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WO2017074263A1 - Dispositifs de mémoire magnétiques et procédés de mise en fonctionnement associés - Google Patents

Dispositifs de mémoire magnétiques et procédés de mise en fonctionnement associés Download PDF

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Publication number
WO2017074263A1
WO2017074263A1 PCT/SG2016/050526 SG2016050526W WO2017074263A1 WO 2017074263 A1 WO2017074263 A1 WO 2017074263A1 SG 2016050526 W SG2016050526 W SG 2016050526W WO 2017074263 A1 WO2017074263 A1 WO 2017074263A1
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Prior art keywords
segment
magnetic
component
writing
domain
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English (en)
Inventor
Wen Siang LEW
Senfu ZHANG
Weiliang GAN
Chu Keong Gerard Joseph LIM
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Nanyang Technological University
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Nanyang Technological University
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    • 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
    • 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
    • G11C11/1673—Reading or sensing 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
    • G11C19/0841—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 using electric current

Definitions

  • the invention relates to magnetic memory devices.
  • the invention also relates to methods of operation of magnetic memory devices.
  • the invention has particular application for the writing of a magnetic memory bit in a memory component such as a nanowire comprising Perpendicular Magnetic Anisotropy (PMA) material.
  • PMA Perpendicular Magnetic Anisotropy
  • Magnetic data storage devices such as domain wall (DW) memory and Magnetic Random Access Memory (MRAM) devices have been dubbed as amongst the most promising candidates that can fulfil the role of a universal memory [1-3].
  • the data bits "1" and "0" are represented by magnetic domains oriented in one of the two possible directions.
  • a magnetic writing component also known as an injection line.
  • injection lines typically comprise a (relatively) thick and conductive nanowire deposited on top of a memory data line, which is the memory component being used to store the data bits.
  • This data line is also typically a nanowire.
  • An electrical pulse is generated and applied to the injection line which, in turn, causes a magnetic field to be induced in the area surrounding the injection line typically in the form of an Oersted field which causes the magnetic data bits to be written in the data line disposed within the generated Oersted field.
  • the direction of the applied electrical pulse (or, rather, the current) can be reversed, with different current directions used to write either "1" or "0" bits [4-6].
  • Magnetic memory devices were first demonstrated in in-plane materials.
  • the first domain wall memory demonstrated in in-plane magnetic anisotropy (IMA) material has very large DW widths of about 100 ⁇ 200 nm which limits its scalability [4, 5].
  • the current-driven domain wall dynamics is very sensitive to external magnetic fields and suffers from a high intrinsic pinning [6-11].
  • Domain Wall memory design has been moving towards the use of high PMA materials. This type of magnetic memory has a small domain size, narrower domain walls, much higher domain wall thermal stability and a much higher pinning field than that of in-plane magnetized systems any or all of which may be advantageous for the thermal stability of the device [7-10] .
  • the current-induced domain wall motion in such systems is dominated by the field-insensitive adiabatic torque which moves the domain wall by changing its structure between Bloch and Neel walls periodically [8, 9, 11, 16, 17]. Therefore, the threshold current density required for domain wall propagation is given by the energy difference between the two types of domain walls. As compared to an I MA system, the threshold current density for DW motion in a PMA system is lower [18-21] .
  • domain wall injection is achieved by applying an electrical current via a thick and conductive strip line deposited on top of the magnetic nanowire.
  • the Oersted field generated by the conductive strip line is used to change the
  • novel arrangements for magnetic writing components which may comprise an injection line such as a micro- coil which has been patterned using, for instance, standard electron beam
  • the geometry of the writing component may generate a highly shaped and focused electric current.
  • This current can produce a high magnitude and localised magnetic field that can easily initiate the nucleation of a magnetic domain in a memory component (such as a nanowire) disposed within the magnetic field.
  • Use of the techniques disclosed herein may mean that the magnetic data bit can be deterministically written bit using only an 8 ns pulse with a current density of, say, 4.97 x 10 11 A/m 2 or a 15 ns pulse with a current density of, say, 5.35 ⁇ 10 11 A/m 2 .
  • the disclosed methods consume less than 30%, perhaps around 28%, of the energy required by known injection designs, such as that disclosed in [23].
  • an improved memory writing component for more efficient magnetic data bit writing is provided.
  • the memory writing component - for instance, an injection line - has a design that can focus and shape the current density distribution to reduce the threshold current needed to write a magnetic data bit.
