Interferometric optical display system with broadband characteristics

Abstract

Broad band white color can be achieved in MEMS display devices by incorporating a material having an extinction coefficient (k) below a threshold value for wavelength of light within an operative optical range of the interferometric modulator. One embodiment provides a method of making the MEMS display device comprising depositing said material over at least a portion of a transparent substrate, depositing a dielectric layer over the layer of material, forming a sacrificial layer over the dielectric, depositing an electrically conductive layer on the sacrificial layer, and forming a cavity by removing at least a portion of the sacrificial layer. The suitable material may comprise germanium, germanium alloy of various compositions, doped germanium or doped germanium-containing alloys, and may be deposited over the transparent substrate, incorporated within the transparent substrate or the dielectric layer.

1 . A device comprising:
 a substrate; and   an interferometric modulator supported by the substrate, wherein the interferometric modulator is configured to reflect at least a portion of incident light passing through the substrate, and wherein the interferometric modulator includes:
 a movable layer over the substrate, and 
 an absorber between the movable layer and the substrate, wherein the absorber has an extinction coefficient (k) below a threshold value for wavelengths of light within an operative optical range of the interferometric modulator, and wherein k remains substantially constant or decreases as the wavelength of light increases within the operative optical range of the interferometric modulator. 
   
     
     
         2 . The device of  claim 1 , wherein the threshold value is about 2.5. 
     
     
         3 . The device of  claim 1 , wherein the interferometric modulator is configured to reflect broadband white light with a reflectance level of about 30% to about 70% across the operative optical range. 
     
     
         4 . The device of  claim 1 , wherein the substrate includes the absorber. 
     
     
         5 . The device of  claim 1 , wherein the absorber is deposited over the substrate. 
     
     
         6 . The device of  claim 1 , wherein the absorber has a refractive index (n), and wherein the absorber has an n to k ratio from about 2.5 to about 6. 
     
     
         7 . The device of  claim 1 , wherein the absorber includes at least one of germanium, germanium alloy, doped germanium, or doped germanium-containing alloy. 
     
     
         8 . The device of  claim 1 , wherein the movable layer includes at least one of aluminum or aluminum alloy. 
     
     
         9 . The device of  claim 1 , wherein the absorber includes a metal layer. 
     
     
         10 . The device of  claim 9 , wherein the metal layer includes at least one of chromium, molybdenum, a refractive metal, and a refractive alloy. 
     
     
         11 . The device of  claim 1 , wherein the absorber has a refractive index (n) that increases as the wavelength of light increases within the operative optical range of the interferometric modulator. 
     
     
         12 . The device of  claim 1 , wherein the operative optical range extends from wavelengths of about 300 nm to about 800 nm. 
     
     
         13 . The device of  claim 1 , further comprising:
 a display;   a processor that is configured to communicate with the display, the processor being configured to process image data; and   a memory device that is configured to communicate with the processor.   
     
     
         14 . The device of  claim 13 , further comprising:
 a driver circuit configured to send at least one signal to the display; and   a controller configured to send at least a portion of the image data to the driver circuit.   
     
     
         15 . The device of  claim 13 , further comprising:
 an image source module configured to send the image data to the processor, wherein the image source module includes at least one of a receiver, transceiver, and transmitter; and   an input device configured to receive input data and to communicate the input data to the processor.   
     
     
         16 . A device comprising:
 a substrate; and   an interferometric modulator supported by the substrate, wherein the interferometric modulator is configured to reflect at least a portion of incident light passing through the substrate, and wherein the interferometric modulator includes:
 a movable layer over the substrate, and 
 an absorber between the movable layer and the substrate, wherein the absorber has an extinction coefficient (k) below a threshold value for visible wavelengths of light, and wherein k remains substantially constant or decreases as the wavelength of light increases for visible wavelengths of light. 
   
     
     
         17 . The device of  claim 16 , wherein the threshold value is about 2.5. 
     
     
         18 . The device of  claim 16 , wherein the interferometric modulator is configured to reflect light at a reflectance level above a reflectance threshold value across the range of visible wavelengths of light, thereby reflecting broadband white light. 
     
     
         19 . The device of  claim 16 , wherein the absorber has a refractive index (n), and wherein the absorber has an n to k ratio of about 3. 
     
     
         20 . The device of  claim 16 , wherein the absorber has a refractive index (n) that increases as the wavelength of light increases for visible wavelengths of light. 
     
     
         21 . A method of making a display device, comprising:
 forming an array of interferometric modulators, wherein forming the array of interferometric modulators includes:
 forming an absorber layer over a transparent substrate, and 
 forming a movable layer over the absorber layer, the absorber layer having an extinction coefficient (k) below a threshold value for wavelengths of light within an operative optical range of the interferometric modulators, wherein k remains substantially constant or decreases as the wavelength of light increases within the operative optical range of the interferometric modulators. 
   
     
     
         22 . The method of  claim 21 , wherein the threshold value is about 2.5. 
     
     
         23 . The method of  claim 21 , wherein the absorber layer also has a refractive index (n) that increases as the wavelength of light increases within the operative optical range of the interferometric modulators. 
     
     
         24 . The method of  claim 21 , wherein the absorber layer has a refractive index (n), and wherein the absorber has an n to k ratio of about 3. 
     
     
         25 . The method of  claim 21 , wherein forming the array of interferometric modulators includes:
 forming an optical stack on the transparent substrate;   depositing a sacrificial layer over the optical stack;   forming an electrically conductive layer over the sacrificial layer; and   removing at least a portion of the sacrificial layer to thereby form a cavity between the substrate and the electrically conductive layer.   
     
     
         26 . The method of  claim 21 , wherein the forming the absorber layer comprises:
 providing a substrate that includes the absorber layer.