Performance Analyses of Micromirror Devices

Abstract

The invention provides a method and apparatus for evaluating the product quality and performances of micromirror array devices through measurements of the electromechanical responses of the individual micromirrors to the driving forces of electric fields. The electromechanical responses of the micromirrors according to the present invention are described in terms of the rotational angles associated with the operational states, such as the ON and OFF state angles of the ON and OFF state when the micromirror array device is operated in the binary-state mode, and the response speed (i.e. the time interval required for a micromirror device to transit form one state to another) of the individual micromirrors to the driving fields.

1 . A method of evaluating a quality of a micromirror array device having an array of micromirrors, each micromirror having a deflectable reflective mirror plate, the method comprising:
 (a) dynamically measuring a mechanical response of a mirror plate of a micromirror in the micromirror array in response to an altering driving force;   (b) determining an instant driving force of the altering driving force under which the mirror plate is at a desired state of the measured mechanical response;   (c) repeating steps (a) and (b) for a number of other micromirrors in the micromirror array; and   (d) evaluating the quality of the micromirror array device based on the determined instant driving forces.   
   
   
       2 . The method of  claim 1 , wherein the step of dynamically measuring the mechanical response further comprises:
 applying an altering voltage to the mirror plate; and   dynamically measuring a sequence of rotation positions of the mirror plate in response to the altering voltage.   
   
   
       3 . The method of  claim 2 , wherein step of determining the instant driving force further comprises:
 determining an instant voltage of the altering voltage under which the mirror plate is at an ON state.   
   
   
       4 . The method of  claim 3 , wherein the ON state is a state wherein the mirror plate is rotated 10° degrees or more relative to a substrate on which the mirror plate is formed. 
   
   
       5 . The method of  claim 4 , wherein the ON state is a state wherein the mirror plate is rotated 12° degrees or more relative to the substrate. 
   
   
       6 . The method of  claim 5 , wherein the ON state is a state wherein the mirror plate is rotated 14° degrees or more relative to the substrate. 
   
   
       7 . The method of  claim 2 , wherein the altering voltage comprises an upward sweeping edge and a downward sweeping edge, wherein the mirror plate rotates towards an ON state during the upwards sweeping edge, and rotates towards an OFF state during downwards sweeping edge. 
   
   
       8 . The method of  claim 7 , wherein the OFF state is a state wherein the mirror plate is parallel to a substrate on which the mirror plate is formed. 
   
   
       9 . The method of  claim 2 , wherein the altering voltage comprises a sequence of voltage cycles, each of which comprises a first and second voltage peak with the first voltage peak having an amplitude higher than a voltage required for rotating the mirror plate to an ON state, and the second voltage peak having an amplitude that varies over time. 
   
   
       10 . The method of  claim 9 , wherein the first voltage peak of a voltage cycle is applied to the mirror plate immediately prior to the application of the second voltage peak of the same cycle. 
   
   
       11 . The method of  claim 9 , wherein the second voltage peak of a voltage cycle is applied to the mirror plate immediately prior to the application of the first voltage peak of the same cycle. 
   
   
       12 . The method of  claim 2 , wherein the altering voltage comprises a sequence of voltages, the amplitude of each of which varies over time. 
   
   
       13 . The method of  claim 2 , wherein the altering voltage comprises a set of voltage sequences, each voltage sequence having a sequence of voltage pulses, wherein a time interval between two consecutive voltage pulses varies over time. 
   
   
       14 . The method of  claim 2 , further comprising:
 directing a light beam to the mirror plates of the micromirrors in the micromirror array;   taking an image of the illuminated micromirrors;   processing the image so as to obtain an edge of each illuminated micromirror; and   selecting a micromirror to be measured.   
   
   
       15 . The method of  claim 1 , further comprising:
 loading the micromirror array device into a vacuum chamber of a measurement system; and   pumping out the vacuum chamber to a particular pressure.   
   
   
       16 . The method of  claim 15 , wherein the particular pressure is 1 atmosphere or less. 
   
   
       17 . The method of  claim 15 , wherein the particular pressure is 20 Torr or less. 
   
   
       18 . The method of  claim 15 , wherein the particular pressure is 50 mTorr or less. 
   
   
       19 . The method of  claim 14 , wherein step of dynamically measuring the mechanical response further comprises:
 dynamically measuring an intensity of a light beam reflected from the mirror plate being inspected; and   from the detected illumination intensity, determining whether the mirror plate reaches to the desired state.   
   
   
       20 . The method of  claim 14 , wherein the step of processing the image further comprises:
 transforming the image into the Fourier space;   locating a plurality of peaks in the image;   approximating a horizontal and vertical pitches of the mirror plate according to the located peaks;   performing the Fourier transformation to the images; and   calculating a geometric center of each mirror plate in the micromirror array.   
   
   
       21 . The method of  claim 20 , wherein the step of approximating the horizontal and vertical pitches further comprises:
 approximating the horizontal and vertical pitches using the Siebel operator.   
   
   
       22 . The method of  claim 21 , further comprising:
 filtering a noise of the image before transforming the image into the Fourier space.   
   
   
       23 . The method of  claim 21 , further comprising:
 filtering a noise of the image immediately after the transformation of the image into the Fourier space.   
   
   
       24 . The method of  claim 13 , further comprising:
 measuring a response time for each micromirror in the micromirror array during which the illumination intensity changes between a minimum value to a maximum value in response to the altering voltage; and   evaluating the quality of the micromirrors based upon the measured response time for all micromirrors of the micromirror array.   
   
   
       25 . The method of  claim 24 , wherein the step of evaluating the quality further comprises:
 calculating a distribution of the response time of the micromirrors; and   evaluating the quality based upon the calculated distribution.   
   
   
       26 . The method of  claim 3 , further comprising:
 calculating a distribution of the measured instant voltages for the micromirrors, wherein the instant voltage of a micromirror is the ON state voltage; and   evaluating the quality of the micromirrors based upon the calculated distribution.   
   
   
       27 . The method of  claim 1 , wherein the step of evaluating the quality further comprises:
 passing the micromirror array device if the determined instant driving force is within a predetermined range; and   failing the micromirror array device if the determined instant driving force is beyond the predetermined range.   
   
   
       28 . The method of  claim 2 , wherein the altering voltage has a maximum value of from 10 to 70 volts. 
   
   
       29 . The method of  claim 2 , wherein the altering voltage has a maximum value of from 25 to 45 volts. 
   
   
       30 . The method of  claim 2 , wherein the altering voltage has a maximum value of from 70 to 100 volts. 
   
   
       31 . The method of  claim 14 , wherein the step of taking an image of the illuminated micromirrors further comprises:
 capturing a reflected light from the illuminated micromirrors in a propagation path of the reflected light, wherein said propagation path of the reflected light has an angle with a propagation path of the illumination light incident onto the micromirrors; and   wherein the angle is 10° degrees or more.   
   
   
       32 . The method of  claim 31 , wherein the angle is 14° degrees or more. 
   
   
       33 . The method of  claim 31 , wherein the angle is 16° degrees or more. 
   
   
       34 . The method of  claim 31 , wherein the angle is 18° degrees or more. 
   
   
       35 . The method of  claim 31 , wherein the angle is 20° degrees or more. 
   
   
       36 . The method of  claim 31 , wherein the angle is 22° degrees or more. 
   
   
       37 - 70 . (canceled)