Dae-Hyuk Kwon

Effects of heat treatment on Ta2O5 sensing membrane for low drift and high sensitivity pH-ISFET

This paper presents a new approach for reducing the drift and improving the sensitivity of a pH-ISFET by varying the heat treatment condition of the Ta 2 O 5 sensing membrane. A Ta 2 O 5 pH-ISFET which was heat-treated at various temperatures, showed very different sensing characteristics such as sensitivity, long-term drift, etc. When heat-treated in O 2 ambient at 400°C for I h, Ta 2 O 5 pH-ISFET showed low drift, which is maybe related to a densification effect of the film in an amorphous state with a low leakage current. Furthermore, the Ta 2 O 5 pH-ISFET which was heat-treated in O 2 , showed good sensitivity, which is maybe associated with an increase of O-sites at the surface. The Ta 2 O 5 pH-ISFET fabricated by the above method showed good linearity, high sensitivity (58-59 mV) over a wide pH range (pH 2-12) and low long-term drift (0.03-0.05 pH/day).

ISFET glucose and sucrose sensors by using platinum electrode and photo-crosslinkable polymers

The ISFET glucose and sucrose sensors containing platinum electrode and photopolymeric enzyme membrane were fabricated. The platinum working electrode was used for the electrolysis of hydrogen peroxide, which was the other product of the enzyme reaction, to improve sensing characteristics of the sensors. In order to improve response time, photo-crosslinkable polymer(PVA-SbQ) was used to the matrix for the enzyme immobilized membrane. The characteristics of glucose and sucrose sensors were investigated according to the variation of platinum electrode area. The response time was about minutes and determinations of glucose and sucrose in the range of about could be possible.

Highly sensitive nano-porous lattice biosensor based on localized surface plasmon resonance and interference

We propose a design for a highly sensitive biosensor based on nanostructured anodized aluminum oxide (AAO) substrates. A gold-deposited AAO substrate exhibits both optical interference and localized surface plasmon resonance (LSPR). In our sensor, application of these disparate optical properties overcomes problems of limited sensitivity, selectivity, and dynamic range seen in similar biosensors. We fabricated uniform periodic nanopore lattice AAO templates by two-step anodizing and assessed their suitability for application in biosensors by characterizing the change in optical response on addition of biomolecules to the AAO template. To determine the suitability of such structures for biosensing applications, we immobilized a layer of C-reactive protein (CRP) antibody on a gold coating atop an AAO template. We then applied a CRP antigen (Ag) atop the immobilized antibody (Ab) layer. The shift in reflectance is interpreted as being caused by the change in refractive index with membrane thickness. Our results confirm that our proposed AAO-based biosensor is highly selective toward detection of CRP antigen, and can measure a change in CRP antigen concentration of 1 fg/ml. This method can provide a simple, fast, and sensitive analysis for protein detection in real-time.

Mild wetting poor solvent induced hydrogen bonding interactions for improved performance in bulk heterojunction solar cells

In this paper, we demonstrate a facile, mild wetting (short residence time) poor solvent [isopropyl alcohol (IPA)] treatment, carried out on the top surface of a spin-cast poly (3-hexylthiopene) (P3HT) and [6,6]-phenyl-C71-butyric acid methyl ester (PCBM) blend film, in order to fabricate high-performance polymer solar cells (PSCs). This method utilizes the hydrophilic and polar/hydrogen bonding interactions of IPA with the blend components (P3HT and PCBM). The photovoltaic (PV) performance of the fabricated PSCs was optimized by utilizing a preheated IPA wetting treatment and devices fabricated with the configuration: ITO/PEDOT:PSS/P3HT:PCBM/M-IPA-T°/Al (T°: 25 °C/45 °C/65 °C/85 °C) (where “M” stands for modified IPA and “T” signifies the temperature used for the IPA wetting). Our investigation encompasses electrical, optical, crystalline, and morphological studies on the P3HT:PCBM blend films ,modified by preheated IPA, to elucidate the associated enhancements in the PV characteristics and performance. The device fabricated with IPA-85 °C (ITO/PEDOT:PSS/P3HT:PCBM/M-IPA-85 °C/Al) exhibited the best power conversion efficiency (PCE) of 3.51%, with an open circuit voltage of 0.65 V, a fill factor of 0.52, and a short-circuit current density of 10.20 mA cm−2. In contrast, the non-modified blend film device showed a PCE of only ∼3.04%. Ultraviolet-visible absorption studies and X-ray diffraction results suggest that the use of the pre-heated mild-wetting IPA treatment improves the crystallinity and self-organization of the blend layer. We rationalize our findings based on the interactions between IPA and the blend components, due to its high polar and hydrogen bonding Hansen solubility parameters to impart supramolecular assembly of P3HT chains during the blend film formation. This is the first report demonstrating that the poor solvent (IPA) can induce an optimal phase separation in a P3HT:PCBM blend through our proposed mild wetting preheated treatment, toward achieving high-performance PSCs.

