Nonvolatile Memory Applications Research Articles

TCAD simulation study of dual ferroelectric gate field-effect transistors with a recessed channel geometry for non-volatile memory applications

TCAD simulation study of dual ferroelectric gate field-effect transistors with a recessed channel geometry for non-volatile memory applications

Evidence for reversible oxygen ion movement during electrical pulsing: enabler of emerging ferroelectricity in binary oxides

Ferroelectric HfO2-based materials and devices show promising potential for applications in information technology but face challenges with inadequate electrostatic control, degraded reliability, and serious variation in effective oxide thickness scaling. We demonstrate a novel interface-type switching strategy to realize ferroelectric characteristics in atomic-scale amorphous binary oxide films, which are formed in oxygen-deficient conditions by atomic layer deposition at low temperatures. This approach can avoid the shortcomings of reliability degradation and gate leakage increment in scaling polycrystalline doped HfO2-based films. Using theoretical modeling and experimental characterization, we show the following. (1) Emerging ferroelectricity exists in ultrathin oxide systems as a result of microscopic ion migration during the switching process. (2) These ferroelectric binary oxide films are governed by an interface-limited switching mechanism, which can be attributed to oxygen vacancy migration and surface defects related to electron (de)trapping. (3) Transistors featuring ultrathin amorphous dielectrics, used for non-volatile memory applications with an operating voltage reduced to ±1 V, have also been experimentally demonstrated. These findings suggest that this strategy is a promising approach to realizing next-generation complementary metal-oxide semiconductors with scalable ferroelectric materials.

Symmetry Engineering of Epitaxial Hf0.5Zr0.5O2 Ultrathin Films.

Robust ferroelectricity in HfO2-based ultrathin films has the potential to revolutionize nonvolatile memory applications in nanoscale electronic devices because of their compatibility with the existing Si technology. However, to fully exploit the potential of ferroelectric HfO2-based thin films, it is crucial to develop strategies for the controlled stabilization of various HfO2-based polymorphs in nanoscale heterostructures. This study demonstrates how substrate-orientation-induced anisotropic strain can engineer the crystal symmetry, structural domain morphology, and growth orientation of ultrathin Hf0.5Zr0.5O2 (HZO) films. Epitaxial ultrathin HZO films were grown on the heterostructures of (001)- and (110)-oriented La2/3Sr1/3MnO3/SrTiO3 (LSMO/STO) substrate. Various structural analyses revealed that the (110)-oriented substrate promotes a higher degree of structural order (crystallinity) with improved stability of the (111)-oriented orthorhombic phase (Pca21) of HZO. Conversely, the (001)-oriented substrate not only induces a distorted orthorhombic structure but also facilitates the partial stabilization of nonpolar phases. Electrical measurements revealed robust ferroelectric properties in epitaxial thin films without any wake-up effect, where the well-ordered crystal symmetry stabilized by STO(110) facilitated better ferroelectric characteristics. This study suggests that tuning the epitaxial growth of ferroelectric HZO through substrate orientation can improve the stability of the metastable ferroelectric orthorhombic phase and thereby offer a better understanding of device applications.

Multilevel resistive switching in hydrothermally synthesized FeWO4 thin film-based memristive device for non-volatile memory application

The memristors offer significant advantages as a key element in non-volatile and brain-inspired neuromorphic systems because of their salient features such as remarkable endurance, ability to store multiple bits, fast operation speed, and extremely low energy usage. This work reports the resistive switching (RS) characteristics of the hydrothermally synthesized iron tungstate (FeWO4) based thin film memristive device. The detailed physicochemical analysis was investigated using Rietveld’s refinement, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM) techniques. The fabricated Ag/FWO/FTO memristive device exhibits bipolar resistive switching (BRS) behavior. In addition, the devices exhibit negative differential resistance (NDR) at both positive and negative bias. The charge-flux relation portrayed the non-ideal or memristive nature of the devices. The reliability in the RS process was analyzed in detail using Weibull distribution and time series analysis techniques. The device exhibits stable and multilevel endurance and retention characteristics which demonstrates the suitability of the device for the high-density non-volatile memory application. The current conduction of the device was dominated by Ohmic and trap controlled-space charge limited current (TC-SCLC) mechanisms and filamentary RS process responsible for the BRS in the device. In a nutshell, the present investigations reveal the potential use of the iron tungstate for the fabrication of memristive devices for the non-volatile memory application.

Modified Donor End Caps for Binary-to-Ternary WORM Memory Conversion in N-Heteroaromatic Systems.

