Abstract:
A magnetoresistive magnetic imaging sensor for identifying a magnetic image comprises a PCB and several magnetoresistive sensor chips, wherein the several magnetoresistive sensor chips are located on the PCB, and the PCB is perpendicular or parallel to the magnetic image detection surface. It has a lateral detection mode and front detection mode. In the lateral detection mode, each side face of the several magnetoresistive sensor chips is parallel or coplanar with the side of the PCB, and parallel to the magnetic image detection surface. The several magnetoresistive sensor chips have the same magnetic sensing direction. In the lateral detection mode, the adjacent magnetoresistive sensor chips are stacked, while in the front detection mode, the adjacent magnetoresistive sensor chips are arranged in a staggered manner, in order to achieve continuity of the detection area in the magnetic image detection surface. The magnetoresistive magnetic imaging sensor may also comprise a permanent magnet assembly and a housing. The sensor has several advantages, including continuity across the detection area, good signal reproduction, high sensitivity, and low power consumption.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to the field of magnetic sensors, and in particular, to a magnetoresistive magnetic imaging sensor for identifying a magnetic image. 
       BACKGROUND ART 
       [0002]    A magnetic image identification sensor is mainly used in the field of finance, for example, in a POS, an ATM, a currency detector, a money counting machine and so on. A magnetic strip of a credit card is made of a hard magnetic material, a magnetic field thereof can be measured directly, a surface image of a banknote is printed by ink containing soft magnetic particles, and the magnetic particles are magnetized, upon application of a bias magnetic field, to be detected by the magnetic image identification sensor, achieving identification of information of the credit card or the image of the banknote. The magnetic image identification sensor generally adopts an audio magnetic head technology or a magnetoresistive head technology. The audio magnetic head uses a coil to wind a ring-like structure with a gap, which uses the principle of electromagnetic induction. A magnetic flux change occurs when the gap rapidly passes through the magnetic particles, and thus an induction current is induced in the coil and distribution signals of magnetic images are established according to changes to the current. Main problems existing in the technology are as follows: 1. the magnetic field sensitivity is low, and only with a method of increasing the number of turns can an effective signal be obtained; 2. the size is large, the size resolution is low, rapid movement is required, and there is no response to static magnetic field signals; and 3. the power consumption is large. The magnetoresistive head, for example, a Hall effect sensor, mainly has the following problems: 1) the Hall effect sensor has low magnetic field sensitivity, and therefore, for magnetic particle detection, a large enough bias magnetic field is required to generate sufficient magnetization intensity so as to be detected by a magnetic sensor, and thus the volume of a financial magnetic head is increased; and 2) the Hall effect sensor has low magnetic field sensitivity, generates low magnetic field output signals, and also has high power consumption. In addition, whether the audio magnetic head technology or the magnetoresistive head technology is adopted, when several magnetic sensors are employed to implement detection on large-scale magnetic images, a form of arranging the magnetic sensors into rows and columns is generally used; as a result, there are undetected areas between adjacent magnetic sensors, and undetected areas are present in the resultant image identification. 
       SUMMARY OF THE INVENTION 
       [0003]    In order to solve the above existing problems, a magnetoresistive magnetic imaging sensor for identifying a magnetic image is provided in the present invention, which uses a magnetoresistive sensor, for example, a TMR magnetic sensor, to implement detection on magnetic nano-particle images of banknotes; TMR sensors have characteristics of high magnetic field sensitivity, small size and low power consumption, and chips can be arranged in a staggered or stacked manner, so as to overcome the above problems. 
         [0004]    A magnetoresistive magnetic imaging sensor for identifying a magnetic image provided in the present invention is used for detecting a magnetic image, the plane where the magnetic image is located being a magnetic image detection surface, the sensor including a lateral/front detection mode image identification sensor; the lateral/front detection mode image identification sensor includes several magnetoresistive sensor chips on a PCB, respectively; each side face of the several magnetoresistive sensor chips of the lateral detection mode image identification sensor is parallel to the magnetic image detection surface; front surfaces of the several magnetoresistive sensor chips of the front detection mode image identification sensor are parallel to the magnetic image detection surface; 
         [0005]    and the adjacent magnetoresistive sensor chips are complementary to or intersect with each other in scanning detection areas along a scanning direction on the magnetic image detection surface. 
         [0006]    The adjacent magnetoresistive sensor chips corresponding to the front detection mode image identification sensor are arranged, in a mutually staggered manner, along edges of the magnetoresistive sensor chips in the front surface of the PCB. 
         [0007]    One side of each of the several magnetoresistive sensor chips on the PCB corresponding to the lateral detection mode image identification sensor is cocked away from the front surface of the PCB, and the other side is obliquely stacked with one side of each of the adjacent magnetoresistive sensor chips. 
