Abstract:
A method of forming a micro-display includes forming a device that includes forming a partially reflecting layer on a first substrate and forming a plate overlying the partially reflecting layer, and adhering the device to a second substrate.

Description:
CLAIM OF PRIORITY 
   This application claims the benefit of U.S. Provisional Application No. 60/621,176, filed on Oct. 21, 2004, entitled MICRO-DISPLAYS AND THEIR MANUFACTURE, and having express mail label number EL871865948 US. 

   BACKGROUND 
   Digital projectors often include micro-displays that include arrays of pixels (e.g., 1280×1024, etc.) Each pixel usually includes a micro-electromechanical system (MEMS) device, such as a micro-mirror, liquid crystal on silicon (LcoS) device, interference-based modulator, etc. A micro-display is used with a light source and projection lens of the digital projector. The micro-display receives light from the light source. When the pixels of the micro-display are ON, the pixels direct the light to the projection lens. When the pixels are OFF, they direct the light from the light source away from the projection lens. The projection lens images and magnifies the micro-display. 
   Micro-displays are usually formed using semiconductor-processing methods that include forming electronic driver circuits on a semiconductor substrate for driving the MEMS devices of the pixels. The electronic driver circuits are often Complementary Metal Oxide Semiconductor (CMOS) devices. After forming the electronic driver circuits, the MEMS devices are formed overlying the electronic driver circuits and a transparent, e.g., glass, cover is formed overlying the MEMS devices for packaging, e.g., sealing and/or protecting, the MEMS devices and the electronic driver circuits. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic of an embodiment of a micro-display, according to an embodiment of the disclosure. 
       FIGS. 2A-2L  are cross-sections of a portion of an embodiment of a micro display at various stages of fabrication, according to another embodiment of the disclosure. 
   

   DETAILED DESCRIPTION 
   In the following detailed description of the present embodiments, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments that may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice disclosed subject matter, and it is to be understood that other embodiments may be utilized and that process, electrical or mechanical changes may be made without departing from the scope of the claimed subject matter. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the claimed subject matter is defined only by the appended claims and equivalents thereof. 
     FIG. 1  is a schematic of a micro-display  100 , e.g., as a portion of a digital projector, according to an embodiment. For one embodiment, micro-display  100  functions as a light modulator of the digital projector. For another embodiment, micro-display  100  includes a device  102  and a driver  104 . For some embodiments, device  102  includes one or more micro-electromechanical system (MEMS) devices  111 , such as micro-mirrors, liquid crystal on silicon (LcoS) devices, interference-based modulators, etc. For other embodiments, device  102  and driver  104  are formed separately and are subsequently bonded together. 
   For one embodiment, device  102  includes a substrate  106 , such as a transparent cover, e.g., of glass. For another embodiment, a transparent layer  108 , e.g., of TEOS (tetraethylorthosilicate) oxide, silicon oxide, etc., is formed on substrate  106 . A partially reflecting layer  110 , e.g., a tantalum-aluminum (TaAl) layer, is formed on transparent layer  108 . For other embodiments, partially reflecting layer  110  may be formed directly on substrate  106 . For other embodiments, partially reflecting layer  110  forms a first capacitor plate of device  102 . 
   Device  102  also includes pixel plates  112 , e.g., as a portion of the MEMS devices  111 , that are suspended by flexures  120  within a gap  114  located between partially reflecting layer  110  and a protective layer  116 , e.g., of TEOS (tetraethylorthosilicate) oxide, silicon oxide, etc. Specifically, a first gap portion  114 , of gap  114  separates a pixel plate  112  from partially reflecting layer  110 , and a second gap portion  114   2  of gap  114  separates a pixel plate  112  from protective layer  116 . For one embodiment, pixel plates  112  form second capacitor plates of device  102 . 
   Flexures  120  electrically connect their respective pixel plates to one or more signal posts  122  that terminate at signal contacts  124  formed on protective layer  116 . For one embodiment, pixel plates  112  are of a aluminum-copper (AlCu) alloy that acts like a mirror. For another embodiment, pixel plates  112  include a layer of TaAl formed on a layer of AlCu, where the AlCu layer faces partially reflecting layer  110 . 
   For one embodiment, a bond ring  126  is electrically connected to partially reflecting layer  110  and terminates at ground contacts  128  formed on protective layer  116 . For some embodiments, bond ring  126  also provides support between substrate  106  and protective layer  116 . For another embodiment, ground posts  127  are also electrically connected to partially reflecting layer  110  and terminate at ground contacts  129  formed on protective layer  116 . Ground posts  127  may also provide support between substrate  106  and protective layer  116 , for some embodiments. 
