Advanced+Functional+Materials
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Ultra-Low Power Flexible Memory Using 2D Materials
(Professor Choi and Ph.D. candidate Jang)
KAIST research team led by Professor Sung-Yool Choi at School of Electrical Engineering and Professor Sung Gap Im at the Department of Chemical and Biomolecular Engineering developed high-density, ultra-low power, non-volatile, flexible memory technology using 2D materials. The team used ultrathin molybdenum disulfide (MoS2) with atomic-scale thickness as the channel material and high-performance polymeric insulator film as the tunneling dielectric material. This research was published on the cover of Advanced Functional Materials on November 17. KAIST graduate Myung Hun Woo, a researcher at Samsung Electronics and Ph.D. candidate Byung Chul Jang are first authors.
The surge of new technologies such as Internet of Things (IoT), Artificial Intelligence (AI), and cloud server led to the paradigm shift from processor-centric computing to memory-centric computing in the industry, as well as the increase in demand of wearable devices. This led to an increased need for high-density, ultra-low power, non-volatile flexible memory. In particular, ultrathin MoS2 as semiconductor material has been recently regarded as post-silicon material. This is due to its ultrathin thickness of atomic-scale which suppresses short channel effect observed in conventional silicon material, leading to advantages in high- density and low-power consumption. Further, this thickness allows the material to be flexible, and thus the material is applicable to wearable devices.
However, due to the dangling-bond free surface of MoS2 semiconductor material, it is difficult to deposit the thin insulator film to be uniform and stable over a large area via the conventional atomic layer deposition process. Further, the currently used solution process makes it difficult to deposit uniformly low dielectric constant (k) polymeric insulator film with sub-10 nm thickness on a large area, thus indicating that the memory device utilizing the conventional solution-processed polymer insulator film cannot be operated at low-operating voltage and is not compatible with photolithography.
The research team tried to overcome the hurdles and develop high-density, ultra-low power, non-volatile flexible memory by employing a low-temperature, solvent-free, and all-dry vapor phase technique named initiated chemical vapor deposition (iCVD) process. Using iCVD process, tunneling polymeric insulator film with 10 nm thickness was deposited uniformly on MoS2 semiconductor material without being restricted by the dangling bond-free surface of MoS2. The team observed that the newly developed MoS2-based non-volatile memory can be operated at low-voltage (around 10V), in contrast to the conventional MoS2-based non-volatile memory that requires over 20V.
Professor Choi said, “As the basis for the Fourth Industrial revolution technologies including AI and IoT, semiconductor device technology needs to have characteristics of low-power and flexibility, in clear contrast to conventional memory devices.” He continued, “This new technology is significant in developing source technology in terms of materials, processes, and devices to contribute to achieve these characteristics.”
This research was supported by the Global Frontier Center for Advanced Soft Electronics and the Creative Materials Discovery Program by funded the National Research Foundation of Korea of Ministry of Science and ICT.
( Figure 1. Cover of Advanced Functional Materials)
(Figure 2. Concept map for the developed non-volatile memory material and high-resolution transmission electron microscopy image for material cross-section )
2018.01.02 View 8016 -
Ultra High Speed Nanomaterial Synthesis Process Developed Using Laser
Dr. Jun-Yeop, Yeo and the research team led by Professor Seung-Hwan, Ko (both of the Department of Mechanical Engineering) successfully developed a process enabling the location-determinable, ultra high speed synthesis of nanomaterials using concentrated laser beams.
The result of the research effort was published as the frontispiece in the July 9th issue of Advanced Functional Materials, a world renowned material science and engineering academic journal.
Application of the technology reduced the time needed to process nanomaterial synthesis from a few hours to a mere five minutes. In addition, unlike conventional nanomaterial synthesis processes, it is simple enough to enable mass production and commercialization.
Conventional processes require the high temperatures of 900~1,000 °C and the use of toxic or explosive vapors. Complex processes such as separation after synthesis and patterning are needed for application in electronic devices. The multi-step, expensive, environmentally unfriendly characteristics of nanomaterial synthesis served as road blocks to its mass production and commercialization.
Exposing the precursor to concentrated continuous laser beam (green wavelength) resulted in the synthesis of nanowires in the desired location; the first instance in the world to accomplish this feat. The technology, according to the research team, makes possible the production, integration and patterning of nanomaterials using a single process. Applicable to various surfaces and substrates, nanowires have been successfully synthesized on flexible plastic substrates and controlled patterning on the surface of 3-dimensional structures.
