Patterned PEDOT:PSS-enabled organic planar microwave resonator sensors

Abstract

The demand for low-cost and environmentally friendly electronics has required novel materials that have high electrical performance while being mechanically stable and sustainable. Capitalizing on the water-dispersibility and high electrical conductivity of intrinsically conductive polymers, we first devise an all organic, environmentally friendly, and reformable microwave split-ring resonator (SRR) using poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), and second optimize its performance in solid and gas sensing applications. The conducting polymer layer is obtained by the solution-processing of PEDOT:PSS with dimethyl sulfoxide (DMSO) and is subsequently able to substitute metal traces used in conventional SRR structures. The performance of the fabricated organic microwave resonators (OMRs) in various sizes demonstrates the scalability of these resonators to be calibrated in a wide range of operational resonant frequencies, similar to their metal-based counterparts while being low-cost, environmentally friendly, and compatible with industrial-scale production. Moreover, by coupling two identical D-PEDOT:PSS resonators, an enhanced notch profile with an amplitude of −48.47 dB at the resonant frequency of 4.76 GHz is achieved, which is four times more sensitive than a single polymeric SRR at the same resonant frequency. The sensing capability of the polymeric microwave resonators is investigated by using solid standard materials, wherein the change in resonant frequency and resonant amplitude is observed in accordance with the permittivity of the test samples. Furthermore, the D-PEDOT:PSS OMRs developed in this study shows great potential when subjected to relative humidity sensing applications as a proof of concept. The performance of the OMRs is investigated for a wide relative humidity range of 3 % to 90 %, which demonstrates a sensitivity of 28 mdB and 300 kHz per unit relative humidity change on the resonant amplitude and the resonant frequency, respectively. The presented D-PEDOT:PSS split ring resonator paves the way for a novel generation of OMRs to be further developed in flexible and wearable microwave sensor applications in a wide variety of scenarios.