Photocatalytic TiO2 films were prepared by reactive gas flow sputtering (GFS), which enables sputter-deposition at a high pressure of about 100 Pa. A pure Ti tube was used as the target, and the O2 gas was supplied in front of the substrate, resulting in a very stable discharge and a high deposition rate of 80 nm/min. The crystal structure and morphology of TiO2 films were found to strongly depend on the flow rate of O2 gas during sputtering. Polycrystalline films composed of rutile and anatase crystallites were deposited at a low O2 flow rate of less than 2 sccm when Ar flow rate was set at 300 sccm, and amorphous films were deposited at higher O2 flow rates. Polycrystalline films composed of very small crystallites showed high levels of photocatalytic activity, while amorphous films showed no activity.

The surface film of a slip ring is important for the sliding contact phenomenon. The surface film is affected by atmospheric temperature, humidity and air pressure. The main objective of our study is to examine the effect of oxygen gas on the sliding contact phenomenon. In the present experiment, we examined the contact voltage drop for continuous sliding when the atmosphere is changed from low pressure to atmospheric pressure by introducing oxygen (O2 20%+N2 80%) or nitrogen gas. As a result, the contact voltage drop increases rapidly with increasing gas pressure, and its fluctuation also becomes large. These phenomena are observed in both cases of oxygen (O2 20%+N2 80%) and nitrogen introduction. The results clearly show that the sudden increase of contact voltage drop is affected by factors other than the oxide film. Actually, the oxide film is not formed in the nitrogen atmosphere. Furthermore, the frictional coefficient of carbon and copper ring is changed at ambient atmosphere. It is inferred from these data that the contact voltage drop may be affected by the frictional coefficient. When the gas pressure decreases again, the contact voltage drop does not suffer from the effect of ambient gas. Therefore, only the resistance of the oxide film appears to affect contact voltage drop. In this paper, the effect of sliding contact phenomenon on the contact voltage drop by gas adsorption and film generation was examined.

Contact resistance of nickel hardened gold electroplate (NiHG) deposited on nickel-underplated phosphor bronze disk coupons (substrate) after thermal aging was measured with a hard gold-plated beryllium copper alloy pin probe by means of a four-point probe technique, compared to that of cobalt-hardened gold electroplate (CoHG). Surface of NiHG plated coupons after aging was analyzed by X-ray photoelectron spectroscopy (XPS) to investigate the influence of the oxide film formation during thermal aging on contact resistance of NiHG electroplate, compared to that of CoHG. Initial contact resistance of the NiHG coupons was less than 10 mΩ at a contact forces more than 0.05 N, increased to 10 mΩ at a contact force of 0.05 N after 100 hours aging at 200. In contrast, contact resistance of the CoHG coupons progressively increased with increase in aging time, reached 1000 mΩ even at a contact force of 0.05 N after 52 hours aging. XPS analysis for the NiHG coupons demonstrated that nickel oxide film was formed on the NiHG surface in conformity with parabolic growth kinetics, as cobalt oxide film formed on CoHG surface. However, a thickness of the latter film was approximately 4-fold larger than that of former after 100 hours aging at 200. The small increase in contact resistance of NiHG coupons after aging suggested to be due to inhibitory of nickel oxide film growth on the surface. The cause of relatively low and steady contact resistance of NiHG during thermal aging was discussed.

This paper describes a new reduction mechanism of the stress induced leakage current that is induced by step tunneling of electrons through the step tunneling sites. The concept of this mechanism is based on the deactivation of step tunneling sites for thin oxide. It is verified that the deactivation is electrically realized by the injected electrons int the sites. It is because the step tunneling probability of electrons though the deactivated sites is suppressed, since the electron capture cross section of the neutralized deactivation sites becomes extremely low. The deactivation scheme is as follows: (1) The deactivation of tunneling sites can be realized that the tunneling sites trapped holes change to neutralized tunneling sites due to electrons injection. (2) The injected electron can deactivate the activation tunneling sites only under energy level than the energy level of the injected electrons. It is shown that the above reduction phenomenon can be quantifiably with formulation. These results are very important for high reliable thin oxide films and for high performance ULSI.

On the surface of contacts which are exposed to the atmosphere, the reaction with gases in the atmosphere produces contaminant films including oxides. The contact reliability is degraded by the contaminant films. Humidity in the atmospheric environment also influences on the surface of contacts. However, influence of humidity on the surface has not been clarified. In the present paper, influence of humidity on the Cu surface and the oxides (CuO + Cu2O) on it were studied with respect to the thickness of the oxide film and contact resistance characteristics both for static and for sliding contacts. The thickness was measured by ellipsometric analysis. Topographic image affected by humidification was also observed by scanning tunneling microscope (STM). In the atmospheric environment, the clean surface of Cu was found to oxidize with fluctuations of the thickness for lapse of exposure time due to the fluctuations of the humidity. It was also found that the thickness of the oxide film decreases immediately after the humidification, and increases under dehumidification. Changes in contact resistance affected by humidity was corresponding to the change in the film thickness. Immediately after humidification contact resistance decreased, and increased with dehumidification both for static and for sliding contacts. For the mechanism of the influence of humidity on the oxide, chemical reduction of hydrogen generated by decomposition of the absorbed water molecule (H2O) was derived. The clean Cu surface was oxidized by oxygen due to absorbed water molecule and atmosphere.

The former experimental results have already shown that it is oxide films formed on contact surface causing the contact resistance to degrade in dc. breaking arcs for Ag and Pd materials. In order to understand the detailed information about it, the experiments are performed to break dc. inductive load at 20 V, 0.5 A and 1.0 A in nitrogen gas with different oxygen concentrations. The contact surface morphology and surface contamination are evaluated by SEM and AES, respectively. The tested results demonstrate that, for Ag contact, the severe oxidation occurs with increasing oxygen concentration, and the critical value of oxygen concentration is found to be about 10% and 5% in 0.5 A and 1.0 A, respectively, above those values the contact resistance degrades due to the oxide films formed on the contact surface, especially on the anode surface. While, for Pd contacts, a remarkable contact resistance degradation is not found even at 1.0 A in oxigen. Evidence shows that the arc duration, in particular the gaseous phase arc duration affects the anode oxidation, which in turn causes the significant fluctuation of contact resistance.

The increase of surface microroughness on Si substrate degrades the electrical characteristics such as the dielectric breakdown field intensity (EBD) and charge to break-down (QBD) of thin oxide film. It has been found that the surface microroughness increases in the wet chemical process, particularly in NH4OH-H2O2-H2O cleaning (APM cleaning). It has been revealed that the surface microroughness does not increase at all if the NH4OH mixing ratio in NH4OH-H2O2-H2O solution is reduced from the conventional level of 1:1:5 to 0.05:1:5, and the room temperature ultrapure water rinsing is introduced right after the APM cleaning. At the same time, the APM cleaning with NH4OH-H2O2-H2O mixing ratio of 0.05:1:5 has been very effective to remove particles and metallic impurities from the Si surface. The surface microroughness dominating the electrical properties of very thin oxide films is strictly influenced by the wafer quality. The increase of surface microroughness due to the APM cleaning has varied among the wafer types such as Cz, FZ and epitaxial (EPI) wafers. The increase of surface microroughness in EPI wafer was very much limited, while the surface microroughness of FZ and Cz wafers gradually increase. As a result of investigating the amount of diffused phosphorus atoms into these wafers, the increase of the surface microroughness in APM cleaning has been confirmed to strongly depend on the silicon vacancy cluster concentration in wafer. The EPI wafer having low silicon vacancy concentration is essentially revealed superior for future sub-half-micron ULSI devices.