Performance and reliability in back-gated CVD-grown MoS2 devices

In this work, the electrical performance and reliability of as-synthesized CVD-grown MoS2 transistors directly grown on SiO2/Si substrate without any transfer process have been evaluated. Transfer and output characteristics, current hysteresis, capacitancevoltage and low-frequency noise signatures have been characterized revealing the huge influence of surface and oxide defects and the disturbance due to the fluctuations of the carrier number on the back-gated transistor response.European Union’sHorizon 2020 research and innovation programme under theMarie Skłodowska-Curie grant agreement No 895322Spanish Government under Juan de la Cierva Formacion grantnumber FJC2018-038264-IThe Spanish Program (TEC2017-89800-R)ASCENT (EU Horizon 2020 GRANT 654384)Science Foundation Ireland: INVEST (SFI-15/IA/3131)Science Foundation Ireland: AMBER (12/RC/2278-P2

Diodo rectificador en silicio

Este proyecto tiene como principal objetivo dotar de material didáctico original al profesorado y al alumnado acerca de la fabricación de dispositivos electrónicos esenciales de forma simplificada en la sala blanca y su caracterización en el laboratorio de nano electrónica. La idea no es tanto obtener dispositivos de calidad sino conseguir dispositivos funcionales empleando el menor número de etapas posible y con el menor grado de complejidad de cara a una mejor comprensión por parte del alumnado. Se pretende por tanto: - Acercar la tecnología de fabricación de dispositivos electrónicos esenciales al estudiantado de una forma simplificada. - Reforzar los conocimientos del alumnado en relación a los dispositivos electrónicos desde un punto de vista práctico. - Facilitar la comprensión de conceptos básicos de los dispositivos electrónicos a nivel teórico y práctico. - Profundizar en los parámetros característicos de los dispositivos electrónicos a través de su caracterización

Improved inter-device variability in graphene liquid gate sensors by laser treatment

We investigate the influence of a visible laser treatment on the electrical performance of CVD-grown graphene-based liquid gate sensors. This method allows to treat locally the graphene sheet, improving the electrical characteristic for biochemical sensing applications. Optimizing the laser exposure, the Dirac point (minimum conductivity voltage) was shifted around 300 mV to lower voltages, together with a decrease of the inter-device electrical variability. These results open the door to use the laser treatment to increase the sensibility and reproducibility of liquid gate graphene-based devices as sensors or biosensors.Grupo de Nanoelectrónica, TIC216, Departamento de Electronica y Tecnología de los ComputadoresEuropean Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 895322Spanish Program (TEC2017-89800-R)SUPERA COVID19 Fund and CRUE-SantanderRegional Program FEDER UGRVID (CV20-36685), P18-RT-4826 projectUGRMADOC CEMIX 2D-EDE

Liquid-gate 2D material-on-insulator transistors for sensing applications

This research investigates the use of 2D materials (specifically graphene) as active channel in liquid-gate transistors used as detectors of biological targets on functionalized surfaces. However, before these sensors can be effectively used, it is crucial to establish a reliable sensing platform within two-dimensional materials as active channels, and to evaluate the fabrication, lithography, and reliability of these devices. In this study, we analyzed the inter-device variability and reliability of the transistors, as well as the potential factors that may exacerbate these issues under operative conditions. We performed structural characterization to confirm the quality of the materials, followed by photolithography and processing to create liquid-gate sensors. We then conducted electrical evaluations of the devices, which revealed significant reliability issues and inter-device variability. To address these problems, we propose the use of an intergate-coupling effect that utilizes both front- and back-gates simultaneously. Our findings have important implications for the design and optimization of 2D materials-based liquid-gate sensors for biological applications.European Union’s Horizon 2020 research and innovation programme under the MSC grant No 895322Spanish and Andalusian Programs DTS20/00038P18-RT-4826, PYC-020-RE-023UGRA-TIC-628-UGR20PID2020- 119668GB-I00. Funding for open access charge: Universidad de Granada / CBU

