Origin of multi-level switching and telegraphic noise in organic nanocomposite memory devices.

The origin of negative differential resistance (NDR) and its derivative intermediate resistive states (IRSs) of nanocomposite memory systems have not been clearly analyzed for the past decade. To address this issue, we investigate the current fluctuations of organic nanocomposite memory devices with NDR and the IRSs under various temperature conditions. The 1/f noise scaling behaviors at various temperature conditions in the IRSs and telegraphic noise in NDR indicate the localized current pathways in the organic nanocomposite layers for each IRS. The clearly observed telegraphic noise with a long characteristic time in NDR at low temperature indicates that the localized current pathways for the IRSs are attributed to trapping/de-trapping at the deep trap levels in NDR. This study will be useful for the development and tuning of multi-bit storable organic nanocomposite memory device systems

Substrate thermal conductivity effect on heat dissipation and lifetime improvement of organic light-emitting diodes

We report substrate thermal conductivity effect on heat dissipation and lifetime improvement of organic light-emitting diodes (OLEDs). Heat dissipation behavior of top-emission OLEDs fabricated on silicon, glass, and planarized stainless steel substrates was measured by using an infrared camera. Peak temperature measured from the backside of each substrate was saturated to be 21.4, 64.5, and 40.5 °C, 180 s after the OLED was operated at luminance of 10 000 cd/m2 and 80% luminance lifetime was about 198, 31, and 96 h, respectively. Efficient heat dissipation through the highly thermally conductive substrates reduced temperature increase, resulting in much improved OLED lifetime.This work supported by the Korea Research Foundation Grant funded by the Korean Government (MOEHRD, Basic Research Promotion Fund) (Grant No. KRF-2008-331-D00216)

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

An inkjet-printed silver electrode and a spin-coated cross-linked poly(4-vinylphenol)(PVP) dielectric layer were used as a gate electrode and a gate insulator for a bottom-gate pentacene thin-film transistor (TFT), respectively. The printing and the curing conditions of the printed silver electrode were optimized and tested on various substrates, such as glass, silicon, silicon dioxide, polyethersulfone, polyethyleneterephthalate, polyimide and polyarylate, to produce a good sheet resistance of 0.2 $\sim$ 0.4 $\Omega$/$\square$ and a good surface roughness of 2.38 nm in RMS value and 20.14 nm in peak-to-valley (P2V) value, which are very similar to those of conventionally-sputtered indium-tin-oxide (ITO) or thermally-evaporated silver electrodes. The coated PVP layer of metal/PVP/metal devices showed a good insulation property of 10.4 nA/$\rm cm^{2}$ at 0.5 MV/cm. The PVP layer further reduced the surface roughness of the gate electrode to provide a good interface to the pentance layer. The pentacene TFT with a structure of glass/printed silver/PVP/pentacene/Au showed a good saturation region mobility of 0.13 $\rm cm^{2}$/Vs and a good on/off ratio of larger than 10$^{5}$, which are similar to the performance of a pentacene TFT with a conventional ITO gate electrode.This work was supported by \SystemIC2010" project of Korea Ministry of Knowledge Economy and by the Seoul R&BD Program (CRO70048)

