CA2270896A1 - Multiple magnetic tunnel structures - Google Patents
Multiple magnetic tunnel structures Download PDFInfo
- Publication number
- CA2270896A1 CA2270896A1 CA002270896A CA2270896A CA2270896A1 CA 2270896 A1 CA2270896 A1 CA 2270896A1 CA 002270896 A CA002270896 A CA 002270896A CA 2270896 A CA2270896 A CA 2270896A CA 2270896 A1 CA2270896 A1 CA 2270896A1
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- Prior art keywords
- layer
- tunnel junction
- ferromagnetic
- spin
- junction
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- 230000005291 magnetic effect Effects 0.000 title claims abstract description 18
- 239000000463 material Substances 0.000 claims description 33
- 230000005294 ferromagnetic effect Effects 0.000 claims description 16
- 239000003302 ferromagnetic material Substances 0.000 claims description 12
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 10
- PXHVJJICTQNCMI-UHFFFAOYSA-N Nickel Chemical compound [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 claims description 6
- 229910052742 iron Inorganic materials 0.000 claims description 5
- 229910017052 cobalt Inorganic materials 0.000 claims description 4
- 239000010941 cobalt Substances 0.000 claims description 4
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 claims description 4
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 claims description 2
- 229910052748 manganese Inorganic materials 0.000 claims description 2
- 239000011572 manganese Substances 0.000 claims description 2
- 229910052759 nickel Inorganic materials 0.000 claims description 2
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 claims description 2
- 229910000889 permalloy Inorganic materials 0.000 claims description 2
- -1 Permadur Inorganic materials 0.000 claims 1
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 claims 1
- 239000000395 magnesium oxide Substances 0.000 claims 1
- AXZKOIWUVFPNLO-UHFFFAOYSA-N magnesium;oxygen(2-) Chemical compound [O-2].[Mg+2] AXZKOIWUVFPNLO-UHFFFAOYSA-N 0.000 claims 1
- 239000002907 paramagnetic material Substances 0.000 claims 1
- 230000015654 memory Effects 0.000 abstract description 2
- 239000007769 metal material Substances 0.000 abstract 1
- 230000005415 magnetization Effects 0.000 description 16
- 239000000126 substance Substances 0.000 description 16
- 239000012212 insulator Substances 0.000 description 5
- 238000009825 accumulation Methods 0.000 description 3
- 229910045601 alloy Inorganic materials 0.000 description 3
- 239000000956 alloy Substances 0.000 description 3
- 239000011810 insulating material Substances 0.000 description 3
- 230000004888 barrier function Effects 0.000 description 2
- 230000005684 electric field Effects 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 239000002674 ointment Substances 0.000 description 2
- 230000005298 paramagnetic effect Effects 0.000 description 2
- 230000002441 reversible effect Effects 0.000 description 2
- 238000012216 screening Methods 0.000 description 2
- 239000010409 thin film Substances 0.000 description 2
- 241000282326 Felis catus Species 0.000 description 1
- 244000287680 Garcinia dulcis Species 0.000 description 1
- 101000637855 Homo sapiens Transmembrane protease serine 11E Proteins 0.000 description 1
- 235000001537 Ribes X gardonianum Nutrition 0.000 description 1
- 235000001535 Ribes X utile Nutrition 0.000 description 1
- 235000016919 Ribes petraeum Nutrition 0.000 description 1
- 244000281247 Ribes rubrum Species 0.000 description 1
- 235000002355 Ribes spicatum Nutrition 0.000 description 1
- 206010041235 Snoring Diseases 0.000 description 1
- 102100032001 Transmembrane protease serine 11E Human genes 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 238000005315 distribution function Methods 0.000 description 1
- 230000014509 gene expression Effects 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 238000000034 method Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 241000894007 species Species 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/127—Structure or manufacture of heads, e.g. inductive
- G11B5/33—Structure or manufacture of flux-sensitive heads, i.e. for reproduction only; Combination of such heads with means for recording or erasing only
- G11B5/39—Structure or manufacture of flux-sensitive heads, i.e. for reproduction only; Combination of such heads with means for recording or erasing only using magneto-resistive devices or effects
- G11B5/3903—Structure or manufacture of flux-sensitive heads, i.e. for reproduction only; Combination of such heads with means for recording or erasing only using magneto-resistive devices or effects using magnetic thin film layers or their effects, the films being part of integrated structures
- G11B5/3906—Details related to the use of magnetic thin film layers or to their effects
- G11B5/3909—Arrangements using a magnetic tunnel junction
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y10/00—Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B82—NANOTECHNOLOGY
- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- B82Y25/00—Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
- G11C11/56—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using storage elements with more than two stable states represented by steps, e.g. of voltage, current, phase, frequency
- G11C11/5607—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using storage elements with more than two stable states represented by steps, e.g. of voltage, current, phase, frequency using magnetic storage elements
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/82—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by variation of the magnetic field applied to the device
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N50/00—Galvanomagnetic devices
- H10N50/10—Magnetoresistive devices
Abstract
A double tunnel junction is disclosed that can be used as a magnetic sensor or as random access memories. The preferred embodiment comprises three magnetic metal materials (16, 18 and 20) separated by two insulating layers (12 and 14). A current is passed through the first tunnel junction thereby developing a voltage in the second junction. The resistance of this device can be changed over a 100 % when an external magnetic field of just a few gauss is applied.
Description
CA 02270896 1999-OS-06 .r ... . .. . ., , ~ .. JW.'. . . ) .. 7 i. ,~~.
SENT BY:CONN.,BOVE,LODGE,&HUTZ; 1- 7-99 : 11:41 . LAW OFFICE ~~ #~ 1~
N 19~~
( 0, TITLE: MULTIPLE MAGNETIC 'TUNNEL STRUCTURES
BACKGRGU1~ID F THE IIVVFNTION
The subject of this invention is a magnetoresistive sensor having a unique combination of elements. This combination of elements results in a substantial change in resistance when even a minimal cxterr>Ftl mabrtetic field is applied. The preferred ermbodiment described below comprises a double tunnel junction, i.e., three magnetic metal sections separated by two insulators with a thickness In the order of 1 U angstroms or two ferromagnets and one paramagnetic materiarl sep~traled by insulators. Application of even a minimum magnetic field to the doubt a tunnel j unction can effectuate a change i.n resistance from as mue;h as l (H) ulun by snore than 100%.
One application of this double tunnel junction is as read heads in hard disks.
Applicant's de~~hlc tnnrtcl Junction providea orders of magnitude change in resistance fear a given change in magnetic held, relative to existing devices.
One example vi' a prior art magnctoresistive device is that described in .Johnson U.S_ Patent No. 5,432,373. The basic trilayer strttctttre of the Johnson patent comprises two electrically conductive ferromagnetic layers separated by a thin conductive parfunabnetic layer. 'The Johnson patent discloses bold as the preferred material for the paratttagrtetic layer.
'This patent theorizes that . a currant pumped between the ferromagnetic layers will force spin up and spin down electrons into the pftraruagnelic layer to slightly magnetize it. Johnson theorizes that his devices can be used trs a current Switch, memory cell ~r a magnetic field delec;tur.
Another magnetoresistivc device disclosed in the art is that described by Moodera et al in an article entitled "Large Magnetoresistance at Rnocn Temperature in r~erromagnelic Thin Film Tunnel lttnctions" which appeared in VulumC 74, Nee. 16 of Plysicsl ReviewL~tte~, pp.
