Dr Karlheinz Bock, Head of Dept, Polytronic Systems
Fraunhofer Inst - Reliability & Mikrointegration, Germany
Apr 20, 2005.
Fraunhofer Presentation (updated)*
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Polymers are already an important material in electronics since more than twenty years. Polymers in electronics are at present widely used as passive materials. There are photoresists for etching and soldering, dielectrics, boards, materials for encapsulating, under-filler and coating, electrically and thermally conductive adhesives for electronic interconnecting. Regarding conductive and semi-conductive polymer materials firstly conductors, than semiconductors, transistors and at present fully functional polymer ICs have been demonstrated. But the mobility of charge carriers in polymers is limited and incomparable to silicon.
During the last 10 years the material properties of conductive and semi-conductive polymers were improved significantly. Visible progress has been reached regarding higher mobility and limited progress with respect to stability against water and oxygen. Spin casting and printing technologies are the most favorable fabrication methods for low cost electronics, however their resolution and control of i.e. layer thickness needs further improvement. Most of these processing steps apply polymeric materials. In particular the application of printing technology, which is a high-volume mass-production technology, could lead to a tremendous benefit in the production of polymer electronics in future.
Reliability and stability of organic TFTs is the major problem at present, especially connected to the process technology integration for the fabrication of integrated organic circuits. In publications the issue of reliability and stability is very less pronounced but increased interest is visible and the stability of the organic TFT is recognized to be crucial. Typical problems which mostly are not yet completely understood are that the mobility is typically reduced, the threshold voltage and the sub threshold region of the TFT are sensitive to environmental conditions. The threshold swing of the TFT typically increases and the threshold voltages shift to more positive voltages and the transfer characteristic of the TFT changes under bias voltage stress. Fraunhofer IZM in Munich has established the Reel to Reel Application Center in order to focus on the cost-efficient aspect of the fabrication of polytronics.
Polytronics will provide a cheap method for the fabrication of simple low-cost electronic, but in most cases these circuits have to be integrated in a system, which may combine different technologies (e.g. a polymer display must be integrated with pixel drivers, processor, power supply, memory I/O-circuits etc.) or different functions (e.g. electronics, sensors and actuators, optics and fluidics are combined for an intelligent medical bandage). In order to make this vision a reality, combined research is necessary in order to overcome the actual problems. At present the development currently still concentrates very much on the optimization of the single elements and their reliable process integration in order to fabricate demonstrators. For the development of systems, a design environment including dedicated simulation possibilities is however urgently required. For production of possible efficient and marketable products, the integration of important elements like NMOS and bipolar transistors has not yet been carried out. The materials properties for the packaging of the polytronic elements are not yet satisfactorily.
For flexible electronics low-cost manufacturing processes with high throughput have to be used. The best seems to be in-line industrial processes, based on the reel-to-reel (R2R) flexible substrates technique, but also fast sheet processes are considered. Continous flow and fast sheet are not necessarily in contradiction since the major substrate materials like plastic foils and paper are on rolls. The 'connecting' question between reel-to-reel (or roll-to-roll) and the fast sheet processes is : At which point is the transition to sheet necessary. Some processes developments consider sheets as the solution and assume that the R2R process is not needed for large volume fabrication. Some process developments are performed with prospect of being applicable in R2R industrial production lines. The R2R process considers advantageously that the polymer electronics already starts during the fabrication process of the substrate material like the plastic foils and the paper or cardboard. In this sense it is needed to keep a roll fabrication and processing capability. At the same time R2R polytronic processes technologies can be transferred to a fast sheet process too.
The promising technology platform polymer + electronics = polytronics opens up the prospect of completely new applications that combine the features of transistor, LED, sensors, detectors, energy-cells, actuators, micro-mechanics, micro-fluidics and interconnect devices with the freedom of design, flexibility and low cost of plastics. In this scope it seems to be possible that polytronics may solve present and coming problems in economical and ecological measures adding functionality to microelectronic circuits and systems to be applied in information and communication but also in life science and medical systems. Polytronics creates a very promising technological area with new applications, products and markets, but it does not compete to existing mainstream electronic technologies like silicon CMOS at all.
The presentation will focus in particular on the following bullets
Dr. Karlheinz Bock studied electronics and communication engineering at the University of Saarbrücken, Germany. From October 1986 to September 1987 he has been a scientific assistant at the Institute for Material Science Saarbrücken, Germany where he was involved in Mössbauer spectroscopy on laser treated metal surfaces. From September 1987 to March 1989 he has been employed as a technical consultant. From September 1989 to March 1994 he has been employed at the University of Darmstadt, Germany as research assistant and doctoral student on the subject of high-frequency communication microelectronics technology and reliability. In 1994 he has been promoted the Dr.-Ing. Degree in RF microelectronics. From August 1994 to August 1995 he has been Japan Society for the Promotion of Science Award (JSPS) invited post-doctoral researcher at the Tohoku University, Japan working on the development of strained SiGe CVD layer growth and corresponding RT-diode devices technology and characterization. From September 1995 to March 1996 he again joined the University of Darmstadt, Germany, Institute of high-frequency communications working in RF HT mechatronics. From March 1996 July 1999 he has been employed at IMECvzw in Leuven, Belgium working on deep-submicron CMOS technology, ESD reliability. From 1999 - 2000 he joined the Fraunhofer Management Gesellschaft in Munich, Germany as business director, Information and Communication technologies. Since January 2001-present he is employed at the Institute for Reliability and Microintegration IZM in Munich, Germany as head of the Polytronic Systems Department working on the development of thin and flexible systems and technologies as well as chemical and biological sensors and bio-analytical systems. From Sept. 2003 he serves as deputy director of the Munich branch of the IZM.
With more than 350 employees at seven locations, the Fraunhofer Institute of Reliability and Microintegration, IZM, is one of the leading institutes for microelectronics and microsystem packaging worldwide.
Main competencies are material science and characterization, design and simulation, high density interconnect and wafer level packaging, chip and board interconnection technologies, 3D-packaging and vertical chip integra-tion, mechatronics, micromechanical systems, reliability and failure analysis, environmental engineering, polymer materials and composites, polytronic and flexible systems.
Emphasis is the transfer of research results into practical applications offering customized packaging solutions. In particular, Fraunhofer IZM know-how contributes to new developments in information and communication (e.g. mobile phones) and automotive technologies (e.g. airbag sensors).