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Register a new userImproving Reproducibility of Sputter Deposited Ferroelectric Wurtzite Al0.6Sc0.4N Films using In-situ Optical Emission Spectrometry
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High-Sc Al1-xScxN thin films are of tremendous interest because of their attractive piezoelectric and ferroelectric properties, but overall film quality and reproducibility are widely reported to suffer as x increases. In this study, we correlate the structure and electrical properties of Al0.6Sc0.4N with in-situ observations of glow discharge optical emission during growth. This in-situ technique uses changes in the Ar(I) and N2(I) emission lines of the glow discharge during growth to identify films that subsequently exhibit unacceptable structural and electrical performance. We show that a steady deposition throughout film growth produces ferroelectric Al0.6Sc0.4N with a reversible 80 {mu}C cm-1 polarization and 3.1 MV cm-1 coercive field. In other films deposited using identical settings, fluctuations in both Ar(I) and N2(I) line intensities correspond to decreased wurtzite phase purity, nm-scale changes to the film microstructure, and a non-ferroelectric response. These results illustrate the power of optical emission spectroscopy for tracking changes when fabricating process-sensitive samples such as high-Sc Al1-xScxN films.
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We grow epitaxial Sm-Co thin films by sputter deposition from an alloy target with a nominal SmCo5 composition on Cr(100)-buffered MgO(100) single-crystal substrates. By varying the Ar gas pressure, we can change the composition of the film from a SmCo5-like to a Sm2Co7-like phase. The composition, crystal structure, morphology and magnetic properties of these films have been determined using Rutherford Backscattering, X-ray diffraction and magnetization measurements. We find that the various properties are sensitive to the sputter background pressure in different ways. In particular, the lattice parameter changes in a continuous way, the coercive fields vary continuously with a maximum value of 3.3 T, but the saturation magnetization peaks when the lattice parameter is close to that of Sm2Co7. Moreover, we find that the Sm content of the films is higher than expected from the expected stoichiometry.
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The first epitaxial ferroelectric wurtzite film with clear polarization-electric field hysteresis behavior is presented. The coercive field of this epitaxial Al0.7Sc0.3N film on W/c-sapphire substrate is 0.4 +- 0.3 MV cm-1 (8 %) smaller than that of a conventional fiber textured film on a Pt/TiOx/SiO2/Si substrate, attributed to the 0.01 +- 0.007 {AA} smaller c-axis lattice parameter in the epitaxial film. The strain and decrease of the coercive field most likely originate from epitaxial strain rather than the mismatch in thermal coefficient of expansion. These results provide an insight for further coercive field reduction of novel wurtzite ferroelectrics using epitaxial mismatch strain.
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