Patent Abstract:
A sensor with unique floating magnet based on magnetic levitation, which can be used for multiple purposes, such as fall detection, tilting monitor and vibration measurement, is proposed. The manufacture method of making such a sensor is also given along with the fall detection methodology.

Full Description:
FIELD OF INVENTION 
       [0001]    The invention is related to sensor, which can be used for fall detection, digital tilting angle measurement respect to local gravity, digital pulse/vibration measurement with great sensitivity. The sensor can be made in volume production with proposed manufacture process disclosed in this patent. 
       BACKGROUND ART 
       [0002]    Fall detection is very important and has widely applications in older care, patient care, child care, disable care as well as safety for outdoor sports event. To develop a reliable fall detection system has huge market potential and great society impact. Conventional fall detection system is designed to detect whether a real fall event happens by matching falling acceleration data with pre-set models or thresholds using enormous different kinds of algorithm. However, a random fall event depends on actual situation and prior falling movement of the host. It is too complicated to have a precise model to mimic the real event. Despite of great efforts, there is no a successful product existing on the market with great impact. The present invention resolves this dilemma by directly measuring/sensing the relative position/orientation between the host body and direction of gravity at the spot where a falling event happens. 
         [0003]    Related to fall detection, measuring the tilt angle respect to local gravity is also very useful. Currently, tilting angle is also indirectly measured with reference to local gravity or ground mostly through measuring acceleration via an accelerometer. 
         [0004]    Detecting vibration with great sensitivity also has many applications. Conventionally, vibration detection is carried out by accelerometer (e.g. piezoelectric sensor or capacitive sensor), velocity sensor (e.g. electromagnetic linear velocity transducer), proximity probes (e.g. capacitance or eddy current), or laser displacement sensor. In this invention, a brand new sensor is proposed, which can be used to fulfill the requirements for the above mentioned tilt sensor or vibration sensor applications. Several embodiments of the designs with respective sensitivity are proposed. 
       SUMMARY OF THE INVENTION 
       [0005]    A new type of sensors, which has multiple applications such as fall detection, dynamic tilting detection, and vibration detection, is disclosed. Several alternative designs of sensor with different sensitivity have been given. The manufacture processes, using semiconductor wafer process together with MEMS technology, have been described. This makes low-cost large scale manufacture of this type of sensors feasible. 
         [0006]    The sensor, having strong preferred uniaxial, can be used to detect the vibration of the membrane or the hard surface along its preferred axle. Based on this sensor, a new class of sonar technology can be developed. 
         [0007]    With additional coil design for energy harvesting as an energy source, this invention becomes a self-powered multi-purpose sensor. 
         [0008]    Coupled with wireless technology, it can be used as a basic key component for large scale wireless sensor network. 
         [0009]    Deploying in large scale in buoyant state in the targeted depth in middle of the sea this sensor can be used to detect earthquake as well as tsunami in the deep sea as part of alarming system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1A  illustrates the relative orientation of host body at normal walking position with respect to local gravity direction, which can be detected by special designed sensor. 
           [0011]      FIG. 1B  illustrates the relative orientation of host body at fall down position with respect to local gravity direction, which can be detected by special designed sensor. 
           [0012]      FIG. 2A  illustrates one of the embodiments for the proposed sensor design. 
           [0013]      FIG. 2B  illustrates the dynamic response of the output emf voltage of the magnetic flux pickup coil  218  shown in  FIG. 2A  to the host body&#39;s movement. 
           [0014]      FIG. 2C  illustrates the dynamic response of the capacitance of the capacitor  205  shown in  FIG. 2A  to the host body&#39;s movement. 
           [0015]      FIG. 3  illustrates one of the embodiments of sensor similar to that shown in  FIG. 2  but with additional permanent magnet. 
           [0016]      FIG. 4A  illustrates one of the embodiments of the proposed sensor design. 
           [0017]      FIG. 4B  illustrates the bird eye view of an AMR sensor used as the transducer  404  in  FIG. 4A . 
           [0018]      FIG. 4C  illustrates the bird eye view of a GMR sensor used as the transducer  404  in  FIG. 4A . 
           [0019]      FIG. 4D  illustrates the detailed zoom-in cross section view of a TMR sensor used as the transducer  404  in  FIG. 4A . 
