Article
Engineering, Electrical & Electronic
Ryun-Han Koo, Wonjun Shin, Kyung Kyu Min, Dongseok Kwon, Jae-Joon Kim, Daewoong Kwon, Jong-Ho Lee
Summary: We investigate the effect of post-metal annealing temperature (T-PMA) on ferroelectric (FE) resistive switching (RS) and non-FE RS in HfOx ferroelectric tunnel junctions. Through conductance analysis and low frequency noise spectroscopy, the effects of T-PMA on RS mechanisms are demonstrated. It is revealed that the non FE RS, redistribution of oxygen vacancies, is suppressed with an increase in T-PMA. The effects of different RS mechanisms on the tunneling electroresistance and cycling endurance characteristics are systematically investigated.
IEEE ELECTRON DEVICE LETTERS
(2023)
Article
Engineering, Electrical & Electronic
Ryun-Han Koo, Wonjun Shin, Kyung Kyu Min, Dongseok Kwon, Dae Hwan Kim, Jae-Joon Kim, Daewoong Kwon, Jong-Ho Lee
Summary: We investigate the effects of temperature and the number of cycles on remnant polarization and carrier transport process to determine the factors that determine the tunneling electroresistance (TER) of the ferroelectric tunnel junction (FTJ). Our fabricated FTJs have a metal/ferroelectric/insulator/semiconductor structure. It is found that the remnant polarization increases with increasing temperature and number of cycles due to oxygen vacancy redistribution. However, the increased remnant polarization does not improve the TER ratio at higher temperature and number of cycles. Using current-voltage characterization and low-frequency noise spectroscopy, we reveal that the carrier transport process at the interface between the ferroelectric and dielectric layers plays a more important role in determining the TER ratio than remnant polarization.
IEEE ELECTRON DEVICE LETTERS
(2023)
Article
Engineering, Electrical & Electronic
Wonjun Shin, Jong-Ho Bae, Dongseok Kwon, Ryun-Han Koo, Byung-Gook Park, Daewoong Kwon, Jong-Ho Lee
Summary: This study investigates the effects of length and width scaling on the low-frequency noise characteristics of ferroelectric tunnel junctions (FTJs). The results show that in the high-resistance state, 1/f noise increases proportionally with length and width scaling, while shot noise is not affected by scaling. In the low-resistance state, the dependence of 1/f noise on length scaling is more sensitive than on width scaling due to the influence of process-induced damaged edge regions on the switching and conduction mechanisms.
IEEE ELECTRON DEVICE LETTERS
(2022)
Article
Engineering, Electrical & Electronic
Pengying Chang, Yiyang Xie
Summary: An innovative resonant ferroelectric tunnel junction (FTJ) with asymmetric barrier-well-barrier structure is proposed. This FTJ exhibits improved ON-current and ON/OFF tunneling electroresistance (TER) ratio while maintaining a low depolarization field. The resonance peak of FTJ can be shifted by enhancing the device asymmetry through resonant band engineering. This work is useful for designing FTJs for large array circuit applications.
IEEE TRANSACTIONS ON ELECTRON DEVICES
(2023)
Article
Engineering, Electrical & Electronic
Pengying Chang, Gang Du, Jinfeng Kang, Xiaoyan Liu
Summary: This study investigates the tunneling processes of ferroelectric tunnel junction (FTJ) based on metal-ferroelectric-insulator-semiconductor (MFIS) stack for both n-type and p-type semiconductor electrodes using an experimentally calibrated model. The research shows that the conduction modes of n-type and p-type MFIS can be classified depending on the contribution of minority carriers in the semiconductor, and the optimal tunneling electroresistance (TER) for each device is achieved under different operating conditions. The findings provide insights into the band structure engineering of the MFIS structure for designing and optimizing FTJ performance.
IEEE TRANSACTIONS ON ELECTRON DEVICES
(2021)
Article
Engineering, Electrical & Electronic
Hsin-Hui Huang, Yueh-Hua Chu, Tzu-Yun Wu, Ming-Hung Wu, I-Ting Wang, Tuo-Hung Hou
Summary: A comprehensive physical model is established to understand the device operation and optimization strategy of the ferroelectric tunnel junction. The model is capable of simulating various operations and has good agreement with experiments. The optimization strategy for the thickness of the ferroelectric layer and nonpolar interfacial layer is discussed, as well as the possible misinterpretation of measured results.
