Jongwan Choi

A Dielectric Biosensor Using the Capacitance Change with AC Frequency Integrated on Glass Substrates

Glass-based microchannel chips were fabricated using photolithographic technology, and Pt thin-film microelectrodes as dielectric biosensors were integrated on them. From capacitance-frequency measurements at various interelectrode distances and ionic concentrations, a significant difference between deionized (DI) water and tris-ethylenediaminetetraacetic acid (EDTA) (TE) buffer was observed in the low-frequency region. Although the capacitance (CM) of the DI water decreased as the interelectrode distance increased, that of the TE buffer was similar up to a frequency of 100 Hz, after which it was spilt in the same manner as the DI water above 100 Hz. As the ionic concentration increased, the CM of the TE buffer increased and the slope in the low frequency region changed from -0.875 to -0.425. The point where the slope changed shifted towards the frequency increase. These observations were clarified from the viewpoint of interfacial phenomena, such as the electrical double layer and Faradaic reactions, the dielectric constant related to conductivity, and the capacitance inversely proportional to the interelectrode distance. The addition of deoxyribonucleic acid (DNA) molecules (10 ng/µl) increased the capacitance and dielectric loss in the TE buffer at low frequency. It is feasible to use dielectric properties for the rapid and direct detection of biomolecules, particularly DNA molecules, without using labels or indicators.

Composition and electrical properties of metallic Ru thin films deposited using Ru(C6H6)(C6H8) precursor

Metallic ruthenium films were prepared by metalorganic chemical vapor deposition (CVD) using a new precursor named (η6-benzene)(η4-1,3-cyclohexadiene)ruthenium (Ru(C6H6)(C6H8)) in Ar atmosphere, and the absolute composition and electrical properties were investigated. The absolute composition including hydrogen was determined by means of the elastic recoil detection time of flight (ERD-TOF). It was found that carbon contents in the films markedly decreased when tetrahydrofuran (THF) was supplied with the precursor during deposition. The variation in carbon content could be interpreted by the formation of hydrocarbon compounds as well as the formation of carbon oxide, resulting from the reaction between carbon and THF. In particular, Ru films contained hydrogen that originated in the hydrogen atoms in the precursor and was involved in the CVD process due to the catalytic effect of ruthenium on hydrocarbon and hydrogen. It was shown that grain size, among several other factors strongly affected the electrical properties of ruthenium films.

Influences of annealing temperature on the optical and structural properties of (Ba,Sr)TiO3 thin films derived from sol–gel technique

Abstract Amorphous and polycrystalline Ba 0.9 Sr 0.1 TiO 3 thin films were deposited on Si(100) and fused quartz substrates by a modified sol–gel technique. X-Ray diffraction analysis clearly shows the formation of a perovskite structure at approximately 700 °C. An amorphous nature was found for films annealed below 600 °C, and their inferior crystallinity suggested the formation of an incomplete perovskite phase. The dominant surface feature was a cone-like protrusion observed by atomic force microscopy. The average grain size was approximately 70 nm for the film annealed at 700 °C. The optical constants were determined from spectrophotometric measurements of the transmittance in the wavelength regime of 200–900 nm at room temperature. The effects of the annealing temperature on the optical and structural properties of the films were investigated.

Dependence of Ferroelectricity on Film Thickness in Nano-Scale Pb(Zr,Ti)O3 Thin Films

We present the dependence of the ferroelectric polarization on the film thickness. Below the film thickness of 21 nm, Pb metallic phase was formed at grain boundary and the pervoskite phase disappeared. As the film thickness decreased, the intensity of phonon modes decreased and the compressive stress in the Pb(Zr,Ti)O3 thin film, which had tetragonal and rhombohedral structures, increased. The remnant polarization decreased from 6 μ C/cm2 to 2.5 μ C/cm2, while the coercive field increased from 50 kV/cm to 150 kV/cm, with the decrease in film thickness from 152 nm to 32 nm. The suppression of ferroelectricity resulted from the crystallinity degradation observed using X-ray photoelectron spectroscopy (XPS) and Raman analysis and size effect derived from the residual compressive stress evaluated using a laser reflectance method. The Pb/(Zr+Ti) ratio would be the important factor determining the crystal structure in PZT thin films, especially nano-scale PZT films.

Effects of Sr/Ti Ratio on the Step Coverage of SrTiO3 Thin Films Fabricated Using Electron Cyclotron Resonance Plasma Enhanced Metal Organic Chemical Vapor Deposition

