CN112305470B

CN112305470B - Annealing method of giant magnetoresistance sensor constructed by giant magnetoresistance structures with different magnetization directions

Info

Publication number: CN112305470B
Application number: CN201910686340.7A
Authority: CN
Inventors: 宋玉哲; 韩根亮; 张彪; 郑礴
Original assignee: INSTITUTE OF SENSOR TECHNOLOGY GANSU ACADEMY OF SCIENCE
Current assignee: INSTITUTE OF SENSOR TECHNOLOGY GANSU ACADEMY OF SCIENCE
Priority date: 2019-07-29
Filing date: 2019-07-29
Publication date: 2022-12-06
Anticipated expiration: 2039-07-29
Also published as: CN112305470A

Abstract

The invention discloses an annealing method of giant magneto-resistance sensor constructed by giant magneto-resistance structures with different magnetization directions, the integrated annealing structure can independently anneal a GMR structure to make the temperature reach the blocking temperature of the GMR structure or even higher, under an external magnetic field, the magnetization direction Mp of a pinned layer in the GMR structure is adjusted to be consistent with the external annealing magnetic field and fixed, thereby adjusting the magnetization direction of the pinned layer in the GMR structure to the desired direction. In some examples, the GMR structures are divided into multiple groups according to the identity of the Mp, the Mp is the same as one group, and the Mp is different from one group to another. GMR structures with different magnetization directions can be realized by separately annealing different groups of GMR structures in different directions of an applied annealing magnetic field.

Description

Annealing method of giant magnetoresistance sensor constructed by giant magnetoresistance structures with different magnetization directions

Technical Field

The present invention relates to giant magnetoresistive sensors, and more particularly to giant magnetoresistive sensors having an integrated anneal structure.

Background

MR sensors, such as Giant Magnetoresistive (GMR) sensors, are widely used and are one of the most promising magnetic sensors. The core structure of a typical GMR structure comprises a "sandwich" structure of two ferromagnetic layers sandwiching a non-ferromagnetic layer. As shown in fig. 1, the GMR structure (10) comprises ferromagnetic layers (a first ferromagnetic layer 12 and a second ferromagnetic layer 16) with an intervening non-ferromagnetic layer (14). The primary composition of the ferromagnetic layers (first ferromagnetic layer 12 and second ferromagnetic layer 16) may be NiFe, coFe, or other suitable magnetic material. The non-ferromagnetic layer (14) may have Cu, mgO, and Al as main components ₂ O ₃ Or other suitable non-magnetic material. The magnetization direction of the second ferromagnetic layer (16) does not change with the magnetic field to be measured, and is therefore called the "pinned layer". The magnetization direction of the first ferromagnetic layer (12) changes with changes in the magnetic field to be measured and is therefore commonly referred to as the "free layer". The angle (relative direction) between the magnetization direction of the free layer and the magnetization direction of the pinned layer (second ferromagnetic layer 16) determines the resistance value of the GMR structure (10). In sensing applications, the magnetization of the pinned layer remains unchanged, and the magnetic field to be measured causes a change in the magnetization of the free layer, thereby causing a change in the angle of the magnetization of the free layer and the magnetization of the pinned layer. By measuring the change in this angle, the magnetic field to be measured can be inferred.

In order to achieve a linear relationship between the change in the relative angles of the magnetization directions of the free layer and the pinned layer and the magnetic field to be measured, the intrinsic magnetization direction Mp of the pinned layer and the intrinsic magnetization direction Mf of the free layer are perpendicular to each other. In the Cartesian coordinate system shown in FIG. 1, mp is along the Y-axis and Mf is along the X-axis.

In practical application, the measuring current passes through the GMR structure (10), and the magnitude of the magnetic field to be measured is calculated by measuring the magneto-resistance of the GMR structure (10). The measurement current may be parallel to the GMR film surface or may be perpendicular to the GMR film surface. The configuration In which the measured Current is parallel to the GMR film surface is generally referred to as "CIP (Current-In-Plane)" type (Current direction In Plane). Typical CIP type GMR structures are Spin-Valve (SV) structures, the composition of the nonmagnetic layer (14) of which is typically Cu.