A series of novel D-π-A type organic small molecules have been designed, synthesized, and demonstrated for non-volatile resistive switching WORM memory application. The electron-deficient phenazine and quinoxaline units were coupled with various functionalized triphenylamine end caps to explore the structure-property correlations. The photophysical investigations displayed considerable intramolecular charge transfer, and the electrochemical analysis revealed an optimum band gap of 2.44 to 2.83 eV. These factors and the thin film morphological studies suggest the feasibility of the compounds as better resistive memory devices. All the compounds indicated potent non-volatile resistive switching memory capabilities with ON/OFF ratios ranging from 103 to 104, and the lowest threshold voltage recorded stands at -0.74 V. A longer retention time of 103 s marks the substantial stability of the devices. The phenazine-based compounds outperformed the others in terms of memory performance. Exceptionally, the compound with -CHO substituted triphenylamine exhibited ternary memory performance owing to its multiple traps. The resistive switching mechanism for the devices was validated using density functional theory calculations, which revealed that the integrated effect of charge transfer and charge trapping contributes significantly to the resistive switching phenomena.

Magnetite–Polyaniline Nanocomposite for Non-Volatile Memory and Neuromorphic Computing Applications

Magnetite–Polyaniline Nanocomposite for Non-Volatile Memory and Neuromorphic Computing Applications

Ferroelastically protected reversible orthorhombic to monoclinic-like phase transition in ZrO2 nanocrystals.

Robust ferroelectricity in nanoscale fluorite oxide-based thin films enables promising applications in silicon-compatible non-volatile memories and logic devices. However, the polar orthorhombic (O) phase of fluorite oxides is a metastable phase that is prone to transforming into the ground-state non-polar monoclinic (M) phase, leading to macroscopic ferroelectric degradation. Here we investigate the reversibility of the O-M phase transition in ZrO2 nanocrystals via in situ visualization of the martensitic transformation at the atomic scale. We reveal that the reversible shear deformation pathway from the O phase to the monoclinic-like (M') state, a compressive-strained M phase, is protected by 90° ferroelectric-ferroelastic switching. Nevertheless, as the M' state gradually accumulates localized strain, a critical tensile strain can pin the ferroelastic domain, resulting in an irreversible M'-M strain relaxation and the loss of ferroelectricity. These findings demonstrate the key role of ferroelastic switching in the reversibility of phase transition and also provide a tensile-strain threshold for stabilizing the metastable ferroelectric phase in fluorite oxide thin films.

Fluorite-structured antiferroelectric hafnium-zirconium oxide for emerging nonvolatile memory and neuromorphic-computing applications

The rapid progress of the internet of things, cloud computing, and artificial intelligence has increased demand for high-performance computing. This demand has led to a focused exploration of novel nonvolatile memory (NVM) and brain-inspired neuromorphic-computing electronics, with research efforts directed at identifying materials compatible with complementary metal-oxide-semiconductor technology. Exploring fluorite-structured hafnium-zirconium oxide (HZO) mixed oxides has revealed promising ferroelectric (FE) and memristor characteristics, suggesting potential applications in emerging technologies. However, certain intrinsic properties of HZO-based FEs, such as high coercive fields (Ec) and polarization metastability, may pose challenges for commercial viability. Recent investigations of fluorite-structured HZO-based antiferroelectrics (AFEs) have highlighted their advantages, including lower energetic barriers, higher switching speeds, and a uniform phase distribution. These inherent benefits position fluorite-structured HZO-based AFEs as potential candidates within the NVM landscape. Furthermore, the accumulated polarization and spontaneous depolarization characteristics of fluorite-structured HZO-based AFEs make them worthy of potential integration into neuromorphic-computing because they resemble certain aspects of neuron behavior. Despite these positive aspects, a more thorough exploration and consideration are needed to address existing challenges. This review aims to present fluorite-structured HZO-based AFE materials and highlight the current challenges, possible applications, and future opportunities and can act as an update for recent developments in these intriguing materials and provide guidance for future researchers in the optimization and design of HZO-based AFE materials and devices for emerging NVM and neuromorphic-computing applications.

