| 1. |
- Bur, Christian, et al.
(författare)
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Detecting Volatile Organic Compounds in the ppb Range with Gas Sensitive Platinum gate SiC-Field Effect Transistors
- 2014
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Ingår i: IEEE Sensors Journal. - 1530-437X .- 1558-1748. ; 14:9, s. 3221-3228
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the use of a platinum gate gas-sensitive SiC field-effect transistor (SiC-FET) was studied for the detection of low concentrations of hazardous volatile organic compounds (VOCs). For this purpose, a new gas mixing system was realized providing VOCs down to sub-parts per billion levels with permeation ovens and gas predilution. Benzene, naphthalene, and formaldehyde were chosen as major indoor air pollutants and their characteristics are briefly reviewed. Measurements have shown that the selected VOCs can be detected by the SiC-FET in the parts per billion range and indicate a detection limit of ~1 ppb for benzene and naphthalene and ~10 ppb for formaldehyde in humid atmospheres. For 10-ppb naphthalene at 20% r.h., the sensor response is high with 12 mV, respectively, a relative response of 1.4%. Even in a background of 2-ppm ethanol, the relative response is still 0.3%. Quantification independent of the humidity level can be achieved using temperature cycled operation combined with pattern recognition, here linear discriminant analysis. Discrimination of benzene, naphthalene, and formaldehyde is also possible.
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| 2. |
- Bur, Christian, et al.
(författare)
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Increasing the Selectivity of Pt-Gate SiC Field Effect Gas Sensors by Dynamic Temperature Modulation
- 2012
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Ingår i: IEEE Sensors Journal. - : Institute of Electrical and Electronics Engineers (IEEE). - 1530-437X .- 1558-1748. ; 12:6
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Tidskriftsartikel (refereegranskat)abstract
- Based on a diode coupled silicon carbide field effect transistor (FET) with platinum as catalytic gate material, the influence of dynamic temperature modulation on the selectivity of gas analysis sensors FETs has been investigated. This operating mode, studied intensively for semiconductor gas sensors, has only recently been applied to FETs. A suitable temperature cycle for detection of typical exhaust gases (CO, NO, C3H6, H-2, NH3) was developed and combined with appropriate signal processing. The sensor data were evaluated using multivariate statistics, e.g., linear discriminant analysis. Measurements have proven that typical exhaust gases can be discriminated in backgrounds with 0, 10, and 20% oxygen. Furthermore, we are able to quantify the mentioned gases and to determine unknown concentrations based on training data. Very low levels of relative humidity below a few percent influence the sensor response considerably but for higher levels the cross interference of humidity is negligible. In addition, experiments regarding stability and reproducibility were performed.
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| 3. |
- Larsson, Andreas, et al.
(författare)
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Thermal Management System for Particle Sensors Design, Performance and Verification
- 2012
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Ingår i: IEEE Sensors Journal. - : Institute of Electrical and Electronics Engineers (IEEE). - 1530-437X .- 1558-1748. ; 12:6, s. 2299-2305
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the thermal performance of a proposed thermal management device (patented in 2009) intended for a thermophoresis-based soot sensor. The performance was studied for temperatures ranging from 50 to 400 degrees C and for exhaust speeds up to 10 m/s. It also presents the design and basic concepts. The performance study and design development were performed with finite element analysis (FEA). The FEA results were then verified with experiments in a heated wind tunnel. The relative performance of the device was found to increase for higher temperatures and lower wind speeds. The main conclusion drawn from this paper was that it is feasible to cool a sensor surface enough for a thermophoresis-based soot sensor in a diesel exhaust system.
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| 4. |
- Wingbrant, Helena, et al.
(författare)
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Using a MISiC-FET sensor for detecting NH3 in SCR systems
- 2005
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Ingår i: IEEE Sensors Journal. - 1530-437X .- 1558-1748. ; 5:5, s. 1099-1105
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Becker, Elin, et al.
(författare)
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Study of the Sensing Mechanism Towards Carbon Monoxide of Platinum-Based Field Effect Sensors
- 2011
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Ingår i: IEEE SENSORS JOURNAL. - : IEEE. - 1530-437X. ; 11:7, s. 1527-1534
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the temperature dependence and the effect of hydrogen on the CO response of MISiC field effect device sensors. The evolution of adsorbates on a model sensor was studied by in situ DRIFT spectroscopy and correlated to sensor response measurements at similar conditions. A strong correlation between the CO coverage of the sensor surface and the sensor response was found. The temperature dependence and hydrogen sensitivity are partly in agreement with these observations, however at low temperatures it is difficult to explain the observed increase in sensor response with increasing temperature. This may be explained by the reduction of a surface oxide or removal of oxygen from the Pt/SiO2 interface at increasing temperatures. The sensing mechanism of MISiC field effect sensors is likely complex, involving several of the factors discussed in this paper.
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| 6. |
- Wingbrant, Helena, et al.
(författare)
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Co-sputtered metal and SiO2 layers for use in thick-film MISiC NH3 sensors
- 2006
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Ingår i: IEEE Sensors Journal. - 1530-437X. ; 6:4, s. 887-897
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Wingbrant, Helena, et al.
(författare)
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The influence of catalytic activity on the phase transition governed binary switch point of MISiC-FET lambda sensors
- 2006
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Ingår i: Applied Surface Science. - : Elsevier BV. - 1530-437X .- 0169-4332. ; 252:20, s. 7473-7486
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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