Abstract:
A multi-motion programmable micromirror control method is provided with the multiple supports in a stepper plate to upholding the micromirror structure. The control system has advantages such that multiple motion can be applied to a micromirror and that the micromirror can be controlled in a low driving voltage and that simple motion control is applied by digital controlling and that the degrees of freedom in motion of the micromirror can be chosen by the number of the stepper plate and that only single voltage is needed for driving the micromirror motion. With many advantages, the multi-motion programmable micromirror control system provides a solution to overcome the difficulties in controlling micromirror motion.

Description:
REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation-in-part of, and claims priority to U.S. patent application Ser. No. 10/872,241 (Docket No. 1802.011) filed Jun. 18, 2004, U.S. patent application Ser. No. 10/893,039 (Docket No. 1802.012) filed Jul. 16, 2004, U.S. patent application Ser. No. 10/072,597 (Docket No. 1802.22) filed Mar. 4, 2005, and U.S. patent application Ser. No. 11/347,590 (Docket No. 1802.38) filed Feb. 4, 2006, all of which are hereby incorporated by reference. 
     
    
     FIELD OF INVENTION  
       [0002]     The present invention relates to micromirror in general and more specifically micromirror control and motion generation.  
       BACKGROUND OF THE INVENTION  
       [0003]     Micromirrors may be used in various optical applications instead of, or in addition to, conventional optoelectronic devices. It is desirable to be able to move the micromirrors by rotation and translation with very fine control.  
         [0004]     Since the micro-electro mechanical systems (MEMS) were developed, many applications in MEMS have been developed and used. Micromirror device is the one of the major development in MEMS field. Devices and application using micromirrors are developed and used in various fields such as optical communication and display. As the applications of micromirrors grow rapidly, the demand on controlling micromirror device becomes increases. It is desirable to have the motion control of the micromirror with many degrees of freedom and simple driving method.  
         [0005]     A phase-only piston-style micromirror has been used for phase adaptive optics applications and a rotational micromirror has been used to deflect light. Most of these micromirrors have been controlled to have continuous displacements, which are determined at the equilibrium between electrostatic force and elastic force. The analog control is more complex than the digital or discrete control, and is not compatible with known semiconductor electronics technologies such as MOS, CMOS, etc. In addition, the micromirrors with continuous displacement actuated by electrostatic force undergo the classical snap-down phenomenon when the electric force exceeds the elastic force of mechanical structure. The snap-down phenomenon limits the translational and rotational ranges of a micromirror.  
         [0006]     The high driving voltage is another disadvantage in controlling the micromirror motion with continuous displacement actuated by electrostatic force. To be compatible with IC components, it is desired that micromirrors are operated at a low voltage which is compatible with the circuit operation or control voltage.  
         [0007]     In a prior art micromirror array, such as, for example, the digital micromirror device (DMD) in U.S. Pat. Nos. 4,566,939, 5,083,857, and 6,232,936, each micromirror is actuated by digital control of a voltage. It has large rotation, low driving voltage, and is compatible with known semiconductor electronics technologies. However, it has only one degree of freedom, that is, rotation about a single axis, and it only has two level positions.  
         [0008]     Therefore, the demand on the simple control of the micromirror with more degrees of freedom has been increased to use the micromirror. The present invention is intended to provide a method with multiple motions, a plurality of degrees of freedom, low driving voltage, and simple activation. This control system can have one degree of freedom rotational motion, one degree of freedom translational motion, one degree of freedom and one degree of freedom translational motion, two degrees of freedom rotational motion, and two degrees of freedom rotational motion and one degree of freedom translational motion.  
