Klaus Steiner

CO and CO2 thin-film SnO2 gas sensors on Si substrates

Abstract Thin-film SnO 2 gas sensors have been structured on Si substrates. The sensors are temperature stable at 900°C in synthetic air for 48 h. No significant outdiffusion of the sensor layers can be observed after annealing. Pt catalysts lead to CO sensors without cross sensitivity to CO 2 . Pt/Ca catalyst combinations also lead to CO 2 gas response. CO 2 sensitivity between 1000 and 10 000 ppm has been demonstrated at 270°C. CO 2 might be indirectly detected via humidity exchange between CO 2 and the heated Ca-catalysed SnO 2 surface.

Contact and sheet resistance of SnO2 thin films from transmission-line model measurements

Abstract Sheet and contact resistances of thin-film SnO 2 gas sensors have been evaluated in different gas atmosphere using transmission-line model measurements. The modified sheet resistance close to the electrode/metal oxide interface exhibits the strongest response due to CO or NO 2 gas reactions. The systematic variation of contact separations and SnO 2 layer widths gives an idea for the design of simple and low-cost integrated sensor arrays. There is no necessity to modify each sensor of the array with different dopants or catalysts.

Thin-film SnO2 sensor arrays controlled by variation of contact potential—a suitable tool for chemometric gas mixture analysis in the TLV range

Abstract The selectivity of SnO2 thin-film gas sensors can be modulated by changing the contact areas of the contact electrodes. The investigated SnO2 arrays have been structured with two mask steps only. Gas mixture analysis in the German threshold limit value (TLV) range has been performed with an integrated thin-film sensor array using principal component regression (PCR) analysis. As an example, NO2, CO, CH4 and H2O mixtures in air have been analyzed. In this case additional doping materials, catalysts, temperature gradients, etc., to enhance selectivity are not necessary.

Ni, In and Sb implanted Pt and V catalysed thin-film SnO2 gas sensors

Abstract Thin-film technologies lead to low cost and reliable microsystems combining electronics and sensors. However, in competition with microelectronic fabrication sensor technologies exhibit a lack of experience creating difficulties in microsystem integration. In this paper a simple implantation process is introduced to improve thin-film sensor performance. In, Ni and Sb-doped thin-film V and Pt catalysed SnO2 gas sensors are presented. The sensor response due to pulses of H2, COx, NH3, NO2 CH4 and C2H5OH is discussed in the temperature range between 100 and 400 °C.

Ca- and Pt-catalysed thin-film SnO2 gas sensors for CO and CO2 detection

Abstract Pt-, Ca- and Pt/Ca-catalyzed thin-film SnO2 gas sensors have been structured on Si substrates. The sensors are temperature stable at 900 °C in synthetic air for 48 h. No significant outdiffusion of the sensor layers or peeling effects can be observed after annealing. Pt/Ca catalyst combinations reduce the sensor-signal drift. Pt/Ca-catalyzed sensors show a weak CO2 gas response. Ca catalysts lead to a strong NH3 response.

Gas-sensitive GaAs-MESFETs

Abstract Gas-sensitive GaAs-MESFETs with catalytic gates have been fabricated. Gas response of I–V output and transfer characteristics are discussed. Pd- and Pt-catalysed MESFETs show NO2 and NH3-sensitivity. There is no cross sensitivity to H2O, CO1, CO2 and CH4 below 100°C operating temperatures. Possible sensor mechanisms are proposed.

Thin-film In-doped V-catalysed SnO2 gas sensors

Abstract Thin-film In-doped V-catalysed SnO2 gas sensors are discussed and compared with Pt-catalysed In-doped or undoped SnO2 gas sensors. The In acceptors are implanted, while the catalysts are directly evaporated onto the active sensor layer. The V/In catalyst/dopant combination leads to thin-film sensors highly sensitive to NO2, while nearly no cross sensitivity to CO, CO2, H2 and CH4 is detectable. The maximum conductivity change of the V-catalyst In-doped SnO2 sensor in NO2-enriched synthetic air occurs at about 200 °C.

Frequency-dependent admittance analysis on amorphous silicon photodetectors for integrated optical waveguides

Amorphous silicon photodetectors are attractive transducers for integrated optical devices on dielectrics. Frequency-dependent admittance analysis is used to analyze the material properties of such detectors. The photodetectors are laterally coupled to channel waveguides in glass substrates. Admittance values are recalculated using a six element small-signal equivalent circuit model. Space charge capacitances, series resistances, residual contact conductances and inductive reactance contributions are evaluated for 633 nm TE and TM modes as well as for dark current conditions.