In this work a novel flexible acetylene (C2H2) gas sensor based on Ag nanoparticles decorated vertical ZnO nanorods (Ag-ZnO NRs) on PI/PTFE substrate has been investigated. The grown structure was synthesized through a simple, rapid, and low-temperature hydrothermal-RF magnetron sputtering method. The successful immobilization of Ag nanoparticles (NPs) onto the surface of ZnO nanorods contributed large effective surface area and facilitated the charge transfer process. The as-fabricated sensor exhibited enhanced C2H2 sensing performances at low temperature (200°C) including a broad detection range (3 - 1000 ppm), and short recovery time (39 sec). Mechanical robustness and device flexibility were investigated at different curvature angle (0 - 90°) and several times bending-relaxing process (0 – 5 × 105 times). The sensor exhibited stable response magnitude with a negligible drift of ~ 2.1% for a maximum bending angle of 90o and a response drop of 8% after 5 × 104 bending/relaxing processes. The superior sensing features along with outstanding flexibility to extreme bending stress indicate the sensor a promising candidate for the development of practical flexible C2H2 gas sensors.
Fabrication and characterizations of a flexible NO2 sensor based on tungsten trioxide nanoparticles-loaded multi-walled carbon nanotubes-reduced graphene oxide hybrid (WO3 NPs-loaded MWCNTs-RGO) on a polyimide/polyethylene terephthalate (PI/PET) substrate have been investigated. A viscous gel of the hybrid materials (WO3-MWCNTs-RGO) was prepared with the assistance of α-terpineol. To observe the physical and crystalline properties of hybrid materials FESEM, TEM and XRD was carried-out. Afterwards, sensor was fabricated by drop casting hybrid solution between two fingers gold (Au) electrodes. Finally, gas sensing properties were taken out in open air environment. The sensor showed excellent sensing performance towards NO2 including a maximum response of 17% (to 5 ppm), a limit of detection (LOD) of 1 ppm, and relatively short response/recovery time (7/15 min). The sensing behaviors of the fabricated flexible sensor were evaluated systematically at different curvature angles (0-90°) and after several times bending and relaxing (0-107). The sensor exhibited excellent mechanical flexibility and sensing properties at room temperature without any significant performance degradation even at a curvature angle of 90° and after 106 times bending and relaxing process. The results indicates that economical, light weight and mechanical robustness of the proposed WO3 NPs-MWCNTs- RGO hybrid based sensor can be a promising building block for the development of high performance flexible NO2 sensors.
This paper describes anodic bonding characteristics of MLCA to Si-wafer using evaporated Pyres #7740 glass thin-films for MEMS applications. Pyrex #7740 glass thin-films with the same properties that were deposited on MLCA under optimum RF magneto conditions (Ar 100%, input power 1 W/cm2). After annealing in 450°C for 1 hr, the anodic bonding of MLCA and Si-wafer was successfully performed at 600 V, 400°C in - 760 mmHg. Then, the MLCA/Si bonded interface and fabricated Si diaphragm deflection characteristics were analyzed through the actuation and simulation test. It is possible to control with accurate deflection of Si diaphragm according to its geometries and its maximum non-linearity being 0.05-0.08 %FS. Moreover, any damages or separation of MLCA/Si bonded interfaces did not occur during actuation test. Therefore, it is expected that the anodic bonding technology of MLCA/Si wafers could be usefully applied for the fabrication process of high-performance piezoelectric MEMS devices.
This paper describes the fabrication process and characteristics of ceramic thin-film pressure sensors based on Ta-N strain gauges for harsh environment applications. The Ta-N thin-film strain gauges are sputter-deposited on a thermally oxidized micromachined Si diaphragm with buried cavities for overpressure tolerance. The proposed device takes advantage of the good mechanical properties of single-crystalline Si as a diaphragm fabricated by SDB and electrochemical etch-stop technology, and in order to extend the temperature range, it has relatively higher resistance, stability and gauge factor of Ta-N thin-films more than other gauges. The fabricated pressure sensor presents a low temperature coefficient of resistance, high-sensitivity, low nonlinearity and excellent temperature stability. The sensitivity is 1.21-1.097 mV/V•kgf/cm2 in temperature ranges of 25-200°C and a maximum non-linearity is 0.43 %FS.