  • novel arrangements disclosed here obviate any issues which might arise from magnetic data bit writing in such high PMA materials consuming increasing amounts of energy. Significantly reduced amounts of energy are required by implementing the techniques disclosed herein.
  • FIG. 1 is a series of schematic representations of memory writing components in accordance with the techniques disclosed herein;
  • FIG. 2 is a schematic representation of another memory writing component in accordance with the techniques disclosed herein;
  • Figure 3 is a schematic representation of a magnetic memory device incorporating a memory writing component according to the principles of the memory writing component of Figure 2;
  • Figure 4 is a series of graphs illustrating properties of a memory component as may be used in the magnetic memory device of Figure 3;
  • Figure 5 is a series of diagrams illustrating domain wall propagation
  • Figure 6 is a series of polar Kerr images of a PMA nanowire after domain injection while sweeping a small magnetic field, normalised Hall resistance measurement of the nanowire after the injection and schematic illustrations of the magnetisation;
  • Figure 7 is a series of curves illustrating domain injection probability in respect of differing properties in the memory writing component;
  • Figure 8 is a series of views providing a comparison of current density distribution, magnetic field and time-resolved magnetisation between the known technique mentioned above and the innovative techniques disclosed herein;
  • Figure 9 is a series of curves illustrating magnetic bit writing performance of the techniques disclosed herein in comparison with a known technique;
  • Figure 10 is a series of representations illustrating the current density distribution and Z-axis magnetic field resulting from variation of the properties of the magnetic writing component according to the techniques disclosed herein;
  • Figure 11 provides an illustrative comparison of one application of the techniques disclosed herein in a magnetic tunnel junction (MTJ) device and a known technique
  • Figure 12 is a schematic representation of a known three-terminal MTJ device
  • Figure 13 is a more detailed schematic representation of an application of the techniques disclosed herein in a MTJ device.
  • MTJ magnetic tunnel junction
  • Writing component 100 comprises a first segment 102 and a second segment 104 and, as best viewed in Figure 1(b), the writing component 100 has a thickness 105.
  • writing component 100 is formed of electrically- conductive material and arranged generally in the shape of the Greek character ⁇ (lambda), or to give it an alternative expression, it can be considered to be arranged in an inverted V-shape, with the first segment 102 and second segment 104 extending away from an apex 106, which comprises a straight or generally straight edge running along the thickness 105 of the writing component 100.
  • the first and second segments 102, 104 extend away from apex 106 at an angle.
  • the first segment 102 and the second segment 104 meet (or merge into one another) at a boundary section 108 between the two segments.
  • an area or volume 110 is formed between the segments 102, 104, with the segments 102, 104 defining, at least in part, this area/volume 110.
  • a memory component 112 (viewed in section in this figure), or at least a part thereof, is disposed in this area/volume 110 between the first and second segments 102, 104.
  • the memory component 112 can take a number of forms, including a cylindrical (or generally cylindrical) magnetic structure, or a cuboidal (or generally cuboidal) magnetic nanowire.
  • the memory component 112 is illustrated being spaced from the first and second segments 102, 104 of the writing component 100, but in alternative arrangements, the memory component 112 may be in contact with one or both of these segments 102, 104.
  • Writing component 100 is manufactured such that the transition between the first segment 102 and the second segment 104 at the boundary section 108 results in generally straight and sharp edges: the apex 106 and an opposed edge 114 which also runs along the thickness 105 of the writing component 100 as perhaps best viewed in Figure 1(b).
  • a "sharp" edge is formed when the edges of the two segments which meet define straight or substantially straight lines, akin to, say, an edge of a cuboid.
  • the edge 114 can be considered an
  • apex 106 may be considered an "exterior" edge. That is, the edge section 116 comprises a sharp edge 114 defining a boundary between the first segment 202 and the second segment 204 of the writing component 100.
  • writing component 100 may be subjected to an electrical pulse. Because of the geometric shape of the writing component 100, particularly because of the edge 114, the current distribution in the writing component 100 is concentrated at an edge section 116 (illustrated schematically only in Figure 1(a)) proximal to the edge 114. As best viewed in Figure 1(b), a part 118 of the surface of the writing component 100 at the edge section 116 is disposed facing towards the memory component 112. A localised magnetic field component represented by arrow 120 is generated by the concentrated current distribution in edge section 114 and emanating from or near surface portion 118. This magnetic field component may initiate nucleation of a magnetic domain in the memory component 112, causing the writing of a magnetic data bit therein.
