Bipolar Switching Characteristics Research Articles

MAPbBr3 Halide Perovskite-Based Resistive Random-Access Memories Using Electron Transport Layers for Long Endurance Cycles and Retention Time.

Recent studies have focused on exploring the potential of resistive random-access memory (ReRAM) utilizing halide perovskites as novel data storage devices. This interest stems from its notable attributes, including a high ON/OFF ratio, low operating voltages, and exceptional mechanical properties. Nevertheless, there have been reports indicating that memory systems utilizing halide perovskites encounter certain obstacles pertaining to their stability and dependability, mostly assessed through endurance and retention time. Moreover, the presence of these problems can potentially restrict their practical applicability. This study explores a resistive switching memory device utilizing MAPbBr3 perovskite, which demonstrates bipolar switching characteristics. The device fabrication procedure involves a low-temperature, all-solution process. For the purpose of enhancing the device's reliability, the utilization of TPBI(2,2',2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) as an electron transfer material on the MAPbBr3 switching layer was implemented for the first time. The formation and rupture of Ag filaments in the MAPbBr3 perovskite switching layer are attributed to reduction-oxidation reactions. The TPBI is involved in the regulation of filaments during the SET and RESET processes. Hence, it can be shown that the MAPbBr3 device incorporating TPBI exhibited about 1000 endurance cycles when subjected to continuous voltage pulses. Moreover, the device consistently maintained ON/OFF ratios above 107. In contrast, the original MAPbBr3 device without TPBI demonstrated a significantly lower endurance with only 90 cycles observed. In addition, the MAPbBr3 device integrated with TPBI exhibited a retention time exceeding 3 × 103 s. The findings of this research provide compelling evidence to support the notion that electron transfer materials have promise for the development of halide perovskite memory systems owing to their favorable attributes of dependability and stability.

Oxygen Vacancy-Induced Ferromagnetism and Resistive-Magnetization Switching Characteristics in In2O3 Films

Ordered porous indium oxide thin films (In2O3) with higher ferromagnetism were prepared by the direct current magnetron sputtering method using porous anodic aluminum oxide thin films as the template. The experiment results show that the saturation magnetization reaches a maximum of about 42.03 emu/cm3 at a sputtering pressure of 3.2 Pa. The room-temperature ferromagnetism of In2O3 films mainly originates from the oxygen vacancies in the films. In addition, the spin can generally only be regulated by a magnetic field, which makes it challenging to realize miniaturization and integration of spin devices, while the regulation by an electric field can solve this contradiction. Based on this, the In2O3 composite thin-film resistive-magnetization switching device (Ag/In2O3/PAA/Al) was successfully prepared, showing bipolar resistive-magnetization switching characteristics and stable electrical and magnetic control characteristics. This research provides a way to develop a new multifunctional memory combining magnetic and resistive-magnetization storage and lays the foundation for the application of In2O3 in spintronic devices.

Silkworm Hemolymph Resistance Random Access Memory with High Stability and Low Power Consumption

AbstractMost current resistive memory has the problems of high and unstable threshold voltages and high device misread rates caused by low current switching ratios. To address these problems, an Al/poly(methyl methacrylate) (PMMA)/silkworm hemolymph:gold nanoparticles/PMMA/indium tin oxide memory device is fabricated by adding PMMA layers above and below the active layer. The device not only has stable bipolar switching characteristics with a high ON/OFF current ratio but also has a lower and more stable threshold voltage. Potentiation, depression, and spike‐time‐dependent plasticity at biological synapses are realized using this device. The device is successfully fabricated on a flexible substrate, and the device can still maintain a stable working state after 104 bending cycles. This research opens a new door for the future realization of artificial synapses in neural network hardware.

Bipolar Switching Characteristics of Transparent WOX-Based RRAM for Synaptic Application and Neuromorphic Engineering.

