High Frequency Sputtering Research Articles

Effect of Preparation Conditions on the Fundamental Absorption Edge of Y2O3 Thin Films

The fundamental absorption edge of Y2O3 thin fi lms obtained by discrete evaporation and high-frequency (HF) onplasma sputtering in various atmospheres was studied using optical spectroscopy. It was ascertained that the optical bandgap Eg increased from 5.65 eV for Y2O3 fi lms obtained by discrete evaporation to 5.77 eV for fi lms obtained by HF sputtering in Ar to 5.90 eV for fi lms obtained by HF sputtering in O2. The effective reduced mass of free charge carriers was estimated. It was found that the concentration of free charge carriers in Y2O3 fi lms obtained by ionplasma sputtering in Ar with 50% O2 was N = 1.34·1017 cm–3 whereas sputtering in 100% O2 gave N = 1.38·1018 cm–3, which was typical of degenerate semiconductors. It was shown that the shift of the fundamental absorption edge in Y2O3 thin fi lms after addition of O2 to the sputtering atmosphere was most likely caused by the Burstein–Moss effect.

Chemical mechanical polishing characteristics of ITO thin film prepared by RF magnetron sputtering

Indium-tin-oxide (ITO) thin films have attracted intensive interest because of their unique properties of good conductivity, high optical transmittance over the visible region and easy patterning ability. ITO thin films have found many applications in anti-static coatings, thermal heaters, solar cells, flat panel displays (FPDs), liquid crystal displays (LCDs), electroluminescent devices, sensors and organic light-emitting diodes (OLEDs). ITO thin films are generally fabricated by using various methods, such as spraying, chemical vapor deposition (CVD), evaporation, electron gun deposition, direct current electroplating, high frequency sputtering, and reactive sputtering. In this research, ITO films were grown on glass substrates by using a radio-frequency (RF) magnetron sputtering method. In order to achieve a high transmittance and a low resistivity, we examined the various film deposition conditions, such as substrate temperature, working pressure, annealing temperature, and deposition time. Next, in order to improve the surface quality of the ITO thin films, we performed a chemical mechanical polishing (CMP) with different process parameters and compared the electrical and the optical properties of the polished ITO thin films. The best CMP conditions with a high removal rate, low nonuniformity, low resistivity and high transmittance were as follows: platen speed, head speed, polishing time, and slurry flow rate of 30 rpm, 30 rpm, 60 sec, and 60 ml/min, respectively.

Mg<SUB>2</SUB>Si Coating Technology on Magnesium Alloys to Improve Corrosion and Wear Resistance

Magnesium silicide (Mg 2 Si) bulky materials are useful to improve the surface function of light metals such as magnesium or aluminum alloys, due to its superior corrosion resistance to the conventional stainless steel, and its high mechanical properties. In this study, Mg 2 Si thin film coated on AZ31 magnesium alloys by using a high frequency sputtering method, was examined. A neutral salt spray test to evaluate the corrosion resistance indicated that AZ31 substrate with Mg 2 Si coating was hardly damaged after 240 h. On the other hand, the non-treated one was corroded in only 1 h. Concerning wear resistance under the oil lubricant test, a friction coefficient of the AZ31 alloy with Mg 2 Si film is remarkably stable in employing S35C steel as a counter specimen. No sticking between both specimens was detected. In the combination of AZ31 alloy disc and S35C pin specimens, seizure and sticking phenomena occurred and the μ value suddenly increased. Accordingly, Mg 2 Si coating technology is a suitable surface modification process to improve corrosion and wear resistance of magnesium alloys.

Low Temperature Synthesis of Extremely Dense and Vertically Aligned Single-Walled Carbon Nanotubes

A novel point-arc microwave plasma chemical vapor deposition (CVD) apparatus was employed to grow single-walled carbon nanotubes (SWNTs) on Si substrates coated with a sandwich-like nano-layer structure of 0.7 nm Al2O3 (top)/0.5 nm Fe/5–70 nm Al2O3 by conventional high frequency sputtering. The growth of extremely dense and vertically aligned SWNTs with an almost constant growth rate of 270 µm/h within 40 min at a temperature as low as 600°C was demonstrated for the first time. The volume density of the as-grown SWNT films is as higher as 66 kg/m3.

Ｍｇ２Ｓｉ焼結体を用いたマグネシウム合金へのＭｇ‐Ｓｉ成膜プロセスと皮膜特性

Coating technology by using magnesium silicide intermetallics (Mg2Si) was developed to improve the surface properties of magnesium alloys. This is because they have superior corrosion resistance to the conventional stainless steel and high Young's modulus and hardness. In this study, Mg-Si thin film deposited on AZ31 magnesium alloys by using a high frequency sputtering method was examined when employing the sintered Mg2Si bulky materials as sputtering targets. The change in the sputtering Ar gas pressure enables the structure control of Mg-Si thin film; crystal structures at lower pressure and amorphous one over 4 Pa. Some results of SST to evaluate the corrosion resistance indicated that AZ31 substrate with Mg-Si coating showed no damage after 240 h. On the other hand, that with no coating was corroded within only 1 h, and showed remarkably damaged surfaces. Pin on disk type wear test under oil lubricant indicated that a friction coefficient, μ was low and stable in using AZ31 alloy disk specimen coated by Mg-Si film. The disk specimen with no coating showed severely damaged surface including seizure or sticking phenomena with S35C pin specimens. In particular, the amorphous Mg-Si film showed superior anti-seizure properties to the crystalline one because of higher hardness and Young's modulus.

