Introduction

In the last 15 years much interest has been diverted to the semiconducting properties of lightly doped or undoped conjugated polymers. Schottky diodes, light-emitting diodes, photodiodes, chemical sensors and organic field-effect transistors (OFETs) have been constructed.

OFETs which are made of conjugated polymers present several potential advantages. First, the deposition techniques for semiconductor films allow large areas to be coated. Many conjugated polymers can be synthesized in a way that they are soluble in organic solvents, so that they can be processed by spin-coating, casting or by various printing methods. Second advantage is that polymers are mechanically tough and flexible, therefore compatible with plastic substrates. This offers the possibility to realise foldable, flexible products with extremely light-weight.

Research in the field of OFETs has been conducted in an interdisciplinary level on many different disciplines, which have to work parallel in good collaboration. Organic chemists work on the synthesis of high-mobility, high-purity, high-stability semiconductors. Electronic engineers are trying to improve circuitry that can be realized by OFETs. Physicist are working on the physical model of OFETs, whereas material scientists are looking for new materials and investigating the interface related issues in OFETs.

Goals

At the institute of OEM at TUHH the research conducted on OFETs can be classified in 4 sections:

1. Characterization of novel dielectric and semiconductor thin-films for OFETs

Various thermosetting and thermoplastic materials are used as dielectric. Compatibility of layers and the electronic properties of transistors are characterized. In cooperation with the company Elantas Beck new dielectric materials are being developed.

2. Influence of interfaces on OFET device properties and interface tuning

Dielectric/semiconductor interface plays a crucial role in OFET performance. Therefore a proper interface should be formed during the deposition of these layers. By means of experimental studies on interfaces, like usage of new solvents or surface modifications, it is tried to extract new information on physical properties of interfaces in OFETs. Charge carrier mobility and interface doping are the main investigated mechanisms.

3. OFET-sensors, for light and chemical sensing

Chemical volatile sensing properties of OFETs are demonstrated. Selective volatile sensing by using organic transistor-sensors is aimed.

4. Ferroelectric OFETs for memory applications

Well known superb ferroelectric and dielectric properties of PVDF/TrFE copolymers were modified by blending barium titanate nanopowder and preparing thin nanocomposite films. The films have up to 50 volume % BT powder and exhibit dielectric constant values of up to 51.5 at 1 kHz. These films are introduced as gate insulator in OFETs where ferroelectric memory and low-voltage operation are demonstrated.

Wissenschaftliche Kontakte und Kooperationen

• Prof.Dr.-Ing. Wolfgang Krautschneider, Arbeitsbereich Mikroelektronik, Elektrotechnik V, TUHH
• Prof.Dr.-Ing. Holger Göbel, Fachbereich Elektrotechnik, Universität der Bundeswehr, Hamburg
• Elantas Beck  http://www.elantas.com/de/