Study Of Transparent & Conductive Indium Tin Oxide (ITO) And ITO Composite Films

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/□.