Organic electronics

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Organic electronics is a branch of electronics that uses electronic circuits made from electrically conductive polymers or smaller organic compounds. Based on the term " plastics electronics ", which is predominantly used in the English-speaking world , the synonym polymer electronics is also used (much less often also plastic electronics or plastic electronics ). The general feature of all concepts is usually the design of the circuits from macromolecules and, compared to conventional electronics, from multi-molecular structures of larger dimensions. Therefore, the new art term of polytronics is also used.

The characteristic of organic electronics is the use of microelectronic components on carrier materials made of organic foils as well as with conductor tracks and components made of conductive organic molecules ( organic semiconductors ). The molecules (in addition to monomers and oligomers , especially polymers ) are printed, glued or otherwise attached to the foils in the form of thin films or small volumes. All processes that are also used for electronics on ceramic or semiconducting carriers can be used for the production of the thin layers .

Flexible, bendable display made of organic electronics

Polymer electronics

Depending on their chemical structure, polymers can have electrically conductive, semiconducting or non-conductive properties. The insulating properties of “normal” polymers in everyday use have been used in electrical engineering since the beginning of the 20th century, for example as the insulating sheath of cables. In the early 1970s, electrically conductive and semiconducting polymers were produced and characterized for the first time. The 2000 Nobel Prize in Chemistry was awarded to Alan J. Heeger , Alan G. MacDiarmid, and Hideki Shirakawa for services in this field . The term “polymer electronics” was coined through the use of these novel materials for electronic applications.

Polymer electronics are still largely in the laboratory or pilot stage. In 2008, the PolyID, a market-ready, printed RFID chip was presented. The first microprocessor made from polymer films was presented by a research team in 2011.

The planned polytronic applications are intended to open up the market for extremely inexpensive ubiquitous electronics, which traditional silicon- based electronics cannot reach due to special requirements and the costs of assembly and connection technology. The manufacturing processes for polymer electronics are therefore being developed in the direction of high quantities, extremely low manufacturing costs and largely free of structural steps. Inexpensive printing processes, roll-to-roll coating and structuring methods form an important basis for future products in this area.

Structure of the polymers

The basic structure of electronic polymers are conjugated polymer main chains , which consist of a strictly alternating sequence of single and double bonds. As a result, these polymers have a delocalized electron system, which enables semiconductor properties and, after chemical doping, conductivity.

Advantages of polymer electronics

The main advantage of these circuits is the lower production costs, which makes them interesting for so-called “ disposable electronics ” (e.g. RFID tags on disposable packaging as electronic price tags). In addition, polymers have properties that are not possible with traditional semiconductors. For example, flexible films with integrated circuits can be produced in this way.

Disadvantages of polymer electronics

So far there is no reliable information on the service life of data stored in electronic polymer assemblies. Unless there is a clear indication of the expected lifespan, tests cannot be performed and polymer electronics therefore remains a largely academic topic. Solutions that can do without memory content are rather rare and consistently of low quality. When the question arises of what practically feasible results research has so far brought, one can feel as though back to the prehistoric times of electronics at the beginning of 1960. With hybrid structures (combination of organic electronics with classic silicon technology), a large part of the special features of polymer electronics is lost.

Small molecules

Small molecules (ger .: small molecules ) are currently used mainly for OLEDs ( SOLED or SMOLED ). In principle, electronic functions such as diodes on the molecule can be implemented with specially structured individual molecules . However, this technology is still at a very early stage of development and is classified as part of the field of nanotechnology .

Applications

In the established application areas of information processing, inorganic semiconductors have , compared to molecule-based technologies, among others. a. the advantages of a much higher charge carrier mobility and stability against environmental influences. The aim of the development of plastic electronics therefore does not (so far) include replacing the classic semiconductor technologies based on inorganic semiconductors. Rather, the focus is on developing electronic areas of application that require very light and / or mechanically flexible carrier materials.

Such applications include B.

or applications that require very inexpensive and simple manufacturing processes for economically viable mass production such. B.

Such areas of application are problematic for the classic manufacturing and structuring technologies of the semiconductor industry, since the necessary processes require extreme conditions of the ultra-high vacuum , great demands on the process control as well as high temperatures - conditions that are very costly and exclude sensitive, flexible substrates based on polymers.

Special applications

In addition to their purely conductive or semiconducting properties, the materials used in polymer electronics can also emit light under certain circumstances. This enables use in organic light-emitting diodes ( OLED ). The reverse effect of absorbing light and converting it into electrical energy enables it to be used in organic solar cells ( organic photovoltaics ). In addition, these polymers can be used as sensors or as organic storage media. Integrated circuits can be built with organic field effect transistors ( OFET ). Applications as electronic paper also appear feasible.

