Thermal Stability of the Ferroelectric Properties in 100 nm-Thick Al_0.72Sc_0.28N

The discovery of ferroelectricity in aluminum scandium nitride (Al 1– x Sc x N) opens technological perspectives for harsh environments and space-related memory applications, considering the high-temperature stability of piezoelectricity in aluminum nitride. The ferroelectric and material properties of 100 nm-thick Al 0.72 Sc 0.28 N are studied up to 873 K, combining both electrical and in situ X-ray diffraction measurements as well as transmission electron microscopy and energy-dispersive X-ray spectroscopy. The present work demonstrates that Al 0.72 Sc 0.28 N can achieve high switching polarization and tunable coercive fields in a 375 K temperature range from room temperature up to 673 K. The degradation of the ferroelectric properties in the capacitors is observed above this temperature. Reduction of the effective top electrode area and consequent oxidation of the Al 0.72 Sc 0.28 N film are mainly responsible for this degradation. A slight variation of the Sc concentration is quantified across grain boundaries, even though its impact on the ferroelectric properties cannot be isolated from those brought by the top electrode deterioration and Al 0.72 Sc 0.28 N oxidation. The Curie temperature of Al 0.72 Sc 0.28 N is confirmed to be above 873 K, thus corroborating the promising thermal stability of this ferroelectric material. The present results further support the future adoption of Al 1– x Sc x N in memory technologies for harsh environments like applications in space missions.