Investigation on formaldehyde gas sensor with ZnO thick film prepared through microwave heating method

ZnO nanopowders were prepared through microwave heating method. ZnO thick film sensors were fabricated by using ZnO nanopowders as sensing materials. The phase composition and morphology of the material particles were characterized by means of X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The gas-sensing properties of the sensors based on ZnO nano-materials were investigated. It was found that the sensor based on ZnO nano-materials (low power, 10× 10 min) exhibited very high responses to benzene and toluene when operating at 440 and 370 °C, respectively; but the sensor based on ZnO (low power, 10× 10 min) showed very low responses to benzene and toluene when operating at 205–215 °C. The sensor based on ZnO (low power, 10× 10 min) showed high response and good selectivity to dilute formaldehyde when operating at 210 °C; especially, the response to 0.001 ppm HCHO attained 7.4 when operating at 210 °C.     

Pulsed laser deposited Y-doped BaZrO3 thin films for high temperature humidity sensors

Pulsed laser deposited (PLD) Y-doped BaZrO₃ thin films (BaZr_1-xY_xO_3-y/2, x = 0.2, y > 0), were investigated as to their viability for reliable humidity microsensors with long-term stability at high operating temperatures (T > 500 °C) as required for in situ point of source emissions control as used in power plant combustion processes. Defect chemistry based models and initial experimental results in recent humidity sensor literature [1] and [2]. indicate that bulk Y-doped BaZrO₃ could be suitable for use in highly selective, high temperature compatible humidity sensors. In order to accomplish faster response and leverage low cost batch microfabrication technologies we have developed thin film deposition processes, characterized layer properties, fabricated and tested high temperature humidity micro sensors using these thin films. Previously published results on sputtering Y-doped BaZrO₃ thin films have confirmed the principle validity of our approach [3]. However, the difficulty in controlling the stoichiometry of the films and their electrical properties as well as mud flat cracking of the films occurring either at films thicker than 400 nm or at annealing temperature above 800 °C have rendered sputtering a difficult process for the fabrication of reproducible and reliable thin film high temperature humidity microsensors, leading to the evaluation of PLD as alternative deposition method for these films.X-ray Photoelectron Spectroscopy (XPS) data was collected from as deposited samples at the sample surface as well as after 4 min of Ar⁺ etching. PLD samples were close to the desired stoichiometry. X-ray diffraction (XRD) spectra from all as deposited BaZrO₃:Y films show that the material is polycrystalline when deposited at substrate temperatures of 800 °C. AFM results revealed that PLD samples have a particle size between 32 nm and 72 nm and root mean square (RMS) roughness between 0.2 nm and 1.2 nm. The film conductivity increases as a function of temperature (from 200 °C to 650 °C) and upon exposure to a humid atmosphere, supporting our hypothesis of a proton conduction based conduction and sensing mechanism. Humidity measurements are presented for 200–500 nm thick films from 500 °C to 650 °C at vapor pressures of between 0.05 and 0.5 atm, with 0.03–2% error in repeatability and 1.2–15.7% error in hysteresis during cycling for over 2 h. Sensitivities of up to 7.5 atm⁻¹ for 200 nm thick PLD samples at 0.058 atm partial pressure of water were measured.     

Polysilicon nanofilm pressure sensor

Utilizing 80 nm polysilicon nanofilm as piezoresistors, a pressure sensor with high performance is developed. The complete fabrication process is described. The pressure properties of the sensor were measured at the temperature from 0 to 200 °C. For 0.6 MPa full scale pressure, the sensitivity is 23.00 mV/V/MPa at 0 °C and 18.27 mV/V/MPa at 200 °C, the temperature coefficient of sensitivity (TCS) is about −0.098%/ °C without any compensation. The temperature coefficient of offset (TCO) is about −0.017%/ °C. Because of the good piezoresistive and temperature characteristics of polysilicon nanofilm, the pressure sensor demonstrates a better performance.     

A SOI-MEMS-based 3-DOF planar parallel-kinematics nanopositioning stage

This paper presents the design, kinematic and dynamic analysis, fabrication and characterization of a monolithic micro/nanopositioning three degrees-of-freedom (DOF) (XYθ) stage. The design of the proposed MEMS (micro-electro-mechanical system) stage is based on a parallel-kinematic mechanism (PKM) scheme that allows for translation in the XY plane and rotation about the Z axis, an increased motion range, and linear kinematics in the operating region (or work area) of the stage. The truss-like structure of the PKM results in higher modal frequencies by increasing the structural stiffness and reducing the moving mass of the stage. The stage is fabricated on a silicon-on-insulator (SOI) wafer using surface micromachining and deep reactive ion etching (DRIE) processes. Three sets of electrostatic linear comb drives jointly actuate the mechanism to produce motion in the X, Y and θ (rotation) directions. The fabricated stage provides a motion range of 18 μm and 1.72° at a driving voltage of 85 V. The resonant frequency of the stage under ambient conditions is 465 Hz. Additionally a high Q factor (66) is achieved from this parallel-kinematics mechanism design.     