A non-ferromagnetic layer (14) of a typical CPP type GMR structure such as MTJ (Magnetic-Tunnel-Junction) is generally composed of MgO, al, and a Current direction Perpendicular to the film surface is generally referred to as "CPP (Current-Perpendicular-to-Plane" type (Current direction Perpendicular to the film surface) ₂ O ₃ Or other suitable non-magnetic, insulating material.

In practical applications based on magnetoresistive measurements, it is often desirable to use a wheatstone bridge configuration to achieve higher sensitivity, stability and linearity. Among the different wheatstone bridge configurations, the wheatstone full bridge configuration has the best linearity and signal levels, as shown in fig. 2. In the figure, four resistors R1, R2, R3 and R4 form a Wheatstone full-bridge structure. The four resistors can be independently changed along with the change of the external signal, and the bridge circuit output voltage signal Vo can be calculated by the following formula 1.

Vb is the voltage

R ₁ ＝R ₄ ＝R-ΔR

R ₂ ＝R ₃ Equation 1 = R + Δ r.. D

Where AR is a magnetic resistance change value caused by a change in an external signal.

When a Wheatstone full bridge circuit is formed by adopting the GMR magneto-resistance structure, the GMR structure in the full bridge circuit needs to have different magnetization directions, as shown in FIG. 3. Fig. 3 is a typical full bridge GMR sensor (18). The GMR sensor (18) is composed of four GMR structures of R1, R2, R3 and R4, and each GMR structure can change along with the change of a magnetic field to be measured. The magnetization direction Mp of the pinned layers of adjacent GMR structures is opposite in direction. For example, the pinned layers Mp of R1 and R2 are opposite in direction, and the pinned layers Mp of R3 and R4 are opposite in direction. R1 and R3 have the same Mp orientation, and R2 and R4 have the same Mp orientation.

In order to make the pinned layers of adjacent GMR structures (e.g. R1 and R2, R3 and R4) have opposite magnetization directions, a local laser annealing method is currently used. The GMR sensor (18) is arranged in an external magnetic field Hb, and the GMR structure is divided into two groups according to the direction of Mp, the direction of Mp is the same, the direction of Mp of one group is opposite to that of the other group. One of the groups (e.g., R1 and R3) is selected and the GMR structures of that group are laser annealed to a temperature above the blocking temperature so that the Mp direction of the GMR coincides with the direction of the applied magnetic field Hb, all GMR structures of that group operating in turn in the same manner. After the first set of GMR structures (e.g. R1 and R3) has been aligned, the GMR sensor (18) is rotated 180 ° to oppose the applied magnetic field Hb. Of course, it is also possible to rotate the applied magnetic field by 180 ° while the GMR sensor is stationary. The second set of GMR structures (e.g. R2 and R4) is then laser annealed to perform the same operations as the first set.

Another process that enables the formation of a GMR full bridge sensor (18) is multi-step photolithography. After depositing the multilayer film of GMR structures, a first set of GMR structures (e.g. R1 and R3) having the same Mp direction are completed using photolithography. The completed first set of GMR structures R1, R3 is protected with a magnetic shielding material. Subsequently, a second set of GMR structures (R2 and R4) is lithographically formed by depositing again a GMR multilayer film with the applied magnetic field Hb reversed. Since the first set of GMR structures (e.g. R1 and R3) are protected by the magnetic shielding material, the reverse magnetic field used when preparing the second set of GMR structures (R2 and R4) does not affect them, thereby forming a plurality of GMR structures having opposite magnetization directions in one GMR sensor.

It can be seen that both the local laser annealing process and the multi-step photolithography process have the disadvantages of low precision and low efficiency, and are particularly difficult to implement in terms of industrial mass production.

Disclosure of Invention

The invention aims to provide an annealing method of a giant magnetoresistance sensor constructed by giant magnetoresistance structures with different magnetization directions.

The technical scheme of the invention is as follows: a method for annealing a GMR sensor constructed from two sets of GMR structures having different magnetization directions. The magnetization direction of the first set of GMR structures is set to a first magnetization direction and the magnetization direction of the second set of GMR structures is set to a second magnetization direction. The method comprises the following steps:

annealing of the first set of GMR structures, step:

applying an external magnetic field along a first magnetization direction;

current is introduced into the annealing structure corresponding to the first group of GMR structure, so that the first group of GMR structure reaches the blocking temperature;

the first set of GMR structures is held at their blocking temperature for a period of time;

and (4) canceling current input, and keeping an external magnetic field to reduce the temperature of the GMR structure to be lower than the blocking temperature. And

annealing the second set of GMR structures, step:

applying an external magnetic field along a second magnetization direction;

current is introduced into the annealing structure corresponding to the second group of GMR structures, so that the second group of GMR structures reach the blocking temperature;

the second group of GMR structures is kept at the blocking temperature for a period of time;

and (4) canceling current input, and keeping an external magnetic field to reduce the temperature of the GMR structure to be lower than the blocking temperature.

