JPS635257Y2 - - Google Patents

Description

[Detailed explanation of the idea]

The present invention detects changes in the strength of a periodic signal magnetic field generated from a magnetic storage medium in which magnetic signals are recorded in the form of magnetization with equally spaced bit lengths P, and in particular, changes in the peak position of the periodic magnetic field or in the vicinity of the peak. ,
The present invention relates to a position detection ferromagnetic magnetoresistive element (hereinafter referred to as a position detection MR element) that detects a change in resistance of a ferromagnetic magnetoresistive thin film (hereinafter referred to as an MR film). The position detection MR element outputs a signal according to the relative position with respect to a magnetic storage medium, and is used in the detection section of a position detector such as a linear encoder or rotary encoder. MR for position detection
In the device, it is necessary to detect signals regardless of the relative speed with the magnetic storage medium, and changes in the electrical resistance of the MR film stripe are detected in a direct current manner as changes in the voltage across both ends due to the drive current. Therefore, fluctuations in the voltage at both ends due to causes other than the magnetic field, that is, offsets and drifts, directly cause malfunctions or a reduction in operating margin. Among these, drift is mainly caused by temperature fluctuations, but it has conventionally been solved by using a differential configuration or a bridge configuration. In other words, by taking advantage of the fact that the resistance values of two MR film stripes spaced apart by P/2 change in opposite phases, where P is the bit length of magnetization of the magnetic storage medium, a differential configuration can be formed with them, or they can be connected to each other. A bridge configuration is made of four MR film stripes spaced apart by P/2 to cancel common-phase changes due to temperature, etc. On the other hand, the cause of the offset is mainly due to variations during manufacturing, that is, variations in the film thickness distribution of the MR film and the patterning of the stripes. In the past, the MR film on the same substrate was improved to some extent by using the differential configuration or bridge configuration as described above, but the importance of the size of the offset and the arrangement of the MR film stripes was not recognized, so it was difficult to reduce the offset. was insufficient, and it became essential to adjust the offset externally. In this way, conventional position detection MR elements have had problems such as an increase in the number of parts for offset adjustment and the need for complicated adjustments. The object of the present invention is to provide an MR element for position detection that has an extremely small offset and does not require adjustment by arranging MR film stripes having a bridge configuration at optimal positions. The MR element for position detection of the present invention detects a periodic magnetic field generated from a magnetic storage medium in which magnetic signals are recorded in the form of magnetization having equally spaced bit lengths P. , and a fourth striped MR film parallel to each other and of equal length, with the first MR film as a reference, the second, third,
The fourth MR film is arranged at a distance of (2n-1)P/2, (2n+2m-1)P/2, (2n+m-1)P (n, m≧1 integer), respectively, using the bit length P as a unit. , the first and fourth MR films are opposite sides, and the second and third MR films are opposite sides.
It is characterized in that it is electrically coupled to form a bridge circuit with the MR film as the other side. Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a plan view showing a first embodiment of the MR element for position detection of the present invention. In this structure, four striped MR films 2, 3, 4, and 5, which are parallel to each other and have the same length, are formed on a smooth substrate 1 and are electrically connected by a conductor portion 6. Furthermore, the electrode terminal 7,
8, 9 and 10. A first MR film stripe 2 and second, third, and fourth MR film stripes 3,
The intervals with 4 and 5 are P/2, 3P/2, and 2P, respectively.
It is. Here, P represents the bit length recorded on the magnetic storage medium. This is the case where n=m=1 in (2n-1)P/2, (2n+2m-1)P/2, and (2n+m-1)P. The conductor part 6 is the first
MR film stripe 2 and fourth MR film stripe 5
and the second and third MR film stripes 3,
Electrode terminals 7, 8, 9, 10 are electrically connected to form a bridge circuit with 4 as the opposite side to the other side, and electrode terminals 7, 8, 9, 10 are used to apply a bridge voltage to each connection point and take out the output. It is said that FIG. 2 shows an equivalent circuit of a bridge circuit using MR film stripes 2, 3, 4, and 5.
Resistors R _A , R _B , R _C , and R _D forming the bridge circuit correspond to MR film stripes 2, 3, 4, and 5, respectively, and resistors R _A and R _D form opposite sides of this bridge circuit. Resistors R _B and R _C form the other opposite sides. Next, the operation of this MR element for position detection is shown in Figure 1.
This will be explained using FIGS. 2, 3, and 4. FIG. 3 is a diagram showing the positional relationship between the position detection MR element and the magnetic storage medium. MR elements for position detection (here simply MR film stripes 2, 3, 4, 5)
(representatively represented by ) are arranged parallel to and facing the surface of the magnetic storage medium 11 . magnetic storage medium 1
1, a magnetic signal is recorded in the form of magnetization with a bit length of P, and the MR is recorded with relative displacement in the x direction.
The signal magnetic field 12 acting on the film stripes 2, 3, 4, 5 changes periodically. This allows each
Similarly, the resistance value of the MR film stripe changes periodically. This is shown in Figure 4a. The resistance value of the MR film stripe is maximum on the magnetization boundary line 13 and minimum in the middle thereof. In this way, due to the positional relationship of MR film stripes 2, 3, 4, and 5, the first and fourth
The resistance values of the MR film stripes 2 and 5 both change like R _A , and the resistance values of the second and third MR film stripes 3 and 4 change like R _B with completely opposite phases. Therefore, due to the bridge circuit in which the first and fourth MR film stripes 2 and 5 and the second and third MR film stripes 3 and 4 are opposite sides, a bridge output that changes around zero with a period P is generated. is obtained. That is, by applying a bridge voltage between electrode terminals 8 and 9 in the position detection MR element shown in FIG. 1 or its equivalent circuit shown in FIG. The bridge output V _MR1 shown in figure b is obtained. Normally this bridge output V _MR1 is pulsed with zero as the threshold,
The pulse train output corresponds to the amount of change relative to the magnetic storage medium. Therefore, there is no problem when the bridge output has no offset like V _MR1 , but if it becomes an output like V _MR2 which has an offset V _pff added to it, it becomes impossible to pulse. Even if this does not happen, the noise tolerance will decrease and the position detection function will not be able to be performed. The MR element for position detection of the present invention is characterized in that this offset V _pff can be made extremely small, and this will be explained next in comparison with the conventional one. Figure 5a shows the conventional arrangement of MR film stripes.
The membrane stripes 14, 15, 16 and 17 are arranged at equal intervals P/2. In this arrangement,
With MR film stripes 14 and 16 as opposite sides,
A bridge circuit is constructed with the MR film stripes 15 and 17 as other opposite sides. In other words, if it corresponds to the equivalent circuit shown in Fig. 2, MR film stripe 1
4, 15, 16, and 17 correspond to resistors _RA , _RB , _RD , and _RC . Further, FIG. 5b shows the arrangement of the MR film stripes according to the present invention, which is the same as that already explained. If the resistance values of the respective MR film stripes 14, 15, 16, 17 and 2, 3, 4, 5 are all equal, no offset V _pff will occur in either case, but in reality, during manufacturing
Variations in the film thickness distribution of the MR film and pattern width during stripe pattern formation occur, which inevitably causes variations in the resistance value. However, in addition to truly random variations in the resistance values of such MR film stripes, there are spatially systematic deviations, and these systematic deviations generally account for a larger portion. Systematic deviations are due to the fact that the thickness of the MR film has a gradual spatial distribution, and the amount of overetching when forming a stripe pattern using photoetching technology also has a gradual spatial distribution. caused by. thus,
There is a correlation between the resistance values of the four MR film stripes, and the arrangement of the present invention using this correlation and the offset V _pff of the conventional one (this is the difference between the offset V′ _pff caused by systematic deviation and the truly random one) This is very different from the offset V'_' due to variations (which is the sum of The deviation in resistance value caused by gradual fluctuations in width (due to overetching, etc.) is also gradual spatially, and within a range of the size of one position detection MR element, it can be approximated linearly as follows. r (x, y) = r _p (1 + ax + by) ... (1) where r is the resistance value of the MR film stripe per unit length at the coordinates (x, y), and r _p can be arbitrarily set. It is the resistance value per unit length at the origin of the ivy coordinates,
a and b are coefficients depending on the distribution of resistance values. Also, truly random variations are omitted here. As a result, the resistance value of one MR film stripe becomes R _i (x) = ∫ ^l _p r _p (1 + ax + by) dy = r _p l (1 + bl / 2 + ax) ... (2) where the stripe length is l. . Table 1 summarizes the resistance values and offset V' _pff obtained by substituting the x-coordinate of each MR film.

