Lina Rambausek

Synthesis and characterization of copper, polyimide and TIPS-pentacene layers for the development of a solution processed fibrous transistor

A study was performed for the development of a flexible organic field effect transistor starting from a polyester fibre as substrate material. Focus of subsequent layer deposition was on low temperature soluble processes to allow upscaling. Gate layer consists out of a pyrrole polymerization and copper coating step. Polyimide dielectric layer was deposited using dipcoating. Gold electrodes were vacuum evaporated and patterned via mask fibre shadowing. The active layer consisted of a soluble p-type TIPS-pentacene organic semiconductor. Different deposition techniques have been examined. Considerable progress in development of a transistor has been made.

Piezoelectric textiles: state of the art

Abstract The textile industry has made significant advances in the fields of intelligent and multifunctional textiles, mainly in the sector of high performance products. Electrotextiles and intelligent textiles present enormous potential in creating a new generation of flexible, comfortable and multifunctional structures for many applications. Therefore, the textile sector is greatly interested in the development of new fibrous forms of sensors, exploring the potential resulting from materials science. Piezoelectric polymer films, monofilaments, multifilaments and fibres are highly suitable and attractive for the development of a new generation of intelligent textiles. The main objective of this paper is to give a comprehensive overview of piezoelectric textiles.

Essential Building Blocks of Fibrous Transistors, Part I: Gate Layer

Abstract. During the last decade, research on intelligent textile systems progressed steadily. Today, science is focusing on full integration of electronics into textiles. E-textiles function like their rigid electronic companions but keep their textile properties. To interconnect components within the system, textile structures need to be equipped with electro-conductive properties. For flexible solar cells or fibrous transistors, electro-conductive coatings are applied. Transistors, acting as electrical switches, are essential for realizing fully integrated intelligent textile systems. By electroless deposition of pyrrole and copper on polyester fibres, conductivity is achieved. A DC conductive gate electrode is designed. In this paper, the development of the gate layer within the fibrous transistor is described. Ideal pH and optimal reaction time are determined as well as the effect of variation in fibre diameter is investigated. A reproducible polypyrrole layer has been obtained. Ideal reaction time was 180 minutes at a temperature of 278K. The electroless copper coating process on the polypyrrole layer showed optimal results when the substrate was immersed into the plating bath coated for 6 minutes at a pH of 13. Analysis through resistance measurements has been completed.

SURFACE MORPHOLOGY OF POLYIMIDE THIN FILM DIP-COATED ON POLYESTER FILAMENT FOR DIELECTRIC LAYER IN FIBROUS ORGANIC FIELD EFFECT TRANSISTOR

Abstract The idea of wearable electronics automatically leads to the concept of integrating electronic functions on textile substrates. Since this substrate type implies certain challenges in comparison with their rigid electronic companions, it is of utmost importance to investigate the application of materials for generating the electronic functions on the textile substrate. Only when interaction of materials and textile substrate is fully understood, the electronic function can be generated on the textile without changing the textile’s properties, being flexible or stretchable. This research deals with the optimization of the dielectric layer in a fibrous organic field effect transistor (OFET). A transistor can act as an electrical switch in a circuit. In this work, the polyimide layer was dip-coated on a copper-coated polyester filament. After thoroughly investigating the process conditions, best results with minimal thickness and roughness at full insulation could be achieved at a dip-coating speed of 50 mm/min. The polyimide solution was optimal at 15w% and the choice for the solvent NMP was made. In this paper, details on the pre-treatment methods, choice of solvent and dip-coating speed and their effect on layer morphology and thickness, electrical properties and roughness are reported. Results show that the use of polyimide as a dielectric layer in the architecture of a fibrous OFET is promising. Further research deals with the application of the semiconductor layer within the mentioned architecture, to finally build an OFET on a filament for application in smart textiles.

Polyimide Dielectric Layer on Filaments for Organic Field Effect Transistors: Choice of Solvent, Solution Composition and Dip-Coating Speed

Abstract In today’s research, smart textiles is an established topic in both electronics and the textile fields. The concept of producing microelectronics directly on a textile substrate is not a mere idea anymore and several research institutes are working on its realisation. Microelectronics like organic field effect transistor (OFET) can be manufactured with a layered architecture. The production techniques used for this purpose can also be applied on textile substrates. Besides gate, active and contact layers, the isolating or dielectric layer is of high importance in the OFET architecture. Therefore, generating a high quality dielectric layer that is of low roughness and insulating at the same time is one of the fundamental requirements in building microelectronics on textile surfaces. To evaluate its potential, we have studied polyimide as a dielectric layer, dip-coated onto copper-coated polyester filaments. Accordingly, the copper-coated polyester filament was dip-coated from a polyimide solution with two different solvents, 1-methyl-2-pyrrolidone (NMP) and dimethylformaldehyde. A variety of dip-coating speeds, solution concentrations and solvent-solute combinations have been tested. Their effect on the quality of the layer was analysed through microscopy, leak current measurements and atomic force microscopy (AFM). Polyimide dip-coating with polyimide resin dissolved in NMP at a concentration of 15w% in combination with a dip-coating speed of 50 mm/min led to the best results in electrical insulation and roughness. By optimising the dielectric layer’s properties, the way is paved for applying the subsequent semi-conductive layer. In further research, we will be working with the organic semiconductor material TIPS-Pentacene