JPH0888423A - Magnetic sensor - Google Patents

Abstract

PURPOSE: To make a magnetic sensor stronger against noise and more sensitive by, with the element's resistance value of at least one of four magnetoresistance effect elements in bridge connection being different, generating offset output voltage so that the offset voltage is superimposed on the output voltage of a magnetic sensor. CONSTITUTION: A silicon substrate on which the surface of an oxide film is formed is heated and a magnetic thin film is formed on it, which becomes the area where a magnetism sensing part pattern is formed by etching. Then, this substrate is heated and a magnetic thin film is formed over the entire surface of it, and a mask pattern is formed, and by ion milling method, the magnetism sensing part pattern is so formed that it becomes magnetoresistance effect elements 21-24. Relating to the four magnetoresistance effect elements 21-24 thus formed, so that 3V offset output voltage is generated at a sensor of them, a photo-mask where the length of a magnetism sensing part element is changed is used so that the resistance values of MR elements of 21 and 23 are 2.02kΩ and those of 22 and 24 1.98kΩ.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present application relates to a magnetic sensor using a magnetoresistive effect used in a position detecting device, a current detecting device, a magnetic field detecting device, or an integrated magnetic sensor including the magnetic sensor and a signal processing circuit.

[0002]

2. Description of the Related Art Conventionally, a magnetic sensor utilizing the magnetoresistive effect has a resistance value of 4 as shown in FIG.
The two magnetic field sensing elements 51 to 54 are bridge-connected, and when the magnetic field is present, the resistance value of the magnetic field sensing element is changed by the magnetoresistive effect, so that the balance of the bridge is disturbed and the midpoint potential generated by this is lost. The configuration is such that the difference is taken out as the output voltage. The magnetic sensing element is N
A ferromagnetic material such as i-Fe, Ni-Co, etc.
It is a thin film having a thickness of about m and is then subjected to patterning. As a production example, the ferromagnetic thin film is formed on a glass or a silicon substrate having an oxide film formed on the surface by using a method such as vacuum deposition or sputtering, and a pattern is formed by a method such as photo-etching and then plating or There is a procedure of forming electrodes by vacuum vapor deposition. Applying 5V between the input terminals of the sensor made in this way, the external magnetic field is 4000A
In the case of / m, about 40 to 100 mV can be obtained between the output terminals. This sensitivity changes depending on the ratio of the length and width of the ferromagnetic thin film forming the magnetic sensing element and the film thickness.

The magnetic sensor described above obtains an analog output voltage. However, a current above a certain level is detected by simply detecting the approach of a magnet or the magnetic field generated around a coil or a conductor. When detecting, the digital output of the sensor is preferable. Therefore, as an integrated magnetic sensor that outputs a digital signal, when the sensor generates an output voltage above a certain threshold value, the output changes from a state of 1 to a state of 2,
After that, a circuit having a function of changing the output from the state of 2 to the state of 1 when the output voltage of the sensor falls below the same or different threshold value (hereinafter referred to as a comparison operation circuit) is provided outside. There is a configuration. Further, there is a configuration in which a circuit in which this circuit is integrated like a silicon IC is formed on the same substrate, or separately manufactured, and then housed in the same package and electrically connected.

[0004]

When a magnetoresistive element using a ferromagnetic thin film is used in the above magnetic sensor, the output voltage is restricted by the upper limit of the resistance change rate of the ferromagnetic thin film, and the pattern or the ferromagnetic Even if the thickness of the thin film is optimized, it is difficult to obtain an output voltage above a certain level. In order to improve the magnetic field sensitivity of the integrated magnetic sensor using such a magnetic sensor, it is conceivable to reduce the threshold value of the comparison operation circuit connected to the magnetic sensor. However, it is difficult to reduce the threshold value of the comparison operation circuit because the noise resistance deteriorates and the characteristics of the comparison operation circuit are likely to become unstable due to disturbance such as temperature and power supply voltage fluctuations. In addition, it is necessary to redesign the circuit in order to change the threshold value, and especially when an integrated circuit is currently used for the comparison operation circuit, a large cost is required for new design and manufacture of the integrated circuit. There is.

When a bias current is supplied to the magnetic sensor side and a comparison operation circuit configured to give a voltage threshold value by the product of the bias current and the resistance value of the magnetic sensor is used, the reason described above is used. Therefore, it is difficult to reduce the bias current value. Therefore, the threshold value must be lowered by decreasing the output resistance value of the magnetic sensor, and at the same time, the input resistance also decreases, making it difficult to reduce the power supply current.

