Patent Application
20080218915
1. Field of the Invention
The present invention relates to a tunnel magnetoresistive (TMR) effect element that provides an output based on resistance change according to the intensity of a signal magnetic field, a thin-film magnetic head including the TMR effect element, a head gimbal assembly (HGA) provided with the thin-film magnetic head, and a magnetic recording/reproducing apparatus provided with the HGA. Especially, the present invention relates to a manufacturing method of the TMR effect element.
2. Description of the Related Art
As magnetic recording/reproducing apparatuses, in particular magnetic disk drive apparatuses, increase in capacity and reduce in size, thin-film magnetic heads are required to have higher sensitivity and larger output. To respond to the requirement, a tunnel magnetoresistive (TMR) effect, which is expected to show extremely high resistance-change ratio, attracts attention, and actually thin-film magnetic heads having the TMR effect element as a read head element for reading data are being intensively developed.
The TMR effect element has a magnetization-pinned layer (pinned layer) in which the magnetization direction is fixed, and a magnetization-free layer (free layer) in which the magnetization direction can change according to an applied magnetic field, and has a structure in which a tunnel barrier layer as an energy barrier in the tunneling effect is sandwiched between the pinned layer and the free layer. The tunnel barrier layer is usually a metal-oxide layer, and therefore, the TMR effect element has an element resistance higher than those of other magnetoresistive (MR) effect elements such as an anisotropic magnetoresistive (AMR) effect element and a giant magnetoresistive (GMR) effect element. A considerably higher resistance of the TMR effect element is likely to increase a shot noise derived from random motions of electrons in the element, to degrade the signal-to-noise (S/N) ratio of the element output.
One measure for decreasing the element resistance may be to reduce the thickness of the tunnel barrier layer. However, an outright reduction of the layer thickness causes the corresponding decrease in the resistance-change ratio. As the measure for both of high resistance-change ratio and low element resistance, for example, Japanese Patent Publication No. 2000-322714A describes a structure provided with a noble metal between a ferromagnetic layer and the a tunnel barrier layer. Further, for example, Japanese Patent Publication No. 2000-266566A describes a structure provided with a non-magnetic layer such as III-V intermetallic compound layer at the position of a tunnel barrier layer.
As the conventional measure without using the above-described special structure needing much man-hour cost for the formation, the thickness of the tunnel barrier layer has been adjusted so that the ratio of the resistance-change ratio and the sheet-resistance of the element becomes as high as possible. Generally, the higher the ratio is, the larger the element output becomes. Here, the sheet-resistance is defined as a product of the element resistance in the layer thickness direction and the area of the layer surface of the element. In fact, used is a tunnel barrier layer with a thickness at which the resistance-change ratio indicates a maximum value or with smaller thickness than the just-described thickness. As a result, in some cases, a new noise may occur due to the formation of pinholes. As the measure against the new noise, the elements are screened in the formation step, and elements showing a noise in a predetermined degree or more are excluded.
However, even if the screening is performed, there have been elements that show a considerably large noise under the condition of high environmental temperature, for example, approximately 85 to 100° C. or of low environmental temperature, for example, approximately −10 to 0° C. The degree of the noise under the condition of high or low environmental temperature (high temperature noise or low temperature noise) has been difficult to be judged in the head manufacturing process.
Therefore, an object of the present invention is to provide a TMR effect element having no special structures needing much man-hour cost for the formation, in which the high temperature noise and the low temperature noise are suppressed and a sufficiently high resistance-change ratio is provided, a thin-film magnetic head with the TMR effect element, an HGA including the thin-film magnetic head, and a magnetic recording/reproducing apparatus including the HGA.
Another object of the present invention is to provide a manufacturing method of a TMR effect element having no special structures needing much man-hour cost for the formation, in which the high temperature noise and the low temperature noise are suppressed and a sufficiently high resistance-change ratio is provided.