Exploring bipolar resistive switching behavior of sprayed BaTiO3 thin films for nonvolatile memory application

The memristive properties of barium titanate (BT) thin films deposited by cost-effective spray pyrolysis technique are explored. The device was configured as Ag/BT/FTO. The electrical measurements unveiled robust bipolar resistive switching (BRS) characteristics in the devices with memory window ∼35. This behavior, attributed to intrinsic defects within BaTiO3, demonstrated the potential of these films for applications in advanced electronic devices like Resistive-Random Access Memory (RRAM). The observed phenomenon arises from the generation of polarized areas within the material, responsive to an applied electric field. Specifically focusing on the memristive aspects, this study indicated promising non-volatile memory performance. All devices undergo the SET process between 0.9 and 1.7 V, and the RESET process takes place between −1.3 to −1.9 V. According to the statistical distribution of SET and RESET voltages, the coefficient of variation (CV) for all devices is less than 18 %. The Ag/BT/FTO memristive device exhibited endurance through 103 cycles of switching, attesting to its reliability. Moreover, the device displayed the capability to maintain stored data for 104 seconds. This establishes the suitability of spray-deposited BaTiO3 thin films for memory-based applications.

Structural and resistive properties of Pt/BiFeO3/La0.5Sr0.5CoO3 heterostructure for storage application

BiFeO3 has promissing application in non-volatile ferroelectric memory, but the dominant mechanism has not been unified. Here, Pt/BiFeO3 (100 nm)/La0.5Sr0.5CoO3 (Pt/BFO/LSCO) heterostructures have been fabricated on (001) SrTiO3 (STO) single crystal substrates by off-axis magnetron sputtering. Both XRD and TEM analyses confirm that the (001) oriented BFO/LSCO heterostructures have been epitaxially grown on STO. In addition, XRD, TEM along with XPS analyses further indicate that the BFO film (001) presents epitaxial perovskite structure. On the basis of electric field regulation of Pt/BFO and BFO/LSCO interface barrier, the switching interface state is controlled by charge filling and trapping in interface potential well, which is responsible for I-V resistance and G-V hysteretic curve. Based on the fitting results of the conduction mechanism of I-V characteristic curve, it proves that the space charges limiting current play a dominant role, and the filling and trapping of interface traps are considered as the main resistance mechanisms. Moreover, ultraviolet irradiation can modulate the I-V resistance curve but does not change its conduction mechanism. This work provides experimental data for the practical application of integrated BFO resistive memories.

Resistive switching memory using buckybowl sumanene-inserted bilayer graphene

The bowl-shaped molecules of the nanocarbon material called sumanene have structural flexibility (bowl inversion). In the case of the sumanene molecule used as an intercalant between graphene layers, it has been predicted that holes and electrons are unevenly distributed according to the bowl inversion. Using the property of sumanene molecules, we expected that resistive switching for the nonvolatile memory applications could be achieved by the sumanene-inserted bilayer graphene. In this study, metal–insulator–metal devices with sumanene-inserted bilayer graphene are fabricated. As a result, it is observed that the resistance of the sumanene-inserted bilayer graphene changes by applying voltage, demonstrating resistive switching characteristics. This result implies the possibility of realizing a novel ultra-thin resistive memory device using nanocarbon technologies.

Non-volatile memory characteristics of flexible ferroelectric field-effect transistors consisting of Sm-doped BiFeO3 thin films

This study investigates the impact of Sm doping on the structural, electrical, and functional properties of BiFeO3 (BFO) thin films. The aim is to improve their non-volatile memory characteristics for use in flexible ferroelectric field-effect transistors (FeFETs). We fabricated Sm-doped BFO (SBFO) thin films on flexible mica substrates with Sm concentrations ranging from 0 to 15 %. The FeFET device structures, which include MoS2 monolayer channels and SBFO thin films with Pt bottom electrodes, were analyzed. The SBFO thin films displayed a (111) preferential orientation due to the influence of underlying Pt electrodes. Notably, the SBFO thin film doped with a 10 % Sm concentration showed optimal enhancements, including a reduction in leakage current density and an increase in remanent polarization to 55.8 μC/cm2, compared to undoped thin film (35.5 μC/cm2). Furthermore, the thin film exhibited superior fatigue resistance for up to 1012 switching cycles and maintained stable values under significant bending stress for ferroelectric polarizations. On the other hand, SBFO thin film with 15 % Sm doping displayed relaxor antiferroelectric behavior, highlighting the importance of doping concentration. Therefore, for non-volatile memory application reliability, the FeFET device featuring a 10 % Sm-doped SBFO thin film not only enhanced the memory window but also showed superior fatigue characteristics over 1012 switching cycles, compared to its undoped counterpart. These findings demonstrate the effect of Sm doping in customizing the properties of BFO thin films for advanced, flexible non-volatile memory devices, offering a novel insight to optimize ferroelectric field-effect transistor performance.

