Super-Nernstian pH sensitivity of TbTaO₄ sensing film for a solid-state pH sensor

In this work, a super-Nernstian pH sensitivity of TbTaO₄ sensing film was developed for an electrolyte-insulator-semiconductor (EIS) solid-state pH sensor. The TbTaO₄ sensitive films deposited on the Si substrates through radio-frequency magnetron co-sputtering were prepared under three various Ta plasma powers (80, 120, and 160 W) and then annealed at 800 °C. To investigate the impact of tantalum plasma power, multiple material analyses including X-ray diffraction, secondary ion mass spectrometry, atomic force microscopy, and X-ray photoelectron spectroscopy were performed. Results indicate that the film processed with the 120 W condition might form a stoichiometric TbTaO₄ structure and possess a rough surface. Therefore, the best sensing performance was observed for the TbTaO₄-based EIS sensor fabricated at the 120 W. In addition, the TbTaO₄-based EIS also showed good selectivity for H⁺ ion over other ions (Na⁺, K⁺, Mg²⁺, and Ca²⁺). The proposed film fabrication process and analysis may represent a promising approach for the exploration of a novel pH-sensitive TbTaO₄ film.