Reversible diode debuts
R. Colin Johnson
EE Times
(02/23/2009 2:17 PM EST)
PORTLAND, Ore. — Rutgers University researchers have demonstrated what they claims in the world's first reversible diode that uses a ferroelectric material. The new material formulation was also found to be photovoltaic in a part of the spectrum not covered by conventional solar cells, opening the door to a potential new green energy source.
The new material is a member of the perovskite class of crystals and is distinguished by using three negative ions of oxygen to bind to two positive ions of very different atomic sizes. Made from bismuth, iron and oxygen, the reversible diode can alter the direction in which it allows current to pass by switching its ferroelectric polarization.
"The same terminals that are used for current flow can also be used to switch the diode's direction of current flow by simply applying a large voltage pulse," said Rutgers professor Sang-Wook Cheong.
A photovoltaic diode whose direction of rectification can be reversed with a high-voltage pulse.
Cheong also claimed that, besides enabling new devices and circuits, solar cells using the new diode could harvest the blue light of the spectrum, which remains bright even on cloudy days. "We haven't measured its efficiency yet, but we know it's sensitive to the blue end of the light spectrum," said Cheong.
Cheong said the process can be used for both discrete devices as well as those integrated onto CMOS chips. The new ferroelectric material, however, will have to be integrated into a semiconductor fab process. The researchers claim that the ferroelectric polarization of the material is a bulk effect, rather than the result of a semiconductor interface, which should ease integration.
"In principle, the reproducibility of a bulk effect is a good thing," said Cheong.
Funding was provided by the National Science Foundation and thorugh a Korea Research Foundation Grant.
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