Investigation of the impact of insulator material on the performance of dissimilar electrode metal-insulator-metal diodes

The performance of thin film metal-insulator-metal (MIM) diodes is investigated for a variety of large and small electron affinity insulators using ultrasmooth amorphous metal as the bottom electrode. Nb₂O₅, Ta₂O₅, ZrO₂, HfO₂, Al₂O₃, and SiO₂ amorphous insulators are deposited via atomic layer deposition (ALD). Reflection electron energy loss spectroscopy (REELS) is utilized to measure the band-gap energy (E_G) and energy position of intrinsic sub-gap defect states for each insulator. E_G of as-deposited ALD insulators are found to be Nb₂O₅ = 3.8 eV, Ta₂O₅ = 4.4 eV, ZrO₂ = 5.4 eV, HfO₂ = 5.6 eV, Al₂O₃ = 6.4 eV, and SiO₂ = 8.8 eV with uncertainty of ±0.2 eV. Current vs. voltage asymmetry, non-linearity, turn-on voltage, and dominant conduction mechanisms are compared. Al₂O₃ and SiO₂ are found to operate based on Fowler-Nordheim tunneling. Al₂O₃ shows the highest asymmetry. ZrO₂, Nb₂O₅, and Ta₂O₅ based diodes are found to be dominated by Frenkel-Poole emission at large biases and exhibit lower asymmetry. The electrically estimated trap energy levels for defects that dominate Frenkel-Poole conduction are found to be consistent with the energy levels of surface oxygen vacancy defects observed in REELS measurements. For HfO₂, conduction is found to be a mix of trap assisted tunneling and Frenkel-Poole emission. Insulator selection criteria in regards to MIM diodes applications are discussed.