In this work, we evaluate the resistive switching (RS) and synaptic characteristics of a fully transparent resistive random-access memory (T-RRAM) device based on indium-tin-oxide (ITO) electrodes. Here, we fabricated ITO/WOX/ITO capacitor structure and incorporated DC-sputtered WOX as the switching layer between the two ITO electrodes. The device shows approximately 77% (including the glass substrate) of optical transmittance in visible light and exhibits reliable bipolar switching behavior. The current-voltage (I–V) curve is divided into two types: partial and full curves affected by the magnitude of the positive voltage during the reset process. In the partial curve, we confirmed that the retention could be maintained for more than 104 s and the endurance for more than 300 cycles could be stably secured. The switching mechanism based on the formation/rupture of the filament is further explained through the extra oxygen vacancies provided by the ITO electrodes. Finally, we examined the responsive potentiation and depression to check the synaptic characteristics of the device. We believe that the transparent WOX-based RRAM could be a milestone for neuromorphic devices as well as future non-volatile transparent memory.

Artificial synaptic and self-rectifying properties of crystalline (Na1-K )NbO3 thin films grown on Sr2Nb3O10 nanosheet seed layers

• Crystalline Na 1-x K x NbO 3 (CNKN) film grown on Sr 2 Nb 3 O 10 (SNO) seed layer at 370 °C. • CNKN film grown on one SNO monolayer shows typical bipolar switching properties. • CNKN film grown on two SNO monolayers shows self-rectifying switching properties. • The CNKN memristor with two SNO monolayers shows artificial synaptic properties. • The CNKN film can be used to fabricate ANNs with a cross-point array structure. Crystalline (Na 1- x K x )NbO 3 (NKN) thin films were deposited on Sr 2 Nb 3 O 10 /TiN/Si (S-TS) substrates at 370 °C. Sr 2 Nb 3 O 10 (SNO) nanosheets served as a template for the formation of crystalline NKN films at low temperatures. When the NKN film was deposited on one SNO monolayer, the NKN memristor exhibited normal bipolar switching characteristics, which could be attributed to the formation and destruction of oxygen vacancy filaments. Moreover, the NKN memristor with one SNO monolayer exhibited artificial synaptic properties. However, the NKN memristor deposited on two SNO monolayers exhibited self-rectifying bipolar switching properties, with the two SNO monolayers acting as tunneling barriers in the memristor. The conduction mechanism of the NKN memristor with two SNO monolayers in the high-resistance state is attributed to Schottky emission, direct tunneling, and Fowler–Nordheim (FN) tunneling. The current conduction in this memristor in the low-resistance state was governed by direct tunneling and FN tunneling. Additionally, the NKN memristor with two SNO monolayers exhibited large ON/OFF and rectification ratios and artificial synaptic properties. Therefore, an NKN memristor with two SNO monolayers can be used for fabricating artificial synaptic devices with a cross-point array structure.

Effect of Au electrode on the resistance change response of HfO x -based ReRAM device under voltage pulse trains

The demand for neuromorphic computing is increasing, and resistive random access memory (ReRAM) devices are intriguing candidates for synaptic applications. We studied a Ti/HfO x /Au ReRAM device with this potential in view, and fabricated a Ti/HfO x /Pt device for comparison. Both devices exhibited bipolar switching characteristics. In response to voltage pulse trains, gradual resistance change was observed in the Ti/HfO x /Au device for both the SET and RESET processes, indicating its suitability for artificial synapse application. In contrast, an abrupt resistance change was observed in the SET process of the Ti/HfO x /Pt device. A significant diffusion of Au atoms occurred in the HfO x layer of the Ti/HfO x /Au device, and the Au atoms were oxidized at the interface. This led to an increase in the O vacancy concentration, which assisted the achievement of the gradual resistance change. The present study indicates that the Ti/HfO x /Au device demonstrates good potential for use as an artificial synaptic device.

Reduced Stochastic Resistive Switching in Organic‐Inorganic Hybrid Memristors by Vapor‐Phase Infiltration

