Oxidant-Dependent Conduction in Early-Cycle Atomic-Layer-Deposited Al₂O₃and Its Impact on the Dielectric Behavior of Al₂O₃/TiO₂Nanolaminates

Nanolaminates─atomically layered stacks of dissimilar oxides─are widely used to engineer dielectric behavior at the nanometer scale. Among these, atomic layer deposition (ALD)-grown Al₂O₃/TiO₂ stacks have been reported to exhibit “giant” dielectric constant (κ ∼ 10³) at subnanometer periods. Here we show that the apparent high-κ is not an intrinsic dielectric enhancement but a measurement artifact arising from electrically percolative Al₂O₃/TiO₂ stacks treated as ideal dielectrics. Using Al₂O₃/TiO₂ nanolaminate metal–insulator–metal (MIM) capacitors and a combination of electrical (C–f, I–V, EIS), spectroscopic (XPS, HAXPES), and structural (TEM) measurements, we found that TMA/H₂O growth yields Al-deficient Al₂O₃ on TiO₂ that appears morphologically continuous yet lacks full atomic closure, forming electronically percolative pathways that recover insulating behavior only after a fully coalesced overlayer develops. In contrast, TMA/O₃ deposition produces fully continuous Al₂O₃ that remains insulating even at subnanometer thickness. These results establish practical design rules, showing that oxidant chemistry and film thickness together govern film continuity and insulating behavior, thereby clarifying when ultrathin ALD Al₂O₃ functions as a true insulator versus a quasi-conductive layer. The insights extend directly to applications in microelectronics (gate stacks, MIM/DRAM capacitors), quantum devices (2DEGs, tunnel barriers), and electrochemical/photovoltaic systems (battery electrodes, electrocatalysts, and perovskite interface engineering), where reliable subnanometer coatings are essential.