           [0020]      FIG. 4E  illustrates the bird eye view of the TMR sensor cut along the line A-A′ in  FIG. 4D . 
           [0021]      FIG. 5  illustrates one of the embodiments of sensor similar to that shown in  FIG. 4A  but with additional permanent magnet. 
           [0022]      FIG. 6A  shows a 3-sensors assembly that the sensors are assembled along 3 orthogonal X, Y and Z directions with front view on left and top view on right. All sensors come from design  FIG. 2A ,  FIG. 3 ,  FIG. 4A  or  FIG. 5 . 
           [0023]      FIG. 6B  illustrated a typical output from transducer of one sensor shown in  FIG. 6A  in time domain. 
           [0024]      FIG. 6C  illustrate the calibrated curve between the tilting angle of the sensor with respect to local gravity direction and the transducer mean output voltage from the sensor. 
           [0025]      FIG. 7  illustrates wafer process to form the proposed sensor with the bottom magnet built on wafer. 
           [0026]      FIG. 8  illustrates a more cost friendly approach with the bottom magnet built in packaging component using conventional mechanical machining. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    The following description is provided in the context of particular designs, applications and the details, to enable any person skilled in the art to make and use the invention. However, for those skilled in the art, it is apparent that various modifications to the embodiments shown can be practiced with the generic principles defined here, and without departing the spirit and scope of this invention. Thus, the present invention is not intended to be limited to the embodiments shown in this disclosure, but is to be accorded the widest scope consistent with the principles, features and teachings disclosed here. 
         [0028]      FIGS. 1A and 1B  illustrates a fall detection mechanism by sensing the relative position or orientation change of host body with the direction of local gravity at the event of fall. The host can be anything such as a human, a robot, a ladder or a vehicle, whose fall is our major concern. The orientation of the host&#39;s body center-line can be used as a general reference for the body orientation of the host. It would be extremely reliable for a fall detection system to sensor only the change of the host&#39;s body center-line respective to the direction of local gravity, and ignore the details happened during the fall event. 
         [0029]    In the particular scenario described here, the host is a human  101 , whose spine  105  is used as a reference for the orientation of the human body.  FIGS. 1A and 1B  describes the situations before and after fall happens, respectively. It is quite noticeable that, regardless of the details of how the fall happens and the details of the speed or the acceleration before and after fall, the direction of local gravity  104  is not changed. However, the relative orientation between the host body ( 105 ) and direction of gravity ( 104 ), shown here as the angle between  105  and  104 , has changed after fall happens. 
         [0030]    Shown in  FIG. 1A  and  FIG. 1B , a proposed sensor  102  is fixed on the waist of human body, whose orientation  103  parallel to the human body  105  is kept without change before and after fall. The change of the proposed sensor&#39;s orientation  103  respective to the direction of local gravity  104  precisely represents the orientation change of the host body  105  respective to the direction of local gravity  104 . Hence, it would be extremely reliable to detect a fall event by sensing the change of the proposed sensor&#39;s orientation  103  respective to the direction of local gravity  104  and ignoring the details happened during the fall event. 
         [0031]      FIG. 2A  illustrates one of the embodiments for the proposed sensor design. The sensor comprises a bottom permanent magnet  201  (e.g. either a continue magnetic film or patterned magnet); an optional non-magnetic space layer  202 ; a hollow space in form of tube  203  formed within the dielectric matrix  204 ; a small permanent magnet  206 , with coating layer  209  for reducing the friction between the magnet  206  and side wall of tube  203 , floating inside tube  203 ; a lid  208  on top of the tube  203  to prevent the magnet  206  from moving out of the tube  203 ; and a pair of electrodes  205 , which forms a capacitance sensor and locates in the vertical equilibrium position of magnet  206  when the center line  217  of tube  203  parallel to direction of local gravity  215 . The magnetization  212  of the permanent magnet (or magnetic layer)  201  is aligned to be opposite to the magnetization  213  of the small magnet  206 . The magnet  206  floats vertically inside tube  203  due to the magnetostatic repelling force  214  applied on magnet  206  from the permanent magnet  201  against the gravity  215  of the magnet  206  shown in  FIG. 2A  when the center line  217  of tube  203  parallel to direction of local gravity  215 . Any interference or disturbing due to external magnetic field is shielded by the soft magnetic shield  216  around the sensor. 
