# US 8,570,797 B2 · Magnetic random access memory (MRAM) read with reduced disturb failure > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,570,797 B2 - Document ID: US8570797B2 - Status: Granted - Kind: B2 - Application number: 13/035,006 - Filed: 2011-02-25 - Published: 2012-08-30 - Granted: 2013-10-29 - Earliest claimed: 2011-02-25 - Assignees: QUALCOMM Incorporated - Applicants: Jung Pill Kim; Tae Hyun Kim; Kangho Lee - Inventors: Jung Pill Kim; Tae Hyun Kim; Kangho Lee - Web page: https://patentgrep.com/patent/US8570797B2 ## CPC - G11C 11/1673: {Reading or sensing circuits or methods} - G11C 11/1693: {Timing circuits or methods} - G11C: STATIC STORES (semiconductor memory devices H10B) ## Abstract Magnetic tunnel junctions (MTJs) in magnetic random access memory (MRAM) are subject to read disturb events when the current passing through the MTJ causes a spontaneous switching of the MTJ due to spin transfer torque (STT) from a parallel state to an anti-parallel state or from an anti-parallel state to a parallel state. Because the state of the MTJ corresponds to stored data, a read disturb event may cause data loss in MRAM devices. Read disturb events may be reduced by controlling the direction of current flow through the MTJ. For example, the current direction through a reference MTJ may be selected based on the state of the reference MTJ. In another example, the current direction through a data or reference MTJ may be alternated such that the MTJ is only subject to read disturb events during approximately half the read operations on the MTJ. ## Claims ### Claim 1 An apparatus, comprising: a magnetic tunnel junction having a first terminal and a second terminal; a first read select transistor coupled between the first terminal of the magnetic tunnel junction and a first multiplexer, the first multiplexer being coupled to a voltage source and coupled to a ground, the first multiplexer being configured to receive a first control signal to toggle the voltage source and the ground to the first terminal via the first read select transistor; a second read select transistor coupled between the second terminal of the magnetic tunnel junction and a second multiplexer, the second multiplexer being coupled to the voltage source, and coupled to the ground, the second multiplexer being configured to receive a second control signal to toggle the voltage source and the ground to the second terminal; and a read select line coupled to the first read select transistor and the second read select transistor and configured to simultaneously turn on the first read select transistor and the second read select transistor. ### Claim 2 (depends on 1) The apparatus of claim 1, in which the magnetic tunnel junction is a reference magnetic tunnel junction having one of a parallel and an anti-parallel configuration, and in which the first multiplexer control signal and the second multiplexer control signal are selected to correspond to the configuration of the reference magnetic tunnel junction. ### Claim 3 (depends on 1) The apparatus of claim 1, in which the magnetic tunnel junction is a data magnetic tunnel junction, and in which the first multiplexer control signal and the second multiplexer control signal are toggled after a read of the data magnetic tunnel junction. ### Claim 4 (depends on 1) The apparatus of claim 1, in which the magnetic tunnel junction is integrated into a magnetic random access memory (MRAM). ### Claim 5 (depends on 1) The apparatus of claim 1, in which the magnetic tunnel junction is integrated into at least one of a mobile phone, a set top box, a music player, a video player, an entertainment unit, a navigation device, a computer, a hand-held personal communication systems (PCS) unit, a portable data unit, and a fixed location data unit. ### Claim 6 A method, comprising: signaling a first multiplexer, the first multiplexer selecting to pass a first current through a parallel reference magnetic tunnel junction from a free layer to a fixed layer of the parallel reference magnetic tunnel junction in response to the signaling of the first multiplexer; signaling a second multiplexer, the second multiplexer selecting to pass a second current through an anti-parallel reference magnetic tunnel junction from a fixed layer to a free layer of the anti-parallel reference magnetic tunnel junction in response to the signaling of the second multiplexer; and reading a data magnetic tunnel junction during the passing of the first current and the passing of the second current. ### Claim 7 (depends on 6) The method of claim 6, in which reading the data magnetic tunnel junction comprises passing a third current through the data magnetic tunnel junction in at least one of a first direction from a free layer of the data magnetic tunnel junction to a fixed layer of the data magnetic tunnel junction and a second direction from the fixed layer of the data magnetic tunnel junction to the free layer of the data magnetic tunnel junction, in which the third current is in the first direction when a previous read of the data magnetic tunnel junction was in the second direction, and in which the third current is in the second direction when the previous read of the data magnetic tunnel junction was in the first direction. ### Claim 8 (depends on 7) The method of claim 7, in which the previous read comprises the previous read immediately preceding the reading the data magnetic tunnel junction. ### Claim 9 (depends on 6) The method of claim 6, further comprising integrating the parallel reference magnetic tunnel junction, the anti-parallel reference magnetic tunnel junction, and the data magnetic tunnel junction into a magnetic random access memory (MRAM). ### Claim 10 (depends on 9) The method of claim 9, further comprising integrating the MRAM into at least one of a mobile phone, a set top box, a music player, a video player, an entertainment unit, a navigation device, a computer, a hand-held personal communication systems (PCS) unit, a portable data unit, and a fixed location data unit. ### Claim 11 A method, comprising: passing current in a first direction, from a free layer to a fixed layer, through a parallel reference magnetic tunnel junction, an anti-parallel reference magnetic tunnel junction, and a data magnetic tunnel junction during a first read operation; and passing current in a second direction, from a fixed layer to a free layer, through the parallel reference magnetic tunnel junction, the anti-parallel reference magnetic tunnel junction, and the data magnetic tunnel junction during a second read operation, the second direction being different from the first direction, and the first read operation and the second read operation form a sequence. ### Claim 12 (depends on 11) The method of claim 11, further comprising integrating the parallel, anti-parallel, and data magnetic tunnel junctions into a magnetic random access memory (MRAM). ### Claim 13 (depends on 11) The method of claim 11, further comprising integrating the parallel, anti-parallel, and data magnetic tunnel junctions into at least one of a mobile phone, a set top box, a music player, a video player, an entertainment unit, a navigation device, a computer, a hand-held personal communication systems (PCS) unit, a portable data unit, and a fixed location data unit. ### Claim 14 An apparatus, comprising: a magnetic tunnel junction having a first terminal and a second terminal; first-means for selecting read circuitry coupled between the first terminal of the magnetic tunnel junction and a first means for multiplexing, the first multiplexing means being coupled to a voltage source and coupled to a ground, the first multiplexing means being configured to toggle the first terminal between the voltage source and the ground via the first selecting means; second means for selecting read circuitry coupled between the second terminal of the magnetic tunnel junction and a second means for multiplexing, the second multiplexing means being coupled to the voltage source and coupled to the ground, the second multiplexing means being configured to toggle the second terminal between the voltage source and the ground; and a read select line coupled to the first selecting means and the second selecting means and configured to simultaneously turn on the first selecting means and the second selecting means. ### Claim 15 (depends on 14) The apparatus of claim 14, in which the first multiplexing means and the second multiplexing means are toggled after each read operation. ### Claim 16 (depends on 14) The apparatus of claim 14, in which the magnetic tunnel junction is integrated into a magnetic random access memory (MRAM). ### Claim 17 (depends on 14) The apparatus of claim 14, in which the magnetic tunnel junction is integrated into at least one of a mobile phone, a set top box, a music player, a video player, an entertainment unit, a navigation device, a computer, a hand-held personal communication systems (PCS) unit, a portable data unit, and a fixed location data unit. ### Claim 18 A method, comprising the steps of: signaling a first multiplexer, the first multiplexer selecting to pass a first current through a parallel reference magnetic tunnel junction from a fixed layer to a free layer of the parallel reference magnetic tunnel junction in response to the signaling of the first multiplexer; signaling a second multiplexer, the second multiplexer selecting to pass a second current through an anti-parallel reference magnetic tunnel junction from a free layer to a fixed layer of the anti-parallel reference magnetic tunnel junction in response to the signaling of the second multiplexer; and reading a data magnetic tunnel junction during the passing of the first current and the passing of the second current. ### Claim 19 (depends on 18) The method of claim 18, further comprising the step of integrating the parallel reference magnetic tunnel junction, anti-parallel reference magnetic tunnel junction, and data magnetic tunnel junction into at least one of a mobile phone, a set top box, a music player, a video player, an entertainment unit, a navigation device, a computer, a hand-held personal communication systems (PCS) unit, a portable data unit, and a fixed location data unit. ### Claim 20 A method, comprising the steps of: passing current in a first direction, from a free layer to a fixed layer, through a parallel reference magnetic tunnel junction, an anti-parallel reference magnetic tunnel junction, and a data magnetic tunnel junction during a first read operation; and passing current in a second direction, from a fixed layer to a free layer, through the parallel reference magnetic tunnel junction, the anti-parallel reference magnetic tunnel junction, and the data magnetic tunnel junction during a second read operation, the second direction being different from the first direction, and the first read operation and the second read operation form a sequence. ### Claim 21 (depends on 20) The method of claim 20, further comprising the step of integrating the parallel reference magnetic tunnel junction, anti-parallel reference magnetic tunnel junction, and data magnetic tunnel junction into at least one of a mobile phone, a set top box, a music player, a video player, an entertainment unit, a navigation device, a computer, a hand-held personal communication systems (PCS) unit, a portable data unit, and a fixed location data unit.