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  • 1.
    Andersson, Mike
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics. Linköping University, The Institute of Technology.
    Buchholt, Kristina
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics. Linköping University, The Institute of Technology.
    Wingbrant, Helena
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics. Linköping University, The Institute of Technology.
    Lloyd Spetz, Anita
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics. Linköping University, The Institute of Technology.
    On the CO response mechanism of SiC based field effect gas sensorsManuscript (Other academic)
    Abstract [en]

    The response characteristics of Metal Insulator Silicon Carbide (MISiC) field effect sensor devices, with platinum (Pt) as the metal contact, towards carbon monoxide (CO) at varying oxygen (O2) concentrations and over a wide range of temperatures have been investigated in detail at atmospheric pressure. The influence of hydrogen (H2) on the CO response was also studied. Sensor devices with thin, porous as well as dense, homogeneous Pt films on top of both silicon dioxide (SiO2) and magnesium oxide (MgO) as insulator materials were investigated in this study. The reaction products generated on the sensor surfaces were also monitored with a mass spectrometer connected to the gas flow just downstream of the sensor location and the results compared to CO oxidation characteristics over Pt/SiO2 and to some extent Pt/MgO catalysts as reported in literature. By correlating the response characteristics of these devices with CO2 formation and hydrogen consumption on the sensor surfaces, strong indications for a CO response mechanism involving a CO induced increased sensitivity to background hydrogen have been obtained, this mechanism being hypothesized to be the only one behind the CO sensitivity of devices with dense Pt metal contacts. The results also give further support to the idea that also other processes than an increased sensitivity to background hydrogen contribute to the CO response of sensor devices with a porous platinum film as the metal contact, one candidate being the removal of oxygen anions from the surface of exposed oxide areas through the oxidation reaction with CO.

  • 2.
    Andersson, Mike
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics. Linköping University, The Institute of Technology.
    Buchholt, Kristina
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics. Linköping University, The Institute of Technology.
    Wingbrant, Helena
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics. Linköping University, The Institute of Technology.
    Lloyd Spetz, Anita
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics. Linköping University, The Institute of Technology.
    On the response mechanism of SiC based field effect gas sensors towards non-hydrogen containing species and specifically NOManuscript (Other academic)
    Abstract [en]

    The response characteristics of Metal Insulator Silicon Carbide (MISiC) field effect sensor devices, with platinum (Pt) as the metal contact, towards nitrogen oxide (NO) for both low as well as relatively high background oxygen (O2) concentrations and different temperatures have been investigated at atmospheric pressure. Devices with both porous and dense Pt metal gate contacts have been investigated and the results seem to confirm the theories and results from earlier measurements regarding the requirement of porous metal films for the existence of a response to NO for this kind of sensor device. The results also suggest that no NO induced increased sensitivity to background hydrogen exists, at least it does not play any role in the observed NO sensitivity, as opposed to what has been suggested in the case of CO. The obtained results are also discussed in relation to some of the proposed sensing mechanisms for non-hydrogen containing substances and in comparison to NO reduction characteristics on Pt/SiO2 catalysts, as reported in literature. The results further give some indications about also some other process/ processes being important for the response of SiC based field effect sensors towards NO than just adsorption/desorption.

  • 3.
    Andersson, Mike
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Wingbrant, Helena
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Lloyd-Spets, Anita
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Study of CO response of SiC based field effect gas sensors2005In: IEEE Sensors 2005,2005, 2005, p. 105-Conference paper (Refereed)
  • 4.
    Briand, D.
    et al.
    Institute of Microtechnology, University of Neuchâtel, P.O. Box 3, CH-2007 Neuchâtel, Switzerland.
    Wingbrant, Helena
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Sundgren, Hans
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Van, der Schoot B.
    Van der Schoot, B., Institute of Microtechnology, University of Neuchâtel, P.O. Box 3, CH-2007 Neuchâtel, Switzerland.
    Ekedahl, Lars-Gunnar
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Lundström, Ingemar
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    De, Rooij N.F.
    De Rooij, N.F., Institute of Microtechnology, University of Neuchâtel, P.O. Box 3, CH-2007 Neuchâtel, Switzerland.
    Modulated operating temperature for MOSFET gas sensors: Hydrogen recovery time reduction and gas discrimination2003In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 93, no 1-3, p. 276-285Conference paper (Other academic)
    Abstract [en]

    This communication presents a modulated mode of operation for MOSFET gas sensors. A low-power micromachined device allows pulsing the temperature of MOSFET gas sensors with a time constant less than 100ms. Modulating the temperature during the gas exposure modifies the kinetics of the gas reactions with the sensing film. The way the sensor response is modified by the temperature modulation depends on the sensor "history", on the nature of the surrounding gaseous atmosphere, and on the type of materials used as catalytic sensing film. Pulsing the temperature up just after the gas exposure can reduce the recovery time for specific applications, such as for hydrogen detection. Cycling the temperature can allow the discrimination between different gas mixtures. Discrimination was shown for gaseous mixtures of hydrogen and ammonia in air. The results obtained indicate that a "smart" combination of sample and temperature profile could be used to expand the information content in the sensor response. © 2003 Elsevier Science B.V. All rights reserved.

  • 5.
    Lloyd-Spets, Anita
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics.
    Andersson, Mike
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics.
    Petersson, Henrik
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics.
    Wingbrant, Helena
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics.
    Unéus, Lars
    Svenningstorp, Henrik
    Löfdahl, Mikael
    Holmberg, Martin
    Gas sensor arrays for combustion control2005In: Encyclopedia of Sensors, eds. / [ed] Professor Rudolph A. Marcus, Nobel Prize Laureate, California: American Scientific Publishers , 2005, p. 139-154Chapter in book (Other academic)
    Abstract [en]

    The applications of sensors range from medical diagnostics to industrial manufacturing and to defense and national security applications. When an area spans such a large diversity of research, and where research from many different countries is also involved, a review of these developments becomes especially useful. Because it bridges science and technology the field also provides a desired interaction between researchers and research in technologically advanced and developing countries. The present series of volumes, "The Encyclopedia of Sensors" , the first of its kind, is intended to provide a timely compendium of the entire field. As such it can be expected to play a significant role in worldwide future progress and understanding."

  • 6.
    Lloyd-Spets, Anita
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics.
    Andersson, Mike
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics.
    Wingbrant, Helena
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics.
    MISiC-FET NH3 sensors for SCR control in exhaust and flue gases2005In: Encyclopedia of Sensors, eds. / [ed] Rudolph A. Marcus, Nobel Prize Laureate, California: American Scientific Publishers , 2005, p. 205-218Chapter in book (Other academic)
    Abstract [en]

        The applications of sensors range from medical diagnostics to industrial manufacturing and to defense and national security applications. When an area spans such a large diversity of research, and where research from many different countries is also involved, a review of these developments becomes especially useful. Because it bridges science and technology the field also provides a desired interaction between researchers and research in technologically advanced and developing countries. The present series of volumes, "The Encyclopedia of Sensors" , the first of its kind, is intended to provide a timely compendium of the entire field. As such it can be expected to play a significant role in worldwide future progress and understanding."

