PVA modified ZnO nanowire based microsensors platform for relative humidity and soil moisture measurement

Abstract

In the present work, we have investigated Polyvinyl Alcohol (PVA) modified Zinc Oxide nanowires (ZnO NW) heterostructure based microsensors platform to measure the relative humidity and gravimetric soil moisture contents for agriculture applications. For this the hydrothermal growth of ZnO NW is carried out on Inter Digitated Electrodes (IDEs) patterned on Si/SiO2 substrates. Further, ZnO NW surface is functionalized by drop casting PVA solution. The surface characterization of the PVA coated ZnO NWs film is carried out by X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Current-Voltage (IV) measurements. These measurements revealed the successful formation of PVA-ZnO NW heterostructure. The microsensors are exposed to different levels of relative humidity (% RH) ranging from 40 to 90% and various moisture contents of bentonite and red soils. It is observed that the microsensors resistance decreases with increase in humidity (% RH) and gravimetric soil moisture contents (red and bentonite), respectively. The sensor exhibited a sensitivity of 4.6 KΩ/0.1% change in RH. Further, sensitivities of 7.5 and 12.2 KΩ/0.1% change in gravimetric water content when exposed to bentonite and red soil samples respectively were achieved. The low cost, good reproducibility, repeatability and good stability with time indicated that PVA modified ZnO NW heterostructure microsensors platform is potentially useful for measurement of humidity and soil moisture contents in agriculture applications.