High-performance Memory Applications Research Articles

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.

Room-temperature orbit-transfer torque enabling van der Waals magnetoresistive memories

The non-volatile magnetoresistive random access memory (MRAM) is believed to facilitate emerging applications, such as in-memory computing, neuromorphic computing and stochastic computing. Two-dimensional (2D) materials and their van der Waals heterostructures promote the development of MRAM technology, due to their atomically smooth interfaces and tunable physical properties. Here we report the all-2D magnetoresistive memories featuring all-electrical data reading and writing at room temperature based on WTe2/Fe3GaTe2/BN/Fe3GaTe2 heterostructures. The data reading process relies on the tunnel magnetoresistance of Fe3GaTe2/BN/Fe3GaTe2. The data writing is achieved through current induced polarization of orbital magnetic moments in WTe2, which exert torques on Fe3GaTe2, known as the orbit-transfer torque (OTT) effect. In contrast to the conventional reliance on spin moments in spin-transfer torque and spin–orbit torque, the OTT effect leverages the natural out-of-plane orbital moments, facilitating field-free perpendicular magnetization switching through interface currents. Our results indicate that the emerging OTT-MRAM is promising for low-power, high-performance memory applications.

Polarization of Bi2Se3 thin film toward non-volatile memory applications

In recent years, topological insulators have drawn growing interest as a unique electronic state of matter toward quantum information technology. Despite the logic devices with magnetization switching through spin–orbit torque or the topological magneto-electric effect, realizing memory devices based on topological insulators has been urged in quantum computing applications. In this work, we report the design and fabrication of a non-volatile memory device that employs polarization of Bi2Se3 thin films achieving fast memory speed, sufficient memory window, and good reliability. The Bi2Se3 film polarizes under an external electrical field with charges accumulated on the top and bottom surfaces separating the electrons and holes. Such polarization is much faster than the carrier tunneling in conventional floating-gate flash memory and ferroelectric-based memory devices. In addition, good memory retention and endurance properties have also been obtained, showing great potential in high-performance memory application in future topological insulator-involved information technology.

Damage-Induced Ferroelectricity in HfOx-Based Thin Film

In the last decade, a surge in research on hafnium oxide (HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> )-based ferroelectricity has become a significant part of the semiconductor research trend. In this work, we present a new factor, that is, process damage to the HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> -based ferroelectric implementation. By reversely exploiting harmful damage in the metal-oxide-semiconductor process, the ferroelectricity in HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> is improved by eliciting early amorphization suitable for orthorhombic phase formation. In addition, through various pulsed polarization measurements, it is found that the damaged HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> film has a fast polarization switching speed, with an initial pinning site that is suitable for domain wall growth motion; advantageous for high-performance memory applications.

Conduction mechanisms of ferroelectric La:HfO2 ultrathin films

Recently, ion-doped HfO2 thin films are highly desirable for the next-generation nonvolatile memories due to excellent compatibility with current complementary metal-oxide-semiconductor processes and robust ferroelectricity persisted down to the nanoscale. In this work, we study conduction mechanisms of 4 and 8 nm-thick La:HfO2 ultrathin films sandwiched between Pt and (La0.67,Sr0.33)MnO3 (LSMO) electrodes based on band alignments of the Pt/La:HfO2/LSMO, measured by x-ray photoelectron spectroscopy, and temperature-dependent current-voltage curves from 50 to 300 K. In a 4 nm-thick La:HfO2 thin-film capacitor, the conduction mechanism is found to be governed by direct tunneling at 50–100 K and phonon-assisted indirect tunneling when the temperature is further increased to 300 K in which the (LaHf4+3+)′ acceptors are served as localized states, facilitating hole hopping through the La:HfO2 barrier. When the thickness is increased to 8 nm, the tunneling through a La:HfO2 layer is suppressed, and the current-voltage character becomes rectifying, which is regulated by the dominated La:HfO2/LSMO interfacial barrier. The transport for a forward bias of the La:HfO2/LSMO barrier is found to be governed by thermionic-field emission, exhibiting a temperature-independent build-in potential of ∼2.77 V. For the reverse bias, the Fowler–Nordheim tunneling is observed. The revealing of conduction mechanisms in terms of band alignments sheds light on leakage problems and facilitates the design of HfO2-based ferroelectric devices with excellent insulating character for high-performance memory applications.

High Performance Flexible Nonvolatile Memory Based on Vertical Organic Thin Film Transistor

AbstractFlexible floating‐gate organic transistor memory (FGOTM) is a potential candidate for emerging memory technologies. Unfortunately, conventional planar FGOTM suffers from weak driving ability and insufficient mechanical flexibility, which limits its commercial application. In this work, a novel flexible vertical FGOTM (VFGOTM) is reported. Benefitting from new vertical architecture, VFGOTM provides ultrashort channel length to afford an extremely high current density. Meanwhile, VFGOTM devices exhibit excellent memory performance and outstanding retention property. The memory properties of VFGOTM devices are comparable or even better than traditional planar FGOTM and much better than the reported organic nonvolatile memory with vertical transistor structures. More importantly, organic nonvolatile memory with vertical transistor structures is investigated for the first time on a flexible substrate. The results show that VFGOTM architecture allows vertical current flow across the channel layer to effectively eliminate the effect of mechanical bending during current transport, which significantly improves the mechanical stability of the flexible VFGOTM. Hence, with a combination of excellent driving ability, memory performance, and mechanical stability, VFGOTM devices meet the practical requirements for high performance memory applications, which have great potential for the application in a wide range of flexible and wearable electronics.