  • 7.
    Lloyd-Spets, Anita
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Nakagomi, S.
    School of Science and Engineering, Ishinomaki Senshu University, Ishinomaki, Miyagi, Japan.
    Wingbrant, Helena
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Andersson, Mike
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Salomonsson, Anette
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Roy, S.
    Wingqvist, G.
    Ångström Laboratory, Uppsala University, Uppsala, Sweden.
    Katardjiev, I.
    Ångström Laboratory, Uppsala University, Uppsala, Sweden.
    Eickhoff, M.
    Walter Schottky Institut, Technishce Universität München, Am. Coulombwall, Garching, Germany.
    Uvdal, Kajsa
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Sensor Science and Molecular Physics .
    Yakimova, Rositsa
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Materials Science .
    New materials for chemical and biosensors2006In: Materials and Manufacturing Processes, ISSN 1042-6914, E-ISSN 1532-2475, Vol. 21, no 3, p. 253-256Article in journal (Refereed)
    Abstract [en]

    Wide band gap materials such as SiC, AlN, GaN, ZnO, and diamond have excellent properties such as high operation temperature when used as field effect devices and a high resonating frequency of the substrate materials used in piezoelectric resonator devices. Integration of FET and resonating sensors on the same chip enables powerful miniaturized devices, which can deliver increased information about a gas mixture or complex liquid. Examples of sensor devices based on different wide band gap materials will be given.

  • 8.
    Lloyd-Spets, Anita
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Sundgren, Hans
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Thunér, Bo
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Wingbrant, Helena
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Belov, I.
    Svenningstorp, H.
    Leisner, P.
    CFD analysis of packaging and mounting solutions for SiC-based gas sensors in automotive applications2006Article in journal (Refereed)
    Abstract [en]

    Simulation-based guidelines were developed for designing tube-mounted gas sensors in the exhaust pipes of diesel and petrol engines, taking into account thermal constraints and gas flow conditions. Different block and tube mounting alternatives for SiC-based gas sensors were studied by means of temperature measurements and simulation of steady state heat transfer and gas flow. Design variables included the number of fins in the heat sink mounted on the inlet tube, the inlet construction, the mounting tube orientation, and the micro-heater substrate placement inside the mounting tube. The most preferable tube mounting design was determined with respect to the thermal performance of the sensor structure and with respect to the gas flow parameters, which are important for the sensor's selectivity, sensitivity and response time. Copyright © 2006 American Scientific Publishers All rights reserved.

  • 9.
    Lloyd-Spets, Anita
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Unéus, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Svenningstorp, H
    SSENCE, SE-58183 Linkoping, Sweden Linkoping Univ, Div Appl Phys, SE-58183 Linkoping, Sweden Ford Motor Co, Dearborn, MI 48124 USA Vattenfall Dev, SE-81426 Alvkarleby, Sweden AppliedSensor AB, SE-58330 Linkoping, Sweden Volvo PV AB, SE-40508 Gothenburg, Sweden ACREO Ab, SE-16440 Kista, Sweden Volvo TU, SE-41288 Gothenburg, Sweden.
    Wingbrant, Helena
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Harris, CI
    SSENCE, SE-58183 Linkoping, Sweden Linkoping Univ, Div Appl Phys, SE-58183 Linkoping, Sweden Ford Motor Co, Dearborn, MI 48124 USA Vattenfall Dev, SE-81426 Alvkarleby, Sweden AppliedSensor AB, SE-58330 Linkoping, Sweden Volvo PV AB, SE-40508 Gothenburg, Sweden ACREO Ab, SE-16440 Kista, Sweden Volvo TU, SE-41288 Gothenburg, Sweden.
    Salomonsson, P
    SSENCE, SE-58183 Linkoping, Sweden Linkoping Univ, Div Appl Phys, SE-58183 Linkoping, Sweden Ford Motor Co, Dearborn, MI 48124 USA Vattenfall Dev, SE-81426 Alvkarleby, Sweden AppliedSensor AB, SE-58330 Linkoping, Sweden Volvo PV AB, SE-40508 Gothenburg, Sweden ACREO Ab, SE-16440 Kista, Sweden Volvo TU, SE-41288 Gothenburg, Sweden.
    Tengstrom, P
    Martensson, P
    Ljung, P
    Mattsson, M
    SSENCE, SE-58183 Linkoping, Sweden Linkoping Univ, Div Appl Phys, SE-58183 Linkoping, Sweden Ford Motor Co, Dearborn, MI 48124 USA Vattenfall Dev, SE-81426 Alvkarleby, Sweden AppliedSensor AB, SE-58330 Linkoping, Sweden Volvo PV AB, SE-40508 Gothenburg, Sweden ACREO Ab, SE-16440 Kista, Sweden Volvo TU, SE-41288 Gothenburg, Sweden.
    Visser, JH
    SSENCE, SE-58183 Linkoping, Sweden Linkoping Univ, Div Appl Phys, SE-58183 Linkoping, Sweden Ford Motor Co, Dearborn, MI 48124 USA Vattenfall Dev, SE-81426 Alvkarleby, Sweden AppliedSensor AB, SE-58330 Linkoping, Sweden Volvo PV AB, SE-40508 Gothenburg, Sweden ACREO Ab, SE-16440 Kista, Sweden Volvo TU, SE-41288 Gothenburg, Sweden.
    Ejakov, SG
    SSENCE, SE-58183 Linkoping, Sweden Linkoping Univ, Div Appl Phys, SE-58183 Linkoping, Sweden Ford Motor Co, Dearborn, MI 48124 USA Vattenfall Dev, SE-81426 Alvkarleby, Sweden AppliedSensor AB, SE-58330 Linkoping, Sweden Volvo PV AB, SE-40508 Gothenburg, Sweden ACREO Ab, SE-16440 Kista, Sweden Volvo TU, SE-41288 Gothenburg, Sweden.
    Kubinski, D
    SSENCE, SE-58183 Linkoping, Sweden Linkoping Univ, Div Appl Phys, SE-58183 Linkoping, Sweden Ford Motor Co, Dearborn, MI 48124 USA Vattenfall Dev, SE-81426 Alvkarleby, Sweden AppliedSensor AB, SE-58330 Linkoping, Sweden Volvo PV AB, SE-40508 Gothenburg, Sweden ACREO Ab, SE-16440 Kista, Sweden Volvo TU, SE-41288 Gothenburg, Sweden.
    Ekedahl, Lars-Gunnar
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Lundström, Ingemar
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Savage, SM
    SSENCE, SE-58183 Linkoping, Sweden Linkoping Univ, Div Appl Phys, SE-58183 Linkoping, Sweden Ford Motor Co, Dearborn, MI 48124 USA Vattenfall Dev, SE-81426 Alvkarleby, Sweden AppliedSensor AB, SE-58330 Linkoping, Sweden Volvo PV AB, SE-40508 Gothenburg, Sweden ACREO Ab, SE-16440 Kista, Sweden Volvo TU, SE-41288 Gothenburg, Sweden.
    MISiCFET chemical gas sensors for high temperature and corrosive environment applications2002In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 389-3, p. 1415-1418Article in journal (Refereed)
    Abstract [en]

