Takeo Nakano

Mode transitions in reactive sputtering of metal (Ti, V) oxides are studied. Under a controlled Ar gas pressure at a flow rate of 10 sccm, direct current sputtering plasma was generated. The oxygen flow rate Q and discharge power P were changed in two ways (Q was varied at fixed P, and vice versa), and the mode transitions were monitored using the state jump in the discharge voltage. When the transition points (P, Q) were plotted as two-dimensional (2D) maps, the metal-to-oxide and oxide-to-metal transition points were found to be located on two corresponding straight lines that passed through the origin, irrespective of how the parameters were varied. The origin of this behavior is discussed and ascribed to the linear relationship between the input power and the sputter etching rate of the target. These results also suggest that the metal-mode, hysteresis, and oxide-mode regions of the 2D map can be determined by a few pilot experiments. By depositing vanadium oxide films under conditions in the oxide-mode region, near its boundary, films with very similar optical properties could be obtained.

Transparent conductive Al-doped Zinc oxide thin films were deposited on glass substrates by conventional radio frequency magnetron sputtering (C-RFMS) and inductively coupled plasma-assisted radio frequency magnetron sputtering (ICP-RFMS) methods. The structural and electrical properties of films were studied as a function of the radial position (r) of the substrate in both methods. A good thickness uniformity was obtained in ICP-RFMS, while a significant decrease in film thickness was observed at r=30 mm (erosion zone) in C-RFMS. The c-axis orientation was achieved in all positions in ICP-RFMS, while crystallinity was degraded at r≧25 mm in C-RFMS. Low resistivity ρ of the order of 10^-4 Ω cm was obtained at all positions in ICP-RFMS, while ρ was rapidly increased at r≧30 mm in C-RFMS. In ICP-RFMS, high-energy ion bombardment is suppressed due to the modified plasma density profile and lower space potential. As for transparency, the sample prepared at r=0 mm in ICP-RFMS showed an average visible transmittance of 81%, higher than that in C-RFMS. Throughout the study, it was demonstrated that ICP-RFMS method was promising to improve the radial distribution of structural, electrical, and optical properties of Al-doped ZnO thin films.

Spindt-type emitters were fabricated with cavities made of Al/Mo/SiO₂ using the triode high power pulsed magnetron sputtering method. We explored the process parameters (gas pressure and voltage of the additional cap electrode) to optimize the sharpness of the emitter shape. We found that the intermediate pressure and voltage were suited to obtain sharp emitters. Further, we elucidated the crucial effect of the cavity dimensions, such as the cavity depth and hole diameter in the cavity ceiling, on the emitter shape. At a cavity depth of 480 nm, the aspect ratio (AR) of the emitter increased monotonously with an increase in the hole diameter. With a large hole diameter (900 nm) and even shallower cavity (380 nm depth), we attempted to reoptimize the process parameters. Consequently, a very sharp emitter cone structure with an AR exceeding 1.3 was obtained. The cap voltage that produced the optimum AR was found to decrease for the larger-hole and shallower-depth cavities. Finally, the applicability of the process for preparing a working emitter is discussed.