A sensitive magnetic field sensor using BPSCCO thick film

A highly sensitive magnetic sensor operating at liquid nitrogen temperature and based on BPSCCO screen-printed thick film, is reported. The sensor resistance for an applied magnetic field of 100 ×10⁻⁴ T (100 gauss) exhibits an increase by 360% of its value in zero field at 77.4 K. The performance of the sensor in presence of magnetic field, the hysteretic features and the effect of thermal cycling, has been discussed.     

Fabrication of a near-infrared sensor using a polyaniline conducting polymer thin film

Near infrared (NIR) photo-responsive polyaniline-based conducting thin films are developed for sensor application. Upon NIR illumination (2.43 W/cm²), the electrical conductance of the polyaniline thin films was enhanced 5.9% and the response time was 20 s. NIR sensing performance of polyaniline conducting polymer thin film is comparable with that of bolometric carbon nanotube (CNT) network devices with the merits of polymers over CNTs such as processability, productivity and economy.     

A flexible and highly sensitive strain-gauge sensor using reversible interlocking of nanofibres

Flexible skin-attachable strain-gauge sensors are an essential component in the development of artificial systems that can mimic the complex characteristics of the human skin. In general, such sensors contain a number of circuits or complex layered matrix arrays. Here, we present a simple architecture for a flexible and highly sensitive strain sensor that enables the detection of pressure, shear and torsion. The device is based on two interlocked arrays of high-aspect-ratio Pt-coated polymeric nanofibres that are supported on thin polydimethylsiloxane layers. When different sensing stimuli are applied, the degree of interconnection and the electrical resistance of the sensor changes in a reversible, directional manner with specific, discernible strain-gauge factors. The sensor response is highly repeatable and reproducible up to 10,000 cycles with excellent on/off switching behaviour. We show that the sensor can be used to monitor signals ranging from human heartbeats to the impact of a bouncing water droplet on a superhydrophobic surface.     

Nondestructive readout in thick magnetic film devices

To study the nondestructive readout properties of thick magnetic film devices, sense voltages are computed for triangular interrogate word pulses. Eddy currents are assumed to be the exclusive damping mechanism. For a given pulse rise time one can obtain a maximum signal peak value with a given optimum film thickness, and the read signal of an optimized film can be approximated by simple analytical functions. In an attempt to describe the nondestructive readout stability, a relation is developed between pulse widths, angle of rotation of the magnetization, and reversibility threshold.     

A highly sensitive thin-film capacitive pressure sensor

Translated from Izmeritel'naya Tekhnika, No. 12, pp. 47–48, December, 1991.     

Temperature sensor using an optical fiber coupler with a thin film

A temperature sensor was demonstrated and fabricated by coating thermosensitive film around a fiber coupler. Based on the multicladding equivalent method, the coated fiber coupler was simplified to a conventional one. With the high thermo-optical coefficient of organic-inorganic solgel material, a good sensing result was achieved. The range of temperature measured is from -50 to 100 degrees C. The resonant wavelength has a shift of about 25 nm. A sensitivity of 0.17 nm/degrees C is achieved. With the advantages of having a simple structure and being unaffected by the instability of the light source, the proposed fiber coupler temperature sensor will find wide applications.     

用激光微细熔覆法直写电阻浆料制备厚膜电阻

介绍了一种激光微细熔覆法直写电阻浆料制备厚膜电阻的新技术,并利用该技术在陶瓷基板上制备出厚膜电阻。文章中展示了部分实验结果．并分析了其附着机理。由于激光微细熔覆直写电阻技术具有无需掩模、图形由计算机控制、分辨率高、柔性化制造程度高等优点,显示谊技术在电子工业中将具有广阔的应用前景。     

Selective detection of hydrogen sulfide using copper oxide-doped tin oxide based thick film sensor array

