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KIST Staff scientists visited two German leading institutes to forge future collaborations. This visit
was part of the Global KIST Program, which is intended to promote collaborative research with
world leading institutes. From March 21st to 25, eight KIST scientists visited the institute for applied
materials (IAM) at Karlsruhe Institute of Technology (KIT) and the Max Planck Institute for Steel
Research (MPIE). The visits were followed by two separate bi-lateral workshops between KIST and
KIT-IAM and between KIST and MPIE. The workshops brought together leading researchers from the
institutes to share common research interests and identify collaboration opportunities in the area of
nanostructured materials and next-generation power plant materials. The directors of MPIE and KIT-
IAM will visit KIST in May and July, respectively, to elaborate and develop a collaboration program.
1. Research Scientists
• Qualifications: Ph.D. degree in science and engineering fields
• Deadlines: Candidates who apply must submit their application packages during 5/16/2011~ 6/17/2011
• For more information, please visit website http://www.kist.re.kr or contact E-mail : recuit@kist.re.kr Tel:+82-2-958-6249
2. KIST Star Postdoctoral Program
• Qualifications: Ph.D. degree in science and engineering fields, Non-Korean citizenship
• Salary and benefit: 52 million won (approx. US$45,000) per year, Basic health insurance and workers’ compensation insurance ,
On-campus housing available on a “space available” basis (monthly rent: US$120-450)
• How to Apply: Applications are accepted year-round. Complete the online application form available at
www.kist.re.kr/en/cy/ns_view.jsp?content_id=17920 and email to starpostdoc@kist.re.kr
KIST held its 45th Anniversary Commemorative Ceremony on Thursday, February 10,
2011. Five hundred KIST members and distinguished guests, including members of
the National Assembly, high-ranking government officials, and ambassadors to Korea,
celebrated the KIST foundation day. President Kil-Choo Moon of KIST emphasized
KIST’s new vision in his speech, “KIST: At the forefront of Korea’s development
over the past half century, it will become the hope of the world with its own unique
development model, as well as a leading global institution that creates new history.”
KIST scientists visited German leading research institutes
Job openings at KIST
KIST Held Its 45th Anniversary Commemorative Ceremony
KISToday MaterialsMaterials Research Quarterly Magazine
Editor-in-ChiefDr. Seok-Jin Yoon sjyoon@kist.re.kr
Editors Dr. Insuk Choi insukchoi@kist.re.kr Dr. Ho Won Jang hwjang@kist.re.kr Dr. Heesuk Kim heesukkim@kist.re.kr Dr. Sang hoon Kim kim_sh@kist.re.kr Dr. Kwan Hyi Lee kwanhyi@kist.re.kr Dr. Jung Ah Lim jalim@kist.re.kr
Editorial OfficeMaterials Research Korea Instite of Science and TechnologyHwarangno 14-gil 5, Seongbuk-gu, Seoul 136-791, KoreaTel +82-2-958-5401 www.kist.re.kr
Materials Research News
KIST 50 years, Global Leading Institute for Future
Special Issue
Pushing the limits of thin films in solid oxide fuel cellsContribution
Spin Devices for Information Technology
Focus inDevelopment of nanostructured amorphous thick coatings by plasma sprayingComprehensive review of the stability of oxide thin film transistors for display applicationsSynthesis of ladder-like polysilsesquioxane with superior opto-/electronic propertiesUltrafast mode-locked lasers incorporating graphene
www.kist.re.kr/materials
Pantone : 1788C 2XProcess Color :Cyan 5%+Magenta 90%+Yellow 100%RGB : R 242+G 25KIST Red
KIST Dark Gray
Pantone : 423CProcess Color : Black 40%RGB : R 153+G 153+B 153KIST Gray
Pantone : 877CKIST Silver
Pantone : 873CKIST Gold
Pantone : 425C Process Color :Magenta 5%+Yellow 10%+Black 70%RGB : R 88+G 84+B 78
Thin film solid oxide fuel cell with graded nanostructure
Materials Research Quarterly Magazine No.2
APRIL
2011
12 K ISToday MATERIALS
500 nm
2 K ISToday MATERIALS APRIL 2011 3
>> Brain Science Institute
Mission : Brain disease treatment mechanisms, new drug development,
molecular-level mechanisms of brain cognitive function
>> Biomedical Research Institute
Mission : Development of artificial organs and human body parts,
development of human intention-oriented rehabilitation systems
>> Future Convergence Technology Research Division
Mission : Frontier research for the future, platform for multidisciplinary
core technologies in the material-, nano-, and bio-sciences, as well as in
the IT field
>> National Agenda Research Division
Mission : meet the challenges identified in the national agenda,
particularly relating to energy and environmental challenges, leadership
in research for global issues.