A technique for monitoring SO2 in combustion exhausts: Use of a non-Nernstian sensing element in combination with an upstream catalytic filter

Detection of sulfur dioxide (SO₂) at high temperature (600–750 °C) in the presence of some interferents found in combustion exhausts (NO₂, NO, CO₂, CO, and hydrocarbon (C₃H₆)) is described. The detection scheme involves use of a catalytic filter in front of a non-Nernstian (mixed-potential) sensing element. The catalytic filter was a Ni:Cr powder bed operating at 850 °C, and the sensing elements were pairs of platinum (Pt) and oxide (Ba-promoted copper chromite ((Ba,Cu)_xCr_yO_z) or Sr-modified lanthanum ferrite (LSF)) electrodes on yttria-stabilized zirconia. The Ni:Cr powder bed was capable of reducing the sensing element response to NO₂, NO, CO, and C₃H₆, but the presence of NO₂ or NO (“NO_x”, at 100 ppm by volume) still interfered with the SO₂ response of the Pt–(Ba,Cu)_xCr_yO_z sensing element at 600 °C, causing approximately a 7 mV (20%) reduction in the response to 120 ppm SO₂ and a response equivalent to about 20 ppm SO₂ in the absence of SO₂. The Pt–LSF sensing element, operated at 750 °C, did not suffer from this NO_x interference but at the cost of a reduced SO₂ response magnitude (120 ppm SO₂ yielded 10 mV, in contrast to 30 mV for the Pt-(Ba,Cu)_xCr_yO_z sensing element). The powder bed and Pt–LSF sensing element were operated continuously over approximately 350 h, and the response to SO₂ drifted downward by about 7%, with most of this change occurring during the initial 100 h of operation.     

Micropatterning of sandwiched FeCuNbSiB/Cu/FeCuNbSiB for the realization of magneto-impedance microsensors

This work presents the fabrication of magnetic field microsensors based on the magneto-impedance phenomenon and dedicated to NDC applications. The multilayer structure, ferromagnetic/conductive/ferromagnetic, is composed of a copper layer sandwiched with two Finemet^? alloy films. The later, initially an amorphous material, is nanocrystallized by heat treatment. The fabrication process has been optimized in order to minimize coercivity and induce transversal anisotropy. The technological defects induced by the lift-off and sputtering processes change the magneto-impedance properties of the sensors. Eliminating these defects permits the sensor to reach to a sensitivity of 1,200 V/T/A at 30 MHz with a bias field larger than the anisotropy field and without hysteresis. The angular dependence of the sensitivity shows that the sensor is only sensitive to the axial component of the magnetic field.     

Detection of amines with chromium-doped WO3 mesoporous material

Chromium-doped mesoporous tungsten trioxide – with KIT-6 structure – was prepared through a chemical route. The resulting material was deposited on a micromechanically fabricated hot-plate and tested as a sensor for ammonia and trimethylamine in the temperature range of 200–500 °C. Maximum response was reached at 350 and 450 °C for ammonia and TMA, respectively. It was also found that the sensor shows a non-linear cross-sensitivity to the gases.     

Plasma assisted thermal bonding for PMMA microfluidic chips with integrated metal microelectrodes

Fracture of integrated metal microelectrodes likely happens during the thermal bonding process of PMMA [poly (methylmethacrylate)] microfluidic chips. In this paper, the fracture behaviors are studied. The fracture is mainly caused by the plastic deformation of the electrode plate (the PMMA plate with microelectrodes) and the thermal stress of microelectrodes, which is due to the high bonding temperature. To decrease the bonding temperature, a plasma assisted thermal bonding method is evaluated and first used to eliminate the fracture of microelectrodes. In this process, the surface of the cover plate (the PMMA plate with microchannels) is modified using oxygen plasma before the electrode plate is thermally bonded to the cover plate. The parameters of the oxygen plasma treatment are optimized, and the contact angle is decreased from 71.7° to 43.6°. The thermal bonding temperature is optimized, which decreases the temperature from 100 °C to 85 °C. Testing of bonding strength shows an average failure pressure of 1.75 MPa, which is comparable to the bonding strength of 1.46 MPa for chips bonded at 100 °C without plasma modification. In order to demonstrate this bonding method, a PMMA microfluidic chip with integrated copper interdigitated microelectrode arrays for AC electroosmotic pump is fabricated.     

