Study of the Chemical and Morphological Characteristics of Al2O3 and HfO2 Surfaces after Immersion in Time-Dependent pH Solutions

After immersion of ALD-Al2O3 materials in time-dependent pH solutions (solutions whose pH is changing over time), any possible change in the chemical and morphological characteristics of Al₂O₃ is correlated to the chemical sensitivity when used as active material in ion-sensitive devices. Morphological changes have been recorded by Atomic Force Microscopy (AFM), while the chemical characteristics have been quantified by Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS). Experimental results suggest that the changes experienced by the films under immersion are highly dependent on immersion time and ion-strength (acidic or basic solutions), and this might be the main cause of drift in ion-sensitive solid state sensors. Moreover, the data shows that HfO₂ and Al₂O₃ exhibit different chemical characteristics after immersion in pH solutions than Si₃N₄. Nonetheless, due to their high chemical sensitivity and higher dielectric constant, these materials are well suited for highly sensitive applications in pH-sensing devices.