Three-dimensional hologram-read-only memory duplication by nanoimprint lithography

Abstract

Because the amount of multimedia data is continually increasing, there is growing demand for high-speed, large-capacity, read-only memory (ROM) to facilitate data distribution. Computer-generated hologram-ROM (CGH-ROM) has received considerable attention in relation to its potential to meet this rising demand. CGH-ROM requires a nanoscale-precision structure, as well as nanosteps. Because of its process simplicity, nanoimprint lithography (NIL) is a promising method for cost-effective fabrication of complex and high-precision patterns. The authors have demonstrated CGH-ROM duplication by ultraviolet NIL (UV-NIL) from a three-dimensional (3D) master mold fabricated by electron-beam lithography (EBL). The calculated depths of the CGH were converted into four tones to permit easy fabrication of the CGH while retaining a high diffraction efficiency. EBL using a spin-on glass and super-resolution technique with a postexposure bake was used to fabricate the 3D master mold. The developed depth was controlled by changing the EB exposure dose, with higher EB doses tending to produce deeper patterns. The pattern was duplicated by means of UV-NIL and the reconstruction image corresponded to the design pattern. Moreover, the authors have succeeded in fabricating a gray-scale multilevel CGH-ROM and in producing its reconstruction.