Before describing the present invention, terms used herein will be defined. In a multilayer structure formed on/above the element formation surface of a substrate in a TMR effect element or a thin-film magnetic head, a layer or a portion of the layer located closer to the substrate than a standard layer is referred to as being located “lower” than, “beneath” or “below” the standard layer, and a layer or a portion of the layer located on the stacking direction side in relation to a standard layer is referred to as being located “upper” than, “on” or “above” the standard layer.
According to the present invention, a TMR effect element is provided, which comprises: a tunnel barrier layer formed by oxidizing a base film; and two ferromagnetic layers stacked so as to sandwich the tunnel barrier layer, the base film having a film thickness larger than a film thickness at which a resistance-change ratio of the TMR effect element indicates a maximum value.
In the above-described TMR effect element, it is preferable that the base film is an aluminum film and a film thickness of the aluminum film is in the range of 0.50 nanometer to 1.5 nanometer. It is also preferable that the base film is a magnesium film and a film thickness of the magnesium film is in the range of 0.60 nanometer to 1.5 nanometer. Further, the base film is also preferably a film including at least one element selected from a group of titanium, hafnium, Zinc, tantalum, zirconium, silicon, molybdenum, tungsten, tin, nickel, gadolinium, niobium, gallium and germanium. Furthermore, the tunnel barrier layer preferably has a non-oxidized or insufficiently oxidized layer in the lower end portion of the tunnel barrier layer.
In the TMR effect element according to the present invention, the high temperature noise and the low temperature noise are suppressed without using no special structures needing much man-hour cost for the formation, and the resistance-change ratio shows a sufficiently large value though slightly decreased compared with the maximum value.
According to the present invention, a thin-film magnetic head is further provided, which comprises: a substrate; and the above-described TMR effect element for reading data formed on/above an element formation surface of the substrate.
According to the present invention, an HGA is further provided, which comprises: the above-described thin-film magnetic head; signal lines for the TMR effect element; and a support means for supporting the thin-film magnetic head.
According to the present invention, a magnetic recording/reproducing apparatus is further provided, which comprises: at least one HGA described above; at least one magnetic recording medium; and a recording/reproducing means for controlling read and write operations of the thin-film magnetic head to the at least one magnetic recording medium.
According to the present invention, a manufacturing method of a TMR effect element is further provided, which comprises steps of: forming a first ferromagnetic layer on/above an element formation surface of a substrate; forming a base film having a film thickness larger than a film thickness at which a resistance-change ratio of the TMR effect element indicates a maximum value, on the first ferromagnetic layer; forming a tunnel barrier layer by oxidizing the base film; and forming a second ferromagnetic layer on the tunnel barrier layer.
In the above-described manufacturing method, an aluminum film with a film thickness in the range of 0.50 nanometer to 1.5 nanometer is preferably formed as the base film. Or a magnesium film with a film thickness in the range of 0.60 nanometer to 1.5 nanometer is preferably formed as the base film. Further, it is also preferable that a film including at least one element selected from a group of titanium, hafnium, Zinc, tantalum, zirconium, silicon, molybdenum, tungsten, tin, nickel, gadolinium, niobium, gallium or germanium is formed as the base film.
By using the manufacturing method according to the present invention, a TMR effect element can be provided, in which the high temperature noise and the low temperature noise are suppressed and the resistance-change ratio shows a sufficiently large value without forming no special structures needing much man-hour cost.
Further objects and advantages of the present invention will be apparent from the following description of preferred embodiments of the invention as illustrated in the accompanying figures. In each figure, the same element as that shown in other figure is indicated by the same reference numeral. Further, the ratio of dimensions within an element and between elements becomes arbitrary for viewability.