3273-3276 (17 April 1995). in this article the author repeats maximum change of about 25% in resistance (~Rli) upon application of a magnetic field utilizing the Mooderti et al sttvctttre.
That structure i~ a sandwich of a thin layer insulation between ferromagnetic materials. As reported in the Mooclerr~
CA 02270896 1999-OS-06 r.-. ,. , . :r;.<.
_ ._ . . . . .. . ..,. ,..,1'. ~~~.::,.... _ ..,.'f.~ -_q:.7-.4~~t~..4;. .
~a:....~~ :....:. . ::~a a ,:. : ~~ __ SEAT BY : CUW. . BUV)=. LUDGE, t~HUTZ,. 1- 7-99 ~ : '11 : 42 ; LaW UFF I CES
~7~ 0~3~~# ~/~79 --- "~ . E~ ~ ,~ A N t999 1 AIl~3S
article this change in resistance sharply declines as applied voltage increases.
SUMMARY OF THE INYF.LHTlON
Applicant has discovered that the change in resistance (~RlR) desired in a tunnel junction can be substantially improved by utilizinb a double funnel junction comprising alternating ferromagnetic materials and insulating materials. In contrast to the Moodcra tunnel junction just descri hcd, applicant has found that his double tunnel junction results in a much greater change in resistance with minimal change in mal,~nctic field. Also, that change is accomplished without the severe decline in resistivity experienced by Moodera as applied voltage increases.
Applicanf5 dcmhle turmel junction 10 comprises two thin film insulating layers 12 and 14 sandwiched between three materials 16, 18 and 20. The first tunnel junction can comprise a first ferromagnetic material 16, a tirst insulator 12 and a secund ferromagnetic material 18. The second tunnel junctiun can comprise ferromagnetic material 18) second insulator 14 and a ferromagnetic material 20. The second material 18 can he replaced by partima.gnetic material, however, the tirst and third materials cannot.
In operation a current Iee is passed through tire first tunnel junction 1 G) 12, 18 with current going into the first fcrrotnagnetic material 16 and coming out of the second ferromagnetic material 18. Voltage is measure across the second tunnel junction 18, 14, 20 with leads attached to the second 18 and third 20 materials. The measured voltage divided by the current is the effective resistance R. This resistance is different from urdirtary resistance wherC the voltage and current are measured across the same tunnel junction.
DESC1<tIYTION OF DRAWINGS
I=lCi. 1 is a cross-sectional view of the five component double tunnel junction of the invention.
FIG. ? ie a schematic diagram of chemical potentials of the spin up and spin down bands .r wrr ~a eu ocT
_ _..~",.
CA 02270896 1999-OS-06 , a.;> ",.;,", s~;;~,~.~
. ~ , . .W ,, .iJ..2~''.i _ . . .._ ..,.. . .. .. . . s::.<z-r,.. _, , ..~y-.~.< =.'r-._. _.... _.._.....~:~..;.c~~~-v-.,.. ._..._..
_.aWa..;,.vr.i.tt1_tir.;si::~
SENT BY : CUNN. , BUVE, LUDGE, t(iHfTZ : 1- 7-99 : 11 : ~2 : LAW OFF 1 Cl=S ~~
. ~ C~ ~~5 ~ 7 '~< ~~9 r- ~' ~N
IPEAIU.S a in a tunnel junction.
DET LEl) DESC PTION OF -ILF YREFE D FMBODIMErI'1'1 The overall structure of the double tttnncl junction of this invention is illustrated in FIG. 1.
Its preferred composition is as previously described) i_e., alternating layers ol' ferromagnetic m~d~ri:~l I6, 18, ZO and insulating material 12) 14_ The ferroma6netic material suitaUle for use in this invention includes: iron, Perrnadur (rrrl alloy of ~4y% iron, 49% cobalt and 2"/~ vanadium), Pcrmalloy (an alloy ~f iron and nickel-), cobalt, nickel and manganese (or alloys of these three componcnta).
1'he insulating material suitable for use in this invention includes aluminum oxide A12O3) and map,rtesium oxide (Mg0). Typically the overall dimensions of each layer of material fall within the ranbe of lU-' to LO-'" squ~rre millimeters or smaller and have a thlCkness oTabout 1 to 10 nanomcters.
Suitable leads ~a, ~.~ arc attached t.o the first tunnel junetiet: !~ur imposing current therethrough.
Similar leads 2G. 28 are attached to the second tunnel junction. Voltage across leads 26, 28 is Subsequently measured.
'I~he underlying operation of the double tunnel junction is as follows. A
ferromagnetic material contains within it electrons with their spin (the magnetic moment is Proportional to the spin) up and electrons with their spin down. For a given tunnel junction, when a current is passed through it, the chemical potentials uC the spin up and the spin down electrons become different. This difference is called the splitting and is proportional to the ntabnilude oC
the external current (Fig.
z j. -1-he ratio 01 this splitting to the current is of the order of the r eststancc of the tunnel junction.
~hhe mathCmali~al analysis is "reversible;" in that when there is a Splitting in the chemical potentials, a current (For closed circuits) or a voltag,c (for open circuits) will be induced. When a current is passed through the first tunnel junction, there is a splitting of the chemical potential in the second material 18. The rw~rse is true of the second h~nnel junction. Because of the "splitting" in the ;rrond material 1 R which is part of the Second tunnel junction I R, 14, 20. a current or a voltabe is ,~rtut~tn C1.?~~X
CA 02270896 1999-OS-06'~. :;~:<- , -.=; t ~~ ~' _,:~~ ".;3.-wr.~~;,~;~i -'_ , . . .. ,. , _, .:- ~. . ~:.'.~-..v : - ~..:: ::: :;~.~ ~ ., ~a:v' . . . . ~..:.. ~t. . , .:~ ~w: . . < ~ .. . . .. _ . ( ~,1_ _. ~ ..... . ~ . , _ , w.. ~.:., : . .. _ . _.. ....._ ....~fx.,~,~y.a."":._..n..r::..,...:....,:r..t!~rrrr~,='". r,.v. ..JCL,-~:ca.f , .u ;......:.. .... .,... n.."."~,.y;"a~,~
SEVT BY : CONN. , BOVE, LODGE, &I1UTZ ; 1- 7-99 ~ .11 : 43 ; LAW OFF I CL~S1 .
. '5 4 ' / 7 I E~,N~U,S ~ ,.1 induced in the second tunnel junction.
The direction of the curreW depends on the direction of the magnetization of the second or third materials 18 or 20, provided certain conditions are met. Lf the direction of the magnetization of these materials 18 or ZU is reversed, which can be caused by an external mayetiv field, the sign of the current or voltage in the second tunnel structure is reversed. Thus, the application of a small external ma6~netic field can result in a substantial change in the resistance of this device.
'The wndilion can be stated in preoise mathematical terms and roul;hly corresponds to the requirement that the spin asymmetry is stronger in the third material 20 than in the second material 18. 'Ibis analysis is performed by sulvit~ a so-called liliearized Landau-Vlasav-Boltana,n equation which describes the transport cat the electrons inside the ferromagnets, taking into account the Coulomb interaction between the elec;tmns. This equation is described in 1.,.
Kadanu1T and G. Bayin, "Quantum 5latistical, Mechanics", Chapter 7, Benjamin, N.Y. (1902). The solutions are then matched across cash of the insulatinb materials 12, 14.
