Abstract:
A magneto-optical head for magneto-optical writing and reading systems having an improved construction for a field modulating coil and a miniature objective lens, and a method of manufacturing the magneto-optical head. The magneto-optical head is mounted at the end of a slide-arm movable over a magneto-optical recording medium by hydrodynamics and includes: a lens mounted at the end of the slide-arm, for focusing incident light to form a light spot on the magneto-optical recording medium; a coil member including at least two stacked coil layers, and an insulating layer interposed between adjacent coil layers for electrically insulating the adjacent coil layers from one another, the stacked coil layers being planar coils with a spiral structure and having electrical contacts for electrical connection therebetween; and a connection member interposed between the lens and the coil member, for connecting the coil member to one side of the lens, facing the magneto-optical recording medium, and for electrically connecting the coil layers to an external power supply. The coil member is manufactured using a semiconductor fabrication process.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Application No. 99-23946, filed Jun. 24, 1999 in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a magneto-optical head for magneto-optical reading and writing systems, with improved structure associated with a field modulation coil and installation of a miniature objective lens, and a method of manufacturing the same. 
     2. Description of the Related Art 
     Magneto-optical reading and writing systems write information onto magneto-optical recording media by magnetic field modulation, and read written information from the media in an optical manner. 
     Referring to FIG. 1, a common magneto-optical reading and writing system is shown. The magneto-optical reading and writing system includes a swing arm  21  mounted to enable it to pivot relative to a base  10 , an actuator  23  for providing a rotary driving force to the swing arm  21 , an air-bearing slider  25 , attached at one end of the swing arm  21 , which flies over a magneto-optical recording medium  1  by hydrodynamics to scan tracks thereof, and a magneto-optical head  30  mounted at the slider  25  to read information optically from the magneto-optical recording medium  1 . The magneto-optical head  30  includes an objective lens  31  for focusing a light spot onto the magneto-optical recording medium  1 , and coils (not shown) for magnetic field modulation. 
     Referring to FIGS. 2 and 3, the conventional magneto-optical head  30  of a magneto-optical reading and writing system includes: the objective lens  31 , which is installed on the slider  25 , for focusing incident laser light onto the magneto-optical recording medium  1 ; a pair of magnetic pole pieces  33  and  35  mounted parallel to and on respective sides of the slider  25 , and also mounted between the objective lens  31  and the surface of the magneto-optical recording medium  1 ; and first and second coils  37  and  39  are wound around the magnetic pole pieces  33  and  35 , respectively. The magnetic pole pieces  33  and  35  are separated from one another, allowing laser light focused by the objective lens  31  to pass through the gap therebetween. The first and second coils  37  and  39  establish horizontal magnetic fields, the orientation of which varies according to the direction of current flowing through the coils  37  and  39 , which enables the magneto-optical head  30  to write information onto the magneto-optical recording medium  1 . 
     As previously described, the conventional magneto-optical head  30  has the construction in which the first and second coils  37  and  39  are wound around the magnetic pole pieces  33  and  35  mounted below the objective lens  31  in a horizontal direction. Due to the structure, there are limitations in miniaturizing the magneto-optical head  30 , which limits the recording density and performance of near-field recording. In addition, winding the first and second coils  37  and  39  around the magnetic pole pieces  33  and  35 , respectively, is ineffective in terms of assembling characteristics, costs and yields, thereby making mass production thereof difficult. 
     SUMMARY OF THE INVENTION 
     To solve the above problems, it is an object of the present invention to provide a magneto-optical head for magneto-optical reading and writing systems and a method of manufacturing the same, in which a thin film type microcoil for field modulation is formed in a semiconductor fabrication process, so that the magneto-optical head can be miniaturized with improved performance of near-field recording. 
     It is a further object of the present invention to provide a magneto-optical head for magneto-optical reading and writing systems and a method of manufacturing the same which simplifies the assembling of miniature coils to lower costs and increases yields to enable mass production of the magneto-optical reading and writing systems. 
     Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
     According to an aspect of the present invention, there is provided a magneto-optical head for a magneto-optical writing and reading system capable of writing information on a magneto-optical recording medium by field modulation and optically reading information from the magneto-optical recording medium, the magneto-optical head being mounted at the end of a slide-arm movable over the magneto-optical recording medium by hydrodynamics, the magneto-optical head comprising: a lens mounted at the end of the slide-arm, for focusing incident light to form a light spot on the magneto-optical recording medium; a coil member including at least two stacked coil layers, and an insulating layer interposed between the two coil layers for electrically insulating the two coil layers from one another, the two stacked coil layers being planar coils with a spiral structure and having electrical contacts for electrical connection therebetween; and a connection member interposed between the lens and the coil member, for connecting the coil member to one side of the lens, facing the magneto-optical recording medium, and for electrically connecting the coil layers to an external power supply. 
     Preferably, the connection member is solder bumps formed projecting from the uppermost coil layer of the coil member, with a conductive material for electrical connection to the external power supply, the solder bumps adhering to the lens by thermal melting. Preferably, the solder bumps are formed of at least one metal alloy selected from the group consisting of a tin-lead (Sn—Pb) alloy, a silver-tin-lead (Ag—Sn—Pb) alloy and a gold-tin (Au—Sn) alloy. 
     According to another aspect of the present invention, there is provided a method of manufacturing a magneto-optical head for a magneto-optical writing and reading system capable of writing information on a magneto-optical recording medium by magnetic field modulation and optically reading information from the magneto-optical recording medium, the magneto-optical head being mounted at the end of a slide-arm movable over the magneto-optical recording medium by hydrodynamics, the method comprising: forming a sacrificial layer over a substrate; forming a coil member over the sacrificial layer, the coil member including at least two coil layers and at least one insulating layer; patterning the coil member and the sacrificial layer to form a through hole; forming a plating mold pattern over the uppermost coil layer of the coil member, and plating solder into the plating mold pattern to form solder bumps; preparing a lens having an emitting portion projecting a predetermined length toward the magneto-optical recording medium, the lens for focusing incident light to form a light spot on the magneto-optical recording layer, and coating a metal thin film having a predetermined pattern on the bottom surface of the lens, except on the emitting portion, to form a conductive reflective layer; inserting the emitting portion into the through hole to place the lens on the solder bumps, and heating the assembly to melt the solder bumps and adhere the lens to the coil member; and removing the sacrificial layer to separate the combined lens and coil member from the substrate. 
     Preferably, forming the coil member comprises: forming a seed layer pattern for plating over the sacrificial layer; depositing a mold over the seed layer pattern to a predetermined thickness, and patterning the mold layer to form a plating mold pattern; plating a metal into the plating mold pattern to form a coil layer having a predetermined thickness; forming an insulating layer over the plating mold pattern and the coil layer; and repeating one or more times the formation of the seed layer, formation of the plating mold pattern, formation of the coil layer and formation of the insulating layer in sequence, to form a stacked multiple coil layer with flatness between every coil layer of the stack. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which: 
     FIG. 1 is a schematic plan view of a conventional magneto-optical reading and writing system; 
     FIG. 2 is a front view of a conventional magneto-optical head of a magneto-optical reading and writing system; 
     FIG. 3 is a bottom view taken along line III—III of FIG. 2; 
     FIG. 4 is a schematic front view showing a magneto-optical head of a magneto-optical reading and writing system according to an embodiment of the present invention mounted on a slider; 
     FIG. 5 is a partial front view of the magneto-optical head shown in FIG. 4; 
     FIG. 6 is a schematic bottom view of the lens in FIG. 5; 
     FIG. 7 is an exploded perspective view of the coil member of the magneto-optical head shown in FIG. 4; 
     FIGS. 8A through 8E are sectional views illustrating a method of manufacturing a magneto-optical head for a magneto-optical reading and writing system according to an embodiment of the present invention; and 
     FIGS. 9A through 9K are sectional views illustrating in greater detail the fabrication method of the coil member for the magneto-optical reading and writing system according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now made in detail to the present preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. 
