Multifunctional Memory Devices Research Articles

Electrically modulated photoresponse and optically modulated electroresistance in a ferroelectric heterostructure with PbZr0.2Ti0.8O3 barriers

Ferroelectric heterostructures hold great promise for developing multifunctional memristors and optoelectronic devices. In this study, we report a ferroelectrically modulated photoresponse and optically modulated electroresistance behaviors in the Pt/PbZr0.2Ti0.8O3(PZT)/Nb-doped SrTiO3 (NSTO) heterostructure. The short-circuit photocurrent rises from 28 nA (after poling at +5 V) to 345 nA (after poling at −5 V) when illuminated with 360 nm of 10 mW·cm−2, exhibiting a massive photocurrent variation ratio of 1230%. This result can be attributed to the modulation of the ferroelectric polarization on the built-in field at the PZT/NSTO interface, which impacts the separation of photogenerated carriers. Furthermore, the heterostructure has a large high/low resistance ratio of 6 × 105%, which decreases to 2 × 104% when illuminated with 360 nm light. This finding is attributed to ferroelectric polarization and light illumination modulating the barrier height and width. Overall, this research suggests a promising strategy for developing self-powered heterojunction photodetectors and multifunctional memory devices.

Improved resistive switching performance and realized electric control of exchange bias in a NiO/HfO2 bilayer structure.

The fluctuation of switching parameters is unavoidable in conductive filaments (CFs)-type resistive switching (RS) devices, which restricts the application in resistive random-access memory. Here, we employed an uninsulated antiferromagnetic (AFM) NiO layer adhered to a well-insulating HfO2 layer to effectively suppress the RS fluctuation by achieving forming-free, narrower set voltage distribution, a more stable on/off ratio, and better endurance in comparison with single-HfO2-layer based RS devices. The conduction scaling behavior indicates that the NiO/HfO2 bilayer has a smaller scale parameter S0 (lateral dimension of the bottleneck for the CFs). Besides this, considering some preexisting conductive paths in the NiO layer, the electric fields and the formation/rupture of CFs can be highly localized, leading to reduced switching fluctuation and improved RS performance in the NiO/HfO2-based RS devices. Moreover, asymmetric I-V curves measured in a high resistance state (HRS) in positively and negatively biased regions and the electric modulation of exchange bias (EB) arising from the Co-NiO interfacial coupling are favorable for revealing the inherent mechanism for RS. The coexistence of RS and EB is also useful to the design of novel multifunctional memory devices.

Ultrafast flash memory with large self-rectifying ratio based on atomically thin MoS2-channel transistor

Abstract Flash memory with high operation speed and stable retention performance is in great demand to meet the requirements of big data. In addition, the realisation of ultrafast flash memory with novel functions offers a means of combining heterogeneous components into a homogeneous device without considering impedance matching. This report proposes a 20 ns programme flash memory with 108 self-rectifying ratios based on a 0.65 nm-thick MoS2-channel transistor. A high-quality van der Waals heterojunction with a sharp interface is formed between the Cr/Au metal floating layer and h-BN tunnelling layer. In addition, the large rectification ratio and low ideality factor (n = 1.13) facilitate the application of the MoS2-channel flash memory as a bit-line select transistor. Finally, owing to the ultralow MoS2/h-BN heterojunction capacitance (50 fF), the memory device exhibits superior performance as a high-frequency (up to 1 MHz) sine signal rectifier. These results pave the way toward the potential utilisation of multifunctional memory devices in ultrafast two-dimensional NAND-flash applications.

Magnetic field effect on the dielectric behavior in SrRuO3/Ba(Zr0.3Ti0.7)O3/FeMn/ Ba(Zr0.3Ti0.7)O3/n-Si heterostructure

Interfacial structure plays a dominant role in physical properties of the oxides and their film. In this study, SrRuO3/Ba(Zr0.3Ti0.7)O3/FeMn/Ba(Zr0.3Ti0.7)O3/n-Si heterostructure was fabricated by utilizing pulsed laser deposition technique. The X-ray diffraction was utilized to analyze the multilayers’ crystalline. Dielectric properties of the heterostructure were studied under various magnetic fields. Giant magnetocapacitance characteristic was gained from the heterostructure. It is found that the interfacial polarization between barium zirconate titanate film and iron manganese alloy film is responsible for giant magnetocapacitance. A possible dielectric polarization mechanism was investigated. This work can provide guidance for the development of the multi-functional memory device.