[0006]

SUMMARY OF THE INVENTION The present application is a magnetic sensor comprising four bridge-connected magnetoresistive effect elements, of which at least one element has a resistance value different from the others and is configured to generate an offset output voltage. Regarding Alternatively, a magnetic sensor chip and a waveform shaping circuit, which are composed of four bridge-connected magnetoresistive effect elements and have a resistance value of at least one element different from the others, and are configured to generate an offset output voltage, are provided on the same substrate. An integrated magnetic sensor formed above and electrically coupled.

Alternatively, a magnetic sensor chip and an integrated waveform shaping circuit which are composed of four magnetoresistive effect elements connected in a bridge structure, at least one of which has a resistance value different from the others, and which is configured to generate an offset output voltage. The present invention relates to an integrated magnetic sensor in which a chip is housed in the same package and electrically coupled. Furthermore, the absolute value of the offset output voltage is 0.3% or more and 50% of the input voltage.
The present invention relates to the magnetic sensor according to any one of the above.

Here, the offset output voltage means a voltage which is a difference between the midpoint potentials of the bridges in the absence of a magnetic field. In the conventional magnetic sensor, since the resistances of the respective elements constituting the magnetic sensor are all made equal and the bridge is balanced, no offset output voltage is generated in the absence of a magnetic field. The offset output voltage referred to in this application is
It is measured when the element is demagnetized.

In the present invention, the resistance value of at least one of the four elements is made different from that of the other three elements to intentionally break the balance of the bridge and generate the offset output voltage. Specifically, it can be realized by, for example, making the total length of the element whose resistance value is to be changed different from that of the other element or making the width of the element different from that of the other element.

In the example of the method for manufacturing the magnetoresistive element described above, a photo-etching technique may be used when patterning the ferromagnetic thin film, and a photomask may be used in which the length or width of the element is changed. Alternatively, a magnetic sensor having a desired offset output voltage may be produced by changing the film thickness of the ferromagnetic thin film or changing the material. When an external magnetic field is applied so that a positive output voltage is obtained in the magnetic sensor, a large output voltage can be obtained by setting the above offset output voltage to be positive. Therefore, it is possible to detect a magnetic field with high sensitivity without reducing the threshold value of the comparison operation circuit.

However, if the offset output voltage is too small, it is difficult to distinguish it from the variation in the offset output voltage that occurs during manufacturing, and the yield of elements that can achieve the object is reduced. Therefore, the lower limit of the offset output voltage must be 0.3% or more of the absolute value of the input voltage, preferably 0.5% or more, and more preferably 0.
It is 8% or more. Further, the upper limit of the offset output voltage can be simply up to the input voltage. However, when the offset output voltage is increased, it is necessary to increase the difference in the resistance value of each element, so the magnetic field sensitivity of the sensor is reduced. For example, if the offset output voltage is set to 25% of the input voltage, the magnetic field sensitivity is reduced by 5%. If the offset output voltage is set to 50% of the input voltage, the magnetic field sensitivity is reduced by 30%. Therefore, the upper limit of the offset output voltage needs to be 50% or less of the input voltage, and more preferably 25% or less.

Further, when a comparison arithmetic circuit configured to give a voltage threshold value by a product of a bias current flowing through the magnetic sensor and a resistance value of the magnetic sensor is used, the output resistance value of the magnetic sensor is high. It is possible to operate even if the threshold value is a large voltage, and it is possible to make an integrated magnetic sensor with a small power supply current. In this case, the magnitude of the offset output voltage to be set is a voltage whose upper limit is the voltage given by the product of the bias current and the output resistance. In addition, when the above-mentioned offset output voltage is negative, a comparator circuit that simply uses a zero voltage as a threshold value is used, and by varying the magnitude of the offset output voltage of the magnetic sensor, various threshold values can be obtained. An integrated magnetic sensor with can be made. In this case, there is an advantage that the circuit is simplified and the number of parts is reduced.

[0013]

Embodiments of the present invention will now be described with reference to the drawings.

