JP2011248997A - Magnetic disk device having microwave assist function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine whether or not an STOAR element for performing microwave assist of the magnetic disk device is surely oscillated.SOLUTION: When the STOAR element is oscillated during current biasing, a resistance value of an element becomes high. Thus, in a head IC outputting the current bias, a voltage applied to the STOAR is detected, and when the voltage is increased to a threshold or more, it becomes possible to determine that the STOAR is being oscillated. On the contrary, when the voltage is equal to or less than the threshold, it can be determined that the STOAR element is not oscillated. Moreover, since it can be determined that oscillation is being weakened when the resistance value is reduced after the voltage reaches a certain threshold or more, the STOAR can be normally oscillated again by boosting with current.

Description

  Embodiments described herein relate generally to a magnetic disk device having a microwave assist function.

  In recent years, with the aim of increasing the recording density of magnetic disk devices such as HDDs, microwave assist has been applied to record information by applying a microwave (high-frequency magnetic field) to the surface of the medium at the time of writing to make the surface of the medium easy to write information. Attention has been paid. Microwave assist is a function of applying a constant current bias to the STOAR element, causing the element to oscillate in the order of several tens of GHz to output microwaves, lowering the Hc of the medium, and making the medium easy to write. Since the bias is a DC current, the control is easy, the threshold for mounting is not high, and this is a necessary function for the next-generation magnetic disk device.

Japanese Patent No. 4348389

  Since the STOAR element oscillates on the order of several tens of GHz, the oscillation signal is attenuated because it is generally higher in frequency than the signal band of the head IC / transmission path, and it is difficult to determine whether the element is oscillating reliably.

  An embodiment of the present invention is intended to determine whether or not a STOAR element that performs microwave assist of a magnetic disk device oscillates reliably.

  When the STOAR element oscillates during current bias, the resistance value of the element increases. This is the same as the mechanism of a GMR head or the like that provides a bias current. Therefore, in the head IC that outputs a current bias, it is possible to detect the voltage applied to the STOAR element and determine that the head IC is oscillating when the voltage increases above a threshold value. Conversely, if the voltage is equal to or lower than the threshold, it can be determined that the STOAR element is not oscillating. Further, when the resistance value decreases after the voltage reaches a certain threshold value or more, it can be determined that the oscillation has weakened. Therefore, the STOAR element can be normally oscillated again by boosting with a current.

It is a block diagram which shows the principal part of the disk drive 10 regarding one Embodiment. 3 is a block diagram showing details of a head 13 and a head amplifier 14. FIG. It is a figure which shows the principle of STOAR oscillation. It is a figure which shows the relationship between the oscillation of a STOAR element, and resistance value. It is a figure which shows the structure of the circuit which confirms the oscillation of a STOAR element. It is a figure which shows the circuit structure of 2nd Embodiment. It is a figure which shows the circuit structure of 3rd Embodiment. It is a figure which shows the circuit structure of 4th Embodiment. It is a figure which shows the circuit structure of 5th Embodiment.

  Hereinafter, a magnetic disk device according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a main part of a disk drive 10 relating to the present embodiment. The disk drive 10 of this embodiment includes a disk 11 that is a magnetic recording medium, a spindle motor 12, a head 13, a head amplifier 14, and a hard disk controller (HDC, simply referred to as a disk controller) 15. The spindle motor 12 rotates the disk 11. The head 13 includes a read head element and a write head element, reads data from the disk 11, and writes data.

  The head amplifier 14 is generally configured as an IC, and amplifies a signal (read data) read by the head 13 and transmits the amplified signal to the disk controller 15. The head amplifier 14 converts a signal (write data) output from the disk controller 15 into a write current and transmits the write current to the head 13.

  The disk controller 15 includes a read / write (R / W) channel 17 and a controller 18. The R / W channel 17 is a signal processing circuit for recording / reproducing data, and has a function of decoding read data read by the head 13 and encoding write data. The controller 18 is an interface that controls data transfer between the R / W channel 17 and the host system 20. The controller 18 controls the data recording / reproducing operation via the R / W channel 17.

  The host system 20 is a digital device such as a personal computer or a digital television that uses the disk drive 10 as an external storage device.

