U.S. patent application number 11/064230 was filed with the patent office on 2005-07-07 for magnetoresistive device and electronic device.
Invention is credited to Coehoorn, Reinder, Giebeler, Carsten, Lenssen, Kars-Michiel Hubert, Zilker, Stephan Johann.
Application Number | 20050145909 11/064230 |
Document ID | / |
Family ID | 8180861 |
Filed Date | 2005-07-07 |
United States Patent
Application |
20050145909 |
Kind Code |
A1 |
Giebeler, Carsten ; et
al. |
July 7, 2005 |
Magnetoresistive device and electronic device
Abstract
A magnetoresistive device (11) having a lateral structure and
provided with a non-magnetic spacer layer (3) of organic
semiconductor material allows the presence of an additional
electrode (19). With this electrode (19), a switch-function is
integrated into the device (11). Preferably, electrically
conductive layers (13,23) are present for the protection of the
ferromagnetic layers (1,2). The magnetoresistive device (11) is
suitable for integration into an array so as to act as an MRAM
device.
Inventors: |
Giebeler, Carsten;
(Edinburgh, GB) ; Lenssen, Kars-Michiel Hubert;
(Eindhoven, NL) ; Zilker, Stephan Johann;
(Eindhoven, NL) ; Coehoorn, Reinder; (Eindhoven,
NL) |
Correspondence
Address: |
PHILIPS INTELLECTUAL PROPERTY & STANDARDS
P.O. BOX 3001
BRIARCLIFF MANOR
NY
10510
US
|
Family ID: |
8180861 |
Appl. No.: |
11/064230 |
Filed: |
February 23, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11064230 |
Feb 23, 2005 |
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10228602 |
Aug 27, 2002 |
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6876574 |
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Current U.S.
Class: |
257/295 ;
257/E21.665; 257/E27.005; 257/E29.323; 365/171 |
Current CPC
Class: |
B82Y 10/00 20130101;
H01L 29/82 20130101; G11C 13/0014 20130101; G11C 11/15 20130101;
H01F 10/3254 20130101; G11B 2005/3996 20130101; H01L 43/10
20130101; G11C 11/16 20130101; H01L 43/08 20130101; G11C 13/025
20130101; G11B 5/3909 20130101; H01F 10/32 20130101; B82Y 25/00
20130101; G11C 11/161 20130101 |
Class at
Publication: |
257/295 ;
365/171 |
International
Class: |
H01L 031/062 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 30, 2001 |
EP |
01203265.2 |
Claims
1-3. (canceled)
4. A device (11) comprising a substrate which carries a first and a
second magnetic layer for providing a magnetoresistive effect, said
first and second layer being interconnected by a non-magnetic
space-layer, wherein the first and second layer are patterned and
laterally spaced apart on the substrate, and the spacer layer
comprises a semiconductor material with a chain-like molecular
structure, and wherein an electrically conducting layer (13) is
present between the magnetic layers (1,2) and the spacer layer
(3).
5. A device (11) as claimed in claim 4, characterized in that a
tunnel barrier layer (21) is present between the electrically
conducting layer (13) and the spacer layer (3).
6. A device (11) as claimed in claim 4, characterized in that the
magnetic layers (1,2) are present between the spacer layer (3) and
the substrate (4).
7. A device (11) comprising a substrate which carries a first and a
second magnetic layer for providing a magnetoresistive effect, said
first and second layer being interconnected by a non-magnetic
space-layer, wherein the first and second layer are patterned and
laterally spaced apart on the substrate, and the spacer layer
comprises a semiconductor material with a chain-like molecular
structure, and wherein an electrode (19) is present for influencing
a charge distribution in a region of the spacer layer (3) located
between the first and the second magnetic layer (1,2), the
electrode being separated from the spacer layer (3) by a dielectric
layer (18).
8-10. (canceled)
Description
[0001] The invention relates to a magnetoresistive device
comprising a substrate which carries a first and a second magnetic
layer for providing a magnetoresistive effect, said first and said
second layers being separated by a non-magnetic spacer layer.
[0002] The invention also relates to an electronic device provided
with a magnetic memory including an array of magnetoresistive
devices.