Hysteresis in As-Synthesized MoS2 Transistors: Origin and Sensing Perspectives

Two-dimensional materials, including molybdenum disulfide (MoS2), present promising sensing and detecting capabilities thanks to their extreme sensitivity to changes in the environment. Their reduced thickness also facilitates the electrostatic control of the channel and opens the door to flexible electronic applications. However, these materials still exhibit integration difficulties with complementary-MOS standardized processes and methods. The device reliability is compromised by gate insulator selection and the quality of the metal/semiconductor and semiconductor/insulator interfaces. Despite some improvements regarding mobility, hysteresis and Schottky barriers having been reported thanks to metal engineering, vertically stacked heterostructures with compatible thin-layers (such as hexagonal boron nitride or device encapsulation) variability is still an important constraint to sensor performance. In this work, we fabricated and extensively characterized the reliability of as-synthesized back-gated MoS2 transistors. Under atmospheric and room-temperature conditions, these devices present a wide electrical hysteresis (up to 5 volts) in their transfer characteristics. However, their performance is highly influenced by the temperature, light and pressure conditions. The singular signature in the time response of the devices points to adsorbates and contaminants inducing mobile charges and trapping/detrapping carrier phenomena as the mechanisms responsible for time-dependent current degradation. Far from being only a reliability issue, we demonstrated a method to exploit this device response to perform light, temperature and/or pressure sensors in as-synthesized devices. Two orders of magnitude drain current level differences were demonstrated by comparing device operation under light and dark conditions while a factor up to 105 is observed at vacuum versus atmospheric pressure environments.European Union’s Horizon 2020 Research and Innovation Programme under the Marie Skłodowska-Curie grant agreement No 895322Spanish Government under Juan de la Cierva Formacion grant number FJC2018-038264-ISpanish Ministry of Economy, Industry and Competitivity under grant TEC2017-89800-RASCENT (EU Horizon 2020 GRANT 654384)Science Foundation Ireland through the AMBER 2 project (12/RC/2278-P2)UGR-MADOC CEMIX 2D-EDE

Project Based Learning in the subject of Energy and sustainable development

[EN] The standards and guidelines for quality assurance in the European Higher Education Area (EHEA) lay down that one of the keys to combining learners¿ knowledge and skills is the implementation of new more student-centred methodologies, and learning based on competences. One of the most widely used and effective active learning methodologies is Project-Based Learning (PBL). This is a practical pedagogical methodology in which the student carries out a project focused on solving a real problem by applying the theoretical concepts from a practical point of view. In this work, projects implanted using the PBL methodology are aligned with the Agenda 2030. This Agenda for Sustainable Development, approved in 2015, establishes that the universities must play a major role in compliance with it, in due consideration of their responsibility in relation to training, research, relations with society and a model for higher education governance. This agenda contains 17 Sustainable Development Goals (SDGs). This proposal is focused on Goal 7, ¿Affordable and Clean Energy¿. In the framework of the PBL methodology and integrating the SDGs of the Agenda 2030, the main goal of this work is the development of project-based learning in the subject "Energy and Sustainable Development" in the bachelor¿s degree in Energy Engineering at the Universitat Politècnica de València. The paper described the developed methodology, the results achieved and the initial conclusions obtained.This work was carried out within the framework of the PIME's Educational Improvement and Innovation Project 2018-2019 Coordination of transversal competences in nuclear subjects of the Energy Engineering Degree, Referencia B16, del Vicerrectorado de Estudios, Calidad y Acreditación de la Universitat Politècnica de València.Marton Lluch, I.; Villanueva López, JF.; Gallardo Bermell, S.; Carlos Alberola, S.; Sánchez Galdón, AI. (2020). Project Based Learning in the subject of Energy and sustainable development. IATED Academy. 4811-4819. https://doi.org/10.21125/edulearn.2020.1266S4811481

Uncertainty analysis of a loss of cooling and loss of coolant accident in a spent fuel pool using TRACE

[EN] In this work the fundamentals and application results of an uncertainty analysis of a loss of coolant and loss of cooling accident in a spent fuel pool are presented. The spent fuel pool was modeled with TRACE V5.0 Patch 5 using a VESSEL 3D component in Cartesian coordinates. A more detailed nodalization was necessary as compared with a previous study of the same accident scenario to better develop the uncertainty analysis in the framework of the Best Estimate Plus Uncertainty (BEPU) approach. First, the model was calibrated using Main Yankee spent fuel pool experimental data of temperatures and flows measured in steady state conditions. Using the calibrated model, the analysis of the accident was performed considering uncertainty in boundary conditions and in all the coefficients included in the TRACE uncertainty quantification data module. The figure of merit selected in this work is the time at which the cladding oxidation reaches 0.17 times the cladding thickness before oxidation (CFR 50.46 b2). The uncertainty analysis was performed using Wilks' method and surrogate models. In particular, the Elastic Net surrogate model has demonstrated its potential not only to predict the evolution of the figure of merit in an appropriate way with lower computational effort than the Wilks' method but also its capability to identify the most relevant uncertain parameters, such as the fuel and cladding specific heats, rod internal pressure coefficient, burst temperature coefficient, a group of fluid regime heat transfer coefficients, the cladding metal-water reaction rate coefficient and the cladding tolerance for the average cores. In addition, the surrogate model provides more information of the distribution of the evolution of the figure of merit. The estimations of the 5/95 tolerance limits, both with the Wilks' method and with the surrogate models, are very similar, ranging from 30.432 to 30.461 h.The authors are grateful to the Spanish "Consejo de Seguridad Nuclear (CSN)" for the financial support they provided for Research MASA Project 2 and STN/4524/2015/640 (CAMP Project).Sanchez-Saez, F.; Carlos Alberola, S.; Villanueva López, JF.; Sánchez Galdón, AI.; Martorell Alsina, SS. (2020). Uncertainty analysis of a loss of cooling and loss of coolant accident in a spent fuel pool using TRACE. Progress in Nuclear Energy. 124:1-8. https://doi.org/10.1016/j.pnucene.2020.1033451812

