Next-generation Memory Devices Research Articles

Tunneling magnetoresistance effect with controlled spin polarization based on Mn3ZnN

Due to their groundbreaking advantages, antiferromagnetics offer superior prospects for next-generation memory devices. However, detecting their Néel vector poses great challenges. Mn3ZnN, an antiperovskite antiferromagnetic, breaks TPτ and Uτ symmetries, exhibiting k -resolved spin polarization at the Fermi surface. It is ideal for generation of the tunneling magnetoresistance (TMR) effect by electrodes, which hinges on electrode–barrier compatibility. Testing various insulators, we obtained 2000% TMR effects in Mn3ZnN/SrTiO3/Mn3ZnN. Additionally, the application of 2% biaxial stress increased the spin polarization to 35.24% in Mn3ZnN, hinting at the potential for higher TMR. These findings provide valuable insights for experimental and industrial developments in the field of spintronics.

Thickness dependent tribological and magnetic behavior of two-dimensional cobalt telluride (CoTe2)

Two-dimensional (2D) layered transition-metal based tellurides (chalcogens) are known to harness their surface atoms’ characteristics to enhance topographical activities for energy conversion, storage, and magnetic applications. The gradual stacking of each sheet alters the surface atoms’ subtle features such as lattice expansion, leading to several phenomena and rendering tunable properties. Here, we have evaluated thickness-dependent mechanical properties (nanoscale mechanics, tribology, potential surface distributions, interfacial interaction) of 2D CoTe2 sheets and magnetic behavior using surface probe techniques. The experimental observations are further supported and explained with theoretical investigations: density functional theory and molecular dynamics. The variation in properties observed in theoretical investigations unleashes the crucial role of crystal planes of the CoTe2. The presented results are beneficial in expanding the use of the 2D telluride family in flexible electronics, piezo sensors, tribo-generators, and next-generation memory devices.

Mutual control of electric and magnetic orders near room temperature in Al doped Y-type hexaferrite single crystals

Realizing robust magnetoelectric (ME) coupling effect near room temperature is still a long-standing challenge for the application of multiferroic materials in next-generation low-power spintronic and memory devices. Here we report a systematic study on the magnetic, dielectric, and ME coupling properties of Y-type hexaferrite Ba0.5Sr1.5Co2Fe12–xAlxO22 (x = 0.0, 0.5, 1.0) single crystals. The Al doping can induce the shifting of the alternating longitudinal conical (ALC)-proper screw (PS) magnetic phase transition temperature from 200 K for x = 0.0 to 365 K for x = 1.0. The most interesting feature is that the Ba0.5Sr1.5Co2Fe11AlO22 single crystal displays a direct and converse ME coupling coefficient with ∼ 3,100 ps/m and ∼ 3,900 ps/m at 250 K, respectively, due to the Al-doped enhanced stability of ALC phase. Moreover, the exchange bias also verifies the strong coupling of electric and magnetic orders. These results provide a valuable insight on the modulation of ALC structure and the mechanism of ME effect in Y-type hexaferrites.

Nanoscale-doped dual-channel for improved performance and reliability of Hf: IGTO / a-IGTO thin film transistor

Amorphous oxide semiconductors are widely used in the backplane thin film transistors (TFTs) of displays and are extensively researched as materials for next-generation memory devices. However, they face reliability degradation due to stress factors such as thermal, bias, and light exposure. To mitigate these issues, extensive research is focused on improvements, including doping, enhancing crystallinity, and applying pre-and post-treatments. This study investigates the significantly improved reliability and electrical properties of amorphous indium gallium tin oxide (a-IGTO) TFTs by adopting a dual-channel configuration through simultaneous co-sputtering of HfO2 and IGTO targets. The device fabrication involved co-sputtering HfO2 and IGTO at the gate oxide interface, followed by depositing an IGTO-only layer, rather than doping the entire channel material. The effect of varying Hf concentration was evaluated by applying different HfO2 sputtering powers. Optimal hafnium doping reduced the threshold voltage of the a-IGTO TFT from −0.85V to 0.15V compared to the pristine a-IGTO TFT, while enhancing the field-effect mobility (μFE). Furthermore, the Hf-doped device exhibited improved stability, with a reduced threshold voltage shift (ΔVth) under positive (+15 V) and negative(-15 V) bias stress at 3000s, decreasing from 11.5 V to 4.8 V, and 4.7 V–1.1 V, respectively. This study proposes a novel device fabrication method to enhance the reliability of amorphous oxide semiconductor, addressing their inherent stress-related issues.

