Maxwell-Wagner Relaxation-Driven High Dielectric Constant in Al2O3/TiO2 Nanolaminates Grown by Pulsed Laser Deposition

Multilayer nanolaminates (NLs) of alternate ultrathin sublayers of Al2O3 and TiO2 (ATA) with the thickness ranging similar to 2 to 0.5 nm were fabricated by optimized pulsed laser deposition (PLD). Maxwell-Wagner (M-W) relaxation-induced interfacial polarization was realized and engineered by precisely controlling the sublayer thicknesses and the number of interfaces. X-ray reflectivity and cross-sectional transmission electron microscopy measurements of ATA NLs revealed an artificial periodicity with well-defined uniformly thick amorphous sublayers with chemically and physically distinct interfaces down to a sublayer thickness of similar to 0.8 nm. The dielectric constants and loss of ATA NLs were found to increase from similar to 60 to 670 and decrease from similar to 0.9 to 0.16, respectively, as sublayer thicknesses reduced from similar to 2 to 0.8 nm. However, for a sublayer thickness below 0.8 nm, the trend was reversed. Furthermore, temperature-dependent impedance spectroscopy studies revealed two distinct thermally activated relaxation processes, corresponding to TiO2 and Al2O3 sublayers, corroborating the M-W relaxation. The conductivity contrast between the sublayers of ATA NLs enhanced with reducing sublayer thickness and plateaued at a sublayer thickness of similar to 0.8 nm, resulting in dominant M-W interfacial polarization and a high cut-off frequency of similar to 50 kHz. These results demonstrate that ATA NLs grown by PLD may find application as potential high-k materials for next-generation nanoelectronic devices.