         [0032]    The capacitance between the pair of electrodes  205  is proportional to EA/d, while A is the facing area of the two electrodes  205 , d is the distance of the two electrodes, and E is permittivity of material between the electrodes. The medium  207  filled inside the tube  203  can be air, a kind of gas, a kind of liquid, or even vacuum. The position of the magnet  206  in stable state inside the tube  203  varies with the orientation of the tube  203  respect to the gravity  215 . Hence, the capacitance between the pair of electrodes  205  in stable state varies too with the orientation of the tube  203  respect to the gravity  215 . The break of the force balance applied on the magnet  206 , such as during falling, vibrating, or tilting, etc., will drive the magnet  206  away from its vertical equilibrium position inside the tube  203 , resulting in the capacitance change between the pair of electrodes  205  due to the change of permittivity E. The dynamic response of the capacitance sensor can be used to detect a falling, tilting or vibrating event. Specially, the capacitance sensor can be used to sense a falling event by detecting the directional change of the center line  217  respect to the gravity  215 . Multiple of capacitance sensor pairs can be arranged along the tube  203  to precisely detect the displacement of magnet  206  from its vertical equilibrium position inside tube  203  during the fall; and thus they can work together to define and characterize the fall event. 
         [0033]    The coil  218  with optional soft magnetic core  221  is used to pick up the change of the magnetic flux within the coil  218  due to the move of the floating magnet  206 .  FIG. 2A  shows one arrangement of the magnetic flux pickup coil  218 . It locates on the top left side of the tube  203 ; and the axis of the coil  218  and its soft magnetic core  221  is perpendicular to the axis of the tube  217 . The axis of the coil  218  and its soft magnetic core  221  can also be parallel to the axis of the tube  217 . The magnetic flux pickup coil  218  can have different arrangements relative to the tube  203 , such as on top of the tube  203 , or on the right of the tube  203 . The magnetic flux pickup coil  218  can also place at different latitude along the tube  203 . The magnetic flux change within the magnetic pickup coil  218  is determined by the change of the floating magnet  206  position inside the tube  203 ; and the rate of the magnetic flux change is determined by the moving velocity of the floating magnet  206 . According to Faraday&#39;s law, the output of the electromotive force (emf) voltage between the two leads  219  and  220  of the coil  218  is proportional to the rate of the magnetic flux change within the coil. Hence, any movement of the floating magnet  206  inside the tube  203  will trigger the dynamic output response of the coil&#39;s emf voltage. 
         [0034]    For the application as a fall sensor, the device is tightly attached on the host body, and the centerline  217  of the sensor is always parallel to the centerline  105  of the host body shown in  FIG. 1  before and after fall. Any host body&#39;s movement will cause the dynamic responses of the coil sensor  218  and capacitor sensor  205  shown in  FIG. 2B  and  FIG. 2C , respectively. As shown in  FIG. 2B , the output emf voltage of the coil sensor  218  breaks the pre-set threshold level (dash line), and dramatically increases at the beginning of the host body falling down due to large acceleration. It gradually drops down to below the pre-set threshold level at the end of the host body falling. For capacitor sensor  205 , it has two distinct stable capacitance levels, i.e., calibrated vertical and horizontal capacitances respect to local gravity direction. The capacitance of the capacitor sensor  205  changes from its calibrated vertical level to its calibrated horizontal level when the host body falls down as shown in  FIG. 2C . Continuously monitoring capacitor sensor  205  is not an economical operation mode due to its nature of energy consuming. Instead, as an economic operation mode, the fall sensor device continuously monitors the response of the coil sensor  218 . The capacitor sensor  205  is used only at the end of a falling event detected by the coil sensor  218  to check whether the fall indeed happens or not. This approach is certainly the most reliable method to determine and sense the fall event. 
         [0035]    All the structures and features shown here in  FIG. 2A  can be made by semiconductor process together with MEMS process, which is well known in the field. Therefore, volume manufacture as well as size reduction of the sensor become feasible with low cost. 
