JP2012159308A - Magnetic sensor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic sensor device which can prevent the insulation breakdown of a TMR element, and use a general-purpose IC.SOLUTION: A magnetic sensor device comprises: a substrate 2; a plurality of tunnel magnetic resistance elements 3 provided on the substrate 2 and having a pair of electrodes 3a; wiring 4 provided on the substrate 2, connecting the plurality of tunnel magnetic resistance elements 3 in series, and having connecting terminals 4a at both ends; and a detection circuit portion 6 for detecting resistance change by applying voltage on the tunnel magnetic resistance elements 3. When estimating the voltage resistance of the whole of the tunnel magnetic resistance elements 3 connected in series as Vb, and the action voltage of an IC 5 as Vdd, the voltage resistance Vb is set to be a relationship of Vdd/2≤Vb≤2Vdd.

Description

  The present invention relates to a magnetic sensor device which can be driven by a general-purpose IC while preventing dielectric breakdown of a tunnel magnetoresistive element having a low withstand voltage.

  In recent years, magnetic sensors and current sensors using tunneling magnetoresistive (TMR) elements have been developed. This TMR element has an element structure including a pair of ferromagnetic layers opposed to each other with a thin insulating layer interposed therebetween, and a magnetization direction of one ferromagnetic layer is fixed to form a fixed magnetization layer (so-called pinned layer). In addition, the magnetization direction of the other ferromagnetic layer is a free magnetic layer (so-called free layer) that changes according to an external magnetic field. In this TMR element, when an external magnetic field is applied, the tunnel current between the pair of ferromagnetic layers changes according to the magnetization directions of the pair of ferromagnetic layers, and the resistance value of the element changes. It is possible to detect an external magnetic field with high accuracy.

Although this TMR element has good magnetic sensitivity, the insulating layer is extremely thin and the withstand voltage of the element is low, so that the TMR element may break down due to static electricity or the like.
For this reason, for example, Non-Patent Document 1 describes a method of suppressing a dielectric breakdown by connecting a shunt resistor to the upper shield layer and the lower shield layer provided above and below the TMR element to limit the parasitic capacitance that causes discharge. Has been.

Anthony Wai Yuen Lai et al., `` Anti-Static Robustness Enhancement and high-Frequency Noise Pickup Immunity by Internal Shunting for Tunneking Magnetoresistive Sensors '' IEEE Trans. On Mgn. JANUARY (2008), VOL.44, NO.l, 104- 106

The following problems remain in the conventional technology.
When the resistance change of a TMR element is monitored using, for example, a general-purpose IC with an operating voltage of 5 V, even with a TMR element that has been treated as described in Non-Patent Document 1, there is a disadvantage that dielectric breakdown occurs due to low withstand voltage. It was. That is, normally, a TMR element is used with an applied voltage of less than 1 V in consideration of the withstand voltage, but when a general-purpose IC with an operating voltage of 5 V is used, the terminal voltage is usually about ½ of the operating voltage. There is a problem that the voltage exceeds the withstand voltage of the TMR element.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a magnetic sensor device that can prevent a dielectric breakdown of a TMR element and use a general-purpose IC.

  The present invention employs the following configuration in order to solve the above problems. In other words, the magnetic sensor device of the first invention includes a substrate, a plurality of tunnel magnetoresistive elements provided on the substrate and having a pair of electrodes, and a plurality of tunnel magnetoresistive elements provided on the substrate in series. The tunnel magnetoresistive element connected in series, and a detection circuit unit having an IC for detecting a change in resistance by applying a voltage to the tunnel magnetoresistive element When the overall withstand voltage is Vb and the operating voltage of the IC is Vdd, the withstand voltage Vb is set to have a relationship of Vdd / 2 ≦ Vb ≦ 2Vdd.

