  HfO2-based ferroelectric tunnel junctions (FTJs) exhibit attractive
properties for adoption in neuromorphic applications. The combination of
ultra-low-power multi-level switching capability together with the low
on-current density suggests the application in circuits for massive parallel
computation. In this work, we discuss one example circuit of a differential
synaptic cell featuring multiple parallel connected FTJ devices. Moreover, from
the circuit requirements we deduce that the absolute difference in currents
(Ion - Ioff) is a more critical figure of merit than the tunneling
electroresistance ratio (TER). Based on this, we discuss the potential of FTJ
device optimization by means of electrode work function engineering in bilayer
HZO/Al2O3 FTJs.
