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Seunghyup Yoo - One of the best experts on this subject based on the ideXlab platform.

  • improvement of on off current ratio in hbox tio _ rm x Active Channel tfts using hbox n _ 2 hbox o plasma treatment
    IEEE Electron Device Letters, 2009
    Co-Authors: Jae-woo Park, Dongyun Lee, Hakyoung Kwon, Seunghyup Yoo
    Abstract:

    Without sacrificing the on-current in the transfer characteristics, we have successfully reduced the off-current part by the optimal N2O plasma treatment to improve the on-off-current ratio in n-type titanium oxide ( TiOx) Active-Channel thin-film transistors. While the high-power (275 W) N2O plasma treatment oxidizes the whole TiOx Channel and results in the reduction of both on- and off-current, the optimized low-power (150 W) process makes the selective oxidation of the top portion in the Channel and reduces only the off-current significantly. Increase in on-off ratio by almost five orders of magnitude is achieved without change in on-current by using the presented method.

  • Improvement of On–Off-Current Ratio in $ \hbox{TiO}_{\rm x}$ Active-Channel TFTs Using $\hbox{N}_{2} \hbox{O}$ Plasma Treatment
    IEEE Electron Device Letters, 2009
    Co-Authors: Jae-woo Park, Dongyun Lee, Hakyoung Kwon, Seunghyup Yoo
    Abstract:

    Without sacrificing the on-current in the transfer characteristics, we have successfully reduced the off-current part by the optimal N2O plasma treatment to improve the on-off-current ratio in n-type titanium oxide ( TiOx) Active-Channel thin-film transistors. While the high-power (275 W) N2O plasma treatment oxidizes the whole TiOx Channel and results in the reduction of both on- and off-current, the optimized low-power (150 W) process makes the selective oxidation of the top portion in the Channel and reduces only the off-current significantly. Increase in on-off ratio by almost five orders of magnitude is achieved without change in on-current by using the presented method.

  • New n-Type $\hbox{TiO}_{2}$ Transparent Active Channel TFTs Fabricated With a Solution Process
    IEEE Electron Device Letters, 2008
    Co-Authors: Jae-woo Park, Seunghyup Yoo
    Abstract:

    New metal-oxide thin-film transistors (MOxTFTs) with a solution-processed TiO2 transparent Active Channel are fabricated with a novel doping process that consists of a deposition of an ultrathin Ti layer on TiO2 films and a brief rapid thermal annealing. Contrary to an as-prepared device which does not show any appreciable TFT actions, devices with the proposed process exhibit a clear n-type TFT behavior with a saturation mobility of 0.12 cm2 V-1ldr s-1 and a threshold voltage of 11 V. A solution processibility and a low-cost manufacturability of TiO2 make the presented TFTs potentially attrActive for cost-sensitive applications.

Giuseppe Caire - One of the best experts on this subject based on the ideXlab platform.

  • fdd massive mimo via ul dl Channel covariance extrapolation and Active Channel sparsification
    IEEE Transactions on Wireless Communications, 2019
    Co-Authors: Mahdi Barzegar Khalilsarai, Saeid Haghighatshoar, Giuseppe Caire
    Abstract:

