Ilsub Chung

Characterization and elimination of dry etching damaged layer in Pt/Pb(Zr0.53Ti0.47)O3/Pt ferroelectric capacitor

The damage of Pb(Zr0.53Ti0.47)O3 thin film due to dry etching process was characterized in terms of the microstructure and electrical properties. The damaged layer seems to be amorphous and the thickness of the damaged layer is about 10 nm. The existence of such a layer in Pt/Pb(Zr0.53Ti0.47)O3/Pt ferroelectric capacitor tends to increase the coercive voltage and the leakage current. The damaged layer was not fully reverted to perovskite phase by the thermal annealing. With the wet cleaning treatment, however, the damaged layer was successfully removed thereby revealing significantly improved electrical properties.

A partially insulated field-effect transistor (PiFET) as a candidate for scaled transistors

Highly manufacturable partially insulated field-effect transistors (PiFETs) were fabricated by using Si-SiGe epitaxial growth and selective SiGe etch process. Owing to these technologies, pseudo-silicon-on-insulator (SOI) structures, partially insulating oxide (PiOX) under source/drain (PUSD) and PiOX under channel (PUC), could be easily realized with excellent structural and process advantages. We are demonstrating their preliminary characteristics and properties. Especially, in the PUSD PiFET, junction capacitance, leakage current, and DIBL in bulk devices could be reduced and the floating body problem in SOI devices was also cleared without any area penalty. Thus, this PiFET structure can be a promising candidate for the future DRAM cell transistor.

Synthesis and characteristics of NH2-functionalized polymer films to align and immobilize DNA molecules

We developed a method to use NH2-functionalized polymer films to align and immobilize DNA molecules on a Si substrate. The plasma-polymerized cyclohexane film was deposited on the Si substrate according to the radio frequency plasma-enhanced chemical vapor deposition method using a single molecular precursor, and it was then treated by the dielectric barrier discharge method in a nitrogen environment under atmospheric pressure. Changes in the chemistry of the surface functional groups were studied using X-ray photoelectron spectroscopy and Fourier transformed infrared spectroscopy. The wettability of the surfaces was examined using dynamic contact angle measurements, and the surface morphology was evaluated using atomic force microscopy.We utilized a tilting method to align λ-DNA molecules that were immobilized by the electrostatic interaction between the amine groups in NH2-functionalized polymer films and the phosphate groups in the DNA. The DNA was treated with positively charged gold nanoparticles to make a conductive nanowire that uses the DNA as a template. We observed that the NH2-functionalized polymer film was useful for aligning and immobilizing the DNA, and thus the DNA-templated nanowires.

Ferroelectric SrBi4Ti4O15 thin films with high polarization grown on an IrO2 layer

Ferroelectric strontium bismuth titanate (SrBi4Ti4O15) thin films with a high remanent polarization were produced by a chemical solution deposition method. Pt and IrO2 layers were used as substrates. It was found that ferroelectric SrBi4Ti4O15 films can be successfully fabricated on IrO2: They demonstrate a saturated hysteresis loop at 5 V with remanent polarization (Pr) of 19 μC/cm2 and coercive field (Ps) of 116 kV/cm. SrBi4Ti4O15 films grown on IrO2 show larger and denser grains and controlled surface morphology. The grains are random oriented, while those of films on Pt are mainly c-axis oriented. It is concluded that the high remanent polarization of the films grown on IrO2 originates from the relatively high concentration of a- and b-axis orientations.

Study on Ag mesh/conductive oxide hybrid transparent electrode for film heaters

Ag mesh-indium tin oxide (ITO) hybrid transparent conductive films were fabricated and evaluated for use in film heaters. PS monolayer templates were prepared using highly mono-dispersed PS spheres (11.2 μm) obtained by a filtering process with micro-sieves. At first, three Ag meshes with different sheet resistances (20, 100, and 300 Ω sq(-1)) and transmittances (70, 73, and 76%) were evaluated for film heaters in terms of voltage and long-term stability. Subsequently, in an effort to obtain better transmittance, Ag mesh-ITO hybrid heaters were fabricated utilizing finite ITO depositions. At the optimised ITO thickness (15 nm), the sheet resistance and the transmittance were 300 Ω sq(-1) and 88%, respectively, which indicates that this material is a good potential candidate for an efficient defroster in vehicles.

A novel multibridge-channel MOSFET (MBCFET): fabrication technologies and characteristics

We have demonstrated a novel three-dimensional multibridge-channel metal-oxide-semiconductor field-effect transistor (MBCFET). This transistor was successfully fabricated using a conventional complementary metal-oxide-semiconductor process. We introduce the fabrication technologies and electrical characteristics of MBCFET in comparison with a conventional planar MOSFET. The MBCFET has more benefits than a conventional MOSFET. It shows 4.6 times larger current drivability than a planar MOSFET. This is due to the vertically stacked multibridge channels. The subthreshold swing of MBCFET is 61 mV/dec, which is almost an ideal value due to the thin body surrounded by gate. Based on a simulation result, we show that the MBCFET will have a large on-off state current ratio at short channel transistors.

