Electrical transport properties of two-dimensional materials on ferroelectrics toward nonvolatile memory devices*

When ferroelectric material is employed as a gate dielectric for the field effect transistor (FET) of a two-dimensional (2D) material such as graphene, MoS₂, and MoTe₂, it is possible to induce a giant amount of carriers in the channel by polarization field of the ferroelectric and also to show a nonvolatile memory operation. In many cases, however, the electrical coupling between 2D material and ferroelectric-oxide had shown abnormal behavior like anti-hysteresis different from 2D material/ferroelectric-polymer cases showing normal hysteresis. In our work, we also observed systematically those phenomena related to the interface by combining ferroelectric oxide material, PMN-PT (i.e. (1-x)Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃) single-crystal with several 2D materials. Through the electrical transport measurement, it is found out that the ferroelectric polarization and trapped charges strongly interacts each other, which is reflected in the conductance of 2D channel. To develop the 2D electronic system in ferroelectric memory device, we should study those properties in detail.