    A chemical gas sensor based on a silicon carbide field effect transistor with a catalytic gate metal has been under development for a number of years. The buried gate design allows the sensor to operate at high temperatures, routinely up to 600degreesC and for at least three days at 700degreesC. The chemical inertness of silicon carbide makes it a suitable sensor technology for applications in corrosive environments such as exhaust gases and flue gases from boilers. The selectivity of the sensor devices is established through the choice of type and structure of the gate metal as well as the operation temperature. In this way NH3 sensors with low cross sensitivity to NOx have been demonstrated as potential sensors for control of selective catalytic reduction (SCR) of NOx by urea injection into diesel exhausts. The hardness of the silicon carbide makes it for example more resistant to water splash at cold start of a petrol engine than existing technologies, and a sensor which can control the air to fuel ratio, before the exhaust gases are heated, has been demonstrated. Silicon carbide sensors are also tested in flue gases from boilers. Efficient regulation of the combustion in a boiler will decrease fuel consumption and reduce emissions.

  • 10. Nakagomi, S
    et al.
    Takahashi, M
    Kokubun, Y
    Unéus, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Savage, S
    Wingbrant, Helena
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Andersson, M
    Lundström, Ingemar
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Löfdahl, Mikael
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Lloyd-Spets, Anita
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Substrate bias amplification of a SiC junction field effect transistor with a catalytic gate electrode2004In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 457-460, p. 1507-1510Article in journal (Refereed)
    Abstract [en]

    The drain current-voltage (I-d-V-D) characteristics of a chemical gas sensor based on a catalytic metal insulator silicon carbide field effect transistor (SiC-FET) were measured in H-2 or O-2 ambient while applying negative substrate bias, V-sub, at temperatures up to 600degreesC. An increase in the negative V-sub gives rise to an increase of the drain voltage at a given drain current level, which can be used to adjust the device baseline. In addition, we found that the difference in drain voltage between H-2 and O-2 ambient at a given drain current level (the gas response to H-2) increases for an increased negative substrate bias. By modifying an equation for the drain current in a SIT (static induction transistor), the influence of substrate bias on the amplification factors, mu and eta, was estimated using the temperature dependence of the I-d-V-D characteristics. From this, the effect of substrate bias on the gas response to hydrogen was calculated. It was clarified that the increase in the gas response caused by the negative substrate bias is due to a substrate bias dependence of the amplification factor of the short channel device.

  • 11.
    Nakagomi, Shinji
    et al.
    School of Science and Engineering Ishinomaki Senshu University.
    Fukumura, Akira
    School of Science and Engineering Ishinomaki Senshu University.
    Kokubun, Yoshihiro
    School of Science and Engineering Ishinomaki Senshu University.
    Savage, Susan
    Acreo AB.
    Wingbrant, Helena
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Andersson, Mike
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Lundström, Ingemar
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Löfdahl, Mikael
    AppliedSensor AB.
    Lloyd-Spets, Anita
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Influence of gate bias of MISiC-FET gas sensor device on the sensing properties2005In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 108, p. 501-507Article in journal (Refereed)
    Abstract [en]

    The influence of gate bias on the gas sensing properties of SiC-based field effect transistors with catalytic gate and a buried short channel has been studied. The drain current-voltage (I-d-V-D) characteristics of the device reveal non-saturation property, which is a consequence of the short channel design. The drain current is larger in hydrogen ambient than in oxygen ambient at the same drain voltage. The threshold voltage decreases with increasing positive gate bias, and increases with increasing negative gate bias. When a positive bias is applied to the gate, the I-d-V-D characteristics reveal a tendency to saturate. A positive gate bias increases the drain voltage response to hydrogen, as compared with a negative applied gate bias. However, a positive gate bias decreases the stability of the device signal. A change in the channel resistivity is the main reason for the change in the electrical properties when a positive gate bias is applied. A physical model that explains the influence of the gate bias has been studied, and the behavior of the barrier height in the channel was estimated by using the temperature dependence of the I-d-V-D characteristics.

  • 12.
    Weidemann, O.
    et al.
    Walter Schottky Institute, Technical University Munich, Am Coulombwall 3, D-85748 Garching, Germany.
    Hermann, M.
    Walter Schottky Institute, Technical University Munich, Am Coulombwall 3, D-85748 Garching, Germany.
    Steinhoff, G.
    Walter Schottky Institute, Technical University Munich, Am Coulombwall 3, D-85748 Garching, Germany.
    Wingbrant, Helena
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Lloyd-Spets, Anita
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Stutzmann, M.
    Walter Schottky Institute, Technical University Munich, Am Coulombwall 3, D-85748 Garching, Germany.
    Eickhoff, M.
    Walter Schottky Institute, Technical University Munich, Am Coulombwall 3, D-85748 Garching, Germany.
    Influence of surface oxides on hydrogen-sensitive Pd: GaN Schottky diodes2003In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 83, no 4, p. 773-775Article in journal (Refereed)
    Abstract [en]

    Influence of surface oxides on hydrogen-sensitive Pd:GaN Schottky diodes was studied. Ex-situ fabricated devices show a sensitivity towards molecular hydrogen, which is about 50 times higher than for in situ deposited diodes. In situ deposited Pd Schottky contacts reveal lower barrier heights and drastically higher reverse currents.

  • 13.
    Wingbrant, Helena
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
    Development of high temperature SiC based field effect sensors for internal combustion engine exhaust gas monitoring2003Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    While the car fleet becomes increasingly larger it is important to lower the amounts of pollutants from each individual diesel or gasoline engine to almost zero levels. The pollutants from these engines predominantly originate from high NOx emissions and particulates, in the case when diesel is utilized, and emissions at cold start from gasoline engines. One way of treating the high NOx levels is to introduce ammonia in the diesel exhausts and let it react with the NOx to form nitrogen gas and water, which is called SCR (Selective Catalytic Reduction). However, in order to make this system reduce NOx efficiently enough for meeting future legislations, closed loop control is required. To realize this type of system an NOx or ammonia sensor is needed. The cold start emissions from gasoline vehicles are primarily due to a high light-off time for the catalytic converter. Another reason is the inability to quickly heat the sensor used for controlling the air-to-fuel ratio in the exhausts, also called the lambda value, which is required to be in a particular range for the catalytic converter to work properly. This problem may be solved utilizing another, more robust sensor for this purpose.

    This thesis presents the efforts made to test the SiC-based field effect transistor (SiC-FET) sensor technology both as an ammonia sensor for SCR systems and as a cold start lambda sensor. The SiC-FET sensor has been shown to be highly sensitive to ammonia both in laboratory and engine measurements. As a lambda sensor it has proven to be both sensitive and selective, and its properties have been studied in lambda stairs both in engine exhausts and in the laboratory. The influence of metal gate restructuring on the linearity of the sensor has also been investigated. The speed of response for both sensor types has been found to be fast enough for closed loop control in each application.

