As theoretically predicted by Prof. Chua, the input signal frequency has a major impact on the electrical behavior of memristors. According with one of the so-called fingerprints of such devices, the ...resistive window, i.e. the difference between the low and high resistance states, shrinks as the frequency increases. Physically, this effect stems from the incapability of ions/vacancies to follow the external electrical stimulus. In terms of the electrical behavior, the collapse of the resistive window can be ascribed to the shift of the set and reset voltages toward higher values. In addition, for a fixed frequency, the resistive window increases with the signal amplitude. In this letter, we show that both phenomena, decrease and increase of the resistive window, can be consistently explained after considering the snapback effect and a balance model equation for the memory state of the device.
Complementary resistive switching (CRS) arises when two bipolar-mode memristive devices are antiserially connected, forming a single functional structure. The combined effect of both memristors leads ...to the appearance of high (HRS) and low (LRS) resistance windows in the current-voltage (<inline-formula> <tex-math notation="LaTeX">{I} </tex-math></inline-formula>-<inline-formula> <tex-math notation="LaTeX">V </tex-math></inline-formula>) characteristic that finds application in fields such as neuromorphic computing and logic circuits. In this work, the electric behavior of HfO 2 -based CRS devices intentionally fabricated with a common central electrode is investigated both from experimental and modeling viewpoints. Experiments reveal that the maximum voltage applied to the structure allows tuning the amplitude of the resistance window following a self-balance dynamics. The origin of the abrupt (digital) and gradual (analog) transitions between the HRS and LRS states is elucidated through the inclusion of the snapback and snapforward effects in the switching dynamics. The <inline-formula> <tex-math notation="LaTeX">{I} </tex-math></inline-formula>-<inline-formula> <tex-math notation="LaTeX">{V} </tex-math></inline-formula> characteristics of the CRS devices are compact modeled with two opposite-biased memdiodes and simulated in LTSpice using an equivalent three-terminal subcircuit. It is shown that the proposed model is able to reproduce with a high degree of accuracy not only the observed CRS behavior for HfO 2 but also the main features exhibited by devices with a wide variety of oxide/electrode materials.
In this work, TiN/Ti/HfO2/W memristors have been investigated to mimic the spike-time dependent plasticity (STDP) of biological synapses at multiple time scales. For this purpose, a smart software ...tool has been implemented to control the instrumentation and to perform a dedicated ultra-fast pulsed characterization. Different time scales, from tens of milliseconds to hundreds of nanoseconds, have been explored to emulate the STDP learning rule in electronic synapses. The impact of such times on the synaptic weight potentiation and depression characteristics has also been discussed.
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•HfO2-based memristors have been fabricated and characterized as electronic synapses.•The conductivity of HfO2-based memristors can be electrically and continuously tuned.•The STDP rule has been successfully implemented at different spike time scales.•The impact of the spike width on the STDP response has been assessed.•STDP characteristics have been analyzed by considering an exponential trend.
This letter reports a compact SPICE model for the electron transport characteristics of Al 2 O 3 /HfO 2 -based nanolaminates for their use in multilevel one-time programmable (M-OTP) memories. The ...model comprises three simulation blocks corresponding to the electrical stimulus applied to the device, the equivalent circuit of the memory cell, and the events generator associated with the dielectric breakdown of the insulating layer. For a clear assessment of the quantum effects occurring in these structures, constant voltage stress was used as the primary electrical stimulus. The antifuse (AF) cell is represented by a combination of series and parallel resistances that account for the formation of filamentary conducting paths with quantum properties across the structure. The arrival of successive breakdown events is simulated using a power-law nonhomogeneous Poisson process. Our study indicates that a M-OTP memory device operating in the quantum regime not only is feasible but also that its stochastic features are addressable by circuit simulations.
We have analyzed variability in resistive memories (Resistive Random Access Memories, RRAMs) making use of advanced numerical techniques to process experimental measurements and simulations based on ...the kinetic Monte Carlo technique. The devices employed in the study were fabricated using the TiN/Ti/HfO2/W stack. The switching parameters were obtained making use of new developed extraction methods. The appropriateness of the advanced parameter extraction methodologies has been checked by comparison to kinetic Monte Carlo simulations; in particular, the reset and set events have been studied and detected. The data obtained were employed to shed light on the resistive switching operation and the cycle-to-cycle variability. It has been shown that variability depends on the numerical technique employed to obtain the set and reset voltages, therefore, this issue must be taken into consideration in RS characterization and modeling studies. The proposed techniques are complementary and depending on the technology and the curves shape the features of a particular method could make it to be the most appropriate.
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•Devices with TiN/Ti/HfO2/W are fabricated and measured.•New numerical techniques for resistive switching parameters extraction are presented.•Cycle-to-cycle reset and set voltage variability depends on the technique considered.
A new model to account for variability in resistive memories is presented. It is included in a previous general current model that considers the main physical mechanisms involved in the conductive ...filament formation and disruption processes that lead to different resistive states. The validity of the model has been proved for different technologies of metal-insulator-metal bipolar resistive memories. The model can be implemented in Verilog-A for circuit simulation purposes.
•A physical model for RRAMs with filamentary conduction is presented.•A detailed thermal model is included in addition to a new variability model.•Three different technologies have been employed to prove the model validity.
In this work the serial combination of two RRAM cells is studied for the generation of a random bit. Measurements confirm that a serial reset operation, in which one of the two RRAMs switches to the ...high resistance state, is an unpredictable and random process. Furthermore, the same device switches during subsequent set and reset operations. This behavior paves the way for the application of this configuration for hardware security purposes.
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•A cell composed of the serial combination of two RRAMs is experimentally evaluated.•During a first serial reset, one of the RRAMs unpredictably switches its state.•The switching of the same RRAM persists for subsequent serial set/reset operations.•This unpredictable behavior is the source for the generation of random bits.•This cell can be leveraged for the implementation of Physical Unclonable Functions.
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