Abstract:
A data storage apparatus includes a controller capable of being coupled to a read/write head. The controller is configured to receive a fault signal from a sensor of the read/write head. The sensor indicates whether an energy source used to heat the recording medium is malfunctioning during a write operation. In response to the fault signal, the controller takes remedial action to protect the data associated with the write operation.

Description:
SUMMARY 
     A data storage apparatus according to various embodiments described within the present disclosure includes a controller capable of being coupled to a read/write head. The controller is configured to receive a fault signal from a sensor of the read/write head. The sensor indicates whether an energy source used to heat the recording medium is malfunctioning during a write operation. In response to the fault signal, the controller takes remedial action to protect the data associated with the write operation. 
     A system according to various embodiments described within the present disclosure includes a read/write head and a controller. The read/write head includes an energy source that is used to heat a recording medium and a sensor that is configured to detect whether the energy source is heating the recording medium during a write operation. The controller is coupled to the read/write head and receives a fault signal from the sensor indicating that the energy source is malfunctioning during the write operation. In response to the fault signal, the controller takes remedial action to protect the data associated with the write operation. 
     A method according to various embodiments described within the present disclosure includes initiating a write operation of data onto a recording medium, sensing whether the recording medium is heated during the write operation, issuing a fault signal if the recording medium is not heated during the operation, and responding to the fault signal by protecting the data associated with the write operation. 
     The above summary is not intended to describe each embodiment or every implementation. A more complete understanding will become apparent and appreciated by referring to the following detailed description and claims in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts an example of a HAMR slider. 
         FIG. 2  depicts an example of a read/write head configuration. 
         FIG. 3  is a block diagram illustrating an example of components used in a write operation. 
         FIG. 4  is a block diagram of a fault detection system according to various embodiments. 
         FIG. 5  is a flowchart illustrating a write operation enhanced with a fault detection system according to various embodiments. 
     
    
    
