Molecule-sized electronics components could soon be on the menu thanks to US research that has led to a simple recipe for sandwiching organic molecules between silicon and metal layers.
Fabricating test structures consisting of a molecular junction held between a layer of gold and a layer of silicon is proving to be no simple task. Now, researchers at the National Institute of Standards and Technology (NIST) and the University of Maryland, have devised an approach that could one day miniaturize the electronics industry in the extreme, with single molecules acting as electronic switches [Coll et al., J. Am. Chem. Soc. (2009) 131, 12451].
The team’s approach side-steps the main problem with making the metal layer stick to the silicon – heat. Previously, researchers have tried to fabricate sandwiches by toasting them, but that damages the molecular structures.
NIST’s Mariona Coll, Christina Hacker, and their colleagues have now found that they can create an ultrasmooth gold surface on a layer of polymer. They then form the molecular layer on to the gold and then flip it over on to a silicon surface to complete the sandwich.
The researchers used a raft of spectroscopic techniques and electrical current-voltage measurements to verify that their silicon flip-chip sandwich has the structure they designed. “Both vibrational and electrical data indicate that electrical contact to the monolayer is formed while preserving the integrity of the molecules without metal filaments,” Coll says.
The approach could now lead the way to making high-quality molecular junctions consisting of dense single layers of molecules bonded chemically to metal and silicon electrodes. Coll calls the technique “flip-chip lamination” and suggests that it may lead to applications beyond microelectronic chip design, including biosensors for environmental and medical diagnostics.
By choosing specific molecules to sandwich between the gold and silicon layers it should be possible to endow the flip-chips with selectivity for different chemicals in a sample, for instance. Moreover, the use of so-called molecular recognition and self assembly in which complementary components of a larger molecular aggregate meet and connect could allow specific functionality to be designed into the sandwich.
“Our goal is to make a molecular junction that would advance the development and metrology of organic molecular electronics,” Hacker told Materials Today, “while being an adaptable fabrication approach that could be widely applied to other technologies.” Prototypes are only a few years away but much development is needed before widespread manufacture and use, she adds.