Random Access Research Articles

Evaluation of the Alinity m CMV assay for detecting and quantifying cytomegalovirus DNA in non-plasma samples.

CMV infection remains a well-recognized threat in immunocompromised patients and is a major cause of congenital infection. If plasma and whole blood are routinely used as clinical samples for detection of CMV infection and disease, CMV laboratory testing in non-blood samples is becoming more and more relevant to support the diagnosis, prognosis and management of CMV infection. Accurate CMV viral load assessment in various body fluids is therefore essential. We evaluated the performance of the Alinity m CMV assay for detecting and quantifying CMV in plasma, amniotic fluid, bronchoalveolar lavage, cerebrospinal fluid, saliva and urine. Using a commercially available CMV reference panel and CMV culture supernatant, we assessed the linearity and accuracy of the Alinity m CMV assay across the different sample types. Excellent linear correlations (r values > 0.98) and a good accuracy (bias < ± 0.50 Log10 IU/mL and SD < 0.23) were observed. In conclusion, the Alinity m CMV assay is suitable to detect and quantify CMV DNA in plasma but also in all non-plasma samples tested. Random and continuous access capabilities of the Alinity m enable rapid and efficient laboratory detection and quantification of CMV DNA.

A new 13N-complexity memory built-in self-test algorithm to balance static random access memory static fault coverage and test time

As memories dominate the system-on-chip (SoC), their quality significantly impacts the chip manufacturing yield. There is a growing need to reduce the chip production time and cost, which mainly depends on the testing phase. Hence, a memory built-in self-test (MBIST) utilizing a low-complexity, high-fault-coverage test algorithm is essential for efficient and thorough memory testing. The March AZ1 algorithm, with 13N complexity, was created earlier to balance the test length and fault coverage. However, poor positioning of a write operation in its test sequence caused the reduction of the transition coupling fault (CFtr) detection. This paper presents the creation of the March AZ algorithm, modified from the March AZ1 algorithm, to increase CFtr coverage while preserving the same complexity. It was accomplished by analyzing the fault coverage offered by the March AZ1 algorithm and then reorganizing its test sequence to address the limitation in detecting CFtr. The newly produced March AZ1 algorithm was successfully implemented in an MBIST controller. The simulation tests validated its functionality and demonstrated that the CFtr coverage was enhanced from 62.5% to 75%, achieving an overall fault coverage of 83.3%. Therefore, with 13N complexity, it offers the best fault coverage among all the existing test algorithms with a complexity below 18N.

Progress, challenges, and perspectives of magnetoelectric composites and devices based on relaxor-PT single crystals

Magnetoelectric (ME) composites exhibit robust ME interfacial coupling because of the strong interaction between piezoelectricity and magnetostriction. The presence of two novel functionalities, i.e., direct and converse ME couplings, makes them ideal candidates for multifunctional devices such as energy harvesters, magnetic field sensors, ME random access memories, and ME antennas. In these ME composites, ME coupling is strongly dependent on the superior physical properties of the piezoelectric and magnetostrictive materials. Therefore, magnetostrictive materials with excellent piezomagnetic coefficients and piezoelectric materials with excellent piezoelectric coefficients are required to achieve a large ME coupling. Among the various piezoelectric materials, ferroelectric relaxor-PbTiO3 (PT) single crystals have been used extensively as piezoelectric constituents because of their ultrahigh piezoelectric and electromechanical properties. Furthermore, the domain structure and crystal orientation of the relaxor-PT single crystals exhibit extraordinarily large piezoelectric and electromechanical properties. Owing to these multifunctional properties, relaxor-PT single-crystal-based ME composites have been widely used for studying direct and converse ME couplings in ME composites in recent years. Relaxor-PT single-crystal-based ME composites show excellent ME coupling, e.g., the highest ME voltage coefficient, equivalent magnetic noise, and output power of 7000 V cm−1 Oe−1@ 23.23 kHz, 6 pT/√Hz @1 Hz, and 19 mW @ 60 Hz, respectively, which are one of the best-reported values in ME composites so far. Considering the vast research on relaxor-PT single-crystal-based ME composites, we present a detailed review of the recent progress, challenges, and perspectives of ME composites and ME devices based on relaxor-PT single crystals.

