Ultrasonic nanoimprint lithography: a new approach to nanopatterning

We report an ultrasonic nanoimprint lithography (U-NIL) method that can overcome the drawbacks of energy consumption and long process times that occur in conventional nanoimprint lithography (NIL) methods. Instead of using heaters in conventional NIL, the proposed U-NIL employs an ultrasonic source located on the top of the mold to generate high-frequency vibrations, causing the increase of temperature to soften and melt the thermoplastic polymer. The ultrasonic source is induced by the transducer, consisting of a number of piezoelectric ceramic disks sandwiched between two aluminum metal blocks. Since the ultrasonic source provides a vibration with tens of kilohertz frequencies, the temperature of the polymer can increase rapidly. Consequently, the process time is significantly reduced. The experimental results demonstrate that vibratory energy could be concentrated in transferring the topography of a mold's surface into the polymer. In addition, we found that under appropriate conditions, such as ultrasonic time, imprinted pressure/force, frequency, and amplitude of vibration, the feature on the mold can replicate into the polymer film in a few seconds. We conclude that the proposed U-NIL process has the potential to become a novel nanoimprinting method with high productivity, energy efficiency, and low cost.