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 . 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. Dielectric constant is important for RF applications, especially antenna designs. Therefore, provided with a range of dielectric constants, these composite substrates are a great promise in RF field for pliable antenna fabrication . For experiment purposes, some of the transmission lines are printed on these composite substrates as well as pure PDMS.
In this study, apart from the fabrication of transmission lines, this novel technique will be applied in a GPS antenna design for demonstration purposes. This antenna design is a single-fed circularly-polarized stacked antenna for tri-band GPS (L1, L2 and L5) applications . For the fabrication of the antenna, polymer-ceramic materials of ε1=16 and ε2=30 will be utilized as the substrates .