Kyun Kyu Kim

All Publications

• Photothermal Lithography for Realizing a Stretchable Multilayer Electronic Circuit Using a Laser. ACS nano Song, S., Hong, H., Kim, K. Y., Kim, K. K., Kim, J., Won, D., Yun, S., Choi, J., Ryu, Y. I., Lee, K., Park, J., Kang, J., Bang, J., Seo, H., Kim, Y. C., Lee, D., Lee, H., Lee, J., Hwang, S. W., Ko, S. H., Jeon, H., Lee, W. 2023

  Abstract

  Photolithography is a well-established fabrication method for realizing multilayer electronic circuits. However, it is challenging to adopt photolithography to fabricate intrinsically stretchable multilayer electronic circuits fully composed of an elastomeric matrix, due to the opacity of thick stretchable nanocomposite conductors. Here, we present photothermal lithography that can pattern elastomeric conductors and via holes using pulsed lasers. The photothermal-patterned stretchable nanocomposite conductor exhibits 3 times higher conductivity (5940 S cm-1) and 5 orders of magnitude lower resistance change (R/R0 = 40) under a 30% strained 5000th cyclic stretch, compared to those of a screen-printed conductor, based on the percolation network formed by spatial heating of the laser. In addition, a 50 μm sized stretchable via holes can be patterned on the passivation without material ablation and electrical degradation of the bottom conductor. By repeatedly patterning the conductor and via holes, highly conductive and durable multilayer circuits can be stacked with layer-by-layer material integration. Finally, a stretchable wireless pressure sensor and passive matrix LED array are demonstrated, thus showing the potential for a stretchable multilayer electronic circuit with durability, high density, and multifunctionality.

  View details for DOI 10.1021/acsnano.3c06207

  View details for PubMedID 37857269

• A substrate-less nanomesh receptor with meta-learning for rapid hand task recognition NATURE ELECTRONICS Kim, K., Kim, M., Pyun, K., Kim, J., Min, J., Koh, S., Root, S. E., Kim, J., Nguyen, B. T., Nishio, Y., Han, S., Choi, J., Kim, C., Tok, J., Jo, S., Ko, S., Bao, Z. 2022

  View details for DOI 10.1038/s41928-022-00888-7

  View details for Web of Science ID 000905510900002

• Energy Harvesting Untethered Soft Electronic Devices ADVANCED HEALTHCARE MATERIALS Kim, K., Choi, J., Ko, S. 2021: e2002286

  Abstract

  Advances in wearable and stretchable electronic technologies have yielded a wide range of electronic devices that can be conformably worn by, or implanted in humans to measure physiological signals. Moreover, various cutting-edge technologies for battery-free electronic devices have led to advances in healthcare devices that can continuously measure long-term biosignals for advanced human-machine interface and clinical diagnostics. This report presents the recent progress in battery-less, wearable devices using a wide range of energy harvesting sources, such as electromagnetic energy, mechanical energy, and biofuels. Additionally, this report also discusses the principles and working mechanisms of near/far-field communications, triboelectric, thermoelectric, and biofuel technologies.

  View details for DOI 10.1002/adhm.202002286

  View details for Web of Science ID 000645651000001

  View details for PubMedID 33929767

• Transparent Soft Actuators/Sensors and Camouflage Skins for Imperceptible Soft Robotics ADVANCED MATERIALS Won, P., Kim, K., Kim, H., Park, J., Ha, I., Shin, J., Jung, J., Cho, H., Kwon, J., Lee, H., Ko, S. 2021; 33 (19): e2002397

  Abstract

  The advent of soft robotics has led to great advancements in robots, wearables, and even manufacturing processes by employing entirely soft-bodied systems that interact safely with any random surfaces while providing great mechanical compliance. Moreover, recent developments in soft robotics involve advances in transparent soft actuators and sensors that have made it possible to construct robots that can function in a visually and mechanically unobstructed manner, assisting the operations of robots and creating more applications in various fields. In this aspect, imperceptible soft robotics that mainly consist of optically transparent imperceptible hardware components is expected to constitute a new research focus in the forthcoming era of soft robotics. Here, the recent progress regarding extended imperceptible soft robotics is provided, including imperceptible transparent soft robotics (transparent soft actuators/sensors) and imperceptible nontransparent camouflage skins. Their principles, materials selections, and working mechanisms are discussed so that key challenges and perspectives in imperceptible soft robotic systems can be explored.

