Lab Accident Could Allow High-Capacity 3D Storage

Conductivity of strontium titanate rises 400-fold with exposure to light.

An accident that left an experimental semiconductor exposed overnight boosted its performance potential by so much that the exposed material could lead to huge increases in data-storage capacity.

Strontium titanate is a crystalline semiconductor once considered a potential replacement for silicon dioxide because its electrical conductivity remains steady, even in very tiny transistors whose size causes silicon dioxide-based versions to choke.

Despite a variety of positive electrical characteristics that should make it invaluable, researchers have found few practical applications for strontium titanate. That may change after a Ph.D. candidate at Washington State University left a chunk of it out in the lab and discovered exposure to light increased the electrical conductivity of the strontium titanate crystal 400-fold.

The phenomenon, called persistent photoconductivity, is rare, but not unheard of; it can be induced in other materials, though never with so dramatic a result, according to a paper describing the incident published in Physical Review Letters.

“No one has ever seen such an increase in conductivity due to exposure to light at room temperature. It’s fine to have an interesting effect at liquid-nitrogen temperatures, but unless you can have it at room temperature, it’s not going to be very practical,” McCluskey said in a video accompanying the announcement.

The reason it works is unclear, though Tarun and Matthew McCluskey, chair of the WSU physics department and co-author of the paper, suggest light might free more electrons from atoms within the material, allowing it to carry more electricity with less resistance. Lowering the temperature of a material can have a similar effect, which is why most superconducting materials being studied work only at temperatures near absolute zero.

Even a leap in conductivity as great as that demonstrated by strontium titanate doesn’t make it a superconductor, but it does give it far more practical potential, McCluskey said.

Photoconductivity could also make possible super-capacity holographic storage systems by allowing individual semiconducting crystals to store data throughout the crystal, rather than only on the surface to which existing storage systems are limited. The sudden change in both properties and potential of the material was a complete surprise, “which makes it very exciting to share,” said Tarun, who is working with the material’s new properties in search of practical applications.


Image: Washington State University