Abstract:
An apparatus and associated method generally relate to data writing and more specifically to writing data to a rotating media. An embodiment of such an apparatus comprises a slider body, a transducer and a write driver. The transducer comprises a writer. The write driver is integrated on the slider body, and directly connected to the writer.

Description:
RELATED APPLICATION 
     This application is a continuation of copending U.S. patent application Ser. No. 12/618,976 filed on Nov. 16, 2009. 
    
    
     SUMMARY 
     Various embodiments are directed to an apparatus comprising a slider body, a transducer and a write driver, and a method for forming the apparatus. The transducer is on the slider body, and comprises a writer. The write driver integrated on the slider body and directly connected to the writer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a magnetic head with an integrated write driver. 
         FIG. 2  is a side view of another magnetic head with an integrated write driver. 
         FIG. 3A  is a cross-sectional view of a transducer with a write driver mounted on the trailing edge. 
         FIG. 3B  is a cross-sectional view of a magnetic head with a write driver located on top of the writer elements. 
         FIG. 4A  is a cross-sectional view of a magnetic head with a write driver located below the writer elements. 
         FIG. 4B  is a cross-sectional view of another magnetic head with a write driver located below the writer elements. 
         FIG. 5A  is a circuit diagram for a write driver. 
         FIG. 5B  is an alternate circuit diagram for a write driver. 
         FIG. 5C  is another alternate circuit diagram for a write driver. 
         FIG. 6A  is series of plots of launch voltage versus time, comparing a direct write driver interconnect to an indirect transmission line connection. 
         FIG. 6B  is a series of plots of write current versus time, comparing direct and indirect write driver connections. 
         FIG. 6C  is a series of plots of write power versus time, comparing direct and indirect write drive connections. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a side view of an example embodiment of a magnetic read/write head  10  with slider body  12 , magnetic transducer  14  and integrated write driver  16 . In this particular embodiment, write driver  16  is formed on driver substrate  18 , and mounted onto external (top) surface  20  of slider body  12 . 
     Slider body  12  is supported by an actuator system with flexure  22  and slider mount  24 , such that magnetic head  10  “flies” along windage produced by the motion of magnetic medium  26 . Medium  26  translates in tracking direction S with respect to magnetic head  10 , from leading edge  28  toward trailing edge  30 . 
     In various disc drive designs, media-facing (bottom) surface  32  provides an air-bearing surface (ABS) to support magnetic head  10 , with top surface  20  positioned opposite media-facing surface  32 . In other embodiments, media-facing surface  32  supports head  10  on a different fluid such as an inert gas or a lubricant, or, alternatively, media-facing surface  32  forms a contact surface between head  10  and data storage medium  26 . 
     Slider body  12  is formed in some embodiments of a two-phase material comprising a continuous host phase such as a dielectric and a discontinuous included phase, which is selected for desired hardness properties. In one particular embodiment, for example, slider body  12  is formed of a polycrystalline AlTiC material in which the host phase is aluminum oxide (Al 2 O 3 , or alumina) and the included phase is titanium carbide (TiC). 
     Transducer  14  comprises reader and writer elements for performing data storage operations on magnetic medium  26 . The transducer is formed, in various non-limiting embodiments, by thin film deposition onto slider body  12 , as described in more detail below. 
     Depending on embodiment, write driver  16  in some embodiments comprises a current source to generate write current for transducer  14 . In some embodiments, external electrode pads  34  connect write driver  16  to a write data buffer or other external data source, in some embodiments via a transmission line connection formed along flexure  22 . Additional pads  34  may form an impedance-matching connection between write driver  16  and transducer  14 , for example using flexible circuit element  38 . 
     The current source and other elements of write driver  16  are formed by thin film deposition onto substrate  18 , which is mountable to slider body  12  using wafer-to-wafer bonding or “pick and place” techniques. In the embodiment of  FIG. 1 , for example, substrate  18  is mounted to top surface  20  of slider body  12  using an adhesive layer or bond pads  36 . Alternatively, write driver  16  is located on leading edge  28 , trailing edge  30  or another external (e.g., side) surface of slider body  12 . 
     To accommodate pick-and-place and wafer-to-wafer bonding techniques, substrate  18  in some embodiments has a thickness of about 10 microns or more, for example a thickness of about 20 microns. Alternatively, the thickness of substrate  18  is reduced by ultrathin wafer processing or wafer thinning techniques, and the placement and bonding methods are adapted for a substrate thickness of less than 10 microns, for example about 2-5 microns. 
