Investigation of ZrO2 – Gd2O3 Based High-k Materials as Capacitor Dielectrics

Abstract

Atomic layer deposition (ALD) of nanolaminates and mixtures was investigated for the preparation of a high permittivity dielectric material. Variation in the relative number of ALD cycles for constituent oxides allowed one to obtain films with controlled composition. Pure films possessed monoclinic and higher permittivity cubic or tetragonal phases, whereas the inclusion of resulted in the disappearance of the monoclinic phase. Changes in phase composition were accompanied with increased permittivity of mixtures and laminates with low Gd content. Further increase in the lower permittivity content above 3.4 cat. % resulted in the decreased permittivity of the mixtures. Leakage currents generally decreased with increasing Gd content, whereby laminated structures demonstrated smaller leakage currents than mixed films at a comparable Gd content. Concerning the bottom electrode materials, the best results in terms of permittivity and leakage currents were achieved with Ru, allowing a capacitance equivalent oxide thickness of and a current density of at 1 V. Charge storage values up to were obtained for mixtures and laminates with thickness below 30 nm. In general, at electric fields below 2–3 MV/cm, normal and trap-compensated Poole–Frenkel conduction mechanisms were competing, whereas at higher fields, Fowler–Nordheim and/or trap-assisted tunneling started to dominate.