Current sensor for printed circuit board

Abstract

The present application relates to a current sensor for a printed circuit board, and provides a non-contact current sensing circuit for sensing current in a conductive line on a dielectric substrate of a printed circuit board (PCB), comprising a plurality of magnetic tunnel junction (MTJ) structures comprising first and second MTJ structures on a first side of the conductive line, and third and fourth MTJ structures on a second side of the conductive line opposite the first side. The MTJ structure is located in an H-field induced by current flowing through the wire.

Description

Technical Field

[0001] Embodiments of the present application relate to current sensing circuits implemented on a printed circuit board (PCB), and more particularly to non-contact current sensing circuits using magnetic tunneling junction (MTJ) structures. Background Art

[0002] Sensing the current flowing through a line on a printed circuit board (PCB) is typically implemented in a circuit by directly measuring the current flowing through a wire using a component (such as a shunt resistor) located in the current path. However, adding a component to the current path has some effect on the current, and typically, a certain amount of power loss is associated with direct current measurement, especially at high current levels. Non-contact current measurement can be performed by a current transformer. However, a current transformer cannot measure direct current, and current transformers are typically large devices that are not suitable for miniaturization.

[0003] Another non-contact measurement is a Hall-effect sensor, which operates on the principle that for a copper trace on a PCB with current flowing through it, a corresponding magnetic field is generated around the current-carrying conductor. By measuring such a magnetic field, information about the current value that generated the magnetic field can be obtained. The sensing element typically has the PCB copper flowing through the sensing element package, while some others place the sensor above the copper trace and sense only by proximity.

[0004] Anisotropic magneto-resistance (AMR) sensors measure the angular variation of a magnetic field by using an iron material. The resistance of the iron material in the AMR sensor depends on the current direction and the magnetization direction. The AMR sensor determines non-contact position measurement in a harsh environment. Giant magneto-resistance (GMR) sensors use the quantum mechanical effect of having a non-magnetic material between two iron material layers. When current passes through one of the two iron material layers, the GMR sensor results in a high resistance for anti-parallel spin alignment and a low resistance for parallel spin alignment. Summary of the Invention

[0005] Embodiments of the present application relate to current sensing circuits implemented on a printed circuit board (PCB), and more particularly to non-contact current sensing circuits using magnetic tunneling junction (MTJ) structures.

[0006] In one embodiment, a current sensing circuit includes a wire and a plurality of magnetic tunneling junction (MTJ) structures. The wire is located on a dielectric substrate of a printed circuit board (PCB). The plurality of magnetic tunneling junction (MTJ) structures include first and second magnetic tunneling junction (MTJ) structures located on a first side of the wire, and third and fourth magnetic tunneling junction (MTJ) structures located on a second side of the wire opposite the first side.

[0007] In one embodiment, a device includes a printed circuit board (PCB), a wire, and a plurality of magnetic tunneling junction (MTJ) structures. The printed circuit board includes a dielectric substrate. The wire is located on the dielectric substrate. The plurality of magnetic tunneling junction structures include first and second magnetic tunneling junction (MTJ) structures located on a first side of the wire and third and fourth magnetic tunneling junction (MTJ) structures located on a second side of the wire opposite the first side.

[0008] In one embodiment, a method for forming a current sensing circuit includes arranging a plurality of magnetic tunneling junction (MTJ) structures on a printed circuit board (PCB) having a wire. The plurality of magnetic tunneling junction structures include first and second magnetic tunneling junction (MTJ) structures located on a first side of the wire, and third and fourth magnetic tunneling junction (MTJ) structures located on a second side of the wire opposite the first side. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 Shows a current sensing circuit according to one embodiment.

[0010] Figure 2A AND 2B Shows the operation of a current sensing circuit according to one embodiment in response to different amounts of current in the wire.

[0011] Figure 3 Shows a schematic circuit diagram of a Wheatstone bridge circuit according to one embodiment.

[0012] Figure 4A AND 4B Shows an embodiment of a current sensing circuit having two chips.