    List of papers
    1. Using a MISiCFET device as a cold start sensor
    Open this publication in new window or tab >>Using a MISiCFET device as a cold start sensor
    Show others...
    2003 (English)In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 63, no 1-3, p. 295-303Article in journal (Refereed) Published
    Abstract [en]

    As a consequence of the formation of water droplets in the car engine at cold start, the fragile ZrO2 λ sensor cannot be heated until the engine is sufficiently warm. A possibility to shorten the time before closed loop λ control would decrease the exhaust emission. As a solution to this problem, the metal insulator silicon carbide field effect transistor (MISiCFET) sensor, which presumably is more thermo shock resistant than the ZrO2 sensor, could be used at cold start. The requirements for a cold start sensor are, among others, sensitivity to λ (air to fuel ratio) close to stochiometry, selectivity to λ and high speed of response. In this communication, the possibility of using the MISiCFET sensor at cold start is treated. The sensor consists of a SiC based MOSFET device with a buried channel design and a catalytic gate metal of 10 nm TaSix and 100 nm Pt. The response depends linearly on λ at 500 °C. The sensitivity of the device has been tested both in artificial atmospheres and in an engine. Two-level factorial designed experiments showed a high selectivity to λ compared to other gases such as CO, hydrocarbons, NOx and H2. The response time was found to be <10 ms at 500 °C when changing from an oxidizing to a reducing atmosphere. The MISiCFET sensor response showed interesting differences in λ stairs when the λ-value was varied by changing the oxygen, hydrogen or CO concentration. The results show that the MISiCFET sensor is a promising choice as a future cold start sensor.

    Keywords
    Field effect device, Gas sensor, Cold start, Exhaust gases, Silicon carbide
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13401 (URN)10.1016/S0925-4005(03)00227-2 (DOI)
    Available from: 2005-11-10 Created: 2005-11-10 Last updated: 2017-12-13
    2. The speed of response of MISiCFET devices
    Open this publication in new window or tab >>The speed of response of MISiCFET devices
    2003 (English)In: Sensors and Actuators B: Chemical, ISSN 0925-4005, Vol. 93, no 1-3, p. 286-294Article in journal (Refereed) Published
    Abstract [en]

    The metal oxide silicon carbide field effect transistor (MISiCFET) sensor has several possible car engine applications, such as an ammonia sensor in selective catalytic reduction (SCR) systems or as a lambda-sensitive device for enhancing catalytic converter efficiency. Both these applications involve closed loop control of the engine and thereby require fast sensors, that is why it is important to investigate the speed of response of the devices. The sensor consists of a SiC-based MOSFET device with a buried channel design and a catalytic gate metal, which makes it sensitive to a wide range of different gases. The selectivity and sensitivity of the sensor to a specific gas depends mainly on the choice of gate metal, its structure and the operating temperature. In this presentation, the speed of response of MISiCFET devices with many different gate metals at several operating temperatures are compared. The tests have been performed in the laboratory using the moving gas outlet (MGO) equipment. The equipment allows two gas outlets to move back and forth under the sensor, which makes it possible to change the atmosphere surrounding the sensor from synthetic air to the test gas quickly. The method is verified by changing the temperature of the device and frequency of the moving gas outlets. The test gas is either ammonia or hydrogen. The time constant of the sensors is shown to be very small; <100 ms when exposing a 25 nm porous Pt sensor to ammonia at 300 °C and <10 ms for a 10 nm TaSix 100 nm Pt device exposed to hydrogen. The temperature is found to have a large influence on the speed of response. The results show that the speed of response is well beyond the current requirements for use in both SCR and lambda control systems, respectively.

    Keywords
    Response time, Chemical sensor, Field effect device, Exhaust, Silicon carbide
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13402 (URN)10.1016/S0925-4005(03)00228-4 (DOI)
    Available from: 2005-11-10 Created: 2005-11-10 Last updated: 2014-01-09
    3. Dependence of Pt gate restructuring on the linearity of SiC Field Effect Transistor lambda sensors
    Open this publication in new window or tab >>Dependence of Pt gate restructuring on the linearity of SiC Field Effect Transistor lambda sensors
    2003 (English)In: Sensor Letters, ISSN 1546-198X, Vol. 1, no 1, p. 37-41Article in journal (Refereed) Published
    Abstract [en]

    To achieve an efficient conversion of pollutants from gasoline-driven cars, the lambda value, or the air-to-fuel ratio, of the exhausts that reach the catalytic converter is required to be close to 1. The composition of the exhaust gases is normally regulated with the use of a zirconia lambda sensor. However, at cold start another, more robust sensor is required, and a SiC-based field effect transistor sensor is currently being developed for this purpose. The SiC field effect transistor sensor has previously been shown to respond in either a linear or a binary fashion to changes in the lambda value, depending on parameters such as the choice of operation temperature and the area of catalytic metal. Here it is shown that the linear behavior of the sensor may appear as a result of the restructuring of the thick Pt film, which is working as its sensitive layer, when exposed to intermittent pulses of reducing and oxidizing gas mixtures. Sensors that have been used only for a short while have a continuous film and show a binary behavior, whereas samples that have been run for a longer time have seriously restructured films and show a linear behavior. A connection between the linear behavior and the decreased catalytic activity of the used films in comparison with fresh samples with a binary behavior is discussed. Some alternative methods for preventing the restructuring of the metal are suggested.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13403 (URN)10.1166/sl.2003.011 (DOI)
    Available from: 2005-11-10 Created: 2005-11-10 Last updated: 2014-01-09
    4. Using a MISiC-FET sensor for detecting NH3 in SCR systems
    Open this publication in new window or tab >>Using a MISiC-FET sensor for detecting NH3 in SCR systems
    Show others...
    2005 (English)In: IEEE Sensors Journal, ISSN 1530-437X, E-ISSN 1558-1748, Vol. 5, no 5, p. 1099-1105Article in journal (Refereed) Published
    Abstract [en]

    One way to decrease the emitted levels of NOx from diesel engines is to add NH3 in the form of urea to the exhausts after combustion. NH3 will react with NOx in the catalytic converter to form N2 and water, which is called selective catalytic reduction (SCR). The amount of NH3 added may be regulated through closed-loop control by using an NH3 sensor. The metal-insulator silicon-carbide field-effect transistor (MISiC-FET) sensor has previously been tested for this application and has been shown to be sensitive to NH3. Here, the sensors have been further studied in engine SCR systems. Tests on the cross sensitivity to N2O and NO2, and studies concerning the influence of water vapor have been performed in the laboratory. The difference between Ir and Pt films, with regard to catalytic activity, has also been investigated. The sensors were found to be sensitive to NH3 in diesel engine exhausts. The addition of urea was computer controlled, which made it possible to add NH3 in a stair-like fashion to the system and detect it with the MISiC-FET sensors. The presence of water vapor was shown to have the largest effect on the sensors at low levels and the NH3 response was slightly decreased by a background level of NO2.