[0003] Such a magnetoresistive device is known from WO-A-00/10024.
The first magnetic layer in said device is preferably a so-called
free layer, the second magnetic layer is a so-called pinned layer,
i.e. a layer with a large uniaxial anisotropy due to the magnetic
exchange interaction with an antiferromagnetic layer. Both the
first and the second magnetic layers are ferromagnetic. The free
layer is a layer whose magnetization direction can be changed by
applying magnetic fields with a strength lower, preferably
substantially lower, than the strength of the field required for
changing the magnetization direction of the pinned layer. The
pinned layer thus has a preferred, substantially fixed
magnetization direction, whereas the magnetization direction of the
free layer can be changed quite easily under an externally applied
field. A change in the magnetization direction of the free layer
changes the resistance of the magnetoresistive device. The effect
produced in the device is either the Giant Magneto-Resistance (GMR)
effect or the Spin-Tunnel Magneto-Resistance (TMR) effect. In a
device utilizing the GMR-effect, the non-magnetic spacer layer is
metallic. In a device utilizing the TMR-effect, the non-magnetic
spacer layer is insulating, for example Al.sub.2O.sub.3. This
spacer layer allows for a significant probability for
quantum-mechanical tunneling of electrons between the first and
second ferromagnetic layers.
[0004] The characteristics of these magnetoresistive devices may be
exploited in different ways. They can be used for advanced hard
disk thin film heads. Magnetic memory devices such as non-volatile
stand-alone or embedded memory devices may also be made, based on
the GMR and the TMR effect. An example of such a memory device is a
Magnetic Random Access Memory (MRAM) device. A further application
is a sensor device. Such sensors are used, for example, in
anti-lock braking (ABS) systems.
[0005] It is a disadvantage of the known magnetoresistive device
that its manufacture is complicated. The device may either be
present as a stack of layers, or as a lateral structure. The stack
of layers has the disadvantage that the spacer layer has to be very
thin, some nanometers only. The lateral structure has the
disadvantage that the distance between the first and second
magnetic layer must be very short, e.g. about 10 nanometers only.
If the thickness of the spacer layer were larger, or if the mutual
distance were larger, then no measurable magnetoresistive effect
would be obtained.
[0006] It is therefore a first object of the invention to provide a
magnetoresistive device of the kind mentioned in the opening
paragraph of which the spacer layer has less critical
dimensions.
[0007] The first object of the invention is achieved in that:
[0008] the first and second layer are patterned and laterally
spaced apart on the substrate, and the spacer layer comprises a
semiconductor material with a chain-like molecular structure.
[0009] A first characteristic of the magnetoresistive device of the
invention is its lateral structure. It is an advantage thereof that
the thickness of the spacer layer is not critically relevant for
the operation of the device; instead, the magnetoresistive effect
is strongly dependent on the distance between the first and the
second magnetic layer. Photolithography or other lithographic
techniques, such as soft lithography, may be used for obtaining a
desired distance.
[0010] A second characteristic of the magnetoresistive device of
the invention is that its spacer layer comprises a semiconductor
material with a chain-like molecular structure. In such a
chain-like, primarily one dimensional molecular structure, the
charge transport is less hindered by interaction with neighbouring
atoms. It is believed to happen primarily via the delocalized
electronic structure and less via vacancies in the lattice. As a
conquence, the spin diffusion length is longer. This means that the
spins of the electrons which are responsible for the
magnetoresistive effect, are maintained in their original direction
much longer than in conventional inorganic materials.
[0011] This has the advantageous effect that the distance between
the first and the second magnetic layer can be larger than some
nanometers. It is preferably in the range of 50 to 500 nanometers,
especially approximately 100 nanometers. Such a distance may be
obtained, for example, with e-beam lithography. Furthermore, the
electrical resistance of a region of the spacer layer located
between the two magnetic layers is small enough for obtaining a
measurable magnetoresistive effect at room temperature. The upper
limit is dependent on the spin diffusion length of the material
used with chain-like molecular structure, but the shorter the
distance, the larger the magnetoresistive effect. For reasons of
clarity, said distance is defined as the shortest distance between
the mutually opposed side faces of the first and the second
magnetic layers.
