Research Topics & Highlights
The research focus in QMDL has largely centered on generating innovative nanomaterials and device architectures for the applications to next-generation electronics systems with an emphasis on the electronics and photonics applications of graphene and other two-dimensional (2D) materials. Currently, QMDL members are exploring the potentials of two-dimensional 2D materials, including graphene, transition metal dichalcogenides (TMDCs), hexagonal boron nitride (h-BN), for flexible electronics, displays, and energy applications
The main research activities can be summarized as follows: (i) synthesis technology for high-quality 2D materials, (ii) process technology for the realization of high-performance 2D devices, (iii) Applications of 2D materials to electronics, displays, and energy devices.
The search for funding has been quite successful, so that, currently, Prof. Choi is leading several national or industrial research projects on graphene and 2D materials as a principal investigator (PI). In the last four years at KAIST, his efforts attracted close to 6.1 Billion Korean Won (~5.1M US$, 1$~1,200 KRW) from external research funds. The funding sources included government agencies such as NRF, KEIT, and ETRI, and LG Display Co. Ltd. To support these activities, Prof. Choi is advising 12 PhD and 10 MS students and also mentoring closely with 2 research professors in QMDL(MNDL) as of July 2017.
1. Synthesis of 2D Materials
For the mass production of large-area graphene, chemical vapor deposition (CVD) is the most popular method, because it enables low-cost growth of the large area, high-quality graphene with good electrical properties. However, there have been difficulties in handling the CVD graphene due to its extremely thin nature when it is applied to the industrial process and several technical issues need to be addressed for the real applications of graphene in electronics and optoelectronics. The direct growth of graphene on an insulating substrate has been a longstanding problem in the synthesis of graphene. In 2014, my group has successfully synthesized multilayer graphene films on an insulating substrate through laser-annealing of SiC. We reported a solid-phase synthesis of doped graphene by means of silicon carbide substrate including a dopant source driven by nanosecond-pulsed laser irradiation. This method provides in situ direct growth of doped graphene on an insulating SiC substrate without an additional transfer step.
On the other hands, the fact that the devices with channels made of graphene show poor performances, which is attributed to the traits that the graphene has no band gap (and further deteriorated by Klein tunneling due to massless feature of electron), has led graphene as an inappropriate material for digital logic applications (i.e. transistors with on/off functions; still it is a powerful component for analog RF applications).
To address the issues, materials with finite band gap are highly demanded, and the most well-known materials of these classes are silicon, compound semiconductors, oxides and organic semiconductors. Recently, new semiconducting 2D materials known as transition metal dichalcogenides (TMDCs) appeared, as represented by MoS2, MoSe2,WS2 and WSe2. Unlike graphene field-effect transistors (FETs) with less than ~10 of on/off ratio, the transistors made of these TMDCs can attain high current on/off ratio, which fulfills the current need for the commercial transistors, and the high mobility of TMDCs make the low power consumption of possible. In 2014, we have demonstrated the synthesis of large area MoSe2 via chemical vapor deposition on arbitrary substrates such as SiO2 and Sapphire for the first time. In addition, we have also developed a facile liquid-phase exfoliation method to improve the exfoliation efficiency for single-layer MoS2 or MoSe2 sheets.
Furthermore, in order to maximize the outstanding electrical properties of 2D materials, we are trying to optimize the 2D material-based device structure such as contact electrodes and gate insulators. Forming a reliable insulating layer and reducing the contact resistance of 2D materials in devices are key technologies enabling reliable operation of field-effect transistors (FETs), flash memory, and so on − key building blocks in modern electronic systems. Ideally, insulating layers should offer high capacitance, low leakage, high break-down field, and resistance to electrical stresses. To provide a high-quality insulating material, we are trying to synthesize a large-area h-BN thin films by using a plasma-enhanced atomic layer depositions.
2. Process Technology for 2D Materials
We are so confident that graphene and 2D materials will play a key role in the development of next-generation nanoscale devices or large-area displays. For the mass production of large-area graphene, CVD is the most popular method. However, handling the CVD-grown 2D materials is difficult due to their extremely thin nature when they are going through the industrial process.
