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

Thorben Ziemer; Gerhard Ziegmann; Christian Rembe

doi:10.1515/teme-2023-0023

Article

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

Thorben Ziemer
Thorben Ziemer is a doctoral student at the Clausthal Centre of Material Technology (CZM) and the Institute for Electrical Information Technology (IEI), TU Clausthal. He studied mechanical engineering and mechatronics (M.Sc.) with an emphasis on metrology and automation control at Clausthal University of Technology. His research focusses on the fabrication of polymer micro sensors.
, Gerhard Ziegmann and Christian Rembe

Published/Copyright: August 7, 2023

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From the journal tm - Technisches Messen Volume 90 Issue 11

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.

Zusammenfassung

Polymere haben großes Potenzial für den Einsatz in Mikrosensoren und organischer Elektronik. Sie sind sehr anpassungsfähig, einfach zu verarbeiten und können neue oder verbesserte Fähigkeiten im Vergleich zu Halbleitern bieten. Auch die direkte UV-Laserlithografie gewinnt zunehmend an Bedeutung. Da sie ohne teure Fotomasken auskommt, ist sie besonders attraktiv, wenn nur kleine Stückzahlen spezialisierter Mikrokomponenten benötigt werden, wie beim Prototyping. Lithografie erfordert Materialien, die durch UV-Strahlung geformt werden können. Für viele Mikrosensorik-Anwendungen besteht außerdem Bedarf an elektrischer Leitfähigkeit, möglichst im selben Material. Um diese beide Anforderungen zu erfüllen, kombinierten wir einen Novolak und Terthiophen, das mit Kupfer(II)-perchlorat dotiert wurde, zu einem interpenetrierenden Polymernetzwerk, welches Eigenschaften beider Bestandteile besitzt. Daraus stellten wir mit dem UV-Laser eines Micro Pattern Generators Teststrukturen her. In früheren Konferenzbeiträgen zeigten wir einen ersten Nachweis des Prinzips. In dieser Veröffentlichung stellen wir die Ergebnisse neuer Experimente vor, welche die Eigenschaften detaillierter demonstrieren. Wir verbesserten unseren elektrischen Aufbau, um vierpolige Messungen durchzuführen. Damit prüften wir das Verhalten des Materials bei Wechselströmen bis zu 10 kHz, um bisherige Ergebnisse zu verifizieren. Darüber hinaus verglichen wir den spezifischen Widerstand unterschiedlich großer Strukturen für Temperaturen zwischen 20 und 90 °C und untersuchten die Langzeitstabilität des elektrischen Widerstands, indem wir Proben über mehrere Stunden Temperaturen bis zu 60 °C aussetzten. Zusätzlich testeten wir den Einfluss von UV-Strahlung auf den Widerstand. Unsere Proben zeigten gute lithografische Eigenschaften. Spezifische Widerstände lagen bei etwa 2 Ω mm und die Temperaturempfindlichkeit bei bis zu −407 Ω K⁻¹. UV-Strahlung führte zu einem teilweise reversiblen Anstieg des elektrischen Widerstands. Die Langzeitstabilität des Materials war temperaturabhängig.

Keywords: direct UV laser lithography; electrically conductive polymer; interpenetrating polymer network; polymer microsensor; temperature sensor; terthiophene

Schlagwörter: elektrisch leitfähiges Polymer; direkte UV-Laserlithografie; polymerer Mikrosensor; Temperatursensor; interpenetrierendes Polymernetzwerk; Terthiophen

Corresponding author: Thorben Ziemer, Clausthaler Zentrum für Materialtechnik, TU Clausthal, Leibnizstraße 9, 38678 Clausthal-Zellerfeld, Germany, E-mail: ziemer@iei.tu-clausthal.de

Funding source: European Regional Development Fund

Award Identifier / Grant number: ZW 3-85021239

About the author

Thorben Ziemer

Thorben Ziemer is a doctoral student at the Clausthal Centre of Material Technology (CZM) and the Institute for Electrical Information Technology (IEI), TU Clausthal. He studied mechanical engineering and mechatronics (M.Sc.) with an emphasis on metrology and automation control at Clausthal University of Technology. His research focusses on the fabrication of polymer micro sensors.

Acknowledgment

Experimental procedures were carried out at the Clausthal Centre of Material Technology (CZM) micro systems lab.

Author contributions: All the authors have accepted responsibility for the entire content of this submitted manuscript and approved submission.
Research funding: Research for this contribution was funded by the European Regional Development Fund (ERDF), in conjunction with NBank, Germany, as part of the project “Sensorentwicklung fur Produkte des baulichen Brandschutzes zur Sicherstellung deren Funktion, für Smart Maintenance und I 4.0” (ZW 3–85021239).
Conflict of interest statement: The authors declare no conflicts of interest regarding this article.

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Received: 2023-02-24

Accepted: 2023-07-03

Published Online: 2023-08-07

Published in Print: 2023-11-26

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https://doi.org/10.1515/teme-2023-0023

Keywords for this article

direct UV laser lithography; electrically conductive polymer; interpenetrating polymer network; polymer microsensor; temperature sensor; terthiophene