Patent Application
20080316656
The instant nonprovisional patent application claims priority to Japanese Patent Application No. 2007-164838 filed Jun. 22, 2007 and which is incorporated by reference in its entirety herein for all purposes.
Recently, the recording density of a magnetic recording/reading device has rapidly increased concurrently with increases in the amount of information to be treated, and a magnetic head having high sensitivity and high output power is increasingly required in accordance with such tendency. To meet such requirement, a magnetic head using a GMR (Giant Magnetoresistive) film, which may provide high output power, has been developed, and furthermore variously improved so far. However, even in the magnetic head using the GMR film, output power may be possibly insufficient for recording density larger than 9.3109 bits/cm2. Therefore, as a next-generation magnetoresistive film subsequent to the GMR film, research and development has focused on a magnetic head using a tunnel magnetoresistive effect (TMR) film, or a CPP (Current Perpendicular to the Plane) GMR film that flows a current so as to penetrate stacked surfaces of GMR.
The magnetic head using the TMR film or the CPP-GMR film has a significantly different structure compared with the magnetic head using the conventional GMR film. In the latter case, the magnetic head has a CIP (Current Into the Plane) structure that flows a sense current in a film plane direction of a magnetoresistive effect film including a GMR film, and electrodes for supplying the sense current are provided in both sides of the magnetoresistive effect film. On the other hand, in the former case, since the magnetic head has a CPP structure in which the sense current is flown in a perpendicular direction to a film plane of the magnetoresistive effect film such as TMR film or CPP-GMR film, electrodes for supplying the sense current are provided to be stacked on the magnetoresistive effect film.
In the magnetic head having the CPP structure, as described below, magnetic properties may be greatly degraded in a process during manufacturing the magnetic head. First, in the magnetic head having the CPP structure, the sense current flows perpendicularly to stacked surfaces in a thickness direction of the magnetoresistive effect film between an upper magnetic shield and a lower magnetic shield. Therefore, when a circuit, which short-circuits the upper magnetic shield as one electrode to the lower magnetic shield as the other electrode, exists in the magnetic head having the CPP structure, the circuit may become a short-circuit of the sense current, resulting in a decrease in reading output of the magnetic head. Moreover, “Broad-band noise spectroscopy of giant magnetoresistive read heads”, IEEE transactions on magnetics, 41, 2307 (2005), Klaas B. Klaassen et al. (“non-patent document 1) describes that when a magnetic head is not appropriately manufactured and thus has some defects in the magnetoresistive effect film, the magnetic head has large noise.
The short circuit or the defects may be formed on an end face of the magnetoresistive effect film. When the magnetoresistive effect film is processed by ion milling or mechanical polishing, a short circuit or a damaged area is formed on an end face to be formed, which may degrade magnetic properties of a magnetic head. Several methods have been proposed for the purpose of inhibiting formation of the short circuit or the damaged area which may degrade original properties of the magnetoresistive effect film. Japanese Patent Publication No. 2003-086861 (“Patent document 1) discloses an approach for removing the short circuit by performing oxidation treatment to a side face of a magnetoresistive effect film after being subjected to ion milling.
An air-bearing surface protection layer formed on an air-bearing surface of a slider of a magnetic head must have sufficient corrosion resistance and sufficient wear resistance to protect the magnetoresistive effect film from corrosion and wear. On the other hand, since magnetic spacing as a distance between the magnetic head and a magnetic disk is essentially reduced in accordance with increase in recording density of the magnetic disk recording/reading device, the air-bearing surface protection layer must be small in thickness.
To concurrently meet the above requirements, studies have been made on a technique for reducing thickness of the air-bearing surface protection layer while keeping the corrosion resistance and wear resistance. Currently, a double-layer film configured by an upper layer of a carbon film and an adhesion layer of an amorphous silicon film is used for the air-bearing surface protection layer. Since the carbon film is tough and chemically inactive, the film has sufficient corrosion resistance and sufficient wear resistance. Since the carbon film generally has high internal stress, the film is hard to be directly adhered to a substrate. On the contrary, since the amorphous silicon film has low internal stress, it reduces the internal, compressive stress of the carbon film, and consequently improves adhesion.
