Patent Description:
<CIT> and discloses a magnetic field sensor which includes built in self-test circuits that allow a self-test of most of, or all of, the circuitry of the magnetic field sensor, including self-test of a magnetic field sensing element used within the magnetic field sensor, while the magnetic field sensor is functioning in normal operation.

<CIT> discloses a magnetic field sensor including a diagnostic circuit that allows a self-test of most of or all of, the circuitry of the magnetic field sensor, including a self-test of a magnetic field sensing element used within the magnetic field sensor.

<CIT> discloses a method for determining an excitation conductor distance from a magnetic field sensor, and a method of calibrating the magnetic field sensor.

<CIT> discloses a magnetic-field sensor adapted to detect an external magnetic field, including a magnetoresistive structure for detection of the external magnetic field, and a magnetic-field generator magnetically coupled to the magnetoresistive structure.

<CIT> discloses a magnetic field sensor integrated in a semiconductor chip. The chip and a magnetic field source e.g. a permanent magnet or a magnetic coil connected with a power supply terminal, are arranged relative to each other in a preset position in an enclosed material, such that the magnetic field produced by the source is detected by the sensor.

<CIT> discloses a magnetic field sensor for a sensor module, which has a magnetoresistive sensor element mounted on a lead frame.

<CIT> discloses a magnetic sensor which is small and low in cost and power consumption. A coil for bias and a coil for negative feedback are integrated with a magnetic impedance element having a magnetic impedance effect by using resin or the like, and the magnetic reluctance between the element and the coils is reduced so as to apply a bias magnetic field and a negative feedback magnetic field with less power consumption.

<CIT> discloses a Hall sensor integrated on a semiconductor chip. A first insulating layer covers the surface of the substrate of the chip, and a metal loop mounted on the insulating layer overlaps the area forming the Hall element. A second insulating layer covers the metal loop and a covering layer of a ferromagnetic material overlies the entire structure.

<CIT> discloses a semiconductor device including a housing defining a cavity, a magnetic sensor chip disposed in the cavity, and mold material covering the magnetic sensor chip and substantially filling the cavity. One of the housing or the mold material is ferromagnetic, and the other one of the housing or the mold material is non-ferromagnetic.

<CIT>, published after the priority date of the present application, discloses a magnetic field sensor including a lead frame, a die supporting a magnetic field sensing element and attached to the lead frame, a non-conductive mold material enclosing the die and a portion of the lead frame, and optionally a ferromagnetic mold material secured to a portion of the non-conductive mold material. The hard or soft ferromagnetic mold material may be tapered and includes a non-contiguous central region, as may contain a separately formed element.

<CIT> relates to a methodology for manufacturing a sensor module including providing a substrate comprising an array of magnetically sensitive elements on a first main face of the substrate. An array of conducting lines is applied over the first main face of the substrate. An array of electrical interconnects is applied over the first main face of the substrate. The substrate is singulated after application of the electrical interconnects.

<CIT> relates to an integrated circuit including a magnetic sensor that comprises a region of conductive material operable to receive a current from a current source and to conduct the current through the region of conductive material. At least one conductive node is electrically connected to the region of conductive material and is operable to allow measurement of a differential voltage arising due to a magnetic field acting on the region of conductive material. A copper conductor is disposed adjacent the region of conductive material such that a current through the copper conductor generates a magnetic field.

In one aspect of the invention, a magnetic field sensor IC package, comprises: a sensing element, an analog circuit path coupled to the sensing element for generating an output voltage proportional to a magnetic field applied to the sensing element, a coil in proximity to the sensing element, the coil having a first terminal that is accessible to provide a direct electrical connection to the coil from external to the magnetic field sensor IC package, wherein the coil is configured to carry a current to generate a magnetic field having an intensity corresponding to a level of the current; and characterized by a threshold module; a device; a diagnostic module; a control module; and a switch, wherein the threshold module is coupled to the diagnostic module and configured to provide a normal operation threshold and a diagnostic threshold, wherein: during a normal operation, a voltage from the sensing element is compared with the normal operation threshold using the device and an output of the normal operation comparison is received by the control module, wherein the control module is configured to control the switch for generating the output voltage based on the normal operation comparison output, and during a diagnostic testing, a voltage from the sensing element is compared to the diagnostic threshold using the device and an output of the diagnostic testing comparison is received by the control module, wherein the control module is configured to control the switch for generating the output voltage based on the diagnostic testing comparison output.

The magnetic field sensor can further include one or more of the following features: the sensing element comprises a magnetic sensing element, the magnetic sensing element comprises a Hall element, the magnetic sensing element comprises a magnetoresistance element, the integrated circuit comprises a linear current sensor, the magnetic field sensor comprises a closed loop magnetic sensor, the coil is located on an opposite side of the lead frame from the die and enclosed in an over molded package, and/or the coil is located on the opposite side of the lead frame from the die and enclosed in a housing.

