HfO^xF^y based ISFETs with reactive fluorine doping for K⁺ ion detection

Electrolyte-insulator-semiconductor (EIS)- and ion-Sensitive field-effect transistors (ISFET)-based sensors with a fluorinated hafnium oxide (HfO₂) thin film treated by thermal carbon tetrafluoride (CF₄) plasma was investigated for potassium (K⁺) ion detection. The HfO₂ thin film was deposited using radio frequency (RF) sputtering and then CF₄ plasma treated on HfO₂ surface with substrate heating at 300°C during processing in the plasma system. The developed fluorinated-HfO₂ (HfOxFy) ISFETs have an average sensitivity of 59.5 mV/pK in the concentration range between 0.01 and 100 mM. To explain the increases of pK sensitivity by thermal CF₄ plasma treatment, the polar dipole formation in HfO₂ thin-film was proposed based on surface analysis by using XPS. The drift rate considered as the long-term stability is 1 mV/h, which is in the acceptable range. The fluorinated-HfO₂ film treated by thermal CF₄ plasma, which is compatible with advanced CMOS technology, could be a potential candidate for preparation of K⁺ ion sensitive layers.