     Referring to FIGS. 4 and 5, a magneto-optical head of a magneto-optical reading and writing system according to an embodiment of the present invention is mounted on an air-bearing slider  110 , which is movable above the surface of a magneto-optical recording medium  100  by hydrodynamics. The magneto-optical head includes a lens  120  for focusing incident light to form a light spot on the magneto-optical recording medium  100 , a coil member  140  attached to one surface of the lens  120 , facing the magneto-optical recording medium  100 , and a connection member  160  for allowing attachment between the coil member  140  and the lens  120  and electrical connection of the coil member  140  to an external power source. 
     For a near-field writing operation, the lens  120  focuses incident light to form a light spot on the magneto-optical reading medium  100 . As the light spot domain of the magneto-optical recording medium  100  is heated to the Curie point temperature or more of the medium, vertical magnetic fields are produced by the coil member  140  and information is recorded by the magnetization. Recorded information is reproduced by exploiting Kerr&#39;s effect. In other words, as the temperature at the light spot is lowered to the Curie point temperature or less, the polarization of the incident beam changes according to the direction of magnetization at the magnetic domain on the medium, so that information can be read from the medium. 
     For these functions, the lens  120  includes a transmitting portion  121 , a first reflective portion  123 , a second reflective portion  125 , an emitting portion  127  and a conductive reflective layer  129 . The transmitting portion  121  is formed in a concave shape to divergently transmit incident light L. The first reflective portion  123 , a plane arranged facing the transmitting portion  121 , reflects the incident light L toward the second reflective portion  125  adjacent to the transmitting portion  121 . The second reflective portion  125  is formed with a concave mirror structure around the transmitting portion  121  such that it focally reflects the incident light reflected by the first reflective portion  123 . The emitting portion  127  is formed extending outward a predetermined length from the center of the first reflective portion  123 , and transmits the focused light from the second reflective portion  125  to form a light spot on the magneto-optical recording medium  100 . For writing and reading operations, the emitting portion  127  is spaced a predetermined distance above the magneto-optical recording medium  100 . As shown in FIG. 6, the conductive reflective layer  129 , which is divided into at least two portions  129   a  and  129   b , is formed on the first reflective portion  123 . Referring to FIG. 5, the conductive reflective layer  129  is made to adhere to the connection member  160  by melting and allows current to flow from an external power supply to the coil member  140 . In addition, the conductive reflective layer  129  assures total reflection of the incident light from the first reflective portion  123  toward the second reflective portion  125 . 
     The coil member  140  includes at least two coil layers  141  and  151 , and an insulating layer  143  for electrically insulating the coil layers  141  and  151 , while being interposed between the same. The coil layers  141  and  151 , which are planar coils having a spiral structure, are connected to each other through electric contact points thereof. 
     In FIGS. 4 and 5, a bilayered coil structure is shown. The detailed construction of the first and second coil layers  141  and  151 , and the insulating layer  143  of the coil member  140  will be described with reference to FIG.  7 . Referring to FIG. 7, the first coil layer  141  has a spiral structure around the emitting portion  127  of the lens  120  (not shown) in a direction, for example, counterclockwise, within a predetermined distance. The first coil layer  141  includes a first contact point  141   a  on the inside end of the spiral structure, and second contact points  141   b  arranged around the circumference of the first coil layer  141 . The first and second contact points  141   a  and  141   b  are electrically connected to the second coil layer  151  through the insulating layer  143 , and in turn to the conductive reflective layer  129  (not shown). The second coil layer  151  is stacked on the first coil layer  141  with the insulating layer  143  interposed therebetween, and has a spiral structure arranged in the reverse direction of the first coil layer  141 . The second coil layer  151  has a third contact point  151   a , which is connected to the first contact point  141   a , and fourth contact points  151   b , which are connected through the connection member  160  to the conductive reflective layer  129  (not shown). Further, the second coil layer  151  has a connection pattern  153  around the circumference of the same, which is electrically insulated from the second coil layer  151 , and is connected to the first coil layer  141  to allow current flow from the conductive reflective layer  129  (not shown) to the first coil layer  141 . Thus, the portion  129   b  of the conductive reflective layer  129  (not shown) is connected through the connection pattern  153  to the second contact points  141   b , while the other portion  129   a  (not shown) thereof is connected to the fourth contact points  151   b . As a result, when current is applied through the portion  129   b  of the conductive reflective layer  129 , the current first flows through first coil layer  141 , and then to the second coil layer  151  through the first contact point  141   a  and then the third contact point  151   a . After the current flows through the second coil layer  151 , it then flows through the fourth contact points  151   b  to the other portion  129   a  (not shown). 
