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In this work, we proposed a novel variability analysis method in nanoscale ferroelectric (FE) Hf $_{{0}.{5}}$ Zr $_{{0}.{5}}$ O2 (HZO) using FE diode. The polarization variability was indirectly evaluated from the variation of Schottky emission (SE) current, which is the dominant conduction mechanism in FE diode. Using this method, we investigated two strategies to improve variability: 1) microwave annealing (MWA) and 2) HfO2 interfacial layer (IL) insertion. Low monoclinic (m-) phase fraction with MWA and scaled HZO grain size with HfO2 IL insertion contribute to the improvement of variability. Effectively reduced thermal budget and improved endurance were also achieved. Our proposed method and strategies demonstrate strong potential for applications in scaled FE memory devices.

We report a bypass resistive random-access memory (B-RRAM), which combines interface switching-based RRAM and an IGZO transistor, providing high compatibility with a vertical NAND (V-NAND) structure for high-density memory. The analog switching properties of the WOx resistive switching (RS) layer for the memory and the low off-state leakage current of the IGZO transistor (Tr) were utilized for the selector device. By utilizing the bypass reading between the RS and Tr layer, B-RRAM exhibits the favorable memory characteristics with a low operation voltage (~ 2 V), outstanding multibit operation (> 3 bits), and robust endurance ( $\sim ~10^{{6}}{)}$ . Furthermore, the B-RRAM also demonstrated a high on/off ( $ > 10^{{6}}{)}$ ratio and reasonable retention characteristics owing to the synergistic effects of RS and Tr layers. These results suggest that the B-RRAM has promising potential as a replacement for V-NAND flash memory.

This study evaluates HfxZr1-xO2 (HZO)-based high-k dielectrics, where dielectric constant (k) is significantly enhanced through structural engineering. The investigation focuses on their dielectric characteristics by pulse operation for DRAM applications. HZO/ZrO2 (HZZ) films with different superlattice structures display different dielectric behaviors, including ferroelectricity, morphotropic phase boundary (MPB), and anti-ferroelectricity. The HZZ film at the MPB condition exhibits exceptionally high k value of 62 even at voltage of 1 V, which is attributed to the abundance of phase boundaries facilitating phase transition in the superlattice structure. Conversely, the HZZ films with ferroelectric and anti-ferroelectric properties exhibit lower-than-expected k values compared to capacitance measurement, due to overestimation caused by polarization switching. Furthermore, the HZZ film at the MPB condition demonstrates robust endurance above 1012 cycles (k>45 @1015 cycles, extrapolation). These findings highlight the potential of HZZ films at the MPB to replace conventional DRAM capacitors, offering superior dielectric properties.

In this study, we report on the subthreshold bias-induced threshold voltage shift (SITS) phenomenon of an ovonic threshold switch (OTS) that can occur during array inhibit operation in a cross-point memory. We found that the threshold voltage ( $\text{V}_{\text {th}}{)}$ of the OTS increases after applying a bias to the subthreshold region of the OTS. In particular, the closer the subthreshold bias is to the $\text{V}_{\text {th}}$ of the OTS, and the longer the width of the bias pulse, the greater the SITS effect. As this SITS phenomenon can occur at half-biased cells during the inhibit operations of read and write, it should be considered as a factor affecting $\text{V}_{\text {th}}$ instability. Based on the changes in drift characteristics after subthreshold biasing and the analysis of off-leakage fitting parameters, it can be concluded that the SITS phenomenon is likely to be associated with the acceleration of the defect annihilation in the OTS film.

In this study, we investigated the effect of material composition on the selector-only memory (SOM) characteristics of ovonic threshold switch (OTS) device. By controlling the selenium (Se) concentration within the chalcogenide film, we were able to optimize the electrical properties. OTS devices co-sputtered with Se exhibited excellent characteristics, including a sufficient memory window (MW > 1.2 V) and fast operation speed ( $\sim $ 10 ns). Furthermore, we found that the desired MW could be obtained by varying the pulse height during the write process. The optical bandgap and bond nature of chalcogenide film were analyzed by UV-vis and Raman spectroscopy, revealing that the Se is the key element to the SOM operation of the OTS device. To understand the correlation between electrical properties and modification of the bond topology, we employed density functional theory (DFT) calculations. Finally, we explained the mechanism of SOM operation by introducing a thermally assisted hopping (TAH) model and analyzing the trap behavior in OTS devices. From our experimental results, we have demonstrated that the stability of delocalized traps formed depending on the polarity of the write pulse plays a crucial role in the operation of the SOM device. Our findings provide valuable insights into the complex relationship between material composition and the electrical characteristics of SOM devices.