       SUMMARY OF THE INVENTION  
       [0009]     The present invention contrives to solve the disadvantages of the prior art for controlling micromirror motion. The present invention provides an advanced method for discretely controlled micromirror (DCM) system. Method for DCM system is provided in U.S. patent application Ser. No. 10/872,241 (Docket No. 1802.011) filed Jun. 18, 2004, U.S. patent application Ser. No. 10/893,039 (Docket No. 1802.012) filed Jul. 16, 2004, U.S. patent application Ser. No. 10/072,597 (Docket No. 1802.22) filed Mar. 4, 2005, and U.S. patent application Ser. No. 11/347,590 (Docket No. 1802.38) filed Feb. 4, 2006. DCM system has many advantages for controlling micromirrors such as that DCM uses simple driving method, and that single voltage or discretely separated voltages are used for actuating the micromirror structure, and that degree of freedom can be increased by the number of the stepper plates and the number of the supports, and that multiple motions can be embedded in one structure, and so on.  
         [0010]     In the present invention, multi-motion programmable micromirror control method is provided. A stepper plate with multiple supports is introduced for generating multiple motions of a micromirror. The stepper plate is inclined by electrostatic force between the electrodes and the stepper plate. When a stepper plate is inclined for a given step toward the selected direction, the support with the pre-programmed position upholds the micromirror to make a desired motion of the micromirror. Each support in a stepper plate gives a pre-programmed micromirror motion with other support or supports in the same step upholding the micromirror together. The desired motions of the micromirror also can be obtained by the positions of the supports under the micromirror not by the positions of the supports on the stepper plate. Also support on the stepper plate and support under the micromirror can be applied to the system altogether. Besides controlling the motion of the micromirror by the support positions, the motion can be selected by different amounts of the rotation angle of the stepper plates for each step. The control system is actuated by the electrostatic force between the stepper plate and the electrodes. Also the electromagnetic and electro-thermal forces can be applied to the system.  
         [0011]     The shape of the stepper plates can be varied to have triangular, square, hexagonal; octagonal, circular or other shapes by the number of the supports, number of the steps and the geometries of the micromirror, electrodes, and stepper plates. The number of the steps in a stepper plate can be determined by the shape of the stepper plate, the electrodes under the stepper plates, desired degrees of freedom for making motions and the required number of the motion steps for a micromirror. If the stepper plate has 8 electrodes, the stepper plates can have up to 8 different steps. If the micromirror should have 8 step motions with 3 degrees of freedom, the number of the supports is at least 24 (8 support in each three stepper plate).  
         [0012]     Because a stepper plate has multiple motions which can be defined by the positions of the supports, the micromirror can have many steps in a small sized volume. The step density of the motion is much higher than the case of multiple stepper plates with one support. Since the micromirror is small in size, the high density of the motions is strongly desirable for controlling the micromirror.  
         [0013]     The control system needs low voltage to control the micromirror due to the multiple electrode usage. Since defining of a step is only determined by the direction of the inclined stepper plate and the support position, one step in a stepper plate can share neighboring electrodes to have stronger electrostatic force as many as the force by the neighboring electrodes does not disturb the required rotation of the stepper plate. By using the multiple electrodes together, the driving voltage can be reduced since the effective area for forming the electrostatic force is increased. Electrostatic force can be increased by doubled or tripled the area of the electrode by applying the driving voltage to the on-step electrode accompanying with neighboring electrodes. By applying the voltage to the multiple electrodes together, the stepper plate with supports can uphold the micromirror with stiffer restoring elastic force or reduce the driving voltage. Each step is controlled by the corresponding electrode or electrodes. Also the plurality of the micromirror can be controlled by the common voltage source.  
         [0014]     Another advantage of the present invention is that the stepper plate is digitally controlled and has simple two states for each step. For controlling the full steps of the micromirror motions, the device needs only the same number of the control channels as that of the motion steps to be required by the micromirror. Since the desired motion is already programmed while fabricating the micromirror structure in the stepper and support geometry, simply applying voltage to the desired electrode makes the desired motion active. The present invention gives a simple way to control the micromirror with multiple steps. The programmable micromirror control system can be made on the CMOS structures and the system is controlled by the CMOS circuit.  
