CN-116322274-B - Magnetic tunnel junction sensing unit, manufacturing method and Wheatstone bridge

CN116322274BCN 116322274 BCN116322274 BCN 116322274BCN-116322274-B

Abstract

The invention discloses a magnetic tunnel junction sensing unit, a manufacturing method and a Wheatstone bridge, wherein the magnetic tunnel junction sensing unit comprises a seed layer, a fixed layer and a potential barrier layer, a first synthetic antiferromagnetic free layer, a second synthetic antiferromagnetic free layer, a first covering layer and a second covering layer, wherein the first surface of the first synthetic antiferromagnetic free layer is arranged on the potential barrier layer, the first surface of the second synthetic antiferromagnetic free layer is connected with the second surface of the first synthetic antiferromagnetic free layer, the first surface of the second covering layer is connected with the second surface of the second synthetic antiferromagnetic free layer, the seed layer, the fixed layer, the potential barrier layer, the first synthetic antiferromagnetic free layer and the first covering layer form an MTJ1, and the seed layer, the fixed layer, the potential barrier layer, the second synthetic antiferromagnetic free layer and the second covering layer form an MTJ2. According to the invention, the MTJ bridge arms with two fixed layers having opposite magnetization directions are realized on one MTJ sensing unit, and the complexity of the structure is reduced. The invention can be widely applied to magnetic tunnel junction sensors.

Inventors

JIANG SHENG
YAO LINRONG

Assignees

华南理工大学

Dates

Publication Date: 20260512
Application Date: 20230208

Claims (8)

1. A magnetic tunnel junction sensing cell, comprising: A seed layer; the first surface of the fixed layer is connected with the second surface of the seed layer; a barrier layer, the first surface of the barrier layer being connected to the second surface of the fixed layer; A first synthetic antiferromagnetic free layer having a first surface disposed on a first boundary of a second surface of the barrier layer; A second synthetic antiferromagnetic free layer having a first surface disposed on a second boundary of the second surface of the barrier layer, wherein the first boundary is opposite the second boundary; a first capping layer having a first surface coupled to a second surface of the first synthetic antiferromagnetic free layer; a second capping layer, the first surface of the second capping layer being coupled to the second surface of the second synthetic antiferromagnetic free layer; the seed layer, the fixed layer, the barrier layer, the first synthetic antiferromagnetic free layer and the first cladding layer form an MTJ1, and the seed layer, the fixed layer, the barrier layer, the second synthetic antiferromagnetic free layer and the second cladding layer form an MTJ2; The seed layer, the fixed layer and the barrier layer form square columns, the synthetic antiferromagnetic free layer and the covering layer are processed into columnar structures, the projection of the columnar structures on the second surface of the barrier layer is rectangular, and the extension line of the long side of the rectangle is perpendicular to the boundary of the barrier layer; The fixed layer is made of ferromagnetic material, and the magnetization directions of the fixed layers are antiparallel because of shape anisotropy, the magnetization directions of the fixed layers of the MTJ1 and the MTJ2 form an X-shaped magnetic domain structure along the in-plane direction and form a magnetic vortex at the center.
2. The magnetic tunnel junction sensing cell of claim 1, wherein the first synthetic antiferromagnetic free layer and the second synthetic antiferromagnetic free layer are identical in structure; the first synthetic antiferromagnetic free layer includes: a free layer, a first surface of the free layer being connected to a second surface of the barrier layer; A non-magnetic metal layer, the first surface of the non-magnetic metal layer being connected to the second surface of the free layer; A weak pinning layer, a first surface of the weak pinning layer being connected to a second surface of the nonmagnetic metal layer; an antiferromagnetic layer having a first surface connected to the second surface of the weak pinned layer and a second surface connected to the first surface of the first capping layer.
3. The magnetic tunnel junction sensor cell of claim 2 wherein the seed layer is a metallic material, the barrier layer is an insulating material, the free layer is a ferromagnetic material, the nonmagnetic metallic layer is a metallic material, the weak pinning layer is a ferromagnetic material, and the antiferromagnetic layer is an antiferromagnetic material.
4. A method of fabricating a magnetic tunnel junction sensor cell according to claim 1, comprising the steps of: Depositing a film layer by layer, photoetching a square column on the deposited film, and etching two rectangular columns with the size far smaller than that of the square column on the basis of the structure; the square column comprises a seed layer, a fixed layer and a barrier layer, and the rectangular column comprises a synthetic antiferromagnetic free layer and a covering layer.
5. The method of manufacturing of claim 4, further comprising the steps of: Optimizing the tunnel magnetoresistance ratio to be more than 10% by adjusting growth conditions, wherein the growth conditions comprise the thickness of the barrier layer and the annealing condition; The thickness of the nonmagnetic metal layer is controlled so as to realize antiferromagnetic coupling between the free layer in the antiferromagnetic free layer and the weak pinning layer, thereby reducing the influence of stray field of the free layer on the magnetization direction of the fixed layer and further improving the linearity of the magnetic sensor; By optimizing the magnitude of the pinning strength, a large-scale linear output and high sensitivity are realized.
6. The Wheatstone bridge is characterized by comprising a first bridge arm, a second bridge arm, a third bridge arm and a fourth bridge arm, wherein one end of the first bridge arm is connected with one end of the second bridge arm, one end of the third bridge arm is connected with one end of the fourth bridge arm, the other end of the first bridge arm is connected with the other end of the third bridge arm, and the other end of the second bridge arm is connected with the other end of the fourth bridge arm; The first bridge arm and the second bridge arm are composed of a first magnetic tunnel junction sensing unit, wherein the first bridge arm is an MTJ1 of the first magnetic tunnel junction sensing unit, and the second bridge arm is an MTJ2 of the first magnetic tunnel junction sensing unit; The third bridge arm and the fourth bridge arm are composed of a second magnetic tunnel junction sensing unit, wherein the third bridge arm is an MTJ1 of the second magnetic tunnel junction sensing unit, and the fourth bridge arm is an MTJ2 of the second magnetic tunnel junction sensing unit; The first magnetic tunnel junction sensing unit and the second magnetic tunnel junction sensing unit are each implemented with a magnetic tunnel junction sensing unit as claimed in any one of claims 1 to 3.
7. The wheatstone bridge according to claim 6, wherein magnetization directions of the fixed layers of the MTJs corresponding to the first, fourth and second, third bridge arms are reversed in the absence of an external magnetic field; the magnetic domain of the fixed layer changes along with the change of the external magnetic field under the application of the external magnetic field, and the magnetic domain change does not change the magnetization direction of the fixed layer under the rectangular column of the free layer in a certain magnetic field range by designing the free layer to be close to the boundary.
8. The wheatstone bridge of claim 6, wherein the total sensing area is increased by forming a sensor matrix from individual magnetic tunnel junction sensing units in series-parallel connection to improve signal-to-noise ratio.

