Memcapacitor Crossbar Array with Charge Trap NAND Flash Structure for Neuromorphic Computing

Abstract The progress of artificial intelligence and the development of large‐scale neural networks have significantly increased computational costs and energy consumption. To address these challenges, researchers are exploring low‐power neural network implementation approaches and neuromorphic computing systems are being highlighted as potential candidates. Specifically, the development of high‐density and reliable synaptic devices, which are the key elements of neuromorphic systems, is of particular interest. In this study, an 8 × 16 memcapacitor crossbar array that combines the technological maturity of flash cells with the advantages of NAND flash array structure is presented. The analog properties of the array with high reliability are experimentally demonstrated, and vector‐matrix multiplication with extremely low error is successfully performed. Additionally, with the capability of weight fine‐tuning characteristics, a spiking neural network for CIFAR‐10 classification via off‐chip learning at the wafer level is implemented. These experimental results demonstrate a high level of accuracy of 92.11%, with less than a 1.13% difference compared to software‐based neural networks (93.24%)

Kernel Mapping Methods of Convolutional Neural Network in 3D NAND Flash Architecture

A flash memory is a non-volatile memory that has a large memory window, high cell density, and reliable switching characteristics and can be used as a synaptic device in a neuromorphic system based on 3D NAND flash architecture. We fabricated a TiN/Al2O3/Si3N4/SiO2/Si stack-based Flash memory device with a polysilicon channel. The input/output signals and output values are binarized for accurate vector-matrix multiplication operations in the hardware. In addition, we propose two kernel mapping methods for convolutional neural networks (CNN) in the neuromorphic system. The VMM operations of two mapping schemes are verified through SPICE simulation. Finally, the off-chip learning in the CNN structure is performed using the Modified National Institute of Standards and Technology (MNIST) dataset. We compared the two schemes in terms of various parameters and determined the advantages and disadvantages of each

Detrimental effect of high-temperature storage on sulfide-based all-solid-state batteries

© 2022 Author(s).The all-solid-state battery (ASSB) has become one of the most promising next-generation battery systems, since the aspect of safety has emerged as a crucial criterion for new large-scale applications such as in electric vehicles. Despite the recent remarkable progress in the performance enhancement, the real-world implementation of the ASSB still requires full comprehension/evaluation of its properties and performance under various practical operational conditions. Unlike batteries employed in conventional electronic devices, those in electric vehicles - the major application that the ASSB is expected to be employed - would be exposed to wide temperature variations (-20 to ∼70 °C) at various states of charges due to their outdoor storage and irregular discharge/rest/charge conditions depending on vehicle drivers' usage patterns. Herein, we investigate the reliability of a Li6PS5Cl-based ASSB system in practically harsh but plausible storage conditions and reveal that it is vulnerable to elevated-temperature storage as low as 70 °C, which, in contrast to the common belief, causes significant degradation of the electrolyte and consequently irreversible buildup of the cell resistance. It is unraveled that this storage condition induces the decomposition of Li6PS5Cl in contact with the cathode material, involving the SOx gas evolution particularly at charged states, which creates a detrimental porous cathode/electrolyte interface, thereby leading to the large interfacial resistance. Our findings indicate that the stability of the solid electrolyte, which has been believed to be failsafe, needs to be carefully revisited at various practical operational conditions for actual applications in ASSBs.11Nsciescopu

A Kinetic Indicator of Ultrafast Nickel-Rich Layered Oxide Cathodes

Elucidating high-rate cycling-induced nonequilibriumelectrodereactions is crucial for developing extreme fast charging (XFC) batteries.Herein, we unveiled the distinct rate capabilities of a series ofNi-rich layered oxide (NRLO) cathodes by quantitatively establishingtheir dynamic structure-kinetics relationships. Contrary toconventional views, we discovered electrode kinetic properties obtained ex-situ near equilibrium states failed to assess the effectiverate capability of NRLOs at ultrafast C rates. Further, the kineticphase heterogeneity, characterized by the dynamic separations in in-situ X-ray diffraction patterns and deviations in NRLO c-axis lattice parameters, exclusively correlated with thecapacity reduction under XFC and became an effective indicator ofthe NRLO rate capability. Enhancing the cycling temperature boostedthe rate capability of studied NRLOs by similar to 10%, which was furtherverified to mitigate the kinetic phase heterogeneity during XFC. Overall,this study lays the groundwork for tuning the kinetic phase heterogeneityof electrodes to develop ultrafast batteries.N

A Kinetic Indicator of Ultrafast Nickel-Rich Layered Oxide Cathodes

Elucidating high-rate cycling-induced nonequilibrium electrode reactions is crucial for developing extreme fast charging (XFC) batteries. Herein, we unveiled the distinct rate capabilities of a series of Ni-rich layered oxide (NRLO) cathodes by quantitatively establishing their dynamic structure–kinetics relationships. Contrary to conventional views, we discovered electrode kinetic properties obtained ex-situ near equilibrium states failed to assess the effective rate capability of NRLOs at ultrafast C rates. Further, the kinetic phase heterogeneity, characterized by the dynamic separations in in-situ X-ray diffraction patterns and deviations in NRLO c-axis lattice parameters, exclusively correlated with the capacity reduction under XFC and became an effective indicator of the NRLO rate capability. Enhancing the cycling temperature boosted the rate capability of studied NRLOs by ∼10%, which was further verified to mitigate the kinetic phase heterogeneity during XFC. Overall, this study lays the groundwork for tuning the kinetic phase heterogeneity of electrodes to develop ultrafast batteries