In another aspect of the invention, a magnetic field sensor IC package, comprises: a lead frame having a first surface and a second opposing surface, a semiconductor die having a first surface in which a magnetic field sensing element is disposed and a second opposing surface attached to the first surface of the lead frame, a non-conductive mold material enclosing the die and at least a portion of the lead frame, a conductive coil secured to the non- conductive mold material, wherein the coil has at least one terminal that is accessible to provide a direct electrical connection to the coil from external to the magnetic field sensor IC package, wherein the coil is configured to carry a current to generate a magnetic field having an intensity corresponding to a level of the current; and characterized by a threshold module; a device; a diagnostic module; a control module; and a switch, wherein the threshold module is coupled to the diagnostic module and configured to provide a normal operation threshold and a diagnostic threshold, wherein: during a normal operation, a voltage from the sensing element is compared with the normal operation threshold using the device and an output of the normal operation comparison is received by the control module, wherein the control module is configured to control the switch for generating an output voltage based on the normal operation comparison output, and during a diagnostic testing, a voltage from the sensing element is compared to the diagnostic threshold using the device and an output of the diagnostic testing comparison is received by the control module, wherein the control module is configured to control the switch for generating the output voltage based on the diagnostic testing comparison output.

The sensor can further include one or more of the following features: the non-conductive mold material encloses the coil, a second mold material, the second mold material is ferromagnetic, and/or a housing encloses said coil.

The foregoing features of this invention, as well as the invention itself, may be more fully understood from the following description of the drawings in which:.

Exemplary embodiments of the invention provide a magnetic field sensor with external control of an on chip coil for generating a magnetic field for diagnostic/self test functionality, calibration, and/or back bias applications. In some embodiments, such conductive coils are formed on the semiconductor die itself. With this arrangement, a user can control a signal on the coil to meet the needs of a particular application. While exemplary embodiments of the invention are shown and described as having particular configurations, elements, and functions, it is understood that embodiments of the invention are applicable to magnetic field sensors in general in which external control of an internal coil is desirable.

In one aspect of the invention, magnetic sensor provides external control of an on chip coil to enable self-testing of a device to improve functional safety levels. Access to the coil also facilitates the manufacture of a closed loop sensor without the need to procure and assemble a compensation coil into a finished assembly.

As is known in the art, IS026262 is a specification for automotive OEMs directed to improving functional safety and achieving higher overall quality levels and lower field failure rates. Providing test modes for functional parameters of an IC in accordance with exemplary embodiments of the invention allows users to implement testing procedures at various stages of manufacture and use, such as after installation in an automobile. Thus, an IC can be tested after installation to ensure proper functioning. Providing test modes also improves functional safety in safety critical applications, such as accelerator pedal positioning. For example, a linear Hall IC having test functionality in accordance with exemplary embodiments of the invention can communicate that the IC is operating properly through self-test processing, which improves the functional safety of the entire throttle system.

In additional embodiments, an on chip coil with externally accessible terminals allows users of the magnetic sensor ICs to apply diagnostic magnetic fields to the sensing element to verify proper operation of the IC on an as needed basis, for example. In one embodiment having a closed loop system, accuracy of the system is increased by nearly eliminating the effects of sensitivity drift over temperature. In exemplary embodiments of the invention, an on-chip coil is used in a closed loop magnetic sensor.

<FIG> shows an exemplary sensor <NUM>, shown as a current sensor linear device, having externally accessible terminals 102a,b for a coil <NUM> proximate a magnetic sensing element <NUM> not in accordance with the claimed invention. The device <NUM> has an analog output voltage VOUT that is proportional to an applied magnetic field. In one embodiment, the device has a linear output that starts at Vcc/<NUM> and swings in a more positive or negative direction depending on the polarity of the applied field. With this arrangement, a user can control a current through the coil <NUM> via the terminals 102a,b to stimulate the sensing element <NUM> for diagnostic testing.

The sensor IC senses current in a manner well known in the art. In general, a magnetic field sensing element, such as a Hall element <NUM>, generates a voltage in response to an applied magnetic field. A dynamic offset cancellation module <NUM> 'chops' the signal and a signal recovery module <NUM> provides an output signal. Exemplary current sensing is shown and described for example, in <CIT>, and U. Patent Publication No. <CIT>. It is understood that other techiques can be used to meet the needs of a particular application.

