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. ●Impact of tantalum content on the structural and sensing properties of TbTaO4 sensing films was studied.●TbTaO4 EIS sensor with the 120 W exhibited the best sensing performance.●Super-Nernstian pH-sensitivity might be attributed to change in oxidation state of Tb3+ from Tb2+.