Temperature Gradients as a Data Storage Principle

In this work, we analyze the thermodynamic principles underlying modern data storage systems, including Random Access Memory (RAM), hard disk drive (HDD), flash memory, magnetic RAM (MRAM), ferroelectric RAM (FeRAM), and phase-change RAM (PCRAM), as well as other less well-known data storage mechanisms. The analysis is conducted in the context of data storage and processing in relation to Landauer’s principle, with special emphasis on hysteresis. Analogous to how heat engines are characterized by thermodynamic cycles, data storage systems are examined in terms of the hysteresis loop of their fundamental data unit. We explore the role of heat in data storage systems. Afterward, we introduce the concept of temperature gradient memory (TeGraM) along with a detailed layout of a realizable device. Experimental results demonstrating this technology are also presented.

Write error ballooning due to anisotropy variation within the free layer in perpendicular magnetic tunnel junctions

Abstract A finite-temperature micromagnetic investigation is conducted to analyze magnetization switching and write error rates in perpendicular spin-transfer torque random access memory (STT-RAM), including the influence of domain wall (DW) pinning arising from variations within the free layer (FL) magnet and stray field from reference layer assembly in the magnetic tunnel junction. The study reveals that uneven perpendicular magnetic anisotropy within the FL could lead to the formation of pinning sites that give rise to metastable states during switching. Such metastable states could result in a significant increase in the write error rates as compared to the ideal situation. Unlike the case with stray fields arising from reference layer assembly, where the DW propagation is hindered only for one switching direction, inhomogeneity within the FL causes the DW pinning to occur in both switching directions. Combined effects of FL inhomogeneity and stray field from the reference layer result in write error ballooning similar to those reported in recent experiments. The impact of free layer inhomogeneity could be further exacerbated by the stray field for one of the switching directions. Surprisingly, the impact of inhomogeneity is also observed to persist at smaller FL dimensions where quasi-coherent switching is expected. These findings provide deeper insights into the potential factors contributing to anomalous write errors in perpendicular STT-RAM.

Hardware‐Efficient Quantum Random Access Memory Design with a Native Gate Set on Superconducting Platforms

AbstractQuantum Random Access Memory (QRAM) is a critical component for enabling data queries in superposition, which is the cornerstone of quantum algorithms. Among various QRAM architectures, the bucket‐brigade model stands out due to its noise resilience. This study presents a hardware‐efficient native gate set for implementing bucket‐brigade QRAM on superconducting platforms. The experimental feasibility of the proposed gate set is demonstrated, showing high fidelity and reduced complexity. By leveraging the complementary control property in QRAM, the approach directly substitutes the conventional gates with the new gate set, eliminating decomposition overhead and significantly reducing circuit depth and gate count.

Recursive Quantum Relaxation for Combinatorial Optimization Problems

Quantum optimization methods use a continuous degree-of-freedom of quantum states to heuristically solve combinatorial problems, such as the MAX-CUT problem, which can be attributed to various NP-hard combinatorial problems. This paper shows that some existing quantum optimization methods can be unified into a solver to find the binary solution which is most likely measured from the optimal quantum state. Combining this finding with the concept of quantum random access codes (QRACs) for encoding bits into quantum states on fewer qubits, we propose an efficient recursive quantum relaxation method called recursive quantum random access optimization (RQRAO) for MAX-CUT. Experiments on standard benchmark graphs with several hundred nodes in the MAX-CUT problem, conducted in a fully classical manner using a tensor network technique, show that RQRAO not only outperforms the Goemans-Williamson and recursive QAOA methods, but also is comparable to state-of-the-art classical solvers. The code is available at https://github.com/ToyotaCRDL/rqrao.

3D Vertical Ferroelectric Capacitors with Excellent Scalability.

Three-dimensional vertically stacked memory is more cost-effective than two-dimensional stacked memory. Vertically stacked memory using ferroelectric materials has great potential not only in high-density memory but also in neuromorphic fields because it secures low voltage and fast operation speed. This paper presents the implementation of a ferroelectric capacitor comprising a vertical two-layer stacked structure composed of a titanium nitride (TiN)/aluminum-doped hafnium oxide/TiN configuration. To enhance the ferroelectric properties influenced by the active area, we propose a structure in which multiple small holes share a common pillar electrode. Comprehensive analyses using transmission electron microscopy and energy-dispersive X-ray spectroscopy were conducted to confirm the chemical composition and physical structure of the device. This newly engineered architecture demonstrated promising characteristics, including a sufficient remnant polarization, small device-to-device variations, high endurance, and excellent retention in 3D vertical structures. Moreover, this structure can be applied to one-transistor n-capacitor ferroelectric random access memory with a vertical transistor.