[0013] Figure 5A AND 5B Shows an embodiment of a current sensing circuit having one chip. Detailed Embodiments

[0014] Embodiments of the present application relate to a current sensing circuit, a device including the current sensing circuit, and a method for forming the current sensing circuit.

[0015] The following provides a detailed description of the embodiments in conjunction with the Figure 1 drawings. The scope of the present invention is limited by the claims and includes various alternatives, modifications, and equivalents. Although the steps of various processes are presented in a given order, the embodiments are not necessarily limited to being executed in the listed order. In some embodiments, specific operations may be performed simultaneously, in an order different from the described order, or not performed at all.

[0016] Various specific details are set forth in the following description. These details are provided by way of specific examples to facilitate a comprehensive understanding of the scope of the present invention, and the embodiments may be implemented in accordance with the claims without some of these specific details. Thus, the specific embodiments of the present invention are exemplary and not intended to be exclusive or restrictive. For clarity, technical materials known in the technical field related to the present invention are not described in detail so as not to unnecessarily obscure the present invention. The drawings are not drawn to scale, and some features are intentionally enlarged or reduced for emphasis and visual clarity.

[0017] Figure 1 An isometric view showing an embodiment of the current sensing circuit 100. The current sensing circuit 100 includes a dielectric substrate 102 of a printed circuit board (PCB) 103 and a wire 104 located on the dielectric substrate 102. Four magnetic tunneling junction (MTJ) structures 106 are located on the PCB 103, with two MTJ structures 106 on one side of the wire 104 and two MTJ structures 106 on the opposite side of the wire 104.

[0018] The PCB 103 may include one or more layers or dielectric substrates 102, each of which may include a polymer material such as epoxy resin, polyester, polyimide, or polytetrafluoroethylene. The polymer material may be reinforced or interwoven with fibers (such as glass or organic fibers). In some embodiments, the PCB 103 is a multi-layer laminate, where one or more layers are layers made of a conductive material (such as copper). In one embodiment, the PCB 103 includes a copper ground plane. The laminated layers may be alternating layers of polymer and fiber. In some embodiments, one or more layers of the PCB 103 are ceramic materials. Examples of the PCB 103 are FR-4, CEM-2, and RF-35.

[0019] The conductive wire 104 can be conductive metal printed or otherwise suitably disposed on the PCB 103. The size of the conductive wire 104 can be determined by the intended application of the current sensor. For example, the thickness of the copper wire 104 can be from about 0.035 mm to 0.31 mm, and the width of the copper wire can be from about 0.25 mm to 7.6 mm. Based on the application of the PCB 103 and the amount of current that the conductive wire 104 is designed to handle, the specific size of the conductive wire 104 can vary between embodiments.

[0020] The MTJ structure 106 includes at least three material layers, and the at least three material layers include two magnetic material layers 108 and 112 separated by a thin insulating layer 110. The magnetic material layer can include a pinned layer 112 with a fixed magnetic orientation and a free layer 108. The magnetization direction of the free layer 108 can be adaptable, so that when exposed to an external electromagnetic field, the magnetization direction changes. The MTJ structure 106 can be a perpendicular MTJ (pMTJ) structure.

[0021] For the tunneling between the magnetic layers 108 and 112 of the MTJ structure 106, when the magnetization directions of these magnetic layers are parallel, the tunneling current is the highest, and when the magnetization directions of these magnetic layers are antiparallel, the tunneling current is the lowest. Therefore, the resistance of the MTJ structure 106 is proportional to the difference in magnetization direction between the pinned layer 112 and the free layer 108. This resistance can be referred to as the tunneling magnetoresistance (TMR) of the MTJ structure 106. When a voltage is applied to these magnetic materials, electrons can tunnel through the insulating layer 110 through quantum mechanics. In Figure 1 it, the magnetization directions are marked by the black arrows on the magnetic layers 108 and 112.

[0022] Figure 2A and 2B show embodiments of the operation of the current sensing circuit 100. As Figure 2A shown in it, when the current 220 flows through the conductive wire 104, the current induces a magnetic field 222 or H field around the wire. The direction of the magnetic field 222 is shown by the semicircular arrow in the figure and conforms to the right-hand rule (also known as Ampere's right-hand grip rule). According to the right-hand grip rule, when the current flows in the direction of the thumb, the direction of the magnetic field is the same as the direction of the remaining fingers in the right hand in the "thumb up" position.