Modulating resistive switching in Ni0.5Zn0.5Fe2O4 memristors: The role of manganese doping concentrations

Memristors, recognized as key devices for mitigating the von Neumann bottleneck, show great potential in non-volatile memory technology. Their performance is fundamentally linked to the chemical composition and structural characteristics of their intermediate dielectric layer. Owing to the inherent advantages of metal oxides, such as their simplistic chemical makeup and superior thermal stability, memristors featuring a Metal-Insulator-Metal (MIM) sandwich structure with metal oxides as the intermediate layer have received extensive focus. In this study, a Pt/Ni0.5Zn0.5MnxFe2-xO4(NZMFO)/Pt composite film was prepared, and its resistance switching behavior was modulated by altering the doping concentration of Mnn+ in NZMFO. The experimental results indicate that altering the Mnn+ doping concentration does significantly impact the content of oxygen vacancies. As the concentration of Mnn+ increases from 0.10 to 0.20 at.%, the content of oxygen vacancies correspondingly rises from 46.58 % to 76.42 %. Concurrently, variations in Mnn+ doping concentration significantly alter the resistance switching properties of the Pt/NZMFO/Pt composite films. This includes elevating the set/reset voltage, diminishing the resistance ratio, and enhancing the durability with the augmentation of Mnn+ concentration. By meticulously adjusting the Mnn+ doping concentration, we can achieve a memristor characterized by superior performance across all metrics. Considering all performance aspects, this study determined that the Pt/NZMFO/Pt thin film memristor with x = 0.15 exhibits adequate endurance (100 cycles), high data retention, and stable set/reset voltage. This work underscores the critical role of Mnn+ doping concentration in optimizing the electrochemical properties of NZFO memristors, illustrating a strategic pathway to engineer memristive devices with enhanced performance for future non-volatile memory applications.

Penggabungan Ti<sub>3</sub>C<sub>2</sub>T<sub>x</sub> dalam Matriks Poli (Metil Metakrilat) untuk Aplikasi Memori Tidak Meruap

MXenes, with their unique surface properties and 2D structure, have demonstrated promising potential in electronic devices, particularly in memory storage. This study explored the potential of 2D Ti<sub>3</sub>C<sub>2</sub>T<sub>x</sub> for the nonvolatile memory (NVM) application. The simple solution process routes were used to fabricate the two-terminal bistable switching devices. The silver nanowires/nanocomposite/ITO structure was deposited on a glass substrate using spin coating and spray coating techniques. The Ti<sub>3</sub>C<sub>2</sub>T<sub>x</sub> MXene flakes were incorporated into a poly(methyl methacrylate) (PMMA) polymer host to form the nanocomposite and act as a charge-trapping layer. Meanwhile, PMMA acts as a dielectric layer. The measured current-voltage data showed a bistable current behavior with the presence of a memory window. The fabricated NVM memory devices were reprogrammable when the endurance test was performed and stable up to 1×104 s cycles with a distinct ON/OFF ratio of 103. The conduction mechanisms were identified using the curve-fitting method with double log plots of current-voltage (I-V) data. Based on the obtained I-V characteristics, various conduction mechanisms, especially Schottky and Poole-Frenkel emission, trapped charge limiting current, and space charge limited current, were proposed to be responsible for the bistable switching behavior. Thus, the results of this study provide an experimental basis for using MXene in non-volatile memory applications.

Tailoring of charge carriers with deposition temperature in pulsed laser deposited BiFeO3 thin films

This research investigates the structural, topological, electrical and optical properties of pulsed laser deposited polycrystalline BiFeO3 thin films on silicon and glass substrate at varying deposition temperatures ranging from 400 °C to 700 °C. X-ray diffraction confirm rhombohedral phase and X-ray photoelectron spectroscopy reveals stoichiometric BiFeO3 films. The optical bandgap of thin films obtained from absorption spectra increases with the substrate temperature. Photoluminescence emission spectrum reveals the defects and Atomic Force Microscopy analysis bring out the surface topography and crystallinity improvement with temperature. The charge transport studies reveal a transition in conductivity from n-type at lower deposition temperature to p-type at higher deposition temperature, attributed to oxygen and bismuth vacancies respectively. The intricate understanding of conductivity tuning and the leaky nature of BiFeO3 thin film opens avenues for applications in non-volatile memories, particularly neuromorphic devices.