a shows a flow chart schematically illustrating an embodiment of the manufacturing method of a TMR effect element according to the present invention;
b shows cross-sectional views for explaining the oxidization process of the base film (step 4) in the flow chart of
a shows a graph of the relation between the film thickness tMF of the Al base film and the resistance-change ratio, whose data are shown in Table 1;
b shows a graph of the relation between the film thickness tMF of the Al base film and the ratio of the resistance-change ratio/the sheet-resistance, whose data are also shown in Table 1;
a to 6c show cross-sectional views of the tunnel barrier layer, schematically explaining the considered mechanism;
a shows a graph of the relation between the film thickness tMF of the Mg base film and the resistance-change ratio, whose data are shown in Table 3;
b shows a graph of the relation between the film thickness tMF of the Mg base film and the ratio of the resistance-change ratio/the sheet-resistance, whose data are also shown in Table 3; and
The magnetic recording/reproducing apparatus shown in
The assembly carriage device 12 is provided for positioning the thin-film magnetic head 21 above a track formed on the magnetic disk 10. In the device 12, the drive arms 14 are stacked along a pivot bearing axis 16 and are capable of angular-pivoting about the axis 16 driven by a voice coil motor (VCM) 15. The numbers of magnetic disks 10, drive arms 14, HGAs 17, and thin-film magnetic heads 21 may be one.
While not shown, the recording/reproducing circuit 13 includes a recording/reproducing control LSI, a write gate for receiving data to be recorded from the recording/reproducing control LSI, an write circuit for outputting a signal from the write gate to an electromagnetic coil element for writing data, which will be described later, a constant current circuit for supplying a sense current to a TMR effect element for reading data, which will also be described later, an amplifier for amplifying output voltage from the TMR effect element, and a demodulator circuit for demodulating the amplified output voltage and outputting reproduced data to the recording/reproducing control LSI.
Also as shown in
The suspension 20 includes a load beam 22, an flexure 23 with elasticity fixed on the load beam 22, a base plate 24 provided on the base portion of the load beam 22, and a wiring member 25 that is provided on the flexure 23 and consists of lead conductors as signal lines and connection pads electrically connected to both ends of the lead conductors. While not shown, a head drive IC chip may be attached at some midpoints of the suspension 20.
Also as shown in
One ends of the TMR effect element 33 and the electromagnetic coil element 34 reach the head end surface 300 on the ABS 30 side. These ends face the surface of the magnetic disk 10, and then, a read operation is performed by sensing a signal magnetic field from the disk 10, and a write operation is performed by applying a write magnetic field to the disk 10. A predetermined area of the head end surface 300 that these ends reach may be coated with diamond like carbon (DLC), etc. as an extremely thin protective film.
In
Also as shown in
The end portion in the head end surface 300 side of the auxiliary magnetic pole layer 345 becomes a trailing shield portion 3450 that has a length in the stacking direction (thickness) larger than that of the other portions. The trailing shield portion 3450 causes a magnetic field gradient between the end portion of the trailing shield portion 3450 and the end portion of the main magnetic pole layer 340 to be steeper. As a result, a jitter of signal outputs becomes smaller, and therefore, an error rate during reading can be reduced.
Further, in the present embodiment, a backing coil portion 36 and an inter-element shield layer 37 are provided between the TMR effect element 33 and the electromagnetic coil element 34. The backing coil portion 36 suppresses a wide area adjacent-track erase (WATE) behavior, which is an unwanted write or erase operation to the magnetic disk, by generating a magnetic flux for negating the magnetic flux loop that arises from the electromagnetic coil element 34 through the upper and lower electrode layers 334 and 330 of the TMR effect element 33.
In
The lower metal layer 40 is provided on the lower electrode layer 330, and electrically connects the TMR effect multilayer 332 to the lower electrode layer 330. Further, the upper metal layer 46 electrically connects the TMR effect multilayer 332 to the upper electrode layer 334 by providing the upper electrode layer 334 on the upper metal layer 46. Therefore, during detecting a signal field, a sense current flows in the direction perpendicular to the surface of each stacked layer of the TMR effect multilayer 332.
The antiferromagnetic layer 42 is provided above the lower metal layer 40 through the base layer 41. The pinned layer 43 is provided on the antiferromagnetic layer 42, and has namely a synthetic-ferri-pinned structure in which a first ferromagnetic film 43a, a non-magnetic film 43b and a second ferromagnetic film 43c are sequentially stacked from the antiferromagnetic layer 42 side. The first ferromagnetic film 43a receives an exchange bias field due to the exchange interaction with the antiferromagnetic layer 42. As a result, the whole magnetization of the pinned layer 43 is stably fixed.