  FIG. 2 is a block diagram showing details of the head 13 and the head amplifier (head IC) 14.

  First, the head amplifier 14 will be described.

  The read amplifier (Read Amp) 21 is an amplifier that amplifies a signal read from the recording medium by the MR element 30. The read amplifier 21 amplifies, for example, a signal of several mVpp into a signal of several hundred mVpp from which a subsequent R channel (Read Channel) can be read. A write driver 22 is a driver that supplies current to the write element 31 in order to write data to the recording medium. For example, the write driver 22 supplies a current of ± tens of mA to the write head.

  A heater driver 23 is a driver for causing the heater 32 provided in the head 13 to generate heat. The STOAR driver 24 is a driver that supplies a current for causing the STOAR element 33 to oscillate. An error indicator (Fault Indicator) 25 has a function of detecting an abnormality in the head amplifier 14 and its surroundings (such as a head). A serial port register 26 is a head amplifier setting register. A mode controller (Mode Control) 27 is a control unit that switches writing / reading of the preamplifier.

  Next, the head 13 will be described.

  The MR element 30 is an element whose resistance value changes depending on the magnetic polarity (N pole / S pole) of the medium, and includes a GMR head and a TMR head. A constant current / voltage is applied to the MR element 30 to convert a resistance value change into a voltage / current change. A write element 31 is an element (coil) for magnetizing the recording medium. When a signal current is passed through the write element 31, a magnetic field is generated in the coil, the recording medium is magnetized to a desired polarity, and a signal is recorded. A heater element 32 generates heat and thermally expands the head to control the distance (flying height) from the medium surface to the head. The element itself is a resistor. The STOAR element 33 oscillates at an internal magnetization of several tens of GHz by supplying a constant current to this element during writing. As a result, a high frequency magnetic field of several tens of GHz is applied to the medium, and the magnetic particles of the medium resonate and are easily inverted. As a result, rewriting of information becomes easy.

  FIG. 3 is a diagram illustrating the principle of STOAR oscillation.

  When electrons flow in the magnetic thin film, electrons having a spin in the same direction as the magnetization of the magnetic material are easily transmitted, and electrons directed in the opposite direction to the magnetization of the magnetic material are easily reflected. The reflected electrons oscillate as the magnetization of the free layer rotates. The oscillation frequency at this time is, for example, several tens of GHz.

  FIG. 4 is a diagram showing the relationship between the oscillation of the STOAR element and the resistance value.

  When a high-frequency magnetic field that matches the magnetic resonance frequency of the medium is applied to the medium, the medium magnetization vibrates and the medium Hc (coercivity) decreases. At this time, data is written by the magnetic field of the write head. When the high-frequency magnetic field is removed, the medium returns to high Hc, and the magnetization of the magnetic material is stabilized.

  FIG. 5 is a diagram showing a configuration of a STOAR element oscillation confirmation circuit for confirming the oscillation of the STOAR element.

  A constant current Ibias supplied from the constant current source 34 flows through the STOAR element 33. The constant current source 34 includes a resistor 35, an FET 36, a comparator 37, and an Ibias adjusting DAC 38. In order to oscillate the STOAR element 33 normally, it is necessary to flow a constant current Ibias having an appropriate magnitude. Therefore, the constant current source 34 has its constant current adjusted in advance by the DAC 38. The configuration of the constant current source 34 is not limited to the configuration shown in FIG. 5, and other general configurations can be applied as long as the constant current Ibias can be accurately adjusted.

  As described above, since the oscillation frequency of the STOAR element 33 is generally several tens of GHz, this oscillation signal is generally attenuated in the signal path from the STOAR element 33 to the comparator 39. Further, the comparator 39 is a general comparator that does not respond to a signal of several tens of GHz. Therefore, the comparator 39 compares the average value Vstor 'of the voltage Vstoar with the threshold voltage Vth. If the voltage Vstoar 'is higher than the threshold voltage Vth1, for example, an L level is output as the signal Fault, and if it is lower, an H level is output. In order to remove the oscillation component and noise, Vstor may be applied to the comparator 39 after passing through a low-pass filter.