     The insulating layer  143  is provided for electrical insulation of the first and second coil layers  141  and  151  from each other, and for electrical connection between the first and second coil layers  141  and  151 . The insulating layer  143  has through holes  143   a  and  143   b  for electrical connections between the first and third contact points  141   a  and  151   a , and between the second contact points  141   b  and the connection pattern  153 . 
     Referring to FIGS. 4 and 5, it is preferable that the length of the emitting portion  127  of the lens  120  is greater than the total height of the coil member  140  and the connection member  160  so as to prevent the coil member  140  from contacting the magneto-optical recording medium  100  as the slider  110  flies over the magneto-optical recording medium  100 . 
     Preferably, as shown in FIG. 5, the connection member  160 , which is formed projecting from the uppermost layer of the coil member  140 , for example, from the second coil layer  151 , is constructed of solder bumps  161  formed of a conductive material, which allows for physical connection between the conductive reflective layer  129  and the coil member  140  by thermal melting, and for electrical connection between the conductive reflective layer  129 , and the first and second coil layers  141  and  151 . A tin-lead (Sn-Pd) alloy, a silver-tin-lead (Ag—Sn—Pb) alloy or a gold—tin (Au—Sn) alloy is preferred as a material for the solder bumps  161 . 
     The solder bumps  161  are arranged such that the first and second coil layers  141  and  151  are separately connected to each of the two divided portions  129   a  and  129   b  (not shown) of the conductive reflective layer  129 . For the solder bumps  161 , a pattern is formed over the second coil layer  151  and then subjected to a plating process to arrange the solder bumps  161  as shown in FIG. 5, which allows for a predetermined contact area with the conductive reflective layer  129 , and electrode separation between the two divided portions  129   a  and  129   b  (not shown). However, a native oxide film exists on the solder bumps  161  formed through these processes, which weakens adhesion to the lens  120  by melting. 
     Considering this negative factor, the connection between the solder bumps  161  and the lens  120  by thermal melting is carried out by fluxless reflow soldering in which heating is performed in the absence of flux in a high purity nitrogen atmosphere or a vacuum. In other words, the heating in a high purity nitrogen atmosphere or a vacuum prevents the formation of the oxide film on the solder bumps  161  at high temperatures, thereby strengthening adhesion to the lens  120 . 
     FIGS. 8A through 8E are sectional views illustrating a method of manufacturing a magneto-optical head employing a bilayered coil member according to an embodiment of the present invention. 
     In the manufacture of the magneto-optical head, as shown in FIG. 8A, a substrate  200 , for example, a silicon wafer, is prepared, and a sacrificial layer  210  is formed over the substrate  200 . After a coil member  140  including a plurality of coil layers, for example, two coil layers, and an insulating layer therebetween is formed over the sacrificial layer  210 , a through hole  220  to be the emitting portion  127  of the lens  120  shown in FIG. 4 is formed. Here, the through hole  220  is formed through both the coil member  140  and the sacrificial layer  210  such that the length of the emitting portion  127  is greater than the height of the coil member  140 . 
     The sacrificial layer  210  is formed of titanium (Ti), chromium (Cr) or photoresist. If photoresist is selected as a material for the sacrificial layer  210 , there is an advantage in that a subsequent removal of the sacrificial layer  210  is easy. If the sacrificial layer  210  is formed of Ti or Cr, a seed layer  230   a , which will be described later, can be easily formed. 
     Following this, as shown in FIG. 8B, a plating mold pattern is formed over the uppermost layer, for example, the second coil layer  151  (see FIG. 7) of the coil member  140 , and solder is plated into the pattern to form the solder bumps  161 . Preferably, the solder bumps  161  are formed of a Sn—Pb alloy, an Ag—Sn—Pb alloy or an Au—Sn alloy. 
