Abstract:
Approaches for a hard-disk drive suspension interconnect having a wide bandwidth. A suspension interconnect includes a substrate layer, a dielectric layer disposed on the substrate layer, and a plurality of transmission-line (TL) conductors disposed within the dielectric layer. Air gaps may be disposed around the TL conductors to minimize the tendency of the dielectric material to act as an electrical shunt, which impedes high bandwidth signal transmission. An air gap may exist in the dielectric layer between adjacent TL conductors. Additionally, the area adjacent to the plurality of TL conductors, along the direction of signal travel, may alternate between dielectric material and air gaps. Indeed, there need not be any solid material enclosing the TL conductors save for a plurality of dielectric cross ties that provide structural support thereto. The substrate layer may also comprise one or more air gaps underneath a portion of the plurality of TL conductors.

Description:
FIELD OF THE INVENTION 
       [0001]    Embodiments of the invention generally relate to a suspension interconnect structure that supports high frequency signal transmission. 
       BACKGROUND OF THE INVENTION 
       [0002]    A hard-disk drive (HDD) is a non-volatile storage device that is housed in a protective enclosure and stores digitally encoded data on one or more circular disks having magnetic surfaces (a disk may also be referred to as a platter). When an HDD is in operation, each magnetic-recording disk is rapidly rotated by a spindle system. Data is read from and written to a magnetic-recording disk using a read/write head which is positioned over a specific location of a disk by an actuator. 
         [0003]    A read/write head uses a magnetic field to read data from and write data to the surface of a magnetic-recording disk. As a magnetic dipole field decreases rapidly with distance from a magnetic pole, the distance between a read/write head and the surface of a magnetic-recording disk must be tightly controlled. To provide the distance between a read/write head and the surface of a magnetic-recording disk, an actuator relies on suspension&#39;s force on the read/write head to provide the proper distance between the read/write head and the surface of the magnetic-recording disk while the magnetic-recording disk rotates. A read/write head therefore is said to “fly” over the surface of the magnetic-recording disk. When the magnetic-recording disk stops spinning, a read/write head must either “land” or be pulled away onto a mechanical landing ramp from the disk surface. 
         [0004]    A write-head of an HDD records data onto the surface of a magnetic-recording disk in a series of concentric tracks. Electrical signals may be carried by electrical conductors (or “traces”) within the HDD to a transducer of the read/write head. The transducer converts the electrical signals, carried by the electrical conductors, into a magnetic write field used to write data to a track on the magnetic-recording disk. The greater the frequency (the “write frequency”) of the magnetic write field, the greater the amount of data that can be stored on the track (referred to as recording density) and the faster the data can be retrieved. It is desirable to store as much data as is safely possible on a magnetic-recording disk. For reading data, a read transducer translates the magnetic signals into electrical signals, which are then carried by electrical conductors (or “traces”) within the HDD to signal processing electronics. 
       SUMMARY OF THE INVENTION 
       [0005]    Until recently, the electrical signals and harmonics received by the transducers which generate the magnetic write fields within a hard-disk drive (HDD) typically did not exceed 4 gigahertz. However, in the future, HDDs may enable or require transducers to receive and/or transmit electrical signals with much higher frequency, such as 10-30 gigahertz. 
         [0006]    It is observed that today&#39;s transmission-line (TL) conductors on the suspension (also referred to as “traces”) within a HDD cannot scale to support higher frequency signals. This is so because, when the transmission-line (TL) conductors conduct signals at higher frequencies, the dielectric material which insulates the transmission-line (TL) conductors itself becomes conductive, thereby causing the dielectric material to act as an electrical shunt that dissipates energy carried by the transmission-line (TL) conductors. 
         [0007]    Advantageously, embodiments of the invention address this issue by reducing or eliminating the dielectric material surrounding, enclosing, or adjacent to the transmission-line (TL) conductors. Embodiments may dispose one or more of air gaps along adjacent transmission-line (TL) conductors (sometimes referred to as an “air spine”), may dispose air gaps in the substrate layer beneath the transmission-line (TL) conductors (sometimes referred to as “substrate windowing”), and may remove the dielectric material adjacent to the transmission-line (TL) conductors except for support structures (referred to as “cross ties”) made out of dielectric material. By reducing or eliminating the dielectric material surrounding, enclosing, or adjacent to the transmission-line (TL) conductors in this manner, the ability of the dielectric material to act as an electrical shunt is reduced, thereby allowing the transmission-line (TL) conductors to support a greater amount of signal bandwidth. 
