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

摘要

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. Nb_2O_5, Ta_2O_5, ZrO_2, HfO_2, Al_2O_3, and SiO_2 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 Nb_2O_5 = 3.8eV, Ta_2O_5 = 4.4eV, ZrO_2 = 5.4eV, HfO_2 = 5.6eV, Al_2O_3 = 6.4eV, and SiO_2 = 8.8eV with uncertainty of ±0.2 eV. Current vs. voltage asymmetry, non-linearity, turn-on voltage, and dominant conduction mechanisms are compared. Al_2O_3 and SiO_2 are found to operate based on Fowler-Nordheim tunneling. Al_2O_3 shows the highest asymmetry. ZrO_2, Nb_2O_5, and Ta_2O_5 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 HfO_2, 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.