Papers by Author: Rodrigo Martins

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Authors: Pedro Barquinha, Elvira Fortunato, Alexandra Gonçalves, Ana Pimentel, António Marques, Luís Pereira, Rodrigo Martins
Abstract: The purpose of this work is to present in-depth electrical characterization on transparent TFTs, using zinc oxide produced at room temperature as the semiconductor material. Some of the studied aspects were the relation between the output conductance in the post-pinch-off regime and width-to-length ratios, the gate leakage current, the semiconductor/insulator interface traps density and its relation with threshold voltage. The main point of the analysis was focused on channel mobility. Values extracted using different methodologies, like effective, saturation and average mobility, are presented and discussed regarding their significance and validity. The evolution of the different types of mobility with the applied gate voltage was investigated and the obtained results are somehow in disagreement with the typical behavior found on classical silicon based MOSFETs, which is mainly attributed to the completely different structures of the semiconductor materials used in the two situations: while in MOSFETS we have monocrystalline silicon, our transparent TFTs use poly/nanocrystalline zinc oxide with grain sizes of about 10 nm.
Authors: Sen Mei, Juan Yang, José Maria F. Ferreira, Rodrigo Martins
Authors: Leandro Raniero, Hugo Águas, Luís Pereira, Elvira Fortunato, Isabel Ferreira, Rodrigo Martins
Authors: S. Zhang, Y. Xu, X. Liao, Rodrigo Martins, Elvira Fortunato, X. Zeng, Z. Hu, G. Kong
Authors: Rodrigo Martins, Hugo Águas, Isabel Ferreira, Elvira Fortunato, Leandro Raniero, Pere Roca i Cabarrocas
Authors: M. Fernandes, M. Vieira, Rodrigo Martins
Authors: Hugo Águas, Luís Pereira, Isabel Ferreira, A.R. Ramos, A.S. Viana, J. Andreu, Paula M. Vilarinho, Elvira Fortunato, Rodrigo Martins
Authors: Patrícia Nunes, Elvira Fortunato, Paula M. Vilarinho, Rodrigo Martins
Authors: Gonçalo Gonçalves, Elvira Fortunato, J.I. Martins, Rodrigo Martins
Abstract: In this work, the relation between oxidant/monomer ratio and the electrical conductivity of polypyrrole was studied using different ratios. We achieved a maximum value for electrical conductivity of 7.5 S/cm for a ratio of 2:1. We also developed a chemical dip-coating process to produce the cathode layer in tantalum capacitors. We obtained capacitances of about 80 µF after 8 cycles using the sequence Monomer/Oxidant.
Authors: Luís Pereira, Pedro Barquinha, Elvira Fortunato, Rodrigo Martins
Abstract: In this work, HfO2 was deposited by r.f. sputtering at room temperature and then annealed for different times at 200°C in a forming gas atmosphere. After annealing for 2 hours the HfO2 layers present a reduction on the flat band voltage of about 1 V, relatively to the as deposited film, decreasing from -2.23V down to -1.28 V. This means an improvement of the interface properties and a reduction on the oxide charge density from 1.33×1012 cm-2 to 7.62×1011 cm-2. The dielectric constant reaches a maximum of 18.3 after 5h annealing due to film’s densification. When annealing for longer times such as 10h a small degradation of the electrical properties is observed. After 10h annealing the dielectric constant, flat band voltage and fixed charge density are respectively, 14.9, -2.96 V and 1.64 ×1012 cm-2 and the leakage current also increases due to film’s crystallization.
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