  As described above, if the STOAR element 33 oscillates, its internal resistance is larger than that when it does not oscillate, so Vstoar becomes a relatively high voltage. At this time, the voltage Vstoar 'is larger than the predetermined voltage Vth, and the comparator 39 outputs, for example, L level.

  On the other hand, if the oscillation of the STOAR element 33 is stopped or weakened, the internal resistance of the STOAR element 33 is smaller than that during oscillation, so that Vstoar becomes a relatively low voltage. At this time, the voltage Vstoar 'is smaller than the predetermined voltage Vth, and the comparator 39 outputs an H level.

  The STOAR element 33 is provided in the head 13 of FIG. 2, and the constant current source 34 and the comparator 39 correspond to the STOAR driver 24 of the head amplifier 14. The signal “Fault” is transmitted to the disk controller 15 via the error indicator 25. In the disk controller 15, when the controller 18 inputs an H level signal as the signal “Fault”, the controller 18 determines that the oscillation of the STOAR element 33 is weakened or stopped, and sets the STOAR element 33 to oscillate normally again. The constant current Ibias is increased by setting a larger value in the Ibias DAC 38 of the current source 34 than before. This resetting operation of the DAC is repeated until the STOAR element 33 oscillates normally.

  As described above, according to the present embodiment, in the STOAR that is the microwave assist function, it is possible to determine whether or not the element oscillates, and even when the STOAR element stops oscillating, it is normally controlled under the control of the controller 18. Oscillation can be resumed.

  Next, a second embodiment of the STOAR element oscillation confirmation circuit according to the present invention will be described.

  FIG. 6 is a diagram showing a circuit configuration of the second embodiment.

  In this circuit configuration, in addition to the configuration of the first embodiment, a series circuit of a resistor 40 and a resistor 41 is connected between the constant current source 34 and GND. Other configurations are the same as those in the first embodiment. The comparator 39 inputs the voltage at the connection point between the resistor 40 and the resistor 41. The voltage Vstoar of the STOAR element 33 is divided by the resistors 40 and 41. A large value is applied to the values of the resistors 40 and 41 so as not to affect the current Ibias flowing through the STOAR element 33 as much as possible. The present embodiment is effective when the voltage Vstoar generated in the STOAR element 33 exceeds the appropriate input range of the comparator 39.

  The voltage V1 divided by the resistors 40 and 41 is expressed by the following equation, where Vstor is a voltage generated in the voltage STOAR element 33 and R40 and R41 are resistance values of the resistors 40 and 41, respectively.

V1 = Vstoar * R41 / (R40 + R41)
The comparator 39 compares the voltage V1 with the predetermined voltage Vth2, and outputs a signal Fault indicating whether the STOAR element 33 is oscillating.

  As described above, according to this embodiment, even when the voltage Vstoar generated in the STOAR element 33 exceeds the input range of the comparator 39, it is possible to determine whether or not the STOAR element oscillates and to stop the oscillation of the STOAR element. Even in this case, oscillation can be resumed under the control of the controller 18.

  Next, a third embodiment of the STOAR element oscillation confirmation circuit according to the present invention will be described.

  FIG. 7 is a diagram showing a circuit configuration of the third embodiment.

  In this circuit configuration, in addition to the configuration of the first embodiment, a series circuit of a second constant current source 32 and a switch 43 is provided between the power supply voltage Vcc and the STOAR element 33. When the oscillation of the STOAR element 33 stops or weakens, the H level fault signal is transmitted to the controller 18 as described above. The controller 18 turns on the boost switch 43 in response to the Fault signal. As a result, the constant current of the second constant current source is added to the current flowing through the STOAR element 33. Accordingly, the STOAR element 33 starts to oscillate again.

  As described above, according to the present embodiment, it is possible to determine whether or not the STOAR element oscillates, and even when the STOAR element stops oscillating, the oscillation can be resumed under the control of the controller 18.

  As a modification of the third embodiment, the output of the comparator 39 may be used as a control input for the boost switch 43 as indicated by a dotted line. In this case, when the oscillation of the STOAR element 33 is stopped or weakened, for example, an H level fault signal is output from the comparator, and the boost switch 43 is turned on. As a result, the current flowing through the STOAR element 33 is increased and oscillation is resumed.