  • the "interior" edge 114 is a sharp edge, as explained above.
  • the edge 114 is a rounded edge having a radius. The radius may be constant or variable across the arc of the curve of the rounded edge. That is, the edge section 116 may comprise a rounded edge 118 were the first segment 102 and the second segment 104 of the writing component 100 meet.
  • first and second segments are formed integrally. In one arrangement, the first and second segments are connected at an angle of between 1 and 150 degrees, preferably at an angle of between 20 and 130 degrees, more preferably at an angle of between 40 and 120 degrees, yet more preferably at an angle of between 60 and 110 degrees, and yet more preferably at an angle of between 80 and 100 degrees.
  • Figure 2 illustrates a further alternative arrangement, where the writing component 200 is not provided in a ⁇ /inverted-V shaped.
  • the writing component 200 is formed generally to resemble the Greek character ⁇ (Pi), or, considered alternatively, generally in the form of an n-shape.
  • writing component 200 in this example comprises three main segments: first segment 202, second segment 204 and third segment 205.
  • first segment 202 and second segment 204 adjoin one another, and are formed at right angles to one another; that is, the first segment 202 and the second segment 204 each extend away from the apex (or corner) 206a at 90 degrees from one another.
  • second segment 204 and third segment 205 are formed at right angles to one another, extending at 90 degrees from one another from apex/corner 206b.
  • first and second segments 202, 204 form an area/volume 210, this time in conjunction with third segment 205 in which at least a part of memory
  • edges 214 are formed where, respectively, the first segment 202 meets (in this case merges into) the second segment 204, and where the second segment 204 meets (merges into) the third segment 205.
  • edge sections are defined in the areas represented
  • edge sections 216 are disposed facing towards the memory component 112. Because of the sharp edge geometry at the edges 114, when the writing component 200 is energised, the current distribution in the edge sections 216 are again concentrated, thereby generating magnetic field components (represented by the arrows 220) which may induce nucleation of a domain wall in memory component 112.
  • the injection line has a ⁇ -shaped or n-shaped portion.
  • the ⁇ -shaped or n-shaped portion may include a first segment 202, a second segment 204 and a third segment 205.
  • the first segment 202 and the third segment 205 may be disposed at or near two opposite ends of the second segment 204.
  • the first segment 202 and the third segment 205 may be parallel or generally parallel to each other.
  • the first segment 202 and the third segment 205 may extend perpendicularly from the second segment 204.
  • the first segment 202 and the third segment 205 may extend perpendicularly from two opposite ends of the second segment 204.
  • the first segment 202, the second segment 204 and the third segment 205 may be formed integrally using, for example, one of the techniques mentioned above.
  • the writing component 200 comprises a third segment 205, the first segment 202 and the third segment 205 extending generally perpendicularly from the second segment 204, thereby forming a volume 210 defined in part by the first segment 202, the second segment 204 and the third segment 205 in which a portion of the memory component 112 is disposed.
  • the angle between the first segment 202 and the second segment 204 may range between 70 and 100 degrees, preferably between 80 and 95 degrees.
  • the angle between the second segment 204 and the third segment 205 may also range between 70 and 100 degrees, preferably between 80 and 95 degrees.
  • the edges 214 may be a sharp edge. However, it will be appreciated that these edges may be a rounded edge, in a similar fashion to the arrangement of Figure 1(c). It may be preferred that the radius of the rounded edge has a radius of up to a width of the second segment 204.
  • the domain wall(s) may be used for magnetic storage.
  • the domain(s) may be used for magnetic storage.
  • Figure 3 is a schematic representation of a magnetic memory device incorporating a magnetic memory writing component. While Figure 2 is given in the context of a memory writing component according to the principles of Figure 2, it will be appreciated that additionally or alternatively, one of the writing components illustrated in Figure 1 may also be used.
  • Figure 3 illustrates a magnetic memory device 300 having a writing component 200 having first, second and third segments 202, 204, 205.
  • the figure illustrates the scanning electron microscopy image of a ⁇ -shaped device, including the proposed writing component/injection line 200 with terminals C-G, two Hall bars 302a, 302b having, respectively, terminals B-H and D-F.
  • the memory component 112 in this instance a PMA nanowire fabricated horizontally across, having electrical terminals A-E 304, 306 acting as a current source and sink across which a Hall Effect bias current may be applied using current source 308.