The carbon film in the air-bearing surface protection layer is formed using chemical vapor deposition (CVD) or filtered cathodic vacuum arc (FCVA) deposition. The carbon film includes a diamond component and a graphite component, and the carbon film formed using the above method is relatively much in diamond component and thus tough, consequently the carbon film exhibits relatively excellent wear resistance even if the thickness is small. When the above method is used, a carbon film having a thickness of 1.5 nm or more is formed, whereby sufficient corrosion resistance and sufficient wear resistance can be achieved. Currently, an air-bearing surface protection layer including a carbon film 1.5 nm thick and a silicon film 1.0 nm thick is formed using these techniques.
To achieve further reduction in thickness of the air-bearing surface protection layer, Japanese Patent Publication No. 2006-107607 (“patent document 2”) discloses a method of manufacturing an air-bearing surface protection layer including only a carbon thin film. By using this technique, an air-bearing surface protection layer is formed with only the carbon film that contributes to corrosion resistance and wear resistance, whereby reduction in thickness can be achieved while keeping corrosion resistance and wear resistance.
It was found that in a magnetic head using the TMR film in which the intermediate layer was a tunnel barrier layer, when the thickness of the air-bearing surface protection layer was made less than 2.5 nm to meet the requirement of increased recording density, a considerably large number of magnetic heads were low in S/N ratio of a read element, and therefore they were not able to exhibit desired properties.
Embodiments of the present invention provide a magnetic head suitable for high density recording at a high yield by reducing the thickness of an air-bearing surface protection layer of a magnetic head and suppressing reduction in the S/N ratio of a read element. According to the embodiment of
Embodiments of the present invention relate to a magnetic head having a magnetoresistive effect element, and a method of manufacturing the magnetic head.
An object of embodiments of the invention is to provide a magnetic head suitable for high density recording at a high yield by reducing the thickness of an air-bearing surface protection layer of a magnetic head, in addition, suppressing reduction in the S/N ratio of a read element.
In conducting a detailed investigation on a conventional manufacturing method in order to achieve a high-yield magnetic head, it was found that reduction in the S/N ratio of a read element of a magnetic head was caused by the following mechanism.
When an intermediate layer, a ferromagnetic pinned layer, or a ferromagnetic free layer in a magnetoresistive effect film is damaged, such a damaged portion becomes a trap site that easily captures an electron. Coulomb potential is different between a case that an electron is trapped in the damaged portion as the trap site, and a case that the damaged portion is empty, and consequently electric resistance is varied (fluctuates). The fluctuation of electric resistance acts as noise in detection of a magnetic field.
The damage is induced by a phenomenon that a material configuring a magnetoresistive effect film chemically reacts with a reactive material at an end face of the film. One end face (recording medium facing surface) of the magnetoresistive effect film is exposed to an air-bearing surface side, and directly contacts to the air-bearing surface protection layer. The carbon film configuring the upper layer of the air-bearing surface protection layer and the silicon film configuring the adhesion film as the lower layer thereof are extremely reactive with the magnetoresistive effect film. Furthermore, when the silicon film is compared to the carbon film, the carbon film more significantly damages the magnetoresistive effect film. From the above, when the conventional air-bearing surface protection layer configured by the silicon film and the carbon film is used, first, increases in noise is observed due to a reaction between silicon configuring the adhesion film and the magnetoresistive effect film. Furthermore, when the thickness of the adhesion film is reduced due to reduction in thickness of the air-bearing surface protection layer, and consequently carbon may contact to the magnetoresistive effect film, more trap sites are formed in a medium facing surface configuring part of the air-bearing surface of the magnetoresistive effect film, resulting in increases in noise, namely, reduction in the S/N ratio.
