A Nonvolatile Memory Operation by Ferroelectric Modulation of Interface Conductance in a Combinatorial Oxide Structure

We have observed a nonvolatile memory effect in interface conductance which can be modulated by polarization of a ferroelectric film stacked in semiconducting oxide films. The memory element is a ferroelectric-gate field-effect transistor (FeFET) with a heteroepitaxially grown stack of ZnO(n-type semiconductor)/Pb(Zr,Ti)O₃(ferroelectric)/SrRuO₃(bottom gate electrode) films, which exhibits a high ON/OFF ratio of 10⁵. In order to construct a memory cell, we have also built a switching element of a Au/Ti(top gate electrode)/SiNx(insulator)/ZnO thin-film transistor (TFT) in the same heteroepitaxial stack together with the FeFET. The FeFET and TFT share the same ZnO layer as a conductive channel so that the memory cell size can be minimized. This is the first report on write and read operations of the combinatorial oxide nonvolatile memory cell.