[0014]

Example 1 A 4-inch φ silicon substrate having a 200 nm oxide film formed on its surface was heated to 300 ° C.
A 200 nm-thick magnetic thin film made of 80% -Fe20% was formed by a sputtering method. This magnetic thin film was etched using an ammonium sulfate-based corrosive liquid to form a region for forming a magnetic sensitive portion pattern. This substrate is then 300
50 ℃ Ni80% -Fe20 over the entire surface of the substrate
% Magnetic thin film is formed by the sputtering method, the mask pattern is formed by the photo-etching method, and the magnetoresistive effect element as shown in FIG. 1 is formed by the ion milling method.
A magnetic sensing part pattern having a certain shape was formed. The width of the magnetically sensitive portion affects the rate of change in magnetic resistance, and the wider the width, the better the magnetic field sensitivity, but on the other hand, the resistance value of the element becomes smaller and the hysteresis becomes larger. Is about 8 μm to 35 μm, preferably 15 to 2
It is about 5 μm. Of the four magnetoresistive elements formed here, the offset output voltage can be generated by making the total length or width or film thickness of at least one element different from the other, but as shown in FIG. It is preferable to equalize the resistance values of the two elements at symmetrical positions in order to obtain the symmetry of the midpoint potential, and here, in order to generate the offset output voltage of 30 mV when the input voltage of 3 V is applied to the sensor. The resistance values of the MR elements 21 and 23 are set to 2.02 kΩ and 2
Photomasks were used in which the length of the magnetic sensing element was changed so that the MR elements 2 and 24 had a resistance value of 1.98 kΩ.

Then, a mask pattern is formed to form electrodes and wirings of the device, and the mask pattern is formed by electroplating.
A gold layer with a thickness of 00 nm and then a nickel layer with a thickness of 1 μm are produced. A silicon oxide film having a thickness of 1.5 μm was formed on this by a plasma chemical vapor deposition method using silane gas and nitrous oxide for the purpose of protecting the magnetic sensitive pattern. A window was formed in the silicon oxide film by a reactive ion etching method using carbon tetrafluoride to open the electrode part of the device, and a wafer was produced. The wafer obtained by this method is 0.96 mm with a dicing saw.
It cut into the element chip of the corner. This chip was fixed on a lead frame, a predetermined position was wire-bonded, a terminal was drawn out, and sealed with an epoxy resin to manufacture a magnetic sensor. When 3 V was applied as an input voltage between the input terminals at room temperature to the magnetic sensor thus obtained, an offset output voltage of 32.2 mV (1.1% with respect to the input voltage) was obtained in the absence of a magnetic field. When a magnetic field was applied to the sensor using a solenoid coil,
55.1 mV at 0 A / m magnetic field, 3000 A / m
An output voltage of 77.6 mV was obtained at.

[0016]

COMPARATIVE EXAMPLE 1 A magnetic sensor was manufactured in the same manner as in Example 1 except that the resistances of all four elements were set to 2 kΩ. The same measurement was performed on this sensor, and when a 3V input voltage was applied and there was no magnetic field, the standard deviation was 3.5 mV variation (0.1% of the input voltage).
2%). 22.1 mV at a magnetic field of 1500 A / m, and 4 at a magnetic field of 3000 A / m.
The output voltage was as low as 6.0 mV.

[0017]

COMPARATIVE EXAMPLE 2 A magnetic sensor was produced in the same manner as in Example 1 except that the offset output voltage was 8 mV (0.27% of the input voltage) when 3 V was input. When the offset output voltage of this sensor was measured, the average value was 7.8 mV and the standard deviation was 3.8 mV.
In addition, 4% of the manufactured sensors have a negative offset output voltage, and the same measurement as in Example 1 was performed on these sensors, and as a result, a magnetic field of 1500 A / m resulted in 19.3 mV and 3000 A. / M at 42.
The output voltage was as low as 0 mV.

[0018]

Example 2 A magnetic sensor element chip was manufactured in the same manner as in Example 1. On the other hand, a constant voltage power supply circuit for driving the magnetic sensor, a circuit for amplifying the output voltage from the magnetic sensor, and when the output voltage of the sensor reaches 70 mV as an operating point, the output changes from the OFF state to the ON state and the ON state.
When the output voltage of the sensor is 50 mV
A silicon integrated circuit of 1 × 1.4 mm square provided with a comparison operation circuit having an action of returning to the OFF state again when the temperature falls below the range and an output circuit was manufactured.

In order to assemble the respective parts obtained as described above into a sensor, the magnetic sensor and the silicon integrated circuit are fixed on one lead frame, and the predetermined position is wire-bonded and electrically coupled to the epoxy. An integrated magnetic sensor was obtained by sealing with a resin. When a power supply voltage of 12 V was applied to this sensor and a magnetic field was applied by a coil, the output switched from a state of 1 to a state of 2 at a magnetic field strength of 2800 A / m at room temperature, and then the magnetic field was gradually reduced to a magnetic field strength of 1400 A. Output again at / m
It was confirmed with good reproducibility that the state of 1 returned to the state of 1. The circuit current at this time was 4.2 mA.

