Eric Yeow Hwee Teo

Electrical Conductance Tuning and Bistable Switching in Poly(N-vinylcarbazole)−Carbon Nanotube Composite Films

By varying the carbon nanotube (CNT) content in poly(N-vinylcarbazole) (PVK) composite thin films, the electrical conductance behavior of an indium-tin oxide/PVK-CNT/aluminum (ITO/PVK-CNT/Al) sandwich structure can be tuned in a controlled manner. Distinctly different electrical conductance behaviors, such as (i) insulator behavior, (ii) bistable electrical conductance switching effects (write-once read-many-times (WORM) memory effect and rewritable memory effect), and (iii) conductor behavior, are discernible from the current density-voltage characteristics of the composite films. The turn-on voltage of the two bistable conductance switching devices decreases and the ON/OFF state current ratio of the WORM device increases with the increase in CNT content of the composite film. Both the WORM and rewritable devices are stable under a constant voltage stress or a continuous pulse voltage stress, with an ON/OFF state current ratio in excess of 10(3). The conductance switching effects of the composite films have been attributed to electron trapping in the CNTs of the electron-donating/hole-transporting PVK matrix.

Electrically Bistable Thin-Film Device Based on PVK and GNPs Polymer Material

We present an electrical-bistability device based on MIM-sandwiched structure. Poly(N-vinylcarbazole) (PVK) mixed with gold nanoparticles (GNPs) serve as the active layer between two metal electrodes. After applying a voltage, the as-fabricated device can transit from low conductivity state to high conductivity state. By simply using a reverse bias, the high conductivity state can return to the low conductivity state. An on/off current ratio as high as 105 at room temperature has been achieved. The memory effect is attributed to electric-field-induced charge transfer complex formed between the PVK and the GNPs. The device shows a good stability under stress test for both states and exhibits a high potential on Flash-type memory applications

WORM-Type Memory Device Based on a Conjugated Copolymer Containing Europium Complex in the Main Chain

A conjugated copolymer of 9,9-dihexylfluorene and Eu-complexed benzoate (PF6Eu) for write-once read-many-times (WORM) memory application was demonstrated in a sandwich structure of Al/PF6Eu/ITO. The device exhibited: a high ON/OFF current ratio up to 10 7 , stable ON and OFF states with read cycles up to 10 8 at a read voltage of 1 V, and projected stability up to 10 years at a constant stress of I V.

Synthesis and memory properties of a conjugated copolymer of fluorene and benzoate with chelated europium complex

A conjugated copolymer of diethylhexylfluorene and europium complex-chelated benzoate (PF8Eu) was synthesized. The device based on an Al/PF8Eu/indium-tin-oxide sandwich structure exhibited nonvolatile, write-once read-many-times (WORM) memory behavior. The fluorene moiety served as the backbone and electron donor, while the europium complex served as the electron acceptor. The as-fabricated device was in its low conductivity state. After applying a voltage of ∼3V, the device underwent a transition to the high conductivity state, which could not be erased by a reverse bias. In the initial low conductivity state, the device showed a charge injection controlled current. At the high conductivity state, the current-voltage characteristics were dominated by a space-charge-limited current. The device had a switching time of ∼1μs and an on/off current ratio as high as 106. No degradation in device performance was observed after 107 read cycles at a read voltage of 1V under ambient conditions. The device also exhi...

Correction to "An Organic-Based Diode-Memory Device With Rectifying Property for Crossbar Memory Array Applications"

An organic-based diode-memory device that has a bistable memory function and a high rectification ratio has been studied. The diode-memory device is fabricated by incorporating an organic-based diode component in series with a polymer memory component. The organic-based diode-memory device performs well as a reliable rectifying memory device, achieving an excellent on/off current ratio of 106 and a high rectification ratio of 103. The conduction models are also fitted to study the proposed conductivity mechanism of the rectifying memory device. The demonstrated organic-based diode-memory device is very promising for use in a passive matrix crossbar polymer memory array.

Molecular Conformation-dependent Memory Effects in Non-conjugated Polymers with Pendant Carbazole Moieties

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 write-once-read-many-times (WORM) memory behavior with an ON/OFF current ratio up to 10 6 , while the device based on poly(9-(2-((4-vinylbenzyl)oxy)ethyl)-9 H -carbazole) (PVBCz) exhibited volatile memory behavior with an ON/OFF current ratio of approximately 10 3 . 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 switching and memory effects observed were attributed to conformation changes of the pendant carbazole groups.