Hf0.5Zr0.5O2 (HZO) faces challenges related to variability and reliability due to the instability of ferroelectric phase crystallization. This instability exacerbates reliability issues in HZO devices, especially as devices scale down to the nanometer level. In this study, we explore a method to tackle these issues in nano-scale ferroelectric HZO devices by directly analyzing switchable polarization. The devices used for the analysis are fabricated through different O3 treatments, and the effects on variability and reliability are demonstrated. We calculate the switchable polarization values from the current responses to Positive Up Negative Down (PUND) voltage pulses. We then compare the device-to-device and cycle-to-cycle uniformity of 500 nm size devices and predict the variability of 100 nm size devices through phase distribution simulation. Additionally, we measure and compare imprint and retention properties using write and read delay tests at 85 °C. Our comprehensive analysis offers insights for fabricating reliable ferroelectric devices with superior uniformity and retention properties.

In this study, we focused on the electrical and reliability characteristics of a ferroelectric diode (FE diode) composed of an InGaZnO (IGZO)/HfxZr1−xO2 (HZO) stack by controlling the bulk and interface defect of IGZO. Initially, to achieve the high ON/ OFF ratio, we reduced the bulk defects in the IGZO film during deposition by adjusting the oxygen partial pressure. This strategy effectively reduced the OFF-state leakage current in the high-resistance state (HRS), as demonstrated by current–voltage ( ${I}$ – ${V}{)}$ characteristics and ${x}$ -ray photoelectron spectroscopy (XPS) analysis. Subsequently, to enhance the endurance characteristics, we considered the application of microwave annealing (MWA) as an alternative to the conventional rapid thermal annealing (RTA) to decrease interface traps. Upon assessing interface trap densities, we confirmed an improved interface quality within double-layered structure. Consequently, the IGZO/HZO FE diode device exhibited a remarkable ON/OFF ratio of $4\times 10^{{5}}$ and cycling endurance of $10^{{10}}$ , underlining the importance of defect management in device performance.

This study investigates the effect of N-doping on the nanoscale (d = 30 nm) BTe ovonic threshold switch (OTS) device to achieve ideal selector characteristics in terms of leakage current, cycling endurance, and variation. Based on our findings, N-doping significantly improves device performance. In particular, the N-doped BTe OTS exhibits an ultra-low leakage current ( $\text{I}_{\textit {off}}$ @ 1/2 V $_{\textit {th}}$ = 750 pA), low threshold voltage ( $\text{V}_{\textit {th}}$ ) variation ( $\sigma < 30$ mV), excellent cycling endurance (> 1011), and low $\text{V}_{\textit {th}}$ drift ( $\gamma $ = 30 mV/dec.) characteristics. From density functional theory (DFT) calculation, we found that an increase in Te-Te lifetime after the N-doping process can improve the reliability characteristics of the OTS device. This study contributes importantly to the development of high-performance OTS devices, providing a fundamental understanding of the role of N-doping in enhancing device properties.

For efficient training of embedded Edge-AI, we demonstrate a compact neuronal dropout by exploiting the inherent stochasticity of a highly scalable ovonic threshold switch (OTS). To implement reliable probabilistic operations, the random nature of OTS is intensively investigated, and a pre-set pulse scheme is presented. We verify successful dropout implementation by a mere 1T3R structure that controls the probability without requiring external circuits. Experimental results reveal its potential for edge applications (i.e., arrhythmia detection) by improving accuracies (up to 11.4 %) with limited training data (100 signals).

In this article, we propose vertical sensing electrochemical random-access memory (VS-ECRAM) with improved synaptic behaviors for the neuromorphic application. This new type of ECRAM uses a monolayer graphene layer located between the electrolyte and channel layer, serving as both a barrier and a drain electrode. Controlled ion doping behavior was achieved through the barrier effect of monolayer graphene, resulting in excellent weight-update linearity. The constant ion injection and uniform ion distribution in the channel were verified through device simulation using ionic current mapping. In addition, the graphene barrier was effective in ensuring robust endurance and retention by obstructing ion mixing at the interface between the channel and electrolyte. Furthermore, based on the excellent scalability of the vertical channel structure, the device was scaled down to $30\times30$ nm2, resulting in reduced read/write energy consumption ( $\sim $ 5 fJ/pulse) and improved read latency ( $\times 20$ ). Finally, a $32\times32$ VS-ECRAM array was fabricated with $4{F}^{\,{2}}$ of cell layout and a high Modified National Institute of Standards and Technology (MNIST) pattern recognition accuracy (95.39%) was evaluated with near-ideal synaptic characteristics.

