Abstract:
A micro-mirror device and associated method, the device including a substrate, address electrodes provided on the substrate, and a micro-mirror facing the substrate and spaced a predetermined distance from the substrate. The micro-mirror device is adapted so that the slope of the micro-mirror can be adjusted by electrostatic attraction forces between the address electrodes and the micro-mirror. The micro-mirror device further includes auxiliary electrodes formed on and projected from the substrate. The upper portions of the auxiliary electrodes are disposed in the vicinity of the micro-mirror, so that distances between the micro-mirror and the auxiliary electrodes can remain small, even when the micro-mirror is inclined by electrostatic attraction forces in one direction. Accordingly, restoration of the micro-mirror is enhanced by electrostatic attraction forces of the auxiliary electrodes.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a micro-mirror device and an associated method, the device adapted so as to change the reflection path of an incident light beam by pivoting a micro-mirror using electrostatic attraction forces. More particularly, the present invention relates to a micro-mirror device and an associated method, the device having an improved structure for restoring the micro-mirror skewed by electrostatic attraction forces to its original position. 
     2. Description of the Related Art 
     A general micro-mirror device array is an array in which a plurality of micro-mirrors are installed so as to be pivoted by electrostatic attraction forces, and to reflect incident light beams at different reflection angles depending on pivoting angles or directions. Applications of micro-mirror device arrays include an image displaying apparatus of a projection television and various laser scanning devices such as a scanner, copier, or facsimile machine. In particular, when a micro-mirror device array is employed in an image displaying apparatus, in the micro-mirror device array, micro-mirrors  1  corresponding to the number of required pixels are arranged in an array in a two-dimensional plane, as shown in FIG.  1 . The micro-mirrors  1  arranged in an array, so as to correspond to respective pixels as described above are independently pivoted according to an image signal, decide respective reflection angles of incident light beams, and, therefore, can form an image. 
     Such micro-mirror devices are disclosed in, for example, U.S. Pat. No. 5,331,454 entitled “LOW RESET VOLTAGE PROCESS FOR DMD” issued Jul. 19, 1994 and assigned to Texas Instruments Incorporated, and U.S. Pat. No. 5,535,047 entitled “ACTIVE YOKE HIDDEN HINGE DIGITAL MICROMIRROR DEVICE” issued Jul. 9, 1996 and assigned to Texas Instruments Incorporated. 
     Briefly, as shown in FIG. 2, each of the disclosed micro-mirror devices comprises a substrate  11 , first and second address electrodes  13  and  14  provided on the substrate  11 , and a micro-mirror disposed to be spaced from and facing the first and second address electrodes  13  and  14 . 
     In the disclosed micro-mirror devices, the micro-mirror  15  is installed on the substrate  11  by means of at least one elastically deformable hinge or post so as to be pivotable, and is maintained in a horizontal position by an elastic restoring force. As the structure of such a hinge or post is described in the above-mentioned inventions, a detailed description thereof is omitted. 
     In the micro-mirror device having the structure as described above, when respective voltages are applied to the first and second address electrodes  13  and  14  and the micro-mirror  15 , the micro-mirror  15  is inclined by electrostatic attraction forces formed according to the differences in electric potentials between the first address electrode  13  and the micro-mirror  15  and between the second address electrode  14  and the micro-mirror  15  to the side having the larger electric potential difference. However, the electrostatic attraction forces must overcome the strength of the hinge or post which tends to keep the micro-mirror in the horizontal position. 
     That is, as shown in FIG. 3, when voltages V 1  and V 2  applied to the first and second address electrodes  13  and  14 , and voltage V 3  applied to the micro-mirror  15  all are zero (0), the micro-mirror  15  is maintained in a horizontal position. Therefore, the distance r 1  between the first electrode  13  and the micro-mirror  15  and the distance r 2  between the second electrode  14  and the micro-mirror  15  are the same. 
     On the other hand, when voltages V 1 , V 2 , and V 3  applied to the first and second address electrodes  13  and  14  and the micro-mirror  15 , respectively, have the relationship of V 1 &lt;V 2 &lt;V 3 , the electrostatic force F 1  acting between the first address electrode  13  and the micro-mirror  15  is greater than the electrostatic force F 2  acting between the second address electrode  14  and the micro-mirror  15 , as shown in FIG.  4 . Accordingly, the micro-mirror  15  is pivoted toward the first address electrode  13  side of the substrate  11 , and is inclined to a position where the electrostatic force F 1  is balanced by the sum of the electrostatic force F 2  and a restoring force of the hinge or post, such that the condition of r 1 &lt;r 2  is satisfied. 
