Abstract:
The invention provides a method for fabricating an optical device comprising at least one optical component formed on a transparent substrate. The method comprises determining an area of the substrate that is to be light-absorbing; and fabricating a light-absorbing mask on the determined area prior to fabricating the at least one optical component. The invention also provides an optical device comprising a substrate; and first and second optical components formed on the substrate, wherein the first optical component has two modes, each mode producing a different optical response to light incident thereupon, and wherein the second optical component absorbs light and is formed on the substrate before the first optical component is formed.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to optical devices. In particular it relates to micro-optical electromechanical devices and to a method for fabricating same.  
         BACKGROUND  
         [0002]    Today, a wide variety of optical devices such as Microelectromechanical Systems (MEMS) devices may be fabricated using micromachining and microelectronic fabrication techniques.  
           [0003]    For example in some cases, MEMS devices may include optical components and are more specifically referred to as micro-opto-electromechanical systems or “MOEMS” devices. One example of such a MOEMS device is the Interferometric Modulator (IMOD) device described in U.S. Pat. No. 5,835,255. The IMOD devices of U.S. Pat. No. 5,835,255 may be fabricated in an array and used in a reflective display wherein each IMOD functions as a pixel to provide a desired optical response.  
           [0004]    In order to improve the desired optical response, the contribution of reflected ambient light from certain inactive areas of the IMODS should be reduced. Thus, these inactive areas of the IMODS should be made to be light-absorbing, typifying a need to mask-off or make light-absorbing inactive areas in optical devices in general.  
         SUMMARY OF THE INVENTION  
         [0005]    According to one aspect of the invention there is provided a method for fabricating a device comprising at least one optical component formed on a transparent substrate, the method comprising determining an area of the substrate that is to be light absorbing; and fabricating a light-absorbing mask on the determined area prior to fabricating at least one optical component.  
           [0006]    According to a second aspect of the invention, there is provided a device comprising a substrate; and first and second optical components formed on the substrate, wherein the first optical component has two modes, each producing a different optical response to light incident thereupon, and wherein the second optical component absorbs the light and is formed on the substrate before the first optical component is formed.  
           [0007]    According to a third aspect of the invention there is provided a method for fabricating a device, the method comprising forming a static optical component on a substrate, wherein the static optical component absorbs light; and forming a dynamic optical component adjacent to the static optical component, wherein the dynamic optical component comprises a driven and an undriven state each having a characteristic optical response to incident light.  
           [0008]    According to a further aspect of the invention there is provided a device comprising a substrate; a static optical component on the substrate, wherein the static optical component absorbs the light; and a dynamic optical component adjacent to the static optical component, wherein the dynamic optical component comprises a driven and an undriven state each having a characteristic optical response to incident light.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 of the drawings shows an end view of a display having inactive areas which have been masked-off in accordance with the present invention;  
         [0010]    [0010]FIG. 2 of the drawings shows a cross-section through a MEMS device having a black mask or light-absorbing region in accordance with one embodiment of the invention;  
         [0011]    [0011]FIG. 3 shows another embodiment of a MEMS device having a black mask or light-absorbing region in accordance with another embodiment of the invention;  
         [0012]    [0012]FIG. 4 shows the various layers making up the light-absorbing or black mask layers of the MEMS device FIG. 2; and  
         [0013]    [0013]FIGS. 5A to  5 G show various steps in the fabrication of a MEMS device in accordance with the invention.  
     
    
     DETAILED DESCRIPTION  
       [0014]    In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the invention. It will be apparent, however, to one skilled in the art that the invention can be practiced without these specific details.  
         [0015]    Reference in this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Moreover, various features are described which may be exhibited by some embodiments and not by others. Similarly, various requirements are described which may be requirements for some embodiments but not other embodiments.  
         [0016]    The present invention discloses, in one embodiment, a MEMS device in the form of a MOEMS device comprising a static optical component and a dynamic optical component, wherein the static optical component acts as “black mask” to absorb ambient or stray light thereby to improve the optical response of the dynamic optical component.  
         [0017]    Although a MEMS device which includes an IMOD will be used to describe the present invention, it is to be understood that the invention covers other optical devices such as various imaging display and optoelectronic devices in general, which have inactive areas which are required to be light-absorbing, but which do not include IMODS.  
         [0018]    Referring now to FIG. 1 of the drawings, an end view of display device  100  is shown. It is to be understood that many components of the display  100  have been omitted so as not to obscure the present invention. The display device  100  includes two active optical components in the form of IMOD devices  104  which typically comprise an arrangement of reflective films which when driven towards a substrate  102  in a direction indicated by arrows  106  produces a desired optical response. The operation of the IMOD devices  104  has been described in U.S. Pat. No. 5,835,255 which is hereby incorporated by reference. Reference numerals  108  indicate inactive areas of the IMOD devices  104  which are required to be light-absorbing or to function as a “black mask” so that when a viewer looks at the display  100  from a direction indicated by arrow  110 , the actual optical response produced by the IMOD devices  104  is not degraded by the reflection of ambient light from the inactive areas  108 .  
         [0019]    Each inactive area  108  may be fabricated from materials selected to have an optical response which absorbs or attenuates light. According to embodiments of the invention, each inactive area  108  may be fabricated as a stack of thin films. For example, in one embodiment, the stack of thin films may comprise a non-light-absorbing dielectric layer sandwiched between two light reflecting chrome layers, as will be more fully described below. In other embodiments, the inactive areas  108  may comprise a single layer of organic or inorganic materials which attenuates or absorbs light.  
