Abstract:
Wafer-scale integration in gallium phosphide (GaP) is used to overcome the assembly difficulties of current optical heads, resulting in significantly improvements in optical performance as well as reduced cost.

Description:
RELATED APPLICATIONS 
     This application is related to and claims priority from Provisional Application Ser. No. 60/129,051 filed Apr. 13, 1999. 
    
    
     FIELD OF THE INVENTION 
     The present invention is related to optical heads and their manufacture in wafer form. 
     BACKGROUND 
     A schematic of an embodiment of an optical head is shown in FIG.  2 . The head comprises a number of discrete parts: a slider body, a movable micro-machined tracking mirror, a fiber, a magnetic writing coil, a molded glass lens, a lens holder, and possibly a quarter-wave plate. The quarter wave-plate plate may be needed when a polarization-maintaining fiber is used, but is not used when a low-birefringence fiber is used. Assembly of this head is complex due to the small size of the components and to tight alignment tolerances. The lens-to-slider and coil-attach processes are particularly time-consuming and tedious. Another disadvantage is that the lenses are molded one piece at a time, leading to high costs and difficulty in handling. Furthermore, the lens is limited to a numerical aperture (NA) less than 0.85, resulting in a maximum areal density of around 4 Gb/in 2  using a 660 nm laser, quad-MO media, and a conventional read channel. 
     What is needed is a head design that makes head assembly more efficient and that offers a path to significantly higher areal densities. 
     SUMMARY 
     The present invention includes an optical head for transferring a light from a source to a storage disk of a storage drive, comprising: a first block; a reflective element, the reflective element coupled to the first block to direct the light to the disk; a second block, the second block coupled to the first block; and a first lens, the first lens for focusing the light onto the disk; and the first lens formed of the second block. The first and/or second blocks may comprise GaP (Gallium Phosphorus). The second lens may comprise a near-field lens. The first block may comprise silicon. The second block may comprise GaP. The optical head may also comprise a third block, the third block disposed between the first and second blocks and coupled thereto. The optical head may also comprise as second lens, wherein the second lens is formed of the third block. The third block may comprise GaP. The first lens and the second lens may provide an NA of at least 1.13. 
     The present invention also includes a storage system comprising: a source, the source providing a light; a storage disk; a head; a first block; a reflective element, the reflective element coupled to the first block to direct the light to the storage disk; a second block, the second block coupled to the first block; and a first lens, the first lens formed of the second block, and the first lens for focusing the light onto the storage disk. The second block may comprise GaP. The first lens may comprise a near-field lens. The first and/or second blocks may comprise GaP. The first block may comprise silicon. The optical head may also comprise a third block, the third block disposed between the first and second blocks and coupled thereto. The optical head may further comprise a second lens, wherein the second lens is formed of the third block. 
     The present invention may also comprise a disk drive head, including: a light directing means for directing a light towards a storage medium; and a focusing means for focusing the light onto the storage means, wherein the light directing means is coupled to the focusing means. 
    
    
     DESCRIPTION OF THE FIGURES 
     FIG. 1 shows a perspective view of a multi-disk optical drive  100 ; 
     FIG. 2 shows an exploded view of a MO head; 
     FIG. 3 shows a steerable micro-machined mirror; 
     FIG. 4 a  shows a far-field MO head embodiment of the present invention; 
     FIG. 4 b  shows a near-field MO head embodiment of the present invention; 
     FIG. 5 shows design, performance specifications, and tolerances for an exemplary embodiment of the lens of the far-field head; 
     FIG. 6 shows an optical ray-trace for the lens corresponding to FIG. 5; 
     FIG. 7 shows design, performance specifications, and tolerances of an embodiment of the lenses of the near-field head; 
     FIG. 8 shows an optical ray-trace for the lens corresponding to FIG. 7; 
     FIG. 9 shows an alternative embodiment of a head of the present invention; 
     FIG. 10 shows a wafer layout for a 2-inch GaP wafer. 
     FIG. 11 shows a pictorial diagram of the far field head fabrication process; and 
     FIG. 12 shows a bearing and coil layout for the far-field head. 
     FIG. 13 shows a lens etched in a thick film deposited on a substrate made from different material. 
    
    
     DESCRIPTION OF THE INVENTION 
     Referring in detail to the drawings wherein similar parts are identified by like reference numbers, there is seen in FIG. 1 a perspective view of a multi-disk optical drive  100 . In this view, a head stack assembly  105  comprises individual heads  125 , each of which is coupled to individual arms  120  through respective suspensions  122 . In the preferred embodiment, the heads  125  comprise flying magneto-optical (MO) heads. The MO heads  125  comprise air bearing surfaces of a type well known in the Winchester disc drive arts. The air bearing surfaces interact to maintain the MO heads above respective rotating disks  155 . While the present invention is described with reference to flying MO heads, it is understood that non flying MO heads used in the disk drive industry are also with the scope of use with the present invention. The head  125  may also comprise an optical head wherein magnetic elements are not utilized (not shown). FIG. 1 further illustrates a group of individual optical fibers  115 , which are all coupled to an optical switch  130  at one end and to individual ones of the MO heads  125  at an opposite end. The optical switch  130  selectively directs a light  160  from a source (not shown) to a particular one of the individual optical fibers  115 . The optical fibers  115  function to route the light  160  between the optical switch  130  and a particular MO head  125 . 
