High-performance MEMS-based gas chromatography column with integrated micro heater

A high-performance MEMS-based gas chromatography (GC) device is proposed comprising a miniature serpentine column with dimensions of 3.2 m × 200 μm × 250 μm (length × width × depth) and with an integrated Pt micro heater. The column is fabricated on a Si die measuring 3.5 × 1.8 mm² using a wet etching process and is bonded to a Pyrex cover plate incorporating the Pt micro heater via a thermal fusion process. The experimental results reveal that an applied voltage of 9.7 V is sufficient to maintain a constant temperature of 85°C for elution purposes. In addition, it is shown that the proposed device successfully detects the concentrations of both pure and mixed samples of four volatile organic compound gases, namely acetone, toluene, methanol, and benzene. Finally, the theoretical plate number obtained by the proposed MEMS-based GC device is shown to be 2–3 times higher than that obtained from a conventional capillary-based GC system under the same injection conditions.     

First Vertical Hall Device in standard 0.35 μm CMOS technology

In order to lower the short-circuit effect due to the measurement contacts, Vertical Hall Devices (VHDs) are generally designed either in bulky N-type silicon or in the deep N-well of high-voltage CMOS technologies. In this last case, VHD can benefit from on chip circuitry for offset and 1/f noise reduction, but HVCMOS remains a costly technology. Using spinning-current, HVCMOS compatible VHDs with a resolution of 76 μT rms over a 1.6-kHz bandwidth have been demonstrated. The VHD presented here is designed in the shallow N-well of a low-cost 0.35 μm standard CMOS technology. Unlike conventional VHD, its measurement contacts are located outside the sensor active area. FEM simulations and experimental results show that the new geometry suppresses the short-circuit effect and strongly reduces the intrinsic offset and noise. Thus, without any noise and offset reduction method, this new small VHD (63 μm²) reaches a resolution of 79 μT rms over a (5 Hz–1.6 kHz) bandwidth, and opens the way to the integration of 3D Hall sensors in low-cost standard CMOS technologies.     

Single-crystalline Te microtubes: Synthesis and NO2 gas sensor application

Tellurium tubular crystals were grown by direct thermal evaporation of tellurium metal in an inert atmosphere on quartz substrates at ambient pressure without employing any catalyst. Tellurium powder was evaporated by heating at 600 °C and was condensed at a substrate temperature of 300–350 °C in the downstream of argon gas at a flow rate of 100 mL/min. The structure and chemical composition of the as-synthesized samples were examined by X-ray diffraction analysis, scanning electron microscopy, energy-dispersive X-rays microanalysis and micro-Raman spectroscopy. Scanning electron microscopy images and X-ray diffraction patterns showed that the as-synthesized Te had a tubular single-crystalline morphology with a hexagonal cross-section. The Te microtubes were typically 0.5–6 mm long, 30–70 μm in external diameter, and 5–20 μm thick. NO₂ gas-sensing properties of the Te microtubes at room temperature were also investigated. They showed a promising sensitivity and response towards tested gas.     

Selective adsorption of solvents in a multiscale device

We have incorporated microspheres, from 50 to 80 μm in diameter, of periodic mesoporous organosilica (inner surfaces up to 1,000 m²/g and pore sizes in the nanometre range) with two types of organic functionalities (benzene and ethane bridges, respectively) inside microstructured channels (each 200 μm wide and 100 μm deep) and, exemplarily, monitored by Raman microscopy (Raman spectroscopy through microscope optics) that the temperature characteristics of the adsorption–desorption equilibria of benzene and ethanol vary significantly with the type of organic functionality of the microspheres and the pore morphology. The integration of this class of nanostructured material into devices by means of microchannels is a promising novel approach to, among others, substance separation in analytics, micro process engineering, and micro chemistry.     

Tensile and high cycle fatigue test of Al–3% Ti thin films

This paper presents the results of tensile and high cycle fatigue tests with stress ratio R = 0.1 for an Al–3% Ti thin film of 1 μm thickness in atmospheric air at room temperature. Specimens with three different widths (50, 100, and 150 μm) were fabricated to study the width effects of each sample. Test results show that tensile and fatigue properties for the Al–3% Ti thin film with different widths are very close, and, thus, width effects were found to be minimal. The elastic moduli ranged from 80 to 82 GPa, and the tensile strengths ranged from 369 to 379 MPa. Fatigue strength coefficients of the specimens with 50, 100, and 150 μm width were 193, 181, and 164 MPa, respectively. In addition, fatigue strength exponents of the specimens with 50, 100, and 150 μm width were −0.023, −0.020, and −0.013, respectively. When present test results are compared with typical properties of bulk aluminium, the Al–3% Ti thin film is found to have longer life at the same stress, but it is more sensitive to the stress level.     

