Selective etching of ITO–PET using a dry film photoresist for large area metamaterial fabrication

Abstract

The selective etching of indium tin oxide (ITO) from a polymer substrate to fabricate rapidly growing flexible electronic devices over a large area is extremely challenging. We have developed a wet etching technique for the removal of ITO films coated over polyethylene terephthalate (PET) substrates, by employing a uniformly coated dry film photoresist (DFPR) and optimized the photolithographic process that is easily scalable for industrial manufacturing units. The substrate was exposed to minimum heat during lamination of the DFPR and the chemical etchant, aqua regia with optimal dilution was used to selectively remove the ITO film without any degradation of the underlying PET. UV-Vis, SEM and 4-probe conductivity measurements have shown that the electrical conductivity and optical transparency of the samples were maintained after exposure to the optimized composition of chemicals during the etching, developing and stripping processes. The fabrication of an X-band FSS-based RADAR absorber composed of repetitive conductive patterns of ITO films over a PET substrate has been demonstrated for approximately unit square feet sample size. The simulated EM performance of the FSS, absorbing more than 90% of EM waves within the frequency range of 7.6–12.2 GHz, was validated by measurements conducted in an anechoic chamber.