US5930164A
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Magnetic memory unit having four states and operating method thereof
Assignee: Everspin Technologies Inc
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Filing: 1998-02-26
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Granted: 1999-07-27
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Expires: 2018-02-26
Abstract
Abstract A new structure of a magnetoresistive random access memory (MRAM) is presented for a high density and fast access operations. The MRAM includes two magnetic memory cells separated by an electrically conductive layer, each cell having two magnetic layers separated by a barrier layer forming a tunneling junction. Each memory cell contains one bit information as directions of magnetic vectors which are switched by an external magnetic field and sensed by a sense current flowing in the MRAM unit. The current creates a drop voltage over the MRAM unit, which indicates four different values according to the states stored in MRAM unit.
Inventors
- 👤 Theodore Zhu
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-01 23:53
CPC Classifications
G; G11; G11C; G11C11/00; G11C11/56; G11C11/5607; H; H10; H10B; H10B61/00; G11C2211/00; G11C2211/56; G11C2211/561; G11C2211/5615
Claims Analysis
Total Claims: 25
Claim 1
Independent Claim
74 words
A magnetoresistive random access memory (MRAM) unit comprising: a first magnetic memory cell including magnetic layers separated by a first barrier layer forming a tunneling junction; a second magnetic memory cell including magnetic layers separated by a second barrier layer forming a tunneling junction, the second magnetic memory cell having a different resistance from one of the first barrier layer; and an electrically conductive layer sandwiched between the first and second magnetic memory cells.
Claim 2
Dependent Claim
74 words
A magnetoresistive random access memory (MRAM) unit comprising: a first magnetic memory cell including magnetic layers separated by a first barrier layer forming a tunneling junction; a second magnetic memory cell including magnetic layers separated by a second barrier layer forming a tunneling junction, the second magnetic memory cell having a different resistance from one of the first barrier layer; and an electrically conductive layer sandwiched between the first and second magnetic memory cells.
Claim 3
Dependent Claim
74 words
The MRAM unit as claimed in claim 1 wherein the magnetic layers in the first magnetic cell include first pinned and free layers, and the magnetic layers in the second magnetic cell include second pinned and free layers, magnetic vectors in the first and second pinned magnetic layers not being switched by an external magnetic field and magnetic vectors in the first and second free magnetic layers being switched by the external magnetic field.
Claim 4
Dependent Claim
23 words
The MRAM unit as claimed in claim 2 further including magnetic layers anti-ferromagnetically coupled with the first and second pinned magnetic layers, respectively.
Claim 5
Dependent Claim
22 words
The MRAM unit as claimed in claim 1 wherein the first barrier layer has a different thickness from the second barrier layer.
Claim 6
Dependent Claim
22 words
The MRAM unit as claimed in claim 4 wherein the second barrier layer is twice as thick as the first barrier layer.
Claim 7
Dependent Claim
24 words
The MRAM unit as claimed in claim 1 wherein the first magnetic memory cell has a different area from the second magnetic memory cell.
Claim 8
Dependent Claim
26 words
The MRAM unit as claimed in claim 1 further including a first conductive line electrically coupled to the first magnetic cell for providing a sense current.
Claim 9
Dependent Claim
24 words
The MRAM unit as claimed in claim 7 further including further including a switch coupled to the MRAM unit for controlling the sense current.
Claim 10
Dependent Claim
29 words
The MRAM unit as claimed in claim 8 further including a second conductive line placed adjacent the MRAM unit for applying an external magnetic field to the MRAM unit.
Claim 11
Dependent Claim
23 words
The MRAM unit as claimed in claim 1 wherein the first barrier layer has a different barrier height from the second barrier layer.
Claim 12
Dependent Claim
156 words
A magnetoresistive random access memory (MRAM) device comprising: a substrate on which the MRAM device is formed; a plurality of MRAM units arranged in rows and columns, each MRAM unit comprising: a first magnetic memory cell including magnetic layers separated by a first barrier layer forming a tunneling junction, a second magnetic memory cell including magnetic layers separated by a second barrier layer forming a tunneling junction, the second magnetic memory cell having a different resistance from one of the first barrier layer, and an electrically conductive layer sandwiched between the first and second magnetic memory cells; a plurality of first conductive lines for providing a sense current, one first conductive line for each row, each first conductive line being electrically coupled to each of the first magnetic memory cell of each MRAM unit in the row; and a plurality of switches electrically coupled to each of the second magnetic memory cell of each MRAM unit.
Claim 13
Dependent Claim
156 words
A magnetoresistive random access memory (MRAM) device comprising: a substrate on which the MRAM device is formed; a plurality of MRAM units arranged in rows and columns, each MRAM unit comprising: a first magnetic memory cell including magnetic layers separated by a first barrier layer forming a tunneling junction, a second magnetic memory cell including magnetic layers separated by a second barrier layer forming a tunneling junction, the second magnetic memory cell having a different resistance from one of the first barrier layer, and an electrically conductive layer sandwiched between the first and second magnetic memory cells; a plurality of first conductive lines for providing a sense current, one first conductive line for each row, each first conductive line being electrically coupled to each of the first magnetic memory cell of each MRAM unit in the row; and a plurality of switches electrically coupled to each of the second magnetic memory cell of each MRAM unit.