'fo better understand the operation of this invention a brief explanation is provided of the mCC;hat~ics by which a ettrrent in a tunnel structure can induce a splitting of the chemical potentials of the spin up and the spin down electrons. Cach of the tunnel junctions can be viewed as having a total thickness 1. comprising a trilayer sizucture of two wupled ferromagnets on the left aurd on the right and an insulator in between. We assume the z direction to be perpendicular to the insulating interface which is located from z=--d/2 to cU2. l-here is an interfacial resistamc~ of mabnitudC r(1 ys) for spin channel s = t 1 caused by the W sulatin6 barrier between the fettomagncts. ~1'hus r is the average resistance of the spin up and the spin down channel. 2yr is the difference between these two channels. We assume that the thickness of our device is less than the spin diffusion length (oC the order of 100 A) so that we; can ignore the conversion of the spin up electrons into spin down electrons or vice verss.
SENT BY:CONN.,BOVE,LODGE,&HUTZ; 1- 7-99 : 11:41 . LAW OFFICE ~~ #~ 1~
N 19~~
( 0, TITLE: MULTIPLE MAGNETIC 'TUNNEL STRUCTURES
BACKGRGU1~ID F THE IIVVFNTION
The subject of this invention is a magnetoresistive sensor having a unique combination of elements. This combination of elements results in a substantial change in resistance when even a minimal cxterr>Ftl mabrtetic field is applied. The preferred ermbodiment described below comprises a double tunnel junction, i.e., three magnetic metal sections separated by two insulators with a thickness In the order of 1 U angstroms or two ferromagnets and one paramagnetic materiarl sep~traled by insulators. Application of even a minimum magnetic field to the doubt a tunnel j unction can effectuate a change i.n resistance from as mue;h as l (H) ulun by snore than 100%.
One application of this double tunnel junction is as read heads in hard disks.
Applicant's de~~hlc tnnrtcl Junction providea orders of magnitude change in resistance fear a given change in magnetic held, relative to existing devices.
One example vi' a prior art magnctoresistive device is that described in .Johnson U.S_ Patent No. 5,432,373. The basic trilayer strttctttre of the Johnson patent comprises two electrically conductive ferromagnetic layers separated by a thin conductive parfunabnetic layer. 'The Johnson patent discloses bold as the preferred material for the paratttagrtetic layer.
'This patent theorizes that . a currant pumped between the ferromagnetic layers will force spin up and spin down electrons into the pftraruagnelic layer to slightly magnetize it. Johnson theorizes that his devices can be used trs a current Switch, memory cell ~r a magnetic field delec;tur.
Another magnetoresistivc device disclosed in the art is that described by Moodera et al in an article entitled "Large Magnetoresistance at Rnocn Temperature in r~erromagnelic Thin Film Tunnel lttnctions" which appeared in VulumC 74, Nee. 16 of Plysicsl ReviewL~tte~, pp.
3273-3276 (17 April 1995). in this article the author repeats maximum change of about 25% in resistance (~Rli) upon application of a magnetic field utilizing the Mooderti et al sttvctttre.
That structure i~ a sandwich of a thin layer insulation between ferromagnetic materials. As reported in the Mooclerr~
CA 02270896 1999-OS-06 r.-. ,. , . :r;.<.
_ ._ . . . . .. . ..,. ,..,1'. ~~~.::,.... _ ..,.'f.~ -_q:.7-.4~~t~..4;. .
~a:....~~ :....:. . ::~a a ,:. : ~~ __ SEAT BY : CUW. . BUV)=. LUDGE, t~HUTZ,. 1- 7-99 ~ : '11 : 42 ; LaW UFF I CES
~7~ 0~3~~# ~/~79 --- "~ . E~ ~ ,~ A N t999 1 AIl~3S
article this change in resistance sharply declines as applied voltage increases.
SUMMARY OF THE INYF.LHTlON
Applicant has discovered that the change in resistance (~RlR) desired in a tunnel junction can be substantially improved by utilizinb a double funnel junction comprising alternating ferromagnetic materials and insulating materials. In contrast to the Moodcra tunnel junction just descri hcd, applicant has found that his double tunnel junction results in a much greater change in resistance with minimal change in mal,~nctic field. Also, that change is accomplished without the severe decline in resistivity experienced by Moodera as applied voltage increases.
Applicanf5 dcmhle turmel junction 10 comprises two thin film insulating layers 12 and 14 sandwiched between three materials 16, 18 and 20. The first tunnel junction can comprise a first ferromagnetic material 16, a tirst insulator 12 and a secund ferromagnetic material 18. The second tunnel junctiun can comprise ferromagnetic material 18) second insulator 14 and a ferromagnetic material 20. The second material 18 can he replaced by partima.gnetic material, however, the tirst and third materials cannot.
In operation a current Iee is passed through tire first tunnel junction 1 G) 12, 18 with current going into the first fcrrotnagnetic material 16 and coming out of the second ferromagnetic material 18. Voltage is measure across the second tunnel junction 18, 14, 20 with leads attached to the second 18 and third 20 materials. The measured voltage divided by the current is the effective resistance R. This resistance is different from urdirtary resistance wherC the voltage and current are measured across the same tunnel junction.
DESC1<tIYTION OF DRAWINGS
I=lCi. 1 is a cross-sectional view of the five component double tunnel junction of the invention.
FIG. ? ie a schematic diagram of chemical potentials of the spin up and spin down bands .r wrr ~a eu ocT
_ _..~",.
CA 02270896 1999-OS-06 , a.;> ",.;,", s~;;~,~.~
. ~ , . .W ,, .iJ..2~''.i _ . . .._ ..,.. . .. .. . . s::.<z-r,.. _, , ..~y-.~.< =.'r-._. _.... _.._.....~:~..;.c~~~-v-.,.. ._..._..
_.aWa..;,.vr.i.tt1_tir.;si::~
SENT BY : CUNN. , BUVE, LUDGE, t(iHfTZ : 1- 7-99 : 11 : ~2 : LAW OFF 1 Cl=S ~~
. ~ C~ ~~5 ~ 7 '~< ~~9 r- ~' ~N
IPEAIU.S a in a tunnel junction.
DET LEl) DESC PTION OF -ILF YREFE D FMBODIMErI'1'1 The overall structure of the double tttnncl junction of this invention is illustrated in FIG. 1.
Its preferred composition is as previously described) i_e., alternating layers ol' ferromagnetic m~d~ri:~l I6, 18, ZO and insulating material 12) 14_ The ferroma6netic material suitaUle for use in this invention includes: iron, Perrnadur (rrrl alloy of ~4y% iron, 49% cobalt and 2"/~ vanadium), Pcrmalloy (an alloy ~f iron and nickel-), cobalt, nickel and manganese (or alloys of these three componcnta).
1'he insulating material suitable for use in this invention includes aluminum oxide A12O3) and map,rtesium oxide (Mg0). Typically the overall dimensions of each layer of material fall within the ranbe of lU-' to LO-'" squ~rre millimeters or smaller and have a thlCkness oTabout 1 to 10 nanomcters.
Suitable leads ~a, ~.~ arc attached t.o the first tunnel junetiet: !~ur imposing current therethrough.
Similar leads 2G. 28 are attached to the second tunnel junction. Voltage across leads 26, 28 is Subsequently measured.
