Oxygen vacancy contributions to the electrical stress response and endurance of ferroelectric hafnium zirconium oxide thin films

Abstract

Despite its scalability and CMOS process compatibility, the limited endurance and sub-optimal stress response of ferroelectric Zr-substituted hafnia [(Hf,Zr)O2] have been one of the key impediments toward its integration into practical device and technology applications. Here, using electrical measurements complemented by photoluminescence spectroscopy, we investigate the underlying mechanisms behind this behavior in 10 nm thick W/Hf0.5Zr0.5O2/W capacitors. Analyzing the evolution of leakage current with stress cycles and the spectroscopic response of the stress-induced leakage current, we attribute the behavior to defect levels, which lie at 0.6 eV from the conduction band edge of the ferroelectric. Photoluminescence spectroscopy, in turn, further corroborates the defect level's position within the bandgap while enabling its attribution to the presence of oxygen vacancies. This work helps to identify oxygen vacancies as the key factor responsible for the degraded endurance and stress response in (Hf,Zr)O2 and subsequently motivates the exploration of methods to reduce the oxygen vacancy concentrations without destabilizing the ferroelectric orthorhombic phase.