[0023] The flow of the magnetic field 222 acts on the magnetization direction 114 of the free layer 108 of the MTJ structure 106 by moving the magnetization direction 114 along the direction of the magnetic field 222. As Figure 2AAs shown, when current 220 flows through wire 104, the magnetic field 222 induced by current 220 causes the magnetization directions 114a and 114c of MTJ structures 106a and 106c located on one side of wire 104 to be oriented upward, and causes the magnetization directions 114b and 114d of MTJ structures 106b and 106d located on the opposite side of wire 104 to be oriented downward.

[0024] In Figure 2A the orientation of magnetization direction 114 represents a maximum value (e.g., the directions 114 being oriented straight up and down will result in the highest and lowest resistance levels in MTJ structure 106), and is for illustrative purposes here. In an embodiment, the elements of current sensing circuit 100 (such as the spacing between MTJ structure 106 and wire 104 and the construction of MTJ structure 106) are configured such that the magnetization orientation 114 is below this maximum value at normal current levels 220.

[0025] Figure 2B An embodiment is shown where current sensing circuit 100 is in a state less than this maximum value (e.g., normal operating conditions of circuit 100). Due to the magnetic field 222 induced by current 220 flowing through wire 104, in Figure 2A the magnetization direction 114 of MTJ structure 106 in Figure 1 changes from the default orientation shown in

[0026]

[0027] Figure 3 As Figure 3 shown, MTJ structures 106a, 106b, 106c, and 106d can be electrically coupled to each other in a Wheatstone bridge circuit. The Wheatstone bridge is well-suited for measuring current 220 in wire 104 based on the different resistances of MTJ structures 106 (which are resistors in this circuit). When voltage V is applied to this Wheatstone bridge circuit, the voltage difference (V out) is proportional to the resistance difference between MTJ structures 106 (such as 106a and 106c) on one side of the wire 104 and MTJ structures 106 (such as 106b and 106d) on the opposite side of the wire 104. Thus, the amount of current 220 flowing through the wire 104 is proportional to the potential difference between the output terminals, but this proportionality may be non-linear. When the current 220 increases, the V of this Wheatstone bridge out also increases, so the current 220 can be measured by measuring V out .

[0028] Figure 4A shows the layout of the current sensing circuit 100, and Figure 4B is a cross-sectional view of the circuit taken along Figure 4A A-A'. In the Figure 4A and 4B embodiment, a first chip 430a including two MTJ structures 106a and 106c is located on one side of the wire 104, and a second chip 430b including two MTJ structures 106b and 106d is located on the opposite side of the wire 104. The first and second chips 430a and 430b are on the same side of the dielectric substrate 102 as the wire 104, and are arranged such that the free layer 108 of the MTJ structure is within the H field 222 induced when current flows through the wire 104.

[0029] As Figure 4B shown, each MTJ structure 106 includes an upper metal contact layer 432 coupled to the free layer 108 and a lower metal contact 434 coupled to the pinned layer 112. The metal contacts 432 and 434 are electrodes that couple the MTJ structure 106 in the Wheatstone bridge circuit as Figure 3 shown. The chip 430 may include additional circuitry and components known in the art. For example, the chip 430 may include circuitry that couples the MTJ structure 106 to ground, the voltage lines of the PCB 103, and appropriate additional devices.

[0030] The chip 430 can be formed by known and existing or future developed processes. For example, the components of the chip 430 can be formed by deposition, lithography, and etching methods.

[0031] In one embodiment, the underlying metal contact 434 is formed by depositing and etching a conductive material on a semiconductor substrate. Each material layer in the MTJ structure 106 can be deposited on top of the underlying metal contact 434 by conventional deposition methods such as physical vapor deposition (PVD) or chemical vapor deposition (CVD) processes. After this deposition process, the resist formed on top of the topmost material is exposed to energy (light) to form a pattern (opening). A selective chemical etching process such as reactive ion etching (RIE) can be used to pattern the material through the opening in the resist, thereby forming the corresponding MTJ structure 106. The resist can be removed by a conventional oxygen ashing process or other known strippers.

