Nanomaterials

Research

13 pages, 2259 KiB

Open AccessArticle

Spike Optimization to Improve Properties of Ferroelectric Tunnel Junction Synaptic Devices for Neuromorphic Computing System Applications

by Jisu Byun, Wonwoo Kho, Hyunjoo Hwang, Yoomi Kang, Minjeong Kang, Taewan Noh, Hoseong Kim, Jimin Lee, Hyo-Bae Kim, Ji-Hoon Ahn and Seung-Eon Ahn

Nanomaterials 2023, 13(19), 2704; https://doi.org/10.3390/nano13192704 - 5 Oct 2023

Viewed by 1242

Abstract

The continuous advancement of Artificial Intelligence (AI) technology depends on the efficient processing of unstructured data, encompassing text, speech, and video. Traditional serial computing systems based on the von Neumann architecture, employed in information and communication technology development for decades, are not suitable [...] Read more.

The continuous advancement of Artificial Intelligence (AI) technology depends on the efficient processing of unstructured data, encompassing text, speech, and video. Traditional serial computing systems based on the von Neumann architecture, employed in information and communication technology development for decades, are not suitable for the concurrent processing of massive unstructured data tasks with relatively low-level operations. As a result, there arises a pressing need to develop novel parallel computing systems. Recently, there has been a burgeoning interest among developers in emulating the intricate operations of the human brain, which efficiently processes vast datasets with remarkable energy efficiency. This has led to the proposal of neuromorphic computing systems. Of these, Spiking Neural Networks (SNNs), designed to closely resemble the information processing mechanisms of biological neural networks, are subjects of intense research activity. Nevertheless, a comprehensive investigation into the relationship between spike shapes and Spike-Timing-Dependent Plasticity (STDP) to ensure efficient synaptic behavior remains insufficiently explored. In this study, we systematically explore various input spike types to optimize the resistive memory characteristics of Hafnium-based Ferroelectric Tunnel Junction (FTJ) devices. Among the various spike shapes investigated, the square-triangle (RT) spike exhibited good linearity and symmetry, and a wide range of weight values could be realized depending on the offset of the RT spike. These results indicate that the spike shape serves as a crucial indicator in the alteration of synaptic connections, representing the strength of the signals. Full article

(This article belongs to the Special Issue Ferroelectric Nanostructures and Thin Films)

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14 pages, 7769 KiB

Open AccessArticle

Synthesis, Characterization and Investigation of Optical and Electrical Properties of Polyaniline/Nickel Ferrite Composites

by Priyanka Kolhar, Basavaraja Sannakki, Meenakshi Verma, Prabhakar S.V., Mansoor Alshehri and Nehad Ali Shah

Nanomaterials 2023, 13(15), 2223; https://doi.org/10.3390/nano13152223 - 31 Jul 2023

Cited by 6 | Viewed by 1406

Abstract

Nickel ferrite nanoparticles are prepared by using a low-temperature self-propagating solution combustion method using urea as fuel. The prepared nickel ferrite nanoparticles were doped with polyaniline in the three different weight ratios of 10%, 30% and 50% by using an in situ polymerization [...] Read more.

Nickel ferrite nanoparticles are prepared by using a low-temperature self-propagating solution combustion method using urea as fuel. The prepared nickel ferrite nanoparticles were doped with polyaniline in the three different weight ratios of 10%, 30% and 50% by using an in situ polymerization method and by adding ammonium persulfate as an oxidizing agent. The obtained samples were characterized by using XRD, FTIR, SEM and a UV–visible spectrophotometer. XRD examined crystalline peaks of ferrites and amorphous peak of polyaniline and confirmed the formation of the composites. FTIR examined the chemical nature of samples and showed peaks due to polyaniline and the characteristic peaks that were less than 1000 cm⁻¹ wavenumber were due to metal–oxygen bond vibrations of ferrites. AC conductivity increased with frequency in all samples and the highest AC conductivity was seen in polyaniline/nickel ferrite 50%. DC conductivity increased in all samples with the temperature showing the semiconducting nature of the samples. Activation energy was evaluated by using Arrhenius plots and there was a decrease in activation energy with the addition of ferrite content. The UV–visible absorption peaks of polyaniline showed shifting in the composites. The optical direct and indirect band gaps were evaluated by plotting Tauc plots and the values of the optical band gap decreased with addition of ferrite in polyaniline and the Urbach energy increased in the samples with 10%, 30% and 50% polyaniline/nickel ferrite composites. The optical properties of these composites with a low band gap can find applications in devices such as solar cells. Full article