    Keywords
    Ammonia, field-effect transistor (FET) sensor, iridium, platinum, selective catalytic reduction (SCR)
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13408 (URN)10.1109/JSEN.2005.854489 (DOI)
    Available from: 2005-11-10 Created: 2005-11-10 Last updated: 2017-12-13
  • 14.
    Wingbrant, Helena
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
    Studies of MISiC-FET sensors for car exhaust gas monitoring2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The increasing size of the car fleet makes it important to find ways of lowering the amounts of pollutants from each individual diesel or gasoline engine to almost zero levels. The pollutants from these engines predominantly originate from emissions at cold start, in the case when gasoline is utilized, and high NOx emissions and particulates from diesel engines.

    The cold start emissions from gasoline vehicles are primarily due to a high light-off time for the catalytic converter. Another reason is the inability to quickly heat the sensor used for controlling the air-to-fuel ratio in the exhausts, also called the lambda value, which is required to be in a particular range for the catalytic converter to work properly. This problem may be solved utilizing another, more robust sensor for this purpose.

    One way of treating the high NOx levels from diesel engines is to introduce ammonia in the exhausts and let it react with the NOx in a special catalytic converter to form nitrogen gas and water, which is called SCR (selective catalytic reduction). However, in order to make this system reduce NOx efficiently enough for meeting future legislations, closed loop control is required. To realize this type of system an NOx or ammonia sensor is needed.

    This thesis presents the efforts made to test the SiC-based field effect sensor device both as a cold start lambda sensor for gasoline engines and as an NH3 sensor for SCR systems in diesel engines.

    The MISiC (metal insulator silicon carbide) lambda sensor has proven to be both sensitive and selective to lambda, and its properties have been studied in lambda stairs both in gasoline engine exhausts and in the laboratory. There is, however, a small cross-sensitivity to CO. The influence of metal gate restructuring on the linearity of the sensor has also been investigated. The metal tends to form islands by time, which decreases the catalytic activity and thereby gives the sensor, which is binary when fresh, a linear behavior. Successful attempts to prevent the restructuring through depositing a protective layer of insulator on top of the metal were made. The influence of increasing the catalytic activity in the measurement cell was also studied. It was concluded that the location of the binary switch point of MISiC lambda sensors could be moved towards the stoichiometric value if the consumption of gases in the measurement cell was increased.

    The MISiC NH3 sensor for SCR systems has been shown to be highly sensitive to ammonia both in laboratory and diesel engine measurements. The influence of other diesel exhaust gas components, such as NOx, water or N2O has been found to be low. In order to make the ammonia sensor more long-term stable experiments on samples with different types of co-sputtered Pt or Ir/SiO2 gas-sensitive layers were performed. These samples turned out to be sensitive to NH3 even though they were dense and NH3 detection normally requires porous films.

    The speed of response for both sensor types has been found to be fast enough for closed loop control in each application.

    List of papers
    1. Using a MISiCFET device as a cold start sensor
    Open this publication in new window or tab >>Using a MISiCFET device as a cold start sensor
    Show others...
    2003 (English)In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 63, no 1-3, p. 295-303Article in journal (Refereed) Published
    Abstract [en]

    As a consequence of the formation of water droplets in the car engine at cold start, the fragile ZrO2 λ sensor cannot be heated until the engine is sufficiently warm. A possibility to shorten the time before closed loop λ control would decrease the exhaust emission. As a solution to this problem, the metal insulator silicon carbide field effect transistor (MISiCFET) sensor, which presumably is more thermo shock resistant than the ZrO2 sensor, could be used at cold start. The requirements for a cold start sensor are, among others, sensitivity to λ (air to fuel ratio) close to stochiometry, selectivity to λ and high speed of response. In this communication, the possibility of using the MISiCFET sensor at cold start is treated. The sensor consists of a SiC based MOSFET device with a buried channel design and a catalytic gate metal of 10 nm TaSix and 100 nm Pt. The response depends linearly on λ at 500 °C. The sensitivity of the device has been tested both in artificial atmospheres and in an engine. Two-level factorial designed experiments showed a high selectivity to λ compared to other gases such as CO, hydrocarbons, NOx and H2. The response time was found to be <10 ms at 500 °C when changing from an oxidizing to a reducing atmosphere. The MISiCFET sensor response showed interesting differences in λ stairs when the λ-value was varied by changing the oxygen, hydrogen or CO concentration. The results show that the MISiCFET sensor is a promising choice as a future cold start sensor.

    Keywords
    Field effect device, Gas sensor, Cold start, Exhaust gases, Silicon carbide
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13401 (URN)10.1016/S0925-4005(03)00227-2 (DOI)
    Available from: 2005-11-10 Created: 2005-11-10 Last updated: 2017-12-13
    2. The speed of response of MISiCFET devices
    Open this publication in new window or tab >>The speed of response of MISiCFET devices
    2003 (English)In: Sensors and Actuators B: Chemical, ISSN 0925-4005, Vol. 93, no 1-3, p. 286-294Article in journal (Refereed) Published
    Abstract [en]

    The metal oxide silicon carbide field effect transistor (MISiCFET) sensor has several possible car engine applications, such as an ammonia sensor in selective catalytic reduction (SCR) systems or as a lambda-sensitive device for enhancing catalytic converter efficiency. Both these applications involve closed loop control of the engine and thereby require fast sensors, that is why it is important to investigate the speed of response of the devices. The sensor consists of a SiC-based MOSFET device with a buried channel design and a catalytic gate metal, which makes it sensitive to a wide range of different gases. The selectivity and sensitivity of the sensor to a specific gas depends mainly on the choice of gate metal, its structure and the operating temperature. In this presentation, the speed of response of MISiCFET devices with many different gate metals at several operating temperatures are compared. The tests have been performed in the laboratory using the moving gas outlet (MGO) equipment. The equipment allows two gas outlets to move back and forth under the sensor, which makes it possible to change the atmosphere surrounding the sensor from synthetic air to the test gas quickly. The method is verified by changing the temperature of the device and frequency of the moving gas outlets. The test gas is either ammonia or hydrogen. The time constant of the sensors is shown to be very small; <100 ms when exposing a 25 nm porous Pt sensor to ammonia at 300 °C and <10 ms for a 10 nm TaSix 100 nm Pt device exposed to hydrogen. The temperature is found to have a large influence on the speed of response. The results show that the speed of response is well beyond the current requirements for use in both SCR and lambda control systems, respectively.