Conventionally, the transfer process is carried out using ‘wet transfer technique’ in which graphene or 2D materials are separated from the growth substrate by etching metals away with a chemical solution (metal etchant) and the transfer is completed by fishing up the floating graphene on the water with a target substrate. From a practical point of view, scale-up of wet transfer method is not an effective way to produce large-area, transferred graphene due to the difficulty in handling and the process-induced damage issues. We are focusing on the transfer technology for 2D materials, in which large-area thin films from CVD processes can be readily transferable onto target substrates, minimizing polymer residues or metal contaminants. My group reported important advances in the transfer process for CVD-grown graphene.
Another important subject of the investigation has been the interface engineering between 2D materials and other parts of devices, like the dielectrics, substrates, and channel or source/drain doping process. Integration of high-quality gate dielectrics on graphene is an important technical challenge because the quality of the interface between the dielectrics and graphene channel affects the electrical characteristics of graphene devices, such as operating voltage, scaling capability, and device reliability. To address these issues, we proposed a new approach for integration of high-k dielectrics on graphene using a functionalized graphene monolayer as an ultra-thin seed layer on top of the graphene channel and novel methods for graphene transfer on various substrates with high degrees of freedom. Graphene transistors with top gate structure using these methods show significantly enhanced device performances in terms of carrier mobility and device reliability. In addition, we demonstrate high-performance graphene transistors on various substrates including flexible substrates. It is expected that our group’s approaches will pave the way for the realization of high-performance electronic devices based on graphene and 2D materials.
3. Device Applications of 2D Materials
Graphene and 2D materials have attracted great attentions because of their potential to overcome the limitations in electronics and many other technological fields. One of the most pursuing goals of my research team is to realize high-performance electronics from atomic/molecular-scale nanomaterials for these applications. Although the study is still in an infant stage, we are expecting to see a great success in a near future. Since 2009, my research group has reported several important applications of graphene and other 2D materials, nonvolatile memory devices, displays and optoelectronic devices, chemical sensors, energy, and biological applications.
Wearable electronics and internet of things (IoT) are hot research topics in these days. In this perspective, we are also studying memristors, because memristor devices can perform the logic-inside-memory concept for which the one memristor device can work simultaneously as a memory and logic gate. It can develop the advanced computer architectures different from the conventional von Neumann architecture in which memory and logic devices are separated. We are planning to optimize 2D materials-based memristor integrated circuits and ultra-thin device for the application of wearable electronics and internet of things (IoT), thus extending the research about soft electronics-based systems in the future.
Graphene/2D Materials Research Center (GRC) at KAIST
Prof. Choi has contributed his efforts and passion towards forming an internationally recognized cross-disciplinary program that incorporates teaching and research in the area of graphene and applications devices. In this goal to build high-impact applications of graphene and 2D materials, he first made a considerable devotion to the establishment of Graphene/2D Materials Research Center (GRC) in 2012, with a founding goal to be a key research center of excellence in Korea as well as to be the global research hub in graphene and 2D materials research.
The research in GRC is focused on the novel synthesis methods for high-quality graphene and 2D materials, as well as the device applications of them for future information and energy technologies. This effort results in a successful convergence research program in the area of graphene and 2D materials in a short span of years.
By pursuing the world-class excellence through the cooperative research activities between outstanding research groups from different disciplines inside or outside of KAIST, I have a strong confidence that the Graphene/2D Materials Research Center will be a national and global research hub in graphene science and technology. I highly expect that the outcome of these efforts will greatly enhance the quality of life and improve national competence.
Center for Advanced Materials Discovery towards 3D Displays (CAMD³) at KAIST
In 2016, Prof. Choi successfully won a 6.5M$ research project funded by national research foundation (NRF), and established the Center for Advanced Materials Discovery towards 3D Displays. (CAMD³).
