Synthesis and memory performance of a conjugated polymer with an integrated fluorene, carbazole and oxadiazole backbone

Abstract

A new soluble conjugated polymer, poly[{9-(4-methoxyphenyl)-9H-carbazole}(9,9-dioctylfluorene)(2,5-diphenyl-1,3,4-oxadiazole)] (PCFO), was synthesized through the Suzuki coupling reaction. The absolute fluorescence quantum yield of PCFO was measured using the integrating sphere of a photoluminescence spectrofluorometer, and changed from 49.1% for a dilute tetrahydrofuran solution to 16.2% for a thin film due to the existence of a strong fluorescence quenching effect in the solid state. The HOMO-LUMO bandgap (3.07 eV) calculated from the electrochemical measurement is nearly identical to the optical bandgap (3.06 eV) estimated from the ultraviolet/visible absorption onset data. This film was attached to aluminum and indium-tin oxide contacts to fabricate a memory device with typical bistable electrical switching, nonvolatile write-once read-many-times memory performance, a turn-on voltage of BÀ2.3 V and an ON/OFF ratio of B10 5 . Degradation of the current density was observed for neither the ON nor OFF states after one hundred million continuous read cycles, which indicates that both states were insensitive to read cycles. Keywords: donor-acceptor system; molecular devices; polymer memory; synthesis INTRODUCTIONPolymer memories are proposed to revolutionize electrical applications by providing extremely inexpensive, lightweight and transparent modules that can be fabricated onto plastic, glass or the top layer of CMOS hybrid integration circuits, 1,2 and have been identified as an emerging memory technology by the International Technology Roadmap for Semiconductors since year 2005. 3 Rather than encoding '0'and '1' as a charge stored in the cell of a silicon device, polymer memory stores data in an entirely different form, such as in a highand low-conductivity response to an applied voltage. 4 The molecular structure of polymers can be tailored by functionalizing them with electron donors (D) and acceptors (A) of different strengths, spacer moieties of different steric effects for the electroactive pendant groups, or nanostructured electroactive materials, to induce different memory behaviors in simple metal/polymer/metal devices. 5,6 Very recently, Liu and Chen 7 highlighted the recent developments in D-A polymers for resistive switching memory device applications including conjugated polymers, functional polyimides, nonconjugated pendent polymers and polymer composites. D/A polymer materials (usually carbazole or

Conjugated polymers for information storage and neuromorphic computing

“…Charge transfer interaction is one of the most common strategies used to construct organic memristors. Conjugated memristive polymers based on this mechanism usually consist of two parts, the electron donor (D) and the electron acceptor (A), either in the conjugated skeleton or in the pendant groups 46,47 . When a suitable voltage is applied to the organic switching layer across the two ends of a device, electrons in the donor unit will be excited and transferred to the acceptor chromophore, increasing the concentration of free charge carriers and thus greatly improving the conductance of the memristor.…”

“…Kang and co‐workers synthesized poly[{9‐(4‐methoxyphenyl)‐9 H ‐carbazole}(9,9‐dioctylfluorene)(2,5‐diphenyl‐1,3,4‐oxadiazole)] (P11) through Suzuki coupling reaction (Fig. 9(a)), and used it as the switching matrix in an Al/P11/ITO sandwich device that displays non‐volatile memory characteristics 46 . When a voltage of −2.3 V is applied to the device, the current density increases abruptly from 10 −7 to 10 −2 , giving rise to an ON/OFF ratio of about 10 5 which is sufficient to reduce the misreading rate during practical operation (Fig.…”

“…Insets of (b) and (c) show device structure and ON/OFF current ratio as a function of applied voltage, respectively (adapted from Ref. 46 ; Copyright 2012, Polymer Journal ).…”

Recent Advances in Resistive Switching Materials and Devices: From Memories to Memristors

“…In particular, the solution processing capability of organic materials allows them to be handled via dip coating, blade casting, spray coating, spin coating, rollercoating and even ink-jet printing, not only making the more elaborated processes of vacuum deposition of functional thin films eliminable, but allowing the fabrication of flexible memory chips. Extensive studies have been performed on the resistance switching in organic materials, wherein focus has been concentrated on the development of novel materials for memory performance [28][29][30][31][32][33][34][35] optimization.…”

“…By incorporating both electron donating (D) and accepting (A) moieties into the chemical structure, a series of electroactive polymer materials exhibiting resistive switching behaviors have been [28][29][30][31][32][33] synthesized successfully.…”