     The position of the micro-mirror can also be changed from the position shown in FIG. 4 to the position shown in FIG. 3, or to a position where the micro-mirror is inclined to a direction opposite to the position shown in FIG.  4 . These operations of the micro-mirror device are described as follows. 
     First, when voltages V 1 , V 2 , and V 3  which all are zero (0) are applied to the first and second address electrodes  13  and  14 , and the micro-mirror  15 , the position of the micro-mirror  15  changes to the position shown in FIG. 3 under the restoring force of the hinge or post which tends to maintain. the micro-mirror in a horizontal position. In this case, since the dimensions of the hinge or post are on the order of □m, the strength of the hinge is relatively weak with respect to torque, and the restoring force of the hinge is very weak. Therefore, the time required to change the position of the micro-mirror is longer than the desired time for driving the micro-mirror device, creating a problem in that the micro-mirror device cannot be driven at high speed. 
     Next, when voltages V 1 , V 2 , and V 3  which have the relationship of V 2 &lt;V 1 &lt;V 3  are applied to the first and second address electrodes  13  and  14  and the micro-mirror  15 , respectively, and the micro-mirror  15  is driven to be inclined in the opposite direction, the position of the micro-mirror  15  is changed by the restoring force of the hinge or post and electrostatic forces. In this case, when electrostatic forces F 1  and F 2  are compared to each other, the fact that the difference between voltages V 2  and V 3  exceeds the difference between voltages V 2  and V 3  does not always mean that the electrostatic force F 2  is greater than the electrostatic force F 1 . The reason is that the electrostatic forces F 1  and F 2  are inversely proportional to respective squares of distances r 1  and r 2  between the first and second address electrodes  13  and  14  and the micro-mirror  15 . Therefore, in this case, until distances r 1  and r 2  become similar to each other due to the restoring force of the hinge, the effect of reducing the time required to change the position of the micro-mirror  15  by applying voltages having reversed values is insignificant. 
     Therefore, the micro-mirror device having the structure as described above requires a relatively long time to change the position of a micro-mirror by forming electrostatic attraction forces. Consequently, the driving speed of the micro-mirrors is limited. 
     SUMMARY OF THE INVENTION 
     To solve the above problem, it is an objective of the present invention to provide a micro-mirror device and an associated method, the device having improved electrode structures, so that the time required to change the position of a micro-mirror, for example, to change from an inclined position of the micro-mirror to an initial position of the micro-mirror, or to an oppositely inclined position of the micro-mirror, can be reduced. 
     Accordingly, to achieve the above objective, the present invention provides a micro-mirror device including a substrate, address electrodes being provided on the substrate, and a micro-mirror facing the substrate and spaced a predetermined distance from the substrate. The micro-mirror is adapted so that the slope of the micro-mirror can be adjusted by electrostatic attraction forces between the address electrodes and the micro-mirror. The micro-mirror device includes auxiliary electrodes that are formed on and projected from the substrate and the upper portions of which are disposed in the vicinity of the micro-mirror so that restoring force and restoring speed can be enhanced by electrostatic forces of the auxiliary electrodes when an inclined micro-mirror is restored. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above objective and advantage of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings, in which: 
     FIG. 1 is a schematic plan view illustrating a conventional micro-mirror device array for an image displaying apparatus; 
     FIG. 2 is a schematic perspective view illustrating a conventional micro-mirror device; 
     FIGS. 3 and 4 are schematic side views for describing the operation of the conventional micro-mirror device; 
     FIG. 5 is a schematic perspective view illustrating a micro-mirror device of an image displaying apparatus according to an embodiment of the present invention; 
     FIGS. 6 and 7 are schematic side views for describing the operation of the micro-mirror device shown in FIG. 5; and 
     FIG. 8 is an exploded perspective view illustrating a micro-mirror device of an image displaying apparatus according to another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 5, a micro-mirror device according to an embodiment of the present invention comprises a substrate  21 , electrodes provided on the substrate  21 , and a micro-mirror  51  disposed to be spaced from and facing the electrodes. The micro-mirror  51  is installed to be pivoted above the substrate  21  by electrostatic attraction forces between the electrodes and the micro-mirror  51 . The micro-mirror  51  is made pivotable by a hinge (not shown) or post (not shown). 
     The electrodes comprise a plurality of address electrodes  30  disposed on the substrate  21 , facing the micro-mirror  51 , and a plurality of auxiliary electrodes  40  disposed on the substrate  21  in the vicinity of the address electrodes  30 , projecting toward the micro-mirror  51 . 