'I~he underlying operation of the double tunnel junction is as follows. A
ferromagnetic material contains within it electrons with their spin (the magnetic moment is Proportional to the spin) up and electrons with their spin down. For a given tunnel junction, when a current is passed through it, the chemical potentials uC the spin up and the spin down electrons become different. This difference is called the splitting and is proportional to the ntabnilude oC
the external current (Fig.
z j. -1-he ratio 01 this splitting to the current is of the order of the r eststancc of the tunnel junction.
~hhe mathCmali~al analysis is "reversible;" in that when there is a Splitting in the chemical potentials, a current (For closed circuits) or a voltag,c (for open circuits) will be induced. When a current is passed through the first tunnel junction, there is a splitting of the chemical potential in the second material 18. The rw~rse is true of the second h~nnel junction. Because of the "splitting" in the ;rrond material 1 R which is part of the Second tunnel junction I R, 14, 20. a current or a voltabe is ,~rtut~tn C1.?~~X
CA 02270896 1999-OS-06'~. :;~:<- , -.=; t ~~ ~' _,:~~ ".;3.-wr.~~;,~;~i -'_ , . . .. ,. , _, .:- ~. . ~:.'.~-..v : - ~..:: ::: :;~.~ ~ ., ~a:v' . . . . ~..:.. ~t. . , .:~ ~w: . . < ~ .. . . .. _ . ( ~,1_ _. ~ ..... . ~ . , _ , w.. ~.:., : . .. _ . _.. ....._ ....~fx.,~,~y.a."":._..n..r::..,...:....,:r..t!~rrrr~,='". r,.v. ..JCL,-~:ca.f , .u ;......:.. .... .,... n.."."~,.y;"a~,~
SEVT BY : CONN. , BOVE, LODGE, &I1UTZ ; 1- 7-99 ~ .11 : 43 ; LAW OFF I CL~S1 .
. '5 4 ' / 7 I E~,N~U,S ~ ,.1 induced in the second tunnel junction.
The direction of the curreW depends on the direction of the magnetization of the second or third materials 18 or 20, provided certain conditions are met. Lf the direction of the magnetization of these materials 18 or ZU is reversed, which can be caused by an external mayetiv field, the sign of the current or voltage in the second tunnel structure is reversed. Thus, the application of a small external ma6~netic field can result in a substantial change in the resistance of this device.
'The wndilion can be stated in preoise mathematical terms and roul;hly corresponds to the requirement that the spin asymmetry is stronger in the third material 20 than in the second material 18. 'Ibis analysis is performed by sulvit~ a so-called liliearized Landau-Vlasav-Boltana,n equation which describes the transport cat the electrons inside the ferromagnets, taking into account the Coulomb interaction between the elec;tmns. This equation is described in 1.,.
Kadanu1T and G. Bayin, "Quantum 5latistical, Mechanics", Chapter 7, Benjamin, N.Y. (1902). The solutions are then matched across cash of the insulatinb materials 12, 14.
'fo better understand the operation of this invention a brief explanation is provided of the mCC;hat~ics by which a ettrrent in a tunnel structure can induce a splitting of the chemical potentials of the spin up and the spin down electrons. Cach of the tunnel junctions can be viewed as having a total thickness 1. comprising a trilayer sizucture of two wupled ferromagnets on the left aurd on the right and an insulator in between. We assume the z direction to be perpendicular to the insulating interface which is located from z=--d/2 to cU2. l-here is an interfacial resistamc~ of mabnitudC r(1 ys) for spin channel s = t 1 caused by the W sulatin6 barrier between the fettomagncts. ~1'hus r is the average resistance of the spin up and the spin down channel. 2yr is the difference between these two channels. We assume that the thickness of our device is less than the spin diffusion length (oC the order of 100 A) so that we; can ignore the conversion of the spin up electrons into spin down electrons or vice verss.
.. ... . _ _ . . CA 02270896 1999v..05._ 06 <-.. . -,~:'; ,~ , _~.-:
n;z~~*<~~~.~~ , ,~. .~ ._ : ., ,;...:..,.: .. . . ,: ,.. _ .. .. : . _. ,.,. , . , .:. .,, ,:.
, . .: :::~,: :. . . ~. :~: : : .. r.. ' .~ a.
,. .
,~.,~:;r=~~'~,~
.i ;
... _ ... _ > , Y.. .. . . . . , ..,:,:-~.;. ' ' ,. x _ . . . ... _ . ._ . . -._ .. ::~~. ~..._ :.:x;:.:...:.-~_..m.,. . .. _ _.:
.~~r'.:.~.~._. _.;r:i~:,:~w SEVT BY : CONN. , BOVE, LODGE, &tiUTZ : 1- 7-99 : 11 : 43 ; L.AW OFF I CE~~ ;
1 ~~~~N
_.
r is of the order of kilo - ohms and is much larger than the resistance of the terroma~.nets r~;.
The chemical potential for spin s on the left and right is represented by ,u,' and p..r', respectively, and the current carried by electrons of spin s by the symbol J,. Superscripts <, >
denote the left and right side of the junction. Because of~ the high interfacial resistance r(1 - ys), most oh voltage drop will occur at the interface. We obta~.n, from Ohm's law, ~~.: - ~.s~(Z - d~2) ~ ~.r'(Z - ..d~2~ ~ r( 1 - ~S).h.
We explain Why ,ui # p. helow.
Associated with the change ofthe chemical potential, there is a change of the electron density of spW s by an amount givCn by dpr _ ~srN, whi:rc N, is cHe dccisity of states at the Fermi surface for electrons of spin s '= f 1. Tliis change in turn implies changes ixt the net charge; (p) and magnetization (a) den.Sities given by ap'' - 8p''~ + gyp', = N'' , ~' , +
N'_~t''_, ~~ '- ap r + ~p'_ N' ~ N'- ~ + N''- ft'- with similar expressions ti>r the right hand side a f' the j unction where the superscript is replaced by >. These induced charbe and spin densities are due to shi fLS
in the chemical potential and not to spin accumulation. Spin accumulation can also cause a splitting of the chemical potential (see column 4 of Johnson U.S. Patent No. 5,432,373). For spin accumulation, an additional magnetization 60' of the order of I",TZII~ is created on the right hand side (of volume ~) due to the injee;tiun magneliiatiun current (m from the Icft hand side which takes a finite time TZ to relax. This 80' is also present in addition iu the So discussed above but is of a much smaller magnitude. The physics of this structure requires that the net charge induced becomes very small, oP the order of r,lr ti mes Ny,u.,. '!'his implies that the shifts in the chemical potentials are opposite in sign. More precisely, 6p = 0.5~, 8p, = U.SE,~,Nr = 0. Thus, ~, _ -N~ulN+. We now turn our attention to why the uet charge induced at the interface is small.
For an external electric field F', the current can be expressed as a sum of a term E/p,,: due lu ~~pEp SHeET
.- , . . CA 02270896 1999-OS-06 ' . ~ :
._. '._...... ..'..'.._._ . :-. ..~...,.H .. f...~..r....... - .... .,r'- - ~;
,.r , . ,.- '. < .: r ~, . ~:"..:... ~ ... : . ~ :~ . .... _ SEVT BY : CONIC , BOVE, LODGE, &HUTZ : 1- 7-99 : 11 : ~~ ; LAW OFF 1 C1=~~S
~3~(~3~ ~~l~l lPEAIUS n ~' JA N f999 the external driving field in the metal and another term .1,, due to the potential caused by the difference between the induced charge densities and that due to the self consistent screening potential T~Tl caused by the Coulomb repulsion between electrons:
J, = J,., + F,Ip,.,.
