Kentaro Utsumi

Low resistivity ITO film prepared using the ultra high density ITO target

Abstract The ultra high density ITO target of 99% or more in relative density has developed by the improvements of the ITO powder and the sintering process. Sputtering test on various densities (90, 97 and 99%) of ITO (SnO2: 10 wt.%) targets was performed in a dc magnetron sputtering system. The minimum resistivity of the thin film was obtained at 0.1% in O2/Ar for each of the targets, and was 149 (μΩ×cm) for the 99% target, 159 (μΩ×cm) for the 97% one and 161 (μΩ×cm) for the 90% one, respectively. Hall effect measurement revealed that the improvement of the resistivity with an increase in the target density is due to the carrier concentration increase. ITO films prepared with different density targets were analyzed by means of EPMA, SEM, XRD and ESCA. However, no differences in microstructure were recognized between them.

Study on In2O3-SnO2 transparent and conductive films prepared by d.c. sputtering using high density ceramic targets

The influence of SnO 2 concentration in the target on the film characteristics was studied in order to make the useful database for the device design when low discharge voltage sputtering method and a high density In 2 O 3 -SnO 2 ceramic targets were used. In the case of the films deposited on unheated substrate, X-ray diffraction profile showed amorphous structure. Minimum resistivity of 358 μΩ cm was obtained by In 2 O 3 film with mobility of 40.1 cm 2 (V s) -1 and carrier density of 4.35E + 20 cm -3 . With the increase of SnO 2 contents, resistivity of the films increased because of the decrease in both carrier density and mobility. Whereas, the films deposited on heated substrates showed polycrystalline structure. Resistivity was reduced, ranging from 5 to 20 wt.% SnO 2 , and minimum resistivity of 136 μΩ cm was obtained at 15 wt.% with mobility of 40.5 cm 2 (V s) -1 and carrier density of 1.13E+21 cm -3 . Transmittance and reflectance of these films strongly depend on carrier density.

Structural, electrical, and optical properties of transparent conductive In2O3–SnO2 films

Transparent conductive In2O3–SnO2 films were deposited by dc magnetron sputtering on unheated glass substrates using high-density ceramic targets with various SnO2 concentrations (0–100 wt. %). These films were subsequently postannealed in various atmospheres [air, Ar (100%) or Ar(97%)+H2(3%)] for 1 h at 200 °C. All the as-deposited films were amorphous by X-ray diffraction (XRD). After the postannealing, XRD profiles of the films deposited using the targets in the range of 0–20 wt. % SnO2 showed bixbyte In2O3 polycrystalline structure, whereas all the films deposited using the targets with 44.5 wt. % SnO2 and 100 wt. % (pure SnO2) were amorphous. Resistivity of the films deposited using the targets in the range of 0–20 wt. % SnO2 went from about 4.0×10−4 to 2.0×10−4Ω∙cm by the postannealing under all atmospheres due to increased carrier density. This implies an increase in the number of the substitutional Sn4+ at In3+ sites during crystallization. The work function of the postannealed films was inversely...

Structure and Internal Stress of Tin-Doped Indium Oxide and Indium–Zinc Oxide Films Deposited by DC Magnetron Sputtering

Representative transparent conductive oxide films, such as tin-doped indium oxide (ITO) and indium–zinc oxide (IZO) films, were deposited by dc magnetron sputtering using corresponding oxide targets under various total gas pressures (Ptot) ranging from 0.3 to 3.0 Pa. The ITO films deposited at a Ptot lower than 0.7 Pa were polycrystalline and were found to have a large compressive stress of about 1.5 ×109 Pa, whereas the ITO films deposited at 1.5–3.0 Pa were amorphous and had a low tensile stress. In contrast, all the IZO films deposited at a Ptot range of 0.3–3.0 Pa showed an entirely amorphous structure, where the compressive stress in the IZO films deposited at a Ptot lower than 1.5 Pa was lower than that in the ITO films. Such compressive stress was considered to be generated by the atomic peening effect of high-energy neutrals (Ar0) recoiled from the target or high-energy negative ions (O-) accelerated in the cathode sheath toward the film surface.

