Bipolar spin-transfer switching
First Claim
1. A magnetic device comprising:
- a polarizing layer magnetized perpendicular to a free magnetic layer;
the free magnetic layer forming a first electrode and separated from the magnetized polarizing layer by a first non-magnetic metal layer, the free magnetic layer having a magnetization vector having at least a first stable state and a second stable state;
a reference layer forming a second electrode and separated from the free-magnetic layer by a second non-magnetic layer;
wherein the magnetization vector is set via application of a unipolar current pulse, having either positive or negative polarity and a selected amplitude and duration, through the magnetic device bipolarly switching the magnetization vector from the first stable state to the second stable state or the second stable state to the first stable state, wherein the unipolar current pulse is orthogonal to the polarizing layer.
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Abstract
Orthogonal spin-transfer magnetic random access memory (OST-MRAM) uses a spin-polarizing layer magnetized perpendicularly to the free layer to achieve large spin-transfer torques and ultra-fast energy efficient switching. OST-MRAM devices that incorporate a perpendicularly magnetized spin-polarizing layer and a magnetic tunnel junction, which consists of an in-plane magnetized free layer and synthetic antiferromagnetic reference layer, exhibit improved performance over prior art devices. The switching is bipolar, occurring for positive and negative polarity pulses, consistent with a precessional reversal mechanism, and requires an energy less than 450 fJ and may be reliably observed at room temperature with 0.7 V amplitude pulses of 500 ps duration.
158 Citations
18 Claims
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1. A magnetic device comprising:
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a polarizing layer magnetized perpendicular to a free magnetic layer; the free magnetic layer forming a first electrode and separated from the magnetized polarizing layer by a first non-magnetic metal layer, the free magnetic layer having a magnetization vector having at least a first stable state and a second stable state; a reference layer forming a second electrode and separated from the free-magnetic layer by a second non-magnetic layer; wherein the magnetization vector is set via application of a unipolar current pulse, having either positive or negative polarity and a selected amplitude and duration, through the magnetic device bipolarly switching the magnetization vector from the first stable state to the second stable state or the second stable state to the first stable state, wherein the unipolar current pulse is orthogonal to the polarizing layer. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. A method of controlling a memory array having a plurality of cells each comprising:
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determining an initial state of a cell within the memory array; determining if the initial state is the same as a write state corresponding to information to be written to the cell; if the initial state is different from the write state, applying a unipolar current pulse of either positive or negative polarity and of a selected amplitude and duration through the magnetic device bipolarly switching the magnetization vector to the write state, wherein the unipolar current pulse is orthogonal to the cell.
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18. A memory array comprising:
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at least one bit cell including; a magnetic device having; a magnetic layer having a fixed magnetization vector; a free magnetic layer having a variable magnetization vector having at least a first stable state and a second stable state; a non-magnetic layer separating the magnetic layer with fixed magnetization vector and the free magnetic layer; wherein the variable magnetization vector is set via application of a unipolar current pulse having either positive or negative polarity and a sufficient amplitude and duration through the magnetic device bipolarly switches the magnetization vector from either the first stable state to the second stable state or from the second stable state to the first stable state, wherein the unipolar current pulse is orthogonal to the polarizing layer; and at least one transistor for current control and readout wherein application of a voltage to the at least one bit cell activates the bit cell.
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Specification