Akira Mitsui

Electrical and optical properties of gallium-doped zinc oxide films deposited by dc magnetron sputtering

Gallium-doped zinc oxide (GZO) films were deposited by dc planar magnetron sputtering using a GZO ceramic target. Deposition was carried out under various conditions of substrate temperature (RT-700 °C), residual water pressure (1.61 × 10 -4 -2.2 × 10 -3 Pa), and H 2 /(Ar + H 2 ) flow ratio (0-15%). A relatively low resistivity of 5 × 10 -4 Ω cm was obtained for films deposited at 400 °C, attributed to an increase in carrier density and Hall mobility. In the case of 100% Ar gas, the grain size and electrical properties of the GZO films deposited on RT substrates were heavily affected by residual water pressure in the deposition chamber. The resistivity increased from 3.0 × 10 -3 to 3.1 × 10 -2 Ω cm and the grain size of the films decreased from 24 to 3 nm when the residual water pressure was increased from 1.6 × 10 -4 to 2.2 × 10 -3 Pa. However, the introduction of H 2 to decrease the resistivity resulted in a decrease of grain size in proportion to H 2 flow ratio.

Properties of Ga-doped ZnO films

Abstract Transparent conductive films of Ga-doped ZnO (GZO) were deposited on glass substrates by dc magnetron sputtering using a ZnO target with Ga 2 O 3 content of 3 to 10 wt%. The dependence of electrical properties on substrate temperature, Ga 2 O 3 contents in the sputtering target and magnetic field strength at the target surface were investigated. It was found that the resistivity depended on both substrate temperature and Ga 2 O 3 content. At substrate temperatures of 100°C, resistivity decreased with increasing Ga 2 O 3 content and 6.5 × 10 −4 ω cm was obtained for a Ga 2 O 3 content of 7.5–10.0 wt%. When the substrate temperature was increased to 300°C, GZO films deposited using 4.5 to 5.7 wt% Ga 2 O 3 targets had a resistivity of 2.7 × 10 −4 ω scm. In addition, the resistivity was found to decrease with increasing magnetic field strength. When the substrate temperature and Ga 2 O 3 content were 100°C and 7.5 wt%, respectively, the resistivity decreased from 6.5 × 10 −4 to 2.9 × 10 −4 ω cm by increasing the magnetic field strength from 3.0 × 10 −2 to 6.5 × 10 −2 T. The minimum resistivity of 2.2 × 10 −4 ω cm was obtained at 250°C (Ga 2 O 3 content:5.7 wt%) for a magnetic field strength of 6.5 × 10 −2 T. The decrease in resistivity was due to the increase both in carrier concentration and mobility.

High rate sputter deposition of TiO2 from TiO2−x target

Abstract A new sputter technique for high rate deposition of TiO2 was developed for applying to common planar magnetron sputter system. With this technique, using plasma sprayed TiO2−x targets and a sputter gas of a few percent of O2 diluted with Ar, TiO2 films are deposited with a high deposition rate efficiency (deposition rate per applied power density) being almost eight times larger than that of the conventional sputter method using Ti target and O2 sputter gas.

High rate deposition of TiO2 by DC sputtering of the TiO2-X target

Abstract A new sputter method for high rate deposition of TiO 2 was developed for application to the common planar magnetron sputter system. In this method, DC power is applied to plasma sprayed TiO 2− X targets using a sputter gas of a few percent of O 2 diluted with Ar and then TiO 2 films are deposited with a high deposition rate (eight times higher than that by the conventional method) and a good uniformity of thickness and refractive-index distribution.

TiO2−X sputter for high rate deposition of TiO2

Abstract A new sputter technique for high rate deposition of TiO2 was developed for applying to conventional planar magnetron DC sputter system. In this technique, TiO2 films are deposited by using a plasma-sprayed TiO2−X target and Ar sputter gas including a few percent of O2 gas. The deposition rate efficiency (deposition rate per applied power density) was almost 8 times larger than that of the conventional sputter method. This technique also has an advantage that there is no damage done to the under layer during the deposition. The Low-E coatings, being multi-stacks of Ag/TiO2, were obtained even in the case of no protective layer on Ag film and their optical properties were better than those of Low-E coatings including ZnO as the dielectric layer, because of the high refractive index of TiO2.

