Sensitivity improvements of HfxWyOz sensing membranes for pK sensors based on electrolyte-insulator-semiconductor structure

In this study, the hydrogen ion and potassium ion sensing properties of mixing hafnium oxide-tungsten oxide (Hf_xW_yO_z) membranes on an electrolyte-insulator-semiconductor (EIS) structure by co-sputtering method were investigated. For tungsten oxide, the increasing of pH-sensitivity (35.47 mV/pH to 46.22 mV/pH), linearity (98.11% to 99.87%), measuring range (pH 6-pH 12 to pH 2-pH 12) and the decreasing of hysteresis (17.63 mV to 2.34 mV) were observed with increasing the ratio of hafnium oxide incorporation. For hafnium oxide, an increasing of pK-sensitivity (7.07 mV mV/ pK to 26.84 mV/ pK in the concentration range between 1 mM to 100 mM) was observed with increasing the ratio of tungsten oxide incorporation. For potassium ion detection, the Hf_xW_yO_z (HfO₂-60%) sensing membrane with good pK sensitivity (26.84 mV/pK) and high linearity (99.67%) in the concentration range between 1 mM and 100 mM and with good selectivity (low pH-sensitivity) over hydrogen ion was chosen as the optimal condition for pK sensor application.