Chi-Yen Shen

Grain Growth and Electrical Properties in ZnO Varistors with Various Valence States of Additions

Grain growth and electrical properties in ZnO system with various valence states of manganese and cobalt were studied. The results were discussed by means of defects produced by the additions. The grain growth was analyzed from the kinetic grain growth equation: Gn=Dtexp (-E/RT). In this work, the grain growth kinetic exponent n was 6 and activation energy was 230±21 kJ/mol. The grain size increased with the valence states of manganese and cobalt. The compositions with lower trap density have higher nonlinear coefficient, higher voltage ratio and lower leakage current. The varistor properties were improved by increasing the sintering temperature and time because of the more obvious tunneling effect.

Surface Acoustic Wave Ammonia Sensors Based on ST-cut Quartz under Periodic Al Structure

Surface acoustic wave (SAW) devices are key components for sensing applications. SAW propagation under a periodic grating was investigated in this work. The theoretical method used here is the space harmonic method. We also applied the results of SAW propagation studied in this work to design a two-port resonator with an Al grating on ST-cut quartz. The measured frequency responses of the resonator were similar to the simulation ones. Then, the chemical interface of polyaniline/WO3 composites was coated on the SAW sensor for ammonia detection. The SAW sensor responded to ammonia gas and could be regenerated using dry nitrogen.

The Microstructure of ZnO Varistor Doped with Antimony Oxide

The effects produced by different valency and amount of antimony ions on the resulting microstructures of ZnO varistors were studied. From the observation of scanning electron microscopy (SEM), the composition originally added with high valency of antimony ion had a larger grain size than that originally added with a low valency of antimony ion. Conversely, the composition originally added with a high valency of antimony ion possessed fewer intragrain particles than that originally added with a low valency of antimony ion. The spinel particle size and number of intragrain particles increased when the sintering temperature was raised. The compositions containing more antimony oxide can form more spinel phases, and result in an increase in grain growth kinetic exponent and activation energy as well as a decrease in grain size. These compositions have fewer intragrain particles and more spinel particles than those containing less antimony oxide.

Viscoelastic properties of polymer films on surface acoustic wave organophosphorous vapor sensors

This work investigates the viscoelastic properties of the fluoropolyol (FPOL) polymer on the surface acoustic wave (SAW) organophosphorous vapor sensors. A complex shear modulus is used to express different polymer types (glassy, glassy-rubbery, and rubbery). The different polymer types leads to different propagating properties of SAW, such as attenuation change and velocity shift. Calculation results indicate that the glassy-rubbery film exhibits the highest sensitivity for detecting organophosphorous vapor. The thicker the glassy and glassy-rubbery film implies a higher sensitivity. Moreover, the SAW vapor sensor based on the rubbery film represents the response of acoustically thick layers which has a peak in attenuation with an increasing vapor adsorption. The selectivity factor between DMMP (10 ppm) and H2O (40%RH) is so low that the selectivity of FPOL film towards water is ineffecient. However, the selectivity factor between ethanol (10 ppm) and DMMP (10 ppm) is as high as 2512, thus confirming that the selectivity of FPOL film towards ethanol is good. Therefore, a precise and dry humidity control in the sensors system with FPOL coating is required.

Grain growth processes in ZnO varistors with various valence states of manganese and cobalt

Grain growth in ZnO ceramics with various valence states of added manganese and cobalt was studied. The results were discussed by means of defects produced by the additions. The grain growth was analyzed from the kinetic grain growth equation: Rn/t = Γo expRn/t=Γo exp( − E/RT). In this work, the grain growth kinetic exponent n was 6 and the activation energy was 301±35 kJ/mol. The grain size increased with the valence states of manganese and cobalt. The addition of CoOx affected not only the mean grain size, grain growth kinetic exponent, and activation energy, but also inhibited the effects of Bi2O3‐liquid phase sintering.

