David H. Seo

Samsung Advanced Institute of Technology, Usan-ri, Gyeonggi Province, South Korea

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Publications (40)223.78 Total impact

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    ABSTRACT: Many attempts have been tried to improve switching characteristics of resistive switching materials such as NiOx because it gives scattered switching current and voltage values [J. F. Gibbons and W. E. Beadle, Solid-State Electron. 7, 785–790 (1964); S. Seo et al., Appl. Phys. Lett. 85, 5655–5657 (2004); H. D. Lee et al., Phys. Rev. B 81, 193202 (2010); S. I. Kim et al., Appl. Phys. Lett. 104, 023513 (2014); M.-J. Lee et al., Nano Lett. 9, 1476–1481 (2009)]. The nature of scattering should be understood based on switching mechanism and the source of scattering in order to improve switching properties. Here, the long tail in scatter data—the data points which are observed only one or two times during switching—was investigated. Techniques such as multiple input pulses are proposed in order to avoid switching missing and size scaling of switching devices are suggested in order to improve data scattering. In addition, discovery of double switching curves in unipolar switching is presented.
    Applied Physics Letters 06/2014; 104(22):222902-222902-4. · 3.52 Impact Factor
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    ABSTRACT: Stackable select devices such as the oxide p-n junction diode and the Schottky diode (one-way switch) have been proposed for non-volatile unipolar resistive switching devices; however, bidirectional select devices (or two-way switch) need to be developed for bipolar resistive switching devices. Here we report on a fully stackable switching device that solves several problems including current density, temperature stability, cycling endurance and cycle distribution. We demonstrate that the threshold switching device based on As-Ge-Te-Si material significantly improves cycling endurance performance by reactive nitrogen deposition and nitrogen plasma hardening. Formation of the thin Si3N4 glass layer by the plasma treatment retards tellurium diffusion during cycling. Scalability of threshold switching devices is measured down to 30 nm scale with extremely fast switching speed of ~2 ns.
    Nature Communications 10/2013; 4:2629. · 10.74 Impact Factor
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    ABSTRACT: The rectifying Schottky characteristics of the metal-semiconductor junction with high contact resistance have been a serious issue in modern electronic devices. Herein, we demonstrated the conversion of the Schottky nature of the Ni-Si junction, one of the most commonly used metal-semiconductor junctions, into an Ohmic contact with low contact resistance by inserting a single layer of graphene. The contact resistance achieved from the junction incorporating graphene was about 10(-8 ~ -9) Ω cm(2) at a Si doping concentration of 10(17) cm(-3).
    Nano Letters 08/2013; · 13.03 Impact Factor
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    ABSTRACT: Until now, the studies about low-frequency noises in electronic devices have mostly relied on the scaling behaviour analysis of current noise measured from multiple devices with different resistance values. However, the fabrication of such multiple devices for noise analysis is a labor-intensive and time-consuming work. Herein, we developed the scanning noise microscopy (SNM) method for nanoscale noise analysis of electronic devices, which allowed us to measure the scaling behaviour of electrical current noises in a graphene-strip-based device. In this method, a conductive atomic force microscopy probe made a direct contact on the graphene strip channel in the device to measure the noise spectra through it. The SNM method enabled the investigation of the noise scaling behaviour using only a single device. In addition, the nanoscale noise map was obtained, which allowed us to study the effect of structural defects on the noise characteristics of the graphene strip channel. Our method should be a powerful strategy for nanoscale noise analysis and play a significant role in basic research on nanoscale devices.
    03/2013;
