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High temperature catalytic metal field effect transistors for industrial applications

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 d ...

Evaluation of on-line flue gas measurements by MISiCFET and metal-oxide sensors in boilers

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/sub 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.

SiC Based Gas Sensors and their Applications

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.

MISiCFET chemical sensors for applications in exhaust gases and flue gases

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.

Evaluation of on-line hot flue gas measurements

Using Metal Insulator Silicon Carbide (MISiC) sensors, Semiconducing Metal Oxide sensors (SMO) and a linear lambda sensor in an electronic nose, we measure hot flue gases on-line. Flue gas from a 500 kW pellets fuelled boiler, which is used for heating apartment blocks, has been used to feed the experimental set-up. Several reference instruments, which measure the flue gases in parallel to the sensor array, are connected to the electronic nose. The gases which are interesting to measure are NO, CO, O2 and hydrocarbons, HC. Results on prediction for CO, NO, and O2 in the flue gases based on PLS- (and ANN-) models are here presented.

Substrate Bias Amplification of a SiC Junction Field Effect Transistor with a Catalytic Gate Electrode

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.

MISiCFET Chemical Gas Sensors for High Temperature and Corrosive Environment Applications

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.

MISiC-FET devices with bias controlled baseline and gas response

The drain current-voltage characteristics of a chemical gas sensor based on a catalytic metal insulator silicon carbide field effect transistor (MISiC-FET) was measured in H/sub 2/ and O/sub 2/ ambient while applying negative substrate bias at temperatures up to 600/spl deg/C. It is reported that the gas sensitivity can be amplified and the position of the base-line controlled by applying a negative substrate bias to the MISiC-FET device, which is a buried short channel device. This is possible in a wide range of drain current levels and over a large temperature range.

Influence of the Gate Material and Temperature on the Diode Properties of Schottky Diodes based on SiC in O 2 or CO Ambient

MSiC sensors with different gate materials, Pt-TaSixOy, porous Pt and Ir, have been investigated as a function of temperature when the ambient was changed between CO and O2. Four parameters have been investigated; the barrier height, ΦBn, the change in barrier height, ΔΦBn, due to different gas ambient, the series resistance, R, and the ideality factor, n. The diodes with porous Pt and Ir electrodes have the largest change in barrier height at 300∼500°C and at 100∼300°C, respectively. The diode with the TaSixOy layer has a higher ideality factor and higher series resistance. In the oxygen ambient the barrier height of the diodes with porous Pt and Ir electrodes have a large temperature dependence.