Ferroelectric Al${}_{1-x}$B${}_x$N sputtered thin films on n-type Si bottom electrodes

Abstract

Ferroelectric Al${}_{1-x}$B${}_x$N 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 130-140 $\mu$C/cm${}^2$ and coercive field values as low as 4 MV/cm at 1 Hz with low leakage. The highest re-sistivity 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${}_{1-x}$B${}_x$N crystallinity and switching. Cross-sectional transmission electron microscopy and electron energy loss spectra reveal an amorphous 3.5 nm SiNx layer at the Al${}_{1-x}$B${}_x$N interface post-plasma treatment and deposition. The first $\sim 5$ nm of Al${}_{1-x}$B${}_x$N is crystallographically defective. Using the n-type Si substrate we demonstrate Al${}_{1-x}$B${}_x$N thick-ness scaling to 25 nm via low frequency hysteresis and CV. Serving as the bottom electrode and sub-strate, the n-type Si enables a streamlined growth process for Al${}_{1-x}$B${}_x$N for a wide range of Al${}_{1-x}$B${}_x$N compositions and layer thicknesses.