Atomic layer deposition of tantalum oxide with controlled oxygen deficiency for making resistive memory structures

Abstract

TaO_x films with controlled ratio of Ta⁴⁺ and Ta⁵⁺ atoms were prepared at different hydrogen concentrations in plasma. As shown by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry, the chemical state of Ta⁴⁺ corresponds to oxygen vacancies in the TaO_x film. Electrophysical studies of the metal–dielectric–metal structures revealed an increase in the leakage current by four orders of magnitude as the hydrogen concentration in the plasma was increased from 7 to 70%, which is due to an increase in the concentration of oxygen vacancies in TaO_x. A test structure of a resistive memory cell was made on the basis of the nonstoichiometric TaO_x obtained. It withstood more than 10⁶ rewriting cycles. The suggested atomic layer deposition process shows promise for solving one of the main problems of resistive memory: extension of its working life.