| ext">MRAM chip design (Credit: Freescale) | | | | data when the computer is suddenly shut off. MRAM |
| In early July 2006, Freescale Semiconductor | | | | has much faster write speeds than Flash and has an |
| announced the first commercial availability of a new | | | | unlimited endurance, meaning that MRAM is not |
| type of memory with the potential to surpass most | | | | subject to the degradation suffered by Flash. |
| existing types in terms of speed, power | | | | Conventional RAM memory is made of transistors |
| consumption, and durability. This article reviews the | | | | and 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 new | | | | Memory 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 industry | | | | which 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 be | | | | charge at a specific address, accordingly. |
| commercially unveiled, improves on and combines the | | | | MRAM 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 be | | | | MRAM works in a different way, more like the read |
| classified in several different ways, the simplest of | | | | write head of a hard drive. But unlike a hard drive, |
| which is the division into volatile and non-volatile | | | | which includes mechanical parts (the moving arm |
| memory. Volatile memory requires constant power to | | | | holding the read/write head and the rotating plates |
| maintain stored information. Most types of RAM | | | | on which the information is stored), MRAM is a solid |
| (random access memory), the most common type | | | | state 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 RAM | | | | composed of transistors but, instead of electrical |
| computer chips are dependent upon electricity | | | | charges, it uses magnetic charges to store |
| flowing through them. When the power is switched | | | | information. An MRAM chip is made up of millions of |
| off (i.e., when the system is "powered down"), unless | | | | pairs 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 retain | | | | layers separated by a very thin insulating layer. Each |
| stored information permanently, absolving the need | | | | magnetic layer has a polarity — a north pole |
| for a constant power supply. ROM (read-only | | | | and a south pole. These can be oriented in a parallel |
| memory), which stores information that does not | | | | orientation, 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 a | | | | orientation, or in an anti-parallel fashion, meaning that |
| hardware such as a BIOS [basic input-output | | | | their poles/magnetic moments are oriented in |
| system]) is typically non-volatile. So, even when the | | | | opposite 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 thumb | | | | either 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 memory | | | | sum of the magnetic fields from both lines is needed |
| highly popular in recent years and it is currently used | | | | to program the bit. (Credit: Freescale) |
| to improve other types of storage such as hard | | | | An MRAM chip reads information by measuring the |
| drives or even replace them altogether. But although | | | | electrical resistance of a specific cell that, in turn, |
| Flash is cheap and non-volatile, it still suffers from a | | | | depends upon the alignment of the magnetic |
| relatively limited lifetime. Though this had improved | | | | moments 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 faster | | | | orientation, then the detected resistance would be |
| volatile memory with the benefits of non-volatile | | | | smaller than if they were in an anti-parallel orientation. |
| memory, Freescale (which originated from Motorola | | | | Write is achieved by the alignment of the magnetic |
| Semiconductor about two years ago) created a new | | | | moments of the two memory layers into one or the |
| type of non-volatile memory - Magnetoresistive | | | | other relative orientation. Current is passed through |
| Random Access Memory, or MRAM. The roots of | | | | two sets of parallel wires or write lines (called a bit |
| MRAM can be traced back to the 1940's at Harvard | | | | line and a digit or word line), which pass over and |
| when physicists An Wang and Way-Dong Woo and | | | | beneath the memory cells, respectively. The bit lines |
| later Jay Forrester and colleagues at MIT worked on | | | | and the digit lines run perpendicular to one another |
| developments that led to Magnetic Core Memory and | | | | and at their intersections lie the magnetic memory |
| later on to the discovery of the "giant | | | | cells, each defined by one particular bit line and one |
| magnetoresistive effect" in thin-film structures by | | | | particular 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 boot | | | | that is generated from current passing through a |
| time of conventional computers when data from the | | | | wire can change the orientation of the magnetic |
| hard drive is transferred to RAM, as well as loss of | | | | moments of the particular memory cell. |