Archives: 연구 > 연구성과

Highly functional and free-form displays are critical components to complete the technological prowess of wearable electronics, robotics, and human-machine interfaces.

A KAIST team created stretchable OLEDs (Organic Light-Emitting Diodes) that are compliant and maintain their performance under high-strain deformation. Their stress-relief substrates have a unique structure and utilize pillar arrays to reduce the stress on the active areas of devices when strain is applied.

Traditional intrinsically stretchable OLEDs have commercial limitations due to their low efficiency in the electrical conductivity of the electrodes. In addition, previous geometrically stretchable OLEDs laminated to the elastic substrates with thin film devices lead to different pixel emissions of the devices from different peak sizes of the buckles.

To solve these problems, a research team led by Professor Kyung Cheol Choi designed a stretchable substrate system with surface relief island structures that relieve the stress at the locations of bridges in the devices. Their stretchable OLED devices contained an elastic substrate structure comprising bonded elastic pillars and bridges. A patterned upper substrate with bridges makes the rigid substrate stretchable, while the pillars decentralize the stress on the device.

Although various applications using micropillar arrays have been reported, it has not yet been reported how elastic pillar arrays can affect substrates by relieving the stress applied to those substrates upon stretching. Compared to results using similar layouts with conventional free-standing, flat substrates or island structures, their results with elastic pillar arrays show relatively low stress levels at both the bridges and plates when stretching the devices. They achieved stretchable RGB (red, green, blue) OLEDs and had no difficulties with material selection as practical processes were conducted with stress-relief substrates.

Their stretchable OLEDs were mechanically stable and have two-dimensional stretchability, which is superior to only one-direction stretchable electronics, opening the way for practical applications like wearable electronics and health monitoring systems.

Professor Choi said, “Our substrate design will impart flexibility into electronics technology development including semiconductor and circuit technologies. We look forward this new stretchable OLED lowering the barrier for entering the stretchable display market.”

This research was published in Nano Letters titled Two-Dimensionally Stretchable Organic Light-Emitting Diode with Elastic Pillar Arrays for Stress Relief. (https://dx.doi.org/10.1021/acs.nanolett.9b03657).  This work was supported by the Engineering Research Center of Excellence Program supported by the National Research Foundation of Korea.

Figure. Photographs of the patterned rigid part of the substrate on the finger joint indicating 2D dimensional stretchability and images of stretchable OLEDs on a finger joint emitting green light

School of EE recorded the most publications and awards at Humantech Paper Award for five years in a row.

Humantech Paper Award, which was the 26th at this time since 1994, is held by Samsung Electronics to find distinguished engineering in the discipline of science and technology.

At Humantech Paper Award, not only the individual prize but also a special prize is given to university or high school with notable accomplishment.

“The special prize for the most publications and awards,” which includes 10 million KRW, is the greatest honor among special prizes.

Moreover, it is recognizable that our department received this astonishing award for five years in a row.

We expect excellent achievements of KAIST EE are revealed extensively to improve the prestige.

Researchers described a new strategy of designing metamolecules that incorporates two independently controllable subwavelength meta-atoms. This two-parametric control of the metamolecule secures the complete control of both amplitude and the phase of light.
 
A KAIST research team in collaboration with the University of Wisconsin-Madison theoretically suggested a graphene-based active metasurface capable of independent amplitude and phase control of mid-infrared light. This research gives a new insight into modulating the mid-infrared wavefront with high resolution by solving the problem of the independent control of light amplitude and phase, which has remained a long-standing challenge.
 
Light modulation technology is essential for developing future optical devices such as holography, high-resolution imaging, and optical communication systems. Liquid crystals and a microelectromechanical system (MEMS) have previously been utilized to modulate light. However, both methods suffer from significantly limited driving speeds and unit pixel sizes larger than the diffraction limit, which consequently prevent their integration into photonic systems.
 
The metasurface platform is considered a strong candidate for the next generation of light modulation technology. Metasurfaces have optical properties that natural materials cannot have, and can overcome the limitations of conventional optical systems, such as forming a high-resolution image beyond the diffraction limit. In particular, the active metasurface is regarded as a technology with a wide range of applications due to its tunable optical characteristics with an electrical signal.
 
However, the previous active metasurfaces suffered from the inevitable correlation between light amplitude control and phase control. This problem is caused by the modulation mechanism of conventional metasurfaces. Conventional metasurfaces have been designed such that a metaatom only has one resonance condition, but a single resonant design inherently lacks the degrees of freedom to independently control the amplitude and phase of light.
 