As a further development of the invention, the first and second set of GMR structures each consist of a spin valve.

As a further development of the invention, the first and second set of GMR structures each consist of one magnetic tunnel junction.

As a further development of the invention, the current with which the first set of GMR structures is annealed is a pulsed current.

As a further improvement of the invention, the first group of GMR structures are insulated by applying intermittent pulse current, and intermittent stagnation exists between pulse trains;

as a further improvement of the invention, a first set of annealed structures is deposited on the substrate, and then a first set of GMR structures is deposited, that is, the first set of GMR structures is deposited right above the first set of annealed structures, and the first set of GMR structures are in one-to-one correspondence from top to bottom.

As a further improvement of the invention, the first and second sets of annealed structures are deposited on the same plane; a second set of GMR structures is deposited on the second set of annealed structures and in one-to-one correspondence above and below the second set of annealed structures.

The integrated annealing structure of the invention can independently anneal the GMR structure to make the temperature reach the blocking temperature of the GMR structure or even higher, under the external magnetic field, the magnetization direction Mp of the pinned layer in the GMR structure is adjusted to be consistent with the external annealing magnetic field and fixed, thereby adjusting the magnetization direction of the pinned layer in the GMR structure to the desired direction. In some examples, the GMR structures are divided into multiple groups according to the identity of the Mp, the Mp is the same as one group, and the Mp is different from one group to another. GMR structures with different magnetization directions can be realized by separately annealing different groups of GMR structures in different directions of an applied annealing magnetic field.

Drawings

FIG. 1 is a schematic diagram of a GMR structure with a sandwich structure;

FIG. 2 is a schematic diagram of a Wheatstone full-bridge configuration of MR resistors;

FIG. 3 is a schematic diagram of a GMR sensor in a Wheatstone full bridge configuration;

FIG. 4 is a wafer composition diagram;

FIG. 5 is a side view of a typical GMR structure with an integrated anneal structure;

FIG. 6 is a side view of a typical bottom-pinned GMR structure with an integrated anneal structure;

FIG. 7 is a side view of a typical top pinned GMR structure with an integrated anneal structure;

FIG. 8 is a perspective view of an integrated annealed structure of three Wheatstone full bridge GMR sensors;

FIG. 9 is a side view of FIG. 8 in the XZ plane;

fig. 10 is a side view of fig. 8 in the YZ plane.

FIG. 11 is a diagram of an exemplary fabrication process for a GMR sensor with an integrated anneal structure;

figure 12 is a diagram of a typical CIP type GMR structure,

FIG. 13 is a conductor pattern of an annealed structure;

FIG. 14 is a flow chart of an exemplary annealing process to cause a GMR structure to have different magnetization directions;

FIG. 15 is an exemplary graph of current applied to an annealed structure to heat up a GMR structure;

FIG. 16 is an exemplary graph of current applied to an annealed structure to keep a GMR structure warm.

Detailed Description

The invention discloses a GMR structure integrated with an annealing structure and a Wheatstone full-bridge GMR sensor formed by utilizing the GMR structure. The integrated annealing structure can anneal the GMR structure to make the temperature reach the blocking temperature or even higher, and under the external annealing magnetic field, the magnetization direction Mp of the pinned layer in the GMR structure is adjusted to be consistent with and fixed by the external annealing magnetic field. In some examples, the GMR structures are divided into a plurality of groups according to the identity of the Mp, wherein the Mp is the same group, and the Mp is different groups. The integrated annealing structure can realize annealing of different GMR structure groups in external magnetic fields in different directions. In particular, such an integrated anneal structure is capable of independently annealing the corresponding GMR structure to adjust the magnetization direction of the pinned layer in the GMR structure to a desired direction. Selected examples of the present invention are described in detail below with reference to the accompanying drawings. Those skilled in the art will appreciate that the following description is for purposes of illustration and should not be construed as a limitation of the present invention. Other variations within the scope of the invention are also encompassed by the invention.