     The figures are not necessarily to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number. 
     DETAILED DESCRIPTION 
     In heat-assisted magnetic recording (HAMR) disk drives, also referred to as thermal-assisted magnetic recording (TAMR) disk drives, heat energy is used in conjunction with magnetic fields applied to a magnetic recording media, e.g., a hard disk drive, to overcome super-paramagnetic effects that limit the areal data density of traditional magnetic media. In a HAMR recording device, information bits are recorded on a storage layer at elevated temperatures. The heated area in the storage layer determines the data bit dimension and linear recording density is determined by the magnetic transitions between the data bits. 
     In order to achieve desired data density, a HAMR recording head, also known as a HAMR slider, includes optical components that direct, concentrate and transform light energy from an energy source to heat on the recording media. An example configuration of a HAMR slider is depicted in  FIG. 1 . The HAMR slider  100  includes an energy source  102 , e.g., a laser diode, configured to produce laser light that energizes an optical antenna  112  of a near field transducer (NFT)  106 . The laser light produced by the energy source  102  is guided to the NFT  106  through an optical waveguide  110 . The head media interface (HMI), also known as an air bearing surface (ABS) is indicated with item number  108 . 
     A detailed view of an exemplary read/write head configuration  120  contained within HAMR slider  100  is provided in  FIG. 2 . The read/write head configuration  120  is positioned with ABS  108  proximate magnetic medium  122 . The read/write head configuration  120  includes a magnetic read head  124  proximate the ABS  108  for reading data from the magnetic medium  122  and a magnetic writer configuration  126  for writing to the magnetic medium  122 . The magnetic writer configuration  126  includes NFT  106  intermediate optical waveguide  110  and write pole  128  and write coil  132 . A hotspot  133  created by the heat emitted by NFT  106  is shown within magnetic medium  122 . The read/write head configuration  120  also includes a heater  134  and may also include at least one sensor. For purposes of illustration, sensors  136   a ,  136   b , and  136   c  are shown; the multitude of sensors indicating possible placement locations within the read/write head configuration  120 . 
     Sensors  136   a ,  136   b , and  136   c  may comprise any variety of sensors including a sensor having a temperature coefficient of resistance (TCR), a varistor, or a thermocouple, for example. One example of a TCR sensor is a dual-ended temperature coefficient of resistance sensor (DETCR). A TCR sensor measures temperature change by measuring the change in resistance, or rate of change of resistance, across the sensor and, as such, can measure the temperature change at the ABS  108  induced by all thermal condition changes from air pressure, clearance, head operation, and contact, among other changes. As described, a TCR sensor may be used to monitor temperature in the HAMR slider  100  but it may also be used during manufacturing to set head-disk spacing and/or may be used for thermal asperity (TA) detection. 
     Sensors  136   a ,  136   b , and  136   c  may alternatively, and/or additionally, comprise any variety of sensors including a light output detection sensor such as a photodiode, phototransistor or bolometer. The light output detection sensor may be used to measure the light output of the energy source  102 , e.g., laser diode, as a feedback mechanism for regulating the output power of the energy source  102 . 
     The locations of sensors  136   a ,  136   b , and  136   c  in  FIG. 2  represent possible locations for a sensor. Other sensor locations may be used as desired or appropriate. For example, the photodiode may be located proximate to the laser diode in order to reduce the complexity of recording head manufacturing. Further, the read/write head configuration  120  need not be limited to a single sensor or a single type of sensor rather multiple sensors and multiple sensor types may be used as desired or appropriate. A read/write head configuration  120  with no sensors is also contemplated and may be suitable as per a specific application. 
     Referring now to  FIG. 3 , a block diagram provides an example of the typical components used by a HAMR drive during a write operation. The components include a host  140 , a controller application-specific integrated circuit (ASIC)  142 , a preamplifier  144  and a write head  146 . The host  140  may comprise a computer or other similar device capable of performing a sequence of logical operations, and may be coupled to the HAMR device via host protocols such as SATA, SaS, SCSI, etc. The controller ASIC  142  generally includes a controller microprocessor  148  operating under control of firmware  150 , a formatter  152  utilizing formatter logic and a write channel  154 . The preamplifier  144  includes a laser driver  156  and writer driver  158  while the write head  146  includes laser diode  102  (see  FIG. 1 ) and writer coil  132  (see  FIG. 2 ). Often, the drive contains more than one write head, and the preamplifier contains multiplexing circuitry (not shown) for selecting and routing signals to a desired head. Other embodiments include more than one preamplifier. 
     In operation, the host  140  initiates a write operation that is communicated to the controller ASIC  142  and specifically to the controller microprocessor  148 . The controller microprocessor  148  has been programmed, via the firmware  150 , to operate on the host instruction and generate a write request to the formatter  152  as well as seek a desired track/position on the magnetic media  122  (see  FIG. 2 ). The formatter  152  asserts the WrGate signal to the write channel  154  which enables the laser driver  156  and writer driver  158  of the preamplifier  144 . In this instance, the write channel  154  provides a laser pulsing signal to the laser driver  156  and the write data is provided to the write driver  158 . The current from each of the drivers  156  and  158  activates the laser diode  102  and writer coil  132 , respectively, allowing the write head  146  to complete the write operation. 
     HAMR drive technology has increased the speed at which data may be recorded in a magnetic media as well as the amount of data that may be recorded in a magnetic media however the technology does present some complexities. For example, the HAMR media hotspot may need to be smaller than a half-wavelength of light available from economic sources, e.g., laser diodes. Due to what is known as the diffraction limit, optical components cannot focus the light at this scale. One way to achieve tiny confined hotspots that are smaller than the half-wavelength of light is to use an NFT, such as a plasmonic optical antenna. The NFT is designed to have a surface plasmonic resonance when energized by laser light. At resonance, a high electrical field surrounds the NFT due to the collective oscillation of electrons in the metal. Part of the electrical field tunnels into the magnetic media and is absorbed, raising the temperature of the magnetic media locally above the Curie point for recording. Without the presence of heat energy, the magnetic media will be below the Curie point, and no effective erasure or re-magnetization will occur, even if the magnetic field from the writer is present. However, it is well understood that the magnetic transitions are defined, i.e., magnetically frozen, at temperatures less than the Curie temperature. 
     Furthermore, while a HAMR drive may use a laser and an NFT to heat the media to aid in the recording process, inefficiencies in the optical transmission path, the laser and the NFT can result in the heating of the overall HAMR head/slider. The heating may originate from the NFT, the light delivery optics and/or from the laser itself. Energy absorbed into these components may be converted to heat, which is conducted to the surrounding materials. This heat can be detected by sensor(s) within the recording head, for example the DETCR sensor(s) described earlier. 
