Evolution of the Ferroelectric Properties of AlScN Film by Electrical Cycling with an Inhomogeneous Field Distribution

Abstract

This work investigates the evolution of the ferroelectric (FE) performance of the sputtered aluminum scandium nitride (AlScN) thin film, which has a high remanent polarization (Pr, > 100 µC cm−2) and coercive field (Ec, > 6 MV cm−1), with the electric field cycling. The work aims at elucidating the underlying origin of the severe fatigue behavior, even with a relatively small number of endurance cycles (<105). When cycled with a low electric field, an internal field is created by charges trapped between the FE layer and the interfacial dielectric layer (non‐FE). On the other hand, fatigue is observed when cycled with a high electric field cycling. This work proposes a new method to simulate a switching current utilizing an inhomogeneous field mechanism and the appropriate circuit model to assess the thickness change of the non‐FE layer. It is concluded that the thickened non‐FE layer after the field cycling results in fatigue.

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

“…The existence of an internal bias field in pristine Al 1−x Sc x N can be explained by injected charge (electrons at the BE/Al 0.85 Sc 0.15 N interface and holes at the Al 0.85 Sc 0.15 N/TE interface) at the interfaces to stabilize the Npolar state. 13,39 The larger initial internal bias field of Al 0.85 Sc 0.15 N compared to the report of Kim et al 13 for Al 0.7 Sc 0.3 N could be explained by the larger P r in Al 0.85 Sc 0.15 N and a lower number of M-polar domains in the pristine state. The positively charged V N that participate in the filamentary VCM resistive switching mechanism could hence be responsible for the reduction of the internal bias field during bipolar ferroelectric switching cycling as well.…”

“…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. In Al 1– x Sc x N, the fatigue effect was explained by depolarization fields and/or domain pinning, while no conclusive evidence about the breakdown has emerged so far. , …”

“…This conclusion would be supported by the favored N-polar state in the capacitor by the deposition conditions (Section S4). Nonetheless, because modified Schottky emission was used to explain the current conduction in Al 1– x Sc x N and an initial electronic activation of the breakdown phenomenon cannot be excluded, another possible explanation for the polarity-dependent E BD would be the asymmetry between the interfaces formed between Al 0.85 Sc 0.15 N and the electrodes. , The interface properties are likely to influence the generation of defects that form the CF if defects are created by carriers injected from the electrodes. Charged defects, material structure, and interface effects impact both the filamentary VCM resistive and the ferroelectric switching; thus, a possible correlation between ferroelectric switching and filament formation could exist …”

“…In Al 1−x Sc x N, the fatigue effect was explained by depolarization fields and/or domain pinning, while no conclusive evidence about the breakdown has emerged so far. 13,14 Tsai et al 14 proposed that the breakdown in Al 0.78 Sc 0.22 N is related to Joule-heating-induced leakage current without involving any conductive filament (CF) formation, in contrast to the case of PZT or hafnia-based ferroelectrics. 16−18 This hypothesis contradicts the experimentally observed enhancement of Al 1−x Sc x N breakdown strength in multilayered films, which can be explained by a CF-driven process.…”

“…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. In Al 1– x Sc x N, the fatigue effect was explained by depolarization fields and/or domain pinning, while no conclusive evidence about the breakdown has emerged so far. , …”