Magnetic memory unit having four states and operating method thereof
First Claim
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1. 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.
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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.
141 Citations
21 Claims
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1. A magnetoresistive random access memory (MRAM) unit comprising:
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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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A magnetoresistive random access memory (MRAM) device comprising:
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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. - View Dependent Claims (12, 13, 14, 15, 16, 17, 19)
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18. 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:
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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.
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20. 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:
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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. - View Dependent Claims (21)
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Specification