Solid-state electrochemical redox control of the optoelectronic properties for SrFeOx thin films

By utilizing redox reactions, the physical properties of several transition metal oxides can be drastically changed, which is useful for developing multifunctional memory devices. Strontium iron oxide (SrFeOx), which exhibits a clear phase transition from antiferromagnetic insulator (x = 2.5) to helimagnetic metal (x = 3), is a good candidate for the active material in multifunctional memory devices. However, practical applications using previous demonstrations of redox reactions in SrFeOx are limited by the use of a liquid electrolyte due to the leakage problem. Here, we demonstrate solid-state electrochemical redox reaction in SrFeOx using a yttria-stabilized zirconia (YSZ) single-crystal substrate as the solid electrolyte. We fabricated the SrFeO2.5 film on the YSZ substrate and the applied electric current using Au electrodes. The phase gradually changed from SrFeO2.5 to SrFeO2.5+x and SrFeO3−x. The color of the film changed from yellowish-transparent to dark brown. Although the as-grown SrFeO2.5 film showed high resistivity (ρ > 101 Ω cm), the ρ dramatically decreased (∼10−2 Ω cm) with increasing the applied charge density. Simultaneously, the thermopower greatly decreased from ∼+200 to ∼−10 μV K−1. The present results would provide a design concept for future SrFeOx-based solid-state multifunctional memory devices.

ZnO Based Resistive Random Access Memory Device: A Prospective Multifunctional Next-Generation Memory

Numerous works that have demonstrated the study and enhancement of switching properties of ZnO-based RRAM devices are discussed. Several native point defects that have a direct or indirect effect on ZnO are discussed. The use of doping elements, multi-layered structures, suitable bottom and top electrodes, controlling the deposition materials, and the impact of hybrid structure for enhancing the switching dynamics are discussed. The potentials of ZnO-based RRAM for invisible and bendable devices are also covered. ZnO-based RRAM has the potential for possible application in bio-inspired cognitive computational systems. Thus, the synapse capability of ZnO is presented. The sneak-path current issue also besets ZnO-based RRAM crossbar array architecture. Hence, various attempts to subdue the bottleneck have been shown and discussed in this article. Interestingly, ZnO provides not only helpful memory features. However, it demonstrates the ability to be used in nonvolatile multifunctional memory devices. Also, this review covers various issues like the effect of electrodes, interfacial layers, proper switching layers, appropriate fabrication techniques, and proper annealing settings. These may offer a valuable understanding of the study and development of ZnO-based RRAM and should be an avenue for overcoming RRAM challenges.

Multifunctional Polymer Memory via Bi-Interfacial Topography for Pressure Perception Recognition.

Emerging memory devices, that can provide programmable information recording with tunable resistive switching under external stimuli, hold great potential for applications in data storage, logic circuits, and artificial synapses. Realization of multifunctional manipulation within individual memory devices is particularly important in the More‐than‐Moore era, yet remains a challenge. Here, both rewritable and nonerasable memory are demonstrated in a single stimuli‐responsive polymer diode, based on a nanohole‐nanowrinkle bi‐interfacial structure. Such synergic nanostructure is constructed from interfacing a nanowrinkled bottom graphene electrode and top polymer matrix with nanoholes; and it can be easily prepared by spin coating, which is a low‐cost and high‐yield production method. Furthermore, the resulting device, with ternary and low‐power operation under varied external stimuli, can enable both reversible and irreversible biomimetic pressure recognition memories using a device‐to‐system framework. This work offers both a general guideline to fabricate multifunctional memory devices via interfacial nanostructure engineering and a smart information storage basis for future artificial intelligence.

Voltage-Driven Room-Temperature Resistance and Magnetization Switching in Ceramic TiO2/PAA Nanoporous Composite Films.

Voltage control of room-temperature ferromagnetism has remained a big challenge which will greatly influence the multifunctional memory devices. In this paper, porous TiO2 thin films were deposited by dc-reactive magnetron sputtering onto ordered porous anodic alumina (PAA) substrates. Voltage-driving room-temperature resistance and magnetization switching without external magnetic field are simultaneously found in an Ag/TiO2/PAA/Al (Ag/TP/Al) device. Further analysis indicates that the formation/rupture of oxygen vacancy defect-based conductive filaments would be responsible for the changes of resistivity and magnetization. Our present results suggest that the TP nanoporous composite film material may therefore be used to achieve voltage control of magnetism and resistance switching in the future multifunctional memory devices. The Ag/TP/Al devices can also be used for new spintronic devices, neuromorphic operations, and alternative logic circuits and computing.