As shown in FIG. 1A, which has some commonality with <FIG>, threshold module <NUM> provides a reference voltage to a device <NUM> under the control of a diagnostic module <NUM>. In the illustrative embodiment, the threshold module <NUM> provides a normal operation threshold and a diagnostic threshold under the control of the diagnostic module <NUM>. A control module <NUM> receives the output to control a switch <NUM> for generating the output voltage VOL. A current limit module <NUM> coupled to the control module <NUM> and the switch <NUM>.

The magnetic field sensing element <NUM> in this and other embodiments can be, but is not limited to, a Hall effect element, a magnetoresistance element, or a magnetotransistor. As is known, there are different types of Hall effect elements, for example, a planar Hall element, a vertical Hall element, and a Circular Vertical Hall (CVH) element. As is also known, there are different types of magnetoresistance elements, for example, a semiconductor magnetoresistance element such as Indium Antimonide (InSb), a giant magnetoresistance (GMR) element, an anisotropic magnetoresistance element (AMR), a tunneling magnetoresistance (TMR) element, and a magnetic tunnel junction (MTJ). The sensing element <NUM> may include a single element or, alternatively, may include two or more elements arranged in various configurations, e.g., a half bridge or full (Wheatstone) bridge. Depending on the device type and other application requirements, the sensing element <NUM> may be a device made of a type IV semiconductor material such as Silicon (Si) or Germanium (Ge), or a type III-V semiconductor material like Gallium-Arsenide (GaAs) or an Indium compound, e.g., Indium-Antimonide (InSb).

As is known, some of the above-described magnetic field sensing elements tend to have an axis of maximum sensitivity parallel to a substrate that supports the magnetic field sensing element, and others of the above-described magnetic field sensing elements tend to have an axis of maximum sensitivity perpendicular to a substrate that supports the magnetic field sensing element. In particular, planar Hall elements tend to have axes of sensitivity perpendicular to a substrate, while metal based or metallic magnetoresistance elements (e.g., GMR, TMR, AMR) and vertical Hall elements tend to have axes of sensitivity parallel to a substrate.

As used herein, the term "magnetic field sensor" is used to describe a circuit that uses a magnetic field sensing element, generally in combination with other circuits. Magnetic field sensors are used in a variety of applications, including, but not limited to, an angle sensor that senses an angle of a direction of a magnetic field, a current sensor that senses a magnetic field generated by a current carried by a current-carrying conductor, a magnetic switch that senses the proximity of a ferromagnetic object, a rotation detector that senses passing ferromagnetic articles, for example, magnetic domains of a ring magnet, and a magnetic field sensor that senses a magnetic field density of a magnetic field.

Exemplary embodments of the invention are appliable to a variety of sensing applications having a range of sensing elements. Exemplary sensors include magnetic field, for example automotive speed and position sensors, current sensors, or package scale NMR devices for use in chemical or biological applications. Exemplary embodiments of the invention are applicable to a wide range of applications in which sensing magnetic fields generated by moving magnets or flowing current are desirable. For example, exemplary embodiments of the invention are useful for performing diagnostic functions for a device installed in an automobile in safety critical applications.

In safety critical applications it is desirable to improve the safety integrity level (SIL) of the sensor, such as by using self-test diagnostics. As described more fully below, in exemplary embodiments of the invention, the analog signal path of a sensor can be stimulated and evaluated. In one embodiment, output accuracy of the device over temperature can be enhanced.

<FIG> shows a sensor <NUM> including a sensing element <NUM>, such as a Hall element, having a coil <NUM> wrapped around the sensing element, which generates an output voltage Vout that is proportional to a magnetic field on the sensing element. In one embodiment, the coil <NUM> is disposed around the Hall element <NUM> on the silicon. The coil <NUM> has a first terminal <NUM> that is externally accessible to allow connection to any suitable signal generator. In the illustrated embodiment of <FIG>, a second terminal <NUM> of the coil is coupled to ground. In the alternate embodiment shown in <FIG>, the second terminal <NUM>' is externally controllable.

<FIG> are shown as a Single In-line Package (SIP) with four leads with the coil taking one additional pin. If the user can drive positive and negative currents into this single pin then they will not require a device with access to both pins. One pin can be tied to GND, as shown in <FIG>. If two pins are used for coil stimulation, as in <FIG>, then the user can drive currents in either direction with a single source by switching the connections of the terminals.

<FIG> shows an exemplary closed loop magnetic sensor <NUM> with a user-test circuit <NUM> attached. The analog output is fed into an amplifier circuit with supply voltages. The sensor output can be fed into a level shifter <NUM> and amplifier <NUM> in the user-test circuit <NUM> land then connected to the coil <NUM> on the device. In this way the amplifier <NUM> can apply a cancellation of the incident magnetic field generated by the application. It is understood that a wide variety of user-test circuits well known to one of ordinary skill in the art can be used. Exemplary applications for such a device include a moving magnet and a current flowing in a conductor that generates a magnetic field.

