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KAIST Develops Room-Temperature 3D Printing Technology for ‘Electronic Eyes’—Miniaturized Infrared Sensors
<(From Left) Professor Ji Tae Kim of the Department of Mechanical Engineering, Professor Soong Ju Oh of Korea University and Professor Tianshuo Zhao of the University of Hong Kong>
The “electronic eyes” technology that can recognize objects even in darkness has taken a step forward. Infrared sensors, which act as the “seeing” component in devices such as LiDAR for autonomous vehicles, 3D face recognition systems in smartphones, and wearable healthcare devices, are regarded as key components in next-generation electronics. Now, a research team at KAIST and their collaborators have developed the world’s first room-temperature 3D printing technology that can fabricate miniature infrared sensors in any desired shape and size.
KAIST (President Kwang Hyung Lee) announced on the 3rd of November that the research team led by Professor Ji Tae Kim of the Department of Mechanical Engineering, in collaboration with Professor Soong Ju Oh of Korea University and Professor Tianshuo Zhao of the University of Hong Kong, has developed a 3D printing technique capable of fabricating ultra-small infrared sensors—smaller than 10 micrometers (µm)—in customized shapes and sizes at room temperature.
Infrared sensors convert invisible infrared signals into electrical signals and serve as essential components in realizing future electronic technologies such as robotic vision. Accordingly, miniaturization, weight reduction, and flexible form-factor design have become increasingly important.
Conventional semiconductor fabrication processes were well suited for mass production but struggled to adapt flexibly to rapidly changing technological demands. They also required high-temperature processing, which limited material choices and consumed large amounts of energy.
To overcome these challenges, the research team developed an ultra-precise 3D printing process that uses metal, semiconductor, and insulator materials in the form of liquid nanocrystal inks, stacking them layer by layer within a single printing platform.
This method enables direct fabrication of core components of infrared sensors at room temperature, allowing for the realization of customized miniature sensors of various shapes and sizes.
Particularly, the researchers achieved excellent electrical performance without the need for high-temperature annealing by applying a “ligand-exchange” process, where insulating molecules on the surface of nanoparticles are replaced with conductive ones.
As a result, the team successfully fabricated ultra-small infrared sensors measuring less than one-tenth the thickness of a human hair (under 10 µm).
<Figure 1. 3D printing of infrared sensors.a. Room-temperature printing process for the electrodes and photoactive layer that make up the infrared sensor.b. Structure and chemical composition of the printed infrared microsensor. c.Printed infrared sensor micropixel array.>
Professor Ji Tae Kim commented, “The developed 3D printing technology not only advances the miniaturization and lightweight design of infrared sensors but also paves the way for the creation of innovative new form-factor products that were previously unimaginable. Moreover, by reducing the massive energy consumption associated with high-temperature processes, this approach can lower production costs and enable eco-friendly manufacturing—contributing to the sustainable development of the infrared sensor industry.”
The research results were published online in Nature Communications on October 16, 2025, under the title “Ligand-exchange-assisted printing of colloidal nanocrystals to enable all-printed sub-micron optoelectronics” (DOI: https://doi.org/10.1038/s41467-025-64596-4).
This research was supported by the Ministry of Science and ICT of Korea through the Excellent Young Researcher Program (RS−2025−00556379), the National Strategic Technology Material Development Program (RS−2024−00407084), and the International Cooperation Research Program for Original Technology Development (RS−2024−00438059).
2025.11.03 View 4518 -
KAIST Research Team Develops Electronic Ink for Room-Temperature Printing of High-Resolution, Variable-Stiffness Electronics
A team of researchers from KAIST and Seoul National University has developed a groundbreaking electronic ink that enables room-temperature printing of variable-stiffness circuits capable of switching between rigid and soft modes. This advancement marks a significant leap toward next-generation wearable, implantable, and robotic devices.
< Photo 1. (From left) Professor Jae-Woong Jeong and PhD candidate Simok Lee of the School of Electrical Engineering, (in separate bubbles, from left) Professor Gun-Hee Lee of Pusan National University, Professor Seongjun Park of Seoul National University, Professor Steve Park of the Department of Materials Science and Engineering>
Variable-stiffness electronics are at the forefront of adaptive technology, offering the ability for a single device to transition between rigid and soft modes depending on its use case. Gallium, a metal known for its high rigidity contrast between solid and liquid states, is a promising candidate for such applications. However, its use has been hindered by challenges including high surface tension, low viscosity, and undesirable phase transitions during manufacturing.
On June 4th, a research team led by Professor Jae-Woong Jeong from the School of Electrical Engineering at KAIST, Professor Seongjun Park from the Digital Healthcare Major at Seoul National University, and Professor Steve Park from the Department of Materials Science and Engineering at KAIST introduced a novel liquid metal electronic ink. This ink allows for micro-scale circuit printing – thinner than a human hair – at room temperature, with the ability to reversibly switch between rigid and soft modes depending on temperature.