This study presents cell design parameters to be considered for a two-terminal ovonic threshold switch (OTS) and phase-change memory (PCM)-based array, with an example of 3-D cross-point array (XPA). The 1-Mb 3-D XPA in this study was simulated using MATLAB. The array characteristics were analyzed using the Monte–Carlo simulation for the variability of OTS characteristics. We observed that the OTS threshold voltage ( ${V}_{\text{th}}$ ) variation further accelerates the IR drop, increasing ${V}_{\text{th}}$ of cells in real XPAs. This further reduces the read window margin (RWM) and inhibit-fail margin (IFM), creating constraints on 1-Mb normal operation. The IR drop is more significant at RESET (RST) than the selected cell is at SET. Furthermore, the higher the RST resistance ( ${R}_{\text{rst}}$ ), the more severe it is, increasing the inhibit bias and worsening inhibit fails. Based on the simulation results, the raw bit error rate (RBER) of the 3-D XPA device can be minimized by balancing ${R}_{\text{rst}}$ of the PCM to minimize the error bits between failures from insufficient RWMs and inhibit fails, as the two errors are directly related to ${R}_{\text{rst}}$ . Finally, we show that the 3-D XPA device can be fabricated when ${R}_{\text{rst}}$ of the memory material is sufficiently large to minimize failures from insufficient RWM, and ${V}_{\text{th}}$ (OTS ${V}_{\text{th}}$ ) of the selector material is adjustable to ${R}_{\text{rst}}$ to minimize inhibit fails.

We presented the ternary logic using a threshold switch (TS) that enabled faster operation than the existing ternary concept and quantitatively compared it to binary logic in a 5-nm node. TS-ternary inverter shows comparable power and performance to the binary inverter in low to high (high to low) operations. Operations passing through the middle state show large delays but still show the fastest speed among existing ternary concepts. Further, our TS-ternary can be applied to various logic applications, and the noise margin can be optimized by adjusting the threshold voltage of the transistor ( $\text{V}_{T,TR}$ ) and threshold current of TS ( $\text{I}_{T}$ ). Moreover, the ternary layout requires a slightly larger area, but the system complexity is reduced to 71.0% compared with binary. Overall, TS-ternary logic is a promising candidate as a future ternary concept, having fast speed, high density, and applicability to diverse logic applications.

Oxygen-based electrochemical random-access memories (O-ECRAMs) are promising synaptic devices for neuromorphic applications because of their near-ideal synaptic characteristics and compatibility with complementary metal–oxide–semiconductor processes. However, the correlation between material parameters and synaptic properties of O-ECRAM devices has not yet been elucidated. Here, we propose the critical design parameters to fabricate an ideal ECRAM device. Based on the experimental data and simulation results, it is revealed that consistent ion supply from the electrolyte and rapid ion diffusion in the channel are critical factors for ideal synaptic characteristics. To optimize these parameters, crystalline WO2.7exhibiting fast ion diffusivity and ZrO1.7exhibiting an appropriate ion conduction energy barrier (1.1 eV) are used as a channel and an electrolyte, respectively. As a result, synaptic characteristics with near-ideal weight-update linearity in the nanosiemens conductance range are achieved. Finally, a selector-less O-ECRAM device is integrated into a 2 × 2 array, and high recognition accuracy (94.83%) of the Modified National Institute of Standards and Technology pattern is evaluated.

In this study, the nano-to bulk-scale fracture behaviors of a dual phase (DP) steel were investigated by combining a micro-digital-image-correlation (micro-DIC) technique and the finite element method (FEM). The emergence of surface cracks and nano-to bulk-scale strain distributions during plastic deformations were investigated using micro-DIC and macro-DIC techniques. FEM simulations were conducted to calculate the stress state of the damaged regions that could not be directly obtained from experiments. By combining nano- and bulk-scale observations, fracture strain and stress triaxiality of both scales were determined into model parameters for predicting the material damage behavior. The accuracy of the present damage model parameters was confirmed by comparing the load–displacement curves obtained from experimental result and proposed method. This new strategy of combining micro-scale deformation behavior and bulk-scale damage analysis facilitates defining damage model parameters through observing a wide range of regions with only one or two specimens, which is opposed to the conventional method that requires bulk-scale observations in multiple loading condition.