(This article belongs to the Special Issue Ferroelectric Nanostructures and Thin Films)

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11 pages, 4608 KiB

Open AccessArticle

Yttrium Doping Effects on Ferroelectricity and Electric Properties of As-Deposited Hf_1−xZr_xO₂ Thin Films via Atomic Layer Deposition

by Youkyoung Oh, Seung Won Lee, Jeong-Hun Choi, Seung-Eon Ahn, Hyo-Bae Kim and Ji-Hoon Ahn

Nanomaterials 2023, 13(15), 2187; https://doi.org/10.3390/nano13152187 - 27 Jul 2023

Cited by 1 | Viewed by 1244

Abstract

Hf_1−xZr_xO₂ (HZO) thin films are versatile materials suitable for advanced ferroelectric semiconductor devices. Previous studies have shown that the ferroelectricity of HZO thin films can be stabilized by doping them with group III elements at low concentrations. While [...] Read more.

Hf_1−xZr_xO₂ (HZO) thin films are versatile materials suitable for advanced ferroelectric semiconductor devices. Previous studies have shown that the ferroelectricity of HZO thin films can be stabilized by doping them with group III elements at low concentrations. While doping with Y improves the ferroelectric properties, there has been limited research on Y-HZO thin films fabricated using atomic layer deposition (ALD). In this study, we investigated the effects of Y-doping cycles on the ferroelectric and electrical properties of as-deposited Y-HZO thin films with varying compositions fabricated through ALD. The Y-HZO thin films were stably crystallized without the need for post-thermal treatment and exhibited transition behavior depending on the Y-doping cycle and initial composition ratio of the HZO thin films. These Y-HZO thin films offer several advantages, including enhanced dielectric constant, leakage current density, and improved endurance. Moreover, the optimized Y-doping cycle induced a phase transformation that resulted in Y-HZO thin films with improved ferroelectric properties, exhibiting stable behavior without fatigue for up to 10¹⁰ cycles. These as-deposited Y-HZO thin films show promise for applications in semiconductor devices that require high ferroelectric properties, excellent electrical properties, and reliable performance with a low thermal budget. Full article

(This article belongs to the Special Issue Ferroelectric Nanostructures and Thin Films)

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12 pages, 4896 KiB

Open AccessArticle

Mechanism of the Wake-Up and the Split-Up in AlO_x/Hf_0.5Zr_0.5O_x Film

by Min-Jin Kim, Cheol-Jun Kim and Bo-Soo Kang

Nanomaterials 2023, 13(14), 2146; https://doi.org/10.3390/nano13142146 - 24 Jul 2023

Viewed by 940

Abstract

Dielectric layers are widely used in ferroelectric applications such as memory and negative capacitance devices. The wake-up and the split-up phenomena in the ferroelectric hafnia are well-known challenges in early-stage device reliability. We found that the phenomena even occur in the bilayer, which [...] Read more.