Solid-state potentiometric SO2 sensor combining NASICON with V2O5-doped TiO2 electrode

A compact tubular sensor based on NASICON (sodium super ionic conductor) and V₂O₅-doped TiO₂ sensing electrode was designed for the detection of SO₂. In order to reduce the size of the sensor, a thick-film of NASICON was formed on the outer surface of a small Al₂O₃ tube; furthermore, a thin layer of V₂O₅-doped TiO₂ with nanometer size was attached on the NASICON as a sensing electrode. This paper investigated the influence of V₂O₅ doping and sintering temperature on the characteristics of the sensor. The sensor attached with 5 wt% V₂O₅-doped TiO₂ sintered at 600 °C exhibited excellent sensing properties to 1–50 ppm SO₂ in air at 200–400 °C. The EMF value of the sensor was almost proportional to the logarithm of SO₂ concentration and the sensitivity (slope) was −78 mV/decade at 300 °C. It was also seen that the sensor showed a good selectivity to SO₂ against NO, NO₂, CH₄, CO, NH₃ and CO₂. Moreover, the sensor had speedy response kinetics to SO₂ too, the 90% response time to 50 ppm SO₂ was 10 s, and the recovery time was 35 s. On the basis of XPS analysis for the SO₂-adsorbed sensing electrode, a sensing mechanism involving the mixed potential at the sensing electrode was proposed.     

An efficient cell count method using a lattice molded on indents of a culture dish

Cell count is an important task for obtaining biological and medical information. In this paper, a novel cell count method is presented for improving the efficiency of the procedure as well as reducing microbial contamination compared to the conventional cell count method using a hemocytometer. The proposed method involves a lattice array consisting of a 50 μm × 50 μm square with lines of 2-μm width and 1.4-μm depth on a surface indented from a culture dish bottom. This configuration enables observation of cells at the same focus as the lattice. Therefore, an instant cell count during incubation is possible without the tedious, error-prone preparation steps such as harvesting and loading required in conventional methods. In addition, cells can be preserved with minimal contact with the external environment. These advantages become magnified with a periodic long-term cell count. A polystyrene culture dish, 35 mm in diameter, was fabricated by injection molding using a nickel mold, wherein indents of 3 mm × 3 mm in area and 1 mm in height were electroplated based on microfabrication technology. For easy separation from the nickel mold, the four sides of the indents in the mold are inclined at 54.74° via anisotropic silicon etching. The usefulness of the suggested method was verified using adhering HeLa (cervical carcinoma cell) cells and floating Jurkat cells. Both were placed in culture dishes and cultivated for 3 days in a carbon dioxide incubator (5% CO₂, 95% air) at 37 °C, and then successfully observed through the divided lattice using an inverted microscope. The dish was also assessed with a hemocytometer by counting HEK 293T (human embryonic kidney) cells and yeast cells.     

Effects of internal electrode composition on the reliability of low-firing PMN–PZT multilayer ceramic actuators

We investigated the effects of internal electrode composition on the reliability of low-firing multilayer ceramic actuators using Ag internal electrodes. Ag–ceramic composite pastes were prepared by adding Pb(Mg_1/3Nb_2/3)O₃–Pb(Zr_0.475,Ti_0.525)O₃ (PMNZT) ceramic powders to a commercial Ag paste at concentrations in the range of 0–60 vol%. PMNZT multilayered laminates were fabricated using tape casting, and then cofired at 925 °C for 10 h. The fatigue behaviors of multilayer actuators with Ag internal electrodes having different PMNZT concentrations were compared by applying a 2 kV/mm ac electric field at 50 °C under a relative humidity of 30%. The failure data were analyzed using Weibull statistics. The addition of PMNZT ceramics enhanced the mean time to failure by reducing the densification mismatch between the piezoelectric ceramic and internal electrode layers during the cofiring process.     

Influence of Cs doping in spray deposited SnO2 thin films for LPG sensors

Detection of low concentrations of petroleum gas was achieved using transparent conducting SnO₂ thin films doped with 0–4 wt.% caesium (Cs), deposited by spray pyrolysis technique. The electrical resistance change of the films was evaluated in the presence of LPG upon doping with different concentrations of Cs at different working temperatures in the range 250–400 °C. The investigations showed that the tin oxide thin film doped with 2% Cs with a mean grain size of 18 nm at a deposition temperature of 325 °C showed the maximum sensor response (93.4%). At a deposition temperature of 285 °C, the film doped with 3% Cs with a mean grain size of 20 nm showed a high response of 90.0% consistently. The structural properties of Cs-doped SnO₂ were studied by means of X-ray diffraction (XRD); the preferential orientation of the thin films was found to be along the (3 0 1) directions. The crystallite sizes of the films determined from XRD are found to vary between 15 and 60 nm. The electrical investigations revealed that Cs-doped SnO₂ thin film conductivity in a petroleum gas ambience and subsequently the sensor response depended on the dopant concentration and the deposition temperature of the film. The sensors showed a rapid response at an operating temperature of 345 °C. The long-term stability of the sensors is also reported.     