         [0015]     Still another advantage is that the control system has many degrees of freedom in motion control. The degrees of the freedom are constraint by the number of the stepper plates. The degrees of the freedom can be varied by adding more stepper plate to obtain the desired motion in the micromirror. When the stepper plate is inclined, the support on stepper plate is raised and upholds the micromirror. If the micromirror needs three degrees of freedom motions, three different stepper plates are applied and three supports define the desire motion. The degrees of freedom in motion are constraint by the number of the supports in a step or by the number of the stepper plates. The motion control system can have one rotational degree of freedom, one translational degrees of freedom, one translational and one rotational degrees of freedom, two rotational and one translational degree of freedom, two rotational degrees of freedom and so on. The control system has a plurality of degrees of freedom in motion control.  
         [0016]     The multi-motion programmable micromirror control method of the present invention has advantages: (1) multiple motion can be applied to the micromirror; (2) high density motions can be applied to the micromirror; (3) the micromirror can be controlled in a low driving voltage; (4) simple motion control is applied by digital controlling; (5) the degrees of freedom in motion of the micromirror can be chosen by the number of the stepper plate; (6) only single voltage is needed for driving the micromirror motion; and (7) the micromirror is controlled in a stepwise way.  
         [0017]     Although the present invention is briefly summarized, the full understanding of the invention can be obtained by the following drawings, detailed description, and appended claims. 
     
    
     DESCRIPTION OF THE FIGURES  
       [0018]     These and other features, aspects and advantages of the present invention will become better understood with reference to the accompanying drawings, wherein:  
         [0019]      FIG. 1  is a schematic diagram showing how prior art controls the micromirrors;  
         [0020]      FIG. 2  show schematic diagrams of discretely controlled micromirror control system of embodiment;  
         [0021]      FIGS. 3A-3C  show schematic diagrams of discretely controlled micromirror control system when the system has motions;  
         [0022]      FIG. 4  shows a stepper plate with quadruple supports and electrodes for generating the multiple motions (4 different motions);  
         [0023]      FIG. 5  shows a stepper plate with multiple supports and electrodes for generating the multiple motions (8 different motions);  
         [0024]      FIG. 6  is a schematic diagram of springless hinge structure.  
         [0025]      FIG. 7  is a schematic diagram showing how three multiple support actuators define micromirror motions with three degrees of freedom (two rotational and one translational);  
         [0026]      FIG. 8  is a schematic diagram showing how a micromirror with a multiple support actuator works as multi-step optical switch;  
         [0027]      FIG. 9  is a schematic diagram showing how micromirrors with multiple support actuator works as a multi-step micromirror array lens;  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0028]      FIG. 1  shows schematic diagram of the prior art of the micromirror control system. Micromirror  11  is controlled to have a continuous rotation  15  or translation  16 , which is determined by the equilibrium between electrostatic force from the electrode  13  and the micromirror  11  structure and elastic force of the translational spring  14  and the rotational spring  17 . The micromirror  11  is rotated along the hinge supported by the supporting structure. Since the motion is determined by the static equilibrium of the electrostatic and elastic forces, complex analog control with active feedback is required to have a fine control of the motion.  
         [0029]     On the other hand, discretely controlled micromirror (DCM) method has simpler control system. Once the motion is defined and programmed in the micromirror structure, the control is just applying the on/off voltage for desired channel with respect to the desired motion. No feedback is required and the motion is reproducible regardless of the environment.  
         [0030]     A multi-motion programmable micromirror control system comprises at least on stepper plate configured to be rotated to uphold micromirror structure, wherein the stepper plate has at least two contact points, wherein the two contact points have different heights to make the stepper plate to have a motion of rotation, a bottom layer configured to have at least one electrodes to control the stepper plate and a micromirror coupled to the stepper plate wherein the micromirror has the multiple motion programmed by the positions of the supports or the rotation angles of the stepper plate.  
