si₃N₄/Si基片等衬底上的生长模式和织构进行了研究。实验结果表明不同的衬底上生长的氧化钒的生长模式和织构存在较大差异。Si₃N₄/Si衬底上生长的氧化钒薄膜晶粒细小,薄膜较为平坦;而玻璃衬底和Si衬底上的晶粒较为粗大,薄膜的柱状生长较为明显。氧化钒薄膜厚度的调整会明显改变薄膜晶粒大小;薄膜的厚度和薄膜的晶粒尺寸的变化会导致薄膜电性能的很大变化。对不同衬底上生长的80nm、440nm、1000nm厚的氧化钒薄膜研究后发现,随着薄膜厚度的增加,薄膜的晶粒尺寸明显增加;不同衬底上生长的二氧化钒薄膜晶粒都呈现一种比较规则的“纺锤”形或“棒”形,晶粒的尺寸也具有一定的变化规律;薄膜的方阻随着薄膜厚度和薄膜晶粒的增大而减小;同时,随着薄膜厚度和薄膜晶粒的增大,薄膜的半导体—金属相变也逐渐趋于明显。实验说明,衬底是影响氧化钒薄膜微观结构和性能的重要因素之一。（4）对不同厚度的氧化钒薄膜,进一步研究了薄膜的光、电性能,发现薄膜厚度对薄膜的折射率和消光系数有较大影响。采用Preisach等理论模型对VO₂薄膜非对称的热滞回线做了分析,确定了氧化钒薄膜的阻值与外加温度以及温度变化导致的晶粒体积的变化密切相关。（5）尝试采用了在纯氩气氛中直流磁控溅射V₂O₅靶材沉积氧化钒薄膜。对沉积的薄膜进行了后续高真空高温退火处理。利用XRD对薄膜的晶相进行了分析,结果表明退火处理前和退火处理后的薄膜都具有VO₂晶面的取向,薄膜的XPS成份分析证明了XRD的物相分析结果。对薄膜的XRD分析和薄膜方阻特性的测试表明生成的薄膜是典型的VO₂（B）薄膜。在此基础上,利用薄膜晶界散射理论,通过改变薄膜厚度和晶粒大小对薄膜的方阻和方阻温度系数进行了有效调控。（6）尝试采用了先直流磁控溅射沉积金属钒膜再对其氧化热处理制备氧化钒薄膜,采用此法时,通过适当的氧化处理可优化薄膜的方阻,改善薄膜的方阻温度系数,使处理后的氧化钒薄膜的方阻温度系数能达到-2%/℃以上;薄膜中各价态钒的比例及钒氧比会通过调整退火条件而得到改善。通过以上研究,我们对氧化钒薄膜的制备、微结构、及其性能有了进一步的认识和了解,为氧化钒薄膜的应用做了较为有益的基础研究工作。更多还原

【Abstract】 Vanadium oxides exist in a large variety of structures with mixed valencies. Most of the VOx materials have the transition properties with low temperature semiconductor phase to high temperature metal phase. As a heat-sensing material, VOx thin films have promising prospect for thermal detectors and IR imaging due to their outstanding physical and chemical properties.In this dissertation, vanadium oxide （VOx） thin films were studied. The VOx thin films for heat-sensing applications were deposited by DC magnetron sputtering method. Preparation, microstructure, and characterization of the VOx thin films were studied. The outline of this dissertation was outspread by the optimization of the preparation technology for the VOx thin films.In the experiments, X-ray photoelectron spectrometer （XPS）, X-ray diffraction （XRD）, scanning electron microscope （SEM）, and atomic force microscope （AFM） were employed to analyze the microstructures and chemical states of the VOx films. The square resistance （R□） and temperature coefficient of square resistance （TCR） were emphasis measured. Moreover, the refractive index （n） and extinction coefficient （k） of the VOx films prepared were investigated. The dissertation was narrated from six aspects as follows:（1） Microstructures of the VOx films have great influence on the film properties. In the dissertation, composition, chemical state, crystallization, and micro-features were first analyzed by XPS, XRD, SEM, and AFM. In this way, the micro-properties of the VOx films were acquainted, which help us to optimize the technology process.（2） In the optimization of the deposition conditions of the VOx films, we first systematically investigated the effects of gas flux of Ar, O₂, and Ar/O₂ on the deposition rate and sputtering voltage. On the basis of the investigations, a new controlling method—sputtering controlling method was proposed. By adjusting the sputtering voltage, the reproductability and stability of the technology were improved obviously. VOx films were deposited under different sputtering voltage by our new method and the properties of the films were analyzed. The results revealed that when the sputtering voltage is 304～318 V, the R□and TCR of the VOx films is 30～150 KΩ/□and -4%/℃～-5%/℃, respectively, and the O/V ratio is 1.91～2.13.（3） The growth mode and texture of VOx films grown on different substrates, including Si, glass, Si₃N₄/Si, were studied. Experiment results demonstrated that both the growth mode and texture are clearly different for the VOx films deposited on different substrates. For the VOx films grown on Si₃N₄/Si substrate, the grain sizes are small and the film is flat. However, for the films grown on glass substrate or Si substrate, the grain sizes are large, and the column-like growth mode is obvious. Moreover, it was confirmed that film thickness has great influence on the film grain size, and the film thermal electrical properties are greatly influenced by the film thickness and the grain size. In addition, the grain size and the crystallization extent increase with increasing the film thickness from 80nm to 1000nm. The growth mode of the VOx was demonstrated an obvious club-shape or spindle-shape for the thick films. With increasing the film thickness, the R□decreases, the TCR increases, and the metal-semiconductor phase transition becomes obvious. These suggest that substrates have great influence on the microstructure and properties of VOx films.（4） The optical and electrical properties were investigated for the VOx films with different thickness. Results proved that the refractive index and extinction coefficient of vanadium oxide thin films are correlated with the film thickness. In the dissertation, the Preisach theory model was adopted to analyze the asymmetrical thermal electrical hysteresis loop. Based on this theory, the interrelations of the film resistance, temperature, and grain volume were determined.（5） On the basis of the studies above, VOx thin films were deposited in pure Ar condition by DC magnetron sputtering method. The target material was vanadium pentoxide. The vanadium oxide thin films deposited were post-annealed with high temperature in high vacuum. Crystallization of the samples was analyzed by XRD and the results showed that the thin films prepared exhibit preferred orientation of VO₂ crystalline plane before and after annealing. XPS results verified the phase analysis obtained by XRD. XRD analysis and square resistance measurements proved that the thin films are VO₂ （B）. Based on these and the theory of grain boundary scattering, the electrical properties of the samples can be controlled by changing the film thickness and grain size.（6） Moreover, we deposited the VOx thin films by a two-step procedure method. In this method, the pure vanadium thin films were first deposited onto the substrates, and then they were post-oxidized to form the VOx thin films. The results suggested that the appropriate oxidation process is helpful to optimize the R□and TCR of VOx thin films, and TCR of VOx films are higher than -2 %/℃. Moreover, the chemical states and V/O ratio of VOx can also be controlled by optimizing the annealing conditions.On the basis of the above researches, preparation, microstructure, and characterization of the VOx thin films were further acquainted and comprehended by us, which are beneficial for the application of the VOx thin films.更多还原