Hong-Kun Lyu

Fabrication and Characteristics of a Field Effect Transistor-Type Charge Sensor for Detecting Deoxyribonucleic Acid Sequence

We have fabricated an field effect transistor (FET)-type deoxyribonucleic acid (DNA) charge sensor which can detect the DNA sequence by sensing the variation of drain current due to DNA hybridization and investigated its electrical characteristics. It is fabricated as a PMOSFET-type because the DNA probe has a negative charge. Au which has a chemical affinity with thiol was used as the gate metal in order to immobilize DNA. The operating principle is very similar to that of MOSFET. The gate potential is determined by the electric charge possessed by the DNA. The variation of the drain current with time was measured. The drain current increased when thiol DNA and target DNA were injected into the solution, because of the field effect due to the electrical charge of DNA molecules. Therefore it is confirmed that the DNA sequence can be detected by measuring the variation of the drain current due to the variation of DNA charge and it is concluded that the proposed FET-type DNA charge sensor might be useful for the implementation of the DNA chip.

Effect of TiO2 Nanoparticle Modification on Ultraviolet Photodetection Properties of Al-Doped ZnO Nanowire Network

This study was conducted in order to observe the changes in the ultraviolet (UV) photodetection characteristic when TiO2 nanoparticles are modified on the surface of an aluminum-doped zinc oxide (AZO) nanowire in an AZO nanowire network with enhanced conductivity. According to the experiment results, the UV photosensitivity under a bias of 5 V was 52-fold in a bare AZO network, and it increased to 147-fold in the case when TiO2 nanoparticles were modified. The UV reset time decreased from 9 to 5 s. The AZO nanowire onto which TiO2 nanoparticles were adsorbed showed an approximately 2-fold faster response time and an approximately 3-fold higher UV photosensitivity than the existing bare AZO nanowire. The faster UV photoresponse time of the AZO nanowire network with adsorbed TiO2 nanoparticles is because the adsorbed TiO2 nanoparticles serve as recombination sites for electrons excited by UV illumination. In addition, with enhanced UV photosensitivity, adsorbed TiO2 nanoparticles serve as electron donation sites that provide additional electrons to the AZO nanowire when UV light is turned on.

Robust heart rate detection method using UWB impulse radar

Non-invasive and non-restrictive methods for measuring the physiological functions of the human body are useful for both patients and healthy people, and will serve to improve quality of life. Among the various methods of this kind, one practical option involves the use of radar technology. In this paper, considering the issues of low power consumption, low implementation complexity, and safety with regard to exposure to the human body, a novel method that detects the human heart rate by utilizing an ultra wideband (UWB) impulse radar is proposed. Further, the interactions between the electromagnetic waves and the human body are analyzed, in order to understand the shape of the reflected pulse and to prevent harmful effects on the body. The radar signal is processed in the time domain for morphological analysis. The experimental results show that the detection of heart rate is possible with high accuracy. In addition, it is confirmed that the proposed method can be used to extract the transient characteristics of the heartbeat from the radar signals.

Formation of Macropore and Three-Dimensional Nanorod Array in p-Type Silicon

We carried out a study on the change in pore wall thickness depending on the current density in p-type silicon. We attempted the formation of a uniform macropore or nanorod array with a high aspect ratio in p-type silicon by electrochemical etching through the optimization of the hydrogen fluoride (HF)/organic electrolyte composition and the design of the mask pattern. The electrochemical etching of p-type silicon in the HF: dimethylsulfoxide (DMSO): deionized (DI) water = 1:5:5 electrolyte can control the velocity of a reaction between an electrolyte and a hole necessary for the electrochemical etching of silicon through the mixing of the protic property of DI water and the aprotic property of DMSO. In this study, we fabricated a p-type silicon nanorod array of three-dimensional structures with an approximately 350 nm diameter from macroporous Si by applying two-step currents (40 mA, 200 s + 38 mA, 1600 s) to a 1.8 cm2 circular area using an optimized HF: DMSO: DI water = 1:5:5 electrolyte composition.

Characteristics and modeling of a nonplanar nonrectangular metal oxide semiconductor field effect transistor for charge sensing in the Si micro-fluidic channel

In this work, a nonplanar, nonrectangular metal-oxide-semiconductor field effect transistor (MOSFET) with an asymmetrical channel structure for sensing charge in the Si micro-fluidic channel was fabricated, and the electrical characteristics of the fabricated three-dimensional (3-D) MOSFET were measured. The device was formed in the convex corner of a Si micro-fluidic channel using tetramethyl ammonium hydroxide (TMAH) anistropic etching solution, so that it would be suitable for combination with a micro-fluidic system. We approximated the nonplanar, nonrectangular 3-D MOSFET to a two-dimensional rectangular structure using the Schwartz-Christoffel transformation. The LEVEL1 device parameters of the 3-D MOSFET were extracted from the measured electrical device characteristics and were used in a simulation program with integrated circuit emphasis (SPICE) simulation. The measured and simulated results for the 3-D MOSFET were compared and found to show good agreement. We also investigated the feasibility of the proposed 3-D MOSFET as a charge sensor for detecting charged biomolecules.

