Abstract:
A head suspension having an active crosstalk attenuation conductor is formed on a load beam for conducting a crosstalk attenuation signal in order to reduce crosstalk interference between first and second conductors on the load beam. Preferably, the active crosstalk attenuation conductor is located in between the first and second conductors along a portion of the load beam and the crosstalk attenuation signal is a function of the first signal so that the electromagnetic field generated by the active crosstalk attenuation conductor reduces or cancels, at the second conductor, the electromagnetic field generated by the first conductor.

Description:
TECHNICAL FILED 
     The present invention relates generally to suspensions for supporting read/write heads over recording media. In particular, the present invention is an integrated lead head suspension having an active crosstalk attenuation conductor for reducing crosstalk interference between conductors formed on the integrated lead head suspension. 
     BACKGROUND OF THE INVENTION 
     Disk drives include disk drive suspensions for supporting read/write heads over information tracks of rotating disks. The well-known and widely used Watrous-type suspensions include a load beam having a mounting region on a proximal end, a flexure on a distal end, a relatively rigid region adjacent to the flexure and a spring region between the mounting region and the rigid region. An air-bearing slider that includes a read/write head is mounted to the flexure. The mounting region is typically attached to a base plate for mounting the load beam to an actuator arm. A motor which is controlled by a servo control system rotates the actuator arm to position the read/write head over desired information tracks on the disk. This type of suspension is used with both magnetic and non-magnetic disks. 
     Disk drive manufacturers continue to develop smaller yet higher storage capacity drives. Storage capacity increases are achieved in part by increasing the density of the information tracks on the disks (i.e., by using narrower and/or more closely spaced tracks). As track density increases, however, it becomes increasingly difficult for the motor and servo control system to quickly and accurately position the read/write head over the desired track. The use of head suspensions having microactuators or fine tracking motors has been proposed to overcome these problems. Such suspensions are disclosed in U.S. Pat. Nos. 5,657,188 and 5,898,544, which are assigned to Hutchinson Technology Incorporated, the assignee of the present application, and which are incorporated by reference herein. 
     However, the signals that are used to control the microactuators are relatively large (for example, having a peak voltage of about 30 V) compared to the sensitive signals (typically in the millivolt range) coming from the head slider. Since the microactuator control conductors (which conduct microactuator control signals between microactuator control circuitry and the microactuator) and the head slider conductors (which conduct the head slider signals) are typically routed near each other along at least a portion of the load beam, the larger microactuator control signals will tend to capacitively couple into the head slider signals. This crosstalk interference will tend to corrupt the sensitive head slider signals. 
     One known approach to reducing crosstalk interference between two signal-carrying conductors formed on a substrate that is used in a wide range of electrical applications is to form a conventional passive guard trace (sometimes referred to herein as a “passive crosstalk attenuation conductor”) in between the two signal-carrying conductors. The conventional passive crosstalk attenuation conductor is a conductor which is grounded, unterminated, or match terminated at its ends and runs between the two signal-carrying conductors. The conventional passive crosstalk attenuation conductor reduces the coupling between the two signal-carrying conductors, which reduces crosstalk interference therebetween. 
     Although conventional passive crosstalk attenuation conductors can reduce crosstalk interference to levels that are acceptable for some applications, conventional passive crosstalk attenuation conductors may not reduce crosstalk interference to acceptable level in other applications, such as when used on head suspensions having microactuator control conductors and head slider conductors. Thus, there is a continuing need for greater reductions in crosstalk interference between microactuator control conductors and head slider conductors. 
     SUMMARY OF THE INVENTION 
     The present invention can be embodied in any head suspension having first and second conductors conducting first and second signals, respectively. The head suspension according to the present invention includes an active crosstalk attenuation conductor formed on a load beam for conducting a crosstalk attenuation signal in order to reduce crosstalk interference between the first and second conductors. The crosstalk attenuation signal is a function of the first signal so that the electromagnetic field generated by the active crosstalk attenuation conductor reduces or cancels, at the second conductor, the electromagnetic field generated by the first conductor. 