(2) ~~r " -~~t.,.a~L~Plm.,. - X~~m..~ Here p,,., the resistivity ul' the ferroanagnet, is given by p,,,.v _ -1.~, z~,JZm,1 x, _ (.~ ~ c~,,~, (e)lrrt=)l( .F~ ;lZrrt~ ) is a deasity of states laclor. ,f,; is the Fermi distribution function; r" m,, are the relaxation time in the ferromagnet and the effective mass. X, a d~;,a/m,_ Recall that the charge density of spW s is a sum of the total charge and magnetization densities dp., = (p + s a)/2, Away froth the interface, the magnetization decays at a rata proportional to the renurmalized spin diffusiuu length I (of the ozder of 1 UU ~) whcrct~s the charge density decays at a faster rate proportional to the screening length ~1 (of the order of a few ~).
Since the charge density dirs off much fastrr than the magneti~tion density, the ratr of change of fip,. is approarimately equal to 0.5~ ~. J,., is thus of the order of magnitude rSpT,lrrt,'~ ~ h~(xopr~t), on usW g the definition of the resistivity p,.,;.
There are two resistances that enter into consideration: the interfacial resistance r and that of the ferromagnets r,.. = p,~lla. For problems of practical interest, for an area a of l O~cm~, r i s of the order of k-ohm whereas pr!la is of the order of 10'S ohm. ~fhus y~ > > p,..llu > > p,:.ilu. We expect that unless there is a cancellation, gyp, and hence 8p is of the order of N,lt, ~
N,rJ,. Substituting this cstitnate of dp into the estimate of.7,, in the previous paragraph, we found that ,7, is of the order of r.l."alpr~ and is much larger than the current due to the external field.
t3ecausc of the rapid decay of the charge densities, an electric field is created that may become much larger than the external tield.
Thin cannot bG aell-c:c~nsislGntly auvl;ained and ~qualiutr (1) cannot be salisrcd unless the chary iu the charge densities of each spin component arv such that the net charge density 8p = ().
In summary, thr net charge induced is smaller than expected. This implies a splitting of the ~' j~n~T
, . . CA 02270896 1999-OS-06.... . .. . . , '.-y. ~ ~t~a=
'- L -. , : . _ - ~.:;
. . _._, . _ . . . . ........ .. . .. ~. ... -n ~'W ..: r ~ _ _, .-. -.r~udxi:c.~-. .., ,.
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1 EAIU.S ~ J A N
chemical potential of the spin up and the spin down electrons right al the interface.
The following argument provides a picture of why the voltage may reverse sign as the magnetization of ferromagnet 20 is reversed. Consider the extreme case that the spin asymmetry in the third ferromagnetic material 20 is such that only a single spin species occurs with enCr~es at the rermi energy. Assume that the chemical potential is split in the see;orad material 18 with the spin up energy above the spin down energy. We expect the chemical potential of the single spin component in the third material 2U to be between the chemical potentials in the second material J Y. if the third material 20 spin component is down, then the electrons will flow from the third mcateri.al 20 to the second material 18 where the chemical potential of the Spin dawn elCClrun iv l~wur than that in third material 20. if we switch the magnetization of the third material 20 so that lhc spin component in that component is now spin up) electrons will flow from second to third material because the chemical potential of the spin up electrons in the second material 18 is now higher. A similar argument also works if we switch the magnetization of the second material 18 while that of third ferromagnetic material Zt) is fixed. A detailed analysis provides the following result for the I73i1~,11Chlat1U11 Ml in the second ferromagnet.
lltslcurrent ~ /(B - y)lN"' - (I - yB)lN,'_J4r f1 /N,,,,N", - llNn,,N~ j ( 3 ) where 1/N" = IlN+ - IlN, IlN,' = 1/N+ + IlN_, IlNx,, = 1/N,,' - IlNr'.
I/N,,;,. _. IlN, > + IIN,~'; .f=D
or S. B = (b'G' -~- b'C')l(C' - C'); G = -0.5(b+~,l(~t~pr.(1-~)~ where we have assumed that the resistivity of the ferromagnet for spin channel s, p,", can be written as p,:
(I- s~. b is a parameter that measures the difference in transport properties between the spin up tmd the spill dowtl electrons given by b = (~'r r"~,slnr,~l(E',rx,,Jm~l. The parameter p foe the asymmetry of the resistivity can be written in a similar fashion as ~ _ -~"v r,/2m,?l~ rl2r.~,s_ Por a fixed magnetisation M~ in the: second ferromagnetic (paramagnetic) material 18 that is created by the current through leads 22-24, as the magnetization of 20 is reversed, N") ~ and y -7_ T ..~ .:.;'.' ;~il~~.~, ~
.-. _ CA 02270896 1999-05-06~ : 't~~~R'~ !'x~..""~~~
~. :.... : ~ . .. -,.:,.y"-'_ :-...:. ....::.. ... ..-: . .x~.a a.: .,.._.-..W.~
~E~T Bf : CO\\ . . BOV)=. LODG>=, &Hf TZ :~ 1- 7- 99 : 11 - ~ 5 : L ~W OFF f CF ~~ p~~~~ ~9 ~ 9~~. ~ 9~1 ~l~.S D 7 .J A N 1999 changes sign. Thus, any possible sign changes will be determined by IV~R and Ni,,,. if the two aides are identical, then for the P (AP) case, quantities with subscripts A (S) are zero. We get fI = 0 (drl = U), no sign change occurs. On the other hand, if there is a band with a low density of states on ttte > side such that j 1IN,;' j > j 1IN"y, then the voltage wi 11 change sign when the > magnetization is changed.
The tuiuiel junction device of this invention can be used as a magnetic sensor or as a non-volatile random access memory (RAM).
Magnetic sensors arc used in different applications. Examples are as read heads in hard disks, as sensors in dillerent parts of the automobile, or in traffic controls. ~1'he external field comes from the magnetic media (ou disk) in a recordW g situation. Ut it caex i:ucw fn~tn rr~egnGla embedded in an mechanical instnunent. In a11 these applications, the external magnetic field is expected to possess a cornpunenl alignec! along the planes of the double tunnel .junction stmcture. When the external field is big enough) the magnetization of one of the ferromagnetic maleria.ls cdn be changed.
With the appropriate choice of ferromagnetic material, such ns Permalloy, in applicant's device, fields as low as a few C iauss can be easily detected.
Depending on the application there are different design possibilities. One can "pin" the magnetization of some of the three ferromagnetic components su that one or two, for example, the Iirst and second materials) do nut rotate under a field of reasonable strength that is encountered in au~ application. This "pinning" can be achieved by using a material of high coercivily such as cobalt or iron or by placing a material of high coereivity in contact with the ferrornagnetie layers, For applications as the read head in hard disks we expect the layers to be parallel to the platters of the media. For longiludi,tlal media where the iriagnetizaliun is mostly along the platter, we expect the stray field on top of the media to cause the switching.
1~ or application as rams, the magnetization states of the three ferromagnets store the _g_ - ~ CA 02270896 1999-OS-06 ~ . ,; ;,.~,~ .,;.-~' ... ~ . , . . ..:r',.y - ., ._..r... w-':r-. . ':",'... "....._.. ~.-: : s: ' ..'. ~ - _ ~ . ~ .. . ". : .
~ .
. ~ ' . ~ ::1 ...._.,-~: ._ . .... .... .. ... _s.".. .:,~.. . F -..i....~ , F....~ _.~. .W ... .:...'. a.-_.... .- . ...-... i.s~..._ ~ : .~. ~.~.. _ . -. . - .:... - ::.,.,: _a.-.