FPGA/DSP-based implementation of a high-performance multi-channel counter

A high-performance configurable multi-channel counter is presented. The system has been implemented on a small-size and low-cost Commercial-Off-The-Shelf (COTS) FPGA/DSP-based board, and features 64 input channels, a maximum counting rate of 45 MHz, and a minimum integration window (time resolution) of 24 μs with a 23 b counting depth. In particular, the time resolution depends on both the selected counting bit-depth and the number of acquisition channels: indeed, with a 8 b counting depth, the time resolution reaches the value of 8 μs if all the 64 input channels are enabled, whereas it lowers to 378 ns if only 2 channels are used. Thanks to its flexible architecture and performance, the system is suitable in highly demanding photon counting applications based on SPAD arrays, as well as in many other scientific experiments. Moreover, the collected counting results are both real-time processed and transmitted over a high-speed IEEE 1394 serial link. The same link is used to remotely set up and control the entire acquisition process, thus giving the system a even higher degree of flexibility. Finally, a theoretical model of general use which immediately provides the overall system performance is described. The model is then validated by the reported experimental results.     

A large-displacement 65Pb(Mg1/3Nb2/3)O3–35PbTiO3/Pt bimorph actuator prepared by screen printing

In this paper we present a novel approach to preparing large-displacement 65Pb(Mg_1/3Nb_2/3)O₃–35PbTiO₃/Pt (65/35 PMN–PT/Pt) bimorph actuators. These “substrate-free”, bending-type actuators were prepared by screen-printing the 65/35 PMN–PT and Pt thick-film pastes as the electrodes on alumina substrates. After this screen printing and the subsequent firing the 65/35 PMN–PT/Pt composites were peeled off from the substrates. Displacements of nearly 100 μm at 18 V were achieved for actuators with dimensions of 1.8 cm × 2.5 mm × 50 μm for the 65/35 PMN–PT layer. The normalized displacement (the displacement per unit length) was 40 μm/cm at 18 V. The experimental results together with a computation procedure were used to obtain the material parameters for a finite-element analysis of the 65/35 PMN–PT/Pt bimorph actuators.     

Silicon-micromachined gas chromatography system used to separateand detect ammonia and nitrogen dioxide. I. Design, fabrication, andintegration of the gas chromatography system

A miniature gas chromatography (GC) system was designed and developed using silicon micromachining and integrated circuit (IC) processing techniques. The micromachined gas chromatography (MMGC) system is composed of a miniature sample injector incorporating a 10-μm-long sample loop; a 0.9-m-long, rectangular-shaped (300 μm width and 10 μm height) capillary column coated with a 0.2-μm-thick copper phthalocyanine (CuPc) stationary phase, and a dual-detector scheme based upon a CuPc-coated chemiresistor and a 125-μm-diameter thermal conductivity detector (TCD) bead. Silicon micromachining was employed to fabricate the interface between the sample injector and the GC column, the GC column itself, and the dual-detector cavity. A novel processing technique was developed to sublime a homogeneous CuPc stationary-phase coating on the GC column walls. The complete MMGC system package is approximately 4 in, square and 100 mils (2.5 mm) thick, [96]     

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.     

Control of the microparticle position in the channel based on dielectrophoresis

We report here the control of the microparticles position within fluid flow based on its size by using dielectrophoresis (DEP) with a microelectrode array consisted of rectangular features with the different size of width and gap. 3 μm- and 10 μm-diameter particles were introduced into the channel with 300 μm height at 30 μl/min. An AC electric field (20 V peak–peak and 2 MHz) was then applied to microelectrode arrays to form dielectrophoretic fluid cage, resulting in a formation of flow paths with low electric fields on the arrays. The microparticles separately flow in line streams along the paths formed between the rectangular features of the arrays, the 3 μm-diameter particles mainly flow through the narrow path and 10 μm-diameter particles through the wide path. These results indicated that positions of two types of microparticles in the fluidic channel were easily separated and controlled using the n-DEP.     

Improved field emission characteristics of screen-printed CNT-FED cathode by interfusing Fe/Ni nano-grains

Carbon nanotube (CNT) cathode with and without interfusing nano-metal particles was prepared using screen-printing technology. For the good electric conductivity of metal, the turn-on electric field of the Fe/Ni and CNT composite film (Fe/CNT film) decreases to 1.42 V/μm comparing with the usual CNT film of 2.45 V/μm, and the emission current increases from 60 μA to 440 μA at an applied electric field of 2.3 V/μm. Furthermore, the field enhancement factor β increases from 1721 to 3242. By characterizing the prepared samples via X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM), it is found that carbide Fe₃C phase is formed in Fe/CNT film, and the metal particles are filled in the interspaces of CNTs. It is evaluated that benefiting from good electrical conductivity and chemical inertness of metal carbide, Fe/CNT film achieves high emission characteristics and emission uniformity.     

