Effect of Al₂O₃ layer thickness on leakage current and dielectric properties of atomic layer deposited Al₂O₃/TiO₂/Al₂O₃ nano-stack

Abstract

In order to develop an alternate high-k and low-loss dielectric material for high density energy storage and gate oxide applications and to address the leakage current issues in single layer oxide thin films, nano-stacked devices with the active oxide layer sandwiched between higher bandgap barrier layers have recently been extensively explored. Here, we report the fabrication of Al₂O₃/TiO₂ (20 nm)/Al₂O₃ (ATA) nano-stacks using an optimized atomic layer deposition technique, where the effect of the Al₂O₃ barrier layer thickness on leakage and dielectric properties was thoroughly explored. The high dielectric loss (> 1) and leakage current values (> 10⁻⁴ A/cm²) exhibited by ~ 20 nm TiO₂ thin film was reduced significantly by encapsulating with Al₂O₃ barrier layer. Introducing barrier layer thickness from 1 to 5 nm, the leakage paths are substantially reduced and the charge carriers are effectively trapped at the interfaces, leading to a significant improvement in leakage current density (reduction from ~ 7.47 × 10⁻⁷ to 1.21 × 10⁻⁹ A/cm² at 1 V applied bias), breakdown field (increase from 0.8 to 1.75 MV/cm) and dielectric loss (reduction from 0.1 to 0.06). Furthermore, the capacitance density of a particular ATA structure was found to be invariant with applied bias voltage (− 1 V to + 1 V) and frequency (10 kHz to 1 MHz), demonstrating its potential in various high frequency capacitive circuit applications. Notably, the ATA structure having barrier layer thickness of ~ 1 nm, demonstrated a significantly high capacitance density (~ 13.2 fF/µm²), low dielectric loss (~ 0.1) and low leakage current density (~ 7.47 × 10⁻⁷ A/cm² @1 V bias), making this ATA stack a promising material for high-density energy storage and gate dielectric applications.