     The integration of write driver  16  directly onto magnetic head  10  provides for improved impedance matching between the current source and the write coil, reducing reflections and jitter while improving signal rise time and reducing overshoot. The pick-and place mounting technique also allows the write driver electronics to be independently designed and manufactured, with write driver  16  integrated onto magnetic head  10  at any point before, during or after the head build process used for transducer  14 . 
     In the externally-mounted embodiment of  FIG. 1 , for example, write driver  16  is in some embodiments mounted after the head build process, and after the wafer is cut into individual slider bodies  12 . This increases the available area for microcircuit components on substrate  18  and improves heat dissipation away from slider body  12 , while providing additional design flexibility when particular components of write driver  16  are incompatible with one or more of the manufacturing steps used to form transducer  14 . Alternatively, write driver  16  is located on trailing edge  30 , and substrate  18  is mounted to slider body  12  at any point before, during or after the head build process as described below. 
     Depending on embodiment, write driver  16  provides microcircuit elements for generating the write current and for forming an impedance-matching connection to the write coil, but data buffering and read signal processing are not necessarily required. This contrasts with fully integrated write driver/preamplifier designs, which perform data buffering and read signal processing, and substantially limits the size footprint and mass envelope of write driver  16  on slider body  12 . 
     In the externally-mounted embodiment of  FIG. 1 , for example, write driver  16  and substrate  18  have overall dimensions of about 1,000 microns (about 1 mm) or less in length and about 400 microns or less in width; that is, no greater than the corresponding dimensions of slider body  12 . In addition, the combined mass of write driver  16  and substrate  18  is less than that of slider body  12 , so the flying and suspension properties of magnetic head  10  are not substantially altered. Typically, this allows precision control of pitch angle and media/head spacing to be maintained without material modifications to flexure  22  and the other components of the actuator and suspension assembly. 
       FIG. 2  is a side view of the magnetic head  10  of  FIG. 1 , with write driver  16  mounted on trailing edge  30 , along with transducer  14 . In this embodiment, write driver  16  is integrated onto magnetic head  10  on a wafer level, before slicing and dicing operations to produce individual slider bodies  12 . In some embodiments, impedance-matching connections to the write coil are provided by internal traces or conducting vias, as formed inside the body of transducer  14 . Alternatively, impedance-matching connections are formed by external pads  34 , or by a combination of internal traces and external pads. 
     In the trailing-edge mounted embodiment of  FIG. 2 , the dimensions of write driver  16  and substrate  18  are in some embodiments limited to about 400 microns or less in width and about 100 micros or less in height, corresponding to the lateral dimensions of trailing edge  30 . This somewhat reduces flexibility in lateral spacing of the write driver elements on substrate  18 , but allows write driver  16  to be mounted to slider body  12  at any point during the head build process, reducing manufacturing time and providing for a range of different arrangements with respect to the other elements of transducer  14 . 
       FIG. 3A  is a cross-sectional view of another embodiment of the magnetic head  10  of  FIG. 1 , with write driver  16  mounted directly to trailing edge  30 , above top dielectric layer(s)  46  of transducer  14 . In this embodiment, write driver  16  is mounted after the head build process is complete, and is exposed to provide increased heat dissipation at trailing edge  30 , with reduced heat dissipation through the body of transducer  14 . 
     Transducer  14  comprises reader portion (reader)  40  and writer portion (writer)  42 . These elements are formed by thin film deposition on the trailing surface of slider body  12 , such that transducer  14  extends to approximately trailing edge  30  of magnetic head  10 . 
     Write driver  16  is formed on substrate  18 , which is mounted to transducer  14  via pick and place or wafer bonding techniques using bond pads or adhesive layer  44 . As shown in  FIG. 3A , for example, adhesive layer or bond pads  44  comprise an organic or hybrid bonding compound such as benzocyclobutene (BCB), an SU8 epoxy resin, or a silver epoxy material, which bonds substrate  18  to a layer of nonmagnetic insulator or dielectric  46 , with write driver  16  located above reader  40  and writer  42  (that is, opposite slider body  12 ). 