Dielectric layers are widely used in ferroelectric applications such as memory and negative capacitance devices. The wake-up and the split-up phenomena in the ferroelectric hafnia are well-known challenges in early-stage device reliability. We found that the phenomena even occur in the bilayer, which is composed of the hafnia and the dielectrics. The phenomena are known to be affected mainly by oxygen vacancies of hafnia. Dielectric layers, which are often metal oxides, are also prone to be affected by oxygen vacancies. To study the effect of the dielectric layer on the wake-up and the split-up phenomena, we fabricated ferroelectric thin-film capacitors with dielectric layers of various thicknesses and measured their field-cycling behaviors. We found that the movement of oxygen vacancies in the dielectric layer was predominantly affected by the polarization state of the ferroelectric layer. In addition, the mechanism of the field-cycling behavior in the bilayer is similar to that in ferroelectric thin films. Our results can be applied in ferroelectric applications that use dielectric layers. Full article

(This article belongs to the Special Issue Ferroelectric Nanostructures and Thin Films)

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13 pages, 5465 KiB

Open AccessArticle

Preparation of Remote Plasma Atomic Layer-Deposited HfO₂ Thin Films with High Charge Trapping Densities and Their Application in Nonvolatile Memory Devices

by Jae-Hoon Yoo, Won-Ji Park, So-Won Kim, Ga-Ram Lee, Jong-Hwan Kim, Joung-Ho Lee, Sae-Hoon Uhm and Hee-Chul Lee

Nanomaterials 2023, 13(11), 1785; https://doi.org/10.3390/nano13111785 - 1 Jun 2023

Cited by 3 | Viewed by 1415

Abstract

Optimization of equipment structure and process conditions is essential to obtain thin films with the required properties, such as film thickness, trapped charge density, leakage current, and memory characteristics, that ensure reliability of the corresponding device. In this study, we fabricated metal–insulator–semiconductor (MIS) [...] Read more.

Optimization of equipment structure and process conditions is essential to obtain thin films with the required properties, such as film thickness, trapped charge density, leakage current, and memory characteristics, that ensure reliability of the corresponding device. In this study, we fabricated metal–insulator–semiconductor (MIS) structure capacitors using HfO₂ thin films separately deposited by remote plasma (RP) atomic layer deposition (ALD) and direct-plasma (DP) ALD and determined the optimal process temperature by measuring the leakage current and breakdown strength as functions of process temperature. Additionally, we analyzed the effects of the plasma application method on the charge trapping properties of HfO₂ thin films and properties of the interface between Si and HfO₂. Subsequently, we synthesized charge-trapping memory (CTM) devices utilizing the deposited thin films as charge-trapping layers (CTLs) and evaluated their memory properties. The results indicated excellent memory window characteristics of the RP-HfO₂ MIS capacitors compared to those of the DP-HfO₂ MIS capacitors. Moreover, the memory characteristics of the RP-HfO₂ CTM devices were outstanding as compared to those of the DP-HfO₂ CTM devices. In conclusion, the methodology proposed herein can be useful for future implementations of multiple levels of charge-storage nonvolatile memories or synaptic devices that require many states. Full article

(This article belongs to the Special Issue Ferroelectric Nanostructures and Thin Films)

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13 pages, 8006 KiB

Open AccessArticle

Characteristics of Hf_0.5Zr_0.5O₂ Thin Films Prepared by Direct and Remote Plasma Atomic Layer Deposition for Application to Ferroelectric Memory

by Da Hee Hong, Jae Hoon Yoo, Won Ji Park, So Won Kim, Jong Hwan Kim, Sae Hoon Uhm and Hee Chul Lee

Nanomaterials 2023, 13(5), 900; https://doi.org/10.3390/nano13050900 - 27 Feb 2023

Cited by 2 | Viewed by 2559

Abstract

Hf_0.5Zr_0.5O₂ (HZO) thin film exhibits ferroelectric properties and is presumed to be suitable for use in next-generation memory devices because of its compatibility with the complementary metal–oxide–semiconductor (CMOS) process. This study examined the physical and electrical properties of [...] Read more.

