Electrochemical transistors have been printed onto paper by ACREO in Sweden and others and paper electronics, including transistors, is being researched by Abo Akademi, The University of Helsinki and others.
Biopolymers such as paper offer the possibility of creating electronics at very low costs that may even be biodegradable. This work traditionally involves organic inks and, because of the challenging topology, the resulting transistors usually have limited performance. Indeed, some take several seconds to switch. Now attention is turning to Field Effect Transistors FETs because, as with traditional silicon chips, they are the favoured structure to give best performance for most of the potential marketplace.
In Portugal, an elegant new field effect transistor with paper as the dielectric layer has now been developed by Elvira Fortunato and her colleagues of the Centro de Ingestigacao de Materiais at Faculdade de Ciencias e Tecnologia, Universidade Nova de Lisboa, Portugal.
Unusually, the new devices have the paper doubling as both dielectric layer and substrate. Paper, being mostly cellulose, is electric insulating and a fairly good dielectric. The team from Cenimat/I3N, led by Elvira Fortunato and Rodrigo Martins, used a single sheet of common paper as dielectric layer on which semiconducting oxides were printing on both sides. IDTechEx wonder what voltage is needed because this is presumably rather thick as dielectric layer and it will not have a very fhigh permittivity. However, the idea is a good one and perhaps the next versions could use the high strength thin paper that we recently featured in an article "Nonopaper is stronger than cast iron" July 22.
"It is a two in one," says Elvira Fortunato regarding the fact that the paper sheet works as substrate and interstrate at the same time. Better still, she says that the electrical characteristics of the new transistor are closely similar to those of inorganic oxide thin film transistors and therefore much better amorphous silicon transistors. Disposable electronic circuits, paper displays, smart labels, smart packaging, biosensing systems, RFID tags and other devices may result. The results will be published in the IEEE Electron Device Letters in September.
Also read papers:
- Next generation of thin film transistors based on zinc oxide by E. Fortunato, P. Barquinha, A. Pimentel, A. Gonçalves, L. Pereira, A. Marques, R. Martins, Materials Science , FCT-UNL Portugal, reports "high performance ZnO thin film transistor (ZnO-TFT) fabricated by rf magnetron sputtering at room temperature with a bottom gate configuration. The ZnO-TFT operates in the enhancement mode with a threshold voltage of 19 V, a field effect mobility of 28 cm2/Vs, a gate voltage swing of 1.39 V/decade and an on/off ratio of 3x105. The ZnO-TFT present an average optical transmission (including the glass substrate) of 80 % in the visible part of the spectrum. The combination of transparency, high field-effect mobility and room temperature processing makes the ZnO-TFT a very promising low cost optoelectronic device for the next generation of invisible and flexible electronics."
- Characterization of transparent and conductive zno:ga thin films produced by rf sputtering at room temperature by E. Fortunato, V. Assunção, A. Marques, I. Ferreira, H. Águas, L. Pereira, and R. Martins.
- "Is the future of TFTs transparent?" by Elvira Fortunato, Pedro Barquinha, Luís Pereira, Gonçlalo Gonçalves and Rodrigo Martins at 2007 International Thin Film Transistors Conference, ITC'07, Session 7.
- High-k Dielectrics for Organic MISFETs," by David Martin Taylor, Janet Lancaster and Henrique Leonel Gomes, at MRS Meeting April 2007, 6.44.
Portugal has many institutions researching printed electronics but we suspect it may not get its fair share of European Community grants because most EC projects are directed at organic electronics to the detriment of inorganic electronics - a frequent focus in Portugal. Inorganic and composite electronics has over half of the potential for business in printed electronics markets.
Portuguese institutions doing excellent work include CEMOP UNINOVA, the University of Lisbon, the New University of Lisbon, the Technical University of Lisbon, the Technology and Nuclear Institute ITN, the University of Algarve and the University of Alveiro. To learn what they are doing and how this shapes up with the rest of Europe read Organic & Printed Electronics in Europe.