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Sensors Journal, IEEE

Issue 4 • Date Aug 2002

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Displaying Results 1 - 15 of 15
  • A direct digital synthesis system for acoustic wave sensors

    Page(s): 288 - 293
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (414 KB) |  | HTML iconHTML  

    Current designs for acoustic wave sensor system electronics are typically based on surface acoustic wave (SAW) oscillators, phase detectors, or phase-locked loops to measure changes in SAW velocity. The advantage of oscillators is a high resolution frequency output, as compared to phase detection systems which are more stable and can more easily provide amplitude information. Phase-locked loops (PLL) offer advantages of both the oscillator and phase detection systems but have the disadvantages of a fixed frequency range and the need for frequency counting circuitry. The objectives of this work were to study the performance of a direct digital synthesis (DDS) based PLL system with the advantages of a programmable frequency range, elimination of the need for frequency counting circuitry, and tolerance of large SAW sensor insertion losses. The DDS system tested had a resolution of 4 Hz and a range of 80 to 120 MHz in SAW humidity and temperature sensing applications indicating that the DDS based PLL is a practical electronic system for SAW sensors. View full abstract»

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  • Design and fabrication of a novel crystal SiGeC far infrared sensor with wavelength 8-14 micrometer

    Page(s): 360 - 365
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (639 KB) |  | HTML iconHTML  

    In this paper, we report the design, fabrication, and performance of a novel crystal SiGeC infrared sensor with wavelength 8-14 μm by bulk micromachining technology for portable far infrared ray (FIR) in rehabilitation system application. The working principle of the sensor is based on the change of thermistor's resistance under the irradiation FIR light. The thermistor in the IR detector is made of Si0.68Ge0.31C0.01 thin films for its large activation energy of 0.21 ev and the temperature coefficient (TCR) of -2.74%, respectively. Finite element method package ANSYS has been employed for analyze of the thermal isolation and stress distribution in the IR detector. The dimension of the microbridge fabricated by anisotropic wet etching is 2000 × 2000 × 25 μm3. The developed FIR sensor exhibits the thermal conductance of 1.85 × 10-1 WK-1 and the heat capacity as 7.4 × 10-7 JK-1 under air ambient at room temperature. The responsivity is 523 VW-1 in the waveband 8-14 μm with nickel absorber under a bias voltage 1.5 V. View full abstract»

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  • Theoretical and experimental mass-sensitivity analysis of polymer-coated SAW and STW resonators for gas sensing applications

    Page(s): 307 - 313
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (383 KB) |  | HTML iconHTML  

    Polymer-coated surface transverse waves (STW) resonators have recently been successfully studied for organic gas sensing applications. The first results indicate increased absolute and even relative sensitivity as compared to similar resonators with surface acoustic waves (SAW). However, the gain in sensitivity is accompanied by the adverse effect of an increased attenuation and the advantage frame is difficult to establish quantitatively. In this paper, a new set of experimental samples with Parylene C-coated quartz substrates are studied. The samples are matched in frequency and wavelength. The results are compared and the obtained features explained using available theoretical algorithms for analyzing layered SAW and Love configurations, and a recently developed STW algorithm. The approximate limits of advantageous applicability of the STW resonator gas sensors are discussed. View full abstract»

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  • Working mechanism of an ethanol filter for selective high-temperature methane gas sensors

    Page(s): 354 - 359
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (631 KB) |  | HTML iconHTML  

    Semiconducting metal-oxide gas sensors are generally nonselective, which limits their use as natural gas detectors in domestic environments when ethanol is present in high background concentrations. Using a thin-film Ga2O3 sensor with a thick-film catalyst filter of Ga2O3 and an operating temperature of 800°C, the cross-sensitivity to ethanol is strongly reduced and the sensor response to methane is enhanced. Detection of natural gas is made reliable and the rate of false alarms is reduced. Oxidation of ethanol and methane over gallium oxide is studied using GC product analysis. These measurements of catalytic activity help to clarify the reactions involved in the filtering mechanism. Elimination of the ethanol cross-sensitivity is attributed to the thermal combustion of ethanol as it passes over the hot filter. The sensor response to methane is enhanced as methane is activated by the active catalytic Ga2O3 thick-film. View full abstract»