     Depending on embodiment, reader  40  comprises read sensor  48  with read shields  50  and  52 . Read sensor  48  in some embodiments comprises a magnetoresistive (MR) spin valve or other MR sensing element configured for perpendicular or longitudinal read operations. In general, the data are decoded as a function of a sense current across MR element  48 , in which the resistance (and thus the voltage) depend upon magnetization orientations in the bit pattern, taking advantage of one or more MR effects including anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR), tunneling magnetoresistance (TMR) and colossal magnetoresistance (CMR). 
     First (bottom) read shield  50  and second (top) read shield  52  are oriented transversely to media-facing surface  32 , and are formed of a soft magnetic shield material such as a nickel-iron (NiFe) or nickel-cobalt-iron (NiCoFe) alloy in order to improve reader sensitivity by absorbing stray magnetic flux. Read sensor  48  is in some embodiments formed as a multilayer MR stack that extends perpendicularly from media-facing surface  32  between read shields  50  and  52 . Dielectric material  46  (or another nonmagnetic insulator) extends from the distal end of MR sensor  48  (that is, opposite media-facing surface  32 ), in the read gap between read shields  50  and  52 . 
     In current-perpendicular-to-plane (CPP) embodiments, MR sensor  48  typically spans the read gap between read shields  50  and  52 , which also function as electrical contacts for the sense current. In this embodiment, the current propagates in a substantially perpendicular sense through the layers of the MR stack. In current-in-plane (CIP) configurations, additional side contacts (not shown) are used to conduct the sense current in a substantially parallel sense through the stack layers, and MR sensor  48  is spaced from read shields  50  and  52  by additional layers of dielectric  46 . Other reader designs are also configurable for use with the integrated write driver designs described herein. 
     Depending on embodiment, writer  42  comprises first (leading) return pole  54 , second (trailing) return pole  56  and main (write) pole  58 , with pole tip  60  formed on the proximal end of write pole  58  and oriented toward media-facing surface  32 . Write pole  58  is formed of a magnetically soft, high magnetic moment material such as a cobalt-iron (CoFe) alloy, in order to direct magnetic flux through pole tip  60  and across media-facing surface  32 . 
     One or more sets of coils  62  are inductively coupled to write pole  58 . Coils  62  are in some embodiments formed of a low resistivity material such as copper (Cu), and positioned about write pole  58  and yoke  64  (or back vias  66 ) in order to generate time-varying magnetic flux when energized by a switching write current or write pulse, as provided by write driver  16 . 
     Yoke  64  and write pole  58  extend from media-facing surface  32  to distal ends proximate back vias  66 . Yoke  64  and back vias  66  are formed of a magnetically soft material such as NiFe or NiCoFe, in order to improve flux delivery to write pole  58  and pole tip  60 . In some embodiments, writer  42  also includes one or more top, bottom or side shields to improve sensitivity or provide additional field shaping. Other writer designs are also configurable for use with the integrated write driver designs described herein. 
     Dielectric material  46  surrounds write pole  58 , insulating coils  62  and spacing write pole tip  60  from return poles  54  and  56 . Protective layer  68  covers pole tip  60  and other elements of reader  40  and writer  42  at media-facing surface  32 , in some embodiments providing a diamond-like coating (DLC) or encapsulant, or both, to protect sensitive structures and reduce hard particle contamination. 
     Reader  40  and writer  42  are formed as a number of closely spaced layers, in some embodiments by thin film deposition onto slider body  12 . In the stacked configuration of  FIG. 3A , for example, writer  42  is stacked on top of reader  40 , with first (bottom) return pole  54  spaced from second (top) read shield  52  by a layer of dielectric insulator  46 . Alternatively, top read shield  52  is merged with first return pole  54   m  or, in side-by-side designs, reader  40  and writer  42  are laterally spaced from one another along media-facing surface  32 , and have a substantially coplanar configuration. 
     In operation magnetic head  10 , writer  42  writes data in response to a current generated by write driver  16 . Write driver  16  drives the write current through coils  62 , which generate magnetic flux in yoke  64  and write pole  58 . Flux loops exit write pole  58  at pole tip  60 , crossing media-facing surface  32  to enter the recording medium and close back through one or both of return poles  54  and  56 , and through one or both of magnetic vias  66 . Magnetic domain orientations in the recording medium are determined by the polarity of the write current generated by write driver  16 , allowing writer  42  to record a bit pattern as a function of the switching write current. 