     Additionally, in some HAMR drive embodiments a technique known as pulsing may be used to control the laser, such a technique was utilized in the configuration of  FIG. 3 . The pulsing operates to flash the laser at a repetitive frequency. Pulsing is usually in synchronization with magnetic transitions from the writer coil, but offset in phase such that the flashes occur between magnetic transitions. The support of pulsing adds control pins and circuitry within the preamplifier, which add additional, potential failure points. 
     Because of the technical complexities involved in HAMR drives, such as those described above, errors in the writing of data to magnetic media can occur. However, in disk drives, especially in “enterprise disk drives”, i.e., drives that are commonly used in industry and commerce, data integrity is given a high priority. In the general sense, disk drive data integrity means returning the same data when read as what was most recently written or, alternatively, returning an error indication that the drive was unable to complete a valid data write, which might occur, for example, on a hardware error or other drive system error. The error indication would thus suggest a data storage failure mode, and the host system would then perform appropriate error recovery. In this disclosure, when it is written “protect data associated with a write operation”, it is meant that either the device has verified the data were properly stored (i.e. by either the lack of a fault detection on a write operation or by performing a read-after-write), or that the host has been notified of the data storage device&#39;s failure to properly store the data. 
     One class of data-integrity failure modes that may occur is that of an “undetected data miscompare.” One class of “undetected data miscompares” is a “stale-data miscompare,” which can occur when the drive fails to write data to the magnetic media due to some fault, and this failure to write is undetected by the drive. In some failure-mode scenarios, the disk drive accepts data from a host for writing on the magnetic media, but fails to write the data on the magnetic media and, even worse, fails to notify the host system of the failure to write the data on the media. Consequently, when the host later wishes to retrieve (read) the data, the drive reads old (stale) data from an earlier write and returns this data to the host, again failing to notify the host system of the error. This failure mode can even occur in the presence of logical block address (LBA) seeded error detecting codes, since the LBA number of the previously written data is usually the same as the LBA number of the data that was intended to be written. 
     In conventional disk drives, i.e., non-HAMR drives, a preamplifier containing fault detection circuitry is typically connected to the drive recording head to help prevent the above-described types of failures. Such a preamplifier can detect faults like an open or short-circuited writer element. If the preamplifier detects one of these faults, the preamplifier asserts a signal back to the disk drive controller and the controller performs error recovery, which can include reporting the error to the host if the drive is unable to correct the fault condition. However, fault detection in conventional disk drives does not contemplate detection of faults related to heat or an energy source. 
       FIG. 4  illustrates a fault detection system  160  for a HAMR disk drive. The fault detection system  160  has the ability to detect faults within the energy delivery system of the HAMR drive, including the NFT, which until the present system has not been reliably performed. The inability to detect faults within the NFT may lead to either compromising data integrity or a loss of performance. The fault detection system  160  provides multiple feedback loops that, when disturbed, alerts the controller ASIC  142  to a fault. The controller ASIC  142  contains logic for mitigating the error or reporting an error status back to the host  140  in event of a hard failure. An example of error mitigation includes retrying a write operation with read verification (read after write); other mitigation techniques may be utilized as appropriate. 
     The fault detection system  160  can interact with host  140 , and incorporates those components described above with reference to the write operation block diagram of  FIG. 3  including a controller ASIC  142  incorporating a controller microprocessor  148  with firmware  150 , a formatter  152  and a write channel  154 , a preamplifier  144  incorporating a laser driver  156  and a writer driver  158 , and a write head  146  incorporating laser diode  102  and writer coil  132 . The fault detection system  160  additionally includes an NFT temperature sensor  162 , e.g., DETCR sensor, and/or a photo detector sensor  164  (see  FIG. 2  and description relating to corresponding sensors  136   a ,  136   b , and  136   c ). The fault detection system  160  further includes a fault detector  166  in each of laser driver  156  and writer driver  158  as well as preamplifier fault logic  168  and controller fault logic  170  within controller ASIC  142 . 
     The additional components within fault detection system  160  provide the opportunity for feedback signals that assist in enabling the fault detection. Specifically, the laser diode  102  now provides a feedback current and/or voltage that can be measured by the preamplifier and acted upon by the preamplifier fault logic  168  and/or the controller fault logic. For example, if the laser diode voltage is out of range, if there is a laser diode voltage shift during write indicating mode hopping, if the laser threshold/bias current is out of range, i.e., too high or too low, or if the laser operating current is out of range, i.e., too high or too low, faults within system  160  can be signaled and responded to appropriately. The writer coil  132  similarly provides a feedback current and/or voltage for fault detection. 
     The NFT temperature sensor  162  and/or photo detector  164  positioned within the write head  146  each provide a signal back to the preamplifier  144  which can be acted upon by the preamplifier fault logic  168  and/or controller fault logic  170 . For example, if the NFT temperature sensor  162  detects no or insufficient thermal heating, if the photo sensor  164  indicates the detected light is out of range, i.e., too high or too low, or if the photo sensor  164  indicates that the detected light has a step discontinuity, i.e., faults can be signaled within system  160  and responded to appropriately. Faults within the write head  146  and those occurring in the preamplifier itself are signaled to the preamplifier fault logic  168  and fed back to the controller fault logic  170 . Fault feedback signals within the controller ASIC itself are provided from the write channel  154  to the controller fault logic  170 . The controller fault logic  170  additionally provides a write enable signal to each of the elements of the preamplifier  144  including the laser driver  156 , the writer driver  158  and the preamplifier fault logic  168 . The write enable signal generally follows the WrGate signal from the formatter logic  152 , asserting when a write is active. Upon reception of a fault, the fault logic  170  aborts the write operation by de-asserting the write enable signal and alerts the controller microprocessor  148  of the fault condition via processor interrupt signal IRQ Fault. The controller microprocessor  148  then performs fault error recovery, which may include rewriting the data and rereading the data to confirm that it was correctly written. 
     A listing of the faults monitored by the fault detection system  160  and the resulting system failure modes are provided in Table 1. The list of faults in Table 1 should not be deemed exhaustive but rather a listing of exemplary faults to which other faults may be added or subtracted. 
     
