Transcript Danielle Hitchen - University of Illinois at Chicago

Temperature-Dependent
Electrical Characterization of
Multiferroic BFO Thin Films
Danielle Hitchen, Sid Ghosh, K. Hassan, K.
Banerjee, J. Huang
Electrical and Computer Engineering
Rutgers University
Outline
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Motivation
Multiferroics
Hysteresis: The Enabling Property
Ferroelectricity
Bismuth Ferrite: Material of Choice
Procedures
Challenges
Data Results
Conclusion
Acknowledgements
Motivation
[1]
[2]
Storage limitations on existing memory devices as well as
the desire for faster write/erase capability on non-volatile
memory devices has increased the demand for better
materials that accord with standard integrated circuit
requirements. [3]
[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 a
previously applied
energy field
[4]
[4] http://www.daviddarling.info/images/hysteresis_loop.jpg
Ferroelectricity
[5]
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
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
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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 thin
films 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 semiconductor
precision 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 from
ten contacts
on a single
sample
taken at room
temperature.
Data: Polarization
Device became
more resistive as
temperature
increased; this is
evidenced by the
shape of the curve.
[4]
Ideal Hysteresis
Data: Remanent Polarization
Polarization shows
an increasing
trend at higher
temperatures; this
is not what is
expected, and may
relate to the
increasing current
leakage.
Data: Current Leakage
At increasing
temperatures,
our device leaks
more current, as
expected.
The curved data
points are
representative of
a dielectric; a linear
slope would be a
purely resistive
device.
Data: Remanent Current Leakage
As temperatures
increase, we see
an increasingly
leaky device.
(All data was taken
At -1.5V.)
Current leakage
is 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
Acknowledgements
I 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.