         [0008]    Embodiments discussed in the Summary of the Invention section are not meant to suggest, describe, or teach all the embodiments discussed herein. Thus, embodiments of the invention may contain additional or different features than those discussed in this section. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Embodiments of the invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
           [0010]      FIG. 1  is a plan view of an HDD according to an embodiment of the invention; 
           [0011]      FIG. 2  is a plan view of a head-arm-assembly (HAA) according to an embodiment of the invention; 
           [0012]      FIG. 3  is a cross-sectional view of a prior art interconnect structure according to the prior art; 
           [0013]      FIG. 4A  is a cross-sectional view of an interconnect structure having an air spine; 
           [0014]      FIG. 4B  is a top view of an interconnect structure having an air spine; 
           [0015]      FIG. 5A  is a top view of an interconnect structure having dielectric cross ties according to an embodiment of the invention; 
           [0016]      FIG. 5B  is a top view of a interconnect structure having an air spine, dielectric cross ties, and substrate windows according to an embodiment of the invention; and 
           [0017]      FIG. 6  is a graph comparing the frequency response for different approaches according to embodiments of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    Approaches for reducing or eliminating the dielectric material surrounding, enclosing, or adjacent to the transmission-line (TL) conductors to increase the signal bandwidth supported by the transmission-line (TL) conductors are described. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the invention described herein. It will be apparent, however, that the embodiments of the invention described herein may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the embodiments of the invention described herein. 
         [0019]    Physical Description of Illustrative Embodiments of the Invention 
         [0020]    While embodiments of the invention may be implemented in a variety of electrical equipment, particular embodiments of the invention shall be described with reference to a hard-disk drive (HDD). In accordance with an embodiment of the present invention, a plan view of a HDD  100  is shown in  FIG. 1 .  FIG. 1  illustrates the functional arrangement of components of the HDD including a slider  110   b  that includes a magnetic-recording head  110   a . The HDD  100  includes at least one head gimbal assembly (HGA)  110  including the head  110   a , a lead suspension  110   c  attached to the head  110   a , and a load beam  110   d  attached to the slider  110   b , which includes the head  110   a  at a distal end of the slider  110   b ; the slider  110   b  is attached at the distal end of the load beam  110   d  to a gimbal portion of the load beam  110   d . The HDD  100  also includes at least one magnetic-recording disk  120  rotatably mounted on a spindle  124  and a drive motor (not shown) attached to the spindle  124  for rotating the disk  120 . The head  110   a  includes a write element and a read element for respectively writing and reading information stored on the disk  120  of the HDD  100 . The disk  120  or a plurality (not shown) of disks may be affixed to the spindle  124  with a disk clamp  128 . The HDD  100  further includes an arm  132  attached to the HGA  110 , a carriage  134 , a voice-coil motor (VCM) that includes an armature  136  including a voice coil  140  attached to the carriage  134 ; and a stator  144  including a voice-coil magnet (not shown); the armature  136  of the VCM is attached to the carriage  134  and is configured to move the arm  132  and the HGA  110  to access portions of the disk  120  being mounted on a pivot-shaft  148  with an interposed pivot-bearing assembly  152 . 
         [0021]    With further reference to  FIG. 1 , in accordance with an embodiment of the present invention, electrical signals, for example, current to the voice coil  140  of the VCM, write signal to and read signal from the PMR head  110   a , are provided by a flexible cable  156 . Interconnection between the flexible cable  156  and the head  110   a  may be provided by an arm-electronics (AE) module  160 , which may have an on-board pre-amplifier for the read signal, as well as other read-channel and write-channel electronic components. The flexible cable  156  is coupled to an electrical-connector block  164 , which provides electrical communication through electrical feedthroughs (not shown) provided by an HDD housing  168 . The HDD housing  168 , also referred to as a casting, depending upon whether the HDD housing is cast, in conjunction with an HDD cover (not shown) provides a sealed, protective enclosure for the information storage components of the HDD  100 . 
