Bo Soo Kang

Bio: Bo Soo Kang is an academic researcher from Hanyang University. The author has contributed to research in topics: Ferroelectricity & Resistive random-access memory. The author has an hindex of 27, co-authored 88 publications receiving 4880 citations. Previous affiliations of Bo Soo Kang include Samsung & Ewha Womans University.

Lanthanum-substituted bismuth titanate for use in non-volatile memories

Abstract: Non-volatile memory devices are so named because they retain information when power is interrupted; thus they are important computer components. In this context, there has been considerable recent interest1,2 in developing non-volatile memories that use ferroelectric thin films—‘ferroelectric random access memories’, or FRAMs—in which information is stored in the polarization state of the ferroelectric material. To realize a practical FRAM, the thin films should satisfy the following criteria: compatibility with existing dynamic random access memory technologies, large remnant polarization (Pr) and reliable polarization-cycling characteristics. Early work focused on lead zirconate titanate (PZT) but, when films of this material were grown on metal electrodes, they generally suffered from a reduction of Pr (‘fatigue’) with polarity switching. Strontium bismuth tantalate (SBT) and related oxides have been proposed to overcome the fatigue problem3, but such materials have other shortcomings, such as a high deposition temperature. Here we show that lanthanum-substituted bismuth titanate thin films provide a promising alternative for FRAM applications. The films are fatigue-free on metal electrodes, they can be deposited at temperatures of ∼650 °C and their values of Pr are larger than those of the SBT films.

Electrical manipulation of nanofilaments in transition-metal oxides for resistance-based memory.

Abstract: The fabrication of controlled nanostructures such as quantum dots, nanotubes, nanowires, and nanopillars has progressed rapidly over the past 10 years. However, both bottom-up and top-down methods to integrate the nanostructures are met with several challenges. For practical applications with the high level of the integration, an approach that can fabricate the required structures locally is desirable. In addition, the electrical signal to construct and control the nanostructures can provide significant advantages toward the stability and ordering. Through experiments on the negative resistance switching phenomenon in Pt-NiO-Pt structures, we have fabricated nanofilament channels that can be electrically connected or disconnected. Various analyses indicate that the nanofilaments are made of nickel and are formed at the grain boundaries. The scaling behaviors of the nickel nanofilaments were closely examined, with respect to the switching time, power, and resistance. In particular, the 100 nm x 100 nm cell was switchable on the nanosecond scale, making them ideal for the basis for high-speed, high-density, nonvolatile memory applications.

2-stack 1D-1R Cross-point Structure with Oxide Diodes as Switch Elements for High Density Resistance RAM Applications

Abstract: We have successfully integrated a 2-stack 8times8 array 1D- lR (one diode-one resistor) structure with 0.5 mumtimes0.5 mum cells in order to demonstrate the feasibility of high density stacked RRAM. p-CuOx/n-InZnOx heterojunction thin film was used for the first time as a oxide diode which shows increased current density of two orders over our previous p-NiOx/n-TiOx oxide diode. And Ti-doped NiO was used for the storage node. No limitation to the number of stacks has been observed from our results. Cell and device properties of our cross-point structure 8times8 array are reported. In addition, all fabrication processes were done at room temperature without other dedicated facilities or processes allowing for compatibility with current CMOS technology. Bi-stable switching for 1D-1R memory was demonstrated for our 2-stack cross-point structures showing excellent behavior for both diode and storage nodes. The forward current density for p-CuOx/n-IZOx diodes was over 104A/cm2, and the operation voltage for the storage node with diode attached was around 3 V.

Effects of metal electrodes on the resistive memory switching property of NiO thin films

Abstract: The effects of various metal electrodes on the resistive switching of NiO thin films were investigated. Contrary to the belief that Pt is used for its high work function, which enables Ohmic contact to p-type NiO, resistive switching was observed in films with Ta or Al electrodes with a low work function in the as-deposited state. The resistive switching of films with a Ag or Cu top electrode with a low work function and high free energy of oxidation shows the importance of the formation of an oxide layer at the metal/NiO interface.

A high-mobility electron gas at the LaAlO3/SrTiO3 heterointerface

Abstract: Polarity discontinuities at the interfaces between different crystalline materials (heterointerfaces) can lead to nontrivial local atomic and electronic structure, owing to the presence of dangling bonds and incomplete atomic coordinations. These discontinuities often arise in naturally layered oxide structures, such as the superconducting copper oxides and ferroelectric titanates, as well as in artificial thin film oxide heterostructures such as manganite tunnel junctions. If polarity discontinuities can be atomically controlled, unusual charge states that are inaccessible in bulk materials could be realized. Here we have examined a model interface between two insulating perovskite oxides--LaAlO3 and SrTiO3--in which we control the termination layer at the interface on an atomic scale. In the simple ionic limit, this interface presents an extra half electron or hole per two-dimensional unit cell, depending on the structure of the interface. The hole-doped interface is found to be insulating, whereas the electron-doped interface is conducting, with extremely high carrier mobility exceeding 10,000 cm2 V(-1) s(-1). At low temperature, dramatic magnetoresistance oscillations periodic with the inverse magnetic field are observed, indicating quantum transport. These results present a broad opportunity to tailor low-dimensional charge states by atomically engineered oxide heteroepitaxy.

Prospects of Colloidal Nanocrystals for Electronic and Optoelectronic Applications

Abstract: Nanocrystals (NCs) discussed in this Review are tiny crystals of metals, semiconductors, and magnetic material consisting of hundreds to a few thousand atoms each. Their size ranges from 2-3 to about 20 nm. What is special about this size regime that placed NCs among the hottest research topics of the last decades? The quantum mechanical coupling * To whom correspondence should be addressed. E-mail: dvtalapin@uchicago.edu. † The University of Chicago. ‡ Argonne National Lab. Chem. Rev. 2010, 110, 389–458 389

Memristive devices for computing

Abstract: Memristive devices are electrical resistance switches that can retain a state of internal resistance based on the history of applied voltage and current. These devices can store and process information, and offer several key performance characteristics that exceed conventional integrated circuit technology. An important class of memristive devices are two-terminal resistance switches based on ionic motion, which are built from a simple conductor/insulator/conductor thin-film stack. These devices were originally conceived in the late 1960s and recent progress has led to fast, low-energy, high-endurance devices that can be scaled down to less than 10 nm and stacked in three dimensions. However, the underlying device mechanisms remain unclear, which is a significant barrier to their widespread application. Here, we review recent progress in the development and understanding of memristive devices. We also examine the performance requirements for computing with memristive devices and detail how the outstanding challenges could be met.

Metal–Oxide RRAM

Abstract: In this paper, recent progress of binary metal-oxide resistive switching random access memory (RRAM) is reviewed. The physical mechanism, material properties, and electrical characteristics of a variety of binary metal-oxide RRAM are discussed, with a focus on the use of RRAM for nonvolatile memory application. A review of recent development of large-scale RRAM arrays is given. Issues such as uniformity, endurance, retention, multibit operation, and scaling trends are discussed.