Nanocrystalline Graphite Humidity Sensors for Wearable Breath Monitoring Applications

A wearable humidity sensing platform based on nanocrystalline graphite (NCG) resistive sensors for continuous breath pattern analysis is reported in this paper. The sensor was fabricated using plasma enhanced chemical vapour deposition (PECVD) to grow graphitic nanocrystals directly onto SiO ₂ substrates without metal catalysts. The resulting sensor shows suitably fast response, and high durability against contaminants. The film also demonstrates good mechanical stability and can be integrated with existing CMOS production technology to produce a complete system on chip (SoC) sensor for smart wearable applications. When exposed to human breath (~100% RH) from room conditions (~40% RH), the sensor experiences a measurable ~100 Ohm drop in resistance, with a 2 seconds response from 100% RH to 40% RH. The resulting sensor is small and can easily be integrated into a wearable smart-mask for breath analysis.