  • one or more of the writing component/injection line and the other electrical connects may be fabricated using, for example, tantalum (Ta) (e.g. 6.3 nm)/copper Cu (93.6 nm)/gold Au (24 nm).
  • Ta tantalum
  • Other materials may also be used, including but not limited to gold (Au), aluminium (Al), tungsten (W), titanium (Ti), chromium (Cr), and ruthenium (Ru) can be used for fabricating the injection line and/or one or more of the electrical connects.
  • the dimensions of the materials can differ according to the materials used or according to the desired dimensions.
  • the resistivity R H of the Hall bars is used to detect the magnetization of the nanowire underneath by exploiting the Anomalous Hall Effect.
  • the Hall resistivity is empirically fitted by the formula [24] :
  • R p H R 0 B + 4nR 5 M (1)
  • B the applied magnetic field
  • M the magnetization per unit volume.
  • R 0 and R s are the ordinary and the anomalous Hall coefficient, respectively. In the example of Figure 3, R s may be substantially larger than R 0 . In such cases, the R Ha n is proportional to the perpendicular component of the local magnetization of the nanowire beneath the Hall bar.
  • Figure 3 illustrates a magnetic memory device 300 comprising: a memory component 112 comprising perpendicular magnetic anisotropy, PMA, material; a writing component 200 comprising electrically- conductive material, the writing component being for writing a magnetic data bit in the PMA material, the writing component comprising a first segment 202 and a second segment 204, the first segment and the second segment meeting at an edge section 216, the edge section 216 being disposed facing the PMA material (in the magnetic component/nanowire 112); and wherein the magnetic memory device 300 is configured to inject an electrical pulse into the writing component 200 for the generation of a localised magnetic field component 220 from the edge section 216.
  • a memory component 112 comprising perpendicular magnetic anisotropy, PMA, material
  • a writing component 200 comprising electrically- conductive material, the writing component being for writing a magnetic data bit in the PMA material, the writing component comprising a first segment 202 and a second segment 204, the first segment and the second segment meeting at
  • This magnetic memory device 300 comprises a memory component 112 comprising perpendicular magnetic anisotropy, PMA, material; and a writing component 200 comprising electrically-conductive material, the writing component 200 comprising a first segment 202 and a second segment 204, the first segment 202 and the second segment 204 meeting at an edge section 216, the edge section 216 being disposed facing the PMA material (in the magnetic component/nanowire 112), the method comprising injecting an electrical pulse into the writing component 200 to generate a localised magnetic field component 220 from the edge section 216.
  • references in the preceding two paragraphs to the edge section 216 formed between the first and second segments 202, 204 may also be substituted by references to the edge section 216 formed between the second and third segments 204, 205.
  • references to the writing component 200 may be substituted by references to the writing component 100, and parts thereof, of Figure 1.
  • a potential pulse of duration t p from pulse generator 310 is applied through the bias-T 312 across the injection line on terminals C-G. Circuit parameters may be observed using one or more of oscilloscope 314 and voltmeter 316.
  • Figures 4(a)-(d) show the measured resistivity R H as a function of sweeping fields.
  • the coercivity of the nanowire may be 190 Oe or thereabouts, as shown in Figures 4(a) and (b).
  • the magnetization of the nanowire may be found to switch at a much lower field of 50 Oe, as shown in Figures 4(c) and (d).
  • Domain walls are topological defects in the magnetization which can propagate swiftly across the nanowire, causing a magnetization reversal even before the coercive field for a uniformly magnetized nanowire is reached. Subsequently, the domain injection probability for each pulse duration t p and potential is illustrated from 20 repeated measurements.
  • Figures 4 (a) and (b) illustrate the Normalized Hall resistance of the PMA nanowire without domain injection, under a 2000 Oe and 370 Oe sweeping magnetic field and Figures 4 (c) and (d) illustrate the Normalized Hall resistance of a PMA nanowire with domain injected in the +z (-z) direction.
  • Figure 4(e) shows the typical R Ha ii measurement while sweeping a 370 Oe external magnetic field in the z-direction, perpendicular to the nanowire. The squa re loop indicates that the nanowire exhibits a strong PMA.
  • the y-axis of the graph is the normalized R Ha n, where 1 and 0 correspond to the complete alignment of the magnetization beneath the Hall bar in the + z and - z magnetization, respectively.
