The research of the differential reference electrode arraved flexible IGZO pH sensor for different Ar/O2 ratios

In this study, we used polyethylene terephthalate (PET) as substrate and we combined with screen-printed technology to achieve miniaturization of sensor. In order to avoid damaging for single sensing window, the sensor device had six sensing windows on polyethylene terephthalate (PET) substrate in this study. The six sensing windows could provide six measurement values, which could provide accurate measurement results. The sensing properties of indium gallium zinc oxide (IGZO) sensing membranes were changed by different sputtering parameters. Therefore, we changed Ar/O₂ flow ratios of IGZO sensing membranes by the radio frequency sputtering system, which investigated about the sensing properties of differential reference electrode arrayed flexible IGZO pH sensor for different Ar/O₂ flow ratios. Furthermore, we also researched on hysteresis effect and drift effect. The hysteresis experiments were carried out by two cycles of pH values, which were pH 7-11-7-3-7 and pH 7-3-7-11-7, respectively. The drift experiments were carried out by immersing IGZO sensor in pH3, pH7, pH11 buffer solutions for 12 hours, respectively. According to the experimental results, we found that Ar/O₂ flow ratio of IGZO pH sensing membranes was set at 16/2 (in seem) by radio frequency sputtering system, which can have better performance. The sensitivity and linearity of the IGZO pH sensor were 54.737 mV/pH and 0.994 in Ar/O₂ flow ambience of 16/2 (in sccm), respectively. The hysteresis values were 8.56 mV and 25.01 mV in cycles of pH 7-11-7-3-7 and pH 7-3-7-11-7 in Ar/O₂ flow ambience of 16/2, respectively. The drift values were 1.06 mV/hr, 3.64 mV/hr, 6.04 mV/hr in pH3, pH7, pH11 buffer solutions from 5 to 12 hours in Ar/O₂ flow ambience of 16/2, respectively. The experimental results demonstrated that IGZO sensing membrane was successfully applied to detect hydrogen ions.