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Unéus, Lars
Publications (10 of 13) Show all publications
Lee, S.-K., Suh, E.-K., Cho, N.-K., Park, H.-D., Unéus, L. & Lloyd-Spets, A. (2005). Comparison study of ohmic contacts to 4H-silicon carbide in oxidizing ambient for harsh environment gas sensor applications. Solid-State Electronics, 49, 1297-1301
Open this publication in new window or tab >>Comparison study of ohmic contacts to 4H-silicon carbide in oxidizing ambient for harsh environment gas sensor applications
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2005 (English)In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 49, p. 1297-1301Article in journal (Refereed) Published
Keywords
Silicon carbide, LTLM structures, Gas sensor, ohmic contacts
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-30144 (URN)10.1016/j.sse.2005.06.005 (DOI)15625 (Local ID)15625 (Archive number)15625 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13
Unéus, L., Artursson, T., Mattsson, M., Ljung, P., Wigren, R., Mårtensson, P., . . . Lloyd-Spets, A. (2005). Evaluation of on-line flue gas measurements by MISiCFET and metal-oxide sensors in boilers. IEEE Sensors Journal, 5(1), 75-81
Open this publication in new window or tab >>Evaluation of on-line flue gas measurements by MISiCFET and metal-oxide sensors in boilers
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2005 (English)In: IEEE Sensors Journal, ISSN 1530-437X, E-ISSN 1558-1748, Vol. 5, no 1, p. 75-81Article in journal (Refereed) Published
Abstract [en]

Metal insulator silicon carbide field-effect transistor sensors, metal-oxide sensors, and a linear Lambda sensor in an electronic nose was used to measure on-line in hot flue gases from a boiler. Flue gas from a 100-MW pellets-fuelled boiler has been used to feed the experimental setup. Several reference instruments, which measure the flue gases in parallel to the sensor array, are connected to the electronic nose. Data was collected during six weeks and then evaluated. Using principal component analysis as the data evaluation method, different operating modes for the boiler have been identified in the data set. The different modes could be described in terms of high or low O 2 and CO concentration. Furthermore, we have shown that it seems possible to use a sensor array to determine the operating mode of the boiler and, by partial least-squares models, measure the CO concentration when the boiler operates in its optimum mode.

Keywords
boilers, ctalytic matals, chemometric methods, field-effect transistor (FET), flue gases, gas sensors, sensor arrays, silicone carbide (SiC)
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-30277 (URN)10.1109/JSEN.2004.839132 (DOI)15794 (Local ID)15794 (Archive number)15794 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13
Janson, M. S., Linnarsson, M. K., Hallen, A., Svensson, B. G., Achtziger, N., Unéus, L., . . . Forsberg, U. (2004). Hydrogen in the wide bandgap semiconductor silicon carbide. Physica Scripta, T108, 99-112
Open this publication in new window or tab >>Hydrogen in the wide bandgap semiconductor silicon carbide
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2004 (English)In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T108, p. 99-112Article in journal (Refereed) Published
Abstract [en]

In this paper we give a review of our recent results related to the incorporation of hydrogen (H) in silicon carbide (SiC) and its interaction with acceptor doping atoms and implantation induced defects. Hydrogen is an abundant impurity in the growth of epitaxial SiC since it is present in the precursor gases and since H-2 is used as the carrier gas. High concentrations of hydrogen are indeed incorporated into highly doped p-type epi-layers and it is shown that the main source is the carrier gas. Furthermore, it is revealed that the entire substrate becomes homogeneously filled with hydrogen during growth and that this hydrogen is more thermally stable than that in the epi-layer. Incorporation of hydrogen from an H-2 ambient, at temperatures considerably lower than those used for epitaxy, is also demonstrated in p-type samples coated with a catalytic metal film. This effect is most likely the cause for the increased series resistance observed in p-type SiC Schottky sensor devices using a catalytic metal gate after annealing at 600 degrees C in a H-2 containing ambient. Hydrogen is found to passivate the acceptors Al and B by forming electrically neutral H-acceptor complexes. Unlike in Si and GaAs, the two H-acceptor complexes in SiC exhibit very different dissociation energies, suggesting that the atomic configurations of the complexes are significantly different. The migration of mobile hydrogen in the presence of externally applied, or internal built-in, electric fields further reveals that hydrogen is present as H+ in p-type SiC. Finally, the redistribution and subsequent out-diffusion of low energy implanted H-1 and H-2 is investigated. Two annealing phases for the redistribution are observed, and the activation energies for the processes are extracted.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-48247 (URN)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12
Nakagomi, S., Takahashi, M., Kokubun, Y., Unéus, L., Savage, S., Wingbrant, H., . . . Lloyd-Spets, A. (2004). Substrate bias amplification of a SiC junction field effect transistor with a catalytic gate electrode. Materials Science Forum, 457-460, 1507-1510
Open this publication in new window or tab >>Substrate bias amplification of a SiC junction field effect transistor with a catalytic gate electrode
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2004 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 457-460, p. 1507-1510Article in journal (Refereed) Published
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.