Current in the coil <NUM> stimulates the Hall element <NUM> at the front end of the sensing circuitry when current flows through the coil by generating a magnetic field. With this arrangement, the entire analog signal path can be tested.

By providing external control over the coil <NUM>, the analog signal path programmed sensitivity can be analyzed by the end user very accurately. By applying a constant current through the coil <NUM>, the magnetic field generated by the coil is fixed. This fixed magnetic field causes a deflection on the output of the analog output proportional to the gain of the analog signal path. Since the gain of the device is programmable and the coil is defined, the device can provide an accurate measurement of the analog signal path by the end user detecting the change in output voltage or output current in response to the applied coil stimulus or current.

Since a user can control the signal on the coil, certain failure modes can be forced to check for detection. In addition, the offset of the device in the offset cancellation module <NUM> can also be tested. Since the zero gauss field analog output voltage is programmed, the zero field output signal as well as the signal path gain can be self-tested with high accuracy. If it were to drift for some reason, the drift can be identified during the user-test.

With external control of the coil, a user can exercise the device to meet the needs of a particular application. For example, some users may want to do a quick functional check and other users may want to determine whether the sensitivity of the device is within some specified window.

It is understood that the ability to control a coil in a magnetic sensor is desirable for various applications. Coils are used in magnetic field sensors for various reasons, for example to generate a magnetic field for diagnostic or self test functionality as described above and in a <CIT>, for calibration as is described in a <CIT>, and/or for resetting a GMR magnetic field sensing element as described in a <CIT>, each of which is assigned to the Assignee of the subject application. In many instances, such conductive coils are formed on the semiconductor die itself.

In another aspect of the invention, a magnetic field sensor includes a coil with externally accessible terminals that functions as a back bias magnet, so as to provide a magnetic field which can be used to detect movement of a proximate target.

Referring to the cross-sectional view of <FIG>, and also to the cross-sectional views of <FIG> and <FIG>, a magnetic field sensor <NUM> includes a semiconductor die <NUM> having a first, active surface 314a in which a magnetic field sensing element or transducer <NUM> is formed and a second, opposing surface 314b attached to a die attach area <NUM> on a first surface 318a of a lead frame <NUM>, a non-conductive mold material <NUM> enclosing the die and at least a portion of the lead frame, and a ferromagnetic mold material <NUM> secured to the non-conductive mold material. The ferromagnetic mold material <NUM> comprises a ferromagnetic material and is tapered from a first end 330a proximate to the lead frame <NUM> to a second end 330b distal from the lead frame. A coil <NUM> is disposed in proximity to the magnet field sensing element <NUM>, as described more fully below. The active die surface 314a is opposite the die surface 314b which is attached to the die attach area <NUM> and thus, this configuration may be referred to as a "die up" arrangement. In other embodiments the die may be flip-chip attached or lead on chip attached, for example.

In use, the magnetic field sensor <NUM> like the other sensor embodiments described herein may be positioned in proximity to a moveable magnetically permeable ferromagnetic article, or target, such as the illustrated gear <NUM>, such that the magnetic field transducer <NUM> is adjacent to the article <NUM> and is thereby exposed to a magnetic field altered by movement of the article. The magnetic field transducer <NUM> generates a magnetic field signal proportional to the magnetic field.

While the magnetic field sensor <NUM> in <FIG> is oriented relative to the target <NUM> such that the transducer <NUM> is closer to the target than the ferromagnetic mold material <NUM>, it will be appreciated that it may be desirable in certain applications to rotate the sensor <NUM> by <NUM>° so that the ferromagnetic mold material is closer to the target than the transducer. Also, the sensor <NUM> may be rotated by <NUM>° so that the major face of the transducer is orthogonal to the target, thereby achieving a different type of magnetically sensitive sensor, as may be desirable when the transducer is a magnetoresistance element for example.

The ferromagnetic article <NUM> may be comprised of a hard ferromagnetic, or simply hard magnetic material (i.e., a permanent magnet such as a segmented ring magnet), a soft ferromagnetic material, or even an electromagnet and embodiments described herein may be used in conjunction with any such article arrangement.

In embodiments in which the article <NUM> is comprised of a soft ferromagnetic material, the ferromagnetic mold material <NUM> is comprised of a hard ferromagnetic material to form a bias magnet; whereas in embodiments in which the article <NUM> is comprised of a hard ferromagnetic material, the ferromagnetic mold material <NUM> may be soft ferromagnetic material to form a concentrator, or a hard magnetic material where a bias field is desired (for example, in the case of a magnetoresistance element that is biased with a hard magnetic material or permanent magnet). In other embodiments the mold material <NUM> may be a non-conductive and non-ferromagnetic mold material similar to the material for the first mold element <NUM>. In embodiments in which the ferromagnetic mold material <NUM> comprises a hard ferromagnetic material to form a bias magnet and in which the sensor <NUM> is oriented relative to the target such that transducer <NUM> is closer to the target than the ferromagnetic mold material <NUM> as shown, the bias magnet may be referred to as a back bias magnet.