[Table] However, in this table, the MR film stripes are shown in the order of resistors R _A , R _B , R _C , and R _D shown in the equivalent circuit of FIG. 2. Also, the offset voltage V' _pff is calculated as V _pff = ( _RB / R _A + _{R B} - R _D / R _C + R _D ) V _p (3), where the bridge voltage is V p. While the offset V' _pff of the conventional MR element for position detection includes aP, that is, the linear term of the deviation ratio of the MR film stripe resistance value at a point separated by P in the MR element for position detection, the position detection of the present invention It can be seen that the offset of the detection MR element is significantly reduced, with only the second-order term of aP remaining. This effect will be shown more concretely by substituting actual numerical values. The value of the bit length P commonly used is from several 100 μm to several mm, and for example, for a bit length of 1 mm, the typical value of aP is about 0.5%. Therefore, the offset V′ _pff (due to systematic deviation) per 1 V of bridge voltage is 1.25 mV for the conventional position detection MR element.
In contrast, the MR element for position detection of the present invention does not even reach 0.01 mV. On the other hand, a typical value of the offset V'' _pff caused by truly random variations is about 0.3 mV (example of P = 1 mm, l = 1 mm, MR film stripe width = 20 μm), and therefore the total offset V In terms of _pff , while the conventional one has a voltage of 1.55 mV, the inventive one has only about 0.3 mV.Comparing this with the output of the position detection MR element, the zero-to-peak of the bridge output V _MR The maximum value is about 14 mV per 1 V of bridge voltage, and in actual use it is about 3 to 10 mV.Therefore, as shown in Figure 4b, conventional position detection
While it is essential for the MR element to adjust the offset V _pff using a circuit, it is clear that there is no need for the position detection MR element of the present invention. In the above embodiment, the second, third, and fourth MR film stripes 3, 4, and 5 are connected to the first MR film stripe 2.
The output waveform of the MR membrane has a periodicity of pitch P as shown in Figure 3a, so taking this point into consideration, these are (2n-1)P/2, (2n+2m-1)P/2, and (2n+m-1)P, the above explanation holds exactly in the same way. For example, the effect is the same even if each of them is 3P/2, 5P/2, or 8P/2, and is particularly effective when it is desired to widen the interval between the MR film stripes due to the wiring of the conductor portion 6. However, as the distance between them increases, the resistance value distribution deviates from the linear approximation of equation (1), so in terms of characteristics, they should be as close to each other as possible, that is,
P/2, 3P/2, and 5P/2 are optimal. The shape and arrangement of the conductor portion 6 and the electrode terminals 7, 8, 9, and 10 are merely examples, and may be of any shape as long as they form a predetermined bridge circuit. For example, if the resistance value of the conductor portion 6 is not negligible compared to the resistance value of the MR film stripes 2, 3, 4, 5, a slight offset will occur, so that the electrode terminals 7, 8,
The outlets 9 and 10 are arranged to be taken from the midpoint of each conductor section 6 connecting each MR film stripe. Here, as the substrate 1 of the MR element for position detection,
Suitable materials include glass or ceramic with a smooth surface, or a silicon plate with an insulating layer formed on the surface.
Single elements such as Fe, Co, etc., or alloys containing them as main components are formed by vapor deposition, sputtering, plating, etc., and unnecessary parts are removed using microfabrication techniques such as photo etching to form a predetermined shape. Typical shapes of MR film stripes include film thickness of 200 to 1000 Å, width of several μm to 100 μm, and length of several
It ranges from about 100 μm to several mm, and the specific values are determined depending on the magnetic storage medium used, the bit length P, etc. For the conductor portion 6 and electrode terminals 7, 8, 9, 10, materials such as Au, Ag, Cu, Al, etc. having a low resistance value are suitable.
It is formed into a predetermined shape in the same manner as the MR film stripe. As explained above, the MR for position detection of this invention
The element detects a periodic signal magnetic field generated from a magnetic storage medium in which magnetic signals are recorded in the form of magnetization with equally spaced bit lengths P. The first MR film stripe is used as a reference, and the second, third, and fourth MR film stripes are each (2n-1)P/2 with the bit length P as a unit. , (2n+2m-1)P/2, (2n+Zm-1)P [n, m≧1 integer] and are arranged with the first and fourth MR film stripes on opposite sides, and the second and third MR film stripes Because they are electrically connected to form a bridge circuit with the membrane stripe as the other side,
Even if there is an unavoidable variation in resistance value when forming an MR film, no offset will occur, so there is no need to adjust it, and the extra components, circuits, and complicated labor required for this adjustment can be eliminated.

