W.J. Maeng

Hybrid nanofabrication processes utilizing diblock copolymer nanotemplate prepared by self-assembled monolayer based surface neutralization

Nanostructures including nanohole and metal dot arrays were fabricated by hybrid processes combing self-assembled diblock copolymer and conventional semiconductor processes. The interfacial energy between polystyrene-b-polymethylmetacrylate (PS-b-PMMA) diblock copolymer and substrate surface was controlled by employing a self-assembled monolayer (SAM), resulting in a polymer template with well-ordered cylindrical nanohole array. The nanohole sizes were controlled within 10 to 22 nm in diameter using block copolymers with different molecular weights. The PS nanotemplates were fabricated on various substrates, including oxides, nitrides, and poly-Si. Nanohole pattern was transferred by dry etching process, producing inorganic nanohole templates. Also, gold nanodot arrays with diameter smaller than 10 nm were fabricated through lift off process.

Low temperature atomic layer deposited Al-doped ZnO thin films and associated semiconducting properties

Semiconducting Al-doped ZnO films were deposited by atomic layer deposition at low deposition temperatures of less than 100u2009°C and used to fabricate transistors. At deposition temperatures of less than 100u2009°C, the carrier concentrations of the Al:ZnO thin films were below 1018u2009cm−3, which corresponds to the transparent semiconducting oxide region. The reduced carrier concentrations at low deposition temperatures were attributed to the activation energy for carrier generation of ∼0.7u2009eV. The devices characteristics of the semiconducting Al:ZnO consisted of mobilities of 1.95 cm2/Vu2005s and on–off ratios of over 106. At a positive gate stress of less than 10u2009V, the Vth shift of the Al:ZnO after 3000u2009s was ∼3u2009V, which is almost 1 order of magnitude lower than that of ZnO thin-film transistors.

Growth characteristics and film properties of gallium doped zinc oxide prepared by atomic layer deposition

We carried out comprehensive studies on structural, optical, and electrical properties of gallium-doped zinc oxide (Ga:ZnO) films deposited by atomic layer deposition (ALD). The gallium(III) isopropoxide (GTIP) was used as a Ga precursor, which showed pure Ga2O3 thin film with high growth rate. Using this precursor, conductive Ga doped ZnO thin film can be successfully deposited. The electrical, structural and optical properties were systematically investigated as functions of the Ga doping contents and deposition temperature. The best carrier concentration and transmittance (7.2u2009×u20091020xa0cm−3 and 83.5xa0%) with low resistivity (≈3.5u2009×u200910−3u2009Ωcm) were observed at 5xa0at.% Ga doping concentration deposited at 250xa0°C. Also, low correlation of deposition temperature with the carrier concentration and film structure was observed. This can be explained by the almost same atomic radius of Ga and Zn atom.

Effects of Fluorine Plasma Treatment on the Electronic Structure of Plasma-Enhanced Atomic Layer Deposition HfO2

We investigated the effects of fluorine treatments on the electrical properties and electronic structures of plasma-enhanced atomic layer deposition HfO 2 gate oxides, depending on the treatment process. Pre- and postoxide-deposition fluorine treatments were carried out using CF 4 plasma. Improved dielectric properties were achieved by predeposition treatment, while degradation of electrical properties was observed for postdeposition treatment. Based on the electronic structure analysis using X-ray photoemission spectroscopy and near-edge X-ray absorption fine structures, we found that the enhanced dielectric properties of the pretreated HfO 2 are induced by the defect passivation and conduction-band offset increase.

Plasma-Enhanced ALD of TiO2 Thin Films on SUS 304 Stainless Steel for Photocatalytic Application

Plasma-enhanced atomic layer deposition (PE-ALD) of TiO 2 thin films using Ti(NMe 2 ) 4 [tetrakis(dimethylamido) Ti] and O 2 plasma were prepared on stainless steel to show the self-cleaning effect. The TiO 2 thin films deposited on stainless steel have high growth rate, large surface roughness, and low impurities. The film deposited below 200°C was amorphous, while the films deposited at 300 and 400°C showed anatase and rutile phases, respectively. The contact angle measurements on crystalline PE-ALD TiO 2 thin films exhibited superhydrophilicity after UV irradiation. The TiO 2 thin film with anatase phase deposited at 300°C showed the highest photocatalytic efficiency, which is higher than on Activ glass or thermal ALD TiO 2 films. We suggest that anatase structure and large surface area of TiO 2 thin film on stainless steel are the main factors for the high photocatalytic efficiency.

Effects of TaN Diffusion Barrier on Cu-Gate ZnO:N Thin-Film Transistors

The effects of TaN Cu diffusion barrier in Cu-gate ZnO:N thin-film transistors (TFTs) were studied. Bias stress tests were performed on Cu-gate TFTs with atomic layer deposited Al2O3 and HfO2 gate insulators. The mobility, the threshold voltage, and the reliability were significantly improved by applying a TaN diffusion barrier at the interface between the Cu gate and the gate insulator. The reduction in Cu diffusion by the diffusion barrier is a key process that increases device stability and results in improved oxide TFT performance.

Lattice reorientation in tetragonal PMN-PT thin film induced by focused ion beam preparation for transmission electron microscopy

Focused ion beam sample preparation for transmission electron microscopy (TEM) can induce relaxation mechanisms in epitaxial thin films. Here, we describe a relaxation mechanism that can occur in materials having a tetragonal structure. We investigated the lattice structure of a 600u2009nm thick 0.4[Pb(Mg1/3Nb2/3)O3]−0.6[PbTiO3] layer grown by epitaxy on (110) GdScO3 substrate using geometrical phase analysis applied to high resolution TEM images. The lattice mismatch at the interface is expected to favor the formation of c-domains. However, it was measured that the out-of-plane lattice parameter can decrease abruptly along the growth direction and the transition depends on the thickness of the TEM lamella. Different observations indicate that the crystal flipped by 90° following the preparation of the sample, so that the c-axis is oriented in the thinning direction. Such a mechanism can easily lead to misinterpretations and might happen in other materials with a similar structure.