[0012] A report on the transport of electronic spins in a GaAs
substrate has been published by J. M. Kikkawa and D. D. Awschalom,
Nature 397, 139 (1999). Although this report discusses this
transport in connection with giant-magnetoresistive systems and
spin-valve transistors, it does not present any magnetoresistive
device. Besides, the transport is studied at a temperature of 1.6
K, which is not a temperature useful in any integrated circuit.
Furthermore, the presence of the spacer layer as a substrate
hinders integration with other elements. In the magnetoresistive
device of the invention, the semiconductor is applied as a separate
layer, preferably at the end of the manufacturing process. Thus
standard Si technology is available for manufacturing
structures.
[0013] It is an advantage of the device of the invention that the
semiconductor material can be deposited by alternative methods
which are easy and relatively inexpensive. Whereas expensive
processes such as MBE deposition in ultrahigh vacuum or chemical
vapor deposition (CVD) must be used for the II-VI and III-V type
semiconductors, spin-coating, dip-coating or vapour deposition may
be used under standard conditions for the deposition of any
semiconductor material of the invention. Furthermore, the
semiconductor material can be applied as the last functional layer,
after the deposition of the electrically conducting and magnetic
layers.
[0014] It is another advantage of the device of the invention that
it can be made flexible. Being a layer that is processable in
solution, the semiconductor is flexible and can be deposited on a
flexible substrate. The magnetic layers in the device are thin
enough, so that they are no obstacle to the flexibility of the
device. Other layers present may be chosen so as to be flexible
magnetic layers.
[0015] In a first embodiment, the material of the spacer layer is
an organic semiconductor material. The material is semiconducting
or electrically conducting. The material is organic, as organic
materials have a more favorable structure and composition for
spin-polarized transport than commonly used inorganic ones. In a
.pi.-conjugated organic system, only p-levels are delocalized and
are consequently mainly responsible for charge transport. Their
wave functions are zero at the site of the nucleus, leading to a
minimal hyperfine interaction. The latter is one of the two main
processes leading to spin-flips. The second one is spin-orbit
coupling which increases with the mass of the involved nuclei. The
latter are comparatively small in organic systems, in particular in
systems in which the heaviest atoms are C or N. Thus charge
carriers in organic materials have a long spin diffusion length,
however, this may vary substantially among different materials.
[0016] Organic semiconductor materials are known per se, and can be
applied by vapour deposition and by spincoating, printing, and
other solution processing techniques. For the solution processing
the organic semiconductor material may be applied as a processor
material or as a blend or contain processing-enhancing side
chains.
[0017] In a second embodiment, the semiconductor material of the
spacer layer is a nanowire. Nanowires, of, for instance, silicon,
carbon, InP, GaAS, are ultrathin, wires of a semiconductor
material, that can be doped, and which exhibit extremely
advantageous semiconductor properties, as is per se known from
Gudliksen et.at, Nature 415(2002), 617-620. They can be made
separately, for instance, by growing in a CVD reactor or by etching
a semiconductor substrate of a desired material.
[0018] A preferred example of a nanowire is a carbon nanotube,
which has a low spin-orbit coupling.
[0019] Nanowires can be provided in a solution, for instance, an
organic solvent, and they can be aligned, if necessary with
electrical means or with chemical means. For instance, positioned
with a monolayer for preferred adhesion or, with channels wherein
the nanowires are positioned by microfluidic transport.
Particularly with nanowires, but more in general, the first and
second layer can be patterned so as to form an interdigitated
structure.
[0020] In an embodiment of the magnetoresistive device of the
invention, an electrically conducting layer is present between the
magnetic layers and the non-magnetic spacer layer. This
electrically conducting layer is present to protect the magnetic
layers against oxidation, especially during manufacture, but also
thereafter. Without such a protection, the complete surface of the
magnetic layers will oxidize, and hence there will not be an
adequate contact between the magnetic layers and the spacer layer.
