1. Field of the Invention
The present invention relates to a magnetic field sensing element for detecting a change in a magnetic field, and more particularly, to the element used in a device for detecting the rotation of a magnetic body.
2. Description of the Related Art
Generally, a magnetic resistance element (hereinafter referred to as an MR element) is an element whose resistance changes depending on an angle formed by the direction of magnetization of a ferromagnetic body (Ni-Fe or Ni-Co, for example) thin film and the direction of an electric current. The resistance of such an MR element is minimum when the direction of an electric current and the direction of magnetization cross at right angles to each other, and is maximum when the angle formed by the direction of an electric current and the direction of magnetization is 0.degree., that is, when the directions are the same or completely opposite. Such a change in resistance is referred to as an MR rate of change, and is typically 2-3% with respect to Ni-Fe and 5-6% with respect to Ni-Co.
FIGS. 34 and 35 are a side view and a perspective view, respectively, showing the structure of a conventional magnetic field sensing device.
As shown in FIG. 34, the conventional magnetic field sensing device comprises a rotation axis 41, a magnetic rotating body 42 which has at least one concavity and convexity and which rotates synchronously with the rotation of the rotation axis 41, an MR element 43 arranged with a predetermined gap between the magnetic rotating body 42, a magnet 44 for applying a magnetic field to the MR element 43, and an integrated circuit 45 for processing an output of the MR element 43. The MR element 43 has a magnetic resistance pattern 46 and a thin film surface (magnetic-sensitive surface) 47.
In such a magnetic field sensing device, rotation of the magnetic rotating body 42 causes a change in the magnetic field penetrating the thin film surface 47 which is the magnetic-sensitive surface of the MR element 43, resulting in a change in the resistance of the magnetic resistance pattern 46.
However, since the output level of the MR element as a magnetic field sensing element used in such a magnetic field sensing device is low, the detection can not be highly accurate. In order to solve this problem, a magnetic field sensing element using a giant magnetic resistance element (hereinafter referred to as a GMR element) having a high output level has been recently proposed.
FIG. 36 is a graph showing the characteristics of a conventional GMR element.
The GMR element showing the characteristics in FIG. 36 is a laminated body (Fe/Cr, permalloy/Cu/Co/Cu, Co/Cu) as a so-called artificial lattice film where magnetic layers and non-magnetic layers with thicknesses of several angstroms to several dozen angstroms are alternately laminated. This is disclosed in an article entitled "Magnetic Resistance Effects of Artificial Lattices," Japan Applied Magnetics Society Transactions, Vol. 15, No. 51991, pp. 813-821. The laminated body has a much larger MR effect (MR rate of change) than the above-mentioned MR element, and, at the same time, is an element which shows the same change in resistance irrespective of the angle formed by the direction of an external magnetic field and the direction of an electric current.
In order to detect a change in the magnetic field, the GMR element substantially forms a magnetic-sensitive surface. Electrodes are formed at the respective ends of the magnetic-sensitive surface to form a bridge circuit. A constant-voltage and constant-current power source is connected between the two facing electrodes of the bridge circuit. The change in the magnetic field acting on the GMR element is detected by converting a change in the resistance of the GMR element into a change in voltage.
FIGS. 37 and 38 are a side view and a perspective view, respectively, showing the structure of a magnetic field sensing device using a conventional GMR element.
In FIGS. 37 and 38, the magnetic field sensing device comprises a rotation axis 41, a magnetic rotating body 42 as a means for imparting a change to a magnetic field, the body having at least one concavity and convexity and having rotatable synchronously with the rotation of the rotation axis 41, a GMR element 48 arranged with a predetermined gap between the magnetic rotating body 42, a magnet 44 as a magnetic field generating means for applying a magnetic field to the. GMR element 48, and an integrated circuit 45 for processing an output of the GMR element 48. The GMR element 48 has a magnetic resistance pattern 49 as a magnetic-sensitive pattern and a thin film surface 50.
