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

Abstract

AlxSc1-xN 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 Al0.72Sc0.28N thin films on epitaxial Pt electrode layers deposited on GaN/Al2O3 substrates. The results are compared both structurally and electrically with similar systems on SiO2/Si substrates. Our X-ray diffraction analysis showed that Al0.72Sc0.28N/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 Al0.72Sc0.28N/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 Al0.72Sc0.28N/Pt/GaN MFM stack with a sharp interface thickness of less than 1 nm.