By Anna Lynn Spitzer
07.25.05 -- Three students at UC Irvine could create some of the smallest transistors ever – if only they could get their zinc-oxide nanowires to grow. The transistors, each separately created from two nanowires, would be years away from commercial use, but that does little to lessen the importance of these particular nanowires or dampen the students’ enthusiasm.
According to Evan Brown, a fourth-year material science & engineering student and IM-SURE research fellow, these nanowires are exciting because theoretically, they could be perfectly ordered.
“It’s something we call self-assembly,” Brown explained. “Instead of taking an atomic force microscope and moving wires with two needles into the position we want, these highly ordered wires will be growing perfectly and it will be repeatable.”
The student scientists are using a method called electrodeposition that utilizes a chip with a top layer of alumina substrate covered with highly ordered vertical pores. Underneath the substrate is a gold plate that acts as an electrode, beneath which is a layer of titanium, and finally, an epoxy holding the structure to silicon.
This substrate is placed in a solution with zinc ions and a metal contact is attached to it in order to pass current through the system. Once the electric potential is applied, the zinc ions will be attracted to the gold and will deposit in each of the pores, creating perfect nanowires. Putting the nanowires in a furnace and flowing diluted oxygen into the system results in zinc-oxide nanowires. In theory at least … for now.
“Some of the chips are good, but we don’t have much density on the wires. Not every pore grows,” said Marco Huang, a fourth-year electrical engineering student and SURF-IT fellow.
The group, composed of Brown, Huang, and Joseph Fan, a chemical engineering & materials science graduate student, and mentored by Jia Grace Lu, assistant professor of chemical engineering & materials science, has spent the last few weeks overcoming one problem after another.
At first, electrodeposition resulted in the zinc ions depositing on the silicon instead of the gold, so they substituted glass for the silicon. Then they encountered problems with the adhesive and the glass, so they sanded the glass. Currently, they believe the epoxy may be causing the gold to strip away, but the students remain optimistic.
“We’re doing it over and over and over again and trying different things and different chemicals, which is all part of research. But we’re getting close,” Brown pointed out.
After growing the zinc-oxide nanowires, the group will measure their properties.
“We’re going to do electrical measurements on the nanowire array and if the results are promising, we can go ahead with the fabrication process,” Fan said. “We can then create transistor arrays, logic gates and memory arrays.”
And those tiny transistors would finally be a reality.