Magnetoresistive effect head with diode in parallel

Details Magnetoresistive effect head with diode in parallel Magnetoresistive effect head with diode in parallel

2000-04-24

2003-01-14

Evans, Jefferson (Department: 2652)

Dynamic magnetic information storage or retrieval

Head

Magnetoresistive reproducing head

Reexamination Certificate

active

06507466

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetoresistive effect head and to a method for manufacturing a magnetoresistive effect head.
2. Description of Related Arts
In the prior art, there has been disclosure of a magnetic reading transducer known as a magnetoresistive (MR) sensor or head, and this was known to be capable of reading data from a magnetic surface with a high linear density.
This type of MR sensor detects a magnetic field signal by means of a change in resistance as a function of the strength and direction of magnetic flux detected by a reading element.
Such an MR sensor operates on the principle of anisotropic magnetic resistance (AMR), which varies in proportion to the square of the cosine of the angle between the direction of magnetization of one component of the resistance of the reading element and the direction of the sensed current flowing in the element.
A detailed description of the AMR effect is found in D. A Thompson et al, “Memory Storage and Related Applications,” IEEE Trans. on Magnetics, MAG-11, p 1039 (1975).
In a magnetic head that uses the AMR effect, to suppress Barkhausen noise, vertical bias is often applied. The vertical bias application material is sometimes an anti-ferromagnetic material such as FeMn, NiMn, or nickel oxide or the like.
Recently, there has been a report of a more prominent magnetoresistive effect attributed to spin-dependent conduction of conduction electrons between magnetic layers with non-magnetic layers therebetween, and an accompanying spin-dependent disturbance in the surface boundary.
This magnetoresistive effect is known variously as the giant magnetoresistive effect and the spin valve effect. Such a magnetic sensor is made of an appropriate material and has improved sensitivity and larger resistance change than sensors that use the AMR effect.
In this type of MR sensor, the planar resistance between a pair of magnetic layers separated by a non-magnetic layer varies in proportion to the cosine of the angle between the magnetization in the two layers.
In the Japanese Unexamined Patent Publication (KOKAI) No. 2-61572, having a claimed priority date of June 1988, there is language with regard to a laminated magnetic structure that imparts a large MR change occurring due to anti-parallel alignment of magnetization within a magnetic layer. In the above-cited specification, a ferromagnetic transition metal and alloy are given as a material usable as in the laminated structure.
Additionally, there is disclosure of a structure in which there is an added layer fixed to at least one of two magnetic layers separated by an intermediate layer and a disclosure that FeMn is suitable for the fixed layer.
In the Japanese Unexamined Patent Publication (KOKAI) No. 4-358310, having a claimed priority day of December 11, 1990, there is disclosure of an MR sensor that is independent of the direction of current flowing therewithin, having two thin-film layers of ferromagnetic material separated by a non-magnetic metal layer, wherein when an applied magnetic field is zero the magnetization directions of the two ferromagnetic layers intersect perpendicularly, the resistance of the two non-linked magnetic layers varying in proportion to the cosine of the angle between the magnetization directions of the two layers.
In the Japanese Unexamined Patent Publication (KOKAI) No. 4-103014, the application for which was filed on Aug. 22, 1990, there is language describing a ferromagnetic tunnel effect film in a multilayer ferromagnetic tunnel junction element in which an intermediate layer is interposed between ferromagnetic layers, wherein a bias magnetic field is applied to at least one of the ferromagnetic layers from an anti-ferromagnetic body.
Shielded spin-valve head and shielded TMR head of the past exhibited great deterioration under excessive current conditions. (Refer to, for example, Abstracts for the 43rd Annual Conference on Magnetism & Magnetic Materials, Miami, Fla., November 1998, p. 170 EB-09.)
Table 1 shown below presents the results of an MR ratio EDD electrostatic discharge test, performed by the inventors and others, with regard to a shielded AMR head, a shield-type spin valve head, and a shielded TMR head.
A human body model was used in the above-noted test, which was performed using a known test apparatus.
A 100-pF ceramic capacitor was used as a capacitor to impart an electrical charge to the above-noted samples, a 1500&OHgr; resistance being inserted between the head (device under test) and the capacitor.
First, a charge was stored in the capacitor using a voltage-application apparatus (HV power supply), after which a switch was switched to the head so as to apply the charge to the head, the R-H loop before and after these events being measured.
With the AMR head, while there was no observed drop in the MR ratio up until a high ESD voltage of 60 volts, with the spin valve head and there was an observed drop in the MR ratio at 25 volts, and with the TMR head, there was a drop observed in the MR ratio at just 1 volt.
This is because in contrast to the magnetically sensitive part of the AMR head, which was a NiFe alloy, that exhibits a drop in the MR ratio when the element temperature is raised by the ESD current to the 660° C., which is the Curie temperature of the NiFe alloy, in the spin valve head, even if the Brocking temperature of the anti-ferromagnetic layers is high, this is approximately 350° C., and when this temperature is exceeded there is a drop in the MR ratio, resulting in a drop in the MR ratio at a lower ESD current and ESD voltage than in the AMR head.
In the case of the TMR head, the element breakdown mode by the ESD voltage is different, the ESD voltage being established by the withstand voltage of the barrier layer, and with current elements, the ESD voltage is approximately 1 V.
TABLE 1
MR Ratio ESD Withstand Voltages for Shielded AMR,
Spin Valve, and TMR Heads
ESD Voltage (V)
AMR (%)
Spin Valve (%)
TMR (%)
0
0.8
1.7
2.4
0.5
0.8
1.7
2.4
0.8
0.8
1.7
2.4
1
0.8
1.7
2.4
2
0.8
1.7
0
5
0.8
1.7
0
8
0.8
1.7
0
10
0.8
1.7
0
15
0.8
1.7
0
20
0.8
1.7
0
25
0.8
1.7
0
30
0.8
0.7
0
60
0.8
0
0
65
0.3
0
0
70
0
0
0
A head is generally subjected to slider processing, is adhered to a suspension, and connected by wiring before shipping, this wiring acting as an antenna, which picks up stray electromagnetic radiation, thereby causing a current to flow.
This current has the same effect as the current that flows in the head during the ESD test, and can destroy the head.
Even after mounting is such equipment as hard disk drives, an excessive sense current can be momentarily imparted because of equipment noise or radiated noise and the like, and this type of excessive current can also destroy the head. Thus, strength exhibited in the ESD test is equivalent to immunity to damage from these types of externally introduced noise.
In the Japanese Unexamined Patent Publication (KOKAI) No. 6-103508 and in Japanese Patent No. 2784460, although there is disclosure of technology for connecting a diode in parallel with a magnetoresistive effect head, in these documents there is no disclosure that can be seen therein with regard to technology for solving the problem of a drop in the MR ratio, which occurs in an SDE test of a magnetoresistive effect head, especially in a magnetoresistive effect element made of a ferromagnetic tunnel junction film or a spin valve film, this occurring at a SDE voltage condition that is lower than a magnetoresistive effect element using AMR, nor is there any disclosure of technology for simplifying the manufacturing process therefor.
Next, in the Japanese Unexamined Patent Publication (KOKAI) No. 4-103014, there is language with regard to technology for applying a bias magnetic field with respect to a magnetic layer in a magnetoresistive effect element. However, there is no disclosure of technology for solving the problem of a drop in the MR ratio, which occurs in an SDE test of a magnetoresistive effect head, this occurring at a SDE voltage condition that is much lo

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