Abstract:
A product comprising a micromirror comprising a reflective layer and a treatment layer overlying the reflective layer, and wherein the treatment layer comprises Ti.

Description:
FIELD OF THE INVENTION 
   This invention relates to micromirrors and products using the same, and more particularly to micromirrors, digital micromirror devices and projection systems. 
   BACKGROUND OF THE INVENTION 
   New advancements in projection systems utilize an optical semiconductor known as a digital micromirror device. A digital micrometer device chip may be the world&#39;s most sophisticated light switch. It contains an array from 750,000 to 1.3 million pivotally mounted microscopic mirrors. Each mirror many measure less than ⅕ of the width of a human hair and corresponds to one pixel in a projected image. The digital micromirror device chip can be combined with a digital video are graphic signal, a light source, and a projector lens so that the micromirrors reflect an all-digital image onto a screen or onto another surface. 
   Although there are variety of digital micromirror device configurations, typically micromirror are mounted on tiny hinges that enable each mirror to be tilted either toward the light source (on) in a projector system to reflect the light or away from the light source (off) creating a darker pixel on the projection surface. A bitstream to image code entering the semiconductor directs each mirror to switch on or off after several times per second. When the mirror is switched on more frequently than off the mirror reflects a light gray pixel. When the mirror is switched off more frequently than on the mirror reflects a darker gray pixel. Some projection systems can deflect pixels enough to generate 1024 shades of gray to convert the video are graphic signal entering the digital micromirror device into a highly detailed grayscale image. In some systems, light generated by a lamp passes through a color wheel as it travels to the surface of the digital micromirror device panel. The color wheel filters to light into red, green and blue. A single chip digital micromirror vice projector systems can create at least 16.7 million colors. When three digital micromirror device chips are utilized, more than 35 trillion colors can be produced. The on and off states of each micromirror are coordinated with the three basic building blocks of color, red, green and blue to produce a wide variety of colors. 
   Huibers et al U.S. Pat. No. 6,396,619 B1 discloses a deflectable spatial light modulator including a mirror plate that is substantially ridge and may be made up of a laminate having layers of silicon nitride and aluminum. In one embodiment, the mirror laminate may include a layer of aluminum sandwiched by two layers of silicon nitride. In other embodiments, include only a layer of aluminum and a layer of silicon nitride. Multi-layer arrangements with multiple layers of aluminum and/or silicon nitride are disclosed. The reference states that other materials besides aluminum (such as conductive and reflective metals) could be used. Other materials besides silicon nitride, such as silicon dioxide are also disclosed. The reference discloses that the silicon nitride layer may be 1400 Å thick and that the aluminum layer may be 700 Å thick. Disclosed also are one or more dielectric films, that act as a reflective coating, may be deposited on the mirror laminate to improve reflectivity. 
   A variety of digital micromirror devices (DMD) are known.  FIG. 1  illustrates one embodiment of a prior art DMD that may be used in the present invention with the substitution of a unique mirror structure according to the present invention. As shown in  FIG. 1 , a DMD  10  may include a semiconductor device  12  such as a CMOS memory device that includes circuitry  13  that is used to activate an electrode(s) in response to a video or graphic signal. A first layer  14  is formed over the semiconductor device  12  and may include a yoke address electrode  16 , and vias  18  formed therein down to the circuitry  13  on the semiconductor device  12 , and a bias-reset bus  20 . A second layer  22  is formed over the first layer  14  and may include a yoke  24  torsion hinge  26  and mirror address electrodes  28 . A micromirror  32  is formed over the second layer  22  and positioned so that the micromirror  32  may be deflected diagonally when one of the electrodes  28  is activate by the semiconductor device  12 . The micromirror include a reflective layer typically including aluminum. The DMD  10  shown in  FIG. 1  while being an excellent engineering accomplishment is very complex, costly to manufacture and has low manufacturing yield. Further, the micromirror  32  may include defects as will be describe hereafter with respect to a second configuration of a DMD. 
     FIG. 2  illustrates a first subassembly  40  for a second type of DMD. The subassembly  40  may include a transparent layer  42  which may be any transparent material including, but not limited to, glass. A hinge  44  is formed on the transparent layer  44  and a micromirror  32  is secured thereto for pivotal movement with respect to the hinge  44  and the transparent layer  42 . 
     FIG. 3  illustrates the first subassembly  40  including a plurality of micromirrors  32  each connected by a hinge  44  to the transparent layer  42 . All of the component and subassemblies of the various DMD devices can be made by semiconductor or MEM micro processing techniques known to those skilled in the art. 
