Microelectromechanical device with thermal expansion balancing layer or stiffening layer

Abstract

An interferometric modulating device is provided with a thermal expansion balancing layer on a side of the movable flexible layer opposite the movable reflector such that when temperature changes the distance between the movable reflector and the optical stack does not change significantly, thereby leading to stable color. Additionally, an interferometric modulating device is provided with a stiffening layer between the movable flexible layer and the movable reflector and at least one hollow void exists on the surface where the movable reflector and the stiffening layer contact each other so that the movable reflector is more rigid to bending, thereby reducing the temperature sensitivity of the movable reflector.

1 . A device comprising:
 an optical stack;   a movable reflector, the movable reflector being movable relative to the optical stack through an interferometric cavity between at least a first position and a second position; and   a thermal expansion balancing layer mechanically coupled to the movable reflector on a side of the movable reflector opposite the interferometric cavity, the thermal expansion balancing layer being configured such that a distance between the movable reflector and the optical stack when the movable reflector is in the first position does not change when the device is heated or cooled.   
     
     
         2 . The device of  claim 1 , wherein the movable reflector has a thickness dimension, wherein the thermal expansion balancing layer has a thickness dimension, and wherein the thickness dimension of the thermal expansion balancing layer is greater than the thickness dimension of the movable reflector. 
     
     
         3 . The device of  claim 1 , wherein the movable reflector has a coefficient of thermal expansion characteristic, wherein the thermal expansion balancing layer has a coefficient of thermal expansion characteristic, and wherein the coefficient of thermal expansion characteristic of the thermal expansion balancing layer is substantially the same as the coefficient of thermal expansion characteristic of the movable reflector. 
     
     
         4 . The device of  claim 3 , wherein the movable reflector and the thermal expansion balancing layer include the same material. 
     
     
         5 . The device of  claim 4 , wherein the movable reflector includes aluminum. 
     
     
         6 . The device of  claim 1 , wherein the movable reflector includes a dielectric layer and a reflective layer, wherein the dielectric layer is disposed between the thermal expansion balancing layer and the reflective layer. 
     
     
         7 . The device of  claim 6 , wherein the thermal expansion balancing layer has a coefficient of thermal expansion greater than or equal to that of the dielectric layer if a coefficient of thermal expansion of the reflective layer is greater than that of the dielectric layer, or a coefficient of thermal expansion less than or equal to that of the dielectric layer if the coefficient of thermal expansion of the reflective layer is less than that of the dielectric layer. 
     
     
         8 . 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.   
     
     
         9 . The device of  claim 8 , further comprising a driver circuit configured to send at least one signal to the display. 
     
     
         10 . The device of  claim 9 , further comprising a controller configured to send at least a portion of the image data to the driver circuit. 
     
     
         11 . The device of  claim 8 , further comprising an image source module configured to send the image data to the processor. 
     
     
         12 . The device of  claim 11 , wherein the image source module comprises at least one of a receiver, transceiver, and transmitter. 
     
     
         13 . The device of  claim 8 , further comprising an input device configured to receive input data and to communicate the input data to the processor. 
     
     
         14 . A device comprising:
 an optical stack;   a movable reflector, the movable reflector being movable relative to the optical stack through an interferometric cavity between at least a first position and a second position; and   means for balancing thermal expansion of the movable reflector such that a distance between the movable reflector and the optical stack when the movable reflector is in the first position does not change when the device is heated or cooled.   
     
     
         15 . The device of  claim 14 , wherein the thermal expansion balancing means is coupled to the movable reflector on a side of the movable reflector opposite the interferometric cavity. 
     
     
         16 . The device of  claim 14 , wherein the movable reflector has a thickness dimension, wherein the thermal expansion balancing means has a thickness dimension, and wherein the thickness dimension of the thermal expansion balancing means is greater than the thickness dimension of the movable reflector. 
     
     
         17 . The device of  claim 14 , wherein the movable reflector has a coefficient of thermal expansion characteristic, wherein the thermal expansion balancing means has a coefficient of thermal expansion characteristic, and wherein the coefficient of thermal expansion characteristic of the thermal expansion balancing means is substantially the same as the coefficient of thermal expansion characteristic of the movable reflector. 
     
     
         18 . A method of making a device, the method comprising:
 forming an optical stack;   forming a movable reflector; and   after forming the movable reflector, mechanically coupling a thermal expansion balancing layer to the movable reflector, the thermal expansion balancing layer being configured to counteract a stress gradient present on the movable reflector caused by thermal expansion or thermal contraction of the movable reflector.   
     
     
         19 . The method of  claim 18 , further comprising forming a sacrificial layer between the optical stack and the movable reflector. 
     
     
         20 . The method of  claim 19 , further comprising removing the sacrificial layer. 
     
     
         21 . The method of  claim 18 , wherein the movable reflector has a thickness dimension, wherein the thermal expansion balancing layer has a thickness dimension, and wherein the thickness dimension of the thermal expansion balancing layer is greater than the thickness dimension of the movable reflector. 
     
     
         22 . The method of  claim 18 , wherein the movable reflector has a coefficient of thermal expansion characteristic, wherein the thermal expansion balancing layer has a coefficient of thermal expansion characteristic, and wherein the coefficient of thermal expansion characteristic of the thermal expansion balancing layer is substantially the same as the coefficient of thermal expansion characteristic of the movable reflector. 
     
     
         23 . The method of  claim 18 , wherein forming the movable reflector includes forming a reflective layer and a dielectric layer. 
     
     
         24 . The method of  claim 23 , wherein mechanically coupling the thermal expansion balancing layer to the movable reflector includes mechanically coupling the thermal expansion balancing layer to the dielectric layer of the movable reflector. 
     
     
         25 . The method of  claim 24 , wherein the thermal expansion balancing layer has a coefficient of thermal expansion greater than or equal to that of the dielectric layer if a coefficient of thermal expansion of the reflective layer is greater than that of the dielectric layer, or a coefficient of thermal expansion less than or equal to that of the dielectric layer if the coefficient of thermal expansion of the reflective layer is less than that of the dielectric layer