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Hyunsang Hwang - One of the best experts on this subject based on the ideXlab platform.

  • demonstration of low power 3 bit multilevel cell characteristics in a tao x based rram by stack engineering
    IEEE Electron Device Letters, 2015
    Co-Authors: Amit Prakash, Jaesung Park, Jeonghwan Song, Jiyong Woo, Euijun Cha, Hyunsang Hwang
    Abstract:

    Multilevel cell (MLC) storage technology is attractive in achieving ultraHigh density memory with low cost. In this letter, we have demonstrated 3-bit per cell storage characteristics in a TaO x -based RRAM. By analyzing the key requirements for MLC operation mainly the switching uniformity and stability of Resistance levels, an engineered stack based on thermodynamics in top electrode/(vacancy reservoir/defect control layer)/switching layer/bottom electrode structure was designed. In the optimized stack with $\sim 10$ -nm Ta layer incorporated at W/TaO x interface, seven low Resistance State levels with same High Resistance State were obtained by controlling the switching current down from $30~\mu $ A enabling low power 3-bit storage in contrast to the control device which shows 2-bit MLC with Resistance saturation. The improved switching and MLC behavior is attributed to the minimized stochastic nature of set/reset operations due to filament confinement by favorable electric field generation and formation of thin but Highly conductive filament which is confirmed electrically.

  • Highly reliable resistive switching without an initial forming operation by defect engineering
    IEEE Electron Device Letters, 2013
    Co-Authors: Jaesung Park, Jeonghwan Song, Kibong Moon, Behnoush Attari, Nusrat Tamanna, Misha Saiful Haque, Hyunsang Hwang
    Abstract:

    The effects of stack and defect engineering of metal-oxide layers on resistive switching uniformity were investigated to obtain resistive random access memory (ReRAM) with excellent switching reliability. Uniform switching, parameters, such as set voltage (Vset), reset voltage (Vreset), low-Resistance State, High-Resistance State, and retention characteristics, were significantly improved by stack and defect engineering. Furthermore, the initial forming operation, which is a nuisance, was removed to realize cross-point ReRAM.

  • multibit operation of hbox tio _ x based reram by schottky barrier height engineering
    IEEE Electron Device Letters, 2011
    Co-Authors: Jubong Park, Kuyyadi P Biju, Seungjae Jung, Wootae Lee, Joonmyoung Lee, Seonghyun Kim, Sangsu Park, Jungho Shin, Hyunsang Hwang
    Abstract:

    We demonstrated multibit operation using a 250-nm Ir/TiOx/ TiN resistive random access memory by Schottky barrier height engineering. A Schottky barrier was formed by the interface between a High-work-function Ir top electrode and n-type TiOx. The conducting path, which was composed of oxygen vacancies, was generated in a low-Resistance State, whereas a Schottky barrier was reproduced in a High-Resistance State (HRS) due to the High concentration of oxygen by the electric field. By changing the reset operation voltage, we successfully engineered the Schottky barrier height, resulting in the modulation of the HRS current and demonstrating the feasibility of multibit applications.

  • improved switching uniformity and speed in filament type rram using lightning rod effect
    IEEE Electron Device Letters, 2011
    Co-Authors: Jubong Park, Seungjae Jung, Jungho Shin, Minseok Jo, Hyunsang Hwang
    Abstract:

    Improved switching uniformity and speed were demonstrated using a filament-type resistive memory. By using a gradual reset operation, a leaky High Resistance, which has a smaller gap distance confirmed by C-AFM, was successfully obtained. The leaky High-Resistance State shows significantly improved switching uniformity compared to the High-Resistance State, which has a Higher Resistance than the leaky High-Resistance State, because of the confinement of the randomly formed conducting filaments. A faster operation speed was achieved using the smaller gap distance. To confirm the improved switching speed, we monitored the real-time oscilloscope response.

  • Resistance switching characteristics of polycrystalline nb sub 2 o sub 5 for nonvolatile memory application
    IEEE Electron Device Letters, 2005
    Co-Authors: Hyunjun Sim, Dooho Choi, Dongsoo Lee, Sunae Seo, Myongjae Lee, Inkyeong Yoo, Hyunsang Hwang
    Abstract:

    The Resistance switching characteristics of polycrystalline Nb/sub 2/O/sub 5/ film prepared by pulsed-laser deposition (PLD) were investigated for nonvolatile memory application. Reversible Resistance-switching behavior from a High Resistance State to a lower State was observed by voltage stress with current compliance. The reproducible Resistance-switching cycles were observed and the Resistance ratio was as High as 50-100 times. The Resistance switching was observed under voltage pulse as short as 10 ns. The estimated retention lifetime at 85/spl deg/C was sufficiently longer than ten years. Considering its excellent electrical and reliability characteristics, Nb/sub 2/O/sub 5/ shows strong promise for future nonvolatile memory applications.

