Faithful Replication of Large-Area
Nanostructures via Pulsed Direct Current
High-Voltage Electrohydrodynamic Phase
Instability
Hyunje Park, Jae Seok Hwang, and, Dae Joon Kang
Department of Physics2
Sungkyunkwan University2066, Seobu-ro, Jangan-gu, Suwon, Gyeonggi-do, 16419 Republic of Korea
E-mail: djkang@skku.edu

As the conventional lithography confronted the physical barrier in reducing the feature size,
intensive efforts for alternative lithographic methods have been dedicated to improving thefeasibility of the well-ordered nanostructure fabrication over a large area. Among varioustypes of nanopatterning techniques, electrohydrodynamic lithography (EHL) has been
considered a promising tool for replicating nano-sized features in a cost-effective manner[1-3]. However, EHL is still facing technical challenges to achieve highly faithful patternreplications over a large area. In addition, poor reproducibility, limited pattern height,
precise control of parameters, and limited available substrates are the outstanding issues tobe resolved. In this regard, we introduced a new lithographic approach based onelectrohydrodynamic instability induced by employing pulsed high-voltage (> 6.0 kV)
with micro-level air gap (> 1.0μm). Compared to the conventional EHL, the high-voltage
method (HV-EHL) using stronger electric field (> 108 𝑉/𝑚) enhances the overall fidelity
including the pattern height [4]. Nonetheless, HV-EHL offsets this influence due to thereduced characteristic time that determines the patterning time for fully-developed pattern(See Figure 1). Accordingly, under the non-constant air gap condition, the patterned area canbe extended over the entire surface of the resist. To support this, we confirmed that theparameter constraints for perfect replication is more relieved in HV-EHL, which implies themore facile replication process in our approach. Our pulsed high-voltage EHL is not only atechnical improvement but also an innovative lithographic approach to achieve bothlithographic requirements and industrial needs by the capability of fabricating a number offunctional nanoscale patterns on a large scale in a facile and cost-effective fashion.
References:[1] T. Ito T; Okazaki S.; “Pushing the limits of lithography,” Nature, 2000 (406), no. 6799,1027–1031, 2000.
[2] Lau C.Y.; Russel W.B.; “Fundamental Limitations on Ordered ElectrohydrodynamicPatterning,” Macromolecules, 2011 (44), no. 19, 7746–7751.
[3] J. J. S. Rickard J.J.S.; I. Farrer I.; Oppenheimer P.G.;“Tunable Nanopatterning ofConductive Polymers via Electrohydrodynamic Lithography,” ACS Nano, 2016 (10), no. 3,3865–3870.
[4] Wang G. et al.; “A Photocurable Leaky Dielectric for Highly Electrical Insulating
Electrohydrodynamic Micro-/Nanopatterns,” Soft Matter, 2016 (12), no. 43, 8819–8824,

2016.

Figure 1. Pattern growth velocity and patterned area as a function of voltage (a) The plots of thereciprocal time constant (1/𝜏) as a function of the wavenumber (𝑞). As seen, the maximum value
increases drastically with increasing voltage (150 V, 1.2, 1.8 and 2.1 kV, respectively). Notably, these1ℎ 3

𝜕𝑝0
plots are based on the dispersion relation given by 𝜏 = − 3𝜂(𝛾𝑞 4 + 𝜕𝑥𝑒𝑙 𝑞 2 ). The inset photographs

indicate that the patterned area is enlarged as the high-voltage increases. The corresponding opticalimages show the different stages of the time-dependent evolution. (b) Two schematics illustrate thatthe pattern replication with different growth velocity in the LV- and HV-EHL (top and bottom). (c)Photographs of diffraction patterns from the monochromatic illumination: the patterned areas tend tobe enlarged as the high-voltage increases.