The free layer 45, which is provided on the tunnel barrier layer 44, has a two-layered structure in which a high polarizability film 45a and a soft-magnetic film 45b are sequentially stacked from the tunnel barrier layer 44 side. The magnetization of the free layer 45 makes a ferromagnetic tunnel coupling together with the magnetization of the pinned layer 43 with the tunnel barrier layer 44 as a barrier of the tunnel effect. Thus, when the magnetization direction of the free layer 45 changes in response to a signal field, a tunnel current increases/decreases due to the variation in the state densities of up and down spin bands of the pinned layer 43 and the free layer 45, and therefore, the electric resistance of the TMR effect multilayer 332 changes. The measurement of this resistance change enables a weak and local signal field to be surely detected with high sensitivity.
The tunnel barrier layer 44 according to the present invention has a layer thickness tML larger than a layer thickness tML0 at which the resistance-change ratio of the TMR effect element 33 indicates a maximum value, as described later in detail. And the tunnel barrier layer 44 may be formed of a layer obtained by oxidizing a base film made of at least one element selected from the group of, for example, Al (aluminum), Mg (magnesium), Ti (titanium), Hf (hafnium), Zn (Zinc), Ta (tantalum), Zr (zirconium), Si (silicon), Mo (molybdenum), W (tungsten), Sn (tin), Ni (nickel), Gd (gadolinium), Nb (niobium), Ga (gallium) or Ge (germanium). The oxidization is performed by exposing the upper surface of the base film in an atmosphere with a predetermined O2 (oxygen) partial pressure. Going through the oxidization, the layer thickness tML of the formed tunnel barrier layer 44 becomes one and a half to four times (1.5 to 4 times) larger than a film thickness tMF of the base film before the oxidization, and is almost proportional to the film thickness tMF. Here, a film thickness of the base film is defined to be tMF0, at which the layer thickness tML0 of the tunnel barrier layer 44 is obtained, which realizes the maximum resistance-change ratio of the TMR effect element 33. Then, to realize the layer thickness of the tunnel barrier layer 44 larger than the layer thickness tML0, it is an essential condition to set the film thickness tMF of the base film to be larger than the film thickness tMF0.
In the case that the tunnel barrier layer 44 is an Al-film-oxidized layer, the film thickness of the Al film before the oxidization is set to be in the range of 0.50 nm (nanometer) to 1.5 nm, as described later in detail using practical examples. In the case that the tunnel barrier layer 44 is a Mg-film-oxidized layer, the film thickness of the Mg film before the oxidization is set to be in the range of 0.60 nm to 1.5 nm.
By applying the tunnel barrier layer with the above-described structure, realized is a TMR effect element having no special structures needing much man-hour cost for the formation, in which the high temperature noise and the low temperature noise are suppressed and a sufficiently high resistance-change ratio is provided, as described later in detail.
As a matter of course, the mode of each layer of the TMR effect multilayer 332 is not limited to the above-described one. For example, the pinned layer 43 may have a monolayer structure of a ferromagnetic film, or a multilayered structure with other number of layers. Further, the free layer 45 may have a monolayer structure without a high polarizability film, or may have a more-than-two-layered structure including a film for adjusting magnetostriction. The antiferromagnetic layer, the pinned layer, the tunnel barrier layer and the free layer may be stacked in the reverse order, that is, the free layer, the tunnel barrier layer, the pinned layer and the antiferromagnetic layer may be stacked in this order. When the pinned layer, the tunnel barrier layer and the free layer may be stacked in this order, the pinned layer and the free layer become the first and the second ferromagnetic layers respectively. On the other hand, when the free layer, the tunnel barrier layer and the pinned layer may be stacked in this order, the free layer and the pinned layer become the first and the second ferromagnetic layers respectively.
