Classifications

• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11C—STATIC STORES
  • G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
  • G11C11/02—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements
  • G11C11/16—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements using elements in which the storage effect is based on magnetic spin effect
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10N50/00—Galvanomagnetic devices
  • H10N50/10—Magnetoresistive devices

Definitions

• the present invention relates to a magnetic memory with spin detection.
• Magnetic memories on silicon also called “MRAM” for the English term “Magnetic Random Access Memory” have experienced very rapid development in recent years and reference may be made to this subject for example in US patent US Pat. They indeed have many advantages such as the non-volatility of the "FLASH” memory, the speed of the "SRAM” memory and the density of the “DRAM” memory. In addition to these numerous advantages, they also offer very low voltage operation.
• a first type of spin transistor such as that described in US Pat. No. 5,654,566 is presented as a field effect transistor except that the source, respectively the drain, are replaced by an injector, respectively a detector. of spin-polarized electrons, both made of magnetic magnetic material.
• the memory is arranged on a semiconductor junction formed by two adjacent zones, the first and the second zone having a conductivity of a first and a second type respectively, this memory comprising a first and a second connection cells arranged on either side of this junction, each cell being provided with a magnetization module; in addition, at least one of these cells has a polarization electrode in addition to its magnetization module.
• one of the magnetization modules adjoins the semiconductor junction.
• At least one of these magnetization modules comprises a buffer layer in contact with the zone in which it appears, a magnetic layer being disposed on this buffer layer.
• this buffer layer is made of an insulating material and, according to an additional characteristic, its thickness is such that it allows conduction by tunnel effect between the magnetic layer and the zone in which it appears.
• the distance between the two magnetization modules of the memory is less than double the spin diffusion length.
• the first zone has a p-type conductivity.
• the magnetic memory is arranged on a semiconductor substrate 100.
• the substrate 100 has a first zone 101 on which a first connection cell 110 is arranged.
• This first zone 101 has a conductivity of a first type, type p in this case, while the rest of the substrate which constitutes a second zone 102, presents a conductivity of the second type, of type n in this case.
• the separation of the two zones thus forms a semiconductor junction 103.
• the first connection cell 110 is here a spin polarized electron injector. It comprises a first magnetization module formed by a first buffer layer 111 in contact with the first zone 101 and by a first magnetic layer 112 disposed on this first buffer layer.
• this first magnetization module is disposed in the immediate vicinity of the semiconductor junction 103.
• the spin-polarized electrons are injected from the first magnetic layer 112 into the first zone 101.
• ferromagnetic materials are naturally good candidates. These materials can be insulating, semiconducting or metallic. For electronic devices such as memories, it is preferable to use ferromagnetic metals because ferromagnetic semiconductors are materials which have been synthesized recently and their technology is not yet well mastered. In addition, the Curie temperature of these materials is quite low, less than 300 ° K, and these materials therefore cannot be used at room temperature. On the other hand, conductive ferromagnetic materials have very high Curie temperatures, well above 300 ° K.
• the first buffer layer 111 is made of an insulating material such as silicon dioxide or alumina.
• the first magnetization cell comprises a polarization electrode 113 in ohmic contact with the first zone 101. It suffices that a relatively low voltage, of the order of a few volts, is applied between the first magnetic layer 112 and the first zone 101 to curve the strips in the semiconductor 101 near the interface with the first buffer layer 111. The injection of electrons into the conduction strip of this semi -conductor is then insured.
• a second connection cell 120 acts as a detector of spin-polarized electrons.
• a second magnetization module which, preferably, is formed of a second buffer layer 121 in contact with the second zone 102 and of a second magnetic layer 122 disposed on this second buffer layer .
• a tunnel junction makes it possible to significantly increase the injection efficiency of polarized electrons. Such a junction similarly improves the detection of these polarized electrons because the probability of an electron passing through a ferromagnetic material through this junction very strongly depends on its spin orientation.
• the second buffer layer 121 is made of insulating material to produce a second tunnel junction materialized by the stacking of the second zone 102, second buffer layer 121, second magnetic layer 122.
• the potential difference between the second magnetic layer 122 and this second electrode polarization is of the order of a few volts.
• the current injected by the first connection cell 110 to the second connection cell is spin polarized.
• it is mainly made up of electrons of a spin type, "spin up” or “spin down".
• the rate of current polarization is determined by the band structure of the magnetic material at the interface with the buffer layer.
• the spin polarization depends on the orientation of the magnetization of the ferromagnetic metal.
• the injected current / has two components G + and G-, each representing the electron current respectively of "spin up” or "spin down”.
• the injected current is subdivided into a detection current picked up by the second magnetic layer 122 and a leakage current picked up by the second polarization electrode 123.
• the detection current and the leakage current depend on the relative magnetization of the two magnetization modules.
