JPH0471352B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a magnetic sensor using a magnetoresistive element.

(b) Conventional technology Semiconductors with high carrier mobility such as Insb, Insb-Nisb, InAs, or Ni-Co, Ni-Fe, Ni-Fe
-Ferromagnetic materials such as Co have the property that the resistance value changes when a magnetic material is applied to it, and this property is used to detect the presence of magnetism, the presence of magnetic material, and the movement of magnetic materials.Magnetic sensors has been put into practical use.

Generally, the conventional magnetic sensor 21 is
Publication No. 157755 (The casing 26 as shown in Figure 3 A and B)
is made of metal and is formed in the shape of a rectangular cylinder with one end closed, the lower end is closed with a lid member, the mount board 27, sensor unit 28, etc. are arranged inside, and the sensor unit 28 and spacer 29 are arranged. The remaining space except the enclosed area was filled with synthetic resin. The sensor unit 28 is formed by fixing a pair of magnetoresistive elements 23 and 24 in parallel on the magnetic substrate 22 on the upper surface of the mount substrate 27 using adhesive resin, and the spacer 29 is attached to the magnetic substrate 22 on the upper surface of the mount substrate 27.
They were installed on all sides of 8.

As for the operating principle, as shown in FIG. 4, a pair of magnetoresistive elements 23 and 24 are placed on the magnetic pole face of a magnet and magnetically biased. When the magnetic body approaches from below and reaches the magnetoresistive element 24, the magnetic flux generated by the magnet concentrates on the magnetic body. Therefore, the resistance of the magnetoresistive element 24 increases. These two magnetoresistive elements 23, 24
When connected as shown in FIG. 4 and connected to a low voltage circuit, an alternating current signal appears at the output terminal as the magnetic material moves, making it possible to detect the magnetic material.

Furthermore, as shown in FIG. 3A, a short-circuit stripe called a raster 25 is attached above the magnetoresistive elements 23 and 24 at right angles to the length direction. This is equivalent to magnetoresistive elements connected in series with a distance between the electrodes that is short compared to the width of the electrodes, and at the same time suppresses the Hall electric field and increases the resistance value by connecting many of them. You can take it.

Financial institutions use this method to read bills, checks, and bills that are printed using special magnetic ink.

(c) Problems to be solved by the invention General banknotes differ in size, color, and ink used;
It is easy to distinguish because of features such as watermarks, but since special banknotes have the same size, ink, color, etc., identification is highly dependent on magnetic patterns using magnetic ink, which makes them easier to identify than current magnetic sensors. Furthermore, it has become necessary to improve performance such as resolution and stability.

For example, as shown in Figure 5A, two magnetoresistive elements
When a character pattern whose width is narrower than the interval P between MR ₁ and MR ₂ arrives, the output signal waveform reaches its maximum value and then returns to the zero level. However, as shown in FIG. 5D, when a character pattern with an interval q and a width s equal to the width r and the interval p of the magnetoresistive elements MR ₁ and MR ₂ , respectively, arrives successively, the signal waveform is as follows. This is the same as when one wide pattern arrives, and therefore the magnetic sensor detects the upper and lower two types of patterns as being the same.

(d) Means for Solving the Problems The present invention has been made in view of the above points, and provides a magnetic sensor having a pair of magnetoresistive elements 3 and 4 fixed on a magnetic substrate 2. This problem is solved by attaching the magnetic body 10 under the magnetoresistive element.

(e) Effect Here, as shown in Figure 6, which shows the change in resistance with respect to the magnetic flux density of the magnetoresistive element, (R _B is the resistance of the magnetoresistive element, and R _O is the resistance of the magnetoresistive element when the magnetic flux density is zero. ) If no magnetic bias is applied, the change in resistance will be small; on the other hand, if a magnetic bias is applied, the change in resistance will be large. Therefore, when the magnetic body 10 is attached under one of the magnetoresistive elements 3 and a magnetic bias is applied, the distance q is equal to the width r of the magnetoresistive element and the interval p thereof, as shown in FIG. 5D.
Even if character patterns having widths s and s arrive consecutively, the outputs are not offset and can be detected.