We present resistive switching (RS) behavior of few-layer hexagonal boron nitride (h-BN) mediated by defects and interfacial charge transfer. Few-layer h-BN is grown by metal–organic chemical vapor deposition and used as active RS medium in Ti/h-BN/Au structure, exhibiting clear bipolar RS behavior and fast switching characteristics about ∼25 ns without an initial electroforming process. Systematic investigation on microstructural and chemical characteristics of the h-BN reveals that there are structural defects such as homoelemental B–B bonds at grain boundaries and nitrogen vacancies, which can provide preferential pathways for the penetration of Tix+ions through the h-BN film. In addition, the interfacial charge transfer from Ti to the h-BN is observed by in situX-ray photoelectron spectroscopy. We suggest that the attractive Coulomb interaction between positively charged Tix+ions and the negatively charged h-BN surface as a result of the interfacial charge transfer facilitates the migration of Tix+ions at the Ti/h-BN interface, leading to the facile formation of conductive filaments. We believe that these findings can improve our understanding of the fundamental mechanisms involved in RS behavior of h-BN and contribute a significant step for the future development of h-BN-based nonvolatile memory applications.

Transition metal oxide-based memristors have widely been proposed for applications toward artificial synapses. In general, memristors have two or more electrically switchable stable resistance states that device researchers see as an analogue to the ion channels found in biological synapses. The mechanism behind resistive switching in metal oxides has been divided into electrochemical metallization models and valence change models. The stability of the resistance states in the memristor vary widely depending on: oxide material, electrode material, deposition conditions, film thickness, and programming conditions. So far, it has been extremely challenging to obtain reliable memristors with more than two stable multivalued states along with endurances greater than ∼1000 cycles for each of those states. Using an oxygen plasma-assisted sputter deposition method of noble metal electrodes, we found that the metal-oxide interface could be deposited with substantially lower interface roughness observable at the nanometer scale. This markedly improved device reliability and function, allowing for a demonstration of memristors with four completely distinct levels from ∼6 × 10–6to ∼4 × 10–8S that were tested up to 104cycles per level. Furthermore through a unique in situ transmission electron microscopy study, we were able to verify a redox reaction-type model to be dominant in our samples, leading to the higher degree of electrical state controllability. For solid-state synapse applications, the improvements to electrical properties will lead to simple device structures, with an overall power and area reduction of at least 1000 times when compared to SRAM.

Emulating essential synaptic working principles using a single electronic device has been an important research field in recent years. However, achieving sensitivity and energy consumption comparable to biological synapses in these electronic devices is still a difficult challenge. Here, we report the fabrication of conjugated polyelectrolyte (CPE)-based artificial synapse, which emulates important synaptic functions such as paired-pulse facilitation (PPF), spike-timing dependent plasticity (STDP) and spiking rate dependent plasticity (SRDP). The device exhibits superior sensitivity to external stimuli andlow-energy consumption. Ultrahigh sensitivity and low-energy consumption are key requirements for building up brain-inspired artificial systems and efficient electronic-biological interface. The excellent synaptic performance originated from (i) a hybrid working mechanism that ensured the realization of both short-term and long-term plasticity in the same device, and (ii) the mobile-ion rich CPE thin film that mediate migration of abundant ions analogous to a synaptic cleft. Development of this type of artificial synapse is both scientifically and technologically important for construction of ultrasensitive highly-energy efficient and soft neuromorphic electronics.

In this paper, we investigated the effects of inserting an N-doped GeSbTe buffer layer on a Cu/Al2O3-based conducting-bridge random-access memory (CBRAM). The N-doped GeSbTe buffer layer induced a limited Cu ion injection during the set process due to Cu-Te bonding and N-doping in the buffer layer. In addition, joule heating confinement resulting from the low-thermal-conductivity buffer layer led to a low-residual conductive filament after the reset process. As a result, the on/off ratio of the Cu/Al2O3-based device increased from 102 to 105. Furthermore, the variability of the switching parameters such as high-resistance state and set/reset voltages distributions was significantly mitigated. The N-doping effects were confirmed by comparing the GeSbTe and the N-doped GeSbTe buffer-layer-inserted devices. The N-doped GeSbTe-inserted CBRAM exhibited an on/off ratio of > 105 up to 300 DC cycles without any noticeable data-state degradation.

