Patent Publication Number: US-2020286507-A1

Title: Shared MAMR and HDI Sensor/Driver

Description:
TECHNICAL FIELD 
     This disclosure relates generally to a microwave assisted magnetic recording (MAMR) device with a spin torque oscillator (STO) connected in parallel with a head-disk interference (HDI) sensor incorporated in a magnetic recording head, that are usually built into a head gimbal assembly, and then further into head stack assembly used in a hard disk drive. 
     BACKGROUND 
     As is known in the art, microwave assisted magnetic recording (MAMR) is a recording method to improve the areal density of a magnetic read/write head for use in a hard disk drive (HDD). MAMR enabled magnetic recording head utilizes a spin torque oscillator (STO) for generating a magnetic field having a microwave frequency. When the magnetic field from the write head is applied and current is conducted through the STO, the STO oscillates and the field is transferred to the medium. The AC magnetic field reduces the coercive force of the recording medium, thus high quality recording by MAMR may be achieved. 
     In hard disk drives, the read/write heads are flying closer and closer to the disk, and it is increasingly important to precisely detect the flying height and head disk impact. To do this, mechanical vibration of the read/write head is usually used to detect contact between the read/write head and the disk, because contact awareness is important to accurate flying height spacing. A dedicated contact sensor provides more accurate contact detection. The contact sensor is commonly referred to as a head-disk interference sensor (HDI). Some head-disk interference sensors are resistive temperature detectors that are configured into the head slider. The temperature change of the HDI sensor is used to indicate contact or the relative flying height of the slider. The HDI sensor has a current flowing through it for putting the sensor at a higher temperature than the local environment and providing a mean for monitoring its resistance change. 
     Both the STO and the HDI sensor require an additional electrical trace connection from the preamplifier to the head slider. Additionally, electrical connection pads are needed on the slider to accommodate both the STO and the HDI sensor. 
     SUMMARY 
     An object of this disclosure is to provide a read/write head on an arm-head assembly that includes a spin torque oscillator (STO) and a head-disk interference (HDI) sensor connected in parallel. 
     To accomplish at least this object, a hard disk drive has a head-gimbal assembly that is configured with an STO situated between a main pole and a trailing shield. An HDI sensor is placed in the vicinity of the main pole and one of the magneto-resistive shields of the magneto-resistive read sensor. A conductive trace is connected between a pad on the preamplifier affixed to the head stack assembly. The preamplifier is configured for providing a first biasing voltage level to the spin torque oscillator (STO) and to the HDI sensor for determining resistance changes in the head-disk interference (HDI) sensor. Further, the preamplifier is configured for determining a resistance change in the HDI sensor based on a change in current through the HDI sensor. 
     The STO and the HDI sensor are connected to a first connector of the trace such that a first terminal of the STO and the HDI sensor receive a first polarity of the first biasing voltage and connected to a second connector of a second trace such that a second terminal of the STO and the HDI sensor receive a second polarity of the first biasing voltage. 
     In another embodiment, the first terminal of the HDI sensor is connected to a first terminal of a first resistor. A second terminal of the first resistor is connected to the first connector of the trace. A second terminal of the HDI sensor is connected to a first terminal of a second resistor. A second terminal of the second resistor is connected to the second connector of the trace. 
     In some embodiments, the first terminal of the STO is connected to a first terminal of a third resistor. A second terminal of the third resistor is connected to the first connector of the trace. A second terminal of the STO is connected to a first terminal of a fourth resistor. A second terminal of the fourth resistor is connected to the second connector of the trace. 
     In some embodiments, a first terminal of a fifth resistor is connected to the second terminals of the first and third resistors and the first connector of the trace. A first terminal of a sixth resistor is connected to the second terminals of the second and fourth resistors and the second connector of the trace. The second terminals of the fifth and sixth resistors are connected to a ground reference terminal. The first, second, third, and fourth, fifth, and sixth resistors are selected to balance out the bias voltage requirements of the STO and the HDI sensor and deliver the desired voltage to the STO and the HDI sensor. 
     In various embodiments, the first, second, third, and fourth, fifth, and sixth resistors are selectively placed inside the head device or on the preamplifier or a hard disk controller circuit. In embodiments, the first and second terminals of the STO and the HDI sensor are connected to individual connectors of the trace and thus to the resistors as described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a representation of a magnetic hard disk drive embodying the principles of the present disclosure. 
         FIG. 2  is a block diagram of a controller and preamplifier embodying the principles of the present disclosure. 
         FIG. 3  is a block diagram of a magnetic head assembly embodying the principles of the present disclosure. 
