Chien-Hung Lin

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 molds 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.

Effects of mold geometries and imprinted polymer resist thickness on ultrasonic nanoimprint lithography

This paper investigated the effects of imprinted resist thickness and mold geometries on the polymer flow and the temperature distribution of ultrasonic nanoimprint lithography (U-NIL) through numerical simulations and experiments. In simulations, the velocity fields in the imprinting stage and the temperature distributions in ultrasonic vibrations are performed under variations of convexity width, cavity width and thickness of the imprinted polymer resist. The study of the velocity field, including the lateral and vertical velocity, is significant because the velocity field can directly describe the mode of the polymer deformation, which is the key role to determine the mechanism of nanoimprint forming. Though the velocity field is crucial for the polymer deformation, it is often ignored and is rarely found in the literature. In ultrasonic vibrations, the temperature distribution of U-NIL is different from that of the thermal NIL and deserves to be investigated. Moreover, the combined effects of the imprinting stage and ultrasonic vibrations in the U-NIL process are discussed. Furthermore, experiments were conducted to verify the results performed by the numerical simulations. In this work, the simulations and experiments provide a deep understanding of polymer flow affected by the velocity field and temperature distribution during U-NIL, which should be well applied to a thermal NIL.

New approaches of mold fabrication for nanoimprint lithography

We present the new mold fabrications for nanoimprint lithography for the application of ordered array of rod or pore patterning. The concave and convex types of the mold are achieved. For this technology, the master is required preparation before the mold fabrication. The master is utilized by step and repeated to achieve the structures over a large area on the mold. The master, mold, and imprint results demonstrate that the new approaches of mold fabrication could be a feasible scheme with low cost and high throughput.

Investigation of Structures of Microwave Microelectromechanical-System Switches by Taguchi Method

The optimal design of microwave microelectromechanical-system (MEMS) switches by the Taguchi method is presented. The structures of the switches are analyzed and optimized in terms of the effective stiffness constant, the maximum von Mises stress, and the natural frequency in order to improve the reliability and the performance of the MEMS switches. There are four factors, each of which has three levels in the Taguchi method for the MEMS switches. An L9(34) orthogonal array is used for the matrix experiments. The characteristics of the experiments are studied by the finite-element method and the analytical method. The responses of the signal-to-noise (S/N) ratios of the characteristics of the switches are investigated. The statistical analysis of variance (ANOVA) is used to interpret the experimental results and decide the significant factors. The final optimum setting, A1B3C1D2, predicts that the effective stiffness constant is 1.06 N/m, the maximum von Mises stress is 76.9 MPa, and the natural frequency is 29.331 kHz. The corresponding switching time is 34 µs, and the pull-down voltage is 9.8 V.

Replication of polyethylene terephthalate (PET) nano/micro structures using ultrasonic nanoimprint

The ultrasonic nanoimprint lithography (U-NIL) were proposed to overcome the drawbacks of energy consumption and long process times comparing with conventional NIL methods. However, the relationship between process condition and imprinting quality has not been completely and systematically investigated. Therefore, it is necessary to study on the optimal process parameters to get good replicated structures in imprinting process. In this study, we have demonstrated the replication nano- and micro- structures on polyethylene terephthalate (PET) in heating-assisted ultrasonic nanoimprint. A highly effective tool of the Taguchi method has been utilized to acquire the optimal process parameters. Using the filling ratio as imprinting quality, the results of orthogonal array experimental layout could determine the optimal process parameters as the best setting. The confirmation test with these optimal parameters shows good filling ration of 96.40 % in replication structures from silicon mold to PET film with high formability and good imprinting quality. This would provide to advance U-NIL and to achieve nano- or micro- structures replication with high throughput and low cost.

Nanofabrication with Ultrasonic Nanoimprint Lithography

The ultrasonic nanoimprint lithography method provides high productivity, energy efficiency, and low cost. We propose a new nanoimprint lithography technique based on direct heating of the polymer resist by ultrasonic vibrations instead of using heaters in conventional nanoimprint lithography. In this paper we demonstrate that ultrasonic stack design is very important to ultrasonic nanoimprint lithography system. Since properties of ultrasonic vibrations obviously affect imprint results. If the diameter of the horn is greater than twice times of the size of the mold, the transferred patterns are completely replicated from the mold. To th best imprint results, the imprinted force, ultrasonic power, and ultrasonic time should be adjusted.

Capacitively catenary feedback control for open-type digital microfluidics

Abstract. With the rapid development and technical support by microelectromechanical systems, a lab-on-a-chip or micrototal analysis system has been widely developed for medical tests due to its low cost, simple, disposable, and less contamination. Comparing to the continuous microfluidics system, a digital microfluidics system has the advantages of being without micropump and easily driven using the alternative change of hydrophilic and hydrophobic properties. A feedback control system is proposed for driving digital microfluidics by using capacitive catenary as a sensor. In the proposed system, the moving droplet can be real-time positioned and controlled to overcome the imperfection of fabricated devices and the environmental disturbance. Furthermore, with the compensation of adjusting the amount of applied voltage online, the droplets can run smoothly toward the desired position in the chip through the feedback control. As a result, the proposed system is capable of moving droplets with higher speed, compared to most of the existing system, and improves the reliability of handling microfluidics. The chip for microfluidics operation has been successfully fabricated. With the self-designed circuit and LabVIEW interface, the experiments for operating microdroplets in an open channel are conducted to verify the performances of proposed devices.

Impact of mold geometries and imprinted resist thickness on velocity fields for nanoimprint lithography

The effects of mold geometries and imprinted resist thickness on the polymer flow using numerical simulations during nanoimprint lithography is investigated. The velocity fields, including the lateral and vertical velocity, is studied to describe the mode of the polymer deformation, which is the key role to determine the mechanism of nanoimprint forming.

Ultrasonics for nanoimprint lithography

In this paper we demonstrate that ultrasonic nanoimprint lithography (U-NIL) method can overcome the drawbacks of energy consumption and long process time occurred in conventional nanoimprint lithography (NIL) methods. Instead of using heaters in conventional NIL, the proposed U-NIL employs ultrasonic vibrations located on the top of mold to generate high frequency vibrations to soften and to melt the thermoplastic polymer. The temperature of polymer can rise rapidly for ultrasonic vibrations with frequency of 27 kHz. A simple but novel imprint apparatus has been designed for feasibility study of our U-NIL system. The experimental results showed that vibratory energy could increase temperature of the polymer in transferring the topography of molds surface into the polymer. We conclude that the proposed U-NIL process has the potential to become a novel nanoimprint method with high productivity, energy efficiency, and low cost.