Molecular Conformation-dependent Memory Effects in Non-conjugated Polymers with Pendant Carbazole Moieties
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1071-F05-01
Molecular Conformation-dependent Memory Effects in Non-conjugated Polymers with Pendant Carbazole Moieties Siew Lay Lim1,2, Qidan Ling2, Eric Yeow Hwee Teo3, Chun Xiang Zhu3, Daniel Siu Hung Chan3, En Tang Kang2, and Koon Gee Neoh2 1 NUS Graduate School of Integrative Sciences and Engineering (NGS), National University of Singapore, Singapore, Singapore 2 Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore, Singapore 3 SNDL, Department of Electrical and Computer Engineering, National University of Singapore, Singapore, Singapore ABSTRACT Single-layer devices of the structure indium-tin-oxide/polymer/aluminum were fabricated from two non-conjugated polymers with pendant carbazole groups in different spacer units. The device based on poly(2-(N-carbazolyl)ethyl methacrylate) (PMCz) exhibited non-volatile writeonce-read-many-times (WORM) memory behavior with an ON/OFF current ratio up to 106, while the device based on poly(9-(2-((4-vinylbenzyl)oxy)ethyl)-9H-carbazole) (PVBCz) exhibited volatile memory behavior with an ON/OFF current ratio of approximately 103. In the absence of a spacer unit between the pendant carbazole group and the main chain, regioregular poly(N-vinylcarbazole) (PVK) exhibited only one conductivity state (ON state). The formation of carbazole excimers resulting from conformation-induced conductance switching under an electric field was revealed in situ by fluorescence spectroscopy. The electrical behavior of the polymer in a device was found to be dictated by the chemical structure and steric effect of the spacer unit between the pendant carbazole group and the main chain. INTRODUCTION Organic materials are promising candidates for future molecular-scale device applications in new information storage technologies as the need to overcome the potentially limiting scaling difficulties present in the semiconductor industries intensifies [1]. In particular, polymer memories have emerged as an active research topic in recent years. Polymer materials possess unique properties, such as good mechanical strength and flexibility, as well as the possibility for molecular design through chemical synthesis. Polymer memory devices are easily fabricated by solution-processing methods, such as spin-coating and ink-jet printing, and a variety of materials, including plastics and metal foils, can be used as substrates for deposition of the polymers. The memory cells can be addressed by two-terminal structures and stacked to form high-density, three-dimensional (3-D) data storage devices. Polymer memories can potentially provide lowcost, low-power, flexible, and light-weight devices with high-capacity data storage [2]. Rather than encoding “0” and “1” from the number of charges stored in a cell in silicon devices, a polymer memory stores data, for example, on the basis of the high and low conductivity responses to an applied voltage [3]. Although conductance switching due to chargetransfer, electro-reduction, charge-tunneling and others has been widely reported
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