         [0036]      FIG. 3  illustrates one of the embodiments of sensor similar to that shown in  FIG. 2A  but with additional top permanent magnet  301 . The magnetization  302  of the top permanent magnet  301  has the same direction as the magnetization  212  of the bottom permanent magnet  201 , and is opposite to the magnetization  213  of the small magnet  206  inside the tube  203  shown in  FIG. 2A . The magnetostatic force  303  pushing the small magnet inside the tube away from the top lid  304  prevents the small magnet inside the tube from touching (e.g. avoid noise generation) and sticking to the top lid  304 . Moreover, this kind of design provides extra knobs to tune the sensitivity of the sensor by adjusting the position and/or strength of the magnet  301 . 
         [0037]      FIG. 4A  illustrates one of the embodiments of the proposed sensor design. The layout of the sensor shown in  FIG. 4A  is very much similar to what is shown in  FIG. 2A . A bottom hard magnet  401  provides expelling magnetostatic force on the floating magnet  406  in the tube  403  to balance its gravity. The proposed sensor design shown in  FIG. 2A  detects the change rate of the magnetic flux within the magnetic flux pickup coil  218 . The design shown in  FIG. 4A  is quite noticeably different from that shown in  FIG. 2A . The solid magnetic field transducer  404  is used to detect the magnetic field strength regardless whether the magnetic field varies or not as long as the frequency of magnetic field variation is below a threshold value (e.g. GHz), which is well above the frequency we are interested in during fall event or the proposed applications. The magnetic field strength sensed by the solid magnetic field transducer  404  has a close correlation with the exact position of the floating magnet  406  in the tube  403  once the relative position of the transducer  404  to the tube  403  is fixed. Any movement of the floating magnet  406  inside the tube  403  will change the magnetic field strength that can be detected by the solid magnetic field transducer  404 . The solid magnetic field transducer  404  can be a Hall sensor, a magneto-impedance (MI) sensor, a reed sensor, an anisotropic magnetoresistive sensor (AMR), a giant magnetoresistive sensor (GMR), or a tunneling magnetoresistive sensor (TMR). The top of the tube  403  over the lid  407  is the best location for Hall Effect magnetic field transducer  404 . For the proposed sensor design shown in  FIG. 4A , the magnetic field strength sensed by the solid magnetic field transducer  404  can be enhanced by the optional structure of flux guide  402 , which collects the magnetic flux from the floating magnet  406 . Again, the electrodes  405  forms a capacitor sensor, which has the same function as that shown in  FIG. 2A . The capacitor sensor  405  is an optional design feature since the field sensor alone is able to detect the all fall events. 
         [0038]    For the application as a fall sensor, the device is tightly attached on the host body, and the centerline  408  of the sensor is always parallel to the centerline  105  of the host body shown in  FIG. 1  before and after the fall. Any host body&#39;s movement, which could lead to potential fall event, will change the magnetic field strength. The change is detected by the transducer  404 , and results in the oscillation output from the transducer  404 . Depending on exact detecting algorithm, the frequency of the oscillation output, the amplitude variation (peak-to-peak value), or both together can be used to detect the fall event. The output changes of the transducer  404  from “above the pre-set threshold levels” to “below the pre-set threshold levels” indicate that either a real fall event or any possible event that could lead to possible falling has finished. The capacitor sensor  405  is used at the end of a falling event detected by the transducer  404  to check whether the fall indeed happens or not. 
         [0039]    Actually, the field transducer  404  itself can be used alone to detect whether the fall indeed happens or not. As mentioned above, the field transducer  404  detects the magnetic field strength that is determined by the position of the floating magnet  406  inside the tube  403 . Similar as the capacitor sensor  405 , the field transducer  404  has two distinct stable outputs corresponding to the orientations of the tube  403  parallel or perpendicular to the gravity. At the end of any possible event, the field transducer  404  will have one stable output. By checking the final stable output of the field transducer  404 , it can be relatively easy to deduce whether the fall indeed happens or not. 
         [0040]      FIG. 4B  to  FIG. 4E  describe three types of magnetoresistive sensors used as the transducer  404  in  FIG. 4A . 
         [0041]      FIG. 4B  illustrates the bird eye view of an AMR sensor used as the transducer  404  in  FIG. 4A . The optional flux guide  411  concentrates incoming magnetic flux  415  towards AMR sensor  410  for improving its sensitivity. The AMR sensor  410  comprises two leads  413 ; AMR sensor stack  412 , which has its sensing current  416  (indicated here by dash line) flowing between leads  413 . The magnetization of the magnetic layer of AMR sensor stack  412 , representing here by arrow  414 , has a pre-fixed angle with the direction of the sensing current  416  in the absence of the external magnetic field. Any change of the magnetic field, due to the movement of the floating magnet  406  in  FIG. 4A , leads to the change of the angle between the magnetization  414  and current  416  thus the output voltage of the AMR sensor  410  between leads  413 . Therefore, the transducer based on AMR sensor described here is capable of detecting the movement as well as final location of the floating magnet  406  in  FIG. 4A . 