The research team made a metaunit by combining two independently controllable metaatoms, dramatically improving the modulation range of active metasurfaces. The proposed metasurface can control the amplitude and phase of the mid-infrared light independently with a resolution beyond the diffraction limit, thus allowing complete control of the optical wavefront.
 
The research team theoretically confirmed the performance of the proposed active metasurface and the possibility of wavefront shaping using this design method. Furthermore, they developed an analytical method that can approximate the optical properties of metasurfaces without complex electromagnetic simulations. This analytical platform proposes a more intuitive and comprehensively applicable metasurface design guideline.
 
The proposed technology is expected to enable accurate wavefront shaping with a much higher spatial resolution than existing wavefront shaping technologies, which will be applied to active optical systems such as mid-infrared holography, high-speed beam steering devices that can be applied for LiDAR, and variable focus infrared lenses.
 
Professor Min Seok Jang commented, “This study showed the independent control amplitude and phase of light, which has been a long-standing quest in light modulator technology. The development of optical devices using complex wavefront control is expected to become more active in the future.”
 
MS candidate Sangjun Han and Dr. Seyoon Kim of the University of Wisconsin-Madison are the co-first authors of the research, which was published and selected as the front cover of the January 28 edition of ACS Nano titled “Complete complex amplitude modulation with electronically tunable graphene plasmonic metamolecules.”

 

This research was funded by the Samsung Research Funding & Incubation Center for Future Technology.

Professor Min-Soo Rhu received the “Facebook Faculty Research Award”, which is awarded by the Facebook headquarters. 167 faculty members from 100 universities in 26 countries around the world have applied for the award and 10 faculty members out of them earned the award. The significance of this award is that Professor Min-Soo Rhu is the only winner in Asia. It is also the first from KAIST.

Professor Min-Soo Rhu won the award in the “Systems for Machine Learning” area for his research titled “A Near-Memory Processing Architecture for Training Recommendation Systems”. He will receive a $50,000 prize money that can be used for research. The awarding ceremony will be held at the “AI Systems Faculty Summit” in fall 2020.

Congratulations again to Professor Min-Soo Rhu!

More information about the award can be found at the link below.   

[Link]

https://research.fb.com/blog/2020/02/announcing-the-winners-of-the-systems-for-machine-learning-rfp/

Professor Min-Soo Rhu’s lab has succeeded in developing an “AI-based recommendation technology” acceleration system and their work has been reported in the media. The system accelerates AI-based recommendation algorithms from 6x up to 17x.

The AI-based recommendation service refers to advertisement recommendations that can be found easily on portal sites such as Google and Naver. This is a service based on a deep learning system and recommends personalized information by using a user’s search history through AI technology. The key element of such service is the “computation time of the algorithm”. Since it is based on real-time information, the quality of the service is determined by how quickly the recommendation results are derived. Besides, this is directly related to user satisfaction and also the profit generation of the company.

Professor Min-Soo Rhu’s research team has devised a solution to effectively reduce execution time by developing an AI accelerator computing system based on memory, which improves the so-called ‘memory bottleneck’. The system proposed by the team is a ‘Processing in Memory (PI614M)’ technology that places an AI accelerator close to the memory. This is noteworthy in that it effectively reduces data transfers and memory access times.

The developed technology is receiving positive reviews and can be utilized in various fields. Professor Min-Soo Rhu has expressed his position to cooperate with domestic companies to win the leadership of the AI accelerator market.

The results of this research are globally recognized for their excellence, including to be listed on the 2019 IEEE Micro Top Picks – Honorable Mention List, which was presented in 26 of the most influential results among the hundreds of papers published in computer system architecture in 2019.

In the meantime, this research was carried out with the support from Samsung Electronics Future Technology Foundation. Congratulations on your achievements.

Our engineering school held the Readers’ Choice Award ceremony. In the ceremony, Professor Changho Suh and Professor Hyunjoo Lee were selected in 2019 spring and autumn, respectively.

The ceremony was at the council chamber of the engineering school on Jan 15th. Including Prof. Choongsik Bae and Prof. Sung-Yool Choi, who is the dean and the deputy head of the engineering school respectively, a cadre of professors participated in the ceremony.

Readers’ Choice Award is for a researcher who enhanced the reputation of the engineering school by promoting research achievement on ‘KAIST Breakthroughs’, which is a Research Webzine published from 2014.

This ceremony was secondly planned, and the best research achievement was voted among the articles which are published in 2019.

This is significantly meaningful because two winners belong to our department. We wish diverse accomplishment to be promoted for further notable articles. 