AbstractResistive random‐access memory (RRAM) is promising for next‐generation data storage and non‐von Neumann computing hardware. However, tuning device switching characteristics and particularly, controlling their stochastic variation remain as critical challenges. Here, new organic‐inorganic hybrid RRAM media are reported whose bipolar switching characteristics and stochasticity can be controlled by vapor‐phase infiltration (VPI), an ex situ hybridization technique derived from atomic layer deposition. Hybrid RRAMs based on AlOx‐infiltrated SU‐8 feature facile tunability of device switching voltages, off‐state current, and on‐off ratio by adjusting the amount of infiltrated AlOx in the hybrid. Furthermore, a significant reduction in the stochastic, cycle‐to‐cycle variations of switching parameters is enabled by AlOx infiltration, driven by the infiltration‐induced changes in mechanical, dielectric, and chemical properties of organic medium and their influence on the dimension and formation characteristics of conductive filaments. Finally, multi‐level analog switching potentially useful for neuromorphic applications are demonstrated, along with direct, one‐step device patterning exploiting the negative‐tone resist feature of SU‐8. With the demonstrated control over switching characteristics and stochastic variation, combined with analog switching and one‐step patterning capabilities, the results not only present a novel hybrid medium for RRAM applications but also showcase the utility of VPI for developing new, high‐performance hybrid RRAM devices.

Protonated g-C3N4-based nonvolatile memories with good environmental robustness assisted by boron nitride

The searching for new memory that can work under harsh conditions will be significant for their application in some important fields such as geothermal, oil and aerospace industries. In this work, memory devices with simple sandwich structures using the g-C3N4 treated by different concentration acids as active layers have been fabricated, which exhibit non-volatile behaviors and bipolar switching characteristics. Protonation treatment can enhance the memory performance efficiently compared with un-protonized device. Among them, the device containing g-C3N4 treated with 8 M HCl presents the best resistive switching performance with ON/OFF ratio of 104 and good retention capability, which might be relative to its texture without violent tortuosity. In addition, the protonated g-C3N4-based memory devices exhibit good environmental robustness, including temperature and ionizing irradiation. Specially, its high tolerant temperature (454 °C) can also be assisted by doping BN for heat dissipation. Their good thermal/irradiating stabilities are assigned to the strong bond energy of CN double bonds localized π-conjugated tri-s-triazine rings. In all, the facial protonation treatment without any functionalization or supporting, the simple sandwich device structure and good environmental robustness endow their promising applications in aerospace and outdoor environment.

Oscillatory Circuits With a Real Non-Volatile Stanford Memristor Model

Stanford memristor model is a widely used model that accurately characterizes real non-volatile metal-oxide resistive random access memory (RRAM) devices with bipolar switching characteristics. The paper studies for the first time the dynamics and bifurcations in a class of nonlinear oscillators with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">real non-volatile memristor devices</i> obeying Stanford model. This is in contrast with papers in the literature considering oscillators with ideal, abstract, or artificial memristor models, that are unable to describe physical memristors implemented in nanotechnology. One main new idea in the paper is to use the memristor as a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">programmable nonlinear resistor</i> . Namely, two principal modes of operation are considered. 1) Analogue transient phase: the oscillator is designed so that in the transient oscillations the voltage on the memristor is below threshold, hence the main memristor state variable, i.e., the gap of the insulating material, is almost constant and the memristor behaves as a static nonlinear resistor. 2) Programming phase: the nonlinear characteristic of the memristor, which depends on the gap, can be changed via the application of voltages above threshold. The paper studies nonlinear oscillations in the transient phase for a fixed gap as well as the bifurcations phenomena displayed when the gap is varied. The paper also discusses the differences between the approach in the paper and those to design other memristor oscillators with non-volatile memristors.

Effect of Oxygen Vacancy on the Conduction Modulation Linearity and Classification Accuracy of Pr0.7Ca0.3MnO3 Memristor.

An amorphous Pr0.7Ca0.3MnO3 (PCMO) film was grown on a TiN/SiO2/Si (TiN–Si) substrate at 300 °C and at an oxygen pressure (OP) of 100 mTorr. This PCMO memristor showed typical bipolar switching characteristics, which were attributed to the generation and disruption of oxygen vacancy (OV) filaments. Fabrication of the PCMO memristor at a high OP resulted in nonlinear conduction modulation with the application of equivalent pulses. However, the memristor fabricated at a low OP of 100 mTorr exhibited linear conduction modulation. The linearity of this memristor improved because the growth and disruption of the OV filaments were mostly determined by the redox reaction of OV owing to the presence of numerous OVs in this PCMO film. Furthermore, simulation using a convolutional neural network revealed that this PCMO memristor has enhanced classification performance owing to its linear conduction modulation. This memristor also exhibited several biological synaptic characteristics, indicating that an amorphous PCMO thin film fabricated at a low OP would be a suitable candidate for artificial synapses.

