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Carbon-Yarn-Based Supercapacitors with In Situ Regenerated Cellulose Hydrogel for Sustainable Wearable Electronics
Publication . Carvalho, José Tiago; Cunha, Inês; Coelho, João; Fortunato, Elvira; Martins, Rodrigo; Pereira, Luís; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); DCM - Departamento de Ciência dos Materiais; UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; ACS - American Chemical Society
Developing sustainable options for energy storage in textiles is needed to power future wearable "Internet of Things" (IoT) electronics. This process must consider disruptive alternatives that address questions of sustainability, reuse, repair, or even a second life application. Herein, we pair stretch-broken carbon fiber yarns (SBCFYs), as current collectors, and an in situ regenerated cellulose-based ionic hydrogel (RCIH), as an electrolyte, to fabricate 1D fiber-shaped supercapacitors (FSCs). The areal specific capacitance reaches 433.02 μF·cm-2at 5 μA·cm-2, while the specific energy density is 1.73 × 10-2μWh·cm-2. The maximum achieved specific power density is 5.33 × 10-1mW·cm-2at 1 mA·cm-2. The 1D FSCs possess a long-life cycle and 92% capacitance retention after 10 »000 consecutive voltammetry cycles, higher than similar ones using the reference PVA/H3PO4gel electrolyte. Additionally, the feasibility and reproducibility of the produced devices were demonstrated by connecting three devices in series and parallel, showing a small variation of the current density in flat and bent positions. An environmentally responsible approach was implemented by recovering the active materials from the 1D FSCs and reusing or recycling them without compromising the electrochemical performance, thus ensuring a circular economy path.
Architecture engineering as a route to enhance performance, stability and reproducibility of oxide TFTs
Publication . Ferreira, Tomás Afonso Carmelo; Martins, Jorge; Barquinha, Pedro
InGaZnO (IGZO) thin-film transistors (TFTs) have gained significant traction in the dis-
play industry due to their excellent electrical performance and adaptability to flexible sub-
strates. This versatility has opened doors to innovative applications like smart surfaces for
health monitoring, wearables, and radiation security. However, since these substrates require
low thermal budgets (< 180 °C), these TFTs often encounter higher defect densities, necessitat-
ing enhancements in device performance and stability.
In this context, the objective of this work centers on dual-gate (DG) TFTs, aiming to
achieve superior mobility, precise threshold voltage control, and improved stability and uni-
formity. These goals are pursued through a concept called bulk accumulation (BA), which can
occur in DG TFTs when the semiconductor layer is sufficiently thin. While the devices could
not be fabricated due to unforeseen circumstances with lab equipment, the research was pro-
pelled by technology computer-aided design (TCAD) simulation tools to gain insights into the
structural changes and material behaviors within the TFTs.
The results show that DG TFTs display increased drain currents and field-effect mobil-
ity, and lower threshold voltage and subthreshold swing. The devices also benefit from in-
creased resistance against semiconductor/dielectric interface defects, which are very promi-
nent in TFTs and decisive in their electrical performance. This is because of the occurrence of
BA, in which carrier accumulation occurs not only at semiconductor/dielectric interfaces but
also in the bulk of the active layer. The results also suggest that this effect is more noticeable
at higher interface defect densities, since the TFT is more reliant on the bulk contributions for
its electric performance. These structures could be used as a way to impose an electrical per-
formance boost on TFTs with high interface defects, using BA to avoid these imperfections.
Screen-printed, flexible, and eco-friendly thermoelectric touch sensors based on ethyl cellulose and graphite flakes inks
Publication . Figueira, J.; Bonito, R. M.; Carvalho, J. T.; Vieira, E. M. F.; Gaspar, C.; Loureiro, Joana; Correia, J. H.; Fortunato, E.; Martins, R.; Pereira, L.; DCM - Departamento de Ciência dos Materiais; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; IOP Publishing
Despite the undoubtable interest in energy conversion, thermoelectric (TE) materials can be approached from a temperature-sensitive perspective, as they can detect small thermal stimuli, such as a human touch or contact with cold/hot objects. This feature offers possibilities for different applications one of them being the integration with scalable and cost-effective, biocompatible, flexible, and lightweight thermal sensing solutions, exploring the combination of sustainable Seebeck coefficient-holding materials with printing techniques and flexible substrates. In this work, ethyl cellulose and graphite flakes inks were optimized to be used as functional material for flexible thermal touch sensors produced by screen-printing. Graphite concentrations of 10, 20 and 30 wt% were tested, with 1, 2 and 3 printed layers on four different substrates—office paper, sticker label paper, standard cotton, and organic cotton. The conjugation of these variables was assessed in terms of printability, sheet resistance and TE response. The best electrical-TE output combination is achieved by printing two layers of the ink with 20 wt% of graphite on an office paper substrate. Subsequently, thermal touch sensors with up to 48 TE elements were produced to increase the output voltage response (>4.5 mV) promoted by a gloved finger touch. Fast and repeatable touch recognition were obtained in optimized devices with a signal-to-noise ratio up to 340 and rise times bellow 0.5 s. The results evidence that the screen-printed graphite-based inks are highly suitable for flexible TE sensing applications.