Study of symmetric microstructures for CMOS multilayer residual stress

This study presents a fabrication-based approach to improve the curl-up effect in complementary metal oxide semiconductor (CMOS) multilayer large-area planar structures. Control of the residual stress of CMOS multilayer microstructures is necessary for development of microelectromechanical systems (MEMS) sensors such as accelerometers and micromirrors. In this work, 3D symmetric geometry can be used to overcome effectively the residual stresses in CMOS multilayer microstructures. To demonstrate this concept, a symmetric multilayer flat-plane is fabricated and release-etched using an isotropic plasma etching process. The isotropic etch characteristics and lateral undercut can be controlled using a chamber pressure of 0.47 ± 0.2 Torr. A flat-plane structure with an area of 500 μm × 500 μm is fabricated using multilayer materials, including four metal and three silicon dioxide layers. Based on this approach, the measured results show the residual stress effect can be minimized in CMOS multilayer microstructures, and furthermore the curl-up effect of flat-plane is less than 2 μm across the 500 μm × 500 μm area.     

Novel tunable laser sources with 1.5-μm and 1.57-μm cascaded DFB reflectors for in situ gas monitoring applications

Novel tunable lasers based on 1.5-μm and 1.57-μm cascaded distributed-feedback reflectors are realized for real-time monitoring of H₂O and CO gas mixtures immediately in multi-gas sensor systems. With simple fabrication procedures, the new design allows the realization of a widely tunable laser source that can cover the H₂O and CO absorption wavelength bands. With the temperature tuning of 0.1 nm/°C and current tuning of 0.014 nm/mA, the laser can be tuned to cover over 3 nm wavelength range in each wavelength band. Experiments verify that the lasers can have more than 38 dB SMSR over the tuning range. The characteristics of high power, excellent spectral purity, and simple wavelength switching control can simplify the analysis procedures of gas sensing and thus reduce the cost. By direct absorption method, the tunable laser has been successfully adopted in a diode laser sensor system for monitoring of water vapor concentration near 1.5 μm and carbon monoxide near 1.57 μm. Less than 15% error in the line strength is observed between the measured data and HITRAN database.     

MEMS半填充气相色谱柱研究

采用MEMS技术设计了一种微型半填充气相色谱柱,运用深反应离子刻蚀(DRIE)技术,对器件刻蚀深250μm,其微型色谱柱总长度为1m,宽度为160μm,槽道内部填充20μm×20μm微型柱。采用静态涂覆法对色谱柱涂覆SE—54固定相。通过理论模拟分析柱结构,得出微型半填充色谱柱具有高分离效率能力。在对酯类化合物分离测试中,选取了含酯类的化学战剂模拟剂和几种酯类食品添加剂,分别对其进行分离,所有组分在75s内被完全分离。实现了微型半填充色谱柱快速并具有高分离率。     

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.     

One-step fabrication of a polyaniline nanofiber vapor sensor

A single-step, bottom-up technique has been used to fabricate sensors, based on conducting polymer nanofibers. A small amount of an aqueous solution containing aniline, a dopant, and an oxidant was placed on an interdigitated electrode array. Ultraviolet (UV)-irradiation of the solutions affected polymerization, yielding a highly porous film of polyaniline nanofibers with a mean diameter of around 100 nm and a length on the order of 1 μm. Solutions that were not irradiated formed bulk-like polyaniline (PANI) films. Nanofibers and bulk polyaniline sensors were exposed to chloroform, a weak proton donor; to toluene, a vapor that causes polymer swelling; and to triethylamine, which alters the doping level. Because of their higher surface areas, the response times of the fiber sensors were about a factor of 2 faster, with the current variations up to 4 times larger than those of the bulk polyaniline sensors. These results suggest methods for the advancement of simple and environment-friendly production of organic nanofiber-based sensors and electronic devices.     

Flexible humidity sensor in a sandwich configuration with a hydrophilic porous membrane

We constructed a wearable and flexible humidity sensor (thickness: 80 μm) in a sandwich configuration, with a hydrophilic poly-tetrafluoroethylene membrane placed between two gold deposited layers, using soft-MEMS techniques. The device was used to measure humidity level, via its electrical conductivity, using a multi-frequency LCR-meter at frequencies ranging from 100 Hz to 100 kHz. The device was calibrated at 100 Hz against moist air over the range of 30–85% RH, which includes normal humidity levels in the atmosphere and physiological air such as breath and evaporating sweat. The response sensitivity of the humidity device was extremely high, even for recovery to dry air; for example response time was less than 1 s for a conductivity shift between humid air of 80% RH and dry air of −60 °C dew point. The sensor performance was reproducible over multiple measurements, with a coefficient of variation of 1.77% (n = 5). The sensor was appropriate for physiological applications, and was successfully used in two non-invasive approaches: to monitor breath air at the mouth, and to measure sweat moisture from the nostrils.     

