Yil-Hwan You

Bio: Yil-Hwan You is an academic researcher from Texas A&M University. The author has contributed to research in topics: Thin film & Atomic layer deposition. The author has an hindex of 10, co-authored 34 publications receiving 336 citations. Previous affiliations of Yil-Hwan You include Samsung & Korea University.

Impedance spectroscopy characterization of resistance switching NiO thin films prepared through atomic layer deposition

Abstract: To understand electrical/dielectric phenomena and the origins of bistable resistive switching, impedance spectroscopy was applied to NiO thin films prepared through atomic layer deposition. The dc current-voltage characteristics of the NiO thin films were also determined. Frequency-dependent characterizations indicated that the switching and memory phenomena in NiO thin films did not originate from the non-Ohmic effect at the electrode/NiO interfaces but from the bulk-related responses, i.e., from an electrocomposite where highly conducting components are distributed in the insulating NiO matrix. Low dielectric constants and bias-independent capacitance appeared to corroborate the bulk-based responses in resistive switching in NiO thin films.

NiO thin films by MOCVD of Ni(dmamb)2 and their resistance switching phenomena

Abstract: We have synthesized the volatile, liquid, nickel precursor Ni(dmamb) 2 , nickel bis(1-dimethylamino-2-methyl-2-butanolate), Ni[OC(CH 3 )(C 2 H 5 )CH 2 N(CH 3 ) 2 ] 2 , and employed it in the MOCVD of nickel oxide (NiO). A stainless steel, cold-wall, low-pressure reactor was employed to grow the NiO films on Si and Pt/SiO 2 /Si substrates. In addition, the resistance switching property of the Pt/NiO/Pt capacitor structure was investigated. The substrate temperature was varied in the range 230–410 °C. The films deposited were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and I – V measurements. They were polycrystalline showing dominantly the NiO(111) peak in their X-ray diffraction patterns. The films were found to be almost stoichiometric with the Ni:O ratio of 1.1:0.9 and no appreciable amount of carbon incorporation was detected by XPS. The I – V measurements revealed an interesting switching property of the NiO films showing low and high resistance states thereby suggesting their application as ReRAM devices.

Composite Hydrogels Containing Bioactive Microreactors for Optical Enzymatic Lactate Sensing

Abstract: Continuously monitoring specific biomarkers offer a promising method to interrogate disease status and progression. In this work we have demonstrated a composite hydrogel-based sensing platform that may be used for optical detection of lactate. The sensor design consists of microsized enzymatic sensors that are embedded in an outer hydrogel matrix. In these engineered microdomains, encapsulated lactate oxidase serves as the bioactive component, phosphorescent metalloporphyrin acts as the optical transducer, and polyelectrolyte multilayers coated on the enzymatic microsensors control the permeation of lactate into the microsensors. The response of the composite hydrogel-based lactate sensors was characterized by subjecting the sensors to lactate concentration challenges at low physiological oxygen levels. The analytical range and the mean sensitivity were determined to be 9.2 ± 0.83 mg/dL and 11 ± 0.90% dL mg–1, respectively. Repeated cyclic exposure to high levels of lactate revealed that these sensors we...

Crystallization of Amorphous Silicon Thin Films Using Self-Limiting ALD of Nickel Oxide

Abstract: The crystallization of amorphous Si (a-Si) thin films was performed using atomic layer deposition (ALD) of nickel oxide. Nickel oxide layers were deposited using nickel aminoalkoxide as a precursor in Ni and water as a precursor in oxygen. The presence of nickel oxide caused significant crystallization to occur in a-Si at 575 °C under a reducing atmosphere. Even one single ALD layer of nickel oxide was high enough to crystallize the a-Si thin films. Self-limiting layer controllability in ALD is useful in providing a catalytic layer for formation of polycrystalline Si thin films for application to large-scale flat panel displays. © 2007 The Electrochemical Society. [DOI: 10.1149/1.2666721] All rights reserved.

