Fabrication of 3D Micro Structures on Nonplanar Substrates and Its Applications for Roll Micro contact Printing
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Fabrication of 3D Micro Structures on Nonplanar Substrates and Its Applications for Roll Micro contact Printing Jongho Park1, Hiroyuki Fujita1, and Beomjoon Kim1 1 Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo, 153-0041, JAPAN. ABSTRACT The purpose of this research is to develop a fabrication technique of microstructures on nonplanar substrates, investigating so called, optical softlithography. In addition, PDMS roller stamps were duplicated from these structures on curved substrates as the mold, roll micro contact printing was performed successfully. Micro structuring on nonplanar substrates has not been fully established yet, although several fabrication methods, such as laser direct writing and modified photolithography, were proposed. Moreover, those techniques require still expensive and complex processes. To overcome those drawbacks, optical softlithography using flexible photomasks was developed [1]. Firstly, SU-8 micro structures were fabricated on concave substrates by optical softlithography using PDMS flexible photomasks. As a result, SU-8 structures with 2.5 µm line width and high aspect ratio over 7.9 were fabricated on a concave substrate. Also, experimental parameters for optical softlithography were investigated and established for further fabrications and applications. In addition, the tilting structures were confirmed due to the vertical UV exposure method. Next, Based on these novel 3D patterning technologies, PDMS roller stamps were fabricated and roll micro contact printing was performed. The roll micro contact printing was investigated by using the customized roll micro contact printing apparatus and the flexible pressure sensor system. We expect this technique can provide various sized roller stamps with various micro patterns for µCP process as well as roll micro contact printing process. INTRODUCTION Micropatterning, the fabrication of micro structures or patterns on a substrate, has been one of important technologies for the development of micro devices. It has been performed usually by utilizing conventional optical photolithography. Optical photolithography has been developed along with the development of semiconductor fabrication technologies from early 20th century [2]. It is the well-established and essential patterning process, especially, for the fabrication of integrated circuits. However, conventional photolithography requires a flat substrate as its starting point, which means it has difficulty in micropatterning on nonplanar substrate. To overcome those difficulties, several techniques for micropatterning with nonplanar substrates have been developed, which include laser lithography [3], photolithography with customized exposure module [4], decal transfer lithography [5], and so on. Recently, the optical soft lithography technique was successfully introduced to fabricate micro patterns onto a curved substrate [1, 6]. Instead of a rigid glass photomask, a flexible PDMS photomask was used, which can be fit uniformly along a curved substrat
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