Keon Jae Lee

Pattern Transfer Printing by Kinetic Control of Adhesion to an Elastomeric Stamp

An increasing number of technologies require large-scale integration of disparate classes of separately fabricated objects into spatially organized, functional systems1,2,3,4,5,6,7,8,9. Here we introduce an approach for heterogeneous integration based on kinetically controlled switching between adhesion and release of solid objects to and from an elastomeric stamp. We describe the physics of soft adhesion that govern this process and demonstrate the method by printing objects with a wide range of sizes and shapes, made of single-crystal silicon and GaN, mica, highly ordered pyrolytic graphite, silica and pollen, onto a variety of substrates without specially designed surface chemistries or separate adhesive layers. Printed p–n junctions and photodiodes fixed directly on highly curved surfaces illustrate some unique device-level capabilities of this approach.

Heterogeneous Three-Dimensional Electronics by Use of Printed Semiconductor Nanomaterials

We developed a simple approach to combine broad classes of dissimilar materials into heterogeneously integrated electronic systems with two- or three-dimensional layouts. The process begins with the synthesis of different semiconductor nanomaterials, such as single-walled carbon nanotubes and single-crystal micro- and nanoscale wires and ribbons of gallium nitride, silicon, and gallium arsenide on separate substrates. Repeated application of an additive, transfer printing process that uses soft stamps with these substrates as donors, followed by device and interconnect formation, yields high-performance heterogeneously integrated electronics that incorporate any combination of semiconductor nanomaterials on rigid or flexible device substrates. This versatile methodology can produce a wide range of unusual electronic systems that would be impossible to achieve with other techniques.

Piezoelectric BaTiO3 Thin Film Nanogenerator on Plastic Substrates

The piezoelectric generation of perovskite BaTiO3 thin films on a flexible substrate has been applied to convert mechanical energy to electrical energy for the first time. Ferroelectric BaTiO3 thin films were deposited by radio frequency magnetron sputtering on a Pt/Ti/SiO2/(100) Si substrate and poled under an electric field of 100 kV/cm. The metal-insulator (BaTiO3)-metal-structured ribbons were successfully transferred onto a flexible substrate and connected by interdigitated electrodes. When periodically deformed by a bending stage, a flexible BaTiO3 nanogenerator can generate an output voltage of up to 1.0 V. The fabricated nanogenerator produced an output current density of 0.19 μA/cm(2) and a power density of ∼7 mW/cm(3). The results show that a nanogenerator can be used to power flexible displays by means of mechanical agitations for future touchable display technologies.

Flexible Nanocomposite Generator Made of BaTiO 3 Nanoparticles and Graphitic Carbons

Outdoor renewable energy sources such as solar energy (15 000 μ W/cm 3 ), [ 3 , 4 ] wind energy (380 μ W/cm 3 ), [ 5 ] and wave energy (1 000 W/cm of wave crest length) [ 6 , 7 ] can provide largescale needs of power. However, for driving small electronics in indoor or concealed environments [ 3 , 8 ] (such as in tunnels, clothes, and artifi cial skin) and implantable biomedical devices, innovative approaches have to be developed. One way of energy harvesting without such restraints is to utilize piezoelectric materials that can convert vibrational and mechanical energy sources from human activities such as pressure, bending, and stretching motions into electrical energy. [ 9–11 ]

Bendable Inorganic Thin-Film Battery for Fully Flexible Electronic Systems

High-performance flexible power sources have gained attention, as they enable the realization of next-generation bendable, implantable, and wearable electronic systems. Although the rechargeable lithium-ion battery (LIB) has been regarded as a strong candidate for a high-performance flexible energy source, compliant electrodes for bendable LIBs are restricted to only a few materials, and their performance has not been sufficient for them to be applied to flexible consumer electronics including rollable displays. In this paper, we present a flexible thin-film LIB developed using the universal transfer approach, which enables the realization of diverse flexible LIBs regardless of electrode chemistry. Moreover, it can form high-temperature (HT) annealed electrodes on polymer substrates for high-performance LIBs. The bendable LIB is then integrated with a flexible light-emitting diode (LED), which makes an all-in-one flexible electronic system. The outstanding battery performance is explored and well supported by finite element analysis (FEA) simulation.

