Temperature-Dependent Electrical Characterization of Multiferroic BFO Thin Films

Danielle Hitchen, Sid Ghosh, K. Hassan, K. Banerjee, J. HuangElectrical and Computer EngineeringRutgers University

Outline Motivation Multiferroics Hysteresis: The Enabling Property Ferroelectricity Bismuth Ferrite: Material of Choice Procedures Challenges Data Results Conclusion Acknowledgements

Motivation

Storage limitations on existing memory devices as well asthe desire for faster write/erase capability on non-volatilememory devices has increased the demand for bettermaterials that accord with standard integrated circuitrequirements. [3]

[1] [2]

[1] http://imgs.tootoo.com/ff/29/ff290e10431d97b15c18ebd08e952f36.jpg[2] http://www.computerrepairmaintenance.com/images/flash-drive.png[3] Zambrano, Raffaele. “Applications and issues for ferroelectric NVMs.” Materials Science in Semiconductor Processing 5 (2003) 305-310.

Multiferroic Materials Discovered less than a century ago,

ferroics relate to the ancient study of magnetism

Ferroic materials can be: Ferroelectric Ferromagnetic Ferroelastic

Multiferroics exhibit two or more of these properties simultaneously

Hysteresis: The Enabling Property

Hysteresis: the ‘memory’a material retains of apreviously applied energy field

[4]

[4] http://www.daviddarling.info/images/hysteresis_loop.jpg

Ferroelectricity

Ferroelectric materials possess a spontaneous, stable polarization that switches hysteretically in an applied electric field.

[5] http://www.fujitsu.com/img/MICRO/fme/microelectronics/fram/ferroelectric_material.jpg

[5]

Ferroelectricity

Polarization characteristics change when subjected to varying Pressure Temperature Applied Voltage

These unique properties make the material useful for many different applications

Bismuth Ferrite: Our Material of Choice BFO is multiferroic at room

temperature– a rarity among multiferroics

Has strong ferroelectric, but weak ferromagnetic properties

Crystalline structure, as well as polarization, alters in varying temperature

We hope to see how well BFO functions as a capacitor

Goal: document the changes in polarization that occur as the temperature changes

Fractal ferroelectric domains in thinfilms of multiferroic BiFeO3. [6]

[6] http://www.esc.cam.ac.uk/teaching/mineral-sciences/minsci-part-IA

Procedure

The probe (left) controls temperature and pressure in the chamber housing the sample.Leakage current is plotted in the semiconductorprecision analyzer (above).

Challenges The samples were not uniformly

dielectric; finding good contacts was difficult

Careful probing was necessary due to the properties of the material

Equipment broke down several times Redeposition of the contacts

appeared to influence the functionality of the devices

Data: Varied Dielectric Behavior

Data is fromten contactson a single sampletaken at room temperature.

Data: Polarization

Device becamemore resistive astemperature increased; this isevidenced by the shape of the curve.

Ideal Hysteresis

[4]

Data: Remanent Polarization

Polarization showsan increasingtrend at highertemperatures; thisis not what is expected, and mayrelate to the increasing currentleakage.

Data: Current Leakage

At increasingtemperatures,our device leaksmore current, asexpected.

The curved datapoints are representative of a dielectric; a linearslope would be apurely resistivedevice.

Data: Remanent Current Leakage

As temperaturesincrease, we seean increasinglyleaky device. (All data was takenAt -1.5V.)

Current leakageis high at high temperatures(20nA/cm2

vs. 2.0E5 nA/cm2).

Conclusion Dielectric behavior did not characterize the

behavior of this material There was non-uniformity in the samples

that DID exhibit capacitive polarization The contact deposition process may have

influenced functionality Dielectric behavior degraded at higher

temperatures, as expected

AcknowledgementsI would like to thank the National Science Foundation and

the US Department of Defense for funding my research (EEC-NSF Grant # 0755115 and CMMI-NSF Grant # 1016002), as well as the University of Illinois at Chicago for hosting my undergraduate research program.

I would also like to express my thanks to the directors of my program, Professors Christos Takoudis and Greg Jursich, as well as to Professor Siddhartha Ghosh who advised me in my research.

Finally, thank you Koushik Banerjee, Jun Huang, Khaled Hassan and Hsu Bo for informing my research, assisting with the equipment, and providing me with necessary literature.