Structurally modulated dielectric relaxation in rhombohedral Cr2O3 mediated by Mn addition

A simple, energy and time efficient, sol–gel based auto-combustion route was employed to synthesize phase pure nanoparticles of Cr2O3 and MnCr2O4 to study structural, dielectric, impedance and ferroelectric properties. Crystal structure, identified through X-ray diffraction, revealed that Cr2O3 had rhombohedral symmetry (R-3c), while MnCr2O4 possessed cubic spinel symmetry with space group, Fd-3m. Data obtained from X-ray diffraction was further utilized to refine the diffraction patterns using Rietveld’s refinement approach to confirm the structural parameters. Frequency dependent dielectric properties have been investigated systematically in a high frequency range from 20 Hz to 20 MHz. Dielectric constant, loss factor and tangent loss were found to decrease with increase in frequency due to hopping and mainly explained on the basis of Maxwell–Wagner’s model followed by Koop’s theory. Impedance studies helped to define the electro-active regions and Nyquist plot thereby was used to evaluate grain and grain boundary resistance of the synthesized samples. Conductivity behavior followed by the typical Jonscher’s power law was confirmed by calculating the exponent in the expression and thus the hopping mechanism of charge carriers inside these chromites was studied. Ferroelectric analysis showed the potential of the synthesized samples in multifunctional memory devices, used in the miniaturized industry.

Ferroelastically and magnetically co-coupled resistive switching in Nd0.5Sr0.5MnO3/PMN-PT(011) multiferroic heterostructures

The phase separation, i.e., the competition between coexisting multi-phases, can be adjusted by external stimuli, such as magnetic field, electric field, current, light, and strain. Here, a multiferroic heterostructure composed of a charge-ordered Nd0.5Sr0.5MnO3 thin film and a ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystal is fabricated to investigate the lattice strain and magnetic field co-control of phase separation in resistive switching. The stable and nonvolatile resistance tuning is realized at room temperature using the electric-field-induced reversible ferroelastic strain effect, which can be enhanced by 84% under the magnetic field. Moreover, the magnetoresistance can be effectively tuned by the electrically driven ferroelastic strain. These findings reveal that the ferroelastic strain and the magnetic field strongly correlate with each other and are mediated by phase separation. Our work provides an approach to design strain-engineered multifunctional memory devices based on complex oxides by introducing an extra magnetic field stimulus.

Low‐Voltage, Optoelectronic CH3NH3PbI3−xClx Memory with Integrated Sensing and Logic Operations

AbstractNonvolatile optoelectronic memories integrated with the functions of sensing, data storage, and data processing are promising for the potential Internet of things (IoT) applications. To meet the requirements of IoT devices, multifunctional memory devices with low power consumption and secure data storage are highly desirable. This study demonstrates an optoelectronic resistive switching memory integrated with sensing and logic operations by adopting organic–inorganic hybrid CH3NH3PbI3−xClx perovskites, which possess unusual defect physics and excellent light absorption. The CH3NH3PbI3−xClx cell exhibits low operation voltage of 0.1 V with the assistance of light illumination, long‐term retention property, and multiple resistance states. Its unique optoelectronic characteristics enable to perform logic operation for inputting one electrical pulse and one optical signal, and detect the coincidence of electrical and optical signal as well. This design provides possibilities for smart sensor in IoT application.

Valence Change Bipolar Resistive Switching Accompanied With Magnetization Switching in CoFe2O4 Thin Film

Resistive Switching in oxides has offered new opportunities for developing resistive random access memory (ReRAM) devices. Here we demonstrated bipolar Resistive Switching along with magnetization switching of cobalt ferrite (CFO) thin film using Al/CFO/FTO sandwich structure, which makes it a potential candidate for developing future multifunctional memory devices. The device shows good retention characteristic time (>104 seconds) and endurance performance, a good resistance ratio of high resistance state (HRS) and low resistance state (LRS) ~103. Nearly constant resistance values in LRS and HRS confirm the stability and non-volatile nature of the device. The device shows different conduction mechanisms in the HRS and LRS i.e. Schottky, Poole Frenkel and Ohmic. Magnetization of the device is also modulated by applied electric field which has been attributed to the oxygen vacancies formed/annihilated during the voltage sweep and indicates the presence of valence change mechanism (VCM) in our device. It is suggested that push/pull of oxygen ions from oxygen diffusion layer during voltage sweep is responsible for forming/rupture of oxygen vacancies conducting channels, leading to switching between LRS and HRS and for switching in magnetization in CFO thin film. Presence of VCM in our device was confirmed by X-ray Photoelectron Spectroscopy at Al/CFO interface.

