Sang-Mun Lee

Fabrication and characterization of micro-gas sensor for nitrogen oxides gas detection

Abstract WO 3 -based thin film micro-gas sensor was fabricated and the NO x gas sensing as well as electrical properties have been investigated. To obtain the optimal heat distribution, the structure of micro-hot plate was designed from the result of finite element simulation and was prepared by backside etching with KOH solution. The micro-hot plate was made out of N/O/N diaphragm with the thickness of 0.6 μm and area of 1.5×1.5 mm 2 . The power consumption to maintain the device temperature of 300°C was about 60 mW. WO 3 thin film was thermally evaporated on micro-diaphragm. The film exhibited a fast response to NO 2 gas and the relationship between sensitivity and NO 2 concentration showed good linearity in the gas concentration range of 0–30 ppm NO 2 . The sensitivity of micro-gas sensor to NO x was correlated with the microstructure of the thin film.

The TiO2-adding effects in WO3-based NO2 sensors prepared by coprecipitation and precipitation method

Abstract Two different sensing materials of TiO 2 –WO 3 system with the grain size of nanometer are synthesized; one is a complete 2-nm-sized coprecipitate ((Ti,W)O 2 ) made by sol-coprecipitation of TiCl 4 and WCl 6 , and the other is a complex 8-nm-sized material (TiO 2 +WO 3 ) by mixing the sol-precipitation of TiCl 4 and WCl 6 . The TiO 2 –WO 3 system showed different characteristics between the coprecipitate and the complex material of TiO 2 and WO 3 . The sensitivity and sorption properties were improved in the coprecipitate. In the coprecipitate, the sensitivity defined as R G / R A , where R G and R A are resistance in gas ambient and in air, respectively, was about 100 for 30 ppm NO 2 at 340°C, which is suited for facility combustion furnace. The coprecipitated sensing materials had different resistance and grain size of 6 nm after calcination in air at 600°C for 2 h. The properties of precursor have been investigated by SEM, X-ray diffraction (XRD) and BET analyses.

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.

Thermally oxidized tin black films for gas sensing

Abstract The tin dioxide (SnO2) films were been prepared by oxidization of tin black film which was deposited by thermal evaporation. This method can be used for a simple and economical fabrication of a SnO2 gas sensor. These films also have an ultra-porous structure and a grain size in the nanometer. The reduction of particle size to nanometers leads to a dramatic improvement in sensitivity. The particle size and structural properties of SnO2 film were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Through the addition of Pt sol as a catalyst, the SnO2/Pt films acquired an appropriate resistance and stable reaction, though sensitivity decreased. The gas sensing characteristics were also investigated using iso-C4H10, CH4, C3H8, and CO gases.

Effects of the Plasma Treatment on the Electrical Properties of Indium Tin Oxide Thin Films

The sheet resistance of the ITO films after oxygen and nitrogen plasma treatments was investigated, based on the change in the lattice characteristics such as the grain size and the lattice strain. The plasma treatment yields an increase in the grain size thence the electrical conductivity in addition to better surface morphology. The decrease in lattice strain is attributable to the increase in the grain size. The experimental results imply that the grain boundary scattering limited mobility plays an important role in the conductivity of ITO films.

Synthesis and Performance of Polyimide Films for the Flexible Organic Light Emitting Diodes

A series of polyimide (PI) and copolyimide (Co-PI) films were prepared by two-step imidization processes from the poly(amicacid) precursors. The color and visible light transmission of the Co-PI films were much better than those of the general Kapton type PI film mainly due to the decrease of the charge transfer complex formation by the presence of the CF3 groups both in the aromatic diamine and dianhydride monomers. In the ITO thin film deposition and subsequent OLED device fabrication, the thermal and mechanical properties of the Co-PI films were more important than the optical property of the Co-PI films.

Effects of Thin Film Deposition on Fabrication of Switchable Mirror

In this paper we studied switchable mirrors for application to transparent flat panel displays. The typical structure of switchable mirror has configuration of MgNi/Pd/Ta2O5/HxWO3/ITO. In this study photocatalyst layer (TiO2 or Nb2O5) was used between Pd and Ta2O5 layers. These layers were prepared by RF magnetron sputtering method utilizing TiO2 and Nb2O5 targets under various conditions and their electrochromic properties were investigated by using FE-SEM, EDAX and Nano View system. The transmittances of the Nb2O5 and the TiO2 thin films, could be optimized in the switchable mirror as photocatalyst layer, where they were deposited under the power of 80 W and 70 W, respectively, by the RF magnetron sputter. The characteristics of Nb2O5 and TiO2 transmittance are the outstanding at 80 W, 70 W respectively.

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.

Gas Barrier of Plastic Substrate and Performance of White OLED

Flexible white OLED (organic light emitting diode) is a subject of intense research due to its application as versatile lightings for housing and flexible backlight unit for TFT-LCD. In order to make flexible OLED, flexible transparent conductor substrate is required which can replace ITO-glass used in current OLED devices. Another important point is a good gas barrier property of the flexible ITO-film, since the water vapor transmission rate (WVTR) of polymer film is much higher than that of ITO-glass and the life time of OLED device is very sensitive to the transmitted water vapor. In this work, a wet process of forming gas barrier layer on polyethersulfone (PES) film was studied utilizing spin coating of polysilazane solution and thermal conversion to thin SiO2 barrier layer. The flexible white OLED fabricated with this ITO-SiO2 (polysilazane)-PES substrate exhibited about equal power and current efficiencies to the OLED made with ITO-glass.

Electrical modelling for thermal behavior and gas response of combustible catalytic sensor

This study provides the electrical model of combustible catalytic gas sensor. Physical characteristics such as thermal behavior, resistance change were included in this model. The finite element method analysis for sensor device structure showed that the thermal behavior of sensor is expressed in a simple electrical equivalent circuit that consists of a resistor, a capacitor and a current source. This thermal equivalent circuit interfaces with real electrical circuit using two parts. One is `power to heat` converter. The other is temperature dependent variable resistor. These parts realized with the analog behavior devices of the SPICE library. The gas response tendency was represented from the mass transferring limitation theory and the combustion theory. In this model, Gas concentration that is expressed in voltage at the model, is converted to heat and is flowed to the thermal equivalent circuit. This model is tested in several circuit simulations. The resistance change of device, the delay time due to thermal capacity, the gas responses output voltage that are calculated from SPICE simulations correspond well to real results from measuring in electrical circuits. Also good simulation result can be produced in the more complicated circuit that includes amplifier, bios circiut, buffer part.