Oxide thin films for sustainable, multifunctional and flexible electronics

The growing range of applications of large-area electronics (LAE) in the last years is starting to require levels of performance, functionality and cost not compatible with the current thin-film technologies, such as a-Si or low-temperature polysilicon (LTPS) thin-film transistors (TFTs). This starts to be even more relevant when low-cost flexible substrates and processing technologies are considered. In this context, amorphous oxide semiconductors (AOS) are becoming essential materials in this field. AOS are recognized for their remarkable features such as good uniformity even when produced at room temperature, enabling applications in large area and flexible electronics; wide band gap (thus high transparency), making them suitable for transparent electronics; and good electrical performance despite their amorphous structure, enabling flexible circuitry operating at high-kHz to MHz range. Since the initial publication by Nomura et al. on indium-gallium-zinc oxide (IGZO) TFTs in 2004, these devices had a tremendous development and are now implemented in Gen10 display fabs for the production of low power consumption, high refresh rate and high resolution displays. But oxide electronics has a great potential for going well beyond display backplane applications: in fact, by combining new materials/structures, processing techniques and circuit design architectures having in mind conventional CMOS concepts adapted to the speed and (typically) unipolar limitations of oxide TFTs, these devices can be seen as a powerful platform for sustainable, multifunctional and flexible electronics. This presentation will precisely address these topics, which are currently being studied at CENIMAT: • Turning oxides into an even more sustainable approach for electronics, by replacing IGZO by indium- and gallium-free semiconductors, such as zinc-tin oxide (ZTO). Even if the initial reports on this material have shown largely inferior TFT performance and superior processing temperature when compared to IGZO TFTs, it will be shown that sputtered ZTO TFTs with On/Off ratio above 106, field effect mobility close to 10 cm2/Vs, subthreshold slope of 0.3 V/dec and non-significant performance variation under bending can now be obtained on PEN foil with only 150 C processing temperature. • Taking oxide TFTs towards the limits of microscale patterning, investigating the peculiarities found for oxide TFTs with channel lengths as low as 1 micron. While short channel effects as channel length modulation or drain induced barrier lowering start to be relevant, cut-off frequencies of oxide TFTs can exceed 100 MHz at this scale. The electrical characterization is being supported by TCAD simulations. [1, 2] • Integrating oxide TFTs in digital, analog and mixed-signal circuits with a significant level of complexity (100s of TFTs). To compensate for the intrinsic performance limitations compared to Si-based CMOS, high-gain topologies are being used to create logic gates, amplifiers, multipliers, phase-generators, among many other blocks. As examples, four-quadrant analog multipliers with a gain improvement of 7.2 dB over the Gilbert cell with the diode-connected load or amplifiers with a gain of 34 dB and a power consumption of 0.576 mW (load of 10 MOhm//16 pF) will be presented [3, 4]. These blocks are being used for different fields of applications, such as smart-bottles or flexible x-ray sensors. For this last application we recently found our oxide TFTs to have excellent ionizing-radiation hardness, showing to be insensitive even to exposure doses of 410 krad(SiO2) [5]. [1] Bahubalindruni, P. G. et al. Journal of Display Technology 12, 515-518 (2016) [2] Martins, J., Barquinha, P. & Goes, J. in Technological Innovation for Cyber-Physical Systems: 7th IFIP WG 5.5/SOCOLNET Advanced Doctoral Conference on Computing, Electrical and Industrial Systems, DoCEIS 2016, Costa de Caparica, Portugal, April 11-13, 2016, Proceedings (eds M. Luis Camarinha-Matos, António J. Falcão, Nazanin Vafaei, & Shirin Najdi) 551-557 (Springer International Publishing, 2016) [3] Bahubalindruni, P. G. et al. Ieee Electron Device Letters 37, 419-421 (2016

All-Standard-Cell-Based Analog-to-Digital Architectures Well-Suited for Internet of Things Applications