As described above with reference to fig. 3, a GMR wheatstone full bridge sensor generally requires four GMR structures, each GMR structure represents one magnetoresistance, adjacent magnetoresistance have opposite Mp directions, and all four magnetoresistance can change with the magnetic field to be measured.

Many times, GMR sensors are fabricated as chips on a wafer, as shown in fig. 4, the wafer (20) is composed of many chips (e.g. 18), and each die is a wheatstone bridge of GMR resistors); the above discussion of the chip (18) containing the GMR sensor or the GMR sensor in the chip (18) is with reference to fig. 3. It is noted that adjacent GMR structures in a GMR wheatstone full bridge sensor chip have opposite Mp directions. In order to more efficiently realize GMR structures with opposite magnetization directions in a GMR sensor, the patent proposes an integrated annealing structure.

The adjustment of the magnetization direction Mp in GMR structures is usually achieved by an annealing process. The temperature of the GMR structure is raised above the blocking temperature and the magnetization direction of the pinned layer is induced to the direction of the annealing magnetic field with an applied magnetic field. During cooling of the GMR structure, an annealing magnetic field is maintained. After cooling down (after a temperature below its blocking temperature) the GMR structure has its magnetization direction fixed.

For sensors or chips on a wafer, GMR structures have different magnetization directions, and it is very difficult to apply magnetic fields of different directions to GMR structures independently of each other. However, applying an applied annealing magnetic field to all GMR structures, and independently heating the GMR structures above the blocking temperature to achieve the adjustment of the magnetization direction is a feasible approach.

For example, FIG. 5 is a GMR structure integrated with an anneal structure. The GMR structure (22) is a sandwich multilayer film structure in which a nonmagnetic layer (14) is sandwiched between a magnetic layer (first ferromagnetic layer 12) and a second ferromagnetic layer 16. The integrated anneal structure (26) is deposited on a substrate (28). An insulating layer (24) may be optionally coated on the annealed structure (26), and a multilayer film composed of the first ferromagnetic layer (12), the second ferromagnetic layer (16), and the non-ferromagnetic layer (14) may be deposited on the insulating layer (24).

The annealed structure (26) in this example uses a metal sheet as a resistor. When current is passed through the metal anneal structure, the metal sheet generates joule heat, which is transferred through the insulating layer (24) to the pinned layer, raising the temperature of the pinned layer to the blocking temperature or even higher.

The metal sheet in the annealed structure (26) may be selected from any suitable material, such as copper, aluminum, gold, and the like. The thickness of the metal sheet may be 50 μm or less, such as 20 μm or less, 10 μm or less, 5 μm or less, 1 μm or less. The metal sheet may be deposited onto the substrate (28) using physical vapor deposition, such as magnetron sputtering or other suitable methods. To increase the resistance of the metal sheet, one or more insulating layers (e.g., oxide layers, etc.) may be incorporated into or over the metal sheet, such as a thin layer of Al ₂ O ₃ Or SiO _x . Other materials, e.g. SiN _x Or the like ceramics may also be added to the metal layer of the annealed structure. In other examples, the metal sheet may be replaced with a resistive wire, such as a serpentine resistor, to increase the resistance value.

The area (top view area) of the annealed structure (26) may be smaller than the area of the GMR structure above it, which is particularly advantageous for avoiding cross-talk between adjacent GMR structures during annealing. For example, the area of the annealed structure (26) may be 90% or less, 80% or less, 70% or less, or 60% or less of the area of the GMR structure (calculated as the area of the ferromagnetic layer).

The annealing structure (26) may be in other suitable forms besides sheet metal, such as a high frequency coil or the like that generates heat during annealing.

When a Direct Current (DC) or Alternating Current (AC) is passed through the annealed structure (26), heat is generated. Either a constant current of direct current or a pulsed current of direct current, which may contain 20 pulses with a pulse length of 1ms, may be passed directly into the annealing structure (26). Joule heat can be generated by the skin effect when the metal sheet of the annealed structure (26) is connected in an alternating current.

The insulating layer (24) may be any suitable insulating material. For example, can adopt

SiO of (2) ₂ As an insulating layer material. The insulating layer (24) can be deposited in a number of waysOnto the substrate (28) and the annealed structure (26), physical vapor deposition techniques such as magnetron sputtering, and the like.

