Nonvolatile Logic Research Articles

Nonvolatile logic inverters based on 2D CuInP2S6 ferroelectric field effect transistors

With the capability of in-memory computing, integrated nonvolatile logic devices can mitigate the back-and-forth movement of data between storage and logic units, thus effectively enhancing computational speed and reducing power consumption. In this work, two-dimensional (2D) CuInP2S6, which reveals robust polarization within a few nanometer thicknesses, was utilized as gate dielectric for ferroelectric field effect transistor (FeFET). Device with a ReS2 channel demonstrated a high on/off ratio of current of 105, accompanied by a substantial hysteresis window of 2.8 V. Additionally, ReS2 FETs, gated with an h-BN layer, exhibited a switch ratio of 108 and minimal hysteresis of 61.6 mV at room temperature, attributed to the atomically flat heterointerface with negligible traps. Leveraging the performance of these devices enabled the creation of a nonvolatile logic inverter, wherein the ReS2/h-BN FET acts as the load transistor, and ReS2/h-BN/CIPS FeFET serves as the driving unit. This configuration stably operates with low power consumption of 0.45 μW and outstanding retention exceeding 1000 s. This work presents a viable device architecture for designing nonvolatile logic circuits applicable in in-memory computing.

Nonvolatile logic gate and full adder based on tri-terminal oxide resistive switching devices

Today's on-chip computing power is constrained by the “memory wall” and “power wall” caused by the Von Neumann bottleneck. As a potential solution, this work has developed nonvolatile logic gates based on field-effect tri-terminal oxide resistive switching memory devices (3T-RRAM). A compact circuit model using a polynomial control source (PCS) is proposed to describe the behavior of the fabricated 3T-RRAM. The 3T-RRAM can be regarded as a nonvolatile transmission gate for constructing nonvolatile logic gates. Additionally, a full adder with input storage functionality has been designed using only eight 3T-RRAMs (four nonvolatile logic gates), and a binarized neural network (BNN) based on 3T-RRAM logic gate arrays has been proposed. This demonstrates the great potential of nonvolatile logic gates in computing-in-memory applications.

Spin-torque vortex-oscillator with modified saturation magnetization in ferromagnetic nanodots

Recent years have seen greater interest in manipulating vortex states in magnetic nanostructures for non-volatile memory and logic networks. We show how reducing saturation magnetization locally in ferromagnetic thick nanodot vortex-based spin-torque nano-oscillators modulates their frequency using micromagnetic simulations. When a spin-polarized current and a static in-plane magnetic field are applied to the vortex core of an isolated thick nanodot, the uniform gyrotropic modes and the first higher-order gyrotropic mode resonate at different frequencies in various saturation magnetization areas. The intensity of the first higher-order mode gets almost suppressed in areas with modified saturation magnetization. With linewidths ranging from 25 to 70 MHz with the considered dimensions, these small spin-torque vortex-oscillator devices made of thick Permalloy nanodots seem promising for use in gigahertz signal processing. Our study suggests that locally modifying saturation magnetization may be a cost-effective technique to build dense oscillator and array networks for neuromorphic computing without lithographical fabrication stages.

Dual-Mode Reconfigurable Split-Gate Logic Transistor through Van der Waals Integration.

As silicon-based transistors approach their physical size limitations, two-dimensional material-based reconfigurable functional electronic devices are considered the most promising novel device architectures beyond Moore strategies. While these devices have garnered significant attention, they often require complex device fabrication processes and extra electric fields. Additionally, the device performance is usually limited by the metal-semiconductor interface properties. In this Letter, we have constructed a reconfigurable logic device based on a WSe2 transistor with a nanofloating gate and split-gates through van der Waals integration. This device achieves a small Schottky barrier height due to the van der Waals contacts. By varying the split-gate biases, we can realize volatile reconfigurable homojunctions as well as AND, OR, NOR, and NAND logic operations with just a single device. Furthermore, with the charge trapping effect of nanofloating gate, we can also achieve nonvolatile reconfigurable homojunctions, as well as AND and OR logic operations. The volatile and nonvolatile logic operations are similar to the short-term plasticity and long-term plasticity, respectively, of synapses in the human brain. This work offers a potential approach for creating novel reconfigurable functional electronic devices with a simple fabrication process and low cost.