Uncertainty analysis of PKL SBLOCA G7.1 test simulation using TRACE with Wilks and GAM surrogate methods

[EN] The Nuclear Energy Agency auspices simulation of experiments in different facilities under several programs. One on them consisted of performing a counterpart test between ROSA/LSTF and PKL facilities, with the main objective of determining the effectiveness of late accident management actions in a small break loss of coolant accident. The results obtained by TRACE code for PKL experiment SBLOCA G7.1 (a scaled model of Konvoi reactor) were in good agreement with the experiments. However, in the simulation process, uncertainty was not accounted. Uncertainty, analysis, following the principles of Best Estimate Plus Uncertainty (BEPU) approach, must be performed to measure the effect of uncertainties on the evolution of safety variables of interest, such as the maximum of the Peak Cladding Temperature (PCTmax) in the experiment. In this paper we present a comparison between two uncertainty analysis techniques. The first technique is based on order statistics that makes use of Wilks' formula. The second technique is based on a Generalized Additive Model (GAM) that substitutes the thermal-hydraulic code, without and with consideration of errors in adjusting the GAM model. The comparison of the uncertainty analysis results makes use of several performance metrics such as coverage, Coefficient of Variation and conservativeness. Based on the results of these metrics it can be concluded that the GAMPE (GAM Plus Error) provides the best performance, in particular, when using small sample size, i.e. n = 59, 93. For larger sample sizes, i.e. n = 124, 153, GAMPE and Wilks' results presents similar performance.This work has been developed partially with the support of Programa de Apoyo a la Investigacion y Desarrollo of UPV (PAID). Authors are grateful to Spanish CSN (Consejo de Seguridad Nuclear) for the financial support of these researches: (Research Project SIN/4078/2013/640; MASA Project) and (Research Project STN/4524/2015/640; CAMP Project).Sánchez Sáez, F.; Carlos Alberola, S.; Villanueva López, JF.; Sánchez Galdón, AI.; Martorell Alsina, SS. (2017). Uncertainty analysis of PKL SBLOCA G7.1 test simulation using TRACE with Wilks and GAM surrogate methods. Nuclear Engineering and Design. 319:61-72. https://doi.org/10.1016/j.nucengdes.2017.04.037S617231

Investigating the transient response of Schottky barrier back-gated MoS2 transistors

Molybdenum disulfide (MoS2) MOSFETs have been widely reported to exhibit hysteresis behavior, which is usually attributed to charge trapping effects due to defective/sub-stoichiometric compositions in the material, or defects near, or at, the oxide/channel interfaces. It is also suggested that defective MoS2 transistors show current limitations caused by the Schottky barrier junctions formed at the contacts. Here, we report on the static and dynamic device response of back-gated MoS2 transistors directly fabricated on a SiO2/Si substrate using chemical vapor deposition synthesis, without film transfer, and standard CMOS optical lithography. The devices exhibit an atypical hysteresis in the transfer characteristics, as well as a delayed response in the formation of the conducting channel in response to voltage pulses applied to the back gate. Analysis of the output characteristic is consistent with two back-to-back Schottky diodes, allowing the Fermi level pinning position at the Ni/MoS2 source and drain contacts and blocking the MoS2 hole channel. Capacitance-voltage characterization demonstrates that the grown MoS2 thin film is p-type, resulting in a nominally-off, inversion mode, n-channel device. Analysis of the transient response and hysteresis as a function of device temperature, illumination and ambient conditions indicates that the dynamic response of the device is determined by the net charge in the MoS2 film combined with the minority carrier generation lifetime in the underlying silicon substrate. The work demonstrates the strong dependence of the device response time on substrate, temperature, illumination, and net charge in the MoS2 layer opening the possibility of applications in photo-detectors and sensors.Spanish National Program (grant No. TEC2017-89800-R)ASCENT access to nanoelectronics infrastructure (EU Horizon 2020 programme grant No 654384)Science Foundation Ireland, through the IvP award INVEST (SFI-15/IA/3131) and AMBER (12/RC/2278-P2).Jose Castillejo mobility (grant No. CAS18/00460)University of Granada Plan Propio Programme 8

Experimental analysis of variability in WS2-based devices for hardware security

This work investigates the variability of tungsten disulfide (WS2)-based devices by experimental characterization in view of possible application in the field of hardware security. To this aim, a preliminary analysis was performed by measurements across voltages and temperatures on a set of seven Si/SiO2/WS2 back-gated devices, also considering the effect of different stabilization conditions on their conductivity. Obtained results show appreciable variability in the conductivity, while also revealing similar dependence on bias and temperature across tested devices. Overall, our analysis demonstrates that WS2-based devices can be potentially exploited to ensure adequate randomness and robustness against environmental variations and then used as building blocks for hardware security primitives.European Union’s Horizon 2020 project ASCENT+ (grant agreement no 871130)Science Foundation Ireland (SFI-12/RC/2278_P2)Italian MUR through the PRIN project FIVE2D (Contract No. 2017SRYEJH_001