High-performance Memory Research Articles

Ferroelectric tunnel junctions: promise, achievements and challenges

Abstract Ferroelectric tunnel junctions (FTJs) have been the subject of ongoing research interest due to its fast operation based on the spontaneous polarization direction of ultrathin ferroelectrics and its simple two-terminal structure. Due to the advantages of FTJs, such as non-destructive readout, fast operation speed, low energy consumption, and high-density integration, they have recently been considered a promising candidate for non-volatile next-generation memory. These characteristics are essential to meet the increasing demand for high-performance memory in modern computing systems. In this review, we explore the basic principles and structures of FTJs and clarify the elements necessary for the successful fabrication and operation of FTJs. Then, we focus on the recent progress in perovskite oxide, fluorite, 2-dimensional van der Waals, and polymer-based FTJs and discuss ferroelectric materials expected to be available for FTJs use in the future. We highlight various functional device applications, including non-volatile memories, crossbar arrays, and synapses, utilizing the advantageous properties of ferroelectrics. Lastly, we address the challenges that FTJ devices currently face and propose a direction for moving forward.

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.

Graphdiyne particles as nano-floating gates for high-performance nonvolatile organic field-effect transistor memory

Graphdiyne particles (GDYP), newcomers of carbon family, were employed as nano-floating gates in organic field-effect transistor (OFET) memories. The charge-trapping layer was prepared by blending GDYP into a polystyrene (PS) matrix. The effect of GDYP doping ratio on memory performances was investigated, and the OFET memory with the optimal doping concentration of the GDYP (0.3 mg/mL) exhibits ambipolar memory behavior with a wide memory window as large as 86 V, excellent retention time over 104 s with a high ON/OFF current ratio of 7.5 × 105. This work demonstrates that graphdiyne is a promising charge-trapping material for high-performance nonvolatile OFET memory devices.

Charge-Localized Retention and Long-Term Memory Enabled by Cooperating Sterically Confined Molecular Crystallization with Spiro[fluorene-9,9'-xanthene]-Based Csp3-Hindrance.

Charge localization of memory materials plays a crucial role in the endurance and retention ability of organic nonvolatile memory, which is completely opposite from the charge delocalization of high-mobility materials. However, charge transfer of both though-space and through-bond based on molecular design principles still faces challenges. Herein, a nonplanar wide-bandgap semiconductor with Csp3-hindrance (DOCH3-DDPA-SFX) has been designed and synthesized. An effective crystallization effect of self-assembled two-dimensional nanosheets on charge trapping dynamics and kinetics is visualized by Kelvin probe force microscopy (KPFM). The trapped charges are localized completely on a single nanosheet, which has better charge trapping and retention properties than an amorphous film. Meanwhile, crystallization also greatly improves structure stability. Combining DFT theoretical calculations, the mechanisms of localization and long-term retention are discussed. The steric crystallization effects on the charge localization will guide the effective design of single-component semiconducting charge-memory materials by molecular assembly and aggregate control for high-performance organic memory.

Epitaxial Strain Enhanced Ferroelectric Polarization toward a Giant Tunneling Electroresistance.

A substantial ferroelectric polarization is the key for designing high-performance ferroelectric nonvolatile memories. As a promising candidate system, the BaTiO3/La0.67Sr0.33MnO3 (BTO/LSMO) ferroelectric/ferromagnetic heterostructure has attracted a lot of attention thanks to the merits of high Curie temperature, large spin polarization, and low ferroelectric coercivity. Nevertheless, the BTO/LSMO heterostructure suffers from a moderate FE polarization, primarily due to the quick film-thickness-driven strain relaxation. In response to this challenge, we propose an approach for enhancing the FE properties of BTO films by using a Sr3Al2O6 (SAO) buffering layer to mitigate the interfacial strain relaxation. The continuously tunable strain allows us to illustrate the linear dependence of polarization on epitaxial strain with a large strain-sensitive coefficient of ∼27 μC/cm2 per percent strain. This results in a giant polarization of ∼80 μC/cm2 on the BTO/LSMO interface. Leveraging this large polarization, we achieved a giant tunneling electroresistance (TER) of ∼105 in SAO-buffered Pt/BTO/LSMO ferroelectric tunnel junctions (FTJs). Our research uncovers the fundamental interplay between strain, polarization magnitude, and device performance, such as on/off ratio, thereby advancing the potential of FTJs for next-generation information storage applications.