Spin injection at MgB2-superconductor/ferromagnet interface

There is a growing interest in mixing spintronics and superconductivity to develop original energy-efficient nonvolatile memory and logic devices. Research works conducted so far have mostly focused on superconductor with critical temperature Tc lower than 10 K. Here, we report on the growth and characterization of MgB2/Ni80Fe20 and MgB2/Co bilayers, where Tc of the MgB2 layer is of the order of 30 K. Ferromagnetic resonance was undertaken to analyze the spin pumping into MgB2. The larger magnetization at saturation in Co, as compared to Ni80Fe20, induces a smaller spin pumping contribution to the damping when MgB2 is normal. A spin pumping reduction was observed for both bilayers when MgB2 becomes superconductor and is attributed to the opening of the superconducting gap. The present results show that MgB2 thin films could be suitable to implement superconducting spintronic at 30 K, which is not only relevant for future technological development but also relaxes experimental constraints related to low-temperature investigations.

Unraveling the negative charge-to-spin conversion in the Heusler alloy Co2FeSi

Recent discoveries of Heusler alloy achieve a strong advantage of the chemically disordered sample in the charge-to-spin conversion and attracted interests for spintronics applications. Here, we observe the negative charge-to-spin conversion in single magnetic layer of Co2FeSi/MgO and prove generations of σy and σx by spin-torque ferromagnetic resonance (ST-FMR). We also report that the change in charge-to-spin conversion efficiency could be controlled by chemical disordering. Furthermore, the thickness dependents of Co2FeSi demonstrated bulk effect is responsible for the generation of spin current. This study contributes to understanding the mechanisms of spin current generation from magnetic full Heusler alloy and also paves the way for the applications of magnetic memory and nonvolatile spin logic technologies.

Nonvolatile photoelectric memristor for reconfigurable Boolean logic operation and data storage

Photoelectric memristors have the advantages of highly parallel computing and large-scale interconnection, which provides a promising method for reconfigurable logic operations and greatly promotes the development of new memory computing technology. In this paper, a photoelectric memristor was fabricated using natural gelatin and water-soluble CdSe/ZnS quantum dots with a shell structure. Under light stimulation, the device undergoes photoelectric effects in the dielectric layer, generating electron–hole pairs and causing the device to transition from a high-resistance state to a low-resistance state. Seven nonvolatile logic functions are achieved using three wavelengths of light excitation devices. Compared with traditional electrically controlled memristors, emerging photoelectric memristors are more attractive because they can integrate the advantages of photons and electrons.

Realization of 2D multiferroic with strong magnetoelectric coupling by intercalation: a first-principles high-throughput prediction

The discovery of novel two-dimensional (2D) multiferroic materials is attractive due to their potential for the realization of information storage and logic devices. Although many approaches have been explored to simultaneously introduce ferromagnetic (FM) and ferroelectric (FE) orders into a 2D material, the resulting systems are often plagued by weak magnetoelectric (ME) coupling or limited room-temperature stability. Here, we present a superlattice strategy to construct non-centrosymmetric AM2X4 multiferroic monolayers, i.e., intercalating transition metal ions (A) into the tetragonal-like vacancies of transition metal dichalcogenide bilayers (MX2). Starting from 960 intercalated AM2X4 compounds, our high-throughput calculations have identified 21 multiferroics with robust magnetic order, large FE polarization, low transition barrier, high FE/FM transition temperature, and strong ME coupling. According to the origin of magnetism, we have classified them into twelve type-a, seven type-b, and two type-c multiferroics, which exhibit different ME coupling behavior. During the switching of polarization, the reversal of skyrmions chirality, the transition of the magnetic ground state from FM to antiferromagnetic, and the changes in spin-polarized electron distribution were observed in type-a, type-b, and type-c 2D multiferroic materials, respectively. These results substantially expand the family of 2D ferroic materials and pave an avenue for designing and implementing nonvolatile logic and memory devices.