  View details for DOI 10.1002/adma.202002397

  View details for Web of Science ID 000580509300001

  View details for PubMedID 33089569

• Recent progress in controlled nano/micro cracking as an alternative nano-patterning method for functional applications NANOSCALE HORIZONS Jung, J., Kim, K., Suh, Y. D., Hong, S., Yeo, J., Ko, S. 2020; 5 (7): 1036-1049

  Abstract

  Generally, cracking occurs for many reasons connected to uncertainties and to the non-uniformity resulting from intrinsic deficiencies in materials or the non-linearity of applied external (thermal, mechanical, etc.) stresses. However, recently, an increased level of effort has gone into analyzing the phenomenon of cracking and also into methods for controlling it. Sophisticated manipulation of cracking has yielded various cutting-edge technologies such as transparent conductors, mechanical sensors, microfluidics, and energy devices. In this paper, we present some of the recent progress that has been made in controlling cracking by giving an overview of the fabrication methods and working mechanisms used for various mediums. In addition, we discuss recent progress in the various applications of methods that use controlled cracking as an alternative to patterning tools.

  View details for DOI 10.1039/d0nh00241k

  View details for Web of Science ID 000543912700002

  View details for PubMedID 32469038

• A deep-learned skin sensor decoding the epicentral human motions NATURE COMMUNICATIONS Kim, K., Ha, I., Kim, M., Choi, J., Won, P., Jo, S., Ko, S. 2020; 11 (1): 2149

  Abstract

  State monitoring of the complex system needs a large number of sensors. Especially, studies in soft electronics aim to attain complete measurement of the body, mapping various stimulations like temperature, electrophysiological signals, and mechanical strains. However, conventional approach requires many sensor networks that cover the entire curvilinear surfaces of the target area. We introduce a new measuring system, a novel electronic skin integrated with a deep neural network that captures dynamic motions from a distance without creating a sensor network. The device detects minute deformations from the unique laser-induced crack structures. A single skin sensor decodes the complex motion of five finger motions in real-time, and the rapid situation learning (RSL) ensures stable operation regardless of its position on the wrist. The sensor is also capable of extracting gait motions from pelvis. This technology is expected to provide a turning point in health-monitoring, motion tracking, and soft robotics.

  View details for DOI 10.1038/s41467-020-16040-y

  View details for Web of Science ID 000531425700030

  View details for PubMedID 32358525

  View details for PubMedCentralID PMC7195472

• Smart Stretchable Electronics for Advanced Human–Machine Interface Advanced Intelligent Systems Kim, K., Suh, Y., Ko, S. 2020

  View details for DOI 10.1002/aisy.202000157

• Transparent wearable three-dimensional touch by self-generated multiscale structure NATURE COMMUNICATIONS Kim, K., Ha, I., Won, P., Seo, D., Cho, K., Ko, S. 2019; 10: 2582

  Abstract

  Pressure-sensitive touch panels can measure pressure and location (3D) information simultaneously and provide an intuitive and natural method for expressing one's intention with a higher level of controllability and interactivity. However, they have been generally realized by a simple combination of pressure and location sensor or a stylus-based interface, which limit their implementation in a wide spectrum of applications. Here, we report a first demonstration (to our knowledge) of a transparent and flexible 3D touch which can sense the 3D information in a single device with the assistance of functionally designed self-generated multiscale structures. The single 3D touch system is demonstrated to draw a complex three-dimensional structure by utilizing the pressure as a third coordinate. Furthermore, rigorous theoretical analysis is carried out to achieve the target pressure performances with successful 3D data acquisition in wireless and wearable conditions, which in turn, paves the way for future wearable devices.

  View details for DOI 10.1038/s41467-019-10736-6

  View details for Web of Science ID 000471226600002

  View details for PubMedID 31197161

  View details for PubMedCentralID PMC6565712

• Highly Sensitive and Stretchable Multidimensional Strain Sensor with Prestrained Anisotropic Metal Nanowire Percolation Networks NANO LETTERS Kim, K. K., Hong, S., Cho, H. M., Lee, J., Suh, Y. D., Ham, J., Ko, S. H. 2015; 15 (8): 5240-5247

  Abstract

  To overcome the limitation of the conventional single axis-strain sensor, we demonstrate a multidimensional strain sensor composed of two layers of prestrained silver nanowire percolation network with decoupled and polarized electrical response in principal and perpendicular directional strain. The information on strain vector is successfully measured up to 35% maximum strain with large gauge factor (>20). The potential of the proposed sensor as a versatile wearable device has been further confirmed.

  View details for DOI 10.1021/acs.nanolett.5b01505

  View details for Web of Science ID 000359613700058

  View details for PubMedID 26150011