Also as shown in
a shows a flow chart schematically illustrating an embodiment of the manufacturing method of a TMR effect element according to the present invention. And
According to
Then, the base film made of a metal such as Al, Mg, Ti, Hf, Zn, Ta, Zr, Mo, W, Sn, Ni, Gd, Nb, Ga or Ge, or Si is formed on the formed second ferromagnetic film 43c by using, for example, a sputtering method (step S3). Here, the important feature of the present invention will be explained by using
Here, the film thickness tMF setting of exceeding the film thickness tMF0 will be explained. Conventionally, the layer thickness of the tunnel barrier layer has been adjusted so that the ratio of the resistance-change ratio and the sheet-resistance of the element becomes as high as possible, as described above. Generally, the higher the ratio is, the larger the element output becomes. In fact, a base film with a thickness at which the resistance-change ratio indicates a maximum value or with smaller thickness than the just-described thickness has been used. In the case of using the base film with such a film thickness, there has been a problem that a noise, especially a high temperature noise or a low temperature noise, is likely to occur by a mechanism described later. On the contrary, the setting to the sufficiently large thickness tMF, which is larger than the thickness tMF0, of the base film according to the present invention can suppress the noise such as the high temperature noise and the low temperature noise.
Next, returning to
Then, returning to
Next, after a photoresist pattern for a lift-off process, etc. is formed on the upper metal layer 46, the formed multilayer is patterned by etching such as an ion milling method. Here, in the case of an embodiment including the above-described hard bias means, after a insulating film and a hard-magnetic film are deposited, the insulating layer 48 and the hard bias layer 47 are formed by removing the photoresist pattern, that is, by using a lift-off method (step S6). Then, by further patterning process, the TMR effect multilayer 332 is formed, and further the insulating layer 333 is formed (step S6). At the last, on the formed TMR effect multilayer 332, formed is the upper electrode layer 334 made of a soft-magnetic conductive material such as NiFe, CoFeNi, CoFe, FeN or FeZrN with a thickness of approximately 0.5 to 5 μm, by using, for example, a frame plating method (step S7). Through these processes, the TMR effect element 33 is completed.
Hereinafter, practical examples of the TMR effect element according to the present invention will be presented, and the influence of the film thickness of the base film on the high and low temperature noises will be explained.
Table 1 shows the relation of the film thickness tMF of an Al base film, the resistance-change ratio and the ratio of the resistance-change ratio/the sheet-resistance in the TMR effect element in which the base film is made of Al.
The TMR effect element used for the measurements included a multilayer in which sequentially stacked are: an antiferromagnetic layer made of IrMn with a thickness of 7 nm; a pinned layer formed by sequentially stacking a CoFe film with a thickness of 2 nm, a Ru film with a thickness of 0.8 nm and a CoFe film with a thickness of 2.5 nm; a tunnel barrier layer formed by oxidizing an Al base film; and a free layer formed by sequentially stacking a CoFe film with a thickness of 3 nm and a NiFe film with a thickness of 1 nm. The oxidization process of the Al base film is performed as the follows: the multilayer in which the Al base film was deposited at the last was set in an oxidization chamber, O2 (oxygen) gas was introduced in the chamber, and the O2 gas was evacuated from the chamber after sealing the O2 gas in the chamber for a predetermined time. The resistance-change ratio ΔR/R0 is defined as a ratio of the maximum amount ΔR of the element resistance change during applying magnetic field and the element resistance R0. Further, the sheet-resistance RA is defined as a product R0×Ss of the element resistance R0 and the area Ss of the layer surface through which a sense current flows effectively. Here, the element resistance R0 is an electric resistance in the case that an electric current flows in the direction of the layer thickness of the element. All samples had the same amount of the area Ss.
a shows a graph of the relation between the film thickness tMF of the Al base film and the resistance-change ratio, whose data are shown in Table 1. And
As shown in
Then, the measurement results of the high temperature noise and the low temperature noise in these TMR effect elements will be shown. Table 2 shows the relation between the film thickness tMF of the Al base film and the percent defective of the high temperature noise, and the relation between the film thickness tMF of the Al base film and the percent defective of the low temperature noise.