Ellipsometry characterization of polycrystalline ZnO layers with the modeling of carrier concentration gradient: Effects of grain boundary, humidity, and surface texture

Spectroscopic ellipsometry (SE) has been applied to study the effects of grain boundary, humidity, and surface texture on the carrier transport properties of Al-doped ZnO layers fabricated by dc and rf magnetron sputtering. In the SE analysis, the variation in the free carrier absorption toward the growth direction, induced by the ZnO grain growth on foreign substrates, has been modeled explicitly by adopting a multilayer model in which the optical carrier concentration (Nopt) varies continuously with a constant optical mobility (μopt). The effect of the grain boundary has been studied by comparing μopt with Hall mobility (μHall). The change in μHall/μopt indicates a sharp structural transition of the ZnO polycrystalline layer at a thickness of d ∼ 500 nm, which correlates very well with the structure confirmed by transmission electron microscopy. In particular, below the transition thickness, the formation of the high density grain boundary leads to the reduction in the μHall/μopt ratio as well as Nopt. ...

Development of Novel Al-Doped Zinc Oxide Films Fabricated on Etched Glass and Their Application to Solar Cells

We have successfully developed novel aluminum-doped zinc oxide (AZO-X) films with a high haze ratio by the combined use of an etched glass substrate and wet-etched AZO-X films. The effects of the use of an etched glass substrate and wet-chemical etching on the properties of AZO-X films were investigated. The texture size and rms roughness of these films largely increased with glass surface roughening. Post-treatment using wet chemical etching slightly increased the texture size and rms roughness. The etched glass approach has been found to be a promising method for achieving an AZO-coated glass substrate with a high haze ratio. Using high-haze ratio AZO-X films as the front transparent conductive oxide (TCO) layers in solar cells, we improved the quantum efficiency (QE) of these solar cells particularly in the long-wavelength region. Thus, the AZO-X films deposited on etched glass have a high potential for use as front TCO layers in silicon-based thin-film solar cells.

Magnetic properties and crystal structure of CoCrTaPt thin film for longitudinal recording media

Magnetic properties and crystal structure of sputtered CoCrTaPt/Cr and CoCrTa/Cr thin films were studied as a function of Pt content and the substrate temperature. It was observed that the coercivity increased with Pt content or the substrate temperature, and that the coercivity was saturated with a small amount of Pt at high substrate temperature compared to at low substrate temperature. X‐ray diffraction study showed that at high substrate temperature, Co(11.0) grew epitaxially on Cr(200). That indicates c axis of hexagonal‐close‐packed Co phase lies in the film plane. It was also shown that diffraction angles of Co planes shifted lower with the addition of Pt. These shifts are attributed to the diffusion of Pt into the Co lattice, and the shifts are promoted by the increase of the substrate temperature. The addition of Pt led to the increase of crystalline magnetic anisotropy constant (Ku), and the increase of Ku was also promoted by the increase of the substrate temperature. The increase of the coerci...

Development of Novel Aluminum-Doped Zinc Oxide Film and Its Application to Solar Cells

We have developed novel aluminum-doped zinc oxide films (AZO-X and AZO-HX films) with a high haze value using wet-chemical etching for various times after dc magnetron sputtering, and have investigated their electrical and optical properties, durability under high-humidity condition, and surface morphology. The AZO-X and AZO-HX films showed good balance between transmittance in the near-infrared area and durability under 85 °C–85%RH condition. These novel films also had a higher haze value after wet chemical etching than normal AZO films. The crater size and haze value of the AZO-HX film increased with increasing etching time in comparison with those of the AZO-X film. The haze value of the AZO-HX film was higher than that of the AZO-X film; their values are 90% at 550 nm and 60% at 800 nm. Furthermore, the AZO-HX film was applied in amorphous silicon (a-Si) single-type solar cells as the front electrode. The short-circuit current of the solar cell using the AZO-HX film was higher than that of the solar cell using the AZO-X film. As an optimization-based result, an efficiency as high as 10.2% was obtained, showing that the new AZO-HX film is a promising material for the front electrode of a-Si solar cells.

Development of novel Al doped zinc oxide film and its application to solar cells

We have developed novel Al doped zinc oxide (AZO) films, AZO-X films, using d.c. magnetron sputtering process and have investigated their electro-optical properties and their surface morphology. AZO-X films showed a good balance between the transmittance in near-infrared area and the durability under 85°C-85%RH condition. And AZO-X film also had higher haze value after wet chemical etching than the value obtained in normal AZO film. Furthermore, AZO-X films have been applied to amorphous Si (a-Si) single-type solar cells as the front electrodes. The efficiency as high as 10.1% with high short-circuit current has been obtained, showing that this novel AZO-X is the new promising material for front electrode of a-Si solar cells.