Interpretation of ferroelectric behavior in AlScN films with TiN and Ta bottom electrodes

Ferroelectric properties of 50-nm-thick Al0.88Sc0.12N films with different bottom electrodes (BEs) of TiN and Ta were characterized. Capacitance–voltage (C–V) curves of the capacitors indicate sharp switching with the Ta BE, whereas partial polarization can be obtained with the TiN BE. By analyzing the electric field distribution of the partial polarization obtained from positive-up negative-down measurements, two kinds of coercive field (Ec) with Lorentzian distributions can be extracted: one high Ec with AlScN domains and another low Ec with defect-incorporated domains. The distribution of the inverted nucleus becomes narrower with the Ta BE and appears to correlate with the degree of c-axis orientation evaluated by rocking-curve x-ray diffraction. The defect-incorporated domains were found to shift their mean Ec to a higher electric field by switching cycles, resulting in the fatigue effect. The present interpretation provides insight into understanding the ferroelectric behavior of AlScN films.