황현상 교수

Hardware artificial neural network (ANN) systems with high density synapse array devices can perform massive parallel computing for pattern recognition with low power consumption. To implement a neuromorphic system with on-chip training capability, we need to develop an ideal synapse device with various device requirements, such as scalability, MLC characteristics, low power operation, data retention, and symmetric/linear conductance changes under potentiation/depression modes. Although various

This letter presents a unique process to grow high quality ultrathin (∼60 Å) gate dielectrics using N2O (nitrous oxide) gas. Compared with conventional rapid thermally grown oxide in the O2, the new oxynitride dielectrics show very large charge-to-breakdown (at +50 mA/cm2, 850 C/cm2 for oxynitride compared to 95 C/cm2 for the control thermal oxide) and less charge trapping under constant current stress. Significantly reduced interface state generation was also observed under constant current str

Abstract This study demonstrates an integrate and fire (I&F) neuron using threshold switching (TS) devices to implement spike‐based neuromorphic system. An I&F neuron can be realized using the hysteric voltage switch characteristics of a TS device. To investigate the effects of various TS devices on neuron behavior, neurons are compared using three different types of TS device: NbO 2 ‐based insulator‐to‐metal transition (IMT) device, B–Te‐based ovonic threshold switching device, and Ag/H

We demonstrate a high-performance selection device by utilizing the concept of crested oxide barrier to suppress the sneak current in bipolar resistive memory arrays. Using a TaO(x)/TiO(2)/TaO(x) structure, high current density over 10(7) A cm(-2) and excellent nonlinear characteristics up to 10(4) were successfully demonstrated. On the basis of the defect chemistry and SIMS depth profile result, we found that some Ta atoms gradually diffused into TiO(2) film, and consequently, the energy band o

A wake-up free Hf0.5Zr0.5O2 (HZO) ferroelectric film with the highest remnant polarization (Pr) value to date was achieved through tuning of the ozone pulse duration, the annealing process, and the metal/insulator interface. The ozone dosage during the atomic layer deposition of HZO films appears to be a crucial parameter in suppressing the mechanisms driving the wake-up effect. A tungsten capping electrode with a relatively low thermal expansion coefficient enables the induction of an in-plane

Efforts to develop scalable learning algorithms for implementation of networks of spiking neurons in silicon have been hindered by the considerable footprints of learning circuits, which grow as the number of synapses increases. Recent developments in nanotechnologies provide an extremely compact device with low-power consumption.In particular, nanoscale resistive switching devices (resistive random-access memory (RRAM)) are regarded as a promising solution for implementation of biological synap

Abstract All solid-state lithium-ion transistors are considered as promising synaptic devices for building artificial neural networks for neuromorphic computing. However, the slow ionic conduction in existing electrolytes hinders the performance of lithium-ion-based synaptic transistors. In this study, we systematically explore the influence of ionic conductivity of electrolytes on the synaptic performance of ionic transistors. Isovalent chalcogenide substitution such as Se in Li 3 PO 4 signific

The electrical and physical characteristics of oxynitride grown in N/sub 2/O gas ambient have been studied. The dielectric growth rate in N/sub 2/O was found to be highly controllable and lower than that in O/sub 2/. Auger electron spectroscopy studies of oxynitride show a nitrogen-rich layer near the Si-SiO/sub 2/ interface. Compared with the control oxide, the oxynitride shows excellent electrical characteristics such as excellent diffusion barrier to dopant (BF/sub 2/), a significant reductio

Wake‐up effect is still an obstacle in the commercialization of hafnia‐based ferroelectric thin films. Herein, the effect of defects, controlled by ozone dosage, on the field cycling behavior of the atomic layer deposited Hf 0.5 Zr 0.5 O 2 (HZO) films is investigated. A nearly wake‐up free device is achieved after reduction of carbon contamination and oxygen defects by increasing the ozone dosage. The sample which is grown at 30 s ozone pulse duration shows about 97% of the woken‐up P r at the p

Creation of nanometer‐scale conductive filaments in resistive switching devices makes them appealing for advanced electrical applications. While in situ electrical probing transmission electron microscopy promotes fundamental investigations of how the conductive filament comes into existence, it does not provide proof‐of‐principle observations for the filament growth. Here, using advanced microscopy techniques, electrical, 3D compositional, and structural information of the switching‐induced con

Abstract NbO 2 has the potential for a variety of electronic applications due to its electrically induced insulator-to-metal transition (IMT) characteristic. In this study, we find that the IMT behavior of NbO 2 follows the field-induced nucleation by investigating the delay time dependency at various voltages and temperatures. Based on the investigation, we reveal that the origin of leakage current in NbO x is partly due to insufficient Schottky barrier height originating from interface defects

Abstract Lithium nanoionic transistors have recently emerged as promising artificial synaptic devices for neuromorphic hardware systems. However, mimicking the essential synaptic functionalities including nonvolatile conductance modulation with a near‐linear analog weight update has been a crucial milestone in those synaptic devices and has a direct impact on pattern recognition accuracy. The volatile channel conductance change due to the instability of the solid electrolyte interface and lithiu

Abstract Atomic‐level control of conductance in a Cu/Ti/HfO 2 /TiN‐based electrically controllable break junction (ECBJ) is demonstrated. The ECBJ is designed through sophisticated stack engineering and refined electrical operation. Control over bias‐induced ion migration is the key to forming the ECBJ. Precise atomic‐level control is accomplished with an optimized high temperature forming (OHTF) scheme. OHTF‐controlled single‐atomic switching in ECBJs has not yet been studied in detail. During

Ovonic threshold switching (OTS) selector device and the material properties analysed by X-ray diffraction (XRD), spectroscopic ellipsometry, and X-ray photoelectron spectroscopy (XPS). The correlation and the key material parameters determining the device performances were investigated. By comparing the experimental data with the calculation results from various analytical models previously developed for OTS materials, the electrical properties of the device were shown to be dependent on the ke

We have investigated the analogue memory characteristics of an oxide-based resistive-switching device under an electrical pulse to mimic biological spike-timing-dependent plasticity synapse characteristics. As a synaptic device, a TiN/Pr0.7Ca0.3MnO3-based resistive-switching device exhibiting excellent analogue memory characteristics was used to control the synaptic weight by applying various pulse amplitudes and cycles. Furthermore, potentiation and depression characteristics with the same spik