【作者】 李世涛；

【导师】 乔学亮；

【作者基本信息】 华中科技大学 ， 材料科学与工程， 2006， 博士

【摘要】 作为应用最为广泛的n型透明导电氧化物(TCOs)——锡掺杂氧化铟(ITO)一直是材料和电子领域研究的热点之一。由于金属铟属于稀缺资源,因此节约铟用量是一项重要的课题。为此,本论文从事了三个方面的研究:(1)用化学共沉淀法制备了四种特殊形貌的纳米ITO粉末,并制作了防红外辐射的纳米ITO/高分子复合涂层;(2)通过降低ITO(9:1)陶瓷靶中In含量,利用rf磁控溅射沉积透光率高、方阻低和表面质量高的ITO(1:1)薄膜;(3)优化设计并制备纳米Ag基ITO(1:1)复合三层膜系IAI薄膜,进一步降低方阻,且透光率高、表面平整。详细分析了合成工艺参数对纳米ITO粉末形貌和晶体结构的影响,深入研究了rf磁控溅射工艺条件对ITO(9:1)、ITO(1:1)、Ag膜和IAI复合膜系的晶体结构、微观形貌/组织和光电性能的影响,用AFM、SEM和XRD表征了ITO材料的微观结构,XPS分析了薄膜的表面化学状态,分光光度计、椭偏仪、四探针测试仪和Hall测试系统测试了薄膜的光电性能。主要结论如下:用化学共沉淀法制备出纳米棒状ITO(9:1)前驱体——In(OH)3-H2[Sn(OH)6],煅烧后获得立方晶型的纳米棒状ITO粉末,Sn4+完全掺杂到In2O3晶格中。水浴温度Tb对前驱体的形貌有重要影响:Tb为40℃时呈球形,Tb为100℃时呈棒状颗粒。延长老化时间,棒状颗粒轴径比增大,说明前驱体沿In(OH)3的[100]方向继续生长。在酸性、碱性、中性环境中,纳米前驱体分别为类块状的In(OH)3+ Sn3O2 (OH)2混合相、方块状的单一In(OH)3相、球形In(OH)3+InOOH混合相。研究表明:前驱体转变为ITO的过程为吸热过程,反应pH值对相转变温度Tc有显著影响。纳米ITO粉末形貌“遗传”了前驱体的形貌,In3+与NH4+络合使前驱体易形成棒状颗粒,而In3+与Cl-络合则易形成方块状颗粒。ITO涂层具有强的紫外吸收性、高可见光的透光率(~80%)和高红外的反射率(~60%),但其导电率较低。所制备的ITO聚合物复合涂层可以代替防红外辐射的Low-E玻璃。将ITO靶材与紫铜板焊接能提高靶的冷却效率,避免其热应力开裂。分析表明:ITO靶的节瘤(Nodule)和中毒起初主要与表面异物有关,后来与Nodule分解引起成分偏析有关。Nodule的形成机制有两种可能:Particle熔点较低时为核长大机制,Particle熔点较高时为遮蔽机制。首次用rf磁控溅射法制备出表面为蜂窝状的ITO(9:1)薄膜,其表面粗糙度低、与靶材中In/Sn一致。研究表明:随着氧流量增加,ITO薄膜表面蜂窝状形貌逐渐消失,沿(222)晶面以柱状晶生长,这是因为氧使薄膜结晶改善、晶格缺陷减少。退火后薄膜沿[111]晶面择优生长,表面为主晶-次晶(grain-subgrain)结构。薄膜(基体不加热)随着溅射负偏压的增加,结晶逐渐完善并沿着[111]方向择优生长,由垂直柱状晶逐渐变为平行于基体的致密纤维状组织。制备出含In量低的ITO(1:1)靶材和非晶态薄膜,研究表明:ITO(1:1)薄膜的折射率与氧流量fo2有关,这是因为薄膜中存在SnO和Sn3O4亚氧化物使其光电性能恶化;ITO薄膜载流子浓度主要受氧空位的影响,因此应严格控制氧流量。溅射氩气压强增加,薄膜电阻率增加,折射率n在1.97～2.21之间变化。溅射时红外辐射温度TIR对薄膜方阻、薄膜透射率和折射率有重要影响。SEM表征发现TIR和溅射方式改变了ITO薄膜表面的grain-subgrain组织和粗糙度Rp-v值,这主要与薄膜生长模式变化有关。退火ITO(1:1)薄膜仍为非晶态,但性能得到改善,薄膜透光率可以达到90%,方阻为Rs=13.1Ω/□。电性能分析和AFM表征说明:随着沉积时间(厚度)的增加,薄膜出现三个生长阶段,对应着三种不同的导电机制,这说明ITO薄膜的电阻率表现出明显的尺寸效应。通过电阻率计算得到的薄膜临界尺寸dc与AFM观察的结果十分接近。根据溅射镀膜的特点对Thornton的结构分区理论进行修正得到ITO薄膜的微观形貌生长机理:氧流量对ITO薄膜微观结构的影响主要是由化学迁移率引起的;负偏压对ITO薄膜微观结构的影响主要是由轰击迁移率引起的。通过理论计算和实验求解得到最优增透膜IAI三层复合膜系的设计方案:60(nm) ITO/12(nm)Ag /60(nm)ITO。IAI膜表面粗糙度Rp-v=8.6nm、Rrms=1.2nm。IAI膜的Rs与dAg值有关:当IAI中的Ag膜为连续膜层时(dAg>12nm),IAI的Rs取决于Ag膜的Rs。当dI=120nm,IAI的透光率最大可达到90%,Rs =2.5Ω/□,ε<0.045。这说明所制备的IAI和ITO(1:1)薄膜的综合光电性能指数高。更多还原

