Abstract: Humidity or a gas concentration or a solvent concentration in at least one gas is detected by a field effect transistor-based gas sensor whose sensor signal is generated by the change in the work function on a sensitive film. Detection is to be provided in a simple, effective and inexpensive manner. An additional change in potential is impressed at a gate of the field effect transistor and a variable of the resulting change in the sensor signal relative to the additional change in potential is evaluated. For example, each variable, which is e.g. a ratio, can be assigned a relative humidity, a gas concentration, or a solvent concentration. Sensitive films having at least one polymer are particularly advantageous.

Abstract: A FET gas sensor having a relatively low operating temperature, for example, room temperature, is free from cross sensitivities from interfering gases by a preceding in-line filter. The sensor's service life is substantially stabilizable by using fabric-like activated charcoal filters which can be regenerated by a moderate temperature increase, and by limiting the diffusion of the analyte gas, which is made possible by the relatively small amount of gas detectable on the sensitive layer of the sensor. This substantially increases the service life of the filters. The gas sensor eliminates cross sensitivities to thereby increase the detection reliability thereof. Also, the gas sensor has relative long term stability and is economical to build. The gas sensor can read relatively weak signals generated by gas-sensitive layers, for example, without other stronger gas signals interfering with the weak signals.

Abstract: The invention relates to a sensor and a method for detecting soot, said method comprising the following steps: a first operating temperature is set on the sensor for a measuring phase, such that soot can be deposited on the surface of the substrate, but depositions interfering with the measurement of the soot are prevented; the time between the beginning of the measurement and the increase in conductivity between the electrodes is recorded; and a second operating temperature is set on the sensor for a regeneration phase, such that the deposited soot is burned with the oxygen in the test gas. The inventive product is a soot sensor for using in the automobile industry.

Abstract: A gas-sensitive field-effect transistor may be formed from a substrate with a gas-sensitive layer and a transistor processed separately and then assembled. The substrate may be patterned to form spacers by which the height of an air gap between the transistor and the sensitive layer may be adjustable to a relatively precise degree. Formation of the spacers can be achieved by patterning the substrate using material-removal techniques. The height of the spacers may be adjusted in the layer thickness of the gas-sensitive layer and for the transistor fabricated using a CMOS process. Suitable techniques for producing recesses between the spacers include, for example, polishing, cutting, sandblasting, lithographic dry etching, or wet-chemical etching. Suitable materials for the substrate may include, for example, glass, ceramic, aluminum oxide, silicon, or a dimensionally stable polymer.

Abstract: The invention relates to a gas sensor which is used to detect ammonia by detecting and evaluating conductivity variations on semi-conductive metal oxides, comprising: a substrate, a gas sensitive layer made of a semi-conductive metal oxide, a catalytic filter which is disposed in front of the metal oxide, said filter being used to convert ammonia, contained in the measuring gas, into a NO/NO2 mixture or to only NO2, measuring electrodes which are arranged on the surface of the substrate in order to detect conductivity variations in the semi-conductive metal oxide which is at least sensitive to NO/NO2, a controllable electric heating device which is used to adjust predetermined temperatures at least for the semi-conductive metal oxide, whereby the formed NO/NO2 can be guided to the metal oxide and the content of ammonia in the measuring gas can be determined from the NO/NO2-measurement by means of the semi-conductive metal oxide.

Abstract: A gas sensor based on a field effect transistor (“FET”) evaluates both a change in work function of a gas-sensitive layer of the FET and a change in the capacitance of the layer. Thus, two physically independent signals are read from the gas-sensitive layer, each signal representing a sensitivity to a different gas. This reduces the effect of cross-sensitivities; that is, of one gas on the target gas. The underlying physical mechanisms, the first causing a change in the work function in a reaction with gases and the second causing a change in the capacitance of the sensitive layer, are widely different. Because of this, the two parameters demonstrate different gas sensitivities. If the reactions to both gases are known, the effect of the interfering gas on the sensor signal can be compensated for, and with this the concentration of the target gas can be determined.

Abstract: A soot sensor includes a plurality of sensor elements including a base body having at least a part that is excitable to produce mechanical oscillations, the base body having at least one defined surface having predefined catalytic properties and subjected to a measurement gas, and a heating element acting on said base body, wherein a change in an oscillation frequency, an oscillation amplitude or the quality of the oscillation which has occurred due to increasing precipitation of soot on the defined surface indicates the presence of soot.

Abstract: A gas-sensitive field-effect transistor (GasFET) for the detection or measurement of an amount of hydrogen sulfide present in ambient air includes a raised gate electrode and a transistor structure. The raised gate electrode may be formed from or coated with a gas-sensitive material such as tin oxide, or silver, silver oxide or mixtures thereof. An insulator layer may be disposed on top of the transistor structure. An air gap is formed between the gas-sensitive layer of the raised gate electrode and the insulator layer on top of the transistor structure.

Abstract: The invention relates to an FET-based gas sensor comprising a gas channel for diffusing a measuring gas to a gas-sensitive layer which is actively connected to a FET for signal readout. According to the invention, an electrochemical element is at least partially inserted into the gas channel for the electrochemical conversion of interfering gases. The arrangement is permeable to the target gas.

Abstract: Method of effecting a readout of a gas-sensitive field-effect transistor having an air gap between a gate electrode with a gas-sensitive layer and the readout transistor, in which a potential occurring on the gas-sensitive layer in the presence of a target gas is passed through a noncontacting floating gate electrode to the transistor, wherein the potential of a reference electrode, which together with the floating gate electrode generates a capacitance Cw, is tracked to the potential of the floating gate electrode in order to eliminate the capacitance Cw during the measurement.

Abstract: A gas-sensitive field-effect transistor may be formed from a substrate with a gas-sensitive layer and a transistor processed separately and then assembled. The substrate may be patterned to form spacers by which the height of an air gap between the transistor and the sensitive layer may be adjustable to a relatively precise degree. Formation of the spacers can be achieved by patterning the substrate using material-removal techniques. The height of the spacers may be adjusted in the layer thickness of the gas-sensitive layer and for the transistor fabricated using a CMOS process. Suitable techniques for producing recesses between the spacers include, for example, polishing, cutting, sandblasting, lithographic dry etching, or wet-chemical etching. Suitable materials for the substrate may include, for example, glass, ceramic, aluminum oxide, silicon, or a dimensionally stable polymer.

Abstract: An ozone sensor has an ozone-sensitive layer containing an ozone-sensitive material which is encapsulated in a polymer or in a polymer mixture or is coated by at least one polymer or polymer mixture. Advantages result from a longer service life of the ozone-sensitive materials which, because of their high hygroscopic properties, would not be stable without encapsulation or coating. Furthermore, a polymer matrix can be selectively used as a filter or in order to eliminate interfering influences.

Abstract: The invention relates to an ozone sensor having an ozone-sensitive layer containing an ozone-sensitive material which is encapsulated in a polymer or in a polymer mixture or is coated by at least one polymer or polymer mixture. Advantages result from a longer service life of the ozone-sensitive materials which, because of their high hygroscopic properties, would not be stable without encapsulation or coating. Furthermore, a polymer matrix can be selectively used as a filter or in order to eliminate interfering influences.