Approach to Low Contact Resistance Formation on Buried Interface in Oxide Thin-Film Transistors: Utilization of Palladium-Mediated Hydrogen Pathway.

Amorphous oxide semiconductors (AOSs) with low off-currents and processing temperatures offer promising alternative materials for next-generation high-density memory devices. The complex vertical stacking process of memory devices significantly increases the probability of encountering internal contact issues. Conventional surface treatment methods developed for planar devices necessitate efficient approaches to eliminate contact issues at deep internal interfaces in the nanoscale complex structures of AOS devices. In this work, we report the pioneering use of palladium thin film as a high-efficiency active hydrogen transfer pathway from the outside to the internal contact interface via low-temperature postannealing in the H2 atmosphere, and the formation of highly conductive metallic interlayer effectively solves the contact issues at the deeply buried interfaces in devices. The application of this method reduced the contact resistance of Pd electrodes/amorphous indium-gallium-zinc oxide (a-IGZO) thin-film by 2 orders of magnitude, and thereby the mobility of thin-film transistor was increased from 3.2 cm2 V-1 s-1 to nearly 20 cm2 V-1 s-1, preserving an excellent bias stress stability. This technology has wide applicability for the solution of contact resistance issues in oxide semiconductor devices with complex architectures.

Electron-Assisted Generation and Straight Movement of Skyrmion Bubble in Kagome TbMn6Sn6.

Topological magnetic textures are promising candidates as binary data units for the next-generation memory device. The precise generation and convenient control of nontrivial spin topology at zero field near room temperature endows the critical advantages in skyrmionic devices but is not simultaneously integrated into one material. Here, in the Kagome plane of quantum TbMn6Sn6, the expedient generation of the skyrmion bubbles in versatile forms of lattice, chain, and isolated one by converging the electron beam, where the electron intensity gradient contributes to the dynamic generation from local anisotropy variation near spin reorientation transition (SRT) is reported. Encouragingly, by utilizing the dynamic shift of the SRT domain interface, the straight movement is actualized with the skyrmion bubble slave to the SRT domain interface forming an elastic composite object, avoiding the usual deflection from the skyrmion Hall effect. The critical contribution of the SRT domain interface via conveniently electron-assisted heating is further theoretically validated in micromagnetic simulation, highlighting the compatible application possibility in advanced devices.

In Situ Unveiling of the Resistive Switching Mechanism of Halide Perovskite-Based Memristors.

The organic-inorganic halide perovskite has become one of the most promising candidates for next-generation memory devices, i.e. memristors, with excellent performance and solution-processable preparation. Yet, the mechanism of resistive switching in perovskite-based memristors remains ambiguous due to a lack of in situ visualized characterization methods. Here, we directly observe the switching process of perovskite memristors with in situ photoluminescence (PL) imaging microscopy under an external electric field. Furthermore, the corresponding element composition of conductive filaments (CFs) is studied, indicating that the metallic CFs with respect to the activity of the top electrode are essential for device performance. Finally, electrochemical impedance spectroscopy (EIS) is conducted to reveal that the transition of ion states is associated with the formation of metallic CFs. This study provides in-depth insights into the switching mechanism of perovskite memristors, paving a pathway to develop and optimize high-performance perovskite memristors for large-scale applications.

