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: To implement low-power gas sensors with low component costs, the principle of work-function read out via a hybrid suspended gate FET (SGFET) is being pursued, whereby a freely selectable sensor film undergoes a reversible work-function change corresponding to the build-up of a potential difference on the surface in response to gas adsorption/reaction. This is read out via an ISFET structure. An innovative design which allows cheap manufacturing will be described for the principle that has already been successfully demonstrated. The starting point of the design is a ceramic Al2O3 substrate coated with conductor patterns and sensitive materials onto which the FET is mounted in flip–chip technology. By means of the freely selectable sensor film and its preparation method, a wide range of applications can be opened up.Sensors and Actuators B: Chemical. 01/2001;