Patent Publication Number: US-6703767-B1

Title: PZT microactuator

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a division of U.S. application Ser. No. 09/772,354 filed on Jan. 29, 2001 U.S. Pat. No. 6,393,681, and further claims the benefit of U.S. Provisional Patent Application Ser. No. 60/263,021 filed Jan. 22, 2001. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable 
     REFERENCE TO A MICROFICHE APPENDIX 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to the manufacture of piezoelectric crystals (PZT) and, more particularly, to the processing of PZT wafers to produce peripherally coated PZT crystals that will not contaminate their use environment, such as disk drive suspensions and hard disk drives. In a particular aspect the invention relates to improved methods of coating the PZT crystals, using a resin coating placed between adjacent crystal precursors in a kerf of a predetermined width that permits subsequent cutting of a narrower kerf that leaves the crystal sides coated upon later separation of the crystals from the wafer. 
     2. Description of the Related Art 
     PZT crystals are used to effect micromovements of the sliders in disk drives. The crystals may flake in this use environment and introduce contamination into the disk drive. To avoid this efforts have been made to shroud the crystals after their separation from the PZT wafer with plasma sprayed coatings. This is a costly expedient requiring expensive equipment, increased manufacturing time, and repeated handling of the individual crystals. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the invention, therefore, to provide a less costly solution to the PZT crystal contamination problem. It is a further object to modify the PZT crystal preparation at the wafer cutting level to have a coating formed on the crystal peripheries as a part of the crystal separation steps normally used. It is a further object to provide a wider first kerf between adjacent crystals, fill the first kerf with coating resin, such as epoxy resin, and then cut a second kerf in the first kerf to isolate the crystals with the coating resin adhered to their peripheries. 
     These and other objects of the invention to become apparent hereinafter are realized in a method for the manufacture of peripherally coated PZT crystals suitable for microactuation of a disk drive suspension from a wafer comprising a plurality of PZT crystal precursors, including cutting in a locus between adjacent precursors a first kerf of a predetermined width to cut apart the precursors and reveal the sides thereof, depositing into the first kerf a coating resin that fills the first kerf and coats the precursor sides, solidifying the coating resin in place, cutting in the solidified coating resin at the locus a second kerf of less width than the first kerf, the second kerf cutting through the coating and between the adjacent precursors in spaced relation to the precursor sides to again cut apart the precursors while maintaining the solidified coating resin in place on the precursor sides, whereby the precursors become PZT crystals having a side coating against flaking of detritus therefrom into a disk drive suspension containing the crystals. 
     In this and like embodiments, typically, the method further includes cutting the wafer in a grid pattern comprising a series of intersecting first kerfs to define the plurality of crystal precursors, and using as the coating resin a flowable resin that cures to a solid, such as an epoxy resin, 
     The invention further provides a peripherally coated PZT crystal made by the above method, and more specifically a PZT crystal suitable for microactuation of a disk drive suspension, in which the crystal has on the vertical sides thereof a peripheral coating of a resin applied at a first thickness and cut to a second thickness to block flaking of detritus from the crystal into a disk drive suspension, the coating resin comprising an epoxy resin. 
     In another aspect the invention provides a wafer comprising a plurality of PZT crystal precursors separated by a first kerf, the first kerf being filled with a coating resin, and in which the first kerf has a second kerf formed therein. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     The invention will be further described in conjunction with the attached drawings in which: 
     FIG. 1 is a plan view of a PZT crystal wafer with a grid cut into it to define the individual crystals; 
     FIG. 2 is a PRIOR ART plan view, greatly enlarged, of a fragment of a PZT wafer with the individual crystals defined by intersecting narrow kerfs; 
     FIG. 3 is a plan view, greatly enlarged, of a fragment of a PZT wafer with the individual crystals defined by intersecting wide firsts kerfs according to the invention; 
     FIG. 4 is a view like FIG. 3 of a portion of the PZT wafer with coating resin in the first kerfs; 
     FIG. 5 is a view like FIG. 4 of a portion of the PZT wafer with second kerfs cut into the coating resin in the first kerfs separating adjacent crystals with the coating resin adhered to the crystal peripheries; and, 
     FIG. 6 is an isometric view of an individual crystal with the coating resin about its periphery. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference now to the drawings in detail, in FIG. 1 a typical PZT crystal wafer is shown at  10 . Individual PZT crystal precursors  12  (labeled PZT in FIGS. 4 and 4) are separated from the bulk of the wafer  10  by cutting a grid pattern  14  of kerfs  16  on the wafer by known means. In FIG. 2 PRIOR ART the heretofore-typical kerf  7  or cut between adjacent precursors  8  is shown to be about 0.003″ in width in the crystal wafer  9 . 
     With reference to FIGS. 3,  4 ,  5  and  6 , the invention method is for the manufacture from wafer  10  of peripherally coated PZT crystals  18  (FIG. 6) that will be suitable for microactuation of a disk drive suspension. The method includes cutting the grid  14  of intersecting kerfs  26  into the wafer  10  that comprises a PZT crystal  22  capable of being subdivided into a plurality of PZT crystal precursors  12 . The cutting is made in a locus  24  between adjacent precursors  12 . In accordance with the invention the first cutting forms a first kerf  26  of about 0.009″ in width, much wider than the previous width of 0.003″ shown in FIG. 2 PRIOR ART. The invention first kerf  26  cuts apart the PZT crystal precursors  12  and reveals the sides  30  thereof. See FIG.  3 . 
     In the next step, shown in FIGS. 4 and 5, a coating resin such as epoxy, or any other curable or hardenable resin  28  that is adherent to the crystal precursors  12 , flowable to be depositable in to the kerf  26 , and chemically compatible with the disk drive application envisioned for the PZT crystals  18 , is deposited into the first kerf  26  to fill the first kerf and coat exposed sides  30  of the PZT crystal precursors  12 . The coating resin  28  is solidified in place filling the first kerf  26 , FIG.  4 . 
     In the next step, the solidified coating resin  28  is cut at a predetermined locus  32  between the crystal precursors  12  for a second kerf  34 . As a part of the invention, the second kerf  34  is of less width than the first kerf  26 . Typically, the first kerf  26 , as noted, is about 0.009″; the second kerf  34  is about one-third the width of the first kerf  26 , or about 0.0003″. Once cut then, the second kerf  34  leaves a peripheral resin coating  36  comprising a portion of the resin  28  on either side of the kerf that is about 0.003: in width or depth. See FIG.  5 . 
     The crystal precursors  12  thus become PZT crystals  18  (FIG. 6) having a side coating  36  of the coating resin  28  against flaking of detritus therefrom into a disk drive suspension containing the crystals. PZT crystals  18  are suitable for microactuation of a disk drive suspension and have on their vertical sides  28  the peripheral coating  36  of resin  28  applied at, a first thickness, FIG. 4, and cut to a second thickness, FIG. 5, to block flaking of detritus from the crystal into a disk drive suspension. 
     As an intermediate product of the invention, there is provided the wafer  10  comprising a plurality of PZT crystal precursors separated by a first kerf  26 , the first kerf being filled with a coating resin  28 , and in which the first kerf has a second kerf  34  formed therein. 
     The invention thus provides a less costly solution to the PZT crystal contamination problem, by modifying the PZT crystal preparation at the wafer cutting level to have a coating formed on the crystal peripheries as a part of the crystal separation steps normally used through the use of a wider first kerf between adjacent crystals, later filled with coating resin, such as epoxy resin, and then cut with a second kerf in the first kerf to isolate the PZT crystals with the coating resin adhered prophylatically to their peripheries. 
     The foregoing objects are thus met.