  • RH C H was observed to change at 197 Oe, which corresponds to the magnetization reversal field.
  • the sudden switch can be explained by the nanowire reversal process - a domain first nucleates at a defect in the nanowire and then, by means of domain wall motion, the domain rapidly expands throughout the nanowire until saturation results. As the threshold field for domain wall motion is less than the domain wall nucleation field of the nanowire, only a single change in R Ha ii was expected for each sweep direction.
  • a perpendicular field of 370 Oe was applied to saturate the nanowire magnetization in the - z direction.
  • Domain wall injection may then be carried out by applying a current pulse to the injection line from C to G without an external magnetic field.
  • the current pulse generates a local Oersted field with perpendicular field components at the sides of the injection line. If the amplitude and duration (t p ) of the pulse reaches the threshold value, a magnetic domain 500 will be introduced in the nanowire as shown in Figure 5(i) between the pair of domain walls 502. In the section 500, the magnetisation direction is up, and in the sections 504, the magnetisation direction is down.
  • the proposed ⁇ -shaped writing component Under an applied electric potential, the proposed ⁇ -shaped writing component generates a highly concentrated current distribution. This creates a highly localized magnetic field that quickly initiates the nucleation of a magnetic domain. The formation and motion of the resulting domain walls can then be electrically detected by means of Hall bars (for example made from tantalum) across the nanowire. Measurements show that the ⁇ -shaped writing component can deterministically write a magnetic data bit in 15 ns even with a relatively low current density. Micromagnetic simulations reveal the evolution of the domain nucleation - first, by the formation of a pair of magnetic bubbles, then followed by their rapid expansion into a single domain. Finally, it is demonstrated experimentally that the injection geometry can perform bit writing using only about 30% of the electrical energy as compared to a conventional injection line.
  • Figure 6(a) shows the polar Kerr images of a 2 ⁇ wide PMA nanowire after domain injection while sweeping a small magnetic field.
  • a nanowire with an injected domain was imaged from 92-102 Oe in 2 Oe steps.
  • An image of the saturated nanowire was then used for background subtraction.
  • the white (black) contrast represents the up (down) magnetization direction.
  • a magnetic domain was successfully injected into the nanowire underneath the injection line and the domain expands gradually with increasing magnetic field. In a defect-free nanowire, the domain walls will keep moving until they reach the end once the threshold propagation field is reached.
  • the proposed ⁇ -shaped structure may be able to deterministically inject a domain wall pair in only 15 ns using a low current density of 5.34 ⁇ 10 11 A/m 2 . Lowering the current density to 4.1 ⁇ 10 11 A/m 2 results in an increased threshold t p of 50 ns.
  • the current pulse must be larger than 7.82 ⁇ 10 11 A/m 2 with t p of 70 ns, or increasing the current density to 9.07 ⁇ 10 11 A/m 2 results in a decreased t p of 32 ns.
  • ⁇ -shaped structure is calculated to consume only about 30% of the energy used in conventional method.
  • the relatively low threshold t p and current density observed in our experiments is attributed to the highly shaped current density and localized magnetic field generated by our proposed injection line.
  • att j ce relaxation time where a is the Gilbert damping parameter, ⁇ is the gyromagnetic ratio and H e ff is the effective magnetic field which is equal to the in-plane saturation field.
  • t 3 ⁇
  • the magnetic moments become almost aligned along the effective field ⁇
  • ⁇ 2.21 ⁇ 10 5 m .
  • Figure 8(a) shows the schematic diagram of the current flow and its corresponding magnetic field.
  • a significant advantage of the ⁇ -shaped writing component is each side of the three segments produce a magnetic field that is oriented in the same direction in the centre, producing an effective magnetic field that is stronger than that of a straight strip line. This compounds the effect of the areas of concentrated distribution arising from the sharp edge geometry.
  • COMSOL Multiphysics (TM) simulation software and mumax [3] micromagnetics were used to model the magnetic field distribution at the threshold injection conditions for both the writing component 200 of Figures 2 and 3 and the prior art writing component 602 comprising of a straight strip line, as illustrated in Figure 8(b).
  • the geometry of the devices-under-test was created in COMSOL to accurately model the spatial distribution of the current density and its resultant Oersted field as shown in Fig. 8(c).
  • the threshold current density for deterministic nucleation (J t ) at 0 K for deterministic nucleation at 0 K was used.