KIST Materials will broaden its coverage, expanding the former Materials
Research Division to cover material science and technology issues in all
research institutes and divisions at KIST.
We are pleased to announce the formation of the Future Convergence
Technology Research Division. This division encompasses the majority of
research centers formerly in the Materials Research Division. The division
is designed to achieve convergence among the nanotechnology (NT),
biotechnology (BT), and informational technology (IT) fields by fostering
multidisciplinary research. The division additionally provides a platform
for blending research approaches in the conventional technologies, which
will lead to the advancement of core technologies.
The division is formed from the NT-based Spin Device Research Center,
Nanomaterials Research Center, Nanophotonics Research Center,
Interfacial Engineering Research Center, high-Temperature Energy
Materials Research Center, and Nanohybrid Research Center, as well
as the IT-based Electronic Materials Research Center, Visual Media
Research Center, Computational Science Research Center, and BT-based
Biomolecular Functions Research Center. The division will act as an
integrating body in support of multidisciplinary research to strengthen the
nation’s competitiveness and support one of the world’s leading research
organizations in multidisciplinary research.
The principal research fields are as follows:
- Interfacial engineering for energy related and environmental materials
- Sustainable hybrid energy conversion materials and devices
- Next-generation oxide electronic materials and plasmonics
- Nanocarbon convergence materials and nanostructured hybrid smart
materials
- Nanomaterials and processing for softronics
- Biomarkers and clinical diagnostic-based OMICs, as well as novel drugs
based on chemical biology
- human–media interaction technologies for virtual reality, ubiquitous
computing, multimodal interactions, and 3D display
- Spin-based memory, communication, energy, and VLSI technologies
- Synthesis, functionalization, and hybridization of nanoparticulates
- Design, synthesis, and applications of nano-bio systems using atomic-
scale and massive computational methods
- Quantum functional optoelectronics based on nano/microstructures.
KIST Reorganization
>> Before >> After
KIST Reorganization
KIST underwent a major reorganization in March 2011
To better meet the growing demands for frontier research in support of global agendas, as well as to establish world class
research institutes in strategic research fields, KIST underwent a full-scale reorganization across the institute in March
2011. Two specialized research institutes were established, and five former research divisions were restructured to form
two new research divisions as follows;President
Vice President for Research
Convergence Research Division
Materials and Device Research Division
Robot and Systems Division
Energy and Environment Division
Bio and Medical Research Division
Technology Policy Research institute
Gangneung Branch
JeonbukBranch
KiST Europe
President
Brain Science institute
Biomedical Research institute
Vice President
Future Convergence Research Division
National Agenda Research Division
Technology Policy Research institute
Gangneung Branch
JeonbukBranch
KiST Europe
4 K ISToday MATERIALS APRIL 2011 5
surfaces cannot be avoided as long as porous electrodes are used
as deposition surfaces. Effective plugging via conformal deposition
technologies can mitigate the problems associated with pinholes.
Using these approaches, reliable gas-tight thin film electrolytes were
successfully obtained, and electrolyte layer thickness reductions
were satisfactorily achieved.
The second challenge was effectively addressed using composite
electrodes. Both the formation of nano-composite electrodes during
the deposition and the employment of a ‘template’ as a structural
support remarkably suppressed the degradation of the nano-porous
electrodes.These electrodes showed stabilities, in terms of structure
and performance, beyond those achievable using single-phase
nanoporous electrodes.
This work was based on highly reliable thin film technologies.