Crystallinity of Gallium-Doped Zinc Oxide Films Deposited by DC Magnetron Sputtering Using Ar, Ne or Kr Gas

Gallium-doped zinc oxide (GZO) films were deposited at RT by dc planar magnetron sputtering under various total gas pressures (Ptot) ranging from 0.25 Pa to 2.5 Pa using Ar as the sputtering gas and a GZO ceramic oxide target. The GZO films showed highest crystallinity at Ptot = 2.0 Pa and showed clear degradation at a lower or higher Ptot. For a comparative study, Ne or Kr was also used as a sputtering gas. The mechanisms of degradation were investigated, considering the effects of bombardment of high-energy particles on the growing film surface and the energy of sputtered particles, where kinetic energies of these particles were estimated by Monte Carlo simulation. It was shown that sputtered particles lost sufficient energy for surface migration to form a crystalline structure at a higher Ptot. The high-energy neutrals of the sputtering gas (Ar0, Ne0, and Kr0) which recoiled from the target surface should be primarily responsible for the structural damage in the film at a lower pressure.

Friction and wear of boride ceramics in air and water

Abstract The tribochemical response of hot-pressed boride ceramics, ZrB 2 , B 4 C, ZrB 2 + B 4 C and ZrB 2 + B 4 C + SiC , has been investigated in air and in de-ionized water. In dry air, the coefficients of friction for all materials tested were about 0.9–0.95, while in humid air of relative humidity (r.h.) 95% they ranged from 0.2–0.3, except for that of ZrB 2 , which was 0.4. Hertzian fractures were noted on the worn surfaces of monolithic boride and ZrB 2 + B 4 C composite, but not on those of SiC-toughened boride or SiC-toughened ZrB 2 + B 4 C . In water, ZrB 2 underwent very severe tribochemical degradation, as suggested by the following reaction: ZrB 2 +10 H 2 O → Zr ( OH ) 4 + 2 H 3 BO 3 + 5 H 2 , while B 4 C, ZrB 2 + B 4 C and ZrB 2 + B 4 C + SiC underwent less tribochemical degradation, and showed lower specific wear rates than ZrB 2 in water.

Effect of a zirconium oxide undercoat on microstructure and properties of tin-doped indium oxide films for organic light emitting devices

Abstract ITO films deposited on ZrO 2 undercoats by sputtering were investigated. The ITO films have a fine grain structure, compared to a grain–subgrain structure of conventional ITO films grown on a glass substrate. The grain structure of the ITO films grown on ZrO 2 consists of 30–50 nm wide almost parallel-sided columns. The surface grains have a good uniformity in shape and size. The microstructure and electrical properties of the ITO films changed with increasing ZrO 2 thickness. This indicates that the microstructure and properties of ITO films can be controlled by the ZrO 2 film thickness. The OLED fabricated on the ITO films on ZrO 2 worked with lower driving voltage than the one fabricated on conventional ITO films at the same luminance.

Zirconium silicon oxide films for durable solar control coatings

Abstract Zirconium silicon oxide films were deposited by dc reactive magnetron sputtering of ZrSi alloy targets. The character and durability of these films were investigated. Thin film X-ray diffraction analysis showed that the film structure changed from crystalline to amorphous with an abrupt decrease of internal stress for an SiO 2 content of more than 20 mol%. Reduction of friction due to the amorphous structure was related to an improved mechanical durability. Films with an SiO 2 content of 30–90 mol% were favorable as a durable protection layer. Taber abrasion of a double-layer system (amorphous ZrSi oxide/TiN x /glass) indicated that not only the reduction of friction but also the oxide thickness was a key factor for the improved mechanical resistance.