         [0042]      FIG. 4C  illustrates the bird eye view of a GMR sensor used as the transducer  404  in  FIG. 4A . The optional flux guide  421  concentrates incoming magnetic flux  425  towards GMR sensor  420  for improving its sensitivity. The GMR sensor  420  comprises two leads  423 ; GMR sensor stack  422 , which has its sensing current  426  (indicated here by dash line) flowing between leads  423 . The magnetization of the magnetic layer of GMR sensor stack  420 , representing here by arrow  424 , is aligned parallel with the sensing current  426  in the absence of the external magnetic field. Any change of the magnetic field, due to the movement of the floating magnet  406  in  FIG. 4A , leads to the change of the angle between the magnetization  424  and current  426  thus the output voltage of the GMR sensor  420  between leads  423 . Therefore, the transducer based on GMR sensor described here is capable of detecting the movement as well as final location of the floating magnet  406  in  FIG. 4A . 
         [0043]      FIG. 4D  illustrates the detailed zoom-in cross section view of a TMR sensor used as the transducer  404  in  FIG. 4A . The optional flux guide  431  is identical to the flux guide  402  shown in  FIG. 4A . The TMR sensor  435  comprises bottom lead  433 , TMR stack  434  and top lead  432 . 
         [0044]      FIG. 4E  illustrates the bird eye view of the TMR sensor cut along the line A-A′ in  FIG. 4D . 
         [0045]    The optional flux guide  443  concentrates incoming magnetic flux  444  towards TMR sensor  445  for improving its sensitivity. The TMR sensor  445  represents here by TMR free layer  441 , which has its sensing current being perpendicular to the sensor free layer  441  flowing between lead  433  and  432  shown in  FIG. 4D . The free layer  441  of TMR sensor  445  is aligned to the direction perpendicular to the potential incoming flux in the absence of the external field, and the alignment represents here by the arrow  442 . 
         [0046]    Any change of the magnetic field, due to the movement of the floating magnet  406  in  FIG. 4A , leads to the change of the magnetization direction of the TMR free layer  441  resulting in the output voltage change between the electrodes  432  and  433  in  FIG. 4D . Therefore, the transducer based on TMR sensor described here is capable of detecting the movement as well as final location of the floating magnet  406  in  FIG. 4A . 
         [0047]    Using TMR sensor as the transducer  404  in  FIG. 4A  can greatly increase the sensitivity of the proposed sensor. The TMR ratio can be as high as ˜600%, which is similar to a big built-in hardware amplifier. The proposed ultra-high sensitivity TMR sensor illustrated here has significant advantages to detect very weak vibration of the surface, or very small angle titling such as building wall tilting. As a basic build sensing unit, it can construct a new type of sonar. 
         [0048]      FIG. 5  to  FIG. 4A  is very much similar to the relationship between  FIG. 3  to  FIG. 2A .  FIG. 5  illustrates one of the embodiments of sensor similar to that shown in  FIG. 4A  but with additional top permanent magnet  501 . The magnetization  502  of the top permanent magnet  501  has the same direction as the magnetization of the bottom permanent magnet  401 , and is opposite to the magnetization of the small magnet  406  inside the tube  403  shown in  FIG. 4A . The magnetostatic force  503  as shown by the arrow pushing away the floating magnet  406  shown in  FIG. 4A  from the top lid  504  prevents the floating magnet from contacting and sticking to the top lid  504 . Moreover, this kind of design provides extra knobs to tune the sensitivity of the sensor by adjusting the position and/or strength of the magnet  501 . 
         [0049]      FIG. 6A  shows a 3-sensors assembly. The sensors are chosen from above designs ( FIG. 2A ,  FIG. 3 ,  FIG. 4A  or  FIG. 5 ). Sensor  601 ,  610  and  620  are assembled along 3 orthogonal X, Y and Z directions, respectively, which are isolated from each other to avoid their interferences. It is up to the assembly application on the choices of these 3 sensors designs. 
