Printed electronics

Printed electronics is the term for a relatively new technology that defines the printing of electronics on common media such as paper, plastic, and textile using standard printing processes. This printing preferably utilizes common press equipment in the graphics arts industry, such as screen printing, flexography, gravure, and offset lithography. Instead of printing graphic arts inks, families of electrically functional electronic inks are used to print active devices, such as thin film transistors. Printed electronics is expected to facilitate widespread and very low-cost electronics useful for applications not typically associated with conventional ("i"."e"., silicon-based) electronics, such as flexible displays, smart labels, animated posters, and active clothing.

The term "printed electronics" is often used in association with organic electronics or plastic electronics, where one or more functional inks are composed of carbon-based compounds. While these other terms refer to the material system, the process used to deposit them can be either solution-based, vacuum-based, or some other method. Printed electronics, in contrast, specifies the process, and can utilize any solution-based material, including organic semiconductors, inorganic semiconductors, metallic conductors, nanoparticles, nanotubes, etc.

Standards development and activities

Several printed electronics industry leaders have established standards and roadmapping initiatives, which are intended to facilitate value chain development (for sharing of product specifications, characterization standards, etc.) This strategy of standards development mirrors the historical development, market introduction, and wide spread acceptance of silicon-based electronics over the past 50 years. As an example of this development of standards for printed electronics, the Institute of Electrical and Electronics Engineers (IEEE) launched an initiative to develop standards to assist in the development of the technology. To date, the IEEE Standards Association has published IEEE 1620-2004 [http://grouper.ieee.org/groups/1620/] and IEEE 1620.1-2006 [http://grouper.ieee.org/groups/1620/1/] , which will enable the continued maturity of printed electronics. In addition, similar to the well-established International Technology Roadmap for Semiconductors (ITRS), the International Electronics Manufacturing Initiative (iNEMI) [http://www.inemi.org/] has published a roadmap for printed and organic electronics.

Technologies

The attraction of printing technology for the fabrication of electronics mainly results from the possibility to prepare stacks of micro-structured layers (and thereby thin-film devices) in a much more simple and cost-effective way compared to conventional electronics. J.R. Sheats, Journal of Materials Research 19 (2004) 1974.] Beside this, also the possibility to implement new or improved functionalities (e.g. mechanical flexibility) plays a role. The selection of used printing methods is determined by requirements concerning printed layers, by properties of printed materials as well as economic and technical considerations in terms of printed products. Among the traditional industrial printing methods mainly inkjet and screen printing as well as the so-called mass-printing methods gravure, offset and flexographic printing are used in printed electronics. A. Blayo and B. Pineaux, Joint sOC-EUSAI Conference, Grenoble, 2005.] While the mass-printing methods are commonly employed as roll-to-roll methods ("web-fed"), inkjet and screen printing are mostly used as sheet-fed methods. However, also the converse variations exist.

The mass-printing methods gravure, offset and flexographic printing are marked by a largely enhanced productivity in comparison with other printing methods, as expressed by a throughput of many 10.000 m²/h. They are therefore especially suitable for a dramatic reduction of fabrication costs when they are applied to printing of electronics. J.R. Sheats, Journal of Materials Research 19 (2004) 1974.] Due to their high level of development and the manyfold mathods and variations they allow at the same time for high resolutions down to 20 µm and below, for high layer qualities as well as for a broad range of achievable layer properties and processable materials. A. Blayo and B. Pineaux, Joint sOC-EUSAI Conference, Grenoble, 2005.] In the field of printed electronics, the methods are considerably developed further, which holds for the other applied printing methods as well. However, the application and adaptation of mass-printing methods for printed electronics requires not only considerable know-how, but also more effort compared to other printing methods, which nevertheless is considerably lower compared to conventional electronics. While offset and flexographic printing are mainly used for inorganic P.M. Harrey et al., Sensors and Actuators B 87 (2002) 226.] J. Siden et al., Polytronic Conference, Wroclaw, 2005.] and organic D. Zielke et al., Applied Physics Letters 87 (2005) 123580.] T. Mäkelä et al., Synthetic Metals 153 (2005) 285.] conductors (the latter also for dielectrics) A. Hübler et al., Organic Electronics 8 (2007) 480.] , gravure printing is, due to the achievable high layer quality, especially suitable for quality-sensitive layers like organic semiconductors and semiconductor/dielectric-interfaces in transistors, A. Hübler et al., Organic Electronics 8 (2007) 480.] but, in connection with the high resolution, also for inorganic S. Leppavuori et al., Sensors and Actuators 41-42 (1994) 593.] and organic T. Mäkelä et al., Synthetic Metals 135 (2003) 41.] conductors. It could be shown, that organic field-effect transistors and integrated circuits consisting thereof can be prepared completely by means of mass-printing methods. A. Hübler et al., Organic Electronics 8 (2007) 480.]

