Yoshihiro Kawasaki

Study on 40 Gbits/inch2 Density Molding Using Heat Insulated Mold

We investigated the high-density molding of a 40 Gbits/inch2 stamper with steep wall pits. This density corresponds to about 60 Gbytes in a 120 mm-diameter disk. We applied the heat-insulated structure to the mold, in which a heat insulating plate was located at the back of the stamper, to reduce the mold temperature. We obtained substrates without pit deformation over the entire pit area as the result of the combination of this mold and the low mold opening speed.

Study on 100 Gbit/inch2 density molding using double-sided heat insulated mold

Previously we showed substrates without any pit deformation in the case of injection molding a 40 Gbit/inch2 read only memory (ROM) substrate using the single-sided heat insulated mold, in which a heat insulating plate was located below a stamper, and the slow mold opening method. This type of mold is characterized by the fact that pits on the substrates can be replicated at a low mold temperature, to avoid the twisting of substrates. However, it was found that the radial tilt was large. Therefore, we investigated this phenomenon using simulations, and fabricated a double-sided heat insulated mold with a symmetric structure in the thickness direction of the substrates. We showed that performing injection molding using this double-sided mold rendered the radial tilt of substrates controllable, so that it was possible to obtain flat disks. Furthermore, we obtained a 120-mm-diameter 100 Gbit/inch2 ROM substrate, which had no pit deformation over the entire pit area even though the pit wall angle was greater than 80 deg. This density corresponds to approximately 140 Gbyte.