02-08-2013, 04:09 PM
Magnetic random access memory (MRAM)
[attachment=56956]
INTRODUCTION
In February -2006. Toshiba and NEC announced a 16 Mbit MRAM chip with a new "power-forking" design. It achieves a transfer rate of 200 MB/s, with a 34 ns cycle time - the best performance of any MRAM chip.
We hit the power button on our television and it instantly comes to life. But do the same thing with our computer and we have to wait a few minutes while it goes through its boot up sequence.
Why can't we have a computer that turns on as instantly as a television or radio? IBM, in cooperation with Infineon, is promising to launch a new technology in the next few years that will eliminate the boot-up process.
Magnetic random access memory (MRAM) has the potential to store more data, access that data faster and use less power than current memory technologies. The key to MRAM is that, as its name suggests, it uses magnetism rather than electrical power to store data. This is a major leap from dynamic RAM (DRAM), the most common type of memory in use today, which requires a continuous supply of electricity and is terribly inefficient.
ATTRACTIONS OF THIS NEW TECHNOLOGY
Consider what happens when power goes off while we are typing on our computer? Unless we are connected to an uninterruptible power supply we lose everything we were working on since we last saved the document. That's because our computer's random access memory (RAM), which stores information for fast access, can't function without power. The same goes for our cell phone and PDA. Both require a battery to keep the RAM intact with our phone numbers and personal data. But IBM researchers have developed a new form of RAM - magnetic RAM (MRAM) - that doesn't forget anything when the power goes out.
MRAM promises to be
•Cheap
•Fast
•Nonvolatile
•Low power alternative
MRAM has these attractions over conventional RAM, which uses electrical cells to store data, as MRAM uses magnetic cells. This method is similar to the way our hard drive stores information. When we remove power from our computer, conventional RAM loses memory, but the data on our hard disk remains intact due to its magnetic orientation, which represents binary information. Because magnetic memory cells maintain their state even when power is removed, MRAM possesses a distinct advantage over electrical.
With DRAM (RAM used in PCs and workstations) we store a charge in a capacitor. That charge will leak away over time and it needs to be refreshed frequently that takes power. But with MRAM we have no such problems .We need no power to maintain the state, and toy only need to pass a small current through the memory to read it Compared with SRAM(RAM used to build fast memory, cache) MRAMs are as fast as SRAM with read/write speeds better than 2.5 nanoseconds. Moreover MRAMs can be build smaller than SRAM and hence would be cheaper.
HOW MRAM WORKS
INSTANT ON COMPUTING
When we turn our computer on, we can hear it revving up. It takes a few minutes before we can actually get to programs to run. If we just want to browse the Internet, we have to wait for our computer is start-up sequence to finish before we can go to our favorite Web sites. We push the computer's power button, there's some beeping and humming, we see flashes of text on the screen and we count the seconds ticking by. It's a very slow process. Why can't it simply turn on like our television? -- hit a button and instantly our Internet browser is ready to go. What is it that our computer has to do when we turn it on? Every computer has a basic input/output system (BIOS) that performs a series of functions during the boot up sequence. The series of functions performed by BIOS includes:-
• A power-on self-test (POST) for all of the different hardware components in the
System to make sure everything is working properly
•Activating other BIOS chips on different cards installed in the computer - For example,
SCSI and graphics card often have their own BIOS chips
•Providing a set of low level routines that the operating system uses to interface different
Hardware devices
MAGNETIC RAM ARCHITECTURE
Like Flash memory, MRAM is a nonvolatile memory -- a solid-state chip that has no moving parts. Unlike with DRAM chips, we don't have to continuously refresh the data on solid-state chips. Flash memory can't be used for instant-on PCs because it hasn't demonstrated long-term reliability. MRAM will likely compete with Flash memory in the portable device market for the same reason that it will replace DRAM -- it reduces power consumption.