   For one embodiment, driver  104  is Complementary Metal Oxide Semiconductor (CMOS) substrate. Driver  104  can be formed using semiconductor-processing methods known to those skilled in the art. Driver  104  includes driver circuits  130  adapted to respectively control the positions of pixel plates  112  and thus the corresponding gaps  114 . Each of driver circuits  130  is connected between a signal supply line  132  and a ground line  136 . Signal supply line  132  terminates at a signal contact  134  formed in a protective layer  135 , e.g., of TEOS (tetraethylorthosilicate) oxide, silicon oxide, etc. Ground line  136  is connected between a main ground line  137  and a ground contact  138  formed in protective layer  135 . 
   Driver  104  is electrically connected to device  102 , for one embodiment, by bonding ground contacts  129  to ground contacts  138  to connect ground posts  127 , and thus partially reflecting layer  110 , to ground, and by bonding signal contacts  124  to signal contacts  134  to connect driver circuits  130  to signal posts  122  and thus to pixel plates  112 . For another embodiment, main ground line  137  may also be separately connected to ground contacts  128  by bonding ground contacts  128  to ground contacts  140  formed in protective layer  135  and connected to main ground line  137 . This connects seal ring  126 , and thus further connects partially reflecting layer  110 , to ground. For another embodiment, the contacts may be soldered together. For other embodiments, protective layers  116  and  135  are bonded together using plasma-enhanced bonding so that the contacts abut each other. 
   For another embodiment, ground posts  127  and/or bond ring  126 , signal posts  122 , pixel plates  112 , and flexures  120  are formed as a part of driver  104  using semiconductor-processing methods. For this embodiment, partially reflecting layer  110  is formed on substrate  106 , e.g., by chemical vapor deposition. Partially reflecting layer  110  is then bonded, e.g., by gluing, plasma-enhanced bonding, or the like, to ground posts  127  and/or bond ring  126 . This acts to reduce the number of processing steps compared to where transparent layer  108  is disposed on the substrate  106  prior to partially reflecting layer  110 , as discussed above and shown in  FIG. 1 . 
   In operation, driver circuits  130  respectively send signals via signal lines  132 , signal posts  122 , and flexures  120  to pixel plates  112 . This creates potentials between partially reflecting layer  110  and the respective pixel plates  112  that deflect the respective pixel plates  112  and thus change the corresponding gap portions  114   1 . 
   Light, e.g., from a light source of a projector, passes through substrate  106  and through transparent layer  108 . Partially reflecting plate  110  passes a portion of the light onto pixel plates  112  and reflects a portion of the light back through transparent layer  108  and substrate  106 . The pixel plates  112  reflect the light back to partially reflecting plate  110 , which passes some of the light through transparent layer  108  and substrate  106  and reflects a portion of the light back to pixel plates  112  and the process repeats. That is, multiple reflections occur between the pixel plates  112  and partially reflecting layer  110 , with some of the reflected light passing through partially reflecting layer  110  and through substrate  106 . This produces optical interference that can be tuned using the gap portions  114   1 . 
     FIGS. 2A-2L  are cross-sections of a portion of a device  200  at various stages of fabrication, according to another embodiment. The device  200  includes a first substrate  206 , such as an insulator, transparent cover, e.g., of glass, etc., as shown in  FIG. 2A . For one embodiment, a transparent layer  208  is formed on first substrate  206  and a partially reflecting layer  210  is formed on transparent layer  208  and is patterned and etched to expose portions of transparent layer  208 . For another embodiment, partially reflecting layer  210  is formed directly on first substrate  206 . In  FIG. 2B , a first sacrificial layer  211  (distinguished by cross-hatching) is formed on partially reflecting layer  210  and for one embodiment is patterned and etched to expose the exposed portions of transparent layer  208  and portions of partially reflecting layer  210 . For one embodiment, the first sacrificial layer  211  may be smoothed and/or flattened prior to patterning and etching using chemical mechanical polishing (CMP). The first sacrificial layer  211  will form a portion of a gap, such as a gap portion  114   1  of  FIG. 1 , between a pixel plate, such as a pixel plate  112  of  FIG. 1 , and partially reflecting layer  210 . 
   A first metal layer  213 , e.g., a layer of TaAl or a layer of TaAl formed on a layer of AlCu is formed on the first sacrificial layer  211  and on the exposed portions of transparent layer  208  and partially reflecting layer  210  in  FIG. 2C . The first metal layer  213  is patterned and etched to define a pixel plate  212 , first portions of ground posts  227 , and signal posts  222  and to expose portions of the first sacrificial layer  211  in  FIG. 2D . Note that the pixel plate  212  contacts the sacrificial layer  211 , the ground posts  227  contact the exposed portions of partially reflecting layer  210 , and the signal posts  222  contact transparent layer  208 , or for embodiments without transparent layer  208 , first substrate  206 . 