IEEE TRANSACTIONS ON ELECTRON DEVICES
(2022)
Article
Engineering, Electrical & Electronic
Pengying Chang, Yiyang Xie
Summary: In order to enhance the performance of HfO2-based ferroelectric (FE) tunnel junctions (FTJs) and their crossbar arrays, we propose using low-barrier Ta2O5 dielectric material to increase device asymmetry. By inserting Ta2O5 between two FE HfO2 barriers for resonant band engineering, both JON and TER ratio are significantly improved, while good retention is maintained due to the high permittivity of Ta2O5. Additionally, high current rectification ratio and negative differential resistance are observed. These abundant physical effects in HfO2/Ta2O5/HfO2 based MFIFM resonant FTJs may enable selector-less crossbar.
IEEE ELECTRON DEVICE LETTERS
(2023)
Article
Engineering, Electrical & Electronic
Ayse Suenbuel, Tarek Ali, Konstantin Mertens, Ricardo Revello, David Lehninger, Franz Mueller, Maximilian Lederer, Kati Kuehnel, Matthias Rudolph, Sebastian Oehler, Raik Hoffmann, Katrin Zimmermann, Kati Biedermann, Philipp Schramm, Malte Czernohorsky, Konrad Seidel, Thomas Kaempfe, Lukas M. Eng
Summary: This article investigates the characteristics and performance of zirconium-doped hafnium oxide-based ferroelectric tunnel junction (FTJ) devices in terms of ferroelectric (FE) switching and reliability. The switching characteristics of FTJ memory, the effects of polarization switching on write conditions, and the impact of pulse width and amplitude on switching are studied. The results show that the maximum FTJ I-ON/I-OFF ratio and reliable performance can be achieved by tuning the stack structure and FE layer thickness.
IEEE TRANSACTIONS ON ELECTRON DEVICES
(2022)
Article
Engineering, Electrical & Electronic
Robin Athle, Mattias Borg
Summary: In this study, we evaluate the importance of the postmetallization annealing (PMA) temperature on the performance of HfxZr1-xO2-based ferroelectric tunnel junctions (FTJs). Our results show significant variations in tunneling electroresistance (TER) ratio and endurance depending on the PMA temperature, despite negligible changes in remanent polarization. We conclude that minimizing conductive oxide defect states is crucial for achieving high performance. Through carefully optimized PMA conditions, we demonstrate FTJs with a TER = 3, low mean cycle-to-cycle variation (< 1.5%), and at least 16 separable conductance states, providing a 4-bit resolution analog FTJ.
IEEE TRANSACTIONS ON ELECTRON DEVICES
(2023)
Article
Engineering, Electrical & Electronic
Ryun-Han Koo, Wonjun Shin, Sangwoo Ryu, Kyungmin Lee, Sung-Ho Park, Jiseong Im, Jong-Hyun Ko, Jeong-Hyun Kim, Dongseok Kwon, Jae-Joon Kim, Daewoong Kwon, Jong-Ho Lee
Summary: In this study, we re-evaluate the performance of p-type ferroelectric tunnel junction and find that it exhibits similar on-current density and higher tunneling electroresistance ratio compared to the n-type counterpart. We demonstrate that non-ferroelectric resistive switching contributes to the improvement of the p-type ferroelectric tunnel junction performance. Furthermore, we discover that the p-type junction has lower read noise than the n-type junction in the operating region governed by the ferroelectric effect.
IEEE ELECTRON DEVICE LETTERS
(2023)
Article
Engineering, Electrical & Electronic
Kitae Lee, Sihyun Kim, Jong-Ho Lee, Byung-Gook Park, Daewoong Kwon
Summary: The scaling effects on FTJ memory reveal changes in the polarization switching mechanism, with domain wall spreading limited switching becoming dominant due to process-induced damaged edge regions, leading to larger remanent polarization and faster switching speed.
