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