Realization of logic operations via spin–orbit torque driven perpendicular magnetization switching in a heavy metal/ferrimagnet bilayer

Programmable and non-volatile spin-based logic devices have attracted significant interest for use in logic circuits. Realization of logic operations via spin–orbit torque (SOT) driven magnetization switching could be a crucial step in the direction of building logic-in-memory architectures. In this work, we demonstrate experimentally, the realization of four logic operations in a heavy metal/ferrimagnet bilayer structure via SOT switching. We also propose a general scheme for choosing input parameters to achieve programmable logic operations. The bulk and tunable perpendicular magnetic anisotropy and relatively lower saturation magnetization in ferrimagnets are found to make them more energy efficient in performing logic operations, as compared to conventional ferromagnets. Thus, ferrimagnets are promising candidates for use in logic-in-memory architectures, leading to the realization of user-friendly spin logic devices in the future.

Experimental Demonstration of Non-Volatile Boolean Logic With Field Configurable 1FeFET-1RRAM Technology

Experimental Demonstration of Non-Volatile Boolean Logic With Field Configurable 1FeFET-1RRAM Technology

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.

Influence of interface on the domain polarization orientation in ferroelectric Hf0.5Zr0·5O2 thin films

Ferroelectric HfO2-based materials have attracted extensive attention in the research of next-generation nonvolatile memories and logic devices due to their superior scaling properties and compatibility with the CMOS process. However, forming the ferroelectric metastable phase in the thin films of a few nanometers requires clamping of the top and bottom electrodes. As a result, the interface can significantly impact domain structure and polarization, leading to imprinting effects and non-uniform space charge distribution. Here, we have demonstrated how the interface affects the ferroelectric polarization in Hf0.5Zr0·5O2 (HZO) thin films produced by ALD and the physical mechanisms behind it. We found that by regulating the quantity of oxygen vacancy content at the top and bottom interfaces of TiN/HZO/TiN ferroelectric capacitors, it is possible to achieve inversion of polarization orientation. By using a spherical aberration-corrected transmission electron microscope and first-principles calculation, we identified that the internal electric field generated by the accumulation of oxygen vacancies at an interface and the asymmetrical electrostatic energy of the interfacial T-phase layer jointly play a role in the ferroelectric polarization orientation. Our results will significantly help the interface engineering of HfO2-based ferroelectric thin films and devices.

Towards fully electrically controlled domain-wall logic

Utilizing magnetic tunnel junctions (MTJs) for write/read and fast spin-orbit-torque (SOT)-driven domain-wall (DW) motion for propagation, enables non-volatile logic and majority operations, representing a breakthrough in the implementation of nanoscale DW logic devices. Recently, current-driven DW logic gates have been demonstrated via magnetic imaging, where the Dzyaloshinskii-Moriya interaction (DMI) induces chiral coupling between perpendicular magnetic anisotropy (PMA) regions via an in-plane (IP) oriented region. However, full electrical operation of nanoscale DW logic requires electrical write/read operations and a method to pattern PMA and IP regions compatible with the fabrication of PMA MTJs. Here, we study the use of a Hybrid Free Layer (HFL) concept to combine an MTJ stack with DW motion materials, and He+ ion irradiation to convert the stack from PMA to IP. First, we investigate the free layer thickness dependence of 100-nm diameter HFL-MTJ devices and find an optimal CoFeB thickness, from 7 to 10 Å, providing high tunneling magnetoresistance (TMR) readout and efficient spin-transfer torque (STT) writing. We then show that high DMI materials, like Pt/Co, can be integrated into an MTJ stack via interlayer exchange coupling with the CoFeB free layer. In this design, DMI values suitable for SOT-driven DW motion are measured by asymmetric bubble expansion. Finally, we demonstrate that He+ irradiation reliably converts the coupled free layers from PMA to IP. These findings offer a path toward the integration of fully electrically controlled DW logic circuits.