Analysis of Shear Horizontal Surface Acoustic Wave Sensors with the Coupling of Modes Theory

This study has investigated a method for accurate analysis and design of shear horizontal surface acoustic wave (SH-SAW) sensors. The coupling of modes (COM) theory was used to develop an analytical model to satisfy Barkhausens criteria for oscillation and avoid mode hopping. The theoretical simulation was highly consistent with the experimental results. The SH-SAW sensor presented here exhibited excellent reversibility, sensitivity, and repeatability when ammonia was at the ppb level.

A Room Temperature Nitric Oxide Gas Sensor Based on a Copper-Ion-Doped Polyaniline/Tungsten Oxide Nanocomposite

The parts-per-billion-level nitric oxide (NO) gas sensing capability of a copper-ion-doped polyaniline/tungsten oxide nanocomposite (Cu2+/PANI/WO3) film coated on a Rayleigh surface acoustic wave device was investigated. The sensor developed in this study was sensitive to NO gas at room temperature in dry nitrogen. The surface morphology, dopant distribution, and electric properties were characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy mapping, and Hall effect measurements, respectively. The Cu2+/PANI/WO3 film exhibited high NO gas sensitivity and selectivity as well as long-term stability. At 1 ppb of NO, a signal with a frequency shift of 4.3 ppm and a signal-to-noise ratio of 17 was observed. The sensor exhibited distinct selectivity toward NO gas with no substantial response to O2, NH3 and CO2 gases.

Design of ST-cut quartz surface acoustic wave chemical sensors

Abstract This research investigates the design rules polymer-based ST-cut quartz surface acoustic wave (SAW) sensors used in detecting organophosphorous compounds. A complex shear modulus is used to represent express different types of polymer (glassy, glassy–rubbery, and rubbery). Different propagation directions lead to different wave propagation properties in SAW devices, such as attenuation and velocity. Hence, the choice of polymer type and wave propagation direction is a very important aspect of sensor design. Calculations indicate that the glassy–rubbery and rubbery film coated on SAW sensors very sensitively detect organophosphorous vapor. However, the glassy–rubbery film is most suitable in sensing applications, because it makes signal attenuation significantly. Although sensitivity is high when an acoustic wave propagates in the Y -direction, the X -direction is preferred at the optimum path on account of the excellent temperature stability in the X -propagation direction. Therefore, SAW vapor sensors with an appropriate chemical interface and wave propagation direction are designed to yield superior performance.

Detection of cartilage oligomeric matrix protein using a quartz crystal microbalance.

Current methods for the accurate diagnosis of osteoarthritis (OA) based on magnetic resonance imaging and enzyme-linked immunosorbent assay method are highly sensitive and specific but require specialised laboratory facilities and highly trained operators to obtain a definitive result. A quartz crystal microbalance (QCM) immunosensor has been developed to detect cartilage oligomeric matrix protein (COMP) in this work. This QCM immunosensor was fabricated to immobilize COMP antibodies in orientation. Its potential dynamically monitored the processes of immunoreaction and could evaluate for the rapid and sensitive detection of COMP in laboratory-cultured preparations and clinical samples. The frequency response of the QCM immunosensor changed 10 kHz to 100 ng/ml COMP. The linear regression equation of frequency shift and COMP concentration is y = 0.0872 x + 1.2138 (R2 =0.9957).

The Effect of Antimony Oxide on the Electrical Properties and Stability of ZnO Varistors

The nonlinear current-voltage characteristics, depression angle and stability of ZnO varistors were investigated as a function of valence and amount of antimony oxide. The nonlinear properties were improved, the depression angle decreased, and the stability under continuous dc bias increased with decreasing valence of the antimony ion. However, the nonlinear properties became worse with an increasing amount of antimony oxide for any valence. The relaxation time was insensitive to the valence of the antimony ion and the amount of antimony oxide, while the increased antimony oxide content enhanced the electrical stability as a function of time. Spinel particles formed by the reaction of antimony oxide and ZnO, were suggested as playing an important role in the improvement of electrical properties and stability by stressing the junction between two ZnO grains.