Patent Abstract:
A system and method for preventing operational and manufacturing imperfections in piezoelectric micro-actuators by physically and electrically isolating conductive layers of the piezoelectric material.

Full Description:
BACKGROUND INFORMATION  
         [0001]    The present invention relates to magnetic hard disk drives. More specifically, the present invention relates to a system and method for preventing piezoelectric micro-actuator manufacturing and operational imperfections.  
           [0002]    In the art today, different methods are utilized to improve recording density of hard disk drives. FIG. 1 provides an illustration of a typical drive arm configured to read from and write to a magnetic hard disk. Typically, voice-coil motors (VCM)  102  are used for controlling a hard drive&#39;s arm  104  motion across a magnetic hard disk  106 . Because of the inherent tolerance (dynamic play) that exists in the placement of a recording head  108  by a VCM  102  alone, micro-actuators  110  are now being utilized to ‘fine-tune’ head  108  placement, as is described in U.S. Pat. No. 6,198,606. A VCM  102  is utilized for course adjustment and the micro-actuator then corrects the placement on a much smaller scale to compensate for the VCM&#39;s  102  (with the arm  104 ) tolerance. This enables a smaller recordable track width, increasing the ‘tracks per inch’ (TPI) value of the hard drive (increased drive density).  
           [0003]    [0003]FIG. 2 provides an illustration of a micro-actuator as used in the art. Typically, a slider  202  (containing a read/write magnetic head; not shown) is utilized for maintaining a prescribed flying height above the disk surface  106  (See FIG. 1). Micro-actuators may have flexible beams  204  connecting a support device  206  to a slider containment unit  208  enabling slider  202  motion independent of the drive arm  104  (See FIG. 1). An electromagnetic assembly or an electromagnetic/ferromagnetic assembly (not shown) may be utilized to provide minute adjustments in orientation/location of the slider/head  202  with respect to the arm  104  (See FIG. 1).  
           [0004]    Utilizing actuation means such as piezoelectrics (see FIG. 3), problems such as electrical sparking and particulate-enabled shortage can exist. It is therefore desirable to have a system for component treatment that prevents the above-mentioned problems in addition to having other benefits. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    [0005]FIG. 1 provides an illustration of a drive arm configured to read from and write to a magnetic hard disk as used in the art.  
         [0006]    [0006]FIG. 2 provides an illustration of a micro-actuator as used in the art.  
         [0007]    [0007]FIG. 3 provides an illustration of a ‘U’-shaped micro-actuator utilizing multi-layered piezoelectric transducers (PZT) to provide slider actuation.  
         [0008]    [0008]FIG. 4 illustrates a potential problem of particulate-enabled shorting between piezoelectric layers.  
         [0009]    [0009]FIG. 5 illustrates various problems affecting PZT performance.  
         [0010]    [0010]FIG. 6 provides a cross-section of the micro-actuator arms with the micro-actuators unseparated and a cross-section of a micro-actuator arm after micro-actuator separation.  
         [0011]    [0011]FIG. 7 provides a cross-section of the micro-actuator arms with the micro-actuators unseparated and a cross-section of a micro-actuator arm after micro-actuator separation under principles of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0012]    [0012]FIG. 3 provides an illustration of a ‘U’-shaped micro-actuator utilizing multi-layered piezoelectric transducers (PZT) to provide slider actuation. A slider (not shown) is attached between two arms  302 , 304  of the micro-actuator  301  at two connection points  306 , 308 . Layers  310  of PZT material, such as a piezoelectric ceramic material like lead zirconate titanate, are bonded to the outside of each arm (actuator finger)  302 , 304 . PZT material has an anisotropic structure whereby the charge separation between the positive and negative ions provides for electric dipole behavior. When a potential is applied across a poled piezoelectric material, Weiss domains increase their alignment proportional to the voltage, resulting in structural deformation (i.e. regional expansion/contraction) of the PZT material. As the PZT structures  310  bend (in unison), the arms  302 , 304  (which are bonded to the PZT structures  310 ), bend also, causing the slider (not shown) to adjust its position in relation to the micro-actuator  301  (for magnetic head fine adjustments).  
         [0013]    [0013]FIG. 4 demonstrates a potential problem of particulate-enabled shorting between piezoelectric layers. During manufacture and/or drive operation, particles may be deposited, and particle(s)  404  may end up bridging conductive layers  406 . Relative humidity can cause the particle(s) to absorb moisture from the air, enabling electrical conduction between PZT layers. This short  404  in the piezoelectric structure  406  can prevent its normal operation, adversely affecting micro-actuator  402  performance.  
         [0014]    [0014]FIG. 5 illustrates various problems affecting PZT performance. FIG. 5 a  provides an image of a stray particle  504  bridging (and potentially shorting) piezoelectric layers  502 . As stated above, humidity can cause the particle  504  to absorb moisture and become electrically conductive. FIG. 5 b  provides an image of damage caused by electrical arcing  506  between piezoelectric layers  508 . Under the right conditions of voltage and air humidity, electricity may arc between piezoelectric layers  508 , causing damage and deformation  506 . FIG. 5 c  provides an image of ‘smearing’  510  (and potentially shorting) between layers  512 . Smearing can occur during manufacture when the micro-actuators are cut for separation. (See FIGS. 6 and 7). Material of the different layers  512  is smeared across one another as the cutting tool passes over the surface exposed by cutting.  