Principally, if even a single layer of adhesion film exists, the air-bearing surface protection layer including a carbon film does not contact to the magnetoresistive effect film. However, in the conventional technique, when the air-bearing surface protection layer is formed, since carbon is irradiated to an air-bearing surface of a magnetic head as ions having energy of about 50 eV, the carbon somewhat enters into the adhesion film, and some of the ions may penetrate the film. Thus, the carbon may react with the magnetoresistive effect film under the adhesion film. In the case of using the conventional technique, when the thickness of the adhesion film is decreased to less than 1.0 nm, the carbon directly contacts to an end face of the magnetoresistive effect film.
Since a carbon film 1.5 nm or more in thickness must be formed to achieve sufficient corrosion resistance and sufficient wear resistance, when an air-bearing surface protection layer less than 2.5 nm in thickness is formed, the adhesion film must be less than 1.0 nm in thickness, causing reduction in the S/N ratio.
In the light of the above mechanism, the inventors found that a magnetic head was configured such that a single-layer silicon nitride film was used for the air-bearing surface protection layer, and carbon was not present in the medium facing surface of the magnetoresistive effect film, whereby in a magnetic head using a magnetoresistive effect film having an intermediate layer including an oxide, even if the thickness of the air-bearing surface protection layer was less than 2.5 nm, a good S/N ratio was obtained.
The silicon nitride film is used for the air-bearing surface protection layer, so that silicon is inactivated by nitrogen in the silicon nitride film. Thus, the reaction between the magnetoresistive effect film and the air-bearing surface protection layer is suppressed, consequently increases in noise can be prevented. A component ratio of nitrogen in the silicon nitride film is preferably 35 atomic percent or more and 60 atomic percent or less.
When the air-bearing surface protection layer is configured to be at least two layers of the silicon nitride film and the carbon film, the thickness of the silicon nitride film is made large compared with the entering depth of carbon in formation of the carbon film, or the energy of carbon in formation of the carbon film is reduced such that the carbon does not penetrate the silicon nitride film, whereby a reaction between the magnetoresistive effect film and the silicon nitride film or the carbon film is suppressed, consequently increases in noise can be prevented. A detailed mechanism of this is described below.
When a carbon film is formed using carbon ions having energy Ei, since the carbon ions are irradiated to the adhesion film, the carbon ions somewhat enter into the adhesion film, resulting in a reaction of the carbon ions with the magnetoresistive effect film under the adhesion film. The entering depth of a carbon ion into the adhesion film can be calculated as follows. After colliding with the adhesion film, the carbon ion enters into the adhesion film while losing the initial energy Ei. The carbon ion stops at a depth at which the energy of the carbon ions becomes zero. In this process, power of the adhesion film for decelerating the carbon ions is called stopping power (dE/dx). The stopping power means energy lost by a particle while the particle enters to a depth of unit length, and as the number of electrons is increased, that is, as the adhesion film is denser, the stopping power is increased. From the stopping power and energy of an injected particle, the entering depth d can be expressed by the following expression.
D=Ei/(dE/dx)
This shows that one of the following conditions may be satisfied to isolate between the carbon film and the magnetoresistive effect film. That is, since it is only necessary that the entering depth d is smaller than the thickness t of the adhesion film, (1) the thickness t of the adhesion film is larger than a quotient obtained by dividing the injection energy of carbon ions by stopping power of the adhesion film, (2) the injection energy of a carbon particle in formation of the carbon film is smaller than a product of multiplying the thickness t of the adhesion film by the stopping power dE/dx, and (3) the stopping power dE/dx of the adhesion film is larger than a quotient obtained by dividing the injection energy Ei of the carbon particle in formation of the carbon film by the thickness t of the adhesion film. The air-bearing surface protection layer is formed such that any one of the three conditions is satisfied, whereby the carbon film can be isolated from the magnetoresistive effect film. It is also means for solving the problem that the air-bearing surface protection layer is configured such that the air-bearing surface protection film (upper layer) does not contain carbon.