    Keywords
    Response time, Chemical sensor, Field effect device, Exhaust, Silicon carbide
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13402 (URN)10.1016/S0925-4005(03)00228-4 (DOI)
    Available from: 2005-11-10 Created: 2005-11-10 Last updated: 2014-01-09
    3. Dependence of Pt gate restructuring on the linearity of SiC Field Effect Transistor lambda sensors
    Open this publication in new window or tab >>Dependence of Pt gate restructuring on the linearity of SiC Field Effect Transistor lambda sensors
    2003 (English)In: Sensor Letters, ISSN 1546-198X, Vol. 1, no 1, p. 37-41Article in journal (Refereed) Published
    Abstract [en]

    To achieve an efficient conversion of pollutants from gasoline-driven cars, the lambda value, or the air-to-fuel ratio, of the exhausts that reach the catalytic converter is required to be close to 1. The composition of the exhaust gases is normally regulated with the use of a zirconia lambda sensor. However, at cold start another, more robust sensor is required, and a SiC-based field effect transistor sensor is currently being developed for this purpose. The SiC field effect transistor sensor has previously been shown to respond in either a linear or a binary fashion to changes in the lambda value, depending on parameters such as the choice of operation temperature and the area of catalytic metal. Here it is shown that the linear behavior of the sensor may appear as a result of the restructuring of the thick Pt film, which is working as its sensitive layer, when exposed to intermittent pulses of reducing and oxidizing gas mixtures. Sensors that have been used only for a short while have a continuous film and show a binary behavior, whereas samples that have been run for a longer time have seriously restructured films and show a linear behavior. A connection between the linear behavior and the decreased catalytic activity of the used films in comparison with fresh samples with a binary behavior is discussed. Some alternative methods for preventing the restructuring of the metal are suggested.

    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13403 (URN)10.1166/sl.2003.011 (DOI)
    Available from: 2005-11-10 Created: 2005-11-10 Last updated: 2014-01-09
    4. Using a MISiC-FET sensor for detecting NH3 in SCR systems
    Open this publication in new window or tab >>Using a MISiC-FET sensor for detecting NH3 in SCR systems
    Show others...
    2005 (English)In: IEEE Sensors Journal, ISSN 1530-437X, E-ISSN 1558-1748, Vol. 5, no 5, p. 1099-1105Article in journal (Refereed) Published
    Abstract [en]

    One way to decrease the emitted levels of NOx from diesel engines is to add NH3 in the form of urea to the exhausts after combustion. NH3 will react with NOx in the catalytic converter to form N2 and water, which is called selective catalytic reduction (SCR). The amount of NH3 added may be regulated through closed-loop control by using an NH3 sensor. The metal-insulator silicon-carbide field-effect transistor (MISiC-FET) sensor has previously been tested for this application and has been shown to be sensitive to NH3. Here, the sensors have been further studied in engine SCR systems. Tests on the cross sensitivity to N2O and NO2, and studies concerning the influence of water vapor have been performed in the laboratory. The difference between Ir and Pt films, with regard to catalytic activity, has also been investigated. The sensors were found to be sensitive to NH3 in diesel engine exhausts. The addition of urea was computer controlled, which made it possible to add NH3 in a stair-like fashion to the system and detect it with the MISiC-FET sensors. The presence of water vapor was shown to have the largest effect on the sensors at low levels and the NH3 response was slightly decreased by a background level of NO2.

    Keywords
    Ammonia, field-effect transistor (FET) sensor, iridium, platinum, selective catalytic reduction (SCR)
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13408 (URN)10.1109/JSEN.2005.854489 (DOI)
    Available from: 2005-11-10 Created: 2005-11-10 Last updated: 2017-12-13
    5. The influence of catalytic activity on the phase transition governed binary switch point of MISiC-FET lambda sensors
    Open this publication in new window or tab >>The influence of catalytic activity on the phase transition governed binary switch point of MISiC-FET lambda sensors
    2006 (English)In: Applied Surface Science, ISSN 1530-437X, Vol. 252, no 20, p. 7473-7486Article in journal (Refereed) Published
    Abstract [en]

    A metal insulator silicon carbide field effect transistor (MISiC-FET) sensor with a catalytic metal gate is currently under development for detecting the lambda value, or air-to-fuel ratio, of gasoline exhausts. It has been noticed that a change from a low to a high signal level of the sensor occurs at a lambda value above 1.00, which is an oxidizing atmosphere. The exact location of the switch point depends both on the kind of gas and gas concentrations chosen to obtain a specific lambda value. The switch point would rather have been expected at 1.00, which is at stoichiometry, irrespective of the composition of the gas mixture. The origin of this phenomenon is studied here by exposing the sensor to lambda stairs while changing different operating parameters. An increase in catalytic activity has been observed to move the switch point of the device towards a lambda value of 1.00. A similar effect is achieved when decreasing the flow or increasing the temperature of operation of the device. The behavior is explained through the introduction of mass transport limitations in the measurement cell, and the difference in diffusion constants and sticking coefficients among the gases when reaction limitation prevails.

    Keywords
    MISiC-FET; Catalytic activity; Binary switch point; Phase transition; Lambda
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13409 (URN)10.1016/j.apsusc.2005.09.003 (DOI)
    Available from: 2005-11-10 Created: 2005-11-10 Last updated: 2014-01-09
    6. Co-sputtered metal and SiO2 layers for use in thick-film MISiC NH3 sensors
    Open this publication in new window or tab >>Co-sputtered metal and SiO2 layers for use in thick-film MISiC NH3 sensors
    Show others...
    2006 (English)In: IEEE Sensors Journal, ISSN 1530-437X, Vol. 6, no 4, p. 887-897Article in journal (Refereed) Published
    Abstract [en]

    High-temperature metal-insulator-silicon-carbide (MISiC) sensors are currently under development for use as NH3 sensors in selective-catalytic-reduction (SCR) systems in diesel engines or non-SCR (NSCR) systems in boilers. The detection of NH3 by these sensors requires the presence of triple points where the gas, the metal, and the insulator meet. These triple points have traditionally been located at the interface between the insulator and a porous metal. However, to facilitate the long-term stability of the devices when used in a harsh environment, a nonporous gate material would be preferred. Here, the behavior of the samples where such triple points have been introduced in a dense film through cosputtering of the insulator (SiO 2), and either Pt or Ir is studied. The NH3 sensitivity of the materials was found to be in accordance with the earlier investigations on Si-based samples with cosputtered gate materials. Several metal-to-insulator ratios for each of the metals Pt and Ir were studied. The sensitivity of the layers as well as their selectivity to different concentrations of NH3 at temperatures ranging from 150 degC to 450 degC was investigated. The films containing 60%-70% Pt or Ir were found to give a high sensitivity toward NH3. These samples were shown to be sensitive also to propylene and H2 but were rather insensitive to NO and CO.

