  The multiple ferroelectric polarization tuned by external electric field
could be used to simulate the biological synaptic weight. Ferroelectric
synaptic devices have two advantages compared with other reported ones: One is
the intrinsic switching of ferroelectric domains without invoking of defect
migration as in resistive oxides contributes reliable performance in these
ferroelectric synapses. Another tremendous advantage is the extremely low
energy consumption because the ferroelectric polarization is manipulated by
electric field which eliminate the Joule heating by current as in magnetic and
phase change memory. Ferroelectric synapses are potential for the construction
of low-energy and effective brain-like intelligent networks. Here we summarize
recent pioneering work of ferroelectric synapses involving the structure of
ferroelectric tunnel junctions (FTJs), ferroelectric diodes (FDs) and
ferroelectric field effect transistors (FeFETs), respectively, and shed light
on future work needed to accelerate their application for efficient neural
network.
