Laminate Al2O3/Ta2O5 Metal/Insulator/Insulator/Metal (MIIM) Devices for High-Voltage Applications

We evaluate for high-voltage (HV) applications a series of metal/insulator/insulator/metal (MIIM) devices with relatively thick asymmetric Al2O3/Ta2O5 bilayer insulator barriers in which the Al2O3:Ta2O5 layer thickness ratio is varied from 1:1 to 1:9, with the thickness of the Al2O3 layer fixed at 30 nm. The impact of Ta2O5 to Al2O3 stack order and layer thickness ratio on current versus voltage asymmetry, reverse leakage, breakdown, and programable resistance ratio is investigated. Regions of operation are distinguished, and the responsible underlying dominant conduction mechanisms, including Schottky emission over the various barriers, ohmic conduction and Fowler-Nordheim tunneling through Al2O3, and defect-based Frenkel-Poole emission through Ta2O5 are identified. It was found that under positive bias, the low-resistance state in one-time programable usage is controlled by the thickness and properties of the Ta2O5 layer while the high-resistance state is determined by the thickness and properties of the Al2O3 layer. These results demonstrate that atomic layer deposition (ALD) bilayers are an effective way to engineer the electrical properties of HV metal-insulator-metal (MIM) devices.