Although 10 years have passed since the initial report of ferroelectricity in hafnia (HfO2), researchers are still intensely fascinated by this material system and the promise it holds for future applications. A wide variety of deposition methods have been deployed to create ferroelectric HfO2 thin films such as atomic layer deposition, chemical solution deposition, and physical vapor deposition methods such as sputtering and pulsed laser deposition. Process and design parameters such as deposition temperature, precursor choice, target source, vacuum level, reactive gases, substrate strain, and many others are often integral in stabilizing the polar orthorhombic phase and ferroelectricity. We examine processing parameters across four main different deposition methods and their effect on film microstructure, phase evolution, defect concentration, and resultant electrical properties. The goal of this review is to integrate the process knowledge collected over the past 10 years in the field of ferroelectric HfO2 into a single comprehensive guide for the design of future HfO2-based ferroelectric materials and devices.

Northrop Grumman Synoptics is de veloping the growth of large single crystal fluoride materials for Faraday rotator / isolator applications. These materials exhibit smaller nonlinear refractive index and thermo optic coefficients, while maintaining Ver det constants near those of the com monly used terbium gallium garnet (TGG) crystals. In particular, the cu bic potassium terbium fluoride, KTF (KTb 3 F 10 ) crystal has low absorption and thermo optic coefficients. The crystal growth and performance of these single crystal fluoride materi als will be discussed as well as recent improvements to the performance of TGG crystals.

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Antiferroelectric thin films have properties ideal for energy storage due to their lower losses compared to their ferroelectric counterparts as well as their robust endurance properties. We fabricated Al-doped HfO2 antiferroelectric thin films via atomic layer deposition at variable thicknesses (20 nm or 50 nm) with varying dopant concentrations (4 at. % or 8 at. %). 50 nm thick 8 at. % Al-doped HfO2 showed a maximum energy storage density of 63 J/cm3 while maintaining an efficiency of 85%. A study comparing these thin films revealed thicker films allowed for higher operating electric fields and thus higher energy storage densities at operating voltage. The loss tangents of the thin films at operating voltage were under 2% over the range of −4 to 4 MV/cm and at frequencies ranging from 500 Hz to 100 kHz. Reliability studies showed the thin films endure up to 106–107 cycles and the breakdown field of the films yielded Weibull moduli greater than 6 for all our thin films. The Weibull modulus provides a measurement of the consistency of the breakdown strength from sample to sample, with higher moduli indicating a more invariable result. These electrical characteristics along with the thin film's cycling endurance and reliability make antiferroelectric-like Al-doped thin films a promising material for energy storage applications.