For sensing applications, the magnetization direction Mp of the pinned layer is fixed and is not affected by the magnetic field to be measured, while the magnetization direction of the free layer changes with the change of the magnetic field to be measured. Wherein the magnetization direction of the pinned layer is fixed by exchanging energy with the pinning layer. For example, the GMR structure (30) of fig. 6 shows the pinned layer pinned by a pinning layer (32) of composition IrMn or PtMn, the pinning between them being by magnetic exchange energy between the two. The GMR structure (30) is a multilayer film structure composed of a ferromagnetic layer, a nonmagnetic spacer layer (14), and a pinning layer (magnetic layer 32). An annealing structure (26) is deposited on a substrate (28). An insulating layer (24) may optionally be coated on the annealed structure (26), and a GMR multilayer film composed of the first ferromagnetic layer (12), the second ferromagnetic layer (16), the non-ferromagnetic layer (14), and the pinning layer (32) may be deposited on the insulating layer (24). This structure is named "bottom pinned" GMR because the pinned layer is located below the free layer.

The integrated anneal structure (26) is deposited on a substrate (28) while protected by an insulating layer (24). The ferromagnetic layer is in turn deposited on the insulating layer (24) and the annealed structure. During annealing, direct current or alternating current generates joule heat through the annealed structure (26). The generated heat is conducted to the pinned layer (16) through the insulating layer (24) and the pinning layer (32), thereby raising the temperature of the pinned layer (16) to a blocking temperature or even higher.

The pinned layer may also be deposited over the free layer, as opposed to the bottom pinned GMR, and such structures are referred to as "top pinned" GMRs. FIG. 7 shows a top pinned GMR structure (30) with the annealed structure (26) deposited on the substrate (28) and protected by the insulating layer (24), the free layer deposited on the insulating layer (24), and the non-magnetic layer (14) deposited on the free layer. The pinned layer is pinned by a pinning layer (32) through magnetic exchange, the pinned layer and the pinning layer (32) being deposited over the nonmagnetic layer (14).

The plurality of GMR structures in the example are interconnected to form a wheatstone full bridge comprising a plurality of GMR structures having different magnetization directions Mp. The GMR structures are divided into a plurality of groups according to the magnetization direction Mp, and the GMR structures in each group have the same magnetization direction Mp. And in the annealing process, one group is selected, an external annealing magnetic field in the same direction as the Mp is applied, and the integrated annealing structure is used for annealing the group of GMR structures. And after the annealing of the first group is finished, selecting the second group, applying an external annealing magnetic field consistent with the Mp direction of the GMR structure of the second group, and carrying out corresponding annealing treatment.

Taking the wheatstone full bridge in fig. 3 as an example, R1 and R3 with the same magnetization direction Mp are selected as the first group, and R2 and R4 with the opposite magnetization direction Mp are selected as the second group. The adjacent R1 and R2 have opposite magnetization directions, and R3 and R4 are the same. Because the integrated annealing structure is embedded in R1, R3, the annealing structure can be energized to anneal R1, R3 to a temperature that is at or above the blocking temperature of the pinned layer (16 in FIG. 5). When the direction of the applied magnetic field is to the right (Mp direction of R1 and R3 in fig. 3), the magnetization direction of R1 and R3 is induced to that direction. After the temperature of R1 and R3 is reduced to below the barrier temperature or room temperature, annealing of R2 and R4 can be carried out.

When R2 and R4 are annealed, the direction of the applied magnetic field is adjusted to the opposite direction, i.e., the left direction in fig. 3, the Mp direction of R2 and R4. The annealing structures corresponding to R2 and R4 are electrified to lead the temperature of the annealing structures to reach or exceed the blocking temperature of the pinned layers, and the magnetization directions Mp of the R2 and R4 are adjusted to the direction under the action of an external reverse magnetic field.

It should be noted that these two directional anneals are required to be operated separately. In particular, the two different annealing structures are capable of allowing current to pass through, but are isolated from each other and need to be run at different times. This requires that the two sets of annealing structures be arranged on separate planes, respectively, fig. 8 being an example.