Hf_0.5Zr_0.5O₂ (HZO) thin film exhibits ferroelectric properties and is presumed to be suitable for use in next-generation memory devices because of its compatibility with the complementary metal–oxide–semiconductor (CMOS) process. This study examined the physical and electrical properties of HZO thin films deposited by two plasma-enhanced atomic layer deposition (PEALD) methods— direct plasma atomic layer deposition (DPALD) and remote plasma atomic layer deposition (RPALD)—and the effects of plasma application on the properties of HZO thin films. The initial conditions for HZO thin film deposition, depending on the RPALD deposition temperature, were established based on previous research on HZO thin films deposited by the DPALD method. The results show that as the measurement temperature increases, the electric properties of DPALD HZO quickly deteriorate; however, the RPALD HZO thin film exhibited excellent fatigue endurance at a measurement temperature of 60 °C or less. HZO thin films deposited by the DPALD and RPALD methods exhibited relatively good remanent polarization and fatigue endurance, respectively. These results confirm the applicability of the HZO thin films deposited by the RPALD method as ferroelectric memory devices. Full article

(This article belongs to the Special Issue Ferroelectric Nanostructures and Thin Films)

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11 pages, 1910 KiB

Open AccessArticle

Improvement of Resistance Change Memory Characteristics in Ferroelectric and Antiferroelectric (like) Parallel Structures

by Wonwoo Kho, Hyunjoo Hwang, Jisoo Kim, Gyuil Park and Seung-Eon Ahn

Nanomaterials 2023, 13(3), 439; https://doi.org/10.3390/nano13030439 - 21 Jan 2023

Cited by 1 | Viewed by 1738

Abstract

Recently, considerable attention has been paid to the development of advanced technologies such as artificial intelligence (AI) and big data, and high-density, high-speed storage devices are being extensively studied to realize the technology. Ferroelectrics are promising non-volatile memory materials because of their ability [...] Read more.

Recently, considerable attention has been paid to the development of advanced technologies such as artificial intelligence (AI) and big data, and high-density, high-speed storage devices are being extensively studied to realize the technology. Ferroelectrics are promising non-volatile memory materials because of their ability to maintain polarization, even when an external electric field is removed. Recently, it has been reported that HfO₂ thin films compatible with complementary metal–oxide–semiconductor (CMOS) processes exhibit ferroelectricity even at a thickness of less than 10 nm. Among the ferroelectric-based memories, ferroelectric tunnel junctions are attracting attention as ideal devices for improving integration and miniaturization due to the advantages of a simple metal–ferroelectric–metal two-terminal structure and low ultra-low power driving through tunneling. The FTJs are driven by adjusting the tunneling electrical resistance through partial polarization switching. Theoretically and experimentally, a large memory window in a broad coercive field and/or read voltage is required to induce sophisticated partial-polarization switching. Notably, antiferroelectrics (like) have different switching properties than ferroelectrics, which are generally applied to ferroelectric tunnel junctions. The memory features of ferroelectric tunnel junctions are expected to be improved through a broad coercive field when the switching characteristics of the ferroelectric and antiferroelectric (like) are utilized concurrently. In this study, the implementation of multiresistance states was improved by driving the ferroelectric and antiferroelectric (like) devices in parallel. Additionally, by modulating the area ratio of ferroelectric and antiferroelectric (like), the memory window size was increased, and controllability was enhanced by increasing the switchable voltage region. In conclusion, we suggest that ferroelectric and antiferroelectric (like) parallel structures may overcome the limitations of the multiresistance state implementation of existing ferroelectrics. Full article

(This article belongs to the Special Issue Ferroelectric Nanostructures and Thin Films)

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13 pages, 3859 KiB

Open AccessArticle

Synaptic Characteristic of Hafnia-Based Ferroelectric Tunnel Junction Device for Neuromorphic Computing Application

by Wonwoo Kho, Gyuil Park, Jisoo Kim, Hyunjoo Hwang, Jisu Byun, Yoomi Kang, Minjeong Kang and Seung-Eon Ahn

Nanomaterials 2023, 13(1), 114; https://doi.org/10.3390/nano13010114 - 26 Dec 2022

Cited by 5 | Viewed by 2391

Abstract

Owing to the 4th Industrial Revolution, the amount of unstructured data, such as voice and video data, is rapidly increasing. Brain-inspired neuromorphic computing is a new computing method that can efficiently and parallelly process rapidly increasing data. Among artificial neural networks that mimic [...] Read more.

