sealPurdue News

August 1999

Findings suggest new oxygen-sensing material

WEST LAFAYETTE, Ind. -- Purdue University research into computer-related technology has yielded unexpected results that could lead to better oxygen sensors for car exhaust systems and medical devices.

The work centers on an experimental technology, called ferroelectric data storage, which showed promise for a new generation of computers that would retain memory even after losing power.

While analyzing the effects of temperature change on the devices, scientists accidentally discovered that the material is surprisingly sensitive to oxygen. To accurately measure temperature, they subjected the material, known as a ferroelectric thin film, to a vacuum. But they found that reducing the atmospheric pressure also reduced the performance of the devices. Further tests showed that the effect was caused specifically by changes in oxygen concentration and in the "partial pressure" of oxygen in the vacuum chamber.

With that discovery, they theorized that the material might be useful as an oxygen sensor. Materials now used in conventional solid-state sensors must be heated to at least 300 degrees Celsius (572 Fahrenheit). But the material used in the research seems to perform well at room temperature, and it continues to function at temperatures as cold as minus 93 Celsius (minus 135 Fahrenheit), making it suitable for environmental and biological applications.

A paper about the findings will be published June 28 in the journal Applied Physics Letters. The paper was written by Purdue physics graduate student Mark Brazier, materials engineer Said Mansour and physicist Michael McElfresh.

Meanwhile, the research showed that the material's sensitivity to oxygen represents a drawback to its potential application in computer memory. For example, the devices -- called ferroelectric capacitors -- will wear out in 15 percent less time when moved from sea level to Colorado Springs, Colo., an elevation change of about 6,000 feet. Such an effect may surprise engineers, who think of solid-state devices -- such as the silicon semiconductors in computers -- as being relatively impervious to most environmental factors.

"It's a variable that had not been considered, the whole idea that the air in the room is going to affect the performance of a device in your computer," McElfresh said.

Researchers have been studying whether the devices might one day be used to design computers with so-called "non-volatile memory." Such computers would retain memory even if they lost power before a file was saved. However, the recent findings suggest that ferroelectric data storage may not be suitable for such an application. That's because reduced oxygen pressure increases the degree of "ferroelectric fatigue," which is the biggest obstacle to developing the technology.

The material is made of lead, zirconium, titanium and oxygen. The Purdue scientists specifically studied two types of the material: one in which the ratio of zirconium to titanium is 55-to-45, and another that has a 75-25 ratio.

The research is funded by the Department of Energy and the National Science Foundation.

Source: Michael McElfresh, (765) 494-6605;

Writer: Emil Venere, (765) 494-4709,

Purdue News Service: (765) 494-2096;

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