Hyeon Gyun Yoo

Performance Enhancement of Electronic and Energy Devices via Block Copolymer Self‐Assembly

The use of self-assembled block copolymers (BCPs) for the fabrication of electronic and energy devices has received a tremendous amount of attention as a non-traditional approach to patterning integrated circuit elements at nanometer dimensions and densities inaccessible to traditional lithography techniques. The exquisite control over the dimensional features of the self-assembled nanostructures (i.e., shape, size, and periodicity) is one of the most attractive properties of BCP self-assembly. Harmonic spatial arrangement of the self-assembled nanoelements at desired positions on the chip may offer a new strategy for the fabrication of electronic and energy devices. Several recent reports show the great promise in using BCP self-assembly for practical applications of electronic and energy devices, leading to substantial enhancements of the device performance. Recent progress is summarized here, with regard to the performance enhancements of non-volatile memory, electrical sensor, and energy devices enabled by directed BCP self-assembly.

Flexible One Diode-One Phase Change Memory Array Enabled by Block Copolymer Self-Assembly

Flexible memory is the fundamental component for data processing, storage, and radio frequency communication in flexible electronic systems. Among several emerging memory technologies, phase-change random-access memory (PRAM) is one of the strongest candidate for next-generation nonvolatile memories due to its remarkable merits of large cycling endurance, high speed, and excellent scalability. Although there are a few approaches for flexible phase-change memory (PCM), high reset current is the biggest obstacle for the practical operation of flexible PCM devices. In this paper, we report a flexible PCM realized by incorporating nanoinsulators derived from a Si-containing block copolymer (BCP) to significantly lower the operating current of the flexible memory formed on plastic substrate. The reduction of thermal stress by BCP nanostructures enables the reliable operation of flexible PCM devices integrated with ultrathin flexible diodes during more than 100 switching cycles and 1000 bending cycles.

Electrical Biomolecule Detection Using Nanopatterned Silicon via Block Copolymer Lithography

An electrical biosensor exploiting a nanostructured semiconductor is a promising technology for the highly sensitive, label-free detection of biomolecules via a straightforward electronic signal. The facile and scalable production of a nanopatterned electrical silicon biosensor by block copolymer (BCP) nano-lithography is reported. A cost-effective and large-area nanofabrication, based on BCP self-assembly and single-step dry etching, is developed for the hexagonal nanohole patterning of thin silicon films. The resultant nanopatterned electrical channel modified with biotin molecules successfully detects the two proteins, streptavidin and avidin, down to nanoscale molarities (≈1 nm). The nanoscale pattern comparable to the Debye screening length and the large surface area of the three-dimensional silicon nanochannel enable excellent sensitivity and stability. A device simulation confirms that the nanopatterned structure used in this work is effective for biomolecule detection. This approach relying on the scalable self-assembly principle offers a high-throughput manufacturing process for clinical lab-on-a-chip diagnoses and relevant biomolecular studies.

Flexible one diode–one resistor resistive switching memory arrays on plastic substrates

Resistive random access memory (RRAM) has been developed as a promising non-volatile memory on plastic substrates for flexible electronic systems owing to its advantages of simple structure and low temperature process. Memory plays an important role in electronic systems for data processing, information storage, and communication, thus flexible memory is an indispensable element to implement flexible electronics. However, cell-to-cell interference existing in a flexible memory array leads to not only undesired power consumption but also a misreading problem, which has been a big hindrance for practical flexible memory application. This paper describes the development of a fully functional flexible one diode–one resistor RRAM device. By integrating high-performance single crystal silicon diodes with plasma-oxidized resistive memory, cell-to-cell interference between adjacent memory cells is effectively prevented, and random access operation of the 1D–1R flexible memory device is successfully achieved on a flexible substrate. The work presented here could provide a useful methodology to realize flexible non-volatile memory with high packing density for flexible electronic applications.

Simultaneous Roll Transfer and Interconnection of Flexible Silicon NAND Flash Memory.

Ultrathin silicon-based flexible 16 × 16 NAND flash memory (f-NAND) is demonstrated utilizing roll-to-plate packaging. The roll-based thermo-compression bonding of the anisotropic conductive film (ACF) transfers and simultaneously interconnects the f-NAND on a flexible printed circuit board. Reliable circuitry operation of the 16 × 16 f-NAND is confirmed with excellent flexibility and stable ACF interconnections.

Flexible GaN LED on a Polyimide Substrate for Display Applications

The flexible GaN-based light emitting diode (LED) has been fabricated on a plastic substrate for flexible display applications. The epitaxial structures of the GaN LED arrays are transferred onto a flexible substrate using standard soft lithography technology and connected to a source-meter by metal lines. To verify the mechanically and optically stable characteristics of the GaN LEDs on the flexible substrates, the electrical properties are characterized during 2000 bending cycles at various bending radius. A white light-emitting phosphor-coated GaN LED shows its potential as a next-generation flexible light source.

Nanotransplantation Printing of Crystallographic-Orientation-Controlled Single-Crystalline Nanowire Arrays on Diverse Surfaces

The fabrication of a highly ordered array of single-crystalline nanostructures prepared from solution-phase or vapor-phase synthesis methods is extremely challenging due to multiple difficulties of spatial arrangement and control of crystallographic orientation. Herein, we introduce a nanotransplantation printing (NTPP) technique for the reliable fabrication, transfer, and arrangement of single-crystalline Si nanowires (NWs) on diverse substrates. NTPP entails (1) formation of nanoscale etch mask patterns on conventional low-cost Si via nanotransfer printing, (2) two-step combinatorial plasma etching for defining Si NWs, and (3) detachment and transfer of the NWs onto various receiver substrates using an infiltration-type polymeric transfer medium and a solvent-assisted adhesion switching mechanism. Using this approach, high-quality, highly ordered Si NWs can be formed on almost any type of surface including flexible plastic substrates, biological surfaces, and deep-trench structures. Moreover, NTPP provides controllability of the crystallographic orientation of NWs, which is confirmed by the successful generation of (100)- and (110)-oriented Si NWs with different properties. The outstanding electrical properties of the NWs were confirmed by fabricating and characterizing Schottky junction field-effect transistors. Furthermore, exploiting the highly flexible nature of the NWs, a high-performance piezoresistive strain sensor, with a high gauge factor over 200 was realized.

ACF-packaged ultrathin Si-based flexible NAND flash memory

In this paper, we demonstrate an ACF-packaged ultrathin Si-based flexible NAND flash memory by adopting a simple method, without using a conventional transfer process. By gently etching the bottom sacrificial silicon of the SOI wafer, flip-chip bonded devices were sufficiently thinned down (roughly to 1 μm) to fabricate highly flexible, fully packaged Si-based NAND flash memory, without any cracks or wrinkles. The work presented here suggests a useful methodology to realize various high-performance, fully packaged Si-based flexible LSI devices.