According to the above configurations, a magnetic head having small noise can be obtained in thickness of the air-bearing surface protection layer of less than 2.5 nm while the magnetoresistive effect film is not contacted to silicon and carbon.
According to embodiments of the invention, the thickness of the air-bearing surface protection layer can be decreased without damaging the magnetoresistive effect film. As a result, a magnetic head that is high in yield and suitable for high recording density can be obtained.
First, a basic configuration of a magnetic head according to embodiments of the invention is described with reference to
While the magnetic head 1 is a recording/reading magnetic head having the read element 12 and the write element 60, the read element may be separated from the write element. In such a case, the magnetic head 1 is configured to have a read element 12 including a TMR film 2.
Next, a configuration of a portion of the read element and a portion of the air-bearing surface protection layer of a magnetic head according to example 1 is described with reference to
As shown in
For the lower magnetic shield layer 14 and the upper magnetic shield layer 16, a soft magnetic material including Ni—Fe alloy is used. For the lower metal layer 3, Ta, Ru, Ni—Fe alloy, or a stacked film of them is used. For the antiferromagnetic layer 4, an antiferromagnetic material such as Pt—Mn alloy or Mn—Ir alloy, or a hard magnetic material such as Co—Pt alloy or Co—Cr—Pt alloy is used. As the hard magnetic material film, a film with high coercivity in antiparallel coupling, so-called self-pinned film may be used. For the ferromagnetic pinned layer 5 and the ferromagnetic free layer 7, a highly-polarized material such as Ni—Fe alloy, Co—Fe alloy, Co—Ni—Fe alloy, magnetite, or Heusler alloy, and a stacked film of them can be used. Moreover, a multilayer film may be used, which includes ferromagnetic layers stacked with a spacer layer 1 nm or less in thickness between them. In the case of using the TMR effect, the intermediate layer 6 acts as a tunnel barrier layer, and specifically an oxide of Al, Mg, Si, Zr, Ti, or a mixture of oxides of them, or a stacked body of the oxides can be used for the intermediate layer, and magnesium oxide (MgO) is used in the example. For the upper metal layer 8, Ta, Ru, Ni—Fe alloy, or a stacked film of them is used.
A stacking order of layers of the TMR film is not limited to the above, and for example, the lower metal layer, ferromagnetic free layer, intermediate layer, ferromagnetic pinned layer, antiferromagnetic layer, and upper magnetic layer may be stacked in this order on the lower magnetic shield layer 14, and then the upper magnetic shield layer 16 may be stacked thereon.
Next, a method of manufacturing the magnetic head according to example 1 is described using
After the mechanical polishing is finished, the magnetic head row bar 50 is guided into a vacuum chamber (step 701). The medium facing surface 9 of the magnetic head row bar 50 is subjected to cleaning by argon ion beam irradiation in the vacuum chamber (step 702). Ions of a noble gas such as neon, helium, krypton, or xenon can be used as the ions in addition to argon ions. An acceleration voltage of an ion beam is 300 V, and an ion incidence angle is 75 degrees from a normal to the medium facing surface. However, such a condition is not restrictive as long as a conductive smear caused by a plastic flow layer, which is formed in a step of the mechanical polishing, can be removed. Moreover, sputter etching by gas plasma can be used in place of ion beam irradiation.
Following the cleaning step, the magnetic head row bar 50 is taken out from the vacuum chamber, then the row bar 50 is carried in a vacuum into a deposition apparatus shown in
Returning to
As a film formation method of the silicon nitride film, in addition to the reactive sputtering, ion-beam deposition in which directional argon ions and directional nitrogen ions are irradiated in a beam to the silicon target so that the silicon target is sputtered for silicon nitride film formation may be used, in addition, thermal evaporation, CVD and the like may be used. Moreover, the thickness of the film may be less than 2.0 nm as long as corrosion resistance is satisfied.