The structural requirements and high-temperature operation
of SOFCs raise several challenges to the use of thin films and
nanostructures for producing reliable thin film SOFCs (TF-SOFC). The
two main challenges have been: 1) to develop thin gas-impermeable
electrolytes over porous electrodes, and 2) to suppress the
intensive degradation of nanoporous electrodes at high operating
temperatures.
To address the first challenge, we employed two distinct approaches.
First, we developed nanostructured electrodes with transition
from dense to porous structures to form a surface beneath an
electrolyte layer. The electrolyte quality was not a major concern in
this case because dense thin film electrolytes were found to form
during deposition over the dense deposition surface. Secondly, we
‘plugged’ the pinholes of the electrolyte layer formed by the porous
deposition surface. The generation of pinholes at thin electrolyte
Solid oxide fuel cells (SOFCs) are fuel cells in which the electrolytes
and electrodes are composed of ceramic material (oxides). Recently,
SOFCs have attracted attention for their use in next-generation
power sources because they can be operated with a variety of fuels
other than pure hydrogen. SOFCs additionally yield the highest
energy conversion efficiencies of all fuel cell types. Traditional
SOFCs operate at high temperatures (≥ 800°C) to secure the oxygen
ion conductivity in ceramic electrolytes. high operating temperatures
promote reactions between the cell components and degrade the
long-term stability of the cell. Reducing SOFC operating temperatures
without compromising performance is an important goal in the
field. The need for improved low-temperature SOFC performances
by introducing thin electrolytes and nanostructured electrodes has
surged over the past several years both in conventional SOFCs for
high-capacity power generation and in micro-SOFCs for portable and
mobile power sources.
Special Issue Special Issue
Pushing the limits of thin films in solid oxide fuel cells
References• H.-S. Noh, J.-S. Park, H. Lee, H.-W. Lee, J.-H. Lee, J.-W. Son, Transmission electron microscopy study on microstructure and interfacial property of thin film electrolyte SOFC. Electrochem. Solid. St. Lett. 14 (2011) B26-B29.• C.-W. Kwon, J.-W. Son, J.-H. Lee, H.-m. Kim, H.-W. Lee, K.-B. Kim, High-performance micro-solid oxide fuel cells fabricated on nanoporous anodic aluminum oxide templates. Adv. Funct. mater.21 (2011) 1154-1159.
These efforts were key to achieving critical performance
advancements and significantly advanced SOFCs along the
commercialization pathway.
200 nm
HAADF
100 nm1 ㎛1 ㎛
The two main challenges have been: 1) to develop thin gas-impermeable
electrolytes over porous electrodes, and 2) to suppress the intensive degradation
of nanoporous electrodes at high operating temperatures.
Ji-Won SonPrincipal Research Scientist jwson@kist.re.kr
>> high Temperature Energy Materials
Fig. 1 First method to obtain gas-impermeable electrolyte: using dense to porous structural transition of electrode
Fig. 2 Second method to obtain gas-impermeable electrolyte: plugging pinholes in electrolyte deposited over porous electrode
Fig. 3 interpenetrating nano-composite electrode with structural stability
6 K ISToday MATERIALS APRIL 2011 7
Focus in Focus in
Comprehensive review of the stability of oxide thin film transistors for display applications >> Electronic Materials
Fig. 2 Stability of various oxide TFTs (BTS test): (a) Zr-in-Zn-O, (b) Hf-in-Zn-O, and (c) Al-in-Zn-Sn-O TFTs.
Fig. 1 A 70-inch 3D Ultra-Definition 240Hz LCD Display using oxide TFTs, manufactured by Samsung Electronics.
Oxide thin film transistors (TFT) have been steadily replacing
Si-based transistors over the past decade. Next-generation
displays, including ultra-definition (UD), 3D, and flexible
displays, require new materials with mobilitiesof 20–30 cm2/
Vs, much higher than those of Si-based transistors (less than
1 cm2/Vs). Using oxide TFTs, 70-inch UD 240Hz LCD displays
were developed in 2010. KIST has supported a research
program that focuses on various oxide semiconductors,
including Zn-Sn-O, In-Zn-O, Si-In-Zn-O, In-Ga-Zn-O, and hf-
In-Zn-O to develop oxide TFTs with performancesthat meet
the needs of next-generation displays.The stability of oxide
TFTs, which is a key issue in practical applications, has also
been studied.
