22-04-2011, 04:43 PM
Presented By
PRADARTTANA PANDA
MRAM.doc (Size: 522.5 KB / Downloads: 69)
ABSTRACT
MRAM (magnetoresistive random access memory) is a method of storing data bits using magnetic charges instead of the electrical charges used by DRAM (dynamic random access memory). Scientists define a metal as magnetoresistive if it shows a slight change in electrical resistance when placed in a magnetic field. By combining the high speed of static RAM and the high density of DRAM, proponents say MRAM could be used to significantly improve electronic products by storing greater amounts of data, enabling it to be accessed faster while consuming less battery power than existing electronic memory. Conventional random access memory (RAM) computer chips store information as long as electricity flows through them. Once power is turned off, the information is lost unless it has been copied to a hard drive or floppy disk. MRAM, however, retains data after a power supply is cut off. Replacing DRAM with MRAM could prevent data loss and enable computers that start instantly, without waiting for software to boot up. The U.S. Defense Advanced Research Projects Agency (DARPA) has provided funding to help private industry conduct research into the potential of MRAM. Beginning in 1995, DARPA began funding three private consortia researching the viability of making MRAM a general-purpose memory with high density, high speed, and low power usage. Leading the three consortia were IBM, Motorola, and Honeywell. Hewlett-Packard, Matsushita, NEC, Fujitsu, Toshiba, Hitachi, and Siemens also have invested in MRAM research. Motorola Labs says its "universal memory" allows the integration of several memory options within a single chip, resulting in a chip that uses less power. The chip is a three-volt MRAM with an address access time of about 15 nanoseconds. IBM and Infineon Technologies AG are working on a proposed 256-megabit chip they say could be on the market in 2004. Development of MRAM basically followed two scientific schools: 1) spin electronics, the science behind giant magnetoresistive heads used in disk drives and 2) tunneling magnetic resistance, or TMR, which is expected to be the basis of future MRAM.
INTRODUCTION:-
Unlike conventional RAM chip technologies, in MRAM data is not stored as electric charge or current flows, but by magnetic storage elements. The elements are formed from two ferromagnetic plates, each of which can hold a magnetic field, separated by a thin insulating layer. One of the two plates is a permanent magnet set to a particular polarity, the other's field can be changed to match that of an external field to store memory. This configuration is known as a spin valve and is the simplest structure for a MRAM bit. A memory device is built from a grid of such "cells".
The simplest method of reading is accomplished by measuring the electrical resistance of the cell. A particular cell is (typically) selected by powering an associated transistor which switches current from a supply line through the cell to ground. Due to the magnetic tunnel effect, the electrical resistance of the cell changes due to the orientation of the fields in the two plates. By measuring the resulting current, the resistance inside any particular cell can be determined, and from this the polarity of the writable plate. Typically if the two plates have the same polarity this is considered to mean "1", while if the two plates are of opposite polarity the resistance will be higher and this means "0".
Data is written to the cells using a variety of means. In the simplest, each cell lies between a pair of write lines arranged at right angles to each other, above and below the cell. When current is passed through them, an induced magnetic field is created at the junction, which the writable plate picks up. This pattern of operation is similar to core memory, a system commonly used in the 1960s. This approach requires a fairly substantial current to generate the field, however, which makes it less interesting for low-power uses, one of MRAM's primary disadvantages. Additionally, as the device is scaled down in size, there comes a time when the induced field overlaps adjacent cells over a small area, leading to potential false writes. This problem, the half-select (or write disturb) problem, appears to set a fairly large size for this type of cell. One experimental solution to this problem was to use circular domains written and read using the giant magnetoresistive effect, but it appears this line of research is no longer active.
Another approach, the toggle mode, uses a multi-step write with a modified multi-layer cell. The cell is modified to contain an "artificial antiferromagnet" where the magnetic orientation alternates back and forth across the surface, with both the pinned and free layers consisting of multi-layer stacks isolated by a thin "coupling layer". The resulting layers have only two stable states, which can be toggled from one to the other by timing the write current in the two lines so one is slightly delayed, thereby "rotating" the field.