Enhancing ferroelectric performance in hafnia-based MFIS capacitor through interface passivation and bulk doping

In recent times, there has been a notable surge of interests in hafnia (HfO2)-based ferroelectrics, primarily due to their remarkable ferroelectric properties employed in ultra-thin configurations, alongside their compatibility with the conventional CMOS manufacturing process. In order to harness the full potential of HfO2-based films for high-performance non-volatile memory applications, it is imperative to enhance their ferroelectric characteristics and durability. This study introduces a straightforward approach aimed at augmenting the ferroelectric performance of Hf x Zr1−x O2 (HZO) films deposited on silicon (Si) substrates through the engineering of oxygen vacancies (V O). The results of this endeavor demonstrate a significant enhancement in ferroelectric performance, characterized by a 2Pr value of 47 μC cm−2 and impressive endurance, enduring up to 108 cycles under an 8 MV cm−1 electric field without the need of a wake-up process. This marked improvement can be attributed to a dual-pronged approach, involving the incorporation of an Al2O3 interlayer and the introduction of Al atoms into the HZO film. The Al2O3 interlayer primarily serves to mitigate the presence of oxygen vacancies at the interface, while the introduction of Al dopants elevates the concentration of oxygen vacancies within the bulk material. This modulation of oxygen vacancy concentration proves instrumental in facilitating the formation of a ferroelectric o-III phase within the HZO-based films, thereby further augmenting their ferroelectric performance. This innovative and effective strategy offers an alternative avenue for enhancing the ferroelectric properties of materials characterized by a fluorite crystal structure.

Multifunctionality in Electrically Poled PMN–PT/Ni–Mn–In Multiferroic Heterostructure for Flexible Magnetic Field Sensing and Nonvolatile Memory Applications

Multifunctionality in Electrically Poled PMN–PT/Ni–Mn–In Multiferroic Heterostructure for Flexible Magnetic Field Sensing and Nonvolatile Memory Applications

Ferroelectric polarization and conductance filament coupling for large window and high-reliability resistive memory and energy-efficient synaptic devices

Ferroelectric capacitors hold great promise for non-volatile memory applications. However, the challenge lies in fabricating resistive switching devices with a high on/off ratio, excellent non-volatility, and a simple manufacturing process. Here, a novel approach is introduced by demonstrating the efficacy of the coupling effect between ferroelectric polarization and oxygen vacancy-based conductive filaments in Hf0.5Zr0.5O2 (HZO) films for the creation of non-volatile resistive switching memory devices, achieving an impressive on/off ratio of 6.8 × 103 at +1.8 V. An in-depth exploration of the resistive switching mechanism is provided and subsequently the outstanding durability and retention characteristics of these devices for resistive switching is validated. Furthermore, the device’s capacity to emulate non-volatile synaptic functionalities is assessed. Our results reveal that under pulsed conditions of 1 V/–2 V with 1 µs pulses spaced 50 ms apart, the device can robustly achieve potentiation/depression synaptic plasticity, while exhibiting energy consumption (0.16 fJ for potentiation, 0.12 fJ for depression) reduced by 1–2 orders of magnitude compared to biological synapses. This work holds significant value as a reference for the fabrication of energy-efficient, non-volatile memory and synaptic devices.

Bistable magnetic nanowires: A new approach to non-volatile memory with single readout and automatic deletion

A novel approach for a non-volatile destructive readout memory application using bistable magnetic nanowire arrays is presented. The encoded information is stored as binary 1 and 0 by groups of NWs magnetized in the positive and negative states, respectively. We leverage the naturally occurring switching field distribution of the NW array and a tailored alternating decreasing magnetic field to program remanent magnetic states. To retrieve the information, the measured remagnetization curve exhibits a star-like behavior with jumps and plateaus and its derivative converts this information to a binary-type format. Two encoding and readout schemes are proposed and validated: binary bits and barcodes. For each case, the implementation and optimization procedures are illustrated, along with the required processing to obtain a useful readout signal. This strategy holds potential for non-volatile memory applications in which the stored information is erased during reading and can be reused indefinitely.Graphical abstract

2D Ferroic Materials for Nonvolatile Memory Applications.

The emerging nonvolatile memory technologies based on ferroic materials are promising for producing high-speed, low-power, and high-density memory in the field ofintegrated circuits. Long-range ferroic orders observed in 2D materials have triggered extensive research interest in 2D magnets, 2D ferroelectrics, 2D multiferroics, and their device applications. Devices based on 2D ferroic materials and heterostructures with an atomically smooth interface and ultrathin thickness have exhibited impressive properties and significant potential for developing advanced nonvolatile memory. In this context, a systematic review of emergent 2D ferroic materials is conducted here, emphasizing their recent research on nonvolatile memory applications, with a view to proposing brighter prospects for 2D magnetic materials, 2D ferroelectric materials, 2D multiferroic materials, and their relevant devices.