Choice of quantum dot materials for fabricating memory devices with longer storage and faster writing of information

We present theoretical modelling and simulation approach for studying the electron and hole dynamics in various III-V quantum dot (QD) device systems for high performance memory applications. A rigorous computation is carried out by developing a self-consistent Schrödinger Poisson solver for obtaining the potential state of the QD for various applied voltages of the device. A detailed capture as well as emission mechanism of the carriers is elucidated at various operating temperatures ranging from 10 to 300 K. Our results showed suitability of holes in GaSb/GaAs dots for 107 times increase in the duration of data storage and 34 times faster writing capability as compared to InAs/GaAs QDs at room temperature operation. A trade-off is necessary between extending the storage time and increasing the write time by incorporation of high bandgap AlAs barrier. However, a technique is proposed to avoid the trade-off and minimize the write and erase time along with longer storage of data for QD memories with barrier layers. Our computation also reveals greater retention capacity of electrons over holes when localized to the same potential barrier. Applications of these QDs at cryogenic temperatures are also elucidated. Thus, based on our comparative analysis, valuable information is being provided to the device scientist in choosing suitable quantum dot material for memory devices and optimizing its performance.

Facile Synthesis of Co9Se8 Quantum Dots as Charge Traps for Flexible Organic Resistive Switching Memory Device

Uniform Co9Se8 quantum dots (CSQDs) were successfully synthesized through a facile solvothermal method. The obtained CSQDs with average size of 3.2 ± 0.1 nm and thickness of 1.8 ± 0.2 nm were demonstrated good stability and strong fluorescence under UV light after being easily dispersed in both of N,N-dimethylformamide (DMF) and deionized water. We demonstrated the flexible resistive switching memory device based on the hybridization of CSQDs and polyvinylpyrrolidone (PVP) (CSQDs-PVP). The device with the Al/CSQDs-PVP/Pt/poly(ethylene terephthalate) (PET) structure represented excellent switching parameters such as high ON/OFF current ratio, low operating voltages, good stability, and flexibility. The flexible resistive switching memory device based on hybridization of CSQDs and PVP has a great potential to be used in flexible and high-performance memory applications.

Cross-Point Resistive RAM Based on Field-Assisted Superlinear Threshold Selector

We report a 3-D-stackable 1S1R passive cross-point resistive random access memory (RRAM). The sneak (leakage) current challenge in the cross-point RRAM integration has been overcome utilizing a field-assisted superlinear threshold selector. The selector offers high selectivity of >10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> , sharp switching slope of <;5 mV/decade, ability to tune the threshold voltage, stable operation at 125°C, and endurance of >10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sup> . Furthermore, we demonstrate 1S1R integration in which the selector-subthreshold current is <;10 pA while offering >10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> memory ON/OFF ratio and >10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> selectivity during cycling. Combined with self-current-controlled RRAM, the 1S1R enables high-density and high-performance memory applications.

Sub-micro watt resistive memories using nano-crystallized aluminum oxynitride dielectric

Using nano-crystallized aluminum oxynitride (nc-AlOxNy) dielectric, the Al/nc-AlOxNy/AlN/n+-Si resistive random access memory (RRAM) with ultralow sub-micro watt power is reported in this study. The RRAM devices exhibit excellent memory characteristics, including reproducible bipolar resistive switching under >100 times memory window, very low set and reset current of ~10 nA, high voltage distributions and good data retention. It is demonstrated that the reset current decreases as the compliance current decreases, which provides an approach to lower the power consumption. The conduction mechanisms for high- and low-resistance states are dominated by Frenkel–Poole conduction and space-charge-limited current, respectively. These good memory characteristics in this RRAM show great potential in future high-performance memory applications.

Highly Reliable Multilevel and 2-bit/cell Operation of Wrapped Select Gate (WSG) SONOS Memory

In this letter, high-performance and reliable wrapped select gate (WSG) polysilicon-oxide-nitride-oxide-silicon (SONOS) memory cells with multilevel and 2-bit/cell operation have been successfully demonstrated. The multilevel storage is easily obtained with fast program/erase speed (10 mus/5 ms) and low programming current (3.5 muA) for our WSG SONOS by a source-side injection. Besides the excellent reliability properties of our multilevel WSG-SONOS memory including unconsidered gate and drain disturbance, long charge retention (>150degC) and good endurance (>104) are also presented. This novel WSG-SONOS memory with a multilevel and 2-bit/cell operation can be used in future high-density and high-performance memory application