There is excellent collaboration between the many institutions in Portugal that are researching printed and potentially printed transistors. Together, they are exploring inorganic, organic and composite thin film transistors and even their potential biological interfaces. CEMOP UNINOVA, the New University of Lisbon (CENIMAT Dept Materials Science), The Technology & Nuclear Institute, The University of Aveiro and The University of Algarve have collaborated for many years on this. Referring to the 80% or more optical transparency of inorganic transistors, which opens up many new applications, several of these organizations together, presented papers "Is the future of TFTs transparent" and "Next generation of thin film transistors based on zinc oxide" earlier this year. Other titles of presentations indicate the thrust of the work this year such as, "Oxide based TFTs produced at room temperature".
High performance ZnO thin film transistors have been fabricated by RF sputtering at room temperature with a bottom gate configuration. This ZnO-TFT operates in the enhancement mode with a threshold voltage of 19 V, a very high field effect mobility of 28 cm2/Vs, a gate voltage swing of 1.39 V/decade and an adequate on/off ratio of 3x105. Optical transmission (including the glass substrate) is 80 % average in the visible part of the spectrum. It is pointed out that "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."
Back in 2003, several of these organizations had already collaborated to produce transparent and conductive ZnO:Ga thin films by RF sputtering at room temperature. From 2000 to 2003 a "BioFET- Field effect transistor array for monitoring electrical activity from single cells in culture," was investigated by several of these institutions working with the University of Glasgow in the UK.
In 2007, the University of the Algarve has published results of collaboration with Italy and China on "Nanocomposite field effect transistors based on zinc oxide/polymer blends" and The University of Lisbon, another organization (there are three universities in Lisbon) has continued work on organic transistors, announcing, "In the near future we expect to do unimolecular electronic devices (one molecule = one transistor)," and giving the dream of:
"Organic Electronics - Plastic Electronics
Multidisciplinary science and technology related to a class of organic materials, both single molecules and polymers which are emerging as the basis for a new technological paradigm, which aims at ultra low-cost, lightweight and flexible electronic devices for displays, circuits and memories that can be printed on anything and placed anywhere.
OrganIC - Fully Patterned Organic Circuits
The target of this project is to demonstrate the possibility of fully patterning by the same photochemical process (spin-coating plus UV light patterning through mask or direct writing), both at the micro and at the sub-micron (c.a. 200 nm) scales, all components of all organic integrated circuits, namely the transistor's source, drain and gate, the dielectric, and the channel. At the end of the project, fully patterned simple circuits, such as inverters, ring oscillators, and the universal logic gates (NAND and NOR), will be delivered, as a proof of concept (demonstrator)."
The remarkable centre of excellence in Portugal for printed and potentially printed transistors deserves more notice.
For more information attend Printed Electronics USA.