    We propose a novel method for massive multiple-input multiple-output (massive MIMO) in frequency division duplexing (FDD) systems. Due to the large frequency separation between uplink (UL) and downlink (DL) in FDD systems, Channel reciprocity does not hold. Hence, in order to provide DL Channel state information to the base station (BS), closed-loop DL Channel probing, and Channel state information (CSI) feedback is needed. In massive MIMO, this typically incurs a large training overhead. For example, in a typical configuration with $M \simeq 200$ BS antennas and fading coherence block of $T \simeq 200$ symbols, the resulting rate penalty factor due to the DL training overhead, given by $\max \{0, 1 - M/T\}$ , is close to 0. To reduce this overhead, we build upon the well-known fact that the angular scattering function of the user Channels is invariant over frequency intervals whose size is small with respect to the carrier frequency (as in current FDD cellular standards). This allows us to estimate the users’ DL Channel covariance matrix from UL pilots without additional overhead. Based on this covariance information, we propose a novel sparsifying precoder in order to maximize the rank of the effective sparsified Channel matrix subject to the condition that each effective user Channel has sparsity not larger than some desired DL pilot dimension ${\sf T_{dl}}$ , resulting in the DL training overhead factor $\max \{0, 1 - {\sf T_{dl}}/ T\}$ and CSI feedback cost of ${\sf T_{dl}}$ pilot measurements. The optimization of the sparsifying precoder is formulated as a mixed integer linear program , that can be efficiently solved. Extensive simulation results demonstrate the superiority of the proposed approach with respect to the concurrent state-of-the-art schemes based on compressed sensing or UL/DL dictionary learning.

  • FDD Massive MIMO: Efficient Downlink Probing and Uplink Feedback via Active Channel Sparsification
    2018 IEEE International Conference on Communications (ICC), 2018
    Co-Authors: Mahdi Barzegar Khalilsarai, Saeid Haghighatshoar, Xinping Yi, Giuseppe Caire
    Abstract:

    In this paper, we propose a novel method for efficient implementation of a massive Multiple-Input Multiple- Output (massive MIMO) system with Frequency Division Duplexing (FDD) operation. Our main objective is to reduce the large overhead incurred by Downlink (DL) common training and Uplink (UL) feedback needed to obtain Channel state information (CSI) at the base station. Our proposed scheme relies on the fact that the underlying angular distribution of a Channel vector, also known as the angular scattering function, is a frequency-invariant entity yielding a ULDL reciprocity and has a limited angular support. We estimate this support from UL CSI and interpolate it to obtain the corresponding angular support of the DL Channel. Finally we exploit the estimated support of the DL Channel of all the users to design an efficient Channel probing and feedback scheme that maximizes the total spectral efficiency of the system. Our method is different from the existing compressed-sensing (CS) based techniques in the literature. Using support information helps reduce the feedback overhead from O(s logM) in CS techniques to O(s) in our proposed method, with s andM being sparsity order of the Channel vectors and the number of base station antennas, respectively. Furthermore, in order to control the Channel sparsity and therefore the DL common training and UL feedback overhead, we introduce the novel concept of Active Channel sparsification. In brief, when the fixed pilot dimension is less than the required amount for reliable Channel estimation, we introduce a pre-beamforming matrix that artificially reduces the effective Channel dimension of each user to be not larger than the DL pilot dimension, while maximizing both the number of served users and the number of probed angles. We provide numerical experiments to assess the performance of our method and compare it with the state-of-the-art CS technique.

  • fdd massive mimo via ul dl Channel covariance extrapolation and Active Channel sparsification
    arXiv: Information Theory, 2018
    Co-Authors: Mahdi Barzegar Khalilsarai, Saeid Haghighatshoar, Giuseppe Caire
    Abstract:

    We propose a novel method for massive Multiple-Input Multiple-Output (massive MIMO) in Frequency Division Duplexing (FDD) systems. Due to the large frequency separation between Uplink (UL) and Downlink (DL), in FDD systems Channel reciprocity does not hold. Hence, in order to provide DL Channel state information to the Base Station (BS), closed-loop DL Channel probing and feedback is needed. In massive MIMO this incurs typically a large training overhead. For example, in a typical configuration with $M \simeq 200$ BS antennas and fading coherence block of $T \simeq 200$ symbols, the resulting rate penalty factor due to the DL training overhead, given by $\max\{0, 1 - M/T\}$, is close to 0. To reduce this overhead, we build upon the observation that the Angular Scattering Function (ASF) of the user Channels is invariant over the frequency domain. We develop a robust and stable method to estimate the users' DL Channel covariance matrices from pilots sent by the users in the UL. The resulting DL covariance information is used to optimize a sparsifying precoder, in order to limit the effective Channel dimension of each user Channel to be not larger than some desired DL pilot dimension $T_{\rm dl}$. In this way, we can maximize the rank of the effective sparsified Channel matrix subject to a desired training overhead penalty factor $\max\{0, 1 - T_{\rm dl} / T\}$. We pose this problem as a Mixed Integer Linear Program, that can be efficiently solved. Furthermore, each user can simply feed back its $T_{\rm dl}$ pilot measurements. Thus, the proposed approach yields also a small feedback overhead and delay. We provide simulation results demonstrating the superiority of the proposed approach with respect to state-of-the-art "compressed DL pilot" schemes based on compressed sensing.