         [0050]    This kind of assembly configuration can be used for lots of applications. For example, the assembly can be used to monitor high building&#39;s tilting as well as the building&#39;s response to the local wind or earthquake in all directions. A typical output of one sensor is shown in  FIG. 6B  in time domain, and its corresponding tilting angle can be calibrated shown in  FIG. 6C . All signals coming from 3 orthogonal directions can be used to monitor the high building&#39;s status, and detect its responses to the local wind or earthquake in all directions. Based on this technology, it is easy and economical to establish a sensor network inside the high building to monitor its safety, and set up its storm or earthquake emergency system. 
         [0051]    This kind of sensor assembly can be used for athletic training too. Athlete&#39;s performance can be in-suit monitored and evaluated when lots of assemblies are attached on the athlete&#39;s body. 
         [0052]    More sophistically, the dynamic information obtained by this kind of sensor assembly can be analyzed to detect all directions&#39; vibrations. Hence, a new type of sonar can be constructed based on this technology to detect earthquake or tsunami. 
         [0053]      FIG. 7  is a schematic of the fabrication flow in wafer process to make one sensor proposed in  FIG. 2A  and  FIG. 4A . It is easy to economically produce large volume of the devices in matured semiconductor/MEMS volume manufacture environment. Right side of drawings in  FIG. 7  are the device project views at different key steps, and left side of drawings are the device cross section views along line B-B′ in its project view drawings. 
         [0054]    Firstly, the permanent magnet  702  with perpendicular magnetic anisotropy is built on the incoming wafer substrate  701 . The material of the permanent magnet  702  can be sputtered alloy thin film, such as CoCrPt, CoPt, CoZrCrPt, etc., or sputtered multilayer film stack, such as Co/Cr, Co/Pt, Co/Pd, etc., or plated CoPt, CoNiMnP, CoNiReP, CoNiP film with proper seeding. The permanent magnet  702  can be a continue film or a patterned structure  702  shown in the Step  1  of  FIG. 7 . For the patterned permanent magnet  702 , wafer surface has to be flatted for subsequent structure fabrications after the pattern formation. It can be carried out by a chemical mechanical planarization (CMP) process. Usually, SiO2 is chosen as the backfilled dielectric material  703  for wafer planarization. 
         [0055]    The incoming substrate  701  can be ceramic wafer, glass wafer, plastic wafer, or normal semiconductor wafer such as normal Si wafer. Usually, normal semiconductor wafer is used as the material of the substrate  701 . The Application-Specific Integrated Circuit (ASIC) for the sensor will be built-in first with proper electrical connections on the substrate  601 . A special diffusion prohibited layer (diffusion barrier layer, such as Ni, W, Ta 2 O 5 .) will be deposited on top of the ASIC layer before the sensor fabrication to avoid any metallic contamination on the ASIC. For simplicity the electrical connections of the top sensor with the bottom ASIC are not included here. For other people familiar with semiconductor and MEMS wafer process, this can be done fairly easy. 
         [0056]    Upon the formation of the permanent magnet  702  and surface planarization, a patterned sacrificial structure  704  shown in the Step  2  of  FIG. 7  is built on the top surface of the permanent magnet  702  by semiconductor/MEMS microfabrication process, i.e., thin film deposition, photolithography pattern definition, and final pattern transfer by reactive ion etching (RIE), or photolithography pattern definition, thin film deposition, and final pattern formation by left-off process. The sacrificial structure  704  is enclosed by the backfill dielectric material  705 , and planarized by CMP. The sacrificial structure  704  will be etched away later by a solution, leaving the backfill dielectric material  705  to form the 1st section (bottom) of the sensor&#39;s tube. The etching solution should not attack both the backfill dielectric material  705  and the bottom permanent magnet  702 . In this disclosure, Al 2 O 3  and SiO 2  are used for sacrificial and backfill dielectric materials, respectively, unless stated otherwise. 
         [0057]    Next shown in Step  3  of  FIG. 7 , the Al 2 O 3  sacrificial structure  706  surrounded by few hundred nanometers to a few or tens micrometers thick SiO2 material  707  is made first to form the 2nd section of the sensor&#39;s tube geometry, which is aligned with the 1st section (bottom)  704 . And then, a pair of electrodes  708  is patterned and plated to form the capacitor sensor. The capacitor sensor is protected by the backfilled SiO2 material, and planarized by CMP. 