H Philip S Wong - One of the best experts on this subject based on the ideXlab platform.

  • a physics based compact model for cbram retention behaviors based on atom transport dynamics and percolation theory
    IEEE Electron Device Letters, 2019
    Co-Authors: Yudi Zhao, Xiao-yan Liu, Peng Huang, H Philip S Wong, Zheng Zhou, Chen Liu, Shengjun Qin, Lifeng Liu, Jin-feng Kang
    Abstract:

    A physics-based compact model for retention behaviors of conductive-bridge random access memory (CBRAM) is developed by modeling: 1) the material-dependent metal atom transport from the conductive filament into the electrolyte; and 2) the conduction percolation controlled by the atom concentration. Considering the material properties of the metal and electrolyte, this compact model can well reproduce the retention behaviors of the CBRAM in both low Resistance State and High Resistance State (HRS) for various material stacks under various operating temperatures. Two types of HRS Resistance shift can be reproduced by accurately modeling the percolation paths. The compact model can enable the reliability projection of cells in a crossbar array.

  • ultrafast accelerated retention test methodology for rram using micro thermal stage
    IEEE Electron Device Letters, 2017
    Co-Authors: Ziwen Wang, Zizhen Jiang, Xin Zheng, Scott W Fong, Hongyu Chen, H Philip S Wong, Yoshio Nishi
    Abstract:

    We proposed an ultrafast accelerated retention test methodology for resistive random access memory (RRAM) using micro thermal stage (MTS). For accelerated retention test using chuck heating, the two major factors that limit the test speed are the attainable temperature range and thermal time constant. To extend these limits, we built MTS with extended temperature range (~800 °C) and short thermal time constant ( $\sim 10\mu \text{s}$ ). Using High Resistance State retention failure of HfOx-based RRAM as an example, we demonstrated that the proposed methodology can reduce accelerated retention test time to <10 ms, achieving a boost of up to six orders of magnitude compared with chuck heating.

  • on the switching parameter variation of metal oxide rram part ii model corroboration and device design strategy
    IEEE Transactions on Electron Devices, 2012
    Co-Authors: Ximeng Guan, H Philip S Wong
    Abstract:

    Using the model developed in Part I of this two-part paper, the simulated dc sweep and pulse transient characteristics of a metal oxide resistive random access memory cell are corroborated with the experimental data of HfOx memory. Key switching features such as the abrupt SET process, gradual RESET process, current fluctuation in the RESET process, and multilevel Resistance State distributions are captured by the simulation. The current fluctuation in the RESET process is caused by the competition between the simultaneous oxygen vacancy recombination and generation processes. The origin of the High-Resistance State variation and the tail bit problem are attributed to the variation of the tunneling gap distances and the stochastic nature of new Vo generation in the tunneling gap region, respectively. The use of the write-verify technique and a bilayer oxide structure are proposed to achieve a tighter Resistance distribution.

  • nanoscale bipolar and complementary resistive switching memory based on amorphous carbon
    IEEE Transactions on Electron Devices, 2011
    Co-Authors: Yang Chai, Hongyu Chen, Kuniharu Takei, P C H Chan, Ali Javey, H Philip S Wong
    Abstract:

    There has been a strong demand for developing an ultradense and low-power nonvolatile memory technology. In this paper, we present a carbon-based resistive random access memory device with a carbon nanotube (CNT) electrode. An amorphous carbon layer is sandwiched between the fast-diffusing top metal electrode and the bottom CNT electrode, exhibiting a bipolar switching behavior. The use of the CNT electrode can substantially reduce the size of the active device area. We also demonstrate a carbon-based complementary resistive switch (CRS) consisting of two back-to-back connected memory cells, providing a route to reduce the sneak current in the cross-point memory. The bit information of the CRS cell is stored in a High-Resistance State, thus reducing the power consumption of the CRS memory cell. This paper provides valuable early data on the effect of electrode size scaling down to nanometer size.