Logic-in-memory application of silicon nanotube-based FBFET with core-source architecture

The performance of a silicon nanotube-based feedback field-effect transistor (SiNT FBFET) with a core-source architecture has been explored in this work for the use in logic-in-memory (LIM) applications. Both n-channel and p-channel FETs with extremely symmetric transfer characteristics and a high ON/OFF current ratio of 109 are implemented in a single structure using the core and outer gates. SiNT FBFET exhibits significant data retention attributes during memory operations for up to 103 s. The SiNT FBFET-based inverter circuit retains output logic states of “1” and “0” for 1.705 s and 1.948 s, respectively, at megahertz operating frequency without standby power consumption. Additionally, SiNT FBFET has also been used to build ternary NAND/NOR logic gates with memory functionality. Numerical mixed-mode simulations of the circuits have been carried out using the commercially available Synopsys “Sentaurus” TCAD tool for examining the performance and memory characteristics of SiNT FBFETs. This study demonstrates the possible use of SiNT FBFET in multivalued logic systems and the development of next-generation memory devices.

Emerging optoelectronic artificial synapses and memristors based on low-dimensional nanomaterials

The Von Neumann architecture has been the foundation of modern computing systems. Still, its limitations in processing large amounts of data and parallel processing have become more apparent as computing requirements increase. Neuromorphic computing, inspired by the architecture of the human brain, has emerged as a promising solution for developing next-generation computing and memory devices with unprecedented computational power and significantly lower energy consumption. In particular, the development of optoelectronic artificial synaptic devices has made significant progress toward emulating the functionality of biological synapses in the brain. Among them, the potential to mimic the function of the biological eye also paves the way for advancements in robot vision and artificial intelligence. This review focuses on the emerging field of optoelectronic artificial synapses and memristors based on low-dimensional nanomaterials. The unique photoelectric properties of these materials make them ideal for use in neuromorphic and optoelectronic storage devices, with advantages including high carrier mobility, size-tunable optical properties, and low resistor–capacitor circuit delay. The working mechanisms, device structure designs, and applications of these devices are also summarized to achieve truly sense-storage-computer integrated optoelectronic artificial synapses.

Imaging of voltage-controlled switching of magnetization in highly magnetostrictive epitaxial Fe-Ga microstructures.

The magnetoelectric behavior of epitaxial Fe-Ga microstructures on top of a (001)-oriented PMN-PT piezoelectric substrate is imaged with magnetic X-ray microscopy. Additionally, the micron-scale strain distribution in PMN-PT is characterized by X-ray microdiffraction and examined with respect to the results of the Fe-Ga magnetoelectric switching. The magnetic reorientation of Fe-Ga is found to be strongly correlated with size, shape, and crystallographic orientation of the microstructures. In the case of square-shaped structures, size dictates the influence of the strain distribution on both the initialization of the ground state and on the magnetic reorientation during application of voltage. On the other hand, elliptical microstructures demonstrate completely different magnetic responses depending on the relative orientation of their long axis with respect to the crystallographic directions of the PMN-PT. This study demonstrates that engineering the behavior of highly magnetostrictive epitaxial microdevices is possible. It further elucidates that voltage-induced actuation can be largely tuned to achieve the desired type of magnetic switching ranging from vortex circulation reversal, domain wall motion, to a large rotation of magnetization. Because of the outstanding properties of the investigated material system, the reported findings are expected to be of great interest for the realization of next-generation energy-efficient magnetic memory and logic devices.