[Brief explanation of the drawing]

Fig. 1 is a plan view showing the first embodiment of the MR element for position detection of the present invention, Fig. 2 is an equivalent circuit of a bridge circuit constituted by MR film stripes, and Fig. 3 shows the MR element for position detection and magnetic Figure 4a is a waveform diagram showing the change in resistance value of the MR film stripe due to displacement between the position detection MR element and the magnetic storage medium, and Figure 4b is a diagram showing the positional relationship with the storage medium. Figure 5a is an output waveform diagram, and Figure 5a is a conventional MR for position detection.
Figure 5 showing the arrangement of the MR film stripes of the device.
FIG. b is a diagram showing the arrangement of MR film stripes according to the present invention. In the figure, 1 is a substrate; 2, 3, 4, and 5 are first, second, third, and fourth MR film stripes, respectively; 6 is a conductor portion; 7, 8, and 9.

Claims (1)

[Claims for Utility Model Registration] In a ferromagnetic magnetoresistive element for position detection that detects a periodic signal magnetic field generated from a magnetic storage medium in which magnetic signals are recorded in the form of magnetization with equally spaced bit lengths P, The ferromagnetic magnetoresistive effect element for position detection is composed of first, second, third, and fourth striped ferromagnetic magnetoresistive thin films parallel to each other and of equal length, and the first ferromagnetic magnetoresistive effect With the thin film as a reference, the second, third, and fourth ferromagnetic magnetoresistive thin films are respectively (2n-1)P/2, (2n+2m-1)P/2, and (2n+m-) with the bit length P as a unit. 1) P (n, m ≧ 1 integer) spaced apart, and the first and fourth ferromagnetic magnetoresistive thin films are on opposite sides, and the second and third ferromagnetic magnetoresistive thin films are on the other side. 1. A ferromagnetic magnetoresistive element for position detection, characterized in that the element is electrically coupled to form a bridge circuit.