         [0031]      FIG. 2  shows a micromirror control system for a discretely controlled micromirror (DCM), according to embodiments of the present invention. The micromirror control system includes stepper plates  22  with multiple supports  23 A,  23 B, coupled to the bottom layer and configured to be rotated to uphold micromirror structure  21 , and a bottom layer configured to have multiple electrodes to control the stepper plate  22 , and a micromirror  21  coupled to the stepper plate  22 . Also the micromirror control system can use different types of stops  24 A,  24 B,  24 C to control the micromirror motion. The micromirror  21  has the multiple motions programmed by the positions of the supports  23 A,  23 B or the rotation angles of the stepper plate  22 . The micromirror motion is defined by the supports. The micromirror motion is programmed in the geometry of the stepper plate and support while fabricating the control system. The support is positioned on the stepper plate or under the micromirror  21 .  
         [0032]     The stepper  22  structure is coupled to the bottom layer with electrodes  25 A. Each electrode  25 A is activated for a given desired motion of the micromirror  21 . The supports  23 A on the stepper plate are positioned for defining the micromirror motion. When the stepper plate is rotated, the height of the support  23 A is varied by in-plane position of the support. The support  23 B under the micromirror is also positioned for defining the micromirror motion with the relative positions of the stepper plate  22  and the support  23 B under micromirror. The motion of the micromirror  21  is defined by contact position of the supports  23 A,  23 B after the stepper plate  22  rotated. To have a stable motion of the micromirror, at least three contacting points by support  23 A,  23 B upholding the micromirror  21  structures are necessary. At the bottom of the stepper plate  22 , stops  24 A,  24 B,  24 C make the settling points of the stepper plate  22 . The stops  24 A,  24 B,  24 C can be used alone or the combinations of the stops  24 A,  24 B,  24 C can be used. The stops  24 A,  24 B,  24 C under the stepper plate  22  adjust the amount of the angle rotated by its position and/or its height. Also the stop  24 B at the bottom layer adjusts the amount of the angle rotated by its position and/or its height. The electrodes  25 A pull the stepper plate  22  until the stepper plate rests on the stops  24 A,  24 B,  24 C. The stops with different heights make the stepper plate to be rotated. Then the micromirror is upheld by the support  23 A on the stepper plate, or by the stepper plate  22 , or the support under the micromirror is upheld by the stepper plates. And the motion of the micromirror  21  is defined by the positions of supports on the stepper plate  23 A, or supports under the micromirror  23 B, or the rotation angle limited by the stops under the stepper plates  24 A,  24 B,  24 C. The micromirror and the stepper plates are restored due to the restoring forces by the flexible springs  26 A,  26 B. The micromirror also can be pulled by the micromirror electrode  25 B, which makes sure that the micromirror  21  contacts with supports  23 A,  23 B in a step. The stepper plate has at least on support, wherein the support is coupled to the micromirror or the micromirror has at least one support, wherein the support is coupled to the stepper plate. The support can be positioned on the stepper plates and/or under the micromirror.  
