Fully Flexible Polymer-Based Microwave Devices: Materials, Fabrication Technique, and Application to Transmission Lines

To achieve fully flexible microwave devices, we investigated flexible polymers in terms of chemical, mechanical, and electrical properties. Moreover, the fabrication techniques for polymer-based microwave devices have been developed to address chemical adhesion and demolding issues. Finally, based on formulated criteria, we have developed recipes for low-loss (0.001), low-Dk (1.73) flexible dielectric materials and have applied them to the microstrip and CPW transmission lines. The transmission losses of the microstrip and CPW lines are as low as 0.065 and 0.034 dB/cm at 2.5 GHz, respectively, which are comparable to those for rigid PCBs. The effects of various materials on microwave performance have been analyzed, from which we show that the acceptable frequency limits for using our fully flexible microwave devices are 7 GHz for microstrip lines and 10 GHz for CPW lines. The proposed molding process allows us to step out from 2-D PCB designs and build 3-D structures or hybrid PCB-3-D components with a certain freedom in material properties. The new material exhibits unique mechanical properties, which extend the material's application to other fields. In addition, it has been found that the polymer-based devices have significant performance improvements at elevated temperatures, which can be exploited in a high-temperature application. © 2021 IEEE.