FIG. 8 is a perspective view of the integrated annealed structure of three Wheatstone full bridge GMR sensors (GMR structures with the same Mp direction are connected in the same plane; GMR structures with opposite Mp directions are connected in different planes), showing three Wheatstone full bridges formed by GMR structures and their corresponding annealed structures (36), in which the open squares (e.g., square 42) represent the annealed structures corresponding to the GMR structures with the first magnetization direction, and the black squares (e.g., square 44) represent the annealed structures corresponding to the GMR structures with the second magnetization direction. The first magnetization direction and the second magnetization direction are different here, and the two directions in fig. 8 respectively refer to two directions differing by 180 ° in the XY plane in the cartesian coordinate system.

The integrated annealed structures (e.g. blank 42) of the first set of GMR structures are all arranged in the same plane (plane 38) and are interconnected (wires 46) by solid black lines in the figure, a and B are their respective terminals, a is the current inlet and B is the current outlet.

The integrated annealed structures (e.g., black boxes 44) of the second set of GMR structures lie on a plane (38) and are interconnected (wires 48) by dashed black lines in the figure, with C and D being their respective entrance and exit terminals. The layout of the annealed structure of fig. 8 is better shown in the side views of fig. 9 and 10.

Fig. 9 is a side view of fig. 8 in the plane of the cartesian coordinate system XZ, with the integrated annealed structures (e.g., black boxes 44) of the second set of GMR structures distributed over plane (38) and interconnected by

wires

52, 54, 48, with wire 52 distributed over plane (38), wire 48 distributed over plane (40), and wire 52 and wire 48 connected by wire 54. In this way, the electrical connection of the integrated annealed structures of the second set of GMR structures is achieved with the aid of two planes (plane 38 and plane 40), also separating the electrical circuits of the first and second set of annealed structures.

Fig. 10 is a side view of fig. 8 in the cartesian coordinate system YZ plane. The circuitry for the integrated anneal structures (e.g., black boxes 44) for the second set of GMR structures is completed through the wires 54 and the two planes, face (38), face (40). The integrated anneal structure (blank block 42) for the first set of GMR structures is done by wires on the plane (38).

GMR sensors with integrated anneal structures can be prepared by a number of methods. Fig. 11 to 13 are typical examples. Referring to fig. 9, fig. 11 is a diagram of a pattern of conductive lines (e.g., conductive lines 48) on a plane (40), which may be accomplished by a number of possible techniques, such as a standard lift-off process. For example, a layer of metallic conductive material may be deposited onto a substrate (28) by PVD, electroplating, etc., and the deposited material may be patterned by photolithography, etc. to form conductive lines, and an insulating material (60) may be deposited over the conductive lines (e.g., conductive lines 48) to protect and insulate the conductive lines from shorting with other conductive materials. Vertical conductors (e.g., conductors 54) disposed within the insulation (60) serve to connect conductors in different planes, e.g., conductors (54) connect conductors (52) on plane (38) to conductors (48) on plane (40). This process can be accomplished by etching a trench in the insulating layer (60) and then filling it with a conductive material.

The annealed structures (44) and conductive lines (52) on the planar surface (38) may be formed by deposition and patterning processes, and the conductive materials selected for the annealed structures and the conductive lines may be the same or different. An insulating layer (62) is deposited over the already formed annealed structure and the conductive line (52). Vertical wires (66) and (64) are formed in the insulating layers (62), (60), respectively, as terminals for passing current through the annealed structure. Subsequently, a GMR structure is deposited on the planar (38) insulating layer (62), as shown in FIG. 12.

Referring to fig. 12, the annealed structures are distributed in a plane (38) and the GMR structures are distributed in a plane (39) above them, and there is one-to-one correspondence above and below them. The GMR structure may be deposited and patterned using well known techniques and will not be described in detail herein. The illustration of fig. 12 is typical CIP type GMR structures such as spin valves (67) and (69). Wherein the connection terminals of the GMR structures (67) are 78 and 80, the connection terminals of the GMR structures (69) are 76 and 74, so that current is allowed to pass through the GMR structures (67) and (69) in the same plane, and the two adjacent GMR structures (67) and (69) are blocked by the insulating layer (61) (see figure 13). And the conductor distribution of the annealing structure is also shown in fig. 13, the vertical conductors (65) and (63) in the insulating layer (61) are respectively communicated with the conductors (66) and (64) at the lower layer, so that the conductors of the annealing structure extend to the outermost layer.