SMART-E-PTDC/CTM-PAM/04012/2022, IDS-PAPER-PTDC/CTM-PAM/4241/2020 and PEST (CTS/UNINOVA)-UIDB/00066/2020. This work also received funding from the European Community’s H2020 program [Grant Agreement No. 716510 (ERC-2016-StG TREND) and 952169 (SYNERGY, H2020-WIDESPREAD-2020-5, CSA)]. Publisher Copyright: © 2022 by the authors.In this paper, the most suited analog-to-digital (A/D) converters (ADCs) for Internet of Things (IoT) applications are compared in terms of complexity, dynamic performance, and energy efficiency. Among them, an innovative hybrid topology, a digital–delta (Δ) modulator (ΔM) ADC employing noise shaping (NS), is proposed. To implement the active building blocks, several standard-cell-based synthesizable comparators and amplifiers are examined and compared in terms of their key performance parameters. The simulation results of a fully synthesizable Digital-ΔM with NS using passive and standard-cell-based circuitry show a peak of 72.5 dB in the signal-to-noise and distortion ratio (SNDR) for a 113 kHz input signal and 1 MHz bandwidth (BW). The estimated (Formula presented.) is close to 16.2 fJ/conv.-step.publishersversionpublishe

Microwave-Assisted Hydrothermal Synthesis of Zn2SnO4 Nanostructures for Photocatalytic Dye Degradation

Zinc-tin oxide (ZTO) nanostructures appear as one of the most promising material systems for a new generation of nanodevices. In this work, a microwave-assisted hydrothermal synthesis to produce different shapes of Zn2SnO4 nanostructures (nanoparticles, octahedrons and nanoplates) is presented. Reproducible and homogeneous results were obtained with the advantage of reducing up to 20 h the synthesis time when compared to using a conventional oven. Furthermore, the photocatalytic activity of the Zn2SnO4 nanostructures in the degradation of rhodamine B under UV light was studied. Zn2SnO4 nanoparticles demonstrated better performance with >90% of degradation being achieved in 2.5 h.publishersversionpublishe

Chapter Hydrothermal Synthesis of Zinc Tin Oxide Nanostructures for Photocatalysis, Energy Harvesting and Electronics

The massification of Internet of Things (IoT) and Smart Surfaces has increased the demand for nanomaterials excelling at specific properties required for their target application, but also offering multifunctionality, conformal integration in multiple surfaces and sustainability, in line with the European Green Deal goals. Metal oxides have been key materials for this end, finding applications from flexible electronics to photocatalysis and energy harvesting, with multicomponent materials as zinc tin oxide (ZTO) emerging as some of the most promising possibilities. This chapter is dedicated to the hydrothermal synthesis of ZTO nanostructures, expanding the already wide potential of ZnO. A literature review on the latest progress on the synthesis of a multitude of ZTO nanostructures is provided (e.g., nanowires, nanoparticles, nanosheets), emphasizing the relevance of advanced nanoscale techniques for proper characterization of such materials. The multifunctionality of ZTO will also be covered, with special attention being given to their potential for photocatalysis, electronic devices and energy harvesters

effect of physical parameters

POCI-01-0145-FEDER-007688. SFRH/BD/131836/2017. SFRH/BD/122286/2016.ZnSnO3 semiconductor nanostructures have several applications as photocatalysis, gas sensors, and energy harvesting. However, due to its multicomponent nature, the synthesis is far more complex than its binary counter parts. The complexity increases even more when aiming for low-cost and low-temperature processes as in hydrothermal methods. Knowing in detail the influence of all the parameters involved in these processes is imperative, in order to properly control the synthesis to achieve the desired final product. Thus, this paper presents a study of the influence of the physical parameters involved in the hydrothermal synthesis of ZnSnO3 nanowires, namely volume, reaction time, and process temperature. Based on this study a growth mechanism for the complex Zn:Sn:O system is proposed. Two zinc precursors, zinc chloride and zinc acetate, were studied, showing that although the growth mechanism is inherent to the material itself, the chemical reactions for different conditions need to be considered.publishersversionpublishe

Accurate determination of band tail properties in amorphous semiconductor thin film with Kelvin Probe Force Microscopy

