Circuits and devices based on enhanced spin hall effect for efficient spin transfer torque

Patent metadata

Field	Value
Publication number	US-10008248-B2
Application number	US-201515327017-A
Country	US
Kind code	B2
Filing date	Jul 17, 2015
Priority date	Jul 17, 2014
Publication date	Jun 26, 2018
Grant date	Jun 26, 2018

Abstract

Devices or circuits based on spin torque transfer (STT) and Spin Hall effect are disclosed by using a spin Hall effect (SHE) metal layer coupled to a magnetic free layer for various applications. The efficiency or strength of the STT effect based on this combination of SHE and STT can be enhanced by an interface modification between the SHE metal layer and the magnetic free layer or by modifying or engineering the SHE metal layer by doping the SHE metal with certain impurities or other means.

First claim

What is claimed is what is described and illustrated, including:

1. A device based on a spin Hall effect (SHE) and spin transfer torque (STT) effect, comprising:
a magnetic structure including a ferromagnetic layer having a magnetization direction that can be changed by spin transfer torque;
a SHE layer that is electrically conducting and exhibits a spin Hall effect to, in response to an applied charge current, generate a spin-polarized current that is perpendicular to the applied charge current, the SHE layer located adjacent to the ferromagnetic layer to inject the spin-polarized current into the ferromagnetic layer; and
a metal insertion layer in contact with and located between, the ferromagnetic layer and the SHE layer, through which the spin-polarized current generated by the SHE layer enters the ferromagnetic layer, the metal insertion layer having a thickness less than a spin diffusion length of the SHE layer and exhibiting an electrical resistivity greater than an electrical resistivity of the SHE layer to enhance a switching of the magnetization direction of the ferromagnetic layer by the spin transfer torque effect, wherein an interface of the metal insertion layer with the magnetic free layer has a spin mixing conductance that is greater than a conductance of the insertion layer.

2. The device as in claim 1 , further comprising:
a first electrical contact in contact with a first location of the SHE layer;
a second electrical contact in contact with a second location of the SHE layer so that the first and second locations are on two opposite sides of the magnetic structure;
a third electrical contact in contact with the magnetic structure;
a magnetic structure circuit coupled between one of the first and second electrical contacts and the third electrical contact to supply a current or a voltage to the magnetic structure; and
a charge current circuit coupled between the first and second electrical contacts to supply the charge current into the SHE layer.

3. A device based on a spin Hall effect (SHE) and spin transfer torque (STT) effect, comprising:
a magnetic structure including a ferromagnetic layer having a magnetization direction that can be changed by spin transfer torque;
a SHE layer that is electrically conducting and exhibits a spin Hall effect to, in response to an applied charge current, generate a spin-polarized current that is perpendicular to the applied charge current, the SHE layer located adjacent to the ferromagnetic layer to inject the spin-polarized current into the ferromagnetic layer; and
a metal insertion layer in contact with and located between, the ferromagnetic layer and the SHE layer, through which the spin-polarized current generated by the SHE layer enters the ferromagnetic layer, the metal insertion layer having a thickness less than a spin diffusion length of the SHE layer and exhibiting an electrical resistivity greater than an electrical resistivity of the SHE layer to enhance a switching of the magnetization direction of the ferromagnetic layer by the spin transfer torque effect, wherein the SHE layer includes:
a SHE metal material that exhibits a first resistivity without any doping or alloying; and
a different metal element doped in or alloyed with the SHE metal material to cause the doped or alloyed SHE metal to exhibit a second resistivity higher than the first resistivity without degrading a spin Hall conductivity of the SHE metal material.

4. The device as in claim 2 , wherein:
the magnetic structure includes a magnetic tunneling junction (MTJ) which includes (1) the ferromagnetic layer as a free layer of the MTJ, (2) a pinned magnetic layer having a fixed magnetization direction and (3) a non-magnetic junction layer between the free layer and the pinned magnetic layer to allow tunneling of electrons between the free layer and the pinned magnetic layer;
the charge current circuit is coupled to supply a constant current as the charge current via the first and second electrical contacts in the SHE layer to cause a precession of the magnetization of the free layer due to the spin-polarized current; and
the magnetic structure circuit is coupled to supply a MTJ current across the MTJ to cause a current tunneling across the MTJ that oscillates due to the precession of the magnetization of the free magnetic layer, wherein magnetic structure circuit is configured to adjust the MTJ junction current to control an oscillation frequency or an amplitude of the oscillation in the current tunneling across the MTJ.

5. A device based on a spin Hall effect (SHE) and spin transfer torque (STT) effect, comprising:
a magnetic structure including a ferromagnetic layer having a magnetization direction that can be changed by spin transfer torque;
a SHE layer that is electrically conducting and exhibits a spin Hall effect to, in response to an applied charge current, generate a spin-polarized current that is perpendicular to the applied charge current, the SHE layer located adjacent to the ferromagnetic layer to inject the spin-polarized current into the ferromagnetic layer, wherein the SHE layer includes a SHE metal material that exhibits a first resistivity without any doping or alloying; and a different metal element doped in or alloyed with the SHE metal material to cause the doped or alloyed SHE metal to exhibit a second resistivity higher than the first resistivity without degrading a spin Hall conductivity of the SHE metal material;
a first electrical contact in contact with a first location of the SHE layer;
a second electrical contact in contact with a second location of the SHE layer so that the first and second locations are on two opposite sides of the magnetic structure;
a third electrical contact in contact with the magnetic structure;
a magnetic structure circuit coupled between one of the first and second electrical contacts and the third electrical contact to supply a small current across the ferromagnetic layer that co-propagates with the spin-polarized current and is insufficient to switch the magnetization of the ferromagnetic layer without the spin-polarized current and the small current and the spin-polarized current together are sufficient to switch the magnetization of the ferromagnetic layer; and
a charge current circuit coupled between the first and second electrical contacts to supply the charge current into the SHE layer,
wherein the different metal element doped or alloyed with the SHE metal material is selected so that the doped or alloyed SHE metal reduces a total power of the magnetic structure circuit magnetic structure circuit that is needed to switch the magnetization of the ferromagnetic layer when comparing a total power needed without the different metal element doped or alloyed with the SHE metal material.

6. The device as in claim 5 , wherein:
the SHE metal material includes Pt, and
the different metal element doped or alloyed with Pt includes (1) Al, B or Si, or (2) Hf, Zr, Cr or Ta.

7. The device as in claim 5 , wherein:
the magnetic structure includes a magnetic tunneling junction (MTJ) which includes (1) the ferromagnetic layer as a free layer of the MTJ, (2) a pinned magnetic layer having a fixed magnetization direction and (3) a non-magnetic junction layer between the free layer and the pinned magnetic layer to allow tunneling of electrons between the free layer and the pinned magnetic layer;
the third electrical terminal is in electrical contact with the MTJ from a side having the pinned magnetic layer to receive a gate voltage that modifies a current threshold of a spin-polarized current flowing across the MTJ for switching the magnetization of the free layer; and
the magnetic structure circuit is coupled to supply (1) the gate voltage across the MTJ causing a small current tunn

Assignees

• Univ Cornell

Inventors

• Buhrman Robert A
• Nguyen Minh-Hai
• Pai Chi-Feng
• Ralph Daniel C

Classifications

• H01L43/10

  Electricity · mapped topic

• H01L43/08

  Electricity · mapped topic

• H01L43/04

  Electricity · mapped topic

• G11C11/161 Primary

  details concerning the memory cell structure, e.g. the layers of the ferromagnetic memory cell · CPC title

• G11C11/1673

  Reading or sensing circuits or methods · CPC title