Tetrakis(alkylthio)-substituted lutetium bisphthalocyanines for sensing NO2 and O3

In this study, the nitrogen dioxide (NO₂) and ozone (O₃) sensing properties of a series bis[tetrakis(alkylthio) phthalocyaninato] lutetium(III) complexes [(C_nH_2n+1S)₄Pc]₂Lu(III) (n = 6, 10, 16) are investigated as a function of concentration in the temperature range between 25 °C and 150 °C. The concentration ranges were 1–10 ppm for NO₂, and 50 ppb–1 ppm for O₃. The response time and the sensor response to NO₂ are measured for approximately 1 min and 100% ppm⁻¹, respectively, for compound 1 at room temperature. At room temperature, all compounds are in the solid phase. The response time decreases to a few seconds with increasing operation temperature to 150 °C. At this temperature, all compounds are in the liquid crystal phase. The fastest response to oxidizing gases is observed at the liquid crystal phase of the Pcs. It has also been observed that the response time and the sensor response depend on the alkyl chain lengths of the Pcs. The doping effect of oxygen has been determined under high purity nitrogen N₂ flow, after exposure to dry air, at a different period of time and after annealing. It has been found that the conductivities of [(C_nH_2n+1S)₄Pc]₂Lu(III) thin films increased after exposure to dry air and the conduction mechanism also changed from ohmic behavior to space-charge-limited conduction.     

Temperature offset drift of GMI sensors

Temperature offset stability of magnetoimpedance sensor is discussed based on experiments accomplished with soft magnetic amorphous material. An amorphous ribbon of Co₆₇Fe₄Cr₇Si₈B₁₄ composition was tested in a magnetic shield with adjustable internal temperature. DC resistance and complex components of impedance at frequencies up to 30 MHz were investigated in the temperature range of −20 to +75 °C. The measured data were used for the evaluation of temperature dependence of transverse permeability that is assumed to be a major contributor to the temperature variations of impedance. We also show that thermal treatments of the amorphous ribbon significantly affect the temperature behaviour of GMI. In case of tested alloy, which has very small negative temperature coefficient of resistivity, the achieved equivalent temperature offset drift is −0.27 A/m/K (−340 nT/K).     

Direct numerical simulations of transverse and spanwise magnetic field effects on turbulent flow in a 2:1 aspect ratio rectangular duct

Magnetic fields are used extensively to direct liquid metal flows in material processing. Continuous casting of steel uses different configurations of magnetic fields to optimize turbulent flows in rectangular cross-sections to minimize defects in the solidified steel product. Realizing the importance of a magnetic field on turbulent flows in rectangular cross-sections, the present work is aimed at understanding the effect of a magnetic field on the turbulent metal flow at a nominal bulk Reynolds number of ∼5300 (based upon full duct height) (Re_τ = 170, based upon half duct height) and Hartmann numbers (based upon half duct height) of 0, 6.0 and 8.25 in a 2:1 aspect ratio rectangular duct. Direct numerical simulations in a non-MHD 2:1 aspect ratio duct followed by simulations with transverse and span-wise magnetic fields have been performed with 224 × 120 × 512 cells (∼13.7 million cells). The fractional step method with second order space and time discretization schemes has been used to solve the coupled Navier-Stokes-MHD equations. Instantaneous and time-averaged natures of the flow have been examined through distribution of velocities, various turbulence parameters and budget terms. Spanwise (horizontal) magnetic field reorganizes and suppresses secondary flows more strongly. Turbulence suppression and velocity flattening effects are stronger with transverse (vertical) magnetic field.     

Quick and reliable estimation of BOD load of beverage industrial wastewater by developing BOD biosensor

An amperometric biosensor for determination of biochemical oxygen demand in wastewater has been developed to overcome the time consuming monitoring procedures. The performance and stability of the immobilized membrane have been investigated at 37 °C and pH 6.8. Immobilized microbial membranes maintain their stability and activity after intermittent use for 400 cycles when stored at 4 °C in sodium phosphate buffer pH 6.8. The response time of the BOD sensor was only 90 min, being independent of the concentration, and the lower detection limit was 1 mg/l. The obtained BOD values showed correlation with that of the conventional method for BOD determination (BOD5) with a deviation of ±10%. Moreover, the sensor exhibits good repeatability (3.39–4.45%) and reproducibility (1.85–2.25%). Software was added to upgrade this sensor and to make it a promising candidate for online monitoring.     

