Paper NM-ThP2
Ultrasonic Nanoimprint on Engineering Plastics

Thursday, October 23, 2008, 6:00 pm, Room Hall D

We have developed a new ultrasonic nanoimprint technology that is superior to the current thermal and UV nanoimprint technologies. In this method an ultrasonic vibration is impressed in the direction of loading force during a molding operation at room temperature. Our nanoimprint system employed a magnetostriction actuator capable of generating ultrasonic vibration with frequencies and amplitudes ranging from DC to 30 kHz, and from 0 to ± 30 µm respectively. Here an electroformed-Ni mold consisting of dot and line/space patterns with a minimum width of 500 nm was employed to endure the mechanical stress by the ultrasonic vibration. The mold was mounted onto the ultrasonic generator with a photoresist. We report on the results of ultrasonic nanoimprinting on various engineering plastics. At first, several optimized imprinting conditions were investigated by using polyethylene terephthalate (PET, Tg = 75 °C) with a comparatively low glass transition temperature (Tg) in engineering plastics. When the frequency of the ultrasonic vibration was varied in steps of 0.1 - 10 kHz, and the amplitude in steps of 0.5 - 3 µm, the height of the imprinted pattern was found to rise with the increase in the frequency and the amplitude. In this case, a rubber sheet serving as a buffer was interposed between the thermoplastic sheet and the bottom loading stage to keep the contact force of mold patterns on the thermoplastic uniform. By employing four kinds of rubbers the hardness of the buffer material was changed to 32, 57, 80, and 90 °. When the low repulsion rubber sheet in the hardness of 57 ° was used without ultrasonic vibration, the height of the imprinted pattern reached a maximum. However, in the presence the ultrasonic vibration the optimized buffer material was a sheet of urethane in the hardness of 90 °. Then under those same molding conditions, polycarbonates (PC, Tg = 150 °C) and polymethyl methacrylates (PMMA, Tg = 105 °C) were successfully imprinted and the pattern was observed by SEM; although in the absence of the ultrasonic vibration it was not possible to mold. The heights of the imprinted pattern were measured to be 1 µm in PET, 750 nm in PMMA, and 370 nm in PC. The assisting effect of the ultrasonic vibration was found to be inversely proportional to Tg. Therefore, it is inferred that the thermoplastic was softened locally with the frictional heat generated by the ultrasonic vibration.