Kap-Duk Song

Fabrication of Functional Nanofibrous Ammonia Sensor

A nanofibrous sensor for ammonia gas is fabricated by electrospinning the composite of poly(diphenylamine) (PDPA) with poly(methyl methacrylate) (PMMA) onto the patterned interdigit electrode. The composite electrospun membrane shows interconnected fibrous morphology. Functional groups in PDPA and the high active surface area of the fibrous membrane make the device detect a lower concentration of ammonia with a good reproducibility. The sensing capability of the device is studied by monitoring the changes in resistance of the membrane with different concentrations of ammonia. The changes in resistance of the membrane shows linearity with the concentration of ammonia in the limit of 10 and 300 ppm. UV-visible spectroscopy reveals the mechanism of sensing ammonia by the membrane.

Classification of workplace gases using temperature modulation of two SnO2 sensing films on substrate

Abstract Two SnO2-based sensing films (pure SnO2 and SnO2/Pt) and a Pt thin film as a temperature sensor were fabricated on an alumina substrate for classifying workplace environmental gases. By controlling the heating power in the shape of a trapezoid, a temperature profile of the SnO2 sensing films was created along with four unique sensing response curves to the tested gases. A principal component analysis (PCA) was performed using variables extracted from the sensing response curves. The results confirmed that the sensor array with the proposed operating mode was extremely effective in classifying workplace environmental gases, such as CO2, C3H8, and C4H10.

Three electrodes gas sensor based on ITO thin film

A three electrode type sensor was fabricated. This sensor consists of two parts. One is a tin doped indium oxide (or indium tin oxide: denoted ITO hereafter) film. It was fabricated by the metal thermal oxidation method. This produces a large surface area and low resistivity. So, this film has two functions, a gas sensitive film and an effective heater. The other part is a platinum resistor line covered with oxidized aluminum film. This part is located in the backside of the sensor. It plays three roles. The first is a load resistor for a measuring system. Secondly, it also acts as a heater. Most of the consumed power in the sensor is used as the thermal energy of gas sensing. The last role is catalytic combustible gas sensing in high gas concentrations. In this paper, the fabrication method of gas sensitive ITO film is researched. A complex sensor structure is fabricated. It acts as a hot wire semiconductor sensor at low gas concentration and a combustible catalytic sensor at high concentration.

CO2 gas sensor using lithium ionic conductor with inside heater

Abstract The raw material for lithium ionic conductor (Li 1+ x Zr 2 Si x P 3− x O 12 , where x is about 2) was synthesized by sol–gel method. Eutectic mixture (Li 2 CO 3 :K 2 CO 3 :Na 2 CO 3 =47.0:25.6:27.4 wt.%) was formed on the sensing electrode as an auxiliary material. For the wide range of CO 2 concentration from 1000 to 10,000 ppm, the emf examined at 420°C showed excellent agreement with theoretical value of a Nernsts equation. The 90% response time was as short as 15–20 s. In 40–90% relative humidity, the emf slope of sensor for CO 2 gas was 64–67 mV/decade. The long-term stability of the sensor was investigated for 60 days.

Fabrication of functional nanofibrous ammonia sensor

Nanofiberous sensor for ammonia gas is fabricated by electrospinning the composite of poly(diphenylamine), PDPA, with poly(methyl methacrylate), PMMA onto the patterned interdigit electrode. Interconnected fibrous morphology is evident for the electrospun membrane. Functional group and high active surface area of fibrous membrane help the device to have good reproducibility and to detect the lower concentration of ammonia. The sensing capability of device is studied by monitoring the changes in resistance with different concentration of ammonia. The resistance changes shows linearity in range of 10 ppm to 300. The mechanism behind the sensing characteristic is studied using UV-Visible spectroscopy.

Thin film micro carbon oxide sensor using MEMS process

Pt/Na/sup +/ ion conductive ceramics thin film/Pt/carbonate a/sub 2/CO/sub 3/:BaCO/sub 3/=1:1.7 mol) structure micro CO/sub 2/ sensors were prepared and their sensing properties were investigated. The thin film Na/sup +/ ion conductors formed by using RF magnetron sputtering technique. The chemical composition of thin film Nae6>/e6> ion conductor was found to be same as that of NASICON(x=2). The nernst slope of 57 mV/decade or CO/sub 2/ concentration range between 1,000 to 10,000 ppm was observed at the operating temperature of 400/spl deg/C.

The fabrication of novel micro hot-wire sensor

Many works to improve the stability and sensitivity of metal oxide based gas sensors have been carried out during last several decades. As one of stability problems, we can present one example that the resistance alters to some extent when the devices are exposed to the normal air, which becomes an obstacle to its practical use. In this paper, we proposed new type of micro gas sensor with single electrode for improving stability and sensitivity. Generally, metal oxide gas sensors have two electrodes for heating and sensing. But this new type sensor has only a single electrode by forming a sensing material onto heating electrode. This micro gas sensor shows low resistance(a few hundred /spl Omega/) for parallel values of Pt resistance and SnO/sub 2/ sensing resistance. Therefore, it is appeared that the deviation of total resistance in the normal air condition is very low and stability is improved. Pt as a heating and sensing electrode is sputtered on glass (pyrex 7740) substrate and SnO/sub 2/ sensing material is thermally evaporated on Pt electrode. SnO/sub 2/ is patterned by lift-off process and then thermally oxidized in O/sub 2/ condition for 1 hr., 600/spl deg/C. The size of fabricated sensor is 2/spl times/2 mm/sup 2/. As a result of CO gas sensing characteristics, this sensor shows 100 mV voltage output for 1,000 ppm and linearity for wide range(0/spl sim/20,000 ppm) of gas concentration. And the sensor shows a good recovery characteristic of 1% deviation compared to initial resistance. The deviation of sensor resistance is about 5% for 6 months and a little influence for humidity of 90 R.H.%.

A field effect transistor type gas sensor based on polyaniline

The researched sensor at this paper is based on gas sensitive conducting polymer. Some types of conducting polymer have gas sensitivity at room temperature (Matsuguchi et al., 2002). These conducting polymers have several shortages such as low sensitivity. The transistor type gas sensor has been studied for several decades. These sensors are based on metal oxide ceramics such as tin dioxide (Wollenstein et al., 2000 and Popova et al., 1991). We researched a polymer FET gas sensor. The sensor structure is similar to thin film transistor (TFT) one. This sensor can detect very low concentration of ammonia gas. The synthesized polyaniline has the resistance change for ammonia gas. Normally IDT electrode resistor sensor can detect several decade ppm or more ammonia gas. The FET type sensor which has the same polyaniline film can detect 5 ppm of ammonia.

Fabrication of low power NO micro gas senor by using CMOS compatible process

Low power bridge type micro gas sensors were fabricated by micro machining technology with TMAH (Tetra Methyl Ammonium Hydroxide) solution. The sensing devices with different heater materials such as metal and poly-silicon were obtained using CMOS (Complementary Metal Oxide Semiconductor) compatible process. The tellurium films as a sensing layer were deposited on the micro machined substrate using shadow silicon mask. The low power micro gas sensors showed high sensitivity to NO with high speed. The pure tellurium film used micro gas sensor showed good sensitivity than transition metal (Pt, Ti) used tellurium film.

The gas sensing characteristic of the porous tungsten oxide thin films based on anodic reaction

In this paper, the gas responses of tungsten oxide films prepared by anodic reaction was discussed. Sensing electrodes and heating electrodes were patterned by photolithography method on quartz substrate. Porous tungsten oxide was fabricated in electrolyte solutions of 5 % HF (HF :