Ballistic transport in spin-valve Si channel demonstrates feasibility of nanoscale spin-MOSFETs

Recent spintronics devices look to overcome many of the limitations that arise in traditional electronics from their dependence on charge mobility, as devices continue to shrink in size. Reported in the Journal of Applied Physics, a nanoscale Si-based lateral spin-valve device makes significant progress toward a spin-transistor as an alternative, low-power solution. Unlike the charge-based counterparts that rely on the diffusive transport of electrons in the form of current, spintronics devices such as this use electron spin phenomena for information storage and manipulation.

The authors used molecular beam epitaxy to fabricate a Fe/MgO/Ge structure that both injects and detects spin. With nanolithography, they fabricated their spin-valve device with a short Si channel just 20 nanometers long and comparable to electrons’ mean-free path. The channel utilizes the ballistic transport of electrons to overcome conductivity mismatches, greatly reducing a common problem that emerges at the interface between a device’s ferromagnetic electrode and diffusive semiconductor channel (and what leads to high idling power consumption from leakage currents).

The device produced a significant improvement of a few hundred percent in spin-valve effects over previous demonstrations, with a final value of 3 percent. The spin output voltage also improved compared to previously studied long-channel devices to values of about 20 millivolts. Temperature affected the spin-valve effect inversely at temperatures less than 200 Kelvin, attributed to a spin-blockade effect of defect states in the MgO layer.

Characterizing spin transport distinguished an intrinsic spin-valve effect from parasitic local effects by using the local spin-valve effect and systematic dependence measurements, such as bias voltage, temperature, and magnetic-field direction dependence of magnetoresistance. This behavior in a Si-based spintronic device is particularly attractive because it already exhibits the advantage of easier integration into existing metal-oxide-semiconductor technology.

Source: “Inverse spin-valve effect in nanoscale Si-based spin-valve devices,” by Duong Dinh Hiep, Masaaki Tanaka, and Pham Nam Hai, Journal of Applied Physics (2017). The article can be accessed at https://doi.org/10.1063/1.4994881 .