JPS60171618A - Test of magnetic resistance element - Google Patents

Abstract

PURPOSE:To decide the quality of an MR element before it is manufactured to obtain the effect to reduce the variation of the manufacturing process by forming the dummy element of the MR head in such a way that its current density, element temperature, strain, etc., are set to equal conditions to those set to actual heads. CONSTITUTION:The degree of dependence on electric current of a magnetic field value Hk is measured by putting the thin film of an MT element on a crystal substrate, on which a dummy element is put, so that the lengthwise and breadthwise dimensions of the thin film become proportional to those of an actual MR element and measuring its characteristic curve by making various electric currents Is to flow to the dummy element formed through the same manufacturing process as that applied to an actual MR head. In the case of a dummy element whose quantity of magnetostriction lambda is negative, the magnetic field value Hk rises as the electric current Is increases. On the other hand, in the case of an MR element whose quantity of magnetostriction lambda is positive, the magnetic field value Hk does not change even when the electric current Is increases. By forming the dummy element of the MR head in such a way that its current density, element temperature, strain, etc., are set to equal conditions to those set to an actual head, variation of the manufacturing process of the MR element can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to a magnetoresistive magnetic head, and more particularly to a test method for measuring the reproduction characteristics of the head using a dummy magnetoresistive element.

(b) Prior art and problems A conventional example will be explained with reference to the drawings. Figure 1 shows a conventional magnetoresistive magnetic head (hereinafter simply referred to as Ml)! This is a perspective view and block diagram of the shunt bias method of the head.

In the figure, numeral 1 indicates a magnetic substrate made of NiZn ferrite, Mnzn7 elite, or the like. In an actual MR head, the substrate may be formed of another non-magnetic material (not shown), and the magnetic substrate may be formed by thin film deposition. 2 is a titanium thin film, 8 is a magnetoresistive element made of NiFe permalloy (
Hereinafter, simply MR element 5 refers to titanium thin film 2 and M element 811.
! The enclosing nonmagnetic insulating layer 6 is a high magnetic permeability thin film such as NiFe permalloy, and magnetically shields the MR element 8 together with the magnetic substrate 1. Reference numerals 7 and 7' denote power supplies, which allow current to flow in opposite directions from both ends of the MR element 3 to the central extraction layer. This current flows to the MR element 8 and also to the titanium thin film 2 according to the resistance ratio. Due to the magnetic field generated by this shunt current, the MR element 8
A bias magnetic field is applied to the Reference numeral 8 denotes a differential amplifier, which uses the fact that the resistivity of the MK element 3 changes in response to an external magnetic field to differentially output changes in the external magnetic field as a signal. It is.

FIG. 2 shows a perspective view and a block diagram of an MR head (hereinafter referred to as mutual bias type) in which 2I-M elements are arranged in parallel. In this figure, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and redundant explanation thereof will be omitted. 3' in the figure
Elements identical to the MR element 3 are arranged in parallel at a required interval, and the interval and periphery thereof are covered with a non-magnetic insulating layer 5, and further magnetically shielded by a magnetic substrate 1 and a high magnetic permeability thin film 6. The extraction layer 4 is connected to both ends of each MR element 3 and 8'. -10,000 are both grounded, and the other lead-out end is connected to the t source 7 and .tau., respectively, and the differential amplifier 8 is connected in the same manner as in FIG. MR elements 8 and 8 by power supplies 7 and 7'
′, and the magnetic field generated by this current causes Ml
A bias magnetic field is mutually applied to the L elements 8 and 3'.

FIG. 3 is a schematic explanatory diagram of the manufacturing process of a multi-element MR head for magnetic tape, in which (a) a high-transparency film corresponding to FIGS. A manufacturing process is shown in which up to the magnetic thin film 4 is formed by vacuum film forming technology, and (b) shows a process in which a cover plate 9 is bonded after all film formation is completed. (C) is a cutting process in which the MR head is cut into individual pieces, and then bonded to the 7L/-mu 10 shown in (d) through a polishing process. Furthermore, the flat cable 11 and the head terminal are connected by wire bonding to complete M and D.