Tunable multistate data storage device based on silkworm hemolymph and graphene oxide

A multistate data memory device can store more than one bit in each cell. Such devices have broad application prospects because they provide a simple and low-cost way to improve memory capacity. As a biomaterial, silkworm hemolymph (SH) has the advantages of being easily accessible, biodegradable and biocompatible. In this study, performance-tunable multistate data storage devices with an indium tin oxide (ITO)/graphene oxide (GO)/SH/GO/Al structure were fabricated with SH and GO as dielectric layers. The results show that the proposed device structure has stable nonvolatile and bipolar switching characteristics. The conductivity and ON/OFF current ratio (1–103) of such a device can be adjusted by modifying the GO concentration. With appropriate control of the compliance current (ICC), the device can be switched to six different resistance states, enabling multistate data storage capabilities and allowing high-density data storage to be realized. These devices have a long retention time (104 s) and extended endurance. Their switching behavior is attributed to the formation and fracture of oxygen vacancy conductive filaments. This research introduces a new approach to the development of biocompatible high-density memory devices.

Solution-Processed Stretchable Ag2 S Semiconductor Thin Films for Wearable Self-Powered Nonvolatile Memory.

Compared with the large plastic deformation observed in ductile metals and organic materials, inorganic semiconductors have limited plasticity (<0.2%) due to their intrinsic bonding characters, restricting their widespread applications in stretchable electronics. Herein, the solution-processed synthesis of ductile α-Ag2 S thin films and fabrication of all-inorganic, self-powered, and stretchable memory devices, is reported. Molecular Ag2 S complex solution is synthesized by chemical reduction of Ag2 S powder, fabricating wafer-scale highly crystalline Ag2 S thin films. The thin films show stretchability due to the intrinsic ductility, sustaining the structural integrity at a tensile strain of 14.9%. Moreover, the fabricated Ag2 S-based resistive random access memory presents outstanding bipolar switching characteristics (Ion /Ioff ratio of ≈105 , operational endurance of 100 cycles, and retention time >106 s) as well as excellent mechanical stretchability (no degradation of properties up to stretchability of 52%). Meanwhile, the device is highly durable under diverse chemical environments and temperatures from -196 to 300 °C, especially maintaining the properties for 168 h in 85% relative humidity and 85 °C. A self-powered memory combined with motion sensors for use as a wearable healthcare monitoring system is demonstrated, offering the potential for designing high-performance wearable electronics that are usable in daily life in a real-world setting.

Effect of ZnS and PbS shell on mem-behavior of CdS quantum dots

In this paper, a systematic study is carried out on mem-behavior of CdS, CdS@ZnS, and CdS@PbS core–shell nanocomposites with emphasis on the effect of ZnS and PbS shell on mem-behavior of CdS quantum dots. From X-ray diffraction, the CdS quantum dots are found to be hexagonal in nature with average crystallite size ~ 10.3 nm. From high-resolution transmission electron microscope images, the particle size is calculated around 3–4 nm for CdS quantum dots. For core–shell nanoparticles, formation of epitaxial shell layer on CdS core is clearly evident with enhancement in particle sizes. Active layer of as-synthesized samples is deposited on Indium tin oxide-coated glass which is used as one electrode. Aluminium is used as counter electrode and deposited over the active layer using thermal evaporation technique. The fabricated devices show bipolar switching characteristics with prominent hysteresis loops. The current–voltage characteristics of the devices show memristive, memcapacitive, and meminductive behavior depending on the type of active layer used. It is also observed that the inclusion of ZnS and $$\mathrm{PbS}$$ shell significantly alters the mem-behavior of the CdS quantum dots which is the major finding of this study. The conduction through the device is found to be due to coulomb blockade which also supports the ON/OFF switching mechanism. The sensitivity of the devices can be determined from RON/ROFF ratio, and it is found to be higher for CdS@ZnS core–shell nanoparticles compared to CdS quantum dots and CdS@PbS nanoparticles.

