Abstract:
The present invention provides a method of fabricating at least one lens. The method comprises providing a substrate with a surface coating. The surface coating is deformable and the method comprises imprinting a structure into the surface coating. The method also comprises etching at least a region of the imprinted structure and the substrate to remove at least a portion of the imprinted structure and the substrate. The structure is shaped so that the etching forms at least a portion of the at least one lens in the structure.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates generally to a method of fabricating a lens.  
       BACKGROUND OF THE INVENTION  
       [0002]     Electronic devices such as computers or television sets have displays for displaying information and images. Such displays often include optical components for imaging the information and images on a screen. In a rear projection display for instance a projector generates an image and a relatively large lens, such as a large Fresnel lens, may be positioned just before the screen to facilitate corner illumination of the screen. Further, the projector itself may include a liquid crystal display (LCD) panel which may be illuminated and imaged using a Fresnel lens.  
         [0003]     Fresnel lenses have the advantage that they are relatively flat compared with other types of optical lenses. A Fresnel lens typically has a plurality of concentric rings and each ring may be formed from a plurality of stacked ring-shaped layers. The ring-shaped layers of each ring typically have the same inner diameter but their outer diameter varies in a manner such that the Fresnel lens has a saw-tooth like profile. Each layer of such a stack of layers may have a different refractive index and the layers of each stack need to be aligned relative to each other.  
         [0004]     Other types of displays have electron emitters which emit electrons for generation of an image on a screen. Electrons emitted from such electron emitters are guided using electron lenses which are aligned with the electron emitters. In either the optical or the electron optical case alignment processing steps associated with the fabrication of the lenses are cumbersome and complicated. There is a need for technological advancement.  
       SUMMARY OF THE INVENTION  
       [0005]     Briefly, an embodiment of the present invention provides a method of fabricating at least one lens. The method includes providing a substrate with a surface coating. The surface coating is deformable and the method includes imprinting a structure into the surface coating. The method also includes etching at least a region of the imprinted structure and the substrate to remove at least a portion of the substrate and the base material. The structure is shaped so that the etching forms at least a portion of the at least one lens in the structure.  
         [0006]     The invention will be more fully understood from the following description of embodiments of the invention. The description is provided with reference to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is a flow chart illustrating a method of fabricating at least one lens according to an embodiment of the present invention;  
         [0008]     FIGS.  2  ( a ) to  2  ( d ) shows cross-sectional representations illustrating processing steps of the method of fabricating at least one lens according to an embodiment of the present invention;  
         [0009]     FIGS.  3  ( a ) to  3  ( d ) shows cross-sectional representations illustrating processing steps of the method of fabricating at least one lens according to another embodiment of the present invention; and  
         [0010]      FIG. 4  is a flow chart illustrating a method of fabricating at least one lens according to a further embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF EMBODIMENTS  
       [0011]     Referring initially to  FIGS. 1 and 2 , a method of fabricating at least one lens according to an embodiment is now described. The method  100  includes step  102  of depositing a layered structure on a base material and coating the layered structure with a deformable surface coating. The layered structure includes layers of different refractive index.  FIG. 2 ( a ) shows an example of such a base material  202 , a layered structure  204  and deformable surface coating  206 . The deformable surface coating  206  may include a polymeric material that is curable using UV radiation. The deformable surface coating  206  typically is single layered, but may alternatively also include a plurality of layers.  
         [0012]     For clarity  FIG. 2  illustrates processing steps of the fabrication of one lens only. In this embodiment the layered structure  204  includes three layers but it is to be appreciated that in variations of this embodiment the layered structure  204  may have any suitable number of layers. Further, the layers of the layered structure  204  may, in variations of this embodiment, not necessarily have differing refractive indices.  
         [0013]     Step  104  imprints a structure into the deformable surface coating. The structure has steps and has a shape that is associated with a shape of the at least one lens. In this embodiment the shape is associated with that of an array of lenses. Each lens of the lens array is in this example a Fresnel lens having stacks of aligned concentric ring-shaped layers.  
         [0014]     Step  106  selects a thickness of the layers of the layered structure and/or a height of the steps of the imprinted structure. The selection is made so that, if the imprinted structure and a portion of the layered structure is etched away and steps are etched in the layered structure, the etched steps have a height that corresponds to the layer thickness of the layered structure.  
         [0015]      FIG. 2 ( b ) shows a stamp  208  which imprints a structure  210  into the deformable surface coating  206 . The structure  210  is in this simplified illustration associated with the structure of only one lens of the array. The structure  210  that is imprinted into the deformable surface coating  206  has steps  212 . After the imprinting the stamp  208  is removed leaving the structure  210  exposed. The structure  210  is then cured using UV radiation.  
         [0016]     Step  108  uses an anisotropic etch process to etch the imprinted structure and a region of the layered structure which removes the imprinted structure and a portion of the layered structure  204 . For example, the anisotropic etching may be conducted using a directional physical etching processes such as ion beam etching (also referred to as ion milling) or anisotropic reactive ion etching (RIE). It is to be appreciated, however, that alternatively any other suitable etching process may be used which may not necessarily be anisotropic. For example, a chemical etching process may be used. Many chemical etching processes are known and the person skilled in the art will appreciate that the suitability of a particular chemical etching process depends on the material of the layer layered structure and dimensions and shape of the lenses that are etched into the layered structure.  