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    ABSTRACT: A graphene charge-trap memory is devised using a single-layer graphene channel with an Al2O3/AlOx/Al2O3 oxide stack, where the ion-bombarded AlOx layer is intentionally added to create an abundance of charge-trap sites. The low dielectric constant of AlOx compared to Al2O3 reduces the potential drop in the control oxide Al2O3 and suppresses the electron back-injection from the gate to the charge-storage layer, allowing the memory window of the device to be further extended. This shows that the usage of a lower dielectric constant in the charge-storage layer compared to that of the control oxide layer improves the memory performance for graphene charge-trap memories.
    Applied Physics Letters 12/2012; 101(24). · 3.52 Impact Factor
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    ABSTRACT: Understanding the breakdown current density is not enough for establishing the reliability performance of graphene interconnects. It is more important to know how graphene wires degrade with time under constant current stress and how that compares with conventional interconnects. This letter investigates the lifetime of graphene interconnect under constant high current stress. Under a stress current density of 20 MA/cm2 at 250°C exposed to air, the mean time to fail of a 3-μm-wide 100-μm-long graphene interconnect is approximately 6 h, slightly worse than the extrapolated electromigration lifetime of a copper interconnect capped with CoWP at the same stress current density. Raman study shows that the interconnect failure is mainly caused by defect formation due to graphene oxidation. This suggests that optimizing the capping material for graphene interconnect will substantially improve the reliability lifetime of graphene interconnects.
    IEEE Electron Device Letters 11/2012; 33(11):1604-1606. · 2.79 Impact Factor
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    ABSTRACT: A transparent and flexible graphene charge-trap memory (GCTM) composed of a single-layer graphene channel and a 3-dimensional gate stack was fabricated on a polyethylene naphtalate substrate below eutectic temperatures (∼110 °C). The GCTM exhibits memory functionality of ∼8.6 V memory window and 30% data retention per 10 years, while maintaining ∼80% of transparency in the visible wavelength. Under both tensile and compressive stress, the GCTM shows minimal effect on the program/erase states and the on-state current. This can be utilized for transparent and flexible electronics that require integration of logic, memory, and display on a single substrate with high transparency and endurance under flex.
    ACS Nano 08/2012; 6(9):7879-84. · 12.03 Impact Factor
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    ABSTRACT: Despite several years of research into graphene electronics, sufficient on/off current ratio I(on)/I(off) in graphene transistors with conventional device structures has been impossible to obtain. We report on a three-terminal active device, a graphene variable-barrier "barristor" (GB), in which the key is an atomically sharp interface between graphene and hydrogenated silicon. Large modulation on the device current (on/off ratio of 10(5)) is achieved by adjusting the gate voltage to control the graphene-silicon Schottky barrier. The absence of Fermi-level pinning at the interface allows the barrier's height to be tuned to 0.2 electron volt by adjusting graphene's work function, which results in large shifts of diode threshold voltages. Fabricating GBs on respective 150-mm wafers and combining complementary p- and n-type GBs, we demonstrate inverter and half-adder logic circuits.
    Science 05/2012; 336(6085):1140-3. · 31.20 Impact Factor
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    ABSTRACT: Graphene-based non-volatile memory devices composed of a single-layer graphene channel and an Al2O3/HfOx/Al2O3 charge-storage layer exhibit memory functionality. The impact of the gate material’s work-function (Φ) on the memory characteristics is investigated using different types of metals [Ti (ΦTi = 4.3 eV) and Ni (ΦNi = 5.2 eV)]. The ambipolar carrier conduction of graphene results in an enlargement of memory window (ΔVM), which is ∼4.5 V for the Ti-gate device and ∼9.1 V for the Ni-gate device. The increase in ΔVM is attributed to the change in the flat-band condition and the suppression of electron back-injection within the gate stack.
    Applied Physics Letters 01/2012; 100(2). · 3.52 Impact Factor
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    ABSTRACT: Lifetime of multi-layer graphene interconnects under constant current stress is studied for the first time. Under a stress current density of 20MA/cm2 at 250°C exposed to air, Mean-Time-To-Fail (MTTF) of uncapped CVD graphene wire is about 6 hours. It is shown that lifetime is mainly limited by defect formation due to graphene oxidation.
