Anisotropic magnetic resistance (AMR) sensor that requires no adjustment / reset device

Description

Technical Field

[0001] The present invention relates to a magnetoresistive sensor configured to detect vector distribution of a magnetic field, including at least one type of anisotropic magnetoresistive device deposited on a substrate, the magnetoresistive device including a plurality of anisotropic magnetoresistive (AMR) elements connected in series through conductive bars. The magnetoresistive device adopts a Barber-pole electrode structure to improve the sensitivity in a weak magnetic field and expand the linear operating range. Moreover, the exchange coupling characteristic of an anti-ferromagnetic layer is used and a reset and set device is not necessary, thereby further reducing the power consumption and the cost of the sensor.Background Art

[0002] An anisotropy magnetoresistance (AMR) effect refers to a phenomenon that the specific resistance in a ferromagnetic material changes as an included angle between a magnetization intensity of the ferromagnetic material and a current direction changes. The AMR effect is first discovered by Thomson in 1857. A sensor prepared by using the AMR effect is referred to as an AMR sensor.

[0003] Generally, a structure called Barber-pole electrode is adopted in the current AMR sensor design. Specifically, some metal conductive electrodes such as aluminum, copper, and gold are disposed on AMR strips, and the electrodes are arranged to form 45°-structures with long axes of the AMR strips. As shown in FIG. 1, a barber-pole electrode achieves the objective of changing the current direction by changing the structures of the electrodes, which is advantageous in a small volume and low power consumption compared with other methods, thereby being widely applied. The patent No. DE3442278A1 has descriptions about the barber-pole electrode.

[0004] The AMR sensor requires an additional magnetic field during use to bias the sensor, so as to improve the linearity and stability of the sensor and at the same time eliminate temperature drift and improve the signal-to-noise rate of the sensor. DE4221385C2 proposed to add a macroscopic permanent magnet near a magnetoresistive layer structure to implement bias by externally adding a permanent magnet. However, the method has the defects of a limited sensor size and complex assembling. Therefore, the externally added permanent magnet is replaced with a permanent magnet film which is deposited near a magnetoresistive film and is isolated from the magnetoresistive film by an insulating film. The method has the defects that a magnetic domain of the permanent magnetic layer is difficult to control and Barkhausen noise will be generated. Another method is to bias by using an exchange coupling function of an anti-ferromagnetic layer, and the method is mentioned in US 20150061658.

[0005] In addition, if an AMR sensor is interfered by an external large magnetic field during work, the magnetic domain distribution on AMR strips will be destroyed, such that the magnetic domains on the AMR strips are distributed randomly along some directions. Therefore, the sensitivity of the sensor is reduced, attenuated, or even failed. A common method at present, e.g., US 20130300408A1, is to deposit a set / reset coil on an AMR sensor to achieve the following objectives: the sensor is enabled to work in a high-sensitivity mode; the polarity of an output response curve is reversed; and the linearity is improved to reduce influences of the vertical axis effect and the temperature. However, the method has the defects of increased power consumption and limited maximum measurement magnetic field.

[0006] WO2015182643 discloses a magnetoresistive element, magnetic sensor and current sensor. This magnetoresistive element is provided with a substrate, an antiferromagnetic layer provided above the substrate, a ferromagnetic layer provided on the antiferromagnetic layer so as to cover the entire principal surface of the antiferromagnetic layer, and multiple barber pole electrodes which are provided on the ferromagnetic layer and spaced apart from one another.US20130320972 discloses a magnetic field sensing device comprising several functionally different layers, wherein a Wheatstone bridge layer comprising at least two resistors of a Wheatstone bridge, each resistor comprises at least one magnetic field sensing element in the form of a resistor sub-element, and a flip conductor layer comprising at least one flip conductor for flipping the internal magnetization state of each magnetic field.

[0007] CN104900801 discloses an anti-ferromagnetic pinning AMR sensor which structurally comprises a substrate layer, a buffer later, a cover layer and an intermediate layer, wherein the substrate layer is placed at the bottom, the buffer layer is placed on the substrate layer, the cover layer placed at the top, and the intermediate layer which comprises an ferromagnetic later and an anti-ferromagnetic layer is placed between the buffer layer and the cover layer.