The magnetic field sensor <NUM> generally includes additional circuitry formed in the active surface 314a of the die <NUM> for processing the magnetic field signal provided by the transducer <NUM>. The lead frame <NUM> includes leads 324a - 324c for coupling the circuitry to system components (not shown), such as a power source or microcontroller. Electrical connection between the leads 324a - 324c and the semiconductor die <NUM> can be provided with wire bonds 326a - 326c, respectively as shown. While the sensor <NUM> is shown to include three leads 324a - 324c, it will be appreciated by those of ordinary skill in the art that various numbers of leads are possible. Other techniques for electrically coupling the lead frame leads to the sensor components include solder bumps or balls or pillar bumps.

The integrated circuit sensor <NUM> may be provided in the form of a two to six pin Single In-Line (SIP) package, or some other number of pins as appropriate. The die attach area <NUM> on the first surface 318a of a lead frame <NUM> is generally a dedicated area of the conductive lead frame to accept the semiconductor die <NUM>. The die attach area <NUM> is sometimes referred to as a die attach paddle or a die attach pad and in some embodiments the die attach pad may be a silver plated or a NiPdAu area for example. Alternatively, as described in a co-pending <CIT> entitled "Methods and Apparatus for a Magnetic Sensor having a Non-conductive Die Paddle" which was filed on January <NUM>, <NUM> and assigned to the Assignee of the subject application, it may be desirable to form the die attach area with a non-conductive material, particularly in applications where Eddy currents can occur. Conventional techniques for securing the die <NUM> to the die attach area <NUM> include the use of adhesives, such as epoxy or an adhesive tape. It will be appreciated by those of ordinary skill in the art that the die attach area may or may not be a contiguous area.

The non-conductive mold material <NUM> is comprised of a non-conductive material so as to electrically isolate and mechanically protect the die <NUM> and the enclosed portion of the lead frame <NUM>. Suitable materials for the non-conductive mold material <NUM> include thermoset and thermoplastic mold compounds and other commercially available IC mold compounds. It will be appreciated that the non-conductive mold material <NUM> can contain a ferromagnetic material, such as in the form of ferromagnetic particles, as long as such material is non-conductive.

The non-conductive mold material <NUM> is applied to the lead frame/die subassembly to enclose the die <NUM> and a portion of the lead frame <NUM>. The non-conductive mold material <NUM> has a first surface 320a and a second, opposing surface 320b. The shape and dimensions of the non-conductive mold material are selected to suit a particular IC package.

In some embodiments as noted above, the ferromagnetic mold material <NUM> is comprised of a hard or permanent magnetic material to form a bias magnet. As will be apparent to those of ordinary skill in the art, various materials are suitable for providing the ferromagnetic mold material <NUM> depending on the operating temperature range and final package size. In some embodiments, it may be desirable for the ferromagnetic mold material to have a coercivity larger than its remanence.

Illustrative hard magnetic materials for the ferromagnetic mold material include, but are not limited to hard magnetic ferrites, SmCo alloys, NdFeB alloy materials, or Plastiform® materials of Arnold Magnetic Technologies Corp. , or other plastic compounds with hard magnetic particles, for example a thermoset polymer such as polyphenylene sulfide material (PPS) or nylon material containing SmCo, NdFeB, or hard ferromagnetic ferrite magnetic particles; or a thermoset polymer such as SUMIKON®EME of Sumitomo Bakelite Co. , Ltd or similar type of thermoset mold material containing hard magnetic particles. In some embodiments it may be desirable to align the hard ferromagnetic particles during molding to form a more isotropic or directional permanent magnetic material by molding in the presence of a magnetic field; whereas, in other embodiments, a sufficient magnet may result without an alignment step during molding for isotropic materials. It will be appreciated that a NdFeB or a SmCo alloy may contain other elements to improve temperature performance, magnetic coercivity, or other magnetic properties useful to a magnetic design.

In other embodiments, the ferromagnetic mold material <NUM> is comprised of a soft ferromagnetic material to form a concentrator. As will be apparent to those of ordinary skill in the art, various materials are suitable for providing the ferromagnetic mold material <NUM> in the form of a soft ferromagnetic material. In some embodiments, it may be desirable for the soft ferromagnetic mold material to have a relatively low coercivity and high permeability. Suitable soft ferromagnetic materials include, but are not limited to permalloy, NiCo alloys, NiFe alloys, steel, nickel, and soft magnetic ferrites.

