Harnessing Phase Transitions in Antiferroelectric ZrO₂ Using the Size Effect

Abstract

hysteresis observed in macroscopic polarization-voltage (P-V) measurements in HfO 2 and ZrO 2 thin films is a signature of AFE device functionality and originates from a complex interplay of favorable crystallization conditions. [3,5] Underlying electric field-induced FE structural phase transitions are hypothesized to be responsible for generating the distinctive features of antiferroelectricity in the fluorite material system, yet little is known about how to best exploit such phase transitions in fluorites. [4,6] Alternative theories of AFE-like behavior, such as oppositely imprinted FE domains and paraelectric-to-paraelectric phase transitions, need to be evaluated since the approach to achieve superior AFE device performance will depend on the underlying cause of macroscopic antiferroelectricity. [7][8][9][10] Due to the simplicity of controlling the film thickness, the size effect may be easily leveraged to influence and gain a better understanding of antiferroelectricity in ZrO 2 , but previous film thickness studies on ZrO 2 and Hf 1−x Zr x O 2 have not quantified the size-effect influence on supercapacitor performance. [11][12][13][14] A theory of AFE crystals was first formulated by Kittel in which two sub-lattices of opposing polarization are described by a Landau-Devonshire free energy model. [15] There is also increasing acceptance for a more general definition of antiferroelectricity to include reversible electric field induced first-order phase transitions between a paraelectric (nonpolar) and a FE (polar) phase that do not necessarily involve an antipolar crystal structure. [3,5,16,17] In this work, AFE is used in the expanded sense of the term to include field-induced phase transitions that may not specifically involve an antipolar crystal phase.While the diverse polymorphism of HfO 2 and ZrO 2 ceramics has been known for decades, [18] the emergence of a FE phase in thin films of these materials over the past decade has revealed fresh insight on new structural phases and interrelationships. [19][20][21] With the identification of the Pca2 1 polar orthorhombic (o) phase in HfO 2 thin films, [22] the possibility of electric-field induced phase transitions in fluorites surfaced with functional electronic AFE properties. [3,6,20] First-order electric field driven phase transitions between the nonpolar tetragonal and polar orthorhombic phases in HfO 2 and ZrO 2 are postulated to be the origin of antiferroelectricity inThe unique nonlinear dielectric properties of antiferroelectric (AFE) oxides are promising for advancements in solid state supercapacitor, actuator, and memory technologies. AFE behavior in high-k ZrO 2 is of particular technological interest, but the origin of antiferroelectricity in ZrO 2 remains questionable. The theory of reversible electric field-induced phase transitions between the nonpolar P4 2 /nmc tetragonal phase and the polar Pca2 1 orthorhombic phase is experimentally tested with local structural and electromechanical characterization of AFE ZrO 2 thin films. Piezoresponse f...

Influence of Si-Doping on 45 nm Thick Ferroelectric ZrO2 Films

“…However, in ZrO 2 films, the t-phase is the most favorable phase for crystallite sizes up to 34 nm . Therefore, size effects play an important role in the stabilization of the t-phase ,, but have less influence compared to the Si-doping concentration and in-plane stress in the 45 nm thick Si-doped ZrO 2 films investigated here.…”

“…According to previous investigations, factors such as biaxial in-plane stress, ,, grain and crystallite size, and doping ,, are hypothesized to influence ferroelectricity in ZrO 2 thin films. However, these factors have been researched independently, and there is still a lack of studies on their interactions.…”

Explicating the irreversible electric-field-assisted ferroelectric phase transition in the otherwise antiferroelectric sodium niobate for energy storage systems

“…[26][27][28][29] We note that although this phenomenological model may not capture key experimental features such as domain orientation, grain boundaries, and strain effects in the actual device, the LD model has been employed in previous reports to describe the (A)FE transitions in e.g., PbZrO 3 and ZrO 2 . 39,72,73 According to the phenomenological LD theory, 71,74 the energy difference taken with respect to a non-polar state, DE, can be expressed as a mathematical expansion of the order parameter -for instance, polarization (P) -with:…”

Memory Window Enhancement in Antiferroelectric RAM by Hf Doping in ZrO₂

“…The wake-up effect in HfO 2 and ZrO 2 -based ferroelectrics is commonly attributed to a fluid, yet irreversible phase transition from the nonpolar tetragonal to the polar orthorhombic phase with electric field cycling [21]. Alternative theories of AFE that could pertain to wake-up include oppositely-imprinted FE domains and ferroelastic switching [22], [23], but the imprint theory is incompatible with piezoresponse force microscopy results showing locally induced phase transitions in AFE ZrO 2 [6]. Since the AFERAM films are cycled at 2.5 V and only the negative voltage branch of the AFE hysteresis loop is switching during cycling, the higher negative electric field stress may cause local defect rearrangement and/or ferroelastic-like mechanisms that stabilize the negative polarization state without influencing the nonpolar to positive polar phase transition.…”

“…memories is surging [2]- [4]. In contrast to HfO 2 , which exhibits FE properties sought after for ferroelectric random access memory (FeRAM) applications, polycrystalline ZrO 2 films thinner than 15 nm are typically AFE with a double polarization-voltage (P-V) hysteresis loop [2], [5], [6].…”