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arXiv · 2105.08331

On the exceptional temperature stability of ferroelectric AlScN thin films

MD Redwanul Islam·Niklas Wolff·Mohammed Yassine·Georg Schönweger·Björn Christian·Hermann Kohlstedt·Oliver Ambacher·Fabian Lofink·Lorenz Kienle·Simon Fichtner
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Abstract

Through its dependence on low symmetry crystal phases, ferroelectricity is inherently a property tied to the lower temperature ranges of the phase diagram for a given material. This paper presents conclusive evidence that in the case of ferroelectric AlScN, low temperature has to be seen as a purely relative term, since its ferroelectric-to-paraelectric transition temperature is confirmed to surpass 1100°C and thus the transition temperature of virtually any other thin film ferroelectric. We arrived at this conclusion through investigating the structural stability of 0.4 - 2 $μ$m thick Al$_{0.73}$Sc$_{0.27}$N films grown on Mo bottom electrodes via in situ high-temperature X-ray diffraction and permittivity measurements. Our studies reveal the wurtzite-type structure of Al$_{0.73}$Sc$_{0.27}$N is conserved during the entire 1100°C annealing cycle, apparent through a constant c over a lattice parameter ratio. In situ permittivity measurements performed up to 1000°C strongly support this conclusion and include what could be the onset of a diverging permittivity only at the very upper end of the measurement interval. Our in situ measurements are well-supported by ex situ (scanning) transmission electron microscopy and polarization and capacity hysteresis measurements. These results confirm the structural stability on the sub-$μ$m scale next to the stability of the inscribed polarization during the complete 1100°C annealing treatment. Thus, AlScN is the first readily available thin film ferroelectric with a temperature stability that surpasses virtually all thermal budgets occurring in microtechnology, be it during fabrication or the lifetime of a device - even in harshest environments.

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MD Redwanul Islam, Niklas Wolff, Mohammed Yassine, Georg Schönweger, Björn Christian, Hermann Kohlstedt, Oliver Ambacher, Fabian Lofink, Lorenz Kienle, Simon Fichtner. 2021-05-18. On the exceptional temperature stability of ferroelectric AlScN thin films. https://doi.org/10.1063/5.0053649

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