Deposition of nanostructured crystalline and corrosion resistant alumina film on bell metal at low temperature by rf magnetron sputtering

Aluminium oxide films deposited by rf magnetron sputtering for protective coatings have been investigated. The alumina films are found to exhibit grainy surface microstructure. The grain size, structure and density depend on different system parameters such as argon and/or oxygen flow rate and applied rf power etc. The effect of transition of the discharge from metallic to reactive mode on the surface characteristics of the alumina film is studied. X-ray diffractometry reveals that in poisoned mode of sputtering and under optimized power and pressure, crystalline alumina film can be grown. Different system conditions are optimized for corrosion resistant aluminium oxide films with good adhesion properties. Nanostructured alumina film is obtained at lower pressure (8 × 10⁻⁴ to 9 × 10⁻⁴ Torr) by rf reactive magnetron sputtering.     

Effect of substrate temperature on the structural, optical and electrical properties of dc magnetron sputtered tantalum oxide films

dc reactive magnetron sputtering technique was employed for deposition of tantalum oxide films on quartz and silicon substrates by sputtering of pure tantalum target in the presence of oxygen and argon gases under various substrate temperatures in the range 303-973 K. The variation of cathode potential with the oxygen partial pressure was systematically studied. The influence of substrate temperature on the chemical binding configuration, crystal structure and optical properties was investigated. X-ray photoelectron spectroscopic studies indicated that the films formed at oxygen partial pressures ≥1 × 10⁻⁴ mbar were stoichiometric. The Fourier transform infrared spectroscopic studies revealed that the films formed up to substrate temperatures <673 K showed a broad absorption band at 750-1000 cm⁻¹ and a sharp band at 630 cm⁻¹ indicated the presence of amorphous phase while at higher substrate temperatures the appearance of bands at about 810 and 510 cm⁻¹ revealed the polycrystalline nature. The effect of substrate temperature on the electrical characteristics of Al/Ta₂O₅/Si structure was investigated. The dielectric constant values were in the range 17-29 in the substrate temperature range of 303-973 K. The current-voltage characteristics showed modified Poole-Frenkel conduction mechanism with a tendency for reduction of the compensation level. The optical band gap of the films decreased from 4.44 to 4.25 eV and the refractive index increased from 1.89 to 2.25 with the increase of substrate temperature from 303 to 973 K.     

Structural and transport properties of cubic spinel ZnCo2O4 thin films grown by reactive magnetron sputtering

We report on the growth of cubic spinel ZnCo₂O₄ thin films by reactive magnetron sputtering and bipolarity of their conduction type by tuning of oxygen partial pressure ratio in the sputtering gas mixture. Crystal structure of zinc cobalt oxide films sputtered in an oxygen partial pressure ratio of 90% was found to change from wurtzite Zn_1−xCo_xO to spinel ZnCo₂O₄ with an increase of the sputtering power ratio between the Co and Zn metal targets, D_Co/D_Zn, from 0.1 to 2.2. For a fixed D_Co/D_Zn of 2.0 yielding single-phase spinel ZnCo₂O₄ films, the conduction type was found to be dependent on the oxygen partial pressure ratio: n-type and p-type for the oxygen partial pressure ratio below ∼70% and above ∼85%, respectively. The electron and hole concentrations for the ZnCo₂O₄ films at 300 K were as high as 1.37×10²⁰ and 2.81×10²⁰ cm⁻³, respectively, with a mobility of more than 0.2 cm²/V s and a conductivity of more than 1.8 S cm⁻¹.     

Electrical and optical properties of silver doped indium oxide thin films prepared by reactive DC magnetron sputtering

Silver doped indium oxide (In_2−x Ag_x O_3−y) thin films have been prepared on glass and silicon substrates at room temperature (300 K) by reactive DC magnetron sputtering technique using an alloy target of pure indium and silver (80: 20 atomic %. The magnetron power (and hence the metal atom sputter flux) is varied in the range 40-80 W. The energy dispersive analysis of X-ray (EDAX) results show that the silver content in the film decreases with increasing magnetron power. The grain size of these films is of the order of 100 nm. The resistivity of these films is in the range 10⁻²-10⁻³ Ω cm. The work function of the silver-indium oxide films (by Kelvin Probe) are in the range: 4.64-4.55 eV. The refractive index of these films (at 632.8 nm) varies in the range: 1.141-1.195. The optical band gap of indium oxide (3.75 eV) shrinks with silver doping. Calculations of the partial ionic charge (by Sanderson's theory) show that silver doping in indium oxide thin films enhance the ionicity.     