That is, in this magnetic sensor device, when the withstand voltage of the whole tunnel magnetoresistive elements connected in series is Vb and the operating voltage of the IC is Vdd, the withstand voltage Vb has a relationship of Vdd / 2 ≦ Vb ≦ 2Vdd. Therefore, even if the withstand voltage of each TMR element is small, the withstand voltage Vb as a whole of a plurality of TMR elements connected in series becomes high and becomes equal to or higher than the terminal voltage (Vdd / 2) of the IC. Can be prevented.
If the withstand voltage Vb of the entire TMR element is less than Vdd / 2, there is a risk that dielectric breakdown will occur when connected to the terminal of the IC, and if the withstand voltage Vb of the entire TMR element exceeds 2 Vdd, Since a large number of TMR elements are connected in series, the resistance increases more than necessary and becomes insignificant compared to the internal resistance of the IC.

The magnetic sensor device according to a second aspect of the present invention is the magnetic sensor device according to the first aspect, wherein the wiring is connected to the pair of connection terminals and extends between the plurality of tunnel magnetoresistive elements in parallel and close to each other. And a plurality of pairs of connection wiring portions extending in parallel and close to each other from the main wiring portion toward the tunnel magnetoresistive element and connected to a pair of the electrodes. Features.
In this magnetic sensor device, the wiring is connected to the pair of connection terminals and is parallel to and close to each other and extends between the plurality of TMR elements, and is parallel to each other from the main wiring part toward the TMR element. In addition, since it has a plurality of pairs of connection wiring portions extending in close proximity and connected to a pair of electrodes, generation of noise due to electromagnetic induction can be suppressed. That is, a large number of wiring portions exist due to the connection of a plurality of TMR elements, but when the magnetic field to be detected includes an alternating magnetic field (or in the case of an alternating magnetic field), electromagnetic induction occurs in the wiring and becomes a noise voltage. , S / N ratio may be reduced. In particular, when the wiring is arranged outside the row of TMR elements, the space between the pair of wirings spreads to form a loop, and noise is likely to occur due to electromagnetic induction. However, in the present invention, in the pair of main wiring portions and the plurality of pairs of connection wiring portions, the current directions of the adjacent wiring portions are staggered and brought close to each other, thereby avoiding loop-shaped wiring and preventing electromagnetic waves in the wiring. Induction is less likely to occur.

According to a third aspect of the present invention, there is provided the magnetic sensor device according to the second aspect, wherein the plurality of tunnel magnetoresistive elements are arranged in a plurality of columns, and the pair of main wiring portions are arranged between the columns of the tunnel magnetoresistive elements. And a plurality of pairs of connection wiring portions are disposed on both sides of the pair of main wiring portions.
That is, in this magnetic sensor device, the pair of main wiring portions are arranged between the columns of the tunnel magnetoresistive elements arranged in a plurality of columns, so that the wiring length is shortened as compared with the case where the wiring is arranged outside the columns. In addition, electromagnetic induction generated in the wiring can be suppressed.

The present invention has the following effects.
That is, according to the magnetic sensor device of the present invention, when the withstand voltage of the entire tunnel magnetoresistive elements connected in series is Vb and the operating voltage of the IC is Vdd, the withstand voltage Vb is Vdd / 2 ≦ Vb. Since the relationship of ≦ 2 Vdd is set, the withstand voltage Vb of the plurality of TMR elements as a whole becomes higher and becomes equal to or higher than the terminal voltage of the IC, thereby preventing dielectric breakdown. Therefore, even if a general-purpose IC with an operating voltage of 5 V is adopted, dielectric breakdown does not occur, high reliability can be obtained, and member costs can be reduced.

It is a lineblock diagram showing one embodiment of a magnetic sensor device concerning the present invention. In this embodiment, it is a schematic perspective view which shows a tunnel magnetoresistive element. In this embodiment, it is a simple equivalent circuit schematic of a magnetic sensor apparatus. In this embodiment, it is an equivalent circuit schematic of a magnetic sensor apparatus. In other examples of the present invention, it is a top view showing a sensor main part. In other examples of this embodiment, it is a top view showing a sensor main part.