         [0008]    The adjacent magnetoresistive sensor chips in the several magnetoresistive sensor chips on the PCB corresponding to the lateral detection mode image identification sensor are on-chip staggered and stacked. 
         [0009]    A permanent magnet assembly is included; magnetic sensing directions of the several magnetoresistive sensor chips of the front detection mode image identification sensor are parallel to the scanning direction, while magnetic sensing directions of the several magnetoresistive sensor chips of the lateral detection mode image identification sensor are perpendicular to the magnetic image detection surface. 
         [0010]    The permanent magnet assembly includes two permanent magnets having the same magnetization direction which are symmetrically located on two sides of the PCB along the scanning direction respectively, and the magnetization direction is perpendicular to the front surface of the PCB. 
         [0011]    For the lateral detection mode image identification sensor, the permanent magnet assembly includes two permanent magnets symmetrically placed on two sides of the front surface of the PCB, magnetization directions thereof are both perpendicular to the magnetic image detection surface, but the magnetization directions of the two permanent magnets are opposite. 
         [0012]    For the lateral detection mode image identification sensor, the permanent magnet assembly includes a permanent magnet and a soft magnet located on two sides of the front surface of the PCB respectively, the magnetization direction of the permanent magnet is perpendicular to the direction of the front surface of the PCB, and the soft magnet is parallel to the front surface of the PCB. 
         [0013]    For the lateral detection mode image identification sensor, the permanent magnet assembly includes a structure having an opening towards the magnetic image detection surface and formed by a permanent magnet and an L-shaped soft magnet, which are located on the same side of the PCB, and the L-shaped soft magnet is located between the permanent magnet and the PCB. The permanent magnet is located on the bottom of the L-shaped soft magnet and the magnetization direction thereof is perpendicular to the magnetic image detection surface, and a side face of the L-shaped soft magnet is parallel to the PCB. 
         [0014]    For the lateral detection mode image identification sensor, the permanent magnet assembly includes a structure having an opening towards the magnetic image detection surface and formed by a permanent magnet and two soft magnets, wherein the magnetization direction of the permanent magnet is perpendicular to the front surface of the PCB, the permanent magnet is located at the bottom of the PCB, and the two soft magnets are symmetrically located on two sides of the front surface of the PCB and two ends of the permanent magnet, and are parallel to the PCB. 
         [0015]    For the front detection mode image identification sensor, the permanent magnet assembly is a concave permanent magnet, wherein a surface of the concave permanent magnet provided with a groove directly faces the back surface of the PCB, the grooving direction is parallel to the magnetic image detection surface and perpendicular to the magnetic sensing directions, and the magnetization direction of the concave permanent magnet is perpendicular to the direction of the PCB. 
         [0016]    For the front detection mode image identification sensor, the permanent magnet assembly includes a back permanent magnet on the back surface of the PCB and two side permanent magnets symmetrically placed on two sides of the PCB along the scanning direction, wherein magnetization directions of the back permanent magnet and the two side permanent magnets are all perpendicular to the magnetic image detection surface, and the magnetization directions of the back permanent magnet and the two side permanent magnets are opposite. 
         [0017]    Magnetic sensing directions of the several magnetoresistive sensor chips of the front detection mode image identification sensor are parallel to or perpendicular to the direction of the magnetic image detection surface, and when the magnetic sensing directions of the several magnetoresistive sensor chips are parallel to the magnetic image detection surface, the magnetic sensing directions are parallel to or perpendicular to the scanning direction. 
         [0018]    The magnetoresistive sensor chips are a half-bridge structure including two, three or four magnetic sensing units arranged into two rows and one column, three rows and one column, or two rows and two columns respectively, and magnetic sensing directions of the various magnetic sensing units are identical; when the magnetoresistive magnetic sensor chips include two magnetic sensing units, the two magnetic sensing units have the same resistance and directly form a half bridge; when the magnetoresistive magnetic sensor chips include three magnetic sensing units, the resistance of the sensing unit in the middle row is half of the resistances of the two sensing units on two side rows, and the two sensing units on the two side rows, after being connected in parallel, form a half-bridge structure with the sensing unit in the middle row; when the magnetoresistive magnetic sensor chips include four magnetic sensing units, resistances of the four sensing units are the same, and two magnetic sensing units in the same row are connected in parallel and then the two rows are connected in series to form a half-bridge structure; in the lateral detection mode image identification sensor, the column direction thereof is perpendicular to the magnetic image detection surface, and during packaging, the magnetic sensing units are located on one side of the chips close to the magnetic image detection surface; and in the front detection mode image identification sensor, the column direction thereof is parallel to the scanning direction. 