[0008] US20150285873A1 discloses a three-axis magnetic sensor or magnetometer. Two magnetic sensor Wheatstone bridges using barber pole AMR structures are fabricated on opposite sides of a bump structure formed on a substrate to provide surfaces that are at a pre-determined angle with respect to the flat surface of the substrate.Summary of the Disclosure

[0009] Embodiments of the invention are set out in the appended claims.

[0010] The present claims provide an AMR sensor without a set and reset coil.

[0011] The AMR sensor without a set and reset coil of the present claims has the following beneficial effects: 1. The anisotropic magnetoresistive (AMR) sensor achieves coupling by using an exchange bias layer, without requiring a reset / set coil. Because a coil is not used, the power consumption of the chip is reduced greatly, and the manufacturing process is simpler, thereby improving the yield of the product and reducing the production costs. 2. The AMR strips are arranged in a parallel direction and a perpendicular direction in the same chip. After magnetic annealing at 45°, the chip can be switched from single-axis operation to double-axis operation, and magnetic fields in multiple directions can be measured at the same time. 3. The design has no gradient effect and the field is measured more accurately. 4. Compared with other designs, the design adopts a resister pair and so on and does not require a resistance adjustment process. Brief Description of the Drawings

[0012] Examples are further described hereinafter with reference to the accompanying drawings, in which: FIG. 1 is a schematic structural diagram of a barber-pole electrode; FIG. 2 is a schematic structural diagram of an AMR sensor chip without a set and reset coil; FIG. 3 is a partially enlarged schematic diagram of FIG. 2; FIG. 4 is a schematic diagram of a connection between AMR strips and barber-pole electrodes; FIG. 5 is a schematic diagram of circuits forming a Wheatstone bridge; FIG. 6 is a sectional diagram of a chip; FIG. 7 is a schematic diagram of a magnetic annealing direction and exchange coupling magnetization of AMR strips; FIG. 8 is an illustration of a design of resister units closely arranged alternately; and FIG. 9 is an illustration of a design of resister units in a conventional sensor.

[0013] In the drawings: 100-AMR sensor without a set and reset coil, 101-electrode, 102-electrode, 103-electrode, 104-electrode, 110-AMR layer, 120-wire, 122-barber-pole electrode, 130-exchange bias layer, 140-substrate, 200-AMR sensor chip, 300-AMR sensor chip.Detailed Description

[0014] The technical solutions in the present embodiments will be described clearly and completely below with reference to the accompanying drawings. The described embodiments are merely some rather than all of the embodiments within the scope of the appended claims.

[0015] The structure of the sensor 100 is shown in FIG. 2 and FIG. 3: multiple groups of AMR strips 110 are arranged in an X-axis direction or a Y-axis direction (in the X-axis direction in the drawings). Barber-pole electrodes 122 are arranged on the AMR strips under certain rules. The barber-pole electrode and the AMR strip are generally arranged at an angle of ±45° to form a resistance-sensitive element. For example, barber-pole electrodes on several AMR strips of R1 and the AMR strips form the same included angle of +45°. The barber-pole electrodes and the AMR strips jointly form the resistance-sensitive elements of the chip. Multiple such resistance-sensitive elements are connected through wires 120 to form a Wheatstone bridge, and the Wheatstone bridge is then connected to four electrodes (101, 102, 103, 104) to form the whole chip, thereby finally forming the structure as shown in FIG. 4 and FIG. 5.

[0016] FIG. 6 shows a sectional diagram of a chip. An exchange bias layer 130 is deposited on a substrate 140, and an AMR layer 110 is deposited above the exchange bias layer 130. If a conventional AMR sensor experiences an external large magnetic field during work, the magnetic domain distribution in AMR strips will be destroyed, such that the sensitivity of the sensor is attenuated. A prior art method is to deposit a set / reset coil on the AMR sensor, and when a current passes through the AMR sensor, the magnetic domain directions in the AMR strips are reunified to one direction by using a magnetic field generated by the coil, thereby ensuring the high sensitivity and repeatability of the sensor. In the present disclosure, the exchange bias layer 130 is made of an anti-ferromagnetic material (PtMn, NiMn, IrMn, etc.). The magnetic moment of the magnetoresistive layer is made firm and stabilized at the original position by using the exchange coupling function between the exchange bias layer 130 and the AMR layer 110. Therefore, the interference from the external magnetic field is avoided, such that the objective of high sensitivity and high repeatability can also be achieved without a set / reset coil.

