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Recently, studies on ReRAMs and their reliability have received increased attention. The reliability issue is due to the nature of oxygen vacancies behaviour under biasing conditions which necessitate further studies to achieve an in-depth understanding. In this work, we fabricated several HfOx ReRAM devices with different structure, material, and thickness, followed by a study of their electrical characteristics under DC biasing. We show an improvement in the switching parameters through engineering of the device structure. Moreover, we demonstrate a certain required thickness for the oxide layer for the ease of oxygen vacancies relocations, thinner oxide layer led to the common ReRAMs performance failure in the low resistance state.

We propose an ultrathin Ti buffer layer in the Cu/Al2O3 interface to overcome the high temperature retention failure and switching non-uniformity of conductive-bridge random access memory (CBRAM) device. The sacrificial effect of Ti resulted significant improvement in retention by minimizing Cu oxidization. A novel mechanism for this improvement on the basis of the difference in the electrode potentials of the Cu and Ti layers was also proposed. The Ti atoms help in retaining the copper filament with higher electrode potential by donating electrons to it. Moreover, device with a Ti buffer layer exhibits better uniformity that can be explained by the controlled diffusion of Cu ions through the buffer layer.

Resistive Random Access Memories (ReRAMs) have been researched intensively in the last past decades as a promising alternatives technology for the next-generation non-volatile memory (NVM) devices. ReRAM’s excellent performance properties such as high switching speed, excellent scalability, and low power consumption together with accessible fabrication techniques has raised increasing interests. One ReRAM device in its most basic structure consists of a thin layer of transition metal oxide layer (TMO) sandwiched between two metal layers (Top and Bottom Electrodes). ReRAMs could be categorized into different groups regarding the implemented materials and their performance. The concept of switching mechanism is straightforward; the as-fabricated devices appeared to be highly resistive (HRS); when the top electrode (TE) is biased, the resistance state of the devices switched to the lower resistance level (LRS) in an operation called SET. This process is commonly reversible through the application of proper negative external stimuli, which can change back the resistance state of the device from LRS to HRS. Oxygen vacancies are recognized as the main elements controlling the device performance. During the set process, the oxygen vacancies rearrange to form conductive bridges between the TE and bottom electrode (BE). Further application of negative biases can partially/ fully dissolve the conductive filaments and led to HRS by disconnecting the two metallic electrodes from one the other. The excellent ReRAMs performance is enabled due to their switching mechanism which is based on relocation and movement of nano-scale oxygen vacancies, but the stochastic nature of the formation of filament also makes it hard to control this phenomenon precisely. As a result, the reported variation issue in the key switching parameters of ReRAMs lessens the reliability of this technology and hinders its commercialization. To suppress the variability hurdle in ReRAMs, it is crucial to have a better understanding of the switching mechanism. Hence, the interaction between deposited materials in the as-fabricated devices and during electrical measurements under external stimuli needs to be intensely studied to obtain an in-depth knowledge of the behavior of the oxygen vacancies. The first purpose of this research is to overcome the variation in the key switching parameters of stand-alone ReRAMs to be used in cross-point structures. In this work, we implemented two main approaches to improve the reliability and uniformity of HfO2-based ReRAMs, the structural engineering, and post-fabrication thermal treatment v and studied the effect of each method on the performance of HfO2-based fabricated ReRAMs. ReRAMs due to their simple structure can be implemented to the cross-point configuration. However, the sneak current through unwanted neighbor cells significantly decreases the system efficiency, deteriorates the read margin, and limits the maximum size of a cross-point array. To overcome the sneak path issue, different strategies could be implemented; among all, serially connecting each memory element to an additional selection device in a 1S1R configuration is an active way to introduce selectivity to the cross-point arrays. In the second part of this work, we introduced a novel one-selector one-resistor (1S1R) configuration, which eliminates the need for the physical wiring and provides valuable information on isolated selector/resistor and the integrated 1S1R.

— A novel neuron circuit using a Cu/Ti/Al2O3-based conductive-bridge random access memory (CBRAM) device for hardware neural networks that utilize nonvolatile memories as synaptic weights is introduced. The neuronal operations are designed and proved using SPICE simulations with a Verilog-A device model based on the measured characteristics of the CBRAM device. The applicability of the neuron is demonstrated by constructing a neural network system and applying it to pattern reconstructions that can recall the original patterns from noisy patterns. With these CBRAM-based neurons, a reduction in the area and power of neuromorphic chips is expected in comparison with CMOS-only neuron implementations.

In this paper, we investigate different methods and approaches in order to improve the electrical characteristics of Pt/HfOx/TiN ReRAM devices. We discuss the improvement of the ReRAM electrical characteristics after the insertion of a Hf and Ti buffer layer. As a result, the resistance window increases more that 10 times, and the set and reset voltages decrease both in absolute value and variability. Furthermore, we show the influence of an annealing step at different temperatures on the Pt/HfOx/Hf/TiN memory devices on forming voltage and HRS. Considering the importance of achieving high density memory, we demonstrated the possibility of multi-level resistance state in the fabricated devices bu controlling the enforced compliance current. In addition, we show the endurance characteristic of the fabricated memories and their error rate. Finally, we report the transient behavior of the memory devices, investigating the device speed and switching mechanism.