Design a self-controlled high-performance evaluation of content addressable memories using 45 nm technology

A special type of random access memory (RAM) array called as content addressable memory (CAM), in which stored data is compared with the search data which can be returning the address. In the applications of highspeed searching, the CAMs are used. NOR type matchline CAMs are helpful for applications requiring faster search speeds. Because the NOR type match line (ML) CAM consumes a lot of power, therefore many published designs have attempted to reduce power consumption. The design self-controlled high-performance content addressable memories (SC-CAM) using 45-nm technology is presented in this paper. The 6T 4×4 CAM arrays in this paper uses SC logic and Tanner tools 45-nm technology. When compared to the conventional CAM, described SC-CAM architecture reduces the number of voltages sources. Described 6T 4×4 SC-CAM design needs less number of MOSFETs than existed 8T 4×4 CAM array and thus reduces the area with high speed.

A CrO₂ and Out-of-Plane Silicene based Sub-10nm MTJ with perfect spin filtering efficiency and high tunnel magnetoresistance

In this paper, properties of spin transport for MTJs (magnetic tunnel junction) consisting of CrO2 Half Metallic Ferromagnetic (HMF) electrodes with out of plane silicene sheet as scattering region are analyzed. The transport phenomena in the proposed structure are purely tunneling due to the absence of transmission states near the Fermi level. This is contrary to the in plane structures where transmission states exist near the Fermi level. The proposed device shows the highest value (100%) of magneto-resistance. Spin-filtering efficiency reported in out-of-plane silicene-based MTJ is also increased because of silicene acting as a perfect barrier, results in feeble spin down current in both parallel and anti-parallel configurations. The proposed device has dimensions below 10-nm. Due to the use of silicene sheet as a scattering region, it is also likely to integrate well with the already existing silicon technology. It can be used for high-performance memory applications similar to MRAMs.

High-performance shape memory epoxy resin with high strength and toughness: Prepared by introducing hydrogen bonds through polycaprolactone and low melting point alloy

Epoxy resin (EP) as common polymers have attracted much attention in the field of shape memory materials due to their excellent properties. However, epoxy-based shape memory polymers suffer from a trade-off between strength, toughness, variable stiffness capability and shape memory properties, and thus are subject to significant limitations in their applications. In this paper, we propose a method to prepare epoxy composites with high strength and toughness and high shape memory properties by introducing a lot of hydrogen bonds. Hydrogen bonding is generated through polycaprolactone (PCL) induced EP phase separation. A low melting point alloy (L) was also added to enhance the shape memory properties of the composites. The synthesis mechanism of EP and the formation mechanism of hydrogen bonding were revealed. The effects of the introduction of hydrogen bonding on the mechanical properties, stiffness and shape memory properties of the composites were investigated. New ideas and design directions are provided for the optimisation of modification of high-performance shape memory epoxy resins.

Improvement of cell transistors in high-k/metal-gate peripheral transistors technology for high-performance graphic memories

We investigated characteristics and reliabilities of cell transistors (Cell Tr) in graphics double data rate 7 (GDDR7) DRAM with high-k/metal gate (HKMG) peripheral transistors (Peri Tr), and we suggest the robust and reliable Cell Tr for the HKMG peripheral (Peri) scheme. In the latest graphic DRAMs, the HKMG Peri scheme is equipped to achieve the highest speed at the lowest power consumption, so the Cell Tr must operate stably at a lower driving voltage than other memories. Furthermore, the intrinsic properties of Cell Tr are negatively affected by the reduced thermal budget in the gate-first HKMG Peri scheme. In this paper, we propose a suitable Cell Tr to overcome the influence of the gate-first HKMG Peri scheme and the lowest driving voltage. In addition, we verify the segmental properties of node resistance in Cell Tr and the mechanism of the last data-in PRE command period (tRDL) degradation in graphic memories.

Assessment of Radiation Tolerance of Flash Memory by γ-Ray Irradiation

The radiation tolerance of a microcontroller (Raspberry Pi) required for the development of decommissioning robots was investigated. We found that the flash memory needed to boot the microcontroller had particularly low-radiation tolerance, significantly reducing the operation duration of the microcontroller in a radiation environment. We also found that certain high-performance flash memories have high radiation tolerance. Investigation of the process by which flash memory becomes inoperable revealed that internal memory information is rewritten owing to irradiation, leading to limited lifetime for memory.

Room-temperature elastocaloric effect in Co49Ni21Ga30 shape memory wires

We demonstrate appreciable room-temperature elastocaloric effect in the Co49Ni21Ga30 microwires prepared using the Taylor-Ulitovsky method. By forming an almost excellent [001]B2-oriented single crystal along the wire axis, extraordinary superelasticity with low critical stress and narrow stress hysteresis was achieved. Moreover, the wire exhibits room-temperature elastocaloric effect (ΔTad = −4.1 K) with no apparent degradation for 100 cycles. Due to its easy fabrication and the small scale, the wire is of great potential for advanced applications in miniature intelligent devices requiring refrigeration. This work also paves the way for developing other high-performance shape memory wires.