[0017] The exchange coupling function involved in the chip is further illustrated below. As shown in FIG. 7, AMR sensor chips 200 and 300 are placed adjacent to each other. The chips use the same design, and the only difference is that long axes of AMR strips in the chip 200 are along the X direction while long axes of AMR strips in the chip 300 are along the Y direction. In order to implement the exchange coupling, it is first required to magnetically anneal the exchange bias layer. An external magnetic field He is applied during annealing, an included angle between the external magnetic field and the X-axis direction being 45°. After the magnetic annealing is finished, there is a magnetization vector K on each strip of the chips 200 and 300 because of the exchange coupling function between the anti-ferromagnetic layer and the magnetoresistive layer. The direction of the magnetization vector K is consistent with the direction of He. Moreover, there are components K x and K y in the X-axis direction and the Y-axis direction respectively. As such, through one annealing process, the two chips 200 and 300 with different sensitive directions can implement the measurement functions at the same time, thereby greatly simplifying the production process.

[0018] In addition, the sensor generally needs multiple resister elements to form a full-bridge or halfbridge structure to work normally. Different magnetoresistive elements in a conventional sensor will be located at different positions. As shown in FIG. 9, there is a position deviation d between resister elements R1 and R2 in the horizontal direction. In this case, if the measured external magnetic field is not uniform and has intensity fluctuations in a tiny distance, there will be a problem of resistance mismatching among R1, R2, R3, and R4. Therefore, output of the sensor is affected, that is, the so-called "gradient effect" is generated. The chip involved in the patent is designed in such a manner that resister units are closely arranged alternately, as shown in FIG. 8, thereby eliminating the position deviation and achieving more accurate field measurement.

[0019] Preferred embodiments of the anisotropic magnetoresistive (AMR) sensor without a set and reset coil are described above. It should be pointed out that for those of ordinary skill in the art, several improvements and modifications can further be made without departing from the scope of the appended claims.

Claims

1. An anisotropic magnetoresistive (AMR) sensor without a set and reset coil, wherein the sensor (100) comprises a substrate (140), an exchange bias layer (130), an AMR layer (110) and a collection of barber-pole electrodes (122); wherein the exchange bias layer is deposited on the substrate, the AMR layer is deposited on the exchange bias layer, characterized in that the AMR layer is composed of four groups of AMR strips, and the barber-pole electrodes are arranged on each AMR strip, wherein the AMR strips in each group of AMR strips are connected in series, wherein the AMR strips are parallel to each other, wherein the same included angle is formed between each AMR strip in the same group of AMR strips and the barber-pole electrode located on the AMR strip, wherein each AMR strip and respective barber-pole electrodes arranged on the AMR strip form a resistance-sensitive element, and wherein said resistance-sensitive elements comprise two types of resistance-sensitive elements, wherein in the first type of resistance-sensitive elements the included angle between the AMR strip and the barber-pole electrode arranged on the AMR strip is +45°, and in the second type of resistance-sensitive elements the included angle between the AMR strip and the barberpole electrode arranged on the AMR strip is -45°, and the resistance-sensitive elements corresponding to each group of AMR strips are connected in series through wires to form each of four serpentine resistor arms (R1, R2, R3, R4) of a Wheatstone bridge, and the four serpentine resistor arms are arranged in an interdigitated arrangement in which the adjacent resistance-sensitive elements of other resistor arms are of the other type of resistance-sensitive element.

2. The AMR sensor without a set and reset coil according to claim 1, wherein said exchange bias layer is made of an anti-ferromagnetic material.

3. A two-axis AMR sensor comprising first and second AMR sensors according to claim 1 or claim 2, wherein the AMR strips of the first AMR sensor (200) are aligned with an X-axis direction, and the AMR strips of the second AMR sensor (300) are aligned with a Y-axis direction, and wherein the AMR strips of the first and second AMR sensors have a common magnetization vector (K).