Established in 2016 Spring, the center for advanced materials discovery towards 3D Displays (CAMD³) aims to share visions and provide solutions to future display technology. Focused on laser-nanomaterials interaction, we are striving to discover noble materials of high-performance that can realize a new type of display composed of multi-stack of panels capable of producing realistic 3D images.
Key Achievements in 2015-2016
1) Insung Choi, Hu Young Jeong, Hyeyoung shin, Gyeongwon Kang, Myunghwan Byun, Hyungjun Kim, Adrian M. Chitu, James S. Im, Rodney S. Ruoff, Sung-Yool Choi & Keon Jae Lee, Laser-induced phase separation of silicon carbide, Nature Communications 7, 13562 (2016)
2) Sung Kyu Kim, Jong Yoon Kim, Byung Chul Jang, Mi Sun Cho, Sung-Yool Choi, Jeong Yong Lee, Hu Young Jeoung, Conductive Graphitic Channel in Graphene Oxide-Based Memristive Devices, Advanced Functional Materials 26, 7406-7414 (2016) [Back Cover]
3) Gwang Hyuk Shin, Choong-Ki Kim, Gyeong Sook Bang, Jong Yun Kim, Byung Chul Jang, Beom Jun Koo, Myung Hun Woo, Yang-Kyu Choi, and Sung-Yool Choi, Multilevel resistive switching nonvolatile memory based on MOS₂ nanosheet-embedded graphene oxide, 2D Materials 3, 034002 (2016)
4) Jaeho Lee, Tae-Hee Han, Min-Ho Park, Dae Yool Jung, Jeongmin Seo, Hong-Kyu Seo, Hyunsu Cho, Eunhye Kim,
Jin Chung, Sung-Yool Choi, Taek-Soo Kim, Tae-Woo Lee, and Seunghyup Yoo, Synergetic electrode architecture for efficient graphene-based flexible organic light-emitting diodes, Nature Communications 7, 11791 (2016)
5) Khang June Lee, Daewon Kim, Byung Chul Jang, Da-Jin Kim, Hamin Park, Dae Yool Jung, Woonggi Hong, Tae Keun Kim, Yang-Kyu Choi, and Sung-Yool Choi, Multilayer Graphene with a Rippled Structure as a Spacer for Improving Plasmonic Coupling, Advanced Functional Materials 26, 5093-5101 (2016)
6) Byung Chul Jang, Hyejeong Seong, Sung Kyu Kim, Jong Yun Kim, Beom Jun Koo, Junhwan Choi, Sang Yoon Yang, Sung Gap Im, and Sung-Yool Choi, Flexible Nonvolatile Polymer Memory Array on Plastic Substrate via Initiated Chemical Vapor Deposition, ACS Applied Materials & Interfaces 8(20), 12951-12958 (2016)
7) Gyeong Sook Bang, Suhyung Cho, Narae Son, Gi Woong Shim, Byung-Kwan Cho, and Sung-Yool Choi, DNA-Assisted Exfoliation of Tungsten Dichalcogenides and Their Antibacterial Effect, ACS Applied Materials & Interfaces 8(3), 1943-1950 (2016)
8) Sung Kyu Kim, Jong Yun Kim, Sung-Yool Choi, Jeong Yong Lee, Hu Young Jeong, Direct Observation of Conducting Nano-filaments in Graphene Oxide Resistive Switching Memory, Advanced Functional Materials 25, 6710 (2015)
[Inside Front Cover]
9) Seung-Bok Yang, HongKyw Choi, Da Som Lee, Choon-Gi Choi, Sung-Yool Choi, Il-Doo Kim, Improved Optical Sintering Efficiency at the Contacts of Silver Nanowires Encapsulated by a Graphene Layer, Small 11, 1293 (2015) [Back Cover]
10) Sang Yoon Yang, Joong Gun Oh, Dae Yool Jung, HongKyw Choi, Chan Hak Yu, Jongwoo Shin, Choon-Gi Choi, Byung Jin Cho, Sung-Yool Choi, Metal-Etching-Free Direct Delamination and Transfer of Single-Layer Graphene with a High Degree of Freedom, Small 11(2), 175-181 (2015) [Cover] [Selected as 'Most accessed paper' in Jan. 2015]
1. Development of Core Materials based on Laser-Materials Interaction for Multi-dimensional, Beyond-Retina
