Impact of oxygen content on phase constitution and ferroelectric behavior of hafnium oxide thin films deposited by reactive high-power impulse magnetron sputtering

Infrared Signatures for Phase Identification in Hafnium Oxide Thin Films

“…The loop shows low leakage-current contributions to polarization. Although the remanent polarization value is lower than typically observed in doped/substituted HfO 2 films, it is consistent with observations of ferroelectric response in pure hafnia. ,− Furthermore, identically processed HfO 2 films have been shown to have a biaxial tensile stress of only 20 MPa, which is 1 to 2 orders of magnitude lower than typically observed in ferroelectric hafnia. Such a low tensile strain state would not favor the out-of-plane orientation of the polar axis and would limit the maximum polarization value.…”

“…Second, the antipolar film exhibits essentially no modes above ∼690 cm –1 while the polar orthorhombic film has a clear signature at 775 cm –1 . These same spectral characteristics were also observed in films where variable oxygen vacancy concentration altered the amount of the polar and antipolar orthorhombic phases (see Supporting Information, Figure S6).…”

“…The TaN was prepared by pulsed dc magnetron sputtering (30 kHz, 4 μs reverse time) from a TaN target in a Denton Discovery 550 system. HfO 2 films were sputtered via high-power impulse magnetron sputtering (HiPIMS) from a 50 mm diameter hafnium metal target of 99.9% purity in a custom sputter chamber, as detailed previously . For HiPIMS depositions, a Starfire Impulse HiPIMS power module was used in conjunction with a dc power supply to deliver square voltage pulses with a duration of 110 μs, a frequency of 200 Hz, and a magnitude of −700 V. These parameters represent a duty cycle of 2.0% and per-pulse peak plasma power density of 600 W/cm 2 .…”

“…Within HfO 2 thin films, the nonequilibrium ferroelectric polar orthorhombic phase is most often reported to coexist with the equilibrium nonpolar monoclinic ( P 2 1 /c ) and nonequilibrium tetragonal ( P 4 2 / nmc ) phases. − Recent reports, meanwhile, have demonstrated a phase transformation from the antipolar orthorhombic phase ( Pbca ) to the polar orthorhombic ( Pca 2 1 ) phase with electric field cycling, suggesting that this often overlooked antipolar orthorhombic phase may play a significant role as a phase impurity, which impacts ferroelectric performance and influences the wake-up behavior observed in HfO 2 -based thin films. The interplay of these four phasesmonoclinic ( P 2 1 / c ), tetragonal ( P 4 2 / nmc ), antipolar ( Pbca ), and polar ( Pca 2 1 ) orthorhombicis necessarily complex and affected by several factors, including dopant/substituent type and concentration, − stress, − oxygen vacancies, , and film thickness or grain size. , Disentangling the interplay of these competing effects is difficult and necessary, and it requires accurate phase identification in thin films that are typically less than 30 nm thick …”

Asymmetric Electrode Work Function Customization via Top Electrode Replacement in Ferroelectric and Field‐Induced Ferroelectric Hafnium Zirconium Oxide Thin Films

“…[16,17] At equilibrium under atmospheric pressures and at room temperature, HfO 2 is stable in a P2 1 /c linear dielectric monoclinic phase, [18][19][20] whereas a P4 2 nmc field-induced ferroelectric tetragonal phase is stable in small crystallite sizes and at high temperatures. [21] At room temperature, the Pca2 1 orthorhombic phase is stabilized with respect to the mono clinic phase by the utilization of small film thicknesses, [22] incorporation of oxygen vacancies, [22][23][24] and imparting of mechanical stress. [16,25,26] Further, chemical substitution has Non-volatile memory device structures such as ferroelectric random-access memory and ferroelectric tunnel junctions employ switchable spontaneous polarization to hold binary states.…”