Sn–3Ag–0.5Cu/TiO2/Ti wire-tube structure with memristive response by ultrasonic soldering

High-performance memristors have become the next generation of memory devices with potential application to ultra-high-speed, large-capacity, high-density computing requirements. However, devices with low operating voltage, high switching ratio, and long cycle life have not yet been achieved. A novel Sn–3Ag–0.5Cu/TiO2/Ti wire-tube memristor was fabricated using ultrasonic soldering. Ultrasound application changes the wetting conditions of the filler by using the instantaneous high temperature and pressure generated by ultrasonic cavitation, which induces Sn–3Ag–0.5Cu filler metal into anodized TiO2 nanotubes to prepare a wire-tube structure. The Sn–3Ag–0.5Cu/TiO2/Ti device showed bipolar hysteresis with a clear storage window. The maximum switching ratio was 33, which is slightly lower than the value of 36 for a Ag/TiO2/Ti device made using a conventional anodizing method. Seventeen cycles were achieved, which is 143% higher that of the Ag/TiO2/Ti device. The operating voltage of the Cu–3Ag–0.5Cu/TiO2/Ti device was significantly lower than that of the Ag/TiO2/Ti device. The structure and electrochemical performance of the device was evaluated by Raman spectrometry (LAMAN), X-ray photoelectron spectroscopy (XPS) and Electrochemical impendence spectroscopy (EIS) analysis. Formation of the conductive channels of the TiO2 wire-tube structure memristor was studied using transmission electron microscopy and high-resolution transmission electron microscopy, and a model of the mechanism of formation of the conductive filaments was established.

Tunable Spin-Polarized States in Graphene on a Ferrimagnetic Oxide Insulator.

Spin-polarized two-dimensional (2D) materials with large and tunable spin-splitting energy promise the field of 2D spintronics. While graphene has been a canonical 2D material, its spin properties and tunability are limited. Here, this work demonstrates the emergence of robust spin-polarization in graphene with large and tunable spin-splitting energy of up to 132 meV at zero applied magnetic fields. The spin polarization is induced through a magnetic exchange interaction between graphene and the underlying ferrimagnetic oxide insulating layer, Tm3 Fe5 O12 , as confirmed by its X-ray magnetic circular dichroism (XMCD). The spin-splitting energies are directly measured and visualized by the shift in their Landau-fan diagram mapped by analyzing the measured Shubnikov-de-Haas (SdH) oscillations as a function of applied electric fields, showing consistent fit with the first-principles and machine learning calculations. Further, the observed spin-splitting energies can be tuned over a broad range between 98 and 166 meV by field cooling. The methods and results are applicable to other 2D (magnetic) materials and heterostructures, and offer great potential for developing next-generation spin logic and memory devices.

Large-Area Growth of Ferroelectric 2D γ-In2 Se3 Semiconductor by Spray Pyrolysis for Next-Generation Memory.

In2 Se3 , 2D ferroelectric-semiconductor, is a promising candidate for next-generation memory device because of its outstanding electrical properties. However, the large-area manufacturing of In2 Se3 is still a big challenge. In this work, spray pyrolysis technique is introduced for the growth of large-area In2 Se3 thin film. A polycrystalline γ-In2 Se3 layer can be grown on 15cm × 15cm glasss at the substrate temperature of 275°C. The In2 Se3 ferroelectric-semiconductor field effect transistor (FeS-FET) on glass substrate demonstrates a large hysteresis window of 40.3V at the ±40V of gate voltage sweep and excellent uniformity. The FeS-FET exhibits an electron field effect mobility of 0.97 cm2 V-1 s-1 and an on/off current ratio of >107 in the transfer curves. The memory behavior of the large-area, In2 Se3 FeS-FETs for next-generation memory is demonstrated.

Growth and characterization of germanium telluride nanowires via vapor–liquid–solid mechanism

