INV-20119 

Background

The concept of using the spin degree of freedom to control electrical current to expand the capabilities of electronic devices has been in use for decades and generates high frequency voltage signals in the GHz range.

3D topological insulators (TIs) possess enhanced spin current to charge current conversion efficiencies which can provide the highest recorded spin orbit torques (SOT) to adjacent magnetic layers to generate magnetization oscillations and switching. 

These advances are highly relevant for SOT‑based magnetic random access (MRAM) units as fast and reliable non-volatile memory (NVM) units. However, boron iodide (Bi) based 3D TI materials are unstable at high temperatures which can arise during operation of these devices and may melt or sublimate at temperatures higher than 280ºC - 300ºC which can lead to phase transformations and change in SOT efficiency. 

Technology Overview

Northeastern Researchers propose the use of a normal metal (NM) such as Ti, Ag, Cu coupled with a TI to reduce the effective resistivity and hence power dissipation of the bilayer by ~90% without compromising the SOT efficiency. This improves the reliability of TI based SOT devices by manyfold when compared with conventional TI/FM heterostructures. 

The NM layer, due to proximity with a TI, attains enhanced Rashba spin splitting which is topologically protected. The enhanced spin splitting in the proximitized NM due to TI acts as a highly efficient spin hall material with SOT efficiency almost the same as or better than a TI. These TI/NM heterostructures solve several problems associated with TI based spintronic devices.

Benefits

• Dramatic reduction of power dissipation due to presence of a NM conduction channel with proximity induced SOC properties; 
• Barrier against migration of magnetic species when metallic alloy based FM is used; 
• Enabling growth of low temperature MI using spin spray technique which requires exposure of the substrate to atmosphere. 

Applications

• Highly efficient SOT nonvolatile memory (SOT-MRAM).
• SOT‑based power‑efficient logic devices.
• High frequency spin torque nano oscillators (STNO)