  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.
