Microelectromechanical device with restoring electrode

Abstract

Light in the visible spectrum is modulated using an array of modulation elements, and control circuitry connected to the array for controlling each of the modulation elements independently, each of the modulation elements having a surface which is caused to exhibit a predetermined impedance characteristic to particular frequencies of light. The amplitude of light delivered by each of the modulation elements is controlled independently by pulse code modulation. Each modulation element has a deformable portion held under tensile stress, and the control circuitry controls the deformation of the deformable portion. Each deformable element has a deformation mechanism and an optical portion, the deformation mechanism and the optical portion independently imparting to the element respectively a controlled deformation characteristic and a controlled modulation characteristic. The deformable modulation element may be a non-metal. The elements are made by forming a sandwich of two layers and a sacrificial layer between them, the sacrificial layer having a thickness related to the final cavity dimension, and using chemical (e.g., water) or a plasma based etch process to remove the sacrificial layer.

1 . A method for resetting at least one mirror comprising:
 applying a reset voltage to an encapsulation membrane in a deflectable mirror assembly; and   discontinuing application of the reset voltage after deflection of a mirror within the mirror assembly from an actuated position to a rest position.   
     
     
         2 . The method of  claim 1 , wherein the mirror assembly comprises:
 an optically transmissive substrate;   an electrode located on the substrate;   at least one deflectable mirror member spaced from the substrate by a first gap and positioned so that the electrode is between the substrate and the at least one deflectable mirror member; and   the encapsulation membrane comprising electrically conductive material, the encapsulation membrane spaced from the at least one deflectable mirror member by a second gap, the at least one deflectable mirror member being positioned between the substrate and the encapsulation membrane.   
     
     
         3 . The method of  claim 2 , wherein applying a reset voltage to the encapsulation membrane comprises applying the reset voltage across the encapsulation membrane and the at least one deflectable mirror member. 
     
     
         4 . The method of  claim 1 , further comprising deflecting the at least one deflectable mirror member towards the encapsulation membrane and to a rest position after the reset voltage is applied to the encapsulation membrane. 
     
     
         5 . The method of  claim 4 , wherein deflecting the at least one deflectable mirror member includes overcoming electrostatic attraction between the at least one deflectable mirror member and the electrode. 
     
     
         6 . The method of  claim 2 , wherein the electrode is positioned on the same side of the at least one deflectable mirror member as the substrate and spaced from the at least one deflectable mirror member, and wherein the electrode comprises optically transparent conductive material. 
     
     
         7 . The method of  claim 1 , wherein the mirror assembly is present in an array and applying the reset voltage comprises applying the reset voltage to a plurality of mirror assemblies in the array. 
     
     
         8 . A method of moving at least one mirror in a mirror assembly, the method comprising:
 applying an actuation voltage across a substrate and the at least one mirror, the at least one mirror spaced from the substrate by a first gap;   actuating the at least one mirror to deflect towards the substrate to an actuated position;   applying a reset voltage to an encapsulation membrane comprising electrically conductive material, the encapsulation membrane spaced from the at least one mirror by a second gap, the at least one mirror being positioned between the substrate and the encapsulation membrane; and   discontinuing application of the reset voltage.   
     
     
         9 . The method of  claim 8 , wherein applying the reset voltage to the encapsulation membrane comprises applying the reset voltage across the encapsulation membrane and the at least one mirror. 
     
     
         10 . The method of  claim 8 , further comprising deflecting the at least one mirror to deflect towards the encapsulation membrane to a rest position after the reset voltage is applied to the encapsulation membrane. 
     
     
         11 . The method of  claim 10 , wherein the mirror assembly comprises at least one electrode located on the substrate and wherein applying an actuation voltage comprises applying an actuation voltage across the at least one electrode and the at least one mirror to move the at least one mirror toward the actuated position. 
     
     
         12 . The method of  claim 11 , wherein deflecting the at least one mirror includes overcoming electrostatic attraction between the at least one mirror and the at least one electrode. 
     
     
         13 . The method of  claim 11 , wherein the at least one electrode comprises optically transparent conductive material. 
     
     
         14 . The method of  claim 13 , wherein the optically transparent conductive material comprises an oxide. 
     
     
         15 . The method of  claim 13 , wherein the transparent conductive material is disposed on the substrate between the substrate and the at least one mirror. 
     
     
         16 . The method of  claim 8 , wherein the mirror assembly is present in an array and applying the reset voltage comprises applying the reset voltage to a plurality of mirror assemblies in the array. 
     
     
         17 . The method of  claim 8 , wherein the encapsulation membrane comprises a substrate. 
     
     
         18 . The method of  claim 8 , wherein the substrate is substantially parallel to the encapsulation membrane. 
     
     
         19 . A method of making a mirror device comprising:
 depositing spacer layers and patterns on a base substrate having address circuitry;   constructing elements of the mirror device on the base substrate, the elements including an electrode and a mirror;   constructing an optically transparent substrate in sealed overlying relationship with the mirror after removal of the spacer layers; and   forming at least one reset electrode, the reset electrode connected to the optically transparent substrate.   
     
     
         20 . The method of  claim 19 , wherein forming the at least one reset electrode comprises attaching an optically transparent conductive material to at least one region of the optically transparent substrate.