2018 iMiD, Busan, Korea

August 28 - 31, 2017 (Tue. - Fri.), Exhibition Center I, BEXCO 

Tandem structured 2-color micro-polymer light-emitting diodes (μ-PLEDs)

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

 Abstract

Recently organic light emitting diodes (OLED) displays have been selected for commercial mobile devices, curved TVs and Virtual Reality (VR) because of their advantages such as high contrast, high response speed, and wide viewing angle. Typically, OLED pixels are fabricated using thermal evaporation and shadow mask. However, using a shadow mask creates a limitation in implementing high-resolution pixels into the display panel. In order to achieve micronsize OLED pixels, many different approaches had been reported for patterning OLED layers into micron-size such as ink-jet printing, imprinting, and adopting orthogonal photo-resisit. however, created addition problems of luminance degradation, limited panel-size, or increased production costs. 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[1]. Using this mechanism, we could successfully fabricated a CMOS circuits with micron-patterned n- and p-type organic semiconductors through sequential solution processes based on standard photolithograph. Through, we confirmed the feasibility of fabrication various electron device by using a sol-gel process. In this paper, we fabricated 2-color PLEDs with micropatterns of light-emitting polymer semiconductor through sequential solution processes. Fig. 1. (a) shows the optical microscopy image of patterned pixels (20 μm×20 μm) of light-emitting polymer semiconductor that were fabricated by using standard photolithography and dry-etch processes. Fig. 1. (b) shows the electroluminescence (EL) operation of 2-color PLEDs with micropatterns of lightemitting polymer semiconductor. Finally, we confirmed that the maximum luminance of the tandem structured 2- color PLEDs was 140 cd/m2 at 8V. 

2018 iMiD, Busan, Korea

August 28 - 31, 2017 (Tue. - Fri.), Exhibition Center I, BEXCO 

Coplanar a-InGaZnO Thin Film Transistors with Photo-Patterned Ionic-Polymer Gate Dielectric

Dayoon Lee, Yongchan Kim, and Hojin Lee

 Abstract

Currently electrolyte-gated thin-film transistors (TFTs) have been actively studied due to their advantages of high-density carrier accumulation in the channel, ultra-low operation voltage, and low-temperature process. For patterning the electrolyte to be used as a gate dielectric, there have been many different approaches reported so far, such as ‘cut and stick’ method, aerosol printing process, or using additional mold to isolate the ionic liquid. However, most of previous methods have challenges on realizing micron-sized fine patterns. In this paper, we adopted photo-patternable ionic-polymer as a gate dielectric for coplanar TFT structures where the gate, source, and drain electrodes deposited by single lift-off process. After electrodes and a-InGaZnO active layer was patterned in sequence, photo-patternable ionic polymer dielectric was patterned using photo cross-linking reactions to UV light. The measured transfer characteristics of the fabricated TFTs are shown in Fig. 1. According to measurement results, we confirmed the high field-effect mobility (~4.36 cm²/V·s), high on-off ratio (~10⁶), and good sub-threshold swing (~108 mV/decade) could be achieved at drain voltage of 1V.

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.

2017 SPIE Photonics West, San Francisco, USA

January 28 - February 2, 2017 (Sat - Thu), The Moscone Center

<Oral Session : Session 1: THz Sources and Detectors I>

Polarization dependent resonance manipulation by terahertz meta-molecules 

Hyunseung Jung, Eunah Heo, Jaemok Koo, Chihun In, Hyunyong Choi, Moon Sung Kang, and Hojin Lee

 Abstract

In this study, we propose polarization dependent resonance manipulation by meta-molecules at terahertz frequencies. The proposed meta-molecules are combined with various numbers of H-shaped meta-atoms, which we refer as ‘moleculization’ of meta-atoms. We confirm that the laterally moleculized H-shaped meta-molecules successfully realize the unique properties that can modulate the resonance frequency for the specific polarization of an incident wave, while can keep one identical resonance frequency for their orthogonal polarization direction, simultaneously. Moreover, for the vertically moleculized H-shaped meta-molecules, we also find that the electromagnetically induced transparency (EIT) –like phenomenon can be achieved for the specific polarization direction, with their exceptional field enhancement properties.

2017 SPIE Photonics West, San Francisco, USA

January 28 - February 2, 2017 (Sat - Thu), The Moscone Center

<Oral Session : Session 7: RF-Submillimeter-Wave II>

Wireless chemical sensor system based on electromagnetically energy-harvesting metamaterials

Wonwoo Lee, Yonghee Jung, Hyunseung Jung, and Hojin Lee

 Abstract

We propose a novel wireless chemical sensor system by using energy-harvesting metamaterials at microwave frequencies. The proposed metamaterial sensor consists of a single split ring resonator and rectifier circuit for harvesting the energy at the specific frequency. We confirmed that the concentration of ethanol mixed with water can be detected by the proposed sensor by resonance property between the source antenna and the metamaterial which induces the variation in the energy-harvesting rate of our sensor system. Finally, we expect that our metamaterial-based wireless sensor can pave the way to the miniaturized wireless sensor systems including biochemical and dielectric environment sensors.