Vacuum Sputtering Process Research Articles

Preparation of indium oxide from waste indium tin oxide targets by oxalic acid

Indium oxide manufacturing process from waste indium tin oxide (ITO) targets by oxalic acid was experimentally studied. The process was composed of precipitation of intermediate (indium-oxalate salt), re-crystallization and its thermal decomposition. The waste ITO targets were generated from vacuum sputtering process. The effects of operating parameters, such as solid dosage, oxalic acid concentration, reaction temperature and time, on the precipitation and re-crystallization of indium-oxalate salt were examined. Thermal decomposition to indium oxide was also investigated. The optimum reaction conditions to indium-oxalate salt were oxalic acid concentration 1.5 M, solid dosage 50 g/L, reaction temperature 80 °C and reaction time 8 hours. The purity of indium-oxalate salt prepared by precipitation and re-crystallization was 99.99% (4 N), and the salts were thermally decomposed to indium oxide at over 600 oC. The purity of the final product, indium oxide, was dependent on that of the intermediate, indium oxalate salt.

Improving the optoelectronic properties of titanium-doped indium tin oxide thin films

The focus of this study is on a sol–gel method combined with spin-coating to prepare high-quality transparent conducting oxide (TCO) films. The structural, morphological, optical and electrical properties of sol–gel-derived pure and Ti-doped indium tin oxide (ITO) thin films were studied as a function of the concentration of the Ti (i.e. 0 at%, 2 at% and 4 at%) and annealing temperatures (150 °C–600 °C). FESEM measurements indicate that all the films are ∼350 nm thick. XRD analysis confirmed the cubic bixbyite structure of the polycrystalline indium oxide phase for all of the thin films. Increasing the Ti ratio, as well as the annealing temperature, improved the crystallinity of the films. Highly crystalline structures were obtained at 500 °C, with average grain sizes of about 50, 65 and 80 nm for Ti doping of 0 at%, 2 at% and 4 at%, respectively. The electrical and optical properties improved as the annealing temperature increased, with an enlarged electronic energy band gap and an optical absorption edge below 280 nm. In particular, the optical transmittance and electrical resistivity of the samples with a 4 at% Ti content improved from 87% and 7.10 × 10−4 Ω.cm to 92% and 1.6 × 10−4 Ω.cm, respectively. The conductivity, especially for the annealing temperature at 150 °C, is acceptable for many applications such as flexible electronics. These results demonstrate that unlike the more expensive and complex vacuum sputtering process, high-quality Ti-doped ITO films can be achieved by fast processing, simple wet-chemistry, and easy doping level control with the possibility of producing films with high scalability.

Investigation of solution-processed bismuth-niobium-oxide films

The characteristics of bismuth-niobium-oxide (BNO) films prepared using a solution process were investigated. The BNO film annealed at 550 °C involving three phases: an amorphous phase, Bi3NbO7 fluorite microcrystals, and Nb-rich cubic pyrochlore microcrystals. The cubic pyrochlore structure, which was the main phase in this film, has not previously been reported in BNO films. The relative dielectric constant of the BNO film was approximately 140, which is much higher than that of a corresponding film prepared using a conventional vacuum sputtering process. Notably, the cubic pyrochlore microcrystals disappeared with increasing annealing temperature and were replaced with triclinic β-BiNbO4 crystals at 590 °C. The relative dielectric constant also decreased with increasing annealing temperature. Therefore, the high relative dielectric constant of the BNO film annealed at 550 °C is thought to result from the BNO cubic pyrochlore structure. In addition, the BNO films annealed at 500 °C contained approximately 6.5 atm. % carbon, which was lost at approximately 550 °C. This result suggests that the carbon in the BNO film played an important role in the formation of the cubic pyrochlore structure.

Process Parameters Optimization: A Design Study for TiO<formula formulatype="inline"><tex Notation="TeX">$_{2}$</tex></formula> Thin Film of Vacuum Sputtering Process

This paper proposes a procedure for process parameters design by combining both modeling and optimization methods. The proposed procedure integrates the Taguchi method, the artificial neural network (ANN), and the genetic algorithm (GA). First, the Taguchi method is applied to minimize experimental numbers and to collect experimental data representing the quality performances of a system. Next, the ANN is used to build a system model based on the data from the Taguchi experimental method. Then, the GA is employed to search for the optimal process parameters. A process parameters design for a titanium dioxide (TiO2) thin film in the vacuum sputtering process is studied in this paper. The quality objective is to form a smaller water contact angle on the TiO2 thin-film surface. The water contact angle is 4° obtained from the system model of the proposed procedure. The process parameters obtained from the proposed procedure were used to conduct the experiment in the vacuum sputtering process for the TiO2 thin film. The water contact angle given from the practical experiment is 3.93°. The difference percent is 1.75% between 4° and 3.93°. The result obtained from the system model of the proposed procedure is promising. Hence, we can conclude that the proposed procedure is a very good approach in solving the problem of the process parameters design.

