Influence of atomic layer deposited Al2O3 thickness on metal/insulator/metal electron energy barriers

It has been reported that the relative dielectric constant, refractive index, and density of certain thin dielectric films, such as Al2O3, degrade with decreasing thickness. We investigated the influence of Al2O3 film thickness on the electron energy barriers at the interfaces of Pt/Al2O3/TiN metal/insulator/metal devices with Al2O3 deposited via atomic layer deposition. Using internal photoemission spectroscopy, we found that both the top Pt/Al2O3 and bottom TiN/Al2O3 electron barriers were a function of Al2O3 thickness. While both electron barriers were roughly constant at ∼3.6 eV for films ≥11.6 nm thick, both decreased by ∼0.5 eV as Al2O3 thickness decreased to 4.5 nm. The degradation of electron barriers with insulator thickness impacts the modeling of leakage currents and optimization of performance in devices with ultrathin insulators.