         [0019]    The magnetoresistive sensor chips are a full-bridge structure including four magnetic sensing units, and magnetic sensing directions of the various magnetic sensing units are identical, the four magnetic sensing units are arranged into two rows and two columns, two sensing units included in two half bridges forming a full bridge are located in two rows but in different columns respectively; in the lateral detection mode image identification sensor, the column direction thereof is perpendicular to the magnetic image detection surface, and during packaging, the sensing units are located on one side of the chips close to the magnetic image detection surface, and in the front detection mode image identification sensor, the column direction thereof is parallel to the scanning direction. 
         [0020]    The magnetoresistive sensor chips of the half-bridge structure are a single magnetoresistive sensor chip integrated with several sensing units, or an interconnected combination of discrete elements of several magnetoresistive sensor chips integrated with one or more sensing units. 
         [0021]    The magnetoresistive sensor chips of the full-bridge structure are a single magnetoresistive sensor chip integrated with several sensing units, or an interconnected combination of discrete elements of several magnetoresistive sensor chips integrated with one or more sensing units. 
         [0022]    The magnetoresistive sensor chips are of a packaging structure adopting a front bonding pad or a TSV via a back bonding pad of the magnetoresistive sensor chips for wirebonding. 
         [0023]    A housing may be further included, in which the PCB and the several magnetoresistive sensor chips are placed; the permanent magnet assembly is partially or wholly placed in the housing, or wholly located outside the housing. 
         [0024]    The magnetic sensing units in the magnetoresistive magnetic sensor chips are one of AMR, Hall, GMR or TMR type magnetoresistive sensor. 
         [0025]    Each side face of the magnetoresistive sensor chips corresponding to the lateral detection mode image identification sensor is coplanar with a side face of the PCB or parallel to the magnetic image detection surface. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]      FIG. 1  is a diagram of a lateral detection mode image identification sensor; 
           [0027]      FIG. 2  is a schematic diagram of a first permanent magnet assembly used in the lateral detection mode image identification sensor; 
           [0028]      FIG. 3  is a schematic diagram of a second permanent magnet assembly used in the lateral detection mode image identification sensor; 
           [0029]      FIG. 4  is a schematic diagram of a third permanent magnet assembly used in the lateral detection mode image identification sensor; 
           [0030]      FIG. 5  is a schematic diagram of a fourth permanent magnet assembly used in the lateral detection mode image identification sensor; 
           [0031]      FIG. 6  is a schematic diagram of a fifth permanent magnet assembly used in the lateral detection mode image identification sensor; 
           [0032]      FIG. 7  is a spaced arrangement diagram of magnetoresistive magnetic sensor chips on a PCB in a lateral detection mode; 
           [0033]      FIG. 8  is a first on-chip stacked arrangement diagram of the magnetoresistive magnetic sensor chips on the PCB in the lateral detection mode; 
           [0034]      FIG. 9  is a second on-chip stacked arrangement diagram of the magnetoresistive magnetic sensor chips on the PCB in the lateral detection mode; 
           [0035]      FIG. 10  is a third on-chip stacked arrangement diagram of the magnetoresistive magnetic sensor chips on the PCB in the lateral detection mode 
           [0036]      FIG. 11  is a diagram of a front detection mode image identification sensor; 
           [0037]      FIG. 12  is a schematic diagram of a first permanent magnet assembly used in the front detection mode image identification sensor; 
           [0038]      FIG. 13  is a schematic diagram of a second permanent magnet assembly used in the front detection mode image identification sensor; 
           [0039]      FIG. 14  is a schematic diagram of a third permanent magnet assembly used in the front detection mode image identification sensor; 
           [0040]      FIG. 15  is a spaced arrangement diagram of magnetoresistive magnetic sensor chips on a PCB in a front detection mode; 
           [0041]      FIG. 16  is a first staggered arrangement diagram of magnetoresistive sensor chips on a substrate in the front detection mode; 
           [0042]      FIG. 17  is a second staggered arrangement diagram of the magnetoresistive sensor chips on the substrate in the front detection mode; 
           [0043]      FIG. 18  is a front view of a slice of a magnetoresistive sensor chip; 
           [0044]      FIG. 19  is a side view of a slice of the magnetoresistive sensor chip; 
           [0045]      FIG. 20  is a back view of a slice of the magnetoresistive sensor chip; 
           [0046]      FIG. 21  is a schematic structural diagram of a magnetoresistive magnetic sensor: a) a half-bridge structure; b) a full-bridge structure; c) a double half-bridge structure; and d) a three-element half-bridge structure; 
           [0047]      FIG. 22  is an arrangement diagram of sensing units on a magnetoresistive sensor chip in a lateral detection mode: a) a half-bridge structure; b) a full-bridge or double half-bridge structure; and c) a three-element half-bridge structure; and 
           [0048]      FIG. 23  is an arrangement diagram of sensing units on a magnetoresistive sensor chip in a front detection mode: a) a half-bridge structure; b) a full-bridge or double half-bridge structure; and c) a three-element half-bridge structure. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0049]    The present invention is described below in detail with reference to the drawings and embodiments. 