Characterization of Young's modulus and residual stress gradient of MetalMUMPs electroplated nickel film

Metal multi-user MEMS processes (MetalMUMPs) offered by MEMSCAP provide a 20 μm thick electroplated nickel film suitable for constructing micro RF tunable capacitors, RF inductors, relays, switches, etc. Currently the Young's modulus and the residual stress gradient of the MetalMUMPs nickel film have not been characterized. In this paper the resonance method is used to characterize the Young's modulus of the MetalMUMPs nickel film. The characterization results show that the nickel film has a Young's modulus of 155–164 GPa with an average of 159 GPa. A stress gradient induced free beam mechanism is proposed in this paper to characterize the residual stress gradient in the MetalMUMPs nickel film. Characterization results show that the residual stress in the electroplated nickel film has a gradient across the film thickness of −5.49 MPa/μm to −4.30 MPa/μm with the average of −4.72 MPa/μm. The residual stress change from the bottom surface to the top surface of the nickel film is −97.7 MPa. The Young's modulus and residual stress gradient of the MetalMUMPs nickel film obtained in this paper provide MetalMUMPs users an important reference for designing, optimizing and analyzing suspended nickel structures. The stress gradient induced free beam mechanism proposed in this paper provides a method of characterizing negative residual stress gradient in thin films without using trenches or through-wafer holes.     

Dynamic evolvement and formation of refractive microlenses self-assembled from evaporative polyurethane droplets

This paper proposed a method of microfabrication for the formation of hemispherical refractive microlenses by depositing a colloid evaporative droplet onto hydrophobic surfaces. The microdroplets made of polyurethane (PU) were self-driven by surface tension to evolve their three-dimensional (3D) shapes on the surface-treated substrate. The substrates were coated with low surface energy material (Teflon) to de-pin the fluids obeying classic Young–Laplace equation until drying. Array and size-variation experiments, corresponding to different placement and droplet volume, were performed for the shaping process in which the polymers of the drops were self-assembled to be hemispherical utilizing general principle of minimal surface energy. Using the hydrophobic surfaces, plano-convex shapes with spherical curvature were fabricated with micrometer dimensions (base radius between 70 and 1016 μm). The formed structures were observed to form themselves hemispherically by the de-wetting (de-pinning) process during most of evaporation. Moreover, the gravity flatting effect was further found for the larger drop (radius = 1016 μm) when compared to that of smaller one (radius = 118 μm). In the cases, both the modeling calculations and experimental results were performed and compared to illustrate the similar geometries with the contact angle (70°) using dimensionless analysis. In addition, one interesting and significant finding, based on close morphological inspection of the SEM picture, showed that the resulting elongational polymer chains (width 200 nm) stretched (extension 5 μm) on the surface nearby the corner of the contact area, indicating a shear stress occurrence. Compared to those previous methods operated on (soft-) photolithographic techniques, this present one could rapidly predict and microfabricate the hemispherical formation in terms of the radius, height, and contact angle. It is also potentially appropriate for smaller and complex placement by using drop-on-demand (DOD) nozzle arrays for mass-production process.     

Controlled synthesis and gas-sensing properties of hollow sea urchin-like α-Fe2O3 nanostructures and α-Fe2O3 nanocubes

Hollow sea urchin-like α-Fe₂O₃ nanostructures were successfully synthesized by a hydrothermal approach using FeCl₃ and Na₂SO₄ as raw materials, and subsequent annealing in air at 600 °C for 2 h. The hollow sea urchin-like α-Fe₂O₃ nanostructures with the diameters of 2–4.5 μm consist of well-aligned α-Fe₂O₃ nanorods with an average length of about 1 μm growing radially from the centers of the nanostructures, have a hollow interior with a diameter of about 2 μm. α-Fe₂O₃ nanocubes with a diameter of 700–900 nm were directly obtained by a hydrothermal reaction of FeCl₃ at 140 °C for 12 h. The response S_r (S_r = R_a/R_g) of the hollow sea urchin-like α-Fe₂O₃ nanostructures reached 2.4, 7.5, 5.9, 14.0 and 7.5 to 56 ppm ammonia, 32 ppm formaldehyde, 18 ppm triethylamine, 34 ppm acetone, and 42 ppm ethanol, respectively, which was excess twice that of the α-Fe₂O₃ nanocubes and the nanoparticle aggregations. Our results demonstrated that the hollow sea urchin-like α-Fe₂O₃ nanostructures were very promising for gas sensors for the detection of flammable and/or toxic gases with good-sensing characteristics.