25th annual computational neuroscience meeting: CNS-2016

The same neuron may play different functional roles in the neural circuits to which it belongs. For example, neurons in the Tritonia pedal ganglia may participate in variable phases of the swim motor rhythms [1]. While such neuronal functional variability is likely to play a major role the delivery of the functionality of neural systems, it is difficult to study it in most nervous systems. We work on the pyloric rhythm network of the crustacean stomatogastric ganglion (STG) [2]. Typically network models of the STG treat neurons of the same functional type as a single model neuron (e.g. PD neurons), assuming the same conductance parameters for these neurons and implying their synchronous firing [3, 4]. However, simultaneous recording of PD neurons shows differences between the timings of spikes of these neurons. This may indicate functional variability of these neurons. Here we modelled separately the two PD neurons of the STG in a multi-neuron model of the pyloric network. Our neuron models comply with known correlations between conductance parameters of ionic currents. Our results reproduce the experimental finding of increasing spike time distance between spikes originating from the two model PD neurons during their synchronised burst phase. The PD neuron with the larger calcium conductance generates its spikes before the other PD neuron. Larger potassium conductance values in the follower neuron imply longer delays between spikes, see Fig. 17.Neuromodulators change the conductance parameters of neurons and maintain the ratios of these parameters [5]. Our results show that such changes may shift the individual contribution of two PD neurons to the PD-phase of the pyloric rhythm altering their functionality within this rhythm. Our work paves the way towards an accessible experimental and computational framework for the analysis of the mechanisms and impact of functional variability of neurons within the neural circuits to which they belong

Transparent ZnO Thin-Film Deposition by Spray Pyrolysis for High-Performance Metal-Oxide Field-Effect Transistors

Solution-based metal oxide semiconductors (MOSs) have emerged, with their potential for low-cost and low-temperature processability preserving their intrinsic properties of high optical transparency and high carrier mobility. In particular, MOS field-effect transistors (FETs) using the spray pyrolysis technique have drawn huge attention with the electrical performances compatible with those of vacuum-based FETs. However, further intensive investigations are still desirable, associated with the processing optimization and operational instabilities when compared to other methodologies for depositing thin-film semiconductors. Here, we demonstrate high-performing transparent ZnO FETs using the spray pyrolysis technique, exhibiting a field-effect mobility of ~14.7 cm2 V−1 s−1, an on/off ratio of ~109, and an SS of ~0.49 V/decade. We examine the optical and electrical characteristics of the prepared ZnO films formed by spray pyrolysis via various analysis techniques. The influence of spray process conditions was also studied for realizing high quality ZnO films. Furthermore, we measure and analyze time dependence of the threshold voltage (Vth) shifts and their recovery behaviors under prolonged positive and negative gate bias, which were expected to be attributed to defect creation and charge trapping at or near the interface between channel and insulator, respectively

Estimates of Internal Forces in Torsionally Braced Steel I-Girder Bridges Using Deep Neural Networks

The bracing components in steel I-girder bridge systems are essential structural components for the bridges to restrain their rotation due to lateral torsional buckling (LTB). Current design specifications require bracing components to be installed to prevent I-girder sections from unexpectedly twisting due to instability. To estimate the bracing internal forces acting on the bracing elements, we can use approximate design equations that provide considerably conservative design values. Otherwise, it is necessary to conduct a thorough finite element analysis considering initial imperfections to obtain accurate bracing internal forces in the steel I-girder bracing systems. This study aims to provide estimation models based on deep neural network (DNN) algorithms to more accurately estimate the internal forces acting on the bracing element compared with the current design methodology when LTB occurs. This is conducted by constructing structural response data based on the geometrically nonlinear analysis with imperfections to provide accurate bracing internal forces, namely bracing moments (Mbr) and bracing forces (Fbr). To propose prediction models, 16 input and three output variables were selected for training the structural response data. Furthermore, a parametric study on the hyperparameters used in DNN models was analyzed for the number of hidden layers, neurons, and epochs. Based on statistical performance indices (i.e., RMSE, MSE, MAE, and R2), the estimated values using DNN models were evaluated to determine the best prediction models. Finally, DNN models that more accurately estimate internal forces (Mbr, Fbr) in bracing elements, and that provide the best prediction results depending on hyperparameters (numbers of hidden layers, neurons, and epochs), are proposed

Recent progress in strain-engineered elastic platforms for stretchable thin-film devices