     One embodiment of a head suspension according to the present invention includes a load beam having a distal end configured for receiving and supporting a head slider. A microactuator control conductor is located on the load beam for conducting a microactuator control signal between microactuator control circuitry and a microactuator mounted on the load beam. Also, a head slider conductor is located on the load beam for conducting a head slider signal between the head slider circuitry and the head slider. An active crosstalk attenuation conductor is positioned on the load beam for conducting a crosstalk attenuation signal to reduce crosstalk interference between the microactuator control conductor and the head slider conductor. Preferably the crosstalk attenuation conductor is located in between the microactuator control conductor and the head slider conductor along a portion of the load beam. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top view of a head suspension having an active crosstalk attenuation conductor according to the present invention. 
     FIG. 2 is a schematic diagram of the head suspension of FIG. 1 electrically connected to servo control system, a crosstalk attenuation signal source, and head slider signal processing circuitry. 
     FIG. 3 is a schematic diagram of a test coupon having no crosstalk attenuation features. 
     FIG. 4 is a schematic diagram of a test coupon having a conventional passive crosstalk attenuation conductor. 
     FIG. 5 is a schematic diagram of a test coupon having an active crosstalk attenuation conductor according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the embodiment of the present invention shown in FIGS. 1-2, an active crosstalk attenuation conductor is used to reduce crosstalk interference between microactuator control conductors and head slider conductors. As shown, a head suspension  10  includes a load beam  12  having an extended base or mounting region  14  on a proximal end, a flexure  16  on a distal end, a relatively rigid region  17  adjacent to the flexure, and a radius or spring region  18  between the mounting region  14  and rigid region  17 . Load beam  12  can be fabricated and formed from a sheet of stainless steel or other resilient material in a conventional manner. 
     A spring connection is provided between a head slider (not shown) and the distal end of load beam  12  by flexure  16 , which permits the head slider to move in pitch and roll directions so that it can compensate for fluctuations of a spinning disk surface above which the slider “flies.” Many different types of flexures, also known as gimbals, are known to provide the spring connection allowing for pitch and roll movement of the head slider and can be used with the present invention. 
     Head suspension  10  has a stationary section  15  and a moving section  19 . In the embodiment of FIGS. 1-2, moving section  19  includes flexure  16 , rigid region  17 , spring region  18 , and a moving portion  42  of mounting region  14 . Stationary section  15  includes a stationary portion  40  of mounting region  14 . Stationary portion  40  has a circular opening  44  to facilitate attachment of mounting region  14  to an actuator arm (not shown). Stationary portion  40  also has first longitudinally extending arm  46  and second longitudinally extending arm  48 . Moving portion  42  of mounting region  14  is suspended between arms  46  and  48  by support beams  50   a ,  50   b , and  50   c  to allow moving portion  42  to pivot with respect to stationary portion  40 . A generally U-shaped gap  52  extends between stationary portion  40  and moving portion  42 . 
     Head suspension  10  has two piezoelectric or electrostrictive elements  60  and  62  that serve as a microactuator mounted on load beam  12  to move flexure  16  and a read/write head  20  (shown schematically in FIG. 2) mounted thereto along either tracking axis  90  or  92 . A first element  60  extends across gap  52  between first longitudinally extending arm  46  and moving portion  42  of mounting region  14 . Element  60  is attached to arm  46  and moving portion  42  by adhesive or other known approaches. A microactuator control conductor  22  is attached to electrical contact  72  to connect, via branch  22   a , the upper surface (that is, the surface not facing the load beam  12 ) of the element  60  to a servo control system  74  (shown in FIG.  2 ). The bottom surface (that is, the surface facing the load beam  12 ) of element  60  is grounded by connecting the bottom surface of element  60  to the load beam  12 . A second element  62  extends across gap  52  between second longitudinally extending arm  48  and moving portion  42  of mounting region  14 . Element  62  is attached to arm  48  and moving portion  42  by adhesive or other known approaches. A branch  22   b  of the microactuator control conductor  22  is attached to the upper surface of element  62  to connect the upper surface of element  62  to the servo control system  74 . The bottom surface of element  62  is also grounded by connecting the bottom surface of element  62  to the load beam  12 . Element  62  is mounted to the load beam  12  so that the polarity of element  62  is reversed with respect to element  60 . For example, if, as shown in FIG. 1, element  60  is mounted to the load beam  12  so that the upper surface of element  60  is the positive pole of element  60 , element  62  is mounted to the load beam  12  so that the upper surface of element  62  is the negative pole of element  62 . 
