Ferroelectricity and resistive switching in BaTiO$_3$ thin films with liquid electrolyte top contact for bioelectronic devices

We investigate ferroelectric- and resistive switching behavior in 18-nm-thick epitaxial BaTiO$_3$ (BTO) films in a model electrolyte-ferroelectric-semiconductor (EFS) configuration. The system is explored for its potential as a ferroelectric microelectrode in bioelectronics. The BTO films are grown by pulsed laser deposition (PLD) on semiconducting Nb-doped (0.5 wt\%) SrTiO$_{3}$ (Nb:STO) single crystal substrates. The ferroelectric properties of the bare BTO films are demonstrated by piezoresponse force microscopy (PFM) measurements. Cyclic voltammetry (CV) measurements in EFS configuration, with phosphate buffered saline (PBS) acting as the liquid electrolyte top contact, indicate characteristic ferroelectric switching peaks in the bipolar current-voltage loop. The ferroelectric nature of the observed switching peaks is confirmed by analyzing the current response of the EFS devices to unipolar voltage signals. Moreover, electrochemical impedance spectroscopy (EIS) measurements indicate bipolar resisitive switching behavior of the EFS devices, which is controlled by the remanent polarization state of the BTO layer. Our results represent a constitutive step towards the realization of neuroprosthetic implants and hybrid neurocomputational systems based on ferroelectric microelectrodes.