arXiv subjects

C. Ferreyra

Publications and source records attributed to C. Ferreyra.

6 recordsLinked to original sources

arXiv2024

Oxygen vacancies kinetics in $TaO_{2-h}$/$Ta_{2}$$O_{5-x}$ memristive interfaces

Oxygen vacancies (OV) are pervasive in metal oxides and play a pivotal role in the switching behaviour of oxide-based memristive devices. In this work we address, through a combination of experiments and theoretical simulations, OV dynamics in $Pt/TaO_{2-h}/Ta_{2}O_{5-x}/TaO_${2-y}$/Pt$ devices. In particular, we focus on the RESET transition (from low to high resistance), induced by the application of electrical pulse(s), by choosing different initial OV profiles and studying their kinetics during the mentioned process. We demonstrate that by selecting specific OV profiles it is possible to tune the characteristic time-scale of the RESET. Finally, we show that the implementation of gradual RESETs, induced by applying many (small) successive pulses, allows estimating the activation energies involved in the OV electromigration process. Our results help paving the way for OV engineering aiming at optimizing key memristive figures such as switching speed or power consumption, which are highly relevant for neuromorphic or in-memory computing implementations.

cond-mat.mes-hall↗

arXiv2024

Memristive response and neuromorphic functionality of polycrystalline ferroelectric Ca:HfO$_{2}$-based devices

Memristors are considered key building blocks for the development of neuromorphic computing hardware. For ferroelectric memristors with a capacitor-like structure, the polarization direction modulates the height of the Schottky barriers -- present at ferroelectric/metal interfaces -- that control the device resistance. Here, we unveil the coexistence of multiple memristive mechanisms in Pt/Ca:HfO$_2$/Pt devices fabricated on silicon by a simple and effective low-toxicity chemical solution method. Depending on the fabrication conditions, either dielectric or ferroelectric devices are obtained, each one presenting a distinct memristive response. The devices are forming-free and can sustain ferroelectric switching and memristive behavior simultaneously. Aided by numerical simulations, we describe this behavior as a competition of different mechanisms, including the effect of the ferroelectric polarization on Schottky interfaces and oxygen vacancy electromigration. Finally, we propose a simple learning algorithm for time-series recognition, designed to take advantage of the resistance relaxations present in the case of the ferroelectric devices.

physics.app-ph↗

arXiv2021

Optimization of the multi-mem response of topotactic redox La$_{1/2}$Sr$_{1/2}$Mn$_{1/2}$Co$_{1/2}$O$_{3-x}$

Memristive systems emerge as strong candidates for the implementation of Resistive Random Access Memories (RRAM) and neuromorphic computing devices, as they can mimic the electrical analog behavior or biological synapses. In addition, complementary functionalities such as memcapacitance could significantly improve the performance of bio-inspired devices in key issues such as energy consumption. However, the physics of mem-systems is not fully understood so far, hampering their large-scale implementation in devices. Perovskites that undergo topotactic transitions and redox reactions show improved performance as mem-systems, compared to standard perovskites. In this paper we analyze different strategies to optimize the multi-mem behavior (memristive and memcapacitive) of topotactic redox La$_{1/2}$Sr$_{1/2}$Mn$_{1/2}$Co$_{1/2}$O$_{3-x}$ (LSMCO) films grown on Nb:SrTiO$_3$ (NSTO). We explored devices with different crystallinity (from amorphous to epitaxial LSMCO), out-of-plane orientation ((001) and (110)) and stimulated either with voltage or current pulses. We found that an optimum memory response is found for epitaxial (110) LSMCO stimulated with current pulses. Under these conditions, the system efficiently exchanges oxygen with the environment minimizing, at the same time, self-heating effects that trigger nanostructural and chemical changes which could affect the device integrity and performance. Our work contributes to pave the way for the integration of LSMCO-based devices in cross-bar arrays, in order to exploit their memristive and memcapacitive properties for the development of neuromorphic or in-memory computing devices

cond-mat.mtrl-sci↗

arXiv2020

On the key role of oxygen vacancies electromigration in the memristive response of ferroelectric devices

Ferroelectric memristors are intensively studied due to their potential implementation in data storage and processing devices. In this work we show that the memristive behavior of metal/ferroelectric oxide/metal devices relies on the competition of two effects: the modulation of metal/ferroelectric interface barriers by the switchable ferroelectric polarization and the electromigration of oxygen vacancies, with the depolarizing field playing a fundamental role in the latter. We simulate our experimental results with a phenomenological model that includes both effects and we reproduce several non-trivial features of the electrical response, including resistance relaxations observed after external poling. Besides providing insight into the underlying physics of these complex devices, our work suggests that it is possible to combine non-volatile and volatile resistive changes in single ferroelectric memristors, an issue that could be useful for the development of neuromorphic devices.

physics.app-ph↗

arXiv2019

Electric selective activation of memristive interfaces in TaO$_x$-based devices

The development of novel devices for neuromorphic computing and non-traditional logic operations largely relies on the fabrication of well controlled memristive systems with functionalities beyond standard bipolar behavior and digital ON-OFF states. In the present work we demonstrate for Ta$_2$O$_5$-based devices that it is possible to selectively activate/deactivate two series memristive interfaces in order to obtain clockwise or counter-clockwise multilevel squared remanent resistance loops, just by controlling the (a)symmetry of the applied stimuli and independently of the nature of the used metallic electrodes. Based on our thorough characterization, analysis and modeling, we show that the physical origin of this electrical behavior relies on controlled oxygen vacancies electromigration between three different zones of the active Ta$_2$O$_{5-x}$ layer: a central -- bulk -- one and two quasi-symmetric interfaces with reduced TaO$_{2-h(y)}$ layers. Our devices fabrication process is rather simple as it implies the room temperature deposition of only one CMOS compatible oxide -- Ta-oxide -- and one metal, suggesting that it might be possible to take advantage of these properties at low cost and with easy scability. The tunable opposite remanent resistance loops circulations with multiple -- analogic -- intermediate stable states allows mimicking the adaptable synaptic weight of biological systems and presents potential for non-standard logic devices.

physics.app-ph↗

arXiv2019

Large memcapacitance and memristance at Nb:SrTiO$_{3}$ / La$_{0.5}$Sr$_{0.5}$Mn$_{0.5}$Co$_{0.5}$O$_{3-\delta}$ Topotactic Redox Interface

The possibility to develop neuromorphic computing devices able to mimic the extraordinary data processing capabilities of biological systems spurs the research on memristive systems. Memristors with additional functionalities such as robust memcapacitance can outperform standard devices in key aspects such as power consumption or miniaturization possibilities. In this work, we demonstrate a large memcapacitive response of a perovskite memristive interface, using the topotactic redox ability of La$_{0.5}$Sr$_{0.5}$Mn$_{0.5}$Co$_{0.5}$O$_{3-\delta}$ (LSMCO, 0 $\leq$ $\delta$ $\leq$ 0.62). We demonstrate that the multi-mem behaviour originates at the switchable n-p diode formed at the Nb:SrTiO3/LSMCO interface. We found for our Nb:SrTiO$_{3}$/LSMCO/Pt devices a memcapacitive effect C$_{HIGH}$/C$_{LOW}$ ~ 100 at 150 kHz. The proof-of-concept interface reported here opens a promising venue to use topotactic redox materials for disruptive nanoelectronics, with straightforward applications in neuromorphic computing technology.

physics.app-ph↗