Nanometer silicon thin films prepared by HF sputtering at low temperature

Nanometer silicon thin films have been developed by high-frequency (HF) sputtering at low temperature. Dark and photo I–V characteristics of the films are measured at room temperature, and the result shows that the films have the Coulomb blockade effect. The average size of the nano-crystallines which are embedded in the amorphous matrix is about 10nm. Optical gap of such films is >2.0eV. All the films are prepared at temperature lower than 150°C.

Low‐Temperature Polycrystalline Silicon Deposition by Very High Frequency Sputtering Using Ar and H 2

Polycrystalline silicon thin films have been deposited on silicon oxide at 300°C by very high frequency (182.5 MHz) sputtering using an Ar and gas mixture and an arsenic‐doped Si wafer target. Characteristics of films are affected by the hydrogen partial pressure, and polysilicon of lowest resistivity is obtained at 20 to 30% hydrogen partial pressure ratio. We found that as the hydrogen content of the film is reduced, resistivity decreases. This is attributed to reduction of amorphous grain boundary regions due to better crystallization. It is also found that the normalized ion flux incident on the growing surface varies with hydrogen partial pressure, an important parameter for determining the properties of as‐deposited polysilicon.

Preliminary results on a novel fabrication route for α-Al 2O 3 single crystal monofilament-reinforced reaction-bonded mullite (RBM)

Owing to their excellent properties, continuous-fibre reinforced mullite-matrix composites are good candidates for applications in which oxidation resistance and damage tolerance at high temperatures (> 1000 °C) are required. To avoid fibre damage, near net-shape fabrication techniques of the composite are required. This has been achieved by using the reaction-bonding process which benefits the oxidation of metal powders producing volume expansion, and hence fully or partially compensating for the sintering-induced shrinkage. Starting materials include Al-Si alloy (80:20), Si metal, α-Al 2O 3 and mullite precursor powders. Due to the variety of starting compounds with different reaction and sintering kinetics, composite fabrication becomes a complex process. Differential scanning calorimetry (DSC) measurements, scanning electron microscopy (SEM) observations, and X-ray diffractometry (XRD) data show that effective milling of metal powder leads to a high degree of mullite formation (≈ 84%) at temperatures as low as 1500 °C, although densification of the ceramic compacts remains rather low (≈ 45% of theoretical density). Single crystal α-Al 2O 3 monofilaments were used to reinforce the reaction-bonded mullite (RBM) matrix. Although no intense reaction between the matrix and the fibres was observed at process temperature, strong bonding develops between uncoated fibres and the matrix. In order to produce a weaker fibre-matrix interface, which is necessary for improvement of the damage tolerance, the fibres were coated with ZrO 2 by means of high frequency sputtering. Microstructural observations of the fibre surfaces before and after the reaction-bonding process indicate that thick coatings (> 10 μm) produce very weak bonding, insufficient for matrix-fibre load transfer due to shrinkage of the low density ZrO 2 layers. Thinner layers (1 μm) produce a better interfacial relation with suitable pull-out of fibres.

Secondary operations

Owing to their excellent properties, continuous-fibre reinforced mullite-matrix composites are good candidates for applications in which oxidation resistance and damage tolerance at high temperatures (> 1000 °C) are required. To avoid fibre damage, near net-shape fabrication techniques of the composite are required. This has been achieved by using the reaction-bonding process which benefits the oxidation of metal powders producing volume expansion, and hence fully or partially compensating for the sintering-induced shrinkage. Starting materials include Al-Si alloy (80:20), Si metal, α-Al2O3 and mullite precursor powders. Due to the variety of starting compounds with different reaction and sintering kinetics, composite fabrication becomes a complex process. Differential scanning calorimetry (DSC) measurements, scanning electron microscopy (SEM) observations, and X-ray diffractometry (XRD) data show that effective milling of metal powder leads to a high degree of mullite formation (≈ 84%) at temperatures as low as 1500 °C, although densification of the ceramic compacts remains rather low (≈ 45% of theoretical density).Single crystal α-Al2O3 monofilaments were used to reinforce the reaction-bonded mullite (RBM) matrix. Although no intense reaction between the matrix and the fibres was observed at process temperature, strong bonding develops between uncoated fibres and the matrix. In order to produce a weaker fibre-matrix interface, which is necessary for improvement of the damage tolerance, the fibres were coated with ZrO2 by means of high frequency sputtering. Microstructural observations of the fibre surfaces before and after the reaction-bonding process indicate that thick coatings (> 10 μm) produce very weak bonding, insufficient for matrix-fibre load transfer due to shrinkage of the low density ZrO2 layers. Thinner layers (1 μm) produce a better interfacial relation with suitable pull-out of fibres.

Thin-film waveguides made of dense crown glass

High-frequency sputtering was used in the preparation of high-quality thin-film waveguides made of various types of dense crown glass. The refractive index of films produced in this way was higher than that of the bulk materials. This was attributed to preferential sputtering of barium oxide.