  • J t was determined to be 220 mA and 129 mA, corresponding to an average current density of 2.9 x 10 A/m and 1.7 x 10 A/m , respectively.
  • the cones indicate the in-plane orientation of the vector fields. From the simulations, it is clear that the ⁇ -shaped injection line has another two advantages.
  • Fig. 8(c) On the bottom right side of Fig. 8(c), the time resolved magnetization dynamics of the ⁇ -shaped injection geometry is shown. Upon application of a magnetic field with a 300 ps rise time, spin wave excitations were observed. After a few oscillations, two metastable magnetic bubble domains are nucleated at the position of the localized magnetic field. The two domains eventually expand in size with the assistance of the Oersted field and form a complete domain wall pair after 600 ps. Given sufficient time for the magnetization to relax, it is apparent that the ⁇ -shaped injection geometry produces a narrower domain.
  • FIG 8(b) illustrates the current density distribution in the writing component/injection line 200, particularly the areas 600 of concentrated current distribution appearing at the sharp edges defined by the geometry of the writing component, in comparison to the uniform current density distribution in the known straight strip line 602.
  • Figure 8(c) illustrates a comparison between known strip line 602 and the magnetic writing component 200 of Figures 2 and 3 for the Z- axis magnetic field, with the magnetic field acting on the magnetic material.
  • the magnetization dynamics shown in Figure 8(d) during the domain wall nucleation process illustrates that while a threshold magnetic field is required to initiate domain wall nucleation, the magnetic field need not be acting uniformly on the memory component/magnetic nanowire.
  • a localized region of high magnetic field can also initiate spin flipping which will eventually spread out to form a larger and more stable domain.
  • the magnetic writing component of Figures 2 and 3 may be used to create an extremely localized magnetic field at each side of the memory component/nanowire 112 to nucleate a metastable magnetic domain. Only a much weaker magnetic field is needed for the expansion of such magnetic domains. Therefore, the magnetic domain formed can expand quickly to form a domain wall pair by the end of the injection pulse.
  • the sharp bends in the writing component/injection lines 100, 200 focus the electric current, allowing a thicker injection line to achieve the current density distribution of a much finer nanowire, without suffering from the negative effects of Joule heating, and the manufacturing difficulties surrounding the formation of the finer nanowire.
  • a focused current is more desirable as the produced magnetic field quickly decays with distance.
  • the magnetic field produced by the writing components 100, 200 is highly asymmetrical. This may result in the creation of only one nucleation point when an appropriate current density is used.
  • the magnetic field produced on both sides of the known injection line is equal and opposite in magnitude, possibly affecting neighboring magnetic bits.
  • Figure 9 shows the threshold injection parameters derived from micromagnetic simulations for the writing component 200 and the known straight strip line designs.
  • Figure 9(a) shows the threshold injection parameters t P and current density as a function of each other and also temperature.
  • Figure 9(b) shows the injection current needed for the magnetic bit writing at different
  • Figure 10 shows the current density distribution and z-axis magnetic field profile resulting from various modifications of the proposed designs for the writing components/injection lines 100, 200 while keeping the injection line width constant at 30 nm and the current at 1 mA.
  • a ⁇ -shaped injection line can create a single localized magnetic field, useful at the 30 nm length-scale where the nucleation of only a single domain is required.
  • the remaining arrangements of Figures 10(b) - (f) show how the varying degree of edge roundedness can affect the magnetic field profile.
  • Figure 10(b) illustrates the performance of a ⁇ - shaped magnetic writing component 200 with sharp or substantially sharp edges.
  • Figures 10(c) - (e) illustrate the performance with rounded edges of increasing radius, respectively with a 5 nm radius in (c), a 10 nm radius in (d) and with a 15 nm radius in (e). With increasing rounding, the focusing effect is diminished and the two localized magnetic field regions gradually merge into a single larger magnetic field. However, even in the case of Figure 10(e), this design still exhibits the advantageous characteristics that allow it to be more efficient than the known design illustrated, for comparison's sake, in Figure 10(f).
  • MRAM magnetic random access memory
  • TMR magnetoresistance
  • the current techniques used to inject domain walls into the MTJ devices utilizes a straight injection line [15], which can easily be replaced with, for example, the ⁇ -shaped magnetic writing component/injection line 200 for a better energy efficiency and with less stochasticity as shown in Figure 11.