Magnetoresistive random access memory (MRAM) stores bits of data by using magnetic charges. MRAM is designed for high density, high speed, and non-volatile devices. MRAM has the potential to replace dynamic random access memory (DRAM), electrically erasable programmable read-only memory (EEPROM), and Flash memory. DRAM uses small capacitors to store each bit of memory in an addressable format that consists of rows and columns. Because capacitors are unable to hold a charge indefinitely, DRAM requires a near-constant pulse of current to retain stored information. EEPROM needs electricity to be erased. Flash does not need a constant power supply to retain data.
MRAM or magnetoresistive RAM is a non-volatile random access memory (RAM) technology made from metals that change only slightly when placed within a magnetic field. To be non-volatile, these types of magnetic RAM retain the data in their memory arrays even when power is turned off. The chief advantage of MRAM over other forms of non-volatile RAM technology is its ability to combine the most commercially appealing attributes of disparate memory technologies (e.g., non-volatility, storage density, and speed) into a single memory solution. Rather than store electrical activity as magnetic charges, the actual magneto-resistive RAM properties store electrical activity as a state, or moment. This is due to the fact that the ferromagnetic material of MRAM allows the binary language of machines (0s and 1s) as polarized electrons, and permits reading of those polarizations against a transistor-type gate known as a tunnel junction.
HISTORY:-
• 2000 - IBM and Infineon established a joint MRAM development program.
• 2000 - Spintec laboratory's first Spin Torque Transfer patent.
• 2002 - NVE Announces Technology Exchange with Cypress Semiconductor.
• 2003 - A 128 kbit MRAM chip was introduced, manufactured with a 180 nm lithographic process
2004
• June - Infineon unveiled a 16-Mbit prototype, manufactured with a 180 nm lithographic process
• September - MRAM becomes a standard product offering at Freescale.
• October - Taiwan developers of MRAM tape out 1 Mbit parts at TSMC.
• October - Micron drops MRAM, mulls other memories.
• December - TSMC, NEC, Toshiba describe novel MRAM cells.
2005
• January - Cypress Semiconductor samples MRAM, using NVE IP.
• March - Cypress to Sell MRAM Subsidiary.
• June - Honeywell posts data sheet for 1-Mbit rad-hard MRAM using a 150 nm lithographic process
• August - MRAM record: memory cell runs at 2 GHz.
• November - Renesas Technology and Grandis collaborate on development of 65 nm MRAM employing spin torque transfer (STT).
• November - NVE receives an SBIR grant to research cryptographic tamper-responsive memory.[12]
• December - Sony announced the first lab-produced spin-torque-transfer MRAM, which utilizes a spin-polarized current through the tunneling magnetoresistance layer to write data. This method consumes less power and is more scalable than conventional MRAM. With further advances in materials, this process should allow for densities higher than those possible in DRAM.
HOW MRAM WORKS:-
MRAM (Magnetoresistive Random Access Memory) uses electron spin to store data. Memory cells are integrated on an integrated circuit chip, and the function of the resulting device is like a semiconductor static RAM (SRAM) chip, with potentially higher density and the added feature that the data are nonvolatile, that is data are retained with power off. Typical “classic”or “conventional” MRAM uses spin-dependent tunnel junction memory cells and magnetic row and column write lines as illustrated below:
The spin-dependent tunnel junction produces a large change in resistance depending on the predominant electron spin in a storage layer. The tunnel barrier (dark green in the figure above) is as thin as a few atomic layers--so thin that electrons can “tunnel” through the normally insulating material, causing a resistance change.
Row and column magnetic write lines allow data to be written to a selected cell in a two-dimensional array:
Data are written by small electrical currents in the write lines that create a magnetic fields, which flip electron spins in the spin-dependent tunnel junction storage layer, thus changing the junction’s resistance. Data is read by the tunneling current or resistance through the tunnel junction.
Next-generation MRAM could reduce cell size and power consumption. Potential next-generation designs include Spin-Momentum Transfer, Magneto-Thermal MRAM, and Vertical Transport MRAM. Spin-Momentum Transfer (also “Spin-Transfer,” “Spin Injection,” or “Spin Torque Transfer”) MRAM is based on changing the spin of storage electrons directly with an electrical current rather than an induced magnetic field. This method has the potential to significantly reduce MRAM write currents, especially with lithographic feature sizes less than 100 nanometers. M-T MRAM uses a combination of magnetic fields and ultra-fast heating from electrical current pulses to reduce the energy required to write data.
