High-Temperature Spin-Field-Effect Transistor Could Help Measure Blood-Sugar Levels

An international team of researchers has combined the spin-helix state and anomalous Hall effect to produce a realistic spin-field-effect transistor (FET) that is operable at high temperatures and features an AND-gate logic device. Because the transistor can directly convert polarization of light into electric voltage signals, it could potentially be employed down the line in such applications as blood-sugar-level measurement in patients and various sensors.

Miniaturization has demanded the establishment of new physical principles of operation for transistors, according to the team. As a result, researchers have shifted their focus from using the detection of electronic charges in a semiconductor to using its elementary magnetic movement as the logic variable. Progress in the field of 'spintronics' has been slow, however, because electrical manipulation and detection of electrons' spin in semiconductors has proven more challenging than expected.

"One of the major stumbling blocks was that to manipulate spin, one may also destroy it," says Jairo Sinova, a physicist at Texas A&M who was involved in the project. "It has only recently been realized that one could manipulate it without destroying it by choosing a particular setup for the device and manipulating the material. One also has to detect it without destroying it, which we were able to do by exploiting our findings from our study of the spin Hall effect six years ago. It is the combination of these basic physics research projects that has given rise to the first spin-FET."

Development of this spin-FET was achieved by designing a planar photodiode and placing it next to the transistor channel; the planar photodiode was used in lieu of the common circularly polarized light source. "By shining light on the diode, they injected photo-excited electrons, rather than the customary spin-polarized electrons, into the transistor channel. Voltages were applied to input-gate electrodes to control the procession of spins via quantum-relativistic effects. These effects--attributable to quantum relativity--are also responsible for the onset of transverse electrical voltages in the device, which represent the output signal, dependent on the local orientation of processing electron spins in the transistor channel," according to a press release from Texas A&M.