In such a magnetic field sensing device, rotation of the magnetic rotating body 42 causes a change in the magnetic field penetrating the thin film surface (magnetic-sensitive surface) 47 of the GMR element 48, resulting in a change in the resistance of the magnetic resistance pattern 49.
FIG. 39 is a block diagram showing the magnetic field sensing device using the conventional GMR element.
FIG. 40 is a block diagram showing the detail of the magnetic field sensing device using the conventional GMR element.
The magnetic field sensing device shown in FIGS. 39 and 40 is arranged with a predetermined gap between the magnetic rotating body 42 and itself, and comprises a Wheatstone bridge circuit 51 using the GMR element 48 to which a magnetic field is applied by the magnet 44, a differential amplification circuit 52 for amplifying the output of the Wheatstone bridge circuit 51, a comparison circuit 53 for comparing the output of the differential amplification circuit 52 with a reference value to output a signal of either "0" or "1," and an output circuit 54 that switches in response to the output of the comparison circuit 53.
FIG. 41 shows an example of the structure of a circuit of the magnetic field sensing device using the conventional GMR element.
In FIG. 41, the Wheatstone bridge circuit 51 has on its respective sides GMR elements 48a, 48b, 48c, and 48d, for example, with the GMR elements 48a and 48c being connected with a power source terminal VCC, the GMR elements 48 and 48d being polished, the other ends of the GMR elements 48a and 48b being connected with a connection 55, and the other ends of the GMR elements 48c and 48d being connected with a connection 56.
The connection 55 of the Wheatstone bridge circuit 51 is connected with an inverting input terminal of an amplifier 59 of a differential amplification circuit 58 via a resistor 57. The connection 56 is connected with a non-inverting input terminal of the amplifier 59 via a resistor 60, and is further connected with a voltage dividing circuit 62 for forming a reference voltage based on the voltage supplied from the power source terminal VCC via a resistor 61.
An output terminal of the amplifier 59 is connected with its own inverting input terminal via a resistor 63, and is further connected with an inverting input terminal of a comparison circuit 64. A non-inverting input terminal of the comparison circuit 64 is connected with a voltage dividing circuit 66 for forming a reference voltage based on the voltage supplied from the power source terminal VCC, and is further connected with an output terminal of the comparison circuit 64 via a resistor 67.
An output end of the comparison circuit 64 is connected with a base of a transistor 69 of an output circuit 68. The collector of the transistor 69 is connected with an output terminal of the output circuit 68 and is further connected with the power source terminal VCC via a resistor 71. The emitter of the transistor 69 is polished.
FIG. 42 shows the structure of the conventional magnetic field sensing element.
FIG. 43 is a graph showing operating characteristics of the conventional magnetic field sensing element.
As shown in FIG. 42, the Wheatstone bridge comprises the GMR element 48 (formed of 48a, 48b, 48c, and 48d).
As shown in FIG. 43, rotation of the magnetic rotating body 42 causes a change in the magnetic field supplied to the GMR element 48 (48a to 48d), and output corresponding to the concavities and the convexities of the magnetic rotating body 42 can be obtained at an output end of the differential amplification circuit 58.
The output of the differential amplification circuit 58 is supplied to the comparison circuit 64, compared with the reference value as the comparison level, converted into a signal of either "0" or "1," and the signal is further made into a waveform by the output circuit 68. As a result, as shown in FIG. 43, an output of "0" or "1" with steep leading and trailing edges can be obtained at the output terminal 70.
However, since the GMR element used above-mentioned magnetic field sensing element is sensitive, it is necessary to, for example, smooth the surface of the underlayer on which the GMR element is formed in order to fully bring out its characteristics. Therefore, it is difficult to, for example, form the GMR element on the same surface the integrated circuit is formed.
This makes it necessary to separately form the GMR element and the integrated circuit and then electrically connect them with each other, which leads to low productivity and high manufacturing costs.
Further, since the output of the comparison circuit depends on the gap between the magnetic rotating body and the magnetic field sensing element, there is a problem in that the so-called gap characteristics are bad.