         FIG. 4  is a block diagram of a magnetic head assembly showing biasing voltage balancing that embodies the principles of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a representation of a magnetic hard disk drive  10  embodying the principles of the present disclosure. Data from an external device is applied to the magnetic hard disk drive  10  through the data input terminal  100 . Data to be transferred to the external device is transferred from the magnetic disk drive  10  through the data output terminal  165 . 
     The data input signal  100  is applied to the disk controller  20 . The disk controller  20  formats the data input signal to set the conditions suitable for writing the magnetic disk  50 . The formatted data input is transferred to the preamplifier for conversion to the head current used to generate the magnetic field for writing the magnetic disk. 
     Further, the controller  20  receives the data read from the magnetic disk  50  through the preamplifier  30 . The preamplifier  30  and the controller  20  condition the signals read from the magnetic disk  50  to decode the output data. The output data is transferred through the terminal  165  to the external device. Control data is applied to the controller  20  through the terminal  125  for communicating control information such as data request, I/O read/write, channel ready, address, data acknowledge, etc. 
     A head arm or head stack assembly  25  has the magnetic read/write head  40  mounted at a distal end of the arm-head assembly  25 . A voice coil  35  is mounted at an opposite end of the head arm or head stack assembly  25 . The voice coil  35  receives control signals from the controller  20  for causing the magnetic read/write head assembly  40  to move across the disk  50 . The magnetic read/write head  40  is then able to read from and record to the disk  50 . 
     The preamplifier  30  is mounted on the head arm assembly  25 . A trace  45  is connected from the preamplifier  30  to the magnetic read/write head  40  to transfer the data and control signals between the preamplifier  30  and the magnetic read/write head  40 . The trace  45  is also secured to the head arm assembly  25 . 
       FIG. 2  is a block diagram of a controller  20  and preamplifier  30  embodying the principles of the present disclosure. The input data received through the terminal  100  is applied to a data formatter circuit  105  for encoding the data to a format acceptable to the hard disk media for writing the data to the hard disk. The encoded data is then transferred to a data conditioner circuit  110  to have conditioning such as precompensation or other adjustments to accommodate the transmission line characteristics of the trace  45  of  FIG. 1 . The conditioned data is transferred to the write driver current amplifier  115  for transformation to a current for transmission to the write head  120 . 
     The write control data transferred through the terminal  125  is received by the disk controller circuit  130  for supervising the encoding, decoding, synchronization control of the hard disk drive  10  of  FIG. 1 . The disk control circuit  130  provides a spindle motor driver control signal  135  for turning on a spindle motor for spinning the disk  50  of  FIG. 1 . The disk control circuit  130  also provides a voice coil motor driver control signal  140  for actuating the voice coil to move the arm-head assembly over the surface of the disk  50  of  FIG. 1 . 
     Read data sensed by the read head  145  is transferred to the read current preamplifier  150 , where the signals are amplified and transmitted to the read analog to digital (A/D) converter  155  where the data voltage signals are converted to a sequence of digital numbers. The converted digital data are transferred to the read decoder  160  for converting the digital read data to the decoded read data. The read output data from the read decoder  160  is transferred to the external device. 
       FIG. 3  is a block diagram of a magnetic read/write head assembly  40  embodying the principles of the present disclosure. The read head  200  is typically a tunneling magneto-resistive (TMR) device that detects the magnetic field of the stored data on the magnetic disk  50 . The sensed signal of the stored data as detected by the read sensor  205  is transferred to the preamplifier  30  by the trace  45  that is connected to the magnetic read/write head  40  and the preamplifier  30  of  FIG. 1 . The preamplifier  30  amplifies the signal sensed by the magnetic read/write head  40  from the data location of the magnetic disk  50  for transfer to the read A/D converter  155  of the controller  20  of  FIG. 2 . Adjacent to the read sensor  205  are two magnetic read shields  210   a  and  210   b . The magnetic read shields  210   a  and  210   b  isolate the read sensor  205  from stray magnetic fields that may corrupt the read data. 
     The write head  215  generates the magnetic field that switches the magnetic domains at the data locations on the magnetic disk  50 . The write head  215  has a return pole  235  and a main pole  225  that form the magnetic circuit with the magnetic media of the magnetic disk  50 . The magnetic field is generated at the tip of the main pole  225 . The coil  230  is wound around the main pole  225 . A current is passed through the coil  230  to induce a magnetic field in the gap between the main pole  225  and the return pole  235 , also some leakage field near the gap and thus in the magnetic media of the magnetic disk  50 . 