    Keywords
    Ammonia, cosputtered films, iridium, metal insulator silicon carbide (MISiC), platinum, selective catalytic reduction (SCR), silicon dioxide (SiO2), thick film
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13410 (URN)10.1109/JSEN.2006.877973 (DOI)
    Available from: 2005-11-10 Created: 2005-11-10 Last updated: 2015-03-24
    7. Modifications of the Gate Material to Increase the Long-Term Stability of Field Effect Transistor Lambda Sensors
    Open this publication in new window or tab >>Modifications of the Gate Material to Increase the Long-Term Stability of Field Effect Transistor Lambda Sensors
    2005 (English)In: Sensor Letters, ISSN 1546-198X, Vol. 3, no 3, p. 225-230Article in journal (Refereed) Published
    Abstract [en]

    The MISiC-FET Pt/TaSix sensor has been shown previously to work well for measuring the lambda value, or the air-to-fuel ratio, of gasoline engine exhausts. However, the catalytic gate metal that is crucial for the sensing properties tends to restructure in harsh exhaust gases, which affects the behavior of the device. To increase the long-term stability of the sensor several modifications of the sensing layer, such as depositing a protective film of SiO2 on top of the metal or co-sputtering the catalytic metal with SiO2, have been studied and are presented here. The sensitivity and long-term stability of these films compared to the Pt/TaSix layers traditionally used for MISiC-FET lambda sensors have been investigated through laboratory measurements and SEM (scanning electron microscope) analyses. It was found that the catalytic metal films with a protective layer restructured much less than those without, but that the protective layer decreased the sensitivity of the sensors. On the other hand, the sensor gained linear characteristics when exposing it to lambda stairs. Mixing Ir and SiO2 also gave less restructuring compared with the reference samples, while maintaining a high sensitivity to lambda.

    Keywords
    Cold start sensors; Sic-fet; Lambda; Long-term stability; Linear
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-13411 (URN)10.1166/sl.2005.034 (DOI)
    Available from: 2005-11-10 Created: 2005-11-10 Last updated: 2014-01-09
  • 15.
    Wingbrant, Helena
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
    Lloyd Spetz, Anita
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
    Dependence of Pt gate restructuring on the linearity of SiC Field Effect Transistor lambda sensors2003In: Sensor Letters, ISSN 1546-198X, Vol. 1, no 1, p. 37-41Article in journal (Refereed)
    Abstract [en]

    To achieve an efficient conversion of pollutants from gasoline-driven cars, the lambda value, or the air-to-fuel ratio, of the exhausts that reach the catalytic converter is required to be close to 1. The composition of the exhaust gases is normally regulated with the use of a zirconia lambda sensor. However, at cold start another, more robust sensor is required, and a SiC-based field effect transistor sensor is currently being developed for this purpose. The SiC field effect transistor sensor has previously been shown to respond in either a linear or a binary fashion to changes in the lambda value, depending on parameters such as the choice of operation temperature and the area of catalytic metal. Here it is shown that the linear behavior of the sensor may appear as a result of the restructuring of the thick Pt film, which is working as its sensitive layer, when exposed to intermittent pulses of reducing and oxidizing gas mixtures. Sensors that have been used only for a short while have a continuous film and show a binary behavior, whereas samples that have been run for a longer time have seriously restructured films and show a linear behavior. A connection between the linear behavior and the decreased catalytic activity of the used films in comparison with fresh samples with a binary behavior is discussed. Some alternative methods for preventing the restructuring of the metal are suggested.

  • 16.
    Wingbrant, Helena
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
    Lloyd-Spetz, Anita
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
    The influence of catalytic activity on the phase transition governed binary switch point of MISiC-FET lambda sensors2006In: Applied Surface Science, ISSN 1530-437X, Vol. 252, no 20, p. 7473-7486Article in journal (Refereed)
    Abstract [en]

    A metal insulator silicon carbide field effect transistor (MISiC-FET) sensor with a catalytic metal gate is currently under development for detecting the lambda value, or air-to-fuel ratio, of gasoline exhausts. It has been noticed that a change from a low to a high signal level of the sensor occurs at a lambda value above 1.00, which is an oxidizing atmosphere. The exact location of the switch point depends both on the kind of gas and gas concentrations chosen to obtain a specific lambda value. The switch point would rather have been expected at 1.00, which is at stoichiometry, irrespective of the composition of the gas mixture. The origin of this phenomenon is studied here by exposing the sensor to lambda stairs while changing different operating parameters. An increase in catalytic activity has been observed to move the switch point of the device towards a lambda value of 1.00. A similar effect is achieved when decreasing the flow or increasing the temperature of operation of the device. The behavior is explained through the introduction of mass transport limitations in the measurement cell, and the difference in diffusion constants and sticking coefficients among the gases when reaction limitation prevails.

  • 17.
    Wingbrant, Helena
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
    Lundström, Ingemar
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
    Lloyd Spetz, Anita
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
    The speed of response of MISiCFET devices2003In: Sensors and Actuators B: Chemical, ISSN 0925-4005, Vol. 93, no 1-3, p. 286-294Article in journal (Refereed)
    Abstract [en]

    The metal oxide silicon carbide field effect transistor (MISiCFET) sensor has several possible car engine applications, such as an ammonia sensor in selective catalytic reduction (SCR) systems or as a lambda-sensitive device for enhancing catalytic converter efficiency. Both these applications involve closed loop control of the engine and thereby require fast sensors, that is why it is important to investigate the speed of response of the devices. The sensor consists of a SiC-based MOSFET device with a buried channel design and a catalytic gate metal, which makes it sensitive to a wide range of different gases. The selectivity and sensitivity of the sensor to a specific gas depends mainly on the choice of gate metal, its structure and the operating temperature. In this presentation, the speed of response of MISiCFET devices with many different gate metals at several operating temperatures are compared. The tests have been performed in the laboratory using the moving gas outlet (MGO) equipment. The equipment allows two gas outlets to move back and forth under the sensor, which makes it possible to change the atmosphere surrounding the sensor from synthetic air to the test gas quickly. The method is verified by changing the temperature of the device and frequency of the moving gas outlets. The test gas is either ammonia or hydrogen. The time constant of the sensors is shown to be very small; <100 ms when exposing a 25 nm porous Pt sensor to ammonia at 300 °C and <10 ms for a 10 nm TaSix 100 nm Pt device exposed to hydrogen. The temperature is found to have a large influence on the speed of response. The results show that the speed of response is well beyond the current requirements for use in both SCR and lambda control systems, respectively.

  • 18.
    Wingbrant, Helena
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
    Lundén, M.
    Lloyd Spetz, Anita
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
    Modifications of the Gate Material to Increase the Long-Term Stability of Field Effect Transistor Lambda Sensors2005In: Sensor Letters, ISSN 1546-198X, Vol. 3, no 3, p. 225-230Article in journal (Refereed)
    Abstract [en]

    The MISiC-FET Pt/TaSix sensor has been shown previously to work well for measuring the lambda value, or the air-to-fuel ratio, of gasoline engine exhausts. However, the catalytic gate metal that is crucial for the sensing properties tends to restructure in harsh exhaust gases, which affects the behavior of the device. To increase the long-term stability of the sensor several modifications of the sensing layer, such as depositing a protective film of SiO2 on top of the metal or co-sputtering the catalytic metal with SiO2, have been studied and are presented here. The sensitivity and long-term stability of these films compared to the Pt/TaSix layers traditionally used for MISiC-FET lambda sensors have been investigated through laboratory measurements and SEM (scanning electron microscope) analyses. It was found that the catalytic metal films with a protective layer restructured much less than those without, but that the protective layer decreased the sensitivity of the sensors. On the other hand, the sensor gained linear characteristics when exposing it to lambda stairs. Mixing Ir and SiO2 also gave less restructuring compared with the reference samples, while maintaining a high sensitivity to lambda.

