Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10B—ELECTRONIC MEMORY DEVICES
  • H10B61/00—Magnetic memory devices, e.g. magnetoresistive RAM [MRAM] devices
• • 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
  • G11C11/161—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 details concerning the memory cell structure, e.g. the layers of the ferromagnetic memory cell
• • 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
  • G11C11/165—Auxiliary circuits
  • G11C11/1675—Writing or programming circuits or methods
• • G—PHYSICS
  • G11—INFORMATION STORAGE
  • G11C—STATIC STORES
  • G11C19/00—Digital stores in which the information is moved stepwise, e.g. shift registers
  • G11C19/02—Digital stores in which the information is moved stepwise, e.g. shift registers using magnetic elements
  • G11C19/08—Digital stores in which the information is moved stepwise, e.g. shift registers using magnetic elements using thin films in plane structure
  • G11C19/0808—Digital stores in which the information is moved stepwise, e.g. shift registers using magnetic elements using thin films in plane structure using magnetic domain propagation
• • 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 general field of the invention is that of spin electronics, also called spintronics, the field of electronics using the magnetic spin properties of electrons.
• the main fields of application are the very high capacity magnetic information storage and the measurement of local magnetic fields.
• the micromagnetic structure of a ferromagnetic element is composed of domains, in which the magnetic moments are all aligned in the same direction, the domains being separated from each other by walls within which the magnetic moments rotate gradually.
• FIG. 1 thus represents a magnetic wall 3 separating two adjacent domains 1 and 2.
• the magnetic moments M are represented by black arrows.
• the magnetic moments of the first domain are oriented in the opposite direction of the magnetic moments of the second domain in this figure.
• the magnetic moments of two domains can have different orientations. Inside the wall, the orientation of the magnetic moments varies progressively, thus moving from the orientation of the first domain to that of the second domain.
• the magnetic element When a sufficiently strong magnetic field is applied, the magnetic element no longer contains walls and is said to be mono-domain. To return the total magnetization, we reverse the direction of the applied magnetic field and the reversal of Magnetization is then carried out by nucleation and propagation of magnetic walls inside the ferromagnetic element. In current devices, the external magnetic field is generated by a current flowing in lines close to the element.
• the controlled reversal of the magnetization of a ferromagnetic element used in spintronics corresponds, for example, to the writing of a magnetic bit.
• the size of the domains as well as the number of magnetic walls present in the magnetic element depend on the dimensions of the ferromagnetic element. When the size of the ferromagnetic element decreases, it then becomes necessary to apply a more intense magnetic field to evolve the magnetic walls. This phenomenon is particularly sensitive when the dimensions of the element are of the order of a few nanometers. Consequently, the miniaturization in the nanometric range of the magnetic bits obtained from ferromagnetic elements causes a sharp increase in the necessary magnetic reversal fields and consequently leads to an energy consumption that is increasingly unacceptable to the proper functioning of the spintronic device. This phenomenon therefore limits the electronic storage capacities associated with this technology.
• the object of the invention is to achieve the reversal of the magnetic moment by using the wall displacement mechanism induced either wholly or partly by a spin current.
• the advantages are, on the one hand, the reduction of the necessary energy and, on the other hand, in the case of a matrix integration of the spintronic devices controlled by control lines and columns, the reduction of the spurious phenomena of still crosstalk called in Anglo-Saxon terminology cross-talk.
• the subject of the invention is a spin-electronic device comprising at least a first structure ferromagnetic comprising a first magnetic switching zone, said structure comprising at least a first magnetic domain in which the magnetic moments are all aligned in a first direction and a second magnetic domain in which the magnetic moments are all aligned in a second direction different from the first direction, the first domain being separated from the second domain by a magnetic wall, characterized in that:
• Said structure comprises means making it possible to stabilize said magnetic wall in two stable positions, the first switching zone being located between these two stable positions, said wall being able to move from the first stable position to the second stable position at least under the second position; effect of a first current C of spin polarized carriers passing through said structure, said switching zone thus belonging either to the first magnetic domain or to the second magnetic domain, and
• the device comprises at least a first magnetic element, the magnetic moments of said first magnetic element not being coupled with the magnetic moments of the first magnetic switching zone.
• at least one second magnetic element is disposed between the first switching zone and the first magnetic element, so that the magnetic moments of said second element are coupled with the magnetic moments of said switching zone, said switching zone belongs to the first magnetic domain or the second magnetic domain.
• the device also comprises at least a first separating layer disposed between the second magnetic element and the first magnetic element.
• the separating layer is made of a non-magnetic material.
• the displacement is obtained by the combined effect of the spin current and a magnetic field whose field lines pass through the magnetic switching zone substantially parallel to the direction of the current, at least the current or the magnetic field being variable.