     As shown in FIG. 1, elements  60  and  62  are generally rectangular in shape. Element  60  has a short side  60   a  and a long side  60   b  and element  62  has a short side  62   a  and a long side  62   b . Element  60  is configured to expand or contract along the long side  60   b  and element  62  is configured to contract or expand in a direction along the long side  62   b  in response to a voltage signal from the servo control system  74  that is applied to the upper surfaces of both elements  60  and  62  in order to develop a voltage across the upper surfaces of element  60  and  62  and ground. Because elements  60  and  62  are connected to the microactuator control conductor  22  and the load beam  12  (i.e., ground) with their polarities reversed with respect to one another, element  60 , which has a positive pole on its upper surface, will expand when the voltage supplied by the microactuator control conductor  22  is increased, while the element  62 , which has a negative pole on its upper surface, will contract. Likewise, element  60  will contract and element  62  will expand as the voltage supplied by the microactuator control conductor  22  is decreased. 
     Elements  60  and  62  can each be biased with a voltage so that when moving portion  19  is in an undeflected state, that is, flexure  16  is not moved along tracking axis  90  or  92 , elements  60  and  62  are in positions approximately halfway between their fully expanded stated and fully contracted states. To move flexure  16  along tracking axis  90 , the voltage signal supplied by the microactuator control conductor  22  is increased so that element  60  expands and element  62  contracts. As element  60  expands, moving portion  42  of mounting region  14  is pushed away from arm  46  and as element  62  contracts, moving portion  42  is pulled towards arm  48  causing the moving section  19  of head suspension  10  to pivot about a point in moving portion  42 . This motion causes flexure  16  and the read/write head  20  mounted thereto to move along tracking axis  90 . Likewise, reducing the voltage signal supplied by the microactuator control conductor  22  causes element  60  to contract and element  62  to expand, which moves moving portion  19  and flexure  16  along tracking axis  92 . 
     As noted above, elements  60  and  62  can be piezoelectric or electrostrictive. Piezoelectric elements can be fabricated from lead-zirconate-titanate and are commercially available from Newport Corporation of Irvine, Calif. Electrostrictive elements can be fabricated of lead-magnesium-niobate and are also commercially available from Newport Corporation of Irvine, Calif. 
     Conductive head slider conductors  80   a  and  80   b  are connected at distal end to the read/write head  20  (shown in FIG. 2) and at a proximal end to electrical contacts  82   a  and  82   b , respectively. Circuitry  78  (shown in FIG. 2) for amplifying and processing the head slider signals carried on the head slider conductors  80   a  and  80   b  is connected to the electrical contacts  82   a  and  82   b.    
     In the embodiment shown in FIGS. 1-2, the microactuator control conductor  22  is arranged parallel and adjacent to the head slider conductors  80   a  and  80   b  along a portion of the stationary portion  40 . An active crosstalk attenuation conductor  84  is arranged on the stationary portion  40  between the microactuator control conductor  22  and the head slider conductors  80   a  and  80   b . The active crosstalk attenuation conductor  84  has a proximal end connected to electrical contact  86  and a distal end that is unterminated (i.e., floating). A crosstalk attenuation signal source  88  (shown in FIG. 2) can be connected to the electrical contact  86  so that a crosstalk attenuation signal can be conducted on the active crosstalk attenuation conductor  84  in order to reduce the crosstalk interference between the microactuator control conductor  22  and the head slider conductors  80   a  and  80   b . The crosstalk attenuation signal source  88  is designed to provide a crosstalk attenuation signal that will reduce the crosstalk interference between the microactuator control conductor  22  and the head slider conductors  80   a  and  80   b . In the embodiment shown in FIGS. 1-2, the crosstalk attenuation signal source comprises an inverting amplifier that generates the crosstalk attenuation signal as a function of the microactuator control signal. 
     The active crosstalk attenuation conductor  84  is positioned on the load beam  12  in between the microactuator control conductor  22  and the head slider conductors  80   a  and  80   b . For such an arrangement of the microactuator control conductor  22 , the head slider conductors  80   a  and  80   b , and the active crosstalk attenuation conductor  84 , experiments have shown that inverting and reducing the amplitude of the microactuator control signal will produce a crosstalk attenuation signal that will reduce crosstalk interference between the microactuator control signals and head slider signals. Although the optimal amplitude of the crosstalk attenuation signal is heavily dependant on several factors including the particular geometry of the conductors that are used and the particular type of signals that are being conducted, an amplitude of about ⅕ the amplitude of the microactuator control signal has been found to be effective for the geometries and signals described below in the Examples. 