By the way, conventionally completed MR heads are often accompanied by variations in properties, and it is said that the main factor controlling these variations in properties is the magnetic anisotropic dispersion of the MR element. Because there was no way to determine the extent of magnetic anisotropy dispersion during the manufacturing process of an actual MR head, the actual head was not made into a finished product through the manufacturing process described above. At that time, the only way to determine whether a manufacturing lot was acceptable was to test the characteristics of an MR head.

Therefore, when a rejected product occurs, a large amount of man-hours consumed in the manufacturing process are wasted, which is a disadvantage that hinders mass production.

(C) Object of the Invention In view of the above-mentioned conventional drawbacks, it is an object of the present invention to provide means for determining the quality of an MR head at the time of completion of film formation in the LIT head manufacturing process.

(d) Structure and object of the invention According to the present invention, a dummy magnet having a predetermined length-width dimension ratio is formed on a non-magnetic substrate having a predetermined thermal conductivity and coefficient of thermal expansion with respect to a magnetoresistive element thin film. A dummy element is constructed by forming a resistive element thin film, and a tangent line and minimum resistivity are established at the inflection point of a characteristic curve showing the relationship between resistivity and magnetic field strength using the current value flowing through the dummy magnetoresistive element as a parameter. A method for testing a magnetoresistive element, characterized in that the quality of the magnetoresistive element is determined by measuring a change in the magnetic field value indicated by the intersection of the lines or a change in the amount of bias magnetic field due to the current value, and , the dummy element is placed on a non-magnetic substrate having a thermal conductivity n times higher than that of the base material constituting the magnetic head and having an equivalent coefficient of thermal expansion, and is placed on a non-magnetic substrate having an aspect ratio of the thin film dimension of the magnetoresistive element which becomes the head. It is also possible to form a film with n times the element width of the dummy magnetoresistive element.
This is achieved by providing a method for testing a magnetoresistive element, characterized in that the value of the current flowing through the dummy magnetoresistive element is measured at least n times the value of the current flowing through the thin film of the magnetoresistive element. .

(6) Examples of the invention Examples of the present invention will be described in detail below using measurement data.

Figure @4 shows the characteristic measurement data of 7 Yant bias dummy elements. A quartz substrate (thermal conductivity of 0.0.
054W/α℃, coefficient of thermal expansion 15.6 x 10-')
A so-called dummy element (so-called dummy element) was formed by forming a titanium thin film and an MR element thin film on the crystal substrate in the same manufacturing process as the actual MR head to the required size that the vertical and horizontal dimensions of the actual mit crystal are similar. Various currents Is were passed through an element M150tzm, element width 1150μm, aspect ratio 23), and its (resistivity ψ/magnetic field strength U) characteristic curve was measured, and the tangent line set at the summer point of the curve and the minimum resistance were measured. Figure 4 shows the measurement data of the magnetic field value (hereinafter abbreviated as ■V) indicated by the intersection of the ratio lines and the current dependence of the bias magnetic field amount.
is expressed by converting it into an angle θ using a calculation formula. Note that ^ indicates the amount of magnetostriction. As a result of the measurement, in the case of an MR element with a negative magnetostriction amount λ, - increases as the current ls increases, and at ls = 80 mA, HV was 1.4 times that in the case of a low current. Therefore, it was found that the bias angle θ does not change any further around 20'. - For a 10,000 MR element with a positive magnetostriction amount λ, there is no change in 11 even when the current ■s is increased, and even when 's = 80 mA, it shows the same Hk as in the case of a low current, so the bias angle θ is 28°. It turned out to be good.

The above-mentioned MR magnetostrictive MR head pattern with two types of positive and negative, so-called shunt bias type MR head pattern, Mnzu7 elite substrate (thermal conductivity 0-081W/ag'c thermal expansion coefficient 12.l)
Xl0-6) k:, and the aspect ratio of the M head is 40 (
The device is processed to have a length of 10 μm and a width of 400 μm. That is, the measurement dummy element has a thermal conductivity 1.74 times that of the actual MR head forming substrate, has an equivalent thermal expansion coefficient, and has an aspect ratio of 1/144 of the actual MR head.
When the head characteristics were measured using a current equal to 115 - 16 mA of the above-mentioned measurement current, it was found that, similar to the measurement results shown in Fig. 4, even if the magnetostriction amount is positive, the bias was applied normally and the reproduction characteristics were good.