Keywords
gas sensor, catalytic gate, substrate bias, buried channel, JFET, SIT, high temperature
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-48313 (URN)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12
Nakagomi, S., Shinobu, H., Unéus, L., Lundström, I., Ekedahl, L.-G., Yakimova, R., . . . Lloyd-Spets, A. (2002). Influence of epitaxial layer on SiC Schottky diode gas sensors operated under high-temperature conditions. In: Materials Science Forum, Vols. 389-393. Paper presented at ICSCRM2001 (pp. 1423-1426). , 389-3
Open this publication in new window or tab >>Influence of epitaxial layer on SiC Schottky diode gas sensors operated under high-temperature conditions
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2002 (English)In: Materials Science Forum, Vols. 389-393, 2002, Vol. 389-3, p. 1423-1426Conference paper, Published paper (Refereed)
Abstract [en]

Schottky diode gas sensors were fabricated on top of the epitaxial layer grown by three different methods, purchased from Cree Research Inc., by hot wall CVD, or by sublimation at a high growth rate. The epitaxial layers have different thickness and doping. The current-voltage characteristics of the gas sensors were compared in different gas ambient during operation in the high temperature region. The temperature dependence of the series resistance of the diodes revealed two types of carrier scattering mechanisms, impurity scattering for the sublimation epitaxial layer at 300-400degreesC and at 400-600degreesC, lattice scattering for all diodes. The ideality factor of the diode fabricated on the Cree substrate is higher than others. The higher ideality factor gives rise to a larger forward voltage change for a change in gas ambient. The amount of change in barrier height caused by a change in the ambient gas is almost the same for the three types of diodes. The value of the barrier height of the diode grown by the sublimation method is lower than for the others, which gives a higher reverse saturation current at temperatures above 400degreesC. The largest saturation current also shows the largest current change when switching between different gas atmospheres.

Keywords
epitaxial layers, gas sensors, high temperature, resistance, scattering, Schottky diodes
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-48832 (URN)
Conference
ICSCRM2001
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2014-10-08
Lloyd-Spets, A., Unéus, L., Svenningstorp, H., Wingbrant, H., Harris, C., Salomonsson, P., . . . Savage, S. (2002). MISiCFET chemical gas sensors for high temperature and corrosive environment applications. Materials Science Forum, 389-3, 1415-1418
Open this publication in new window or tab >>MISiCFET chemical gas sensors for high temperature and corrosive environment applications
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2002 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 389-3, p. 1415-1418Article in journal (Refereed) Published
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.

Keywords
ammonia, catalytic metal, combustion, FETs, flue gases, gas sensors, high temperature, SCR
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-48830 (URN)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12
Wingbrant, H., Unéus, L., Andersson, M., Cerda, J., Savage, S., Svenningstorp, H., . . . Lloyd-Spets, A. (2002). MISiCFET chemical sensors for applications in exhaust gases and flue gases. Materials Science Forum, 433-4, 953-956
Open this publication in new window or tab >>MISiCFET chemical sensors for applications in exhaust gases and flue gases
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2002 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 433-4, p. 953-956Article in journal (Refereed) Published
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.