     The address electrodes  30  include first and second address electrodes  31  and  35  provided on the substrate  21 , spaced a predetermined distance from each other and independently supplied with electric power. 
     The auxiliary electrodes  40  are provided in the vicinity of the first and second address electrodes  31  and  35 , respectively, and include first and second auxiliary electrodes  41  and  45  each of which has one end projecting beyond the micro-mirror  51 , and each of which is independently supplied with electric power. Here, the first address electrode  31  and the first auxiliary electrode  41  may be independently or simultaneously supplied with electric power, and the second address  35  and the second auxiliary electrode  45  are supplied with electric power in a similar manner. In addition, the first and second auxiliary electrodes  41  and  45  are formed vertically around the outside of the first and second address electrodes  31  and  35 , respectively, and each is corner shaped. In this configuration, because distances between the first and second auxiliary electrodes  41  and  45  and the micro-mirror are small and the effective surfaces of the first and second auxiliary electrodes  41  and  45  are large, electrostatic attraction forces between the first and second auxiliary electrodes  41  and  45  and the micro-mirror  51  can be strengthened. 
     The first and second auxiliary electrodes  41  and  45  are formed to project beyond the micro-mirror  51  as described above so that when the micro-mirror  51  is inclined in a direction, for example, toward the first auxiliary electrode  41 , the distance between the opposite auxiliary electrode, i.e., the second auxiliary electrode  45  and the micro-mirror  51  can be kept small. Therefore, when the micro-mirror  51  is restored to its original position, the restoring speed of the micro-mirror  51  can be enhanced by, in addition to the restoring force of the hinge or post, an electrostatic attraction force between the second auxiliary electrode  45  and the micro-mirror  51 . In this case, by applying electric power to the second address electrode  35 , the restoring speed can be enhanced by an electrostatic attraction force between the second address electrode  35  and the micro-mirror  51 . 
     The operation of the micro-mirror device having the structure as described above will be described with reference to FIGS. 6 and 7 as follows. 
     FIG. 6 depicts the micro-mirror  51  maintained in a horizontal position. In FIG. 6, voltages V 11  and V 21  applied to the first and second address electrodes  31  and  35 , respectively, voltages V 12  and V 22  applied to the first and second auxiliary electrodes  41  and  45 , respectively, and voltage V 4  applied to the micro-mirror all are zero (0). Therefore, the micro-mirror  51  is maintained in a horizontal state by the strength of the hinge or post. Consequently, distances r 11  and r 21  between the first and second address electrodes  31  and  35  and the micro-mirror  51  are the same. Also, distances r 12  and r 22  between the first and second auxiliary electrodes  41  and  45  and the micro-mirror  51  are the same. Here, the distances r 12  and r 22  are much smaller than the distances r 11  and r 21 , and even when the micro-mirror  51  is inclined, the distances r 12  and r 22  remain smaller than the distances r 11  and r 21  when the micro-mirror  51  is in a horizontal state. 
     On the other hand, when voltages V 11 , V 21 , and V 4  applied to the first and second address electrodes  31  and  35  and the micro-mirror  51  have the relationship, V 11 &lt;V 21 &lt;V 4 , the electrostatic force F 11  acting between the first address electrode  31  and the micro-mirror  51  is greater than the electrostatic force F 21  acting between the second address electrode  35  and the micro-mirror  51 , as shown in FIG.  7 . Accordingly, the micro-mirror  51  rotates toward the first address electrode  31  side of the substrate  21 , and is inclined to a position where the electrostatic force F 11  is balanced by the sum of the electrostatic force F 21  and the restoring force of the hinge or post, such that the condition of r 11 &lt;r 21  is satisfied. Here, voltages V 12  and V 22  are applied to the first and second auxiliary electrodes  41  and  45  and voltage V 4  is applied to the micro-mirror  51  so that the voltages V 12 , V 22 , and V 4  have the relationship V 12 &lt;V 22 &lt;V 4 . When voltages V 12  and V 22  are applied as above, the voltages V 12  and V 22  are the same voltages applied to the first and second address electrodes  31  and  35 , respectively. In this case, the first address electrode  31  and the first auxiliary electrode  41 , and the second address electrode  35  and the second auxiliary electrode  45  are integrally formed, respectively. 
     In addition, when voltages V 11 , V 21 , and V 4  applied to the first and second address electrodes  31  and  35  and the micro-mirror  51  respectively, have the relationship of V 11 &gt;V 21 &gt;V 4 , the result as shown in FIG. 7 can also be obtained. 