  • investigating the switching dynamics and multilevel capability of bipolar metal oxide resistive switching memory
    Applied Physics Letters, 2011
    Co-Authors: H Philip S Wong
    Abstract:

    HfOx/AlOx bilayer resistive switching devices were fabricated for the study of the switching dynamics of the metal oxide memory. An exponential voltage-time relationship was experimentally observed as follows: the programming pulse widths need for switching exponentially decreased with the increase in the programming pulse amplitudes. Two following programming schemes were proposed to modulate the High Resistance State values: (1) exponentially increase the programming pulse width; (2) linearly increase the programming pulse amplitude. Although both of these schemes were effective to achieve the target Resistance, the transient current response measurements suggest the second scheme consumes considerably less energy in the programming. A field-driven oxygen ions migration model was utilized to elucidate the above experimentally observed phenomenon.

S Fung - One of the best experts on this subject based on the ideXlab platform.

  • conduction mechanisms at low and High Resistance States in aluminum anodic aluminum oxide aluminum thin film structure
    Journal of Applied Physics, 2012
    Co-Authors: Wei Zhu, T P Chen, Yong Liu, S Fung
    Abstract:

    In this work, conduction mechanisms of Al/anodic Al oxide/ Al structure, which exhibits resistive switching behavior, have been investigated. The low-Resistance State shows ohmic conduction with a metal-like behavior similar to that of pure aluminum. The situation can be explained by the existence of the metallic filament formed by the excess Al in the Al oxide. On the other hand, the High-Resistance State (HRS) shows two distinct regimes: ohmic conduction at low fields with a semiconductor-like behavior; and a non-ohmic conduction at High fields. The ohmic conduction of HRS at low fields is attributed to the electron hopping between the States in the oxide with the activation energy of ∼0.23 eV. It is suggested that the conduction of HRS at High fields (the maximum voltage is lower than the set voltage) is due to the field-enhanced thermal excitation of the electrons trapped in the States of the metallic Al nano-phase into the conduction band of the Al oxide or the electron emission from the potential we...

  • resistive switching behavior of partially anodized aluminum thin film at elevated temperatures
    IEEE Transactions on Electron Devices, 2012
    Co-Authors: Wei Zhu, T P Chen, Ming Yang, Yang Liu, S Fung
    Abstract:

    Resistive switching behavior of partially anodized aluminum thin film has been investigated at temperatures of 25 $^{\circ}\hbox{C}$ –250 $^{\circ}\hbox{C}$ . Both the reset and set voltages decrease with increasing temperature, showing Arrhenius-like dependence with small activation energies. The pulse voltage experiment also suggests that the conductive filament breaking/reconnection is easier to occur at a Higher temperature. Some possible mechanisms for the phenomena are discussed. On the other hand, at elevated temperatures without continuous electric field applied, while the High-Resistance State exhibits no significant change with time, the low-Resistance State (LRS) shows a continuous degradation, and there is a sudden failure. The LRS failure time shows Arrhenius dependence with an activation energy of $\sim$ 1.3 eV, suggesting that the LRS failure could be due to the migration of the excess Al atoms at High temperatures.

  • resistive switching in aluminum anodized aluminum film structure without forming process
    Journal of Applied Physics, 2009
    Co-Authors: Wei Zhu, T P Chen, Zhitian Liu, Mo Yang, Yingli Liu, S Fung
    Abstract:

    Metal-insulator-metal (MIM) structure was fabricated by partially anodizing aluminum film followed by deposition of another aluminum film. Unipolar resistive switching between a High-Resistance State and a low-Resistance State with a High Resistance ratio (>∼104) was observed from the structure. The switching occurred without the requirement of a forming process, which was attributed to the pre-existing conductive filaments in the Al-rich AlxOy layer formed by the anodization. Each Resistance State exhibited Ohmic behavior which could be explained by the metallic conduction and electron hopping from one isolated State to the next in the Al-rich AlxOy layer. The MIM structure showed good memory characteristics.

Cheol Seong Hwang - One of the best experts on this subject based on the ideXlab platform.