  Hereinafter, an embodiment of a magnetic sensor device according to the present invention will be described with reference to FIGS. In each drawing used for the following description, the scale is appropriately changed in order to make each member recognizable or easily recognizable.

  As shown in FIG. 1, a magnetic sensor device 1 according to this embodiment includes a substrate 2 and a plurality of tunnel magnetoresistive elements (hereinafter also referred to as TMR elements) 3 provided on the substrate 2 and having a pair of electrodes 3a. A wiring 4 provided on the substrate 2 for connecting a plurality of tunnel magnetoresistive elements 3 in series and having connection terminals 4a at both ends, and an IC 5 for detecting a resistance change by applying a voltage to the tunnel magnetoresistive element 3. And a detection circuit unit 6 provided. The sensor body 7 is composed of the substrate 2, the TMR element 3 and the wiring 4, and the sensor body 7 and the detection circuit unit 6 are connected by a pair of lead wires 8 connected to a pair of connection terminals 4 a of the wiring 4. Has been.

  The wiring 4 is connected to the pair of connection terminals 4a and extends between the plurality of tunneling magnetoresistive elements 3 in parallel and close to each other, and the tunneling magnetoresistive element 3 from the main wiring part 4A. And a plurality of pairs of connection wiring portions 4B extending in parallel and close to each other and connected to the pair of electrodes 3a.

The plurality of tunnel magnetoresistive elements 3 are arranged in two rows, a pair of main wiring portions 4A are arranged between the columns of the tunnel magnetoresistive elements 3, and a plurality of pairs of connection wiring portions 4B. Are arranged on both sides of the pair of main wiring portions 4A. In these main wiring portion 4A and connection wiring portion 4B, current flows alternately between adjacent lines at any location.
The pair of lead wires 8 are twisted pair wires (so-called twisted pair cables).

  Further, in this magnetic sensor device 1, when the withstand voltage of the entire tunnel magnetoresistive element 3 connected in series is Vb and the operating voltage of the IC 5 is Vdd, the withstand voltage Vb is Vdd / 2 ≦ Vb ≦ 2Vdd. Set in a relationship. For example, when a general-purpose IC having an operating voltage Vdd of 5V is used as IC5, the withstand voltage Vb of the entire tunnel magnetoresistive element 3 is set to be in a range of 2.5V ≦ Vb ≦ 10V.

  As shown in FIG. 2, the TMR element 3 has a structure in which, for example, a fixed-side electrode layer 11, a fixed magnetic layer 12, an insulating layer 13, a free magnetic layer 14, and a free-side electrode layer 15 are stacked in this order. . For example, the fixed-side electrode layer 11 is composed of a stacked layer of a Ta layer (thickness 30 nm) / CoFe layer (thickness 3 nm) / IrMn layer (thickness 15 nm), and the fixed magnetic layer 12 is a CoFe layer (thickness 2 nm). ) / Ru layer (thickness 0.8 nm) / CoFeB layer (thickness 3 nm). The insulating layer 13 is an MgO layer (thickness 1.2 nm), and the free magnetic layer 14 is a CoFeB layer (thickness 3 nm). Furthermore, the free-side electrode layer 15 is composed of a stack of Ta layer (thickness 10 nm) / Ru layer (thickness 15 nm). The fixed-side electrode layer 11 and the free-side electrode layer 15 are directly connected to the pair of connection wiring portions 4B to form a pair of electrodes 3a, or a pair of separately provided via other wiring such as wire bonding. It is electrically connected to the electrode 3a.

The substrate 2 is a printed circuit board on which a plurality of TMR elements 3 can be mounted, and a wiring 4 is formed with a copper pattern or the like on a mounting surface of a substrate body of an insulating material formed of glass epoxy resin or the like. In the present embodiment, six TMR elements 3 are mounted on the substrate 2 in two rows.
The wiring 4 is connected to a pair of connection terminals 4 a and is parallel to and adjacent to each other and extends between the plurality of TMR elements 3, and the main wiring part 4 A toward the TMR element 3. A plurality of pairs of connection wiring portions 4B extending in parallel and close to each other and connected to the pair of electrodes 3a.

