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Clues to the Electrical Switching Mechanism of Carbazole-Containing Polyimide Thin Films
Ree, Brian J.,Kwon, Wonsang,Kim, Kyungtae,Ko, Yong-Gi,Kim, Young Yong,Lee, Hoyeol,Ree, Moonhor American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.23
<P>The mechanism behind electrical memory behavior of carbazole-containing polyimides (PIs) in nanoscale thin films was investigated. For this investigation, a series of poly(3,3′-dihydroxy-4,4′-biphenylene-<I>co</I>-3,3′-bis(<I>N</I>-ethylenyloxycarbazole)-4,4′-biphenylene hexafluoro-isopropylidenedi-phthalimide)s (6F-HAB-HABCZ<SUB><I>n</I></SUB> PIs) with various compositions was synthesized as a model carbazole-containing polymer system. The thermal properties, band gaps, and molecular orbital levels of the PIs were determined. Furthermore, the chemical compositions, as well as the nanoscale thin film morphologies and electron densities, were analyzed, providing detailed information on the population and positional distribution of carbazole moieties in thin films of the PIs. PI Devices were fabricated with aluminum electrodes and tested electrically. The PI thin film layers in the devices exhibited electrically permanent memory behavior, which was driven by trap-limited space-charge limited conduction and ohmic conduction. The permanent memory characteristics were found to be attributed to the incorporated carbazole moieties rather than from the other chemical components. Furthermore, the memory characteristics depended significantly on the population and positional distribution of carbazole moieties in the PI layer, as well as the film thickness. Considering that the backbone is not conjugated, the present results collectively indicate that the electrical switching behavior of the PI films is driven by the carbazole moieties acting as charge traps and a hopping process using the carbazole charge-trap sites as stepping-stones.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-23/am506915n/production/images/medium/am-2014-06915n_0010.gif'></P>
Imprinting well-controlled closed-nanopores in spin-on polymeric dielectric thin films
Ree, Moonhor,Yoon, Jinhwan,Heo, Kyuyoung Royal Society of Chemistry 2006 Journal of materials chemistry Vol.16 No.7
<P>The use of low dielectric constant (low-<I>k</I>) interdielectrics in multilevel structure integrated circuits (ICs) can lower line-to-line noise in interconnects and alleviate power dissipation issues by reducing the capacitance between the interconnect conductor lines. Because of these merits, low-<I>k</I> interdielectric materials are currently in high demand in the development of advanced ICs. This article reviews recent developments in the imprinting of closed nanopores into spin-on materials to produce low-<I>k</I> nanoporous interdielectrics for the production of advanced ICs.</P> <P>Graphic Abstract</P><P>Recent developments in the imprinting of closed nanopores into spin-on materials to produce low dielectric constant nanoporous dielectrics for the production of advanced integrated circuits in multilevel structure are reviewed. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=b511301f'> </P>
High Performance Polyimides for Applications in Microelectronics and Flat Panel Displays
Ree Moonhor The Polymer Society of Korea 2006 Macromolecular Research Vol.14 No.1
Polyimides (PIs) exhibit excellent thermal stability, mechanical, dielectric, and chemical resistance properties due to their heterocyclic imide rings and aromatic rings on the backbone. Due to these advantageous properties, PIs have found diverse applications in industry. Most PIs are insoluble because of the nature of the high chemical resistance. Thus, they are generally used as a soluble precursor polymer, which forms complexes with solvent molecules, and then finally converts to the corresponding polyimides via imidization reaction. This complexation with solvent has caused severe difficulty in the characterization of the precursor polymers. However, significant progress has recently been made on the detailed characterization of PI precursors and their imidization reaction. On the other hand, much research effort has been exerted to reduce the dielectric constant of PIs, as demanded in the microelectronics industry, through chemical modifications, as well as to develop high performance, light-emitting PIs and liquid crystal (LC) alignment layer PIs with both rubbing and rubbing-free processibility, which are desired in the flat-panel display industry. This article reviews this recent research progresses in characterizing PIs and their precursors and in developing low dielectric constant, light-emitting, and LC alignment layer PIs.
Synchrotron Grazing Incidence X-ray Scattering and its Applications in Polymer Nanotechnology
Moonhor Ree,Byeongdu Lee,Jinhwan Yoon,Kyuyoung Heo,Kyeong Sik Jin,Sangwoo Jin,Hyunchul Kim,Ghahee Kim,Seung Chul Choi,Weontae Oh,Young-Hee Park,Yongtaek Hwang,Jong-Seong Kim,Jehan Kim,Kwang-Woo Kim,Ta 한국고분자학회 2006 한국고분자학회 학술대회 연구논문 초록집 Vol.2006 No.10
Self-assembly of novel lipid-mimicking brush polymers in nanoscale thin films
Jung, Jungwoon,Kim, Heesoo,Ree, Moonhor The Royal Society of Chemistry 2014 SOFT MATTER Vol.10 No.5
<P>A series of well-defined poly(oxy(11-phosphorylcholineundecylthiomethyl)ethylene-<I>ran</I>-oxy(<I>n</I>-dodecylthiomethyl)ethylene) (PECH-PC<I>m</I>: <I>m</I> = 0–100 mol% phosphorylcholine (PC)) polymers were used to prepare nanoscale thin films that were characterized by synchrotron X-ray reflectivity (XR) analysis. The quantitative XR analysis provided structural insights into the PECH-PC<I>m</I> thin films. The PECH-PC0 polymer film formed a well-ordered in-plane oriented molecular multibilayer structure, whose individual layers consisted of two sublayers. One sublayer was composed of the fully extended backbones and inner part of the bristles, exhibiting a relatively low electron density, whereas the other sublayer was composed of a bilayer of the outer parts of the bristles without interdigitation. The PECH-PC100 polymer film also formed a well-ordered in-plane oriented molecular multibilayer structure, the individual layers of which were composed of four sublayers rather than two. The bristles in the layer were interdigitated in part <I>via</I> the zwitterionic interactions of the PC end groups. Surprisingly, regardless of the copolymer composition, the PECH-PC<I>m</I> random copolymer molecules in the thin films self-assembled to form a multilayered structure that resembled the structure formed by the PECH-PC100 polymer. These properties have not been observed in other conventional random brush copolymer films. The remarkable multibilayer structures originated from the zwitterionic PC end groups and their favorable interactions and interdigitated structures, which overcame any negative contributions caused by the heterogeneity of the bristles. The unique self-assembly properties of the PECH-PC<I>m</I> polymers always provide a PC-rich surface. The PECH-PC<I>m</I> random copolymers successfully mimicked the molecular bilayer structures formed by natural lipids.</P> <P>Graphic Abstract</P><P>Well-defined lipid-mimicking brush polymers, which contain phosphorylcholine (PC) moieties, have been demonstrated to favorably self-assemble at a molecular level and form a multibilayer structure in thin films, providing a PC-rich surface. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3sm52263f'> </P>