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Projeto de investigação
Materials Synergy Integration for a Better Europe
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A Low-Power Rail-to-Rail Row/Column Selector Operating at 2V Using a-IGZO TFTs for Flexible Displays
Publication . Santos, Ângelo; Tiwari, Bhawna; Martins, Jorge; Santa, Ana; Chapagai, Kamal; Bahubalindruni, Pydi; Barquinha, Pedro; UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); DCM - Departamento de Ciência dos Materiais
This paper presents design and implementation of 8-bit shift register with low-voltage amorphous Indium Gallium Zinc Oxide (a-IGZO) thin-film transistors (TFTs) for row/column selection of pixel matrix in flexible displays. This circuit is capable of ensuring complete rail-to-rail operation by employing novel NAND gates that were developed based on capacitive bootstrapping load. As a first step, a positive edge triggered D-flip flop (D-FF) is designed using these logic gates, then a complete 8-bit shift register is designed and simulated using in-house low-voltage IGZO TFT models in Cadence Virtuoso. During these circuit simulations a power supply voltage of 2V and a channel length of 2 μm were used. Simulation outcome of 8-bit shift register has shown a power consumption of 72.15 μW with output voltage swing of 95% of V dd at 20 kHz operating frequency, going well beyond the state of the art for oxide TFT technology at very low supply voltage. The proposed circuit can be used as a row/column selector in flexible displays that can operate at low supply voltage and allows small active-area.
Metal oxide nanostructures for sensor applications
Publication . Nunes, D.; Pimentel, A.; Gonçalves, A.; Pereira, S.; Branquinho, R.; Barquinha, P.; Fortunato, E.; Martins, R.; DCM - Departamento de Ciência dos Materiais; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; Institute of Physics Publishing
Electrorheological fluids have been paying a lot of attention due to their potential use in active control of various devices in mechanics, biomedicine or robotics. An electrorheological fluid consisting of polarizable particles dispersed in a non-conducting liquid is considered to be one of the most interesting and important smart fluids. This work presents the effect of the dopant, camphorsulphonic acid or citric acid, on the electrorheological behaviour of suspensions of doped polyaniline nanostructures dispersed in silicone oil, revealing its key role. The influence of carbon nanoparticle concentration has also been studied for these dispersions. All the samples showed an electrorheological effect, which increased with electric field and nanostructure concentration and decreased with silicone oil viscosity. However, the magnitude of this effect was strongly influenced not only by carbon nanoparticle concentration but also by the dopant material. The electrorheological effect was much lower with a higher carbon nanoparticle concentration and doped with citric acid. The latter is probably due to the different acidities of the dopants that lead to a different conductivity of polyaniline nanostructures. Furthermore, the effect of the carbon nanoparticles could be related to its charge trapping mechanism, while the charge transfer through the polymeric backbone occurs by hopping. Polyaniline/camphorsulphonic acid composite nanostructures dispersed in silicone oil exhibited the highest electrorheological activity, higher than three decades increase in apparent viscosity for low shear rates and high electric fields, showing their potential application as electrorheological smart materials.
A High Speed Programmable Ring Oscillator Using InGaZnO Thin-Film Transistors
Publication . Tiwari, Bhawna; Martins, Jorge; Kalla, Shivam; Kaushik, Shashwat; Santa, Ana; Bahubalindruni, Pydi Ganga; Tavares, Vitor Grade; Barquinha, Pedro; UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); DCM - Departamento de Ciência dos Materiais
This paper presents a high speed digitally programmable Ring Oscillator (RO) using Indium-gallium-zinc oxide thin-film transistors (IGZO TFTs). Proposed circuit ensures high speed compared to the conventional ROs using negative skewed scheme, in which each inverter delay is reduced by pre-maturely switching on/off the transistors. In addition, by controlling the load capacitance of each inverter through digital control bits, a programmable frequency of oscillation was attained. Proposed RO performance is compared with two conventional designs under same conditions. From simulation, it has been observed that the proposed circuit has shown a higher frequency of oscillations (283 KHz) compared to the conventional designs (76.52 KHz and 144.9 KHz) under same conditions. Due to the programmable feature, the circuit is able to generate 8 different linearly spaced frequencies ranging from 241.2 KHz to 283 KHz depending upon three digital control bits with almost rail-to-rail voltage swing. The circuit is a potential on-chip clock generator in many real-world flexible systems, such as, smart packaging, wearable devices, RFIDs and displays that need multi frequencies.