Write error reduction in magnetic tunnel junctions for voltage-controlled magnetoresistive random access memory by using exchange coupled free layer

Voltage-controlled magnetoresistive random access memory (VC-MRAM) is an emerging nonvolatile memory based on the voltage-controlled magnetic anisotropy (VCMA) effect. It has been garnering considerable attention because of its fast and low-power operation. However, two major issues must be addressed for practical applications. First, the voltage-induced switching of the free layer magnetization is sensitive to ultrashort voltage pulse duration. Second, the write error rate (WER) of the voltage-induced switching is high. To address these issues, a magnetic tunnel junction (MTJ) structure with an exchange coupled free layer, consisting of a precession layer with the VCMA effect and an anchor layer without the VCMA effect, is proposed. The anchor layer prevents the precession layer from returning to its initial direction, thereby reducing the WER without requiring the voltage pulse duration to be precisely controlled. The write operation of the proposed MTJ with an exchange coupled free layer was analyzed using the macrospin model. Using optimized MTJ parameters, a low WER of approximately 10−6 was obtained for an 80 nm MTJ without requiring the pulse duration to be precisely controlled. These results facilitate the reduction of the WER for VC-MRAM and improve its usability, thereby expanding its range of applications.

Spin transfer torque switching in double magnetic tunnel junctions based on dual MgO layers

We report fabrication and characterization of double magnetic tunnel junction (DMTJ) magneto-resistive random access memory cells that exhibit characteristic about 2X reduction of switching current compared to single reference layer junctions, but maintain high tunneling magnetoresistance ratio exceeding 120 %, high coercive fields of the free layer of more than 2 kOe for 65 nm cells, and magnetically stable reference layers with pinning fields above 6 kOe. Switching analysis performed for two different relative magnetization orientations of the reference layers shows that the net switching current is the result of combined spin transfer torque effects of the individual reference layers, with tunneling and spin-valve-like contributions adding constructively. Our work shows that efficient reduction of switching current can be achieved in double magnetic tunnel junctions with dual MgO layers where one of the layers has significantly lower resistance-area product to enable high magnetoresistance ratio.

Capacitorless Dynamic Random Access Memory with 2D Transistors by One-Step Transfer of van der Waals Dielectrics and Electrodes.

Dynamic random access memory (DRAM) has been a cornerstone of modern computing, but it faces challenges as technology scales down, particularly due to the mismatch between reduced storage capacitance and increasing OFF current. The capacitorless 2T0C DRAM architecture is recognized for its potential to offer superior area efficiency and reduced refresh rate requirements by eliminating the traditional capacitor. The exploration of two-dimensional (2D) materials further enhances scaling possibilities, though the absence of dangling bonds complicates the deposition of high-quality dielectrics. Here, we present a hexagonal boron nitride (h-BN)-assisted process for one-step transfer of van der Waals dielectrics and electrodes in 2D transistors with clean interfaces. The transferred aluminum oxide (Al2O3), formed by oxidizing aluminum (Al), exhibits exceptional flatness and uniformity, preserving the intrinsic properties of the 2D semiconductors without introducing doping effects. The MoS2 transistor exhibits an extremely low interface trap density of about 3 × 1011 cm-2 eV-1 and a leakage current density down to 10-7 A cm-2, which enables effective charge storage at the gate stack. This method allows for the simultaneous fabrication of two damage-free MoS2 transistors to form a capacitorless 2T0C DRAM cell, enhancing compatibility with 2D materials. The ultralow leakage current optimizes data retention and power efficiency. The fabricated 2T0C DRAM exhibits a rapid write speed of 20 ns, long data retention exceeding 1,000 s, and low energy consumption of approximately 0.2 fJ per write operation. Additionally, it demonstrates 3-bit storage capability and exceptional stability across numerous write/erase cycles.