In this work, copper oxide-doped (1, 3 and 5 wt%) tin oxide powders have been synthesised by sol–gel method and thick film sensor array has been developed by screen printing technique for the detection of H₂S gas. Powder X-ray diffraction pattern shows that the tin oxide (SnO₂) doped with 3 wt% copper oxide (CuO) has smaller crystallite size in comparison to 0, 1 and 5 wt% CuO-doped SnO₂. Furthermore, field emission scanning electron microscopy manifests the formation of porous film consisting of loosely interconnected small crystallites. The effect of various amounts of CuO dopant has been studied on the sensing properties of sensor array with respect to hydrogen sulfide (H₂S) gas. It is found that the SnO₂ doped with 3 wt% CuO is extremely sensitive (82%) to H₂S gas at 150 °C, while it is almost insensitive to many other gases, i.e., hydrogen (H₂), carbon monoxide (CO), sulphur dioxide (SO₂) and liquefied petroleum gas (LPG). Moreover, at low concentration of gas, it shows fast recovery as compared to response time. Such high performance of 3 wt% CuO-doped SnO₂ thick film sensor is probably due to the diminishing of the p–n junction and the smallest crystallite size (11 nm) along with porous structure.     

Fabrication and modeling of high-frequency PZT composite thick film membrane resonators

High-frequency, thickness mode resonators were fabricated using a 7 microm piezoelectric transducer (PZT) thick film that was produced using a modified composite ceramic sol-gel process. Initial studies dealt with the integration of the PZT thick film onto the substrate. Zirconium oxide (ZrO2) was selected as a diffusion barrier layer and gave good results when used in conjunction with silicon oxide (SiO2) as an etch stop layer. Using these conditions, devices were produced and the acoustic properties measured and modeled. The resonators showed a resonant frequency of about 200 MHz, an effective electromechanical coupling coefficient of 0.34, and a Q factor of 22. Modeling was based on a Mason-type model that gave good agreement between the experimental data and the simulations. The latter showed, for the PZT thick film, an electromechanical coupling coefficient of 0.35, a stiffness of 8.65 x 10(10) N x m(-2) and an e33,f piezoelectric coefficient of 9 C x m(-2).     

Fabrication of copper nanoparticles in a thick polyimide film cured by rapid thermal annealing

We investigated the imidization of a polyimide (PI) and the formation of Cu nanoparticles in a PI film by curinga precursor of PI (polyamic acid (PAA) dissolved in n-methyl-2-pyrrolidinone) in a reducing atmosphere in the rapid thermal annealing (RTA) system. A Cu film was deposited onto the SiO2/Si substrate, and the PAA was spin-coated onto the Cu film. After the PAA reacted with the Cu film, soft-baking was performed to evaporate the solvent. Finally, the PAA was imidized to PI at 450 degrees C by curing in a reducing atmosphere with the RTA. Fourier transform infrared spectroscopy showed that the PAA was successfully imidized by the RTA. X-ray diffraction patterns revealed that Cu nanoparticles formed by RTA curing at 450 degrees C for 5 minutes in a reducing atmosphere, and transmission electron microscopy showed that Cu nanoparticles about 6.5 nm in size were uniformly dispersed in the PI film. Curing by RTA is an attractive method because it takes only a few minutes.     

基于溶胶-凝胶的两种旋涂方法制备PZT厚膜

采用溶胶-凝胶法,研究了两种在Au/Cr/SiO2/Si基底上沉积PZT(Pb(Zr0.52Ti0.48)O3)厚膜的方法.把与PZT澄清溶胶成分相同的PZT纳米粉混入澄清PZT溶胶,然后超声混合形成PZT浆料,PZT纳米粉的粒径为50～100nm.XRD分析表明两种方法得到的PZT厚膜都获得了单相钙钛矿结构.SEM结果显示两种厚膜厚度大约4μm,第一种旋涂方法制得的PZT厚膜表面粗糙,第二种旋涂方法制得的厚膜表面致密,无裂纹.在1 kHz的测试频率下,第一种和第二种厚膜的矫顽场分别为30 kV/cm和50 kV/cm,饱和极化分别为45 μC/cm2和54 μC/cm2,剩余极化分别为25μC/cm2 and 30μC/cm2.第二种厚膜有较高的直流耐压性能,在300 kV/cm的电场下,仍然保持较好的铁电性能.因而,第二种旋涂方法能够改善PZT厚膜的表面形貌和铁电性能.     