     Referring now to FIG.  2  and preceding Figures as needed, there is an exploded view of a previous embodiment of a MO head  125  in which is shown attached to a body  150 , the optical fiber  115 , a steerable micro-machined mirror  140 , and a focusing lens  145 . FIG. 2 also shows a path of the light  160  as it travels along the optical fiber  115 . The light  160  is directed and reflected by a steerable micro-machined mirror  140  in a radial direction  199  of the disk  155 . During normal drive operation, the light  160  is focused by the lens  145  onto a surface of a particular disk  155 , and reflected light  161  is returned from the disk  155  to the optical switch  130  for processing by optics and electronics. 
     Referring now to FIG.  3  and preceding Figures as needed, the steerable micro-machined mirror  140  of FIG. 2 is seen to include a moveable portion  146  attached to a body  147  by beams  142 . Bond pads  143  and  144  are connected electrically to drive-electrodes (not shown) located underneath and separated from the moveable portion  146  by an air gap. When a voltage is applied to pad  143  or  144  relative to a ground pad  148 , an electrostatic force is applied to the moveable portion  146  to cause it to torsionally vector about the beams  142  by a desired angle  141  about axis  149 . 
     Referring now to FIG. 4 a  and preceding Figures as needed, there is seen a far-field MO head embodiment of the present invention. In FIG. 4 a,  the MO head  125  of FIGS. 1 and 2 is replaced by a far-field head  201  design of the present invention. The far-field head  201  has an advantage that its fly height can be on the order of  10 - 15  uin. The far-field head allows use of preformatted plastic disks  155 . The head designs of the present invention may comprise parts made from gallium phosphide (GaP) wafers. GaP is a convenient material to work with because it has a high refractive index and because it can be etched to form various lens designs. By using GAP, the manufacture of the MO head  201  may be simplified. Use of GAP also provides a design path to significantly higher areal densities. 
     In one embodiment of the far-field head  201 , the head comprises a bottom block  208  made from a piece of a GaP wafer, with a lens  209  etched into the block&#39;s top surface and an air bearing  210  etched into its bottom surface. The lens  209  may comprise a plano-convex lens. The lens  209  may be designed such that a bottom of the lens is coplanar with the air-bearing surface. Anti-reflection coatings are preferred on the lens surfaces. A top block  202  comprises a silicon wafer processed to include an integrated tilt-up micro-machined tracking mirror  203  and an etched channel  205  for receiving the optical fiber  115 . The top block  202  can be designed to also include etched slots  206  for holding a quarter-wave plate and/or a wave-plate  207  that may be used to compensate for phase shift introduced by optical components. The far-field head design  201  may be further fabricated to provide a magnetic coil  211  directly below the lens  209  and inside a cavity of the bottom block  208 . Fabrication of the coil  211  may utilize thin film patterning and cured photo-resist insulators. The coil is  211  designed so that a high magnetic field is generated near the focal point of the light  160  that passes through the lens  209 . Bond pads  212  for the coil  209  may be patterned directly on the top. block  202  for accessibility during wire bonding. Connections from the bond pads  212  to the coil  209  can be made by etching or laser drilling vias through the head  201 , and by using an electroless plating technique to establish the current path. 
     Referring now to FIG.  5  and preceding Figures as needed, design, performance specifications, and tolerances for an exemplary embodiment of the lens  209  of the far-field head  201  are given in table format. In this embodiment, the lens  209  provides a numerical aperture (NA) of approximately 0.83 and a corresponding spot size of 0.46 um for an areal density target of about 4 Gb/in 2 ; however, the far-field embodiment should be extendable to an NA of at least 0.9. 
     Referring now to FIG.  6  and preceding Figures as needed, an optical ray-trace for the lens  209  corresponding to the specifications of the table of FIG. 5 is shown. 
     Referring now to FIG. 4 b  and preceding Figures as needed there is seen a near-field MO head embodiment of the present invention. In the near-field embodiment of the present invention, the head  125  of FIGS. 1 and 2 is replaced by a near-field head  221  that comprises top  222  and bottom  223  blocks that are similar in design to the far-field head  201 . The near field head  201  has an advantage that its fly height can be on the order of less than 5 uin. The reduced fly height distance over that of the far field head  101  enables focusing of the light  160  with a smaller spot size. The head  221  also comprises a third block  231  that comprises a lens  232 . The lens  232  is used in combination with an embodiment of the lens  209  to provide the head  221  with a high numerical aperture (NA), while at the same time achieving a wide enough image field-of-view. 
     Referring now to FIG.  7  and preceding Figures as needed, the design, performance specifications, and tolerances of an embodiment of the lenses  209 / 231  of the near-field head  221  are given in table format. The lenses  209 / 231  preferably exhibit an effective NA of approximately 1.3 and a spot size of about 0.29 um for an areal density target of about 11 Gb/in 2 . The two-element near-field concept should be extendable up to a NA of about 2.5. 