 

The research team of Professor Hyunchul Shim accomplished the 3rd place in the final of AlphaPilot Orlando Race held by Lockheed Martin on last Dec. 6th.

Lockheed Martin held AlphaPilot Orlando Race at the beginning of this year and awarded a million USD (1.2 billion KRW) to the race winner-drone which cruises fast on the intricate course. Over 420 teams challenged to participate in the final of the race, but only nine teams were selected for the final.

The research team of Prof. Shim was chosen confidently for the final as one of the nine teams among 420 teams who attended last April.

A drone race is already popular enough to be shown live by such as ESPN in the US. A participant wears a first-person view (FPV) goggle, which shows the real-time image transferred from the camera on the drone, for control.

Congratulations to Prof. Shim and his research team for the great accomplishment against distinguished teams.

Information related to the race and detail can be found through the link below.

 

[Link]

https://www.lockheedmartin.com/en-us/news/events/ai-innovation-challenge.html

Professor Sang-Hyun Kim’s lab has developed a 60,000 PPI ultra-high-resolution micro-LED display production technology.

Dr. Dae-Myeong Geum has participated as the first author and their work has been published as a cover paper of international journal ‘Nanoscale’, December 28^th edition. (Title of the paper: Strategy toward the fabrication of ultrahigh-resolution micro-LED displays by bonding interface-engineered vertical stacking and surface passivation)

To solve the problem of the existing development of ultra-high-resolution displays, the research team stacked a red-green-blue LED active layer in three dimensions, and then proposed a device manufacturing method that can cope with ultra-high resolution micro-LED displays using a semiconductor patterning process. Also, they have proposed a solution that can improve overall efficiency in a small pixel and solve a color interference which is problematic for vertical stacking.

The research team used a substrate bonding technology for three-dimensional stacking, and designed an insulating film with filter characteristics on the bonding surface to minimize color interference, eliminating 97% of the red-blue interference light.

Their work has shown that even vertically combined pixels can achieve high purity pixels without light interference by incorporating an insulating film. The research team demonstrated the ability to achieve resolutions above 60,000 PPI using the vertical patterning followed by semiconductor patterning technology.

Besides, the non-luminescent recombination phenomenon on the semiconductor surface, which can be problematic in the small LED pixels, was thoroughly investigated through time-resolved photoluminescence analysis and computational simulation to provide a meaningful direction to improve the efficiency of the small LED.

Professor Sang-Hyun Kim said, “This is the first research to demonstrate the possibility of producing ultra-high resolution pixels using a semiconductor process. This research shows the importance of cooperation between the semiconductor and display industry. We will continue to work on the development of ultra-high-resolution future displays through future research.

The research was supported by the Korea Research Foundation’s basic research projects in science and engineering, and climate change response technology development projects.

Congratulations on your achievements.

Professor C​hul Soon Park​ and Prof. Wan Choi were named IEEE Fellows in 2020.

IEEE Fellows are elected less than only 0.1 % of total IEEE members, and this great honor implies the verification of achievement as a top-notch professional in a specific discipline.

Professor C​hul Soon Park​ was honored for the development of low power millimeter-wave circuits and packages.

On the other hand, Professor. Wan Choi was awarded for the contribution to the analysis and design of multi-cell communication systems.

Congratulations on both professors’ appointment as 2020 IEEE Fellows.

Two award achievements of Prof. Junil Choi in our department enhanced the reputation of KAIST EE. The Korean Institute of Communications and Information Sciences (KICS) selected Prof. Choi for the 9th Haedong Young Engineering Researcher Award. He researched the realization of massive MIMO systems, which is essential in 5G wireless communication, based on signal processing and communication theory. With this study, he received IEEE Signal Processing Society Best Paper Award in 2015. He is recently conducting projects such as communication between vehicles and a fusion system of communication and radar. The accomplishment was yield by his 34 papers published in international journals and 26 patents registered in the US.

Furthermore, Prof. Choi was awarded the Stephen O. Rice Prize at the Global Communications Conference (GLOBECOM), which is the best prize in the conference, in Hawaii on December 10th. The Stephen O. Rice Prize with a top-notch reputation is given only once a year considering novelty, citations, and influence of the papers in IEEE Transactions on Communications in the last three years. Prof. Choi received the award with the paper about one-bit ADCs in massive MIMO systems. He proposed technology to save power in massive MIMO systems, which is fundamental in 5G and other developed communication systems. This paper was cited about 230 times by various papers in journals and conferences, and multiple follow-up studies are actively ongoing.

Congratulations on the outstanding performance of the research, and we also expect future academic outcomes.