Characterization of K+ and Na+-Sensitive Membrane Fabricated by CF4 Plasma Treatment on Hafnium Oxide Thin Films on ISFET

Abstract

In this paper, we report the effects of fluorine incorporation on the alkali ion sensing properties of a HfO2 dielectric material. The fluorinated-HfO2 film prepared by the postdeposition CF4 plasma treatment was used as a sensing layer of ion sensitive field-effect transistors (ISFET) for K+ and Na+ ion detection. The fluorinated-HfO2 gate ISFET is sensitive to K+ (25.86 mV/M) and Na+ (33.77 mV/M) ions for both in the concentration range between 3 and 135 mM. In comparison with the same structure without plasma treatment, the sensitivity was improved fivefold, and lower selectivity coefficients of K+ and Na+ ions against H+ ion were obtained. In the stability test, the result of time-dependent drift measurements showed that this low power plasma process could not degrade the sensing performance, and lifetime evaluated based on analysis sensitivity change in time was over 15 months. The chemical states of the HfO2 film after CF4 plasma treatment were examined by x-ray photoelectron spectroscopy. Analysis of the spectra of F 1s, O 1s, and Hf 4f showed that the fluorine atoms are incorporated into the HfO2 film. This fluorinated-HfO2 film fabricated by inorganic CF4 plasma is compatible with advanced complementary metal oxide semiconductor technology and possible biosensor applications.