Potentiometric RuO2–Ta2O5 pH sensors fabricated using thick film and LTCC technologies

• Binary metal oxide pastes based on RuO2–Ta2O5 were developed.
• Thick film potentiometric pH sensors were fabricated on alumina and LTCC substrates.
• Structural and composition studies were performed.
• Nonlinear characteristics of thick film pH sensors were investigated.
• LTCC technology was utilized for wireless pH sensor application.

The paper reports on the preparation, properties and application of potentiometric pH sensors with thick film RuO2–Ta2O5 sensing electrode and Ag/AgCl/KCl reference electrode screen printed on an alumina substrate. Furthermore, it presents fabrication procedure and characterization of a new miniaturized pH sensor on LTCC (low temperature cofired ceramics) substrate, destined for wireless monitoring. The crystal structure, phase and elemental composition, and microstructure of the films were investigated by X-ray diffractometry, Raman spectroscopy, scanning electron microscopy and energy dispersive spectroscopy. Potentiometric characterization was performed in a wide pH range of 2–12 for different storage conditions and pH loops. The advantages of the proposed thick film pH sensors are: (a) low cost and easy fabrication, (b) excellent sensitivity close to the Nernstian response (56 mV/pH) in the wide pH range, (c) fast response, (d) long lifetime, (e) good reproducibility, (f) low hysteresis and drift effects, and (g) low cross-sensitivity towards Li+, Na+ and K+ as interfering ions. The applicability of the sensors for pH measurement of river, tap and distilled water, and some drinks was also tested.

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