Abstract
Enhanced hydrogen sensing performance of Pt Schottky diodes on ZnO single crystal wafers in humid ambient conditions is reported using a polymethylmethacrylate (PMMA) membrane layer. ZnO diode sensors showed little change in forward current when switching to wet ambient H2 conditions with 100% relative humidity. This sensitivity drop in the presence of water vapor can be attributed to surface coverage of hydroxyl groups on the Pt surface in humid ambient conditions. The hydrogen sensitivity of PMMA-coated diode sensors recovered up to 805% in wet H2 ambient conditions at room temperature. The PMMA layer can selectively filter water vapor and allow H2 molecules to pass through the membrane layer. It is clear that the PMMA layer can effectively serve as a moisture barrier because of low water vapor permeability and its hydrophobicity. In both dry and wet conditions, ZnO diodes exhibited relatively fast and stable on/off switching in each cycle with good repeatability.
Highlights
Gas sensors based on metal oxide (MOX) semiconductors have been widely used for toxic gas detection and quality air control
We investigated the hydrogen sensing performance in high humidity conditions using protective layers directly coated on Pt/ZnO Schottky diode sensors
This sensitivity drop in the presence of water vapor resulted from the surface coverage of water vapor
Summary
Gas sensors based on metal oxide (MOX) semiconductors have been widely used for toxic gas detection and quality air control. The been proposed to solve the humidity problem in gas sensing, including polymer-based membrane layers permeability and its selectivity of polymer membrane are significantly influenced by various factors, such as polyvinyl fluoride, polytetrafluoroethylene, polymethylmethacrylate (PMMA), and polyimide, such as the polarity of membrane materials, the degree of crystallization, and glass transition as well as inorganic membranes [24,25,26,27]. Non-polar polymers exhibit a lower permeability to coefficient for moisture to water vapor by reducing water adsorption on the oxide surface In this water vapor and polar gas molecules. A hydrophobic PMMA layer can serve as a selective filter paper, we investigated the hydrogen sensing performance in high humidity conditions using PMMA due to its low permeability coefficient for moisture to water vapor by reducing water adsorption on protective layers directly coated on Pt/ZnO Schottky diode sensors. PMMA protective layers directly coated on Pt/ZnO Schottky diode sensors
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