Dielectric Properties of Ceramic Thin Films

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Dielectric Properties of Ceramic Thin Films

• Mara Howell
• Materials Science and Engineering
• Junior, Purdue University
• Professor Kvam, Research Advisor

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Presentation Outline

• Background
• Project Goals
• Experimental Procedure
• Tests
• Results
• Future Work

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Background Capacitors

• Q CV
• Dielectric materials increase the amount of
  stored charge

• Enhanced capacitance is related to original
  capacitance by the dielectric constant, ?
• A material with a higher ? will hold more charge

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Background Barium Titanate

• Titanium ion is slightly displaced at room temp.
  (spontaneous polarization)
• Dielectric constant is dependent on dipole moment
  and magnitude of movement

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Background Ferroelectrics

• Barium Titanate exhibits typical characteristics
• Tetragonal structure
• Movement of central atom
• Randomly oriented domains result in neutral net
  charge
• Applied voltage shifts domains

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Project Goals

• Create Barium Titanate thin films using a Sol-Gel
  processing method
• Refine the Sol-Gel process
• Analyze Barium Titanate thin films
• Modify the process and analyze the resulting
  films
• Dopants
• Varying annealing temperatures

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Experimental Procedure Film Deposition

• Bottom electrode created by sputtering Pt.
• Sol-Gel process used to create Barium Titanate
  thin films
• Stochiometric amounts of Barium hydroxide, acetic
  acid, ethylene glycol, 1-butanol and
  titanium-4-butoxide
• Spin coating
• Low temperature annealing
• Repeat for thicker films
• High temperature annealing at 850C

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Experimental Procedure Top Electrode
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Silicon substrate vs. Glass substrate

• Glass substrates used initially
• Inexpensive, accessible
• Warping of the substrate prevented successful
  deposition of top electrode
• Warping of substrate caused the film to crack
• Low melting temperature prevented completion of
  high temperature anneal
• Silicon substrates solved these problems

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Tests Performed

• XRD analysis
• Optical Microscopy
• Polarization hysteresis
• Capacitance vs. Voltage (CV)
• Current vs. Voltage (IV)
• AFM images

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XRD Analysis
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Optical Microscopy Sample Characteristics
200 µm
100 µm
500 µm
200 µm
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Optical Microscopy Top Electrode
500 µm
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Optical Microscopy Porosity
100 µm
200 µm
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Electrical Properties

• Properties tested using microprobe system
• LabView programs written by Mark McCormick
• Samples with known characteristics were tested

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Accuracy
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Ferroelectric Sample
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Barium Titanate Sample
Fig. 2 Published CV plot ( N.V. Giridharan, R.
Jayavel, P. Ramasamy)
Fig. 1 Measured Capacitance vs. Voltage for
sample 8
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Dielectric Constant

• C is measured at the top point of the curve
• d is estimated to be 400 nm
• A is calculated from optical microscopy
• Average of tested samples is 160

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Voltage vs. CurrentBreakdown Voltage
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Atomic Force Microscopy
Average grain size 0.16 microns
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Atomic Force Microscopy
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Conclusions

• Replacing glass substrate with silicon improves
  quality
• 100 concentration for first layer
• Annealing at higher temperature leads to better
  quality
• Breakdown voltage appears to be 40V

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Future Work

• Examine the relationship between processing and
  grain growth
• Examine the relationship between grain size and
  the dielectric constant
• Examine the effects of dopants on the electrical
  properties of the material

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Acknowledgments

• Thomas Key
• Jacob Jones
• NSF REU grant DMR-0243830

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Questions??