MoS2 decorated carbon fiber yarn hybrids for the development of freestanding flexible supercapacitors
Publication . Carvalho, José Tiago; Correia, Afonso; Cordeiro, Neusmar J. A.; Coelho, João; Lourenço, Sidney A.; Fortunato, Elvira; Martins, Rodrigo; Pereira, Luís; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); DCM - Departamento de Ciência dos Materiais; UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; Nature Publishing Group
Academic and industrial efforts have focused on developing energy storage devices for wearable and portable electronics using low-cost, scalable, and sustainable materials and approaches. In this work, commercially available stretch-broken carbon fiber yarns (SBCFYs) were hybridized with mixed phases of 1 T and 2H MoS2 nanosheets via conventional and microwave-assisted heating (CAH, MAH) without the use of binders to fabricate symmetric freestanding 1D fiber-shaped supercapacitors (FSCs). Electrochemical characterization performed in a three-electrode configuration showed promising results with specific capacitance values of 184.41 and 180.02 F·g−1, at 1 mV·s−1 for CAH and MAH, respectively. Furthermore, after performing 3000 CV cycles at 100 mV·s−1, the capacitance retention was 79.5% and 95.7%, respectively. Using these results as a reference, symmetric 1D FSCs were fabricated by pairing hybridized SBCFYs with MoS2 by MAH. The devices exhibited specific capacitances of approximately 58.60 ± 3.06 F·g−1 at 1 mV·s−1 and 54.81 ± 7.34 F·g−1 at 0.2 A·g−1 with the highest power density achieved being 15.17 W·g−1 and energy density of 5.06×10–4Wh·g−1. In addition, five 1D FSCs were hand-stitched and connected in series onto a cotton fabric. These supercapacitors could power a temperature and humidity sensor for up to six minutes, demonstrating the practicality and versatility of the prepared 1D FSCs for powering future electronic systems.
A Paradigm Shift in the Design of Analog Circuits Targeting Nanoscale CMOS and Large-scale TFT Technologies
Publication . Correia, Ana Paula Pinto; Goes, João; Barquinha, Pedro
Despite the strong developments in complementary metal-oxide-semiconductor (CMOS) or non-CMOS technologies such as, in oxide thin-film transistors (TFTs), their nonidealities and constraints impact on the circuits performance. This aspect is even more relevant in complex circuits, such as in analog-to-digital converters (ADCs), where the design is thorough. Then, using techniques capable to attenuate the impact of these limitations such as, negative feedback, or recurring to almost passive or digital (synthesizable and scalable) circuitry, it is possible to design outstanding ADCs in different technologies. Therefore, two ADCs were designed in this work, using two distinct technologies.
A Digital-delta-modulator (DM) with noise-shaping (NS) was designed using a deep-nanoscale CMOS technology. Employing almost passive and digital-circuitry, this topology comprises a split-capacitor 10-bit digital-to-analog converter (DAC) with embedded sample-and-hold (S/H), a pseudo-differential inverter-based switched-capacitor (SC) integrator with a fully-passive SC common mode feedback (CMFB) circuit, a single-bit comparator, an accumulator and a clock and phase generators. Simulations revealed a signal-to-noise-and-distortion ratio (SNDR) close to 74 dB, a 12-bit effective number of bits (ENOB), with a Walden figure-of-merit (FoM), FoMWalden, of 12.5 fJ/conv.-step.
Using oxide TFTs, a 2nd-order delta-sigma modulator (DSM) was designed. Given the technology limitations, an almost passive structure was considered, with a design that relied essentially on the comparator project. During schematic simulations, a SNDR close to 69 dB, corresponding to an ENOB of ≈ 11:3-bit, was achieved (FoMWalden of 40 nJ/conv.-step). After the fabrication, individual transistors were characterised but they provided completely different electrical properties from the devices used to create the simulation model. The circuits, where comparators are included, were also measured but fabrication problems were detected. Strategies to mitigate these effects are currently being implemented.
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Fundação para a Ciência e a Tecnologia
Programa de financiamento
3599-PPCDT
Número da atribuição
PTDC/CTM-PAM/4241/2020