       FIG. 3B  is a cross-sectional view of an embodiments of the magnetic head  10  of  FIG. 1  with write driver  16  located within the body of transducer  14 . In this particular embodiment, write driver  16  is spaced from trailing edge  30  by a layer of nonmagnetic insulator/dielectric  46 . 
     As shown in  FIG. 3B , substrate  18  is mounted after the head build process is substantially complete, but before the deposition of the top layer(s) of dielectric  46  at trailing edge  30 . This allows for fully internal impedance-matching connections between write driver  16  and coil  62  of writer  42 . In addition, dielectric  46  provides protective layers of thickness d 1  and d 2 , respectively, between write driver  16  and one or both of trailing edge  30  and media-facing surface  32 . 
     The particular location of write driver  16  with respect to reader  40  and writer  42  depends on head design and processing considerations, thermal dissipation requirements, and the location of power, signal and grounding connections to coils  62 . In addition, depending upon location of the respective elements, the impedance-matching connection between write driver  16  and writer  42  utilizes various internal conducting traces, vias, external bonding pads and combinations thereof, as described above with respect to  FIGS. 1 and 2 , and as further illustrated below with respect to  FIGS. 5A ,  5 B and  5 C. 
       FIG. 4A  is a cross-sectional view of the example magnetic head  10 , with write driver  16  located below reader  40  and writer  42 , between slider body  12  and first (bottom) read shield  50 . In this embodiment, write driver substrate  18  is mounted relatively early in the head build process, but after deposition of dielectric layer  46 , which spaces write driver  16  and substrate  18  from the trailing surface of slider body  12 . The impedance-matching connection is in some embodiments formed internally to the body of transducer  14 , and relatively more heat is dissipated through slider body  12  than in the top-mounted configurations of  FIGS. 3A and 3B , above. 
       FIG. 4B  is an alternate side view of magnetic head  10 , with write driver  16  mounted directly to slider body  12 , for example using bond pads or adhesive layer  44 . In this embodiment, heat dissipation through slider body  12  is increased, with relatively less heat transfer through the body of transducer  14 . Comparison of  FIG. 4B  to  FIG. 4A  also illustrates that in some embodiments media-facing surface  32  is provided with protective layer  68 , while in other embodiments media-facing surface  32  is formed without a protective layer. 
     In both the external-surface mounted configuration of  FIG. 1  and  FIG. 3A , and in the transducer-mounted embodiments of  FIGS. 2 ,  3 B,  4 A and  4 B, the integration of write driver  16  onto magnetic head  10  provides a shorter, more direct connection to writer  42 , with better impedance matching and reduced timing jitter. This reduces power requirements while producing a more uniform bit pattern, enabling faster, more reliable readback with improved SNR and lower BER. 
       FIG. 5A  is a circuit diagram for write driver  16 , illustrating an impedance-matching connection to writer  42 . Write drive  16  is formed on substrate  18 , which is located on magnetic head  10 . 
     In this embodiment, write driver  16  comprises current source  70  with a direct (on-slider) impedance-matching connection to coil  62  and an external (off-slider) connection to write data buffer (prebuffer)  72 , for example utilizing a transmission line connection along flex circuit  74 . Microelectronic current source  70  comprises thin-film transistor (three-terminal) or diode (two-terminal) components, or both, with differential (bi-polar) current outputs I+ and I−. In the particular embodiment of  FIG. 5A , current source  70  has differential digital inputs D 1  and D 2 , and is powered by differential (two-ended) supply lines V+ and V−. 
     Prebuffer  72  is located off magnetic head  10 , for example mounted on the suspension/actuator assembly, or integrated onto flex circuit  74 . Prebuffer  72  comprises a data buffer for buffering write data inputs S 1  and S 2 , and a signal generator for transmitting write signals D 1  and D 2  to write driver  16 , based on the buffered data. 
     Writer  42  is located on the trailing edge of slider body  12 , and is represented here by an equivalence circuit with inductance L and series resistances R 1  and R 2 , parallel (leakage) resistance R 3  and capacitance C W . These parameters model not only coil  62  but also reflect the complex (phase-dependant) impedance of writer  42 , including the particular physical configuration of coil  62  with respect to the main pole, yoke, shields and other write head components. 
     Flex circuit  74  provides power, ground and data connections between prebuffer  72  and current source  70 . Digital write signals D 1  and D 2  are connected to current source  70  via data pads P. Impedance-matching resistors R are sometimes provided to reduce reflections at current source  70  and prebuffer  72 , for example reflections from transistor-transistor logic (TTL) devices and other high-impedance elements. 