Description

Magnetic tunnel junction sensing unit, manufacturing method and Wheatstone bridge Technical Field The invention relates to a magnetic tunnel junction sensor, in particular to a magnetic tunnel junction sensing unit, a manufacturing method and a Wheatstone bridge. Background The sensor based on the Magnetic Tunnel Junction (MTJ) has high sensitivity, small size, low power consumption and extremely low resistance noise, is expected to become a mainstream magnetic sensor in the future, and has wide application prospect in the fields of magnetic storage, power grid transportation, automatic driving and the like. Tunnel Magnetoresistive (TMR) sensors need to achieve a linearized output while being connected in a wheatstone bridge configuration, which is a challenge in achieving high performance TMR sensors. At present, the MTJ sensing unit for realizing the linearization output has five main implementation modes, namely, shape anisotropy of a free layer, bias field generation of an integrated Permanent Magnet (PM), anisotropic orthomagnetization, double pinning and superparamagnetism, and all the methods have limitations. The shape anisotropy of the free layer is utilized to form a special size ratio, the free layer is a detection layer and can cause instability of magnetic field detection, the integrated PM not only increases the process flow, the cost and the device area, but also is not suitable for a sensor array, the Magnetic Resistance (MR) of an orthogonal magnetization device is lower than that of an in-plane magnetization device and only can detect a magnetic field in the vertical direction, double pinning needs to be performed for two times, coercivity (Hc) is easy to remain, and the super paramagnetic layer is formed to be extremely thin, so that the MR is reduced and the noise level is greatly improved. Furthermore, the connection in a wheatstone bridge configuration requires that the MR on adjacent legs varies inversely with the external magnetic field, which means that the MTJs making up the adjacent legs have opposite fixed layer magnetization directions, while the thin film fixed layer magnetization directions deposited on the same wafer are uniform. The current realization method firstly utilizes laser radiation or pulse current to locally heat a bridge arm with the magnetization direction needing to be changed and then applies an external magnetic field with the opposite direction to realize the magnetization direction of the opposite fixed layer, and secondly deposits films with the opposite magnetization directions of the two fixed layers on the same wafer through a specific technological process. The first method needs to introduce laser equipment or a current coil and is not suitable for a sensor array, and the second method needs an additional process flow and is complex in process. Disclosure of Invention In order to solve at least one of the technical problems existing in the prior art to a certain extent, the invention aims to provide a magnetic tunnel junction sensing unit, a manufacturing method and a wheatstone bridge. The technical scheme adopted by the invention is as follows: a magnetic tunnel junction sensing unit comprising: A seed layer; the first surface of the fixed layer is connected with the second surface of the seed layer; a barrier layer, the first surface of the barrier layer being connected to the second surface of the fixed layer; A first synthetic antiferromagnetic free layer having a first surface disposed on a first boundary of a second surface of the barrier layer; A second synthetic antiferromagnetic free layer having a first surface disposed on a second boundary of the second surface of the barrier layer, wherein the first boundary is opposite the second boundary; a first capping layer having a first surface coupled to a second surface of the first synthetic antiferromagnetic free layer; a second capping layer, the first surface of the second capping layer being coupled to the second surface of the second synthetic antiferromagnetic free layer; the seed layer, fixed layer, barrier layer, first synthetic antiferromagnetic free layer and first capping layer comprise MTJ1, and the seed layer, fixed layer, barrier layer, second synthetic antiferromagnetic free layer and second capping layer comprise MTJ2. Further, the first synthetic antiferromagnetic free layer and the second synthetic antiferromagnetic free layer are identical in structure; the first synthetic antiferromagnetic free layer includes: a free layer, a first surface of the free layer being connected to a second surface of the barrier layer; A non-magnetic metal layer, the first surface of the non-magnetic metal layer being connected to the second surface of the free layer; A weak pinning layer, a first surface of the weak pinning layer being connected to a second surface of the nonmagnetic metal layer; an antiferromagnetic layer having a first surface connected to the second surface of the weak pinned