Here, the percent HTN defective and the percent LTN defective will be defined. First, a noise value is defined as an integral value (μVrms) of the noise in the range of 10 to 100 MHz. Next, the noise value at room temperature (25° C.) is defined to be NRT, the noise value at 85° C. is defined to be NHT, and the noise value at 0° C. is defined to be NLT, and then, a high temperature noise dNsh(HT) and a low temperature noise dNsh(LT) are defined as follows:
dNsh(HT)=(NHT−NRT)/NRT (1)
dNsh(LT)=(NLT−NRT)/NRT (2)
When the high temperature noise dNsh(HT) exceeds 35%, the TMR effect element with the dNsh(HT) value is judged as a defective in respect to the high temperature noise. Then, a percent HTN (high temperature noise) defective is defined as a ratio of the defective among 200 element samples. Further, when the low temperature noise dNsh(LT) exceeds 35%, the TMR effect element with the dNsh(LT) value is judged as a defective in respect to the Low temperature noise. Then, a percent LTN (low temperature noise) defective is defined as a ratio of the defective among 200 element samples.
As shown in Table 2, the values of both the percent HTN and LTN defectives at the film thickness tMF0=0.500 nm become excellently smaller than those at the film thickness tMF0=0.475 nm. In the actually manufacturing floor of the TMR effect element, the control of the film thickness on the order of 0.1 nm is considerably difficult, and so the difference of 0.025 nm is almost a control limit. Therefore, it is understood that the high temperature noise and the low temperature noise can be sufficiently suppressed by setting the film thickness tMF of the base film to be more than the tMF0 at which the resistance-change ratio ΔR/R0 indicates a maximum value, specifically by setting the film thickness tMF of the Al base film to be 0.500 nm or more. As just described, when the film thickness tMF of the base film is set to be more than the tMF0, the resistance-change ratio ΔR/R0 is slightly decreased from the maximum value, as shown in
Next, a mechanism for suppressing the high and low temperature noises according to the present invention, which the present inventors have considered, will be explained.
As shown in
As shown in
As shown in
According to the above-described mechanism, in
Table 3 shows the relation of the film thickness tMF of an Mg base film, the resistance-change ratio and the ratio of the resistance-change ratio/the sheet-resistance in the TMR effect element in which the base film is made of Mg.
The TMR effect element used for the measurements had the same structure as the above-described TMR effect element formed by using the Al base film except for the base film made of Mg. Further, the definitions of the resistance-change ratio ΔR/R0 and the sheet-resistance RA are also the same as those explained above in Table 1.
a shows a graph of the relation between the film thickness tMF of the Mg base film and the resistance-change ratio, whose data are shown in Table 3. And
As shown in
Then, the measurement results of the high temperature noise in these TMR effect elements will be shown. Table 4 shows the relation between the film thickness tMF of the Mg base film and the percent HTN (high temperature noise) defective.
Here, the definition of the percent HTN defective is the same as that explained above in Table 2.
As shown in
As described above, the result about the regulation of the base film thickness tMF is common between the cases of the Al and Mg base films, which supports the validity of the above-described mechanism for suppressing the high and low temperature noises. Further, according to the mechanism, the high and low temperature noises are considered to be greatly dependent on the base film thickness (on the thickness of the tunnel barrier layer) rather than the oxidization condition, which gives an understanding for the above-described result that the values of the tMF0 and tMF1 are almost independent of the oxidization condition.
In addition, in both cases of using the Al and Mg base films, it has been understood that, when the film thickness tMF exceeds 1.5 nm, another noise may be induced due to the degradation of the flatness of the upper surface of the tunnel barrier layer after oxidization. Further, the larger thickness tMF causes the significant generation of a shot noise, as well as the reduction of the element output due to the great increase in the element resistance. Therefore, the film thicknesses tMF of the Al and Mg base films are required to be set to 1.5 nm or less.
All the foregoing embodiments are by way of example of the present invention only and not intended to be limiting, and many widely different alternations and modifications of the present invention may be constructed without departing from the spirit and scope of the present invention. In fact, the TMR effect element according to the present invention has applicability to magneto-sensitive parts of magnetic sensors, magnetic switches, magnetic encoders and so on, as well as the read head element of the thin-film magnetic head. Accordingly, the present invention is limited only as defined in the following claims and equivalents thereto.
