SnO₂-Based Ultra-Flexible Humidity/Respiratory Sensor for Analysis of Human Breath

Area of Science:

• Materials Science
• Sensor Technology
• Nanotechnology

Background:

• Fabricating ultraflexible metal oxide sensors is hindered by high-temperature annealing requirements.
• Developing low-temperature fabrication methods is crucial for integrating sensors into flexible electronics.

Purpose of the Study:

• To develop an ultraflexible relative humidity (RH) sensor using low-temperature near-infrared (NIR) laser annealing.
• To investigate the fabrication of a tin oxide (SnO2) based RH sensor on food plastic wrap.
• To demonstrate the sensor's capability for real-time breath pattern analysis.

Main Methods:

• Utilized 808 nm NIR laser annealing at low temperatures (26.2-40.8 °C) for 1 minute to fabricate SnO2 sensors on plastic wrap.
• Modulated the wettability of plastic wraps for uniform sol-gel coating.
• Investigated surface morphology, local temperature, and electrical properties under varying NIR power densities (16-84 W/cm2).
• Employed X-ray photoelectron spectroscopy (XPS) to analyze surface binding conditions and sensing response.

Main Results:

• Achieved an optimal ultraflexible RH sensor capable of detecting RH from 15% to 70% with small incremental changes (0.1-2.2%).
• Demonstrated successful real-time human breath pattern analysis (slow, normal, fast) when the sensor was attached to a face mask.
• Established a correlation between surface binding conditions and the sensor's sensing response via XPS analysis.

Conclusions:

• Low-temperature NIR laser annealing offers a viable method for fabricating ultraflexible metal oxide sensors on unconventional substrates like plastic wrap.
• The developed RH sensor shows significant potential for applications in wearable electronics and non-invasive respiration monitoring.
• The study highlights the importance of surface properties in dictating sensor performance for humidity detection.