Donggeun Jung

Large nonlinear dielectric properties of artificial BaTiO3/SrTiO3 superlattices

BaTiO3(BTO)/SrTiO3(STO) artificial superlattices have been made on MgO (100) substrates. The periodicity of the BTO/STO layers in the superlattice was varied from one-unit cell to 125-unit cell thickness. The dielectric constant and its nonlinearity (or voltage tunability) showed similar behavior as the periodicity was varied. The voltage tunability of the superlattice increased with decreasing stacking periodicity of the BTO/STO within the critical thickness. Similarly, the lattice distortion, i.e., the ratio of the lattice parameter along surface normal to parallel, of the BTO and STO layers increased with decreasing the periodicity. Remarkable enhancement of the voltage tunability has been achieved. The superlattice exhibited large voltage tunability (94%, the highest value to date) at the periodicity of BTO2-unit cell/STO2-unit cell at which the maximum lattice distortion of each layer was obtained. This suggests that the nonlinear dielectric property of the superlattice is closely related with the la...

Strain manipulation in BaTiO3/SrTiO3 artificial lattice toward high dielectric constant and its nonlinearity

Enhancement of dielectric properties has been demonstrated in BaTiO3 (BTO)/SrTiO3 (STO) strained artificial lattice. Large variation of lattice distortion in the consisting BTO and STO layers was achieved by varying a stacking sequence of BTO and STO layers. From this strain manipulation, it is found that BTO and STO lattices have a dielectric constant sensitively influenced by the lattice distortion and, more importantly, maximum dielectric constant at a certain degree of lattice distortion. An appropriate degree of lattice distortions of the consisting layers is needed to obtain the large dielectric constant and its nonlinearity of the artificial lattice. The artificial lattice exhibited the large dielectric constant (1230) and extremely large nonlinearity (94%) at the periodicity of BTO2 unit cell/STO2 unit cell. These results suggest that the strain is a macroscopically important factor to influence the dielectric properties and can be manipulated via oxide artificial lattice to obtain large dielectri...

Solution-processed InGaZnO-based thin film transistors for printed electronics applications

This letter reports the utility of using the sol-gel process for exploring the library of multicomponent ZnO-based oxides as an active layer of thin film transistors. We chose InGaZnO as a starting material and modulated the Ga content to examine the potential of this material. Increasing the Ga ratio from 0.1 to 1 brought about a dynamic shift in the electrical behavior from conductor to semiconductor. This exploratory work critically helped us fabricate a device with robust device performance (a mobility of 1∼2 cm2 V−1 s−1 for the 400 °C-sintered samples and 0.2 cm2 V−1 s−1 for the 300 °C-sintered samples).

Paper as a Substrate for Inorganic Powder Electroluminescence Devices

Alternating-current-type inorganic powder electroluminescence (PEL) devices were successfully fabricated on four kinds of paper substrates, i.e., glossy paper, sticker paper, magazine paper, and newspaper. To protect the paper from wet chemical and heating processes during the formation of the PEL device, the paper substrate was coated with a spin-on-glass layer that served as a buffer layer. In spite of the fragility of paper, quite satisfactory results were obtained-the performance of paper-based PEL devices was almost equivalent to that of PEL devices on a plastic substrate. Extension of a substrate to paper, even to flimsy daily newspaper, will widen the opportunity of PEL devices as one of flexible and disposable displays.

Protein immobilization on plasma-polymerized ethylenediamine-coated glass slides

For protein chip construction, protein immobilization on the surface of the glass slide is essential. It was previously reported that glass slides are embedded with chemicals that contain primary amines and aldehydes for protein immobilization. We fabricated a plasma-polymerized ethylenediamine (PPEDA)-coated slide that exposed primary amines. For the plasma polymer deposition on the glass slide, the inductively coupled plasma (ICP) power was found to be a critical factor in sustaining a high density of amine on the surface of the PPEDA films. We prepared PPEDA-coated slides at three different ICP powers (3, 30, or 70 W). In the slide that was prepared at a low ICP power (3 W), we detected a high density of primary amine. Therefore, the fluorescein isothiocyanate-conjugated immunoglobulin G (IgG) was highly immobilized to the PPEDA-coated slide that was prepared at the low ICP power. For protein immobilization, 1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride (EDC) was used as a cross-linker. The immobilization of the protein to the PPEDA-coated slide was carried out by consecutive incubations with 1 mg/ml EDC for 5 min and 0.1 mg/ml IgG for 1 h. This efficiently produced the functionally active protein-immobilized slide. Therefore, this work shows that the plasma technique can be applied to produce a high-quality glass surface for the immobilization of proteins and other materials.