FIG. 5 shows measurement data of a dummy element using a mutual bias method. The dummy element in the figure is the one used in Figure 4, and the thin film of the M element (element length 50 μm) is placed on the same crystal substrate as the dummy element.
, the element width is 1150 μm, and the aspect ratio is 23), so that the vertical and horizontal dimensions are similar to the actual MR element, and various currents Is are applied to the so-called dummy element, which is formed in the same manufacturing process as the actual Mit head. A characteristic curve (resistivity ψ/magnetic field strength h) was measured, and the current dependence of LLk was measured in the same manner as in FIG.

As a result, for an M)L element with a negative magnetostriction amount λ, [k increases as the current Is increases, and 's=80m
At A, Hk was 1.67 times that at low current. -10,000M
It was found that for R elements with a positive magnetostriction amount, Iik does not change as the current Is increases.

The so-called mutual bias type MR head pattern in which the above-mentioned MR element has two types of magnetostriction λ, positive and negative, is fabricated on a -Zn-y elite substrate (thermal conductivity 0.081W/ff, thermal expansion coefficient 12, l
X10) and processed to have an aspect ratio of 4 degrees (element length: 10 μm, element width: 400 μm).
When measured at s=16mA, the above test results showed ■
Even though the magnetostriction amount λ was positive and had no - current dependence, the bias was applied normally and the reproduction characteristics were good.

Effects of the Invention As explained in detail above, according to the test method of the magnetoresistive element of the present invention, the dummy element of Ml (metal) is
By forming the element temperature, stress, etc. under the same conditions as the actual head, it is possible to check the quality of the MR element in the head (
Since it can be determined before commercialization, it is effective in reducing variations in the manufacturing process of MR elements.

[Brief explanation of drawings]

Fig. 1 is a perspective view and block diagram of a shunt bias type MR head, Fig. 2 is a perspective view and block diagram of a mutual bias type MR head, Fig. 8 is a schematic explanatory diagram of the manufacturing process of the MR head, and Fig. 4 The figure shows characteristic measurement data of a shunt bias type dummy element, and FIG. 5 shows characteristic measurement data of a mutual bias type dummy element. In the figure, 1 is a magnetic substrate, 2 is a titanium thin film, 3 and 3' are Mlt elements, 4 is an extraction layer, 5 is a non-magnetic insulating layer 6 is a high permeability thin film, 7 and τ are power supplies, 8 is a differential amplifier, 9 is a cover plate, 10 is a 7-ram cable, and 11 is a 7-rat cable. Figure 1 Question 3

Claims (3)

[Claims] (1) A dummy magnetoresistive element is constructed by forming a dummy magnetoresistive element thin film having a predetermined length-to-width dimension ratio with respect to the magnetoresistive element thin film surrounding the head on a nonmagnetic substrate having a predetermined thermal conductivity and coefficient of thermal expansion. , a change in the magnetic field value indicated by the intersection of a tangent line provided at an inflection point of a characteristic curve showing the relationship between resistivity/magnetic field strength and a minimum resistivity line using the current value flowing through the dummy magnetoresistive element as a parameter; or A method for testing a magnetoresistive element, characterized in that the quality of the magnetoresistive element is determined by measuring changes in the amount of bias magnetic field depending on the current value. (2) The dummy element is the n of the substrate constituting the magnetic head.
A patent characterized in that a film is formed on a non-magnetic substrate having twice the thermal conductivity and the same coefficient of thermal expansion at an aspect ratio of l/n times the aspect ratio of the thin film of the magnetoresistive element that becomes the head. A method for testing a magnetoresistive element according to claim (1). (3) The element width of the dummy magnetoresistive element is n times the element width of the magnetoresistive element thin film serving as the head, and the current value flowing through the dummy magnetoresistive element is at least n times the element width of the magnetoresistive element thin film serving as the head. A method for testing a magnetoresistive element according to claim (1), characterized in that the measurement is performed at a magnification of 1.