The stability of oxide TFTs may be improved by developing
robust oxide channel layers and novel channel structures
or by using passivation layers. TFT stabilitiesare evaluated
using bias temperature stress (BTS) tests, which measure
the threshold voltage shift (ΔVth) under thermal and bias
conditionsover a period of time. The instability mechanisms
mainly arise from traps in or on the channel layer. Among
the various robust oxide materials, indium (In)-containing
Zn-O channel layers show high mobility, and other elements
may be added to improve the performance and enhance
the stability. Various oxide materials, including Zr-In-Zn-O,
hf-In-Zn-O, and Al-In-Zn-Sn-O, have been studied and have
shown good stability in BTS tests. Novel oxide channel layer
structures have been developed to enhance the performance
and long-term stability of oxide TFTs. Introduction of a
highlydoped buried layer into an amorphous indium-
gallium-zinc oxide (a-IGZO) TFT channel layer dramatically
improved the performance and prolonged the biasstability
without the need for high temperature treatments. To
eliminate environmental effects and improve stability,
various passivation layers have been studied. Recently, we
developed an amorphous hf-In-Zn-O TFT with an enhanced
stability, and we compared this TFT to the published
properties of other TFTs. New channel materials composed
of binary, ternary, and quaternary oxide materials have been
studied with different composition ratios, and element-
doped oxide materials, including doping with Al, N, and Mn,
have been studied for their stability enhancement properties.
At KIST, we combine fundamental and applied research
into new oxide semiconductors to improve TFT performance
and stability for next-generation display applications. high
mobilities and good stabilities have been achieved using
robust channel layers, such as hIZO and SIZO, with a buried
structure channel layer. Passivation layers, such as PMMA
and SiO2, prevent environmental effects and enhance device
stability. These advances in oxide semiconductorsenable the
development of future generation displays.
Sang Yeol LeePrincipal Researcherlsy@kist.re.kr
References• S. Y. Lee, et al., Appl. Phys. Lett. 98, 122105 (2011) • E. Chong, et al., Electrochem. Solid-State Lett. 14, H96 (2011) • E. Chong, et al., Appl. Phys. Lett. 96, 152102 (2010) • J. K. Jeonget al., Adv. mater. 21, 329 (2009)• J. K. Jeong et al., IEEE Electron Dev. Lett. 31, No. 2, 144 (2010)
Plasma spraying is a complex process that combines
several sequential steps: the injection of solid particles
into a high-temperature plasma flame (15,000 K), melting
and acceleration of the particles, and consolidation of
the sprayed molten droplets onto a substrate to form a
coherent coating. This process has unique advantages.
Few restrictions apply to the coating area, thickness, and
materials, and the method is cost-effective.
Recently, plasma-sprayed ceramic coatings, such as Al2O3
and Y2O3 have been applied on metal or ceramic parts
of semiconductor, LCD, LED, and solar cell fabrication
equipment including the PE-CVD coater and reactive ion
etcher because ceramic coatings have strong resistance
against plasma erosion and induces the harmful elements
or reaction products. however, it is difficult to fabricate ideal
ceramic coatings by plasma spraying because micro voids
and micro cracks inevitably form due to volume contraction
of the coating materials during the rapid quenching stages
of the process.
We designed new materials that include both metallic
elements (such as Al, Y, Zr) and non-metallic elements (such
as N, O) which easily formed in nanostructured amorphous
coatings with few microcracks and microvoids via plasma
spraying. The plasma-sprayed nanostructured amorphous
coatings was clearly showed a five-fold improvement in
plasma corrosion resistance, a
50-100% improvement in micro-
hardness, and a five- to ten-fold
improvement in wear resistance
compared to existing ceramic
coatings, such as Al2O3 and Y2O3.