First-principles study of resistive random access memory based on single-layer black phosphorous resistive layer

In this work, Ti3C2/single-layer black phosphorus (BP)/Ti3C2 resistive random access memory (RRAM) was studied based on the first-principles theory. First, after determining the size of the material, the Ti3C2/BP(100) interface was built. By studying the electrostatic potential of the interface, it was found that there was a Schottky barrier at the interface, and the barrier height was obtained by calculating the work function and the band structure of the interface. Next, a Ti3C2/BP(100)/Ti3C2 RRAM device was designed based on the mechanism of the Schottky barrier at the interface. The bipolar switching characteristics were confirmed after calculating the I–V curve of the device, in which the turn-on threshold voltage is about 1.5 V, the turn-off threshold voltage is about 0.5 V, and the switch ratio is greater than 105. However, there are still shortcomings such as insufficient drive current. So, in the end, the optimization program is determined through a series of studies of device doping and vacancy, and it is found that after a certain concentration of Mg atoms are adsorbed, the conductivity of the resistive switching layer can be increased, the interface barrier can be adjusted, and the device performance such as the turn-on voltage, drive current, and switching ratio can be improved. This work may have guiding significance and value for the experimental research of manufacturing a new two-dimensional material RRAM.

Characteristic of Flexible Reram with Al2O3/TiO2 Active Layer By ALD and PDA Process at Low Temperature

1. Introduction The resistive random access memory (ReRAM), which is a nonvolatile memory device, on flexible plastic substrate have been widely investigated for future wearable device. The flexible ReRAM based on metal-insulator-metal (MIM) structure is generally fabricated at relatively low temperature (~250°C) from the viewpoint of heat resistance of plastics. Numerous active layers, including Al2O3-TiO2, Al2O3-HfO2, and Al2O3-Ta2O5 bilayers have been studied in a aim of improving resistive swithing reliability. In our previous paper, we found that Pt/Al2O3/TiO2/Pt capacitor fabricated on Si substrate by atomic layer deposition (ALD) and a post-deposition annealing (PDA) process at 200°C, exhibited bipolar resistive swithing charactreistics with a high resistive state (HRS) and a low resisitive state (LRS) in a small switching voltage of ±0.8V.In this paper, we fabricated Pt/Al2O3/TiO2/Pt capacitors on polyimide (PI) substrate by ALD and PDA process at 200°C and examined reliabilities of resistive swithing properties under tensile stress. 2. Experiment MIM capacitors with Al2O3/TiO2 active layer were prepared as follows. First, a 200-nm-thick SiO2 layer as gas barrier was deposited on PI substrate. Pt bottom electrode (BE-Pt) was deposited on PI/SiO2 layer by DC sputtering. A 5-nm-thick Al2O3 layer was deposited on BE-Pt by ALD at 200°C using Al(CH3)3 precursor and H2O gas and subsquently PDA was carried out at 200°C in N2. Next, a 60-nm-thick TiO2 layer was deposited on Al2O3 layer by ALD at same temperature, using Ti[N(CH3)2]4 precursor and H2O gas and PDA was performed at 200°C in O2. Finally, Pt top electrode (TE-Pt) was fabricated on the TiO2 layer by DC sputtering. The area of the TE-Pt was approximately 1.5 ´ 10-4 cm-2. 3. Results and discussion Each of Al2O3 and TiO2 layer of the flexible Pt/Al2O3/TiO2/Pt capacitor on PI had an amorphous structure because no spotty electron diffraction pattern was observed by TEM and EDS measurement. There were no severe chemical reactions in any of the layers.Fig 1 shows the J-V characterestics of the flexible Pt/Al2O3/TiO2/Pt capacitor. The first forming process was performed to occur the irreversible breakdown of the Al2O3 layer when applied voltage was increased to + 7V. The second forming process was the creation of a TiO2-x layer due to the oxygen vacancies (Vo) near the TE-Pt and TiO2 layer when voltage was applied -3V. The set process (switching from the HRS to the LRS) caused at an applied voltage of about +1V and the reset process (switching from the LRS to the HRS) occurred at about -1V. These set and reset processes appeared due to the Vo transfer into TiO2 layer when voltage applied in positive and negative directions. Stable bipolar switching properies between the HRS and the LRS was obtained until the number of swithing cycles of 20. We also observed resistive swithing characteristics of about 2 orders of magnitude between the HRS and the LRS under tensile stress condition. 4. Summary We conclude that flexible Pt/Al2O3/TiO2/Pt capacitors on PI exhibited stable bipolar switching characteristics of the HRS and LRS after two forming steps of breaking Al2O3 layer and creating a TiO2-x layer due to the Vo. Furthermore, a similar resistive switching property was obtained regardless of tensile stress. Acknowledgement This work was partially supported by JSPS KAKENHI Grant Number of JP20H02189. The authors thank all staff members of the Nanofabrication group of the National Institute for Materials Science (NIMS) for their support. Figure 1