As can be seen from fig. 13, the terminals of the annealed structures (e.g., 44) and their wires (48) are 57 and 63, and when current is passed through the circuit, joule heat is generated by the annealed structures (44) and anneals the corresponding GMR structures above (GMR structure (67) corresponds to annealed structure (44)). The magnetization direction of another set of GMR structures (42 in fig. 8, not shown in fig. 13) is different from that of the GMR structures in fig. 13, and the annealing structures and the conductive wires corresponding to the set of GMR structures are distributed on the same plane, and the

connection terminals

65 and 59 connected to the annealing structures can anneal the corresponding GMR structures.

A typical anneal process flow is shown in fig. 14. As discussed above, adjusting the magnetization direction of a GMR structure using an annealing process requires two conditions: blocking temperature and an applied magnetic field. When the temperature of the pinned layer of the GMR structure reaches or exceeds the blocking temperature thereof, the magnetization direction of the pinned layer is induced to the direction of the applied magnetic field; after this process has lasted for a few minutes or hours, the magnetization direction of the pinned layer will be perfectly aligned with the direction of the applied magnetic field; the GMR structure is gradually cooled under the action of the external magnetic field, and the magnetization direction of the pinned layer is kept unchanged even if the external magnetic field is removed.

In order to enable the GMR structure on the Wheatstone full-bridge GMR sensor to obtain different magnetization directions, the GMR structure is divided into a plurality of groups according to the identity of Mp, the Mp direction in the same group is the same, and the Mp directions in different groups are different. The GMR structures in the same group need to be annealed in an external magnetic field in the same direction by the same process; the GMR structures of different groups adopt different applied magnetic field directions and are independently annealed.

According to the flow chart of FIG. 14, an applied magnetic field is applied to the sensor containing the two sets of GMR structures (step 84). Current is passed through

terminals

57 and 63 in fig. 13 to anneal the first set of GMR structures of the sensor, raising it to a temperature even higher than the blocking temperature of the pinned layer (second ferromagnetic layer 16 in fig. 6, 7) (step 86). The current used may be of any suitable form, such as a constant current of fixed amplitude, or a pulsed current as shown in fig. 15, or the like.

The pulse current shown in fig. 15 has a duty cycle of 20ns to 10ms and an amplitude of 100uA to 100mA per pulse.

Referring again to fig. 14, after the temperature of the pinned layer of the first set of GMR structures reaches its blocking temperature, the annealing structure corresponding to the set of GMR structures changes the current form to maintain the annealing structure at its temperature for a certain time, thereby ensuring that the pinned layer of the GMR structures is maintained at the blocking temperature for a certain time. This period of time may be ten minutes to several hours (step 88), ensuring that the pinned layer has sufficiently adjusted its magnetization to be perfectly aligned with the direction of the applied magnetic field. This incubation can be accomplished in a number of ways, one of which is by using an intermittent pulse current as shown in FIG. 16.

As shown in fig. 16, the intermittent pulse current is composed of a plurality of pulse trains, each pulse train containing one or more pulses. The application time of each pulse train is Th and the interval dead time of adjacent pulse trains is Tc. The magnitude of Tc is determined by many factors, such as the thermal capacity, electrical conductance, thermal conduction efficiency, etc. of the GMR and annealed structures, as well as other factors related to the thermal performance of the insulating layer, the environment in which the GMR structure is located.

The intermittent pulse current is withdrawn after a dwell time and the GMR structure is allowed to cool gradually with continued application of the external magnetic field (step 90). The above process completes the annealing of the first set of GMR structures. The second set of GMR structures is then annealed, beginning at step 92.

Because the magnetization direction of the second set of GMR structures is different from that of the first set, the direction of the applied magnetic field of the second set is different (step 92), such as reversed, from the direction of the applied magnetic field of the first set of GMR structures when annealed. A constant current or a pulsed current as discussed in fig. 15 is applied to the corresponding annealed structure of the second GMR structure and the temperature of the pinned layer of the second GMR structure is raised for annealing (step 94) with

current terminals

59 and 65 as shown in fig. 13. After the temperature of the pinned layer of the second set of GMR structures reaches its blocking temperature, the temperature is maintained for a period of time using the intermittent pulse current discussed with respect to FIG. 16 to ensure that the magnetization direction of the pinned layer is fully aligned with the direction of the applied magnetic field (step 96). Finally, the current is stopped in the presence of the applied magnetic field, allowing the second set of GMR structures to cool (step 98).