       Embodiment 1 
       [0050]      FIG. 1  is a structural diagram of a lateral detection mode image identification sensor, including a PCB  1  and several magnetoresistive sensor chips  2 . A surface having a greater area on the PCB  1  is its front surface  1 ( 2 ), while a surface adjacent to the front surface  1 ( 2 ) is its side face  1 ( 1 ), and the direction of the front surface  1 ( 2 ) of the PCB  1  is generally referred to as the direction of the PCB  1  Similarly, the magnetoresistive sensor chips  2  also have their front surfaces and side faces  2 ( 1 ). The several magnetoresistive sensor chips  2  are located on the front surface  1 ( 2 ) of the PCB  1 , and the front surface  1 ( 2 ) of the PCB  1 , where the magnetoresistive sensor chips  2  are located, is perpendicular to a magnetic image detection surface  3 . The magnetic image detection surface  3  is a plane where an image to be scanned and detected is located. Each side face  2 ( 1 ) of the several magnetoresistive sensor chips  2  may be or not be coplanar with the side face  1 ( 1 ) of the PCB  1  close to the magnetic image detection surface  3  but is parallel to and close to the magnetic image detection surface  3  as much as possible, magnetic sensing directions  7  of the several magnetoresistive sensor chips  2  are perpendicular to the magnetic image detection surface  3 , and  4  in  FIG. 1  is a scanning direction. The lateral detection mode magnetoresistive image identification sensor of the structure may be directly used for reading magnetic images made of permanent magnet materials, for example, it may be used in a magnetic head in a POS machine to read a permanent magnet strip on a credit card. 
       Embodiment 2 
       [0051]      FIGS. 2-6  are schematic structural diagrams when a lateral detection mode image identification sensor is applied to reading magnetic images formed by soft magnetic materials, and further includes a permanent magnet assembly  5  and a housing  6 . The housing  6  covers the outside of the PCB  1  and the several magnetoresistive magnetic sensor chips  2 , and the permanent magnet assembly  5  may be wholly located in the housing  6  and may also be partially located in the housing  6  or wholly located outside the housing  6 ; for ease of description,  FIGS. 2-6  only present the situation where the permanent magnet assembly  5  is wholly located in the housing  6 . The function of the permanent magnet assembly  5  is to generate a magnetic field to magnetize soft magnetic materials in a magnetic image detection surface  3  made of the soft magnetic materials, to enable the soft magnetic materials to be detected by the several magnetoresistive magnetic sensor chips  2 . The function of the housing  6  is to protect the magnetoresistive sensor chips  2  and the PCB  1 . That the permanent magnet assembly  5  is wholly or partially located outside the housing  6  can reduce the volume of the image identification sensor. 
         [0052]    The permanent magnet assembly  5  in the lateral detection mode image identification sensor shown in  FIG. 2  includes two permanent magnets  5 ( 1 ) and  5 ( 2 ) which are symmetrically located at two sides of the front surface  1 ( 2 ) of the PCB  1  and have the same magnetization direction, wherein the magnetization direction is perpendicular to the front surface  1 ( 2 ) of the PCB  1 . 
         [0053]    The permanent magnet assembly  5  in the lateral detection mode image identification sensor shown in  FIG. 3  includes two permanent magnets  5 ( 3 ) and  5 ( 4 ) which are symmetrically located at two sides of the front surface  1 ( 2 ) of the PCB  1  and have anti-parallel magnetization directions, wherein their magnetization directions are parallel to magnetic sensing directions  7  of the several magnetoresistive sensor chips  2 , that is, perpendicular to the magnetic image detection surface  3 . 
         [0054]    The permanent magnet assembly  5  in the lateral detection mode image identification sensor shown in  FIG. 4  includes a permanent magnet  5 ( 5 ) and a soft magnet  5 ( 6 ) which are located at two sides of the PCB  1  respectively, wherein the magnetization direction of the permanent magnet  5 ( 5 ) is perpendicular to the front surface  1 ( 2 ) of the PCB  1 , while the soft magnet  5 ( 6 ) is parallel to the front surface  1 ( 2 ) of the PCB  1 . 