[0032] The free layer 108 and the pinned layer 112 of the MTJ structure 106 can include alloys and / or multiple layers composed of cobalt, iron, cobalt-iron alloys, nickel, nickel-iron alloys, and cobalt-iron-boron alloys. The thin insulating layer 110 can include an oxide material such as an oxide of magnesium or aluminum. The magnetization direction of the pinned layer 112 can be fixed by an adjacent synthetic anti-ferromagnetic (SAF) layer that includes one or more material layers composed of one or more of Mn, Pt, Ir, Cr, or Fe. In addition, the MTJ structure 106 can include one or more layers such as a buffer layer that includes one or more layers composed of a non-magnetic material such as Ru or Ta. The MTJ structure 106 can be composed of various layers of these materials and other materials known in the art to obtain desired performance characteristics and to conform to desired deposition and etching processes.

[0033] The upper metal contact 432 (and other circuitry) can be formed on top of the MTJ structure 106 by similar deposition and etching processes. After forming the device and circuitry structure, they can be encapsulated in a polymer encapsulation material such as an epoxy molding compound (EMC), exposing external connections such as pins or lead frames to attach the chip 430 to the circuitry of the PCB 103.

[0034] Figure 5A and 5B shows a layout of the current sensing circuit 100 according to another embodiment. In Figure 5A and 5BIn an embodiment, the MTJ structure 106 is encapsulated within a single chip 430, and the chip 430 and the wire 104 (sensing its current) are located on opposite sides of the dielectric substrate 102. The chip 430 is configured such that the free layer 108 of the MTJ structure 106 is within the H field 222 induced when current flows through the wire 104. The advantage of this single-chip structure is that the chip 430 can include additional circuitry between the MTJ structures on both sides of the wire 104, potentially reducing the number of traces on the PCB 103 used to form the Wheatstone bridge circuit.

[0035] In Figure 5B an example, the MTJ structure 106 is electrically coupled to a wire 440 (which is on the same side of the dielectric substrate 102 as the wire 104) through a pin 436 that is soldered to a plated through-hole 438 extending through the substrate 102. The wire 440 can be used for an input voltage V or an output line. Each chip 430 can be coupled to multiple wires 440 of the PCB 103 for input / output voltages and for circuitry between the MTJ structures 106 located in separate chips 430. Additionally, one or more chips 430 can be coupled to the ground plane of the PCB 103 through the plated through-holes 438. Although Figure 5B the wires 104 and 440 located on the dielectric substrate 102 are shown as exposed, in some embodiments, one or more of the wires 104 and 440 are sandwiched between two dielectric substrates 102 in a multi-layer PCB 103.

[0036] Those skilled in the art will realize that the circuit 100 can be implemented in various configurations without departing from the scope of the invention. For example, in some embodiments, each MTJ structure 106 is encapsulated within a separate chip 430. In another embodiment, each resistor in the Wheatstone bridge circuit can be implemented by serially connecting two or more MTJ structures 106. In another embodiment, the MTJ structure 106 is included in a single chip 430 that is on the same side of the dielectric substrate 102 as the wire 104 (sensing its current) and is arranged above the wire 104. Thus, embodiments can be implemented using different numbers of chips 430, and the one or more chips 430 can be on the same side of the dielectric substrate 102 as the wire 104 or on opposite sides of the dielectric substrate 102.

[0037] The circuit 100 can be incorporated into an electronic device. The device can be any product that measures the current in the wires of the PCB in the device, ranging from toys and other low-end applications to advanced computer products having a display, keyboard, or other input devices and a central processing unit. The device can be a household appliance, a portable or fixed computing device, a vehicle or a component of a vehicle, an image capture device, etc.

[0038] The solution of the present invention has been described in connection with specific embodiments of the present invention presented as examples. Various alternatives, modifications, and variations can be made to the embodiments described herein without departing from the scope of the claims set forth below. Therefore, the embodiments described herein are intended to be illustrative and not restrictive.

