Investigations on terthiophene as an electrically conductive polymer for UV laser lithography

Abstract

Polymers hold great potential for the use in microsensors and organic electronics. They are highly adaptable, easy to process and can contribute new or improved capabilities compared to semiconductors. Direct UV laser lithography also gains increasing attention. Because it avoids expensive photomasks, it is especially attractive where small numbers of specialized microcomponents are needed, like in prototyping. Lithography necessitates materials, which can be shaped by UV radiation. For many microsensor applications, there is the additional requirement of electric conductivity, preferably in the same material. We approached this demand by combining a novolak and terthiophene doped with copper(II) perchlorate to form an interpenetrating polymer network, which possesses properties of both of its constituents. From this, we manufactured test structures with the UV laser of a micro pattern generator. In previous conference contributions, we showed a first proof of principle. In this publication, we present results of new experiments that demonstrate the characteristics in more detail. We improved our electrical setup to conduct four-terminal measuring. We used it to first verify previous results and investigated the material’s response to alternating currents up to 10 kHz. We then compared the electrical resistivity of differently sized structures for temperatures between 20 and 90 °C and examined long-term stability of their resistance by subjecting samples to temperatures of up to 60 °C for several hours. Additionally, we tested the influence of UV radiation on the resistance. Our samples exhibited good lithographic qualities. Resistivities were around 2 Ω mm and temperature sensitivity up to −407 Ω K−1. UV radiation induced a partially reversible increase of the electric resistance. The long-term stability of the material was temperature-dependent.