Multistability in Bistable Ferroelectric Materials toward Adaptive Applications

Traditionally thermodynamically bistable ferroic materials are used for nonvolatile operations based on logic gates (e.g., in the form of field effect transistors). But, this inherent bistability in these class of materials limits their applicability for adaptive operations. Emulating biological synapses in real materials necessitates gradual tuning of resistance in a nonvolatile manner. Even though in recent years few observations have been made of adaptive devices using a ferroelectric, the principal question as to how to make a ferroelectric adaptive has remained elusive in the literature. Here, it is shown that by locally controlling the nucleation energy distribution at the ferroelectric–electrode interface multiple-addressable states in a ferroelectric can be created, which is necessary for adaptive/synaptic applications. This is realized by depositing a layer of nonswitchable ZnO on top of thin film ferroelectric PbZr x Ti(1– x )O3. This methodology of interface-engineered ferroelectric should enable realising brain-like adaptive/synaptic memory in complementary metal-oxide-semiconductor (CMOS) devices. Furthermore, the temporally stable multistability in ferroelectrics should enable the designing of multistate memory and logic devices