         [0022]    With further reference to  FIG. 1 , in accordance with an embodiment of the present invention, other electronic components (not shown), including a disk controller and servo electronics including a digital-signal processor (DSP), provide electrical signals to the drive motor, the voice coil  140  of the VCM and the head  110   a  of the HGA  110 . The electrical signal provided to the drive motor enables the drive motor to spin providing a torque to the spindle  124  which is in turn transmitted to the disk  120  that is affixed to the spindle  124  by the disk clamp  128 ; as a result, the disk  120  spins in a direction  172 . The spinning disk  120  creates a cushion of air that acts as an air-bearing on which the air-bearing surface (ABS) of the slider  110   b  rides so that the slider  110   b  flies above the surface of the disk  120  without making contact with a thin magnetic-recording medium of the disk  120  in which information is recorded. The electrical signal provided to the voice coil  140  of the VCM enables the head  110   a  of the HGA  110  to access a track  176  on which information is recorded. Thus, the armature  136  of the VCM swings through an arc  180  which enables the HGA  110  attached to the armature  136  by the arm  132  to access various tracks on the disk  120 . Information is stored on the disk  120  in a plurality of concentric tracks (not shown) arranged in sectors on the disk  120 , for example, sector  184 . Correspondingly, each track is composed of a plurality of sectored track portions, for example, sectored track portion  188 . Each sectored track portion  188  is composed of recorded data and a header containing a servo-burst-signal pattern, for example, an ABCD-servo-burst-signal pattern, information that identifies the track  176 , and error correction code information. In accessing the track  176 , the read element of the head  110   a  of the HGA  110  reads the servo-burst-signal pattern which provides a position-error-signal (PES) to the servo electronics, which controls the electrical signal provided to the voice coil  140  of the VCM, enabling the head  110   a  to follow the track  176 . Upon finding the track  176  and identifying a particular sectored track portion  188 , the head  110   a  either reads data from the track  176  or writes data to the track  176  depending on instructions received by the disk controller from an external agent, for example, a microprocessor of a computer system. 
         [0023]    Embodiments of the present invention also encompass HDD  100  that includes the HGA  110 , the disk  120  rotatably mounted on the spindle  124 , the arm  132  attached to the HGA  110  including the slider  110   b  including the head  110   a . Therefore, embodiments of the present invention incorporate within the environment of the HDD  100 , without limitation, the subsequently described embodiments of the invention for reducing or eliminating the dielectric material between transmission-line (TL) conductors to increase the signal bandwidth supported by the transmission-line (TL) conductors as further described in the following discussion. Similarly, embodiments of the present invention incorporate within the environment of the HGA  110 , without limitation, the subsequently described embodiments of the invention for reducing or eliminating the dielectric material between transmission-line (TL) conductors to increase the signal bandwidth supported by the transmission-line (TL) conductors as further described in the following discussion. 
         [0024]    With reference now to  FIG. 2 , in accordance with an embodiment of the present invention, a plan view of a head-arm-assembly (HAA) including the HGA  110  is shown.  FIG. 2  illustrates the functional arrangement of the HAA with respect to the HGA  110 . The HAA includes the arm  132  and HGA  110  including the slider  110   b  including the head  110   a . The HAA is attached at the arm  132  to the carriage  134 . In the case of an HDD having multiple disks, or platters as disks are sometimes referred to in the art, the carriage  134  is called an “E-block,” or comb, because the carriage is arranged to carry a ganged array of arms that gives it the appearance of a comb. As shown in  FIG. 2 , the armature  136  of the VCM is attached to the carriage  134  and the voice coil  140  is attached to the armature  136 . The AE  160  may be attached to the carriage  134  as shown. The carriage  134  is mounted on the pivot-shaft  148  with the interposed pivot-bearing assembly  152 . 