Paper-based nanoplatforms for multifunctional applications
Publication . Matias, M. L.; Nunes, D.; Pimentel, A.; Ferreira, S. H.; Borda D’Agua, R.; Duarte, M. P.; Fortunato, E.; Martins, R.; DCM - Departamento de Ciência dos Materiais; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); MEtRICS - Centro de Engenharia Mecânica e Sustentabilidade de Recursos; DCTB - Departamento de Ciências e Tecnologia da Biomassa (ex-GDEH); John Wiley and Sons Ltd
In this work, zinc oxide (ZnO) and titanium dioxide (TiO2) nanostructures were grown on different cellulose paper substrates, namely, Whatman, office, and commercial hospital papers, using a hydrothermal method assisted by microwave irradiation. Pure ZnO and TiO2 nanostructures were synthesized; however, the growth of TiO2 above ZnO was also investigated to produce a uniform heterostructure. Continuous ZnO nanorod arrays were grown on Whatman and hospital papers; however, on office paper, the formation of nanoplates originating nanoflower structures could be observed. TiO2 nanoparticles homogeneously covered all the substrates, in some conditions forming uniform TiO2 films. Structural characterization was carried out by scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and Raman spectroscopy. The optical characterization of all the materials was carried out. The produced materials were investigated for multifunctional applications, like photocatalyst agents, bacterial inactivators, and ultraviolet (UV) sensors. To evaluate the photocatalytic activity under UV and solar radiations, rhodamine B was the model-test contaminant indicator and the best photocatalytic activity was achieved with Whatman paper. Hospital paper with TiO2 nanoparticles showed significant antibacterial properties against Staphylococcus aureus. ZnO-based UV sensors demonstrated a responsivity of 0.61 μA W-1.
TiO2 nanostructured films for electrochromic paper based-devices
Publication . Nunes, Daniela; Freire, Tomas; Barranger, Andrea; Vieira, João; Matias, Mariana; Pereira, Sónia; Pimentel, Ana; Cordeiro, Neusmar J. A.; Fortunato, Elvira; Martins, Rodrigo; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); DCM - Departamento de Ciência dos Materiais; MDPI - Multidisciplinary Digital Publishing Institute
Electrochromic titanium dioxide (TiO2) nanostructured films were grown on gold coated papers using a microwave-assisted hydrothermal method at low temperature (80 °C). Uniform nanostructured films fully covered the paper substrate, while maintaining its flexibility. Three acids, i.e., acetic, hydrochloric and nitric acids, were tested during syntheses, which determined the final structure of the produced films, and consequently their electrochromic behavior. The structural characteristics of nanostructured films were correlated with electrochemical response and reflectance modulation when immersed in 1 M LiClO4-PC (lithium perchlorate with propylene carbonate) electrolyte, nevertheless the material synthesized with nitric acid resulted in highly porous anatase films with enhanced electrochromic performance. The TiO2 films revealed a notable contrast behavior, reaching for the nitric-based film optical modulations of 57%, 9% and 22% between colored and bleached states, at 250, 550 and 850 nm, respectively in reflectance mode. High cycling stability was also obtained performing up to 1500 cycles without significant loss of the electrochromic behavior for the nitric acid material. The approach developed in this work proves the high stability and durability of such devices, together with the use of paper as substrate that aggregates the environmentally friendly, lightweight, flexibility and recyclability characters of the substrate to the microwave synthesis features, i.e., simplicity, celerity and enhanced efficiency/cost balance.
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Entidade financiadora
European Commission
Programa de financiamento
H2020
Número da atribuição
692373