    VLSI Technology (VLSIT), 2012 Symposium on; 01/2012
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    ABSTRACT: A The non-volatile gEOTMs are fabricated using a single-layer graphene (SLG) channel with an Al2O3 gate oxide layer, in which an ion-bombarded AlOx layer is intentionally formed by oxygen ion bombardment (OIB) to create the charge trap sites. The whole processes are carried out at temperature below 120°C to exploit gEOTM's compatibility to the flexible substrates. The devices shows a large memory window (> 11.0 V), attributing to the effective electron-injection into the trap sites in AlOx. The results suggest that the gEOTM has potential applications for the high-density-memory devices and modules in flexible electronics.
    01/2012;
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    ABSTRACT: A Flexible and Transparent charge trap Memory (FTM) based on a single-layer graphene (SLG) channel with a ITO gate electrode was fabricated on a flexible and transparent poly-ethylene naphtalate (PEN) substrate. Triple high-k dielectric stacks Al2O3- AlOx-Al2O3 (AAA) were used as a data storage layer. The FTM shows memory characteristics with a memory window larger than 7V while maintaining ~80% of its transparency in the visible wavelength. The adoption of an AAA gate stack effectively suppressed the electron back injection from the gate electrode. This can be utilized for transparent and flexible electronics that require integration of logic, memory and display on a single flexible substrate with high transparency.
    01/2012;
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    ABSTRACT: One of the key components of modern device structures is the metal-semiconductor (MS) contact with low symmetric contact resistance. We report on a MS contact structure utilizing graphene insertion. In this strategy, graphene reduces or even eliminates in ideal conditions, the Fermi-level pinning at a MS junction. Since the metal, Ni, deposited on graphene reduced the work function of graphene, the doped graphene was able to lower the Schottky barrier at the MS junction. The Schottky barrier height of metal-graphene-Si (MGS) junction was obtained from temperature dependent I-V characteristics. We confirmed that the graphene doped with Ni reduced the Schottky barrier height from 0.67 eV to 0.20 eV in wafer scale test. We also demonstrated the formation of an ideal MGS Ohmic contact via conductive atomic force microscopy. The contact resistance of the ideal MGS was less than 1.0×10-6 Ω cm2 with low doped Si (1015 cm3). The resistance is comparable to that of a current device contact with highly doped Si. Since it only requires the insertion of a single layer of graphene, this method can be directly applied to the current Si technology to reduce the contact resistance at MS junctions.
    Nanotechnology Materials and Devices Conference (NMDC), 2012 IEEE; 01/2012
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    ABSTRACT: We developed a scanning noise microscopy (SNM) method and demonstrated the nanoscale noise analysis of a graphene strip-based device. Here, a Pt tip made a direct contact on the surface of a nanodevice to measure the current noise spectrum through it. Then, the measured noise spectrum was analyzed by an empirical model to extract the noise characteristics only from the device channel. As a proof of concept, we demonstrated the scaling behavior analysis of the noise in graphene strips. Furthermore, we performed the nanoscale noise mapping on a graphene channel, allowing us to study the effect of structural defects on the noise of the graphene channel. The SNM method is a powerful tool for nanoscale noise analysis and should play a significant role in basic research on nanoscale devices.
    ACS Nano 11/2011; 5(11):8620-8. · 12.03 Impact Factor
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    ABSTRACT: We report a graphene-polymer hybrid nanostructure-based bioenergy storage device to turn on and off biomotor activity in real-time. In this strategy, graphene was functionalized with amine groups and utilized as a transparent electrode supporting the motility of biomotors. Conducting polymer patterns doped with adenosine triphosphate (ATP) were fabricated on the graphene and utilized for the fast release of ATP by electrical stimuli through the graphene. The controlled release of biomotor fuel, ATP, allowed us to control the actin filament transportation propelled by the biomotor in real-time. This strategy should enable the integrated nanodevices for the real-time control of biological motors, which can be a significant stepping stone toward hybrid nanomechanical systems based on motor proteins.