Fabrication of a highly sensitive aptasensor for potassium with a nicking endonuclease-assisted signal amplification strategy

A novel strategy to fabricate an aptasensor for potassium with high sensitivity and selectivity by using nicking endonuclease is proposed in this work. A nicking endonuclease (Nt.CviPII), which may recognize specific nucleotide sequences in double-stranded DNA formed by a potassium-binding aptamer and a linker DNA but cleave only the linker strand, may transfer and amplify the quantitative information of the potassium detection to that of the linker DNA through elaborate strand-scission cycles. Since the technique for gene assay is much more mature, the linker DNA can thereby be detected by a number of available methods. Here, taking advantage of a simple and fast gold nanoparticles-based sensing technique, we are able to assay the linker and consequently potassium ion simply by UV-vis spectroanalysis and even with the naked eye. Results show that a 2 μL sample containing 0.1 mM of potassium is enough to induce distinct color appearance of the nanoparticles, and the potassium ion can be easily distinguished from many other ions. The strategy proposed in this work shows some unique advantages over some traditional methods and may be further developed for the detection of some other chemicals in the future.     

A nitrite sensor based on a highly sensitive nitrite reductase mediator-coupled amperometric detection

Highly sensitive nitrite sensors have been developed for the first time based on mediator-modified electrodes. Tetraheme cytochrome c nitrite reductase from Sulfurospirillum deleyianum and cytochrome cd(1) nitrite reductase from Paracoccus denitrificans are able to accept electrons from artificial electron donors, which simultaneously act as electron mediators between the enzyme and an amperometric electrode. In addition to methyl viologen, redox-active compounds such as phenazines (phenosafranin, safranin T, N-methylphenazinium, 1-methoxy-N-methylphenazinium) and triarylmethane redox dyes (bromphenol blue and red) were selected from a range of redox compounds exhibiting the most efficient performance for nitrite detection. After precipitation, the electron mediators were incorporated in a graphite electrode material. Enzyme immobilization is performed by entrapment in a poly(carbamoyl sulfonate) (PCS) hydrogel. Diffusion coefficients and apparent heterogeneous rate constants of the mediators as well as homogeneous rate constants of nitrite sensors were determined by chronoamperometry and cyclic voltammetry. The phenosafranin-modified electrode layered with the PCS hydrogel immobilization of tetraheme cytochrome c nitrite reductase yielded linear current responses up to 250 μM nitrite with a sensitivity of 446.5 mA M(-)(1) cm(-)(2). The detection limit of the enzymatic nitrite sensor was found to be 1 μM nitrite.     

Novel gold-capped nanopillars imprinted on a polymer film for highly sensitive plasmonic biosensing

Herein, a nanoporous alumina was fabricated to use as a mold in transforming nanopillar structures onto a thin film polymer by thermal nanoimprint lithography (NIL). The size of the pores was successfully controlled by varying the applied voltages and etching time. These nanoporous structures were transferred to the Cyclo-olefin polymer (COP) film surface from the porous mold by a thermal nanoimprinting process. A plasmonic substrate was fabricated by sputtering a thin layer of gold onto this nanopillar polymer structure, and the refractive index response in a variety of media was evaluated. Finally, the biosensing capacity of this novel plasmonic substrate was verified by analysis of Human immunoglobulin and achieved a minimum detection limit of 1.0 ng/mL. With the advantages of mass production with consistent reproducibility stemming from the nanoimprint fabrication process, our gold-capped polymeric pillars are ready for the transition from academic interest into commercialization systems for practical use in diagnostic applications.     

Two-dimensional array transducers using thick film connection technology

A connection technique for two-dimensional array ultrasound transducers developed by combining a conductive lambda/4 mismatching layer with a multi-layer ceramic (MLC) connector using thick-film microelectronic technology is described. The connector consists of 20 thick films of alumina and screen printed metallization with customized interconnections between the layers called vias. Ten ground layers are interleaved between ten signal layers to reduce elecrical crosstalk. A lambda/4 mismatching layer of conductive epoxy is bonded between each PZT element and the silver metal pad of the MLC connector to provide an effective low impedance backing. In the current configuration, a 16x16 transducer array, 0.6 mm element spacing, is expanded to a 16x16 grid of connector pins at a standard spacing of 2.5 mm. Vector impedance, sensitivity, bandwidth, interelement uniformity, and crosstalk are all in good agreement with arrays of conventional fabrication. However, an array with MLC connector can be fabricated more quickly independent of the number of elements.     