Owing to the 4th Industrial Revolution, the amount of unstructured data, such as voice and video data, is rapidly increasing. Brain-inspired neuromorphic computing is a new computing method that can efficiently and parallelly process rapidly increasing data. Among artificial neural networks that mimic the structure of the brain, the spiking neural network (SNN) is a network that imitates the information-processing method of biological neural networks. Recently, memristors have attracted attention as synaptic devices for neuromorphic computing systems. Among them, the ferroelectric doped-HfO₂-based ferroelectric tunnel junction (FTJ) is considered as a strong candidate for synaptic devices due to its advantages, such as complementary metal–oxide–semiconductor device/process compatibility, a simple two-terminal structure, and low power consumption. However, research on the spiking operations of FTJ devices for SNN applications is lacking. In this study, the implementation of long-term depression and potentiation as the spike timing-dependent plasticity (STDP) rule in the FTJ device was successful. Based on the measured data, a CrossSim simulator was used to simulate the classification of handwriting images. With a high accuracy of 95.79% for the Mixed National Institute of Standards and Technology (MNIST) dataset, the simulation results demonstrate that our device is capable of differentiating between handwritten images. This suggests that our FTJ device can be used as a synaptic device for implementing an SNN. Full article

(This article belongs to the Special Issue Ferroelectric Nanostructures and Thin Films)

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16 pages, 3720 KiB

Open AccessArticle

On the Reliability of HZO-Based Ferroelectric Capacitors: The Cases of Ru and TiN Electrodes

by Roman R. Khakimov, Anna G. Chernikova, Aleksandra A. Koroleva and Andrey M. Markeev

Nanomaterials 2022, 12(17), 3059; https://doi.org/10.3390/nano12173059 - 3 Sep 2022

Cited by 10 | Viewed by 3644

Abstract

Despite the great potential of Hf_0.5Zr_0.5O₂ (HZO) ferroelectrics, reliability issues, such as wake-up, fatigue, endurance limitations, imprint and retention loss, impede the implementation of HZO to nonvolatile memory devices. Herein, a study of the reliability properties in HZO-based [...] Read more.

Despite the great potential of Hf_0.5Zr_0.5O₂ (HZO) ferroelectrics, reliability issues, such as wake-up, fatigue, endurance limitations, imprint and retention loss, impede the implementation of HZO to nonvolatile memory devices. Herein, a study of the reliability properties in HZO-based stacks with the conventional TiN top electrode and Ru electrode, which is considered a promising alternative to TiN, is performed. An attempt to distinguish the mechanisms underlying the wake-up, fatigue and retention loss in both kinds of stacks is undertaken. Overall, both stacks show pronounced wake-up and retention loss. Moreover, the fatigue and retention loss were found to be worsened by Ru implementation. The huge fatigue was suggested to be because Ru does not protect HZO against oxygen vacancies generation during prolonged cycling. The vacancies generated in the presence of Ru are most likely deeper traps, as compared to the traps formed at the interface with the TiN electrode. Implementing the new procedure, which can separate the depolarization-caused retention loss from the imprint-caused one, reveal a rise in the depolarization contribution with Ru implementation, accompanied by the maintenance of similarly high imprint, as in the case with the TiN electrode. Results show that the mechanisms behind the reliability issues in HZO-based capacitors are very electrode dependent and simple approaches to replacing the TiN electrode with the one providing, for example, just higher remnant polarization or lower leakages, become irrelevant on closer examination. Full article

(This article belongs to the Special Issue Ferroelectric Nanostructures and Thin Films)

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