Structural phase transitions in hafnia and zirconia at ambient pressure

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Title: Structural phase transitions in hafnia and zirconia at ambient pressure
Author: Luo, Xuhui
Abstract: In recent years , both hafnia and zirconia have been looked at closely in the quest for a high permittivity gate dielectric to replace silicon dioxide in advanced metal oxide semiconductor field effect transistors (MOSFET ) . Hafnium dioxide or HfO2 is chosen for its high dielectric constant (five times that of SiO2 ) and compatibility with stringent requirements of the Si process . As deposited , thin hafnia films are typically amorphous but turn polycrystalline after a post -deposition anneal . To control the phase composition in hafnia films understanding of structural phase transitions is a first step . In this dissertation using first principles methods we consider three phase transitions of hafnia and zirconia : monoclinic to tetragonal , tetragonal to cubic and amorphous to crystalline . Because the high surface to volume ratio in hafnia films and powders plays an important role in phase transitions , we also study the surface properties of hafnia . We discuss the mechanisms of various phase transitions and theoretically estimate the transition temperatures . We find two types of amorphous hafnia and show that they have different structural and electronic properties . The small energy barrier between the amorphous and crystalline structures is found to cause the low crystallization temperature . Moreover , we calculate work functions and surface energies for hafnia surfaces and show the surface suppression of the phase transitions .
URI: http : / /hdl .handle .net /2152 /ETD -UT -2010 -08 -1553
Date: 2010-10-26

Citation

Structural phase transitions in hafnia and zirconia at ambient pressure. Doctoral dissertation, University of Texas at Austin. Available electronically from http : / /hdl .handle .net /2152 /ETD -UT -2010 -08 -1553 .

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