An adequate contact reduces the contact resistance, but also the
spin flip scattering that would otherwise occur in the oxide. The
electrically conducting layer preferably comprises gold, but may
comprise, among other materials, platinum, tungsten, copper,
titanium nitride and tantalum nitride as well. The embodiment is
especially suitable for those magnetic layers which are very
sensitive to oxidation, such as Co, Fe, Ni and alloys thereof.
[0021] It is a first advantage of the embodiment that the
manufacture of the lateral device is simplified. The half-ready
device can be taken from a vacuum environment without disastrous
consequences for the magnetic layers. This allows the use of
different machines for the deposition of the different kinds of
materials used for the magnetic layers, for the as spacer layer and
for further layers.
[0022] It is a second advantage of the embodiment that the spacer
layer of organic material can be deposited by any kind of coating
or printing process. Examples of coating processes are spin-coating
and dip-coating. An example of a printing process is ink jet
printing. Combining printing with the deposition in vacuo of the
magnetic layers does not seem feasible realizable otherwise, as
printing cannot be done in vacuo. Furthermore, without an
electrically conductive layer the--generally organic--solvents used
in printing and coating would reach the magnetic layers. This would
have a detrimental effect on the magnetic layers. Printing and
coating processes have the advantage over evaporation and sputter
deposition that they are cheaper and easier to control.
[0023] In a further embodiment, a tunnel barrier layer is present
between the magnetic layers and the electrically conducting layer.
This is especially preferable if the contribution of the resistance
of the organic spacer layer to the total resistance is larger than
the contribution of the resistance of the magnetic layers. This
improves the spin polarization of the current injected from the
magnetic layers, as was explained by E. I. Rashba (Physical Review
B62, 16267 (2000)) for the general case of a system in which the
spacer layer between the two magnetic electrodes has a low
conductance. Preferably, the tunnel barrier layer is an insulating
layer, for example of Al.sub.2O.sub.3 with a thickness of the order
of 1 to 3 mn.
[0024] In a yet further embodiment, the magnetic layers are present
between the non-magnetic spacer layer and the substrate. This
implies that the magnetic layers are deposited before the spacer
layer. As an organic layer is generally sensitive to various
chemicals, it is most practical to deposit such a layer on top of
the others. The organic layer, is for example, sensitive to etching
compositions, which are in common use for to patterning the
magnetic layer.
[0025] The organic semiconductor material may be doped in order to
let it act as an electrically conducting material. Examples of such
materials are doped poly (3,4-ethylenedioxythiophene), polyaniline
and polyacetylenes. Altternatively, a polymer filled with
electrically conducting particles or powder may be used. Examples
of organic semiconductors include polythiophenes, polyfuranes,
polypyrroles, polythienylene-vinylenes, polyphenylene-vinylenes,
polyfuranylene-vinylenes, copolymers of these compounds, pentacene,
oligothiophenes, polyarylamines and charge-transfer complexes such
as tetracyanoquinodimethane-tetrathiafulvalene. Alternatively,
substituted derivatives of these compounds can be used. Examples of
suitable substituents include alkyl and alkoxy groups and cyclic
groups, such as alkylenedioxy groups. Preferably, the substituent
groups have a carbon chain of 1 to 10 carbon atoms. Suitable and
preferred materials comprise poly-3-alkylthiophenes, pentacene and
oligothiophenes.
[0026] In an advantageous embodiment, the semiconductor material is
doped, and an electrode is in contact with the spacer layer such
that charge transport between the first and second magnetic layers
can be modified through the application of a suitable voltage to
the electrode. The magnetoresistive device of this embodiment is a
so-called Johnson spin-switch device.
[0027] If the organic semiconductor material is not or not
intentionally doped to let it act as a semiconducting material, an
electrode ("gate") may be present. This gate is meant to influence
the charge distribution in a region of the spacer layer located
between the first and the second magnetic layer. The electrode is
separated from the organic semiconductor by a layer of dielectric
material. The electrode may be present at the first side or at the
second side of the spacer layer.
[0028] In this embodiment, the magnetoresistive device is a
three-terminal device, which is analogous to a field-effect
transistor. It can be switched on or off by means of said third
electrode. If it is switched on, the magnetoresistive effect can be
measured. Since this switch function is incorporated, no
independent transistor is needed to act as a switch. Such a switch
is, for example, necessary for the operation of an MRAM device.