  As shown in FIGS. 3 and 4, the detection circuit unit 6 includes, for example, an IC 5 operating at Vdd: 5 V and a reference resistor R connected in series to the TMR element 3 (all TMR elements 3 connected in series). And. The IC 5 includes an AMP 16 that is connected between the TMR element 3 and the reference resistor R and amplifies the detected signal, and an A / D converter 17 that converts the amplified signal from analog to digital.

The A / D converter 17 has a resolution of 128 bits in a range of 0.5 to 4.5V, for example. Therefore, the A / D converter 17 can be used effectively by setting the voltage across the TMR elements 3 connected in series within the range of 0.5 to 4.5V. For this reason, it is preferable to set the reference resistance R so that the resistance R ₀ of the entire TMR element 3 in a state where no magnetic field is applied is at a midpoint of 0.5 to 4.5V.

  If the withstand voltage Vb of the TMR element 3 as a whole is less than Vdd / 2, there is a risk of dielectric breakdown when connected to the terminal of the IC 5, and the withstand voltage Vb of the TMR element 3 as a whole exceeds 2 Vdd. Then, since many TMR elements 3 are connected in series, the resistance increases more than necessary and becomes a size that cannot be ignored compared to the internal resistance of the IC. For example, assuming that the withstand voltage of one TMR element 3 is 1V, when 11 TMR elements 3 are connected in series so as to exceed 2Vdd: 10V, the resistance value of the entire TMR element 3 is 110 kΩ or more than necessary. If the internal resistance of the IC 5 is 10 MΩ, it exceeds 1%, so that it becomes a non-negligible size that affects the S / N ratio.

  As described above, in the magnetic sensor device 1 according to the present embodiment, when the withstand voltage of the whole TMR element 3 connected in series is Vb and the operating voltage of the IC 5 is Vdd, the withstand voltage Vb is Vdd / 2 ≦ Vb ≦. Since the relationship of 2Vdd is set, even if the withstand voltage of each TMR element 3 is small, the withstand voltage Vb as a whole of the plurality of TMR elements 3 connected in series is increased and becomes higher than the terminal voltage (Vdd / 2) of the IC5. Thus, dielectric breakdown can be prevented.

  In addition, the wiring 4 is connected to the pair of connection terminals 4 a and is parallel and close to each other and extends between the plurality of TMR elements 3, and from the main wiring part 4 A to the TMR element 3. Since there are a plurality of pairs of connection wiring portions 4B extending in parallel and close to each other and connected to the pair of electrodes 3a, the generation of noise due to electromagnetic induction can be suppressed. That is, when a plurality of TMR elements 3 are connected, a large number of wiring portions exist, but when the magnetic field to be detected includes an alternating magnetic field (or in the case of an alternating magnetic field), electromagnetic induction occurs in the wiring 4 and noise occurs. There is a risk that the S / N ratio is lowered due to the voltage.

In particular, as in the other example of the present invention shown in FIG. 5, when the wiring 4 is arranged around the outside of the TMR element 3 column, the space between the pair of wirings 4 expands to form a loop, and electromagnetic induction Due to this, noise is likely to occur. However, in the present embodiment, in the pair of main wiring portions 4A and the plurality of pairs of connection wiring portions 4B, the current directions of the adjacent wiring portions are staggered and brought close to each other, thereby avoiding loop-shaped wiring and wiring. 4 is less likely to cause electromagnetic induction.
Further, since the main wiring portion 4A is arranged between the rows of the TMR elements 3 arranged in a plurality of rows, the wiring length can be shortened compared with the case where the wiring is arranged outside the row, and further, the electromagnetic induction generated in the wiring Can be suppressed.

Next, the result of actually producing and evaluating the magnetic sensor device according to the present invention will be described.
As this example, a TMR element with a withstand voltage Vb: 1 V was connected in series to a general-purpose IC with an operating voltage Vdd: 5 V, and whether or not dielectric breakdown occurred was evaluated. The element resistance of the TMR element is 10 kΩ.

