Study on the internal field and conduction mechanism of atomic layer deposited ferroelectric Hf0.5Zr0.5O2 thin films

Abstract

The internal field (E_int) in ferroelectric films is an important factor which can affect the reliability of practical devices utilizing two memory states which results from the remanent polarizations of ferroelectric films. In the current work, the E_int in TiN/Hf_0.5Zr_0.5O₂/TiN capacitors was controlled by changing the annealing atmosphere (N₂, O₂, and forming gas). The magnitude of negative E_int in O₂-annealed samples was the largest, whereas that in the forming gas-annealed sample was the smallest. The magnitude of E_int can be understood based on the asymmetric distribution of oxygen vacancies near top and bottom TiN electrodes. Despite the large magnitude of E_int, the two remanent polarizations can be reliably retained due to the large coercive electric field of Hf_0.5Zr_0.5O₂ films, and this is expected to be beneficial for application in semiconductor memory devices. During the repetitive electric field cycling for the wake-up process, the change in E_int in O₂- and forming gas-annealed samples showed the opposite tendency: the magnitude of E_int in the O₂-annealed Hf_0.5Zr_0.5O₂ film decreased, whereas that in the forming gas-annealed film increased. This difference is believed to be due to the redistribution of oxygen vacancies with electric field high enough for the migration of oxygen vacancies. The conduction mechanism of electrons through Hf_0.5Zr_0.5O₂ films was also examined, and the results fitted best with the Poole–Frenkel emission model with the shallow traps for all the samples with a reasonable optical dielectric constant value for Hf_0.5Zr_0.5O₂.