Therefore, a substantial reduction in cost for the individual
transistors and for the assembly is achieved with the
embodiment.
[0029] Proposals that aim at integrating the switching and
magnetoresistive functions in a single device by combining
ferromagnetic and inorganic semiconductor materials in a single
device are known, for example, from Datta and Das (Appl. Phys.
Lett. 56, 665 (1990)). However, the known proposal is strictly
theoretical.
[0030] It is important to counteract any leakage through the spacer
layer from one magnetoresistive element with a first and a second
magnetic electrode to another especially in the embodiment with a
gate, but also without a gate. Therefore, in an advantageous
embodiment, the spacer layer of organic material is
relief-structured. The structuring of the spacer layer may be
realized in various ways, e.g. photochemically or by printing.
[0031] The magnetic layers in the device of the invention are
generally ferromagnetic. However, it is not to be excluded that at
least one of the magnetic layers is antiferromagnetic.
[0032] An electronic device of the kind mentioned in the opening
paragraphs is known from Tehrani et al., Journal of Applied
Physics, 85 (1999), 5822. The known electronic device is an MRAM
device, in which a large number of identical GMR elements is
integrated on a substrate in the form of a matrix of essentially
identical cells. The matrix comprises parallel horizontal and
vertical current lines--generally referred to as word lines and bit
lines, with the magnetoresistive devices at the points of
intersection. A preferred method of addressing a specific cell, in
order to retrieve the digital information written in the cell, is
to provide a voltage difference between the end terminals of the
horizontal and the vertical current line, and to measure the
resulting current. In order to ensure that the measurement current
flows only through the magnetoresistive device at the intersection
of the two contacted lines, and not through other elements via more
comples paths, a diode or a transistor with a high on/off ratio is
combined with each magnetoresistive device.
[0033] It is a disadvantage of the known electronic device that the
necessity of an independent diode or transistor makes the
manufacturing cost for MRAM comparatively high. It is a second
object of the invention to provide an electronic device of the kind
described in the opening paragraph into which magnetoresistive
devices can be easily integrated.
[0034] The second object of the invention, i.e. to provide an
electronic device with an improved magnetic memory, is realized in
that the magnetoresistive device of the invention is present. The
electronic device incorporates all advantages of the individual
magnetoresistive devices of the invention and especially the
advantage of lower manufacturing costs. Furthermore, the
magnetoresistive device of the invention can be flexible.
Therefore, the magnetoresistive device of the invention is very
suitable for use in handheld, flexible, and inexpensive electronic
devices. Examples of these are smartcards, transponders and the
like.
[0035] As in the known electronic device, word lines and bit lines
are necessary for addressing the individual magnetoresistive
devices. Of these mutually crossing wordlines and bit lines, one
may be present below and the other on top of the magnetoresistive
devices, for example at the first and at the second side of the
spacer layer. However, it is advantageous if both the word lines
and the bit lines are present in the substrate. Such a substrate
may be a multilayer ceramic substrate or a multilayer laminate.
Alternatively, it is a multilayer interconnect structure that is
present at a surface or in an integrated circuit. As will be
understood by those skilled in the art, the MRAM of the present
invention may contain other lines next to or instead of word lines
and bit lines. An example of this is a scheme with discrete
magnetoresistive devices and discrete transistors as published by
P. K. Naji et al., Proceedings of the IEEE International
Solid-State Circuits Conference, p. 122-123 (2001).
[0036] It is preferable that the magnetoresistive device of the
invention is provided with a gate electrode. However, this is not
necessary. Owing to its lateral structure, the magnetoresistive
device can be integrated into an interconnect structure of a
semiconductor device in an efficient manner.
[0037] These and other aspects of the magnetoresistive device of
the invention will be apparent from and elucidated with reference
to the embodiments described hereafter. In the drawings:
[0038] FIG. 1 diagrammatically and in cross-section shows the
magnetoresistive device according to the prior art;
[0039] FIG. 2 grammatically and in cross-section shows a first
embodiment of the magnetoresistive device;
[0040] FIG. 3 grammatically and in cross-section shows a second
embodiment of the magnetoresistive device;
[0041] FIG. 4 grammatically and in cross-section shows a third
embodiment of the magnetoresistive device; and
[0042] FIG. 5 grammatically and in cross-section shows a fourth
embodiment of the magnetoresistive device.
