Physical Modelling of the SET/RESET characteristics and analog properties of TiOx/HfO2-x/TiOx-based RRAM devices

Understanding the origins of switching effect is of great importance, since it can enlighten our perspectives and offers guidance for novel device design. In contrast with the common electronic devices which rely their operation only at electron transport properties, resistive switching effect exhibits a strong dependence from the local distribution of ions. Here, we present a quantitative analysis, both at DC and AC domains, which can account for the analog properties of our trilayer-based devices. Our approach can capture the gradual SET/RESET responses, which stem from the balance between drift and diffusion effect, and highlight the crucial role of temperature, electric field and oxygen vacancy density on the switching pattern

Investigating the origins of high multilevel resistive switching in forming free Ti/TiO 2???x -based memory devices through experiments and simulations

Although multilevel capability is probably the most important property of resistive random access memory (RRAM) technology, it is vulnerable to reliability issues due to the stochastic nature of conducting filament (CF) creation. As a result, the various resistance states cannot be clearly distinguished, which leads to memory capacity failure. In this work, due to the gradual resistance switching pattern of TiO2-x-based RRAM devices, we demonstrate at least six resistance states with distinct memory margin and promising temporal variability. It is shown that the formation of small CFs with high density of oxygen vacancies enhances the uniformity of the switching characteristics in spite of the random nature of the switching effect. Insight into the origin of the gradual resistance modulation mechanisms is gained by the application of a trapassisted-tunneling model together with numerical simulations of the filament formation physical processes. Published by AIP Publishing

Experiments and simulation of multilevel resistive switching in forming free Ti/TiO2-x RRAM devices

We report high multilevel resistive switching in forming free resistive random access memory (RRAM) using Ti (4 nm) as top electrode. We demonstrate that at least six-level resistance states could be obtained by modifying the amplitude of the voltage pulse applied on the memory cell or the compliance current, exhibiting excellent resistance uniformity and retention capability. The resistive switching mechanism is believed to be associated with the generation/dissolution of conducting filaments (CFs) that mainly consist of oxygen vacancies, while the gradual transitions indicate the manifestation of trap-assisted conduction model. During DC scan low power resistive switching was recorded for both SET (about 50 mW) and RESET (about 50 mu W) processes, while for pulse voltages even lower power was achieved (0.4 mW and 30 nW respectively) for 100 ns switching duration. A numerical approach is also presented in order to elaborate on the origins of the switching effect. The self-rectification characteristics in conjunction with the room temperature fabrication process render our device attractive for future high-density crossbar memory arrays applications

Pulse-stream impact on recognition accuracy of reservoir computing from SiO2-based low power memory devices

Reservoir computing (RC)-based neuromorphic applications exhibit extremely low power consumption, thus challenging the use of deep neural networks in terms of both consumption requirements and integration density. Under this perspective, this work focuses on the basic principles of RC systems. The ability of self-selective conductive-bridging random access memory devices to operate in two modes, namely, volatile and non-volatile, by regulating the applied voltage is first presented. We then investigate the relaxation time of these devices as a function of the applied amplitude and pulse duration, a critical step in determining the desired non-linearity by the reservoir. Moreover, we present an in-depth study of the impact of selecting the appropriate pulse-stream and its final effects on the total power consumption and recognition accuracy in a handwritten digit recognition application from the National Institute of Standards and Technology dataset. Finally, we conclude at the optimal pulse-stream of 3-bit, through the minimization of two cost criteria, with the total power remaining at 287 µW and simultaneously achieving 82.58% recognition accuracy upon the test set

Experiments and simulation of multilevel resistive switching in forming free Ti/TiO2-x RRAM devices

We report high multilevel resistive switching in forming free resistive random access memory (RRAM) using Ti (4 nm) as top electrode. We demonstrate that at least six-level resistance states could be obtained by modifying the amplitude of the voltage pulse applied on the memory cell or the compliance current, exhibiting excellent resistance uniformity and retention capability. The resistive switching mechanism is believed to be associated with the generation/dissolution of conducting filaments (CFs) that mainly consist of oxygen vacancies, while the gradual transitions indicate the manifestation of trap-assisted conduction model. During DC scan low power resistive switching was recorded for both SET (about 50 mW) and RESET (about 50 mu W) processes, while for pulse voltages even lower power was achieved (0.4 mW and 30 nW respectively) for 100 ns switching duration. A numerical approach is also presented in order to elaborate on the origins of the switching effect. The self-rectification characteristics in conjunction with the room temperature fabrication process render our device attractive for future high-density crossbar memory arrays applications

Engineering amorphous-crystalline interfaces in TiO 2???x /TiO 2???y -based bilayer structures for enhanced resistive switching and synaptic properties

The operating principle of resistive random access memories (RRAMs) relies on the distribution of ionic species and their influence on the electron transport. Taking into account that formation and annihilation of conducting filaments (CFs) is the driving mechanism for the switching effect, it is very important to control the regions where these filaments will evolve. Thus, homolayers of titanium oxide with different oxygen contents were fabricated in order to tune the local electrical and thermal properties of the CFs and narrow down the potential percolation paths. We show that the oxygen content in the top layer of the TiO2-x/TiO2-y bilayer memristors can directly influence the morphology of the layers which affect the diffusion barrier and consequently the diffusivity and drift velocity of oxygen vacancies, yielding in important enhancement of switching characteristics, in terms of spatial uniformity (sigma/mu< 0.2), enlarged switching ratio (similar to 10(4)), and synaptic learning. In order to address the experimental data, a physical model was applied, divulging the crucial role of temperature, electric potential and oxygen vacancy density on the switching effect and offering physical insights to the SET/RESET transitions and the analog switching. The forming free nature of all the devices in conjunction with the self-rectifying behavior, should also be regarded as important assets towards RRAM device optimization. Published by AIP Publishing