Amorphous oxide semiconductors are receiving significant attention due to their relevance for large area electronics. Their disordered microscopic structure causes the formation of band tails in the density of states (DOS) that strongly affect charge transport properties. Bandtail properties are crucial to understand for optimizing thin film device performance. Among the available techniques to measure the DOS, KPFM is exceptional as it enables precise local electronic investigations combined with microscopic imaging. However, a model to interpret KPFM spectroscopy data on amorphous semiconductors of finite thickness is lacking. To address this issue, we provide an analytical solution to the Poisson's equation for a metal-insulator-semiconductor (MIS) junction interacting with the AFM tip. The solution enables us to fit experimental data for semiconductors with finite thickness and obtain the DOS parameters, such as band tail width (E_t), doping density (N_D), and flat band potential. To demonstrate our method, we perform KPFM experiments on Indium-Gallium-Zinc Oxide (IGZO) thin film transistors (IGZO-TFTs). DOS parameters compare well to values obtained with photocurrent spectroscopy. We demonstrate the potentials of the developed method by investigating the impact of ionizing radiation on DOS parameters and TFT performance. Our results provide clear evidence that the observed shift in threshold voltage is caused by static charge in the gate dielectric leading to a shift in flat band potential. Band-tails and doping density are not affected by the radiation. The developed methodology can be easily translated to different semiconductor materials and paves the way towards quantitative microscopic mapping of local DOS parameters in thin film devices

Microwave-Assisted Synthesis of Zn2SnO4 Nanostructures for Photodegradation of Rhodamine B under UV and Sunlight

Funding Information: This work is funded by National Funds through FCT—Portuguese Foundation for Science and Technology, Reference UIDB/50025/2020-2023. This work also received funding from the European Community’s H2020 program under grant agreement No. 716510 (ERC-2016-StG TREND) and No. 101008701 (EMERGE). Publisher Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland.The contamination of water resources by pollutants resulting from human activities represents a major concern nowadays. One promising alternative to solve this problem is the photocatalytic process, which has demonstrated very promising and efficient results. Oxide nanostructures are interesting alternatives for these applications since they present wide band gaps and high surface areas. Among the photocatalytic oxide nanostructures, zinc tin oxide (ZTO) presents itself as an eco-friendly alternative since its composition includes abundant and non-toxic zinc and tin, instead of critical elements. Moreover, ZTO nanostructures have a multiplicity of structures and morphologies possible to be obtained through low-cost solution-based syntheses. In this context, the current work presents an optimization of ZTO nanostructures (polyhedrons, nanoplates, and nanoparticles) obtained by microwave irradiation-assisted hydrothermal synthesis, toward photocatalytic applications. The nanostructures’ photocatalytic activity in the degradation of rhodamine B under both ultraviolet (UV) irradiation and natural sunlight was evaluated. Among the various morphologies, ZTO nanoparticles revealed the best performance, with degradation > 90% being achieved in 60 min under UV irradiation and in 90 min under natural sunlight. The eco-friendly production process and the demonstrated ability of these nanostructures to be used in various water decontamination processes reinforces their sustainability and the role they can play in a circular economy.publishersversionpublishe

High-performance flexible hybrid field-effect transistors based on cellulose fiber paper

IEEE Electron Device Letters, VOL. 29, NO. 9,Abstract—In this letter, we report for the first time the use of a sheet of cellulose-fiber-based paper as the dielectric layer used in oxide-based semiconductor thin-film field-effect transistors(FETs). In this new approach, we are using the cellulose–fiber-based paper in an “interstrate” structure since the device is built on both sides of the cellulose sheet. Such hybrid FETs present excellent operating characteristics such as high channel saturation mobility (> 30 cm2/Vs), drain–source current on/off modulation ratio of approximately 104, near-zero threshold voltage, enhancement n-type operation, and subthreshold gate voltage swing of 0.8 V/decade. The cellulose-fiber-based paper FETs’ characteristics have been measured in air ambient conditions and present good stability, after two months of being processed. The obtained results outpace those of amorphous Si thin-film transistors (TFTs) and rival with the same oxide-based TFTs produced on either glass or crystalline silicon substrates. The compatibility of these devices with large-scale/large-area deposition techniques and low–cost substrates as well as their very low operating bias delineates this as a promising approach to attain high-performance disposable electronics like paper displays, smart labels, smart packaging, RFID, and point-of-care systems for self-analysis in bioapplications, among others.This work was supported in part by the Fundação para a Ciência e a Tecnologia (FCT), Ministério da Ciência, Tecnologia e Ensino Superior (MCTES), under Project PTDC/CTM/73943/2006 and Project PTDC/EEA-ELC/64975/2006 and in part by the Electronic and Telecommunications Research Institute (ETRI),Korea. The work of P. Barquinha was supported by FCT under Fellowship SFRH/BD/17970/2004. The work of G. Gonçalves was supported by FCT under Fellowship SFRH/BD/27313/2006

