# US 2019/0245136 A1 · Multi-resistance mram > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2019/0245136 A1 - Document ID: US20190245136A1 - Status: Published application - Kind: A1 - Application number: 15/891,370 - Filed: 2018-02-08 - Published: 2019-08-08 - Earliest claimed: 2018-02-08 - Assignees: SanDisk Technologies LLC - Applicants: SanDisk Technologies LLC - Inventors: YOUNG-SUK CHOI; WON HO CHOI - Web page: https://patentgrep.com/patent/US20190245136A1 ## CPC - H10N 50/80: Constructional details - G11C 11/005: {comprising combined but independently operative RAM-ROM, RAM-PROM, RAM-EPROM cells} - G11C 11/16: using elements in which the storage effect is based on magnetic spin effect - G11C 11/161: {details concerning the memory cell structure, e.g. the layers of the ferromagnetic memory cell} - G11C 11/1675: {Writing or programming circuits or methods} - G11C 11/54: using elements simulating biological cells, e.g. neuron - H10N 50/01: Manufacture or treatment - H10N 50/10: Magnetoresistive devices - G11C 11/401: forming cells needing refreshing or charge regeneration, i.e. dynamic cells - G11C 11/41: forming {static} cells with positive feedback, i.e. cells not needing refreshing or charge regeneration, e.g. bistable multivibrator or Schmitt trigger - H10N: ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR - G11C: STATIC STORES (semiconductor memory devices H10B) ## Abstract Apparatuses, systems, and methods are disclosed for magnetoresistive random access memory. A magnetic tunnel junction for storing data may include a reference layer, a barrier layer, and a free layer. A barrier layer may be disposed between a reference layer and a free layer. A free layer may include a nucleation region and an arm. A nucleation region may be configured to form a magnetic domain wall. An arm may be narrower than a nucleation region and may extend from the nucleation region. An arm may include a plurality of pinning sites formed at predetermined locations along the arm for pinning a domain wall. ## Claims ### Claim 1 An apparatus comprising: a magnetic tunnel junction (MTJ) for storing data, the magnetic tunnel junction comprising a reference layer, a barrier layer, and a free layer, the barrier layer disposed between the reference layer and the free layer, the free layer comprising: a nucleation region configured to form a magnetic domain wall; and an arm, narrower than the nucleation region and extending from the nucleation region, the arm comprising a plurality of pinning sites formed at predetermined locations along the arm for pinning the domain wall. ### Claim 2 (depends on 1) The apparatus of claim 1, wherein the plurality of pinning sites of the arm comprises one or more intermediate pinning sites of a first pinning strength and a terminal pinning site of a second pinning strength, the second pinning strength greater than the first pinning strength. ### Claim 3 (depends on 2) The apparatus of claim 2, wherein the free layer further comprises a second arm extending from the nucleation region, the second arm comprising an initial arm selection pinning site of a third pinning strength, the third pinning strength greater than the second pinning strength. ### Claim 4 (depends on 3) The apparatus of claim 3, wherein the second arm further comprises one or more intermediate pinning sites of the first pinning strength and a terminal pinning site of the second pinning strength. ### Claim 5 (depends on 4) The apparatus of claim 4, wherein the free layer further comprises one or more further arms extending from the nucleation region. ### Claim 6 (depends on 5) The apparatus of claim 5, wherein the one or more further arms comprise one or more intermediate pinning sites of the first pinning strength, one or more terminal pinning sites of the second pinning strength, and one or more initial arm selection pinning sites of increasing pinning strengths relative to the third pinning strength. ### Claim 7 (depends on 1) The apparatus of claim 1, wherein the domain wall forms at the nucleation region in response to a write current. ### Claim 8 (depends on 7) The apparatus of claim 7, wherein the domain wall migrates along the arm from one pinning site to a subsequent pinning site in response to an increased write current. ### Claim 9 (depends on 7) The apparatus of claim 7, wherein the write current controls a magnetic field applied to the free layer. ### Claim 10 (depends on 7) The apparatus of claim 7, wherein the write current controls a spin current injected into the free layer. ### Claim 11 (depends on 7) The apparatus of claim 7, further comprising a controller configured to supply the write current. ### Claim 12 (depends on 1) The apparatus of claim 1, wherein a resistance state for the MTJ is based on where the domain wall is pinned. ### Claim 13 (depends on 12) The apparatus of claim 12, wherein the MTJ provides four or more possible resistance states. ### Claim 14 (depends on 1) The apparatus of claim 1, wherein the MTJ is configured as a multi-weight synapse that couples two artificial neurons in a neuromorphic computing array. ### Claim 15 A system comprising: a neuromorphic computing die, the neuromorphic computing die comprising a plurality of artificial neurons and a synapse array of multi-state magnetic memory cells coupling the artificial neurons, wherein a magnetic storage layer for a multi-state magnetic memory cell comprises: a pad-shaped region for forming a magnetic domain wall; and one or more arms, narrower than the pad-shaped region and extending from the pad-shaped region, the one or more arms comprising a plurality of notches for pinning the domain wall. ### Claim 16 (depends on 15) The system of claim 15, further comprising a controller that modifies synapse weights for the synapse array by controlling write currents for the multi-state magnetic memory cells. ### Claim 17 (depends on 15) The system of claim 15, wherein a number of states for a multi-state magnetic memory cell is based on a number of notches for the one or more arms. ### Claim 18 (depends on 15) The system of claim 15, wherein at least one of the one or more arms comprises an initial arm selection notch deeper than a maximum notch depth for another arm. ### Claim 19 An apparatus comprising: means for forming a magnetic domain wall in a free layer for a magnetic tunnel junction; and means for pinning the domain wall at one or more predetermined locations along one or more arms in the free layer. ### Claim 20 (depends on 19) The apparatus of claim 19, further comprising means for modifying a resistance state of the magnetic tunnel junction by depinning the domain wall from a first location, and causing the domain wall to migrate and pin to a second location. ### Claim 21 An apparatus comprising: a magnetoresistive random access memory (MUM) die, the MRAM die comprising a plurality of memory cells, a memory cell comprising a fixed layer, a barrier layer, and a free layer, the barrier layer disposed between the fixed layer and the free layer, the free layer comprising: a nucleation region configured to form a magnetic domain wall in response to a write current; a wall extension region configured to provide a plurality of resistance states for the memory cell corresponding to positions of the domain wall within the wall extension region; and a plurality of pinning sites formed at predetermined locations in the wall extension region and configured to pin the domain wall such that the domain wall migrates from one pinning site to a subsequent pinning site in response to an increased write current. ### Claim 22 (depends on 21) The apparatus of claim 21, further comprising a controller configured to apply write currents to the memory cells. ### Claim 23 (depends on 21) The apparatus of claim 21, wherein the free layer further comprises a second wall extension region configured to provide additional resistance states for the memory cell corresponding to positions of a second domain wall within the second wall extension region. ### Claim 24 A method comprising: applying a first write current to a magnetic tunnel junction to form a magnetic domain wall in a nucleation region of a free layer of the magnetic tunnel junction, wherein the domain wall migrates to a first pinning site in the free layer; applying a second write current to the magnetic tunnel junction to move the domain wall from the first pinning site to a second pinning site in the free layer, wherein the pinning sites are formed at predetermined locations in the free layer. ### Claim 25 (depends on 24) The method of claim 24, further comprising applying an erase current to the magnetic tunnel junction to magnetically saturate the free layer in an erased state with no domain wall.