• the device then comprises a conductive line disposed beneath the magnetic switching zone and substantially perpendicular to the direction of the spin current, said line being traversed by a second current so as to generate the magnetic field in the magnetic switching zone.
• the current is located beyond a certain threshold value sufficient to cause the wall to move from the first stable position to the second stable position, said switching zone thus belonging either to the first magnetic domain or to the second domain magnetic.
• the device comprises a second ferromagnetic structure comprising a second magnetic switching zone located opposite the first switching zone of the first ferromagnetic structure, said second structure comprising at least a third magnetic domain in which the magnetic moments are all aligned in a third direction and a fourth magnetic domain in which the magnetic moments are all aligned in a fourth direction different from the third direction, the third domain being separated from the fourth domain by a second magnetic wall, said second structure also having means for stabilizing said magnetic wall on a stable third and fourth position, the second switching zone being located between these two stable positions, said second wall being movable from the third stable position to the fourth position; under the effect of a second stream of spin carriers traversing said second structure, said second current being above a certain threshold value, the second switching zone thus belonging either to the third magnetic domain or to the fourth magnetic field, said second switching zone of said second structure being separated from the first switching zone of the first ferromagnetic structure by at least one separating layer.
• Each threshold current is between a thousand amperes per square centimeter and one million amperes per square centimeter.
• the first structure or the second ferromagnetic structure are ferromagnetic ribbons whose widths are between a few nanometers and a few microns and the thicknesses are between a few nanometers and a few tens of nanometers.
• Each ferromagnetic strip may comprise at each stable position a local change of geometry, said local change of geometry being either a narrowing or a thinning or an enlargement of the ferromagnetic strip.
• Each ferromagnetic strip may also comprise at each stable position a local change of structure. Said local change of structure is obtained, for example, by oxidation.
• the ferromagnetic structure comprises under the switching zone a set of magnetic and non-magnetic layers for concentrating the spin flux in the switching zone.
• this assembly comprises at least two ferromagnetic pads located on either side of the switching zone and separated by a first non-magnetic layer, the assembly consisting of the two pads and the non-magnetic layer being isolated from the ferromagnetic structure by a second non-magnetic layer.
• the ferromagnetic pads have a width equivalent to that of the ribbon and a thickness greater than that of the ribbon, typically ten times the thickness of the ribbon.
• the magnetization directions of the two ferromagnetic pads form a non-zero angle, typically substantially equal to 180 degrees, the magnetizations of the two pads being thus antiparallel.
• the second non-magnetic layer has a thickness of a few nanometers and the material of the non-magnetic layers is gold.
• spin polarized carriers are either electrons or holes.
• FIG. 1 represents a schematic diagram of a magnetic domain wall separating two magnetic domains
• FIG. 2 represents the displacement of said wall when it is subjected to a spin polarized current
• FIG. 3 represents the variations in the orientation of the spins carried by the current and magnetic moments inside the magnetic walls
• FIGS. 4a, 4b and 4c represent the principle of magnetic domain change by wall displacement
• FIGS. 5a, 5b and 5c show a first variant embodiment according to this principle
• FIGS. 6a and 6b show the diagram of a device according to the invention
• FIG. 7 represents a first embodiment variant according to the invention.
• FIG. 8 represents a second variant embodiment according to the invention.
• FIG. 9 represents the principle of change of magnetic domain when a current and a magnetic field are applied.
• FIG. 10 represents the principle of a digital matrix memory comprising a device according to the invention.
• FIG. 11 represents a possible embodiment of a means for stabilizing the magnetic walls
• Figure 12 shows an embodiment of the device for reducing the value of the threshold currents.
• the physical principle at the heart of the invention is based on the wall displacement mechanism induced, either partially or totally, by a spin current.
• the physical mechanism at the origin of the phenomenon of wall displacement by a spin polarized current is called spin transfer.
• FIG. 2 represents a magnetic wall 3 separating two adjacent domains 1 and 2.
• the magnetic moments M are represented by black arrows in bold lines.
• the magnetic moments of the first domain are oriented in the opposite direction of the magnetic moments of the second domain in this figure. Good heard, the magnetic moments of two domains can have different orientations.
• the orientation of the magnetic moments varies progressively, thus moving from the orientation of the first domain to that of the second domain.
• the spin m represented by a thin line arrow of the electronic carriers aligns with the magnetic moment of the material.
• These carriers can be either electrons or holes.
• FIG. 3 thus represents the variation of the magnetic moment in two adjacent points of the magnetic wall.
• the magnetic moments in these two points being denoted M1 and M2.
• M1 and M2 The magnetic moments in these two points.