It is noted that when annealing the first set of GMR structures (steps 84 to 90), the direction of the applied magnetic field is along the selected first magnetization direction. Furthermore, an externally applied magnetic field is applied to all GMR structures including the first and second groups. And annealing the first group of GMR structures to adjust the magnetization direction of the first group of GMR structures to be completely consistent with the direction of the external magnetic field. At this point, because the second set of GMR structures is not annealed, they are not affected because their temperature is much lower than their blocking temperature, even in the presence of an applied magnetic field. For the same reason, the magnetization direction of the first set of GMR structures is not affected when the second set of GMR structures is annealed.

The invention discusses a method for controlling the magnetization direction of a GMR structure through an integrated annealing structure, and the integrated annealing structure can anneal different GMR structure groups in external magnetic fields in different directions, so that the aim that different GMR structures of one GMR sensor have different magnetization directions is fulfilled. Those skilled in the art will appreciate that the foregoing discussion is for the purpose of illustration, and that the examples presented above are some of many possible examples, and that other variations are possible.

Reference in the specification to "one embodiment," "an example embodiment," etc., means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is submitted that it is within the purview of one skilled in the art to effect such feature, structure, or characteristic in connection with other ones of the embodiments. Moreover, for ease of understanding, some method steps are described as separate steps; however, the steps described separately are not to be considered to have to be performed in a certain order. That is, some steps may be performed in another order at the same time. Further, the exemplary diagrams illustrate various methods according to embodiments of the invention. Such exemplary method embodiments are described herein with and can be applied to corresponding apparatus embodiments. However, these method examples are not intended to limit the present invention.

Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention. The foregoing embodiments are, therefore, to be considered in all respects illustrative rather than limiting of the invention described herein. The scope of the invention is indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the specification are to be embraced within their scope. The term "preferably" as used in this specification is not exclusive and means "preferably but not limited to". The terms in the claims, consistent with the general concepts of the invention as described in the specification, should be interpreted in their broadest scope. For example, the terms "connected" and "coupled" (and derivatives thereof) mean directly and indirectly connected/coupled. As another example, "having" and "including" as well as derivatives and variations thereof or phrases having the same meaning as "comprising" (i.e., both being "open" terms) -the only phrase "consisting of …" and "consisting essentially of …" should be considered "closed".

Claims

1. The annealing method of giant magneto-resistance sensor constructed by giant magneto-resistance structures with different magnetization directions, GMR sensor is divided into two groups according to the same or different magnetization directions, the same magnetization direction is one group, the different magnetization directions are different groups, GMR sensor is constructed by two groups of GMR structures with different magnetization directions, the magnetization direction of the first group of GMR structure is set as the first magnetization direction, the magnetization direction of the second group of GMR structure is set as the second magnetization direction; the method comprises the following steps:

annealing of the first set of GMR structures, step:

applying an external magnetic field along a first magnetization direction;

current is introduced into the annealing structure corresponding to the first group of GMR structures, so that the first group of GMR structures reach the blocking temperature;

canceling current input, and keeping an external magnetic field to reduce the temperature of the GMR structure to be lower than the blocking temperature; and

annealing the second set of GMR structures, step:

applying an external magnetic field along a second magnetization direction;

current is introduced into the annealing structure corresponding to the second group of GMR structure, so that the second group of GMR structure reaches the blocking temperature;

canceling current input, and keeping an external magnetic field to reduce the temperature of the GMR structure to be lower than the blocking temperature;

the first and second sets of GMR structures are each comprised of a spin valve;

the first and second groups of GMR structures are each comprised of a magnetic tunnel junction;

the current at which the first set of GMR structures is annealed is a pulsed current;

the first group of GMR structures is insulated by applying intermittent pulse current, and intermittent stagnation exists between pulse trains;

depositing a first group of annealing structures on the substrate, and depositing a first group of GMR structures, namely depositing the first group of GMR structures right above the first group of annealing structures, wherein the first group of GMR structures are in one-to-one correspondence from top to bottom;

the first group of annealing structures and the second group of annealing structures are deposited on the same plane, and the current wiring terminals of the first group of annealing structures and the second group of annealing structures are on different planes; the second group of GMR structures are deposited on the second group of annealing structures and correspond to each other up and down; two different sets of annealing structures are capable of allowing current to pass through, but are isolated from each other and need to be run at different times.