Flexible 3D memristor array for binary storage and multi‐states neuromorphic computing applications

AbstractThe demand of flexible neuromorphic computing electronics is increasing with the rapid development of wearable artificial intelligent devices. The flexible resistive random‐access memory (RRAM) is one excellent candidate of high‐density storage devices. However, due to the limitations of fabrication process, materials system and device structure, it is difficult to prepare flexible 3D high‐density network for neuromorphic computing. In this paper, a 3D flexible memristors network is developed via low‐temperature atomic layer deposition (ALD) at 130°C, with potential of extending to various flexible electronics. The typical bipolar switching characteristics are verified in RRAM units of 3D network, including first, second and third layers. Besides binary storage, the multibit storage in single unit is demonstrated and the storage density is further increased. As a connection link between binary storage and brain‐inspired neuromorphic computing, the multibit storage capability paves the way for the tunable synaptic plasticity, for example, long‐term potentiation/depression (LTP/LTD). The 3D memristors network successfully mimicked the typical neuromorphic functionality and realized ultra‐multi conductance states modulation under 600 spikes. The robust mechanical flexibility is further demonstrated via LTP/LTD emulation under bending states (radius = 10 mm). The 3D flexible memristors network shows significant potential of applications in high‐performance, high‐density and reliable wearable neuromorphic computing system.image

Design of Ion-Implanted Junction Termination Extension for Vertical GaN Pin Rectifiers

Gallium-nitride and related materials have become suitable semiconductor platforms for next-generation power electronic devices. This materials system leverages unique properties of wider energy bandgap, higher carrier mobility, and ultrashort carrier recombination lifetime to achieve much improved bipolar switching characteristics when compared to Si- or SiC-based counterparts. In recent years, vertical GaN switches such as PIN rectifiers, junction barrier Schottky (JBS) diodes, and junction field-effect transistors (JFETs) have been actively sought in hopes to achieve low-loss device performance at kilo-volt (kV) operation range. Over the years, significant progresses in low-defect-density substrate preparation and high-quality epitaxial growth using metalorganic chemical vapor deposition (MOCVD) reactors, along with robust fabrication processing techniques helped achieve many impressive GaN-based power device demonstrations. As vertical GaN devices operate at the kV ranges, proper engineering of the electric field is a key to exploiting the ultimate device performance. To this end, several device-level design strategies such as field plates, beveled sidewalls, and junction termination extensions have been studied. In the context of realizing a planar device topology in GaN materials systems, ion implantation into GaN materials systems offer new opportunities to provide precise control of inhomogeneous carrier distribution for the creation of versatile doping profiles and geometries such as selectively doped regions or highly resistive regions at arbitrary locations in GaN devices.In this presentation, we will discuss a study of the floating guard rings (FGRs) designs that utilize a nitrogen-ion implantation isolation technique. The designs can effectively mitigate the electric field crowding effect and enable robust avalanching capability in vertical GaN PIN rectifiers. Using 1.2-kV GaN PIN rectifiers as design examples, a set of numerical simulation study was performed using a TCAD-Sentaurus software package. The results showed that a closely packed FGRs with a gap of adjacent FGRs in the range of 1-3 microns, a width of the FGRs in the range of 4 to 6 microns, along with a variable-width FGR design toward the outer rings can effectively suppress the peak electric field distribution at edge of the main junction and the surface of junction termination extensions. For example, consider a GaN PIN rectifier structure with a drift layer that consists of 6 microns of unintentionally doped (UID) GaN (n= 5×1015 cm-3) and a 4-micron-thick lightly doped GaN (n = 2×1016 cm-3). The FGR structures can be formed by creating highly resistive GaN regions in the epitaxially grown p-GaN layer using an ion implantation technique. In this design, five of the FGRs have 1-micron-wide undoped GaN and a 6-micron-wide p-GaN region in the p-GaN layer. The outermost FGR (the 6th FGR) is designed to have a 2-micron-wide undoped GaN and 5-micron-wide p-GaN extension. The resulting field distribution showed an effective suppression of the field crowding effect at the edge of the main junction (Figure 1(a)) and a smooth electric potential drop along the lateral direction can be achieved (Figure 1(b)). As shown in Figure 2, the electric field distribution at the vertical junction was plotted for two FGR designs with and without a metal plate on top of the p-GaN region. The electric field distribution of the main junction was also plotted for comparison. It is clearly shown that the peak electric field at the vertical junction is effectively reduced with the metal-plated FGRs by >10% when compared to a non-plated FGRs. Reduced peak electric field in typically high-electric-field regions can safeguard the device from experiencing premature breakdown for robust switching operations. We found that 6 FGRs with a total lateral extension of <45 microns from the main pn junction are sufficient to provide effective junction termination for 1.2 kV devices. Such designs could also support for devices with a blocking voltage up to 1.6 kV.FGR designs were implemented in GaN PIN rectifiers for experimental validation. The fabrication processing of vertical GaN PIN rectifiers was grown on n-type free-standing or bulk GaN substrates using a MOCVD reactor. The cathode was formed by depositing Ti/Al-based ohmic contact on the backside of the wafer, and the anode electrode was formed on the topside p-type GaN layer. Nitrogen-ion implantation was employed to create FGR structures and served as a mean of inter-device isolation. Detailed design strategies of the FGRs, device processing and device characterizations will be discussed in the conference. Figure 1