Fabrication of 3-Dimensional Structure of Metal Oxide Semiconductor Field Effect Transistor Embodied in the Convex Corner of the Silicon Micro-Fluidic Channel

As micro-fluidic systems and biochemical detection systems are scaled to smaller dimensions, the realization of small and portable biochemical detection systems has become increasingly important. In this paper, we propose a 3-dimensional structure of a metal oxide semiconductor field-effect transistor(3-D MOSFET) using tetramethyl ammonium hydroxide (TMAH) anisotropic etching, which is a suitable device for combining with a micro-fluidic system. After fabricating a trapezoidal micro-fluidic channel, the 3-D MOSFET embodied in the convex corner of the micro-fluidic channel was fabricated. The length of the gate is about 20 µm and the width is about 9 µm. The depth and top width of the trapezoidal micro-fluidic channel are about 8 µm and 60 µm, respectively. The measured drain saturation current of the 3-D MOSFET was about -22 µA at VGS=-5 V and VDS=-5 V, and the device characteristics exhibit a typical MOSFET behavior. Moreover, a gold layer was used for the MOSFETs gate metal to detect charged biochemical samples using the affinity between gold and thiol.

Effects of Hole-Collecting Buffer Layers and Electrodes on the Performance of Flexible Plastic Organic Photovoltaics

Here we report the influences of the sheet resistance () of a hole-collecting electrode (indium tin oxide, ITO) and the conductivity of a hole-collecting buffer layer (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), PEDOT:PSS) on the device performance of flexible plastic organic photovoltaic (OPV) devices. The series resistance () of OPV devices steeply increases with increasing of the ITO electrode, which leads to a significant decrease of short-circuit current density () and fill factor (FF) and power conversion efficiency, while the open-circuit voltage () was almost constant. By applying high-conductivity PEDOT:PSS, the efficiency of OPV devices with high values of 160 Ω/□ and 510 Ω/□ is greatly improved, by a factor of 3.5 and 6.5, respectively. These results indicate that the conductivities of ITO and PEDOT:PSS will become more important to consider for manufacturing large-area flexible plastic OPV modules.

Integration of Ag/AgCl reference electrode with MOSFET-type biosensor

In this study, a CMOS process-compatible MOSFET-type biosensor with a built-in Ag/AgCI thin film reference electrode have been fabricated on the same chip. Au was used as the gate metal of the MOSFET-type biosensor in order to immobilize biomolecules. Electrical characteristics of the MOSFET-type biosensor is quite stable and similar to the characteristics of the biosensor with the conventional Ag/AgCI glass electrode. Therefore, it is concluded that the Ag/AgCI thin film reference electrode might replace the voluminous Ag/AgCI glass reference electrode for realization of miniature biosensors and micro total analysis systems.

Noninvasive heartbeat extraction from IR UWB radar signals

Modern society faces problems of increasing healthcare expenditure due to increases in numbers of chronic patients and an aging population. As so-called smart patients become proactive, they require individualized treatment and interactive care. A type of healthcare using ICT (Information & Communication Technology) is gaining interest as the best technological alternative for solving those problems. At DGIST, ICT-medical convergence technologies suitable for pervasive sensing and advanced healthcare services are under development. Impulse radio ultra-wideband complementary metal-oxide silicon (IR UWB CMOS) radar technology is considered a good candidate for sensing features of the human body. In this paper, a novel method that detects vital signals such as respiratory rate and heart rate using IR UWB radar is proposed and the feasibility of it being an appropriate technology for non-invasive biometric sensing is presented.

Simulation of the influence of asymmetrical metallic apertures of the plasmonic infrared filter

In recent times, much research in the field of complementary metal oxide semiconductor (CMOS) image sensors (CISs) regarding plasmonic color filters (PCFs) has been reported. In this paper, we investigated the influence of vertically asymmetrical metallic apertures on the extraordinary optical transmission of PCFs. We designed a structural model of the asymmetric cylindrical aperture. In addition, we simulated the spectral variation in the wavelength transmission. For the simulation, we used a commercial computer simulation tool utilizing the FDTD method. SiO2 was used as the substrate insulator, top-side insulator, and the fill material in the cylindrical aperture. We applied Au as the metal layer; dispersion information for Au was derived from the Lorentz–Drude model. We also presented the electric field distribution under several different conditions at the peak wavelength of the calculated transmission spectrum. Furthermore, we determined the transmittance spectral characteristics and the peak transmittance under several different conditions.