Gold nanoparticles make memory-transistors
【纳米科技世界快讯】French researchers have made a "two-in-one" memory and transistor device from gold nanoparticles on pentacene. The memory-transistor has a large threshold voltage shift of 22 V and an on/off drain current ratio of 3 × 104 – values that compare well with previously made two-terminal organic memory devices.
Organic devices are already beginning to be used in applications like low-cost, large-area and flexible electronics. Although organic field-effect transistors and light-emitting diodes have been widely studied, organic memories – which will be crucial for storing electronic data in such devices – are less well known.
au nps trans.jpg (36.37 KB)
Au/pentacene memory FET
2008-05-14 07:55
For more details, please see "Molecular Nanostructures & Devices" Group at Lille. Credit: D Vuillaume.
Researchers have made memory devices from metal nanoparticles embedded in organic materials before now. These devices consist of a vertical structure where the active layer – an organic semiconductor containing metal nanoparticles – is sandwiched between two metal electrodes. However, the problem here is that the switching effects come from the formation and breaking of the metallic nanoparticles rather than from the nanoparticles charging and discharging.
Dominique Vuillaume of the University of Lille and colleagues, in collaboration with a team at the CEA, have now overcome this problem by making a three-terminal transistor in which the nanoparticles, acting as quantum dots, are controlled by a third (gate) electrode. The device is better than the previously made two-terminal transistors because the third electrode can drive the electrical state of the device.
Vuillaume's team's approach was to immobilize the nanoparticles into the source-drain channel of the device using classic surface chemistry. The researchers then used self-assembled organic monolayers to functionalize both the source and drain electrodes and the surface of the gate dielectric. Next, they covered the nanoparticles with pentacene, a well-known organic semiconductor, by vacuum sublimation.
Vuillaume told nanotechweb.org: "To store and erase electronic charges into the nanoparticles, we applied a voltage pulse to the command gate electrode and then recorded the device behaviour by measuring its usual characteristics – transconductance (drain current vs gate voltage) and the output drive capability (drain current vs drain voltage). When electrostatic charges are stored in the nanoparticles they modify the (drain) current flow in the transistor."
Simplified memory-cells?
The two-in-one organic memory-OFET could be used in circuit design and integration of low-cost organic electronics, adds Vuillaume. This could simplify memory-cells because a charge retention capacitance is no longer required. Usually, two transistors and a capacitance are needed to design a one-bit memory cell, he explains. Similarly, such a single device could be used to drive an OLED (in flat panel displays, for example) instead of the two or more OFETs generally employed in such drive cells.
The team now plans to try and increase the retention time of 4500 seconds in its device because it is shorter than that reported for vertical two-terminal organic memory devices. The researchers also hope to improve the memory's performance by more careful design of the nanoparticles/organic interfaces. "And, very importantly for us, we will carry out more detailed studies on the electronic processes involved in trapping and de-trapping charges into the nanoparticles, including those at the single nanoparticle level," said Vuillaume.
The results were published in
Appl. Phys. Lett. 92 103314.
来源： nanotechweb.org
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