     Referring now to FIG.  8  and preceding Figures as needed, an optical ray-trace for the lens  209 / 231  combination corresponding to the specs of FIG. 7 is shown. 
     Referring now to FIG.  9  and preceding Figures as needed, an alternative embodiment of a head of the present invention is shown. One advantage of the previous embodiments of the present invention discussed above is that the air bearing surface (ABS), lens, and coil are integrated together in one piece and may be are created at the wafer level. In other embodiments it may be advantageous to make the other parts in discrete form for economic reasons or until suitable wafer-scale processes can be developed. In the embodiment of FIG. 9, a micro-machined mirror  301  comprises a discrete component that may be placed on either at the row-bar or individual head level during the manufacturing process of making a head  300 . The mirror  301  may be attached to a top block  302  by an attach process that could be automated using pick-and-place technology. The top block  302  could be made from silicon, GaP, AlTiC or other suitable material. A GaP top block  302  would minimize stresses due to thermal expansion mismatch during a wafer bond process to a GAP lower block  303 . The upper and lower blocks  302 / 303  could be assembled at wafer, row-bar, or individual head level. 
     Referring now to FIG.  10  and preceding Figures as needed, a wafer layout for a 2-inch GAP wafer is shown. The present invention identifies that for either of the heads  201 / 221 , if a discrete micro-machined mirror  301  is used, the remaining constituent parts may be fabricated in a set of two GAP wafers  250 . The wafers  250  may be aligned and bonded together and then the bonded assembly may be diced to yield individual heads  201 / 221 . One possible method of bonding the wafers  250  in the fabrication process is glass frit bonding, wherein, a glass in a paste form is applied to a first GA wafer  250 , which may be lithographed using a screen-printing process. Next, the GAP wafer  250  may be heat-treated (glazed) to burn out organic components of the paste. A second GAP wafer  250  may be placed in contact with the glass side of the first wafer. Next, heat and pressure are applied to the wafer stack, causing the glass paste to reflow and adhere to the two wafers. The glass frit approach can be used for bonding wafers of the same materials or for bonding dissimilar materials. 
     The wafers  255  may also be bonded in a direct wafer fusion bond. Fusion bonding involves placing two like materials in contact and applying heat and pressure to cause their surfaces to chemically react or fuse together. This method has been employed to bond silicon to silicon and silicon to silicon dioxide and may be applicable to GaP-to-GaP bonding. 
     A third possibility is an anodic bond. Anodic bonding typically involves a doped ceramic (such as a sodium-ion-rich glass) and a conductive substrate (such as silicon or metal). The substrates are placed in contact using pressure. Heat (to reach the softening temperature of the glass) and an electric field are applied. The electric field causes the charged ions in the ceramic/glass to move away: from the interface of the two substrates, leaving a space charge region. This space charge region causes the second substrate to be attracted, setting a strong bond. 
     The possibility of using additional bonding techniques exists. Eutectic Au-Si, PECVD oxides and nitrides, and even photo-resist or adhesives may have potential as “frit” layers to attach substrates. 
     Referring now to FIG.  11  and preceding Figures as needed, a pictorial diagram of the far field head  101  fabrication process is shown. 
     Referring now to FIG.  12  and preceding Figures as needed, the bearing and coil layout for the far-field head  201  is shown. 
     Other features and advantages of the present invention may become apparent to a person of skill in the art who studies the present invention disclosure. For example, the optical designs presented above are only examples. Other surface shapes are possible and may be desired. For example, a diffractive surface may be useful in certain applications in place of the lens surfaces described above. There are also a number of ways to pattern the lenses in GaP. One is to deposit photo-resist, expose with a gray-scale mask, and etch. Another possibility is to deposit photo-resist, reflow the photo-resist, and etch. A third approach is to pattern a binary structure and use a mass transport process to form a continuous profile. GaP is a convenient material to work with because it has a high refractive index and it has been demonstrated that lenses can be etched in it. It may be reasonable to consider other materials for the lens wafers. For example, a lens wafer could be molded in glass. Lenses could be etched in silica or some other glass. Other semiconductor materials like ZnSe or ZnS could be used instead of GaP. Lenses could also be etched in a thick film of material deposited on a substrate made from different material, as shown in FIG.  13 . This approach may be. viable when the desired lens material is not available in bulk form. The index difference between the substrate and the film would have to be taken into account in the optical design. The etching processes could utilize wet chemistry or dry chemistry, such as RIE or ion milling. The quarter wave-plate could be incorporated as a separate wafer, and bonded into the stack. A head for use with phase-change media could be made by leaving out the coil fabrication steps. Bond pads could be connected to the coil leads using a shadow mask technique across an edge of the head. Additional grooves or features can be added to expose coil leads, bond pads, or through-holes to facilitate the electrical connection of the coil to the top of the slider. Therefore, the scope of the present invention is to be limited only by the following claims.