The new ink combines printable viscosity with excellent electrical conductivity, enabling the creation of complex, high-resolution multilayer circuits comparable to commercial printed circuit boards (PCBs). These circuits can dynamically change stiffness in response to temperature, presenting new opportunities for multifunctional electronics, medical technologies, and robotics.
Conventional electronics typically have fixed form factors – either rigid for durability or soft for wearability. Rigid devices like smartphones and laptops offer robust performance but are uncomfortable when worn, while soft electronics are more comfortable but lack precise handling. As demand grows for devices that can adapt their stiffness to context, variable-stiffness electronics are becoming increasingly important.
< Figure 1. Fabrication process of stable, high-viscosity electronic ink by dispersing micro-sized gallium particles in a polymer matrix (left). High-resolution large-area circuit printing process through pH-controlled chemical sintering (right). >
To address this challenge, the researchers focused on gallium, which melts just below body temperature. Solid gallium is quite stiff, while its liquid form is fluid and soft. Despite its potential, gallium’s use in electronic printing has been limited by its high surface tension and instability when melted.
To overcome these issues, the team developed a pH-controlled liquid metal ink printing process. By dispersing micro-sized gallium particles into a hydrophilic polyurethane matrix using a neutral solvent (dimethyl sulfoxide, or DMSO), they created a stable, high-viscosity ink suitable for precision printing. During post-print heating, the DMSO decomposes to form an acidic environment, which removes the oxide layer on the gallium particles. This triggers the particles to coalesce into electrically conductive networks with tunable mechanical properties.
The resulting printed circuits exhibit fine feature sizes (~50 μm), high conductivity (2.27 × 10⁶ S/m), and a stiffness modulation ratio of up to 1,465 – allowing the material to shift from plastic-like rigidity to rubber-like softness. Furthermore, the ink is compatible with conventional printing techniques such as screen printing and dip coating, supporting large-area and 3D device fabrication.
< Figure 2. Key features of the electronic ink. (i) High-resolution printing and multilayer integration capability. (ii) Batch fabrication capability through large-area screen printing. (iii) Complex three-dimensional structure printing capability through dip coating. (iv) Excellent electrical conductivity and stiffness control capability.>
The team demonstrated this technology by developing a multi-functional device that operates as a rigid portable electronic under normal conditions but transforms into a soft wearable healthcare device when attached to the body. They also created a neural probe that remains stiff during surgical insertion for accurate positioning but softens once inside brain tissue to reduce inflammation – highlighting its potential for biomedical implants.
< Figure 3. Variable stiffness wearable electronics with high-resolution circuits and multilayer structure comparable to commercial printed circuit boards (PCBs). Functions as a rigid portable electronic device at room temperature, then transforms into a wearable healthcare device by softening at body temperature upon skin contact.>
“The core achievement of this research lies in overcoming the longstanding challenges of liquid metal printing through our innovative technology,” said Professor Jeong. “By controlling the ink’s acidity, we were able to electrically and mechanically connect printed gallium particles, enabling the room-temperature fabrication of high-resolution, large-area circuits with tunable stiffness. This opens up new possibilities for future personal electronics, medical devices, and robotics.”
< Figure 4. Body-temperature softening neural probe implemented by coating electronic ink on an optical waveguide structure. (Left) Remains rigid during surgery for precise manipulation and brain insertion, then softens after implantation to minimize mechanical stress on the brain and greatly enhance biocompatibility. (Right) >
This research was published in Science Advances under the title, “Phase-Change Metal Ink with pH-Controlled Chemical Sintering for Versatile and Scalable Fabrication of Variable Stiffness Electronics.” The work was supported by the National Research Foundation of Korea, the Boston-Korea Project, and the BK21 FOUR Program.
2025.06.04 View 9778 -
Professor Bae of Industrial Design Wins Good Design Award.
Professor Bae Sang Min’s research team of the Industrial Design Department received a G-Mark on the Product Design Section from the Good Design Awards 2010 organized by the Japan Industrial Design Promotion Organization through the exhibition of a Green Sharing Project, Heartea.
Heartea is a tumbler that allows the user to easily know the temperature of the liquid contained inside. Heartea is a name that combines Heart and Tea to refer to a tumbler that contains heart-warming tea.
Heartea was designed and produced by Professor Bae’s research team and was funded by GS Caltex. World Vision selected charity targets and oversaw distribution, and all of the sales income (about 200 million won) was donated as a scholarship to teenagers with financial difficulties.
The project has begun in 2006, and its accumulative sales are 1.7 billion won. Twenty million won is donated to 147 teenagers every year as scholarship, and through annual sharing camp, social leaders mentor teenagers to help them achieve their dreams.
The Good Design Award organized annually by Japan Industrial Design Promotion Organization has a fifty year tradition and is one of the world’s top four design contests with 6,000 submissions from 50 different countries participated.
Professor Bae’s team has won three of the top four design contests including the German Red Dot Product Award and the American IDEA Product Award.
Along with Heartea, both of foldable MP3 in 2008 and natural humidifier Lovepot in 2009 won an award from these four contests.
