Researchers from the University of Utah developed a new spintronic transistor that can be used to align electron spin for a record period of time in silicon chips at room temperature. The research was funded by the National Science Foundation.
The researchers used electricity and magnetic fields to inject "spin polarized carriers" - namely, electrons with their spins aligned either all up or all down - into silicon at room temperature. The new technique was to use magnesium oxide as a "tunnel barrier" to get the aligned electron spins to travel from one nickel-iron electrode through the silicon semiconductor to another nickel-iron electrode. Without the magnesium oxide, the spins would get randomized almost immediately, half up and half down.
The experiment used a flat piece of silicon about 1 inch long, about 0.3 inches wide and one-fiftieth of an inch thick. An ultra-thin layer of magnesium oxide was deposited on the silicon wafer. Then, one dozen tiny transistors were deposited on the silicon wafer so they could be used to inject electrons with aligned spins into the silicon and later detect them. Each nickel-iron transistor had three contacts or electrodes: one through which electrons with aligned spins were injected into the silicon and detected, a negative electrode and a positive electrode used to measure voltage.
During the experiment, the researchers send direct current through the spin-injector electrode and negative electrode of each transistor. The current is kept steady, and the researchers measure variations in voltage while applying a magnetic field to the apparatus.
The electrons retained their spins for 276 picoseconds, or 276 trillionths of a second. And based on that lifetime, the researchers calculate the spin-aligned electrons moved through the silicon 328 nanometers, which is 328 billionths of a meter or about 13 millionths of an inch.