Impact of Iridium Oxide Electrodes on the Ferroelectric Phase of Thin Hf_0.5Zr_0.5O₂ Films

Abstract

Thin film metal–ferroelectric–metal capacitors with an equal mixture of hafnium oxide and zirconium oxide as the ferroelectric material are fabricated using iridium oxide as the electrode material. The influence of the oxygen concentration in the electrodes during crystallization anneal on the ferroelectric properties is characterized by electrical, chemical, and structural methods. Forming gas, O2, and N2 annealing atmospheres significantly change the ferroelectric performance. The use of oxygen‐deficient electrodes improves the stabilization of the ferroelectric orthorhombic phase and reduces the wake‐up effect. It is found that oxygen‐rich electrodes supply oxygen during anneal and reduce the amount of oxygen vacancies, but the nonferroelectric monoclinic phase is stabilized with a negative impact on the ferroelectric properties.

Chemical Stability of IrO2 Top Electrodes in Ferroelectric Hf0.5Zr0.5O2‐Based Metal–Insulator–Metal Structures: The Impact of Annealing Gas

“…HAXPES, thereby, provides the large information depth required to probe the entire capacitor stack; [15,30] even signals from the IrO 2 bottom electrode could be detected. [16] For a depth-dependent analysis, we recorded HAXPES spectra at the photoelectron emission angles of 10 (more bulk sensitive) as well as for 36 and 41 (more surface sensitive) relative to the surface normal. Binding energies (E B ) are referred to the Fermi level of gold.…”

“…The results may stimulate further investigations and finally aid to a better understanding and control of performance instabilities, such as wakeup, imprint, and fatigue. [16]…”

“…Figure 5. Ferroelectric polarization versus switching cycles of FG (9:1 N 2 :H 2 ratio)-, N 2 -, and O 2 -annealed samples (see also Mittmann et al[16] ).…”

Interplay between oxygen defects and dopants: effect on structure and performance of HfO2-based ferroelectrics

“…Their measurements showed neither structural nor electrical strong differences, leading to the conclusion that the oxygen vacancies amount did not influence ferroelectricity. Experiments on the impact of annealing atmosphere with different oxygen content were also conducted by Mittmann et al, 51 where Hf 0.5 Zr 0.5 O 2 layers were instead deposited by ALD between two symmetrical IrO 2 electrodes to avoid oxidation of the electrode during oxygen anneal. In their case, the combination between oxide electrodes and oxygen rich annealing atmosphere seemed to be detrimental for the ferroelectric properties, encouraging the stabilization of the m-phase with respect to the polar o-phase, which was instead formed when H 2 was provided during the annealing treatment.…”

“…As a result, the ferroelectric phase could only be stabilized for low Hf 0.5 Zr 0.5 O 2 thicknesses. IrO 2 was used as both top and bottom electrode in the work by Mittmann et al51 and, differently from the PZT case, the use of an oxide electrode was rather detrimental for the capacitor performance, since the extra provided oxygen decreased the po-phase portion in favour of the non-polar m-phase. A low reactivity of Ru with Hf 0.5 Zr 0.5 O 2 was ascribed by Cao et al78 as the cause for the better performance observed in Ru/ Hf 0.5 Zr 0.5 O 2 /Ru capacitors as compared to TiN/Hf 0.5 Zr 0.5 O 2 /TiN capacitors, especially in terms of measured leakage current and device endurance to field cycling.…”