         [0055]    The permanent magnet assembly  5  in the lateral detection mode image identification sensor shown in  FIG. 5  includes a permanent magnet  5 ( 7 ) and an L-shaped soft magnet  5 ( 8 ). The permanent magnet  5 ( 7 ) and the L-shaped soft magnet  5 ( 8 ) are located at the same side of the PCB  1 , and a gap facing the magnetic image detection surface  3  is formed between the permanent magnet  5 ( 7 ) and the L-shaped soft magnet  5 ( 8 ). The L-shaped soft magnet  5 ( 8 ) is located at one side close to the PCB  1 , and has a side portion and a bottom portion perpendicular to each other. The side portion of the L-shaped soft magnet  5 ( 8 ) is parallel to the permanent magnet  5 ( 7 ), and the bottom portion of the L-shaped soft magnet  5 ( 8 ) is perpendicular to the front surface  1 ( 2 ) of the PCB  1 . The magnetization direction of the permanent magnet  5 ( 7 ) is parallel to the magnetic sensing direction  7 , and the permanent magnet  5 ( 7 ) is located on the bottom portion of the L-shaped soft magnet  5 ( 8 ) so as to form the gap facing the magnetic image detection surface  3 . 
         [0056]    The permanent magnet assembly  5  in the lateral detection mode image identification sensor shown in  FIG. 6  includes a permanent magnet  5 ( 9 ) and soft magnets  5 ( 10 ) and  5 ( 11 ). The soft magnets  5 ( 10 ) and  5 ( 11 ) are located on two ends of the permanent magnet  5 ( 9 ), are symmetrically distributed at two sides of the front surface  1 ( 2 ) of the PCB  1 , and are parallel to the PCB  1 , and the permanent magnet  5 ( 9 ) is located at the bottom of the PCB  1 . A gap formed between the soft magnets  5 ( 10 ) and  5 ( 11 ) is opened towards the magnetic image detection surface  3 , and the magnetization direction of the permanent magnet  5 ( 9 ) is perpendicular to the front surface  1 ( 2 ) of the PCB  1 . 
       Embodiment 3 
       [0057]      FIGS. 7-10  are arrangement diagrams of the several magnetoresistive sensor chips  2  in the side mode image identification sensor on the PCB 1 . 
         [0058]    All the magnetoresistive sensor chips  2  in  FIG. 7  are arranged into one row on the PCB  1 ,  FIG. 7( a )  is a side view,  FIG. 7( b )  is a front view, side faces  2 ( 1 ) of the magnetoresistive sensor chips  2  are arranged sequentially along a side face  1 ( 1 ) of the PCB  1 , and there are gaps among them or the gaps are 0. Such an arrangement method has the following disadvantages: even if in the situation where the gaps are 0, in the presence of packaging materials, scanning detection areas  2 ( 30 ) and  2 ( 31 ) formed on the magnetic image detection surface  3  by adjacent magnetoresistive sensor chips  2  along the scanning direction  4  do not intersect with each other, and thus it is impossible to form continuous detection areas in the scanning direction; therefore, there are undetected areas in the detection of the magnetic image. 
         [0059]    In  FIGS. 8-10 , new arrangement methods of the magnetoresistive sensor chips  2  on the PCB  1  are provided with respect to the problem of the existence of undetected areas of the magnetic image in  FIG. 7 , that is, the magnetoresistive sensor chips  2  are arranged on the PCB  1  in a manner of enabling scanning detection areas formed on the magnetic image detection surface  3  by adjacent magnetoresistive sensor chips  2  along a scanning direction to be complementary to or intersect with each other; the arrangements are specifically as follows. 
         [0060]    The first arrangement method of the magnetoresistive sensor chips  2  that can be employed is as follows: the adjacent magnetoresistive sensor chips  2  are on-chip staggered and stacked. As shown in  FIG. 8  and  FIG. 9 , on the basis of sequential arrangement of the side faces  2 ( 1 ) of a first layer of magnetoresistive sensor chips  2  along the side face  1 ( 1 ) of the PCB  1 , as shown in  FIG. 7 , a second layer of magnetoresistive sensor chips  2  are added, which are located on the first layer of magnetoresistive sensor chips  2 , and each magnetoresistive sensor chip  2  is located in an area between two adjacent magnetoresistive sensor chips  2  in the first layer, so as to form a staggered and stacked structure, such that scanning detection areas  2 ( 32 ) and  2 ( 33 ) formed by the two adjacent magnetoresistive sensor chips  2  in the scanning direction  4  are areas complementary to or overlapping with each other, thus ensuring that there is no undetected area in the detection of the magnetic image during scanning. 
