Magnetoresistive Random Access Memory

Magnetoresistive Random Access Memory (MRAM ) is a non-volatile memory technology that has been developed since the 1990s.

Principle of operation

Unlike conventional storage techniques, such as DRAM or SRAM, the information is not stored by electric, magnetic charge but with elements, that is, it is the property of certain materials used to change the electrical resistance under the influence of magnetic fields. In principle, different mechanisms can be used:

  • The anisotropic magnetoresistance (English: Anisotropic Magnetoresistance, AMR )
  • Giant magnetoresistance (English: giant magnetoresistance, GMR)
  • Tunnelling Magnetoresistance (English: tunneling magnetoresistance TMR )

The latter is currently the favored technology for the development of magnetoresistive RAM.

The advantage of MRAM technology is that it is non-volatile, which means that the chips retain their stored data even after switching off the power supply. This allows electronic devices such as computers, can be realized that are immediately ready for operation after power and not only download the necessary data from a read-only memory as a hard disk, need to load into memory. In contrast to established non-volatile memory technologies such as Flash, MRAM as conventional DRAM / SRAM can be described practically infinite number of times. Read and write access times are in the range of DRAM to SRAM. MRAM is to combine so the benefits of various established storage technologies, and thus have the potential for so-called " universal memory ", DRAM, SRAM and Flash could replace.

Currently ( August 2012) is the company Ever Spin Technologies the only commercial supplier of MRAM memory chips. Ever textile used to 16 Mbit TMR technology in the so-called "Toggle Write" variant. In this case, the magnetic bit is set by the magnetic field of two external write lines in the crossing point, the magnetic field is added, thus achieving a strength with which the magnetic polarization of the cell is changed. For the beginning of 2013 the introduction of so-called "spin torque " building blocks is announced. Here, the polarization of the cell is changed by means of a current flowing through the cell. The spin torque technology enables the production of MRAM in smaller structure sizes, and therefore is considered promising. Almost all other major memory manufacturers like Samsung, Hynix, etc. have announced plans to invest in the MRAM development and manufacturing.

Application

Due to the high price is MRAM since 2008 primarily for use in industrial systems to prevent critical data loss. Typical applications include programmable logic controllers ( PLC), POS / Electronic Cash, GPS tracker or as a cache in server systems. Also in the aerospace industry are MRAM due to their high resistance to radiation levels in that. First use found MRAM memory in slot machines to replace battery-backed SRAM memory.

History

In summer 2003, a 128- kilobits - MRAM chip was introduced, which was made with the 0.18 -micron technology.

In June 2004, Infineon has the first 16 -Mbit MRAM chip, also presented in 0.18 -micron technology,

Freescale Semiconductor (formerly Motorola Semiconductor) commenced delivery of 4 -Mbit prototype (0.18 microns ) in late 2004. After years of research and development and a long sampling phase is scheduled to begin at Freescale now the series production of the 4 -Mbit MRAM MR2A16A. This memory chip is very expensive compared to SDR or DDR SDRAMs with about 25 U.S. dollars, which greatly restricts its application. A Lese-/Schreibzyklus takes 35 ns, so many times longer than SDRAM or even newer RAM technologies.

As part of a management buy-out Freescale's MRAM technology is now produced and distributed by Ever Spin Technologies. There are different products available, which differ both in overall memory size (256 Kbytes to 16 Mbytes ) and in memory word width (8 bits or 16 bits).

The series production of the MRAM has been announced by various companies (IBM, Infineon, Motorola) already for the years 2004/2005. Many renowned companies have withdrawn completely from this branch because of problems in the mass production of chips or have the series production moved to the end of the decade. Due to the cost position and magnitude MRAM was far more suitable for niche applications. With the introduction of spin torque MRAM (ST- MRAM) is to be expected that MRAM gain market share in the coming years.

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