     Then, referring to FIG. 8C, the lens  120 , which has the emitting portion  127  protruding a predetermined length toward the magneto-optical recording medium  100  (see FIG. 4) for focusing incident light to form a light spot on the magneto-optical recording medium  100 , is prepared. Then, a metal thin film is coated on the outside of the first reflective portion  123  of the lens  120 , facing the coil member  140 , surrounding the region of the emitting portion  127 , which results in the conductive reflective layer  129 . 
     Then, the emitting portion  127  of the lens  120  is inserted into the through hole  220  to seat the lens  120  over the solder bumps  161  as shown in FIG. 8D, and then the assembly is subjected to heating, which allows connection between the lens  120  and the coil member  140  by melting. Here, the heating to melt the solder bumps  161  for adhesion to the lens  120  is performed by fluxless reflow soldering in a pure nitrogen atmosphere or a vacuum. The heating in a high purity nitrogen atmosphere or a vacuum prevents the formation of an oxide film on the solder bumps  161  at high temperatures, thereby improving adhesion strength with respect to the lens  120 . 
     As the last process, the sacrificial layer  210  shown in FIG. 8D is removed to separate the assembly of the lens  120  and the coil member  140  from the substrate  200 , which results in the magneto-optical head having the construction as shown in FIG.  8 E. 
     The formation of the coil member  140 , which was described with reference to FIG. 8A, will be described in greater detail with reference to FIGS. 9A through 9K. 
     Referring to FIG. 9A, a first seed layer  230  is formed over a sacrificial layer  210  on a substrate  200 . The first seed layer  230  acts as an electrode for plating the first coil layer  141  (see FIG.  9 D), and is formed by vacuum depositing a material having a superior conductivity, for example, copper (Cu), over the sacrificial layer  210 . If the sacrificial layer  210  is formed of a photoresist, it is preferable that prior to the deposition of the first seed layer  230 , an adhesive layer  215  of Cr or Ti is deposited over the sacrificial layer  210  in order to enhance adhesion strength with respect to the first seed layer  230 . A Cr—Cu alloy or Ti—Cu alloy is preferred as a material for the first seed layer  230   a.    
     Following this, as shown in FIG. 9B, the first seed layer  230   a  is patterned according to the desired shape of the first coil layer  141 . In other words, the first seed layer  230   a  is patterned to form first insulating grooves  231 , which will form a first plating pattern  240  shown in FIG. 9C later. 
     Referring to FIG. 9C, a plating mold is deposited over the first seed pattern  230   a  to a predetermined thickness and patterned to be negative with respect to the shape of the first coil layer  141  shown in FIG. 7, so that the first plating pattern  240  is completed. Here, because the first seed pattern  230   a  is as thin as about 1000 Å, a spin coating technique is preferred for the deposition of a plating mold to ensure that the surface of the mold layer is flat. The first plating pattern  240  is formed of an insulating material such as photoresist. For this case, the patterning of the first plating pattern  240  can be completed by only one photolithography process. 
     Referring to FIG. 9D, a metal is plated into the first plating pattern  240  to a predetermined thickness, which results in the first coil layer  141  having a spiral structure with a predetermined line width. Here, the first coil layer  141  is a relatively thick metal layer, which is more durable in a large current flow environment, and thus a plating technique is preferred for the formation of such a thick metal layer. Here, both electroplating techniques and electroless plating techniques are applicable. 
     Following this, the first plating pattern  240  is subjected to heating. This heating process removes all of the remaining solvent from the first plating pattern  240 , and minimizes potential deformation of the first plating pattern  240  by the solvent. As a result of the heating it process, the height of the first plating pattern  240   a  is lowered as shown in FIG.  9 E. Taking this into account, it is preferable that the first plating pattern  240  is formed to be higher than the height of the first coil layer  141  as shown in FIG.  9 D. For example, assuming that after the heating process the height of the first plating pattern  240  is reduced by 70% of the original height of the same before, the first plating pattern  240  can be formed to be about 140% higher than the height of the first coil layer  141 , such that the top surface of the first plating pattern  240   a  becomes nearly level with the first coil layer  141  after the heating process, as shown in FIG.  9 E. 
     The heating process can be performed by an oven, a flat heating device, an ultra-violet curing device, or an electron-beam heating device. 