  • ICC - FDD Massive MIMO: Efficient Downlink Probing and Uplink Feedback via Active Channel Sparsification
    2018 IEEE International Conference on Communications (ICC), 2018
    Co-Authors: Barzegar Khalilsarai, Saeid Haghighatshoar, Giuseppe Caire
    Abstract:

    In this paper, we propose a novel method for efficient implementation of a massive Multiple-Input Multiple- Output (massive MIMO) system with Frequency Division Duplexing (FDD) operation. Our main objective is to reduce the large overhead incurred by Downlink (DL) common training and Uplink (UL) feedback needed to obtain Channel state information (CSI) at the base station. Our proposed scheme relies on the fact that the underlying angular distribution of a Channel vector, also known as the angular scattering function, is a frequency-invariant entity yielding a ULDL reciprocity and has a limited angular support. We estimate this support from UL CSI and interpolate it to obtain the corresponding angular support of the DL Channel. Finally we exploit the estimated support of the DL Channel of all the users to design an efficient Channel probing and feedback scheme that maximizes the total spectral efficiency of the system. Our method is different from the existing compressed-sensing (CS) based techniques in the literature. Using support information helps reduce the feedback overhead from O(s logM) in CS techniques to O(s) in our proposed method, with s andM being sparsity order of the Channel vectors and the number of base station antennas, respectively. Furthermore, in order to control the Channel sparsity and therefore the DL common training and UL feedback overhead, we introduce the novel concept of Active Channel sparsification. In brief, when the fixed pilot dimension is less than the required amount for reliable Channel estimation, we introduce a pre-beamforming matrix that artificially reduces the effective Channel dimension of each user to be not larger than the DL pilot dimension, while maximizing both the number of served users and the number of probed angles. We provide numerical experiments to assess the performance of our method and compare it with the state-of-the-art CS technique.

  • FDD Massive MIMO: Efficient Downlink Probing and Uplink Feedback via Active Channel Sparsification
    arXiv: Information Theory, 2017
    Co-Authors: Barzegar Khalilsarai, Saeid Haghighatshoar, Giuseppe Caire
    Abstract:

    In this paper, we propose a novel method for efficient implementation of a massive Multiple-Input Multiple-Output (massive MIMO) system with Frequency Division Duplexing (FDD) operation. Our main objective is to reduce the large overhead incurred by Downlink (DL) common training and Uplink (UL) feedback needed to obtain Channel state information (CSI) at the base station. Our proposed scheme relies on the fact that the underlying angular distribution of a Channel vector, also known as the angular scattering function, is a frequency-invariant entity yielding a UL-DL reciprocity and has a limited angular support. We estimate this support from UL CSI and interpolate it to obtain the corresponding angular support of the DL Channel. Finally we exploit the estimated support of the DL Channel of all the users to design an efficient Channel probing and feedback scheme that maximizes the total spectral efficiency of the system. Our method is different from the existing compressed-sensing (CS) based techniques in the literature. Using support information helps reduce the feedback overhead from O(s*log M) in CS techniques to O(s) in our proposed method, with $s$ and $M$ being sparsity order of the Channel vectors and the number of base station antennas, respectively. Furthermore, in order to control the Channel sparsity and therefore the DL common training and UL feedback overhead, we introduce the novel concept of Active Channel sparsification. In brief, when the fixed pilot dimension is less than the required amount for reliable Channel estimation, we introduce a pre-beamforming matrix that artificially reduces the effective Channel dimension of each user to be not larger than the DL pilot dimension, while maximizing both the number of served users and the number of probed angles. We provide numerical experiments to compare our method with the state-of-the-art CS technique.