  • 19.
    Wingbrant, Helena
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
    Persson, M.
    Åbom, A. E.
    Eriksson, Mats
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
    Andersson, B.
    Simko, S.
    Kubinski, D.
    Visser, J. H.
    Lloyd Spetz, Anita
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
    Co-sputtered metal and SiO2 layers for use in thick-film MISiC NH3 sensors2006In: IEEE Sensors Journal, ISSN 1530-437X, Vol. 6, no 4, p. 887-897Article in journal (Refereed)
    Abstract [en]

    High-temperature metal-insulator-silicon-carbide (MISiC) sensors are currently under development for use as NH3 sensors in selective-catalytic-reduction (SCR) systems in diesel engines or non-SCR (NSCR) systems in boilers. The detection of NH3 by these sensors requires the presence of triple points where the gas, the metal, and the insulator meet. These triple points have traditionally been located at the interface between the insulator and a porous metal. However, to facilitate the long-term stability of the devices when used in a harsh environment, a nonporous gate material would be preferred. Here, the behavior of the samples where such triple points have been introduced in a dense film through cosputtering of the insulator (SiO 2), and either Pt or Ir is studied. The NH3 sensitivity of the materials was found to be in accordance with the earlier investigations on Si-based samples with cosputtered gate materials. Several metal-to-insulator ratios for each of the metals Pt and Ir were studied. The sensitivity of the layers as well as their selectivity to different concentrations of NH3 at temperatures ranging from 150 degC to 450 degC was investigated. The films containing 60%-70% Pt or Ir were found to give a high sensitivity toward NH3. These samples were shown to be sensitive also to propylene and H2 but were rather insensitive to NO and CO.

  • 20.
    Wingbrant, Helena
    et al.
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
    Svenningstorp, H.
    Salomonsson, P.
    Volvo Technology Corporation (VTEC), Department 06130, Emission Control and Catalysis, Chalmers Science Park, Göteborg, Sweden.
    Tengström, P.
    Volvo Car Corporation, Exhaust Gas Aftertreatment Systems, Department 97621, Göteborg, Sweden.
    Lundström, Ingemar
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
    Lloyd Spetz, Anita
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
    Using a MISiCFET device as a cold start sensor2003In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 63, no 1-3, p. 295-303Article in journal (Refereed)
    Abstract [en]

    As a consequence of the formation of water droplets in the car engine at cold start, the fragile ZrO2 λ sensor cannot be heated until the engine is sufficiently warm. A possibility to shorten the time before closed loop λ control would decrease the exhaust emission. As a solution to this problem, the metal insulator silicon carbide field effect transistor (MISiCFET) sensor, which presumably is more thermo shock resistant than the ZrO2 sensor, could be used at cold start. The requirements for a cold start sensor are, among others, sensitivity to λ (air to fuel ratio) close to stochiometry, selectivity to λ and high speed of response. In this communication, the possibility of using the MISiCFET sensor at cold start is treated. The sensor consists of a SiC based MOSFET device with a buried channel design and a catalytic gate metal of 10 nm TaSix and 100 nm Pt. The response depends linearly on λ at 500 °C. The sensitivity of the device has been tested both in artificial atmospheres and in an engine. Two-level factorial designed experiments showed a high selectivity to λ compared to other gases such as CO, hydrocarbons, NOx and H2. The response time was found to be <10 ms at 500 °C when changing from an oxidizing to a reducing atmosphere. The MISiCFET sensor response showed interesting differences in λ stairs when the λ-value was varied by changing the oxygen, hydrogen or CO concentration. The results show that the MISiCFET sensor is a promising choice as a future cold start sensor.

  • 21.
    Wingbrant, Helena
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
    Svenningstorp, Henrik
    Salomonsson, Per
    Kubinski, David
    Visser, Jacobus H.
    Löfdahl, Mikael
    Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
    Lloyd Spetz, Anita
    Linköping University, Department of Physics, Chemistry and Biology, Applied Physics . Linköping University, The Institute of Technology.
    Using a MISiC-FET sensor for detecting NH3 in SCR systems2005In: IEEE Sensors Journal, ISSN 1530-437X, E-ISSN 1558-1748, Vol. 5, no 5, p. 1099-1105Article in journal (Refereed)
    Abstract [en]

    One way to decrease the emitted levels of NOx from diesel engines is to add NH3 in the form of urea to the exhausts after combustion. NH3 will react with NOx in the catalytic converter to form N2 and water, which is called selective catalytic reduction (SCR). The amount of NH3 added may be regulated through closed-loop control by using an NH3 sensor. The metal-insulator silicon-carbide field-effect transistor (MISiC-FET) sensor has previously been tested for this application and has been shown to be sensitive to NH3. Here, the sensors have been further studied in engine SCR systems. Tests on the cross sensitivity to N2O and NO2, and studies concerning the influence of water vapor have been performed in the laboratory. The difference between Ir and Pt films, with regard to catalytic activity, has also been investigated. The sensors were found to be sensitive to NH3 in diesel engine exhausts. The addition of urea was computer controlled, which made it possible to add NH3 in a stair-like fashion to the system and detect it with the MISiC-FET sensors. The presence of water vapor was shown to have the largest effect on the sensors at low levels and the NH3 response was slightly decreased by a background level of NO2.

  • 22.
    Wingbrant, Helena
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Unéus, Lars
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    Andersson, M
    Cerda, J
    Savage, S
    Svenningstorp, H
    Salomonsson, P
    Ljung, P
    Mattsson, M
    Visser, JH
    Kubinski, D
    Soltis, R
    Ejakov, SG
    Moldin, D
    Löfdahl, Mikael
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology.
    Einehag, M
    Persson, M
    Lloyd-Spets, Anita
    Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Applied Physics .
    MISiCFET chemical sensors for applications in exhaust gases and flue gases2002In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 433-4, p. 953-956Article in journal (Refereed)
    Abstract [en]

    A chemical gas sensor based on a silicon carbide field effect transistor with a catalytic gate metal has been under development for a number of years. The choice of silicon carbide as the semiconductor material allows the sensor to operate at high temperatures, for more than 6 months in flue gases at 300degreesC and for at least three days at 700degreesC. The chemical inertness of silicon carbide and a buried gate design makes it a suitable sensor technology for applications in corrosive environments such as exhaust gases and flue gases from boilers. The selectivity of the sensor devices is established through the choice of type and structure of the gate metal as well as the operation temperature. In this way NH3 sensors with low cross sensitivity to NOx have been demonstrated as potential sensors for control of selective catalytic reduction (SCR) of NOx by urea injection into diesel exhausts. Here we show that sensors with a porous platinum or iridium gate show different temperature ranges for NH3 detection. The hardness of the silicon carbide makes it for example more resistant to water splash at cold start of a petrol engine than existing technologies, and a sensor which can control the air to fuel ratio, before the exhaust gases are heated, has been demonstrated. Silicon carbide sensors are also tested in flue gases from boilers. Efficient regulation of the combustion in a boiler will decrease fuel consumption and reduce emissions.

1 - 22 of 22
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