Junhee Cho - Academia.edu (original) (raw)

Papers by Junhee Cho

Research paper thumbnail of Stretchable Low Resistance Thick Silver Electrode on Poly(dimethylsiloxane) Compliant Elastomeric Substrate

Japanese Journal of Applied Physics, 2010

In this paper, we demonstrated a stretchable, low resistive thick silver electrode directly depos... more In this paper, we demonstrated a stretchable, low resistive thick silver electrode directly deposited on a roughened poly(dimethylsiloxane) (PDMS) substrate and analyzed its surface crack evolution under the tensile stress. Improvement in the stretching property of the electrode was explained by analyzing changes in the stress distribution when the surface roughness is introduced on the PDMS substrate. It was found

Research paper thumbnail of All-Inkjet-Printed Organic Thin-Film Transistors with Silver Gate, Source/Drain Electrodes

Japanese Journal of Applied Physics, 2011

We report high-performance all-inkjet-printed organic thin-film transistors (OTFTs), where inkjet... more We report high-performance all-inkjet-printed organic thin-film transistors (OTFTs), where inkjet-printed silver electrodes, cross-linked poly(4-vinylphenol) (PVP) and 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) were used as gate/source/drain electrodes, a gate dielectric layer and an active semiconductor layer, respectively. To evaluate quality of the active semiconductor layer, we also fabricated OTFTs by using spin-coating and drop-casting methods for TIPS-pentacene layer on the inkjet-printed PVP gate dielectric layer. Comparable TFT electrical performances were obtained and well-crystallized TIPS-pentacene layer was formed for all cases. All TIPS-pentacene OTFTs show lower sub-threshold swing values than OTFTs with an evaporated pentacene active semiconductor layer on the inkjet-printed PVP gate dielectric layer. By using optimized inkjet-printing conditions, we obtained mobility of 0.06 cm2 V-1 s-1 and on/off ratio of 104 for all-inkjet-printed OTFT.

Research paper thumbnail of Stable Stretchable Silver Electrode Directly Deposited on Wavy Elastomeric Substrate

IEEE Electron Device Letters, 2009

We demonstrated a stable operation of stretchable silver (Ag) electrodes under fast cycling strai... more We demonstrated a stable operation of stretchable silver (Ag) electrodes under fast cycling strain stress conditions. Relatively thick Ag electrodes (700 nm) were directly deposited on an elastomeric polydimethylsiloxane (PDMS) substrate with vertical wavy patterns that were formed by using an aluminum mold. The large surface roughness of PDMS substrate that was transferred from an intentionally roughened mold surface enhanced the adhesion between thick electrode and PDMS layer. Top PDMS layer was coated on the Ag electrode for encasement. During a slow stretching test (16.7 μm/s), the resistance of the Ag electrode on the wavy substrate was increased only by three times for 50% tensile strain. The change in Ag electrode resistance was monitored during 10 000 times of fast (1 mm/s) cycling of 10% tensile strain. The maximum resistance was increased by less than five times during the stress test and returned to its initial value after the stress was removed.

Research paper thumbnail of Effect of Cadmium Arachidate Layers on the Growth of Pentacene and the Performance of Pentacene-Based Thin Film Transistors

Langmuir, 2009

The effect of cadmium arachidate (CdA) layers deposited by Langmuir-Blodgett technique on the gro... more The effect of cadmium arachidate (CdA) layers deposited by Langmuir-Blodgett technique on the growth of pentacene thin films and the performance of pentacene-based thin film transistors has been investigated. The hydrophobicity of the SiO2 gate dielectric surface was increased (surface energy reduced) with the deposition of CdA layers as a result of the presence of long hydrophobic alkyl chains attached to the cadmium atoms. The change in surface wetting properties of SiO2 strongly influenced the growth mechanism of pentacene thin films. The grain size and root-mean-square surface roughness of pentacene was decreased with an increase in the number of CdA layers compared to the pentacene deposited on a bare SiO2 surface. Organic thin film transistors (OTFTs) with seven layers of CdA on SiO2 showed the highest mobility of 0.27 cm2/Vs and the lowest subthreshold slope of 2.4 V/dec. The enhanced electrical properties of the OTFTs with SiO2/CdA as the dielectric is attributed to the better intermolecular connection, tight packing, and improved surface quality of the pentacene, as evident from the X-ray diffraction (XRD) and atomic force microscopy (AFM) results.

Research paper thumbnail of Inkjet-Printed Silver Gate Electrode and Organic Dielectric Materials for Bottom-Gate Pentacene Thin-Film Transistors

Journal of The Korean Physical Society, 2009

Gallium doped zinc oxide (GZO) thin films have been prepared by a simple sol-gel spin coating tec... more Gallium doped zinc oxide (GZO) thin films have been prepared by a simple sol-gel spin coating technique. XRD results showed the preferential c-axis orientation of the crystallites and the presence of the wurtzite phase of ZnO. A lowest resistivity of 3.3 × 10 −3 cm was obtained for the ZnO film doped with 2 at% of Ga after post-annealing at 500 • C for 45 min in a H 2 atmosphere. All the films showed more than 80% of transparency in the entire visible region. Blue shifting of the optical band gap was observed with an increase in Ga doping, which can be explained on the basis of the Burstein-Moss effect. OLED devices were fabricated using 2 at% Ga-doped ZnO thin films as anodes. Preliminary results obtained demonstrated that spin-coated GZO films can be used as a promising TCO for optoelectronic device applications.