The ferromagnetic mold material <NUM> is secured to the non-conductive mold material <NUM>. The ferromagnetic mold material contacts the second surface 320b of the non-conductive mold material and also a portion of the sides of the non-conductive mold material between the first and second surfaces 320a, 320b, as shown.

In some embodiments, a portion of the non-conductive mold material <NUM> that contacts the ferromagnetic mold material <NUM> and/or the portion of the ferromagnetic mold material that contacts the non-conductive mold material has a securing mechanism in order to improve the adhesion between the two materials and to prevent or reduce lateral slippage or shear between the materials. As one example, the lead frame <NUM> has extensions 318c which extend beyond the non-conductive mold material and are enclosed by the ferromagnetic mold material, as shown. Such lead frame extensions additionally enhance the adhesion of the ferromagnetic mold material to the lead frame itself. In such embodiments utilizing lead frame portions as a securing mechanism such that the ferromagnetic mold material contacts such lead frame portions, it will be appreciated that the ferromagnetic mold material should be non-conductive or have a sufficiently low conductivity to prevent the leads from electrically shorting resulting in the device not operating as intended. Alternative forms of securing mechanisms are shown in other embodiments.

As is shown in <FIG>, a portion of the leads 324a - 324c is enclosed by the non-conductive mold material <NUM>. The non-conductive mold material surrounds the leads out to the edge of the package in order to isolate the ferromagnetic mold material <NUM> from the leads (since the ferromagnetic mold material may be electrically conductive).

According to the alternative cross-sectional view of <FIG>, portions of the non-conductive mold material <NUM> adjacent to the leads 324a - 324c may be "cut out" around the leads so as to follow the contours of the leads, as shown. This arrangement may be desirable in some applications for magnetic performance reasons, to thereby increase the amount of the hard ferromagnetic material of the ferromagnetic mold material in proximity to the transducer <NUM>. Also shown in <FIG> is an alternative securing mechanism in the form of lead frame tabs 318c'. The tabs 318c' may be planar and may have an eye as shown. With this arrangement, the ferromagnetic mold material <NUM> flows through the eye of the tabs and around the tabs to improve the adhesion of the ferromagnetic mold material to the lead frame and non-conductive mold material.

The illustrative coil <NUM> on the other hand is positioned relative to the magnetic field sensing element <NUM> to function as a back bias magnet, so as to provide a magnetic field which can be used to detect movement of a proximate target. To this end, the coil <NUM> is positioned adjacent to the second surface 320b of the non-conductive mold material <NUM> so that the transducer <NUM> is closer to the target <NUM> than the coil <NUM>, as shown. Here again, it will be appreciated that it may be desirable in certain applications to rotate the sensor by <NUM>° so that the coil <NUM> is closer to the target than the transducer or to rotate the sensor by <NUM>° so that the major face of the transducer is orthogonal to the target, thereby achieving a different type of magnetically sensitive sensor, as may be desirable when the transducer is a magnetoresistance element for example which has a different axis of sensing element sensitivity than a planar Hall element. It may also be desirable in an embodiment to rotate coil <NUM> such that its central axis is parallel to the surface of the die <NUM> for certain sensor configurations and sensing element combinations.

Various techniques and materials can be used to form the coil <NUM>. For example, the coil can be formed from copper wire of various sizes and with various automated processes so as to provide an insulator between coil windings. The coil material selection, wire gauge selection, number of turns, and other design choices can be readily varied to suit a particular application so as to produce a magnetic field of a desired strength. The coil <NUM> may be formed so that each turn is in the shape of a circle, rectangle, or other shapes such as an oval, as desirable to suit a particular application and packaging arrangement.

The coil <NUM> may be secured to the second surface 320b of the non-conductive mold material <NUM> by various means. As one example, an adhesive, such as an epoxy, may be used to secure the coil in place. Once secured in place, the mold material <NUM> may be formed in the manner described above, such as by injection molding for example.

In operation, a bias current may be applied to the coil <NUM> which causes a bias magnetic field to be generated. The transducer <NUM> is responsive to perturbations in the magnetic field caused by movement of the target <NUM>. It will be appreciated by those of ordinary skill in the art that the mold material <NUM> can be provided in the form of a hard ferromagnetic material, a soft ferromagnetic material, or even a non-conductive material. For example, in embodiments in which the material <NUM> is a soft ferromagnetic material, the magnetic field generated by the coil <NUM> can be focused or otherwise concentrated as desired by the soft ferromagnetic mold material <NUM>. Alternatively, in embodiments in which the material <NUM> is a hard ferromagnetic material, the magnetic field provided by the coil <NUM> can be used to modulate the magnetic field provided by the hard ferromagnetic material <NUM>, in order to thereby reduce the peak current otherwise required to provide the same peak value of magnetic field strength when compared to the case of the coil alone (i.e., if the hard ferromagnetic mold material <NUM> were not present). In another embodiment, a separately formed element may be disposed in the central aperture <NUM>.

