Millimeter wave materials processing in Japan by high power gyrotron

Summary form only given, as follows. Firstly, innovative materials processing in Japan using high power mm-wave radiation of gyrotrons is reviewed briefly. Secondly extensive research results conducted on ceramics sintering and modification by 28 GHz mm-wave is described with emphasis on the unique characteristics inherent to mm-wave irradiation to materials. In the mm-wave processing of bulk materials low temperature sintering of Si/sub 3/N/sub 4/ with Yb/sub 2/O/sub 3/ and Al/sub 2/O/sub 3/ is demonstrated as a typical example of selective heating process of rare-earth metal oxides bringing efficient liquid phase sintering by mm-wave radiation. Low temperature energy saving sintering of AlN is also studied in which dense AlN is obtained at a sintering temperature of 1600/spl deg/C with a soaking time of only 40 min and the thermal conductivity reached to a value over 200 W/mK for the sample sintered at 1700/spl deg/C for 120 min under a reduction gas environment of N/sub 2/ + 3% H/sub 2/. In the thin film processing by mm-wave radiation it was found that SrTiO/sub 3/ and (Ba,Sr)TiO/sub 3/ perovskite structure amorphous films of about 100 nm in thickness, prepared on Si substrates by ECR plasma sputtering, could be crystallized well by the mm-wave irradiation at a low temperature of about 300/spl deg/C. The electrical property was also improved drastically, in which dielectric constant of SrTiO/sub 3/ films could be increased to a value nearly equal to the bulk one by the post annealing with mm-wave radiation at a temperature of 300/spl deg/C. Finally future trend of the mm-wave materials processing will be discussed.