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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Electronic Materials".

Deadline for manuscript submissions: closed (15 December 2024) | Viewed by 15760

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Special Issue Editors

Prof. Dr. Sungjun Kim

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Guest Editor

Division of Electronics and Electrical Engineering, Dongguk University, Seoul 04620, Republic of Korea
Interests: emerging memory; memristor; resistive switching; synaptic devices; neuromorphic; metal oxides
Special Issues, Collections and Topics in MDPI journals

Dr. Jung-Kyu Lee

E-Mail Website
Guest Editor

Division of Electronics and Electrical Engineering, Dongguk University, Seoul 04620, Republic of Korea
Interests: memristor; resistive switching; ferroelectric; synaptic devices; neuromorphic; RRAM; FTJ; device reliability; 1/f noise; low-frequency noise

Special Issue Information

Dear Colleagues,

There is always a need for high-performance information and data storage systems, which emerging memory technology has made possible. With new developments in architecture innovation and performance optimization, memory device design, systems, and materials play an essential role in emerging memory technology. This Special Issue mainly focuses on the advances in materials and devices for memory applications. We welcome articles, communications, and reviews on the state of the art in emerging memory applications, such as advanced fabrication based on various materials and memory types, improvement of electrical performances and functions of memory devices, as well as implementation for neuromorphic computing.

The potential topics include, but are not limited to, the following:

Promising memory devices and technology, such as resistive random-access memory (RRAM), ferroelectric RAM (FRAM), magnetoresistive RAM (MRAM), phase-change memory (PCM), spin-transfer torque RAM (STTRAM), FeFET memory, etc.;
Functional materials for memory applications, including metal and metal oxides/nitrides, silicon and titanium compounds, thin films, nanoparticles, polymers, organic/inorganic–organic hybrids and composites, ferroelectric materials, graphene, carbon nanotubes, carbon-based materials, quantum dots, perovskites, phase change and 2D materials, etc.

Prof. Dr. Sungjun Kim
Dr. Jung-Kyu Lee
Guest Editors

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Keywords

memory devices and materials
non-volatile memory (NVM)
semiconductor memory devices
resistive random-access memory (RRAM)
ferroelectric random-access memory (FeRAM/FRAM)
magnetoresistive random-access memory (MRAM)
phase-change memory (PCM)
spin-transfer-torque random-access memory (STTRAM)
FeFET memory
resistive switching
memristors
neuromorphic computing systems
synaptic devices

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Published Papers (10 papers)

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Research

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13 pages, 3951 KiB

Open AccessArticle

Exploring the Reconfigurable Memory Effect in Electroforming-Free YMnO₃-Based Resistive Switches: Towards a Tunable Frequency Response

by Xianyue Zhao, Nan Du, Jan Dellith, Marco Diegel, Uwe Hübner, Bernhard Wicht and Heidemarie Schmidt

Materials 2024, 17(11), 2748; https://doi.org/10.3390/ma17112748 - 5 Jun 2024

Viewed by 734

Abstract

Memristors, since their inception, have demonstrated remarkable characteristics, notably the exceptional reconfigurability of their memory. This study delves into electroforming-free

{YMnO}_{3}

(YMO)-based resistive switches, emphasizing the reconfigurable memory effect in multiferroic YMO thin films with metallically conducting electrodes and their pivotal role [...] Read more.

Memristors, since their inception, have demonstrated remarkable characteristics, notably the exceptional reconfigurability of their memory. This study delves into electroforming-free

{YMnO}_{3}

(YMO)-based resistive switches, emphasizing the reconfigurable memory effect in multiferroic YMO thin films with metallically conducting electrodes and their pivotal role in achieving adaptable frequency responses in impedance circuits consisting of reconfigurable YMO-based resistive switches and no reconfigurable passive elements, e.g., inductors and capacitors. The multiferroic YMO possesses a network of charged domain walls which can be reconfigured by a time-dependent voltage applied between the metallically conducting electrodes. Through experimental demonstrations, this study scrutinizes the impedance response not only for individual switch devices but also for impedance circuitry based on YMO resistive switches in both low- and high-resistance states, interfacing with capacitors and inductors in parallel and series configurations. Scrutinized Nyquist plots visually capture the intricate dynamics of impedance circuitry, revealing the potential of electroforming-free YMO resistive switches in finely tuning frequency responses within impedance circuits. This adaptability, rooted in the unique properties of YMO, signifies a paradigm shift heralding the advent of advanced and flexible electronic technologies. Full article