  • Memristor crossbar array for binarized neural networks
    AIP Publishing LLC, 2019
    Co-Authors: Yong Kim, Won Hee Jeong, Son Bao Tran, Hyo Cheon Woo, Jihun Kim, Cheol Seong Hwang, Kyeong-sik Min, Byung Joon Choi
    Abstract:

    Memristor crossbar arrays were fabricated based on a Ti/HfO2/Ti stack that exhibited electroforming-free behavior and low device variability in a 10 x 10 array size. The binary States of High-Resistance-State and low-Resistance-State in the bipolar memristor device were used for the synaptic weight representation of a binarized neural network. The electroforming-free memristor was confirmed as being suitable as a binary synaptic device because of its Higher device yield, lower variability, and less severe malfunction (for example, hard break-down) than the electroformed memristors based on a Ti/HfO2/Pt structure. The feasibly working binarized neural network adopting the electroforming-free binary memristors was demonstrated through simulation

  • 32 32 crossbar array resistive memory composed of a stacked schottky diode and unipolar resistive memory
    Advanced Functional Materials, 2013
    Co-Authors: Gun Hwan Kim, Jung Ho Yoon, Jun Yeong Seok, Seul Ji Song, Jongho Lee, Youngbae Ahn, Woojin Jeon, Kyung Jean Yoon, Tae Joo Park, Cheol Seong Hwang
    Abstract:

    Various array types of 1-diode and 1-resistor stacked crossbar array (1D1R CA) devices composed of a Schottky diode (SD) (Pt/TiO2/Ti/Pt) and a resistive switching (RS) memory cell (Pt/TiO2/Pt) are fabricated and their performances are investigated. The unit cell of the 1D1R CA device shows High RS Resistance ratio (≈103 at 1.5 V) between low and High Resistance State (LRS and HRS), and High rectification ratio (≈105) between LRS and reverse-State SD. It also shows a short RS time of <50 ns for SET (Resistance transition from HRS to LRS), and ≈600 ns for RESET (Resistance transition from LRS to HRS), as well as stable RS endurance and data retention characteristics. It is experimentally confirmed that the selected unit cell in HRS (logically the “off” State) is stably readable when it is surrounded by unselected LRS (logically the “on” State) cells, in an array of up to 32 × 32 cells. The SD, as a Highly non-linear resistor, appropriately controls the conducting path formation during the switching and protects the memory element from the noise during retention.

  • concurrent presence of unipolar and bipolar resistive switching phenomena in pnictogen oxide sb2o5 films
    Journal of Applied Physics, 2012
    Co-Authors: Youngbae Ahn, Cheol Seong Hwang, Gun Hwan Kim, Jongho Lee, Ji Woon Park, Jaeyeong Heo, Seung Wook Ryu, Youngseok Kim, Hyeong Joon Kim
    Abstract:

    The concurrent presence of unipolar resistive switching (URS) and bipolar resistive switching (BRS) characteristics of the Sb/Sb2O5/Pt structure were examined. It was discovered that the BRS phenomenon was driven by the abnormal reset process during URS cycles which was induced by the rupture and recovery of the conducting filament (CF) in the localized region near the anode. The electrical conduction behavior in the High Resistance State of URS and BRS was explained by the Schottky emission and space-charge-limited current mechanism, meaning that the URS and BRS phenomena are induced by the extent of reoxidaton and reduction regarding the local CF-ruptured region.

  • study on the electrical conduction mechanism of bipolar resistive switching tio2 thin films using impedance spectroscopy
    Applied Physics Letters, 2010
    Co-Authors: Min Hwan Lee, Jung Ho Yoon, Kyungmin Kim, Gun Hwan Kim, Jun Yeong Seok, Seul Ji Song, Cheol Seong Hwang
    Abstract:

    The electrical conduction mechanism within a resistive switching TiO2 film in its bipolar High Resistance State was examined by ac impedance spectroscopy and dc current-voltage measurements. Bipolar switching, which can be initiated from a unipolar High Resistance State, was attributed to both modulation of the Schottky barrier height at the film-electrode interface and the electronic energy State in the film. Numerical fittings of the impedance data revealed two distinct RC domains in series, which were attributed to an interfacial barrier (activation energy ∼0.1 eV) and a nonconducting layer (activation energy ∼0.5 eV), respectively.

  • anode interface localized filamentary mechanism in resistive switching of tio2 thin films
    Applied Physics Letters, 2007
    Co-Authors: Kyungmin Kim, Byung Joon Choi, Yong Cheol Shin, Seol Choi, Cheol Seong Hwang
    Abstract:

    The filamentary Resistance switching mechanism of a Pt∕40nm TiO2∕Pt capacitor structure in voltage sweep mode was investigated. It was unambiguously found that the conducting filaments propagate from the cathode interface and that the Resistance switching is induced by the rupture and recovery of the filaments in the localized region (3–10nm thick) near the anode. The electrical conduction behavior in the High Resistance State was well explained by the space charge limited current (SCLC) mechanism that occurs in the filament-free region. The various parameters extracted from the SCLC fitting supported the localized rupture and formation of filaments near the anode.