Jae-woo Park - One of the best experts on this subject based on the ideXlab platform.

  • improvement of on off current ratio in hbox tio _ rm x Active Channel tfts using hbox n _ 2 hbox o plasma treatment
    IEEE Electron Device Letters, 2009
    Co-Authors: Jae-woo Park, Dongyun Lee, Hakyoung Kwon, Seunghyup Yoo
    Abstract:

    Without sacrificing the on-current in the transfer characteristics, we have successfully reduced the off-current part by the optimal N2O plasma treatment to improve the on-off-current ratio in n-type titanium oxide ( TiOx) Active-Channel thin-film transistors. While the high-power (275 W) N2O plasma treatment oxidizes the whole TiOx Channel and results in the reduction of both on- and off-current, the optimized low-power (150 W) process makes the selective oxidation of the top portion in the Channel and reduces only the off-current significantly. Increase in on-off ratio by almost five orders of magnitude is achieved without change in on-current by using the presented method.

  • Improvement of On–Off-Current Ratio in $ \hbox{TiO}_{\rm x}$ Active-Channel TFTs Using $\hbox{N}_{2} \hbox{O}$ Plasma Treatment
    IEEE Electron Device Letters, 2009
    Co-Authors: Jae-woo Park, Dongyun Lee, Hakyoung Kwon, Seunghyup Yoo
    Abstract:

    Without sacrificing the on-current in the transfer characteristics, we have successfully reduced the off-current part by the optimal N2O plasma treatment to improve the on-off-current ratio in n-type titanium oxide ( TiOx) Active-Channel thin-film transistors. While the high-power (275 W) N2O plasma treatment oxidizes the whole TiOx Channel and results in the reduction of both on- and off-current, the optimized low-power (150 W) process makes the selective oxidation of the top portion in the Channel and reduces only the off-current significantly. Increase in on-off ratio by almost five orders of magnitude is achieved without change in on-current by using the presented method.

  • New n-Type $\hbox{TiO}_{2}$ Transparent Active Channel TFTs Fabricated With a Solution Process
    IEEE Electron Device Letters, 2008
    Co-Authors: Jae-woo Park, Seunghyup Yoo
    Abstract:

    New metal-oxide thin-film transistors (MOxTFTs) with a solution-processed TiO2 transparent Active Channel are fabricated with a novel doping process that consists of a deposition of an ultrathin Ti layer on TiO2 films and a brief rapid thermal annealing. Contrary to an as-prepared device which does not show any appreciable TFT actions, devices with the proposed process exhibit a clear n-type TFT behavior with a saturation mobility of 0.12 cm2 V-1ldr s-1 and a threshold voltage of 11 V. A solution processibility and a low-cost manufacturability of TiO2 make the presented TFTs potentially attrActive for cost-sensitive applications.

Mahdi Barzegar Khalilsarai - One of the best experts on this subject based on the ideXlab platform.

  • fdd massive mimo via ul dl Channel covariance extrapolation and Active Channel sparsification
    IEEE Transactions on Wireless Communications, 2019
    Co-Authors: Mahdi Barzegar Khalilsarai, Saeid Haghighatshoar, Giuseppe Caire
    Abstract:

    We propose a novel method for massive multiple-input multiple-output (massive MIMO) in frequency division duplexing (FDD) systems. Due to the large frequency separation between uplink (UL) and downlink (DL) in FDD systems, Channel reciprocity does not hold. Hence, in order to provide DL Channel state information to the base station (BS), closed-loop DL Channel probing, and Channel state information (CSI) feedback is needed. In massive MIMO, this typically incurs a large training overhead. For example, in a typical configuration with $M \simeq 200$ BS antennas and fading coherence block of $T \simeq 200$ symbols, the resulting rate penalty factor due to the DL training overhead, given by $\max \{0, 1 - M/T\}$ , is close to 0. To reduce this overhead, we build upon the well-known fact that the angular scattering function of the user Channels is invariant over frequency intervals whose size is small with respect to the carrier frequency (as in current FDD cellular standards). This allows us to estimate the users’ DL Channel covariance matrix from UL pilots without additional overhead. Based on this covariance information, we propose a novel sparsifying precoder in order to maximize the rank of the effective sparsified Channel matrix subject to the condition that each effective user Channel has sparsity not larger than some desired DL pilot dimension ${\sf T_{dl}}$ , resulting in the DL training overhead factor $\max \{0, 1 - {\sf T_{dl}}/ T\}$ and CSI feedback cost of ${\sf T_{dl}}$ pilot measurements. The optimization of the sparsifying precoder is formulated as a mixed integer linear program , that can be efficiently solved. Extensive simulation results demonstrate the superiority of the proposed approach with respect to the concurrent state-of-the-art schemes based on compressed sensing or UL/DL dictionary learning.

  • FDD Massive MIMO: Efficient Downlink Probing and Uplink Feedback via Active Channel Sparsification
    2018 IEEE International Conference on Communications (ICC), 2018
    Co-Authors: Mahdi Barzegar Khalilsarai, Saeid Haghighatshoar, Xinping Yi, Giuseppe Caire
    Abstract:

    In this paper, we propose a novel method for efficient implementation of a massive Multiple-Input Multiple- Output (massive MIMO) system with Frequency Division Duplexing (FDD) operation. Our main objective is to reduce the large overhead incurred by Downlink (DL) common training and Uplink (UL) feedback needed to obtain Channel state information (CSI) at the base station. Our proposed scheme relies on the fact that the underlying angular distribution of a Channel vector, also known as the angular scattering function, is a frequency-invariant entity yielding a ULDL reciprocity and has a limited angular support. We estimate this support from UL CSI and interpolate it to obtain the corresponding angular support of the DL Channel. Finally we exploit the estimated support of the DL Channel of all the users to design an efficient Channel probing and feedback scheme that maximizes the total spectral efficiency of the system. Our method is different from the existing compressed-sensing (CS) based techniques in the literature. Using support information helps reduce the feedback overhead from O(s logM) in CS techniques to O(s) in our proposed method, with s andM being sparsity order of the Channel vectors and the number of base station antennas, respectively. Furthermore, in order to control the Channel sparsity and therefore the DL common training and UL feedback overhead, we introduce the novel concept of Active Channel sparsification. In brief, when the fixed pilot dimension is less than the required amount for reliable Channel estimation, we introduce a pre-beamforming matrix that artificially reduces the effective Channel dimension of each user to be not larger than the DL pilot dimension, while maximizing both the number of served users and the number of probed angles. We provide numerical experiments to assess the performance of our method and compare it with the state-of-the-art CS technique.

  • fdd massive mimo via ul dl Channel covariance extrapolation and Active Channel sparsification
    arXiv: Information Theory, 2018
    Co-Authors: Mahdi Barzegar Khalilsarai, Saeid Haghighatshoar, Giuseppe Caire
    Abstract:

