Indium Zinc Oxide pH Sensors: Fabrication, Measurement, and Applications

Abstract

In this study, indium zinc oxide (IZO) thin films were deposited at different pressures by RF sputtering. The IZO thin films were examined using X-ray diffraction (XRD), SEM, and AFM instruments. The observed crystal orientations [(100), (101), and (008)] were obtained near 31°. The experimental results also reveal slight height variations on the surfaces of the IZO thin films, with average roughness (Ra) values of 2.431, 3.873, and 5.682 nm for sputtering pressures of 10, 20, and 30 mTorr, respectively. In addition, the IZO/Si sensor head and reference electrode were immersed in buffer solutions with various pH values (1, 3, 5, 7, 9, and 11) to measure pH sensitivity. A series of current-voltage (I-V) characteristic curves were obtained using a semiconductor parameter analysis instrument. The pH sensitivity of the IZO extended-gate field-effect transistor (EGFET) was calculated to be approximately 58.9, 56.4, and 52.3 mV/pH for 10, 20, and 30 mTorr sputtering pressures, respectively. The IZO pH-EGFET showed superior pH sensitivity and linear response and has great potential as a disposable pH sensor.