MEMS micro fluxgate sensors with mutual vertical excitation coils and detection coils

As a classic Earth magnetic field sensor, fluxgate magnetic sensors have great potential applications in many fields. This paper presents a new 3D micro-solenoid fluxgate magnetic sensor based on the MEMS technique. The excitation coils were placed vertically to the detection coils on the chip plane, around a rectangular shaped magnetic core. Polyimide was used to insulate coils and magnetic core. Width of copper conductor lines is 50 μm, and line space is 50 μm. The design of such fluxgate magnetic sensor followed second harmonic signal selecting method. Phase-lock amplifier was used to get second harmonic signal output by detection coils. The linear range of 0–80 μT with sensitivity of 6.7 V/T was achieved from the fabricated sensor with excitation current of 430 mA and the operational frequency of 40 KHz. As the excitation current was 470 mA, linear range of 0–50 μT with sensitivity of 21.7 V/T was achieved.     

Streamline generation code for particle dynamics description in numerical models of turbulence

Streamline Version 4 is a versatile Fortran 77 & C++ program for calculating charged test particle trajectories or field-lines for user-specified fields using the test-particle method. The user has the freedom to specify any type of field (analytical, tabulated in files, time dependent, etc.) and maintains complete control over initial conditions of trajectories/field-lines and boundary conditions of specified fields. The structure of Streamline was redesigned from previous versions in order to know not only particle or field-lines positions and velocities at each step of the simulations, but also the instantaneous field values as seen by particles. This was made to compute the instantaneous value of the particle’s magnetic moment, but other applications are possible too. Accuracy tests of the code are shown for different cases, i.e., particles moving in constant magnetic field, magnetic plus constant electric field and wave field. In addition in the last part of the paper we concentrate our discussion on the study of velocity space diffusion of charged particles in turbulent slab fields, paying attention to the discretization of the fields and the temporal discretization of the dynamical equations. The diffusion of charged particles is a very common topic in plasma physics and astrophysics since it plays an important role in many different phenomena such as stochastic particle acceleration, diffusive shock acceleration, solar energetic particle propagation, and the scattering required for the solar modulation of galactic cosmic rays.     

Fiber Bragg grating weighing sensor of beam with two parallel holes

Due to the strains of fiber Bragg gratings mounted on the gauge hole of beam with two parallel holes excited by the weight, a fiber Bragg grating weighing sensor is developed. During the double differential operation of the relation shifts of Bragg wavelength of these four mounted gratings, the shifts of Bragg wavelengths caused by the temperature fluctuation and the bending moment caused by the deflection load can be compensated. The loading and unloading experiments indicate that the delay of grating weighing sensor is 0.28%FS, and the repetition is 0.32%FS. Through the least-square algorithm fitting, the load response sensitivity of grating weighing sensor is 9.992 × 10⁻⁶ kg f⁻¹, and the fitting linearity is 0.6%FS. The temperature drift of grating weighing sensor is 0.02%FS/°C at the range of 20–60 °C. The fitting linearity is 1.5%FS under the action of deflection load.     

Characterization of intermediate In/Ag layers of low temperature fluxless solder based wafer bonding for MEMS packaging

Low temperature fluxless solder for wafer bonding has received a lot of attention due to its great potential in hermetic MEMS packaging. Previous research activities mainly deploy solder alloy of eutectic composition to achieve low bonding temperature. We proposed new intermediate bonding layers (IBLs) of rich Ag composition in In–Ag materials systems. In this study, we investigated the intermetallic compounds (IMCs) at the bonding interface with respect to the bonding condition, post-bonding room temperature storage and post-bonding heat treatment. With this IBL, the IMCs of Ag₂In and Ag₉In₄ with high temperature resist to post-bonding process are derived under process condition of wafer bonding at 180 °C, 40 min and subsequent 120–130 °C annealing for 24 h. Low melting temperature IMC phase of AgIn₂ is formed in the interface after long term room temperature storage or 70 °C aging treatment. This low melting temperature IMC phase can be completely converted into high melting temperature IMCs of Ag₂In and Ag₉In₄ after 120 °C additional annealing. Based on our results, we can design the packaging process flow so as to get reliable hermetic packaged MEMS devices by using low temperature fluxless In–Ag wafer bonding.