FR-IBC: Flipping and Rotation Intra Block Copy for Versatile Video Coding

Screen content has become increasingly important in multimedia applications owing to the growth of remote desktops, Wi-Fi displays, and cloud computing. However, these applications generate large amounts of data, and their limited bandwidth necessitates efficient video coding. While existing video coding standards have been optimized for natural videos originally captured by cameras, screen content has unique characteristics such as large homogeneous areas and repeated patterns. In this paper, we propose an enhanced intra block copy (IBC) method for screen content coding (SCC) in versatile video coding (VVC) named flipping and rotation intra block copy (FR-IBC). The proposed method improves the prediction accuracy by using flipped and rotated versions of the reference blocks as additional references. To reduce the computational complexity, hash maps of these blocks are constructed on a 4 × 4 block size basis. Moreover, we modify the block vectors and block vector predictor candidates of IBC merge and IBC advanced motion vector prediction to indicate the locations within the available reference area at all times. The experimental results show that our FR-IBC method outperforms existing SCC tools in VVC. Bjøntegaard-Delta rate gains of 0.66% and 2.30% were achieved under the All Intra and Random Access conditions for Class F, respectively, while corresponding values of 0.40% and 2.46% were achieved for Class SCC, respectively.

A low‐complexity block EP‐based detector for iterative detection and decoding in unsourced random access

AbstractHere, a multi‐user signal iterative detection and decoding scheme named LBEP based on block expectation propagation (BEP) is proposed for LDPC‐coded two‐phase unsourced random access (URA) scheme. In the iterative process, the approximation of matrix inversion is used to facilitate expectation propagation (EP). In addition, this idea is also applied to the double EP (DEP) scheme. The simulation results show that, in the two‐phase URA scheme, the performance of the proposed LBEP scheme is similar to the BEP scheme for LDPC codes, but the complexity of the receiver is greatly reduced.

The show must go on: a reliability assessment platform for resistive random access memory crossbars.

Resistive random access memory (ReRAM) holds promise for building computing-in-memory (CIM) architectures to execute machine learning (ML) applications. However, existing ReRAM technology faces challenges such as cell and cycle variability, read-disturb and limited endurance, necessitating improvements in devices, algorithms and applications. Understanding the behaviour of ReRAM technologies is crucial for advancement. Existing platforms can either only characterize single cells and do not support CIM operations, or lack a comprehensive software stack for simple system integration. This article introduces NeuroBreakoutBoard (NBB), a versatile, integrable and portable instrumentation platform for ReRAM crossbars. The platform features a software stack enabling experiments via Python from a host PC. In a case study, we demonstrate the capabilities of NBB by conducting diverse experiments on TiN/Ti/HfO2/TiN cells. Our results show that NBB can characterize individual cells and perform CIM operations with a relative measurement error below 2%.This article is part of the theme issue 'Emerging technologies for future secure computing platforms'.

Concealable physical unclonable function generation and an in-memory encryption machine using vertical self-rectifying memristors.

The importance of hardware security increases significantly to protect the vast amounts of private data stored on edge devices. Physical unclonable functions (PUFs) are gaining prominence as hardware security primitives due to their ability to generate true random digital keys by exploiting the inherent randomness of the physical devices. Traditional approaches, however, require significant data movement between memory units and PUF generation circuits to perform encryption, presenting considerable energy efficiency and security challenges. This study introduces an innovative approach where PUF key generation and encryption are accomplished in the same vertically integrated resistive random access memory (V-RRAM), alleviating the data movement issue. The proposed V-RRAM encryption machine offers concealable PUFs, high area efficiency, and multi-thread data handling using parallel XOR logic operations. The encryption machine is compared with other machines, demonstrating the highest spatiotemporal cost-effectiveness.

Uncoupled Unsourced Random Access: Exploiting Geographical Diversity of Access Points

Uncoupled Unsourced Random Access: Exploiting Geographical Diversity of Access Points

Massive Random Access Control for VLC: A Reinforcement Learning Driven Approach

Massive Random Access Control for VLC: A Reinforcement Learning Driven Approach

Feedback-Aided Coded Random Access With Intentional Power Unbalance

Feedback-Aided Coded Random Access With Intentional Power Unbalance

Spatial Performance Analysis and Design Principles of Random Access based Wireless Mutual Broadcast in Various Spectral Environments

Spatial Performance Analysis and Design Principles of Random Access based Wireless Mutual Broadcast in Various Spectral Environments

Performance Analysis and Optimization of Grant-Free Random Access with Capture Effect for Cell-Free Massive MIMO

Performance Analysis and Optimization of Grant-Free Random Access with Capture Effect for Cell-Free Massive MIMO