When checking the part the for proper operation, such as or safety integrity level (SIL) the current applied to the coil is changed, for example, by a change in the input current applied to the coil externally from the package. As noted above, the coil current can be controlled via connection to one or two (or more) external pins of the package. The change in output voltage of the part should change due to the change in magnetic field caused by the change of coil current. The output voltage changed can be monitored, such as by user-test circuitry (see <FIG>, for example) and evaluated for proper functionality. This operation works even if the coil is not used for a bias feature during operation of the part and with or without the ferromagnetic mold material.

In some embodiments, since the back bias functionality is provided by the coil, the mold material <NUM> may be eliminated entirely in which case the non-conductive mold material <NUM> with the coil <NUM> attached to its second surface 320b can be packaged to provide the resulting sensor IC. Such an arrangement can be provided in a package of the type described in a <CIT> or a <CIT>, each of which is assigned to the Assignee of the subject application.

Referring now to <FIG> an alternative magnetic field sensor <NUM> includes a semiconductor die <NUM> having a first active surface 462a in which a magnetic field sensing element <NUM> is disposed and a second, opposing surface 462b attached to a die attach area <NUM> on a first surface 470a of a lead frame <NUM>, a non-conductive mold material <NUM> enclosing the die and at least a portion of the lead frame, and a mold material <NUM> secured to a portion of the non-conductive mold material.

The non-conductive mold material <NUM> has a protrusion <NUM> extending away from a second surface 470b of the lead frame <NUM> as shown. The protrusion <NUM> may prevent there being a void in the bottom surface of the sensor <NUM> (adjacent to the second end 480b of the ferromagnetic mold material), since the presence of a void may make overmolding more difficult. It will be appreciated by those of ordinary skill in the art that the protrusion may extend all or only part of the way to the second end 480b of the mold material.

The sensor includes a coil <NUM> that may the same as or similar to the coil <NUM> of <FIG>. Here, the coil <NUM> is positioned concentrically with respect to the protrusion <NUM> of the non-conductive mold material <NUM>, although it will be appreciated that concentric positioning is not required. It will be appreciated that the taper to the protrusion <NUM> may be eliminated or altered as suitable for a particular application. Here again, the coil <NUM> may be secured to the mold material <NUM> by an adhesive. Alternatively however, the coil <NUM> may be sized and shaped to provide an interference fit with respect to the protrusion <NUM> such that adhesive is not necessary and the coil <NUM> may be sufficiently held in place relative to the mold material <NUM> by the interference fit when the subassembly, including the mold material <NUM>, lead frame <NUM> and die <NUM>, are placed into the mold cavity for formation of the mold material <NUM>.

While the sensor <NUM> is shown to have a protrusion extending only partially through the mold material <NUM> to terminate before the second end 480b of the mold material, it will be appreciated that a similar sensor including a coil that may be (although is not required to be) concentrically disposed with respect to a protrusion of the non-conductive mold material can be provided with a protrusion extending to the second end 480b of the mold material <NUM>.

In operation, a bias current may be applied to the coil <NUM> which causes a bias magnetic field to be generated. The transducer <NUM> is responsive to perturbations in the magnetic field caused by movement of a target. The bias current may be changed to cause a change in the output voltage at a known time in order to check the functionality of the package sensor by looking for a change in response of the output voltage. It will be appreciated by those of ordinary skill in the art that the mold material <NUM> can be provided in the form of a hard ferromagnetic material, a soft ferromagnetic material, or even a non-conductive material. For example, in embodiments in which the material <NUM> is a soft ferromagnetic material, the magnetic field generated by the coil <NUM> can be focused or otherwise concentrated as desired by the soft ferromagnetic mold material <NUM>. Alternatively, in embodiments in which the material <NUM> is a hard ferromagnetic material, the magnetic field provided by the coil can be used to modulate the magnetic field provided by the hard ferromagnetic material <NUM>, in order to thereby reduce the peak current otherwise required to provide the same magnetic field strength with just the coil (i.e., if the hard ferromagnetic mold material <NUM> were not present).

Here again, since the back bias functionality is provided by the coil, the mold material <NUM> may be eliminated entirely (as is shown in FIG. <NUM>) in which case the non-conductive mold material <NUM> with the coil <NUM> attached to its surface can be packaged to provide the resulting sensor IC. Such an arrangement can be provided in a package of the type described in one of the above-referenced U.