In MRAM only a small amount of electricity is needed to store bits of data. This small amount of electricity switches the polarity of each memory cell on the chip. A memory cell is created when word lines (rows) and bit lines (columns) on a chip intersect. Each one of these cells stores a 1 or a 0, representing a piece of data. MRAM promises to combine the high speed of static RAM (SRAM), the storage capacity of DRAM and the non-volatility of Flash Memory.
READING DATA
To read the bit of information stored in this memory cell, we must determine the orientation of the two magnetic moments. Passing a small electric current directly through the memory cell accomplishes this. When the moments are parallel, the resistance of the memory cell is smaller than when the moments are not parallel. Even though there is an insulating layer between the magnetic layers, the insulating layer is so thin that electrons can "tunnel" through it from one magnetic layer to the other.
WRITING DATA
To write to the device, we pass currents through wires close to (but not connected to) the magnetic cells. Because any current through a wire generates a magnetic field, we can use this field to change the direction of the magnetic moment. The arrangement of the wires and cells is called cross-point architecture: the magnetic junctions are set up along the intersection points of a grid. Wires - called word lines -run in parallel below the magnetic cells. Another set of wires - called bit lines - runs above the magnetic cells and perpendicular to the set of wires below.Like coordinates on a map, choosing one particular word line and one particular bit line uniquely specifies one of the memory cells. To write to a particular cell (bit), a current is passed through the two independent wires (one above and one below) that intersect at that particular cell. Only the cell at the cross point of the two wires sees the magnetic fields from both currents and changes state.
MAGNETIC TUNNEL JUNCTIONS
MRAM works by etching a grid of crises-crossing wires on a chip in two layers-with the horizontal wires being placed just below the vertical wires. At each intersection, a "magnetic tunnel junction" (MTJ) is created that serves as a switch-and thus as a repository for a single bit of memory. The MTJ is essentially a small magnet whose direction is easily flipped.
Common materials for the MTJ include chromium dioxide and iron-cobalt alloys. Current runs perpendicularly, "tunneling" through the insulator that separates it from a sheath of copper. At the base of one of the electrodes is a fixed anti-ferromagnetic layer that creates a strong coupling field. When a magnetic field is applied, electrons flow from one electrode to another, creating 0 and 1 states.
[attachment=56956]
INTRODUCTION
In February -2006. Toshiba and NEC announced a 16 Mbit MRAM chip with a new "power-forking" design. It achieves a transfer rate of 200 MB/s, with a 34 ns cycle time - the best performance of any MRAM chip.
We hit the power button on our television and it instantly comes to life. But do the same thing with our computer and we have to wait a few minutes while it goes through its boot up sequence.
Why can't we have a computer that turns on as instantly as a television or radio? IBM, in cooperation with Infineon, is promising to launch a new technology in the next few years that will eliminate the boot-up process.
Magnetic random access memory (MRAM) has the potential to store more data, access that data faster and use less power than current memory technologies. The key to MRAM is that, as its name suggests, it uses magnetism rather than electrical power to store data. This is a major leap from dynamic RAM (DRAM), the most common type of memory in use today, which requires a continuous supply of electricity and is terribly inefficient.
ATTRACTIONS OF THIS NEW TECHNOLOGY
Consider what happens when power goes off while we are typing on our computer? Unless we are connected to an uninterruptible power supply we lose everything we were working on since we last saved the document. That's because our computer's random access memory (RAM), which stores information for fast access, can't function without power. The same goes for our cell phone and PDA. Both require a battery to keep the RAM intact with our phone numbers and personal data. But IBM researchers have developed a new form of RAM - magnetic RAM (MRAM) - that doesn't forget anything when the power goes out.
MRAM promises to be
•Cheap
•Fast
•Nonvolatile
•Low power alternative
MRAM has these attractions over conventional RAM, which uses electrical cells to store data, as MRAM uses magnetic cells. This method is similar to the way our hard drive stores information. When we remove power from our computer, conventional RAM loses memory, but the data on our hard disk remains intact due to its magnetic orientation, which represents binary information. Because magnetic memory cells maintain their state even when power is removed, MRAM possesses a distinct advantage over electrical.