Fabrication of ordered anodic aluminum oxide with matrix arrays of pores using nanoimprint

Anodic aluminum oxide (AAO) with matrix arrays of pores was obtained using nanoimprint and anodizing. Si3N4 imprint stamps were fabricated using electron-beam lithography. The Si3N4 stamps were imprinted into Al films grown on Si wafers by applying a force of 250 kg for 10 s. Two different diameters (45 and 80 nm) and two different periodic distances (100 and 200 nm) of the square patterns in Si3N4 imprint stamp were transferred into an Al film as a form of shallow pores. The Al films were then anodized in 0.3M oxalic acid under conditions of 4 °C at 40 V. The authors found a linear relationship between the interpore distance and anodizing voltage (2.5 nm V−1) to obtain a square array in AAO. In addition, the matrix pores in AAO tend to form a natural hexagonal pattern as the anodizing time increases. The surface images are obtained using field-emission secondary-electron microscope and scanning probe microscopy.

Comparison of motor-evoked potentials monitoring in response to transcranial electrical stimulation in subjects undergoing neurosurgery with partial vs no neuromuscular block†

BACKGROUND There have been no evidence-based comparisons of motor-evoked potential (MEP) monitoring with no and partial neuromuscular block (NMB). We compared the effects of different levels of NMB including no NMB on MEP parameters. METHODS MEP-monitored 120 patients undergoing neurosurgery were enrolled. The patients were randomly allocated to four groups: Group A was to maintain two train-of-four (TOF) counts; Group B was to maintain a T(1)/Tc of 0.5; Group C was to maintain a T(2)/Tc of 0.5 (T(1,2), first or second twitch height of TOF; Tc, control twitch height); Group D did not maintain NMB. The mean MEP amplitude, coefficient of variation (CV), the incidence of spontaneous respiration or movement, the efficacy of MEP, and haemodynamic parameters were compared. RESULTS The median [inter-quartile range (IQR)] amplitudes of the left leg for Groups A, B, C, and D were 0.23 (0.15-0.57), 0.44 (0.19-0.79), 0.28 (0.15-0.75), and 0.75 (0.39-1.35) mV, respectively. The median (IQR) CVs of the left leg were 71.1 (56.9-88.8), 76.1 (54.2-93.1), 59.8 (48.6-95.6), and 25.2 (17.3-35.0), respectively. The differences between groups of the mean amplitudes of the left arm and both legs were statistically significant (Kruskal-Wallis test, P=0.011 for the left leg). For all limbs, the differences between groups of the CVs were significant (P<0.001, for the left leg). Other parameters were not different. CONCLUSIONS If NMB is used during MEP monitoring, a target T(2)/Tc of 0.5 is recommended. In terms of the MEP amplitude and variability, no NMB was more desirable than any level of partial NMB.

Investigation of hydrogen-induced degradation in Pb(ZrxTi1−x)O3 thin film capacitors for the application of memory devices

Hydrogen-induced degradation in Pb(ZrxTi1−x)O3 (PZT) thin film capacitors is investigated in terms of three process parameters, such as electrode structures (Pt/PZT/Pt and Ir/IrO2/PZT/Pt/IrO2), Zr/Ti compositional ratios (60/40, 53/47, 40/60, 30/70), and the domain poling states (±5 V). It was found that the hydrogen-induced degradation is enhanced when PZT films have high Ti portion, and can be suppressed by domain poling prior to the hydrogen anneal. From secondary ion mass spectroscopy analysis, it can be concluded that the hydrogen-induced degradation originates mainly from the interface of PZT and Pt electrodes. Hysteresis loop shifts in PZT capacitors indicate that negative charge develops at interfaces by the hydrogen anneal. Chemically, hydrogen-induced degradation can be elucidated as the formation of negatively charged hydroxyl group (OH−).

Effect of pre-annealing on physical and electrical properties of SrBi2Ta2O9 thin films prepared by chemical solution deposition

Abstract SrBi2Ta2O9 (SBT) thin films with Bi layered-perovskite structure were formed by chemical solution deposition method. The effects of pre-annealing on physical and electrical properties of SBT thin films were investigated by employing rapid thermal annealing (RTA) and furnace annealing. SBT thin films pre-annealed by furnace after each spin-coating exhibited better surface morphology and electrical properties than those pre-annealed by RTA. The crystallization mechanisms of SBT thin films with pre-annealing by RTA and furnace were examined by X-ray diffraction (XRD) analysis and scanning electron micrograph (SEM). Finally, the optimum condition of furnace pre-annealing (700°C for 30 min) was found to give remanent polarization (2Pr) of about 20 μC/cm2, leakage current density of less than 10−7 A/cm2, and breakdown voltage of 15 V.