         [0058]    Following the formation of the capacitor sensor, the small structure with hard magnet  709  is patterned and plated on the top of the sacrificial structure  706  shown in Step  4  of  FIG. 7 . Their centerlines are aligned together. The small hard magnet  709  is enclosed by Al 2 O 3  sacrificial material  710 ; and the 3rd section of the sensor&#39;s tube is formed by backfilling SiO 2  material and CMP. PVD deposited Co alloy or plated CoPt can be used to make the small hard magnet  709  to ensure their coercivity H c  are significantly different from that of the permanent magnet  702  from magnetics point of view. 
         [0059]    The transducer  712 , the optional magnetic flux guide  713 , and the 4th sacrificial feature  714  are built by semiconductor/MEMS microfabrication process in Step  5  of  FIG. 7 . The sacrificial feature  714  is aligned with its bottom feature  709 . They are protected by backfilled SiO 2  material  715 . The surface is flatted by CMP for subsequent layer fabrication. 
         [0060]    The sacrificial feature  716  built on the top of the 4th sacrificial feature  714  enclosed by backfilled SiO 2  material  719  will form the top section of the sensor&#39;s tube shown in Step  6  of  FIG. 7 . Both sacrificial features  716  and  714  are aligned together. After surface planarization, an addition sacrificial feature  717  and a sacrificial ring pattern  718  are built on the top of the feature  716 . The sacrificial features  717  and  718  will be used to release the small hard magnet  709  after subsequently backfilled SiO2 material  720  and CMP. Finally, the sensor is sealed by depositing top layer SiO 2  material  621  after the release of the small hard magnet  709  by etching away all sacrificial materials in NaOH or KOH solution shown in Step  7  of  FIG. 7 . 
         [0061]    For sensors proposed in  FIG. 3  and  FIG. 5 , one more process step is needed to make a permanent magnet ( 301  in  FIG. 3 and 500  in  FIG. 5 ) on top of the sensor. 
         [0062]    Once the completion of the sensor fabrication magnetization alignments have to be performed in order to reach desirable magnetization directions. All 3 magnets (top and bottom permanent magnets and small floating hard magnet) will be aligned magnetically first in the same direction by applying a large magnetic field to along the long axle of the sensor tube. Then a smaller reversed magnetic field is applied to flip the magnetic orientation of the magnet(s) with lower coercivity (H c ) without disturbing the magnetic orientation of the magnet(s) with much higher coercivity so that the floating hard magnet and bottom or/and top magnet have opposite magnetization orientations. 
         [0063]    Alternatively, the manufactures of bottom permanent magnet ( 201  in  FIG. 2A and 401  in  FIG. 4A ) and the top permanent magnet ( 301  in  FIG. 3 and 501  in  FIG. 5 ) can be separated from the wafer process described above. As shown in  FIG. 8 , they can be made economically by classical massive mechanical machining alone, and packaged together with the sensor&#39;s key components fabricated by volume wafer processes described above. 
         [0064]      FIG. 8  shows the whole package of the multi-purpose sensor including the bottom packaging frame  801 , top packaging frame  802  and sensor body  803 . The bottom packaging frame  801  comprises main body  804 , non-magnetic bottom separation layer  805 , bottom permanent magnet  806 , bottom enclosing structure  808 , bottom male mating connector  809 , and solder pad  810 . The top packaging frame  802  comprises main body  814 , non-magnetic top separation layer  815 , optional top permanent magnet  817 , top enclosing structure  811 , top female mating connector  812 , and solder pad  813 . From system reliability and stability points of view, soft magnetic material is preferred for the frame components of  804 ,  808 ,  809 ,  811 , and  814  to shield the external magnetic field away from the sensor as well as to form a closed magnetic loop to further stabilize the internal magnetic configuration. The bottom and top magnetizations  807  and  816  are set in the same direction, which is opposite to that of the small floating hard magnet in the tube before the completion of the sensor packaging assembly. There are only one pair of mating connectors and one pair of solder pads shown in  FIG. 8 . On the really system, there are multiple pairs of mating connectors as well as solder pads to ensure solid packaging and closed magnetic loop formation.

Technology Classification (CPC): 6