Dramatic impact of pressure and annealing temperature on the properties of sputtered ferroelectric HZO layers

The crystallization of ferroelectric (Hf,Zr)O2 thin films is achieved by playing on the deposition pressure during reactive magnetron sputtering from a Hf/Zr metallic target. Postdeposition annealing was tried at different temperatures in order to optimize the quality of the samples. Structural characterizations are performed by transmission electron microscopy (TEM) and electrical characterizations are carried out. TEM analyses reveal that the samples deposited at a low working pressure show no orthorhombic phase, and thus are not ferroelectric, whereas the samples deposited at higher working pressure show the orthorhombic ferroelectric phase. The maximum remnant polarization is 6 µC/cm2 and is obtained for the sample annealed at 600 °C. The maximum cycles to breakdown is higher than 2 × 1010 cycles and is reached for the sample annealed at 400 °C. These results are discussed in the matter of phase transition and oxygen vacancies redistribution.