         [0017]     In a variation of this embodiment the shape of the structure may be selected so that only a portion of the lens is formed in the layered structure. In this case the etching typically does not remove the entire imprinted structure but a portion of the imprinted structure remains and forms a part of the lens array.  
         [0018]      FIG. 2 ( d ) shows a cross-sectional view of one Fresnel lens which is exemplary for the lenses of the lens array. The shown Fresnel lens  216  includes stacks  218  of concentric-rings. In this embodiment each stack  218  includes three concentric rings  220 ,  222  and  224  which are formed from respective layers of the layered structure  204 . In this example the materials of the layered structure  204  are selected so that the layer  220  has a refractive index that is lower than that of the layer  222 . Further, the materials of the layered structure  204  are selected so that the layer  222  has a refractive index that is lower than that of the layer  224 .  
         [0019]     The method  100  has the advantage that a lens having aligned layers, such as stacks  220 ,  222  and  224 , or an array of such lenses can be fabricated in a simplified manner. The combination of imprinting the structure  210  into the deformable material  206  and the subsequent etching make it possible to fabricate a lens having such aligned layers without separate processing steps in which the layers are aligned relatively to each other.  
         [0020]     The method  100  further includes the step  110  of fabricating a display which includes fabricating the array of Fresnel lenses as described above. It is to be appreciated by the person skilled in the art that the fabricated lens array may be incorporated into many types of displays. Once the array has been fabricated, known fabrication steps may follow to fabricate the display. Further, it is to be appreciated that the display may include an array of the lens  216  which are fabricated in accordance with an embodiment of the method  100 .  
         [0021]     The base material  202  may be formed from a hard material but typically is formed from a flexible material such as a polymeric material that is optically transmissive. The concentric rings  220 ,  222  and  224  are also composed of optically transmissive polymeric materials and have respective refractive indices as described above.  
         [0022]     The method  100  is described in the context of fabrication of a lens array. It is to be appreciated by the person skilled in the art, however, that a variation of the method  100  may be not necessarily fabricate a lens array, but may fabricate a plurality of lenses which may form any suitable arrangement. Further, the arrangement may include any number of lenses and in one specific variation of the method  100  only one lens may be fabricated.  
         [0023]     Referring now to  FIGS. 3 and 4 , a method of fabricating at least one lens according to a further embodiment is now described. Method  400  includes step  402  of depositing an electrically insulating layer on a conducting base material and an electrically conductive layer on the electrically insulating layer. In this embodiment the electrically insulating layer is composed of silica or another suitable insulating material and the electrically conductive layers are metallic.  
         [0024]     Step  404  coats the exposed electrically conductive layer with a deformable surface coating. Again, the deformable surface coating may include a polymeric material that is curable using UV radiation.  
         [0025]     Step  406  imprints a structure into the deformable surface coating. The imprinted structure is then cured using UV radiation. In this embodiment the structure has a shape that is associated with that of an array of electron lenses and electron emitters. Each lens of the array is in this example an electrostatic electron lens having respective electrodes. It is to be appreciated that in variations of this embodiment the structure may only be associated with the shape of the electron lenses and not with the shape of the electron emitters. For example, a variation of the method  400  may only fabricate the electron lenses and the electron emitters may be fabricated separately.  
         [0026]      FIG. 3 ( a ) shows the conductive base material  302  coated with electrically insulating layer  303 , electrically conductive layer  304  and a surface coating of deformable material  306 .  FIG. 3 ( b ) shows a stamp  308  during the process of imprinting the structure  310  and  311  into the deformable material  306 . The stamp  308  is removed after imprinting the structure  310 .  FIG. 3 ( c ) shows the base material  302  with the layers  303  and  304  after the stamp  308  has been removed and the structure  310  and  311  is exposed.  
         [0027]     Step  408  etches the imprinted structure and a region of the layers and the base material to form the array of electrodes in the electrically conductive layer and corresponding electron emitters in the base material. In this embodiment the etching is anisotropic and is performed in the same manner as described above in the context of method  100 .  
         [0028]      FIG. 3 ( d ) show a cross-sectional representation of the formed electron lens array  314 . The lens array  314  includes conductive base material  318  in which electron emitters  320  were formed, insulating layers  322  and conductive layers  324  which form electrodes of each electron lens. In this embodiment the insulating layers  322  and the conductive layers  324  form concentric rings positioned around respective electron emitters  320 .  
         [0029]     The array of electron lenses  314  may include a few electron lenses, but typically includes a relatively large number of electron lenses such as more than 1000 electron lenses. The method  400  is described in the context of fabrication of a lens array. It is to be appreciated by the person skilled in the art, however, that a variation of the method  400  may be not necessarily fabricate a lens array, but may fabricate a plurality of lenses which may form any suitable arrangement. Further, the arrangement may include any number of lenses, with or without electron emitters, and in one specific variation of the method  400  only one lens may be fabricated.  
         [0030]     Although the embodiments have been described with reference to particular examples, it is to be appreciated by those skilled in the art that the embodiments may take other forms. For example, the Fresnel lens array may be formed from a material other than a polymeric material. Further, the Fresnel lens array may include any number of concentric rings each being formed from a stack of aligned layers. Each concentric ring may also be formed from only one layer. In addition, it is to be appreciated that only one specific design of the electron lens array has been described and various other designs may be fabricated in variations of the method  400 .