     Head suspension  10  can be fabricated as an integrated lead type head suspension by etching a laminate having a spring layer (formed from stainless steel, for example), an insulator layer (formed from a polyimide or a other dielectric, for example), and a conductor layer (formed from a copper alloy, for example). One suitable method for fabricating an integrated lead type head suspension that can be used to fabricate a head suspension  10  according to the present invention is disclosed in U.S. Pat. No. 5,839,193, which is assigned to Hutchinson Technology Incorporated, the assignee of the present application, and which is incorporated by reference herein. Alternatively, head suspension  10  can be fabricated using other conventional fabrication techniques, for example, depositing or otherwise forming insulator and conductor features on a load beam. 
     EXAMPLES 
     Test coupons comprising a laminate structure of a stainless steel ground plane, a polyimide dielectric layer formed on top of the stainless steel ground plane, and a plurality of parallel conductors formed on top of the polyimide layer were fabricated. Three different types of test coupons were fabricated. Test coupon  110 , shown in FIG. 3, models a conventional head suspension that does not have any kind of crosstalk attenuation features, test coupon  112 , shown in FIG. 4, models a conventional head suspension having a conventional passive crosstalk attenuation conductor, and test coupon  114 , shown in FIG. 5, models a head suspension having an active crosstalk attenuation conductor according to the present invention. 
     Each of the test coupons shown in FIGS. 3-5 have a first conductor  116  that models the microactuator control conductor  22  shown in FIGS. 1-2. Conductor  116  on each of the test coupons is connected to a voltage source  118  that generates a signal, which is representative of a microactuator control signal, in order to drive a piezoelectric capacitive load (Cpzt)  120  of 0.75 nanofarads, which models the piezoelectric microactuator shown in FIGS. 1-2. Each of the test coupons also has second and third conductors  122  and  124  that model the head slider conductors  80   a  and  80   b  shown in FIGS. 1-2. Conductors  122  and  124  are connected at their proximal ends to first and second resistive loads Rpr1  126  and Rpr2  128 , respectively. A third resistive load Rhead  130  electrically connects the second and third conductors  122  and  124  at their distal ends and models the head slider  20  shown in FIGS. 1-2. 
     Test coupon  110 , shown FIG. 3, was designed to include no additional features for reducing crosstalk interference; consequently, the first and second conductors  116  and  122  have no conductive elements formed therebetween. Test coupon  112  shown in FIG. 4 includes a fourth conductor  132  in between the first and second conductors  116  and  122 . The fourth conductor  132  has a proximal end that is grounded and a distal end that is unterminated so as to model a conventional passive crosstalk attenuation conductor. 
     Test coupon  114  shown in FIG. 5 includes an active crosstalk attenuation conductor  134  in between the first and second conductors  116  and  122  and models the active crosstalk attenuation conductor  84  shown in FIGS. 1-2. A crosstalk attenuation signal is applied to the active crosstalk attenuation conductor  134  by an inverting amplifier  136  that is connected to the first conductor  116 . The crosstalk attenuation signal is an inverted and reduced-amplitude version of the signal conducted on the first conductor  116 . 
     In the experiments described below, a 30 Vpk, 10 KHz signal was applied to the first conductor  116  of each of the test coupons  110 ,  112 , and  114  by the voltage source  118 . The crosstalk attenuation signal applied to the active crosstalk attenuation conductor  134  of test coupon  116  had about ⅕ the amplitude of the signal provided by the voltage source  118 . However, as noted above, the optimal amplitude of the crosstalk attenuation signal is heavily dependant on several factors including the particular geometry of the conductors that are used and the particular type of signals that are being conducted. 
     Example 1 
     A first set of test coupons  110 ,  112 , and  114  were fabricated with the conductors spaced 40 micrometers apart. Each test coupon was tested with Rhead  130 , Rpr1  126 , and Rpr2  128  open (the results of which are provided in TABLE 1 under the subheading “op-op”), with Rhead  130  set to 50 Ohms and Rpr1  126  and Rpr2  128  open (the results of which are provided in TABLE 1 under the subheading “50-op”), and with Rhead set to 50 Ohms and Rpr1  126  and Rpr2  128  set to 1 kiloohm (the results of which are provided in TABLE 1 under the subheading “50-1 k”). The signal levels on the second and third conductors  122  and  124  were measured and are shown in TABLE 1 in the columns labeled V2 and V3, respectively. Also, an oscilloscope was used to mathematically subtract the signals on the second and third conductors  122  and  124  to determine the voltage difference across the second and third conductors  122  and  124 , which is the voltage typically used by the head slider signal processing circuitry  78 . The amplitude of this mathematical waveform is shown in TABLE 1 in the column labeled Vdif. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 40 micrometer Spacing 
               