In principle, polymer electronics opens up the entire field of electronics, which until now has essentially been characterized by silicon-based components. Because the mobility of the charge carriers at approx. 0.2 cm² / Vs is three to four orders of magnitude lower than in silicon, extremely short switching times with OFETs cannot be achieved for the foreseeable future. Applications such as powerful microprocessors are therefore not to be expected, at least in the medium term.

In medical technology, thromboses, pulmonary embolisms and strokes can be detected early with a polytronically equipped analyzer. In practical terms, this can be implemented, for example, with a small blood laboratory for the jacket pocket, which quickly analyzes the risk of a blood clot in the legs before a long-haul flight, or in a sensor bracelet that can measure electrosmog and warns patients with pacemakers of life-threatening radiation.

production method

In contrast, organic molecules and polymers can be applied over a large area to a wide variety of substrates and structured in the micrometer range using comparatively simple processes at relatively low processing temperatures (<120 ° C) . Such procedures include

These processes require that the conductive organic molecules are present as a solution . However, only a few of these molecules have a relevant solubility , so that most substances have to be chemically modified to achieve solubility or soluble precursor molecules are used that are only chemically converted after landfilling ( precursor method ).

The physical vapor deposition (PVD) is another possible preparation, but these are for building advanced compared coating techniques, usually by thermal evaporation or modifications as the organic chemical vapor deposition ( OPVD ), and in connection with these proceedings as structuring method usually shadow masks are used.

Functional elements

The functional elements that could be implemented as an active unit for plastic electronics include:

  • Organic field effect transistor / thin film transistor (OFET / OTFT): In many development approaches, only the semiconductor layer is built up from organic compounds (using monomers, using oligomers or using polymers) and the electrodes are conventional or e.g. B. made of metallic substances by metal transfer stamp printing. However, approaches can also be implemented in which all components consist of polymers.
  • organic light-emitting diode (OLED), can be realized using monomers and polymers.
  • organic solar cell , realizable by means of monomers and by means of polymers.

Individual evidence

  1. ↑ PolyIC: PolyID product information ( memento from July 1, 2013 in the web archive archive.today ), accessed on July 22, 2011.
  2. ^ Complete plastic microprocessor Article in Elektor magazine from July 21, 2011
  3. ↑ Fraunhofer Institute for Reliability and Microintegration ( Memento from June 13, 2007 in the Internet Archive )
  4. ^ HE Katz, Z. Bao, S. Gilat: Synthetic chemistry for Ultrapure, Processable, and High-Mobility Organic Transistor Semiconductors . In: Accounts of Chemical Research . 34, 2001, pp. 359-369.
  5. ^ D. Filmore: Carbon electronics . In: Today's Chemist at Work . 11, 2002, pp. 25-27.
  6. ↑ a b H. Kobayashi et al .: A novel RGB multicolor light-emitting polymer display . In: Synthetic Metals . 111-112, 2000, pp. 125-128.
  7. ↑ a b J. A. Rogers et al .: Paper-like electronic displays: Large-area rubber-stamped plastic sheets of electronics and microencapsulated electrophoretic inks . In: PNAS . 98, 2001, pp. 4835-4840.
  8. ↑ HEA Huitema et al .: Active-Matrix Displays Driven by Solution Processed Polymeric Transistors . In: Advanced Materials . 14, 2002, pp. 1201-1204.
  9. ^ BK Crone et al .: Organic oscillator and adaptive amplifier circuits for chemical vapor sensing . In: Journal of Applied Physics . 9, 2002, pp. 10140-10146.
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  12. ↑ R. Enderlein: Microelectronics . Spectrum Academic Publishing House, Heidelberg / Berlin / Oxford 1993.
  13. ↑ PolyIC: polymer electronics ( Memento from 1 July 2013 Web archive archive.today ), accessed on May 21, 2013.
  14. ^ Z. Bao, JA Rogers HE Katz: Printable organic polymeric semiconducting materials and devices . In: Journal of Materials Chemistry . 9, 1999, pp. 1895-1904.
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  16. ↑ H.-J. Butt, K. Graf, M. Kappl: Physics and Chemistry of Interfaces . Wiley-VCH 2003, p. 138
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  23. ↑ CD Dimitrakopoulos, PRL Malenfant: Organic Thin Film Transistors for Large Area Electronics . In: Advanced Materials . 14, 2002, pp. 99-118.
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  31. ↑ J. Blochwitz et al .: Non-polymeric OLEDs with a doped amorphous hole transport layer and operating voltages down to 3.2 V to achieve 100 cd / m 2 . In: Synthetic Metals . 2002, pp. 1-5.
  32. ↑ JGC Veinot, et al .: Fabrication and Properties of Organic Light-Emitting “Nanodiode” Arrays . In: Nano Letters . 2, 2002, pp. 333-335.
  33. ^ RH Friend et al .: Electroluminescence in conjugated polymers . In: Nature . 397, 1999, pp. 121-128.
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