Investigation of honey thin film as a resistive switching material for nonvolatile memories

In this paper, we report, for the first time, honey thin film as a resistive switching material and its memory behaviors. A dried honey film was sandwiched in between a CuxO bottom electrode and a Cu top electrode to form a metal-insulator-metal structure on a glass substrate. Current-voltage measurements showed that the device exhibited bipolar switching characteristics with Ohmic conduction behavior and a read memory window of 2.6 V. When biased at a read voltage of 0.2 V, the data retention time is over an interval of 104 s and ON/OFF ratio is in the order of 107. These properties prove the potential of honey based organic resistive switching devices for “green” electronics and nonvolatile memory applications.

Interfacial layer assisted, forming free, and reliable bipolar resistive switching in solution processed BiFeO3 thin films

BiFeO3 based resistive random access memory (RRAM) devices are fabricated using a low-cost solution process to study the effect of an Al top electrode on switching behavior and reliability. Fabricated devices demonstrated bipolar switching characteristics with a moderate Ion/Ioff ratio, set and reset voltages of ∼−1.3 V and ∼0.8 V, DC and AC endurance of more than 250 cycles and 7100 cycles, respectively, and a retention time of over 104 s, confirming the non-volatile resistive switching behavior. The ohmic and trap filled space charge limited conduction dominates the conduction mechanism in the devices at lower and higher voltages, respectively. Moreover, impedance spectroscopy measurements substantiate the presence of an AlOx layer at the Al/BiFeO3 interface resulting from the Al–O interaction at the junction, which is the possible rationale of reliable complementary switching in these RRAM devices. The switching mechanism is elucidated using the formation and rupture of the oxygen vacancy mediated filament, assisted by the participation of a thin AlOx layer at the Al/BFO interface. The role of the thin AlOx layer is explained by modeling of impedances.

High endurance of bipolar resistive switching in a Pt/LaNiO3/Nb:SrZrO3/Cu stack: The role of Cu modulating layer

A bipolar resistive switching characterizes in Pt/LaNiO3/0.2%Nb:SrZrO3/Cu (Pt/LNO/Nb:SZO/Cu) structure was investigated, as the Cu and LNO layers were employed as the capping and buffering layers, respectively. Interestingly, the bistable bipolar switching characteristic was achieved a high endurance performance up to 1.2 × 103 times at room temperature. The Cu layer was served as reservoir layer to influence the distribution of oxygen vacancies and traps inside the films, and leads to a stabilized resistive switching behavior. The Pt/LNO/Nb:SZO/Cu device with low operating voltage, high operating speed, and long retention time, exhibits a high potential in future nonvolatile memory application.