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information. In principle) the structure can store more than a single bit because there are S possible combinations for the direction of the magnetization of the three materials 16, 18, 2l? in the double barrier junction. For the simplest example, we assume that two of the three materials are pinned so that only one (for example, the third) can be reversed. I n a typical r~pplicatinn, we expect an a.iray of these junctions to be created by, for example, lithographic techniques. The direction of the magnetization can be switched ("written") by an external field along the planes of the junction generated by a current in an external wire. This inibrmation can be read by applying a current to the first tunnel junction 16, 12, 18 and then checking the sign of the voitagc across the second junction 18, 14, 20.
n;z~~*<~~~.~~ , ,~. .~ ._ : ., ,;...:..,.: .. . . ,: ,.. _ .. .. : . _. ,.,. , . , .:. .,, ,:.
, . .: :::~,: :. . . ~. :~: : : .. r.. ' .~ a.
,. .
,~.,~:;r=~~'~,~
.i ;
... _ ... _ > , Y.. .. . . . . , ..,:,:-~.;. ' ' ,. x _ . . . ... _ . ._ . . -._ .. ::~~. ~..._ :.:x;:.:...:.-~_..m.,. . .. _ _.:
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1 ~~~~N
_.
r is of the order of kilo - ohms and is much larger than the resistance of the terroma~.nets r~;.
The chemical potential for spin s on the left and right is represented by ,u,' and p..r', respectively, and the current carried by electrons of spin s by the symbol J,. Superscripts <, >
denote the left and right side of the junction. Because of~ the high interfacial resistance r(1 - ys), most oh voltage drop will occur at the interface. We obta~.n, from Ohm's law, ~~.: - ~.s~(Z - d~2) ~ ~.r'(Z - ..d~2~ ~ r( 1 - ~S).h.
We explain Why ,ui # p. helow.
Associated with the change ofthe chemical potential, there is a change of the electron density of spW s by an amount givCn by dpr _ ~srN, whi:rc N, is cHe dccisity of states at the Fermi surface for electrons of spin s '= f 1. Tliis change in turn implies changes ixt the net charge; (p) and magnetization (a) den.Sities given by ap'' - 8p''~ + gyp', = N'' , ~' , +
N'_~t''_, ~~ '- ap r + ~p'_ N' ~ N'- ~ + N''- ft'- with similar expressions ti>r the right hand side a f' the j unction where the superscript is replaced by >. These induced charbe and spin densities are due to shi fLS
in the chemical potential and not to spin accumulation. Spin accumulation can also cause a splitting of the chemical potential (see column 4 of Johnson U.S. Patent No. 5,432,373). For spin accumulation, an additional magnetization 60' of the order of I",TZII~ is created on the right hand side (of volume ~) due to the injee;tiun magneliiatiun current (m from the Icft hand side which takes a finite time TZ to relax. This 80' is also present in addition iu the So discussed above but is of a much smaller magnitude. The physics of this structure requires that the net charge induced becomes very small, oP the order of r,lr ti mes Ny,u.,. '!'his implies that the shifts in the chemical potentials are opposite in sign. More precisely, 6p = 0.5~, 8p, = U.SE,~,Nr = 0. Thus, ~, _ -N~ulN+. We now turn our attention to why the uet charge induced at the interface is small.
For an external electric field F', the current can be expressed as a sum of a term E/p,,: due lu ~~pEp SHeET
.- , . . CA 02270896 1999-OS-06 ' . ~ :
._. '._...... ..'..'.._._ . :-. ..~...,.H .. f...~..r....... - .... .,r'- - ~;
,.r , . ,.- '. < .: r ~, . ~:"..:... ~ ... : . ~ :~ . .... _ SEVT BY : CONIC , BOVE, LODGE, &HUTZ : 1- 7-99 : 11 : ~~ ; LAW OFF 1 C1=~~S
~3~(~3~ ~~l~l lPEAIUS n ~' JA N f999 the external driving field in the metal and another term .1,, due to the potential caused by the difference between the induced charge densities and that due to the self consistent screening potential T~Tl caused by the Coulomb repulsion between electrons:
J, = J,., + F,Ip,.,.
(2) ~~r " -~~t.,.a~L~Plm.,. - X~~m..~ Here p,,., the resistivity ul' the ferroanagnet, is given by p,,,.v _ -1.~, z~,JZm,1 x, _ (.~ ~ c~,,~, (e)lrrt=)l( .F~ ;lZrrt~ ) is a deasity of states laclor. ,f,; is the Fermi distribution function; r" m,, are the relaxation time in the ferromagnet and the effective mass. X, a d~;,a/m,_ Recall that the charge density of spW s is a sum of the total charge and magnetization densities dp., = (p + s a)/2, Away froth the interface, the magnetization decays at a rata proportional to the renurmalized spin diffusiuu length I (of the ozder of 1 UU ~) whcrct~s the charge density decays at a faster rate proportional to the screening length ~1 (of the order of a few ~).
Since the charge density dirs off much fastrr than the magneti~tion density, the ratr of change of fip,. is approarimately equal to 0.5~ ~. J,., is thus of the order of magnitude rSpT,lrrt,'~ ~ h~(xopr~t), on usW g the definition of the resistivity p,.,;.
There are two resistances that enter into consideration: the interfacial resistance r and that of the ferromagnets r,.. = p,~lla. For problems of practical interest, for an area a of l O~cm~, r i s of the order of k-ohm whereas pr!la is of the order of 10'S ohm. ~fhus y~ > > p,..llu > > p,:.ilu. We expect that unless there is a cancellation, gyp, and hence 8p is of the order of N,lt, ~
N,rJ,. Substituting this cstitnate of dp into the estimate of.7,, in the previous paragraph, we found that ,7, is of the order of r.l."alpr~ and is much larger than the current due to the external field.
t3ecausc of the rapid decay of the charge densities, an electric field is created that may become much larger than the external tield.
Thin cannot bG aell-c:c~nsislGntly auvl;ained and ~qualiutr (1) cannot be salisrcd unless the chary iu the charge densities of each spin component arv such that the net charge density 8p = ().
In summary, thr net charge induced is smaller than expected. This implies a splitting of the ~' j~n~T
, . . CA 02270896 1999-OS-06.... . .. . . , '.-y. ~ ~t~a=
'- L -. , : . _ - ~.:;
. . _._, . _ . . . . ........ .. . .. ~. ... -n ~'W ..: r ~ _ _, .-. -.r~udxi:c.~-. .., ,.
.. . . . ,. . . .,. .~ e'~, ~ - ' __ ~c.\T BY : CO~. ( BUVE, LODGE, &HfTZ : 1- 7-99 : 11 : ~-1 : Lad' OFF I CE ~
~~: ~_ 1t~
~_, ~ . ~ 19~~
1 EAIU.S ~ J A N
chemical potential of the spin up and the spin down electrons right al the interface.
