Sodium and potassium ion sensing properties of EIS and ISFET structures with fluorinated hafnium oxide sensing film

The potassium (K⁺) and sodium (Na⁺) ion-sensitive membranes treated by the carbon tetrafluoride (CF₄) plasma by using plasma-enhanced chemical vapor deposition (PECVD) on the single HfO₂ sensing films based on electrolyte-insulator-semiconductor (EIS) and ion sensitive filed-effect transistor (ISFET) were proposed in this work. With CF₄ plasma treatment, the fluorinated-EIS exhibits higher pK-sensitivity and pNa-sensitivity, wide sensing concentration range of potassium and sodium ion and high linearity. Before plasma treatment, the same ion sensitivity with 7 mV/pX (X = Na or K) in the concentration between 1 mM and 10 mM of K⁺ and Na⁺ was observed. After plasma treatment, the sensitivity of K⁺ and Na⁺ were increasing with increasing plasma time. The optimal sensitivity of potassium ion (49.38 mV/pK) and sodium ion (50.47 mV/pNa) was obtained during 5 min plasma treatment in the concentration range between 0.1 mM to 100 mM. For the results of fluorinated-ISEFT, the obvious changes as a function of potassium and sodium ion concentration were observed during titration.