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  • Piezoresistive sensors on plastic substrates using doped microcrystalline silicon

    Page(s): 336 - 341
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (393 KB) |  | HTML iconHTML  

    The piezoresistive behavior of n-type and p-type microcrystalline silicon films deposited on polyethylene terephthalate plastic substrates by hot-wire, and radio-frequency, plasma-enhanced chemical vapor deposition, at a substrate temperature of 100°C, is studied. The crystallite size was 10 nm for hot-wire films and 6.5 nm for radio-frequency films and the crystalline fraction varied between 50 to 80%. A four-point bending jig allowed the application of positive and negative strains in the films. Repeated measurements of the relative changes in the resistance of the samples during the strained condition showed reversible behavior, with p-type microcrystal line films having positive gauge factor in the range from 25 to 30 and n-type μc-Si:H films having negative values of gauge factor from -40 to -10. The induced strain in the films varied in the interval between 0 and ±0.3%. The films were used in the as-deposited size (50 mm × 10 mm) as sensors, utilizing their piezoresistive properties to map the contour of an acrylic model with the shape of an Archimedes' spiral. Micron-sized devices were patterned and used to map the shape of the same model. View full abstract»

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  • Eliminating contaminants with a piezoelectric transducer in the design of low-cost smart kitchen range hoods

    Page(s): 314 - 321
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (428 KB) |  | HTML iconHTML  

    The exhaust fan in a kitchen range hood is required to generate an adequate suction flow to eliminate the especially high levels of cooking contaminants in Chinese kitchens. Reducing the range hood noise and its power consumption down to an acceptable level is an important issue. In this paper, a low-cost smart range hood system is proposed. A sensitive piezoelectric transducer senses the level of the cooking contaminants and the output regulates the speed of the exhaust fan. Under several cooking conditions, the speed of the exhaust fan, its noise level, and the power consumption were examined. Results showed that the noise level and power consumption can be markedly reduced with the transducer and the control circuit. The average noise level is 65.66 dB and the power consumption 123.97 W, both lower than those of the conventional range hood system, which are 72 dB and 216 W, respectively. View full abstract»

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  • The influence of the electrode size on the electrical response of a potentiometric gas sensor to the action of oxygen

    Page(s): 349 - 353
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB) |  | HTML iconHTML  

    As a part of our research on new gas sensors, an original potentiometric gas sensor was developed. This gas sensor is made of a solid electrolyte (beta alumina) associated with two different metallic electrodes (gold and platinum) located in the same gas mixture. Tests performed under oxygen pressure show that the potential difference read between the electrodes depends on the experimental conditions, oxygen pressure, and temperature, but also on the electrodes surface area ratio. Then, we studied the electrical responses of devices composed of electrodes of the same nature (gold or platinum) but of different size. These electrode size influences are analyzed in terms of different capacitive effects occurring at the electrode-solid electrolyte interface. If we consider that the adsorption of oxygen species is responsible for the electrostatic potential, the proposed model is able to account for the experimental results. It is then possible to explain and to better understand the importance of the electrodes on the electrical response of such a device. View full abstract»

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  • A comparison of layered metal-semiconductor optical position sensitive detectors

    Page(s): 372 - 376
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (496 KB)  

    Position sensitive detectors (PSDs), utilize the lateral photovoltaic effect to produce an electrical output that varies linearly with the position of a light spot incident on a semiconductor junction. In fabricating PSDs, two key elements are optimized: the sensitivity, (mV/increment) and the linearity of the electrical output. Sensitivity is optimized by varying properties of the junction layers, particularly resistivity, while linearity is determined primarily by junction uniformity. In this paper, Schottky barrier PSDs are fabricated from the electron-beam deposition of titanium, tantalum and aluminum on to p-type silicon substrates. Devices were tested under focused broad-band white light and the sensitivities and linearities, for the different metals with varying thicknesses, are compared. Overall, Ti and Ta PSDs performed very well over a large range of film thicknesses, 50 to 2000 Å, while Al was more limited. The best of all the devices fabricated so far was one with 380 Å film of Ti, giving a sensitivity, or output, of 10.62 mV/mm while maintaining excellent linearity and spatial resolution. The best aluminum devices were obtained with a 100 Å film and resulted in a sensitivity of 8.84 mV/mm and a spatial resolution of better than 10 μm. Of the tantalum devices, film thicknesses of around 200 Å produced the highest sensitivities. View full abstract»

