Patent Application
20210065739
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-153794, filed Aug. 26, 2019, the entire contents of which are incorporated herein by reference.
Embodiments described herein relate generally to a magnetic disk device.
For magnetic disk devices, microwave assisted magnetic recording (MAMR) is considered in which, in order to improve recording density, a high-frequency magnetic field is applied to a recording medium with high magnetic anisotropy, a medium coercive force (Hc) is lowered, and a recording is made. In a recording head used in this method, a spin torque oscillation (STO) element in which a field generation layer (FGL), a spin injection layer (SIL), and the like are laminated is mounted between recording poles to apply a high-frequency magnetic field. In a magnetic disk device having such a configuration, a bias voltage is applied to the STO element to pass electrons from the FLG to the SIL, thereby the spin torque effect is caused to oscillate the FGL, reducing the coercive force of a recording medium. Therefore, record data can be recorded even with a weak recording magnetic field generated by a smaller recording element.
On the other hand, shingled magnetic recording (SMR) is provided as a recent technology for improving recording density. In a conventional magnetic recording (CMR), data tracks are recorded with a spacing therebetween according to a magnetic writer width (MWW) of a recording element, but in the SMR, data tracks are written so as to overlap with each other on one side with a spacing smaller than that according to the MWW. Therefore, high-density recording is enabled while maintaining recording quality. However, since track scanning is limited in one direction in recording, when record data from a host requires random write, the record data is temporarily recorded in a cache area which is provided partially in a medium and can be used for the CMR, and after the record data is shaped in data usable for sequential write, the shingled recording is performed. Thus, the SMR requires a longer time than the CMR to record the record data.
It is considered that, in the future, a magnetic recording device employs microwave assisted magnetic recording and includes both of a region for data recording using the SMR and a region for data recording using the CMR. However, in the microwave assisted magnetic recording, the bias voltage applied to the STO element has an optimum value being different between the CMR and the SMR. Therefore, when the bias voltage is applied to the STO element to be suitable for one of the CMR and the SMR, the bias voltage becomes unsuitable for the other. Such a state also occurs, for example, in a magnetic disk device adopting heat-assisted magnetic recording.
It is an object of the present invention to provide a magnetic disk device which includes a magnetic recording head configured to assist in data recording, and a magnetic disk having thereon a data recording area for a first method and a data recording area for a second method different from the first method and which has a large capacity, high reliability, and high manufacturing yield.
In general, according to one embodiment, a magnetic disk device includes a magnetic disk, a write head which includes an assist unit configured to assist in writing data to the magnetic disk, a read head configured to read data from the magnetic disk, and a control unit configured to control writing data to the magnetic disk by the write head and reading data from the magnetic disk by the read head. The magnetic disk includes a first region in which reading/writing data is performed by a first processing method and a second region in which reading/writing data is performed by a second processing method different from the first processing method. The control unit is operable to change assist power of the assist unit between the first region and the second region when writing data to the magnetic disk by the write head.
Hereinafter, embodiments will be described with reference to the drawings. Note that the disclosure is merely an example, and the invention is not limited by the contents described in the following embodiments. Modifications and variations readily conceivable by those skilled in the art are naturally included in the scope of the disclosure. In the drawings, each portion may be schematically illustrated by changing the size, shape, and the like thereof from those in actual embodiments, for clarity of description. In a plurality of drawings, corresponding elements are denoted by the same reference numerals, and a detailed description thereof may be omitted.
The magnetic disk device 100 includes a magnetic disk 11 configured to write data. The magnetic disk 11 is rotationally driven by a spindle motor (SPM) 12. The magnetic disk 11 has two data surfaces of an upper data surface 11a and a lower data surface 11b. Data is written to each of the data surfaces 11a and 11b. On each of the data surfaces 11a and 11b of the magnetic disk 11, a large number of concentric tracks are formed, and each of the tracks has a servo area in which servo data used for positioning control and the like is written and a data area in which data is written. A reproducing/recording composite heads (hereinafter referred to as “magnetic heads”) 13a or 13b used to write data to the magnetic disk 11 and read data from the magnetic disk 11 are provided for both sides of the magnetic disk 11. The magnetic heads 13a and 13b are respectively mounted on sliders 14a and 14b configured to fly over the rotating magnetic disk 11. The magnetic heads 13a and 13b are each moved in a radial direction of the magnetic disk 11 by a slider movement mechanism (voice coil motor: VCM) 15, seek a target position on the magnetic disk 11, and are positioned at the target position. The VCM 15 is operated based on an instruction from a CPU 19. The magnetic heads 13a and 13b each include a read head and a write head. The read head is an MR head using a magnetoresistive effect element, and the write head uses a magnetic recording head including an assist unit configured to assist in writing data with high-frequency. Note that
Here, structures of the magnetic heads 13a and 13b will be described with reference to
As illustrated in
The write head 40 further includes the STO element 46 between the main magnetic pole 41 and the auxiliary magnetic pole 45, as detailed in
In the magnetic disk device 100, when writing data, a recording current for generating a recording magnetic field is applied to the magnetic poles of the write coils 42 and 43, and in the main magnetic pole 41 and the auxiliary magnetic pole 45, bias voltage is applied to the STO element 46 by an STO drive power source, not illustrated, so that current passes from the SIL 46d to the FGL 46b, thus recording data on the magnetic disk 11. Therefore, change of the bias voltage applied to the STO element 46 enables change of assist power for assisting in data writing. The bias voltage applied to the STO element, namely, STO bias voltage, has a magnitude adjusted and determined by an optimization method for each of a CMR region where processing is performed by a CMR method (first method) and an SMR region where processing is performed by an SMR method (second method). Details of this optimization method will be described later.