The switching uniformity and reliability of the TaOx based resistive random access memory (RRAM) device were investigated with varying nitrogen doping concentration. The nitrogen doped samples shows excellent electrical and reliability characteristics such as small switching variability for 3-bit multilevel per cell (MLC), low power operation and good retention properties. Compared with control sample, improved device characteristics of nitrogen doped device can be explained by nitrogen induced filament confinement.

The origin of high leakage current in NbO2 is investigated on the basis of grain size and grain boundary distribution. We used thermally grown and sputtered NbO2 films on polycrystalline niobium microwires. The off-current of the thermally grown film was significantly decreased. This is attributed to the large size of grains in thermally grown film over sputtered one and better quality of oxide film could be grown in the thermal process than sputtering. Our assumptions are supported by Conductive Atomic Force Microscopy studies and simulations. In addition, by introducing 15 nm HfO2 dielectric layer further reduction of the off-current was achieved.

Bipolar-threshold switching was demonstrated using volatile-atomic switches (VAS) for cross-point selector applications. The VAS (Cu/Cu2S/W) exhibits asymmetric current-voltage (I-V) characteristics. An abrupt conductance change occurs by the formation of a Cu filament when a positive voltage is applied to the Cu electrode. Meanwhile, nonlinear I-V characteristics are observed because of the high concentration of vacancy of Cu under a negative voltage. We thus introduce the complementary-VAS configuration for the self-compliance characteristics at both polarities. Furthermore, the increased the switching voltage at a fast sweeping rate allows the VAS to show a strong immunity to electrical disturbance.

The reset breakdown of resistive random access memory (RRAM) significantly degrades device endurance. We suppressed reset breakdown by optimizing the reset operation in an HfO2-based 1T1R RRAM device. The effective gate-to-source voltage VGSeff is reduced by increasing the RRAM resistance during the reset operation. By applying the optimum VGS, we can both guarantee a sufficient reset current and suppress reset breakdown. The experimental results confirmed improved endurance characteristics without a degraded resistance ratio.

In this study, we demonstrate a systematic way to obtain a bidirectional selector for cross point Resistive Random Access Memory (ReRAM) application by engineering material's properties. The nitrogen doping can control carrier density and increase electrical resistivity of zinc oxide. By introducing nitrogen at the both ends of ZnO film, Pt/N-ZnO/ZnO/N-ZnO/Pt structure was fabricated which exhibits very stable selector characteristics. An intensive analysis was performed to analyse the effect of nitrogen percentage and the thickness of N-ZnO on selector characteristics.

We demonstrate a high-performance selection device by utilizing the concept of crested oxide barrier to suppress the sneak current in bipolar resistive memory arrays. Using a TaOx/TiO2/TaOxstructure, high current density over 107A cm–2and excellent nonlinear characteristics up to 104were successfully demonstrated. On the basis of the defect chemistry and SIMS depth profile result, we found that some Ta atoms gradually diffused into TiO2film, and consequently, the energy band of the TiO2film was symmetrically bent at the top and bottom TaOx/TiO2interfaces and modified as a crested oxide barrier. Furthermore, the one selector–one resistor device exhibited significant suppression of the leakage current, indicating excellent selector characteristics.

Memory performances, especially uniformity and reliability of resistance random access memory (RRAM) devices with W/NbOx/Pt structures were investigated. Scaling down the active device area (ø= 250 nm) can significantly minimize extrinsic defects related to nonuniform switching and also demonstrate low‐voltage SET/RESET operations due to increased Joule heating. Electromigration of oxygen ions under the bipolar electric field, bilayer formation, and lightning‐rod effect localized at WOx/NbOxinterface can explain the improved switching behavior in this novel stack. Excellent device characteristics such as lower switching voltage, fast switching speed (100 ns), high‐temperature retention (>104s, 85 °C), stable cycling endurance (107cycles), almost 100% device yield and excellent switching uniformity are obtained.