         [0020]    [0020]FIG. 2 of the drawings shows a cross section through an IMOD device  200  in accordance with one embodiment of the invention. The IMOD device  200  includes an active component comprising a chrome reflective layer  204 , a silicon oxide layer  206 , an air gap  208 , and a mechanical membrane  210  fabricated on a substrate  202 . The mechanical membrane  210  is supported by polymer posts  212 . In use, mechanical membrane  210  is driven to contact silicon oxide layer  206  to produce a desired optical response when viewed from the direction indicated by arrow  214 .  
         [0021]    Areas of each IMOD  200  on which the polymer posts  212  are formed are not part of the active component of the IMOD and therefore need to be light-absorbing in order to reduce stray or ambient light interfering with the desired optical response of the active IMOD components. These inactive areas define static components which are indicated by encircled areas  216 , and are fabricated to form a stack of films selected so that the stack has the optical property that it is light-absorbing. In one embodiment, the invention involves determining which areas of substrate  202  needs to be light-absorbing and fabricating a light-absorbing or black mask on the determined areas prior to forming the active optical components of the IMODS. The black mask may include a stack of thin films which in one embodiment may comprise a chrome base  218 , an oxide middle layer  220  and the chrome layers  204 .  
         [0022]    Referring now to FIG. 3 of the drawings, reference numeral  300  generally indicates another embodiment of an IMOD device in accordance with one aspect of the invention. IMOD device  300  is similar to the IMOD device  200  and accordingly like or similar reference numerals have been used to indicate like or similar components. The main difference between the IMOD  300  and the IMOD  200  is that the entire polymer post  212  comprises of an organic material e.g., a photo-definable black resin such as the material known as DARC  100  by Brewer Science Inc., that functions effectively as a light-absorbing or black mask. One advantage of the IMOD  300  is that the posts  212  perform two functions. Firstly, the posts  212  function as a mechanical support for mechanical membrane  210 . Secondly the posts  212  function as an optical mask to mask off or make light-absorbing inactive areas of the IMOD.  
         [0023]    [0023]FIG. 4 shows a schematic drawing wherein various layers making up thin film black mask in accordance with one embodiment of the invention is shown.  
         [0024]    Referring to FIG. 4, a thin film black mask  402  shown fabricated on substrate  400 . The black mask  402  comprises three layers of film which includes a chrome layer  404 , a silicon oxide layer  406  and an aluminum layer  408 . Various materials may be selected to produce the black mask. In one embodiment, the films which make up the black mask are the same films which are used in the fabrication of the active IMOD components, thus making it possible to use the same deposition parameters to fabricate the inactive and the active components.  
         [0025]    The various stages in the manufacture of the thin film black mask  402  will now be described with reference to FIGS.  5 A- 5 G of the drawings.  
         [0026]    Referring to FIG. 5A, after an initial preparatory step wherein a glass substrate  500  is prepared, e.g. cleaned, a reflective chrome layer  502  is deposited, e.g. by sputter coating it onto substrate  500 . In one embodiment, the thickness of chrome layer  502  may be about 60 angstroms.  
         [0027]    Thereafter, the chrome layer  502  is patterned and developed using conventional techniques to leave outcrops of chrome which will serve as a base layer for a thin film stack which serves as a black mask (see FIG. 5B).  
         [0028]    A black mask oxide layer, e.g. SiO 2 , typically about 300 to 800 angstroms is then deposited by sputter coating. The thickness of the black mask oxide layer depends on the quality of the black state that is required.  
         [0029]    Next, a further reflective chrome layer  506  is sputter coated on the black mask oxide layer  504 . The layer  506  is typically about 60 angstroms thick, its exact thickness being dependent on the required brightness of the ultimate display, a thinner layer yielding a brighter display.  
         [0030]    Thereafter, layers  508  and  510  are respectively sputter coated on layer  506 . Layer  508  comprises silicon oxide and is about 300 to 800 angstroms whereas the layer  510  is a sacrificial layer comprising molybdenum and will typically be about 0.2 to 1.2 microns thick. Thus, layers  504  to  510  define a thick film stack on substrate  502  as can be seen in FIG. 5C.  
         [0031]    Referring to FIG. 5D, a patterning and an etching step is performed to form recesses  512  which extend through the thin film stack to chrome outcrops  502 .  
         [0032]    Referring to FIG. 5E, polymer posts  514  are formed in recesses  512  by spinning a negative photo-resist material, e.g. the material known as NR7-350P by Futurex Inc., over the thin film stack; exposing it through a suitable mask and developing to form posts  514 . These steps are conventional and therefore have not been further described.  
         [0033]    Referring now to FIG. 5F, a mechanical membrane  516  comprising an aluminum alloy, in one embodiment, is deposited by sputter coating it onto the molybdenum layer  510 .  
         [0034]    Thereafter, the molybdenum layer  510  is etched leaving an air gap  516  as shown in FIG. 5G of the drawings.  
         [0035]    Although the present invention has been described with reference to specific exemplary embodiments, it will be evident that the various modification and changes can be made to these embodiments without departing from the broader spirit of the invention as set forth in the claims. Accordingly, the specification and drawings are to be regarded in an illustrative sense rather than in a restrictive sense.