Jiyoung Oh

Ultrathin Film Encapsulation of an OLED by ALD

Fabrication of barrier layers on a PES film and an organic light emitting diode (OLED) based on a glass substrate by atomic layer deposition (ALD) have been carried out. Deposition of 30 nm of film on both sides of PES film at 90°C gave film MOCON value of The passivation performance of the double layer consisting of deposited by plasma-enhanced chemical vapor deposition and by ALD on the OLED has been investigated using the OLED based on a glass substrate. Preliminary life time of two pairs of double layer coated OLED to 65% of initial luminance was 600 h at the initial luminance of

Deep-level defect characteristics in pentacene organic thin films

Organic thin-film transistors using the pentacene as an active electronic material have shown the mobility of 0.8 cm2/V s and the grains larger than 1 μm. To study the characteristics of electronic charge concentrations and the interface traps of the pentacene thin films, the capacitance properties were measured in the metal/insulator/organic semiconductor structure device by employing the capacitance–voltage and deep-level transient spectroscopy (DLTS) measurements. Based on the DLTS measurements, the concentrations and the energy levels of hole and electron traps in the obtained pentacene films were formed to be approximately 4.2×1015 cm−3 at Ev+0.24 eV, 9.6×1014 cm−3 at Ev+1.08 eV, 6.5×1015  cm−3 at Ev+0.31 eV and 2.6×1014 cm−3 at Ec−0.69 eV.

Photolithography-Based Patterning of Liquid Metal Interconnects for Monolithically Integrated Stretchable Circuits

We demonstrate a new patterning technique for gallium-based liquid metals on flat substrates, which can provide both high pattern resolution (∼20 μm) and alignment precision as required for highly integrated circuits. In a very similar manner as in the patterning of solid metal films by photolithography and lift-off processes, the liquid metal layer painted over the whole substrate area can be selectively removed by dissolving the underlying photoresist layer, leaving behind robust liquid patterns as defined by the photolithography. This quick and simple method makes it possible to integrate fine-scale interconnects with preformed devices precisely, which is indispensable for realizing monolithically integrated stretchable circuits. As a way for constructing stretchable integrated circuits, we propose a hybrid configuration composed of rigid device regions and liquid interconnects, which is constructed on a rigid substrate first but highly stretchable after being transferred onto an elastomeric substrate. This new method can be useful in various applications requiring both high-resolution and precisely aligned patterning of gallium-based liquid metals.

Flexible Organic LED and Organic Thin-Film Transistor

In this paper, a plastic organic thin-film transistor (OTFT) with high mobility formed on the polymeric gate dielectrics is presented. Flexible organic LEDs (OLEDs) operated by an OTFT are fabricated with a novel lamination method and the results are also presented. Fabrication method and the performances of white (consisting of R, G, and B) OLEDs with high efficiency, stability, and good color purity are discussed.

Organic blue light emitting materials based on spirobifluorene

Abstract Spirobifluorene derivative, which is useful for obtaining small molecule or polymer blue light emitting materials, has been prepared. To improve the solubility of final materials, long alkoxy side chains were introduced to spirobifluorene moiety. Coupling reaction with biphenyl led to small molecule blue light emitting material. A polymer blue light emitting material was obtained through Ni(0) mediated polymerization. Using vacuum deposition and spin coating methods, small molecule and polymer light emitting devices were fabricated and their device characteristics were investigated. In this paper, the detailed preparation methods of small molecule and polymer materials, and the device characteristics will be discussed.

Facile one-step synthesis of magnesium-doped ZnO nanoparticles: optical properties and their device applications

In this study, magnesium-doped (Mg-doped) zinc oxide (ZnO) nanoparticles were successfully synthesized by a sonochemical process under mild conditions. The x-ray diffraction pattern indicated that the Mg-doped ZnO nanoparticles maintain a wurtzite structure without impurities. We observed a blue-shift of the bandgap of the Mg-doped ZnO nanoparticles as the Mg-doping ratio increased. We also fabricated thin-film transistor (TFT) devices with the doped-ZnO nanoparticles. Devices using Mg-doped ZnO nanoparticles as a channel layer showed insensibility to white-light irradiation compared with undoped ZnO TFTs.

Save energy on OLED lighting by a simple yet powerful technique

Due to the very low light extraction efficiency of conventional organic light-emitting diodes (OLEDs), the application of OLEDs for next-generation lighting remains limited. Therefore, in order to enhance the light extraction efficiencies that result in improving the luminous efficacy (LE, lm W−1) and external quantum efficiency (ηEQE, %) of OLEDs, three different geometrically profiled, negatively nanostructured periodic semi-pyramid polydimethylsiloxane (PDMS) layers are used to create a hole at depths of 500 nm, 650 nm, and 1000 nm; these are designated as the polymeric lighting extraction film (PLEF) I, PLEF II, and PLEF III, respectively. These layers are placed directly on the backside of the green emissive bottom-emitting OLED (BE-OLED) glass substrates as an outcoupling enhancement PLEF that improves the glass substrate/air interface. Through the simple combination with three different nanostructures on each green emissive BE-OLED, a maximum enhancement of up to 50% is achieved in the LE and ηEQE measured at the same brightness, which is 1.5 times higher than the reference green emissive BE-OLED without a PLEF. Therefore, global energy saving can be achieved through reducing the power consumption by up to 30% possibly estimated from LE using the integrated PLEFs.

Non-volatile organic ferroelectric memory transistors fabricated using rigid polyimide islands on an elastomer substrate

The authors fabricated stretchable organic ferroelectric memory transistors (OFMTs) on a polydimethylsiloxane substrate using rigid polyimide island structures. The OFMTs exhibited a field-effect mobility of 4 × 10−2 cm2 V−1 s−1 and a current on/off ratio of 105 with a notably low threshold voltage. Furthermore, our memory TFTs exhibit excellent mechanical stability, showing no noticeable change in electrical performance up to a large strain of 50%. These results indicated the feasibility of a promising device for stretchable electronic systems.

Flexible nonvolatile memory transistors using indium gallium zinc oxide-channel and ferroelectric polymer poly(vinylidene fluoride-co-trifluoroethylene) fabricated on elastomer substrate

The authors demonstrated flexible memory thin-film transistors (MTFTs) with organic ferroelectric polymer poly(vinylidene fluoride-co-trifluoroethylene) and an amorphous oxide semiconducting indium gallium zinc oxide channel on the elastomer substrates. The carrier mobility, memory on/off ratio, and subthreshold swing of the flexible MTFTs showed 21 cm2V−1s−1, 107, and 0.5–1 V/decade, respectively. The memory window of 13 V at ±20 V programming was confirmed for the device without any interface layer. These obtained values did not significantly change when the substrate was bent with a radius of curvature of 10 mm. The memory on/off ratio was initially 5 × 104 and maintained at 102 even after a lapse of 3600 s. The fabricated MTFTs exhibited encouraging characteristics on the elastomer that are sufficient to realize mechanically flexible nonvolatile memory devices.

Organic–inorganic hybrid gate dielectric for solution-processed ZnO thin film transistors

The preparation of a hybrid dielectric film was carried out by blending sol–gel-derived sodium beta alumina (SBA) and poly(4-vinylphenol) (PVP) to enhance the capacitance of a gate dielectric film. PVP-SBA was cured at a temperature sufficiently low enough to apply to a plastic substrate, while maintaining good electrical properties and uniformity. Addition of sol–gel-derived SBA improved the film density, resulting in good PVP-SBA thermal stability. The prepared PVP-SBA was used for high-performance aqueous solution-based ZnO transistors at 200 °C.