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Numerical solution of predator-prey models by the multistage differential transform method
Cheolmin Bae,Kyunghoon Kim,Donghoon Lee,Sanghyup Lee,Kanghyun Lim,Bongsoo Jang 한국산업응용수학회 2010 한국산업응용수학회 학술대회 논문집 Vol.5 No.2
In this work, we present an dynamic behavior of the predator-prey models by using efficient computational algorithm, namely the multistage differential transform method(MDTM). The standard DTM is based on the Taylor series, but it differs from the conventional Taylor series in calculating coefficients. Because of nonlinearity as wall as large size of domain, it is difficult to obtain accurate numerical approximation for many problems by the standard DTM. To overcome these difficulties, we introduce an auxiliary function to apply the DTM for solving nonlinear problems and employ domain refinement to increase accuracy of approximate solution. Several illustrated examples of Holling types predator-prey models are demonstrated and numerical results are compared with those obtained by other numerical methods such as finite-difference and RK4.
Bae, Insung,Kang, Seok Ju,Park, Youn Jung,Furukawa, T.,Park, Cheolmin Elsevier 2010 Current Applied Physics Vol.10 No.1
<P>Among the many ferroelectrics polymers, poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)] has drawn a great attention with its promising memory properties such as large remanent polarization, good fatigue and retention properties. Since the ferroelectric layer plays a critical role in the operation of memory device, it is important to control the structure of ferroelectric thin film. In order to improve the performance of a ferroelectric device, in this contribution we employed P(VDF-TrFE) layers blended with various compositions of an amorphous poly(methyl methacrylate) (PMMA) from 0 wt.% to 20 wt.%. In metal/ferroelectric/metal capacitor structure, we observed the decrease of remanent polarization from 9.13 mu C/cm(2) to 4.7 mu C/cm(2) and increase of coercive voltage from 9.5 V to 15.2 V with PMMA. Polarization switching time of the ferroelectric blend films estimated from the switched polarization vs. time curves increases with the amount of PMMA. Furthermore, ferroelectric field-effect transistors (FeFETs) based on ferroelectric P(VDF-TrFE) and PMMA blend films with single-crystalline tri-isopropylsilylethynyl pentacene (TIPS-PEN) channels show that both ON and OFF currents of the transistors are maintained with the PMMA contents despite the reduction of remanent polarization of P(VDF-TrFE)/PMMA films. (C) 2009 Elsevier B.V. All rights reserved.</P>
Bae, Insung,Hwang, Sun Kak,Kim, Richard Hahnkee,Kang, Seok Ju,Park, Cheolmin American Chemical Society 2013 ACS APPLIED MATERIALS & INTERFACES Vol.5 No.21
<P>Nonvolatile ferroelectric-gate field-effect transistors (Fe-FETs) memories with solution-processed ferroelectric polymers are of great interest because of their potential for use in low-cost flexible devices. In particular, the development of a process for patterning high-performance semiconducting channel layers with mechanical flexibility is essential not only for proper cell-to-cell isolation but also for arrays of flexible nonvolatile memories. We demonstrate a robust route for printing large-scale micropatterns of solution-processed semiconducting small molecules/insulating polymer blends for high performance arrays of nonvolatile ferroelectric polymer memory. The nonvolatile memory devices are based on top-gate/bottom-contact Fe-FET with ferroelectric polymer insulator and micropatterned semiconducting blend channels. Printed micropatterns of a thin blended semiconducting film were achieved by our selective contact evaporation printing, with which semiconducting small molecules in contact with a micropatterned elastomeric poly(dimethylsiloxane) (PDMS) mold were preferentially evaporated and absorbed into the PDMS mold while insulating polymer remained intact. Well-defined micrometer-scale patterns with various shapes and dimensions were readily developed over a very large area on a 4 in. wafer, allowing for fabrication of large-scale printed arrays of Fe-FETs with highly uniform device performance. We statistically analyzed the memory properties of Fe-FETs, including ON/OFF ratio, operation voltage, retention, and endurance, as a function of the micropattern dimensions of the semiconducting films. Furthermore, roll-up memory arrays were produced by successfully detaching large-area Fe-FETs printed on a flexible substrate with a transient adhesive layer from a hard substrate and subsequently transferring them to a nonplanar surface.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2013/aamick.2013.5.issue-21/am402852y/production/images/medium/am-2013-02852y_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am402852y'>ACS Electronic Supporting Info</A></P>
Bae, Insung,Kim, Richard Hahnkee,Hwang, Sun Kak,Kang, Seok Ju,Park, Cheolmin American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.17