The following argument provides a picture of why the voltage may reverse sign as the magnetization of ferromagnet 20 is reversed. Consider the extreme case that the spin asymmetry in the third ferromagnetic material 20 is such that only a single spin species occurs with enCr~es at the rermi energy. Assume that the chemical potential is split in the see;orad material 18 with the spin up energy above the spin down energy. We expect the chemical potential of the single spin component in the third material 2U to be between the chemical potentials in the second material J Y. if the third material 20 spin component is down, then the electrons will flow from the third mcateri.al 20 to the second material 18 where the chemical potential of the Spin dawn elCClrun iv l~wur than that in third material 20. if we switch the magnetization of the third material 20 so that lhc spin component in that component is now spin up) electrons will flow from second to third material because the chemical potential of the spin up electrons in the second material 18 is now higher. A similar argument also works if we switch the magnetization of the second material 18 while that of third ferromagnetic material Zt) is fixed. A detailed analysis provides the following result for the I73i1~,11Chlat1U11 Ml in the second ferromagnet.
lltslcurrent ~ /(B - y)lN"' - (I - yB)lN,'_J4r f1 /N,,,,N", - llNn,,N~ j ( 3 ) where 1/N" = IlN+ - IlN, IlN,' = 1/N+ + IlN_, IlNx,, = 1/N,,' - IlNr'.
I/N,,;,. _. IlN, > + IIN,~'; .f=D
or S. B = (b'G' -~- b'C')l(C' - C'); G = -0.5(b+~,l(~t~pr.(1-~)~ where we have assumed that the resistivity of the ferromagnet for spin channel s, p,", can be written as p,:
(I- s~. b is a parameter that measures the difference in transport properties between the spin up tmd the spill dowtl electrons given by b = (~'r r"~,slnr,~l(E',rx,,Jm~l. The parameter p foe the asymmetry of the resistivity can be written in a similar fashion as ~ _ -~"v r,/2m,?l~ rl2r.~,s_ Por a fixed magnetisation M~ in the: second ferromagnetic (paramagnetic) material 18 that is created by the current through leads 22-24, as the magnetization of 20 is reversed, N") ~ and y -7_ T ..~ .:.;'.' ;~il~~.~, ~
.-. _ CA 02270896 1999-05-06~ : 't~~~R'~ !'x~..""~~~
~. :.... : ~ . .. -,.:,.y"-'_ :-...:. ....::.. ... ..-: . .x~.a a.: .,.._.-..W.~
~E~T Bf : CO\\ . . BOV)=. LODG>=, &Hf TZ :~ 1- 7- 99 : 11 - ~ 5 : L ~W OFF f CF ~~ p~~~~ ~9 ~ 9~~. ~ 9~1 ~l~.S D 7 .J A N 1999 changes sign. Thus, any possible sign changes will be determined by IV~R and Ni,,,. if the two aides are identical, then for the P (AP) case, quantities with subscripts A (S) are zero. We get fI = 0 (drl = U), no sign change occurs. On the other hand, if there is a band with a low density of states on ttte > side such that j 1IN,;' j > j 1IN"y, then the voltage wi 11 change sign when the > magnetization is changed.
The tuiuiel junction device of this invention can be used as a magnetic sensor or as a non-volatile random access memory (RAM).
Magnetic sensors arc used in different applications. Examples are as read heads in hard disks, as sensors in dillerent parts of the automobile, or in traffic controls. ~1'he external field comes from the magnetic media (ou disk) in a recordW g situation. Ut it caex i:ucw fn~tn rr~egnGla embedded in an mechanical instnunent. In a11 these applications, the external magnetic field is expected to possess a cornpunenl alignec! along the planes of the double tunnel .junction stmcture. When the external field is big enough) the magnetization of one of the ferromagnetic maleria.ls cdn be changed.
With the appropriate choice of ferromagnetic material, such ns Permalloy, in applicant's device, fields as low as a few C iauss can be easily detected.
Depending on the application there are different design possibilities. One can "pin" the magnetization of some of the three ferromagnetic components su that one or two, for example, the Iirst and second materials) do nut rotate under a field of reasonable strength that is encountered in au~ application. This "pinning" can be achieved by using a material of high coercivily such as cobalt or iron or by placing a material of high coereivity in contact with the ferrornagnetie layers, For applications as the read head in hard disks we expect the layers to be parallel to the platters of the media. For longiludi,tlal media where the iriagnetizaliun is mostly along the platter, we expect the stray field on top of the media to cause the switching.
1~ or application as rams, the magnetization states of the three ferromagnets store the _g_ - ~ CA 02270896 1999-OS-06 ~ . ,; ;,.~,~ .,;.-~' ... ~ . , . . ..:r',.y - ., ._..r... w-':r-. . ':",'... "....._.. ~.-: : s: ' ..'. ~ - _ ~ . ~ .. . ". : .
~ .
. ~ ' . ~ ::1 ...._.,-~: ._ . .... .... .. ... _s.".. .:,~.. . F -..i....~ , F....~ _.~. .W ... .:...'. a.-_.... .- . ...-... i.s~..._ ~ : .~. ~.~.. _ . -. . - .:... - ::.,.,: _a.-.
~E~T BY : CU\V . , BUVE. LUDGE, &H~TZ ; 1- 7-99 : 11 : -t~ : LW' UFF I
CES~~'~~ ; ~~~~ 1~:' v 9 1PEAIU.S o 7 ,~A,~
information. In principle) the structure can store more than a single bit because there are S possible combinations for the direction of the magnetization of the three materials 16, 18, 2l? in the double barrier junction. For the simplest example, we assume that two of the three materials are pinned so that only one (for example, the third) can be reversed. I n a typical r~pplicatinn, we expect an a.iray of these junctions to be created by, for example, lithographic techniques. The direction of the magnetization can be switched ("written") by an external field along the planes of the junction generated by a current in an external wire. This inibrmation can be read by applying a current to the first tunnel junction 16, 12, 18 and then checking the sign of the voitagc across the second junction 18, 14, 20.
Claims (7)
1. A double tunnel junction comprising:
a first ferromagnetic layer;
a first insulating layer disposed on the first ferromagnetic layer;
a second layer consisting of a ferromagnetic or paramagnetic material disposed on the first insulating layer and aligned with the first ferromagnetic layer;
a second insulating layer disposed on the second layer;
a third ferromagnetic layer disposed on the second insulating layer and aligned with the second layer; and means for passing a biasing current from the first ferromagnetic layer to the second layer, wherein a resultant voltage across the second layer and the third ferromagnetic layer is measured.
a first ferromagnetic layer;
a first insulating layer disposed on the first ferromagnetic layer;
a second layer consisting of a ferromagnetic or paramagnetic material disposed on the first insulating layer and aligned with the first ferromagnetic layer;
a second insulating layer disposed on the second layer;
a third ferromagnetic layer disposed on the second insulating layer and aligned with the second layer; and means for passing a biasing current from the first ferromagnetic layer to the second layer, wherein a resultant voltage across the second layer and the third ferromagnetic layer is measured.
2. The double tunnel junction of claim 1, wherein an external magnetic field is imposed on the second layer and the third ferromagnetic layer.
3. The double tunnel junction of claim 2, wherein a change in the external magnetic field causes a change in the resistance across the double tenet junction.
4. The double tunnel junction of claim 3, wherein a change of 100 oersted (Oe) in the magnetic field results in a 100% change in resistance across the double tunnel junction.
5. The double tunnel junction of claim 1, wherein the ferromagnetic. material is iron, Permadur, Permalloy, cobalt, nickel or manganese.
6. The double tunnel junction of claim 1, wherein the first and second insulating layers comprise aluminum oxide and magnesium oxide.
