Magnetic random access memory capable of writing information with reduced electric current

Claim 2

A magnetic random access memory, comprising: a word line extending in a first direction; a bit line extending in a second, different direction; and a tunneling magneto-resistive sensor provided between said word line and said bit line in a part where said word line and said bit line cross with each other, said tunneling magneto-resistive sensor comprising: a first ferromagnetic layer having a fixed magnetization; a second ferromagnetic layer having a variable magnetization; and a tunneling insulation film interposed between said first ferromagnetic layer and said second ferromagnetic layer, wherein said first ferromagnetic layer comprising a ferromagnetic material having a spin polarization of 0.9 or higher, and wherein said second ferromagnetic layer has a spin polarization of about 0.5 or less.

Claim 3

A magnetic random access memory as claimed in claim 1 , wherein said first ferromagnetic layer has a spin polarization of about 1.0.

Claim 4

A magnetic random access memory as claimed in claim 1 , wherein said first ferromagnetic layer comprises a ferromagnetic material selected from the group consisting of Fe 3 O 4 , NiMnSb, PtMnSb, CrO 2 and (La,Sr)MnO 3 .

Claim 5

A ferromagnetic random access memory as claimed in claim 1 , wherein said second ferromagnetic layer has a spin polarization of about 0.4 or less.

Claim 6

A ferromagnetic random access memory as claimed in claim 1 , wherein said second ferromagnetic layer has a spin polarization of about 0.2 or less.

Claim 7

A magnetic random access memory, comprising: a word line extending in a first direction; a bit line extending in a second, different direction; a magneto-resistive sensor provided between said word line and said bit line in a part where said word line and said bit line cross with each other, said magneto-resistive sensor comprising a ferromagnetic memory layer storing therein information in the form of magnetization; and a magnetic source applying an offset magnetic field to said ferromagnetic memory layer of said magneto-resistive sensor in the direction of a hard axis of magnetization of said ferromagnetic memory layer.

Claim 8

A magnetic random access memory, comprising: a word line extending in a first direction; a bit line extending in a second, different direction; a magneto-resistive sensor provided between said word line and said bit line in a part where said word line and said bit line cross with each other, said magneto-resistive sensor comprising a ferromagnetic memory layer storing therein information in the form of magnetization; and a magnetic source applying an offset magnetic field to said ferromagnetic memory layer of said magneto-resistive sensor in the direction of a hard axis of magnetization of said ferromagnetic memory layer.

Claim 9

A magnetic random access memory as claimed in claim 6 , wherein said magnetic source applies said offset magnetic field so as to satisfy a relationship (δ H x /H x0 ) ⅔ +((δ H y +H yOffset )/ H y0 ) ⅔ <1, where H yOffset represents said offset magnetic field in the direction of said hard axis of magnetization of said ferromagnetic memory layer, δH x and δH y represent magnetic field components induced by a word line current in said word line and a bit line current in said bit line, respectively in the direction of an easy axis of magnetization of said ferromagnetic memory layer and in the direction of said hard axis of magnetization of said ferromagnetic memory layer, H x0 and H y0 represent a coercive force of said ferromagnetic memory layer respectively in the direction of said easy axis of magnetization and in the direction of said hard axis of magnetization.

Claim 10

A magnetic random access memory as claimed in claim 7 , wherein said offset magnetic field H yOffset further satisfies the relationship:  δ   H x  <  H x0   H yOffset  <  H y0   δ   H y + H yOffset   <  H y0  ( δ   H x / H x0 ) 2 / 3 + ( H yOffset / H y0 ) 2 / 3 < 1.

Claim 11

A magnetic random access memory as claimed in claim 6 , wherein said magnetic source comprises a pair of permanent magnets disposed so as to oppose with each other across said magneto-resistive sensor.

Claim 12

A magnetic random access memory as claimed in claim 6 , wherein said magnetic source comprises a pair of solenoids disposed so as to oppose with each other across said magneto-resistive sensor.

Claim 13

A magnetic random access memory as claimed in claim 6 , wherein said magneto-resistive sensor comprises a first ferromagnetic layer having a fixed magnetization, a second ferromagnetic layer having a variable magnetization, and a tunneling insulation film interposed between said first ferromagnetic layer and said second ferromagnetic layer, said second ferromagnetic layer being used as said ferromagnetic memory layer.

Claim 14

A magnetic random access memory as claimed in claim 6 , wherein said magneto-resistive sensor form, together with further magneto-resistive sensors each having a construction identical with a construction of said magneto-resistive sensor, to form a memory cell array, and wherein said magnetic source comprises a pair of permanent magnets disposed at both lateral sides of said memory cell array.

Claim 15

A magnetic random access memory as claimed in claim 6 , wherein said magneto-resistive sensor form, together with further magneto-resistive sensors each having a construction identical with a construction of said magneto-resistive sensor, to form a memory cell array, and wherein said magnetic source comprises a pair of solenoids disposed at both lateral sides of said memory cell array.

Claim 16

A magnetic random access memory as claimed in claim 6 , wherein said magneto-resistive sensor form, together with further magneto-resistive sensors each having a construction identical with a construction of said magneto-resistive sensor, to form a plurality of memory blocks, and wherein said magnetic source comprises a pair of permanent magnets disposed at both lateral sides of each of said memory blocks.

Claim 17

A magnetic random access memory as claimed in claim 6 , wherein said magnetic source produces said offset magnetic field with a magnitude of about 40 Oe.