Intrinsic multiferroic semiconductors with magnetoelastic coupling: two-dimensional MoTe<i>X</i> (<i>X</i> = F, Cl, Br, I) monolayers

Two-dimensional materials with both ferromagnetism and ferroelasticity present new possibilities for developing spintronics and multifunctional devices. These materials provide a novel method for controlling the direction of the magnetization axis by switching the ferroelastic state, achieving efficient and low-power operation of magnetic devices. Such properties make them a promising candidate for the next generation of non-volatile memory, sensors, and logic devices. By performing the first-principles calculations, the ferromagnetism, ferroelasticity, and magnetoelastic coupling in MoTe<i>X</i> (<i>X</i> = F, Cl, Br, I) monolayers are systematically investigated. The results indicate that the MoTe<i>X</i> monolayers are intrinsic semiconductors holding both ferromagnetism and ferroelasticity. The pronounced in-plane magnetic anisotropy suggests that the MoTe<i>X</i> monolayers can resist thermal disturbances and maintain long-range magnetic order. The Curie temperatures of MoTe<i>X</i> monolayers are 144.75 K, 194.55 K, 111.45 K, and 92.02 K, respectively. Our calculations show that the four MoTe<i>X</i> monolayers possess two stable ferroelastic states, with their easy magnetization axes perpendicular to each other. The ferroelastic transition barriers between the two ferroelastic states of MoTeF, MoTeCl, MoTeBr, MoTeI monolayers are 0.180 eV/atom, 0.200 eV/atom, 0.209 eV/atom, and 0.226 eV/atom, respectively, with their corresponding reversible strains of 54.58%, 46.32%, 43.06%, and 38.12%. These values indicate the potential for reversible magnetic control through reversible ferroelastic transition at room temperature. Owing to their unique magnetoelastic coupling properties, MoTe<i>X</i> monolayers exhibit the ability to control reversible magnetization axis at room temperature, laying the foundation for the development of highly controllable and stable spintronic devices.

Universal skyrmion logic gates and circuits based on antiferromagnetically coupled skyrmions without a topological Hall effect

Nanoscale skyrmions are spin-based quasiparticles that are promising for nonvolatile logic applications.

Exploitable magnetic anisotropy and half-metallicity controls in multiferroic van der Waals heterostructure

Two-dimensional (2D) XY ferromagnets have drawn pronounced interest in recent years, but the characteristic of easy-plane magnetization restricts their application in spintronics to some extent. Here, we propose a general strategy for constructing multiferroic van der Waals heterostructures, aiming to achieve electrical control over the magnetic anisotropy in 2D XY ferromagnets. The validity of this strategy is verified by the heterostructure composed of ferromagnetic VBi2Te4 and ferroelectric In2Se3 monolayers. By manipulating the polarized states of In2Se3, the VBi2Te4 can be reversibly transformed between 2D XY and Heisenberg ferromagnets, characterized by the switching of easy magnetization axis between in-plane and out-of-plane directions. More interestingly, accompanied by the changes in magnetic anisotropy, the VBi2Te4 also demonstrates a phase transition from a semiconductor to a half-metal state, which can be ascribed to the band alignment and interfacial charge transfer. The switchable magnetic and electronic properties enable the heterostructure to be utilized in nonvolatile memory and logic devices. Additionally, the half-metallicity and magnetocrystalline anisotropy energy of the heterostructure can be effectively tuned by biaxial strain. These findings not only pave the way for electrically nonvolatile control of 2D XY ferromagnet, but also facilitate the development of interfacial magnetoelectric physics and applications.

In-plane charged antiphase boundary and 180° domain wall in a ferroelectric film

The deterministic creation and modification of domain walls in ferroelectric films have attracted broad interest due to their unprecedented potential as the active element in non-volatile memory, logic computation and energy-harvesting technologies. However, the correlation between charged and antiphase states, and their hybridization into a single domain wall still remain elusive. Here we demonstrate the facile fabrication of antiphase boundaries in BiFeO3 thin films using a He-ion implantation process. Cross-sectional electron microscopy, spectroscopy and piezoresponse force measurement reveal the creation of a continuous in-plane charged antiphase boundaries around the implanted depth and a variety of atomic bonding configurations at the antiphase interface, showing the atomically sharp 180° polarization reversal across the boundary. Therefore, this work not only inspires a domain-wall fabrication strategy using He-ion implantation, which is compatible with the wafer-scale patterning, but also provides atomic-scale structural insights for its future utilization in domain-wall nanoelectronics.