Fully Solution‐Processed Transparent Nonvolatile and Volatile Multifunctional Memory Devices from Conductive Polymer and Graphene Oxide

A transparent multifunctional memory array with the configuration of m‐poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS)/graphene oxide (GO)/m‐PEDOT:PSS is fabricated through a full‐solution process. Dimethyl sulfoxide‐doped PEDOT:PSS thin films as the top and bottom electrodes are facilely prepared by spray coating, and a GO film as the active medium layer is obtained by spin coating. The thus‐fabricated device exhibits nonvolatile and volatile multifunctional memory effects, with an ON/OFF current ratio of 104 and 102 for the nonvolatile and volatile modes, respectively. Both the ON and OFF states are stable under the retention test in the nonvolatile memory mode, as well as during the endurance test in the volatile memory mode, demonstrating advantageous features of stable operation, permanent lifetime, excellent reproducibility, and reliable switching endurance. Moreover, the devices also show a 70% transmission of visible light. Their high transparency, combined with the multifunctional property and simple device configuration, makes these devices promising carbon‐based building blocks in a variety of electronic systems such as transparent electronics, electronic labels, radio frequency identification, internal memory, and databases. Most importantly, the simple full‐solution fabrication process is anticipated to potentially afford industrial‐scale low‐cost fabrication of future electronic devices.

Multilevel resistance in ZnO nanowire memristors enabled by hydrogen annealing treatment

In non-volatile memory technology, various attempts to overcome both technology and physical limits have led to development of neuromorphic devices like memristors. Moreover, multilevel resistance and the potential for enhanced memory capability has attracted much attention. Here, we report memristive characteristics and multilevel resistance in a hydrogen annealed ZnO nanowire device. We find that the memristive behavior including negative differential resistance arises from trapped electrons in an amorphous ZnO interfacial layer at the injection electrode that is formed following hydrogen annealing. Furthermore, we demonstrate that it is possible to control electrons trapping and detrapping by the controlled application of voltage pulses to establish a multilevel memory. These results could pave the way for multifunctional memory device technology such as the artificial neuromorphic system.

Light regulated I–V hysteresis loop of Ag/BiFeO3/FTO thin film

A hysteresis loop of current–voltage characteristics based multiferroic BiFeO3 nanoribbons memory device is observed. Moreover, the white-light can greatly regulate both the current–voltage hysteresis loop and the ferroelectric hysteresis loop. The stored space charges within the electrodes/BiFeO3 interface can lead to hysteresis-type I–V characteristics of Ag/BiFeO3/FTO devices. The white-light controlled I–V loop and ferroelectric loop result from photon-generated carries. Since the I–V hysteresis loop and ferroelectric hysteresis loop have a potential application prospect to the memory devices, these two white-light controlled the hysteresis loops curves are likely to provide promising opportunity for developing the multi-functional memory devices.

Polarization-induced resistive switching behaviors in complex oxide heterostructures

Complex oxide heterostructures are fabricated by growing La0.67Ca0.33MnO3 films on ferroelectric 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (011) single-crystal substrates. The nonvolatile or pulsed resistive switching behaviors induced by an electric field are achieved simultaneously. Further analyses indicate that the different resistive switching behaviors are resulted from co-control of piezostrain and polarization current effects. With decreasing in-plane read current from 0.1 mA to 0.001 mA, the polarization current effect gradually begins to play a more important role than the piezostrain effect. Consequently, the nonvolatile resistive switching behavior is converted to pulse resistive switching behavior. The results further enhance the application of complex oxides in multifunctional memory devices.

Electric field modification of magnetism in Au/La2/3Ba1/3MnO3/Pt device.

The La2/3Ba1/3MnO3 film is deposited in a CMOS-compatible Pt/Ti/SiO2/Si substrate with the oxygen pressure of 10 Pa for investigating magnetoelectric effect. Bipolar resistive switching effect with excellent endurance and retention is observed in this Au/La2/3Ba1/3MnO3/Pt device. Through this effect, a significant nonvolatile change of magnetization is obtained in this device as well. The change of magnetization can be understood by the break and repair of the -Mn3+-O2−-Mn4+- chains induced by the electric field through the oxygen vacancies migration. The resistance and magnetization of the Au/La2/3Ba1/3MnO3/Pt device can be simultaneously manipulated by the electric field, which makes it to be a promising candidate for the multifunctional memory devices.

Electric field manipulation of nonvolatile magnetization in Au/NiO/Pt heterostructure with resistive switching effect

The electrical field manipulation of magnetization is investigated in an Au/NiO/Pt heterostructure, which is fully compatible with the standard complementary metal-oxide semiconductor process. Reversible and stable unipolar resistive switching effects as well as a significant nonvolatile change of the magnetization are observed in this device during the set and reset processes at room temperature. Further analysis indicates that the formation and rupture of metallic Ni conducting filaments caused by the electric field would be responsible for the changes of resistivity and magnetization. The coexistence of the electric field control of magnetization change and resistive switching makes Au/NiO/Pt heterostructure a promising candidate for the multifunctional memory devices.