PRADARTTANA PANDA
MRAM.doc (Size: 522.5 KB / Downloads: 69)
ABSTRACT
MRAM (magnetoresistive random access memory) is a method of storing data bits using magnetic charges instead of the electrical charges used by DRAM (dynamic random access memory). Scientists define a metal as magnetoresistive if it shows a slight change in electrical resistance when placed in a magnetic field. By combining the high speed of static RAM and the high density of DRAM, proponents say MRAM could be used to significantly improve electronic products by storing greater amounts of data, enabling it to be accessed faster while consuming less battery power than existing electronic memory. Conventional random access memory (RAM) computer chips store information as long as electricity flows through them. Once power is turned off, the information is lost unless it has been copied to a hard drive or floppy disk. MRAM, however, retains data after a power supply is cut off. Replacing DRAM with MRAM could prevent data loss and enable computers that start instantly, without waiting for software to boot up. The U.S. Defense Advanced Research Projects Agency (DARPA) has provided funding to help private industry conduct research into the potential of MRAM. Beginning in 1995, DARPA began funding three private consortia researching the viability of making MRAM a general-purpose memory with high density, high speed, and low power usage. Leading the three consortia were IBM, Motorola, and Honeywell. Hewlett-Packard, Matsushita, NEC, Fujitsu, Toshiba, Hitachi, and Siemens also have invested in MRAM research. Motorola Labs says its "universal memory" allows the integration of several memory options within a single chip, resulting in a chip that uses less power. The chip is a three-volt MRAM with an address access time of about 15 nanoseconds. IBM and Infineon Technologies AG are working on a proposed 256-megabit chip they say could be on the market in 2004. Development of MRAM basically followed two scientific schools: 1) spin electronics, the science behind giant magnetoresistive heads used in disk drives and 2) tunneling magnetic resistance, or TMR, which is expected to be the basis of future MRAM.
INTRODUCTION:-
Unlike conventional RAM chip technologies, in MRAM data is not stored as electric charge or current flows, but by magnetic storage elements. The elements are formed from two ferromagnetic plates, each of which can hold a magnetic field, separated by a thin insulating layer. One of the two plates is a permanent magnet set to a particular polarity, the other's field can be changed to match that of an external field to store memory. This configuration is known as a spin valve and is the simplest structure for a MRAM bit. A memory device is built from a grid of such "cells".
The simplest method of reading is accomplished by measuring the electrical resistance of the cell. A particular cell is (typically) selected by powering an associated transistor which switches current from a supply line through the cell to ground. Due to the magnetic tunnel effect, the electrical resistance of the cell changes due to the orientation of the fields in the two plates. By measuring the resulting current, the resistance inside any particular cell can be determined, and from this the polarity of the writable plate. Typically if the two plates have the same polarity this is considered to mean "1", while if the two plates are of opposite polarity the resistance will be higher and this means "0".
Data is written to the cells using a variety of means. In the simplest, each cell lies between a pair of write lines arranged at right angles to each other, above and below the cell. When current is passed through them, an induced magnetic field is created at the junction, which the writable plate picks up. This pattern of operation is similar to core memory, a system commonly used in the 1960s. This approach requires a fairly substantial current to generate the field, however, which makes it less interesting for low-power uses, one of MRAM's primary disadvantages. Additionally, as the device is scaled down in size, there comes a time when the induced field overlaps adjacent cells over a small area, leading to potential false writes. This problem, the half-select (or write disturb) problem, appears to set a fairly large size for this type of cell. One experimental solution to this problem was to use circular domains written and read using the giant magnetoresistive effect, but it appears this line of research is no longer active.
Another approach, the toggle mode, uses a multi-step write with a modified multi-layer cell. The cell is modified to contain an "artificial antiferromagnet" where the magnetic orientation alternates back and forth across the surface, with both the pinned and free layers consisting of multi-layer stacks isolated by a thin "coupling layer". The resulting layers have only two stable states, which can be toggled from one to the other by timing the write current in the two lines so one is slightly delayed, thereby "rotating" the field.
