Interdigitated electrolyte-conductivity sensors with an added top layer of insulating Ta2O5 have been realized. The electrode-substrate structure under the Ta2O5 film has been planarized in order to obtain a totally flat top surface. In addition, the electrodes have been applied on a totally insulating substrate, thus reducing the parasitic sensor capacitance by a factor of ten.
Olthuis, W., Sprenkels, A. J., Bomer, J. G., & Bergveld, P. (1997). Planar interdigitated electrolyte-conductivity sensors on an insulating substrate covered with Ta2O5. Sensors and actuators. B: Chemical, 1997(43), 211-216. https://doi.org/10.1016/S0925-4005(97)00157-3