Structure and electrical properties of CdIn2O4 thin films prepared by DC reactive magnetron sputtering

CdIn₂O₄ thin films were prepared by direct-current (DC) reactive magnetron sputtering. The structure, surface morphology and the chemical composition of the thin films were analyzed by X-ray diffraction (XRD), atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS), respectively. The electrical properties of the films prepared in different oxygen concentration and annealing treatment were determined, and the effects of the preparing conditions on the structure and electrical properties were also explored. It indicates that the CdIn₂O₄ thin films with uniform and dense surface morphology contain mainly CdIn₂O₄, In₂O₃ phases, and CdO phase is also observed. The XPS analysis confirms the films are in oxygen-deficient state. The electrical properties of these films significantly depend on the preparing conditions, the resistivity of the films with the oxygen concentration of 4.29% is 2.95 × 10⁻⁴ Ω cm and the Hall mobility is as high as 60.32 cm²/V s. Annealing treatment can improve the electrical performance of the films.     

Development of structural and optical properties of WOx films upon increasing oxygen partial pressure during reactive sputtering

WO_x films were prepared by reactive dc magnetron sputtering using tungsten target. Sputtering was carried out at a total pressure of 1.2 Pa using a mixture of argon plus oxygen in an effort to determine the influence of the oxygen partial pressure on structural and optical properties of the films. The deposition rate decreases significantly as the surface of the target is oxidized. X-Ray diffraction revealed the amorphous nature of all the films prepared at oxygen partial pressures higher than 1.71×10⁻³ Pa. For higher oxygen partial pressures, fully transparent films were deposited, which showed a slight increase in optical band gap with increasing oxygen partial pressure, while the refractive index was simultaneously decreased.     

A study of the optical properties of titanium oxide films prepared by dc reactive magnetron sputtering

TiO₂ thin films were deposited on the glass substrates by dc reactive magnetron sputtering technique at different sputtering pressures (2 × 10⁻³ to 2 × 10⁻² mbar). The films prepared at low pressures have an anatase phase, and the films prepared at high pressures have an amorphous phase. The optical properties were studied by measuring the transmittance and the ellipsometric spectra. The optical constants of the films in the visible range were obtained by fitting the transmittance combined with the ellipsometry measurements using the classical model with one oscillator. The refractive index of the films decreases from 2.5 until 2.1 as the sputtering pressure increases from 2 × 10⁻³ to 2 × 10⁻² mbar. The films prepared at the pressure higher than 6 × 10⁻³ mbar show a volume inhomogeneity. This volume inhomogeneity has been calculated by fitting the transmittance and the ellipsometric spectra. The volume inhomogeneity of the film prepared at the highest sputtering pressure is about 10%. Although the films prepared at high pressures show a large volume inhomogeneity, they have low extinction coefficients. It is suggested that the anatase phase results in more light scattering than amorphous phase does, and then a high extinction coefficient.     

Preparation and characterization of p-type transparent conducting tin-gallium oxide films

p-Type transparent conducting tin-gallium oxide (TGO) films were successfully fabricated on quartz substrates by DC magnetron sputtering of GaSn alloy films followed by thermal oxidation. XRD characterization indicated that the TGO films maintain rutile structure of the tin oxide (SnO₂). UV-vis transmittance spectra indicated that the films have a transmittance higher than 85% in the visible region, with an optical band-gap around 3.8 eV. Hall effect measurement showed that electrical properties of the TGO films were dependent on oxidation temperature. Oxidation at too high or low temperature was unfavorable for p-type conduction. It is found that the optimum oxidation temperature for highest hole concentration (8.84 × 10¹⁸ cm⁻³) was in the range of 600-650 °C.     

Effect of substrate temperature on the growth of ITO thin films

Indium tin oxide (ITO) thin films were deposited onto glass substrates by rf magnetron sputtering of ITO target and the influence of substrate temperature on the properties of the films were investigated. The structural characteristics showed a dependence on the oxygen partial pressure during sputtering. Oxygen deficient films showed (4 0 0) plane texturing while oxygen-incorporated films were preferentially oriented in the [1 1 1] direction. ITO films with low resistivity of 2.05 × 10⁻³ Ω cm were deposited at relatively low substrate temperature (150 °C) which shows highest figure of merit of 2.84 × 10⁻³ square/Ω⋅     

Influence of charged particle bombardment and sputtering parameters on the properties of HfO2 films prepared by dc reactive magnetron sputtering

HfO₂ films prepared on glass substrates by dc reactive magnetron sputtering in an Ar + O₂ atmosphere are investigated. The films are polycrystallized with a pure monoclinic phase, and the crystallization strongly relates to the technology environment. Charged particle bombardment mainly caused by negative oxygen ions during sputtering on the films results in rougher surface morphology and worse crystalline property. Influence of sputtering pressure, substrate temperature and Ar:O₂ flow ratio is studied. The main orientations of the films are (−1 1 1) and (1 1 1). The (−1 1 1) orientation is stable, but (1 1 1) orientation is very sensitive to the sputtering condition, and it can be suppressed effectively by introducing charged particle bombardment, lowing sputtering pressure and increasing oxygen concentration.