Keywords
ammonia, catalytic metals, combustion, exhaust gases, field effect transistor, flue gases, gas sensor, high temperature, SCR
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-48564 (URN)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12
Unéus, L., Nakagomi, S., Linnarsson, M., Jensen, M., Svensson, B., Yakimova, R., . . . Lloyd-Spets, A. (2002). The effect of hydrogen diffusion in p- and n-type SiC Schottky diodes at high temperatures. In: Materials Science Forum, Vols. 389-393. Paper presented at ICSCRM2001 (pp. 1419-1422). , 389-3
Open this publication in new window or tab >>The effect of hydrogen diffusion in p- and n-type SiC Schottky diodes at high temperatures
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2002 (English)In: Materials Science Forum, Vols. 389-393, 2002, Vol. 389-3, p. 1419-1422Conference paper, Published paper (Refereed)
Abstract [en]

We present here the effect of a hydrogen anneal at 600degreesC for Schottky sensor devices based on n- and p-type 4H SiC. The devices have gate contacts of Ta/Pt, or TaSix/Pt. The catalytic metal gate dissociates hydrogen and thus promotes diffusion of hydrogen atoms into the SiC, where the atoms will trap or react with different impurities, defects or surface states. This will change parameters such as the carrier concentrations, the defect density of the material or the surface resistivity at the SiC/SiO2 interface. The current-voltage and the capacitance-voltage characteristics were measured before and after annealing in hydrogen and oxygen containing atmosphere, and the results show a reversible effect in the I-V characteristics.

Keywords
annealing, gas sensors, high temperature, hydrogen diffusion, Schottky diodes
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-48831 (URN)
Conference
ICSCRM2001
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2014-10-08
Lloyd-Spets, A., Unéus, L., Svenningstorp, H., Tobias, P., Ekedahl, L.-G., Larsson, O., . . . Lundström, I. (2001). SiC based field effect gas sensors for industrial applications. Physica status solidi. A, Applied research, 185(1), 15-25
Open this publication in new window or tab >>SiC based field effect gas sensors for industrial applications
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2001 (English)In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 185, no 1, p. 15-25Article in journal (Refereed) Published
Abstract [en]

The development and field-testing of high-temperature sensors based on silicon carbide devices have shown promising results in several application areas. Silicon carbide based field-effect sensors can be operated over a large temperature range, 100-600 degreesC, and since silicon carbide is a chemically very inert material these sensors can be used in environments like exhaust gases and flue gases from boilers. The sensors respond to reducing gases like hydrogen, hydrocarbons and carbon monoxide. The use of different temperatures, different catalytic metals and different structures of the gate metal gives selectivity to different gases and arrays of sensors can be used to identify and monitor several components in gas mixtures. MOSFET sensors based on SIC combine the advantage of simple circuitry with a thicker insulator, which increases the long term stability of the devices. In this paper we describe silicon carbide MOSFET sensors and their performance and give: examples of industrial applications such as monitoring of car exhausts and flue gases. Chemometric methods have been used for the evaluation of the data.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-49228 (URN)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12
Lloyd-Spets, A., Tobias, P., Unéus, L., Svenningstorp, H., Ekedahl, L.-G. & Lundström, I. (2000). High temperature catalytic metal field effect transistor for industrial applications. Sensors and actuators. B, Chemical, 70(1-3), 67-76
Open this publication in new window or tab >>High temperature catalytic metal field effect transistor for industrial applications
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2000 (English)In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 70, no 1-3, p. 67-76Article in journal (Refereed) Published
Abstract [en]

Field effect chemical sensors, utilising silicon carbide as semiconductor, can be operated at high temperature and in rough environments. Gas sensitive field effect transistors, MISiCFET, are now developed (ACREO, Kista in Sweden). This will increase the number of possible applications for field effect gas sensors. The first batch of MISiCFET devices is possible to operate in intermittent pulses of hydrogen/oxygen up to 775°C. At temperature above 600°C, the gas response of the MISiC devices has very short time constants for a change between oxidising and reducing atmosphere and cylinder specific monitoring of a combustion engine has been demonstrated. Other industrial applications, like exhaust diagnosis and flue gas monitoring, have been demonstrated by the use of MISiC Schottky diodes at lower temperatures, 200°C-500°C.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-47556 (URN)10.1016/S0925-4005(00)00559-1 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
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