         [0061]    The second arrangement method of the magnetoresistive sensor chips  2  that can be employed is as follows: the adjacent magnetoresistive sensor chips  2  are obliquely on-chip stacked. In  FIG. 10 , one side of each magnetoresistive sensor chip  2  is cocked away from the front surface  1 ( 1 ) of the 
         [0062]    PCB  1 , while the other side is on the PCB  1 , that is, each magnetoresistive sensor chip  2  is disposed obliquely, such that, in the adjacent magnetoresistive sensor chips  2 , a non-cocked side of one magnetoresistive sensor chip  2  is obliquely stacked with a cocked side of the other magnetoresistive sensor chip  2  at an edge, thus ensuring that scanning detection areas  2 ( 34 ) and  2 ( 35 ) formed by the adjacent magnetoresistive sensor chips  2  in the scanning direction  4  have overlapping areas and guaranteeing that there is no undetected area in the detection of the magnetic image during scanning. 
       Embodiment 4 
       [0063]      FIG. 11  shows a structure of a front detect mode image identification sensor, including a PCB  11  and several magnetoresistive sensor chips  21 , wherein the several magnetoresistive sensor chips  21  are located on a front surface  11 ( 2 ) of the PCB  11 , and front surfaces  21 ( 2 ) thereof are parallel to a magnetic image detection surface  3 . If the front detect mode image identification sensor is applied to detection of a hard magnet, the magnetic sensing direction thereof may be parallel or perpendicular to the magnetic image detection surface  3 , and when the magnetic sensing direction is parallel to the magnetic image detection surface  3 , the direction may be parallel or perpendicular to a scanning direction  4 . When a magnetic image is formed by a hard magnet, a magnetic field generated by the hard magnet will act on the magnetoresistive sensor chips  21  and convert their magnetic field distribution features along the scanning direction  4  to electric signals, thus achieving reading of the magnetic image. 
       Embodiment 5 
       [0064]      FIGS. 12-14  show application of the front detection mode image identification sensor in detection of a magnetic image made of a soft magnetic material. 
         [0065]    The front detection mode image identification sensor shown in  FIGS. 12-14  further includes a permanent magnet assembly  51  and a housing  6 . 
         [0066]    The PCB  11  and the several magnetoresistive sensor chips  21  are located in the housing  6 , and the permanent magnet assembly  51  may be located in the housing  6  and may also be partially or wholly located outside the housing  6 ; the latter may be conducive to reduction of the size of the image identification sensor. In the presence of the permanent magnet assembly  51 , magnetic sensing directions  71  of the magnetoresistive sensor chips  21  are identical with the scanning direction  4  and parallel to the magnetic image detection surface  3 . 
         [0067]    The permanent magnet assembly  51  in the front detection mode image identification sensor shown in  FIG. 12  is a concave permanent magnet, of which the geometrical structure is a rectangular groove provided on an upper surface of a block. On the PCB  11  of the front detection mode image identification sensor, a surface having a greater area and opposite to the front surface  11 ( 2 ) is its back surface. An upper surface of the concave permanent magnet directly faces the back surface of the PCB  11  and is directly in contact with the back surface of the PCB  11 , the magnetization direction of the concave permanent magnet is perpendicular to the front surface  11 ( 2 ) of the PCB  11 , and the penetration direction of the rectangular groove, that is, the grooving direction, is perpendicular to the scanning direction  4  and parallel to the magnetic image detection surface  3 . 
         [0068]    The permanent magnet assembly  51  in the front detection mode image identification sensor shown in  FIG. 13  includes two permanent magnets  51 ( 1 ) and  51 ( 2 ) which are symmetrically located on two sides of the magnetoresistive sensor chips  21  along the scanning direction  4  respectively, wherein magnetization directions thereof are perpendicular to the magnetic image detection surface  3  and the front surface  11 ( 2 ) of the PCB  11 , and the magnetization directions are the same. 
         [0069]    The permanent magnet assembly  51  in the front detection mode image identification sensor shown in  FIG. 14  includes three permanent magnets  51 ( 3 ),  51 ( 4 ) and  51 ( 5 ), wherein two permanent magnets  51 ( 3 ) and  51 ( 4 ) are symmetrically distributed on two sides of the magnetoresistive sensor chips  21  along the scanning direction  4 , which are referred to as side permanent magnets, and their magnetization directions are the same and are perpendicular to the magnetic image detection surface  3 ; another permanent magnet  51 ( 5 ) is located directly below the PCB  11 , that is, the back surface, which is referred to as a back permanent magnet, and its magnetization direction is reverse-parallel to the permanent magnets  51 ( 3 ) and  51 ( 4 ). 
       Embodiment  6   
       [0070]      FIGS. 15-17  are arrangement diagrams of several magnetoresistive sensor chips  21  of the front detection mode image identification sensor on the PCB  11 . 