Inkjet printing is a flexible and versatile digital printing method, which can be set up with relatively low effort and also at laboratory scale. Therfore it is probably the most commonly used printing method for printed electronics. R. Parashkov et al., Proceedings IEEE 93 (2005) 1321.] However, it is inferior to mass-printing methods in terms of throughput (typically 100 m²/h) as well as in terms of resolution (ca. 50 µm). A. Blayo and B. Pineaux, Joint sOC-EUSAI Conference, Grenoble, 2005.] It is well suited for low-viscosity, soluble materials like organic semiconductors. With high-viscosity materials, like organic dielectrics, and dispersed particles, like inorganic metal inks, repetedly difficulties due to clogging of the nozzles occur. Due to the drop-wise deposition of layers their homogeneity is limited. These problems can be moderated by suited measures. By means of parallelization (i.e. simultaneous usage of many nozzles) and pre-structuring of the substrate improvements in terms of productivity and resolution, respectively, can be achieved. However, in the latter case non-printing methods must be employed for the actual patterning step. B.-J. de Gans et al., Advanced Materials 16 (2004) 203.] Inkjet printing is preferably used for organic semiconductors in organic field-effect transistors (OFETs) and organic light-emitting diodes (OLEDs), but also OFETs completely prepared by means of this method have been demonstrated. V. Subramanian et al., Proceedings IEEE 93 (2005) 1330.] Furthermore, frontplanes S. Holdcroft, Advanced Materials 13 (2001) 1753.] and backplanes A.C. Arias et al., Applied Physics Letters 85 (2004) 3304.] of OLED-displays, integrated circuits, H. Sirringhaus et al., Science 290 (2000) 2123.] organic photovoltaic cells (OPVCs) V.G. Shah and D.B. Wallace, IMAPS Conference, Long Beach, 2004.] and other devices can be prepared by means of inkjet printing.

Due to the possibility to prepare thick layers from paste-like materials, screen printing has been using since many years for the fabrication of electrics and electronics in industrial scale. Mainly conducting lines from inorganic materials (e.g. for circuit boards and antennas), but also insulating and passivating layers are prepared by means of this method, whereby a relatively high layer thickness, but not a high resolution is important. Throughput (ca. 50 m²/h) and resolution (ca. 100 µm) are limited, similar to inkjet printing. A. Blayo and B. Pineaux, Joint sOC-EUSAI Conference, Grenoble, 2005.] Also in printed electronics this versatile and comparatively simple method is used mainly for conductive and dielectric layers, K. Bock et al., Proceedings IEEE 93 (2005) 1400.] Z. Bao et al., Chemistry of Materials 9 (1997) 1299.] but also organic semiconductors, e.g. for OPVCs, S.E. Shaheen et al., Applied Physics Letters 79 (2001) 2996.] and even complete OFETs S. Holdcroft, Advanced Materials 13 (2001) 1753.] can be printed.

Beside the conventional methods new methods with similarities to printing are employed, among them micro-contact printing and nano-imprint lithography. B.D. Gate et al., Chemical Reviews 105 (2005) 1171.] Here, µm- and nm-sized layers, respectively, are prepared by means of methods similar to stamping with soft and hard forms, respectively. Often the actual structures are prepared in a subtractive manner, e.g. by deposition of etch masks or by lift-off processes. Thereby for example electrodes for OFETs can be prepared D. Li and L.J. Guo, Applied Physics Letters 88 (2006) 063513.] G. Leising et al., Microelectronics Engineering 83 (2006) 831.] Sporadicly pad printing is used in a similar manner. A. Knobloch et al., Journal of Applied Physics 96 (2004) 2286.] Occasionally also the application of so-called transfer methods, where solid layers from a carrier are transferred to the substrate, are rated among printed electronics. D.R. Hines et al., Journal of Applied Physics 101 (2007) 024503.] Electrophotography is currently not used in printed electronics.

Printed photovoltaics

Gifu University (Prof. Tsukasa Yoshida) and National Chiao Tung University (Prof. Fang-Chung Chen) are working in printed photovoltaics.

See also

* Amorphous
* Anilox rollers
* Chip famines
* Chip tag
* Chipless tag
* Crystalline
* Dip pen nanolithography
* Disposable flexible circuits
* Electronic paper
* Electronic paper display
* Electrophoretic display
* Encapsulation
* Indium tin oxide
* Iontophoresis
* Laminar electronics
* Magnetic stripe cards
* Magneto-striction
* Marubeni
* Microbattery
* Microcontact printing.
* Nanotube
* Oligomer
* Organic semiconductor
* Organic electronics
* Pedestal antennas
* Roll up displays
* Transdermal
* Vacuum deposition

References

External links

* [http://www.funmat.fi Center for Functional Materials - Finnish Center of Excellence]
*For a history of the field, see "Printed Organic and Molecular Electronics", edited by D. Gamota, P. Brazis, K. Kalyanasundaram, and J. Zhang (Kluwer Academic Publishers: New York, 2004). ISBN 1-4020-7707-6
* [http://www.printedelectronicsworld.com Printed Electronics World]
* [http://www.oe-a.org Organic Electronics Association]
* [http://www.flextech.org The US Alliance for Flexible, Printed Electronics and Displays] - home page
* [http://www.dea.brunel.ac.uk/cleaner/Electronics_Projects/Handbook_1.htm Cleaner Electronics Research Group - Brunel University]
* [http://www.kovio.com Kovio Inc.] , a nano silicon printed electronics company.
* [http://printedelectronics.idtechex.com/research/reports/encyclopedia_of_printed_electronics_000111.asp Encyclopedia of Printed Electronics] (IDTechEx)
* [http://printedelectronics.idtechex.com/printedelectronicsasia08/en/ Printed Electronics Asia]
* [http://printedelectronics.idtechex.com/printedelectronicsusa08/en/ Printed Electronics USA]