Clear semiconductor paves way for smart displays
By Nolan Fell
Electronics Times
(01/30/01 01:01 a.m. PST)
The possibility of a flexible electronic display is a step closer following work at the Tokyo Institute of Technology. Hideomi Koinuma and colleagues have developed a ferromagnetic semiconductor which operates at room temperature and is totally transparent.
Developed using titanium dioxide (TiO2) doped with cobalt, the device was designed to integrate the spin properties of an electron into a semiconductor.
Traditional semiconductors rely purely on an electron's charge to transmit information. A ferromagnetic device, using an electron's spin, can be used to construct magnetic random access memory.
Many ferromagnetic materials only operate at very low temperatures, but this semiconductor still maintains its magnetic qualities at room temperature. In developing the TiO2-based semiconductor, Koinuma and the team also discovered that the material does not absorb any light in the visible spectrum.
The authors published their findings in the journal Science.
Koinuma said: "We were using combinatorial synthesis to develop new materials for catalysts. TiO2 can cleave water using UV. Many people are interested in finding a way to modify it so it works with sunlight. We developed a machine to create many new catalysts.
"A couple of months ago, we developed cobalt-doped TiO2. A colleague has a superconducting quantum interference device — a highly sensitive magnetometer — which he used to sense the material's magnetic qualities."
Commenting on the work, Hideo Ohno of Tokyo University, a leading researcher in the ferromagnetic semiconductor field (Electronics Times, 8/1/01), said: "The ideal scenario would be the integration of the electronics circuits and magnetic storage with the user interface in a single flat panel display."
The combinatorial synthesis technique Koinuma and his colleagues used to produce the cobalt-doped TiO2 involves beaming intense UV light on to specific materials. This caused some of the material to be released from the substrate.
They then placed the ablated material on a separate substrate in an oxygenated atmosphere, creating doped oxide material. A whole series of thin films was produced, with the cobalt-doped TiO2 showing surprising properties.
"We haven't considered applications too much yet," said Kionuma. "But because of its transparency, there must be some applications where charge, magnetism and light interact with each other."
One obvious possible application is the integration of transistors with semiconducting and magnetic properties into a thin film display.
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