The description returns to
Next, a recording area of the magnetic disk 11 will be described.
The description returns to the magnetic disk device 100 of
The magnetic heads 13a and 13b are connected to a head amplifier circuit 16. The head amplifier circuit 16 manages input/output of a read/write signal between the magnetic heads 13a and 13b. The head amplifier circuit 16 has a reproduction signal amplification function for amplifying a signal from the read head 30, recording amplification section for supplying a recording current to the write head 40 in synchronization with a recording signal from a read/write circuit 17, a flying control function for supplying power to the read heater 34 and write heater 47 and adjusting the flying height of the magnetic heads 13a and 13b, and further an STO drive function for applying bias voltage to the STO element 46, and these functions are achieved according to an instruction from the CPU 19, which is described later. The read/write circuit 17 is connected to the head amplifier circuit 16. The read/write circuit 17 includes a read channel having a decoding function performing signal processing necessary for data reproduction operation, on an input read signal amplified by the head amplifier circuit 16 and sent from the magnetic heads 13a and 13b, and a write channel having record compensation section for encoding record data or adjusting a signal inversion position. The read/write circuit 17 is connected to a hard disk controller (hereinafter referred to as “HDC”) 18 and the CPU 19.
The HDC 18 serves as an interface with a host 101. The HDC 18 controls a command and data communication with the host 101 and also controls data communication with the magnetic disk 11 via the read/write circuit 17 and the head amplifier circuit 16.
The CPU (control unit) 19 serves as a main control device configured to control each unit in the magnetic disk device 100 according to a control program or control parameter stored in a memory 20. The control parameter, for example, an STO bias voltage value is adjusted or set for magnetic heads 13 and zones, in each of the SMR region A1 and the CMR region A2, at a manufacturing stage, and the STO bias voltage values having been adjusted or the like are registered in the form of a matrix table in the memory 20. Details of the matrix table will be described later.
A servo processing circuit 21 is connected to the read/write circuit 17 and the CPU 19. The servo processing circuit 21 performs processing so that the magnetic heads 13a and 13b seek a target position on the magnetic disk 11 and are positioned thereto.
Next, the optimization method for bias voltage applied to the STO element 46 will be described.
Firstly, the CPU 19 performs initial adjustment of a read heater value DFH R and a write heater value DFH_W (ST101). More specifically, the read heater value DFH R and the write heater value DFH_W are adjusted and set so that each of the read head 30 and the write head 40 have a desired spacing from a surface of the magnetic disk 11 with no STO bias voltage or no recording current applied.
Next, the CPU 19 sets STO bias voltage (ST102) and then sets ADC/BPI/TPI and write current (ST103). Here, ADC/BPI/TPI settings will be described. Bits per inch (BPI) and tracks per inch (TPI) are settings of a format of the magnetic disk 11, and ADC (BPI×TPI) is a setting of recording density.
Next, the CPU 19 measures IwPTP which is a change in spacing of the write head and sets DFH_W (ST104). More specifically, after setting STO bias voltage, the CPU 19 sets the recording density, format, and recording current, measures the STO bias voltage during writing or a change in spacing of the write head 40 caused by heat generated by the recording current, and determines the write heater value (DFH_W=DFH_W−IwPTP) upon writing. After setting the conditions in this way, the CPU 19 writes/reads data and measures a bit error rate (BER) (hereinafter referred to as “BER1”) (ST105).
Next, the CPU 19 writes data on both adjacent tracks a plurality of times with a space corresponding to the set TPI (ST106) and measures BER (hereinafter referred to as “BER2”) again (ST107). Then, the CPU 19 determines whether both BER1 and BER2 are equal to or more than a predetermined reference value (ST108). If it is determined that both of BER1 and BER2 are equal to the predetermined reference value (ST108: YES), the CPU 19 determines whether ADC measured this time satisfies ADC>ADCmax (ST109). If it is determined that ADC>ADCmax (ST109: YES) is satisfied, the ADC is set as ADCmax (ST110).