Fabrication and characterization of thermoelectric thick film prepared from p-type bismuth telluride nanopowders

In this study, bismuth telluride (Bi2Te3)-based nanopowders with particle size ranging from 100 to 300 nm are prepared by high-energy ball milling. Then, the prepared nanopowders are homogeneously mixed with organic binders to form a paste; this paste is used as the raw material to prepare thick-film thermoelectric modules. The thick film prepared by screen printing followed by hot pressing of p-type pastes show reproducible thermoelectric properties, exhibiting an electrical resistivity of 2.0 m Omega cm and a Seebeck coefficient of 298 muVK-1. The prepared p-type Bi2Te3 thick film has a high power factor because its Seebeck coefficient is significantly higher than that of Bi2Te3 based-bulk materials. These results indicate that a thick film prepared from bismuth telluride nanopowders has potential for use as high-performance thermoelectric modules in practical applications such as power generation and cooling system in electronic devices.     

采用简便方法制备快速响应的聚吡咯复合薄膜传感器

在叉指碳电极上采用原位制备的方法构筑了聚吡咯复合薄膜气敏传感器,对其在三甲基胺气氛中的电响应性能进行了研究.结果表明,对5.14×10-7mol/mL的三甲基胺,其敏感性可达3～6个数量级的变化, 远高于同等实验条件下酞菁、卟啉等及其氟代衍生物的气敏性.该薄膜传感器具有好的重现性和选择性,在室温下可用氮气完全恢复.     

Surface plasmon resonance-based highly sensitive optical touch sensor with a hybrid noise rejection scheme

A surface plasmon resonance (SPR)-based optical touch sensor structure is proposed that provides high switch sensitivity and requires a weak activating force. Our proposed SPR-based optical touch sensor is arranged in a compact Kretschmann-Raether configuration in which the prism acting as our sensor head is coated with a metal nanofilm. Our optical-based noise rejection scheme relies on wavelength filtering, spatial filtering, and high reflectivity of the metal nanofilm, whereas our electrical-based noise reduction is obtained by means of an electrical signal filtering process. In our experimental proof of concept, a visible laser diode at a 655 nm centered wavelength and a prism made from BK7 with a 50 nm thick gold layer on the touching surface are used, showing a 7.85 dB optical contrast ratio for the first touch. An estimated weak mechanical force of <0.1 N is also observed that sufficiently activates the desired electrical load. It is tested for 51 operations without sensor malfunction under typical and very high illumination of 342 and 3000 lx, respectively. In this case, a measured average optical contrast of 0.80 dB is obtained with a +/-0.47 dB fluctuation, implying that the refractive index change in a small 3.2% of the overall active area is enough for our SPR-based optical touch sensor to function properly. Increasing optical contrast in our SPR-based optical touch sensor can be accomplished by using a higher polarization-extinction ratio and a narrower-bandwidth optical beam. A controlled environment and gold-coated surface using the thin-film sputtering technique can help improve the reliability and the durability of our SPR-based optical touch sensor. Other key features include ease of implementation, prevention of a light beam becoming incident on the user, and the ability to accept both strong and weak activating forces.     

Lead-free thick film resistors: an explorative investigation

Pastes prepared with seven lead-free glass particles were screen-printed and fired on 96%-Al₂O₃ substrates. The fired films were studied in terms of sintering, devitrification, crack propagation and bleeding. The most promising glass compositions were selected for the preparation of RuO₂-based thick film resistors (TFRs), on pre-fired PtAu- or PdAg-based terminations; electrical properties of the resistors (sheet resistance vs. RuO₂ volume fraction, temperature coefficient of resistance and size effects) were investigated. The study evidenced a myriad of complex phenomena, including devitrification, relevant bleeding of the glass on alumina substrates, anomalous distribution of conductive grains in the glassy matrix, phase separations. Contrarily to what happens in traditional systems, it is difficult to get a wide resistance range simply by changing the fraction of the conductive phase. These results emphasize the criticality in the choice of the glass composition for the preparation of lead-free thick film resistors.