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  • Molecular recognition for electronic noses using surface acoustic wave immunoassay sensors

    Page(s): 294 - 300
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (635 KB) |  | HTML iconHTML  

    In this paper, we present the results of a series of experiments on vapor phase surface acoustic wave (SAW) sensors using a layer of antibodies as the chemically sensitive film. For these experiments, the sensor component was a ST-quartz resonator with a center frequency of approximately 250 MHz. Anti-FITC antibodies were attached to the electrodes on the device surface via a protein-A crosslinker. SAW resonator devices with various coatings were mounted in TO-8 packages, inserted into a sensor head module and subjected to various fluorescent analyte gases. Numerous controls were performed including the use of coated and uncoated devices along with devices coated with antibodies which were not specific for the target analyte. The SAW immunosensor response was monitored and a baseline frequency shift was observed when the analyte being presented was the antigen for the immobilized antibody. To provide an independent measure of antibody/antigen binding, the devices were removed from the sensor head, washed with a buffer solution to remove any unbound analyte, and then inspected using a confocal laser scanning microscope (CLSM). Since all the analytes being used in these experiments were fluorescent, this afforded us the opportunity to visualize the attachment of the analyte to the antibody film. Given the high resolution of the CLSM, we were able to identify the location of the attachment of the fluorescent analytes relative to the 1.5 μm wide electrodes of the SAW device. We believe that these experiments demonstrate that we have achieved real time molecular recognition of these small molecules in the vapor phase. View full abstract»

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  • Carbon monoxide detector fabricated on the basis of a tin oxide novel doping method

    Page(s): 322 - 328
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (456 KB) |  | HTML iconHTML  

    Toxic gas detection is a common issue of interest in domestic as well as industrial environments. There are, in fact, accurate methods to measure gas concentrations (Fourier transform infrared, gas chromatographs, or mass spectrometers) but they are too expensive and require skilled operators. Therefore, these complex detection systems are not useful for many applications, such as hazardous gas level detection in domestic appliances. In this paper, investigations lead to the fabrication of a micromachined tin oxide device for carbon monoxide detection in domestic environments. Relevant parameters that influence gas detection are analyzed and thus the device fabrication process defined by means of microtechnologies. Throughout the material optimization for CO detection, three different additive adding methods by dc sputtering PVD technique are studied and compared for two additives: Pt and Pd. View full abstract»

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  • Ion-sensitive field-effect transistors in standard CMOS fabricated by post processing

    Page(s): 279 - 287
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (543 KB) |  | HTML iconHTML  

    Highly integrated ion-sensitive field-effect transistor (ISFET) microsystems require the monolithic implementation of ISFETs, CMOS electronics, and additional sensors on the same chip. This paper presents new ISFETs in standard CMOS, fabricated by post-processing of a standard CMOS VLSI chip. Unlike CMOS compatible ISFETs fabricated in a dedicated process, the new sensors are directly combined with state-of-the-art CMOS electronics and are subject to continuous technology upgrading. The ISFETs presented include an intermediate gate formed by one or more conducting layers placed between the gate oxide and the sensing layer. The combination of the highly isolating gate oxide of the MOS with a leaky or conducting sensing layer allows the use of low temperature materials that do not damage the CMOS chip. The operation of ISFETs with an intermediate gate and sensing layers fabricated at low temperature is modeled. ISFETs with a linear pH response and drift as low as 0.3 mV/h are reported. View full abstract»

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  • Development of a protected gas sensor for exhaust automotive applications

    Page(s): 342 - 348
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (609 KB) |  | HTML iconHTML  