IEEE ELECTRON DEVICE LETTERS
(2021)
Article
Engineering, Electrical & Electronic
Jiajie Yu, Tianyu Wang, Kangli Xu, Yongkai Liu, Jialin Meng, Zhenhai Li, Pei Liu, Hao Zhu, Qingqing Sun, David Wei Zhang, Lin Chen
Summary: This study proposes an effective method to enhance the nonlinearity ratio of ferroelectric tunneling junctions (FTJs) by constructing a special energy band structure. Experimental results show that compared to reference devices, the proposed device exhibits reduced coercive electric field, increased residual polarization, and significant switching effect. Simulations also demonstrate significant improvements in nonlinearity and crosstalk issues for the proposed device.
IEEE TRANSACTIONS ON ELECTRON DEVICES
(2023)
Article
Engineering, Electrical & Electronic
Junghyeon Hwang, Youngin Goh, Sanghun Jeon
Summary: In this study, a high 2P(r) value of 44.4 mu C/cm(2) and a notable TER ratio of 11.6 were observed for 6-nm thick hafnia films with 1-nm thick TiO2 films, demonstrating the potential for enhanced ferroelectricity in FTJ operations.
IEEE TRANSACTIONS ON ELECTRON DEVICES
(2021)
Article
Engineering, Electrical & Electronic
Zuopu Zhou, Leming Jiao, Jiuren Zhou, Qiwen Kong, Sheng Luo, Chen Sun, Zijie Zheng, Xiaolin Wang, Dong Zhang, Gan Liu, Gengchiau Liang, Xiao Gong
Summary: The researchers have developed a comprehensive ferroelectric tunnel junction (FTJ) model that considers dynamic and multi-domain switching behaviors. By combining the Time-Dependent Landau-Ginzburg equations and the Non-Equilibrium Green Function, they were able to successfully reproduce experimental results and predict the dynamic and multi-state switching of FTJ. This model shows promise for applications in high-density data storage and analog computing.
IEEE ELECTRON DEVICE LETTERS
(2022)
Article
Engineering, Electrical & Electronic
Fenning Liu, Yue Peng, Yan Liu, Genquan Han, Wenwu Xiao, Bobo Tian, Ni Zhong, Hui Peng, Chungang Duan, Yue Hao
Summary: An amorphous ZrO2 based tunneling junction memristor (TJM) demonstrated a tunneling electroresistance (TER) ratio above 400, attributed to the modulation of tunneling barrier width induced by the accumulation of oxygen vacancies (V-O+) and negative charges near the ZrO2/semiconductor interface. The ferroelectric-like behaviors characterized by a polarization-voltage test in ZrO2 TJM showed excellent performance under various conditions.
IEEE ELECTRON DEVICE LETTERS
(2021)
Article
Engineering, Electrical & Electronic
Sung Yun Woo, Dongseok Kwon, Byung-Gook Park, Jong-Ho Lee, Jong-Ho Bae
Summary: A positive-feedback (PF) device and its operation scheme for implementing pulse width modulation (PWM) function were demonstrated. By adjusting the charge stored in the n(-) floating body (Q(n)), the potential of the floating body changes linearly with time. The voltage-to-pulse width conversion for PWM function was achieved by utilizing the linear time-varying property of Q(n) and the gate bias dependency of Q(th). This approach allows for the reduction of the area required for a PWM neuron.
IEEE ELECTRON DEVICE LETTERS
(2023)
Article
Engineering, Electrical & Electronic
Ryun-Han Koo, Wonjun Shin, Kyung Kyu Min, Dongseok Kwon, Dae Hwan Kim, Jae-Joon Kim, Daewoong Kwon, Jong-Ho Lee
Summary: We investigate the effects of temperature and the number of cycles on remnant polarization and carrier transport process to determine the factors that determine the tunneling electroresistance (TER) of the ferroelectric tunnel junction (FTJ). Our fabricated FTJs have a metal/ferroelectric/insulator/semiconductor structure. It is found that the remnant polarization increases with increasing temperature and number of cycles due to oxygen vacancy redistribution. However, the increased remnant polarization does not improve the TER ratio at higher temperature and number of cycles. Using current-voltage characterization and low-frequency noise spectroscopy, we reveal that the carrier transport process at the interface between the ferroelectric and dielectric layers plays a more important role in determining the TER ratio than remnant polarization.
