Ultrahigh sensitive and ultrafast relative humidity sensing using surface enhanced microcantilevers

Abstract

Active control of relative humidity (RH) and real-time monitoring in a sustained manner are of paramount importance in numerous fields and it is necessary to develop state-of-the-art RH sensors with high sensitivity and fast response times. In the present work, we propose and experimentally demonstrate a high-performance RH sensor using SiO2 microcantilevers (MCs) with controlled micro-patterns on their surface. SiO2 MCs with and without controlled surface micro-patterns were fabricated using direct laser writer and wet chemical etching methods. RH sensing experiments were performed, by measuring the shift in resonance frequency of MCs, when RH is varied between 20% and 90%. RH sensitivity of micro-patterned MCs was found to be significantly higher than the unpatterned ones and is explained on the basis of gel-like water layer formation inside the micro-patterns which facilitates the enhanced uptake of water molecules. Micro-patterned MCs exhibited an unprecedented RH sensitivity (10.45 Hz/% RH), ultrafast response/recovery times (∼ 1 s) and outstanding stability (variation < 5%) along with low hysteresis error (< 3%RH). These superior characteristics of micro-patterned MCs allowed the real-time monitoring of human respiration during normal and slow inhale/exhale cycles. Introduction of controlled micro-patterns on MC surface provides a simple and efficient way to enhance the sensitivity of MC based sensors without compromising other sensor characteristics such as response and recovery times.