     The position of the micro-mirror  51  can also be changed from the position shown in FIG. 7 to the position shown in FIG. 6, or to a position where the micro-mirror  51  is inclined in a direction opposite to the position shown in FIG.  7 . These operations of the micro-mirror device are described as follows. 
     Voltages V 12 , V 22 , and V 4  which have the relationship of V 22 &lt;V 12 &lt;V 4  are applied to the first and second auxiliary electrodes  41  and  45  and the micro-mirror  51 , respectively, so that the micro-mirror  51  is driven to be inclined in the opposite direction. In this case, the position of the micro-mirror  51  is changed by the restoring force of the hinge or post, which supports the micro-mirror  51 , and by electrostatic forces. In this case, because distances r 12  and r 22  between the first and second auxiliary electrodes  41  and  45  and the micro-mirror  51  are very short, and the difference between V 22  and V 4  exceeds the difference between V 12  and V 4 , the electrostatic force F 22  is greater than the electrostatic force F 12 . The time required to change the position of the micro-mirror  51  using the electrostatic attraction force between the first and second auxiliary electrodes  41  and  45  and the micro-mirror  51  can be reduced, as above. 
     In addition, when the slope of the micro-mirror  51  is to be changed, desired voltages, i.e., voltages V 11  and V 21  which have the relationship V 21 &lt;V 11 &lt;V 4  are applied to the first and second address electrodes  31  and  35 , respectively, so that the micro-mirror  51  is driven to be inclined in a direction opposite to the direction of inclination shown in FIG.  7 . In this case, because electrostatic attraction forces between the first and second auxiliary electrodes  41  and  45  and the micro-mirror  51  act in addition to the electrostatic attraction forces between the first and second address electrodes  31  and  35  and the micro-mirror  51 , the time required to change the position of the micro-mirror  51  can be further reduced. Here, voltages applied to the first address electrode  31  and the first auxiliary electrode  41  can be the same, and voltages applied to the second address electrode  35  and the second auxiliary electrode  45  can also be the same. 
     In addition, when the micro-mirror  51  is operated and restored, sequential application of voltages to the first and second auxiliary electrodes  41  and  45  and the first and second address electrodes  31  and  35  is possible. 
     Referring to FIG. 8, a micro-mirror device according to another embodiment of the present invention comprises a substrate  121 , electrodes provided on the substrate  121 , and a micro-mirror  151  supported by a hinge or post on the substrate  121  so as to be spaced a predetermined distance from the substrate  121 . The electrodes comprise address electrodes  130  disposed on the substrate  121  and spaced a predetermined distance from each other, and auxiliary electrodes  140  disposed on the substrate  121  in the vicinity of the address electrodes  130 , projecting toward the micro-mirror  151 . In this embodiment, the address electrodes  130  include first and second address electrodes  131  and  135  driven independently of each other and spaced a predetermined distance from each other. In addition, the auxiliary electrodes  140  include first and second auxiliary electrodes  141  and  145  provided in the vicinity of the first and second address electrodes  131  and  135 , respectively, for enhancing the restoring speed of the inclined micro-mirror  151  by electrostatic attraction forces. Here, because the substrate  121 , the first and second address electrode  131  and  135 , and the micro-mirror  151  are substantially the same as members described with reference to FIGS. 5 through 7, detailed descriptions thereof are omitted. 
     This embodiment differs from the micro-mirror device according to the previously described embodiment in that the first and second auxiliary electrodes  141  and  145  have a cylindrical shape or a polygonal pillar shape. When the first and second auxiliary electrodes  141  and  145  are provided as above, electrostatic attraction forces can be reinforced without markedly lowering the efficiency of utilizing light, since the spaces occupied by the first and second auxiliary electrodes  141  and  145  are small, and, therefore, most of an incident beam can travel to the micro-mirror  151 . 
     Since the micro-mirror device having the structure described above is provided with auxiliary electrodes disposed in the vicinity of the respective address electrodes and projected toward the micro-mirror, the restoring speed of an inclined micro-mirror can be enhanced by electrostatic attraction forces between the auxiliary electrodes and the micro-mirror, and, therefore, the micro-mirror device can be widely utilized in image displaying apparatuses requiring high response speed. 
     The above description of the preferred embodiments has been given by way of example. From the disclosure given, those skilled in the art will not only understand the present invention and its attendant advantages, but will also find apparent various changes and modifications to the structures disclosed. It is sought, therefore, to cover all such changes and modifications as fall within the spirit and scope of the invention, as defined by the appended claims, and equivalents thereof.