Silicon-Compatible Ferroelectric Tunnel Junctions with a SiO2/Hf0.5Zr0.5O2 Composite Barrier as Low-Voltage and Ultra-High-Speed Memristors.

The big data era requires ultrafast, low-power, and silicon-compatible materials and devices for information storage and processing. Here, ferroelectric tunnel junctions (FTJs) based on SiO2/Hf0.5Zr0.5O2 composite barrier and both conducting electrodes are designed and fabricated on Si substrates. The FTJ achieves the fastest write speed of 500ps under 5V (2 orders of magnitude faster than reported silicon-compatible FTJs) or 10ns speed at a low voltage of 1.5V (the lowest voltage among FTJs at similar speeds), low write current density of 1.3 × 104 A cm-2, 8 discrete states, good retention >105 s at 85°C, and endurance >107. In addition, it provides a large read current (88 A cm-2) at 0.1V, 2 orders of magnitude larger than reported FTJs. Interestingly, in FTJ-based synapses, gradually tunable conductance states (128 states) with high linearity (<1) are obtained by 10ns pulses of <1.2V, and a high accuracy of 91.8% in recognizing fashion product images is achieved by online neural network simulations. These results highlight that silicon-compatible HfO2-based FTJs are promising for high-performance nonvolatile memories and electrical synapses.

Phase transition and electrical conversion properties of Ge/Sb nano-multilayer films on flexible substrates

Flexible information memory is the key component of flexible electronic devices and the core of intelligent wearable devices. In this paper, Ge/Sb multilayer phase change films of various thickness ratios were prepared using polyether ether ketone as substrate, and their flexible phase change properties and device conversion characteristics were studied. After bending for 100000 times and bending experiments with different bending radius, the film can still realize the transition from amorphous to crystalline states, and the resistance fluctuation was small. Bending, stretching and pressing of the film resulted in grain refinement and increasing of crystalline resistance. The flexible electronic devices using Ge/Sb multilayer films were prepared. The phase change memory device can realize reversible conversion between SET and RESET states with different pulse widths in flat, bent states and after bending many times. All findings show that Ge/Sb multilayer films on PEEK substrate have broad application prospects in high-performance flexible memory in the future.

Influence of martensitic transformation on the surface integrity aspects during sustainable turning of NiTi-SMA

With the development of the equipment manufacturing industry towards the direction of intelligence, the demand for the use of intelligent materials is increasing, and high-performance shape memory alloy (SMA) products are getting more and more attention. However, the current machining quality of shape memory alloy products can not meet the existing quality requirements. The mechanism of surface integrity of NiTi SMA needs to be revealed. The influence of martensitic transformation on microstructure, roughness, hardness, and superelasticity was explored. The occurrence of martensitic transformation is determined by controlling the cutting speed (lower and higher cutting speeds) and machining conditions (dry and liquid nitrogen conditions). The superelasticity was expressed quantitatively by the remnant depth ratio. The occurrence of martensitic transformation promoted the formation of the affected layer and work hardening. Meanwhile, it is an important reason for the increase in roughness and the decrease in superelasticity.

Rcmp: Reconstructing RDMA-Based Memory Disaggregation via CXL

Memory disaggregation is a promising architecture for modern datacenters that separates compute and memory resources into independent pools connected by ultra-fast networks, which can improve memory utilization, reduce cost, and enable elastic scaling of compute and memory resources. However, existing memory disaggregation solutions based on remote direct memory access (RDMA) suffer from high latency and additional overheads including page faults and code refactoring. Emerging cache-coherent interconnects such as CXL offer opportunities to reconstruct high-performance memory disaggregation. However, existing CXL-based approaches have physical distance limitation and cannot be deployed across racks. In this article, we propose Rcmp, a novel low-latency and highly scalable memory disaggregation system based on RDMA and CXL. The significant feature is that Rcmp improves the performance of RDMA-based systems via CXL, and leverages RDMA to overcome CXL’s distance limitation. To address the challenges of the mismatch between RDMA and CXL in terms of granularity, communication, and performance, Rcmp (1) provides a global page-based memory space management and enables fine-grained data access, (2) designs an efficient communication mechanism to avoid communication blocking issues, (3) proposes a hot-page identification and swapping strategy to reduce RDMA communications, and (4) designs an RDMA-optimized RPC framework to accelerate RDMA transfers. We implement a prototype of Rcmp and evaluate its performance by using micro-benchmarks and running a key-value store with YCSB benchmarks. The results show that Rcmp can achieve 5.2× lower latency and 3.8× higher throughput than RDMA-based systems. We also demonstrate that Rcmp can scale well with the increasing number of nodes without compromising performance.

