Nickel stamp origination from generic SU-8 nanostructure arrays patterned with improved thermal development and reshaping

Abstract

In this study, we show that rapid, reliable, and scalable custom-input colour patterning and eye-readable data storage can be achieved through high-throughput nanoimprinting-exposure-thermal-treatment (NETT) and thermal development and reshaping (TDR) techniques. The main impediment for commercial realization of high-resolution metasurfaces using NETT and TDR is the cost and speed of stamp origination as well as the quality and durability of the fabricated stamp. In order to accelerate the patterning process, lower the fabrication costs, and obtain patterns with high-resolution, we introduce and optimize a new method for origination of durable Ni stamps by electroplating on an SU-8 master fabricated according to custom-input colour patterns via NETT and TDR. In these processes, laser exposure is used to locally activate the generic RGB pixels fabricated on SU-8 via thermal nanoimprint lithography (NIL), according to the custom design. Upon TDR treatment, the exposed regions crosslink while the unexposed areas flatten. TDR is optimized to find the fastest processing condition that results in minimum nanocone height reduction and maximum diffraction efficiency. AFM results show that the TDR-processed nanocones in all red, green, and blue subpixels witness minimal shrinkage in comparison with the corresponding as-imprinted RGB pixels. Among three different sets of direct baking and ramping temperature TDR experiments, direct 55 °C-10 min TDR is found to be the optimal recipe. As a proof-of-concept, the originated stamp was employed to replicate colour images on PET and glass substrates using UV-thermal NIL. The reproduced colour image, photographed at pre-defined lighting and viewing angles, bears vivid diffractive colours with different RGB ratios that are in good match with the custom-input image. Furthermore, the red, green, and blue diffraction peaks from the TDR-55 °C-baked sample exhibit either trivial or no distinguishable difference as compared to the corresponding peaks in the as-imprinted sample.

Fabrication of Planar Microelectrode Array Using Laser-Patterned ITO and SU-8

“…Although IrO X electrodes are verified only for 3 weeks, the degradation and stability issue will not be problematic because they are used only for detection of neural activity without any active charge transfer reaction for stimulation. SU-8 is an epoxy-based negative photoresist that is commonly used in microelectromechanical systems (MEMS) for soft lithography or imprinting techniques [40,41]. Since SU-8 is proven to be biocompatible and chemically stable, it is used as a material of microfluidics for life science applications.…”

Structural colour QR codes for multichannel information storage with enhanced optical security and life expectancy

“…Also, unlike the costly patterning techniques for manufacturing nanostructures in security devices such as electron beam lithography (EBL), NETT is quite cost-effective. Moreover, mass-production of the proposed structural colour QR code is feasible using the Ni stamp origination approach demonstrated previously by our group [52]. Additionally, in terms of life expectancy, in comparison with conventional colour pixels using ink or dyes, which fade away with time, these anticounterfeiting pixels are fabricated using laser-patterned structural colours imprinted on the long-lasting photocrosslinkable SU-8, which is resistant to extreme environmental conditions such as high temperature.…”

“…Due to their colour chromaticity [50], ultrahigh resolution [51], and durability [52,53], structural colours, which are generated from interaction of light waves with subwavelength structures, have become very appealing in nano-optics in recent years. Structural colouration can be obtained from diverse optical media, e.g.…”

“…Structural colouration can be obtained from diverse optical media, e.g. dielectric metasurfaces [54], photonic crystals (PC) [55], plasmonic nanostructures [56], and diffractive periodic nanostructures [52,53]. Structural colour-based anticounterfeiting codes have been generated in various studies.…”

“…In our previous works, new approaches for scalable fabrication of structural colours based on NETT [52,53], inkjet printing [64][65][66], and photolithography patterning [67] were demonstrated using single or multilayer RGB-pixelated nanostructures. In this paper, we introduce a new scheme for generating durable anticounterfeiting structural colour QR codes containing multiplexed RGB channels with high optical security based on the NETT technique.…”