Observing large ferroelectric polarization in top-electrode-free Al:HfO2 thin films with Al-rich strip structures

Abstract

We report a large ferroelectric polarization of Al:HfO2 films in metal-ferroelectric-semiconductor structures with a top-electrode free annealing configuration. Annealing an uncapped film at the Al concentration of 7.7 mol. % shows a large remnant polarization up to 50.5 μC/cm2. The film has a unique microscopically laminar distribution of dopant atoms. We find that the formation of the paraelectric monoclinic phase is suppressed in films with laminar distribution. The uniaxial confinement due to the microscopic stress introduced by the Al-rich strip structures is suggested. It is regarded as a possible explanation for enhancing the remnant polarization of the ferroelectric Al:HfO2 film by increasing the atomic layer deposition cycles for dopant layers. The results elucidate a growth procedure to produce high performance ferroelectric Al:HfO2 nanofilms without the postcapping process.