         [0033]     In  FIG. 3A , the motion defined by the support  33 A,  33 B on the stepper plates  32 A,  32 B are described. The supports  33 A,  33 B on the stepper plates  32 A,  32 B push the micromirror  31  to have the desired micromirror motion. The opposite side electrode  35 A,  35 B are applied by the driving voltage. The motion of the micromirror is defined by the support position on the stepper plate  
         [0034]      FIG. 3B  shows the motion defined by supports  36 A,  36 B under the micromirror  31 . Supports  36 A,  36 B under the micromirror  31  are upheld by the stepper plates  32 A,  32 B and the micromirror  31  has motion defined by the contacting positions of the support  36 A,  36 B under the micromirror and stepper plate. When the driving voltage is applied to the electrodes  35 A,  35 B, the stepper plates  32 A,  32 B are inclined by the pre-programmed angle. The rotated stepper plates  32 A,  32 B push the supports  36 A,  36 B under the micromirror to the positions where the micromirror motion occurs. The micromirror electrode  38  is used to make the supports to be rested on steppers  32 A,  32 B. The motion of the micromirror is defined by support position under the micromirror  
         [0035]      FIG. 3C  shows the motion obtained by the stops  39 A under the stepper plate  32 A. A mechanical stop is applied to the system to determine the amounts of the rotated angle of the stepper plate. In the figure, one stepper plate has the stop  36 A under the stepper plate  32 A. And the other  32 B does not have the stop under the stepper plate  32 B. The amounts of the rotation angles are different as the stop position or the height of the stop or even the existence of the stop under the stepper plate. The amount of the rotation of the stepper plate is determined by the stop. Also stop  39 B at the bottom layer can define the stepper  32 B rotation angle thus the motion of the micromirror  31 . While the rotation amount of the stepper is defined, the inside stops  39 C plays a role as a contact point to define a plane of the stepper plate  32 . And the stepper plate  32  upholds the micromirror. The motion of the micromirror is defined by the rotation amounts of the stepper plate  32  which is determined by the height and/or the position of the stops  34 A,  34 B,  34 C. The motion of the micromirror is defined by the amounts of the rotation of the stepper plate constraint by the position and height of the stops under the stepper plate and/or at the bottom layer. The micromirror has at least one motion programmed by the amount of the rotation of the stepper plate. The stepper plate has at least one stop, wherein the stop is coupled to the bottom layer or the bottom layer has at least one stop, wherein the stop is coupled to the stepper plate. The micromirror has at least one motion programmed by amount of the rotation of the stepper plate and the position of the support. The motion of the micromirror is defined by contact position of the supports on the stepper plate or the support under the micromirror after the stepper plate is rotated. The motion of the micromirror is defined by rotation angle restricted by the stops. The amount of rotation of the stepper plate is determined by the stop and wherein the motion of the micromirror is defined by the mixture of support and stop types. Any combination of supports and stops can be possible even though  FIGS. 3A, 3B , and  3 C don&#39;t show all cases. For example, the motion of the micromirror can be defined by amount of the rotation of the stepper plate and the position of the support or by contact position of the supports on the stepper plate and the support under the micromirror after the stepper plate is rotated.  
         [0036]      FIG. 4  shows a stepper plate  43  with quadruple supports  42  on a stepper plate  43  and electrodes  41  for generating four different direction of rotations. The angle amount of the each directional rotation can be same and each motion of the micromirror is controlled by position of support. Also, the angle amount of the each directional rotation can be controlled by using the stop (not shown). The multiple motions of the micromirror are obtained by the supports  42  with respect to the inclination direction of the stepper plate. The micromirror has at least one motion programmed by the position of the support. If the voltage is applied on one of the electrode  41 , the stepper plate  43  is inclined and snapped down to the direction of the voltage applied electrode  41 . Then the support  42  in opposite side is rotated and raises its tip position by the inclination of the stepper plate  43 . The raised support  42  upholds the micromirror to the desired position. Since there are four electrodes, the stepper plate  43  is inclined to the corresponding directions of the electrodes  41 . For each inclination direction, the position of the support  42  is determined for generating the desired motion of the micromirror. The position and the height of the support  42  is determined to have the pre-programmed motions and fabricated during making process of the micromirror system. To have larger electrostatic force or lower driving voltage, electric bias can be applied to two or three electrodes at the same time. Since the area of the electrode is doubled or tripled, the electrostatic force becomes larger than that of one electrode case. Each motion of the micromirror can be controlled by using the amount of the each directional rotation and position of support  
         [0037]      FIG. 5  shows another example of a stepper plate  53  with discretely controlled micromirror method. Eight supports  52  and electrodes  51  for generating eight different heights for generating motions. If the voltage is applied on one of the eight electrodes  51 , the stepper plate  52  is inclined and snapped down to the direction of voltage applied electrode  51 . Then the support  52  in opposite side is raised by the inclination of the stepper plate  52 . The raised support  52  upholds the micromirror to the desired position. Since there are eight electrodes, the stepper plate is inclined to the corresponding directions of the electrodes. For each inclination direction, the position of the support  52  is determined for generating the desired motion of the micromirror. Also, each directional rotation of the stepper plate is controlled by multiple electrodes by sharing electrodes to have larger electrostatic force or lower driving voltage at the same time. Since the area of the electrode  51  is increased, the electrostatic force becomes larger than that of one electrode case. The system has multiple motions which are constraint by the number of the supports in the stepper plates  53 . Since the stepper plate contacts the bottom layer structure, the surface forces can cause the stiction problems even though the stepper plate is wholly grounded. To reduce the possible stiction problem, the stepper plate has the tip  54  structure to reduce the contact area of stepper plate. Also the contacting structures have the same potential to prevent stiction problem.  
