Low-Voltage High-Frequency Vertical Organic Transistors

• Applicants: Professor Dr. Johann-Wolfgang Bartha; Professor Dr.-Ing. Frank Ellinger; Professor Dr. Karl Leo
• Subject Area: Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering ; Experimental Condensed Matter Physics
• Term: from 2014 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 240553371

Organic field effect transistors (OFETs) hold the promise of enabling a low cost, flexible electronics. Driven by a fundamental understanding of the working principles, a significant improvement in performance has been reached. However, OFETs are still limited by the low charge carrier mobility of organic semiconductors, leading to low operational frequencies and driving currents, which render many applications out of reach. The performance of OFETs could be increased by scaling the channel length into the sub-micrometer region, which however involves costly structuring techniques and is inhibitive considering the strengths of organic electronics as a low cost technology.In this project we propose a novel technology to overcome these limits of conventional organic transistors. Instead of the horizontal structure of conventional OFETs, the transistors are structured vertically. This allows defining the channel length by the thickness of organic or metallic layers which can be controlled with nanometer precision. Thus, it is possible to aggressively scale the channel length down to the sub 100nm region without the need for costly structuring techniques.The project will cover all research aspects needed to enable such a vertical technology, ranging from materials science, device optimization, to circuit design. In particular, the project aims at a) improving the performance of vertical organic transistors already developed by IAPP by doping the source/drain contacts and advanced insulating layers developed by IHM (IAPP/Leo, IHM/Bartha), b) characterizing and improving the high-frequency performance of these transistors (IAPP/Lüssem, CCN/Ellinger), and c) realizing a fully organic amplifier operating at high frequencies (CCN/Ellinger, IAPP/Lüssem). The four partners have a unique combination of expertise needed to challenge this demanding project. The IAPP (Prof. Leo, Dr. Lüssem) developed several vertical transistor concepts and is well known for its doping technology, which is essential for the improvement of vertical OFETs. The IHM is an expert in atomic and molecular layer deposition (ALD and MLD), which will be used to develop novel ultrathin organic/inorganic nanohybride layers used as gate insulator to allow for low voltage operation. Finally the CCN is devoted to the design of integrated circuits using CMOS and BiCMOS technologies as well as advanced "Beyond and Beside Moore" technologies like carbon nano tubes, nanowires and organic & polymer devices. The expertise of the CCN is essential for the design of the organic amplifier and the high-frequency characterization of the transistors.The cooperation of these groups across the boundaries of applied physics, materials science, electrical engineering, and circuit design will lead to novel perspectives in research in organic transistors and to novel, unconventional solutions that enable a breakthrough in organic electronics.

• DFG Programme: Research Grants
• Participating Person: Professor Dr.-Ing. Björn Lüssem