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.

Infrared Signatures for Phase Identification in Hafnium Oxide Thin Films

“…In the sub-band gap region of each Tauc plot, small humps are seen at around 2 and 4 eV. Recent photoluminescence (PL) spectroscopy measurements of hafnium zirconium oxide films have identified PL modes with energies ranging from 2.3–3.0 eV that correspond to defect states resulting from oxygen vacancies . Additionally, prior work has attributed the 4 eV absorption in hafnia to transitions between oxygen point defect states .…”

Impact of Electric Field Pulse Duration on Ferroelectric Hafnium Zirconium Oxide Thin Film Capacitor Endurance

“…The first possible mechanism is the motion of charged oxygen vacancies to the electrode interfaces, allowing for states at the interface through which tunneling at high voltage can occur, as depicted in Figure 7a. [ 32 ] The second transport path is through the bulk and terminates at the grain boundaries, ultimately creating a percolation path for electrons to transport through the HZO capacitor layer and short the device, as seen in Figure 7b. [ 14 ] Most likely, a combination of factors is contributing.…”

Enhanced polarization switching characteristics of HfO2 ultrathin films via acceptor-donor co-doping

“…Despite the superb effect in triggering ferroelectricity, the role of oxygen vacancies remains a double-edged sword. While being effective in stabilizing the polar phase, oxygen vacancies can induce local structural/field inhomogeneities, thereby hindering domain wall motion 22 , 23 and thus impeding the polarization response of HfO 2 -based devices 24 . As a result, the polarization switching characteristics of HfO 2 thin films often fall behind conventional perovskite ferroelectrics like Pb(Zr,Ti)O 3 25 .…”