Abstract
Here in we demonstrate the design of a low- cost zinc oxide (ZnO) thin-film planar transistor-based pH sensor controlled by the bottom gate fabricated by a fairly simple fabrication approach. The performance of the fabricated device is evaluated by electrical as well as surface characterization. The surface morphology is analyzed by scanning electron microscope (SEM) and atomic force microscopy (AFM) and it shows surface properties that are essential for a device to function as a pH sensor. The fabricated thin-film FET comprises Zinc Oxide (ZnO) as a channel layer of length 6 µm and thickness 200 nm, Silicon Nitride (Si3N4) as a pas- sivation layer, and Aluminum (Al) as a contact layer. The effect on pH sensitivity for varied channel lengths (6 µm, 12 µm, and 15 µm) is also examined and opti- mum results have been achieved at channel length = 6 µm. The change in threshold voltage (ΔVth) & change in current (ΔImax) are used as a sensing metrics to an- alyze the sensing performance of the device. The device shows excellent pH sensitivity in terms of average cur- rent and average voltage sensitivity 120.97 mA/pH and 97.85 mv/pH respectively at pH ranging from 3.2 to 11.1 with best pH stability (linearity) for pH value 4 to 10. The voltage sensitivity is higher than the Nernstian value (59 mv/pH) at room temperature.
pH Sensing Characteristics of CuS/ZnO Thin Film Implemented as EGFET