“Through continuous research, I hope to create the world’s best philanthropy design research center to help Third World countries and the neglected. I want to participate in creating a better world through design,” said Professor Bae.
2010.11.05 View 17778 -
"Supersolidity flows back," Nature, September 2, 2010
Supersolidity, discovered for the first time in 2004 by two physicists—one of them is Professor Eun-Seong Kim from the Department of Physics, KAIST—was discussed once again in the September 2, 2010 issue of Nature, an internationally well-known science journal.
The article mentioned “supersolidity” as one of the rare examples of quantum effects on a macroscopic scale, together with “superconductivity” and “superfluidity.” The phenomenon of supersolidity was evidenced by Professor Kim and his colleague through an experiment of placing helium-4 in a torsional oscillator under a low temperature.
The phenomenon, however, has been in debate among scientists in the physics community since the discovery, and Professor Kim has recently released his research results to further support his claim. For the full article, please click the link below:
http://www.nature.com/news/2010/100902/full/news.2010.443.html.
2010.09.08 View 13411 -
Prof. Cho Wins Best Paper Award
KAIST Prof. Nam-Zin Cho of the Department of Nuclear and Quantum Engineering, won the Best Thesis Award in the nuclear reactor physics category at the 2008 Winter Meeting of the American Nuclear Society held on Nov. 9-13 in Reno, Nevada.
His paper, entitled "Thermal Feedback Transient Analysis of a Pebble Fuel Based on the Two-Temperature Homogenized Model," was jointly authored by Hwi Yu and Jong-Un Kim under the guidance of Prof. Cho.
Prof. Cho was elected a fellow of the American Nuclear Society in 2001 and has served as the deputy editor of the Nuclear Science and Engineering, the research journal of the American Nuclear Society, since 1999.
2008.12.09 View 21249 -
Storing Stably Hydrogen Atoms in Icy Materials Discovered
KAIST, Aug. 8, 2008 -- A KAIST research team led by Prof. Huen Lee of the Department of Chemical & Biomolecular Engineering has discovered that icy organic hydrates, which contain small cages that can trap guest molecules, can be used to create and trap hydrogen atoms at higher temperatures.
The properties and reactions of single hydrogen atoms are of great scientific interest because of their inherent quantum mechanical behavior; experimentally, they can be generated and stabilized at very low temperatures (4 K) by high-energy irradiation of solid molecular hydrogen.
The finding was reported in the journal of American Chemical Society and featured in the "Editor"s Choice" in the July 11 issue of Science as a recent research highlight.
Hydrogen is a clean and sustainable form of energy that can be used in mobile and stationary applications. Hydrogen has the potential to solve several major challenges today: depletion of fossil fuels, poor air quality, and green house gas emissions.
However, the trapping of hydrogen atoms in crystalline solid matrix has never been attempted mainly because of experimental difficulties in identifying the generated hydrogen atoms with either spectroscopic or microscopic technique.
"To overcome the barriers and limitations of the existing storage approaches, we have continuously attempted to find the new hydrogen storage media such as icy powders and other related inclusion compounds," said Prof. Lee
The discovery follows the breakthrough concept Prof. Lee"s research team proposed in Nature in 2005 to use pure ice to capture and store hydrogen molecules. At moderate temperature and pressure conditions small guest molecules are entrapped in pure ice powders to form the mixed icy hydrate materials.
"Stable existence of single hydrogen molecule/radical in icy crystalline matrices may offer significant advantages in exploring hydrogen as a quantum medium because icy hydrogen hydrates can be formed at milder conditions when compared with pure solid hydrogen, which requires the ultra low temperature of 4.2 K," said Prof. Lee.
The novel design and synthesis of ionic and radicalized icy hydrates are expected to open a new field for inclusion chemistry and ice-based science and technology. Specifically, the fact that hydrogen atoms can be stably stored in icy materials might provide versatile and practical applications to energy devices including fuel cells, ice-induced reactions, and novel energy storage process, according to the KAIST professor.
2008.08.07 View 18657 -
Prof. Kim Receives Lee Osheroff Prize
Professor Eun-Seong Kim of the Department of Physics has been selected as the winner of the Lee Osheroff Richardson Prize for 2008.
The award was established in honor of the 1996 Nobel Prize laureates in Physics David Lee, Douglas Osheroff, and Robert Richardson for their discovery in superfluidity in helium-3. The annual prize sponsored by Oxford Instruments NanoScience is awarded to a young scientist who has made a notable achievement in the field of low temperatures and high magnetic fields.
Kim was chosen as the winner of this prestigious award for his contributions to the understanding of solid helium. Through research, Professor Kim found superfluid-like behavior in solid helium and with this discovery it is shown that all three states of matter can exhibit superfluid behavior.
The Lee Osheroff Richardson Prize recipient is selected by the North American Prize Committee which is composed of prominent figures in the low temperature and high magnetic fields including Professor Bruce Gaulin of McMaster University, who chairs the Prize Committee. The award ceremony was held on March 11 in New Orleans.
2008.03.18 View 19118