Ferroelectricity in Wurtzite Atomic Layer Annealed Aluminum Nitride Thin Films

Abstract

Investigation of aluminum nitride-based ferroelectric thin films for non-volatile memory applications has largely focused on various thin film solid solutions grown by reactive sputtering. The growth process leads to significant DC electrical leakage related to mosaic disorder and point defects in this class of materials; extrinsic alloying elements such as scandium or boron are used to facilitate ferroelectric switching at lower electric fields to limit these deleterious effects. We take a different approach focusing on growth via atomic layer annealing using a nitrogen remote inductively coupled plasma (ICP). We demonstrate ferroelectric behavior in nanocrystalline wurtzite aluminum nitride (AlN) films with neither additional alloying components nor post-process annealing grown using a 350°C CMOS-compatible growth process. The films do not exhibit hard dielectric breakdown even under electric fields in excess of 10 MV cm^-1. Electrical property characterization using positive-up-negative-down (PUND) measurements shows remanent polarization (P_r) in excess of 30 µC cm^-2. Piezoresponse force microscopy (PFM) DC bias poling experiments yield behavior consistent with ferroelectricity. Structural characterization was performed using Scanning/Transmission Electron Microscopy, X-ray Photoelectron Spectroscopy depth profiling, and spectroscopic ellipsometry. An ALD-based growth approach to ferroelectric aluminum nitride-based films holds significant advantage from a device scaling standpoint and provides an alternative route towards aluminum nitride-based thin films.