       
         
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Monitored Faults 
                 Failure Mode 
               
               
                   
               
             
             
               
                 1. Monitor DETCR heating during write; 
                 Laser Diode Failure 
               
               
                 Fault if thermal heating is not detected 
               
               
                 2. Monitor photodiode feedback during 
                 Laser Diode Failure 
               
               
                 write; Fault if out of range 
                 Optical Waveguide Failure 
               
               
                   
                 Preamp Laser Driver Failure 
               
               
                 3. Monitor photodiode feedback during 
                 Mode Hopping Failure 
               
               
                 write; Fault if step discontinuity is 
               
               
                 detected 
               
               
                 4. Fault if no laser pulsings are 
                 Pulsing Control Signal Failure 
               
               
                 received when write transitions or 
                 (write without laser) 
               
               
                 over time period 
               
               
                 5. Laser diode open Fault 
                 Laser Diode Failure 
               
               
                   
                 Interconnection Failure 
               
               
                 6. Laser diode shorted Fault 
                 Laser Diode Failure 
               
               
                   
                 Interconnection Failure 
               
               
                 7. Laser diode shorted to ground 
                 Laser Diode Failure 
               
               
                 Fault 
                 Interconnection Failure 
               
               
                 8. Laser diode forward voltage out 
                 Laser Diode Failure 
               
               
                 of range Fault 
                 Interconnection Failure 
               
               
                 9. Laser diode forward voltage 
                 Mode Hopping Failure 
               
               
                 shift during write Fault 
               
               
                 10. Laser threshold/bias current 
                 Firmware bug 
               
               
                 register out of range Fault 
                 Microprocessor Malfunction 
               
               
                   
                 Communication Error 
               
               
                 11. Laser I add  (I op ) current register 
                 Firmware bug 
               
               
                 out of range Fault 
                 Microprocessor Malfunction 
               
               
                   
                 Communication Error 
               
               
                 12. Write without laser enable 
                 Firmware bug 
               
               
                 Fault 
                 Microprocessor Malfunction 
               
               
                   
                 Communication Error 
               
               
                   
               
             
          
         
       
     
     Referring now to  FIG. 5 , a flowchart illustrates an example embodiment of the write operation with the fault detection system  160  implemented. Initially, a write operation is issued from the host, per block  200 . The firmware within the controller microprocessor sets up the preamplifier fault detection registers, per block  202 . The firmware seeks to a desired track on the magnetic media and programs the formatter for the write operation, per block  204 . The magnetic media rotates to the desired starting sector of the write, per block  206 . The formatter asserts the write gate, per block  208 . The question of whether a fault occurred during the write operation is posed, per decision block  210 . If a fault has occurred, as detected by the fault detection system  160 , the data on the magnetic media sector is read back, per block  212 . The question of whether the data was written correctly is posed, per decision block  214 . If the data has not been written correctly (or has not been written at all), a “bad” status on the write is reported to the host, per block  216 . If no fault occurred during the write operation or the data was written correctly even though a fault occurred, a “good” status on the write is reported to the host, per block  218 . Not shown, additional error recovery steps, for example reprogramming preamplifier registers, rewriting data multiple times, adjusting laser current, etc. may be attempted prior to returning status to the host. 
     Additional and/or alternative features of the above-described HAMR drive fault detection system  160  include the ability set and adjust operational threshold windows during operation of the drive, e.g., programmable time and amplitude constants for threshold detectors. The sliding window capability allows for temperature, laser power, currents, etc., to change over time without needlessly triggering the fault system. Another feature includes gradual adaptation of fault windows to accommodate for component aging but only if read reads after writes confirm the writes were successful. 
     Systems, devices or methods disclosed herein may include one or more of the features structures, methods, or combination thereof described herein. For example, a device or method may be implemented to include one or more of the features and/or processes above. It is intended that such device or method need not include all of the features and/or processes described herein, but may be implemented to include selected features and/or processes that provide useful structures and/or functionality. 
     Various modifications and additions can be made to the disclosed embodiments discussed above. Accordingly, the scope of the present disclosure should not be limited by the particular embodiments described above, but should be defined only by the claims set forth below and equivalents thereof.