Research paper thumbnail of Stretchable Low Resistance Thick Silver Electrode on Poly(dimethylsiloxane) Compliant Elastomeric Substrate

Japanese Journal of Applied Physics, 2010

In this paper, we demonstrated a stretchable, low resistive thick silver electrode directly depos... more In this paper, we demonstrated a stretchable, low resistive thick silver electrode directly deposited on a roughened poly(dimethylsiloxane) (PDMS) substrate and analyzed its surface crack evolution under the tensile stress. Improvement in the stretching property of the electrode was explained by analyzing changes in the stress distribution when the surface roughness is introduced on the PDMS substrate. It was found

Research paper thumbnail of All-Inkjet-Printed Organic Thin-Film Transistors with Silver Gate, Source/Drain Electrodes

Japanese Journal of Applied Physics, 2011

We report high-performance all-inkjet-printed organic thin-film transistors (OTFTs), where inkjet... more We report high-performance all-inkjet-printed organic thin-film transistors (OTFTs), where inkjet-printed silver electrodes, cross-linked poly(4-vinylphenol) (PVP) and 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-pentacene) were used as gate/source/drain electrodes, a gate dielectric layer and an active semiconductor layer, respectively. To evaluate quality of the active semiconductor layer, we also fabricated OTFTs by using spin-coating and drop-casting methods for TIPS-pentacene layer on the inkjet-printed PVP gate dielectric layer. Comparable TFT electrical performances were obtained and well-crystallized TIPS-pentacene layer was formed for all cases. All TIPS-pentacene OTFTs show lower sub-threshold swing values than OTFTs with an evaporated pentacene active semiconductor layer on the inkjet-printed PVP gate dielectric layer. By using optimized inkjet-printing conditions, we obtained mobility of 0.06 cm2 V-1 s-1 and on/off ratio of 104 for all-inkjet-printed OTFT.

Research paper thumbnail of Stable Stretchable Silver Electrode Directly Deposited on Wavy Elastomeric Substrate

IEEE Electron Device Letters, 2009

We demonstrated a stable operation of stretchable silver (Ag) electrodes under fast cycling strai... more We demonstrated a stable operation of stretchable silver (Ag) electrodes under fast cycling strain stress conditions. Relatively thick Ag electrodes (700 nm) were directly deposited on an elastomeric polydimethylsiloxane (PDMS) substrate with vertical wavy patterns that were formed by using an aluminum mold. The large surface roughness of PDMS substrate that was transferred from an intentionally roughened mold surface enhanced the adhesion between thick electrode and PDMS layer. Top PDMS layer was coated on the Ag electrode for encasement. During a slow stretching test (16.7 μm/s), the resistance of the Ag electrode on the wavy substrate was increased only by three times for 50% tensile strain. The change in Ag electrode resistance was monitored during 10 000 times of fast (1 mm/s) cycling of 10% tensile strain. The maximum resistance was increased by less than five times during the stress test and returned to its initial value after the stress was removed.

Research paper thumbnail of Effect of Cadmium Arachidate Layers on the Growth of Pentacene and the Performance of Pentacene-Based Thin Film Transistors

Langmuir, 2009

The effect of cadmium arachidate (CdA) layers deposited by Langmuir-Blodgett technique on the gro... more The effect of cadmium arachidate (CdA) layers deposited by Langmuir-Blodgett technique on the growth of pentacene thin films and the performance of pentacene-based thin film transistors has been investigated. The hydrophobicity of the SiO2 gate dielectric surface was increased (surface energy reduced) with the deposition of CdA layers as a result of the presence of long hydrophobic alkyl chains attached to the cadmium atoms. The change in surface wetting properties of SiO2 strongly influenced the growth mechanism of pentacene thin films. The grain size and root-mean-square surface roughness of pentacene was decreased with an increase in the number of CdA layers compared to the pentacene deposited on a bare SiO2 surface. Organic thin film transistors (OTFTs) with seven layers of CdA on SiO2 showed the highest mobility of 0.27 cm2/Vs and the lowest subthreshold slope of 2.4 V/dec. The enhanced electrical properties of the OTFTs with SiO2/CdA as the dielectric is attributed to the better intermolecular connection, tight packing, and improved surface quality of the pentacene, as evident from the X-ray diffraction (XRD) and atomic force microscopy (AFM) results.

Research paper thumbnail of Inkjet-Printed Silver Gate Electrode and Organic Dielectric Materials for Bottom-Gate Pentacene Thin-Film Transistors

Journal of The Korean Physical Society, 2009

Gallium doped zinc oxide (GZO) thin films have been prepared by a simple sol-gel spin coating tec... more Gallium doped zinc oxide (GZO) thin films have been prepared by a simple sol-gel spin coating technique. XRD results showed the preferential c-axis orientation of the crystallites and the presence of the wurtzite phase of ZnO. A lowest resistivity of 3.3 × 10 −3 cm was obtained for the ZnO film doped with 2 at% of Ga after post-annealing at 500 • C for 45 min in a H 2 atmosphere. All the films showed more than 80% of transparency in the entire visible region. Blue shifting of the optical band gap was observed with an increase in Ga doping, which can be explained on the basis of the Burstein-Moss effect. OLED devices were fabricated using 2 at% Ga-doped ZnO thin films as anodes. Preliminary results obtained demonstrated that spin-coated GZO films can be used as a promising TCO for optoelectronic device applications.