Ming Liu - One of the best experts on this subject based on the ideXlab platform.

  • evolution of conductive filament and its impact on reliability issues in oxide electrolyte based resistive random access memory
    Scientific Reports, 2015
    Co-Authors: Hongtao Liu, Ruoyu Liu, Qi Liu, Writam Banerjee, Haitao Sun, Shibing Long, Ming Liu
    Abstract:

    The electrochemical metallization cell, also referred to as conductive bridge random access memory, is considered to be a promising candidate or complementary component to the traditional charge based memory. As such, it is receiving additional focus to accelerate the commercialization process. To create a successful mass product, reliability issues must first be rigorously solved. In-depth understanding of the failure behavior of the ECM is essential for performance optimization. Here, we reveal the degradation of High Resistance State behaves as the majority cases of the endurance failure of the HfO2 electrolyte based ECM cell. High resolution transmission electron microscopy was used to characterize the change in filament nature after repetitive switching cycles. The result showed that Cu accumulation inside the filament played a dominant role in switching failure, which was further supported by measuring the retention of cycle dependent High Resistance State and low Resistance State. The clarified physical picture of filament evolution provides a basic understanding of the mechanisms of endurance and retention failure, and the relationship between them. Based on these results, applicable approaches for performance optimization can be implicatively developed, ranging from material tailoring to structure engineering and algorithm design.

  • improving the electrical performance of resistive switching memory using doping technology
    Chinese Science Bulletin, 2012
    Co-Authors: Qi Liu, Shibing Long, Yan Wang, Wei Wang, Sen Zhang, Wentai Lian, Jianhong Yang, Ming Liu
    Abstract:

    In this paper, improvements of resistive random access memory (RRAM) using doping technology are summarized and analyzed. Based on a Cu/ZrO2/Pt device, three doping technologies with Ti ions, Cu, and Cu nanocrystal, respectively, are adopted in the experiments. Compared to an undoped device, improvements focus on four points: eliminating the electroforming process, reducing operation voltage, improving electrical uniformity, and increasing device yield. In addition, thermal stability of the High Resistance State and better retention are also achieved by the doping technology. We demonstrate that doping technology is an effective way of improving the electrical performance of RRAM.

  • organic nonpolar nonvolatile resistive switching in poly 3 4 ethylene dioxythiophene polystyrenesulfonate thin film
    Organic Electronics, 2009
    Co-Authors: Xinghua Liu, Ming Liu, Liwei Shang, Jiang Liu, Changqing Xie
    Abstract:

    Abstract In this paper, the reproducible nonpolar resistive switching is demonstrated in devices with the sandwiched structure of Au/poly(3,4-ethylene-dioxythiophene): polystyrenesulfonate/Au for nonvolatile memory application. The switching between High Resistance State (OFF-State) and low Resistance State (ON-State) does not depend on the polarity of the applied voltage bias, which is different from both the WORM characteristics and the bipolar switching characteristics reported before. The resistive ratio between the ON- and OFF-State is on the order of 103 and increases with the device area decreasing. Both the ON- and OFF-State of the memory devices are stable, showing no significant degradation over 104 s under continuous readout testing. It is proposed that the reduction and oxidation of PEDOT: PSS film might be the switching mechanism.

  • nonvolatile resistive switching memory utilizing gold nanocrystals embedded in zirconium oxide
    Applied Physics Letters, 2007
    Co-Authors: Weihua Gua, Shibing Long, Rui Jia, Ming Liu
    Abstract:

    Resistive switching characteristics of ZrO2 films containing gold nanocrystals (nc-Au) are investigated for nonvolatile memory applications. The sandwiched top electrode/ZrO2 (with nc-Au embedded)/n+ Si structure exhibits two stable Resistance States (High-Resistance State and low-Resistance State). By applying proper voltage bias, resistive switching from one State to the other State can be achieved. This resistive switching behavior is reproducible and the ratio between the High and low Resistances can be as High as two orders. The intentionally introduced nc-Au in ZrO2 films can improve the device yield greatly. ZrO2 films with gold nanocrystals embedded are promising to be used in the nonvolatile resistive switching memory devices.