    ACS Nano 11/2011; 5(11):8656-64. · 12.03 Impact Factor
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    ABSTRACT: We report a simple but efficient method to prepare metallic nanowire-graphene (MN-G) hybrid nanostructures at a low temperature and show its application to the fabrication of flexible field emission devices. In this method, a graphene layer was transferred onto an anodic alumina oxide template, and vertically aligned Au nanowires were grown on the graphene surface via electrodeposition method. As a proof of concept, we demonstrated the fabrication of flexible field emission devices, where the MN-G hybrid nanostructures and another graphene layer on PDMS substrates were utilized as a cathode and an anode for highly flexible devices, respectively. Our field emission device exhibited stable and high field emission currents even when bent down to the radius of curvature of 25 mm. This MN-G hybrid nanostructure should prove tremendous flexibility for various applications such as bio-chemical sensors, field emission devices, pressure sensors and battery electrodes.
    Nanotechnology 09/2011; 22(35):355709. · 3.84 Impact Factor
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    ABSTRACT: With the motivation of realizing an all graphene-based circuit for low power, we present a reliable nonvolatile graphene memory device, single-layer graphene (SLG) ferroelectric field-effect transistor (FFET). We demonstrate that exfoliated single-layer graphene can be optically visible on a ferroelectric lead-zirconate-titanate (PZT) substrate and observe a large memory window that is nearly equivalent to the hysteresis of the PZT at low operating voltages in a graphene FFET. In comparison to exfoliated graphene, FFETs fabricated with chemical vapor deposited (CVD) graphene exhibit enhanced stability through a bi-stable current state operation with long retention time. In addition, we suggest that the trapping/de-trapping of charge carriers in the interface states is responsible for the anti-hysteresis behavior in graphene FFET on PZT.
    Applied Physics Letters 08/2011; · 3.52 Impact Factor
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    ABSTRACT: Suspended few-layer graphene beam electro-mechanical switches (SGSs) with 0.15 μm air-gap are fabricated and electrically characterized. The SGS shows an abrupt on/off current characteristics with minimal off current. In conjunction with the narrow air-gap, the outstanding mechanical properties of graphene enable the mechanical switch to operate at a very low pull-in voltage (VPI) of 1.85 V, which is compatible with conventional complimentary metal-oxide-semiconductor (CMOS) circuit requirements. In addition, we show that the pull-in voltage exhibits an inverse dependence on the beam length.
    Applied Physics Letters 07/2011; 99(2):023103-023103-3. · 3.52 Impact Factor
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    ABSTRACT: Recent developments in wafer scale synthesis and transfer of graphene have made it possible to fabricate electrodes for versatile flexible devices. However, a flexible and transparent graphene-based field emission device has not been explored yet. Herein, we report the fabrication of flexible and transparent field emission devices based on graphene-nanowire hybrid structures. In this work, we successfully grew vertically-aligned Au nanowires on graphene surface using an electrochemical method and utilized it as a cathode. We also utilized a graphene electrode for an anode resulting in a transparent and flexible field emission device. Our field emission devices can be bent down to 22 mm radius of curvature without any significant change in its field emission currents. This flexible and transparent field emission device based on graphene-nanowire hybrid structures will utilized for various applications such as field emission displays, x-ray tubes, and pressure sensors.
    03/2011;

Publication Stats

861 Citations
223.78 Total Impact Points

Institutions

  • 2004–2013
    • Samsung Advanced Institute of Technology
      Usan-ri, Gyeonggi Province, South Korea
  • 2011–2012
    • University of California, Los Angeles
      • Department of Electrical Engineering
      Los Angeles, CA, United States
    • Seoul National University
      • Department of Physics and Astronomy
      Seoul, Seoul, South Korea
  • 2010
    • Stanford University
      • Solid State and Photonics Laboratory
      Palo Alto, CA, United States