         [0038]      FIG. 6  is a schematic diagram of springless hinge structure. The stepper plate  61  is attached to a flexible spring, and the flexible spring is attached to a fixed structure in  FIG. 2 . But the spring can be omitted by using hinge structure as  FIG. 6 . The stepper plate  62  is confined in the hinge structure  63 , while the stepper plate  62  has a motion with inclination.  
         [0039]     In  FIG. 7 , configuration with three degrees of freedom  95 ,  96  is presented. The motion has two degrees of freedom rotation  95  and one degree of translation  96 . For representing three degrees of freedom motion, at least three supports  94  are needed from different stepper plates  92 . In-plane position and/or height of each support  94  from three stepper plates  92  define a specific motion in three dimensional space. These three points by the three supports  94  make a plane for the micromirror  91  representing micromirror motion. Every motion can be specified as a step. In a step, three supports  94  from different stepper plate  92  define a plane of micromirror. In the same way, three other positions by the three other supports define another plane for the micromirror  91 . As many planes as the numbers of the supports in a stepper plate  92  can be defined by three stepper plates  92 .  
         [0040]     An example of light modulation is presented in  FIG. 8 . The micromirror  102  in the figure has four different motions  103  which are defined by the supports from one or two or three stepper plates. The motions can be controlled by applying voltage to the corresponding electrodes under the stepper plates. Each motion represents the specified micromirror angle  103  for reflecting incident light  101 . The micromirror is rotated as the motion is changed and finally changes the path of the reflected light from the micromirror. The reflected light goes to the different positions  105  in the screen  104 . By using a micromirror with multiple support stepper plate, a micromirror can act as multi-channel optical switch for deflecting the incident light into multiple directions  105 . The multi-channel optical switch deflects the incident light to the desired direction by rotating the micromirror or micromirrors. Since the micromirror motion is not restricted in one dimensional motion, the micromirror can reflect the incident light in a plane with multiple axis change by the rotational motions even with time delay by the translational motion of the micromirror.  
         [0041]     In  FIG. 9 , another example of the spatial light modulation by the micromirror array lens  112 . Plurality of micromirrors  112  are controlled by the common voltage electrodes. Micromirror array lens has many micromirrors  113  which are optically coupled to form a lens and controlled to have steps representing various focal lengths. In each step of the motion, each micromirror forms a different focal length lens surface which gives a specified focusing power to the lens. As the figure shows, each step makes the incident beam  111  focused at the screen  114  with the different focal length of the micromirror array lens  112 . The focused light pattern  115  by each step of the motion is given in the screen  114 . Since the micromirror array lens needs to be controlled to have rotational freedom and translational freedom together, the multi-motion programmable micromirror control is a good solution for having focal length variation. Also the focal length of the micromirror array lens can be programmed during the fabrication process of the micromirrors and the focal length change can be obtained by easily applying the driving voltages on the corresponding electrodes.  
         [0042]     While the invention has been shown and described with reference to different embodiments thereof, it will be appreciated by those skills in the art that variations in form, detail, compositions and operation may be made without departing from the spirit and scope of the invention as defined by the accompanying claims.