This study demonstrates a simple and fast method of the operation mode control for ZnO nanowire field effect transistors (FETs) with hydrogen peroxide (H2O2, 10%) solution treatment for 5--10 s. With this H2O2treatment, the surface of ZnO nanowires was roughened as confirmed by transmission electron microscopy images and the defect level-related emission was increased from photoluminescence (PL) data. Correspondingly, the threshold voltage of H2O2-treated ZnO nanowire FETs shifted to the positive gate bias direction, leading a transition of the operation mode from depletion-mode to enhancement-mode. This H2O2solution treatment can be a useful method for controlling the operation mode of ZnO nanowire FETs with a wide threshold voltage shift in a few second solution treatment.

Uniformity is by far an important issue for the application of resistive random access memory (RRAM). In this letter, we explore a prototype RRAM device for switching uniformity improvement. Compared to W/WO3[?]x/Pt structure, after the introduction of a thin NbOx film between WO3[?]x and Pt bottom electrode, the device exhibits much better resistive hysteresis and switching uniformity. The main composition of the interface layer is NbO2 suboxide showing insulator-metal phase transition. A combined filamentary conduction model is proposed to clarify the role of NbOx layer on the resistive switching stabilization during the forming process.

We investigated the resistive switching behavior of a Pt/CuC/buffer oxide(BO)/Pt stack. By inserting an ultrathin BO layer, the resistance value at the off-state was increased, resulting in improved on/off resistance ratio. Furthermore, no high forming voltage was required because the Cu atoms diffused into the BO layer through the post metal annealing process, and changed in the effective switching layer into the ultrathin BO layer, where the actual formation and rupture of the Cu filaments take place. On the basis of results, it seems to be a promising candidate for FPGA applications, considering the forming-free operation and high on/off ratio.

This work presents the investigation of resistive switching memory in a perovskite heterostructure composed of an active Al-Nb codoped Pb(Zr0.52Ti0.48)O3 ferroelectric thin film and a semiconducting Pr0.7Ca0.3MnO3 manganite-based oxide film, both sandwiched between Pt electrodes in a parallel capacitor-like structure. Bipolar resistive switching nature was confirmed from the measured characteristics of the DC I-V hysteresis loop and resistance switching in the pulse mode. The active ferroelectric layer has been demonstrated to play a crucial role in controlling the switching memory performance (resistance state stability and high switching endurance). Ferroelectric polarization and corresponding piezoelectric effect-induced lattice strains are found to be responsible for the resistive switching characteristics in this ferroelectric/manganite heterojunction.

It is known that (PCMO)/Pt structures show no hysteresis loops in current-voltage curves due to the symmetric top and bottom interfaces. Here, we prepared an asymmetric memory device using bi-layer PCMO thin films with different oxygen content. The repeatable and stable resistive switching is observed. The excellent resistive switching characteristics such as a large (where HRS is the high resistance state and LRS is the low resistance state) ratio , sweeping endurance , and long retention time can be obtained using a bipolar operation mode. It is suggested that the switching process can be elucidated to the formation and rupture of localized conductive filament along with the migration of oxygen ions.

We successfully fabricated perovskite oxide‐based resistance random access memory (RRAM) with improved resistance switching characteristics, at a low temperature. A high‐pressure oxygen‐annealed (HPOA) W/Al/Pr0.7Ca0.3MnO3(PCMO)/Pt device shows good memory characteristics such as device uniformity, endurance, and improved switching speed. X‐ray photoelectron spectroscopy reveals large amounts of oxygen effectively incorporated into the PCMO layer during HPOA, enhancing the crystallization of PCMO at low temperature. X‐ray diffraction analysis confirmed that an amorphous PCMO layer was converted to a polycrystalline structure. These results suggest that HPOA is a promising method for fabricating reliable perovskite oxide‐based RRAM at a low temperature.

Resistive switching characteristics of low temperature sol-gel processed thin films are investigated. The device exhibits bipolar switching with a uniform high resistance state compared to the low resistance state. Reliability and stability of the device is significantly improved by choosing a proper compliance current in the first set operation. The film shows excellent switching properties such as high on/off ratio , good cycling endurance, and long retention at . The enhanced switching properties are explained by a physical model based on localized generation/recovery of oxygen vacancy defects near the bottom electrode interface.

