| Magnetic
Random
Access Memory |
Definition
MRAM is a nonvolatile random access memory which uses magnetic storage and
magnetoresistance (MR) to read the stored data. Magnetoresistive material is a
resistor made of common ferromagnetic material which will change in resistance
in the presence of a magnetic field. The magnetoresistive property gives a small
but sufficient signal to distinguish between a "1" and "0".
MRAM results from combining MR storage elements with standard semiconductor fabrication
processes. The magnetic devices are integrated with support circuits on a single
silicon chip to duplicate the function of a static semiconductor RAM chip. The
magnetic storage elements are formed from a layer of permalloy thin film where
the intersection of the permalloy (sense line) and metal layer (word line) form
a memory bit. The general attributes of MRAM
are:
1. Nonvolatility
2. Infinite write cycling without wearout
3. Fast write (few nanoseconds for
advanced modes)
4. Low write energy
5. Nondestructive read.
When
combined with the high density of advanced GMR cells, these attributes lead to
the "perfect memory" with speed, density and limited cycling of SRAM
and DRAM and the nonvolatility of EEPROM, flash and other nonvolatile memories.
In random access magnetoresistive memories (MRAM), storing data is accomplished
by applying magnetic fields and thereby causing a magnetic material in a cell
to be magnetized into either of two possible memory states. Recalling data is
accomplished by sensing resistance changes in the cell when magnetic fields are
applied. The magnetic fields are created by passing currents through strip lines
(word lines) external to the magnetic structure, or through the magnetic structures
themselves (sense lines). MRAM cells are narrow stripes etched into a multi-layer
thin film stack of permalloy-copper-permalloy. Data is stored by magnetizing the
stripe.
MRAM
is a non-volatile random access memory which uses magnetisation direction in a
ferromagnetic material for data storage and magnetoresistance to read the stored
data. The development of MRAM started with
Anisotropic Magnetoresistace materials. Dr.Pohm,Dr.Doughton and others at the
Nonvolatile Electronics,Inc. continued to improve the basic MRAM technology and
innovated new techniques which take advantage of revolutionary advances in magnetoresistive
devices namely, Giant Magnetoresistance (GMR) and Spin Dependent Tunneling (SDT
) memories.
The general attributes of MRAM
are:
a.Non-volatility
b.Fast write (few nanoseconds for advanced modes)
c.Low power consumption
d.High density
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