         [0015]    [0015]FIG. 6 provides a cross-section of the micro-actuator arms with the micro-actuators unseparated and a cross-section of a micro-actuator arm after micro-actuator separation. FIG. 6 a  illustrates a cross-section  604  of a portion  602  of a micro-actuator block structure. The cross-section  604  illustrates alternating layers  628  of conductive material  622  and PZT (insulating) material  624  applied to-the micro-actuator. FIG. 6 b  illustrates a cross-section  608  of a micro-actuator arm  606  after separating the micro-actuator  610  from others. Separation may be performed in one embodiment by mechanical means (e.g., a rotating wheel blade or a straight edge knife). Other embodiments involve electrical means for micro-actuator separation (e.g., electric sputtering or ion milling). Further, chemical means may be used (e.g., chemical vapor deposition (CVD)). Note that the sides of the micro-actuator arm (finger)  606  expose the piezoelectric layers, including the electrically-conductive layers  622 .  
         [0016]    [0016]FIG. 7 provides a cross-section of the micro-actuator arms with the micro-acuators unseparated and a cross-section of a micro-actuator arm after micro-actuator separation and ending with conductive layer application under principles of the present invention. FIG. 7 a  illustrates a cross-section  704  of a portion  702  of a micro-actuator block structure. FIG. 7 b  illustrates a cross-section  708  of a micro-actuator arm  706  after separating the micro-actuator  710  from others. In one embodiment of the present invention, after a set of conductive strips (conductive material)  712 , such as gold, platinum or copper, are placed upon the micro-actuator arm  706 , a PZT layer (insulative layer)  714  is applied over and between the conductive strips  712 , physically and electrically isolating the conductive strips  712 . Another set of conductive strips  712  and a PZT layer  714  are applied and the process is repeated until the number of layers and/or thickness is appropriate for the micro-actuator&#39;s application and performance. In one embodiment, the last layer applied is the conductive strip  712 , followed by the placement of a bonding pad  716  upon the piezoelectric layers (and on opposite ends  717  of the micro-actuator finger  706 , see also FIG. 9). In one embodiment, four to six layers PZT layers are utilized (five to seven conductive layers).  
         [0017]    In one embodiment, upon separation of the micro-actuators  710 , the PZT layers  714  physically isolate the conductive strips  712  from each other, and thus, prevent ‘smearing’ (and potential shorting). Further, the PZT layers  714  electrically insulate the sides of the piezoelectric layers, preventing ‘arcing’ damage and particulate contamination (electrical bridging/shorting).  
         [0018]    [0018]FIG. 8 provides a cross-section of the micro-actuator arms with the micro-actuators unseparated and a cross-section of a micro-actuator arm after micro-actuator separation and ending with PZT layer application under principles of the present invention. FIG. 8 a  illustrates a cross-section  804  of a portion  802  of a micro-actuator block structure. FIG. 8 b  illustrates a cross-section  808  of a micro-actuator arm  806  after separating the micro-actuator  810  from others. In one embodiment of the present invention, after a set of conductive strips (conductive material)  812 , such as gold, platinum or copper, are placed upon the micro-actuator arm  806 , a PZT layer (insulative layer)  814  is applied over and between the conductive strips  812 , physically and electrically isolating the conductive strips  812 . Another set of conductive strips  812  and a PZT layer  814  are applied and the process is repeated until the number of layers and/or thickness is appropriate for the micro-actuator&#39;s application and performance. In one embodiment, the last layer applied is a PZT layer  815 . In one embodiment, the last PZT layer  815  provides a ‘window’ (gap in insulation) for the bonding pad  816  to be attached within. (See FIG. 8). In one embodiment, four to six PZT layers and four to six conductive layers are utilized.  
         [0019]    In one embodiment, upon separation of the micro-actuators  810 , the PZT layers  814 , 815  physically isolate the conductive strips  812  from each other, and thus, prevent ‘smearing’ (and potential shorting). Further, the PZT layers  814 , 815  electrically insulate the sides of the piezoelectric layers, preventing ‘arcing’ damage and particulate contamination (electrical bridging/shorting)  
         [0020]    [0020]FIG. 9 provides a cross-section of a finger of a micro-actuator under principles of the present invention. In an embodiment, a window  902  is provided in the last PZT layer of  915  to give a conduction path between the top conductive layer (strip)  904  and the bonding pad  906 .  
         [0021]    Although several embodiments are specifically illustrated and described herein, it will be appreciated that modifications and variations of the present invention are covered by the above teachings and within the purview of the appended claims without departing from the spirit and intended scope of the invention.

Technology Classification (CPC): 8