Millimeter-Wave Materials Processing in Japan by High-Power Gyrotron.

This paper summarizes recent research activities on materials processing using millimeter-waves in Japan with emphasis on the work performed at the Joining and Welding Research Institute (JWRI), Osaka University. Extensive research results conducted at the JWRI on ceramics sintering and modification of thin film properties with millimeter-wave radiation from a 28-GHz gyrotron are described. In the sintering of pure Al[SUB2]O[SUB3], it was found that al a similar density and grain size a big difference in the bending strength appeared in the sample after millimeter-wave sintering as compared with that after conventional sintering. This result was attributed to come from the difference in the grain boundary structures due to the unique millimeter-wave effect. We have also obtained highly dense sintered Si[SUB3]N[SUB4] and Aluminum Nitride (AIN) by the millimeter-wave method with new sintering aids containing Yb[SUB2]O[SUB3] at a temperature lower by about 200 °C-400°C than that by ibc conventional method. It was verified that selective heating of b[SUB2]O[SUB3] by millimeter-waves around the grain boundary promoted a densification process in its liquid phase. A high thermal conductivity of 210 W/m °C could he obtained in AIN samples sintered at 1700°C for 180 mtn in N[SUB2]+ 3% H[SUB2] gas environment. In the research of thin-film modification the millimeter-wave irradiation to Strip[SUB3] films prepared by mirror-confinement-type electron cyclotron resonance (MCECR) plasma sputtering method could drastically improve their crystallinity and electrical properties at remarkably lower temperatures than by the conventional thermal methods. The crystallization temperature of amorphous films on Si substrates were 300°C and the dielectric constant reached to about 260. [ABSTRACT FROM AUTHOR]