(F) Embodiment An embodiment of the magnetic sensor according to the present invention will be described below with reference to FIGS. 1 and 2.

First, a method for manufacturing the pair of magnetoresistive elements 3 and 4 fixed on the magnetic substrate 2 shown in FIG. 1 will be briefly described.

After slicing the InSb ingot into wafers approximately 300 μm thick using a diamond saw or the like, mirror polishing is performed to remove distortion of the wafers. Next, the wafer is etched to form grooves in which copper is laminated in a raster pattern. Here, the photoresist is formed into a desired pattern, and grooves (not shown here) are dug in stripes on the magnetoresistive elements 3 and 4 so as to be perpendicular to the length direction. Subsequently, electroplating is performed using copper sulfate to laminate copper 5 in the groove. Further, after removing the photoresist, the InSb wafer is treated with the photoresist and etched deeper than the grooves in order to cut out the shape of the magnetoresistive elements 3 and 4 as shown in FIG. Here, approximately 10 μm of etching is performed. Finally the above using adhesive on the glass substrate
Glue the surface of the InSb wafer downward and back-lap it. As a result, the magnetoresistive elements 3 and 4 on which the raster 5 is formed come out in the shape shown in FIG.

Next, the configuration of the magnetic sensor 1 according to the present invention will be shown.
The casing 6 is made of metal and is formed into a rectangular tube shape with one end closed, and the lower end opening is closed with a lid member.
A mount board 7, a sensor unit 8, etc. are arranged inside, and the space other than the part surrounded by the sensor unit 8 and spacer 9 is filled with synthetic resin. The sensor unit 8 is formed by fixing the pair of magnetoresistive elements 3 and 4 in parallel on the magnetic substrate 2 on the upper surface of the mount substrate 7 using adhesive resin, and spacers 9 are installed on all sides of the sensor unit 8. There is. Furthermore, a magnetic body 10 for applying a magnetic bias is provided under one of the magnetoresistive elements 3.
Here, as in the magnetic substrate 2 shown in FIG. 2, a cut may be provided on the lower surface to prevent magnetic flux from leaking.

The feature of the present invention lies in the magnetic body 10 that applies a magnetic bias under the one magnetoresistive element 3. One magnetoresistive element 3 to which magnetic bias is applied
The resistance of the other magnetoresistive element 4 to which no magnetic bias is applied changes small. Therefore, as shown in FIG. 5D, even if character patterns having a spacing q and a width s that are equal to the width r and the spacing p of the magnetoresistive element arrive in succession, the outputs can be detected without being canceled out.

(G) Effects of the Invention As is clear from the above description, the present invention provides a magnetic body 10 that applies a magnetic bias under one of the magnetoresistive elements 3, so that the magnetoresistive elements 3,
Even if the resistance changes of 4 are different, and character patterns with spacing q and width s equal to the width r and spacing p of the magnetoresistive element, respectively, arrive in succession as shown in FIG. 5D, the outputs do not cancel each other out. Detection becomes possible, and more advanced identification becomes possible.

[Brief explanation of the drawing]

FIG. 1 is a partially fragmented plan view of a magnetic sensor that is an embodiment of the present invention, FIG. 2 is a partially fragmented side view of a magnetic sensor that is an embodiment of the invention, and FIG. 3B is a partially exploded side view of a conventional magnetic sensor, FIG. 4 is a circuit diagram of the magnetic sensor, and FIGS. 5A to 5D show the relationship between character patterns and output signal waveforms. 6 are diagrams showing the relationship between magnetic flux density and resistance ratio. 1 is a magnetic sensor, 2 is a magnetic substrate, 3 and 4 are magnetoresistive elements, 5 is a raster, 6 is a housing, 7 is a mount board, 8 is a sensor unit, 9 is a spacer, 1
0 is a magnet.

Claims (1)

[Scope of Claims] 1. A casing having a detection surface; a magnetic substrate fixed inside the casing so as to face the detection surface and forming at least one pair of magnetoresistive elements; and one of the magnetic resistance elements. A magnetic sensor, comprising: a magnetic body fixed below the element and selectively applying a magnetic bias to the one magnetoresistive element, the other magnetoresistive element being unbiased.