http://hdl.handle.net/10362/2711 2013-05-21T12:18:27Z 2013-05-21T12:18:27Z Martins, Rodrigo Barquinha, Pedro Pereira, Luís Correia, Nuno Gonçalves, Gonçalo Ferreira, Isabel Fortunato, Elvira http://hdl.handle.net/10362/3962 2010-07-05T15:11:57Z 2008-10-01T00:00:00Z

Title: Write-erase and read paper memory transistor Authors: Martins, Rodrigo; Barquinha, Pedro; Pereira, Luís; Correia, Nuno; Gonçalves, Gonçalo; Ferreira, Isabel; Fortunato, Elvira Abstract: We report the architecture and the performances of a memory based on a single field-effect transistor built on paper able to write-erase and read. The device is composed of natural multilayer cellulose fibers that simultaneously act as structural support and gate dielectric; active and passive multicomponent amorphous oxides that work as the channel and gate electrode layers, respectively,complemented by the use of patterned metal layers as source/drain electrodes. The devices exhibit a large counterclockwise hysteresis associated with the memory effect, with a turn-on voltage shift between 1 and −14.5 V, on/off ratio and saturation mobilities of about 104 and 40 cm2 V−1 s−1, respectively, and estimated charge retention times above 14 000 h. Description: Applied Physics Letters, Vol.93, issue 20

2008-10-01T00:00:00Z Fortunato, Elvira Assunção, V. Marques, A. Águas, H. Martins, R. Costa, M. E. V. http://hdl.handle.net/10362/3263 2010-03-23T10:49:07Z 2003-01-01T00:00:00Z

Title: Influence of the deposition pressure on the properties of transparent and conductive ZnO: Ga thin-film produced by r.f. sputtering at room temperature Authors: Fortunato, Elvira; Assunção, V.; Marques, A.; Águas, H.; Martins, R.; Costa, M. E. V. Abstract: Highly conducting and transparent gallium doped zinc oxide thin films have been deposited at high growth rates by r.f. magnetron sputtering at room temperature on inexpensive soda lime glass substrates. The argon sputtering pressure was varied between 0.15 and 2.1 Pa. The lowest resistivity was 2.6=10y4 V cm (sheet resistance f6 Vysq. for a thickness f600 nm) and was obtained at an argon sputtering pressure of 0.15 Pa and a r.f. power of 175 W. The films present an overall transmittance in the visible spectra of approximately 90%. The increase on the resistivity for higher sputtering pressures is due to a decrease of both, mobility and carrier concentration, and is associated to a change on the surface morphology. The low resistivity, accomplished with a high growth rate (290 A˚ ymin) and with a room temperature deposition enables these films deposition onto polymeric substrates for flexible optoelectronic devices. Description: Thin Solid Films, vol. 427, nº 1-2

2003-01-01T00:00:00Z Fortunato, Elvira Nunes, P. Tonello, P. Fernandes, F. Braz Vilarinho, P. Martins, R. http://hdl.handle.net/10362/3255 2010-03-18T15:46:14Z 2002-01-01T00:00:00Z

Title: Effect of different dopant elements on the properties of ZnO thin films Authors: Fortunato, Elvira; Nunes, P.; Tonello, P.; Fernandes, F. Braz; Vilarinho, P.; Martins, R. Abstract: In this work we studied the influence of the dopant elements and concentration on the properties of ZnO thin film deposited by spray pyrolysis. The results show that the doping affects the thin films properties mainly the electrical ones, function of dopant concentration and nature. The most important changes were observed for films doped with 1 at% of indium which exhibit a resistivity of 1.9 10 1Ocm associated with a transmitance of 90%. After the annealing treatment, the resistivity of the film decreases to 5.9 10 3Ocm without significative changes in the optical properties. The films were also used to produce amorphous silicon solar cells where the best results were obtained for ZnO : In. Description: Vacuum, Vol. 64

2002-01-01T00:00:00Z Fortunato, Elvira Barquinha, P. M. C. Pimentel, A. C. M. B. G. Gonçalves, A. M. F. Marques, A. J. S. Pereira, L. M. N. Martins, R. F. P. http://hdl.handle.net/10362/3254 2010-03-18T15:47:37Z 2005-03-01T00:00:00Z

Title: Fully transparent ZnO thin-film transistor produced at room temperature Authors: Fortunato, Elvira; Barquinha, P. M. C.; Pimentel, A. C. M. B. G.; Gonçalves, A. M. F.; Marques, A. J. S.; Pereira, L. M. N.; Martins, R. F. P. Abstract: Fully transparent thin-film transistors (TFTs) are produced at room temperature by radiofrequency magnetron sputtering. Measuring the drain current (IDS) as a function of drain voltage (VDS) at different gate voltages (VGS) shows the TFTs possess hard saturation with on-currents of about 0.2 mA (see Figure) and saturation mobilities of 20 cm2 V-1 s-1. The optical and electrical properties and the compatibility of the fabrication process with low-cost plastic substrates show promise for invisible and flexible electronic circuits. Description: Advanced Materials, Vol. 17, nº 5

2005-03-01T00:00:00Z