Ga Ordering and Electrical Conductivity in Nanotwin and Superlattice-Structured Ga-Doped ZnO

Abstract: We have investigated the Ga-ordering controlled by structural changes from nanotwin to superlattice in Ga-doped ZnO (GZO) targets for transparent conductive oxides (TCOs) and discussed the distribution effect of Ga atoms on electrical conductivities of GZOs. The nanotwin and superlattice structures were preferentially formed by Ga-doping and sintering at high temperature. The relative fraction of nanotwin increased above transition concentration (TC ≈ 5.6 wt % Ga). Here, we found that Ga atoms at nanotwin are distributed as clustered and disordered states, while they are completely ordered in superlattice. Ultimately, the superlattice leads to high electrical conductivity in GZOs rather than the nanotwin.

Semiconductor device, and manufacturing method thereof

Abstract: An object is to provide a semiconductor device of which a manufacturing process is not complicated and by which cost can be suppressed, by forming a thin film transistor using an oxide semiconductor film typified by zinc oxide, and a manufacturing method thereof. For the semiconductor device, a gate electrode is formed over a substrate; a gate insulating film is formed covering the gate electrode; an oxide semiconductor film is formed over the gate insulating film; and a first conductive film and a second conductive film are formed over the oxide semiconductor film. The oxide semiconductor film has at least a crystallized region in a channel region.

Crystallinity of inorganic films grown by atomic layer deposition: Overview and general trends

Abstract: Atomic layer deposition (ALD) is gaining attention as a thin film deposition method, uniquely suitable for depositing uniform and conformal films on complex three-dimensional topographies. The deposition of a film of a given material by ALD relies on the successive, separated, and self-terminating gas–solid reactions of typically two gaseous reactants. Hundreds of ALD chemistries have been found for depositing a variety of materials during the past decades, mostly for inorganic materials but lately also for organic and inorganic–organic hybrid compounds. One factor that often dictates the properties of ALD films in actual applications is the crystallinity of the grown film: Is the material amorphous or, if it is crystalline, which phase(s) is (are) present. In this thematic review, we first describe the basics of ALD, summarize the two-reactant ALD processes to grow inorganic materials developed to-date, updating the information of an earlier review on ALD [R. L. Puurunen, J. Appl. Phys. 97, 121301 (2005)], and give an overview of the status of processing ternary compounds by ALD. We then proceed to analyze the published experimental data for information on the crystallinity and phase of inorganic materials deposited by ALD from different reactants at different temperatures. The data are collected for films in their as-deposited state and tabulated for easy reference. Case studies are presented to illustrate the effect of different process parameters on crystallinity for representative materials: aluminium oxide, zirconium oxide, zinc oxide, titanium nitride, zinc zulfide, and ruthenium. Finally, we discuss the general trends in the development of film crystallinity as function of ALD process parameters. The authors hope that this review will help newcomers to ALD to familiarize themselves with the complex world of crystalline ALD films and, at the same time, serve for the expert as a handbook-type reference source on ALD processes and film crystallinity.

Innovation in Layer-by-Layer Assembly.

Abstract: Methods for depositing thin films are important in generating functional materials for diverse applications in a wide variety of fields. Over the last half-century, the layer-by-layer assembly of nanoscale films has received intense and growing interest. This has been fueled by innovation in the available materials and assembly technologies, as well as the film-characterization techniques. In this Review, we explore, discuss, and detail innovation in layer-by-layer assembly in terms of past and present developments, and we highlight how these might guide future advances. A particular focus is on conventional and early developments that have only recently regained interest in the layer-by-layer assembly field. We then review unconventional assemblies and approaches that have been gaining popularity, which include inorganic/organic hybrid materials, cells and tissues, and the use of stereocomplexation, patterning, and dip-pen lithography, to name a few. A relatively recent development is the use of layer-by...