Advantages of the example 1 are described with a relationship with comparative example 1. A magnetic head of the comparative example 1 has the same configuration as in the example 1 except for a composition and a formation method of an air-bearing surface protection layer, and it was prepared by the same manufacturing method. The air-bearing surface protection layer in the comparative example 1 was formed as follows: a magnetic head row bar was subjected to mechanical polishing, then carried into a vacuum chamber and subjected to cleaning by ion beam irradiation therein, and then the air-bearing surface protection layer was formed using the deposition apparatus shown in
Next, the magnetic head of the example 1 and the magnetic head of the comparative example 1 were subjected to noise measurement. Noise of the magnetic head was measured using the following method. First, lead wires, which are connected to the lower magnetic shield layer 14 and the upper magnetic shield layer 16 provided below and above the TMR film 2 of the magnetic head respectively, are connected to a voltage meter. Then, a sense current is flown into the TMR film 2 using a constant-current power supply, and fluctuation of a voltage is measured for 0.1 sec at a sampling frequency of 5 MHz through a bandpass filter of 1 MHz to 50 MHz. Standard deviation of voltage values measured in such a way may be an index of noise. In
As described above, according to the example 1, the air-bearing surface protection layer is reduced in thickness, and reduction in S/N ratio of the read element is suppressed, whereby a magnetic head suitable for high density recording can be provided at a high yield. Moreover, it was able to be confirmed that a silicon nitride film having a high component ratio of nitrogen was excellent in corrosion resistance and wear resistance, and exhibited sufficient corrosion resistance and sufficient wear resistance in thickness of 2.0 nm.
Next, a configuration of a portion of the read element and a portion of an air-bearing surface protection layer of a magnetic head according to example 2 is described with reference to
Next, a method of manufacturing the magnetic head according to example 2 is described with reference to
Following a cleaning step (702) by an ion beam, the adhesion film 112 including silicon nitride is formed by sputtering (step 704). The thickness of the adhesion film 112 is 1.0 nm. A film formation method is the same as in the example 1. The film formation method of the adhesion film 112 is not limited to sputtering, and ion-beam deposition, thermal evaporation, and CVD may be used. After formation of the adhesion film 112, the air-bearing surface protection film 114 of 1.0 nm in thickness including carbon is formed as an upper layer using cathodic vacuum arc deposition (step 706). The cathodic vacuum arc deposition is performed using an apparatus shown in
Some kinds of surface treatment may be performed after formation of the air-bearing surface protection film 114 as long as sufficient corrosion resistance and sufficient wear resistance are provided. After the air-bearing surface protection film 114 is formed, the magnetic head row bar is taken out from a vacuum chamber (step 706).
In the magnetic head 1′ according to the example 2, the thickness of the silicon nitride film as the adhesion film 112 is not limited to the above 1.0 nm if carbon ions may not reach the TMR film 2 through the adhesion film 112 in the relevant thickness in a subsequent step of forming the air-bearing surface protection film 114 including carbon. That is, when it is assumed that stopping power of the adhesion film 112 is dE/dx, the thickness of the film is t, and the energy of the carbon ion is Ei, it is enough that t is given so as to satisfy the following expression.
t>Ei/(dE/dx)
The cathodic vacuum arc deposition is used to form the carbon film 114 in the example 2, in which an average value of energy of carbon ions is about 50 eV. While the energy of carbon ions is somewhat distributed, most of the ions have energy of 100 eV or less. Here, since the stopping power dE/dx of the silicon nitride film 112 is about 100 eV/nm, if the thickness of the silicon nitride film 112 is 1.0 nm or more, the carbon ions do not damage the TMR film 2 through the adhesion film 112 including the silicon nitride film, consequently a magnetic head having a good S/N ratio can be manufactured.