• i p respectively i ap
• j p respectively j ap
• the leakage current when the magnetizations of the two modules are parallel, respectively antiparallel.
• the transmission probabilities of the “spin up” and “spin down” electrons in the second magnetic layer are characterized by the coefficients ⁇ + and ⁇ -, the probability of passing to the ohmic contact being characterized by the coefficient ⁇ which is independent of spin polarization.
• G + + n + + ⁇ n + ;
• G _ a _ n _ + ⁇ n _
• n- _ G n + - ⁇ ⁇ - + ⁇ ⁇ + + ⁇
• G + G + ⁇ G;
• G- G- ⁇ G;
• the quantity which characterizes the sensitivity of the detector is Aili, relative variation of the detection current for two magnetization configurations:
• AG / G characterizes the spin polarization of the injected electrons.
• ⁇ a / a characterizes the anisotropy of transmission of the detector.
• the ratios AG / G and ⁇ / ⁇ are worth a few tenths of a unit, around 0.4 for an alloy of iron and cobalt.
• the sensitivity limit therefore depends solely on the properties of the ferromagnetic structures. It is reached for a "or for /" j.
• the detector therefore has a lower current (compared to the injected current), but with maximum sensitivity to spin polarization in the semiconductor. For a detected current representing 10% of the injected current, the sensitivity of the detector will be equal to 90% of the limit sensitivity, given by the choice of ferromagnetic materials.
• this collector By qualifying as a collector the space appearing between the two magnetization modules, this collector contains a non-negligible concentration of non-polarized electrons of spin when the injected current is zero. As spin-polarized electrons are injected, these electrons gradually replace non-polarized electrons. In the collector in steady state, a spin polarization distribution P is established which has the following form:
• the distance d which separates the two magnetization modules is less than the scattering length L s , although this distance d may be greater, twice the scattering length L s for example, this at detriment to the sensitivity of the detector.
• L s the length of diffusion
• the memory according to the invention can in particular be manufactured in the following manner.
• the process up to the contact part is a traditional CMOS manufacturing process.
• An additional step is introduced.
• An insulator a few nanometers thick is deposited; this insulator can be silicon dioxide, alumina or any other known dielectric.
• the ferromagnetic material is deposited, an alloy of cobalt and iron for example.
• the two constraints imposed on the materials are to have an abrupt interface with the dielectric while maintaining a high electronic polarization at the interface.
• the thickness of deposited magnetic material can vary from a few tens to a few hundred nanometers.
• the process can then resume its traditional course.
• the memory is written or erased with a magnetic field which returns the magnetization of the first 112 or of the second 122 magnetic layer. Since the current passing through the detector depends on the relative orientation of the magnetizations of the injectors and detectors, the magnetic state of the cell is read with the current passing through the detector. As in the state of the art, the writing of the memory can be accomplished by the passage of a current through two insulated metallic conductors which cross over the magnetic layer which it is magnetize.
• the magnetic field generated at the intersection of these is sufficient to change the magnetization configurations from a parallel state to an antiparallel state.
• the saturation current is chosen so that the combined magnetic field exceeds the critical field of the ferromagnetic metal, predominantly determined by magnetic anisotropy.
• this saturation current is applied to only one of the two conductors, the magnetic field generated is insufficient to return the magnetization.
• the arrangement of the conductors is such that the field generated by the saturation current is very localized. This field is less than the field necessary to modify the magnetization of other magnetic elements which would be located near the intersection of the two conductors.
• the two possible directions of magnetization then define two possible logical states (commonly denoted 0 or 1) of the memory.
• the memory according to the invention it becomes possible to manufacture non-volatile memories with a conventional CMOS process, without considerably increasing the different levels of masking.
• the memory according to the invention operates at low voltage and does not require a charge pump. This is a decisive advantage for mobile applications.
• the invention is particularly suitable for so-called “System On Chip” or “SOC” technology.
• SOC technology integrates all of the components on a single chip: micro-controller, “SRAM” and “DRAM” memories, dedicated logic, “MEMS”, chemical sensors and of course, non-volatile memories. It is therefore necessary to have the most standardized manufacturing process possible.
• the embodiment of the invention presented above was chosen for its concrete character. However, it would not be possible to exhaustively list all the embodiments covered by this invention. In particular, any means described may be replaced by equivalent means without departing from the scope of the present invention.

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• Engineering & Computer Science (AREA)
• Computer Hardware Design (AREA)
• Hall/Mr Elements (AREA)
• Mram Or Spin Memory Techniques (AREA)
• Bipolar Transistors (AREA)
• Semiconductor Memories (AREA)

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• 2002
  • 2002-12-27 FR FR0216844A patent/FR2849526B1/fr not_active Expired - Fee Related
• 2003
  • 2003-12-22 CN CNA2003801092621A patent/CN1745430A/zh active Pending
  • 2003-12-22 JP JP2004564294A patent/JP2006512763A/ja active Pending
  • 2003-12-22 EP EP03814485A patent/EP1595263A2/de not_active Withdrawn
  • 2003-12-22 WO PCT/FR2003/003863 patent/WO2004061856A2/fr not_active Ceased
  • 2003-12-22 AU AU2003303658A patent/AU2003303658A1/en not_active Abandoned

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