[0020]

Comparative Example 3 An integrated magnetic sensor was manufactured by the method of Example 2 using the magnetic sensor chip manufactured in Comparative Example 1 and the silicon IC manufactured in Example 2. When this was measured by the same method, the output state was not switched even in a magnetic field of 5000 A / m, and it could not be operated.

[0021]

[Third Embodiment] According to the method of the first embodiment, a magnetic sensor which is different only in that the offset output voltage is -30 mV at the time of inputting 3 V is manufactured.
Was applied and measured in the same manner as in the above-mentioned embodiment. As a result, at room temperature, there was no magnetic field of −28.1 mV (0.
9%), an output of 18.0 mV was obtained in a parallel magnetic field of 3000 A / m. A zero-cross type comparison operation circuit that turns on when the input voltage is 0 V or more and turns off when the input voltage is less than 0 V is connected to this sensor, and a magnetic field is applied.
The output was switched between ON and OFF at / m.

[0022]

[Example 4] A magnetic sensor was produced by the method of Example 1 except that the offset output voltage was -40 mV at the time of inputting 3 V. A power supply voltage of 3 V was applied to this magnetic sensor.
Was applied and measured in the same manner as in the above-mentioned embodiment, it was −37.9 mV (1.
3%), an output of 9.3 mV was obtained in a parallel magnetic field of 3000 A / m. Similar to the third embodiment, a zero-cross type comparison operation circuit that turns on when the input voltage is 0 V or more and turns off when the input voltage is less than 0 V is connected to this sensor, and when a magnetic field is applied, the output turns on and off at 2600 A / m. It switched.

[0023]

By using the magnetic sensor of the present invention, it becomes possible to detect a magnetic field using a comparison operation circuit having a large threshold voltage. In addition, when a bias current is applied to the magnetic sensor and a threshold value is used as a product of the resistance value of the magnetic sensor and the comparison operation circuit of the type,
Since the offset output voltage of the magnetic sensor can compensate for the increase in the threshold voltage caused by increasing the resistance value of the magnetic sensor, an integrated magnetic sensor with high sensitivity and low circuit current can be manufactured. Further, by taking the offset output voltage in the negative direction with respect to the output, it is possible to inexpensively manufacture a magnetic sensor assembly or an integrated magnetic sensor having different sensitivities by using only a simple zero-cross detection circuit.

[Brief description of drawings]

FIG. 1 is a front view showing an example of the arrangement of magnetic field sensing elements of a magnetic sensor of the present invention.

FIG. 2 is a front view showing another example of the arrangement of the magnetic sensing element of the magnetic sensor of the present invention.

FIG. 3 is a block diagram of an example of an integrated magnetic sensor.

FIG. 4 is a front view of an integrated magnetic sensor of Example 2.

FIG. 5 is a front view showing an example of an arrangement of magnetic field sensing elements of a conventional magnetic sensor.

[Brief description of reference numerals]

 11-14 Magnetic Sensing Element 15 Bonding Pad 16 Wiring 21-21 Magnetic Sensing Element 25 Bonding Pad 26 Wiring 31 Constant Voltage Source 32 Magnetoresistive Effect Element 33 Amplifier 34 Comparator with Hysteresis 35 Output Transistor 36 Power Supply Terminal 37 Ground terminal 38 Output terminal 41 Molded outer shape 42 Lead frame 43 Lead frame 44 Magnetoresistive effect element 45 Integrated circuit 46 Bonding pad 47 Bonding pad 48 Wires 51-54 Magnetic sensing element 55 Bonding pad 56 Wiring section

Claims (4)

[Claims] 1. A magnetic sensor comprising four magnetoresistive effect elements connected in a bridge structure, wherein at least one of the magnetoresistive effect elements has a resistance value different from the others, and is configured to generate an offset output voltage. 2. A magnetic sensor chip comprising four magnetoresistive effect elements connected in a bridge structure, wherein at least one of the magnetoresistive effect elements has a resistance value different from the others, and is configured to generate an offset output voltage. An integrated magnetic sensor in which the waveform shaping circuit is formed on the same substrate and electrically coupled. 3. A magnetic sensor chip comprising four magnetoresistive effect elements bridge-connected, wherein at least one of the magnetoresistive effect elements has a resistance value different from the others, and is configured to generate an offset output voltage. An integrated magnetic sensor in which an integrated waveform shaping circuit chip and an integrated waveform shaping circuit chip are housed in the same package and electrically coupled. 4. The magnetic sensor according to claim 1, wherein the absolute value of the offset output voltage is 0.3% or more and 50% or less of the input voltage.