Toward More Reliable Molecular Electronics

A new technique for making molecular junctions could give rise to molecular electronics with consistent, stable, and reliable properties. The simple, potentially low-cost approach ???could pave the way for practical molecular electronics,??? according to the scientists who developed it (Nature 2006, 441, 69).

Electronics researchers have spent years trying to use self-assembled monolayers, or SAMs, as the insulating material in molecular metal-insulator-metal junctions. The electrical properties of these devices, however, tend to be unreliable because of poor electrical contact between the SAM and the metal electrodes. The devices also frequently short out from direct contact between the two metal electrodes.

Bert de Boer, Hylke B. Akkerman, and Paul W. M. Blom of the University of Groningen, in the Netherlands, along with Dago M. de Leeuw of Philips Research were able to overcome these problems by introducing two innovations to the junction fabrication process. First, the group deposits the SAM within lithographically produced cylindrical pores 10???100 µm in diameter. These pores penetrate an insulating plastic film, exposing the gold electrode beneath. The pores protect the SAM from stray currents and from the environment.

The group???s second innovation was to sandwich a layer of conducting polymer between the SAM and the top metal electrode. This layer acts like a cushion and helps to prevent electrical shorts.

The resulting molecular junctions have unprecedented diameters of up to 100 µm. The technique is compatible with standard integrated-circuit fabrication processes, the researchers say, and ???can be scaled up and extended to any molecule and any metal bottom electrode on which an ordered SAM can be formed.???