Printing of Patterned Copper on Pliable, Microtextured PDMS/Ceramic Composites
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Printing of Patterned Copper on Pliable, Microtextured PDMS/Ceramic Composites Elif Apaydin1, Yijun Zhou2, Derek Hansford1, Stavros Koulouridis2, and John Volakis2 1 Biomedical Engineering, The Ohio State University, Suite 100 Science Village, 1381 Kinnear Road, Columbus, OH, 43212 2 Electrical and Computer Engineering, The Ohio State University, ElectroScience Lab, 1320 Kinnear Road, Columbus, OH, 43212 ABSTRACT In this work, we present a novel printing technique that enables the usage of PDMS and ceramic powder mixed PDMS composites (we refer as “PDMS-ceramic composites” in this context), as a substrate for printing of copper conduction layers. This technique is based on microtransfer molding (μTM) and lift-off for pattern formation [4]. Another key feature is the usage of microtextured PDMS and PDMS-ceramic composites before any copper film deposition. Our microtextured surface is composed of pyramid shaped wells (100 μm depth and 150 μm sides on PDMS surface). The poor adhesion between PDMS and copper is overcome by oxygen plasma application and titanium deposition before copper layer. In order to demonstrate the convenience of this technique in RF applications, copper conduction lines (5 mm wide, different lengths) were printed on microtextured PDMS substrates. These transmission lines successfully maintained a low resistance during large strain. The printed lines have the DC resistance of 0.5 Ω and conductivity of 1.3e6 S/m, and the transmission analysis of these lines show good results especially in the MHz range when compared to copper tape measurements. Apart from the conduction lines, the substrates can have ranging dielectric constants from 3 (no powder) to 23 (50% D270 powder, provided by TransTech) by volume mixing rule of ceramic powder and PDMS. Dielectric constant is important for RF applications, especially for antenna designs. Therefore, provided with a range of dielectric constants, these composite substrates are a great promise in RF field for pliable antenna fabrication [5]. For experiment purposes, some of the transmission lines are printed on these composite substrates as well as on pure PDMS. In this study, apart from the fabrication of transmission lines, this technique will be applied in a GPS antenna design for demonstration purposes. The antenna design is a single-fed circularly-polarized stacked antenna for tri-band GPS (L1, L2 and L5) applications [6]. For the fabrication of the antenna, polymer-ceramic materials of ε1=16 and ε2=30 will be utilized as the substrates [6].
INTRODUCTION Pliable electronics has useful applications in various areas of research from biological sensors in close contact with tissues to complex RF circuits for conformable antennas [1, 2]. Polymers and their composites have been considered as good candidates in the category of pliable materials. Polydimethylsiloxane (PDMS) is one of the most widely used silicon-based organic polymers [3]. However, due to the poor adhesion between PDMS and metal layers, it has been considered as a challenging task t
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