Jong-Hyeon Jeong

Development of plasma-on-chip: Plasma treatment for individual cells cultured in media

A device consisting of Si microwells and microplasma sources has been fabricated for plasma treatment of individual cells cultured in media. We named the device plasma-on-chip. The microwells have through-holes at the bottom where gas–liquid interfaces form when they are filled with media containing biological samples. The microplasma sources, which supply reactive species, are located on the back of each microwell. Through the gas–liquid interface, the reactive species are supplied to the cells. Chlorella cells were used to demonstrate the feasibility of the device and after three minutes of plasma treatment, the fluorescence intensity of Chlorella cells appeared to be decreased. Optical emission spectroscopy identified O and OH radicals in the plasma, which can affect the cells. In the analysis of biological samples such as human cells or tissues, this device raises the possibility of revealing the mechanisms of plasma medicine in more detail.

Effect of Magnetic Field on Permeability of Electroplated Permalloy for Microdevices

We have investigated the effect of a magnetic field on an electroplated Ni79Fe21 film. We have succeeded in the formation of a Ni79Fe21 (permalloy) film with high permeability by applying the magnetic field vertical to the electric field during the electroplating process. In a conventional NiFe electroplating process, annealing is required to obtain a stable Ni79Fe21 film after electroplating. This process without annealing is useful for fabricating Ni79Fe21 films for flexible devices and complementary metal oxide semiconductor (CMOS) integration.

Micromechanical IR thermal detector using torsional oscillation: Improvement of resonator profile for high sensitivity

An infrared (IR) thermal detector, which used the torsional oscillation of a micromechanical resonator, was developed to achieve a high sensitivity. The detector has a bimaterial structure consisting of a tense Si film (oscillating body) and a metal film (IR absorber). Owing to the difference in thermal expansion between the two materials, the resonator is bent by light incidence. Because the axis of torsion is bent from the initial flat state, the spring for torsional oscillation hardens and resonant frequency shifts. To enhance bending, an Al film with a large coefficient of thermal expansion was used. In addition, the tension in the polycrystalline Si film was enhanced by metal-induced lateral crystallization using biomineralized Ni nanoparticles. The fabricated detector was flat under initial conditions and showed a bending response to the light incidence and heating. The present IR detector achieved a thermal coefficient of frequency of 1000 ppm/K, which was one order larger than that of the conventional micromechanical IR sensors.

Formation and Characterization of P(VDF-TeFE) Films Using Sol-Gel Methods for Application to Micro-Generators

In order to apply the P(VDF-TeFE) piezoelectric polymer to the micro-generator based on MEMS technology, we have established a process condition of the film formation. A solvent which is used to cast P(VDF-TeFE) solution is important factor for film formation, and MEK solvent has some problems such as low adhesion for low concentration and drying on a coating process for high concentration. Some problems are suppressed by adding a DMA solvent. However, a DMA solvent affected a molecular structure of the film. A thermal treatment is also an important factor since film stretching cannot be allowed in a spin-coating process. In order to compare the single-solvent solution with the mixed-solvent solution, we have carried out qualitative analysis of the film in formation processes.

Effects of an Electric Field and a Solvent during Thermal Treatment in Film Formation of Poly(vinylidene fluoride–tetrafluoroethylene)

In order to apply a poly(vinylidene fluoride–tetrafluoroethylene) piezoelectric polymer to a micro generator as a membrane, the polymer is deposited by spin coating on a substrate. To improve the stability of the film surface, the film is annealed at a temperature higher than its melting point. In this process, the chain structure of the polymer is transmuted by O atoms, and remanent polarization also decreases. We have attempted to enforce the rearrangement of the polymer chain through an electric field in an annealing process. By applying an electric field to an annealing process, O atoms and unnecessary bonds are eliminated. As a result, the remanent polarization of the film annealed with an electric field is measured twice and compared with that of the film annealed without an electric field.

Rapid and Highly Sensitive Detection of Bacteria Sensor Using a Porous Ion Exchange Film

A biological and chemical sensor with a rapid response in microlevel tests is required for health and environmental monitoring. Our approach to developing a high-performance sensor is to use a porous monolith-type ion exchanger having three-dimensional acceptors to sense bacteria. This porous monolith-type ion exchanger has an open-cellular structure with 5–50-µm-diameter pores. The concentration of bacteria in the solution can be detected by measuring the impedance of the monolith. We have succeeded in sensing bacteria Bacillus subtilis with a concentration as low as 8×102 cells/ml. The porous ion exchanger is a potential high-performance device for biological and chemical sensing.

Influences of Intensity of Electric Field on Properties of Poly(vinylidene fluoride-tetrafluoroethylene) Thin Films during Annealing Process

In the annealing of a poly(vinylidene fluoride–tetrafluoroethylene) thin film, the electrical properties of the film was improved by application of a certain electric field. The aim of this study was to investigate changes in characteristics following the application of an electric field. For an electric field lower than a critical intensity, the influence can be slight. For an electric field higher than a critical intensity, on the other hand, the recombination of monomers can be affected. On the basis of these predictions, we have attempted to measure the critical intensity of an electric field and investigate the influences of an electric field application by X-ray photoelectron spectroscopy (XPS) in this study. Moreover, in order to control the contamination by impurities, we have carried out the annealing process using a vacuum chamber.

Cu Electroplating Process with Magnetic Field for Flexible Device

We have investigated the effect of a magnetic field during Cu electroplating. We have succeeded in a large grain growth without annealing and additives by using a Cu electroplating process involving the vertical application of a magnetic field to an electric field. In addition, we have found that this process is effective in the suppression of Cu oxidation and the incorporation of residual impurities of chlorine into the Cu film. In a conventional Cu electroplating process, annealing is required to obtain a stable Cu film after electroplating. This low temperature process without annealing is useful for the Cu interconnection of flexible devices.

Characterization of vibration-type infrared thermal detector on temperature, light, and thermal infrared

A micromechanical infrared (IR) thermal detector using a torsional resonator was fabricated to achieve sensitive detection of a thermal IR radiation. The resonator has a bimaterial structure consisting of an oscillating body and an IR absorber. The suspended resonator is heated and deformed by IR radiation. The deformation generates a hard spring effect for torsional oscillation, thereby shifting its resonant frequency by a hard spring effect. In this study, to improve thermal sensitivity, the resonator was composed of a tension-enhanced poly-crystalline silicon and aluminum. Using a laser-based measuring system, the fabricated device was characterized in terms of responses to visible light irradiation, substrate heating, and thermal IR irradiation. Resonant frequency shift of 7,400 ppm was observed when a thermal source of 570 °C was placed 15 cm away from the detector.

Designing positions of grain boundaries in Si thin-film for low-energy-loss optical MEMS/NEMS devices

Polycrystalline Si (poly-Si) thin-film is widely used in optical MEMS/NEMS devices. However, the device performance depends on the crystallized structure in the poly-Si thin-film. We performed metal-induced lateral crystallization (MILC) to design the positions of grain boundaries in the poly-Si thin-film. Thin-film cantilever resonators were fabricated to discuss how grain boundaries affect the oscillation characteristics. Compared with a reference resonator, a resonator in which crystallization was well-designed achieved two-fold increase in Q factor.