In applications including the mold material <NUM>, such mold material may be tapered from a first end 480a proximate to the lead frame <NUM> to a second end 480b distal from the lead frame and the sensor may, optionally, include a third mold material <NUM> in the form of an overmold in order to protect and electrically insulate the device. In another embodiment a housing may be used as in <CIT> and <CIT>, which are assigned to the assignee of the present invention. In such an embodiment, the third mold material may be replaced by the housing which is pre-molded and the welded to the plastic package, for example. In other embodiments the pre-molded, or otherwise manufactured, housing may be used in place of the second mold material where only the first and second mold versions are used, in such an embodiment the coil is enclosed by the pre-molded housing.

Referring to <FIG> an alternative magnetic field sensor <NUM>' includes a semiconductor die <NUM> having a first active surface 462a in which a magnetic field sensing element <NUM> is disposed and a second, opposing surface 462b attached to a die attach area <NUM> on a first surface 470a of a lead frame <NUM> and a non-conductive mold material <NUM> enclosing the die and at least a portion of the lead frame.

The sensor includes a coil <NUM>' that may the same as or similar to the coil <NUM> of <FIG>. The coil <NUM>' is secured to, and more particularly, in the embodiment of <FIG> is enclosed by, the non-conductive mold material <NUM>. The wire of the coil <NUM>' may be wound around a mandrel or bobbin <NUM>, as shown. In one illustrative embodiment, the mandrel <NUM> may be comprised of a soft ferromagnetic material or a plastic and remain part of the final device. In other embodiments, the mandrel <NUM> is used during coil winding but then not made a part of the final package, for example in the case of <FIG> and <FIG>. The mandrel <NUM> and coil <NUM>' may be secured to the surface 470b of the lead frame <NUM> that is opposite the die <NUM> with an adhesive or other securing mechanism, such that the coil is secured to the lead frame when the subassembly is placed in a mold cavity and the non-conductive mold material <NUM> is formed.

In operation, a bias current is applied to the coil <NUM>' which causes a bias magnetic field to be generated and the transducer <NUM> is responsive to perturbations in the magnetic field caused by movement of a proximate target. The bias current may be changed to cause a change in the output voltage at a known time in order to check the functionality of the package sensor by looking for a change in response of the output voltage. While the ferromagnetic mold material is eliminated in the sensor <NUM>' of <FIG>, it will be appreciated by those of ordinary skill in the art that a ferromagnetic mold material may be provided as explained in connection with any foregoing embodiments in order to concentrate the magnetic field generated by the coil (in the case of a soft ferromagnetic mold material) or to provide a magnetic field for modulation by a coil-generated magnetic field (in the case of a hard ferromagnetic mold material).

In another embodiment, the coil may be used to create a closed loop current sensor. In this embodiment the packaged magnetic field sensor and at least one coil inside the package (either on the die, in the package, or both), in any package form or style such as SIP, SOIC, QFN, or other package of interest, are connected externally to the package with a circuit. The user circuit applies a current to the coil inside the package (or on the die of the sensor) to maintain the output voltage of the sensor at a known voltage (or current for a current output device such as a "two-wire" part). This has the advantage of allowing higher current to be used in the coil, particularly for the case of the coils describe in <FIG>, than would otherwise be typical for a magnetic field sensor.

Claim 1:
A magnetic field sensor IC package (<NUM>, <NUM>; <NUM>), comprising:
a sensing element (<NUM>; <NUM>);
an analog circuit path coupled to the sensing element for generating an output voltage proportional to a magnetic field applied to the sensing element;
a coil (<NUM>; <NUM>) in proximity to the sensing element, the coil having a first terminal that is accessible to provide a direct electrical connection to the coil from external to the magnetic field sensor IC package, wherein the coil is configured to carry a current to generate a magnetic field having an intensity corresponding to a level of the current;
a device (<NUM>);
a diagnostic module (<NUM>);
a control module (<NUM>);
a switch (<NUM>); and
a threshold module (<NUM>),
wherein the threshold module is coupled to the diagnostic module and configured to provide a normal operation threshold and a diagnostic threshold,
wherein:
during a normal operation, the device is configured to compare a voltage from the sensing element with the normal operation threshold and the control module is configured to receive an output of the normal operation comparison, and
the control module is configured to control the switch for generating the output voltage based on the normal operation comparison output;
characterized in that:
during a diagnostic testing, the device is configured to compare a voltage from the sensing element to the diagnostic threshold and the control module is configured to receive an output of the diagnostic testing comparison, and
wherein the control module is configured to control the switch for generating the output voltage based on the diagnostic testing comparison output.