Strain-engineered elastic platforms that can efficiently distribute mechanical stress under deformation offer adjustable mechanical compliance for stretchable electronic systems. By fully exploiting strain-free regions that are favourable for fabricating thin-film devices and interconnecting with reliably stretchable conductors, various electronic systems can be integrated onto stretchable platforms with the assistance of strain engineering strategies. Over the last decade, applications of multifunctional stretchable thin-film devices simultaneously exhibiting superior electrical and mechanical performance have been demonstrated, shedding light on the realization of further reliable human-machine interfaces. This review highlights recent developments in enabling technologies for strain-engineered elastic platforms. In particular, representative approaches to realize strain-engineered substrates and stretchable interconnects in island-bridge configurations are introduced from the perspective of the material homogeneity and structural design of the substrate. State-of-the-art achievements in sophisticated stretchable electronic devices on strain-engineered elastic platforms are also presented, such as stretchable sensors, energy devices, thin-film transistors, and displays, and then, the challenges and outlook are discussed.N

A High-Speed Inkjet-Printed Microelectromechanical Relay With a Mechanically Enhanced Double-Clamped Channel-Beam

We report a high-speed inkjet-printed three-terminal microelectromechanical (MEM) relay with a double-clamped beam that exploits the enhanced stiffness of the double-clamped structure to improve electrical performance. To minimize mechanical delay and pull-in voltage, the contact gap between the channel-beam and drain, and the stiffness of the beam and shape of the drain was carefully designed and optimized through a 3-D finite element simulation. The double-clamped beam prevents stiction-related failure between the channel-beam and drain despite the contact gap being only 370 nm for a > 500μm long beam. The resulting printed relay delivers a turn-ON delay of 8μs at a gate voltage of 10 V, a pull-in voltage of only 7.2 V, immeasurable off-leakage, excellent subthreshold swing, and a small hysteresis window of 2 V without any bending or collapsing of the beam. The device also shows reliable operation over 105 cycles while maintaining a high ON/OFF ratio of 108, and extremely low ON-state resistance of 3.7 Ω. [2016-0180] © 1992-2012 IEEE.1

Efficient Surface Treatment to Improve Contact Properties of Inkjet-Printed Short-Channel Organic Thin-Film Transistors

In this paper, we report contact properties of fully inkjet-printed organic thin-film transistors (OTFTs) with various channel lengths and their improvement by introducing an organo-compatible interlayer between the organic channel and inkjet-printed metallic contacts. To realize all-inkjet-printed OTFTs, a highly conductive metal-organic precursor type silver ink, poly(4-vinylphenol), chlorosilane-terminated polystyrene (PS) and 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS pentacene) solutions were printed by using a commercial piezoelectric inkjet-printer for gate and source/drain (S/D) electrodes, a gate dielectric layer, an interface engineering layer, and a semiconductor layer, respectively. Especially, since the contact resistance more dominantly affects a carrier injection property as channel length gets short, a short-channel length of 7 mu m was formed by using 1 picoliter volume ink cartridge to investigate effects of the organo-compatible interlayer obviously. To evaluate contact properties of the inkjet-printed short-channel OTFTs, transmission line method and Y-function method analyses were used for various channel lengths and low drain-to-source voltage (V-DS) regime of -5 V, respectively. The contact properties between inkjet-printed silver S/D electrodes and TIPS pentacene semiconductor were drastically enhanced showing contact resistance lowered by an order of magnitude and a good linearity at low V-DS regime after inserting an end-functionalized PS layer.OAIID:RECH_ACHV_DSTSH_NO:T201718200RECH_ACHV_FG:RR00200001ADJUST_YN:EMP_ID:A077977CITE_RATE:1.354FILENAME:발표논문_Efficient Surface Treatment to Improve Contact Properties of Inkjet-Printed Short-Channel Organic Thin-Film Transistors.pdfDEPT_NM:전기·정보공학부EMAIL:[email protected]_YN:YFILEURL:https://srnd.snu.ac.kr/eXrepEIR/fws/file/eb888933-b4a3-46db-9f2e-235e7e69b5de/linkN