  According to this modification, it is possible to determine whether the STOAR element oscillates or not, and even when the STOAR element stops oscillating, the STOAR driver 24 itself can restart the oscillation.

  Next, a fourth embodiment of the STOAR element oscillation confirmation circuit according to the present invention will be described.

  FIG. 8 is a diagram showing a circuit configuration of the fourth embodiment.

  In this circuit configuration, a series circuit of a band pass filter (BPF) 44 and a peak hold circuit 45 is provided between the STOAR element 33 and the comparator 39 in addition to the configuration of the first embodiment. When the transmission efficiency of the path from the STOAR element 33 to the BPF 44 is good, the oscillation signal of the STOAR element 33 reaches the BPF 44. The BPF 44 extracts and amplifies the oscillation band signal of the STOAR element 33.

  The peak hold circuit 45 holds the peak value of the output signal of the BPF 44 for a predetermined time, and outputs a peak-held signal Vp. If the STOAR element 33 is oscillating, the amplitude of the signal Vp is higher than the predetermined threshold Th3, and if the oscillation is stopped, the amplitude of the signal Vp is lower than the predetermined threshold Th3. The comparator 39 compares this signal Vp with a predetermined threshold Th3 and outputs the comparison result as a signal “Fault”.

  Based on the signal “Fault”, the controller 18 changes the setting of the Ibias DAC as described above and restarts the oscillation of the STOAR element 33.

  According to the present embodiment, it is possible to determine whether or not the STOAR element oscillates, and it is possible to resume oscillation under the control of the controller 18 even when the STOAR element stops oscillating.

  Next, a fifth embodiment of the STOAR element oscillation confirmation circuit according to the present invention will be described.

  FIG. 9 is a diagram showing a circuit configuration of the fifth embodiment.

  This circuit configuration is a combination of the third embodiment and the fourth example. Therefore, the operation is the same as that described in the third and fourth embodiments. Also in this embodiment, the presence or absence of oscillation of the STOAR element can be determined, and even when the oscillation of the STOAR element stops, the oscillation can be resumed by the STOAR driver 24 itself.

  As described above, according to the embodiment of the present invention, when the oscillation of the STOAR element is detected to be reduced or stopped, the continuous oscillation of the microwave or the microwave is stopped by changing the constant current setting. Can be automatically resumed.

  The above description is an embodiment of the present invention, and does not limit the apparatus and method of the present invention, and various modifications can be easily implemented. For example, as a modified example of the present invention, it is possible to change to a system in which the fluctuation of the resistance value is directly observed by acquiring not only the voltage of the STOAR element but also the current and converting it to the resistance value by a divider.

  DESCRIPTION OF SYMBOLS 11 ... Disk, 12 ... Spindle motor, 13 ... Head, 15 ... Disk controller, 33 ... STOAR element, 35, 40, 41 ... Resistor, 37, 39 ... Comparator.

Claims (5)

A head including a microwave assist element;
A current source for supplying current to the microwave assist element;
A microwave assist element voltage generated by supplying the current to the microwave assist element is compared with a predetermined voltage. When the microwave assist element voltage is lower than the predetermined voltage, the microwave assist element oscillates. A detection unit for detecting that it is not,
A magnetic disk device comprising:   The magnetic disk apparatus according to claim 1, further comprising a controller that increases an output current of the current source when the detection unit detects that the microwave assist element is not oscillating.   The first and second resistance elements connected in parallel with the microwave assist element and connected in series with each other, and the detection unit compares a voltage at a connection portion of the first and second resistance elements with a predetermined voltage. 3. The magnetic disk device according to 1 or 2.   And further comprising a switch connected between the second current source and the second current source and the microwave assist element, and the detection unit switches the switch when the microwave assist element voltage is lower than a predetermined voltage. 4. The magnetic disk device according to claim 1, wherein the magnetic disk device is set to an on state.   A band pass filter that filters the microwave assist element voltage; and a peak hold circuit that holds a peak value of an output voltage of the band pass filter; and the detection unit outputs an output signal of the peak hold circuit and a predetermined voltage. The magnetic disk device according to claim 1, wherein the magnetic disk devices are compared with each other.

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