Development and characterization of miniaturized LTCC pH sensors with RuO2 based sensing electrodes

This work describes the development of a low cost miniaturized solid state pH sensor using LTCC (low temperature cofired ceramic) technology. Thick film sensing electrodes screen printed on LTCC substrates were made of RuO2 and RuO2-Ta2O5-glass based pastes. The Ag/AgCl/KCl reference electrode for the potentiometric sensor was deposited by screen printing on the same LTCC substrate. The sensing performance and mechanism were investigated by using the potentiometric method and electrochemical impedance spectroscopy (EIS). The fabricated potentiometric sensors show close to the Nernstian behavior with the sensitivity being 56 mV/pH for RuO2 layer and 58 mV/pH for RuO2-Ta2O5-glass layer in a wide pH range (2-11). The sensors exhibit very fast response and excellent stability. A wireless system for online solution monitoring operating together with the fabricated sensor was successfully tested. Good performance of the prepared LTCC sensors suggests their applicability in the next generation of solid state pH sensors destined for online solution monitoring.