   A second sacrificial layer  231  (distinguished by cross-hatching) is formed on the first metal layer  213 , i.e., on pixel plate  212 , ground posts  227 , and signal posts  222 , and on the exposed portions of the first sacrificial layer  211  in  FIG. 2E . The second sacrificial layer  231  is patterned and etched to expose portions of pixel plate  212  and to expose ground posts  227  and signal posts  222 . For one embodiment, the second sacrificial layer  231  may be smoothed and/or flattened prior to patterning and etching using CMP. 
   A second metal layer  233 , e.g., of TaAl, is formed on the second sacrificial layer  231 , on the exposed portions of pixel plate  212 , and on the exposed ground posts  227  and signal posts  222  in  FIG. 2F . The second metal layer  233  is patterned and etched to form flexures  220  and second portions of ground posts  227  and to expose portions of the second sacrificial layer  231  in  FIG. 2G . Note that flexures  220  electrically and physically connect signal posts  222  to the exposed portions of pixel plate  212 . Note further that flexures  220  directly overlie pixel plate  212 , meaning that when the device  200  is inverted and connected to a second substrate, such as driver  104 , as shown in  FIG. 1 , flexures  220  will be located under the pixel plate  212 . That is, flexures  220  are aligned behind pixel plate  212  so that pixel plate  212  obstructs flexures  220  from being viewed through cover  206 . This helps to conserve device real estate. 
   A third sacrificial layer  261  (distinguished by cross-hatching) is formed on flexures  220 , ground posts  227 , and the exposed portions of the second sacrificial layer  231  and is patterned and etched to expose portions of flexures  220  and ground posts  227  in  FIG. 2H . For one embodiment, the third sacrificial layer  261  may be smoothed and/or flattened prior to patterning and etching using CMP. A third metal layer  264 , e.g., AlCu, TaAl, or the like, is formed on the third sacrificial layer  261  and on the exposed portions of flexures  220  and on ground posts  227  in  FIG. 2I . The third metal layer  264  is patterned and etched to form ground contacts  229  in physical and electrical contact with ground posts  227  and signal contacts  224  in physical and electrical contact with flexures  220  and to expose portions of the third sacrificial layer  261  in  FIG. 2J . Alternatively, for another embodiment, CMP forms the ground contacts  229 . 
   A protective layer  216 , e.g., of TEOS (tetraethylorthosilicate) oxide, silicon oxide, etc., is formed on the exposed portions of the third sacrificial layer  261  and on ground contacts  229  and signal contacts  224  and is patterned and etched to expose portions of the third sacrificial layer  261  and ground contacts  229  and signal contacts  224  in  FIG. 2K . For one embodiment, CMP follows patterning and etching to smooth and flatten protective layer  216  and ground contacts  229  and signal contacts  224  so that ground contacts  229  and signal contacts  224  are substantially flush with protective layer  216 . For another embodiment, CMP may be used to expose the portions of the third sacrificial layer  261  and ground contacts  229  and signal contacts  224 . 
   The first sacrificial layer  211 , the second sacrificial layer  231 , and the third sacrificial layer  261  are removed in  FIG. 2L  to form the portion of the device  200  that includes a gap  214 , as indicated by removal of the cross-hatching. Gap  214  contains pixel plate  212  and flexures  220 . Note that removal of the first sacrificial layer  211  forms a first gap portion  214   1  between pixel plate  212  and partially reflecting layer  210 . Removal of the second sacrificial layer  231  and the third sacrificial layer  261  forms a second gap portion  214   2  between pixel plate  212  and protective layer  216 . Note that flexures  220  are contained within the second gap portion  214   2 . Flexures  220  support pixel plate  212  within gap  214  and provide a restoring force against which pixel plate  212  returns from an electrostatic actuation driving force applied to pixel plate  212  for some embodiments. 
   The device is inverted and bonded to the second substrate, such as driver  104  of  FIG. 1 . This electrically connects signal contacts  224  to a signal line of the second substrate, such as a signal line  132  of a driver circuit  130  of driver  104 . Ground contacts  229  are connected to a ground line of the second substrate, such as ground line  136  of driver  104 . Note that partially reflecting layer  210  is at a ground state and acts as a first capacitor plate. When electrical signals are applied to pixel plate  212 , via signal contacts  224  and flexures  220 , pixel plate  212  acts as a second capacitor plate and moves within gap  214  against the restoring force provided by flexures  220 . This regulates the size of gap portion  214   1 . 
   It will be appreciated that the bond ring  126  of device  102  of  FIG. 1  may be formed, for one embodiment, as described above for ground posts  227 . 
   CONCLUSION 
   Although specific embodiments have been illustrated and described herein it is manifestly intended that the scope of the claimed subject matter be limited only by the following claims and equivalents thereof.