7. The double tunnel junction of claim 1, wherein the first and second insulating layers, the first and third ferromagnetic layers, and the second layer each have a thickness of 1 to manometers.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US08/745,815 US5757056A (en) | 1996-11-12 | 1996-11-12 | Multiple magnetic tunnel structures |
| US08/745,815 | 1996-11-12 | ||
| PCT/US1997/020419 WO1998024163A2 (en) | 1996-11-12 | 1997-11-04 | Multiple magnetic tunnel structures |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2270896A1 true CA2270896A1 (en) | 1998-06-04 |
Family
ID=24998356
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002270896A Abandoned CA2270896A1 (en) | 1996-11-12 | 1997-11-04 | Multiple magnetic tunnel structures |
Country Status (4)
| Country | Link |
|---|---|
| US (1) | US5757056A (en) |
| EP (1) | EP0948819A2 (en) |
| CA (1) | CA2270896A1 (en) |
| WO (1) | WO1998024163A2 (en) |
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| JP3258241B2 (en) * | 1996-09-30 | 2002-02-18 | 株式会社東芝 | Single electron control magnetoresistive element |
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| FR2791814A1 (en) * | 1999-03-31 | 2000-10-06 | Univ Pasteur | MICROELECTRONIC DEVICE WITH TUNNEL JUNCTIONS AND MEMORY NETWORK AND SENSOR INCLUDING SUCH DEVICES |
| US6381171B1 (en) | 1999-05-19 | 2002-04-30 | Kabushiki Kaisha Toshiba | Magnetic element, magnetic read head, magnetic storage device, magnetic memory device |
| JP3477638B2 (en) * | 1999-07-09 | 2003-12-10 | 科学技術振興事業団 | Ferromagnetic double quantum well tunnel magnetoresistive device |
| US6611405B1 (en) * | 1999-09-16 | 2003-08-26 | Kabushiki Kaisha Toshiba | Magnetoresistive element and magnetic memory device |
| GB0006142D0 (en) * | 2000-03-14 | 2000-05-03 | Isis Innovation | Spin transistor |
| DE10019697A1 (en) * | 2000-04-20 | 2001-11-15 | Sebastian T B Goennenwein | Spin polarization of charge carrier systems in solid bodies comprises applying a inhomogeneous magnetic field produced by a structure in the region of a solid body or on the surface of a solid body |
| DE10031401C2 (en) * | 2000-07-03 | 2002-05-29 | Forschungszentrum Juelich Gmbh | Three-gate device, in particular spin injection transistor |
| JP4309075B2 (en) * | 2000-07-27 | 2009-08-05 | 株式会社東芝 | Magnetic storage |
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| US6541792B1 (en) * | 2001-09-14 | 2003-04-01 | Hewlett-Packard Development Company, Llp | Memory device having dual tunnel junction memory cells |
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| US7916435B1 (en) | 2003-05-02 | 2011-03-29 | Hitachi Global Storage Technologies Netherlands B.V. | Magnetic tunnel transistor having a base structure that provides polarization of unpolarized electrons from an emitter based upon a magnetic orientation of a free layer and a self-pinned layer |
| US6956763B2 (en) * | 2003-06-27 | 2005-10-18 | Freescale Semiconductor, Inc. | MRAM element and methods for writing the MRAM element |
| US6967366B2 (en) * | 2003-08-25 | 2005-11-22 | Freescale Semiconductor, Inc. | Magnetoresistive random access memory with reduced switching field variation |
| US7268986B2 (en) * | 2004-03-31 | 2007-09-11 | Hitachi Global Storage Technologies Netherlands B.V. | Double tunnel junction using self-pinned center ferromagnet |
| US7315041B2 (en) * | 2004-05-21 | 2008-01-01 | The Regents Of The University Of California | Switching devices based on half-metals |
| JP2006093432A (en) * | 2004-09-24 | 2006-04-06 | Sony Corp | Memory element and memory |
| CN1606170A (en) * | 2004-09-24 | 2005-04-13 | 中国科学院物理研究所 | Transistor based on double barrier tunnel junction resonant tunneling effect |
| US7129098B2 (en) * | 2004-11-24 | 2006-10-31 | Freescale Semiconductor, Inc. | Reduced power magnetoresistive random access memory elements |
| US7298597B2 (en) | 2005-03-29 | 2007-11-20 | Hitachi Global Storage Technologies Netherlands B.V. | Magnetoresistive sensor based on spin accumulation effect with free layer stabilized by in-stack orthogonal magnetic coupling |
| US7453084B2 (en) * | 2005-05-24 | 2008-11-18 | Seagate Technology Llc | Spin transistor with ultra-low energy base-collector barrier |
| US10347709B2 (en) * | 2016-12-27 | 2019-07-09 | Ferric Inc. | Methods of manufacturing integrated magnetic core inductors with vertical laminations |
| JP7208504B2 (en) * | 2019-03-11 | 2023-01-19 | ｃＴａｎｇｅｎｔ株式会社 | soundproof material |
| US11735349B2 (en) | 2019-08-30 | 2023-08-22 | Ferric Inc. | Magnetic core with vertical laminations having high aspect ratio |
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| NL7608003A (en) * | 1976-07-20 | 1978-01-24 | Philips Nv | MAGNETIC DEVICE WITH DOMAINS. |
| US5218512A (en) * | 1991-08-16 | 1993-06-08 | Rohm Co., Ltd. | Ferroelectric device |
| US5390142A (en) * | 1992-05-26 | 1995-02-14 | Kappa Numerics, Inc. | Memory material and method for its manufacture |
| US5432373A (en) * | 1992-12-15 | 1995-07-11 | Bell Communications Research, Inc. | Magnetic spin transistor |
| US5477482A (en) * | 1993-10-01 | 1995-12-19 | The United States Of America As Represented By The Secretary Of The Navy | Ultra high density, non-volatile ferromagnetic random access memory |
| US5629922A (en) * | 1995-02-22 | 1997-05-13 | Massachusetts Institute Of Technology | Electron tunneling device using ferromagnetic thin films |
| US5629549A (en) * | 1995-04-21 | 1997-05-13 | Johnson; Mark B. | Magnetic spin transistor device, logic gate & method of operation |
| US5565695A (en) * | 1995-04-21 | 1996-10-15 | Johnson; Mark B. | Magnetic spin transistor hybrid circuit element |
| US5638252A (en) * | 1995-06-14 | 1997-06-10 | Hughes Aircraft Company | Electrical device and method utilizing a positive-temperature-coefficient ferroelectric capacitor |
| US5640343A (en) * | 1996-03-18 | 1997-06-17 | International Business Machines Corporation | Magnetic memory array using magnetic tunnel junction devices in the memory cells |
| US5650958A (en) * | 1996-03-18 | 1997-07-22 | International Business Machines Corporation | Magnetic tunnel junctions with controlled magnetic response |
-
1996
- 1996-11-12 US US08/745,815 patent/US5757056A/en not_active Expired - Fee Related
-
1997
- 1997-11-04 WO PCT/US1997/020419 patent/WO1998024163A2/en not_active Application Discontinuation
- 1997-11-04 CA CA002270896A patent/CA2270896A1/en not_active Abandoned
- 1997-11-04 EP EP97948214A patent/EP0948819A2/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| EP0948819A4 (en) | 1999-11-10 |
| WO1998024163A2 (en) | 1998-06-04 |
| US5757056A (en) | 1998-05-26 |
| EP0948819A2 (en) | 1999-10-13 |
| WO1998024163A3 (en) | 1998-10-08 |
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| Date | Code | Title | Description |
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| FZDE | Discontinued |