(This article belongs to the Special Issue Advanced Semiconductor/Memory Materials and Devices)

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13 pages, 3445 KiB

Open AccessArticle

Deposition and Optical Characterization of Sputter Deposited p-Type Delafossite CuGaO₂ Thin Films Using Cu₂O and Ga₂O₃ Targets

by Akash Hari Bharath, Ashwin Kumar Saikumar and Kalpathy B. Sundaram

Materials 2024, 17(7), 1609; https://doi.org/10.3390/ma17071609 - 1 Apr 2024

Cited by 2 | Viewed by 1272

Abstract

CuGaO₂ thin films were deposited using the RF magnetron sputtering technique using Cu₂O and Ga₂O₃ targets. The films were deposited at room temperature onto a quartz slide. The sputtering power of Cu₂O remained constant at 50 W, while the sputtering power of Ga₂O₃ was systematically varied from 150 W to 200 W. The films were subsequently subjected to annealing at temperatures of 850 °C and 900 °C in a nitrogen atmosphere for a duration of 5 h. XRD analysis on films deposited with a Ga₂O₃ sputtering power of 175 W annealed at 900 °C revealed the development of nearly single-phase delafossite CuGaO₂ thin films. SEM images of films annealed at 900 °C showed an increasing trend in grain size with a change in sputtering power level. Optical studies performed on the film revealed a transmission of 84.97% and indicated a band gap of approximately 3.27 eV. The film exhibited a refractive index of 2.5 within the wavelength range of 300 to 450 nm. Full article

(This article belongs to the Special Issue Advanced Semiconductor/Memory Materials and Devices)

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14 pages, 4836 KiB

Open AccessArticle

Defects Contributing to Hysteresis in Few-Layer and Thin-Film MoS₂ Memristive Devices

by Saadman Abedin, Vladislav Kurtash, Sobin Mathew, Sebastian Thiele, Heiko O. Jacobs and Jörg Pezoldt

Materials 2024, 17(6), 1350; https://doi.org/10.3390/ma17061350 - 15 Mar 2024

Cited by 1 | Viewed by 1414

Abstract

Molybdenum disulfide, a two-dimensional material extensively explored for potential applications in non-von Neumann computing technologies, has garnered significant attention owing to the observed hysteresis phenomena in MoS₂ FETs. The dominant sources of hysteresis reported include charge trapping at the channel–dielectric interface and the adsorption/desorption of molecules. However, in MoS₂ FETs with different channel thicknesses, the specific nature and density of defects contributing to hysteresis remain an intriguing aspect requiring further investigation. This study delves into memristive devices with back-gate modulated channel layers based on CVD-deposited flake-based and thin-film-based MoS₂ FETs, with a few-layer (FL) and thin-film (TF) channel thickness. Analysis of current–voltage (

I - V

) and conductance–frequency (

G_{p} / ω - f

) measurements led to the conclusion that the elevated hysteresis observed in TF MoS₂ devices, as opposed to FL devices, stems from a substantial contribution from intrinsic defects within the channel volume, surpassing that of interface defects. This study underscores the significance of considering both intrinsic defects within the bulk and the interface defects of the channel when analyzing hysteresis in MoS₂ FETs, particularly in TF FETs. The selection between FL and TF MoS₂ devices depends on the requirements for memristive applications, considering factors such as hysteresis tolerance and scaling capabilities. Full article

(This article belongs to the Special Issue Advanced Semiconductor/Memory Materials and Devices)

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12 pages, 29373 KiB

Open AccessArticle

Demonstration of 10 nm Ferroelectric Al_0.7Sc_0.3N-Based Capacitors for Enabling Selector-Free Memory Array

by Li Chen, Chen Liu, Hock Koon Lee, Binni Varghese, Ronald Wing Fai Ip, Minghua Li, Zhan Jiang Quek, Yan Hong, Weijie Wang, Wendong Song, Huamao Lin and Yao Zhu

Materials 2024, 17(3), 627; https://doi.org/10.3390/ma17030627 - 27 Jan 2024

Cited by 4 | Viewed by 1852

Abstract

In this work, 10 nm scandium-doped aluminum nitride (AlScN) capacitors are demonstrated for the construction of the selector-free memory array application. The 10 nm Al_0.7Sc_0.3N film deposited on an 8-inch silicon wafer with sputtering technology exhibits a large remnant polarization exceeding 100 µC/cm² and a tight distribution of the coercive field, which is characterized by the positive-up-negative-down (PUND) method. As a result, the devices with lateral dimension of only 1.5 μm show a large memory window of over 250% and a low power consumption of ~40 pJ while maintaining a low disturbance rate of <2%. Additionally, the devices demonstrate stable multistate memory characteristics with a dedicated operation scheme. The back-end-of-line (BEOL)-compatible fabrication process, along with all these device performances, shows the potential of AlScN-based capacitors for the implementation of the high-density selector-free memory array. Full article