The outstanding nanostructured
amorphous coatings manufactured
b y p l a s m a s p r a y i n g w e r e
successfully deployed on the
commercial scale in items that
include metal and/or ceramic
Fig. 2 Comparison of the wear properties of nanostructured amorphous and CNT-reinforced coatings.
Development of nanostructured amorphous thick coatings by plasma spraying >> Advanced Functional Materials
Fig. 1 Amorphous nanostructuring mechanism.
← Volum
e
Temperature →
(nano/amorphous)Solid
(crystalline) Solid
(amorphous) Liquid← Volum
e contraction →
New materialsHigh cooling rate
Melting Temperature
Wea
r rat
e, X
10-8
[Kg/
Nm
]
components in semiconductor equipment.
Furthermore, we developed methods for effectively adding
carbon nanotubes (CNTs) to nanostructured amorphous
coatings with minimal damage to the CNTs during the
high-temperature plasma spraying process. To do so, the
processing atmosphere was controlled to minimize the
oxygen present in the plasma jet. As a result, the micro-
hardness, elastic modulus and fracture toughness of the
coatings were dramatically improved upon addition of the
CNTs. The wear resistance of CNT-reinforced amorphous
coatings showed a ten-fold improvement over the bare
nanostructured amorphous coatings.
References• J. –h. Jeong et al., J. Phys. D: Appl. Phys. 42, 035104 (2009) • S. Lee et al., J. Electrochem. Soc.156, H612 (2009) • Z. Wu et al., Appl. Phys. Lett. 96, 133510-1 (2010) • J. Choi et al., Appl. Phys. Lett. 95, 081905-1 (2009) • J. -h. Jeong et al., Appl. Phys. Lett. 94, 011902-1 (2009) • Z. Wu et al., unpublished work • S. Lee et al., Appl. Phys. Lett. 92, 243507-1 (2008)
Fig. 3 Representative samples of commercialized semiconductor fabrication equipment parts with plasma sprayed nanostructured amorphous coatings.
Hyun Kwang SeokPrincipal ResearcherCenter for Biomaterialsdrstone@kist.re.kr
Eun Young ChoiResearch AssistantCenter for Biomaterials
Jeong HoonResearch AssistantCenter for Biomaterials
Fig. 3 Enhanced stability of a-HiZO TFT by KiST compare to other published results.
Stress Time (Hrs)
delta
Vth
(V)
0 5 10 15 20 25 30 35 40 45 50 55 60
10
8
6
4
2
0
ZnO (refAPL, 89, 263513)
a-HIZO at 350˚C
a-HIZO (refAdv. Master. 21, 329 2009)
VGS (V)
(a) Zr-In-Zn-O (c) Al-In-Zn-Sn-O
-8 -4 0 4 8 12
Gate Voltage (V)
(b) Hf-In-Zn-OCu
rren
t (A
)
I DS1/
2 [x10
-3A
1/2 ]
10-6
10-8
10-10
10-12
-10 0 10 20 30 40 0
1
0h60hLeakage
Gate Voltage (V)
Dra
in C
urre
nt (A
) VDS = 5.1V
VDS = 0.1V
10-4
10-5
10-6
10-7
10-8
10-9
10-10
10-11
10-4
10-6
10-8
10-10
10-12
10-14
-30 -20 -10 0 10 20 30 40
Before stressAfter 60hrs stress
I DS (
A)
0.09Nanostructured
AmorphousCoating (APS)
CNT-reinforcedAmorphous
Coating (APS)
CNT-reinforcedAmorphous
Coating (ECPS)
• Counter part : Ruby Ball• Load : 1,000gf• Sliding distance : 226.08m• Sliding rpm : 100rpm• Track diameter : 12mm
0.198590.08576
0.93429Five-fold
Ten-fold
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
8 K ISToday MATERIALS APRIL 2011 9
Focus in Focus in
Polysilsesquioxanes comprise a class of organosilicon polymers
of molecular formula (RSiO1.5)n. These unique materials exhibit a
plethora of advantageous properties, including excellent thermal
stability, easy processability, excellent mechanical strength,
chemical and oxidative resistance, and biocompatibility.