    We propose a novel method for massive Multiple-Input Multiple-Output (massive MIMO) in Frequency Division Duplexing (FDD) systems. Due to the large frequency separation between Uplink (UL) and Downlink (DL), in FDD systems Channel reciprocity does not hold. Hence, in order to provide DL Channel state information to the Base Station (BS), closed-loop DL Channel probing and feedback is needed. In massive MIMO this incurs typically a large training overhead. For example, in a typical configuration with $M \simeq 200$ BS antennas and fading coherence block of $T \simeq 200$ symbols, the resulting rate penalty factor due to the DL training overhead, given by $\max\{0, 1 - M/T\}$, is close to 0. To reduce this overhead, we build upon the observation that the Angular Scattering Function (ASF) of the user Channels is invariant over the frequency domain. We develop a robust and stable method to estimate the users' DL Channel covariance matrices from pilots sent by the users in the UL. The resulting DL covariance information is used to optimize a sparsifying precoder, in order to limit the effective Channel dimension of each user Channel to be not larger than some desired DL pilot dimension $T_{\rm dl}$. In this way, we can maximize the rank of the effective sparsified Channel matrix subject to a desired training overhead penalty factor $\max\{0, 1 - T_{\rm dl} / T\}$. We pose this problem as a Mixed Integer Linear Program, that can be efficiently solved. Furthermore, each user can simply feed back its $T_{\rm dl}$ pilot measurements. Thus, the proposed approach yields also a small feedback overhead and delay. We provide simulation results demonstrating the superiority of the proposed approach with respect to state-of-the-art "compressed DL pilot" schemes based on compressed sensing.

Sung-min Yoon - One of the best experts on this subject based on the ideXlab platform.

  • Flexible vertical-Channel thin-film transistors using In-Ga-Zn-O Active Channel and polyimide spacer on poly(ethylene naphthalate) substrate
    Journal of Vacuum Science & Technology B, 2019
    Co-Authors: Hyeong-rae Kim, Ji-hee Yang, Gi-heon Kim, Sung-min Yoon
    Abstract:

    A flexible vertical-Channel thin-film transistor (VTFT) with a Channel length of 400 nm was fabricated on a poly(ethylene naphthalate) substrate. The vertical gate-stack composed of gate electrode/gate insulator/Active Channel was prepared by a conformal atomic layer deposition and a dry etching process of an organic polyimide spacer. The transfer characteristics of the fabricated flexible VTFT were well confirmed after the postannealing process at 200 °C, in which the on/off ratio was obtained to be 1.8 × 102. The threshold voltage shifts were estimated to be +6.1 and −4.5 V under the positive and negative bias-stress conditions for 104 s, respectively. The device characteristics showed no remarkable degradation when delaminating from the carrier glass substrate. Furthermore, there were no marked changes in transfer curves even when the device was bent with a radius of curvature of 10 mm. A suitable choice of spacer material, optimization of the dry etching process, and employment of ultra-thin flexible film substrate were suggested to appropriate solutions for enhancing the device performance of the proposed flexible VTFTs.A flexible vertical-Channel thin-film transistor (VTFT) with a Channel length of 400 nm was fabricated on a poly(ethylene naphthalate) substrate. The vertical gate-stack composed of gate electrode/gate insulator/Active Channel was prepared by a conformal atomic layer deposition and a dry etching process of an organic polyimide spacer. The transfer characteristics of the fabricated flexible VTFT were well confirmed after the postannealing process at 200 °C, in which the on/off ratio was obtained to be 1.8 × 102. The threshold voltage shifts were estimated to be +6.1 and −4.5 V under the positive and negative bias-stress conditions for 104 s, respectively. The device characteristics showed no remarkable degradation when delaminating from the carrier glass substrate. Furthermore, there were no marked changes in transfer curves even when the device was bent with a radius of curvature of 10 mm. A suitable choice of spacer material, optimization of the dry etching process, and employment of ultra-thin flexible ...

  • Nonvolatile Ferroelectric Memory Thin-Film Transistors Using a Poly(Vinylidene Fluoride Trifluoroethylene) Gate Insulator and an Oxide Semiconductor Active Channel
    Topics in Applied Physics, 2016
    Co-Authors: Sung-min Yoon
    Abstract:

    Nonvolatile memory thin-film transistor using an organic ferroelectric gate insulator and oxide semiconductor Active Channel is proposed as a promising memory element embedded onto the next-generation flexible and transparent electronic systems. In this chapter, some important technical issues for this device, such as device structure, process optimization, and memory array integration, are extensively discussed. Feasible applications and remaining technological issues to be solved for practical applications are also reviewed.

