| 1. |
- Lloyd-Spets, Anita, et al.
(författare)
-
MISiCFET chemical gas sensors for high temperature and corrosive environment applications
- 2002
-
Ingår i: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 389-3, s. 1415-1418
-
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.
|
|
| 2. |
- Nakagomi, S, et al.
(författare)
-
Influence of epitaxial layer on SiC Schottky diode gas sensors operated under high-temperature conditions
- 2002
-
Ingår i: Materials Science Forum, Vols. 389-393. ; , s. 1423-1426
-
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.
|
|
| 3. |
- Unéus, Lars, et al.
(författare)
-
The effect of hydrogen diffusion in p- and n-type SiC Schottky diodes at high temperatures
- 2002
-
Ingår i: Materials Science Forum, Vols. 389-393. ; , s. 1419-1422, s. 1419-1422
-
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.
|
|
| 4. |
- Unéus, Lars, 1971-
(författare)
-
Development and Characterisation of SiC Based Sensors for Harsh Environments
- 2002
-
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.
|
|
| 5. |
- Wingbrant, Helena, et al.
(författare)
-
MISiCFET chemical sensors for applications in exhaust gases and flue gases
- 2002
-
Ingår i: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 433-4, s. 953-956
-
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.
|
|
