Study on the internal field and conduction mechanism of atomic layer deposited ferroelectric Hf0.5Zr0.5O2 thin films
Abstract
The internal field (Eint) 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 Eint in TiN/Hf0.5Zr0.5O2/TiN capacitors was controlled by changing the annealing atmosphere (N2, O2, and forming gas). The magnitude of negative Eint in O2-annealed samples was the largest, whereas that in the forming gas-annealed sample was the smallest. The magnitude of Eint can be understood based on the asymmetric distribution of oxygen vacancies near top and bottom TiN electrodes. Despite the large magnitude of Eint, the two remanent polarizations can be reliably retained due to the large coercive electric field of Hf0.5Zr0.5O2 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 Eint in O2- and forming gas-annealed samples showed the opposite tendency: the magnitude of Eint in the O2-annealed Hf0.5Zr0.5O2 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 Hf0.5Zr0.5O2 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 Hf0.5Zr0.5O2.