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??