Spin-transfer torque

From Wikipedia, the free encyclopedia
Jump to: navigation, search
A simple model of spin-transfer torque for two anti-aligned layers. Current flowing out of the fixed layer is spin-polarized. When it reaches the free layer the majority spins relax into lower-energy states of opposite spin, applying a torque to the free layer in the process.
A schematic diagram of a spin valve/magnetic tunnel junction. In a spin valve the spacer layer (purple) is metallic; in a magnetic tunnel junction it is insulating.

Spin-transfer torque is an effect in which the orientation of a magnetic layer in a magnetic tunnel junction or spin valve can be modified using a spin-polarized current.

Charge carriers (such as electrons) have a property known as spin which is a small quantity of angular momentum intrinsic to the carrier. An electrical current is generally unpolarized (consisting of 50% spin-up and 50% spin-down electrons); a spin polarized current is one with more electrons of either spin. By passing a current through a thick magnetic layer, one can produce a spin-polarized current. If a spin-polarized current is directed into a magnetic layer, angular momentum can be transferred to the layer, changing its orientation. This can be used to excite oscillations or even flip the orientation of the magnet. The effects are usually only seen in nanometer scale devices.

Spin-transfer torque memory[edit]

Spin-transfer torque can be used to flip the active elements in magnetic random-access memory. Spin-transfer torque random-access memory (STT-RAM) has the advantages of lower power consumption and better scalability over conventional magnetoresistive random-access memory (MRAM) which uses magnetic fields to flip the active elements. The name STT-RAM was first coined by Grandis, Inc.[citation needed] Spin-transfer torque technology has the potential to make possible MRAM devices combining low current requirements and reduced cost; however, the amount of current needed to reorient the magnetization is at present (2008) too high for most commercial applications, and the reduction of this current density alone is the basis for current academic research in spin electronics.[1]

Hynix Semiconductor and Grandis formed a partnership in April 2008 to explore commercial development of STT-RAM technology.[2][3] On August 1, 2011, Grandis announced that it had been purchased by Samsung Electronics for an undisclosed sum.[4]

Hitachi and Tohoku University demonstrated a 32-Mbit STT-RAM in June 2009.[5]

In 2011, Qualcomm presented a 1 Mbit Embedded STT-MRAM, manufactured in TSMC's 45 nm LP technology at the Symposium on VLSI Circuits.[6]

Other companies working on STT-RAM include Everspin Technologies,[7] Crocus Technology[8] and Spin Transfer Technologies.[9] In May 2011, Russian Nanotechnology Corp. announced an investment of $300 million in Crocus Nano Electronics (a joint venture with Crocus Technology) which will build an MRAM factory in Moscow, Russia.

See also[edit]


  1. ^ Ralph, D. C.; Stiles, M. D. (April 2008). "Spin transfer torques". Journal of Magnetism and Magnetic Materials 320 (7): 1190–1216. arXiv:0711.4608. doi:10.1016/j.jmmm.2007.12.019. ISSN 0304-8853. Retrieved 2009-05-22. 
  2. ^ "Grandis press release describing partnership with Hynix" (PDF). Grandis. 2008-04-01. Archived from the original on 2012-04-14. Retrieved 2008-08-15. 
  3. ^ "Hynix press release describing partnership with Grandis". Hynix. 2008-04-02. Retrieved 2008-08-15. [dead link]
  4. ^ [1][dead link]
  5. ^ "Session 8-4: 32-Mb 2T1R SPRAM with localized bi-directional write driver and '1'/'0' dual-array equalized reference cell". vlsisymposium.org. Archived from the original on 12 March 2012. 
  6. ^ Kim, J.P.; Qualcomm Inc., San Diego, CA, USA; Taehyun Kim; Wuyang Hao; Rao, H.M.; Kangho Lee; Xiaochun Zhu; Xia Li; Wah Hsu; Kang, S.H.; Matt, N.; Yu, N. (15–17 June 2011). "A 45nm 1Mb embedded STT-MRAM with design techniques to minimize read-disturbance". 2011 Symposium on VLSI Circuits (VLSIC),ieeexplore.ieee.org (IEEE). ISBN 978-1-61284-175-5. ISSN 2158-5601. 
  7. ^ "Everspin Technologies". everspin.com. Retrieved 2014-07-30. 
  8. ^ "Crocus press release describing MRAM new prototype". crocus-technology.com. Crocus. 2009-10-01. Archived from the original on 20 April 2012. 
  9. ^ "Interview with Vincent Chun from Spin Transfer Technologies". Mram-info.com. Retrieved 2014-02-07. 

External links[edit]