         [0071]      FIGS. 15( a ) and 15( b )  are a side view and a front view respectively, in which the magnetoresistive sensor chips  21  are arranged into one row on the PCB  11 , and the direction of the row is perpendicular to the scanning direction  4  or the magnetic sensing directions  71 . In the presence of the packaging material in the magnetoresistive sensor chips  21 , even if the gap between the adjacent magnetoresistive sensor chips  21  is 0, scanning detection areas  21 ( 30 ) and  21 ( 31 ) formed on the magnetic image detection surface  3  by the adjacent magnetoresistive sensor chips  21  along the scanning direction  4  do not intersect with each other, and thus there are undetected areas on the magnetic image detection surface  3 . 
         [0072]    In order to make up for the problem of undetected areas,  FIG. 16  and  FIG. 17  improve the arrangement method of the magnetoresistive sensor chips  21  on the PCB  11 . 
         [0073]    An arrangement method of the magnetoresistive sensor chips  21  that can be employed is as follows: on the front surface  11 ( 2 ) of the PCB  11 , the adjacent magnetoresistive sensor chips  21  are arranged in a manner that edges are mutually staggered.  FIGS. 16( a ) and 16( b )  are a side view and a front view of one arrangement method respectively, the scanning direction  4  and the magnetic sensing directions  71  of the magnetoresistive sensor chips  21  are the same, the magnetoresistive sensor chips  21  are disposed obliquely on the front surface  11 ( 2 ) of the PCB  11 , the adjacent magnetoresistive sensor chips  21  are arranged in a staggered manner, and edges of the magnetoresistive sensor chips  21  are mutually staggered, such that scanning detection areas  21 ( 32 ) and  21 ( 33 ) formed on the magnetic image detection surface  3  by the adjacent magnetoresistive sensor chips  21  along the scanning direction  4  can overlap with each other, which solves the problem of missed detection. 
         [0074]      FIGS. 17( a ) and 17( b )  are a side view and a front view of another arrangement method respectively, a third magnetoresistive sensor chip  21  is inserted in a middle position of the row direction of two adjacent magnetoresistive sensor chips  21  and overlaps with the two adjacent magnetoresistive sensor chips  21  at edges, such that scanning detection areas  21 ( 34 ) and  21 ( 35 ) of the adjacent magnetoresistive sensor chips  21  overlap with each other, thereby solving the problem of missed detection. 
         [0075]      FIGS. 18-20  are a front view, a side view and a back view of wafer slices of the magnetoresistive sensor chips in the above embodiments. It can be seen that the magnetoresistive sensor chips each include a magnetic sensing unit  42 , the magnetoresistive sensing unit  42  is in the front surface of a Si slice  41 , and a signal and power pin  43  may be located in the front surface of the Si slice  41  and is led out through wirebonding; a pin  45  may also be formed on the back surface of the Si slice  41  by passing through the Si slice  41  via a TSV via  44 . That is, the magnetoresistive sensor chips are of a packaging structure adopting a front bonding pad or a TSV via a back bonding pad of the magnetoresistive sensor chips for wirebonding. The connection between upper and lower layers of magnetoresistive sensor chips  2  in  FIG. 9  may be implemented by connecting onto the PCB  1  through wirebonding, or by direct connection via a pin between the front surface and the back surface. In the front detection mode image identification sensor, employing a TSV back pin, compared with the front wirebonding, can reduce a detection distance between the magnetoresistive sensor  21  and the magnetic image detection surface  3  and increase magnetic field intensity. 
         [0076]      FIG. 21  is a composition structure diagram of the magnetic sensing unit  42  in the magnetoresistive sensor chip  2  or  21 , and  FIG. 21( a )  shows a half-bridge structure including two sensing units R 1  and R 2 . The two sensing units R 1  and R 2  are arranged into two rows and one column, and the two magnetic sensing units R 1  and R 2  have the same resistance and directly form a half bridge.  FIG. 21( b )  shows a full-bridge structure including four sensing units R 1 , R 2 , R 3  and R 4  and having two outputs Vout+ and Vout−. The four magnetic sensing units R 1 , R 2 , R 3  and R 4  are arranged into two rows and two columns. Two sensing units included in two half bridges forming a full bridge are located in two rows but in different columns respectively. In the lateral detection mode image identification sensor, the column direction thereof is perpendicular to the magnetic image detection surface  3 , and during packaging, the sensing units are located on one side of the chips close to the magnetic image detection surface  3 . In the front detection mode image identification sensor, the column direction thereof is parallel to the scanning direction  4 .  FIG. 21( c )  shows a half-bridge structure including four sensing units R 1 , R 2 , R 3  and R 4  arranged into two rows and two columns, two magnetic sensing units in the same row are connected in parallel, and then the two rows are connected in series to form a half-bridge structure; two half bridges R 1 , R 2  and R 3 , R 4  share a power source respectively and are grounded, but have a common output end.  FIG. 21( d )  shows a three-sensing-element half-bridge structure arranged into three rows and one column, including three sensing units R 1 , R 2  and R 3 , wherein two sensing units R 1  and R 3  located in two side rows have the same resistance, and the resistance is twice that of the sensing unit R 2  in the middle row, the sensing units R 1  and R 3  are connected in parallel and then connected in series with R 2  to form a half bridge, and output signal voltages are output from a common end in the middle of R 1 , R 2  and R 3 . The magnetoresistive sensing units may be one of TMR, Hall, AMR or GMR unit. Magnetic sensing directions of various magnetic sensing units are the same. 