IEEE ELECTRON DEVICE LETTERS
(2023)
Article
Engineering, Electrical & Electronic
In-Seok Lee, Hyeongsu Kim, Min-Kyu Park, Joon Hwang, Ryun-Han Koo, Jae-Joon Kim, Jong-Ho Lee
Summary: This study proposes a novel XNOR-AND hybrid binary neural network (BNN) using a TFT-type synaptic device to reduce the area and power consumption of the synaptic array. Replacing some parts of the network from the XNOR operation to the AND operation allows for expressing weight and input with a single cell and single word line. When replacing the operation of the fully-connected (FC) layer with the AND operation, the accuracy of VGG9 BNN for CIFAR-10 datasets drops by approximately 1%, while the number of cells in the synaptic array decreases by 33.7%. Utilizing the previously proposed TFT-type synaptic devices, the proposed method reduces power consumption by around 25%.
IEEE ELECTRON DEVICE LETTERS
(2023)
Article
Engineering, Electrical & Electronic
Min-Kyu Park, Won-Mook Kang, Ryun-Han Koo, Jeong-Hyun Kim, Joon Hwang, Jong-Ho Bae, Jae-Joon Kim, Jong-Ho Lee
Summary: This study proposes and verifies a novel method of integrating an AND-type flash synaptic array with CMOS circuits. By reducing the number of masks and fabrication steps, the proposed method successfully integrates the synaptic array and CMOS peripheral circuits on a single wafer. This research is of great significance for the efficient implementation of hardware-based neural networks.
IEEE TRANSACTIONS ON ELECTRON DEVICES
(2023)
Article
Engineering, Electrical & Electronic
Sung-Tae Lee, Jong-Ho Lee
Summary: This work proposes using separate synaptic string arrays for error backpropagation in NAND flash memory-based synaptic architecture. Forward and backward propagations are processed in separate synaptic devices in forward and backward synaptic arrays. The optimal conductance response is investigated, and reliability characteristics are verified. Hardware-based neural networks with random synaptic weight achieve a high inference accuracy comparable to that of transposed weight. The proposed on-chip learning scheme maintains high inference accuracy even with increasing device variation.
IEEE TRANSACTIONS ON ELECTRON DEVICES
(2023)
Article
Physics, Applied
Dongseok Kwon, Hyeongsu Kim, Kyu-Ho Lee, Joon Hwang, Wonjun Shin, Jong-Ho Bae, Sung Yun Woo, Jong-Ho Lee
Summary: This work proposes positive feedback (PF) device-based synaptic devices for reliable binary neural networks (BNNs). The fabricated PF device shows a high on/off current ratio (2.69 x 10(7)) due to PF operation. The PF device has a charge-trap layer for adjusting the turn-on voltage (V-on) through program/erase operations and implementing long-term memory function. The steep switching characteristics of the PF device provide tolerance to retention time and turn-on voltage variation, enabling high accuracy (88.44% for CIFAR-10 image classification) in hardware-based BNNs using PF devices as synapses.
APPLIED PHYSICS LETTERS
(2023)
Article
Physics, Applied
Wonjun Shin, Eun Chan Park, Ryun-Han Koo, Dongseok Kwon, Daewoong Kwon, Jong-Ho Lee
Summary: We investigate the low-frequency noise characteristics of indium-gallium-zinc oxide ferroelectric thin-film transistors (FeTFTs) with a metal-ferroelectric-metal-insulator-semiconductor (MFMIS) structure. The noise generation mechanism differs depending on the operation region and metal-to-FE area ratios (A(M)/A(F)). Excess noise in the low I-D region is observed in the MFMIS FeTFTs with A(M)/A(F) of 4 and 6 due to carrier mobility fluctuations. In the high I-D region, the carrier number fluctuation generates the 1/f noise of the devices regardless of the A(M)/A(F).
APPLIED PHYSICS LETTERS
(2023)
Article
Engineering, Electrical & Electronic
Ryun-Han Koo, Wonjun Shin, Kyung Kyu Min, Dongseok Kwon, Jae-Joon Kim, Daewoong Kwon, Jong-Ho Lee
Summary: We investigate the effect of post-metal annealing temperature (T-PMA) on ferroelectric (FE) resistive switching (RS) and non-FE RS in HfOx ferroelectric tunnel junctions. Through conductance analysis and low frequency noise spectroscopy, the effects of T-PMA on RS mechanisms are demonstrated. It is revealed that the non FE RS, redistribution of oxygen vacancies, is suppressed with an increase in T-PMA. The effects of different RS mechanisms on the tunneling electroresistance and cycling endurance characteristics are systematically investigated.
