Chemical analysis of thin ALD-Al2O3 films and their applications as pH-sensitive layers in CMOS-compatible Ion-Sensitive Capacitors (ISCAP)

This work reports the surface chemical characterization of thin aluminum oxide (Al₂O₃) layers after immersion in pH buffer and no-buffer solutions, and the fabrication of Ion-Sensitive Capacitors (ISCAP) employing these layers as the sensitive gate dielectric. We relate Al₂O₃ chemical changes with the ISCAP´s sensing characteristics, i.e. the density of surface/bulk chemical bonds present in these films with the sensitivity of ISCAPs to pH. In our fabricated chip, different ISCAP geometries are proposed for these sensors and these are integrated along with quasi-reference electrodes (using a thin metal layer directly exposed to the electrolytic solution), thus providing different pH sensitivities and flexibility with measurements in aqueous solutions.