     Following this, as shown in FIG. 9F, the insulating layer  143  is formed over the first plating pattern  240   a  and the first coil layer  141  for electrical insulation between the first coil layer  141  and the second coil layer  151  (see FIG. 9J) to be formed later. The insulating layer  143  has apertures  143   a  and  143   b , which allow the first coil layer  141  to be electrically connected with the second coil layer  151  and the conductive reflective layer  129  (not shown) through the first and second contact points  141   a  and  141   b  (see FIG. 7) thereof. Preferably, the insulating layer  143  is formed of a dielectric material, such as SiO 2  and Si 3 N 4 , or a polymer such as photoresist and polyimide. 
     Then, as shown in FIG. 9G, a second seed layer  250  is formed over the insulating layer  143 . The second seed layer  250  acts as an electrode for plating the second coil layer  151  shown in FIG. 9J, and is formed by vacuum depositing a material having a superior conductivity, for example, copper (Cu), over the insulating layer  143 . Here, the apertures  143   a  and  143   b  shown in FIG. 7 are filled with the conductive material, which allows the first and second coil layers  141  and  151  to be electrically connected through the contact points thereof. 
     Then, as shown in FIG. 9H, the second seed layer  250  is patterned according to the desired shape of the second coil layer  151  shown in FIG.  9 J. In other words, the second seed layer  250  is patterned to form second insulating grooves  251 , which will form a second plating pattern  260  (see FIG. 9I) later. The second seed layer  250  is formed of a Cr—Cu alloy or Ti—Cu alloy, which also can be used to form the first seed layer  230  as described previously. 
     Following this, referring to FIG. 9I, a plating mold is deposited over the second seed pattern  250   a  to a predetermined thickness and patterned to be negative with respect to the shape of the second coil layer  151 , so that the second plating pattern  260  is completed. 
     Referring to FIG. 9J, a metal is plated into the second plating pattern  260  to a predetermined thickness, which results in the second coil layer  151  having a spiral structure with a predetermined line width. Here, the second coil layer  151  is a relatively thick metal layer, which is more durable in a large current flow environment, and thus a plating technique is preferred for the formation of such a thick metal layer. Here, both electroplating techniques and electroless plating techniques are applicable. 
     Following this, the second plating pattern  260  is subjected to heating. This heating process removes all of the remaining solvent from the second plating pattern  260 , and minimizes potential deformation of the second plating pattern  260  by the solvent. As a result it of the heating process, the height of the second plating pattern  260  is lowered as shown in FIG.  9 K. Taking this into account, it is preferable that the second plating pattern  260  is formed to be higher than the height of the second coil layer  151  as shown in FIG. 9J in order that the top surface of the second plating pattern  260   a  becomes nearly level with the second coil layer  151  after the heating process, as shown in FIG.  9 K. Then, the portion A is removed to form a through hole that is to be the emitting portion  127  of the lens  120  (see FIG.  8 D), so that the formation of the coil member  140  is completed. 
     As described above, in the magneto-optical head of a magneto-optical reading and writing system according to the present invention having the construction described previously, a thin film type microcoil is combined with a lens by solder bumps, and thus the assembly process is easy to perform and adhesion strength therebetween is strong. In addition, there is no need for additional interconnection, thereby reducing the number of processes in the manufacture of magneto-optical heads. 
     Also, the adoption of a thin film type microcoil enables miniature heads to be manufactured through common semiconductor manufacturing processes, such as thin film formation and plating, thereby reducing the manufacturing while increasing yield. 
     In addition, the technique used to form the coil member for a magneto-optical head maintains the flatness over the top of every coil layer. Thus, after a lower coil layer is completed and a seed layer for an upper coil layer is plated, the focal depth of an exposure light system for patterning the seed layer can be maintained, avoiding reduction in resolution of the pattern. In addition, a problem of disconnection of the metal seed layer for the upper coil layer can be prevented. Thus, the distance between different coil layers can be maintained over line and space regions thereof within a desired range, so that multiple thin film layers can be easily stacked into a microcoil structure. 
     While this invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made thereto without departing from the spirit and scope of the invention as defined by the appended claims.