Equipped with an organic R functional group, these polymers are
physically and chemically mutable in ways not observed in other
organic–inorganic hybrid materials. Three structural classes of
polysilsesquioxanes have been identified: random branched,
polyhedral caged, and ladder-like. Of these classes, ladder-
like polysilsesquioxanes (LPSQs) give the largest number of
functional groups without the need for thermal curing processes.
however, synthetic difficulties have rendered these materials
problematic for industrial applications.
To take advantage of the superior properties of LPSQs, KIST
researchers at the Polymer hybrid Center have worked toward
the controlled facile syntheses of such materials. As shown
in Figure 1, a base catalyst was used in a controlled in situ
hydrolysis-condensation reaction to synthesize well-defined
ladder-like silsesquioxanes.
The introduction of carbazole moieties into LPSQs (PPCSQ)
enhanced the photoluminescence (PL) properties over its organic
analog, polyvinylcarbazole(PVK). The PL spectrum of PPCSQ,
shown in Figure 2(b), revealed two sharp peaks. Moreover, the
PL quantum yield of PPCSQ was twice that of PVK, even though
the UV-vis absorption intensity of PPCSQ was only 10% that of
PVK. These physical properties of the LPSQs were attributed to
the isolating effect of the rigid linear siloxane chain in the LPSQ
backbone, which afforded the carbazole moieties more degrees
Synthesis of ladder-like polysilsesquioxane with superior opto-/electronic properties >> Nano hybrid Materials
Fig. 1 Novel synthetic route to the ladder-like polysilsesquioxanes.
of freedom, as shown in Figure 2(a).
The isolating effects were unequivocally observed when PPCSQ
and PVK were incorporated into devices. Although fewer
carbazole moieties were present in PPCSQ, Figure 3 shows that
the material displayed a higher luminous efficiency compared
to devices fabricated from PVK. Compared with the organic
materials, PPCSQ exhibited far greater thermal stability (up to
400°C), with high transparency due to the inorganic siloxane
backbone.
Such excellent physical, optical, and thermal properties,
coupled with a facile synthetic method, will invariably facilitate
its use in a variety of industrial applications. This research was
recently published in the Journal of Materials Chemistry and
Macromolecular Research.
References• K. –Y. Baek et al., “High Photo- and Electroluminescence Efficiencies of Ladder-like Structured Polysilsesquioxane with Carbazole Groups”, J. mater. Chem. 20, 9852 (2010) • S. S. Hwang et al., “Synthesis and Characterization of Ladder-like Structured Polysilsesquioxane with Carbazole Group” macromol. Res, 19, 3 (2011)
Kyung-Youl BaekSenior Researcherbaek@kist.re.kr
Seung-Sock ChoiResearch Assistantxy7ab5@kist.re.kr
He Seung LeeResearch AssistantSeaung@kist.re.kr
Albert S. LeeResearch Assistantalbert.ss.lee@gmail.com
Seung Sang HwangPrincipal Researchersshwang@kist.re.kr
Fig. 3 Voltage–luminous efficiency of PPCSQ and PVK in an EL device.
VLum
inou
s ef
ficen
cy(C
d/A
)
Voltage0 1 2 3 4 5 6 7 8 9 10 11
10
9
8
7
6
5
4
3
2
1
0
PVKPPCSQ
100
90
80
70
60
50
40
30
20
10
0
Fig. 2 (a) isolated carbazole moieties tethered to ladder-like polysilsesquioxanes (b) UV-vis absorption and photoluminescence spectra of PPCSQ and PVK in solid thin films.
(a) (b)PVK
PPCSQ
Abs
. Nor
m.
PVKPPCSQ
300 350 400 450 500
Wavelength(nm)
1.0
0.8
0.6
0.4
0.2
0.0
PL intensity. Norm
.