Claim 14
Dependent Claim
78 words
The MRAM device as claimed in claim 11 wherein the magnetic layers in the first magnetic cell include first pinned and first free magnetic layers, and the magnetic layers in the second magnetic cell include second pinned and second free magnetic layers, magnetic vectors in the first and second pinned magnetic layers not being switched by an external magnetic field and magnetic vectors in the first and second free magnetic layers being switched by the external magnetic field.
Claim 15
Dependent Claim
22 words
The MRAM unit as claimed in claim 11 wherein the first barrier layer has a different thickness from the second barrier layer.
Claim 16
Dependent Claim
24 words
The MRAM unit as claimed in claim 11 wherein the first magnetic memory cell has an different area from the second magnetic memory cell.
Claim 17
Dependent Claim
42 words
The MRAM device as claimed in claim 11 further including a plurality of second conductive lines being placed adjacent each of the MRAM units in the column, for applying an external magnetic field generated by a current therein to the MRAM unit.
Claim 18
Dependent Claim
20 words
The MRAM device as claimed in claim 11 further including a current source being coupled to the first conductive lines.
Claim 19
Dependent Claim
23 words
The MRAM unit as claimed in claim 11 wherein the first barrier layer has a different barrier height from the second barrier layer.
Claim 20
Independent Claim
186 words
A method for writing first, second, third, and fourth states in a magnetoresistive random access memory (MRAM) unit including a conductive layer sandwiched between two magnetic tunnel junction cells, each magnetic tunnel junction cell storing one bit information, the method comprising the steps of: applying a first magnetic field having a first strength in a first direction to the MRAM unit when the first state (00) is stored in the MRAM unit; applying a second magnetic field having a second strength in a second direction opposite to the first direction to the MRAM unit when the second state (11) is stored in the MRAM unit; applying the first magnetic field and then applying a third magnetic field having a third strength lower than the second strength in the second direction, to the MRAM unit, when the third state (01) is stored in the MRAM unit; and applying the second magnetic field and then applying a fourth magnetic field having a fourth strength lower than the first strength in the first direction, to the MRAM unit, when the fourth state (10) is stored in the MRAM unit.
Claim 21
Independent Claim
186 words
A method for writing first, second, third, and fourth states in a magnetoresistive random access memory (MRAM) unit including a conductive layer sandwiched between two magnetic tunnel junction cells, each magnetic tunnel junction cell storing one bit information, the method comprising the steps of: applying a first magnetic field having a first strength in a first direction to the MRAM unit when the first state (00) is stored in the MRAM unit; applying a second magnetic field having a second strength in a second direction opposite to the first direction to the MRAM unit when the second state (11) is stored in the MRAM unit; applying the first magnetic field and then applying a third magnetic field having a third strength lower than the second strength in the second direction, to the MRAM unit, when the third state (01) is stored in the MRAM unit; and applying the second magnetic field and then applying a fourth magnetic field having a fourth strength lower than the first strength in the first direction, to the MRAM unit, when the fourth state (10) is stored in the MRAM unit.
Claim 22
Dependent Claim
65 words
The method as claimed in claim 17 wherein the step of applying the second magnetic field is a step of applying a magnetic field having a strength equivalent to the first strength in the second direction, and the step of applying the fourth magnetic field is a step of applying a magnetic field having a strength equivalent to the third strength in the first direction.
Claim 23
Independent Claim
78 words
A method for sensing first, second, third, and fourth states in a magnetoresistive random access memory (MRAM) unit including a conductive layer sandwiched between two magnetic tunnel junction cells, each magnetic tunnel junction cell storing one bit information, the method comprising the steps of: providing a sense current to the MRAM unit; sensing a drop voltage over the MRAM unit; and determining the state stored in the MRAM unit from the drop voltage in accordance with predetermined criteria.
Claim 24
Independent Claim
78 words
A method for sensing first, second, third, and fourth states in a magnetoresistive random access memory (MRAM) unit including a conductive layer sandwiched between two magnetic tunnel junction cells, each magnetic tunnel junction cell storing one bit information, the method comprising the steps of: providing a sense current to the MRAM unit; sensing a drop voltage over the MRAM unit; and determining the state stored in the MRAM unit from the drop voltage in accordance with predetermined criteria.
Claim 25
Dependent Claim
94 words
The method as claimed in claim 20 wherein the step of determining the state stored in the MRAM unit from the drop voltage in accordance with predetermined criteria includes a step of determining the state stored in the MRAM unit as the first state when the drop voltage falls within a first voltage range, the second state when the drop voltage falls within a second voltage range, the third state when the drop voltage falls within a third voltage range, and the fourth state when the drop voltage falls within a fourth voltage range.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 2002-07-26 | 2003-01-25 | 2003-07-27 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 2006-07-26 | 2007-01-25 | 2007-07-27 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 2010-07-26 | 2011-01-25 | 2011-07-27 | $7700.00 | Window Closed / Lapsed |