     Power supply lines V+ and V− are connected across slider ground G S  using bypass capacitors C, which prevent voltage drop during high-speed write cycles. This enables a faster rise time for write current outputs I+ and I−, as compared to a relatively slower (essentially DC) response of power lines V+ and V− across flex circuit  74 . Ground connection GND is in some embodiments provided between flex circuit ground G F  and slider ground G S , sometimes with ground resistance R G  to reduce cross-talk or the tendency to form ground loops. 
     Impedance-matching element(s)  76  are sometimes connected between current outputs I+ and I− of current source  70  and coil  62  of writer  42 , with complex impedance Z* to improve response time and increase voltage transfer while reducing reflections and power dissipation. In general, impedance-matching elements  76  include resistive, inductive or capacitive (RLC) components, or a combination thereof, for matching the complex impedance of writer  42  according to the desired transmission characteristics between current source  70  and coil  62 . These RLC components are coupled in series or parallel (or both) with respect to current outputs I+ and I− (compare, e.g.,  FIGS. 5B and 5C ), and positioned according to desired connection properties and the available real estate on write driver substrate  18  and slider body  12 . 
     In general, resistive loads associated with writer  42  are addressed via broadband matching to reduce reflections, and reactive loads are addressed by complex conjugate matching to increase power transfer. Both techniques are relevant to writer response, because power delivery is a critical factor in writer performance and because sharp write transitions implicate a broad Fourier spectrum, so impedance matching must address a broadband frequency range. Resistive impedance bridging techniques are also utilized, for example when voltage transfer is a limiting factor in overall writer performance. 
     In contrast to off-slider (non-integrated) write driver designs, the signal transmission length between current source  70  and coil  62  is relatively short, for example about 1,000 microns (1 mm) or less, as compared to off-slider transmission lines (e.g., flex circuit  74 ) that extend for lengths of a few mm or more, or 1 cm or more. This limits both the resistive and reactive impedance of the write loop, allowing impedance matching to be achieved within the relatively small available area on write driver substrate  18  and slider body  12 . 
     Shorter transmission paths also limit dispersion in the write current signal, reducing jitter and improving response time by maintaining sharper, more uniform write pulses with reduced power dissipation. In addition, better impedance matching between write driver  16  and writer  42  also reduces overshoot (that is, when the leading edge of the write signal spikes above the write plateau), further reducing jitter and unnecessary power dissipation without increasing response time. 
       FIG. 5B  is an alternate circuit diagram for write driver  16 , in an embodiment having single-ended power source V C , buffered with bypass capacitor C across slider ground G S . In this configuration, current source  70  is connected directly across line V C  and slider ground G S , with impedance-matching elements  76  provided between write driver  16  and writer  42 . 
       FIG. 5C  is another alternate circuit diagram for write driver  16 , in an embodiment having single-sided data input D 1 . In this embodiment, write data input S 1  is either single-sided (as shown) or double-sided (differential), and the data transmission line is connected across flex circuit ground G F  at prebuffer  72  and slider ground G S  at current source  70 . In addition complex impedance matching elements  76  are used to increase power or voltage transfer from prebuffer  72  to write driver  16  and current source  70 . 
       FIG. 5C  also illustrates the use of control line CTRL for additional write driver functionality. Typical control applications include a scaling signal for scaling current outputs I+ and I−, or for “zeroing” (turning off) current source  70  during non-write operations such as data reads, disc idling and load/unload or shutdown events. Additional control functions including a shaping signal for current outputs I+ and I−, for example to improve rise time or control overshoot, or to adapt the write current signal to the particular impedance properties of writer  42  and impedance-matching elements  76 . 
     The response and rise times of current outputs I+ and I− (and thus the attainable SNR, BER and data rate) also depend upon the semiconductor properties of current source  70  and the other components of write driver  16 . These properties include band gap, breakdown potential, electron/hole mobility and electron/hole saturation velocity of the relevant semiconductor materials, for which representative values are given in Table 1. 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Semiconductor Properties (Representative Values) 
               
