In accordance with the corrosion protection of Cu by n-TiO2 coating under illumination, the relation between the structural characterization and the photoelectrochemical properties of sol-gel-derived TiO2 coating has been investigated utilizing glow discharge spectroscopy, x-ray diffraction, and x-ray photoelectron spectroscopy analysis techniques. As a result of the well-known shrinkage of the gel under heat-treatment, the thickness of the TiO2 coating decreased with increasing heating temperature, about a 50% decrease from 200 to 800~ Amorphous TiO2 gel was found to be crystallized above 400~ which gave rise to a great enhancement of the photocurrent of the TiO2 coating. In relating these results to the photoelectrochemical behavior of TiO2-coated Cu, it was revealed that both the significant change in the photocurrent and the existence of Cu oxides in the coating were not the direct reasons which accounted for the critical temperature for TiQ to impose its photoeffect on the Cu substrate. The dramatic change in the photopotential of TiO2-coated Cu would be explained by the change of Schottky barrier at the TiO2/Cu interface in terms of the Fermi level pinning at the Ti ~ § defect level. Nevertheless, the increase in the photocurrent of TiO2 coating was beneficial to move the photopotential of TiO2coated Cu to a much less noble level. The degradation of the photoeffect of TiO2 coating heated above 800~ was due to the significant diffusion of Cu into the coating.
Negative bias temperature instability (NBTI) of pMOSFETs with ultra-thin gate dielectrics was investigated from four points of view: basic mechanism of NBTI, dependence of NBTI on gate dielectric thickness, mechanism of NBTl enhancement caused by addition of nitrogen to the gate dielectrics, and possibility of applying SiON gate dielectrics with a high concentration of nitrogen. By investigating the behavior of FET characteristics after NBT stresses were stopped, it was clarified that a portion (60%, in our case) of hydrogen atoms released by the NBT stress remain in the gate dielectric in the case of a 1.85-nm-thick NO-oxynitride gate dielectric. The existence of the hydrogen was shown to lead to the generation of. positive fixed charges in the gate dielectric. It was also found that NBTI depends little on gate dielectric thickness. Moreover, we revealed that the origin of NBTl enhancement by incorporating nitrogen into gate dielectrics is the property of attracting H,O or OH. We speculate this property of attracting H,O or OH is due to the existence of positive fixed charges induced by undesirable nitrogen. We evaluated NBTl immunity of SiN gate dielectrics with oxygen-enriched interface (01-SiN) in which high carrier mobility was obtained by reducing positive fixed charges. The 01-SiN gate dielectrics with EOTs of 1.4 and 1.6 nm were found to have sufticient.lifetime for practical use under 1 V operation.
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