Ultrafast pulsed lasers using passive mode-locking have been
rapidly developed over the past decade. A paradigm shift in
the field has been accelerated by the use of carbon nanotube
(CNT)-based devices to replace conventional semiconductor-
based saturable absorber mirrors (SESAMs). CNTs have several
advantages, including a nano-scale foot-print and extremely high
and fast optical nonlinear properties. Unfortunately, they require
bandgap tuning via control over their diameter and chirality,
along with requirements for a homogeneous dispersion in liquid
media. Quite recently, graphene, a 2-dimensional honeycomb
crystal structure of carbon atoms, has emerged as a promising
photonic material with notable advantages, such as (i) a broad
nonlinear operating spectral range covering the telecomm and
VIS bands, (ii) ultrafast recovery times, (iii) a saturable absorption
threshold lower than that of CNTs, and (iv) facilitated preparation
processes. In order for graphene to act as a nonlinear intensity
modulating component particularly in the high power regime,
direct interaction between graphene and the penetrating light
should be avoided to protect the thermally fragile nanostructures.
Researchers at KIST demonstrated a novel scheme in which the
evanescent field of a laser interacts with graphene to provide
mode-locking operation (see Fig. 1) [1,2]. Because only a small
portion of the propagating mode is involved in pulse formation,
graphene can guarantee the high-power operation with the
intracavity powers up to 21.41 dBm. The resultant graphene-
based mode-locked fiber laser has a center wavelength of 1561.6
nm, a spectral width of 1.96 nm, a repetition rate of 6.99 MHz,
and an estimated pulse duration of 1.3 ps. KIST researchers
also achieved the deformation-suppressed optical deposition
of graphene by co-dissolving polyvinyl acetate (PVAc) into
dimethylformamide (DMF). The PVAc played a critical role during
the deposition as a buffer medium to suppress the deformation
and/or distortion of graphene, which is closely correlated with its
nonlinearity [3]. Deposition of the graphene/PVAc composite on
an optical fiber by laser radiation proceeded via three correlated
mechanisms: optical trapping, thermally-induced convection flow,
and thermodiffusion. The preserved nonlinearity of graphene
successfully formed a 91.5-MHz (higher harmonic) pulsed laser.
A dramatically simplified but elegant graphene preparation
method based on mechanical exfoliation of bulk graphite using
a strip of scotch tape was employed to achieve ultrafast passive
mode-locking by the KIST researchers [4]. After verifying that the
chromatic dispersion in the multilayered graphene was negligible,
optical-intensity-dependent absorption modulation in a laser
cavity was demonstrated with a fundamental repetition rate of
10.92 MHz and a peak-to-background ratio of >40 dB at 1576 nm.
Ultrafast mode-locked lasers incorporating graphene >> Optoelectronic Materials
References• Y. W. Song, et al., “A graphene mode-locker for fiber lasers passively pulsed by evanescent field interaction,” Appl. Phys. Lett., 96, 051122 (2010). • Nature Photonics Research Highlight, “Graphene: under high energy,” Nature Photon., 4, 196 (2010). • Y. W. Song, et al., “Deformation-immunized optical deposition of graphene for ultrafast pulsed lasers,” Appl. Phys. Lett., 98, 021104 (2011). • Y. W. Song, et al., “multilayered graphene efficiently formed by mechanical exfoliation for ultrafast photonics,” Appl. Phys. Lett., 97, 211102 (2010).
Fig. 2 Conceptual explanation of the optical deposition setup and mechanism using PVAc-coated graphene.
Yong-Won SongSenior Researcherysong@kist.re.kr
DFBLaser EDFA ATT
Fig. 1 Fiber mode-locked laser setup and output laser pulse train. The schematic diagram illustrates that the guided mode in the fiber core can be broadened by removing the clad so that the evanescent field of the mode can interact with the graphene layer to form ultrafast laser pulses.
10/90Coupler
Graphenemode-locker
Isolator
Output
Out
put(
a.u.
)
SMFPC
Time Delay (nsec)-300 -400 0 400 300
HO-EDFA
GrapheneLayer
Evanescent field ofbroadened mode
Side-polishedfiber
Guided modeSMF
Core
→ OUTIN→
Fig. 3 AFM analysis of few-layered graphene prepared by mechanical exfoliation. The 3D image (left) and height analysis on selected regions (right) are presented.
