Ultrafast humidity sensor based on liquid phase exfoliated graphene

TL;DR

This paper presents a fast, flexible, and transparent graphene-based humidity sensor created via liquid phase exfoliation and Langmuir-Blodgett assembly, suitable for real-time respiration and proximity monitoring.

Contribution

It introduces a novel, simple fabrication method for high-performance, large-area, flexible humidity sensors with rapid response times and minimal interference from other air constituents.

Findings

Resistance changes up to 10% with humidity variation

Response time of 30 milliseconds

High transparency of nearly 80%

Abstract

Humidity sensing is important to a variety of technologies and industries, ranging from environmental and industrial monitoring to medical applications. Although humidity sensors abound, few available solutions are thin, transparent, compatible with large-area sensor production and flexible, and almost none are fast enough to perform human respiration monitoring through breath detection or real-time finger proximity monitoring via skin humidity sensing. This work describes chemiresistive graphene-based humidity sensors produced in few steps with facile liquid phase exfoliation (LPE) followed by Langmuir-Blodgett assembly that enables active areas of practically any size. The graphene sensors provide a unique mix of performance parameters, exhibiting resistance changes up to 10% with varying humidity, linear performance over relative humidity (RH) levels between 8% and 95%, weak response to other constituents of air, flexibility, transparency of nearly 80%, and response times of 30 ms. The fast response to humidity is shown to be useful for respiration monitoring and real-time finger proximity detection, with potential applications in flexible touchless interactive panels.