    A β-alumina-based gas sensor for automotive exhaust application (hydrocarbon, CO, NO2 detection in 10-1000 ppm concentration range) has been developed by thick film technology (screen-printing) in the frame of a European project. The sensing device consists of a solid electrolyte (β alumina) and of two metallic electrodes having different catalytic properties, the whole system being in contact with the surrounding atmosphere to be analyzed. The detection principle is based on the chemisorption of oxygen which leads to a capacitance effect at the metal-electrolyte interface, resulting in a measurable difference of potential depending on nature and concentration of pollutants and on the sensor temperature. For application in exhaust pipe, a porous protective layer based on α-alumina for preserving the sensing material and the metal electrodes from contamination and deterioration was screen-printed on the sensing element. For limiting the possible interface interactions between the overlapped layers, a new concept of screen -printable ink was set up based on mixing the oxide powder and its gelly precursor without any inorganic binder addition. The performances of the sensor were tested both on laboratory and engine bench. The sensitivity is relevant for exhaust application, and the long-term stability is improved by the protective layer. View full abstract»

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  • Structural and gas-sensing properties of WO3 nanocrystalline powders obtained by a sol-gel method from tungstic acid

    Page(s): 329 - 335
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (381 KB)  

    WO3 nanocrystalline powders were obtained from tungstic acid following a sol-gel process. Evolution of structural properties with annealing temperature was studied by X-ray diffraction and Raman spectroscopy. These structural properties were compared with those of WO3 nanopowders obtained by the most common process of pyrolysis of ammonium paratungstate, usually used in gas sensors applications. Sol-gel WO3 showed a high sensor response to NO2 and low response to CO and CH4. The response of these sensor devices was compared with that of WO3 obtained from pyrolysis, showing the latter a worse sensor response to NO2. Influence of operating temperature, humidity, and film thickness on NO2 detection was studied in order to improve the sensing conditions to this gas. View full abstract»

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  • A novel integrated acoustic gas and temperature sensor

    Page(s): 301 - 306
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (382 KB)  

    Acoustic temperature sensors have the advantages of a high-resolution frequency output and ease of integration with other acoustic sensors but require hermetic packaging to prevent sensor contamination. Surface-skimming bulk-wave (SSBW) devices have been found to be much less sensitive to surface contamination than other acoustic devices, and although their temperature response has been studied extensively, they have not been studied specifically as temperature sensors. Surface acoustic wave (SAW) based chemical sensors requiring temperature measurement or control are susceptible to temperature measurement error because the temperature cannot be measured in the same location as the chemical sensor. The objectives of this work were to examine the temperature characteristics and performance of a SSBW temperature sensor when integrated with a SAW condensation and humidity sensor in a novel design. The SSBW temperature sensor had over an order of magnitude less sensitivity to condensation and water uptake in certain polyimide films than an integrated SAW gas sensor indicating that this design is practical for sensing films in the delay path where film thickness is carefully considered. View full abstract»

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  • GaN metal-semiconductor-metal ultraviolet sensors with various contact electrodes

    Page(s): 366 - 371
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (387 KB) |  | HTML iconHTML  

    Indium-tin-oxide (ITO), Au, Ni, and Pt layers were deposited onto n-GaN films and/or glass substrates by electron-beam evaporation. With proper annealing, it was found that we could improve the optical properties of the ITO layers and achieve a maximum transmittance of 98% at 360 nm. GaN-based MSM UV sensors with ITO, Au, Ni, and Pt as contact electrodes were also fabricated. It was found that we could achieve a maximum 0.12 A photocurrent and a photocurrent to dark current contrast higher than five orders of magnitude for the 600°C-annealed ITO/n-GaN MSM UV sensor at a 5-V bias voltage. We also found that the maximum responsivity at 345 nm was 7.2 A/W and 0.9 A/W when the 600°C-annealed ITO/n-GaN MSM UV sensor was biased at 5 V and 0.5 V, respectively. These values were much larger than those observed from other metal/n-GaN MSM UV sensors. However, the existence of photoconductive gain in the 600°C-annealed ITO/n-GaN MSM UV sensor also results in a slower operation speed and a smaller 3-dB bandwidth as compared with the metal/n-GaN MSM UV sensors. View full abstract»

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The IEEE Sensors Journal is a peer-reviewed, monthly online/print  journal devoted to sensors and sensing phenomena

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Meet Our Editors

Editor-in-Chief
Krikor Ozanyan
University of Manchester
Manchester, M13 9PL, U.K.