Phase-change material opens new path for data storage

A research team from A*STAR Data Storage Institute has found that materials made of iron and tellurium can change their property known as optical reflectivity depending on their crystalline state. They showed that the change between the crystalline and the non-crystalline form—and therefore between high and low reflectivity—can be induced simply and reversibly by heating the material, for example, by using a laser pulse. The switchable reflectivity offers a way for managing data in a small area, and they also showed that the change between the non-crystalline and crystalline phases can happen extremely fast, within tens of nanoseconds.

Memory is a central component of any computer or mobile device. Digital memories must not only store large amounts of data in a small space—and in a way that it is conveniently written, read and erased—but also meet ever-increasing demands on their size as well as their speed and energy efficiency. Phase-change materials, which switch their physical properties depending on whether they are in their crystalline or non-crystalline form, are being used to meet these requirements.

Digital data requiring storage in a memory is generated in the form of ones and zeroes. This means that the storage material should be able to switch between two distinct states, one encoding '1' and the other '0'. This is typically accomplished by altering either magnetic properties, or, as is the case for phase-change materials, optical or electrical behaviour.

"Also, by altering the relative amount of iron and tellurium in the material, the temperature at which the phase change happens can be tuned and therefore adjusted for specific applications," noted Wen Dong Song, a researcher at A*STAR DSI.

Other researchers have observed related behaviours in other phase-change materials, but Song and his team observed properties that are unique to their system. "To our surprise we found that in its non-crystalline state our material has a higher reflectivity than in its crystalline state," added Song. Normally, the opposite is true. "We [also] found that our material exhibits not only anomalous optical behaviour, but also has anomalous electrical properties. These unique characteristics may lead to novel applications in data storage, such as new optical media and solid-state memories," he noted.