Kimin Hong

An Approach to the Development of Organic Additives for Electrodeposition of Narrow Copper Interconnects

We have characterized the electrochemical properties and wetting effects of various organic materials, including selected accelerators, suppressors, and wetters, for the electrodeposition of submicrometer-wide copper interconnects. An additive composition consisting of the following organic chemicals was tested: bis(3-sulfopropyl)-disulfide, disodium salt as an accelerator, polyethylene glycol as a suppressor, and a cross-linked polyamide as a second suppressor (working also as a wetter). Copper films plated using this makeup exhibited a surface roughness of ∼35 nm after annealing, with grain sizes on the order of 0.1-0.5 μm, and an electrical resistivity of ∼ 1.9 μΩ cm. Using this made-up solution, 120 nm wide trenches were successfully gap-filled.

Planarity Improvement and Reduction of Coercivity by Organic Additives in Electroplated Ni – Fe Permalloy Thin Films

We studied the effect of organic additives on the surface planarity and magnetic properties of electroplated Ni-Fe Permalloy thin films. Compared to thin films prepared with a pure inorganic electrolyte, the Ni-Fe permalloy thin films electroplated with electrolytes containing additives showed changes in their crystalline orientations, surface roughnesses, and coercivities. The reduction in coercivity showed a strong correlation with the observed improvement of the surface planarity. We observed that the surface planarity of the thin films could be improved by 50-60% and that coercivity could be adjusted between 0.33 and 0.05 Oe by changing the concentration of additives.

Structure analysis of inorganic crystals by energy-filtered precession electron diffraction

We performed structure analysis of Si single crystal and CaMoO(4) inorganic crystal by energy-filtered precession electron diffraction (PED). Structure analysis was performed using conventional selected area electron diffraction, PED and energy-filtered PED (EF-PED). The EF-PED method proved to be advantageous in determining the crystal structures and accurate cell parameters of inorganic crystals due to resolution enhancement by sharpening the peak shapes and reducing inelastic scattering. Among the EF-PED methods, zero-loss PED was most useful for structure analysis by minimizing inelastic scattering intensities, while plasmon-loss PED could be used effectively to determine crystal symmetry by closely observing the conditions of forbidden reflections.

Programmable synthesis of shape-, structure-, and composition-modulated one-dimensional heterostructures by galvanic displacement reaction

One-dimensional heterostructures consisting of periodically modulated bismuth telluride tube/wire were synthesized by galvanic displacement reaction of Co/Ni multi-segmented sacrificial nanowires. Utilizing the difference in redox potential and corrosion behavior of Co and Ni, segments, dimension, composition, and structure of the individual segments were also precisely engineered. The programmable ability to synthesize heterostructures with simultaneously modulation of various dimensions in ambient conditions may lead to an effective route to synthesize high performance nanodevices including nanoelectronics, optoelectronics, sensors, and thermoelectrics.

Effects of Saccharine N-Propane Sulfonate on the Microstructures, Magnetic Properties, and Magnetoimpedance of Electroplated Ni – Fe Permalloy Thin Films

We have studied the effects of an organic additive, saccharine N-propane sulfonate, on the microstructures, magnetic properties, and magnetoimpedance of electroplated Ni-Fe Permalloy thin films. Compared to thin films prepared with a pure inorganic electrolyte, the Ni-Fe Permalloy thin films electroplated with electrolytes containing the additive have different crystalline orientation, grain size, surface roughness, coercivity, permeability, and magnetoimpedance. There is a strong correlation between the observed structural changes and the changes in the magnetic properties, such as in the coercivity and permeability. The changes are also dependent on the structure of the electroplating cells. By using an appropriate plating cell, the coercivity can be reduced from 0.36 to 0.08 Oe. These changes in the magnetic properties result in an increase in the magnetoimpedance by 31%.

Magnetoimpedance of Galvanostatically Electroplated Ni-Fe Permalloy Wires

We studied the magnetoimpedance of narrow Ni-Fe Permalloy wires prepared by electrodeposition. The wires were fabricated by lithographical patterning and chemical etching of electroplated thin films. The microstructure and magnetic property of the deposit were adjusted by using an organic additive added to the electrolyte. Aspect ratio of the wires was varied between 10 and 50 by changing the length of the wire while the thickness and width were fixed. The magnetoimpedance exhibited highest value at 30 MHz and was 18-25% depending on the aspect ratio. The magnetic fields for the highest magnetoresistance increased in proportion to the frequency in the range between 1 and 100 MHz.

Control of Material Properties and Magnetism of Electroplated Nickel-iron Thin Films

We have studied a means to control the composition of nickel-iron thin films. By changing current and voltage applied to a electroplating electrolyte we could manipulate the relative concentration of nickel and iron in the thin films, which caused variations of coercivity, squareness, and saturation magnetic field. As we increase the content of iron in the thin films by using potentiostatic and galvanostatic plating, the grain size was increased and the coercivity was reduced.

Erratum to: Branch length similarity entropy-based descriptors for shape representation (Journal of the Korean Physical Society, (2017), 71, 10, (727-732), 10.3938/jkps.71.593)

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Multiple and Mass Transfer of Magnetic Particles for Use in Biosensors

We studied a method of collecting small magnetic particles on a narrow metallic wire and transferring them between wires by using magnetic fields of electrical currents. By applying currents to a grid pattern of wires in specified directions, we could adjust direction of thermal drift of the particles in a fluid. We could collect a large amount of particles on a wire at an elevated speed aided by the drift. Gradual changes of the currents in two parallel wires enabled us to transfer the particles between the wires at a fast rate. The transfer could be reversed multiple times by switching the direction of currents. The multiple and mass control of the magnetic particles could be used for high sensitivity biosensors.

Electron emission from PZT and PLZT ferroelectric ceramics by external pulsed electric field

Electron emission from poled PZT and PLZT ferroelectric ceramics has been observed under the application of negatively driven voltage pulse. The flashover plasma has been also shown which is formed along the patterned electrode on the emitting surface. It is inferred that the source of the emission current is the plasma of uncompleted surface discharge which is initiated at the metal-vacuum-dielectric triple points by both the field electron emission and the polarization reverse emission. We present the measured data of the electron current and charge density emitted from PZT and PLZT ferroelectrics as a function of the applied pulse amplitude, the gas pressure, the A-K gap distance, and the acceleration voltage. We also discuss the influence of those key operating parameters.