Hydrothermal Processing of Ba X Sr (1-X) TiO 3 Presented By: Adam Chamberlain Advisors: Elliot...
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Transcript of Hydrothermal Processing of Ba X Sr (1-X) TiO 3 Presented By: Adam Chamberlain Advisors: Elliot...
Hydrothermal Processing of BaXSr(1-X)TiO3
Presented By:
Adam Chamberlain
Advisors:
Elliot Slamovich
Mark McCormick
Outline
• Applications• Background• Procedure• Results
– Composition vs. Leakage, Dielectric Constant & Loss– Annealing vs. Leakage, Dielectric Constant & Loss– Thickness Reduction– Dopant effect
• Conclusions• Acknowledgements
Applications
• BST’s tunable ´, high dielectric strength, low leakage and loss has made it desirable in electrical applications– Dynamic random access memory (DRAM),
multilayer capacitors, microelectromechanical systems (MEMS)
Background
• BST is processed using sputtering, MOCVD, or CSD– These methods sometimes require high vacuum
systems or heat treatments above 500oC
• Hydrothermal processing allows for crystalline BST to form at temperatures below 100oC
Procedure
• Titanium Dimethoxy Dineodeconate (TDD) is used as the precursor
• TDD is spin-coated onto a Pt coated glass substrate
• After each layer the precursor is pyrolyzed at 400oC
SiO2
PtTiO2~300 nm
• Films are reacted in Ba,Sr(OH)2 (aq) @ 90°C for 24 h
• Using (110) XRD peak the composition is determined (Vegard’s Law)
• Photolithography is used for sputtering Pt electrodes onto surface
• Electrical contact are made to form planar capacitors
SiO2
PtBST
Pt
1 m
BST
Pt
SiO2
1 m
Planar SEM micrograph Cross-section SEM micrograph
Optical micrograph of electroded sample
• Using a LCR meter tanand capacitance are measured at room temperature
• DC voltage is applied and the resulting leakage current is measured (I-V curve)
Results
• Composition vs. leakage, dielectric constant & loss
• Annealing vs. leakage, dielectric constant & loss
• Thickness Reduction
• Dopant effect
Composition vs. Leakage
%Ba(OH)2
in solution
Composition vs. Dielectric Constant
Composition vs. Dielectric Loss
Annealing vs. Leakage
Data from sample 50-4
Data from sample 90-4
• Types of conduction– Ohmic– Schottky– Poole-Frenkel
• If Poole-Frenkel contributes to leakage then removal of defects should reduce it
Annealing vs. Dielectric Constant
• OH- are on oxygen sites– Ion jump polarization is available
• Annealing removes OH-
– Ion jump not available– Decrease in
O O2-__H+ O
O O O
AC
Annealing vs. Dielectric Loss
Thickness Reduction
• Reducing thickness increases capacitance
• Thickness is limited by particle size• pH• Reaction Temperature
• Precursor thickness
dC
1~
Planar view of barium titanate thin film Cross-section of barium titanate thin film (~85 nm)
Dopant Effect
• Five atomic percent of magnesium oxide was added to the precursor
• Magnesium will sit on barium or titanium sites
• BaBa MgBa
• TiTi + OO MgTi + VO
x x
x x -2 ..
Conclusions
• Composition does not effect the electrical properties
• Annealing decreases the dielectric constant, loss, and leakage
• Small additions of Mg increases the dielectric constant
Acknowledgements
• Dr. Elliot Slamovich
• Mark McCormick
• Purdue University