PORTLAND, Ore. — Spintronic devices hold promise as atom-scale, nonvolatile devices by encoding information on the spin of electrons -- either "up" or "down" -- instead of charge, potentially enabling ultra-low-power operation of circuitry that remembers its state even when turned off. Unfortunately, silicon compatibility has not been reported for most of these so-called dilute magnetic semiconductors.
Now a new silicon-compatible room-temperature dilute magnetic semiconductor has been discovered by researchers at North Carolina State University (NCSU). Called strontium tin oxide, the researchers have successfully deposited it on silicon substrate atop a thin zirconia interface.
A cross-section image from high-resolution transmission electron microscope shows the interface of epitaxial strontium tin oxide (Sr3SnO) and cubic yttria-stabilized zirconia (c-YSZ) atop a silicon substrate.
(Source: North Carolina State University)
"Dilute magnetic semiconductors hold great promise for spintronic devices, which store information on the magnetic spin of an electron," said professor Jay Narayan at North Carolina State University in an interview with EE Times. He continued:
Other materials like zinc oxide are also dilute magnetic semiconductors, but they cannot be easily deposited on silicon. However because of the cubic symmetry and lattice constant of strontium tin oxide is close to that of silicon, it can be more easily integrated with silicon substrates.
Other research groups are experimenting with dilute magnetic semiconductor (DMS), but many are using III-V materials like indium arsenide or gallium arsenide. Others have reported that germanium quantum dots hold promise for silicon compatibility, but not at room temperature. Now this NCSU lab reports both silicon compatibility and room temperature operation.
Ironically, the researchers -- which included fellow NCSU professor Justin Schwartz -- were not searching for a silicon-compatible material for spintronics, but rather were searching for a topological insulator -- a semiconductor whose bulk properties are that of an insulator, but whose top layer is conductive. However, as they characterized strontium tin oxide, the researchers discovered that it was a dilute magnetic semiconductor too.
"Strontium tin oxide [SSO] has been predicted theoretically to be a topological insulator [TI] and experimentally we have found certain TI characteristics in thin SSO films," said Narayan. "We also discovered it to be room-temperature dilute magnetic semiconductor whose properties can be tuned by annealing in an oxygen ambient."
Next, the researchers plan to start fashioning spintronic transistors in the material to prove the concept that strontium tin oxide can offer a promising new direction for silicon semiconductors.