A Comparative Study of Pt/Al_0.72Sc_0.28N/Pt-Based Thin-Film Metal-Ferroelectric-Metal Capacitors on GaN and Si Substrates

Abstract

Al x Sc 1−x N is a nitride-ferroelectric compatible with both CMOS and GaN technology. The origin of ferroelectricity in these ternary nitrides relies on the full inversion of nitrogen atom positions, which is a significantly different structural mechanism than conventional perovskites. Therefore, its ferroelectric characteristics exhibit a high remanent polarization and a tunable coercive field but suffer heavily from leakage currents during the switching event. In this article, we studied epitaxially grown Al 0.72 Sc 0.28 N thin films on epitaxial Pt electrode layers deposited on GaN/Al 2 O 3 substrates. The results are compared both structurally and electrically with similar systems on SiO 2 /Si substrates. Our X-ray diffraction analysis showed that Al 0.72 Sc 0.28 N/epi-Pt/GaN is always a complete epitaxial stack without any significant strain gradient. Electrically, this system has an overall lower leakage current and coercive field compared to directly grown, highly crystalline, strained epitaxial Al 0.72 Sc 0.28 N/ GaN, despite having a lower crystalline quality of the ferroelectric layer. In addition, decreasing the epi-Pt thickness from 100 to 10 nm resulted in further improvement of the leakage profile, which we attribute to a decrease in surface roughness in the thinner Pt. In contrast, the dominant factor of leakage in a fiber-textured system on Si substrates is the Pt(111) texture. Finally, with the combination of in-plane X-ray diffraction and high-resolution scanning transmission electron microscopy, we have demonstrated an all-epitaxial 20 nm Al 0.72 Sc 0.28 N/Pt/GaN MFM stack with a sharp interface thickness of less than 1 nm.

In‐Grain Ferroelectric Switching in Sub‐5 nm Thin Al0.74Sc0.26N Films at 1 V

“…Here, the use of the ABF detector allows to routinely image atomic positions of light elements such as nitrogen, which is the crucial prerequisite to observe the polarity on the unit cell level in ferroelectric Al 1−x Sc x N. [ 41 ] Figure 5b depicts atomic models of the N‐ and M‐polar oriented wurtzite‐type structures sketched along the [2‐1‐10] viewing direction required for the investigation of unit cell polarity. As already discussed in related work, [ 18,26,41 ] sputtered nanocrystalline films of Al 1−x Sc x N exhibit small grain diameters of 2 – 6 nm featuring an in‐plane tilt between the individual grains in the order of 6° which restricts the observable area to single grains with exact orientation to the incident electron beam. [ 14 ] In this respect, the ABF‐STEM image contrast formation crucially depends on exact orientation conditions.…”

“…[ 17 ] Structurally, the epitaxial films with a 10 nm thin Pt bottom electrode layer also have superior crystalline quality compared to non‐epitaxial ones, that is, higher c ‐axis texture, which we investigate in detail in a separate work. [ 18 ] Nonetheless, the films deposited on Si substrates exhibit more pronounced ferroelectric switching peaks (Figure 1b). Thus, despite their higher interface roughness and poorer interface texture compared to the epitaxial ones, a complete polarization inversion is demonstrated for the non‐epitaxial 10 nm thin Al 0.74 Sc 0.26 N grown on Pt/Ti/SiO 2 /Si, yet not for the epitaxial films.…”

Perspectives of Ferroelectric Wurtzite AlScN: Material Characteristics, Preparation, and Applications in Advanced Memory Devices

“…Empirically, adjusting E c can be effectively achieved by altering the thickness of the thin film. So, we have summarized recent research on the thickness of AlScN films [ 23 , 34 , 36 , 43 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 ], as depicted in Figure 1 c. Such research of thickness reveals a significant downward trend, while the corresponding Sc components gradually concentrate around 0.3. In 2023, it appears to represent a new milestone, with thickness even dropping below 5 nm.…”

“…Copyright 2021, AIP Publishing. ( c ) Research trends in AlScN film thickness in recent years [ 23 , 34 , 36 , 43 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 ]. ( d ) The cross-sectional TEM image of Al/AlScN/Al and interfaces between layers [ 69 ].…”

Strain-Controlled Formation Energy and Migration of Nitrogen Vacancy in Al1–xScxN: A First-Principles Study

“…The continuous advancement of information technology demands the development of storage technologies that can efficiently manage the ever-increasing amount of data. In contrast to conventional semiconductor storage methods, ferroelectric memory storage presents a multitude of advantages including high charge density, low power consumption, rapid access speeds, and nonvolatility. − As a result, ferroelectric memory storage has emerged as a field of great potential for further investigation and development. The key part of ferroelectric memory is the ferroelectric material.…”