Phase-change materials (PCMs), which can transition reversibly between crystalline and amorphous phases, have shown great promise for next-generation memory devices due to their nonvolatility, rapid switching periods, and random-access capability. Several groups have investigated phase-change nanowires for memory applications in recent years. The ability to regulate the scale of nanostructures remains one of the most significant obstacles in nanoscience. Herein, we describe the growth and characterization of germanium telluride (GeTe) nanowires, which are essential for phase-change memory devices. GeTe nanowires were produced by combining thermal evaporation and vapor–liquid–solid (VLS) techniques, using 8 nm Au nanoparticles as the metal catalyst. The influence of various growth parameters, including inert gas flow rate, working pressure, growth temperature, growth duration, and growth substrate, was examined. Ar gas flow rate of 30 sccm and working pressure of 75 Torr produced the narrowest GeTe nanowires horizontally grown on a Si substrate. Using scanning electron microscopy, the dimensions, and morphology of GeTe nanowires were analyzed. Transmission electron microscopy and energy-dispersive x-ray spectroscopy were utilized to conduct structural and chemical analyses. Using a SiO2/Si substrate produced GeTe nanowires that were thicker and lengthier. The current–voltage characteristics of GeTe nanowires were investigated, confirming the amorphous nature of GeTe nanowires using conductive atomic force microscopy. In addition, the effects of the VLS mechanism and the Gibbs–Thomson effect were analyzed, which enables the optimization of nanowires for numerous applications, such as memory and reservoir computing.

Enhanced physical and electrical properties of HfO2 deposited by atomic layer deposition using a novel precursor with improved thermal stability

With the increased application range of Hf-based oxides in memory devices, such as high-k capacitors, gate dielectrics, and ferroelectric devices, improvement in the properties of HfO2 thin films have been received considerable attention. To achieve improved properties HfO2 thin films deposited by atomic layer deposition (ALD), one strategic way is to develop a process incorporating a new precursor with improved thermal stability. In this paper, HfO2 thin films were deposited by ALD process using a novel precursor modified with a cyclopentadienyl-based ligand to improve thermal stability, and the improved properties were investigated. The ALD process window has been extended to higher temperatures. In addition, with increases in deposition temperature, the impurity concentration, surface roughness, density, and crystallinity of HfO2 were improved. Finally, the HfO2 thin film deposited at a high temperature significantly reduced the leakage current (from 5.2 × 10−7 A/cm2 to 3.1 × 10−9 A/cm2 measured at 0.7 V) without a significant change in dielectric constant, and the remanent polarization characters were also observed. Therefore, we suggest that HfO2 deposited using the proposed hafnium precursor can be applied as a key high-k component in next-generation memory devices and ferroelectric-based semiconductor devices.

Improved Uniformity of TaOx-Based Resistive Switching Memory Device by Inserting Thin SiO2 Layer for Neuromorphic System.

RRAM devices operating based on the creation of conductive filaments via the migration of oxygen vacancies are widely studied as promising candidates for next-generation memory devices due to their superior memory characteristics. However, the issues of variation in the resistance state and operating voltage remain key issues that must be addressed. In this study, we propose a TaOx/SiO2 bilayer device, where the inserted SiO2 layer localizes the conductive path, improving uniformity during cycle-to-cycle endurance and retention. Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) confirm the device structure and chemical properties. In addition, various electric pulses are used to investigate the neuromorphic system properties of the device, revealing its good potential for future memory device applications.

Laser-modulated formation of conduction path for the achievement of ultra-low switching voltage in resistive random-access memory (RRAM)

Energy saving is one of critical issues that must be seriously considered for the development of next-generation memory devices. In this study, an ultralow-power resistive random-access memory (RRAM) device is fabricated through use of a successful modulation of the AlOX layer by a laser treatment optimized for the energy saving in resistive switching (RS). The device shows not only multilevel memory properties but also a high on/off ratio (∼106), good endurance (300 cycles), and excellent retention (>104 s). Most importantly, the laser-modulated device achieves ultra-low set and reset voltages (0.06 V and −0.04 V), leading to a very low-power consumption. It was observed that the amorphous phase in the AlOX layer is transformed into the polycrystalline phase and a concentration gradient of oxygen vacancies is secured. The grain boundaries in the polycrystalline act as pathways to facilitate the movement of oxygen vacancies. Meanwhile, the concentration gradient accelerates the diffusion mobility of the oxygen vacancies. The highly potential application of the laser-modulation to the flexible RRAM devices has been demonstrated by a strong level of RS performance maintenance from a device fabricated using the polyethylene terephthalate (PET) substrate.