The interface formation and adhesion of metals (Cu, Ta, and Ti) and low dielectric constant polymer-like organic thin films deposited by plasma-enhanced chemical vapor deposition using para-xylene precursor

Abstract The interface formation, adhesion and diffusion properties of metals (Cu, Ta, and Ti) and low dielectric constant (low k ) polymer-like organic thin films (POTFs) deposited by plasma-enhanced chemical vapor deposition (PE-CVD) using the para -xylene precursor were investigated. Cu, Ta and Ti deposited on the surfaces of POTFs treated by O 2 and N 2 plasmas generated in a magnetically-enhanced inductively coupled plasma (ME-ICP) reactor. X-ray photoelectron spectroscopy (XPS) was used to study the chemical interactions between metals and POTFs. As a result of formation of new binding states by plasma treatment, the adhesion strength of metals and POTFs was increased. Diffusion properties of metals into POTFs were investigated using Rutherford backscattering spectroscopy (RBS) for the vacuum-annealed Cu/POTFs and Ta/POTFs for 1 h at 450°C. Also, from the RBS spectra, it was observed that Cu and Ta in the post-annealed samples were not diffused into both POTFs with and without plasma surface treatments.

Effects of deposition parameters on the crystallinity of CeO2 thin films deposited on Si(100) substrates by r.f.-magnetron sputtering

Deposition temperature, r.f.-power and seed layer deposition time were important parameters effecting the crystallinity of CeO2 thin films deposited by r.f.-magnetron sputtering on Si(100) substrates. The CeO2 (200) peak was notable for a deposition temperature above 600°C. With decreased r.f.-power and thus lower deposition rate, the intensity of the CeO2(200) peak increased. When the seed layer deposition time was less than 20 s, the CeO2(200) peak dominated. Transmission electron microscopy (TEM) diffraction revealed that the deposited CeO2 thin film had a polycrystalline structure. Annealing at 950°C in O2 atmosphere for 30 min increased and sharpened the CeO2(200) peak.

Polymer-like Organic Thin Films Deposited by Plasma Enhanced Chemical Vapor Deposition Using the Para-xylene Precursor as Low Dielectric Constant Interlayer Dielectrics for Multilevel Metallization

Polymer-like organic thin films were deposited by plasma enhanced chemical vapor deposition (PECVD) using the para-xylene precursor. The effect of the plasma power on the dielectric constant and thermal stability was significant. As the plasma power was increased from 5 W to 60 W, the relative dielectric constant increased from 2.70 to 3.21. The film deposited at a higher plasma power showed higher thermal stability. The film deposited at 60 W was stable up to 450°C. All the deposited films were insulating under an applied field of ≤1 MV/cm.

Controllable capacitance–voltage hysteresis width in the aluminum–cerium-dioxide–silicon metal–insulator–semiconductor structure: Application to nonvolatile memory devices without ferroelectrics

The Al/CeO2/Si metal–insulator–semiconductor (MIS) structure showed a capacitance–voltage (C–V) hysteresis, which could be controlled by variation of the CeO2 thickness. For a sample with 3000 A CeO2, hysteresis width as high as ∼1.8 V was obtained. For nonvolatile field-effect transistors, the Al/CeO2/Si MIS structure with a reliable and controllable C–V hysteresis could be an alternative to metal–ferroelectric–semiconductor structures containing unstable, multicomponent ferroelectric materials.

Polarization of strained BaTiO3∕SrTiO3 artificial superlattice: First-principles study

We performed first-principles calculation to investigate the effect of epitaxial strain on lattice instabilities and polarization behavior of BaTiO3∕SrTiO3 artificial lattice with very short stacking period, i.e., BaTiO31unitcell∕SrTiO31unitcell(BTO∕STO). The structural analysis of BTO∕STO artificial superlattice under in-plane compressive state showed enhanced stability of the tetragonal phase. On the other hand, the stability of monoclinic phase was enhanced when the BTO∕STO was in the in-plane tensile state. The phase transition from tetragonal to the monoclinic phase occurs at the misfit strain of −0.25%. As the misfit strain of BTO∕STO superlattice increases from −0.25%to−1.5% (in-plane compressive state), the tetragonal superlattice exhibits an increasing polarization along the [001] direction. In the monoclinic phase, the polarization of the superlattice rotates progressively toward [110] direction with increasing the misfit strain, and the magnitude of the polarization simultaneously increases wit...