10 K ISToday MATERIALS APRIL 2011 11
of MRAM: GMR, anisotropic magneto resistance (AMR), and
tunneling magneto resistance (TMR). GMR and AMR cells
are composed of metal structures characterized by a low
resistance change, which is not attractive for high-density
memory devices. however, TMR cells are composed of a
magnetic tunnel junction (MTJ) with two ferromagnetic layers
separated by a thin dielectric layer, which acts as a DRAM
capacitor. Recently, spin transfer torque MRAM (STT-MRAM)
has been extensively investigated to solve the high cell
writing current and large cell size problems posed by MRAM
devices. The MTJ structure includes two ferromagnetic layers
and an MgO tunneling barrier layer. Switching MTJ states
from antiparallel or “1” to parallel or “0” and vice versa is
performed by running a polarized electron current from the top
to the bottom of the MTJ and vice versa. The polarized current
transfers angular momentum to the spins in the magnetic free
layer, causing it to switch. The read operation of STT-MRAM
is essentially the same as that used with MRAM. The current
STT-MRAM technology has been picked up by leading memory
companies as a serious contender that may replace the
conventional DRAM technology. Several consortia, both local
and abroad, are competing for the potential market share,
including the Samsung-hynix STT-MRAM co-development
project launched in 2009. MRAM displays non-volatility,
endurance, speed, and density, and may potentially function as
a universal memory medium for a host of applications that rely
on embedded memory. Leading groups are now turning their
focus to spintronic VLSI applications, which integrate the MTJ
technology with the conventional CMOS technology to enable
high-performance programmable logic circuits.
a creative research field characterized by high risks and high
rewards. In 2009, the Center for Spintronics Research at KIST
first demonstrated the successful operation of a spin-FET,
the long sought-after goal of spintronics. The achievements
are scientifically noteworthy because spin-FETs rely on the
modulation of spin information. The spin-FET may be used as
an active device in switching and logic devices as well as in
non-volatile devices. Furthermore, it can potentially replace
conventional electronic devices.
The magnetic random access memory (MRAM) technology
combines a spintronic device with standard silicon-based
microelectronics to obtain a combination of attributes not
found in any other memory technology, such as dynamic RAM
(DRAM). MRAM utilizes the magnetization direction in the
free layer of a two-layer magneto resistive structure for data
storage and the resulting resistance difference for information
readout. Three physical effects are required for the realization
C oonventional semiconductor-based electronics that
rely only on charge properties are approaching their
physical size reduction limits due to the importance
of direct tunneling on the nanoscale. The field of spintronics
provides a double-edged sword that may provide a solution
to the scaling problems by relying on spin and its associated
magnetic moment. The technology benefits from other
properties of electron spin systems, such as the non-volatility
of electron spin, the high speed of transmittance, and the low
power consumption requirements of spintronic devices. These
provide a major driving force for the development of next-
generation electronic devices.
Among the spin technologies under development, two large
areas in the field are led by KIST.
Spin field effect transistors (spin-FETs), which are lateral
semiconducting channels with two ferromagnetic electrodes,
lie at the heart of spintronics applications. First proposed in
1990, demonstrations of spin-FETs have required good spin
injection and detection using ferromagnetic sources and
drains, as well as gate voltage control over the spin precession
of injected spins. Purely electrical (rather than optical) spin
injection and detection are necessary to implement spin-
FETs. The development of spin-FETs began in 2002, and
the program has constituted one of the largest spintronics
projects in the world, driven by KIST. The goal of the project
was to demonstrate operational spin-FETs, which had been
unsuccessful at that junction. The project was embedded in
Hyung-jun KimSenior researchermbeqd@kist.re.kr
Spintronics is an emerging technology that exploits both the fundamental electronic charge and the intrinsic spin of the electrons. A representative product was realized as a hard disk drive (HDD) in personal computers, which employs giant magnetoresistance (GMR) effect of 2007 Nobel Prize winner in physics.
Conventional CMOS
Fig. 1 MRAM
Fig. 2 Spin-FET
Contribution Contribution
Spin Devices forinformation Technology
Spin-VLSI
Leakage Current
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