     An HDI sensor  240  is normally placed between the read head  200  and element write head  215 . The HDI sensor  240  is a resistive element such as a physical resistor or a spin torque device placed at the slider surface of the magnetic read/write head  40  to detect the separation and/or contact of the write head assembly  40  from the disk  50 . The resistance of the HDI sensor  240  will decrease as the HDI sensor  240  moves closer to the disk  50  as a result of more effective cooling. The resistance of the HDI sensor  240  will increase when the HDI sensor  240  hits the disk due to heat generation from friction of magnetic read/write head  40  dragging on the disk  50 . The HDI sensor  240  has a pair of wiring traces  242  and  244  that are connected respectively to the connectors  250   a  and  250   b  that are part of the connector of the trace  45  of  FIG. 4 . 
     An STO  245  is placed between the main pole  225  and the trailing shield  235 . The STO  245  has wiring trace  247  and  249  that are connected respectively to the connectors  250   a  and  250   b , thus making the STO  245  in parallel to the HDI sensor  240 . 
     The STO  245  consists of a magnetic layer that serves as a polarizer, a non-magnetic spacer, and a magnetic “free” layer. A DC biasing voltage is applied across the STO  245  that is large enough to transfer a sufficient magnitude of spin torque to the free layer to cause its magnetic moment to precess around the gap field direction. The precession frequency is usually in the microwave frequency range. This STO  245  generates an AC microwave magnetic field that travels to the disk  50  to assist the switching of the magnetic domain in the region of the disk  50  beneath the STO  245 . This allows more data to be written to the disk for a given area. 
     Referring back to  FIGS. 2 and 3 , the parallel connections of the HDI sensor  240  and the STO  245  feed through the trace  45  to the preamplifier  30 . The disk control circuit  130  is connected to the microwave assisted magnetic recording (MAMR) driver  180  to activate a biasing voltage source that transfers a biasing voltage to the trace  45  and thus to the STO  245  for activating the microwave radiation of the STO  245 . The current resulting from the biasing voltage flows through the HDI sensor  240  for determining the resistance of the HDI sensor  240 . The biasing voltage is adjusted to allow the control of the MAMR driver  180  and HDI sensor  240  performance. The HDI sense circuit  175  will detect the relatively low frequency (&lt;1 MHz) changes in the current flowing through the HDI sensor  240  that results from the changes in the resistance of the HDI sensor  240  as the magnetic read/write head  40  fluctuates in spacing above the disk  50  as the disk rotates. The sense signal from the HDI sense circuit  175  is transferred to the disk control circuit  130  for determining if the magnetic read/write head  40  is flying too close to the disk and/or if any contact has occurred. This information is used to control the spacing between the head  40  and disk  50  either with or without active feedback. 
       FIG. 4  is a block diagram of a magnetic head assembly showing biasing voltage balancing that embodies the principles of the present disclosure.  FIG. 4  is identical to  FIG. 3  in terms of structure and function of the magnetic read/write head assembly  40 . The difference being in the addition of the resistors R 1 , R 2 , R 3 , R 4 , R 5 , and R 6 . Resistor R 1  has a first connection that is connected through the wiring trace  242  to the first terminal of the HDI sense circuit  175 . The second terminal of the resistor R 1  is connected to the first connector  250   a  of the trace  45 . Resistor R 2  has a first connection that is connected through the wiring trace  244  to the first terminal of the HDI sense circuit  175 . The second terminal of the resistor R 2  is connected to the second connector  250   b  of the trace  45 . 
     Resistor R 3  has a first connection that is connected through the wiring trace  247  to the first terminal of the STO  245 . The second terminal of the resistor R 3  is connected to the first connector  250   b  of the trace  45 . Resistor R 4  has a first connection that is connected through the wiring trace  249  to the second terminal of the STO  245 . The second terminal of the resistor R 4  is connected to the second connector  250   b  of the trace  45 . The connections as described place the HDI sensor  240  and the STO  245  in parallel with the HDI sense circuit  175  and the microwave assisted magnetic recording (MAMR) driver  180  of  FIG. 2  functioning as described above. 
     The first terminal of the resistor R 5  is connected to the second terminals of the resistors R 1  and R 3 . The first terminal of the resistor R 6  is connected to the second terminals of the resistors R 2  and R 4 . The second terminals of the resistors R 5  and R 6  are connected to a ground reference terminal of the trace  45  or to the structure of the head arm assembly  25 . The resistances of the resistors R 1 , R 2 , R 3 , R 4 , R 5 , and R 6  are adjusted such that the biasing voltage across the microwave assisted magnetic recording (MAMR) STO sensor  245  and the bias voltage on the HDI sensor are both at the desired level for a certain output from the preamp. 
     While this disclosure has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the disclosure.