Magnetoresistive random access memory (MRAM) stores bits of data by using magnetic charges. MRAM is designed for high density, high speed, and non-volatile devices. MRAM has the potential to replace dynamic random access memory (DRAM), electrically erasable programmable read-only memory (EEPROM), and Flash memory. DRAM uses small capacitors to store each bit of memory in an addressable format that consists of rows and columns. Because capacitors are unable to hold a charge indefinitely, DRAM requires a near-constant pulse of current to retain stored information. EEPROM needs electricity to be erased. Flash does not need a constant power supply to retain data.
MRAM or magnetoresistive RAM is a non-volatile random access memory (RAM) technology made from metals that change only slightly when placed within a magnetic field. To be non-volatile, these types of magnetic RAM retain the data in their memory arrays even when power is turned off. The chief advantage of MRAM over other forms of non-volatile RAM technology is its ability to combine the most commercially appealing attributes of disparate memory technologies (e.g., non-volatility, storage density, and speed) into a single memory solution. Rather than store electrical activity as magnetic charges, the actual magneto-resistive RAM properties store electrical activity as a state, or moment. This is due to the fact that the ferromagnetic material of MRAM allows the binary language of machines (0s and 1s) as polarized electrons, and permits reading of those polarizations against a transistor-type gate known as a tunnel junction.
HISTORY:-
• 2000 - IBM and Infineon established a joint MRAM development program.
• 2000 - Spintec laboratory's first Spin Torque Transfer patent.
• 2002 - NVE Announces Technology Exchange with Cypress Semiconductor.
• 2003 - A 128 kbit MRAM chip was introduced, manufactured with a 180 nm lithographic process
2004
• June - Infineon unveiled a 16-Mbit prototype, manufactured with a 180 nm lithographic process
• September - MRAM becomes a standard product offering at Freescale.
• October - Taiwan developers of MRAM tape out 1 Mbit parts at TSMC.
• October - Micron drops MRAM, mulls other memories.
• December - TSMC, NEC, Toshiba describe novel MRAM cells.
2005
• January - Cypress Semiconductor samples MRAM, using NVE IP.
• March - Cypress to Sell MRAM Subsidiary.
• June - Honeywell posts data sheet for 1-Mbit rad-hard MRAM using a 150 nm lithographic process
• August - MRAM record: memory cell runs at 2 GHz.
• November - Renesas Technology and Grandis collaborate on development of 65 nm MRAM employing spin torque transfer (STT).
• November - NVE receives an SBIR grant to research cryptographic tamper-responsive memory.[12]
• December - Sony announced the first lab-produced spin-torque-transfer MRAM, which utilizes a spin-polarized current through the tunneling magnetoresistance layer to write data. This method consumes less power and is more scalable than conventional MRAM. With further advances in materials, this process should allow for densities higher than those possible in DRAM.
HOW MRAM WORKS:-
MRAM (Magnetoresistive Random Access Memory) uses electron spin to store data. Memory cells are integrated on an integrated circuit chip, and the function of the resulting device is like a semiconductor static RAM (SRAM) chip, with potentially higher density and the added feature that the data are nonvolatile, that is data are retained with power off. Typical “classic”or “conventional” MRAM uses spin-dependent tunnel junction memory cells and magnetic row and column write lines as illustrated below:
The spin-dependent tunnel junction produces a large change in resistance depending on the predominant electron spin in a storage layer. The tunnel barrier (dark green in the figure above) is as thin as a few atomic layers--so thin that electrons can “tunnel” through the normally insulating material, causing a resistance change.
Row and column magnetic write lines allow data to be written to a selected cell in a two-dimensional array:
Data are written by small electrical currents in the write lines that create a magnetic fields, which flip electron spins in the spin-dependent tunnel junction storage layer, thus changing the junction’s resistance. Data is read by the tunneling current or resistance through the tunnel junction.
Next-generation MRAM could reduce cell size and power consumption. Potential next-generation designs include Spin-Momentum Transfer, Magneto-Thermal MRAM, and Vertical Transport MRAM. Spin-Momentum Transfer (also “Spin-Transfer,” “Spin Injection,” or “Spin Torque Transfer”) MRAM is based on changing the spin of storage electrons directly with an electrical current rather than an induced magnetic field. This method has the potential to significantly reduce MRAM write currents, especially with lithographic feature sizes less than 100 nanometers. M-T MRAM uses a combination of magnetic fields and ultra-fast heating from electrical current pulses to reduce the energy required to write data.