Angular-dependent magnetoresistance characteristics in Si(001)/NiO(300A)/NiFe(tequals450, 1000, 1350A) thin films was investigated in terms of an angle between current and applied magnetic field. The samples were grown by RF-sputtering and DC-sputtering methods on naturally oxidised Si(001) substrates. First, NiO layer(300A) was grown on Si substrate, followed by the deposition of NiFe layers as a function of NiFe thickness under the condition of in-situ magnetic bias-field of approximately 500G. The measurement of angular magnetoresistance in Si(001)/NiO(300A)NiFe(tequals450, 1000, 1350A) thin films were carried out in variation of an angle between current direction and external magnetic field. Also, on the base of single magnetic domain model, the comparison between the measured and the calculated MR profiles was made. For tNiFe equals 450A, symmetrical MR characteristics were observed as sweeping external magnetic field proceed. However, for tNiFe equals 1000A, asymmetric MR profiles were shown.
Great interest is given in developing magnetoresistance(MR) sensor, using ferromagnetic, electrically non-magnetic conducting and antiferromagnetic films, especially for the use in weak magnetic fields. Here, we report single and Wheatstone-bridge type of MR sensors made in Si(001)/NiO(300A)/NiFe bilayers. Angular dependence of MR profiles was measured in Si(001)/NiO(300A)/NiFe(450A) films as a function of an angle between current and applied field direction, also, linearity was determined. AMR characteristics of single MR sensors was well explained with single domain model. Good linearity in 45 degree(s) Wheatstone-bridge type of MR sensors consisting of 4 single MR sensors made in Si(001)/NiO(300A)/NiFe(450A) was shown in the range of about +/- 50 Oe.
This paper presents the optimized design, fabrication and thermal characteristics of micro-heaters for thermal MEMS (micro electro mechanical system) applications using SDB and SOI membranes and trench structures. The micro-heater is based on a thermal measurement principle and contains for thermal isolation regions a 10 micrometers thick Si membrane with oxide-filled trenches in the SOI membrane rim. The micro- heater was fabricated with Pt-RTD on the same substrate by using MgO as medium layer. The thermal characteristics of the micro-heater with the SOI membrane is 280 degree(s)C at input power 0.9 W; for the SOI membrane with 10 trenches, it is 580 degree(s)C due to reduction of the external thermal loss. Consequently, the micro-heater with trenches in SOI membrane rim provides a powerful and versatile alternative technology for improving the performance of micro-thermal sensors and actuators.
This paper presents the fabrication of high-yield Si micro- diaphragms using electrochemical etch-stop method in TMAH/IPA/pyrazine solution. When IPA was added TMAH solution, the flatness of etching front is improved and undercutting is reduced, but the etch rate of (100) Si is decreased. The (100) Si etch rate is improved with addition of pyrazine. The (100) Si etch rate of 0.8/min which is faster by 13 percent than pure TMAH 20 wt percent solution is obtained using TMAH 20 wt percent/pyrazine 0.5 g and the etch rate of (100) Si is decreased with more additive quantity of pyrazine. Addition of pyrazine to TMAH 25 wt percent solution, the flatness variations of etching front is not observed and undercutting ratio is reduced about 30- 50 percent. Addition of pyrazine to TMAH increases the etch ratio f(100) Si, thus the elapsed time for etch-stop was shortened. I-V curves of n- and p-type Si in TMAH/IPA/pyrazine solution were obtained. OCP and PP of n- and p-type Si were also obtained, and applied potential was selected between n- and p-type Si's PP. 801 Si micro- diaphragms having 20 thick were fabricated on 5 inch Si wafer using electrochemical etch-stop method in TMAH/IPA/pyrazine solution. The average thicknesses of micro-diaphragms were 20.03 and standard deviation was +/- 0.26.
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