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

AlSc_1-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_0.72Sc_0.28N 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 Al_0.72Sc_0.28N/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 Al_0.72Sc_0.28N/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 Al_0.72Sc_0.28N/Pt/GaN MFM stack with a sharp interface thickness of less than 1 nm.