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

Abstract

The discovery of ferroelectricity in aluminum scandium nitride (Al1–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 Al0.72Sc0.28N 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 Al0.72Sc0.28N 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 Al0.72Sc0.28N 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 Al0.72Sc0.28N oxidation. The Curie temperature of Al0.72Sc0.28N 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 Al1–x Sc x N in memory technologies for harsh environments like applications in space missions.

Impact of operation voltage and NH3 annealing on the fatigue characteristics of ferroelectric AlScN thin films grown by sputtering

“…Guido et al also reported the wake-up phenomenon of AlScN when the measurement was performed at a high temperature (600 °C). 13 However, the wake-up phenomenon disappeared when the film was cooled down. Therefore, additional research is required to understand why AlScN exhibits wake-up characteristics at room temperature after 900 °C NH 3 annealing.…”

“…12 The FE properties of AlScN have demonstrated remarkable stability with thermal treatment, even above 1000 °C. 13,14 In addition, AlScN has the advantage of exhibiting ferroelectricity in its stable wurtzite structure, eliminating the need for additional heat treatment and other complicated steps to induce a FE phase. 9 In contrast, HfO 2 -based films require complex thermal treatment to exhibit ferroelectricity, leading to a high degree of variability in material parameters across different grains due to inhomogeneous film stress and multiple phases.…”

A Comparative Study of Pt/Al0.72Sc0.28N/Pt-Based Thin-Film Metal-Ferroelectric-Metal Capacitors on GaN and Si Substrates

“…1,6,7 Thin-film w-Al x Sc 1−x N may also be integrated into GaNbased high-electron-mobility transistors and high-frequency power electronics. 8 The high temperature stability of the solid solution 9,10 and the ferroelectric Curie temperature crossing 1000 °C11 can be appealing for microwave and harshenvironment electronics. 12 However, ferroelectricity in Al x Sc 1−x N is not without limitations.…”

Role of Defects in the Breakdown Phenomenon of Al1–xScxN: From Ferroelectric to Filamentary Resistive Switching

“…3 In this context, aluminum scandium nitride (Al 1−x Sc x N) with its large P r (>80 μC/cm 2 ) is a promising material for future applications, even in harsh environments due to its excellent thermal stability. 4,5 As a result of the high coercive fields (E c ) in Al 1−x Sc x N, very thin films are required to switch the ferroelectric layer between the two stable states (nitrogen (N)-polar and metal (M)-polar) at reasonable voltages for low-power memory applications. 4,6 Recent reports demonstrate that ferroelectric switching is achievable in 5 nm thick films with voltages below 6 V. 7−9 However, because E c is close to the breakdown field (E BD ) of the material, the cycling endurance still remains a critical reliability concern to address.…”

“…The ferroelectric random-access memory (FeRAM) concept is frequently implemented in a single transistor–single capacitor (1T1C) cell, similar to a dynamic random-access memory cell except that the dielectric in the storage capacitor is replaced by a ferroelectric. , In a FeRAM array, the voltage difference sensed by a sense amplifier between the two memory states is directly proportional to the remanent polarization ( P r ) and the area of the ferroelectric capacitor; hence, ferroelectrics with large P r can increase the memory array density . In this context, aluminum scandium nitride (Al 1– x Sc x N) with its large P r (>80 μC/cm 2 ) is a promising material for future applications, even in harsh environments due to its excellent thermal stability. , As a result of the high coercive fields ( E c ) in Al 1– x Sc x N, very thin films are required to switch the ferroelectric layer between the two stable states (nitrogen (N)-polar and metal (M)-polar) at reasonable voltages for low-power memory applications. , Recent reports demonstrate that ferroelectric switching is achievable in 5 nm thick films with voltages below 6 V. − However, because E c is close to the breakdown field ( E BD ) of the material, the cycling endurance still remains a critical reliability concern to address . The reported cycling endurance for Al 1– x Sc x N capacitors is far below the 10 13 cycles achievable in doped hafnia and lead zirconate titanate (PZT). − The two major reliability aspects that determine capacitor endurance are the fatigue effect, which describes the reduction in P r with electric field cycling, and breakdown of the ferroelectric film.…”