Dr. Yeo commented that the research effort has “yielded the creation of a nanomaterial synthesis process capable of synthesis, integration, pattern, and material production using light energy” and has “reduced the synthesis process time of nanomaterial to one tenths of the conventional process.” Dr. Yeo continues to devise steps to commercialize the new multifunctional electronic material and methods for mass production.
The research effort, led by Dr. Yeo and Professor Ko, received contribution from Professor Hyung-Jin Sung (KAIST Department of Mechanical Engineering), Seok-Joon Hong, a Ph.D. candidate, Hyun-Wook Kang, also a Ph.D. candidate, Professor Costas Grigoropoulos of UC Berkeley, and Dr. Dae Ho Lee. In addition, the team received support from the National Research Foundation, Ministry of Knowledge Economy, Global Frontier Program, and KAIST EEWS.
Picture I: Synthesized nanomaterials produced at a desirable location by laser beams
Picture 2: Synthesized nanomaterials built on the 3D structure by using the developed technology
Picture 3: Functional electric circuit made with synthesized nanomaterials
Picture 4: Cover page of July 9th issue of Advanced Functional Materials
2013.08.23 View 9412 -
High Speed Nanomanufacturing Process Developed using Laser
Dr. Yeo Jun Yeop from KAIST’s Department of Mechanical Engineering, in a joint research project with Prof. Seung Hwan Ko, has developed a technology that speeds up the nanomanufacturing process by using lasers. Their research is published in the frontispiece of Advanced Functional Materials (July 9th issue).
Fig. The frontispiece of Advanced Functional Materials(July 9th issue)
The research group put a nanomaterial precursor on the board, illuminated it with a continuous-wave laser in the green wavelength range, and succeeded in synthesizing a nanowire at the point they wanted for the first time in the world.
Currently nanomaterials are difficult to mass produce and commercialize due to their complex and costly manufacturing processes which also use toxic gases. However, their new technology simplified the process and so reduced the manufacturing time from some hours to five minutes (1/10th times reduced).
Furthermore, this technology will apply regardless of the type of the board. Such nanometerials can be synthesized at any point on a flexible plastic board or even in three dimensional structures by illuminating them with a simple laser. Academics and industries expect mass production and commercialization of nanomaterials in near future.
Dr. Yeo said he intends to research further to promote early commercialization of multifunctional electronic devices by combining various nanomaterials
This research is sponsored by the National Research Foundation of Korea, the Ministry of Trade, Industry and Energy and KAIST EEWS
Fig. A nanomaterial synthesized after illuminated by lasers
Fig. A nanomaterial synthesized on a three dimensional structure using the developed technology
Fig. Functional electron device manufactured by using the synthesized nanomaterials
2013.08.02 View 8253 -
Nanofiber sensor detects diabetes or lung cancer faster and easier
Metal-oxide nanofiber based chemiresistive gas sensors offer greater usability for portable real-time breath tests that can be available on smart phones or tablet PCs in the near future.
Daejeon, Republic of Korea, June 11, 2013 -- Today"s technological innovation enables smartphone users to diagnose serious diseases such as diabetes or lung cancer quickly and effectively by simply breathing into a small gadget, a nanofiber breathing sensor, mounted on the phones.
Il-Doo Kim, Associate Professor of Materials Science and Engineering Department at the Korea Advanced Institute of Science and Technology (KAIST), and his research team have recently published a cover paper entitled "Thin-Wall Assembled SnO2 Fibers Functionalized by Catalytic Pt Nanoparticles and their Superior Exhaled Breath-Sensing Properties for the Diagnosis of Diabetes," in an academic journal, Advanced Functional Materials (May 20th issue), on the development of a highly sensitive exhaled breath sensor by using hierarchical SnO2 fibers that are assembled from wrinkled thin SnO2 nanotubes.
In the paper, the research team presented a morphological evolution of SnO2 fibers, called micro phase-separations, which takes place between polymers and other dissolved solutes when varying the flow rate of an electrospinning solution feed and applying a subsequent heat treatment afterward.