We propose a solution-processed transparent -based resistive switching random access memory (ReRAM) device. Electronically active was prepared by sol-gel spin coating of a titanium(IV) isopropoxide precursor on an indium tin oxide-coated glass. The prepared film is completely transparent in the visible range and has an amorphous structure. The fabricated -based ReRAM device exhibits distinct resistive switching under consecutive dc voltage sweeps of . The device also exhibits good memory performance, including fast switching speed with a pulse width of , stable pulse endurance over 1000 cycles, and excellent retention characteristics at up to . In addition, based on the plot and X-ray photoelectron spectroscopy analysis, we postulate that the fabricated device is operated by the reversible formation/rupture of the conducting filament in the oxygen-deficient layer.

Electrical characteristics of TiN/HfO2/TiN capacitors have been investigated by means of leakage current and Random Telegraph Noise measurements. Trap assisted transport simulation allowed the extraction of relevant parameters like trap density and trap energy position. The extracted parameters show striking similarities with those reported for HfO2 deposited on a Si surface (i.e., MOSFET applications). Additionally, even low bias Constant Voltage Stress was found to induce leakage current degradation on current vs voltage characteristics, preferentially at low voltage. The leakage current degradation is explained by preexisting defect precursors or by involvement of hydrogen in creating defects as observed on thermal SiO2 layers.

A back-to-back Schottky diode configuration employing an ultrathin TiO2 layer has been assessed for application as a bi-polar selector in resistive random access memory by considering such factors as its working principle and scaling trends. Although higher rectification was achieved with an extremely low leakage current by the formation of a Schottky barrier, the maximum current remained low. This lower driving current can, however, be improved through engineering the properties of the TiO2 layer. Finally, the device characteristics of a scaled-down to [?]30 nm were observed, the results of which strongly suggest that the device characteristics are governed by its whole area.

We show that the motion of Ag atoms in an Ag2S-based conductive bridge RAM system can be utilized for threshold-type selector applications. We found that the instability of an Ag filament could be increased in low current operation, where only few limited Ag ions are allowed to form a filament, and this resulting small filament enables the transition of a non-volatile memory system to a volatile mode. Furthermore, the enhanced activity of Ag atoms at elevated temperatures promotes the self-dissolution process when the bias is removed. As a result, threshold switching behavior with suppressed hysteresis can be achieved.

This paper proposes using hourglass-shaped metal filaments to improve the ON/OFF resistance ratio and retention characteristics of switching devices used in reconfigurable logic applications. These filaments are obtained by controlling the Cu-ion mobility in multi-layer oxide electrolytes. By adopting an upper AlOX and lower TiO2 electrolyte layers with respectively low and high Cu-ion mobility, we could form hourglass-shaped filaments as a result of suppressed Cu-ion injection and enhanced filament lateral growth. The hourglass-shaped metal filaments induced local Joule heating at the filament constriction, thus accelerating RESET operations. We confirmed that, as a result, Cu/AlOX/TiO2/W devices show high ON/OFF resistance ratios (>106) and [?]10-year retention properties at 80degC.

For the device application of resistive change memory, device performance as well as uniformity and understanding of the mechanism is necessary. The resistance change due to filament formation is undesirable, as it is hard to apply for practical application. In order to have a nonlocalized, uniformly distributed, nonfilamentary-type resistance change memory device, a switching mechanism based on oxide formation and deformation is beneficial. This phenomenon largely depends on the metal electrode on top of the memory oxides. In this study both the device performance, such as pulse switching speed, and the switching mechanism were understood with different metal electrode-oxide combinations. The switching speed is determined by the slowest process step, which in this case is the dissolving of oxide during the set process. A set pulse width of and reset pulse width of were shown. Pulse switching speed was also confirmed by monitoring the delay time, comparing the output signal pulse with the input signal. The devices showed good uniformity and data retention over . Overall the combination of with a carefully designed metal electrode stack has great potential for future nonvolatile memory device applications.

An artificial synapse based on oxygen-ion-driven electrochemical random-access memory (O-ECRAM) devices is a promising candidate for building neural networks embodied in neuromorphic hardware. However, achieving commercial-level learning accuracy in O-ECRAM synapses, analog conductance tuning at fast speed, and multibit storage capacity is challenging because of the lack of Joule heating, which restricts O2–ionic transport. Here, we propose the use of an atomically thin heater of monolayer graphene as a low-power heating source for O-ECRAM to increase thermally activated O2–migration within channel-electrolyte layers. Heating from graphene manipulates the electrolyte activation energy to establish and maintain discrete analog states in the O-ECRAM channel. Benefiting from the integrated graphene heater, the O-ECRAM features long retention (>104s), good stability (switching accuracy <98% for >103training pulses), multilevel analog states for 6-bit analog weight storage with near-ideal linear switching, and 95% pattern-identification accuracy. The findings demonstrate the usefulness of 2D materials as integrated heating elements in artificial synapse chips to accelerate neuromorphic computation.