【Abstract】 As one of n-type transparent conductive oxides widely used, tin doped indium oxide (ITO) is always the hotspot of study fields of materials and electrons. Because of being lack in metal source Indium, saving indium wastage in ITO thin films is an important topic. Thereby, there were three aspects studied by us as follow: (1) Nano- crystalline ITO powders with four micro-morphologies were prepared by a co- precipitation process and were used as additive for nano ITO composite macro- molecule coatings shielding IR irradiation. (2) ITO(1:1) thin films, with high transmittance, low sheet resistance and good surface quality, were prepared by radio frequency (rf) magnetron sputtering with ITO(1:1) target of low in content. (3) We designed and prepared the nano Ag based ITO three-layer films (IAI) with high transmittance and well smooth surfacein order to reduce the sheet resistance. In this thesis, it was studied in detail that synthetical technical parameters dependent of nano ITO powder morphology and crystalline structure. It was also investigated completely that effects of sputtering parameters on the micro-morphology, crystalline structure and photoelectric properties. Microstructure of ITO materials was characterized by AFM, SEM and XRD. The chemical composition and valency states of ITO surface were analyzed and investigated by X-ray photoelectron spectroscopy (XPS). The photoelectric properties were measured by UV-spectrophotometer, ellipsometer, four-point probe system and Hall effect measurement system. The main concerned results and conclusions are as follow:The ITO (9:1) precursors—In(OH)3-H2[Sn(OH)6] were prepared by a chemical co-precipitation process, we obtained the cubic structure ITO powder with Sn4+ completely doped In2O3 lattice by calcinations. A bath temperature (Tb) had an important influence on the precursors’morphologies: spherical and rods shapes were obtained at Tb of 40℃and 40℃respectively. After prolonging aging time of ITO precursor, the axial and sectional ratio of rods increased, which showed that rod precursor grew along [100] orientation of In(OH)3 phase. Under different pH values of reactive solution, we obtained mixed phases of In(OH)3+ Sn3O2 with cubic like shape, single In(OH)3 phase with good cubic shape and mixed phases of In(OH)3+InOOH with spherical shape respectively. Our investigations suggested that the transformation of co-precipitated indium tin hydroxides to ITO was endothermic reaction, which corresponding transformation temperature (Tb) was related with pH value. Nano ITO powders’shapes inherited the precursors’after calination in Ar gas. Rod shaped particles grew due to NH4+ complexing In3+ and cubic shaped particles grew due to the influence of Cl- on the orientation of crystalline.Nano ITO composite macromolecule coatings showed strong absorption for ultraviolet light, high transmittance in visible light range(~80%) and high IR light reflectance(~60%) although its resistance was high. It showed that ITO composite coatings could substitute for Low-E glass for energy conserving application.Cool efficiency of ITO ceramic target had been improved by ITO target jointed with pure copper plate, which could avoid target cracked by thermal stress. Analytical results illuminated that during sputtering process, at first nodules on surface of ITO ceramic target were resulted from the particles, latter from the element segregation caused by nodules decomposing. Nodules growth mechanisms may be as follow: nodule growth-up mechanism of nucleus with low melting particles and shielding mechanism of nodule with high melting particles.ITO(9:1) thin films with smooth surface is consistent with commercial target with regard to chemical element. For the first time, we found the honeycomb morphology on the surface of ITO thin films. The investigation indicated that with the increase in oxygen flow rate, honeycomb boundaries of ITO film surface disappeared gradually and ITO thin films grew into columnar crystal in orientation of (222) because oxygen reduced the oxygen vacancies in lattice and improved the crystalline of ITO thin films. Annealing treatment made ITO films crystallize along preferential orientation of [111] and the surface morphology appeared grain-subgrain structure. With the increase of the sputtering bias voltage, ITO thin films sputtered without heat at glass not only crystallized gradually and showed preferential orientation of [111] but also turned into fibrous structure.We prepared amorphous ITO(1:1) thin films by rf magnetron sputtering with self-made ceramic target. The investigations said that the refractive index and transmittance of ITO(1:1) thin films were strong dependent of fo2 value because of sub-oxides, SnO and Sn3O4 in films deteriorating the photoelectrical properties. On the other hand, carrier concentration of ITO(1:1) thin films is mainly dependent of the oxygen vacancies. Thereby, oxygen flow rate should be accurately controlled during sputtering process. The films’resistivity increased and the refractive index varied in the range of 1.97～2.21 with Ar gas pressure increasing. Sheet resistance, transmittance and refractive index were as function of IR irradiation temperature (TIR). The SEM study showed that TIR and sputtering method made the surface“grain-subgrain”morphology and surface roughness Rp-v change, which was related with the growth model of ITO thin films. The microstructure of amorphous ITO(1:1) thin films were improved and showed maximum transmittance of 90% and sheet resistance of 13.1Ω/□.Electronic properties’analysis and AFM characterization indicated that ITO thin films show three growth stage corresponding to three different conductive mechanisms, it is that resistance of ITO films shows dimensional effect. We modified and corrected the structure zone model theory (Thornton theory) and obtained the tow models at oxygen flow and bias voltage respectively: oxygen flow have an important influence on the microstructure and growth of ITO thin films because of chemical mobility, however bias voltage alter bombardment surface.We designed and prepared the optimized antireflective IAI composite films with three layer structure: 60(nm)ITO/12(nm)Ag/60(nm)ITO. IAI multilayer film had good surface quality, Rp-v of 8.6nm and Rrms of 1.2nm. The sheet resistance Rs of IAI multilayer film is strong related with the thickness dAg of nano Ag film, Rs of IAI is determined by Rs of Ag film when dAg is in excess of 12nm. IAI multilayer film with ITO thickness of 120nm have maximum transmittance of 90% and sheet resistance of Rs =2.5Ω/□.更多还原