Displays (1st year in 1st Phase)
Creative Materials Discovery Program, National Research Foundation (NRF), Ministry of Science, ICT and Future
Planning (MSIP, Korea)
[2016.05 ~ 2017.01]
2. Graphene synthesis and defect-control technology for innovative graphene devices (1st Year in 2nd Phase)
National Research Foundation (NRF), Ministry of Science, ICT and Future Planning (MSIP, Korea)
[2015.09 ~ 2016.08]
3. Novel soft devices and integrated circuit architectures (3rd Year in 2nd Phase)
Global Frontier Center for Advanced Soft Electronics (CASE), MSIP
[2015.09 ~ 2016.06]
4. Development of OLED panel using graphene (3rd Year in 1st Phase)
Ministry of Trade, Industry, and Energy (MOTIE, Korea)
[2015.05 ~ 2016.04]
5. Planning for the Development of Core Materials for Beyond-Retina 3D Display through Laser-Materials
[2015.07 ~ 2015.11]
6. High Mobility 2D Semiconductor Materials
LG Display Ltd.
[2015.03 ~ 2016.02]
7. Graphene synthesis and defect-control technology for innovative graphene devices (3rd Year in 1st Phase)
[2014.09 ~ 2015.08]
8. Novel soft devices and integrated circuit architectures (2nd Year in 2nd Phase)
[2014.09 ~ 2015.08]
9. Development of OLED panel using graphene (2nd Year in 1st Phase)
Ministry of Trade, Industry, and Energy (MOTIE, Korea),
[2014.05 ~ 2015.04]
10. Graphene synthesis and defect-control technology for innovative graphene devices (2nd Year in 1st Phase)
[2013.09 ~ 2014.08]
11. Novel soft devices and integrated circuit architectures (1st Year in 2nd Phase)
[2013.09 ~ 2014.08]
12. High Mobility Semiconductor Materials
[2013.06 ~ 2014.05]
13. Graphene synthesis and defect-control technology for innovative graphene devices (1st Year in 1st Phase)
[2012.09 ~ 2013.08]
14. Novel soft devices and architectures (2nd Year in 1st Phase)
[2012.09 ~ 2013.08]
15. High Mobility Semiconductor Materials
[2012.03 ~ 2013.02]
16. Basic Research on synthesis, control of material properties, and applications of graphene
KAIST Institute for NanoCentury
[2012.01 ~ 2015.12]
17. Basic Research on Catalyst-free Synthesis and Electrical Properties of Graphene
[2012.01 ~ 2016.12]
18. Novel soft devices and architectures (1st Year in 1st Phase
CASE, Ministry of Science and Technology (MOST)
[2012.09 ~ 2013.08]
19. Creative research for graphene electronic devices via atomic level control of material properties
ETRI, Ministry of Knowledge Economics (MKE)
20. Flexible devices based on graphene materials
[2010.01 ~ 2012.12]
21. Core technology for flexible polymer memory devices
[2007.08 ~ 2011.07]
22. IT-BT-NT Convergent Core Technology for Advanced Optoelectronic Devices and Smart Bio/Chemical Sensors
(Cambridge-ETRI Joint R&D Center Program)
Ministry of Information and Communications (MIC, Korea)
[2005.09 ~ 2007.06]
23. Development of organic materials for the nanoimprinted organic electronic devices (21st Frontier
[2005.04 ~ 2008.03]
24. Development of novel organic materials for gigabit organic memory devices
Ministry of Commerce, Industry and Energy (MOCIE, Korea)
[2004.08 ~ 2007.07]
25. Basic Research on single molecular transistors
[2002.09 ~ 2005.08]
26. Development of Molecular Scale Electronic Devices
[2001.12 ~ 2004.11]
27. Development of microwave power amplifier using carbon nanotubes for wireless communications
[2000.02 ~ 2001.12]