MOSFET–BJT hybrid mode of the gated lateral bipolar junction transistor for C-reactive protein detection

In this study, we propose a novel biosensor based on a gated lateral bipolar junction transistor (BJT) for biomaterial detection. The gated lateral BJT can function as both a BJT and a metal-oxide-semiconductor field-effect transistor (MOSFET) with both the emitter and source, and the collector and drain, coupled. C-reactive protein (CRP), which is an important disease marker in clinical examinations, can be detected using the proposed device. In the MOSFET-BJT hybrid mode, the sensitivity, selectivity, and reproducibility of the gated lateral BJT for biosensors were evaluated in this study. According to the results, in the MOSFET-BJT hybrid mode, the gated lateral BJT shows good selectivity and reproducibility. Changes in the emitter (source) current of the device for CRP antigen detection were approximately 0.65, 0.72, and 0.80 μA/decade at base currents of -50, -30, and -10 μA, respectively. The proposed device has significant application in the detection of certain biomaterials that require a dilution process using a common biosensor, such as a MOSFET-based biosensor.

Effect of fluorine on chemical and electrical properties of room temperature oxide films prepared by plasma enhanced chemical vapor deposition

The effect of fluorine on SiO2 films was investigated by comparing chemical and electrical properties of fluorinated silicon oxide (SiOF) films with those of SiO2 films. The SiOF films were prepared at room temperature by plasma enhanced chemical vapor deposition incorporating CF4 as the fluorine source into the deposition process of the SiO2 films using Si2H6 and N2O. The relative dielectric constant of the as-deposited SiO2 films was reduced from 5.95 to 4.43 by the incorporation of fluorine and with postmetallization anneal. The breakdown measurements on the SiOF films showed no early failures at a field strength of ⩽3 MV/cm, resulting in an average breakdown field strength of 7.11 MV/cm.

Properties of low dielectric constant fluorinated silicon oxide films prepared by plasma enhanced chemical vapor deposition

The chemical and electrical properties of fluorinated silicon oxide films prepared by plasma enhanced chemical vapor deposition at 180°C were studied. The deposition of these films was made by incorporating CF 4 as the fluorine source into the deposition process of SiO 2 films using Si 2 H 6 and N2O. With increasing CF 4 flow, the deposition rate of these films decreased; meanwhile, the P-etch rate increased. With post-deposition anneal, the thickness of the films without CF 4 slightly decreased; meanwhile, the thickness slightly increased with the incorporation of CF 4 , The Fourier transform infrared (FTIR) spectroscopy showed that the characteristic peak around 940 cm -1 due to the Si-F stretching bonds increased with increasing CF 4 flow, also the Si-O stretching wave number increased but its full width at half maximum decreased with increasing CF 4 flow. The dielectric constant evaluated by high frequency capacitance-voltage measurements decreased from 4.13 to 3.52 as the CF 4 flow increased. In addition, the effective oxide charge density and interface trap density also decreased with increasing CF 4 flow. The ramp current-voltage measurements showed that the leakage current density of the films decreased with increasing CF 4 flow. However, high average breakdown field strength with low early failures was observed for medium flow of CF 4 .

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A chemical ion sensing using a gated lateral bipolar junction transistor (LBJT) has been performed. This letter reports the basic characteristics of the proposed device and the physical differences between a pure MOSFET-based device and gated LBJT, in giving consideration to an ion sensing. The operation in the linear region, the positive polarity between input bias and output signal, and the direct proportional relationship between pH value and output signal were achieved by the bias configuration and the proposed device using an unmodified standard CMOS process. When the base current is set at -50 muA and VRG of -4 V, this device shows a sensitivity of 6.18 muA/pH.

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We propose a quantum dots (QDs)/poly(N-vinylcarbazole) (PVK) hybrid light-emitting diode (LED) to improve the electron and hole confinement in the QDs layer. QDs used as monochromatic emitters are dispersed in a PVK matrix with a wide bandgap for quantum wells. The HOMO and LUMO level of the PVK can act as a hole transport buffer and an electron-blocking buffer in the hybridized layer. We fabricate an LED using a simplified QDs/PVK hybrid emissive layer (EML) and compare its performance with that of the hybrid LED with controlled QDs concentration. From the result, it is found that the 1.0 wt% QDs within the PVK hybrid LED show the best performance among the compared LEDs, with a luminance of 5989

Ion-Sensitive Transistor Driving With MOS Hybrid Mode Operation

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