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The authors acknowledge the Consejería de Conocimiento, Investigación y Universidad, Junta de Andalucía (Spain), European Regional Development Fund (ERDF) under projects A-TIC-117-UGR18, B-TIC-624-UGR20, and IE2017-5414. Support from the Government of the Russian Federation under Megagrant Program (agreement no. 074-02-2018-330 (2)) and the Ministry of Science and Higher Education of the Russian Federation under “Priority-2030” Academic Excellence Program of the Lobachevsky State University of Nizhny Novgorod (N-466-99_2021- 2023) is also acknowledged. Memristive devices were designed in the frame of the scientific program of the National Center for Physics and Mathematics (project “Artificial intelligence and big data in technical, industrial, natural and social systems”)., Variability is an inherent property of memristive devices based on the switching of resistance in a simple metal–oxide–metal structure compatible with the standard complementary metal–oxide–semiconductor fabrication process. For each specific structure, the variability should be measured and assessed as both the negative and positive factors for different applications of memristive devices. In this report, it is shown how this variability can be extracted and analyzed for such main parameters of resistive switching as the set and reset voltages/cur- rents and how it depends on the methodology used and experimental conditions. The obtained results should be taken into account in the design and predictive simulation of memristive devices and circuits., Consejería de Conocimiento, Investigación y Universidad, Junta de Andalucía (Spain), European Regional Development Fund (ERDF) under projects A-TIC-117-UGR18, B-TIC-624-UGR20, and IE2017-5414, Government of the Russian Federation under Megagrant Program (agreement no. 074-02-2018-330 (2)), Ministry of Science and Higher Education of the Russian Federation under “Priority-2030” Academic Excellence Program of the Lobachevsky State University of Nizhny Novgorod (N-466-99_2021- 2023)

Variability is an inherent property of memristive devices based on the switching of resistance in a simple metal–oxide–metal structure compatible with the standard complementary metal–oxide–semiconductor fabrication process. For each specific structure, the variability should be measured and assessed as both the negative and positive factors for different applications of memristive devices. In this report, it is shown how this variability can be extracted and analyzed for such main parameters of resistive switching as the set and reset voltages/currents and how it depends on the methodology used and experimental conditions. The obtained results should be taken into account in the design and predictive simulation of memristive devices and circuits., Junta de Andalucia, European Commission A-TIC-117-UGR18 B-TIC-624-UGR20 IE2017-5414, Government of the Russian Federation 074-02-2018-330 (2), Ministry of Science and Higher Education of the Russian Federation N-466-99_2021-2023

Developing Materials that can change their shape in response to external signals, like heat or humidity, is a critical concern for architectural design as it enables designers to develop building components that can be programmed to transform in response to changing environmental conditions. However, developing a stimulus-responsive material requires the architect to extend its level of engagement from the macroscale of the building into the much smaller scale of the material’s micro- and meso-structure. In this thesis, a novel approach for the 4D printing (4DP) of hygroscopic responsive shape-changing mechanisms is proposed and analysed. This approach engages the design of mesoscale technical structures, via a precise material deposition, that harness the anisotropic properties inherent to the fabrication process and the constitution of the printing material itself. Organization models from biological organisms, such as motile plant structures, are abstracted into smart 4D printed techniques to preprogram water induced shape-change using copolymers with embedded cellulose fibrils. This principle enables expansion or contraction forces, whose direction and strength are dependent on the architecture of the 3D printed structure. A series of experiments are described that validate the transfer of known hygroscopic bilayer principles from lamination processes to 3D printing (3DP). They demonstrate the increased programmable control of the 4DP technique through functional gradation, moisture control and multi-phase motion; and present the augmented kinematic capacity of the novel 4DP technique. In addition to the self-shaping mechanisms, the possibilities and challenges of using 4DP structures in architectural applications, such as aperture assemblies and flap mechanisms are discussed. The presented techniques, and bio-inspired approach to material organization, demonstrate the first successful application of differentiated Wood Polymer Composite (WPC) 3DP for programmable hygroscopic shape-change. The experiments can help to form the basis for complex stimulus-responsive building components capable of performing autonomous transformations in technical applications for thermal and moisture regulation.

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.

The efforts in this doctoral thesis have been focused on the characterization and modeling of memristive devices fabricated using different technologies. Among all the memristive devices, we will focus on resistive random access memories (RRAM), also known as resistive memories. To do so, devices based on metal-insulator-metal and metal-insulator-semiconductor structures have been studied in depth. A simulator based on circuit breakers has also been developed and tested to analyse RRAM variability and operation., Tesis Univ. Granada., Ministerio de Economía y Competitividad de España FEDER TEC2014-52152-C3-2-R y TEC2017-84321-C4-3-R, Junta de Andalucía FEDER A-TIC-117-UGR18 y B-TIC-624-UGR20

The variability of memristive devices using multilayer hexagonal boron nitride (h-BN) coupled with Ti and Au electrodes (i.e., Au/Ti/h-BN/Au) is analyzed in depth using different numerical techniques. We extract the reset voltage using three different methods, quantified its cycle-to-cycle variability, calculated the charge and flux that allows to minimize the effects of electric noise and the inherent stochasticity of resistive switching, described the device variability using time series analyses to assess the “memory” effect, and employed a circuit breaker simulator to understand the formation and rupture of the percolation paths that produce the switching. We conclude that the cycle-to-cycle variability of the Au/Ti/h-BN/Au devices presented here is higher than that previously observed in Au/h-BN/Au devices, and hence they may be useful for data encryption., Ministry of Science and Technology of China (2019YFE0124200, 2018YFE0100800), National Natural Science Foundation of China (61874075), Consejería de Conocimiento, Investigación y Universidad, Junta de Andalucía (Spain) and European Regional Development Fund (ERDF) under projects A-TIC-117-UGR18, A-FQM-66-UGR20, A-FQM-345- UGR18, B-TIC-624-UGR20 and IE2017-5414, Grant PGC2018-098860-B-I00 supported by MCIU/AEI/FEDER, Maria de Maeztu” Excellence Unit IMAG, reference CEX2020-001105-M, funded by MCIN/AEI/10.13039/501100011033, King Abdullah University of Science and Technology