Electronic behavior of native oxide films on Ti and TiN during 90-day immersion in electrolytes with different pH levels

Abstract

This work presents the electronic behavior of Ti and TiN thin films when exposed to electrolytes with pH levels of 2, 7 and 13 for 90 days. Staircase potentio-electrochemical impedance spectroscopy tests were performed on the 100-nm Ti and TiN monolithic films, and Mott–Schottky analysis of these tests was used to determine the films’ semiconductive behavior and changes in the donor/acceptor density. In addition, the flat-band potential of each film’s surface oxide was also characterized. No attempt was made to control oxide formation, and therefore, these tests reflected the native surfaces of these films. While the TiN films exhibited n-type semiconductivity in all electrolytes, the Ti films only showed n-type behavior in the acidic (pH = 2) and neutral (pH = 7) electrolytes. The semiconductivity of the Ti films transitioned to p-type during exposure to the basic electrolyte (pH = 13) after reaching 60 days. Furthermore, there was a significant increase in the donor densities for both Ti and TiN films when immersed in the basic electrolyte relative to the acidic and neutral electrolytes.