Variability and power enhancement of current controlled resistive switching devices

Producción CientíficaIn this work, the unipolar resistive switching behaviour of Ni/HfO2/Si(n+) devices is studied. The structures are characterized using both current and voltage sweeps, with the device resistance and its cycle-to-cycle variability being analysed in each case. Experimental measurements indicate a clear improvement on resistance states stability when using current sweeps to induce both set and reset processes. Moreover, it has been found that using current to induce these transitions is more efficient than using voltage sweeps, as seen when analysing the device power consumption. The same results are obtained for devices with a Ni top electrode and a bilayer or pentalayer of HfO2/Al2O3 as dielectric. Finally, kinetic Monte Carlo and compact modelling simulation studies are performed to shed light on the experimental results.Junta de Andalucía - FEDER (B-TIC-624-UGR20)Consejo Superior de Investigaciones Científicas (CSIC) (project 20225AT012)Ramón y Cajal (grant RYC2020-030150-I

Thermal Compact Modeling and Resistive Switching Analysis in Titanium Oxide-Based Memristors

Resistive switching devices based on the Au/Ti/TiO2/Au stack were developed. In addition to standard electrical characterization by means of I-V curves, scanning thermal microscopy was employed to localize the hot spots on the top device surface (linked to conductive nanofilaments, CNFs) and perform in-operando tracking of temperature in such spots. In this way, electrical and thermal responses can be simultaneously recorded and related to each other. In a complementary way, a model for device simulation (based on COMSOL Multiphysics) was implemented in order to link the measured temperature to simulated device temperature maps. The data obtained were employed to calculate the thermal resistance to be used in compact models, such as the Stanford model, for circuit simulation. The thermal resistance extraction technique presented in this work is based on electrical and thermal measurements instead of being indirectly supported by a single fitting of the electrical response (using just I-V curves), as usual. Besides, the set and reset voltages were calculated from the complete I-V curve resistive switching series through different automatic numerical methods to assess the device variability. The series resistance was also obtained from experimental measurements, whose value is also incorporated into a compact model enhanced version. © 2024 The Authors. Published by American Chemical Society.We acknowledge grant PID2022-139586NB-44 funded by MCIN/AEI/10.13039/501100011033 and by ERDF, a way of making Europe. M.L. acknowledges the generous support from the Baseline funding scheme of the King Abdullah University of Science and Technology.Supporting informationPeer reviewe

Key Factors Associated With Pulmonary Sequelae in the Follow-Up of Critically Ill COVID-19 Patients

Introduction: Critical COVID-19 survivors have a high risk of respiratory sequelae. Therefore, we aimed to identify key factors associated with altered lung function and CT scan abnormalities at a follow-up visit in a cohort of critical COVID-19 survivors. Methods: Multicenter ambispective observational study in 52 Spanish intensive care units. Up to 1327 PCR-confirmed critical COVID-19 patients had sociodemographic, anthropometric, comorbidity and lifestyle characteristics collected at hospital admission; clinical and biological parameters throughout hospital stay; and, lung function and CT scan at a follow-up visit. Results: The median [p25–p75] time from discharge to follow-up was 3.57 [2.77–4.92] months. Median age was 60 [53–67] years, 27.8% women. The mean (SD) percentage of predicted diffusing lung capacity for carbon monoxide (DLCO) at follow-up was 72.02 (18.33)% predicted, with 66% of patients having DLCO < 80% and 24% having DLCO < 60%. CT scan showed persistent pulmonary infiltrates, fibrotic lesions, and emphysema in 33%, 25% and 6% of patients, respectively. Key variables associated with DLCO < 60% were chronic lung disease (CLD) (OR: 1.86 (1.18–2.92)), duration of invasive mechanical ventilation (IMV) (OR: 1.56 (1.37–1.77)), age (OR [per-1-SD] (95%CI): 1.39 (1.18–1.63)), urea (OR: 1.16 (0.97–1.39)) and estimated glomerular filtration rate at ICU admission (OR: 0.88 (0.73–1.06)). Bacterial pneumonia (1.62 (1.11–2.35)) and duration of ventilation (NIMV (1.23 (1.06–1.42), IMV (1.21 (1.01–1.45)) and prone positioning (1.17 (0.98–1.39)) were associated with fibrotic lesions. Conclusion: Age and CLD, reflecting patients’ baseline vulnerability, and markers of COVID-19 severity, such as duration of IMV and renal failure, were key factors associated with impaired DLCO and CT abnormalities

An experimental and simulation study of the role of thermal effects on variability in TiN/Ti/HfO2/W resistive switching nonlinear devices

An in-depth simulation and experimental study has been performed to analyze thermal effects on the variability of resistive memories. Kinetic Monte Carlo (kMC) simulations, that reproduce well the nonlinearity and stochasticity of resistive switching devices, have been employed to explain the experimental results. The series resistance and the transition voltages and currents have been extracted from devices based on the TiN/Ti/HfO2/W stack we have fabricated and measured at temperatures ranging from 77 K to 350 K. We observed that the variability for all the magnitudes analyzed was much higher at low temperatures. In the kMC simulations, we obtained conductive filaments (CFs) with less compactness at low temperatures. This led us to explain the higher variability, based on the variations of the CF morphology and density seen at low temperatures.Spanish Ministry of Science, Innovation and Universities and the FEDER program through projects TEC2017-84321-C4-1-R, TEC2017-84321-C4-2-R, TEC2017-84321-C4-3-R, and projects A.TIC.117.UGR18, B-TIC-624-UGR20 and IE2017-5414 funded by the Consejería de Conocimiento, Investigación y Universidad, Junta de Andalucía (Spain) and the FEDER progra

Variability and power enhancement of current controlled resistive switching devices

Producción CientíficaIn this work, the unipolar resistive switching behaviour of Ni/HfO2/Si(n+) devices is studied. The structures are characterized using both current and voltage sweeps, with the device resistance and its cycle-to-cycle variability being analysed in each case. Experimental measurements indicate a clear improvement on resistance states stability when using current sweeps to induce both set and reset processes. Moreover, it has been found that using current to induce these transitions is more efficient than using voltage sweeps, as seen when analysing the device power consumption. The same results are obtained for devices with a Ni top electrode and a bilayer or pentalayer of HfO2/Al2O3 as dielectric. Finally, kinetic Monte Carlo and compact modelling simulation studies are performed to shed light on the experimental results.Consejería de Conocimiento, Investigación y Universidad, Junta de Andalucía (Spain) and the FEDER program for the project B-TIC-624-UGR20, as well as the Spanish Consejo Superior de Investigaciones Científicas (CSIC) for the intramural project 20225AT012. M.B. González acknowledges the Ramón y Cajal grant No. RYC2020-030150-