Responsible Humidity Sensor by Direct Laser Writing on Cork Substrate

Abstract

A novel laser-induced graphene (LIG) resistive relative humidity (RH) sensor is successfully fabricated by direct laser writing on a common natural cork sheet. In this work, a straightforward fabrication is presented where LIG, porous multilayer graphene, is generated by a laser photothermal process on a carbon-based substrate, in this case, an agglomerate cork sheet. The formation of LIG material is revealed by structural and morphological characterization using various analyses, including Raman spectroscopy, X-ray Photoelectron spectroscopy (XPS), and Scanning Electron Microscopy (SEM). The electrical analyses are conducted to measure the resulting sheet resistance, getting results as low as 31 Ω sq−1. With the laser parameter optimized, a LIG resistive humidity transducer is manufactured and characterized in a climate chamber. This biodegradable sensor shows good linearity with a sensitivity of 0.015%/%RH from 40 to 80% RH. Additionally, the influence of temperature is studied and demonstrated a low impact on the sensor's response toward RH. Furthermore, a proof of concept is successfully implemented by integrating the transducer onto a cork stopper. Considering all, the prospect of creating an easy, fast, scalable, and cost-effective transducer combined with the use of natural and abundant materials, leads the way for future large-scale production of sustainable sensors.