• this exchange mechanism is symbolized in Figure 3 by a vector ⁇ m and the spin m1 becomes m2, but on the other hand, this spin m1 exerts a torque ⁇ symbolized by the hollow arrow in FIG. 3 on the moment M2 of the wall, which tends to turn it towards the direction of the initial magnetic moment M1.
• This rotation of the moments inside the wall causes a displacement d of the wall in the direction of propagation of the electrons.
• This displacement is symbolized by a straight arrow striped in Figure 2.
• the initial position of the wall is represented by dashed lines.
• This propagation therefore depends on the direction of the current.
• Wall displacement only occurs, however, if the current densities are sufficient.
• the threshold current is between a thousand amperes per square centimeter and one million amperes per square centimeter. Given the small size of the spintronic devices, a current of a few milliamperes is sufficient to achieve the desired wall displacement.
• This mechanism makes it possible to locally reverse a magnetization by wall displacement without applying a large external magnetic field.
• Figures 4a, 4b and 4c show an elementary spintronic device implementing this principle. It comprises a first ferromagnetic structure 4 comprising a first switching zone
• This structure comprises at least a first magnetic domain 1 in which the magnetic moments M are all aligned in a first direction and a second magnetic domain 2 in which the magnetic moments are all aligned in a second direction different from the first direction, the first domain being separated from the second domain by a magnetic wall 3 shown in bold lines in the figures, said structure also comprising means not shown in the figures for stabilizing said magnetic wall in two stable positions.
• the first switching zone 5 bounded by two dashed lines in FIG. 4a is situated between these two stable positions.
• Said wall can move from the first stable position to the second stable position under the effect of a current C of spins passing through said structure. Conversely, when the current C is reversed, the wall moves from the second stable position to return to the first stable position.
• the wall displacements d are represented in FIG. 4b and 4c according to the direction of the current C. Said current is located beyond the threshold value allowing the displacement of walls.
• the switching zone belongs either to the first magnetic domain 1 or to the second magnetic domain 2 depending on the position of the wall 3.
• a spintronic device capable of storing for example, a magnetic bit.
• the magnetic structure 4 is in the form of a ribbon or bar.
• the thickness of the bar is between a few nanometers and a few tens of nanometers. It may consist of a single thin film of magnetic material or a more complex structure consisting of several magnetic films or not.
• the lateral dimensions of the bar are between a few nanometers and a few microns aside.
• different forms of ribbon are possible.
• the propagation speed is of the order of a few nanometers per nanosecond to a few microns per nanosecond. It is therefore possible to switch several magnetic gigabits per second with this technique.
• FIGS. 5b and 5c show a variation of the basic layout described above.
• a magnetic element 6 On the previous switch zone 5 as illustrated in Figure 5a, a magnetic element 6 has been arranged. There is then a strong direct magnetic coupling between the bar 4 and the magnetic element 6.
• the magnetization in the element 6 will instantly turn around as illustrated in FIGS. 5b and 5c where the magnetization M in the element symbolized by a thick arrow changes direction when the magnetic wall passes from one stable position to the other according to the meaning of the current flowing through it.
• the magnetization in the element is thus reproducibly switched between two directions of magnetization which can be identified as logical states "0" or "1".
• the magnetic element 6 may or may not consist of the same material as the bar in which the wall flows under the influence of the current.
• the thickness of the element is between a few atomic planes and a few tens of nanometers.
• the element to be switched is a simple magnetic object defining a magnetic bit.
• this magnetic element controllable by the wall displacement is part of a more complex structure such as a magnetic tunnel junction, a spin valve or any other elementary device of spin electronics.
• FIGS. 6a, 6b and 7 show structures of the spin valve or magnetic tunnel junction type according to the invention.
• the structure of FIGS. 6a and 6b comprises a ferromagnetic bar 4 comprising a switching zone 5, a first magnetic element 7, and finally a second magnetic element 6 arranged between the switching zone and the first magnetic element 7.
• the second magnetic element 6 is controlled by the displacement of a wall 3 separating two magnetic domains 1 and 2 of the ferromagnetic rod 4.
• the direction of the magnetization of the first magnetic element 7 is not modified by the displacement of the wall in the bar as shown in Figure 6b where the displacement of the wall under the effect of a current of carriers causes the switching of the magnetic moments of the second element without changing the orientation of the moments
• the magnetic configuration of the entire device may be probed either by local magneto- optical measurement or by magneto-resistive measurement by taking electrical contact over the first element and measuring the resistance between this contact and the magnetic bar.
• the second element has the same geometric characteristics as the first magnetic element.
• the first magnetic element 7 is composed of a single film made of a single magnetic material. It may also have a more complex structure comprising several films of different materials including for example a ferromagnetic layer and an anti-ferromagnetic layer.