Design of small volume and low power consumption logic gates based on 4-terminal multilevel magnetic cell

Spintronics is an emerging technology for designing logic circuits. The non-volatile logic based on the magnetic tunnel junction (MTJ) cell is a suitable solution to overcome the leakage power problem, which has become a major obstacle for CMOS technology. Here, we introduce a new style of magnetic gate (mGate) logic, which is built by a four-terminal cell. This cell operated by motion of domain wall that is based on spin transfer torque (STT) in a multi-level cell (MLC) structure. To reduce the complexity, a static circuit with a resistive load in ratioed logic style has been used. The use of MLC Gate logic in the static ratioed logic circuit is a suitable solution to reduce the complexity level of structure and power consumption in logic circuits in the field of spintronics. The performance of different magnetic logic gates have been investigated by simulations. The simulation results show that the MLC Gates offer a smaller area and lower power consumption and lower energy in comparison with the previous mGate and magnetic computing in memory.

Reconfigurable Multifunctional van der Waals Ferroelectric Devices and Logic Circuits.

Emerging reconfigurable devices are fast gaining popularity in the search for next-generation computing hardware, while ferroelectric engineering of the doping state in semiconductor materials has the potential to offer alternatives to traditional von-Neumann architecture. In this work, we combine these concepts and demonstrate the suitability of reconfigurable ferroelectric field-effect transistors (Re-FeFETs) for designing nonvolatile reconfigurable logic-in-memory circuits with multifunctional capabilities. Modulation of the energy landscape within a homojunction of a 2D tungsten diselenide (WSe2) layer is achieved by independently controlling two split-gate electrodes made of a ferroelectric 2D copper indium thiophosphate (CuInP2S6) layer. Controlling the state encoded in the program gate enables switching between p, n, and ambipolar FeFET operating modes. The transistors exhibit on-off ratios exceeding 106 and hysteresis windows of up to 10 V width. The homojunction can change from Ohmic-like to diode behavior with a large rectification ratio of 104. When programmed in the diode mode, the large built-in p-n junction electric field enables efficient separation of photogenerated carriers, making the device attractive for energy-harvesting applications. The implementation of the Re-FeFET for reconfigurable logic functions shows how a circuit can be reconfigured to emulate either polymorphic ferroelectric NAND/AND logic-in-memory or electronic XNOR logic with a long retention time exceeding 104 s. We also illustrate how a circuit design made of just two Re-FeFETs exhibits high logic expressivity with reconfigurability at runtime to implement several key nonvolatile 2-input logic functions. Moreover, the Re-FeFET circuit demonstrates high compactness, with an up to 80% reduction in transistor count compared to standard CMOS design. The 2D van de Waals Re-FeFET devices therefore exhibit promising potential for both More-than-Moore and beyond-Moore future of electronics, in particular for an energy-efficient implementation of in-memory computing and machine learning hardware, due to their multifunctionality and design compactness.

Non-volatile reconfigurable spin logic functions in a two-channel Hall bar by spin–orbit torque-based magnetic domains and directional read current

A long-standing goal of CMOS-based logic devices is to meet the needs of key markets, including ultralow-power operation and high operation speed, along with the continuing miniaturization of the architecture. However, despite significant progress in their development, conventional CMOS-based devices still suffer from drawbacks such as introducing large unintended leakage currents and volatile behavior. Thus, reconfigurable logic gates based on magnetic domain (MD) have emerged as a highly promising option because they offer fast operation speeds, nonvolatility, and diverse logic functions in a single-device configuration. Here, we address multiple reconfigurable MD logic gates in a single two-channel Hall bar device by varying the voltage-driven read-current directions and selecting a non-inverting or inverting comparator in W/CoFeB/MgO/Ta stacks. The non-volatile MD switching behavior induced by spin–orbit torque significantly affects our logic gate functions, which are not necessarily synchronized to a single clock. By adapting MD switching by spin-orbit torque and anomalous Hall effect voltage outputs, we identified eight reconfigurable logic gates, including AND, NAND, NOR, OR, INH, Converse INH, Converse IMP, and IMP, in a single device. These experimental findings represent a significant step forward in a wide range of MD-based logic applications in the near future.