<Example 1>
When four TMR elements are connected in series, the resistance of the entire TMR element is 40 kΩ and the withstand voltage is 4 V, which is higher than 2.5 V, which is 1/2 of the operating voltage Vdd of general-purpose IC: 5 V. Did not occur.
<Example 2>
When 10 TMR elements are connected in series, the resistance of the entire TMR element is 100 kΩ and the withstand voltage is 10 V, which is higher than 2.5 V, which is 1/2 of the operating voltage Vdd of general-purpose IC: 5 V. Did not occur. Further, since the resistance of the entire TMR element is 1% or less compared to the internal resistance of 10 MΩ of the general-purpose IC, it can be ignored, and the S / N ratio is not greatly affected.

<Comparative Example 1>
When two TMR elements are connected in series, the resistance of the entire TMR element is 20 kΩ, the withstand voltage is 2 V, and it is lower than 2.5 V, which is 1/2 of the operating voltage Vdd of general-purpose IC: 5 V. Occurred.
<Comparative example 2>
When 20 TMR elements are connected in series, the resistance of the entire TMR element is 200 kΩ, and the withstand voltage is 20 V, which is higher than 2.5 V, which is 1/2 of the operating voltage Vdd of general-purpose IC: 5 V. Did not occur. However, the resistance of the entire TMR element exceeds 1% compared to the internal resistance of 10 MΩ of the general-purpose IC, which is a non-negligible magnitude, affecting the S / N ratio and making high-precision measurement difficult.

  The technical scope of the present invention is not limited to the above-described embodiments and examples, and various modifications can be made without departing from the spirit of the present invention.

For example, in the above embodiment, a plurality of TMR elements are mounted on a printed circuit board and connected in series by pattern wiring. However, a plurality of TMR elements are integrated on one chip using integrated circuit technology, lithography technology, or the like. They may be electrically connected in series with a fine wiring pattern.
In the above embodiment, six TMR elements are arranged in two rows and connected in series, but may be connected in series in other arrangements. For example, as shown in FIG. 6 as another example, 15 TMR elements 3 are divided into 3 pieces of 5 pieces on a substrate 2 and mounted in a dendrite shape (dendritic shape). May be connected in series.

  DESCRIPTION OF SYMBOLS 1 ... Magnetic sensor apparatus, 2 ... Board | substrate, 3 ... Tunnel magnetoresistive (TMR) element, 3a ... Electrode, 4 ... Wiring, 4a ... Connection terminal, 4A ... Main wiring part, 4B ... Connection wiring part, 5 ... IC, 6 ... Detection circuit

Claims (3)

A substrate,
A plurality of tunnel magnetoresistive elements having a pair of electrodes provided on the substrate;
A wiring provided on the substrate for connecting the plurality of tunnel magnetoresistive elements in series and having connection terminals at both ends;
A detection circuit unit having an IC for detecting a resistance change by applying a voltage to the tunnel magnetoresistive element;
When the withstand voltage of the entire tunnel magnetoresistive elements connected in series is Vb and the operating voltage of the IC is Vdd, the withstand voltage Vb is set to have a relationship of Vdd / 2 ≦ Vb ≦ 2Vdd. A magnetic sensor device. The magnetic sensor device according to claim 1,
A pair of main wiring portions connected to the pair of connection terminals and extending between the plurality of tunnel magnetoresistive elements in parallel and close to each other;
A magnetic sensor device comprising: a plurality of pairs of connection wiring portions extending in parallel and close to each other from the main wiring portion toward the tunnel magnetoresistive element and connected to the pair of electrodes. . The magnetic sensor device according to claim 2,
A plurality of the tunnel magnetoresistive elements are arranged in a plurality of rows,
A pair of main wiring portions are arranged between the tunnel magnetoresistive element columns, and a plurality of pairs of connection wiring portions are arranged on both sides of the pair of main wiring portions. Sensor device.

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