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.

Aug 19 - 23, 2018 (Sun - Thu), San Diego Convention Center

<Poster Session>

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

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

 Abstract

In this study, we proposed a tandem structured 2-color micro-polymer light-emitting diodes (μ-PLEDs) for super high-resolution organic light-emitting diodes (OLEDs) micro displays. The proposed 2-color polymer light-emitting diodes consisted of red and green colored polymers patterned to 20 μm. For the tandem structure, we adopted the recently developed 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. Experimental results showed that we could achieve the maximum luminance of the tandem structured 2-color PLEDs up to 140 cd/m² at 8V

2018 SPIE Optics + Photonics, San Diego, United States

Aug 19 - 23, 2018 (Sun - Thu), San Diego Convention Center

<Oral Session>

Electrically controlled terahertz funneling for electromagnetically induced transparency analogue

Hyunseung Jung, Hyunwoo Jo, Wonwoo Lee, Moon Sung Kang, and Hojin Lee

 Abstract

In this study, we propose an electrically switchable funneling of terahertz waves for electrically induced transparency (EIT) analogue by actively controllable metamaterial. The proposed EIT metamaterials consist of the orthogonally combined metallic cut-wire (CW) pair and pseudo complimentary cut-wire (CCW), where graphene lines are laid on the center of pseudo-CCW to control the funneling of terahertz waves at the transmission resonance of the EIT structure by using ion-gel coplanar gating system. In experimental results, we successfully show the modulation depth of 54.9% and the group delay change by 1 ps at the transmission peak of our EIT analogue.

2018 SPIE Photonics West, San Francisco, United States

January 29 - February 1, 2018 (Mon - Thur), The Moscone Center

<Oral Session>

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

Dayoon Lee, Yongchan Kim, and Hojin Lee

 Abstract

We propose novel solution-processed coplanar amorphous indium-gallium-zinc-oxide (a-InGaZnO) thin-film transistors (TFTs) with photo-patterned ionic-polymer gate dielectric. We fabricated and measured the electrical characteristics of our coplanar TFTs, and confirmed the high field-effect mobility (~ 4.36 cm-2/V·s), high on-off ratio (~ 107) and good electrical stability. Based on the developed coplanar a-InGaZnO TFTs, we also have designed and fabricated a NMOS inverter with clear signal inversion for flexible electronics and sensor applications. Through this study, we expect that highly flexible and transparent advanced analog circuits and systems can be realized based on the proposed solution processible coplanar TFTs for human-machine interactions.