With DRAM (RAM used in PCs and workstations) we store a charge in a capacitor. That charge will leak away over time and it needs to be refreshed frequently that takes power. But with MRAM we have no such problems .We need no power to maintain the state, and toy only need to pass a small current through the memory to read it Compared with SRAM(RAM used to build fast memory, cache) MRAMs are as fast as SRAM with read/write speeds better than 2.5 nanoseconds. Moreover MRAMs can be build smaller than SRAM and hence would be cheaper.
HOW MRAM WORKS
INSTANT ON COMPUTING
When we turn our computer on, we can hear it revving up. It takes a few minutes before we can actually get to programs to run. If we just want to browse the Internet, we have to wait for our computer is start-up sequence to finish before we can go to our favorite Web sites. We push the computer's power button, there's some beeping and humming, we see flashes of text on the screen and we count the seconds ticking by. It's a very slow process. Why can't it simply turn on like our television? -- hit a button and instantly our Internet browser is ready to go. What is it that our computer has to do when we turn it on? Every computer has a basic input/output system (BIOS) that performs a series of functions during the boot up sequence. The series of functions performed by BIOS includes:-
• A power-on self-test (POST) for all of the different hardware components in the
System to make sure everything is working properly
•Activating other BIOS chips on different cards installed in the computer - For example,
SCSI and graphics card often have their own BIOS chips
•Providing a set of low level routines that the operating system uses to interface different
Hardware devices
MAGNETIC RAM ARCHITECTURE
Like Flash memory, MRAM is a nonvolatile memory -- a solid-state chip that has no moving parts. Unlike with DRAM chips, we don't have to continuously refresh the data on solid-state chips. Flash memory can't be used for instant-on PCs because it hasn't demonstrated long-term reliability. MRAM will likely compete with Flash memory in the portable device market for the same reason that it will replace DRAM -- it reduces power consumption.
In MRAM only a small amount of electricity is needed to store bits of data. This small amount of electricity switches the polarity of each memory cell on the chip. A memory cell is created when word lines (rows) and bit lines (columns) on a chip intersect. Each one of these cells stores a 1 or a 0, representing a piece of data. MRAM promises to combine the high speed of static RAM (SRAM), the storage capacity of DRAM and the non-volatility of Flash Memory.
READING DATA
To read the bit of information stored in this memory cell, we must determine the orientation of the two magnetic moments. Passing a small electric current directly through the memory cell accomplishes this. When the moments are parallel, the resistance of the memory cell is smaller than when the moments are not parallel. Even though there is an insulating layer between the magnetic layers, the insulating layer is so thin that electrons can "tunnel" through it from one magnetic layer to the other.
WRITING DATA
To write to the device, we pass currents through wires close to (but not connected to) the magnetic cells. Because any current through a wire generates a magnetic field, we can use this field to change the direction of the magnetic moment. The arrangement of the wires and cells is called cross-point architecture: the magnetic junctions are set up along the intersection points of a grid. Wires - called word lines -run in parallel below the magnetic cells. Another set of wires - called bit lines - runs above the magnetic cells and perpendicular to the set of wires below.Like coordinates on a map, choosing one particular word line and one particular bit line uniquely specifies one of the memory cells. To write to a particular cell (bit), a current is passed through the two independent wires (one above and one below) that intersect at that particular cell. Only the cell at the cross point of the two wires sees the magnetic fields from both currents and changes state.
MAGNETIC TUNNEL JUNCTIONS
MRAM works by etching a grid of crises-crossing wires on a chip in two layers-with the horizontal wires being placed just below the vertical wires. At each intersection, a "magnetic tunnel junction" (MTJ) is created that serves as a switch-and thus as a repository for a single bit of memory. The MTJ is essentially a small magnet whose direction is easily flipped.
Common materials for the MTJ include chromium dioxide and iron-cobalt alloys. Current runs perpendicularly, "tunneling" through the insulator that separates it from a sheath of copper. At the base of one of the electrodes is a fixed anti-ferromagnetic layer that creates a strong coupling field. When a magnetic field is applied, electrons flow from one electrode to another, creating 0 and 1 states.