Byung-Woog Cho

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.

All solid type ISFET glucose sensor with fast response and high sensitivity characteristics

Abstract An all solid type ISFET glucose sensor using the electrolysis of hydrogen peroxide has been fabricated and the characteristics investigated. By forming thin-film type three electrodes on the ISFET chip for amperometric actuation, miniaturized solid-type sensor could be achieved. The sensor with a specially designed ladder-type working electrode showed improved operation in response time and response magnitude.

Electronic and magnetic properties of the electron-doped superconductorSm1.85Ce0.15CuO4−δ

Temperature-dependent magnetization (M(T)) and specific heat (C_p(T)) measurements were carried out on single crystal Sm_{1.85}Ce_{0.15}CuO_{4-delta} (T_c = 16.5 K). The magnetic anisotropy in the static susceptibility, chi {equiv} M/H, is apparent not only in its magnitude but also in its temperature dependence, with chi_{perp} for H{perp}c larger than chi_{parallel} for H{parallel}c. For both field orientations, chi does not follow the Curie-Weiss behavior due to the small energy gap of the J = 7/2 multiplet above the J = 5/2 ground-state multiplet. However, with increasing temperature, chi_{parallel}(T) exhibits a broad minimum near 100 K and then a slow increase while chi_{perp}(T) shows a monotonic decrease. A sharp peak in C_p(T) at 4.7 K manifests an antiferromagnetic ordering. The electronic contribution, gamma, to C_p(T) is estimated to be gamma = 103.2 (7) mJ/moleSmK^2. The entropy associated with the magnetic ordering is much smaller than Rln2, where R is the gas constant, which is usually expected for the doublet ground state of Sm^{+3}. The unusual magnetic and electronic properties evident in M(T) and C_p(T) are probably due to a strong anisotropic interaction between conduction electrons and localized electrons at Sm^{+3} sites.

A ISFET cartridge for electrolyte measurement by micromachinery

Abstract A small size cartridge is designed and fabricated for ISFET-based electrolyte sensor applications. The designed cartridge is fabricated by using micromachining techniques including silicon etching and glass bonding. Photosensitive polymer (THB 30) is used both to define a micropool and to encapsulate the sensor surface. A differential amplification method utilizing REFET (reference electrode field-effect transistor) and QRE (quasi-reference-electrode) are introduced in order to substitute the conventional Ag/AgCl reference electrode, which is unsuitable to be applied in this cartridge because of its large size. Total size of the fabricated cartridge is 2.4 cm×2.5 cm, and the dead volume of a micro flow-channel inside the cartridge is only 8.5 μl. The pH-ISFET inserted into the cartridge showed stable operation and reasonable nernstian characteristics [55 mV/pH].

A New Approch To Low Drift Ta/sub2/O/sub5/ By pH Reactive Sputtering And Sol-gel Method

Thin films, such as SiOz, 21-02, A1203, Si3N4 and TazO5, were known as hydrogen ion sensing membranes for pH-ISFET[lI. Among them, TazO5 thin film was reported to have the better sensing characteristics than those of other hydrogen ion sensing membranes. In this research, the TazOs hydrogen ion sensing membrane were formed by RF reactive sputtering and Sol-Gel method. Taz05 pH-ISFETs by R F reactive sputtering and Sol-Gel method showed a good linearity in wide pH range(pH 2 to 12) and had high sensitivities of 58 -59mV/pH and 57mV/pH, respectively. Especially, TazOs pH-ISFET by RF reactive sputtering showed stable long-term sensitivity(5759mV/pH) during 45 days and long-term stability during 60 days (0.05pWday).