[0043] The Figures are diagrammatic and not drawn to scale, and, in
general, like reference numerals refer to like parts. The
embodiments represent a device in which the first ferromagnetic
layer 1 is the free layer and the second ferromagnetic layer 2 is
the pinned layer. However, other embodiments known to those skilled
in the art of magnetoresistive devices are possible as well. These
embodiments may be integrated into the systems of the invention
according by techniques known to those skilled in the art. For
example, the whole sensing system or data storage system may be
integrated on one semiconductor integrated circuit with the layers
of the magnetoresistive device being grown or deposited on the
chip. Said layers are preferable grown or deposited in the back end
of the process of manufacturing the IC. In the back end process,
part of the IC is planarized and the ferromagnetic layers are grown
or deposited thereon. The non-magnetic spacer layer of organic
material is deposited. Appropriate connections by bonding or via
structures are made in order to transfer the signals of the
magnetoresistive device to the part of the IC containing the
signalprocessing logic. It will be apparent to those skilled in the
art that alternative, equivalent embodiments of the invention may
be conceived and put into practice without departing from the true
spirit of the invention, the scope of the invention being limited
by the appended claims only.
[0044] FIG. 1 diagrammatically and in cross-section shows a
magnetoresistive device 10 of the prior art. The known
magnetoresistive device 10 comprises a stack of a first, free
ferromagnetic layer 1, a metallic non-magnetic spacer layer 3, a
second, pinned ferromagnetic layer 2, and a fixing layer 5 of an
antiferromagnetic material, which stack 10 is present on a
substrate 4 (e.g. glass, a semiconductor material such as Si, or a
ceramic material such as Al.sub.2O.sub.3).
[0045] The first and second ferromagnetic layers 1,2 can be
manufactured as known in the art. They may comprise a ferromagnetic
metal such as Fe, Ni, Co or an alloy thereof. Alternatively, they
mau comprise a metalloid ferromagnet such as PtMnSb, NiMnSb,
Fe.sub.3O.sub.4 or CrO.sub.2. Preferably, the first ferromagnetic
layer is pinned and the second one is free. In order to have an
adequate pinning, the pinned ferromagnetic layer is preferably
exchangebiased with the fixing layer of a antiferromagnetic
material such as Ni--Mn, Pt--Mn, Ir--Mn, Fe--Mn or NiO, or a
ferrimagnetic layer such as Tb-Fe. Alternatively, an artificial
antiferromagnet, generally referred to as AAF, is present as the
pinned ferromagnetic layer. Said AAF is a layer structure
comprising alternating ferromagnetic and non-magnetic layers which
have such an exchange coupling, owing to the choice of materials
and layer thicknesses, that the magnetization directions of the
ferromagnetic layers are antiparallel in the absence of an external
magnetic field. An even more preferable structure for pinning the
second ferromagnetic layer (F2) is a combination of an
antiferromagnetic layer (AF) and an AAF. The AAF then preferably
consists of two ferromagnetic layers separated by a
non-ferromagnetic spacer layer that strongly couples these two
layers antiferromagnetically. The layer structure is then
AF/AAF/F2.
[0046] Owing to the GMR effect, the resistance for the
configurations, in which the magnetizations of the electrodes are
parallel or antiparallel, is different. The state of the memory
(`1` or `0`) can be determined by measuring the resistance of the
magnetoresistive device, as is known by those skilled in the art of
GMR devices. To this end the relation between a reading or sensing
current Ir and an applied voltage is measured.
[0047] FIG. 2 diagrammatically and in cross-section shows a first
embodiment of the magnetoresistive device of the invention; in the
invention the non-magnetic spacer layer 3 has a first side 31 and
an opposite second side 32, at which first side 31 the spacer layer
is in contact with the free ferromagnetic layer 1 and with the
pinned ferromagnetic layer 2, both of which ferromagnetic layers 1,
2 are patterned. The magnetoresistive device 11 is a lateral
structure. In this specific embodiment, the substrate 4 is present
at the second side 32 of the spacer layer 3. The non-magnetic
spacer layer is made of an organic semiconductor material. An
antiferromagnetic pinning layer 29 of Ir--Mn is present on top of
the second ferromagnetic layer 2.
