Mram

ext">MRAM chip design (Credit: Freescale)data when the computer is suddenly shut off. MRAM
In early July 2006, Freescale Semiconductorhas much faster write speeds than Flash and has an
announced the first commercial availability of a newunlimited endurance, meaning that MRAM is not
type of memory with the potential to surpass mostsubject to the degradation suffered by Flash.
existing types in terms of speed, powerConventional RAM memory is made of transistors
consumption, and durability. This article reviews theand capacitors that are paired to create a memory
advantages of MRAM and its future potential.cell, which represents one bit of data (0 or 1).
With the continual release in recent years of newMemory cells are aligned in columns and rows, the
types of computer memory (RAM, ROM, DRAM,intersections of which are known as addresses in
Flash, SRAM, PRAMÂ…), the memory chip industrywhich information is stored. Reading and writing
has become an ever more bewildering world.information occurs by measuring or changing the
Freescale's MRAM, one of the latest to becharge at a specific address, accordingly.
commercially unveiled, improves on and combines theMRAM read process - Current is passed through the
advantages of two types of conventional memory.bit, resistance of the bit is sensed (Credit: Freescale)
The various types of computer memory can beMRAM works in a different way, more like the read
classified in several different ways, the simplest ofwrite head of a hard drive. But unlike a hard drive,
which is the division into volatile and non-volatilewhich includes mechanical parts (the moving arm
memory. Volatile memory requires constant power toholding the read/write head and the rotating plates
maintain stored information. Most types of RAMon which the information is stored), MRAM is a solid
(random access memory), the most common typestate device and, as such, has much greater speed
of memory used by modern computers are volatile,and durability. Like conventional RAM, MRAM is
Thus, to store information, conventional RAMcomposed of transistors but, instead of electrical
computer chips are dependent upon electricitycharges, it uses magnetic charges to store
flowing through them. When the power is switchedinformation. An MRAM chip is made up of millions of
off (i.e., when the system is "powered down"), unlesspairs of tiny ferromagnetic plates (like the one
the information has been copied to the hard drive,covering hard drives) called memory cells, i.e.,
the information is lost.magnetic sandwiches consisting of two magnetic
Non-volatile memory, on the other hand, can retainlayers separated by a very thin insulating layer. Each
stored information permanently, absolving the needmagnetic layer has a polarity — a north pole
for a constant power supply. ROM (read-onlyand a south pole. These can be oriented in a parallel
memory), which stores information that does notorientation, meaning that both have their respective
require frequent changing (i.e., doesn't need rewriting),poles (or 'magnetic moments') in the same
such as Firmware (a software embedded inside aorientation, or in an anti-parallel fashion, meaning that
hardware such as a BIOS [basic input-outputtheir poles/magnetic moments are oriented in
system]) is typically non-volatile. So, even when theopposite directions. These relative magnetic pole
system is off, the data is stored.orientations correspond to the binary memory states,
Modern types of ROM such as Flash, used in thumbeither 0 or 1.
drives and many MP3 players, are also non-volatile,MRAM write process - Current is passed through the
but easily rewritable, making them more like RAM.programming lines generating magnetic fields. The
This combination of qualities has made Flash memorysum of the magnetic fields from both lines is needed
highly popular in recent years and it is currently usedto program the bit. (Credit: Freescale)
to improve other types of storage such as hardAn MRAM chip reads information by measuring the
drives or even replace them altogether. But althoughelectrical resistance of a specific cell that, in turn,
Flash is cheap and non-volatile, it still suffers from adepends upon the alignment of the magnetic
relatively limited lifetime. Though this had improvedmoments of the layers of the cell. To read a bit of
considerably in the last few years, more importantly,information, a current is passed through the memory
Flash still has a much lower write speed than RAM.cell. If the magnetic moments are in a parallel
In an attempt to combine the speed of the fasterorientation, then the detected resistance would be
volatile memory with the benefits of non-volatilesmaller than if they were in an anti-parallel orientation.
memory, Freescale (which originated from MotorolaWrite is achieved by the alignment of the magnetic
Semiconductor about two years ago) created a newmoments of the two memory layers into one or the
type of non-volatile memory - Magnetoresistiveother relative orientation. Current is passed through
Random Access Memory, or MRAM. The roots oftwo sets of parallel wires or write lines (called a bit
MRAM can be traced back to the 1940's at Harvardline and a digit or word line), which pass over and
when physicists An Wang and Way-Dong Woo andbeneath the memory cells, respectively. The bit lines
later Jay Forrester and colleagues at MIT worked onand the digit lines run perpendicular to one another
developments that led to Magnetic Core Memory andand at their intersections lie the magnetic memory
later on to the discovery of the "giantcells, each defined by one particular bit line and one
magnetoresistive effect" in thin-film structures byparticular digit line. To write to a particular memory
researchers from IBM in the late 1980's. Like Flash,cell (bit), current is passed through the two wires
MRAM retains data after a power supply is cut off,that intersect at that memory cell. The magnetic field
potentially eliminating that seemingly endless bootthat is generated from current passing through a
time of conventional computers when data from thewire can change the orientation of the magnetic
hard drive is transferred to RAM, as well as loss ofmoments of the particular memory cell.