All-printed humidity sensor based on gmethyl-red/methyl-red composite with high sensitivity

To monitor the most common constituted H2O in the air for health and environment applications, we propose a highly sensitive humidity sensor consisted of silver inter-digital electrodes and graphene (G)/methyl-red (M-R) composite layer. Dimension of the proposed silver inter-digital electrodes is 200 mm finger width, 400 mm spacing, and 400 nm thickness, which is fabricated on a low cost transparent polyethyleneterephthalate (PET) substrate through commercialized Dimatix material inkjet printer (DMP-3000). To achieve a high sensitivity and wide sensing range, the composite thin film layer is deposited over the silver inter-digital electrodes through electrohydrodynamic (EHD), and its thickness is similar to 300 nm. The sensor electrical resistance inversely varies from 11 MU to 0.4 MU against the relative humidity (RH) content from 5% to 95%. The proposed humidity sensor showed 96.36% resistive and 2869500% capacitive sensitivity against humidity. The response and recovery time of the proposed sensor is 0.251s and 0.35s, respectively. (C) 2016 Elsevier Ltd. All rights reserved.