(This article belongs to the Special Issue Advanced Semiconductor/Memory Materials and Devices)

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12 pages, 5472 KiB

Open AccessArticle

Leakage Mechanism and Cycling Behavior of Ferroelectric Al_0.7Sc_0.3N

by Li Chen, Qiang Wang, Chen Liu, Minghua Li, Wendong Song, Weijie Wang, Desmond K. Loke and Yao Zhu

Materials 2024, 17(2), 397; https://doi.org/10.3390/ma17020397 - 12 Jan 2024

Cited by 4 | Viewed by 1659

Abstract

Ferroelectric scandium-doped aluminum nitride (Al_1-xSc_xN) is of considerable research interest because of its superior ferroelectricity. Studies indicate that Al_1-xSc_xN may suffer from a high leakage current, which can hinder further thickness scaling and long-term reliability. In this work, we systematically investigate the origin of the leakage current in Al_0.7Sc_0.3N films via experiments and theoretical calculations. The results reveal that the leakage may originate from the nitrogen vacancies with positively charged states and fits well with the trap-assisted Poole-Frenkel (P-F) emission. Moreover, we examine the cycling behavior of ferroelectric Al_0.7Sc_0.3N-based FeRAM devices. We observe that the leakage current substantially increases when the device undergoes bipolar cycling with a pulse amplitude larger than the coercive electric field. Our analysis shows that the increased leakage current in bipolar cycling is caused by the monotonously reduced trap energy level by monitoring the direct current (DC) leakage under different temperatures and the P-F emission fitting. Full article

(This article belongs to the Special Issue Advanced Semiconductor/Memory Materials and Devices)

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12 pages, 3038 KiB

Open AccessArticle

Analog Memory and Synaptic Plasticity in an InGaZnO-Based Memristor by Modifying Intrinsic Oxygen Vacancies

by Chandreswar Mahata, Hyojin So, Soomin Kim, Sungjun Kim and Seongjae Cho

Materials 2023, 16(24), 7510; https://doi.org/10.3390/ma16247510 - 5 Dec 2023

Cited by 2 | Viewed by 1359

Abstract

This study focuses on InGaZnO-based synaptic devices fabricated using reactive radiofrequency sputtering deposition with highly uniform and reliable multilevel memory states. Electron trapping and trap generation behaviors were examined based on current compliance adjustments and constant voltage stressing on the ITO/InGaZnO/ITO memristor. Using O₂ + N₂ plasma treatment resulted in stable and consistent cycle-to-cycle memory switching with an average memory window of ~95.3. Multilevel resistance states ranging from 0.68 to 140.7 kΩ were achieved by controlling the V_RESET within the range of −1.4 to −1.8 V. The modulation of synaptic weight for short-term plasticity was simulated by applying voltage pulses with increasing amplitudes after the formation of a weak conductive filament. To emulate several synaptic behaviors in InGaZnO-based memristors, variations in the pulse interval were used for paired-pulse facilitation and pulse frequency-dependent spike rate-dependent plasticity. Long-term potentiation and depression are also observed after strong conductive filaments form at higher current compliance in the switching layer. Hence, the ITO/InGaZnO/ITO memristor holds promise for high-performance synaptic device applications. Full article

(This article belongs to the Special Issue Advanced Semiconductor/Memory Materials and Devices)

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12 pages, 5192 KiB

Open AccessArticle

Improved Resistive Switching Characteristics and Synaptic Functions of InZnO/SiO₂ Bilayer Device

by Dongyeol Ju, Minsuk Koo and Sungjun Kim

Materials 2023, 16(23), 7324; https://doi.org/10.3390/ma16237324 - 24 Nov 2023

Viewed by 1305

Abstract

This paper investigates the bipolar resistive switching and synaptic characteristics of IZO single-layer and IZO/SiO₂ bilayer two-terminal memory devices. The chemical properties and structure of the device with a SiO₂ layer are confirmed by x-ray photoemission spectroscopy (XPS) and transmission electron microscopy (TEM) imaging. The device with the SiO₂ layer showed better memory characteristics with a low current level, as well as better cell-to-cell and cycle-to-cycle uniformity. Moreover, the neuromorphic applications of the IZO/SiO₂ bilayer device are demonstrated by pulse response. Paired pulse facilitation, excitatory postsynaptic current, and pulse-width-dependent conductance changes are conducted by the coexistence of short- and long-term memory characteristics. Moreover, Hebbian rules are emulated to mimic biological synapse function. The result of potentiation, depression, spike-rate-dependent plasticity, and spike-time-dependent plasticity prove their favorable abilities for future applications in neuromorphic computing architecture. Full article

