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Research

Research Fields

Flexible optoelectronics
Self-powered energy
Flexible drug delivery
Laser-material interaction
Flexible LSI & Memristor
Flexible Piezo Sensor

 

      Flexible Large Scale Integration (f-LSI)

    

    Silicon-based semiconductors have played significant roles of signal processing, nerve stimulation, memory storage, and wireless communication in implantable electronics. However, the rigid and bulky LSI chips have limited its uses in invivo and flexible devices.

     We has developed silicon-based flexible large scale integrated circuits (LSI) for bio-medical applications.We fabricated flexible LSI  interconnected with thousand nano-transistors on silicon wafer by state-of-the-art 0.18 CMOS process, and then the entire bottom substrate except top 100 nm active circuit layer was removed by wet chemical etching. This work could provide an approach to flexible LSI for an ideal artificial retina system and other bio-medical devices. Also the result represents an exciting technology with the strong potential to realize fully flexible consumer electronics such as application processor (AP) for mobile operating system, high-capacity memory, wireless communication in the near future.

  • Related References

"Simultaneous Roll Transfer and Interconnection of Flexible silicon NAND Flash Memory" Adv. Mater., 28, 8371, 2016 PDF, [IF=19.8]

"ACF Packaged Flexible NAND Flash Memory" IEDM, Washington DC, 19.3, 1, 2015 PDF

"Flexible Crossbar Resistive Memory Arrays via Inorganic-based Laser Lift-off "  Adv. Mater., 26, 7480, 2014  PDF, [IF=19.8]

"In vivo Silicon-Based Flexible Radio Frequency Integrated Circuits Monolithically Encapsulated with Bio-compatible Liquid Crystal Polymers" ACS Nano, 7(5), 4545, (2013).  PDF  [IF=13.9]

   Flexible ACF packaging

 

  Flexible inorganic electronics including LSI and optoelectronics have attracted great attention owing to their merits such as low weight, high portability, low fragility, and high performance. In contrast to the outstanding achievement of active device level researches, however, there still remains a critical issue to develop packaging technology for commercializing flexible devices including electrical interconnections, mechanical protection, and power distribution during bending conditions. We have developed innovative flexible packaging technology using flip-chip (FC) bonding with anisotropic conductive film (ACF) as an elastic and resilient packaging materials. In 2014, our group demonstrated flexible optoelectronics of GaAs light-emitting diode (LED) interconnected by ACF technology to a plastic substrate.  Additionally, we introduced fully-packaged Si-based flexible NAND flash memory, presented in International Electron Device Meetings (IEDM, 2015), which showed stable flexible interconnection in various stress conditions and reliable bending operations.

  • Related References

"ACF Packaged Flexible NAND Flash Memory" IEDM, Washington DC, 19.3, 1, 2015 PDF

"Self-powered Fully-Flexible Light Emitting Systems enabled by Flexible Energy Harvester", Energy Environ. Sci., 7(12), 4035, 2014, PDF[IF=29.5]

    Flexible Memory

        

        Memory is an essential part in electronic systems, as it is used for data processing, information storage and communication with external devices. Therefore, the development of flexible memory has been a challenge to the realization of flexible electronics.

        We have developed the first fully functional flexible non-volatile resistive random access memory (RRAM) where a memory cell can be randomly accessed, written, and erased on a plastic substrate. Our flexible memory  is not affected by cell-to-cell interference, through integrating a memristor with a high-performance single-crystal silicon transistor on flexible substrates. Combining these advanced technologies, we successfully demonstrated that all memory functions in a matrix memory array (writing/reading/erasing) worked perfectly.

  • Related References

"Flexible Phase Change Memory Array"  ACS Nano, 9, 4120, 2015, PDF  [IF=13.9]

"Flexible Crossbar Resistive Memory Arrays via Inorganic-based Laser Lift-off "  Adv. Mater., 26, 7480, 2014,  PDF, Cover Article.[IF=19.8]

"Flexible Memristive Memory Array on Plastic Substrates", Nano Letters, 11(12) , 5438 (2011). PDF [IF=12.7]

"Flexible One Diode-One Resistor Resistive Switching Memory Arrays on Plastic Substrates" RSC Advances  4(38), 20017, 2014. PDF [IF=3.1]

    Neuromorphic Computing

  KAIST 융합프로젝트: Neuromorphic Electronic Brain (인간 뇌모방 전자두뇌 개발)

  Current computer is a fast computing machine, not a thinking device like our brain capable of intelligent recognition. Some brain functions such as speech recognition have often been emulated by computers, but the way they are implemented on computers is inherently different from the way the brain realizes these functions. The brain is a vast array of neurons and synapses. Each neuron receives stimuli from adjacent neurons connected through synapses; once a neuron is adequately stimulated, it in turn stimulates (or fires) other neurons that it connects to. The way a set of neurons is connected through synapses and how they stimulate other neurons determines a particular function.

  Our research goal is to discover the best way of realizing neurons and synapses, and how to extract the connections and firing rules for each particular target function. This can be done collaboration including memristors (synapses), devices and circuits (neurons), algorithms (connections and firing rules), and systems (target functions). Especially, we focused on memristor based neuromorphic computing system, emulating the potentiation and depression process based on identical pulses called Spike-timing dependent plasticity (STDP). Our memristor-based synapse show gradual resistance transition between Low Resistance State (LRS) to High Resistance State (HRS) which is essential for multi-level cell (MLC) behavior needed for complex neuromorphic computing.

  • Related References

"Reliable Memristive-Switching Memory Devices Enabled by Densely-Packed Silver Nanocone Arrays as Electric-Field Concentrators" ACS Nano, 10, 9478, 2016.  PDF  [IF=13.9]

"Self-Structured Conductive Filament Nanoheater for Phase Change Memory" ACS Nano, 9, 6587, 2015.  PDF  [IF=13.9]

"Reliable Control of Filament Formation in Resistive Memories by Self-assembled Nano-insulators Derived from a Block Copolymer"  ACS Nano, 8, 9492, 2014, PDF. [IF=13.9]

"Flexible Crossbar Resistive Memory Arrays via Inorganic-based Laser Lift-off "  Adv. Mater., 26, 7480, 2014,  PDF, [IF=19.8]

"Self-assembled Incorporation of Modulated Block Copolymer Nanostructures in Phase-change Memory for Switching Power Reduction", ACS Nano, 7(3), 2651, (2013). PDF  [IF=13.9]

"Flexible Memristive Memory Array on Plastic Substrates", Nano Letters, 11(12) , 5438 (2011). PDF  [IF=12.7]