| 1. |
- Lloyd-Spets, Anita, et al.
(författare)
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High temperature catalytic metal field effect transistor for industrial applications
- 2000
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Ingår i: Sensors and actuators. B, Chemical. - 0925-4005 .- 1873-3077. ; 70:1-3, s. 67-76
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Lloyd-Spets, Anita, et al.
(författare)
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MISiCFET chemical gas sensors for high temperature and corrosive environment applications
- 2002
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Ingår i: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 389-3, s. 1415-1418
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Lloyd-Spets, Anita, et al.
(författare)
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SiC based field effect gas sensors for industrial applications
- 2001
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Ingår i: Physica status solidi. A, Applied research. - 0031-8965 .- 1521-396X. ; 185:1, s. 15-25
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 4. |
- Nakagomi, S, et al.
(författare)
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Influence of epitaxial layer on SiC Schottky diode gas sensors operated under high-temperature conditions
- 2002
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Ingår i: Materials Science Forum, Vols. 389-393. ; , s. 1423-1426
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 5. |
- Savage, S, et al.
(författare)
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SiC based gas sensors and their applications
- 2000
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Ingår i: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 353-3, s. 747-752
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Tidskriftsartikel (refereegranskat)abstract
- The development and field-testing of hardy high-temperature sensors based on silicon carbide devices has to date shown promising results in several application areas. As the need to take care of the environment becomes more urgent, these small and relatively cheap sensors could be used to increase the monitoring of gases, or to replace or complement larger and more expensive sensor technologies used today. In this paper the development of Silicon Carbide MOSFET transistor sensors and Schottky diode sensors is described. The devices are tested in industrial applications such as monitoring of car exhausts and flue gases.
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| 6. |
- Svenningstorp, H, et al.
(författare)
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High temperature gas sensors based on catalytic metal field effect transistors
- 2000
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Ingår i: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 338-3, s. 1435-1438
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Tidskriftsartikel (refereegranskat)abstract
- Catalytic metal insulator silicon carbide field effect devices, MISiCFET, have been developed as gas sensitive devices. They functioned in a corrosive atmosphere of hydrogen / oxygen alternating pulses up to 775 degreesC. At 600 degreesC some devices operated with full gas response to hydrogen for 17 hours. Below a temperature of 500 degreesC the gas response of the devices was very stable with no base line drift for several days. MISiC Schottky diodes have been used for cylinder specific monitoring of an engine and exhausts and flue gas diagnosis. The MISiCFET devices will increase the number of possible applications for FET gas sensor devices.
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| 7. |
- Unéus, Lars, et al.
(författare)
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The effect of hydrogen diffusion in p- and n-type SiC Schottky diodes at high temperatures
- 2002
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Ingår i: Materials Science Forum, Vols. 389-393. ; , s. 1419-1422, s. 1419-1422
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 8. |
- Janson, Martin S., et al.
(författare)
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Hydrogen in the wide bandgap semiconductor silicon carbide
- 2004
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Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; T108, s. 99-112
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 9. |
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| 10. |
- Lloyd-Spets, Anita, 1951-, et al.
(författare)
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Gas sensor arrays for combustion control
- 2005
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Ingår i: Encyclopedia of Sensors, eds.. - California : American Scientific Publishers. - 158883056X ; , s. 139-154
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- 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."
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| 11. |
- Nakagomi, S, et al.
(författare)
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Substrate bias amplification of a SiC junction field effect transistor with a catalytic gate electrode
- 2004
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Ingår i: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 457-460, s. 1507-1510
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 12. |
- Unéus, Lars, 1971-
(författare)
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Development and Characterisation of SiC Based Sensors for Harsh Environments
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The introduction of chemical gas sensors in our environment is a process that started many years ago. However, although the process has been rather slow over the years, the interest for chemical gas sensors is rising due to the growing environmental awareness. The need to measure gas components in our surrounding is becoming more and more important as the technological level increases in the world.The development of gas sensors for different type of combustion control has been the focus in this thesis. To be able to measure in harsh environments such as flue gases or diesel exhausts, extremely robust sensors have to be developed. By using silicon carbide, a wide band gap material and chemically inert material, sensors that can withstand the harsh environment was developed and manufactured. Since SiC is a rather new material in the world of sensors, a great deal of work was performed on the design and basic understanding of the device. Several different ohmic contacts were studied thoroughly and it was shown that the ohmic contacts on the device could be improved. The effect of hydrogen diffusion into a SiC gas sensor device has also been investigated.Much effort was spent on optimisation of the design and measurement parameters for the sensor when detecting different gas components. The device design parameters are the choice of catalytic metal for the sensor, the thickness of the metal and the porosity of the metal. The operating parameters are the sensor temperature and the annealing procedure before use. It was shown that different pre-treatment of the sensor could have large influence on the ammonia response.Selected gas sensors were used in the flue gas project where the intention is to use the information about the gas concentrations to regulate the boiler for a better power-economy. SiC based Schottky diodes or transistors combined with commercial sensors and a linear lambda sensor was used in a high temperature electronic nose to measure in the flue gases. By using multivariate methods it was possible to evaluate the large amount of data from the continuous measurements in the flue gases. The results showed that it might be possible to use a small array of different gas sensors to identify different modes of operation of the boiler. Furthermore, predictions of the concentrations of a few specific gas components in the flue gases could be made.
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| 13. |
- Unéus, Lars, 1971-, et al.
(författare)
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Evaluation of on-line flue gas measurements by MISiCFET and metal-oxide sensors in boilers
- 2005
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Ingår i: IEEE Sensors Journal. - 1530-437X .- 1558-1748. ; 5:1, s. 75-81
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 14. |
- Unéus, Lars, et al.
(författare)
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Schottky diodes with thin catalytic gate metals for potential use as ammonia sensors for exhaust gases
- 1999
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Ingår i: Sensors and materials. - : Scientific Publishing Division Myu. - 0914-4935. ; 11:5, s. 305-318
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Tidskriftsartikel (refereegranskat)abstract
- Selective catalytic reduction (SCR) is a method in which ammonia reacts with nitric oxides in a catalytic converter to form water and nitrogen. We show that catalytic Metal Insulator Silicon Carbide (MISiC) devices can be used as ammonia sensors for a SCR system in a diesel engine. Different catalytic metals, Pt and Ir, with a thickness of 30 or 50 nm were investigated. The temperature dependence of the ammonia response of the sensors was characterized. Maximum responses were found at temperatures between 225-250 degrees C. Preliminary experiments were performed to investigate how annealing in different gas ambient influences the response-temperature curve of the sensors. In synthetic diesel exhausts with ammonia added, the sensors showed very good selectivity for ammonia and a small interaction effect with oxygen. The influence of other gas components was almost negligible. Temperature in the diesel exhaust system can reach 550 degrees C; however, operating at temperatures above 400 degrees C limited the lifetime of the sensor. Anger electron spectroscopy (AES) revealed that island formation of the metal due to structural changes was the main reason for failure of the sensor.
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| 15. |
- Wingbrant, Helena, et al.
(författare)
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MISiCFET chemical sensors for applications in exhaust gases and flue gases
- 2002
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Ingår i: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 433-4, s. 953-956
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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