Highly‐Efficient, Flexible Piezoelectric PZT Thin Film Nanogenerator on Plastic Substrates

A highly-efficient, flexible piezoelectric PZT thin film nanogenerator is demonstrated using a laser lift-off (LLO) process. The PZT thin film nanogenerator harvests the highest output performance of ∼200 V and ∼150 μA·cm(-2) from regular bending motions. Furthermore, power sources generated from a PZT thin film nanogenerator, driven by slight human finger bending motions, successfully operate over 100 LEDs.

Self-Powered Cardiac Pacemaker Enabled by Flexible Single Crystalline PMN-PT Piezoelectric Energy Harvester

A flexible single-crystalline PMN-PT piezoelectric energy harvester is demonstrated to achieve a self-powered artificial cardiac pacemaker. The energy-harvesting device generates a short-circuit current of 0.223 mA and an open-circuit voltage of 8.2 V, which are enough not only to meet the standard for charging commercial batteries but also for stimulating the heart without an external power source.

High-speed mechanically flexible single-crystal silicon thin-film transistors on plastic substrates

This letter describes the fabrication and properties of bendable single-crystal-silicon thin film transistors formed on plastic substrates. These devices use ultrathin single-crystal silicon ribbons for the semiconductor, with optimized device layouts and low-temperature gate dielectrics. The level of performance that can be achieved approaches that of traditional silicon transistors on rigid bulk wafers: effective mobilities>500cm/sup 2//V/spl middot/s, ON/OFF ratios >10/sup 5/, and response frequencies > 500 MHz at channel lengths of 2 /spl mu/m. This type of device might provide a promising route to flexible digital circuits for classes of applications whose performance requirements cannot be satisfied with organic semiconductors, amorphous silicon, or other related approaches.

Flexible Memristive Memory Array on Plastic Substrates

The demand for flexible electronic systems such as wearable computers, E-paper, and flexible displays has recently increased due to their advantages over present rigid electronic systems. Flexible memory is an essential part of electronic systems for data processing, storage, and communication and thus a key element to realize such flexible electronic systems. Although several emerging memory technologies, including resistive switching memory, have been proposed, the cell-to-cell interference issue has to be overcome for flexible and high performance nonvolatile memory applications. This paper describes the development of NOR type flexible resistive random access memory (RRAM) with a one transistor-one memristor structure (1T-1M). By integration of a high-performance single crystal silicon transistor with a titanium oxide based memristor, random access to memory cells on flexible substrates was achieved without any electrical interference from adjacent cells. The work presented here can provide a new approach to high-performance nonvolatile memory for flexible electronic applications.

A Hyper‐Stretchable Elastic‐Composite Energy Harvester

C. K. Jeong, G.-T. Hwang, D. Y. Park, J. H. Park, Dr. M. Byun, Prof. K. J. Lee Department of Materials Science and Engineering Korea Advanced Institute of Science and Technology (KAIST) 291 Daehak-ro , Yuseong-gu , Daejeon 305-701 , South Korea E-mail: keonlee@kaist.ac.kr Dr. J. Lee, Dr. S. Han, Prof. S. H. Ko Department of Mechanical Engineering Seoul National University 1 Gwanak-ro , Gwanak-gu , Seoul 151-742 , South Korea E-mail: maxko@snu.ac.kr Dr. J. Lee, Prof. S. S. Lee Department of Mechanical Engineering Korea Advanced Institute of Science and Technology (KAIST) 291 Daehak-ro , Yuseong-gu , Daejeon 305-701 , South Korea Dr. J. Ryu Functional Ceramic Group Korea Institute of Materials Science (KIMS) 797 Changwon-daero Seongsan-gu Changwon , Gyeongsangnam-do 642–831 , South Korea