Claims

1. A circuit, characterized in that: include: Conductive wires, located on a dielectric substrate of a printed circuit board; a plurality of magnetic tunneling junction structures, including first and second magnetic tunneling junction structures located on a first side of the conductive line; as well as The third and fourth magnetic tunnel junction structures are located on a second side of the conductive line opposite to the first side.

2. The circuit according to claim 1, characterized in that The plurality of magnetic tunneling junction structures are packaged in a single chip above the dielectric substrate.

3. The circuit according to claim 2, characterized in that The single chip and the conductive line are located on opposite sides of the dielectric substrate.

4. The circuit according to claim 3, characterized in that The single chip is coupled to an input voltage line, a first output voltage line, and a second output voltage line, and the input voltage line, the first output voltage line, the second output voltage line and the conductive line are located on a same side of the dielectric substrate.

5. The circuit according to claim 1, characterized in that The first and second magnetic tunnel junction structures are packaged independently of the third and fourth magnetic tunnel junction structures.

6. The circuit according to claim 5, characterized in that The first and second magnetic tunnel junction structures are packaged in a first chip, and the third and fourth magnetic tunnel junction structures are packaged in a second chip.

7. The circuit according to claim 5, characterized in that The first magnetic tunnel junction structure is packaged in a first chip, the second magnetic tunnel junction structure is packaged in a second chip, the third magnetic tunnel junction structure is packaged in a third chip, and the fourth magnetic tunnel junction structure is packaged in a fourth chip.

8. The circuit according to claim 5, characterized in that The individual packages are located on the same side of the dielectric substrate as the conductive line.

9. The circuit according to claim 1, characterized in that The conductors are copper traces printed on the printed circuit board.

10. The circuit according to claim 1, characterized in that The dielectric substrate is a polymer material, a fiber-reinforced polymer material, a fiber and polymer laminate, or a ceramic material.

11. The circuit according to claim 1, characterized in that The first, second, third and fourth magnetic tunnel junction structures are resistors in a Wheatstone bridge circuit.

12. The circuit according to claim 11, characterized in that The free layers of the plurality of magnetic tunnel junction structures are located within an H field induced when current flows through the conductive line, and are configured to change magnetization directions in the presence of the H field.

13. A device, characterized in that include: Printed circuit boards, including dielectric substrates; A conductor located on the dielectric substrate; a plurality of magnetic tunneling junction structures, including first and second magnetic tunneling junction structures located on a first side of the conductive line; and The third and fourth magnetic tunnel junction structures are located on a second side of the conductive line opposite to the first side.

14. The device according to claim 13, characterized in that The plurality of magnetic tunneling junction structures are packaged in a single chip above the dielectric substrate.

15. The device according to claim 14, characterized in that The single chip and the conductive line are located on opposite sides of the dielectric substrate.

16. The device according to claim 15, characterized in that The single chip is coupled to an input voltage line, a first output voltage line, and a second output voltage line, and the input voltage line, the first output voltage line, the second output voltage line and the conductive line are located on a same side of the dielectric substrate.

17. The device according to claim 13, characterized in that The first and second magnetic tunnel junction structures are packaged independently of the third and fourth magnetic tunnel junction structures.

18. The device according to claim 17, characterized in that The first and second magnetic tunnel junction structures are packaged in a first chip, and the third and fourth magnetic tunnel junction structures are packaged in a second chip.

19. A method for forming a current sensing circuit, characterized in that, The method includes: A plurality of magnetic tunnel junction structures are arranged on a printed circuit board having a conductive line, the plurality of magnetic tunnel junction structures including first and second magnetic tunnel junction structures located on a first side of the conductive line, and third and fourth magnetic tunnel junction structures located on a second side of the conductive line opposite to the first side.

20. The method of claim 19, wherein: Arranging the plurality of magnetic tunnel junction structures on the printed circuit board includes arranging a single chip including the plurality of magnetic tunnel junction structures on the printed circuit board, and coupling the single chip to the ground, input voltage line, first output voltage line and second output voltage line of the printed circuit board.

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