Dielectric Properties of Ceramic Thin Films Mara Howell Materials 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

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 µ m

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

Optical Microscopy: Sample Characteristics 200 µm 100 µm 500 µm

Optical Microscopy: Top Electrode 500 µm

Optical Microscopy: Porosity 200 µm 100 µm

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

Accuracy

Ferroelectric Sample

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

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

Voltage vs. Current Breakdown Voltage

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

Questions??