Vanadium oxide thin film deposited on Si by atomic layer deposition for non-volatile resistive switching memory devices

Vanadium dioxide (VO2) is a representative metal–insulator-transition (MIT) material that undergoes a reversible phase transition at 68 °C, which is close to room temperature. This shows the bias-triggered volatile resistance changes driven by MIT so that many studies have been made to implant VO2 as selectors for solving the sneak current problem of resistive random-access memory (ReRAM). However, the non-volatile switching of VO2 for non-volatile memory (NVM) application has not been demonstrated yet but if realized, this is truly breakthrough for low power and ultrafast NVM application. Herein, we report a successful formation of multiphase vanadium oxide on Si wafer via atomic layer deposition followed by a post-deposition annealing (PDA) process and demonstrate its applicability as a NVM device. It was confirmed that the multiphase vanadium oxide has MIT-driven abrupt resistance switching (i.e., low- and high-resistance state) at ± 1.6 V due to increased oxygen vacancies responsible for non-volatile memory property. The alternating current (AC) endurance upto 30,000 cycles and charge retention upto 3,000 sec are achieved at 2ⅹ102 of LRS/HRS current ratio. As a result, it opens the possibility of application to next-generation memory devices by reliable non-volatile MIT switching scheme.

High-Speed Optoelectronic Nonvolatile Memory Based on van der Waals Heterostructures.

High-performance optoelectronic nonvolatile memory is promising candidate for next-generation information memory devices. Here, a floating-gate memory is constructed based on van der Waals heterostructure, which exhibits a large storage window ratio (≈75.5%) and an extremely high on/off ratio (107 ), as well as an ultrafast electrical writing/erasing speed (40ns). The enhanced performance enables as-fabricated devices to present excellent multilevel data storage, robust retention, and endurance performance. Moreover, stable optical erasing operations can be achieved by illuminating the device with a laser pulse, showcasing outstanding optoelectronic storage performance (optical erasing speed ≈ 2.3ms). The nonvolatile and high-speed characteristics of these devices hold significant potential for the integration of high-performance nonvolatile memory.

Flexible magnetoelectric sensor and nonvolatile memory based on magnetization-graded Ni/FSMA/PMN-PT multiferroic heterostructure

Flexible multiferroic heterostructures are promising to unveil technological developments in wearable magnetic field sensing, nonvolatile memory, soft robotics, and portable energy harvesters. Here, we report an enhanced and a zero-biased magnetoelectric (ME) effect in flexible, cost-effective, and room temperature sensitive Ni/FSMA/PMN-PT magnetization-graded ME heterostructure. Flexible Ni foil with −q (piezomagnetic coefficient) and the ferromagnetic shape memory alloy (FSMA; Ni-Mn-In) layer with +q offers the desired q-grading. The temperature-dependent dielectric behavior shows an anomaly in the martensite transformation regime of the FSMA layer. The Ni/FSMA/PMN-PT ME heterostructure exhibits noteworthy ME output of ∼3.7 V/cm Oe, significantly higher than Ni/PMN-PT (∼1 V/cm Oe). The q-grading-induced bending moment impedes the asymmetry-related flexural strain and strengthens the ME interaction. The zero-bias ME output of ∼0.4 V/cm Oe is ascribed to the interaction between q-grading-induced transverse magnetization and AC magnetic field. Ni/Ni-Mn-In/PMN-PT ME heterostructure displays excellent magnetic field sensing parameters: correlation coefficient, sensitivity, inaccuracy, and hysteresis of 0.99916, ∼0.74 mV/Oe, 1.5% full-scale output (FSO), and 1.8% FSO, respectively. The reversible and repeatable nonvolatile switching of the ME coefficient obtained with positive and negative electric fields is useful for next-generation memory devices. The flexible ME heterostructure shows no degradation in performance up to 1500 bending cycles. Such Ni/FSMA/PMN-PT based ME heterostructures are propitious for multifunctional flexible magnetic field sensors and nonvolatile memory applications.