Enhanced tunneling electroresistance effects in HfZrO-based ferroelectric tunnel junctions by high-pressure nitrogen annealing

Abstract

Greatly improved ferroelectricity with an excellent remanent polarization of 20 μC/cm2 and enhanced tunneling electroresistance (TER) were achieved with TiN/HfZrO(HZO)/p-type Ge ferroelectric tunnel junctions (FTJs) annealed at a high pressure of 200 atmosphere (atm.). We found that the enhanced ferroelectric characteristics can be ascribed to the effective formation of an orthorhombic phase at high pressures. This was verified by the combined study of grazing angle incidence X-ray diffraction, transmission electron microscopy, and hysteresis polarization curve analyses. In addition, using pulse switching measurements, we quantitatively evaluated the interfacial paraelectric capacitance (Ci) of HZO FTJs according to the annealing temperature. HZO films annealed at 550 °C and 200 atm. exhibited an excellent TER effect ratio of 20 due to the extra paraelectric layer between the ferroelectric layer and the bottom electrode and a relatively high remanent polarization.