The morphological change results in nanofibers that are shaped like an open cylinder inside which thin-film SnO2 nanotubes are layered and then rolled up. A number of elongated pores ranging from 10 nanometers (nm) to 500 nm in length along the fiber direction were formed on the surface of the SnO2 fibers, allowing exhaled gas molecules to easily permeate the fibers. The inner and outer wall of SnO2 tubes is evenly coated with catalytic platinum (Pt) nanoparticles. According to the research team, highly porous SnO2 fibers, synthesized by eletrospinning at a high flow rate, showed five-fold higher acetone responses than that of the dense SnO2 nanofibers created under a low flow rate. The catalytic Pt coating shortened the fibers" gas response time dramatically as well.
The breath analysis for diabetes is largely based on an acetone breath test because acetone is one of the specific volatile organic compounds (VOC) produced in the human body to signal the onset of particular diseases. In other words, they are biomarkers to predict certain diseases such as acetone for diabetes, toluene for lung cancer, and ammonia for kidney malfunction. Breath analysis for medical evaluation has attracted much attention because it is less intrusive than conventional medical examination, as well as fast and convenient, and environmentally friendly, leaving almost no biohazard wastes.
Various gas-sensing techniques have been adopted to analyze VOCs including gas chromatography-mass spectroscopy (GC-MS), but these techniques are difficult to incorporate into portable real-time gas sensors because the testing equipment is bulky and expensive, and their operation is more complex. Metal-oxide based chemiresistive gas sensors, however, offer greater usability for portable real-time breath sensors.
Il-Doo Kim said, "Catalyst-loaded metal oxide nanofibers synthesized by electrospinning have a great potential for future exhaled breath sensor applications. From our research, we obtained the results that Pt-coated SnO2 fibers are able to identify promptly and accurately acetone or toluene even at very low concentration less than 100 parts per billion (ppb)."
The exhaled acetone level of diabetes patients exceeds 1.8 parts per million (ppm), which is two to six-fold higher than that (0.3-0.9 ppm) of healthy people. Therefore, a highly sensitive detection that responds to acetone below 1 ppm, in the presence of other exhaled gases as well as under the humid environment of human breath, is important for an accurate diagnosis of diabetes. In addition, Professor Kim said, "a trace concentration of toluene (30 ppb) in exhaled breath is regarded to be a distinctive early symptom of lung cancer, which we were able to detect with our prototype breath tester."
The research team has now been developing an array of breathing sensors using various catalysts and a number of semiconducting metal oxide fibers, which will offer patients a real-time easy diagnosis of diseases.
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Youtube Link: http://www.youtube.com/watch?v=t_Hr11dRryg
For further inquires:
Il-Doo Kim, Professor of Materials Science and Engineering, KAIST
Advanced Nanomaterials and Energy Laboratory
Tel: +82-42-350-3329
Email: idkim@kaist.ac.kr
Clockwise from left to right: left upper shows a magnified SEM image of a broken thin-wall assembled SnO2 fiber. Left below is an array of breath sensors (Inset is an actual size of a breath sensor). The right is the cover of Advanced Functional Materials (May 20th issue) in which a research paper on the development of a highly sensitive exhaled breath sensor by using SnO2 fibers is published.
This is the microstructural evolution of SnO2 nanofibers as a function of flow rate during electrospinning.
2013.06.20 View 13415 -
From Pencil Lead to Batteries: the Unlimited Transformation of Carbon
Those materials, like lead or diamond, made completely up of Carbon are being used in numerous ways as materials or parts. Especially with the discovery of carbon nanotubes, graphemes, and other carbon based materials in nanoscale, the carbon based materials are receiving a lot of interest in both fields of research and industry.
The carbon nanotubes and graphemes are considered as the ‘dream material’ and have a structure of a cross section of a bee hive. Such structure allows the material to have strength higher than that of a diamond and still be able to bend, be transparent and also conduct electricity. However the problem up till now was that these carbon structures appeared in layers and in bunches and were therefore hard to separate to individual layers or tubes.
Professor Kim Sang Wook’s research team developed the technology that can assemble the grapheme and carbon nanotubes in a three dimensional manner.
The team was able to assemble the grapheme ad carbon nanotubes in an entirely new three dimensional structure. In addition, the team was able to efficiently extract single layered grapheme from cheap pencil lead.
Professor Kim is scheduled to give a guest lecture in the “Materials Research Society” in San Francisco and the paper was published in ‘Advanced Functional Materials’ magazine as an ‘Invited Feature Article’.
2011.05.11 View 10182