Byung-Ki Sohn

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.

ISFET glucose sensor based on a new principle using the electrolysis of hydrogen peroxide

Abstract An ISFET glucose sensor based on a new principle using the electrolysis of hydrogen peroxide, one of the by-products of the oxidation of glucose, and a Pt electrode actuator is proposed and the characteristics investigated. Compared with the conventional ISFET glucose sensor, the proposed sensor shows an improvement of four times the sensitivity, an extension of the dynamic range to 5 mM glucose concentration, and a faster response of 3 min in 10 mM phosphate buffer solution (pH 7.4, 100 mM NaCl). In addition, the baseline of the sensor response can also be checked, so that the influences of drift of the ISFET and pH change in the sample solution can be eliminated. The sensor shows a large dependence on the buffer concentration. When the buffer concentration is changed from 5 to 20 mM, the sensitivity decreases by a factor of four. However, the high sensitivity, 9 mV mM 1 even in 20 mM buffer concentration, will still allow the sensor to measure glucose concentrations of human blood without the need for dilution.

A new pH-ISFET based dissolved oxygen sensor by employing electrolysis of oxygen

A new dissolved oxygen sensor based on a pH-ISFET is discussed. A working electrode surrounding a pH-sensing gate of the pH-ISFET electrolyzes dissolved oxygen, resulting in a corresponding pH change near the pH-sensing gate. The pH-ISFET is expected to determine dissolved oxygen concentration by detecting this pH change. The results suggest that the proposed sensor operated by a combined mechanism of an amperometric sensor (Clark type sensor) and a potentiometric sensor (pH-ISFET) is feasible to determine the content of dissolved oxygen. The dependence of sensor output on several factors, such as buffering capacity, bulk pH and stirring of the solution, is investigated and a comparison between the Clark type sensor and proposed sensor is also discussed.

Effects of added TiO2 on the characteristics of SnO2-based thick film gas sensors

Abstract Tin oxide-based thick films were prepared by a screen printing technique for sensing hydrocarbon gases. An SnO 2 -based raw material was obtained by the coprecipitation method. A conductive sensing material was synthesized by SbCl 5 addition to the precipitating solution. The suspension coprecipitated was dried by hot air drying which dried the material at 110°C in a gravity convection oven or by a freeze drying method. The effects of drying method on the morphology and sensing characteristics of the thick film were investigated. The addition of TiO 2 to the thick film had a substantial influence on the characteristics of the films. The sensitivities of the thick film to hydrocarbon gases were enhanced by adding TiO 2 to SnO 2 -based materials at loading rates between 3 and 5 mol.%. TiO 2 was transformed from glass or anatase to the rutile structure and this phase transformation affected the gas sensitivity of the thick film. Platinum added to the raw material during coprecipitation (as H 2 PtCl 6 ·6H 2 O) decidedly improved the sensitivities to hydrocarbon gases.

High sensitivity and selectivity methane gas sensors doped with Rh as a catalyst

Abstract SnO 2 (Rh) thick-film devices for detecting methane gas selectively have been prepared by the screen-printing technique, and their characteristics have been investigated. The sensitivity of an SnO 2 thick film with added Rh to CH 4 (1000 ppm) is about 90% at an operating temperature of 400 °C, which is higher than those of SnO 2 thick-film devices with added Pt or Pd.

Low power thick film CO gas sensors

Abstract SnO2/Pt thick film CO gas sensors were fabricated by a screen printing method. The sensors were fired in the temperature range 500 to 1000 °C wit a mixing ratio of Pt to SnO2 of 0.2 – 1.0 wt.%. The sensitivity, selectivity and response time for CO gas in air of the sensors with various compositions and sintering temperatures were investigated as a function of operating temperature. The sensors showed a low operating temperature (about 100 °C) and high sensitivity of CO gas. The sensors fired at 600 °C exhibited the highest sensitivity when the SnO2/Pt ratio was 99.5/0.5 by weight. They showed good sensitivity to CO gas in comparison with those for other gases (H2, C4H10 and C3H8) at 100 °C. They had a short respose time (about 2 s for 200 ppm of CO gas at 100 °C).

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.

Effect of membrane structure on the performance of field-effect transistor potassium-sensitive sensor

Abstract An FET-type K + -sensitive sensor with a membrane composed of a hydrophobic inner layer and a hydrophilic outer layer has been fabricated by a photolithographic process. The base chip for the sensor is a pH-ISFET with a thin Si 3 N 4 layer. Negative photoresist (OMR-83) is used as the inner layer and poly (vinyl pyrrolidinone-co-vinyl acetate) solution in tetrahydrofuran containing valinomycin and 2,6-bis-( p -azidobenzylidene) cyclohexanone photosensitizer is used as the outer sensing membrane material. The K-ISFET sensor with double-layered membrane shows a high sensitivity (56 mV/decade) toward K + ion, rapid response (1–2 s) and low interference (less than 3 mV/decade) from the competing H + ion.

Some Improvements In Isfet-based Chemical Sensors

A new ISFET-based dissolved oxygen sensor using an amperometric stimulus technique and a hydrogen peroxide electrolysis method for performance enhancement are presented. These techniques are performed by orienting the electrolysis or redox process with a built-on Pt working electrode. Also, the discussion is extended to photolithographically patterning the sensing membranes onto the ISFET gates by utilizing photocrosslinkable polymers.