  We propose new designs of plasmonic modulators, which can be utilized for
dynamic signal switching in photonic integrated circuits. We study performance
of plasmonic waveguide modulator with bismuth ferrite as an active material.
The bismuth ferrite core is sandwiched between metal plates
(metal-insulator-metal configuration), which also serve as electrodes so that
the core changes its refractive index under applied voltage by means of partial
in-plane to out-of-plane reorientation of ferroelectric domains in bismuth
ferrite. This domain switch results in changing of propagation constant and
absorption coefficient, and thus either phase or amplitude control can be
implemented. Efficient modulation performance is achieved because of high field
confinement between the metal layers, as well as the existence of mode cut-offs
for particular values of the core thickness, making it possible to control the
signal with superior modulation depth. For the phase control scheme, {\pi}
phase shift is provided by 0.8-{\mu}m length device having propagation losses
0.29 dB/{\mu}m. For the amplitude control, we predict up to 38 dB/{\mu}m
extinction ratio with 1.2 dB/{\mu}m propagation loss. In contrast to previously
proposed active materials, bismuth ferrite has nearly zero material losses, so
bismuth ferrite based modulators do not bring about additional decay of the
propagating signal.
