In‐Grain Ferroelectric Switching in Sub‐5 nm Thin Al_0.74Sc_0.26N Films at 1 V

Abstract

Analog switching in ferroelectric devices promises neuromorphic computing with the highest energy efficiency if limited device scalability can be overcome. To contribute to a solution, one reports on the ferroelectric switching characteristics of sub‐5 nm thin Al0.74Sc0.26N films grown on Pt/Ti/SiO2/Si and epitaxial Pt/GaN/sapphire templates by sputter‐deposition. In this context, the study focuses on the following major achievements compared to previously available wurtzite‐type ferroelectrics: 1) Record low switching voltages down to 1 V are achieved, which is in a range that can be supplied by standard on‐chip voltage sources. 2) Compared to the previously investigated deposition of ultrathin Al1−xScxN films on epitaxial templates, a significantly larger coercive field (Ec) to breakdown field ratio is observed for Al0.74Sc0.26N films grown on silicon substrates, the technologically most relevant substrate‐type. 3) The formation of true ferroelectric domains in wurtzite‐type materials is for the first time demonstrated on the atomic scale by scanning transmission electron microscopy (STEM) investigations of a sub‐5 nm thin partially switched film. The direct observation of inversion domain boundaries (IDB) within single nm‐sized grains supports the theory of a gradual domain‐wall driven switching process in wurtzite‐type ferroelectrics. Ultimately, this should enable the analog switching necessary for mimicking neuromorphic concepts also in highly scaled devices.

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

“…The STEM image further suggests a similar interface, also with epi-Pt and GaN. These sharp interfaces in the epitaxial films are known to reduce the overall leakage current for the capacitors. − In addition, the low contrast at the grain boundaries also indicates a relatively stronger grain-to-grain bond in epitaxial Al 0.72 Sc 0.28 N films compared to the fiber-textured films grown on Si (previously published). ,, The in-plane X-ray diffraction scan proves that the Al 0.72 Sc 0.28 N grows with an average lattice parameter of ∼3.24 Å, meaning a complete epitaxially relaxed 20 nm film on epi-Pt. The fitted 2θ–χΦ profile of the RSM (shown in Figure d­(i)) shows the contributions of both the GaN and AlScN (01–10) reflections to the recorded peak intensity.…”

Demonstration and STEM Analysis of Ferroelectric Switching in MOCVD‐Grown Single Crystalline Al0.85Sc0.15N

“…In one of our recent studies, we reported on hysteretic current contributions likely arising due to domain wall formation and conduction during polarization inversion. [23] Also in this MOCVD-grown film, polarization domain walls with horizontal components are evidenced in the cone-like shape domain patterns by STEM analysis (see Figure 4). However, in contrast to tail-to-tail domain walls (i.e., polarization direction of the adjacent domains pointing apart, resulting in a negatively charged domain wall) present in 5 nm thin films reported in our previous study, [23] in this heterostructure, head-to-head domain walls (i.e., polarization direction of the adjacent domains pointing toward each other, resulting in a positively charged domain wall) are forming during the switching process.…”

“…This results in N-polar residues at the latter when transitioning from M-polarity. [23,28] As a consequence, only tail-to-tail domain walls were observed.…”

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.…”