IEEE ELECTRON DEVICE LETTERS
(2023)
Article
Physics, Applied
Wonjun Shin, Jihyun Shin, Jong-Ho Lee, Hocheon Yoo, Sung-Tae Lee
Summary: This study investigates the low-frequency noise characteristics of a 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene organic thin-film transistor (OTFT) with a CYTOP dielectric layer. The fabricated OTFT displays 1/f noise, which can be explained by a carrier number fluctuation model. Furthermore, the volume trap density (N-T) of the gate dielectric is quantitatively evaluated and compared with a transistor using a SiO2 dielectric layer. The results indicate that the hydrophilic nature of the dielectric layer strongly affects the N-T, with CYTOP having a lower N-T than SiO2.
APPLIED PHYSICS LETTERS
(2023)
Article
Multidisciplinary Sciences
Dongseok Kwon, Sung Yun Woo, Kyu-Ho Lee, Joon Hwang, Hyeongsu Kim, Sung-Ho Park, Wonjun Shin, Jong-Ho Bae, Jae-Joon Kim, Jong-Ho Lee
Summary: In this work, a reconfigurable neuromorphic computing (NC) block using a flash-type synapse array, emerging positive feedback (PF) neuron devices, and CMOS peripheral circuits is proposed and experimentally demonstrated. The flash memory enables easy calibration of the NC block for output signals, and the super-steep switching characteristics of the PF neuron device reduce the area overhead of the NC block. The NC block shows high energy efficiency (37.9 TOPS/W) and high accuracy (91.80%) for CIFAR-10 image classification, outperforming previous works. This work showcases the engineering potential of integrating synapses and neurons in terms of system efficiency and high performance.
Article
Automation & Control Systems
Wonjun Shin, Kyung Kyu Min, Jong-Ho Bae, Jaehyeon Kim, Ryun-Han Koo, Dongseok Kwon, Jae-Joon Kim, Daewoong Kwon, Jong-Ho Lee
Summary: In recent years, the development of neuromorphic computing has faced the limitations of von Neumann architecture. Therefore, there is a growing demand for high-performance synaptic devices that possess high switching speeds, low power consumption, and multilevel conductance. Among various synaptic devices, ferroelectric tunnel junctions (FTJs) have emerged as promising candidates. While previous studies have focused on improving the reliability of FTJs to enhance synaptic behavior, the low-frequency noise (LFN) of FTJs and its impact on the learning accuracy in neuromorphic computing have not been thoroughly investigated. This study explores the LFN characteristics of FTJs fabricated on n- and p-type Si and evaluates the impact of 1/f noise on the learning accuracy of convolutional neural networks (CNNs). The results demonstrate that FTJs on p-type Si exhibit significantly lower 1/f noise than those on n-type Si. Consequently, the FTJs on p-type Si achieve a significantly higher learning accuracy (86.26%) compared to those on n-type Si (78.70%) due to their low-noise properties. This study provides valuable insights into the LFN characteristics of FTJs and offers a potential solution to enhance the performance of synaptic devices by drastically reducing 1/f noise.
ADVANCED INTELLIGENT SYSTEMS
(2023)
Article
Computer Science, Artificial Intelligence
Dongseok Kwon, Sung Yun Woo, Joon Hwang, Hyeongsu Kim, Jong-Ho Bae, Wonjun Shin, Byung-Gook Park, Jong-Ho Lee
Summary: Neuromorphic hardware using nonvolatile analog synaptic devices can reduce energy and time consumption for large-scale vector-matrix multiplication operations. However, existing training methods have reduced accuracy and high training costs. This study proposes a novel hybrid training method that efficiently trains the hardware using nonvolatile analog memory cells, demonstrating high performance in the fabricated hardware.
IEEE TRANSACTIONS ON NEURAL NETWORKS AND LEARNING SYSTEMS
(2023)