  • the MTJ device comprises a metal oxide and top electrode 1100, the memory component 112 (also a nanowire in this example) and the magnetic writing component/injection line 200 of Figure 2.
  • the known arrangement is illustrated having a known straight strip line 1102.
  • the domain is nucleated under the injection line and can be shifted within the magnetic nanowire.
  • the resistance can be varied.
  • the application is general to all types of domain wall based MTJs including for neuromorphic memory or magnetic logic applications.
  • FIG. 13 Another MRAM technology which may benefit from the ⁇ -shaped writing component/injection line 200 is the Toggle MRAM as illustrated in Figure 13 made commercially available by EverSpin.
  • a pair of injection lines produces orthogonal magnetic fields that flip the magnetization of the magnetic free layer as shown in the figure. This is in contrast with the spin transfer torque MRAM in which the free layer is switched by the spin transfer torque from the spin polarized current acting on the magnetic free layer.
  • most of the write power is dissipated by the injection line. Therefore the use of the ⁇ -shaped writing component/injection line instead of a known straight injection line for magnetic field generation may reduce the current densities required to switch an MRAM cell, and in the process greatly reducing power consumption while likely also decreasing device footprint.
  • a silicon wafer with a 300-nm-thick Si0 2 layer was used as a substrate.
  • Co/Ni multilayer was deposited using DC magnetron sputtering deposition technique at room temperature.
  • the stack structure was, from the substrate side, Ta(5 nm)/Pt(5 nm)/[Co(0.25 nm)/Ni(0.5 nm)] 4 /Co(0.25 nm)/Ta(5 nm).
  • the device was fabricated in three processes: first, the 350 nm wide nanowire was patterned by electron beam lithography and Ar ion milling from the Co/Ni multilayer film. Secondly, two Ta(10 nm) hall bars were patterned using electron beam lithography technique followed by resist lift-off. Third, Ta(6 nm)/Cu(94 nm)/Au(24 nm) electrodes as well as the injection line were also fabricated using electron beam lithography technique and lift-off. Argon reverse sputtering was employed before the second and third processes to obtain a better Ohmic contact.
  • the Hall resistance measurements and domain wall injection were carried out on a Cascade Microtech probe station.
  • a Picosecond 10300B pulse generator was used to inject domain walls by applying pulsed current from E to E'.
  • the Hall resistance is determined by measuring the voltage with a
  • m is the unit vector of the local magnetization
  • y is the gyromagnetic ratio
  • H e is the effective magnetic field
  • a is the Gilbert damping parameter.
  • the unit cell size is set to 5 nm ⁇ 5 nm ⁇ 3.25 nm.
  • the damping constant value a 0.02.
  • the rise time was taken to be 300 ps.

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

Abstract

La présente invention concerne un dispositif de mémoire magnétique (300) comprenant un composant de mémoire (112) comprenant un matériau d'anisotropie magnétique perpendiculaire. Le composant d'écriture comprend un matériau électriquement conducteur, le composant d'écriture étant destiné à l'écriture d'un bit de données magnétique dans le matériau PMA, le composant d'écriture comprenant un premier segment (102, 202) et un second segment (104, 204), le premier segment et le second segment rejoignant sur une section de bord (114, 214), la section de bord étant disposée en regard du matériau PMA. Le dispositif de mémoire magnétique injecte une impulsion électrique dans le composant d'écriture pour générer une composante de champ magnétique localisée (120, 220) depuis la section de bord. Lors de son fonctionnement, celui-ci peut écrire le bit de données magnétique dans le matériau PMA en induisant dans celui-ci une nucléation et/ou un domaine magnétique. L'invention concerne également des procédés de mise en fonctionnement.
PCT/SG2016/050526 2015-10-26 2016-10-26 Dispositifs de mémoire magnétiques et procédés de mise en fonctionnement associés Ceased WO2017074263A1 (fr)

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JP2023022731A (ja) * 2021-08-03 2023-02-15 日本放送協会 磁性細線メモリ

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US11362268B2 (en) 2017-10-30 2022-06-14 Taiwan Semiconductor Manufacturing Company Ltd. Semiconductor structure and associated operating and fabricating method
TWI783018B (zh) * 2017-10-30 2022-11-11 台灣積體電路製造股份有限公司 半導體結構以及相關操作和製造方法
JP2023022731A (ja) * 2021-08-03 2023-02-15 日本放送協会 磁性細線メモリ

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