GasFET for the detection of reducing gases
ABSTRACT A new gas sensor technology based on the signal read out of the work function change on sensitive films of thin or thick film SnO2 or Ga2O3 is used for the detection of reducing gases. The thick films are catalytic activated with Pd. The sensor device consists of a field effect transistor (FET) with suspended gate electrode prepared in hybrid flip chip technology (HFC-FET).Measurements with a Kelvin probe for testing the sensitive properties of the films and with complete assembled GasFET were performed. The SnO2 thick films activated with Pd show a high sensitivity to CO, hence concentrations lower than 1 vpm can be detected. The sensor response decreases with increasing temperature. A high cross sensitivity to oxygen and humidity is found only for very low oxygen concentrations (∼0 vol.%) or low humidity (∼0% r.h.). Thick films of SnO2 show a similar behavior to changes in the gas atmosphere in measurements performed using the Kelvin probe and with completely assembled GasFET sensors.
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ABSTRACT: This status report overviews activities of the German gas sensor research community. It highlights recent progress in the field of potentiometric, amperometric, conductometric, impedimetric, and field effect-based gas sensors. It is shown that besides step-by-step improvements of conventional principles, e.g. by the application of novel materials, novel principles turned out to enable new markets. In the field of mixed potential gas sensors, novel materials allow for selective detection of combustion exhaust components. The same goal can be reached by using zeolites for impedimetric gas sensors. Operando spectroscopy is a powerful tool to learn about the mechanisms in n-type and in p-type conductometric sensors and to design knowledge-based improved sensor devices. Novel deposition methods are applied to gain direct access to the material morphology as well as to obtain dense thick metal oxide films without high temperature steps. Since conductometric and impedimetric sensors have the disadvantage that a current has to pass the gas sensitive film, film morphology, electrode materials, and geometrical issues affect the sensor signal. Therefore, one tries to measure directly the Fermi level position either by measuring the gas-dependent Seebeck coefficient at high temperatures or at room temperature by applying a modified miniaturized Kelvin probe method, where surface adsorption-based work function changes drive the drain-source current of a field effect transistor.Sensors 01/2009; 9(6):4323-65. · 2.05 Impact Factor
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ABSTRACT: A series of cobalt oxyhydroxide (CoOOH) nano-films (250–450 nm thick) containing a small percentage of Au by mass were prepared from the component oxides through special precipitation and were sintered on the sensor substrate between Pt electrodes at 300 °C for 2 h. The sensor response to CO and other combustion by-product pollutants typical for early stages of fire, defined as Rg/Ra, where Rg and Ra denote the sensor electrical resistance in the sample gas and in air, respectively, was strongly promoted by addition of a small amount of Au to the CoOOH nanostructures. The results revealed that the sensors attached with Au-doped CoOOH sensing electrode (SE) have good sensitivity to CO in the temperature range of 60–110 °C with the maximum CO response near 80 °C. Cross-sensitivity investigation of these sensors to various gases has shown that the sensitivity of the nanostructured Au-loaded CoOOH-SE to CO is the highest among other gases. As the amount of Au loaded increased up to 0.5%, the device was found to be more sensitive to CO, whilst the addition of 1 mass% Au substantially degraded the sensing properties of the device. The promoting effects of Au were discussed based on the behaviour of electrical resistance of the Au-loaded sensors. The results of this work may be applicable to further development of carbon monoxide sensors for fire detection at its earlier stages.Sensors and Actuators B Chemical 01/2008; · 3.54 Impact Factor
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ABSTRACT: A new gas sensor based on ultrathin SnO2-films with high sensitivity for humidity and carbon monoxide has been developed. The SnO2-sensing films are fabricated by a spray pyrolysis process with a thickness between 50 and 100 nm on oxidized silicon substrates. The SnO2-sensing films are finally processed in arrays of parallel bars to achieve the sensor device. The structure of SnO2-layers has been characterized by SEM, AFM and XPS analysis. The sensors are operated at temperatures of 250–400 °C, show high sensitivity to humidity and are able to detect carbon monoxide down to a concentration of less than 5 ppm. The fabrication process of the gas sensor is fully compatible with silicon process technology. The spray pyrolysis technique is a simple and flexible process and thus is suitable for the cost efficient fabrication of a new gas-sensing device. Strategies to improve sensitivity and selectivity of the sensor toward different gas species are discussed.Sensors and Actuators B: Chemical. 01/2008;