Mram

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

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