Low-thermal-budget processes are required for Ti electrode in the present gate-first n-channel metal-oxide-semiconductor field effect transistor (nMOSFET) applications because of its thermal stability problem. In this article, the effects of laser annealing on Ti electrodes (in nMOSFET) are discussed. The processes of Ti electrode degradation and crystallization are optimized effectively. nMOSFET with Ti electrode displayed an effective work function , corresponding to the conduction bandedge and an equivalent oxide thickness of by controlling the laser annealing.

We have investigated electrical and structural properties of high-pressure hydrogen postannealed (HPHA) Pt-Er alloy metal gate on HfO2 film. It is shown that the HPHA process causes the removal of micro-voids formed near interface between Pt-Er alloy and HfO2 films, resulting in the increase of gate electrode contact areas. It is further shown that the HPHA process plays a role in the reduction of PtOx and the interface trap density, leading to the negative shift of flat- band voltage and the improvement of the HfO2 interface quality, respectively. By considering the presence of an interfacial layer (IL) between the HfO2 film and a Si substrate and a negative charge at the HfO2/IL interface, the effective metal work function values of the Pt-Er alloy metal gate before and after HPHA are calculated to be ~ 4.6 and ~ 4.8 eV, respectively.

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.

The non-linear current voltage (I-V) characteristics in low-resistance state (LRS) of resistive random access memory is the most important device parameter for cross-point memory applications. An ultrathin TiOy tunnel barrier can significantly improve non-linear characteristics of resistive random access memory. Based on mathematical modeling, we verified that direct tunneling and trap assisted tunneling of TiOy layer are dominant in low voltage regime and high voltage regime, respectively. To maximize non-linearity, we need to reduce direct tunneling at low voltage by increasing film thickness and increase trap assisted tunneling at high voltage by increasing trap density.

Recently, based on the phase‐field modeling, it is predicted that Hf1‐xZrxO2(HZO) exhibits the morphotropic phase boundary (MPB) in its compositional phase diagram. Herein, the effect of structural changes between tetragonal (t) and orthorhombic (o) phases on the ferroelectric (FE) and dielectric properties of HZO films is investigated to probe the existence of MPB region. The structural analysis shows that by adjusting the ozone dosage during the atomic layer deposition process and annealing conditions, different ratios of t‐ to o‐phases (fto)are achieved, which consequently affect the FE and dielectric properties of the samples. Polarization versus electric field measurements show a remarkable increase in FE characteristics (Prand Ec) of the sample that contains the minimum t‐phase fraction (fto≈0.04). This sample shows the lowest ϵrcompared with the other samples, which is due to the formation of FE o‐phase. The sample that contains the maximum fto≈0.41demonstrates the highest dielectric response. By adjusting fto, a large ϵrof ≈55 is achieved. The study reveals a direct relation between ftoand ϵrof HZO thin films, which can be understood by considering the density of MPB region. An experimental investigation on the ferroelectric and dielectric properties of Hf0.5Zr0.5O2(HZO) thin films with different tetragonal (Antiferroelectric) to orthorhombic (Ferroelectric) phase ratios (ft/o), provides strong evidence supporting the existence of the morphotropic phase boundary throughout the HZO films. Moreover, the ft/ocontrols the electric field‐induced increase of dielectric constant in HZO films.

In this research, we propose a method that can significantly improve the linearity of current-voltage characteristics (L-IV) of synapse devices. Considering that analog input data are dependent on the L-IV, synapse devices having non-linear current-voltage characteristics can result in drastic conductance variations during inference operations. It means that the L-IV is one of the key parameters in the synapse device. To improve the L-IV, a triode region of a metal oxide semiconductor field effect transistor (MOSFET) was utilized with a Li-ion-based memristor as a gate voltage divider, which results in gradual channel conductance changes (analog synaptic weights). The channel conductance of the MOSFET can be selectively controlled based on Li-ion intercalation and de-intercalation. A notably improved L-IVand analog synaptic weights were achieved, which enhanced the MNIST data set recognition accuracy from 35.8% to 92.03%.