Seed-Layer Free Zinc Tin Oxide Tailored Nanostructures for Nanoelectronic Applications: Effect of Chemical Parameters

POCI-01-0145-FEDER-007688Semiconductor nanowires are mostly processed by complex, expensive, and high temperature methods. In this work, with the intent of developing zinc tin oxide nanowires (ZTO NWs) by low-cost and low-complexity processes, we show a detailed study on the influence of chemical parameters in the hydrothermal synthesis of ZTO nanostructures at temperatures of only 200 degrees C. Two different zinc precursors, the ratio between zinc and tin precursors, and the concentration of the surfactant agent and of the mineralizer were studied. The type and the crystallinity of the nanostructures were found to be highly dependent on the used precursors and on the concentration of each reagent. Conditions for obtaining different ZTO nanostructures were achieved, namely, Zn2SnO4 nanoparticles and ZnSnO3 nanowires with length similar to 600 nm, with the latter being reported for the first time ever by hydrothermal methods without the use of seed layers. Optical and electrical properties were analyzed, obtaining band gaps of 3.60 and 3.46 eV for ZnSnO3 and Zn2SnO4, respectively, and a resistivity of 1.42 k Omega.cm for single ZnSnO3 nanowires, measured using nanomanipulators after localized deposition of Pt electrodes by e-beam assisted gas decomposition. The low-temperature hydrothermal methods explored here proved to be a low-cost, reproducible, and highly flexible route to obtain multicomponent oxide nanostructures, particularly ZTO NWs. The diversity of the synthesized ZTO structures has potential application in next-generation nanoscale devices such as field effect nanotransistors, nanogenerators, resistive switching memories, gas sensors, and photocatalysis.proofpublishe

Parylene C as a Multipurpose Material for Electronics and Microfluidics

Funding Information: This work was financed by national funds from FCT—Fundação para a Ciência e a Tecnologia, I.P., in the scope of the projects LA/P/0037/2020, UIDP/50025/2020 and UIDB/50025/2020 of the Associate Laboratory Institute of Nanostructures, Nanomodelling and Nanofabrication—i3N. Furthermore, the work received funding from FCT in the scope of projects UIDP/04378/2020 and UIDB/04378/2020 of the Research Unit on Applied Molecular Biosciences—UCIBIO and the project LA/P/0140/2020 of the Associate Laboratory Institute for Health and Bioeconomy—i4HB. This work also received funding from the European Community’s H2020 program under grant agreements 716510 (ERC-2016-StG TREND), 787410 (ERC-2019-AdG DIGISMART) and 952169 (SYNERGY, H2020-WIDESPREAD-2020-5, CSA), 101008701 (EMERGE, H2020-INFRAIA-2018-2020). B. J. Coelho acknowledges FCT for the attribution of grant SFRH/BD/132904/2017 and grant COVID/BD/152453/2022. Publisher Copyright: © 2023 by the authors.Poly(p-xylylene) derivatives, widely known as Parylenes, have been considerably adopted by the scientific community for several applications, ranging from simple passive coatings to active device components. Here, we explore the thermal, structural, and electrical properties of Parylene C, and further present a variety of electronic devices featuring this polymer: transistors, capacitors, and digital microfluidic (DMF) devices. We evaluate transistors produced with Parylene C as a dielectric, substrate, and encapsulation layer, either semitransparent or fully transparent. Such transistors exhibit steep transfer curves and subthreshold slopes of 0.26 V/dec, negligible gate leak currents, and fair mobilities. Furthermore, we characterize MIM (metal–insulator–metal) structures with Parylene C as a dielectric and demonstrate the functionality of the polymer deposited in single and double layers under temperature and AC signal stimuli, mimicking the DMF stimuli. Applying temperature generally leads to a decrease in the capacitance of the dielectric layer, whereas applying an AC signal leads to an increase in said capacitance for double-layered Parylene C only. By applying the two stimuli, the capacitance seems to suffer from a balanced influence of both the separated stimuli. Lastly, we demonstrate that DMF devices with double-layered Parylene C allow for faster droplet motion and enable long nucleic acid amplification reactions.publishersversionpublishe