               
                 (all values are in mV peak) 
               
             
          
           
               
                   
                 V2 
                 V3 
                 V-dif 
               
               
                   
                   
               
             
          
           
               
                   
                 Op-op 
                   
                   
                   
               
               
                   
                 Test Coupon 110 
                 212 
                 20.7 
                 191 
               
               
                   
                 Test Coupon 112 
                 16.75 
                 9.5 
                 7.3 
               
               
                   
                 Test Coupon 114 
                 8 
                 8.75 
                 0.75 
               
               
                   
                 50-op 
               
               
                   
                 Test Coupon 110 
                 115.5 
                 115 
                 1.5 
               
               
                   
                 Test Coupon 112 
                 13.1 
                 13.05 
                 0.15 
               
               
                   
                 Test Coupon 114 
                 1.1 
                 1.1 
                 0.06 
               
               
                   
                 50-1k 
               
               
                   
                 Test Coupon 110 
                 0.75 
                 0.72 
                 0.07 
               
               
                   
                 Test Coupon 112 
                 0.17 
                 0.18 
                 0.05 
               
               
                   
                 Test Coupon 114 
                 0.13 
                 0.13 
                 0.05 
               
               
                   
                   
               
             
          
         
       
     
     Example 2 
     A second set of test coupons  110 ,  112 , and  114  were fabricated with the conductors spaced 70 micrometers apart. The test coupons were tested in the same way as with Example 1 and the results are shown in TABLE 2. 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 70 micrometer Spacing 
               
               
                 (all values are in mV peak) 
               
             
          
           
               
                   
                 V2 
                 V3 
                 V-dif 
               
               
                   
                   
               
             
          
           
               
                   
                 Op-op 
                   
                   
                   
               
               
                   
                 Test Coupon 110 
                 86 
                 16.3 
                 69.6 
               
               
                   
                 Test Coupon 112 
                 14.25 
                 7.95 
                 6.3 
               
               
                   
                 Test Coupon 114 
                 6.8 
                 6.95 
                 1.4 
               
               
                   
                 50-op 
               
               
                   
                 Test Coupon 110 
                 50.9 
                 50.5 
                 0.59 
               
               
                   
                 Test Coupon 112 
                 11.1 
                 11.05 
                 0.14 
               
               
                   
                 Test Coupon 114 
                 0.95 
                 0.95 
                 0.05 
               
               
                   
                 50-1k 
               
               
                   
                 Test Coupon 110 
                 0.37 
                 0.36 
                 0.05 
               
               
                   
                 Test Coupon 112 
                 0.17 
                 0.17 
                 0.05 
               
               
                   
                 Test Coupon 114 
                 0.13 
                 0.13 
                 0.05 
               
               
                   
                   
               
             
          
         
       
     
     Example 3 
     A third set of test coupons  110 ,  112 , and  114  were fabricated with the conductors spaced  100  micrometers apart. The test coupons were tested in the same way as with Example 1 and the results are shown in TABLE 
     
       
         
               
             
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 100 micrometer Spacing 
               
               
                 (all values are in mV peak) 
               
             
          
           
               
                   
                 V2 
                 V3 
                 V-dif 
               
               
                   
                   
               
             
          
           
               
                   
                 Op-op 
                   
                   
                   
               
               
                   
                 Test Coupon 110 
                 53.4 
                 14.4 
                 39.1 
               
               
                   
                 Test Coupon 112 
                 11.6 
                 6.85 
                 4.8 
               
               
                   
                 Test Coupon 114 
                 5.85 
                 5.75 
                 0.44 
               
               
                   
                 50-op 
               
               
                   
                 Test Coupon 110 
                 33.9 
                 33.7 
                 0.28 
               
               
                   
                 Test Coupon 112 
                 9.25 
                 9.2 
                 0.15 
               
               
                   
                 Test Coupon 114 
                 0.84 
                 0.82 
                 0.06 
               
               
                   
                 50-1k 
               
               
                   
                 Test Coupon 110 
                 0.26 
                 0.26 
                 0.05 
               
               
                   
                 Test Coupon 112 
                 0.14 
                 0.15 
                 0.05 
               
               
                   
                 Test Coupon 114 
                 0.13 
                 0.13 
                 0.05 
               
               
                   
                   
               
             
          
         
       
     
     The results from these three Examples show that excessive crosstalk interference levels are present when no crosstalk attenuation features are used. The results also show that although use of a conventional passive crosstalk attenuation conductor reduces crosstalk interference dramatically, use of an active crosstalk attenuation conductor according to the present invention reduces crosstalk interference by an order of magnitude more than the conventional passive crosstalk attenuation conductor. 
     Although the present invention has been described with reference to a preferred embodiment, those skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the invention. For example, although the present invention has been described as being used to reduce crosstalk interference between microactuator control conductors and head slider conductors, it is to be understood that the present invention may also be useful in reducing crosstalk interference between other conductors formed on a head suspension.