Per Salomonsson

SiC Based Field Effect Gas Sensors for Industrial Applications

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 °C, 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.

Using a MISiC-FET sensor for detecting NH/sub 3/ in SCR systems

One way to decrease the emitted levels of NO/sub x/ from diesel engines is to add NH/sub 3/ in the form of urea to the exhausts after combustion. NH/sub 3/ will react with NO/sub x/ in the catalytic converter to form N/sub 2/ and water, which is called selective catalytic reduction (SCR). The amount of NH/sub 3/ added may be regulated through closed-loop control by using an NH/sub 3/ 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 NH/sub 3/. Here, the sensors have been further studied in engine SCR systems. Tests on the cross sensitivity to N/sub 2/O and NO/sub 2/, 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 NH/sub 3/ in diesel engine exhausts. The addition of urea was computer controlled, which made it possible to add NH/sub 3/ 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 NH/sub 3/ response was slightly decreased by a background level of NO/sub 2/.

Response of metal-oxide-silicon carbide sensors to simulated and real exhaust gases

Field effect devices based on catalytic metal-oxide-silicon carbide (MOSiC) structures can be used as high temperature gas sensors. The devices are sensitive to hydrocarbons and hydrogen and can be ...

Influence of catalytic reactivity on the response of metal-oxide-silicon carbide sensor to exhaust gases

Abstract Catalytic metal insulator silicon carbide, MISiC, Schottky diodes are promising devices for on board exhaust diagnosis in cars. These sensors show a direct or indirect sensitivity to gases like H2, CO, HC (hydrocarbons) and O2. The catalytic reactivity of the sensor will effect the gas sensing conditions. In some situations knowledge about the reactivity of the catalytic surface may give more information about the exhaust gas composition. For instance, the sensor signal normally moves to a lower voltage in an ambient containing H2 and HC, however, under certain conditions when exposed to rich gas mixtures, the HC response is opposite the one for H2. Measurements performed by the MISiC sensors on simulated exhaust gas mixtures, either rich or lean, are shown here. Some fundamental studies of the HC response have been performed. Reaction limitation conditions are suggested as an explanation for the response of HC opposite the one of H2.

Detection of HC in exhaust gases by an array of MISiC sensors

Future legislations for car emissions make direct measurements in exhaust gases of hydrocarbon (HC) as well as CO and NOx interesting. Robust sensors that can stand the high temperature and rough environment in the exhaust gases are needed. Silicon carbide has the advantage of being a chemically very inert material, which, due to its high band gap, is a semiconductor even at temperatures around 800°C. Catalytic metal insulator silicon carbide Schottky diode sensors respond to gases like H2, HC, NOx in exhaust gases. The choice of catalytic metal, structure of the metal, and the operation temperature determines the response pattern to different gases. Here we will demonstrate that an array of different MISiC sensors to some extent predicts the HC concentration in gasoline exhaust gases. Chemometric methods are used for the evaluation of the signals.

Response of metal–insulator–silicon carbide sensors to different components in exhaust gases

The effects of different components in simulated car exhaust gases on silicon carbide based field effect sensors are studied using a two-level factorial design. Strong effects are observed for H-2, ...

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.

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.

MISiCFET sensor arrays for on line diagnosis

Catalytic Metal Insulator Silicon Carbide Field Effect Transistor (MISiCFETs) sensors can be processed as a sensor array on a SIC-chip. Different selectivity of the sensors is achieved by the use of different combinations of catalytic metals and insulators. The response patterns are used to evaluate for example different states of a combustion (low/high emissions, efficient/less efficient combustion) or monitoring different components in the exhausts from the combustion.