Effective Design and Fabrication of Harsh Environment and Biomedical Gas Sensors

Solid-state electrochemical devices composed of stabilized zirconia electrolytes (YSZ), e,g, oxygen sensor is used extensively for sensing in combustion environments. However, sensors for detecting other gases have not been as forthcoming. We will present our work in the area of NOx sensors based both on potentiometric and resistive strategies. We find that the heterogeneous catalytic activity of WO₃, yttria-stabilized zirconia (YSZ), and Pt containing zeolite Y (PtY) have a significant influence on the performance of solid-state potentiometric gas sensors. Pt electrodes covered with PtY and WO₃ are used as the reference and working electrodes because of the significant reactivity difference. Using highly catalytic active PtY to filter incoming gas mixtures can effectively remove interferences from 2000ppm CO, 800ppm propane, 10ppm NH₃, as well as minimize effects of 1~13% O₂, CO₂, and H₂O. A second strategy involves the use of p and n-type semiconducting oxides to cancel contributions of oxidizing gases, while enhancing the response to NO, thus leading to sensitivity of ppb levels. The improvement in sensitivity has led to new applications, particularly monitoring human breath for diagnosis of asthma and upper airway inflammation. We will present MEMS-based strategies for manufacture of miniaturized harsh environment tolerant gas sensors.