Title page for ETD etd-9997-12315


Type of Document Master's Thesis
Author Dickerson, Bryan Douglas Jr.
Author's Email Address brdicker@vt.edu
URN etd-9997-12315
Title Characterization of Ferroelectric Films by Spectroscopic Ellipsometry
Degree Master of Science
Department Materials Science and Engineering
Advisory Committee
Advisor Name Title
Desu, Seshu B. Committee Chair
Curtin, William A. Jr. Committee Member
Kenik, Edward A. Committee Member
Keywords
  • microstructure
  • porosity
  • composition
  • SBT
  • modeling
  • ellipsometry
Date of Defense 1997-09-10
Availability unrestricted
Abstract
Process dependent microstructural effects in ferroelectric SrBi2Ta2O9 (SBT) thin films

were characterized and distinguished from material dependent optical properties using a

systematic multi-layer modeling technique. Variable angle spectroscopic ellipsometry

(VASE) models were developed by sequentially testing Bruggeman effective-media

approximation (EMA) layers designed to simulate microstructural effects such as

surface roughness, porosity, secondary phases, and substrate interaction.

Cross-sectional analysis by atomic force microscopy (AFM), transmission and scanning

electron microscopy (TEM) and (SEM) guided and confirmed the structure of

multi-layer models for films produced by pulsed laser deposition (PLD), metal-organic

chemical vapor decomposition (MOCVD), and metal-organic deposition (MOD).

VASE was used to estimated the volume percentage of second phase Bi2O3 in SBT

thin films made by MOD. Since Bi2O3 was 10 orders of magnitude more conductive

than SBT, second phase Bi2O3 produced elevated leakage currents. Equivalent circuits

and percolation theory were applied to predict leakage current based on Bi2O3 content

and connectivity. The complex role of excess Bi2O3 in the crystallization of SBT was

reviewed from a processing perspective. VASE helped clarify the nature of the

interaction between SBT films and Si substrates. When SBT was deposited by MOD

and annealed on Si substrates, the measured capacitance was reduced from that of SBT

on Pt due mainly to the formation of amorphous SiO2 near the SBT/Si interface. VASE

showed that the thickness and roughness of the SiO2 reaction layer increased with

annealing temperature, in agreement with TEM measurements. Unlike PZT, SBT

crystallization was not controlled by substrate interaction.

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