Yosuke Fujita

Patterning Characteristics of ITO Thin Films

The relationship between patterning characteristics and other (such as microstructural and electroptical) characteristics which depend on sputtering conditions, especially the substrate temperature and oxygen partial pressure, was investigated in ITO films prepared by the rf magnetron sputtering method. Sputtering conditions that satisfied both the patterning and electroptical characteristics were found to exist and ought to be precisely controlled since the postannealing of ITO films does not necessarily improve the patterning characteristics. The films showing superior patterning characteristics had dense microstructures without pores and simultaneously exhibited fairly low etching rates and low resistivities.

Electrical Properties of Perovskite Type Oxide Thin-Films Prepared by RF Sputtering

Oxide thin-films with perovskite structure are prepared by rf magnetron sputtering in argon-oxygen mixed gas at substrate temperature below 500°C using the Sr(Zr, Ti)O3 and Ba(Sn, Ti)O3 solid solution ceramic targets. The dielectric properties and the microstructure of the sputtered thin-films depend on the substrate temperature, oxygen partial pressure, and target compositions. The dielectric constant and the electrical breakdown strength of the thin-films sputtered by using Sr(Zr0.2Ti0.8)O3 and Ba(Sn0.2Ti0.8)O3 targets is about 100 and 3 MV/cm, respectively. These thin-films with the high dielectric constant and the high electrical breakdown strength are useful for the dielectic layer of the ac TFEL panel.

New efficient phosphor material ZnS:Sm,P for red electroluminescent devices

Thin‐film electroluminescent devices employing a new phosphor material ZnS:Sm,P have been found to exhibit bright red emission. Luminous efficiency of ZnS:Sm,P phosphor films is higher than that of ZnS:Sm phosphor films in the range of annealing temperature above 500 °C. A brightness of 1000 cd/m2 and an efficiency of 8×10−2 lm/W have been obtained in the devices with ZnS:Sm(1 at. %),P(0.5 at. %) phosphor films annealed at 600 °C. These results indicate that P is an efficient co‐activator for Sm in ZnS.

A Study of the Crystallographic and Luminescent Characteristics of ZnS:Mn Films Prepared by an RF Magnetron Sputtering Method for AC Thin-Film Electroluminescent Devices

Characteristics of ZnS:Mn films prepared by an rf sputtering method for electroluminescent devices were examined in detail; the features were clarified by a comparison with films produced by an electron-beam method. It was found that the incident species to the substrate during sputtering were composed of ZnS, Zn2, Zn2S, MnS and ZnMn in addition to Zn and S atoms; in the case of the electron-beam method, they were composed of Zn and S2. We confirmed that preparative, crystallographic, microstructural , chemical, and eventually electroluminescent characteristics in sputtered ZnS:Mn films were different from those in electron-beam films, according to the fundamental difference of the incident species to the substrate, which affected film growth.

An XPS Study of Blackening of Indium-Tin Oxide Film during Deposition of Dielectric Films by RF Magnetron Sputtering

The blackening phenomenon of an indium-tin oxide (ITO) film when Sr(Zr0.2Ti0.8)O3 dielectric film was deposited on it by the rf magnetron sputtering method has been examined by X-ray photoelectron spectroscopy. It was found that the blackening took place in the thin surface layer of the ITO film near the Sr(Zr0.2Ti0.8)O3/ITO interface and originated from preferential reduction of the Sn4+ ion to Sn0 rather than of In3+.

Interdiffusion Phenomena Caused by Postannealing of ZnS:Mn Films in Thin-Film Electroluminescent Device

In the electroluminescent device laminated with the following thin films, ITO/Sr(Zr0.2Ti0.8)O3/ZnS:Mn/Y2O3/Al2O3/Al, diffusions of In, Sr and Ti ions to the ZnS:Mn film were observed at high postannealing temperature of the ZnS:Mn films. We confirmed that an optimized annealing temperature needed to obtain the highest luminance was located at 450°C, where pronounced diffusions did not take place. The diffusion of the Ti ion into the ZnS:Mn film was considered to affect the performance of the EL device.

Influence of Oxygen and Metal Oxide Impurities in ZnS:Mn Film on Characteristics of Electroluminescent Devices

The effects of an oxygen and some metal oxide impurities introduced into the ZnS:Mn film at its postannealing process were examined with respect to the characteristics of an electroluminescent device. Depending on the oxygen pressure at the postannealing, the oxygen either decreases the emission threshold field strength in the ZnS:Mn film or forms an additional insulating film such as ZnSO4. The metal oxide impurities Fe, V, and Co caused a decrease in luminance via a killer effect on the Mn emission center. On the other hand, Ti, In, Na, and V decreased the emission threshold voltage by lowering the emission threshold field strength in the ZnS:Mn film.

Concentration profiles of composing ions in radio frequency sputtered Sr (Zr0.2Ti0.8)O3 films

Sr(Zr0.2 Ti0.8 )O3 dielectric thin film for electroluminescent devices was prepared by in‐line‐type rf magnetron sputtering method using oxide target. Novel phenomenon of periodic concentration fluctuations of the composing ions was observed in SIMS in‐depth profiles. Partial concentration anomaly with Sr deficiency was also observed in the first‐to‐grow region of the film. The periodic concentration fluctuations were confirmed to be ascribed to periodic appearance of Sr(Zr1−x Tix )O3 with x larger than 0.8.

Electric Resistance Change Mechanism of Indium-Tin Oxide Film During Deposition of Dielectric Oxide Films by RF Magnetron Sputtering

Electric resistance change of indium-tin oxide (ITO) film was investigated when dielectric oxide films such as Sr(Zr0.2Ti0.8)O3 and Y2O3 for an electroluminescent device were deposited on the ITO by the rf magnetron sputtering method using oxide ceramic targets. In order to understand the mechanism of the resistance change, a dc voltage of -70~+70 V was biased to an ITO film during the sputtering of dielectric oxide films. The resistance of the ITO film became higher in the positive bias region. The cause of the increase in resistance of the ITO films was confirmed to be oxidation by the oxide targets and the sputtering gas. The amount of the resistance change could be qualitatively explained by the ratio of the oxygen introduced into the ITO film and the combined oxygen forming O2 gas at the ITO surface incident to the ITO film at the sputtering of the dielectric oxide films.