Novel hafnium oxide (HfO 2 )-based ferroelectrics reveal full scalability and complementary metal oxide semiconductor integratability compared to perovskite-based ferroelectrics that are currently used in nonvolatile ferroelectric random access memories (FeRAMs). Within the lifetime of the device, two main regimes of wake-up and fatigue can be identified. Up to now, the mechanisms behind these two device stages have not been revealed. Thus, the main scope of this study is an identification of the root cause for the increase of the remnant polarization during the wake-up phase and subsequent polarization degradation with further cycling. Combining the comprehensive ferroelectric switching current experiments, Preisach density analysis, and transmission electron microscopy (TEM) study with compact and Technology Computer Aided Design (TCAD) modeling, it has been found out that during the wake-up of the device no new defects are generated but the existing defects redistribute within the device. Furthermore, vacancy diffusion has been identified as the main cause for the phase transformation and consequent increase of the remnant polarization. Utilizing trap density spectroscopy for examining defect evolution with cycling of the device together with modeling of the degradation results in an understanding of the main mechanisms behind the evolution of the ferroelectric response.

Resistive switching (RS) is an interesting property shown by some materials systems that, especially during the last decade, has gained a lot of interest for the fabrication of electronic devices, with electronic nonvolatile memories being those that have received the most attention. The presence and quality of the RS phenomenon in a materials system can be studied using different prototype cells, performing different experiments, displaying different figures of merit, and developing different computational analyses. Therefore, the real usefulness and impact of the findings presented in each study for the RS technology will be also different. This manuscript describes the most recommendable methodologies for the fabrication, characterization, and simulation of RS devices, as well as the proper methods to display the data obtained. The idea is to help the scientific community to evaluate the real usefulness and impact of an RS study for the development of RS technology.

By combining electrical, physical, and transport/atomistic modeling results, this study identifies critical conductive filament (CF) features controlling TiN/HfO2/TiN resistive memory (RRAM) operations. The leakage current through the dielectric is found to be supported by the oxygen vacancies, which tend to segregate at hafnia grain boundaries. We simulate the evolution of a current path during the forming operation employing the multiphonon trap-assisted tunneling (TAT) electron transport model. The forming process is analyzed within the concept of dielectric breakdown, which exhibits much shorter characteristic times than the electroforming process conventionally employed to describe the formation of the conductive filament. The resulting conductive filament is calculated to produce a non-uniform temperature profile along its length during the reset operation, promoting preferential oxidation of the filament tip. A thin dielectric barrier resulting from the CF tip oxidation is found to control filament resistance in the high resistive state. Field-driven dielectric breakdown of this barrier during the set operation restores the filament to its initial low resistive state. These findings point to the critical importance of controlling the filament cross section during forming to achieve low power RRAM cell switching.

The use of two dimensional (2D) materials to improve the capabilities of electronic devices is a promising strategy that has recently gained much interest in both academy and industry. While the research on 2D metallic and semiconducting materials is well established, the knowledge and 2 applications of 2D insulators are still very scarce. In this report we study the presence of resistive switching (RS) in multilayer hexagonal boron nitride (h-BN) using different electrode materials, and we engineer a family of h-BN based resistive random access memories with tunable capabilities.The devices show the coexistence of forming-free bipolar and threshold type RS with low operation voltages down to 0.4 V, high current on/off ratios up to 10 6 , long retention times above 10 hours, as well as low variability. The RS is driven by the grain boundaries (GBs) in the polycrystalline h-BN stack, which allow the penetration of metallic ions from adjacent electrodes. This reaction can be boosted by the generation of B vacancies, which is more abundant at the GBs. To the best of our knowledge, h-BN is the first 2D material showing the coexistance of bipolar and threshold RS, which may open the door to additional functionalities and applications.Received: ((will be filled in by the editorial staff))Revised: ((will be filled in by the editorial staff))

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