     FIG. 4  illustrates a second subassembly  46  of the second type of DMD and may include a semiconductor device  12  such as, but not limited to, a CMOS memory device. A plurality of electrodes  48 , one for each micromirror  32  are formed over the semiconductor device  12  for communication with the circuitry (not shown) contained therein so that the electrode  48  may be selectively activated in response to a video or graphic signal. 
     FIG. 5  illustrates a DMD structure  10  that may be utilized by the present invention with the substitution of a unique micromirror according to the present invention. The DMD of FIG.  5  includes the first subassembly  40  flipped over and overlying the second subassembly  46  so the micromirrors  32  of the first subassembly  40  face and are closest to the electrodes  48  of the second subassembly  46 . Spacers  50  are provided to position so that the micromirrors  32  are spaced a distance from the electrodes  48  and so that micromirror  32  is free to be defected or pivotally moved by the activation of an associated electrode  48 . As illustrated in  FIG. 5 , when light is director on to the micromirrors  32 , an electrode  48  associated with for each micromirror  32  may be activated cause the micromirror to pivotally move about the hinge  44 . As a result, the light will be reflected or not depending on whether the electrode  48  associated with the micromirror  32  has be activated or not. As described above, depending on how fast and often a particular micromirror  32  is deflected by the electrode  48 , the image projected by the micromirror  32  (pixel) will appear light or dark on the projection screen or other surface. 
   However, prior art micromirror structures often were troubled by the present of hillocks (raised features or bumps)  54  or voids  52  in the aluminum layer as shown in  FIGS. 6 and 7 . Typically the micromirror  32  include a sputtered on aluminum coating which may often include hillocks (raised features or bumps)  54  or voids  52 . The hillocks  54  or voids  52  can cause artifacts or distortions in the projected image. 
   The present invention provides alternatives to and improvements over the micromirror, DMD and projection systems of the prior art. 
   SUMMARY OF THE INVENTION 
   One embodiment of the invention includes a product comprising a micromirror comprising a reflective layer and a treatment layer overlying the reflective layer, and wherein the treatment layer comprises Ti. 
   One embodiment of the invention includes a product including a micromirror wherein the treatment layer comprises TiN. 
   One embodiment of the invention includes a product including a micromirror wherein the reflective layer comprises at least one of aluminum and silver. 
   One embodiment of the invention includes a product including a micromirror wherein the reflective layer includes hillocks. 
   One embodiment of the invention includes a product including a micromirror wherein the reflective layer includes voids. 
   One embodiment of the invention includes a product including a micromirror wherein the reflective layer comprises Al, Si and Cu. 
   One embodiment of the invention includes a product including a micromirror wherein the treatment layer is 20–200 Å thick. 
   One embodiment of the invention includes a product including a micromirror wherein the treatment layer is 40–60 Å thick. 
   One embodiment of the invention includes a product including a micromirror and further comprising a first protective layer, and wherein the reflective layer overlies the first protective layer. 
   One embodiment of the invention includes a product including a micromirror wherein the first protective layer comprises silicon oxide. 
   One embodiment of the invention includes a product including a micromirror wherein the first protect layer comprise plasma enhanced silicon oxide. 
   One embodiment of the invention includes a product including a micromirror wherein and further comprising a second protective layer, and wherein the second protective layer overlies the treatment layer. 
   One embodiment of the invention includes a product including a micromirror wherein the second protective layer comprises silicon oxide. 
   One embodiment of the invention includes a product including a micromirror wherein the second protective layer comprises plasma enhanced silicon oxide. 
   One embodiment of the invention includes a product including a micromirror wherein the thickness of the second protective layer ranges from about 200 to about 1000 Å. 
   One embodiment of the invention includes a product including a micromirror wherein the thickness of the second protective layer ranges from about 200 to about 600 Å. 
   One embodiment of the invention includes a product including a micromirror wherein the thickness of the second protective layer ranges from about 400 to about 600 Å. 
   One embodiment of the invention includes a product including a micromirror and further comprising a semiconductor device, an electrode and a hinge, and wherein the micromirror is connected to the hinge for pivotal movement thereabout when the electrode is activated by the semiconductor device. 
   One embodiment of the invention includes a product comprising a micromirror comprising a reflective layer and a first protective layer overlying a first face of the reflective layer and a second protective layer overlying a second face of the reflective layer, and wherein the second protective layer comprises plasma enhance silicon dioxide having a thickness ranging from 200–1000 Å. 
   These and other embodiments of the present invention will become apparent from the following brief description of the drawings, detailed description of the preferred embodiments, and appended claims and drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded view of a prior art digital micromirror device in which a micromirror according to the present invention may be incorporated. 