             
          
           
               
                   
                   
                 Breakdown 
                 Mobility (min)  
                 Saturation Velocity 
               
               
                   
                 Band 
                 Potential 
                 (10 3  cm 2 / 
                 (min)  
               
               
                   
                 Gap 
                 (min) 
                 V · s) 
                 (10 7  cm/s) 
               
             
          
           
               
                 Material 
                 (eV) 
                 (10 5  V/cm) 
                 e 
                 hole 
                 e 
                 hole 
               
               
                   
               
             
          
           
               
                 Si 
                 1.12 
                 3 
                 1.5 
                 0.6 
                 1 
                 0.7 
               
               
                 GaAs 
                 1.42 
                 4 
                 8 
                 0.4 
                 0.8 
                 0.9 
               
               
                 InP 
                 1.35 
                 5 
                 5 
                 0.2 
                 0.7 
                 0.5 
               
               
                 In 0.5 Ga 0.5 As 
                 0.75 
                 0.4-1.0 
                 12 
                 0.3 
                 0.7 
                 0.5 
               
               
                 GaN 
                 3.40 
                 30 
                 1.2 
                 0.05 
                 1.5 
                 0.5 
               
               
                 InS 
                 0.36 
                 0.4 
                 25 
                 0.5 
                 0.9 
                 0.5 
               
               
                   
               
             
          
         
       
     