         [0077]      FIG. 22  is an arrangement diagram of sensing units in the magnetoresistive sensor chips  2  of the lateral detection mode image identification sensor. 
         [0078]      FIG. 22( a )  shows a half-bridge structure, wherein sensing units R 1  and R 2  form an arrangement of two rows and one column, R 1  is located in one row close to the magnetic image detection surface  3  and parallel to the magnetic image detection surface  3 , R 2  is located in the other row, their magnetic sensing directions are the same and are both in directions  71 , the column direction is perpendicular to the magnetic image detection surface  3 , and  4  is a scanning direction. 
         [0079]      FIG. 22( b )  shows a full-bridge structure or two half-bridge structures, wherein sensing units R 1 -R 4  are arranged into two rows and two columns, wherein R 1  and R 3  are located in one row close to the magnetic image detection surface  3 , R 2  and R 4  are located in the other row, R 1  and R 2  form a half bridge, and R 3  and R 4  form a half bridge. 
         [0080]      FIG. 22( c )  shows a three-resistor half-bridge structure including three sensing units R 1 , R 2  and R 3  arranged into a structure of three rows and one column, wherein R 1  is located in one row close to the magnetic image detection surface  3 , R 2  is located between R 1  and R 3 , and magnetic sensing directions of R 1 , R 2  and R 3  are directions  71  and perpendicular to the magnetic image detection surface  3 , and  4  is a scanning direction. 
         [0081]    In the TMR magnetic sensor chip  2  or  21  corresponding to  FIG. 22 , during packaging, the sensing units R 1 , R 2 , R 1 -R 4  or R 1 -R 3  are located on one side close to the magnetic image detection surface  3 . 
         [0082]      FIG. 23  is an arrangement diagram of sensing units in the magnetoresistive sensor chips  21  of the front detection mode image identification sensor, wherein  FIGS. 23 ( a   1 ),  23 ( a   2 ) and  23 ( a   3 ) are side views, 
         [0083]      FIGS. 23 ( b   1 ),  23 ( b   2 ) and  23 ( b   3 ) are front views of the chips  21 , and the scanning direction is  4 .  FIG. 23 ( b   1 ) shows a half-bridge structure including two sensing units R 1  and R 2 , and their arrangement directions are parallel to the sensing directions  71  and identical to the scanning direction  4 .  FIG. 23 ( b   2 ) shows a full-bridge structure, R 1  and R 2  are corresponding to one bridge arm therein, R 3  and R 4  are corresponding to the other bridge arm, and R 1 , R 2  and R 3 , R 4  are arranged along the sensing directions  71 .  FIG. 23 ( b   3 ) shows a three-element half-bridge structure, the sensing units R 1 , R 2  and R 3  are arranged into rows along the scanning direction  4 , R 2  is located between R 1  and R 3 , and magnetic sensing directions of R 1 -R 3  are  71 . The contour of the chips  21  in  FIG. 23  is a parallel arrangement structure relative to the sensing units, and when the chips are obliquely superposed and arranged, the shape of the chips may rotate by a certain angle relative to arrangement of the sensing units. 
         [0084]    It should be noted that the magnetoresistive sensor chips of the full-bridge structure or half-bridge structure may be a single magnetoresistive sensor chip integrated with several sensing units, and may also be replaced with discrete elements of several magnetoresistive sensor chips. For the latter, discrete magnetoresistive sensor chips are integrated with one or more sensing units, and the discrete magnetoresistive sensor chips form a half-bridge or full-bridge structure through interconnection. 
         [0085]    In addition, when an image formed by a hard magnet is detected in  FIG. 23 , magnetic sensing directions of the sensing units of the magnetoresistive sensor  21  may be parallel or perpendicular to the magnetic image detection surface  3 , and when the magnetic sensing directions are parallel to the magnetic image detection surface  3 , the direction thereof may be parallel to or perpendicular to the scanning direction  4 .