Next, advantages of the example 2 are described with a relationship with comparative example 2. Here, description is made on a magnetic head of the comparative example 2 to be compared to the magnetic head of the example 2. The magnetic head of the comparative example 2 has an air-bearing surface protection layer 2.0 nm in thickness as in the example 2, and was prepared as follows. A magnetic head row bar was subjected to mechanical polishing, then carried into a vacuum chamber and subjected to cleaning by ion beam irradiation therein, and then silicon nitride films 0 nm, 0.2 nm, 0.4 nm, 0.6 nm, and 0.8 nm in thickness respectively were formed by reactive sputtering as adhesion films 112. Then, carbon films 2.0 nm, 1.8 nm, 1.6 nm, 1.4 nm, and 1.2 nm in thickness respectively were formed using cathodic vacuum arc deposition. The total thickness of each of the air-bearing surface protection layers formed according to the five conditions is 2.0 nm.
Next, the magnetic heads prepared in the example 2 and the comparative example 2 were subjected to noise measurement. Noise of the magnetic head was measured by the same method as the method carried out in comparison between the example 1 and the comparative example 1. In
In the case that the air-bearing surface protection layer 110 has a double-layer structure of the adhesion film 112 including the silicon nitride film and the air-bearing surface protection film 114 including the carbon film as in the example 2, noise is reduced with increases in the component ratio of nitrogen in the silicon nitride film, and the component ratio of nitrogen is preferably 35 atomic percent or more and 60 atomic percent or less as in the example 1.
According to the example 2, the air-bearing surface protection layer is reduced in thickness, and reduction in S/N ratio of the read element is suppressed, whereby a magnetic head suitable for high density recording can be provided at a high yield as in the example 1. Moreover, since the carbon film is formed as the air-bearing surface protection film (upper layer), corrosion resistance and wear resistance are excellent compared with the example 1.
Next, description is made on another example of a formation method of an air-bearing surface protection layer of the magnetic head according to the example 2. This method is characterized in that the air-bearing surface protection layer 110 is configured by the adhesion film 112 including the silicon nitride film and the air-bearing surface protection film 114 including the carbon film, and when the air-bearing surface protection film 114 is formed, the carbon film is formed by sputtering a carbon target using Ar gas plasma.
Following a cleaning step by an ion beam, the adhesion film 112 including silicon nitride is formed by sputtering. The thickness of the adhesion film 112 is 0.4 nm. A film formation method of the adhesion film 112 is not limited to sputtering, and ion-beam deposition, thermal evaporation, and CVD may be used. After formation of the adhesion film 112, the air-bearing surface protection film 114 1.6 nm in thickness including carbon is formed using sputtering. The formation of the carbon film by sputtering is performed using an apparatus shown in
According to this sputtering method, an atom of carbon, which was sputtered and adhered to the silicon nitride film, has energy of about several electron volts, that is, the atom does not have sufficient energy to penetrate a single layer of the silicon nitride film. Therefore, even if the thickness of the silicon nitride film is 0.4 nm, no reaction occurs between an end face of the TMR film and carbon, and therefore no damage is induced in the TMR film. A magnetic head having the air-bearing surface protection layer formed in this way had a good S/N ratio.
A film formation method of the carbon film need not be limited to the above sputtering, and ion-beam deposition in which directional argon ions are irradiated in a beam to a carbon target so that the carbon target is sputtered for carbon film formation, in addition, thermal evaporation, CVD and the like may be used.
According to the above examples, a magnetic head having a high S/N ratio can be achieved without causing magnetic spacing loss. As a result, a magnetic head suitable for high density recording can be obtained at a high yield.
While the TMR film was used as the magnetoresistive film of the read element in the above examples, the CPP-GMR film may be used. In the case of the CPP-GMR film, the intermediate layer is a conductive layer or a conductive layer having a current confining region. Specifically, Al, Cu, Ag, Au, or a mixture of them or a stacked body of them may be used for the conductive layer, in addition, a region for current confining may be inserted into the conductive layer by partially oxidizing or nitriding part of the conductive layer. Again in this case, the air-bearing surface protection layer is reduced in thickness, and reduction in the S/N ratio of the read element is suppressed, whereby a magnetic head suitable for high density recording can be provided at a high yield.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-164838 | Jun 2007 | JP | national |