High mobility of surface atoms and induced anisotropy in very thin permalloy films

The induced uniaxial anisotropy field H/sub k/ in very thin Ni/sub 79/Fe/sub 21/ films, sandwiched by seed and protective Ta layers, was investigated. Films prepared by an ultra-high vacuum sputtering process show a very sharp fiber texture of fcc-<111> perpendicular to the film plane, even with a thin film of 3 nm. The H/sub k/ value was found to decrease as the film thickness decreased below 20 nm, even after an annealing procedure in a magnetic field. The change in the induced anisotropy energy K/sub u/ was measured as a function of the temperature while applying a dc magnetic field parallel to the hard axis of magnetization. The value of K/sub u/ of as-deposited thin films decreases significantly with increasing temperature from 50/spl deg/C to 100/spl deg/C and the K/sub u/ reduction in a film of 5 nm reaches /spl sim/40%. It is likely that this K/sub u/ reduction is mainly caused by realignment of atom pairs at film surfaces along the field direction. This is supported by the low activation energy of the K/sub u/ reduction process. It is successfully shown that the high mobility of surface atoms should disrupt the alignment of atom-pairs parallel to the field direction during the film deposition and annealing process, resulting in the formation of magnetically isotropic layers at surfaces. The thickness of this isotropic layer was estimated to be /spl sim/0.8 nm and the isotropic surface-layer is likely to reduce the H/sub k/ value of very thin films.

The probability scheme of constructing the mathematical model of shadowed sputtering

The probability scheme of examination of the shadowed vacuum sputtering process is suggested. If one restricts the consideration by non-scattering part of the scheme the resulting model would be equivalent to geometro-optical shadowing model used by our predecessors. At the same time the scheme gives the possibility for the model improvement. Instead of complicating the model by using the multi-particle scattering it is possible to include all the deviations from geometro-optical model into the distribution function of sputtered particle.

Spin valve films with PdPtMn antiferromagnetic layer fabricated using ultrahigh vacuum sputtering process

We investigated the background pressure (P/sub BG/) dependence of the unidirectional anisotropy field (H/sub ua/) of spin valve films with a PdPtMn antiferromagnetic layer fabricated by an ultrahigh vacuum (UHV) sputtering process. The H/sub ua/ increased with decreasing P/sub BG/ until P/sub BG/ reached 2/spl times/10/sup -7/ Pa. The UHV deposition, such as below 2.0/spl times/10/sup -7/ Pa of P/sub BG/, improved the fct [111] texture of PdPtMn, the fcc[111] of NiFe/CoFeB/Cu/CoFeB layers, enlarged the grains of spin valve films, and reduced an absorption of residual oxygen component into the spin valve films. Consequently, the exchange coupled CoFeB/PdPtMn layers exhibited large H/sub ua/ of 620 Oe, in spite of a quite thin PdPtMn (15 nm) as an ordered antiferromagnetic material, and the spin valve films show a large MR ratio of 7.8% and a sheet resistance change of 1.6 /spl Omega/.

Duoplasmatron Ion Beam Source for Vacuum Sputtering of Thin Films

A variation of the von Ardenne type of a duoplasmatron ion source is described. Here the arc discharge is maintained between the cathode in the high pressure and the anode in the vacuum chamber, as opposed to the conventional arrangement in which the arc discharge is confined primarily to the high pressure chamber. This modification allows the extraction, through apertures, of a well defined ion beam of current up to 500 mA over an area ∼1 cm2 into a vacuum chamber at a pressure of ∼10−5 Torr. The ion beam is accelerated and made to impinge on a target material for sputtering. Sequential sputtering of different targets inside the vacuum chamber is possible with the help of suitable magnetic fields. The ion beam has been used to sputter conducting, semiconducting, and insulating target materials. Typical rate of deposition of silver films at a distance of 8 cm from the target with a 50 mA, 2 kV ion beam of 8 mm diam is ∼400 Å/min. Deposition rates of ∼50 Å/min are obtained for SiO2 and TiO films. Vacuum sputtered films adhere to the subtrates much more strongly than the evaporated films do. Gold and silver films grow epitaxially on rock salt substrates at ambient or lower temperatures. This vacuum sputtering process has been found to induce and stabilize new structures. For example, sputtered films of molybdenum, tantalum, tungsten (normally bcc), and hafnium, rhenium and zirconium (normally hcp) have been observed to exist in an fcc phase. Fcc structure films as thick as 2 μ have been prepared. Epitaxial growth of the fcc structures on rock salt substrates at temperatures of ∼400°C are observed.