Ferroelectric Al_1−xB_xN sputtered thin films on n-type Si bottom electrodes

Ferroelectric Al_1−xB_xN thin films are grown on highly doped and plasma treated (100) n-type Si. We demonstrate ferroelectricity for x = < 0.01, 0.02, 0.06, 0.08, 0.13, and 0.17 where the n-type Si is both the substrate and bottom electrode. Polarization hysteresis reveals remanent polarization values between 130 and 140 μC/cm² and coercive field values as low as 4 MV/cm at 1 Hz with low leakage. The highest resistivity and most saturating hysteresis occurs with B contents between x = 0.06 and 0.13. We also demonstrate the impact of substrate plasma treatment time on Al_1−xB_xN crystallinity and switching. Cross-sectional transmission electron microscopy and electron energy loss spectra reveal an amorphous 3.5 nm SiN_x layer at the Al_1−xB_xN interface post-plasma treatment and deposition. The first ~ 5 nm of Al_1−xB_xN is crystallographically defective. Using the n-type Si substrate, we demonstrate Al_1−xB_xN thickness scaling to 25 nm via low-frequency hysteresis and CV. Serving as the bottom electrode and substrate, the n-type Si enables a streamlined growth process for Al_1−xB_xN for a wide range of Al_1−xB_xN compositions and layer thicknesses.