     The pick-and place mounting techniques described herein provide substantial flexibility in the selection of these semiconductor materials, independently of those used for the head build process of writer  42  and the other component of read/write head  10 . In some embodiments, for example, slider body  12  comprises a polycrystalline AlTiC substrate, as described above, while write driver substrate  18  comprises a single-crystalline silicon-based (Si) or silicon-on-insulator (SOI) material. This allows write driver  16  to utilize silicon-based microelectronic components, some of which are not easy to form on a polycrystalline or non Si-based slider body material. 
     Alternatively, write driver  16  and substrate  18  comprise a different combination of compatible gallium (Ga) or indium (In) based substrate and semiconductor materials, including, but not limited to, gallium arsenide (GaAs), indium phosphide (InP), indium-gallium arsenide (e.g., In 0.5 Ga 0.5 As), gallium nitride (GaN), and indium sulfide (InS). In these embodiments, the relevant semiconductor properties vary accordingly, as illustrated by Table 1. In further embodiments, substrate  18  is formed as a multi-component structure having two or more different substrate materials, for example to accommodate both silicon-based and non-silicon (e.g., Ga or In) based semiconductor components. 
       FIGS. 6A-6B  are plots of launch voltage, write current and write power versus time, respectively, illustrating the effect of a direct (on-slider) impedance-matching connection between the write driver and the write coil, as compared to an indirect (off-slider) transmission line connection. Launch voltage V 0 , write current I and power dissipation PWR are shown on the vertical axes with time (t) on the horizontal, and with all axes scaled in arbitrary units. 
     Representative plots for the direct impedance-matching connection (solid lines  81 ) and the indirect transmission line connection (dashed lines  82 ) were obtained by a combination of bench testing and computer modeling. For an integrated write driver located directly on the read/write head, as described above, the connection length between the current source and the write coil is in some embodiments about 1,000 microns (1 mm) or less, or about 400 microns or less in trailing edge-mounted configurations. For the indirect transmission-line (off-slider) comparison, the connection length is in some embodiments a few mm or more, or 1 cm or more. 
     As shown in  FIG. 6A , launch voltage V 0  (as measured at the current source) is less for the direct impedance-matching connection (solid lines  81 ) than for the indirect transmission line (dashed lines  82 ). This reduces overshoot, and provides for better voltage matching and power deliver to the write coil. 
     As shown in  FIG. 6B , the reduction in launch voltage V 0  does not substantially affect the amplitude of write current I (the difference between differential outputs I+ and I− at write coil  62 ; see  FIGS. 5A-5C ). In particular, the maximum write current is substantially similar for the direct impedance-matching connection (solid lines  81 ) and the indirect or transmission line connection (dashed lines  82 ), producing the same degree of write pole magnetization with lower launch voltage V 0 . 
     In addition, shorter transmission length and better impedance matching result in reduced or limited dispersion in the write pulse, improving rise time and decreasing jitter. Sharper, more uniform write pulses, in turn, improve both the SNR and BER. 
     As shown in  FIG. 6C , power dissipation PWR is substantially lower for the direct impedance-matched connection. Reduced power consumption not only increase battery life and enhances “green drive” design flexibility, but also lowers heat dissipation in write driver  16  and writer  42 . This allows for smaller, more compact head designs, with reduced thermal effects on fly height and pitch angle. 
     Generally, power dissipation PWR is approximately the product of launch voltage V 0  and write current I, but the particular result depends on signal phase and other impedance-matching effects. In one particular embodiment, for example, write current I is about 120 mA and launch voltage V 0  (that is, the write voltage) is about 710 mV, with power dissipation PWR of about 85 mW or less. In other embodiments, write current I is about 100 mA or more and launch voltage V 0  is about 750 mV or less, with power dissipation PWR maintained at about 100 mW or less, or about 85 mW or less, depending on the voltage, power and current transmission characteristics of the impedance-matching connection to the write coil. 
     While this disclosure has been described with reference to particular embodiments, the terminology used is for the purposes of description, not limitation. Workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the discussed technology, including the substitution of various equivalents for particular elements and adaptation of the teachings to different materials, situations and circumstances. Thus the present disclosure is not limited to the particular embodiments disclosed herein, but encompasses all embodiments falling within the scope of the appended claims.