[0048] As an example, the magnetoresistive device 11 comprises the
substrate 4 of polyimide, the free ferromagnetic layer 1 of the
alloy Co.sub.90Fe.sub.10 (indicated below briefly as CoFe) having a
thickness of about 10 nanometers and a size of about 500.times.2000
nanometers, the non-magnetic spacer material 3 of
polythienylene-vinylene having a thickness 7 of 50 nanometers, the
pinned ferromagnetic layer 2 of CoFe having a thickness of about 10
nanometer and a size of about 500.times.2000 nanometers. The
distance 9 between the free and the fixed ferromagnetic layers 1,2
is 200 nanometers.
[0049] Said device is manufactured by spincoating the non-magnetic
spacer layer 3 from a precursor polymer of polythienylene-vinylene
onto the substrate 4 and converting it into
polythienylene-vinylene. Said deposition and the conversion are
known to those skilled in the art of organic devices, such as
organic displays and organic transistors. Subsequently, the
substrate 4 with the spacer layer 3 is brought into a dc magnetic
sputtering machine, where in an atmosphere of about 10.sup.-7 Torr
first a layer of Au with a thickness of 3 nm and then a layer of
CoFe are sputtered at a deposition rate of 0.2 nm/s. Then, a resist
layer is deposited, which is exposed/irridiated and developed. The
layer of CoFe is etched into a pattern, thus creating the first
ferromagnetic layer 1. Subsequently, another layer of CoFe and a
layer of Ir--Mn are sputtered. These layers are patterned by means
of photolithography so as to form the second ferromagnetic layer 2
and the pinning layer 29. An acidic substance such as dilute
sulphuric acid is suitable for the etching process.
[0050] Altematively, a resist layer, for example the commercially
available novolak photoresist HPR504, may be spincoated onto the
spacer layer 3 of polythienylene-vinylene. The novolak resist layer
is heated to 100.degree. C. for one minute to produce a dry film
thickness of 50 nm. The novolak is then patterned by exposure to UV
radiation and developed using aqueous base PD 523 to create
openings. Subsequently, the structure of the substrate 4, the
spacer layer 3 and the novolak pattern is transferred to the
sputtering machine to deposit the layer of CoFe, therewith forming
the first and the second ferromagnetic layers 1,2. On top of the
CoFe, Cu is deposited to provide terminals. After deposition of the
Cu, any superflous CoFe and Cu on top of the novolak are removed by
rinsing the novolak. Alternatively, the structure may be
polished.
[0051] FIG. 3 diagrammatically and in cross-section shows a second
embodiment of the magnetoresistive device of the invention. In this
specific embodiment, the ferromagnetic layers 1,2 and the substrate
4 are present at the first side 31 of the spacer layer 3. A
protective coating 15 is present at the second side 32.
[0052] The ferromagnetic layers 1,2 are present on the substrate 4.
The substrate 4 also contains the contacts, with which the
magnetoresistive device is connected to a power supply. An
electrically conductive coating 13 of gold is present in a
thickness of 3 nm on top of both ferromagnetic layers 1,2, at the
first side 31 of the spacer layer. The conductive coating 13 is
deposited by means of sputter deposition in an atmosphere of
10.sup.-7 Torr. This coating protects the ferromagnetic layers 1,2
against oxidation by air or by any other oxidant. On top of the
conductive coating 13, the non-magnetic spacer layer 3 is present
in a thickness 7 of 50 nm. In this example, the spacer layer 3
comprises the organic semiconductor material poly-3-hexylthiophene.
An insulating layer 14 and a protective black coating 15 are
present at the second side 32 of the spacer layer 3. The protective
black coating 15 protects the organic semiconductor material
against the influence of oxygen and light. It comprises, for
example, carbon ink.
