IMID 2019, Gyeongju, Korea

August 27 - 30, 2019 (Tue. - Fri.), HICO

Micropatterned polymer light-emitting diodes (μ-PLEDs) based on Orthogonal Polymer Semiconductors

Kyun-Yeong Choi, Han Wool Park, Do Hwan Kim, and Hojin Lee

Abstract

  In this paper, a micro-patterned 2-color OLED was fabricated through a sequential solution process based on standard photolithography. Previously, we

developed a sol-gel process to obtain the orthogonality of organic semiconductor against the solvents and chemicals so that we could apply the standard photo-lithography and dry-etch process to achieve micron-size patterns of light-emitting polymers with MEH-PPV and F8T2-based orthogonal polymer semiconductor gel (OPSG) through sequential solution processes.

2016 iMiD, Jeju, Republic of Korea

August 24 - 26, 2016 (Wed - Fri), ICC Jeju

<Oral Session : 60. Driving Circuit and Panel Design>

Low-Dropout Regulator based on a-InGaZnO Thin-Film Transistor for Display Driving Systems

Yongchan Kim, Hojin Lee

Abstract

Among various thin-film transistor (TFT) technologies developed so far for integrating the display driving system onto TFT arrays and, therefore, to eliminate the IC assembly, amorphous Indium-Gallium-Zinc-Oxide (a-InGaZnO) TFTs have shown favorable electrical characteristics to achieving the integrated driving circuitry. Previously, we had demonstrated a fully adaptive DC-DC converter circuit could be built with a-InGaZnO TFT based operational amplifier (op-amp). However, in order to make the adaptive DC-DC converter functional, it required an external circuit block made of commercial passive devices on a printed circuit board (PCB). Different from the reported DC-DC converter, Low-Dropout (LDO) regulators are well known to have simple structures with small occupied area, accurate output voltages, and low output ripples. In this paper, we designed a fully integrated LDO regulator on glass substrate for supplying the designated power to display systems.

2018 CLEO, San Jose, United States

May 13 - 17, 2018 (Mon - Fri), San Jose Convention Center

<Oral Session>

Electrically Controllable Reconfiguration of Terahertz Meta-Atoms into Meta-Molecules

Hyunseung Jung, Jaemok Koo, Wonwoo Lee, Moon Sung Kang, and Hojin Lee

 Abstract

We report structural methodology for electrically switchable terahertz metamaterials between atom- and molecule-states by using limited conductance variation of graphene bridges. Based on experimental verification, we confirmed 39% of wide resonance tuning of terahertz metamaterials.

PIERS 2023, Prague, Czech

July 3 - July 6, 2023 (Mon. - Thur.), Prague Congress Center

Patch-Type Electromagnetic Wave Focusing Metasurface for Wireless Power Transfer in Bio-Implantable Devices 

Wonwoo LEE, Semin Jo, and Hojin Lee

Abstract

 With the advances in biomedical technologies, convenient, long-term operable, and sustainable implantable devices are required to be used within the human body, including drug delivery, stimulators, sensors, and post-stimulation monitoring. In general, batteries are used as power sources in these implantable devices, but bioimplantable devices using batteries have challenges in limited lifetime, bulky size, and need for replacement that essentially requires surgical operations. In this regard, wireless power transfer systems (WPT) have been employed as alternatives method to eliminate the use of battery and inevitable surgery for replacement. Recently, WPT systems using metasurfaces exhibiting exotic electromagnetic (EM) characteristics were introduced in bioimplantable devices to enhance the efficiency and to reduce the geometrical dimension. Herein, we propose a patch-type metasurface that improves the power transmission to the tissue by reducing the reflection loss of electromagnetic waves at the air–skin interface and forming a focal point at a specific location. The subwavelength-thickness (< λ/10) metasurface is introduced that focuses electromagnetic waves to a desired depth in multilayered biological tissues to enhance the transferred power for implantable devices. The stable focusing performance is demonstrated by confirming the robust focal point and field intensity profiles for varying incident angles and polarization directions with enhanced field of approximately 11.1 dBmV at a depth of 10 mm in in-vitro environment. By applying the patch-type metasurface to an actual wireless power transfer system, transmission coefficient is improved by 6.37 dB at a depth of 10 mm compared with that of a system without the metasurface patch.

SID Display Week 2023, Los Angeles, USA

May 22 - May 26, 2023 (Mon. - Fri.), Los Angeles Convention Center

Ultra-high Resolution Full-Color OLEDs Patterned by Photo-Lithography

Ryungyu Lee, Keun-Yeong Choi, Hyukmin Kweon, Borina Ha, Do Hwan Kim, and Hojin Lee

Abstract

   In this paper, we present an ultra-high resolution organic light-emitting diodes (OLEDs) pixels patterned by conventional photo-lithography via imbuing high chemical and physical resistance to commercial light-emitting polymers through the silicon networked orthogonal gel process. Especially, when silicon networked orthogonal polymers gel layers are pattered by reactive ion etch, a in-situ non-volatile etch-blocking layer (EBL) is formed to prevent pattern distortion or damage. This unique feature not only slows the etch rate but also enhances the anisotropy of etch direction, leading to achieve ultra-high resolution multicolor OPSG-based OLED patterns (up to 4,500 pixels per inch) through photolithography. This patterning strategy is expected to provide a novel paradigm toward ultrahigh-resolution OLED microdisplays.