If the ADC is set to ADCmax in this way or if the CPU 19 determines in step ST108 that both BER1 and BER2 have values not equal to or more than the predetermined reference value (ST108: NO) and if the CPU 19 determines in step ST109 that ADC having been measured this time does not satisfy ADC>ADCmax (ST109: NO), the CPU 19 determines whether the measurement of write current has completed entirely for BPI/TPI/ADC (ST111). If it is determined that the measurement of the write current has not been completed entirely for BPI/TPI/ADC (ST111: NO), the process returns to step ST103, and the above-described steps subsequent to step ST103 are repeated.
On the other hand, if it is determined that the measurement of the write current has been completed entirely for BPI/TPI/ADC (ST111: YES), the CPU 19 finishes the process. Thus, the same measurement is performed for all prepared formats and write current conditions, and ADCmax is calculated as a maximum recording density satisfying the predetermined reference value for both BER1 and BER2.
In
As a graph g1 shows, on the low voltage side (the left side in the figure), the recording density is improved as the STO bias voltage increases. On the other hand, on the high voltage side (right side in the figure), the influence of data writing on an adjacent track is large, and the recording density is saturated or reduced. In the present embodiment, in
The STO bias voltage is optimized for the SMR region A1 as in the CMR region A2, but multiple writes on both adjacent tracks before measuring BER2 (step ST106 described above) is changed to one write on one track. This is because writing data by the SMR method mitigates the influence of writing data to an adjacent track. Therefore, as illustrated in graphs g2 and g3 of
In the present embodiment, the above-described optimization of the STO bias voltage is performed for all the heads in the CMR/SMR region A2 or A1, during a manufacturing process of the magnetic disk device 100. Then, STO bias voltage values applied to the STO element 46 by the head amplifier circuit 16, upon writing are stored in the memory 20 in the form of a matrix table illustrated in
In a matrix table T1, a head number T11 and an STO bias voltage value T12 are associated with each other. The head number T11 represents the number of a magnetic head 13. In the STO bias voltage value T12, bias voltages Vs_opt and Vc_opt are set for an SMR region T121 and a CMR region T122, respectively.
In the magnetic disk device 100, when data is written on the magnetic disk 11 after shipment from a manufacturer, an STO bias voltage value is read from the memory 20 based on a head number from which writing data is performed and the SMR region or CMR region to which the data is to be written, and the read STO bias voltage value is set as an STO bias voltage value to be applied to the STO element 46 by the head amplifier circuit 16, and thus, the data is written. As described above, an optimum STO bias voltage value in writing data can be set according to the SMR region A1 or the CMR region A2, and thus, the magnetic disk device 100 having a large capacity, high reliability, and high manufacturing yield can be obtained.
Note that, in the above embodiment, the setting of the STO bias voltage values stored in the memory 20 for the respective head numbers T11, SMR regions T121, and CMR regions T122 is described as illustrated in
As illustrated in
Furthermore, the STO bias voltage may be optimized not for all the magnetic heads 13 but for a predetermined number of heads, and in the manufacturing process, an average value of the STO bias voltage may be set as a fixed value for each of the heads or each of the heads/zones in the memory 20, as in matrix tables T3 and T4, which are illustrated in
In the above embodiment, in a case where the fixed value is used as the STO bias voltage value (see
Next, processing for setting the STO bias voltage will be described.
As illustrated in
Specifically, the CPU 19 calculates the STO bias voltages Vc_opt and Vs_opt, from Vc_opt=Vc_opt_e×(R1+R2)/R1 and Vs_opt=Vs_opt_e×(R1+R2)/R1, respectively. The CPU 19 stores the STO bias voltage value for the CMR/SMR region, calculated in this way, in a memory 20 in the form of a matrix table T5 illustrated in
With this configuration, when writing data, the magnetic disk device 100 keeps the STO element voltage constant for each of the SMR region A1 and the CMR region A2 of the magnetic disk 11, reducing variations in characteristics. Note that the calculation formula for calculating the STO bias voltage value is presented as an example, and the calculation formula for the STO bias voltage differs depending on a circuit connected to the STO element 46.
Furthermore, in the above embodiments, the magnetic heads 13a and 13b adopting microwave assisted magnetic recording as a method of assisting in recording data have been described, but the method of assisting in recording data Is not limited thereto. For example, the techniques described in the above embodiments can be also applied to a magnetic disk device adopting heat-assisted magnetic recording as a method of assisting in recording data.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-153794 | Aug 2019 | JP | national |