Solid-state quantum nodes based on color centers and rare-earth ions coupled with fiber Fabry–Pérot microcavities

High-performance optical quantum memories serving as quantum nodes are crucial for the distribution of remote entanglement and the construction of large-scale quantum networks. Notably, quantum systems based on single emitters can achieve deterministic spin-photon entanglement, greatly simplifying the difficulty of constructing quantum network nodes. Among them, optically interfaced spins embedded in solid-state systems, as atomic-like emitters, are important candidate systems for implementing long-lived quantum memory due to their stable physical properties and robustness to decoherence in scalable and compact hardware. To enhance the light-matter-interaction strength, optical microcavities can be exploited as an important tool to generate high-quality spin-photon entanglement for scalable quantum networks. They can enhance the photon collection probability and photon generation rate of specific optical transitions and improve the coherence and spectral purity of emitted photons. For solid-state systems, open Fabry-Pérot cavities can couple single emitters that are not in proximity to the surface, avoiding significant spectral diffusion induced by the interfaces while maintaining the wide tunability, whichenables addressing of multiple single emitters in the frequency and spatial domain within a single device. This review describes the characteristics of single emitters as quantum memories with a comparison to atomic ensembles, the cavity-enhancement effect for single emitters and the advantages of different cavities, especially fiber Fabry-Pérot microcavities. Finally, recent experimental progress on solid-state single emitters coupled with fiber Fabry-Pérot microcavities is reviewed, with a focus on color centers in diamond and silicon carbide, as well as rare-earth dopants.

A high-performance magnetoelectric non-volatile light-emitting memory device

A novel magnetoelectric light-emitting memory (LEM) device that can control the output light intensity and electrical signal based on the input magnetic and electric field strengths has been proposed and demonstrated.

Synthesis of air-stable 1T-CrS2 thin films and their application in high-performance floating-gate memory

A high-quality layered 1T-CrS2 floating-gate memory was fabricated, which exhibits a high switching ratio (∼107), a large window ratio (79%), excellent optical and electrical storage capabilities, and potential integratable for CMOS circuits.

High-performance flexible resistive random-access memory based on SnS2 quantum dots with a charge trapping/de-trapping effect.

The application of resistive random-access memory (RRAM) in storage and neuromorphic computing has attracted widespread attention. Benefitting from the quantum effect, transition metal dichalcogenides (TMD) quantum dots (QDs) exhibit distinctive optical and electronic properties, which make them promising candidates for emerging RRAM. Here, we show a high-performance forming-free flexible RRAM based on high-quality tin disulfide (SnS2) QDs prepared by a facile liquid phase method. The RRAM device demonstrates high flexibility with a large on/off ratio of ∼106 and a long retention time of over 3 × 104 s. The excellent switching behavior of the memristor is elucidated by a charge trapping/de-trapping mechanism where the SnS2 QDs act as charge trapping centers. This study is of significance for the understanding and development of TMD QD-based flexible memristors.

A Study on Film Properties Control of Atomic Layer Deposition Amorphous Carbon for PRAM Electrode Application

As the amount of data usage increases with the development of technologies such as artificial intelligence, Internet of Things (IoT), and big data, the need for development of high-performance memory devices and improvement of density is increasing. Phase change memory is a next-generation memory device that stores and erases information by the resistance difference generated by reversibly and rapidly changing the crystal structure of the memory cell. Recently, research on the material engineering aspect to increase thermal efficiency by using various electrode materials and the structural aspect to increase the degree of integration by making a 3D structure is attracting attention. As an electrode material to increase the thermal efficiency of PRAM devices, carbon, which has various resistances (conductor (graphite, sp2 bond) – insulator (diamond, sp3 bond)) depending on the state of atomic bonding is an attractive material. Therefore, research using carbon as an electrode by using PVD and CVD processes has been conducted, but there is a problem that it is difficult to use it for devices with a complex 3D structure with the existing process. Therefore, in this study, an a-C ALD process that can be uniformly deposited in a 3D structure was developed using the CBr4 precursor. And by analyzing the bonding state and physical properties of the deposited thin film, the mechanism of how the a-C thin film grows according to the thin film deposition conditions is studied.