Abstract:
A liquid crystal over silicon light modulator may include a trenched cover glass. The trenched cover glass enables the provision of regions between adjacent dice on the wafer level. These regions facilitate sealing of the individual modulators and dicing of the individual modulators from the overall wafer. In some embodiments this may reduce contamination of the liquid crystal with the sealing material and losses at the dicing stage.

Description:
BACKGROUND 
   This invention relates generally to light modulation devices. 
   A silicon light modulator is an electro-optical device with a liquid crystal material driven by electronics located under each pixel. High resolution, very large scale integration silicon light modulation devices have practical applications, including rear projection television light engines, computer monitors, and direct view personal viewing devices, to mention a few examples. 
   Actuation of individual pixel elements in a liquid crystal on silicon microdisplay is accomplished by modulation of the electric field applied to the liquid crystal material in the gap between a pixel electrode and a common electrode. Control of the gap between the pixel and common electrode is critical to electro-optical performance. 
   Existing modulators suffer from high assembly losses in the dicing step, liquid crystal contamination by sealing epoxy, and losses in the wire bond attach step. 
   Thus, there is a need for alternate ways of forming liquid crystal on silicon light modulators. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an enlarged, cross-sectional view of one embodiment of the present invention; 
       FIG. 2  is an enlarged, cross-sectional view of a top plate at the wafer level in accordance with one embodiment of the present invention; 
       FIG. 3  is an enlarged, cross-sectional view of the bottom plate at the wafer level in accordance with one embodiment of the present invention; 
       FIG. 4  is an enlarged, cross-sectional view of the assembly of top and bottom plates in accordance with one embodiment of the present invention; 
       FIG. 5  is an enlarged, cross-sectional view of the attachment of top and bottom plates in accordance with one embodiment of the present invention; 
       FIG. 6  is an enlarged, cross-sectional view of filling one embodiment of the present invention; 
       FIG. 7  is an enlarged, cross-sectional view of sealing one embodiment of the present invention; 
       FIG. 8  is an enlarged, cross-sectional view of dicing one embodiment of the present invention; 
       FIG. 9  is an enlarged, cross-sectional view showing the result of dicing in accordance with one embodiment of the present invention; 
       FIG. 10  is an enlarged, cross-sectional view showing wafer probing in accordance with one embodiment of the present invention; 
       FIG. 11  is an enlarged, cross-sectional view showing wafer dicing in accordance with one embodiment of the present invention; 
       FIG. 12  is one embodiment of the unpackaged modulator in accordance with one embodiment of the present invention; 
       FIG. 13  is an enlarged, cross-sectional view of packaging one embodiment of the present invention; and 
       FIG. 14  is an enlarged, cross-sectional view of the embodiment shown in  FIG. 13  after further processing. 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1 , a liquid crystal on silicon (LCOS) microdisplay silicon light modulator  10  includes a packaging surface  12 , a silicon substrate  14 , a wire bond pad  18 , a conductive epoxy  20 , an indium tin oxide (ITO) coated glass  22 , a wire  24 , a wire bond pad  26 , and another wire bond pad  28  on the silicon substrate  14 . A potting compound  21  protects the wire bonds  24 . A plurality of pixel electrodes  30  are formed on the silicon substrate  14 . A liquid crystal material  32  is trapped between the glass  22 , the silicon substrate  14 , the end-most spacers  34 , and the sealing epoxy gasket  38 . A layer of transparent conductive material  36 , such as indium tin oxide (ITO) is formed on the glass  22 . A fill hole  40  is provided for filling the modulator  10  with liquid crystal material  32  and a seal  42  is provided to prevent outflow of liquid crystal material. 
   Circuitry in the silicon substrate  14  selectively operates the electrodes  30  to actuate particular cells between electrode  30  and the overlying electrode  32 . As a result of electrical actuation, different images can be visible through the glass  22 . 
   Fabrication of the modulator  10  may begin by forming, on a wafer scale, a grooved cover glass  22  coated with indium tin oxide  36 . Grooves  48  are formed at periodic intervals to separate out of the wafer, one adjacent modulator  10  from the next. Filling holes  44  are provided along the length of the glass  22 . 
   The silicon substrate  14 , shown in  FIG. 3 , in wafer form, may include a plurality of pixel electrodes  30  and integrated spacers  36  formed thereon. The spacers  36  define the cell size between the silicon substrate  14  and the cover glass  22 . Certain spacers  36  are covered in a sealing epoxy ball  38 . 
   Referring now to  FIG. 4 , the cover glass  22 , on a wafer scale, may be positioned on the wafer scale substrate  14 . The grooves  48  line up with the sealing epoxy gasket  38  covered spacers  36 . 
   As shown in  FIG. 5 , the cover glass  22  may subsequently be adhesively secured to the substrate  14  through the sealing epoxy gasket  38  and integrated spacers  36 . Upon assembly, the regions between successive grooves  48  are effectively sealed from the grooves  48  and from adjacent modulators by the end spacer  36   a  and the epoxy ball  38  thereon. 
   The entire structure, on the wafer scale, is then filled through the openings  44  by injecting liquid crystal material  32  into the sealed region between adjacent grooves  48 . Thereafter, as shown in  FIG. 7 , the openings  44  may be closed with a sealant  42 . 
   Next, individual modulators  10  may be diced from the wafer using the dicing apparatus indicated at B in  FIG. 8 . The dicing is done into the grooved regions  48  between modulators  10 . The use of the grooved regions  48  provides for alignment and ready location of the dicing location to avoid damaging the individual modulators. In particular, the provision of what now appears to be an upstanding surface feature enables easy location of the dicing area and provides room for dicing without damaging components. 
   As a result, segregated modulators  10  may be formed by a dicing hole  50 , shown in  FIG. 9 , between adjacent modulators  10 . An electrode  52  is now exposed between adjacent modulators  10 . The electrode  52  may be accessed by a probing tool C for probe level testing of the devices  10  before packaging, as shown in  FIG. 10 . Bad die may be appropriately marked to prevent further application and use. 
   Subsequently, the individual dies are separated from the rest of the silicon substrate  14 , as shown in FIG.  11 , using a dicing tool D. The resulting die  54  is shown in  FIG. 12 . 
   The die  54  may then be placed on a packaging surface  12  as shown in  FIG. 13 . The surface  12  may have already formed thereon the wire bond pads  18  and  26 . As shown in  FIG. 14 , a conductive epoxy  20  couples the pad  18  to the indium tin oxide layer  36 . A wire bond  24  may be applied from the pad  28  on the substrate  14  to the pad  26  on the packaging surface  12 . Thereafter, the wire bond  24  may be potted with material  21  to achieve the structure shown in  FIG. 1 . 
   In accordance with some embodiments of the present invention, losses in the dicing step may be reduced by providing the trenched structure in the glass plate  22 . Contamination of the liquid crystal material  32  by the sealing epoxy gasket  38  may be reduced by placing the sealing epoxy gasket  38  outbound of the sealed region that includes the liquid crystal material  32 . Losses in the wire bond attach step may be reduced by enabling early testability in some embodiments of the present invention. 
   While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.