研究目的
To develop and evaluate tungsten oxide based chemiresistive sensors for monitoring oxygen at low temperatures in dry and humid air, as an alternative to lead-based sensors.
研究成果
Tungsten oxide thin-film sensors demonstrated good linear response to oxygen concentrations up to 20%, with optimal performance at 350°C. Humidity negatively affects response but remains usable. This represents a significant improvement over previous work and advances the development of lead-free, metal-oxide-based oxygen sensors for various applications.
研究不足
Sensors showed reduced response in humid conditions compared to dry air, and performance decreased at temperatures above 350°C due to oxygen desorption. The study is limited to oxygen concentrations up to 20% and temperatures up to 400°C, with potential for optimization in material composition and fabrication processes.
1：Experimental Design and Method Selection:
The study involved fabricating thin-film sensors using spin coating and photolithography to define the sensing area, followed by gas sensing tests to evaluate performance in varying oxygen concentrations and humidity conditions at temperatures from 150°C to 400°C.
2：Sample Selection and Data Sources:
Sensors were fabricated on alumina substrates with gold interdigitated electrodes; gas mixtures were generated using zero air and nitrogen, with humidity introduced via a water bubbler.
3：List of Experimental Equipment and Materials:
Equipment includes spin coater, fast mill, hot plate, UV exposure system, gas mixture instrument with MFCs, water bubbler, data logger, and sensor management system. Materials include tungsten oxide powder, negative photoresist, deionized water, alumina substrates, gold electrodes, zero air, nitrogen gas.
4：Experimental Procedures and Operational Workflow:
Ink preparation by milling photoresist and tungsten oxide mixture, spin coating onto substrates, drying, UV exposure through a mask, development with DI water, drying, repeating for a second layer, sintering at high temperatures, then gas sensing tests with controlled oxygen concentrations and humidity, measuring resistance changes.
5：Data Analysis Methods:
Sensor response calculated as ΔR/Ra, where Ra is baseline resistance in N2 and Rg is resistance in oxygen; data logged and analyzed for linear relationships and temperature effects.
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Spin Coater
G3P-8
Specialty Coating Systems
Used for depositing ink onto substrates by spinning at high speeds to create thin films.
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Laboratory Fast Mill
Speedy
Nannetti srl
Used for milling the mixture of photoresist and tungsten oxide powder to create a smooth ink.
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Negative Photoresist
Dirasol 22
Fujifilm Sericol Ltd.
Used in the photolithographic process to define the sensing area on the substrate.
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Tungsten Oxide Powder
Treibacher Industrie Ag
Primary sensing material for the chemiresistive sensors.
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Mass Flow Controllers
Used to control and mix gases for generating different oxygen concentrations in the gas sensing tests.
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Software
LabVIEW
National Instrument
Used to control the mass flow controllers for gas mixture generation.
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Data Logger
Lascar Electronics
Used to monitor humidity levels in the gas mixture.
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Sensor Management System
AS-330
Atmospheric Sensor Ltd.
Used to monitor and log the resistance changes of the sensors during gas exposure, and control temperature.
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