(This article belongs to the Special Issue Advanced Semiconductor/Memory Materials and Devices)

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11 pages, 4067 KiB

Open AccessArticle

Amorphous BN-Based Synaptic Device with High Performance in Neuromorphic Computing

by Juyeong Pyo, Junwon Jang, Dongyeol Ju, Subaek Lee, Wonbo Shim and Sungjun Kim

Materials 2023, 16(20), 6698; https://doi.org/10.3390/ma16206698 - 15 Oct 2023

Cited by 1 | Viewed by 1489

Abstract

The von Neumann architecture has faced challenges requiring high-fulfillment levels due to the performance gap between its processor and memory. Among the numerous resistive-switching random-access memories, the properties of hexagonal boron nitride (BN) have been extensively reported, but those of amorphous BN have been insufficiently explored for memory applications. Herein, we fabricated a Pt/BN/TiN device utilizing the resistive switching mechanism to achieve synaptic characteristics in a neuromorphic system. The switching mechanism is investigated based on the I–V curves. Utilizing these characteristics, we optimize the potentiation and depression to mimic the biological synapse. In artificial neural networks, high-recognition rates are achieved using linear conductance updates in a memristor device. The short-term memory characteristics are investigated in depression by controlling the conductance level and time interval. Full article

(This article belongs to the Special Issue Advanced Semiconductor/Memory Materials and Devices)

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13 pages, 3774 KiB

Open AccessEditor’s ChoiceArticle

Double-Forming Mechanism of TaO_x-Based Resistive Memory Device and Its Synaptic Applications

by Dongyeol Ju, Sunghun Kim, Subaek Lee and Sungjun Kim

Materials 2023, 16(18), 6184; https://doi.org/10.3390/ma16186184 - 13 Sep 2023

Viewed by 1240

Abstract

The bipolar resistive switching properties of Pt/TaO_x/InO_x/ITO-resistive random-access memory devices under DC and pulse measurement conditions are explored in this work. Transmission electron microscopy and X-ray photoelectron spectroscopy were used to confirm the structure and chemical compositions of the devices. A unique two-step forming process referred to as the double-forming phenomenon and self-compliance characteristics are demonstrated under a DC sweep. A model based on oxygen vacancy migration is proposed to explain its conduction mechanism. Varying reset voltages and compliance currents were applied to evaluate multilevel cell characteristics. Furthermore, pulses were applied to the devices to demonstrate the neuromorphic system’s application via testing potentiation, depression, spike-timing-dependent plasticity, and spike-rate-dependent plasticity. Full article

(This article belongs to the Special Issue Advanced Semiconductor/Memory Materials and Devices)

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Review

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34 pages, 9070 KiB

Open AccessReview

A Review of β-Ga₂O₃ Power Diodes

by Yongjie He, Feiyang Zhao, Bin Huang, Tianyi Zhang and Hao Zhu

Materials 2024, 17(8), 1870; https://doi.org/10.3390/ma17081870 - 18 Apr 2024

Cited by 13 | Viewed by 2597

Abstract

As the most stable phase of gallium oxide, β-Ga₂O₃ can enable high-quality, large-size, low-cost, and controllably doped wafers by the melt method. It also features a bandgap of 4.7–4.9 eV, a critical electric field strength of 8 MV/cm, and a Baliga’s figure of merit (BFOM) of up to 3444, which is 10 and 4 times higher than that of SiC and GaN, respectively, showing great potential for application in power devices. However, the lack of effective p-type Ga₂O₃ limits the development of bipolar devices. Most research has focused on unipolar devices, with breakthroughs in recent years. This review mainly summarizes the research progress fora different structures of β-Ga₂O₃ power diodes and gives a brief introduction to their thermal management and circuit applications. Full article

(This article belongs to the Special Issue Advanced Semiconductor/Memory Materials and Devices)

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