  • Brain-like synaptic operations of thin-film transistors using In-Ga-Zn-O Active Channel and PVP-SBA electrolytic gate insulator
    2016 23rd International Workshop on Active-Matrix Flatpanel Displays and Devices (AM-FPD), 2016
    Co-Authors: Yeo-myeong Kim, Eom-ji Kim, Won-ho Lee, Sung-min Yoon
    Abstract:

    We proposed a synapse thin film transistors with a bottom-gate structure composed of an In-Ga-Zn-O (IGZO) Active Channel and a poly 4(vinylphenol)-sodium beta-alumina (PVP-SBA) gate insulator. The physical and electrical properties of the PVP-SBA were demonstrated as an electrolytic gate insulator for the synapse TFTs. Paired-pulse facilitation (PPF), short-term memory (STM), and long-term memory (LTM) operations were successfully confirmed in the fabricated synapse TFTs, in which output drain currents were effectively modulated with various input pulse conditions owing to the electrostatic coupling between the carriers in IGZO Channel and sodium ions in PVP-SBA in the STM operation and electrochemical doping in the LTM operation, respectively.

  • Short-term and long-term memory operations of synapse thin-film transistors using an In–Ga–Zn–O Active Channel and a poly(4-vinylphenol)–sodium β-alumina electrolytic gate insulator
    RSC Advances, 2016
    Co-Authors: Yeo-myeong Kim, Eom-ji Kim, Won-ho Lee, Sung-min Yoon
    Abstract:

    We proposed synapse thin-film transistors with a bottom-gate structure using an In–Ga–Zn–O Active Channel and a poly(4-vinylphenol)–sodium β-alumina gate insulator. The proposed synapse TFT is a three-terminal electronic device whose conductance can be modulated with various input pulse conditions owing to the movements of sodium ions within the PVP–SBA electrolytic gate insulator. Paired-pulse facilitation (PPF), short-term memory (STM), and long-term memory (LTM) operations were well emulated in the fabricated synapse TFTs, in which output currents were effectively modulated due to the electrostatic coupling in the STM mode and the electrochemical doping in the LTM mode.

  • Process Optimization and Device Characterization of Nonvolatile Charge Trap Memory Transistors Using In–Ga–ZnO Thin Films as Both Charge Trap and Active Channel Layers
    IEEE Transactions on Electron Devices, 2016
    Co-Authors: Da-jeong Yun, Han-byeol Kang, Sung-min Yoon
    Abstract:

    Charge-trap memory thin-film transistors (CTM-TFTs) using In–Ga–ZnO (IGZO) thin films as Active Channel and charge trap layers (CTLs) were fabricated and characterized. Technical strategies to optimize the device design parameters were categorized into the following three parts. At first, $P_{\textrm {O}2}$ conditions during the sputtering deposition of IGZO CTL were varied to 1%, 2%, and 5% to modulate the electronic natures of the IGZO films. The device using the CTL deposited at $P_{\textrm {O}2}$ of 1% obtained the largest memory window and exhibited the fastest program speed. Second, to investigate the thickness effects of double-layered tunneling oxide, the configuration was varied to 3/3 nm and 5/5 nm. From the viewpoints of process window, the 5/5 nm configuration was chosen for stable device characteristics. At last, the effects of CTL thickness, which affects the number of trap sites and carrier concentration of the film, was carefully investigated. A 30-nm-thick CTL showed most desirable behaviors, including superior memory operation and uniformity. The CTM-TFTs fabricated with optimum conditions exhibited the memory margin in programmed currents between ON- and OFF-states of $2.9\times 10^{5}$ at 1- $\mu \text{s}$ program voltage pulses with ±20 V. Furthermore, the $I_{\mathrm{\scriptscriptstyle ON}/\mathrm{\scriptscriptstyle OFF}}$ of five-orders-of-magnitude was obtained even after the lapse retention time for $10^{4}$ s.