         [0025]    Reducing or Eliminating the Dielectric Materials Between Signal Conductors to Increase Bandwidth Support 
         [0026]    Embodiments of the invention enable transmission-line (TL) conductors to support higher signal bandwidth than prior approaches. Transmission-line (TL) conductors according to embodiments of the invention may be used in a variety of different locations within a HDD. For example, transmission-line (TL) conductors of certain embodiments may electronically connect a transducer (which may be implemented in head  110   a ) to a read/write integrated circuit (IC) (which may be implemented in AE module  160 . As another example, transmission-line (TL) conductors of other embodiments may electronically connect a read/write integrated circuit (IC) (which may be implemented in AE module  160  to flexible cable  160 . Transmission-line (TL) conductors according to embodiments of the invention may be employed in a variety of different suspension interconnect structures or arrangements, including, for example, a coplanar interconnect structure or a bi-layer interconnect structure. 
         [0027]    To understand how embodiments of the invention may be implemented, it may be helpful to understand how prior transmission-line (TL) conductors have been implemented.  FIG. 3  is a cross-sectional view of a differential interconnect structure according to the prior art. As shown in  FIG. 3 , transmission-line (TL) conductors  310  are fully enclosed in dielectric layer  320  that is disposed on substrate layer  330 . Substrate layer  330  may be formed using a poor conductor, such as stainless steel. Dielectric layer  320  may be formed using polyimide, which has a relative permittivity between 3 and 4 (ε r , ε=ε r ε 0 , where ε 0 =8.85×10 −12  F/m for vacuum). Transmission-line (TL) conductors  310  may be formed using a conductive material, such as a copper alloy. 
         [0028]    As transmission-line (TL) conductors carry higher signal frequencies, such as 1 gigahertz or greater, the dielectric losses (tan δ, where tan ε=ε″/ε′, and ε=ε′−jε″) begin to dominate the attenuation of the signal transfer, as the dielectric material adjacent to the transmission-line (TL) conductor  310 , which typically insulates transmission-line (TL) conductors  310 , itself becomes conductive. This causes the dielectric material to act as an electrical shunt and energy carried by transmission-line (TL) conductors  310  is dissipated. To address this issue, embodiments of the invention (not depicted in  FIG. 3  and explained in further detail below) advantageously remove as much of the dielectric material adjacent to or enclosing the transmission-line (TL) conductors as possible by using an air dielectric. 
         [0029]    For purposes of providing a clear description,  FIGS. 3-5B  depict two different transmission-line (TL) conductors. Each of the two different transmission-line (TL) conductors in these figures are either labeled “N” or “P,” signifying that transmission-line (TL) conductors  310  are operating in a differential mode by carrying complimentary signals. While not depicted in  FIGS. 3-5B , embodiments of the invention may also be employed where transmission-line (TL) conductors operate in a single-ended mode, i.e., where each transmission-line (TL) conductor carries a voltage varying representing a signal and another transmission-line (TL) conductor carries a reference voltage (such as ground). 
         [0030]    One approach for employing an air dielectric is depicted in  FIG. 4A , which is a cross-sectional view of an interconnect structure having an air spine. The term “air spine” refers to area between adjacent transmission-line (TL) conductors where the dielectric material of dielectric layer  420  is removed, thereby leaving air in-between the adjacent transmission-line (TL) conductors. For example, the interconnect structure shown in  FIG. 4A  comprises air spine  440  between transmission-line (TL) conductors  410 . The dielectric in air spine  440  is air (as opposed to the dielectric material comprising dielectric layer  420 , which may be polyimide). The location of air spine  440  corresponds to where the concentration of the electric field is greatest, namely the area between the adjacent transmission-line (TL) conductors  410 . 
         [0031]      FIG. 4B  is a top view of the interconnect structure of  FIG. 4A . While  FIGS. 4A and 4B  depicts air spine  440  as encompassing the entirety of the area between the transmission-line (TL) conductors, in other embodiments of the invention (not depicted), air spine  440  may be implemented such that a certain amount of the dielectric material comprising dielectric later  420  may remain in the area between transmission-line (TL) conductors, although the amount of dielectric material remaining between the transmission-line (TL) conductors should not be sufficient to reduce the bandwidth of the transmission-line (TL) conductors  410 . 