<P>We present a simple but robust nondestructive process for fabricating micropatterns of thin ferroelectric polymer films with controlled crystals. Our method is based on utilization of localized heat arising from thin Ge<SUB>8</SUB>Sb<SUB>2</SUB>Te<SUB>11</SUB> (GST) alloy layer upon exposure of 650 nm laser. The heat was generated on GST layer within a few hundred of nanosecond exposure and subsequently transferred to a thin poly(vinylidene fluoride-<I>co</I>-trifluoroethylene) film deposited on GST layer. By controlling exposure time and power of the scanned laser, ferroelectric patterns of one or two microns in size are fabricated with various shape. In the micropatterned regions, ferroelectric polymer crystals were efficiently controlled in both degree of the crystallinity and the molecular orientations. Nonvolatile memory devices with laser scanned ferroelectric polymer layers exhibited excellent device performance of large remnant polarization, ON/OFF current ratio and data retention. The results are comparable with devices containing ferroelectric films thermally annealed at least for 2 h, making our process extremely efficient for saving time. Furthermore, our approach can be conveniently combined with a number of other functional organic materials for the future electronic applications.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-17/am503397j/production/images/medium/am-2014-03397j_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am503397j'>ACS Electronic Supporting Info</A></P>
Bae, Insung,Kang, Seok Ju,Shin, Yu Jin,Park, Youn Jung,Kim, Richard Hahnkee,Mathevet, Fabrice,Park, Cheolmin WILEY‐VCH Verlag 2011 Advanced Materials Vol.23 No.30
<P><B>Single crystalline triisopropylsilylethynyl pentacene (TIPS‐PEN) arrays</B> are fabricated with both size and shape of each patterned domain precisely tailored by selective contact evaporation printing (SCEP), which exhibit sufficient ON/OFF current ratio as well as high field effect mobility.</P>
Nonvolatile Polymer Memory with Nanoconfinement of Ferroelectric Crystals
Kang, Seok Ju,Bae, Insung,Shin, Yu Jin,Park, Youn Jung,Huh, June,Park, Sang-Min,Kim, Ho-Cheol,Park, Cheolmin American Chemical Society 2011 Nano letters Vol.11 No.1
<P>We demonstrate significantly improved performance of a nonvolatile polymeric ferroelectric field effect transistor (FeFET) memory using nanoscopic confinement of poly(vinylidene fluoride-<I>co</I>-trifluoroethylene) (PVDF-TrFE) within self-assembled organosilicate (OS) lamellae. Periodic OS lamellae with 30 nm in width and 50 nm in periodicity were templated using block copolymer self-assembly. Confined crystallization of PVDF-TrFE not only significantly reduces gate leakage current but also facilitates ferroelectric polarization switching. These benefits are due to the elimination of structural defects and the development of an effective PVDF-TrFE crystal orientation through nanoconfinement. A bottom gate FeFET fabricated using a single-crystalline triisopropylsilylethynyl pentacene channel and PVDF-TrFE/OS hybrid gate insulator shows characteristic source-drain current hysteresis that is fully saturated at a programming voltage of ±8 V with an ON/OFF current ratio and a data retention time of approximately 10<SUP>2</SUP> and 2 h, respectively.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2011/nalefd.2011.11.issue-1/nl103094e/production/images/medium/nl-2010-03094e_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl103094e'>ACS Electronic Supporting Info</A></P>
Hwang, Sun Kak,Bae, Insung,Cho, Suk Man,Kim, Richard Hahnkee,Jung, Hee Joon,Park, Cheolmin WILEY‐VCH Verlag 2013 Advanced functional materials Vol.23 No.44
<P><B>Abstract</B></P><P>Polymer ferroelectric‐gate field effect transistors (Fe‐FETs) employing ferroelectric polymer thin films as gate insulators are highly attractive as a next‐generation non‐volatile memory. Furthermore, polymer Fe‐FETs have been recently of interest owing to their capability of storing data in more than 2 states in a single device, that is, they have multi‐level cell (MLC) operation potential for high density data storage. However, among a variety of technological issues of MLC polymer Fe‐FETs, the requirement of high voltage for cell operation is one of the most urgent problems. Here, a low voltage operating MLC polymer Fe‐FET memory with a high dielectric constant (<I>k</I>) ferroelectric polymer insulator is presented. Effective enhancement of capacitance of the ferroelectric gate insulator layer is achieved by a simple binary solution‐blend of a ferroelectric poly(vinylidene fluoride‐co‐trifluoroethylene) (PVDF‐TrFE) (<I>k</I> ≈ 8) with a relaxer high‐<I>k</I> poly(vinylidene‐fluoride–trifluoroethylene–chlorotrifluoroethylene) (PVDF‐TrFE‐CTFE) (<I>k</I> ≈ 18). At optimized conditions, a ferroelectric insulator with a PVDF‐TrFE/PVDF‐TrFE‐CTFE (10/5) blend composition enables the discrete six‐level multi‐state operation of a MLC Fe‐FET at a gate voltage sweep of ±18 V with excellent data retention and endurance of each state of more than 10<SUP>4</SUP> s and 120 cycles, respectively.</P>