Role of Defects in the Breakdown Phenomenon of Al_1–xSc_xN: From Ferroelectric to Filamentary Resistive Switching

Abstract

Aluminum scandium nitride (Al1–x Sc x N), with its large remanent polarization, is an attractive material for high-density ferroelectric random-access memories. However, the cycling endurance of Al1–x Sc x N ferroelectric capacitors is far below what can be achieved in other ferroelectric materials. Understanding the nature and dynamics of the breakdown mechanism is of the utmost importance for improving memory reliability. The breakdown phenomenon in ferroelectric Al1–x Sc x N is proposed to be an impulse thermal filamentary-driven process along preferential defective pathways. For the first time, stable and robust bipolar filamentary resistive switching in ferroelectric Al1–x Sc x N is reported. A hot atom damage defect generation model illustrates how filament formation and ferroelectric switching are connected. The model reveals the tendency of the ferroelectric wurtzite-type Al1–x Sc x N system to reach internal symmetry with bipolar electric field cycling. Defects generated from bipolar electric field cycling influence both the energy barrier between the polarization states and that required for the filament formation.

Kinetics of N‐ to M‐Polar Switching in Ferroelectric Al1−xScxN Capacitors

“…Thus, both defect distribution and interface phenomena are suspected to play a decisive role in defining the energy required for ferroelectric switching in wurtzite-type systems. [26,37,43,44] By comparing the electric field magnitude at which the pristine to M-polar and subsequent N-to M-polar switching are achieved in Figure 3, it can be observed that the full N-to M-polar state reversal is attained with ≈0.3 MV cm −1 smaller electric field magnitude in the second switching transition. The decrease of the energy barrier for polarization reversal between the N-and M-polar states raises significant reliability concerns for both non-volatile memory applications and precise weight update in neuromorphic computing architectures.…”

“…[26] The continuously faster N-to M-polar switching could be explained by the alteration of the local electric field profile due to defect generation and redistribution. [26] The defect distribution could also influence the number of nucleation sites and density of domain walls, which are considered responsible for the origin of wakeup phenomenon in aluminum boron nitride (Al 1−x B x N). [23,40,41] In agreement with this hypothesis, Figure 3 shows that the first M-polar domains nucleate at different regions between the two consecutive N-to M-polar switching transitions.…”

“…Mapping the domain structure dynamics during N-to M-polar switching down to the nanoscale is required to improve the reliability of ferroelectric devices, as well as to develop multilevel memories and artificial synapses for neuromorphic computing. [24][25][26] Piezoresponse force microscopy (PFM) enables nondestructive visualization, control, and measurement of local physical characteristics of ferroelectrics. [27] In this work, transient current integration measurements performed by a pulse switching method are combined with domain imaging by PFM to investigate the kinetics of domain nucleation and wall motion during polarization reversal in Al 0.85 Sc 0.15 N capacitors.…”

Reactive sputtering of ferroelectric AlScN films with H2 gas flow for endurance improvement

“…15,16) Various topics concerning Al 1−x Sc x N thin film have been actively investigated. For instance, sputter deposition, 17,18) epitaxial growth, 19,20) thickness scaling, [21][22][23][24][25][26] low-voltage operation, 27,28) thermal stability, 16,29) field cycling, 30,31) breakdown mechanism, 32) diode memory, 33) ferroelectric FET (FeFET), 34) etc. Low-temperature deposition by Al 1−x Sc x N sputtering down to RT was also reported, which reveals its compatibility with microelectronic integration.…”

Structural characterization of epitaxial ScAlN films grown on GaN by low-temperature sputtering

“…[6][7][8][9][10] Moreover, the inherent ferroelectricity of ScAlN is useful in fabricating nitride semiconductor-based ferroelectric field-effect transistors (FeFETs). [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] Despite its significant potential, ScAlN remains a relatively new material with various unresolved questions regarding the interplay between its structural attributes, such as crystal structure, lattice constants, and physical properties. Notably, ScAlN predominantly crystallizes into a wurtzite structure at lower Sc compositions, and a Sc composition of 18% results in a lattice constant that matches that of GaN.…”