Paraelectric SrTiO3 and (Ba,Sr)TiO3 (BST) thin films have been intensively investigated for giga-bit-scale dynamic random access memory (DRAM) applications because of their high dielectric constants at high frequencies, excellent chemical and thermal stability and outstanding insulting properties. A number of methods have been used to fabricate SrTiO3 and BST thin films. Electron cyclotron resonance plasma enhanced metal organic chemical vapor deposition (ECR-PEMOCVD) has gained significant importance for depositing a variety of dielectric thin-film materials, and MOCVD is often considered to be the best technique for actual applications due to its excellent features, such as easy scale up to industrial levels and the uniform coverage of surface irregularities for stacked capacitor structures to be used in giga-bit-scale DRAM. Up to now, studies on SrTiO3 and BST thin films consist mainly of studies on the dielectric properties of the films fabricated under different deposition conditions (deposition temperature and pressure) and postannealing conditions (annealing temperature and annealing atmosphere). 2, 3, 7, 11) Three-dimensional structures are certainly needed as the DRAM device density increases to achieve the required capacitance in a given area. Thus the step coverage (conformity) of the films is very important in three-dimensional structures. However, there are which are mostly few studies on the effects of process parameters on step coverage, 9) and most of them are based on simulation, and the effects of deposition temperature. There are few studies concerning the effects of composition on step coverage. The properties of SrTiO3 thin films such as crystallinity, however dielectric properties and step coverage depend on their composition. However, controlling the composition of SrTiO3 thin films using MOCVD is not easy. In this study, the composition of SrTiO3 thin films was controlled by varying the flow rate of the carrier gas for the Ti precursor, and we investigated the effects of composition on the step coverage of SrTiO3 thin films. 2. Experimental A schematic diagram of the ECR-PEMOCVD system is shown in Fig. 1. Sr-ditetramethylheptanedionato [or Sr(TMHD)2] and Ti-isopropoxide [or TIP] were used as the metal organic precursors, and oxygen was used as the oxidant. NH3 and Ar gases were used as carrier gases for Sr(TMHD)2 and TIP, respectively. The stainless steel bubbler containing TIP was maintained at 40 ◦ C in an oil bath. A modified membrane evaporator instead of a conventional boat-type evaporator was used in order to increase the vapor pressure of Sr(TMHD)2 by increasing the contact area between the precursor and carrier gas. A stainless steel membrane with 5 µm pores was used that allow may passage of the NH3 carrier gas but not that of the precursor melt. Si(p-type 100), Pt(1000A)/SiO2/Si and stepped Pt(800 A)/ SiO2/Si substrates were used for different purposes. The step coverage was measured for the SrTiO3 thin films deposited on stepped Pt(800A)/SiO2/Si substrates. Figures 2 shows the definition of step coverage used in this study. For the DRAM structure, both the capacitors on the top and the side of the structure are used, so that this definition of step coverage is practical for stacked capacitors. The deposition parameters used in this study were the deposition temperature and the

Effects of etching time and thickness on the performance of the microstrip line resonator of YBa2Cu3Ox thin films

Microstrip transmission lines in the form of an open-ended half-wavelength resonator were fabricated by depositing YBa2Cu3Ox thin films on MgO substrates using the pulsed laser deposition method. All YBa2Cu3Ox thin films had c-axis orientation. The effects of etching time and thickness on the performance of the microstrip line resonator were investigated. As the etching time increased, the loaded quality factor decreased and the surface resistance increased due to the undercut and the increase in roughness of the etched surface. The quality factor and the surface resistance showed a strong dependence on the film thickness. The superconducting properties and the microwave characteristics correlated well with the microstructure.

Fabrication and characterization of BaxSr1-xTiO3/YBa2Cu3Ox/SrTiO3 structure

BaxSr1-xTiO3 (BST)/YBa2Cu3Ox (YBCO)/SrTiO3 (STO) structures were deposited, and the microstructure, orientation and electrical characteristics were investigated. (00l) oriented YBCO thin films were deposited on STO substrates using pulsed laser deposition, and (h00) oriented BST thin films were deposited on YBCO/STO substrates using electron cyclotron resonance (ECR) plasma assisted metal organic chemical vapor deposition (MOCVD). A new phase was formed at the interface between YBCO and BST films and was speculated to be (BaxY1-x)(TiyY1-y)O3. Ba-rich BST films showed a higher dielectric loss than Sr-rich BST films did, which indicates that Sr-rich BST films are more suited for application to microwave devices. The dielectric loss of the films was reduced as temperature decreased, which may be due to the conductivity change of YBCO film and the formation of a conduction path rather than a dielectric property change of the BST film itself. The capacitance vs voltage and the dielectric loss vs bias voltage curves of BST film showed a polarity dependence, which may be speculated to be because of the barrier height difference between the interfaces.

The effects of Sr/Ti ratio on the step coverage of SrTiO/sub 3/ thin films fabricated using ECR-PEMOCVD

SrTiO/sub 3/ thin films were deposited on Si(p-type 100), Pt(1000 /spl Aring/)/SiO/sub 2//Si and stepped Pt(800 /spl Aring/)/SiO/sub 2//Si substrates using ECR-PEMOCVD to study the effects of the deposition temperature and the composition on the properties of SrTiO/sub 3/ thin films. The crystallinity and the dielectric properties of SrTiO/sub 3/ thin films were improved as the deposition temperature increased. But we could observe a distinct correlation not between the step coverage and the deposition temperature but between the step coverage and the composition. The composition of the film was changed by changing the flow rate of carrier gas of one precursor but fixing the other, being the deposition temperature fixed at 550/spl deg/C. The step coverage was improved as the composition (Sr/Ti ratio) increased up to the stoichiometric composition, and showed a saturated value of about 55% as the Sr/Ti ratio increased beyond the stoichiometric composition. This correlation was speculated using the sticking coefficients of the precursor vapors.

Polaron conduction loss in microwave dielectric ceramics

However, it is suggested in this study that this universal parametershould be modified due to the presence of the polarons. From the frequency dependenceof the unloaded quality factor, it is possible to extract the factor determined only by thephonon scattering effects, and we denoted this parameter by