       FIG. 2  illustrates a prior art digital micromirror device subassembly in which a micromirror according to the present invention may be incorporated. 
       FIG. 3  illustrates a prior art digital micromirror device subassembly in which a micromirror according to the present invention may be incorporated. 
       FIG. 4  illustrates a prior art digital micromirror device subassembly. 
       FIG. 5  is an exploded view of a prior art digital micromirror device in which a micromirror according to the present invention may be incorporated. 
       FIG. 6  illustrates a prior art micromirror having hillocks and voids. 
       FIG. 7  illustrates a prior art micromirror having hillocks and voids. 
       FIG. 8  illustrates a micromirror structure according to the present invention. 
       FIG. 9  is a graphic representation of the reflectance spectra of various micromirror films including a micromirror according to the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 8  illustrates a micromirror structure  100  according to the present invention. In one embodiment a micromirror  100  may include a first protective layer  56  which may be any known protective layer including, but not limited to, silicon nitride or silicon oxide or silicon oxynitride. In one embodiment, the first protective layer  56  includes plasma enhanced silicon oxide or silicon oxide. The first protective layer  56  may be present in any thickness including a thickness ranging from 200–600 Å. 
   The micromirror  100  may include a reflective layer  58  overlying the first protective layer  56 . As used herein the description of a first layer “overlying” or “overlies” (or similar language) a second layer means that the first layer may be in direct contact with the second layer or that additional layers may be interposed between the first and second layers. The reflective layer  58  includes a light reflecting material such as, but not limited to, at least of aluminum or silver. In one embodiment the reflective layer  58  may be 2000–4000 Å (angstroms) thick, and preferably 2400–3000 Å thick and most preferably 2500 Å thick. In one embodiment the reflective layer  58  includes aluminum, silicon and copper. In another embodiment the reflective layer  58  includes 98.5 weight percent aluminum, 1 weight percent silicon and 0.5 weight percent copper. The reflective layer  58  may be formed by any method known to those skilled in the art, including screen printing, chemical vapor deposition, by securing a foil to the first protective layer  56 , but preferably is formed by sputtering a reflective material onto the first protective layer  56  or onto another surface from which the reflective layer  58  can be removed. 
   The micromirror  100  may include a treatment layer  60  overlying the reflective layer  58 . The treatment layer  60  include a material formed to a thickness sufficient to effectively eliminate or substantially reduce the effective number of hillocks and voids in the reflective layer  58  thereby reducing the number of artifacts and distorts produced in the projected image from the micromirror  100 . Preferably the treatment layer  60  comprises at least one of Ti or TiN. The treatment layer  60  may be formed by any method known to those skilled in the art but preferably is sputtered onto the reflective layer  58  or onto a layer overlying the reflective layer  58 . The treatment layer  60  may be present in any thickness including but not limited to 20–200 Å and preferably 40–60 Å and most preferably 50 Å thick. The treatment layer  60  may also provide stress relief or lubricating functions. 
   A second protective layer  62  may overlie the treatment layer  60 . The second protective layer  62  may include but is not limited to silicon nitride, silicon oxide or silicon oxynitride. Preferably the second protective layer  62  is silicon oxide deposited by plasma enhanced methods to a thickness ranging from 200–1000 Å, preferably 200–600 Å and most preferably 400 Å thick. When the second protective layer  62  is PEOX (plasma enhanced silicon oxide) the micromirror has an improve reflectance compared to just the treatment layer  60  being present. 
     FIG. 9  is a graphic representation of the reflectance of a variety of films. Line  102  illustrates the reflectance of a AlSiCu film without a protective coating. Line  104  illustrates the reflectance of a AlSiCu film with a 1000 Å thick PEOX protective film. Line  106  illustrates the reflectance of a AlSiCu film with a 400 Å thick PEOX protective film. Line  108  illustrates the reflectance of a AlSiCu film with a 1000 Å thick SiN protective film. Line  110  illustrates the reflectance of a AlSiCu film with a 400 Å thick SiN protective film. Line  112  illustrates the reflectance of a AlSiCu film with a 50 Å thick Ti coating thereon. A protective coating of PEOX can retain 90 percent of the reflectance of a film. 
   The micromirror  100  may be substituted for the micromirror  32  shown in  FIGS. 1 and 2  to create a DMD according to the present invention. The micromirror  100  may also be substituted for the micromirror shown in Huibers et al, U.S. Pat. No. 6,396,619 issued May 28, 2002, the disclosure of which is hereby incorporated by reference, to create a DMD according to the present invention