Vibrational fingerprints of ferroelectric hafnia

TL;DR

This study characterizes the vibrational properties of yttrium-stabilized hafnia crystals, providing spectroscopic fingerprints for different phases, which aids in understanding their dielectric and ferroelectric behaviors for chip applications.

Contribution

It offers the first detailed vibrational analysis and spectral fingerprints of various hafnia phases, combining experimental Raman/infrared spectra with lattice dynamics calculations.

Findings

Identified vibrational modes for multiple hafnia phases.

Compared experimental spectra with theoretical calculations.

Revealed signatures of polar orthorhombic hafnia.

Abstract

Hafnia (HfO2) is a promising material for emerging chip applications due to its high-k dielectric behaviour, suitability for negative capacitance heterostructures, scalable ferroelectricity, and silicon compatibility. The lattice dynamics along with phononic properties such as thermal conductivity, contraction, and heat capacity are under-explored, primarily due to the absence of high quality single crystals. Herein, we report the vibrational properties of a series of HfO2 crystals stabilized with yttrium (chemical formula HfO2:xY, where x = 20, 12, 11, 8, and 0%) and compare our findings with a symmetry analysis and lattice dynamics calculations. We untangle the effects of Y by testing our calculations against the measured Raman and infrared spectra of the cubic, antipolar orthorhombic, and monoclinic phases and then proceed to reveal the signature modes of polar orthorhombic hafnia. This work provides a spectroscopic fingerprint for several different phases of HfO2 and paves the way for an analysis of mode contributions to high-k dielectric and ferroelectric properties for chip technologies.