         [0032]      FIG. 5A  is a top view of an interconnect structure  500  according to another embodiment of the invention. Interconnect structure  500  of  FIG. 5A  has an air spine  540  similar to air spine  440  of  FIG. 4B . However, the interconnect structure  500  also has a plurality of cross ties  550  formed out of the dielectric material that comprises the dielectric layer. As shown in  FIG. 5A , the area adjacent to the plurality of transmission-line (TL) conductors  510  alternates between cross ties  550  and a sequence of air gaps  552  along the direction of travel of signals carried by plurality of transmission-line (TL) conductors  510 . 
         [0033]    In the embodiment of  FIG. 5A , the sequence of air gaps  552  which are interspersed around plurality of transmission-line (TL) conductors  510  are (a) of relatively equal size and shape, and (b) disposed in regular intervals along the plurality of transmission-line (TL) conductors. However, this need not be the case for all implementations. For example, in certain implementations, air gaps  550  may have a variety of different shapes and sizes and/or may be disposed in irregular intervals. Indeed, the only limitation to the dimensions of air gaps  550  is that the cross ties  550  must provide sufficient structural support to the transmission-line (TL) conductors  510 , as the transmission-line (TL) conductors  510  traverse through the cross ties  550  without making contact with the substrate layer. While cross ties  550  may be formed at a variety of different angles relative to transmission-line (TL) conductors  510 , most implementations will position cross ties  550  perpendicular to transmission-line (TL) conductors  510 , as shown in  FIG. 5A . 
         [0034]    The use of cross ties  550  enables the transmission-line (TL) conductors  510  to support a greater amount of signal bandwidth, as the sequence of air gaps  550 , naturally resulting from use of cross ties  550 , reduces the dielectric material surrounding, enclosing, or adjacent to the transmission-line (TL) conductors  510 , which minimizes the ability of the dielectric material to act as an electrical shunt. Cross ties  550  also provide sufficient structural support to transmission-line (TL) conductors  510  to ensure that they are fixed in desired positions. 
         [0035]    In addition to the use of air spines and cross ties, certain embodiments of the invention also use substrate windowing to reduce the dielectric material enclosing, surrounding, or adjacent to the transmission-line (TL) conductors.  FIG. 5B  is a top view of an interconnect structure  580  having air spine  540 , dielectric cross ties  550 , and substrate windows  560  according to an embodiment of the invention. As shown by  FIG. 5B , substrate windowing refers to an approach where one or more air gaps (or substrate windows  560 ) are disposed in the substrate layer underneath a portion of plurality of transmission-line (TL) conductors  510 . Substrate windows  560  reduce the dielectric material surrounding, enclosing, or adjacent to transmission-line (TL) conductors  510 , which minimizes the ability of the dielectric material to act as an electrical shunt. 
         [0036]    Substrate windows  560  may have a variety of different shapes and sizes. For example, substrate windows  560  may be of relatively equal size and shape and be disposed in regular intervals within the substrate layer. Alternately, substrate windows  560  may correspond to a small number (or even just one) of air gaps disposed in the substrate layer that are disposed underneath the transmission-line (TL) conductors. For example, a small number (or even just one) substrate window may result in the absence of the majority of the substrate layer underneath the plurality of transmission-line (TL) conductors. 
         [0037]      FIG. 6  is a graph comparing the frequency response for different approaches according to embodiments of the invention.  FIG. 6  illustrates the frequency response and benefits of utilizing embodiments of the invention in suspension interconnects. As shown by  FIG. 6 , reducing or removing the dielectric material surrounding, enclosing, or adjacent to the transmission-line (TL) conductors increases the ability to the transmission-line (TL) conductors to carry higher frequency signals. As shown in  FIG. 6 , the best results are achieved by using an air spine with substrate windows. By using embodiments of the invention discussed herein, signal frequencies up to at least 30 gigahertz may be carried by transmission-line (TL) conductors. 
         [0038]    In the foregoing specification, embodiments of the invention have been described with reference to numerous specific details that may vary from implementation to implementation. Thus, the sole and exclusive indicator of what is the invention, and is intended by the applicants to be the invention, is the set of claims that issue from this application, in the specific form in which such claims issue, including any subsequent correction. Any definitions expressly set forth herein for terms contained in such claims shall govern the meaning of such terms as used in the claims. Hence, no limitation, element, property, feature, advantage or attribute that is not expressly recited in a claim should limit the scope of such claim in any way. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.