• Figure 7 is a variant of the previous structure. It comprises a ferromagnetic rod 4, a second magnetic element 6, a first separating layer 8 and finally a first magnetic element 7 disposed on said separating layer and having the same properties as the magnetic element 7 of FIGS. 6a and 6b.
• the second magnetic element 6 is controlled by the displacement of a wall 3 separating two magnetic domains 1 and 2 of the ferromagnetic rod 4. It is separated from the first magnetic element by the separation layer 8.
• This layer 8 is made of a material which can be a non-magnetic conductor or an insulator. In the case where the material is non-magnetic, it may be a metal or a semiconductor.
• the direction of the magnetization of the first magnetic element is not modified by the displacement of the wall in the bar.
• the magnetic configuration of the entire device can be probed by the means described above.
• the separating layer 8 has a thickness between a few atomic planes and a few nanometers. The lateral dimensions of the separating layer 8 and of the first element 7 are equivalent to those of the second magnetic element 6.
• the structure of Figure 8 shows a dual magnetic control device. It successively comprises a first ferromagnetic bar 4 comprising two magnetic domains 1 and 2 separated by a wall 3 and having a first switching zone 5, then a second magnetic element 6, a separation layer 8, a first magnetic element 7 and finally a second ferromagnetic bar 13 also comprising two magnetic domains 9 and 10 separated by a second wall January 1 and having a second switching zone 12.
• the separation layer 8 makes it possible to isolate the magnetic state of the second element magnetic device 6 of the magnetic state of the first magnetic element 7. It is thus possible to obtain a device having several possible magnetic states according to the direction of the currents applied in the first bar 4 or the second ferromagnetic bar 13.
• the single spin current it is possible by means of the single spin current to provide switching by displacement of the wall.
• the use of the single spin current may have disadvantages.
• the threshold value of the current required to move the wall can be high.
• this principle does not simply make it possible to carry out matrix commands making it possible, for example to address a memory composed of a matrix of spintronic devices, in particular when the number of matrix elements is high.
• the ferromagnetic structure 4 then comprises a conductive line 20 disposed under the magnetic switching zone 5 and substantially perpendicular to the direction of the spin current C, said line being traversed by a second current C so as to generate a magnetic field B having field lines parallel to the direction of the current C in the magnetic switching zone.
• the lines of field are indicated by semicircular concentric full arrows and currents by solid arrows.
• the matrix represented in FIG. 10 comprises a plurality of lines comprising ferromagnetic structures 4 arranged in series and a plurality of control columns 20 perpendicular to the lines, arranged beneath them. Magnetic switching areas are located at intersections of control lines and columns. It is then possible to address a particular ferromagnetic switching zone by controlling the line and the corresponding column.
• FIG. 11 represents a geometrical configuration of the ferromagnetic bar 4 where two constrictions 14 located on either side of the switching zone 5 make it possible to stabilize or trap the wall 3 separating the first domain. 1 of the second domain 2 at said narrowing. In this case, under the effect of a stream of spin carriers, the wall 3 can move from one narrowing 14 to the other.
• the shape and position of the constrictions is not limited to those shown in FIG. 9. It is possible to envisage any other type of geometrical modification of the shape of the bar, such as, for example, an asymmetric narrowing of its width, an expansion of its width or a thinning of its thickness. It is also possible to modify the structure locally by a chemical process such as oxidation.
• Threshold currents enabling wall displacements are generally high.
• it is added under the switching zone 5 in which the wall 3 will move between the magnetic domains 1 and 2, a set of magnetic and non-magnetic layers which make it possible to concentrate the spin flux in the zone. of commutation.
• FIG. 12 a structure of the device according to this embodiment is presented in FIG. 12. It comprises, under a ferromagnetic structure 4 in the form of a ribbon comprising the switching zone 5, two ferromagnetic studs 15 and 17 located on the one side. and other of the switching zone 5 and separated by a non-magnetic layer 16, for example gold. These pads 15 and 17 have a width equivalent to that of the ribbon and a thickness greater than that of the ribbon, typically ten times the thickness of the ribbon.
• the layer 16 has a length of between a few nanometers and a few microns.
• the magnetizations in the two ferromagnetic pads 15 and 17 are not aligned in parallel in order to obtain the effect of reducing the threshold currents, the most favorable case being the antiparallel alignment of the magnetizations in the two ferromagnetic pads, as shown in FIG. Figure 12 where the magnetic moments are represented by black arrows in opposite directions.
• the assembly consisting of the pads and the gold layer is isolated from the ribbon by a non-magnetic layer 18 which must be as thin as possible, typically a few nanometers. This provision makes it possible to reduce the threshold currents by a significant factor, at least equal to 5.

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• 2004
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• 2005
  • 2005-12-14 WO PCT/EP2005/056786 patent/WO2006064022A1/fr active Application Filing
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