[0053] In the manufacture of the device, the structure comprising
the substrate 4, the still unpatterned ferromagnetic layer
comprising the layers 1,2, and the conductive coating 13, is taken
out of the low-pressure environment. The spacer layer 3 of organic
material, the insulating layer 14 of polyimide or the like, and the
black protective coating 15 are then deposited thereon.
[0054] FIG. 4 diagrammatically and in cross-section shows a third
embodiment of the magnetoresistive device of the invention. In this
specific embodiment, a "gate" electrode 19 is present for
influencing a charge distribution in a region of the spacer layer 3
located between the first and the second ferromagnetic layer 1,2.
In this embodiment, the spacer layer is not or not intentionally
doped. In this specific embodiment, the substrate 4 is present at
the second side 32 of the spacer layer 3. The gate electrode 19 is
present between the substrate 4 and the spacer layer 3. It is
separated from the spacer layer 3 by the dielectric layer 18. The
first and the second ferromagnetic layers 1,2 are present at the
first side 31 of the spacer layer 3. They are protected from the
spacer layer 3 and the substrate 4 by electrically conductive
layers 13, 23. The first ferromagnetic layer 1 is connected to a
word line 25. The second ferromagnetic layer 2 is connected to a
ground line 24. The ground line 24 and the word line 25 extend in
directions which are preferably mutually perpendicular. They are
present in an array with a plurality of magnetoresistive devices
11. The gate electrode 19 is connected to a bit line via the
substrate 4. The spaces between the ground line 24 and the word
line 25 are filled with a dielectric material which has a low
dielectric constant in order to limit parasitic capacitive
coupling.
[0055] FIG. 5 diagrammatically and in cross-section shows a fourth
embodiment of the magnetoresistive device of the invention. In this
specific embodiment, a "gate"-electrode 19 is present for
influencing a charge distribution in a region of the spacer layer 3
located between the first and the second ferromagnetic layer 1,2.
In this embodiment, the spacer layer is not or not intentionally
doped. In this specific embodiment, the ferromagnetic layers 1,2
and the substrate 4 are present at the first side 31 of the spacer
layer 3. The gate electrode 19 is present at the second side 32 of
the spacer layer 3. It is separated from the spacer layer 3 by the
dielectric layer 18. The ferromagnetic layers are protected from
the spacer layer 3 and from the substrate 4 by electrically
conductive layers 13, 23. Tunnel barrier layers 21 are present
between the electrically conducting layers 13 and the ferromagnetic
layers 1,2. The tunnel barrier layers 21 have a thickness of 1.5
nm. The electrically conducting layers 13 have a thickness of 3 nm.
The electrically conducting layer 23 has a thickness of 20 nm. It
acts not only as a protective layer, but also as a contact pad to
vias 26 and interconnects 25. The first ferromagnetic layer 1 is
connected to a word line 25 which is present in or on top of the
substrate 4. The second ferromagnetic layer 2 is connected to a
ground line 24 through a vertical interconnect area 26 in the
substrate 4. The ground line 24 and the word line 25 extend in
directions which are preferably mutually perpendicular. They are
present in an array with a plurality of magnetoresistive devices
11. The gate electrode 19 is connected to a bit line. The spaces
between the gate electrode 19 and the ground line 24 are filled
with a dielectric material.
[0056] In a further embodiment (not shown), the gateelectrode 19
and the connections to the ground line 24 and the word line 25 are
all present in the substrate 4, which in that case is an multilayer
interconnect structure. The interconnect structure is present on a
semiconductor--especially silicon--substrate at a surface of which
a plurality of transistors is defined. An insulating layer 14 and a
protective coating 15 are present on the spacer layer 3. The
insulating layer 14 also acts as a passivating layer. The
protective coating is covered by a conventional IC package of, for
example, an epoxy mold.
[0057] In the summary, the invention presents a magnetoresistive
device having a lateral structure and provided with a non-magnetic
spacer layer of organic semiconductor material allows the presence
of an additional electrode. With this electrode, a switch-function
is integrated into the device. Preferably, electrically conductive
layers are present for the protection of the ferromagnetic layers
(1,2). The magnetoresistive device is suitable for integration into
an array so as to act as an MRAN device
* * * * *