dielectric properties of ceramic thin films mara howell materials science and engineering junior,...
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Dielectric Properties of Ceramic Thin Films
Mara HowellMaterials Science and Engineering
Junior, Purdue University
Professor Kvam, Research Advisor
Presentation Outline
• Background• Project Goals• Experimental Procedure• Tests• Results• Future Work
Background: Capacitors
• Q = CV
• Dielectric materials increase the amount of stored charge
• Enhanced capacitance is related to original capacitance by the dielectric constant, ĸ
• A material with a higher ĸ will hold more charge
oCC
oQ C V
Background: Barium Titanate
• Titanium ion is slightly displaced at room temp. (spontaneous polarization)
• Dielectric constant is dependent on dipole moment and magnitude of movement
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
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
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 850°C
Experimental Procedure: Top Electrode
200 µm
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
Tests Performed
• XRD analysis• Optical Microscopy• Polarization hysteresis• Capacitance vs. Voltage (CV)• Current vs. Voltage (IV)• AFM images
XRD Analysis
0
500
1000
1500
2000
2500
3000
3500
4000
20 25 30 35 40 45 50 55 60
2-theta
Inte
nsity
850 C
Platinum
Barium Titanate
650 C
Optical Microscopy: Sample Characteristics
200 µm
200 µm
100 µm
500 µm
Optical Microscopy: Top Electrode
500 µm
Optical Microscopy: Porosity
200 µm100 µm
Electrical Properties
• Properties tested using microprobe system
• LabView programs written by Mark McCormick
• Samples with known characteristics were tested
AccuracyCurrent vs. Voltage
y = 3E-07x + 6E-09
R2 = 0.9998
0.00
1.00
2.00
3.00
0.00 5.00 10.00
Voltage (V)
Curr
ent (u
A)
Theoretic Resistance: 3.9 MΩMeasured Resistance: 3.3 MΩMaximum Allowed Tolerance: 10%Error: 17%
Ferroelectric Sample
150
350
550
-15.00 -5.00 5.00 15.00Voltage (V)
Cap
acitan
ce (pF)
-150
-100
-50
0
50
100
150
-15 -10 -5 0 5 10 15
Voltage (V)
Pol
ariz
atio
n
Barium Titanate Sample
Fig. 1: Measured Capacitance vs. Voltage for sample 8
Fig. 2: Published CV plot( N.V. Giridharan, R. Jayavel, P. Ramasamy)
45.50
46.50
47.50
-12.00 -6.00 0.00 6.00 12.00Voltage (V)
Cap
acita
nce
(pF)
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
oA
Cd
45.50
46.50
47.50
-12.00 -6.00 0.00 6.00 12.00Voltage (V)
Cap
acitan
ce (pF)
Voltage vs. CurrentBreakdown Voltage
-0.15
-0.10
-0.05
0.00
0.05
0.10
0.15
-50.00 -25.00 0.00 25.00 50.00
Voltage (V)
Curr
ent (m
A)
Atomic Force Microscopy
Average grain size:0.16 microns
Atomic Force Microscopy
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
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
Acknowledgments
Thomas Key
Jacob Jones
NSF REU grant DMR-0243830
Questions??