Analog Control of Retainable Resistance Multistates in HfO₂ Resistive-Switching Random Access Memories (ReRAMs)

Abstract

Resistive-switching random access memory (ReRAM) technologies are nowadays a good candidate to overcome the bottleneck of Von Neumann architectures, taking advantage of their logic-in-memory capability and the ability to mimic biological synapse behavior. Although it has been proven that ReRAMs can memorize multibit information by the storage of multiple internal resistance states, the precise control of the multistates, their nonvolatility, and the cycle-to-cycle reliability are still open challenges. In this study, the analog resistance modulation of Pt/HfO2/Ti/TiN devices is obtained and studied in response to different programming stimuli, linking the electrical response to the internal dynamics of the ReRAM cells. The resistance modulation during RESET operation is explained by the progressive dissolution of the conducting filament, whose switching kinetics is inspected in detail, describing the filament evolution during voltage sweep measurements and under the effect of 1 μs pulses. Exploiting the gradual nature of the RESET process, which is an intrinsic property of our devices, a linear resistance modulation over the wide operating window of 103 is obtained by negative pulse ramping. The intermediate resistance states are characterized by small spatial and temporal variability and stable retention over time. To explore the synaptic long-term plasticity properties, the resistance variation over 102 consecutive depression–potentiation cycles is presented and up to 15 discrete distinguishable states are defined through the evaluation of the maximum step-to-step variability. The linear resistance modulation over a wide resistance window coupled with the stable retention of intermediate states represents a fundamental step forward to enhance HfO2 ReRAM performance in neuromorphic applications.

Multi-Level Analog Resistive Switching Characteristics in Tri-Layer HfO2/Al2O3/HfO2 Based Memristor on ITO Electrode

“…Modulation of a multi-level conduction state is a very essential aspect for the synaptic device to realize the high-density memory storage. To achieve multilevel memory states, gradual RESET has been controlled by V reset-stop , as shown in Figure 5 d. A similar approach has been shown in recent works on bilayer and tri-layer RRAM structures to obtain multi-state resistance by controlling V reset-stop [ 21 , 33 , 39 , 40 ]. Here, the positive RESET voltage was slowly increased to get a gradual RESET process in the HfO 2 /Al 2 O 3 /HfO 2 tri-layer RRAM device, which leads to multiple HRS.…”

Effect of Dielectric Thickness on Resistive Switching Polarity in TiN/Ti/HfO2/Pt Stacks

“…One can propose that the filament is weak near the Pt electrode, where the iterative breaking and forming of the CF occurs. This has been studied by Goux et al [28][29][30] and Giovinazzo et al [31] in Pt/HfO2/TiN and TiN/Ti/HfO2/Pt devices, respectively. Both studies concluded that the CF formed between the metal electrodes is weakened near the Pt.…”

“…Both studies concluded that the CF formed between the metal electrodes is weakened near the Pt. As this metal is chemically inert, it does not form oxides and thus, no oxygen vacancy-rich zone is generated near the interface [28][29][30][31][32][33]. Meanwhile, both TiN and Ti are good oxygen reservoirs, which generate vacancy-rich zones in the hafnium oxide near the HfO 2 /Ti or HfO 2 /TiN interface [14,28,29,34].…”

Influences of the Temperature on the Electrical Properties of HfO2-Based Resistive Switching Devices

“…However, metal oxides are the most widely studied materials [9]. Among them, HfO x -based devices have been found to be highly scalable, CMOS compatible, and robust; and they are capable of ultrafast and low-energy consumption operation [10,11]. In lowtemperature applications, such as aerospace applications, the lack of low-cost, high-density, and endurable NVM has been a main limiting factor [12].…”