Micro-mirror device

Abstract: A micro-mirror device includes a substrate (21), address electrodes (30) provided on the substrate, and a micro-mirror (51) disposed to face the substrate (21) and to be spaced a predetermined distance from the substrate (21); and is adapted so that the slope of the micro-mirror (51) can be adjusted by electrostatic attraction forces between the address electrodes (30) and the micro-mirror (51). The micro-mirror device includes auxiliary electrodes (40) which are formed on and projected from the substrate (21) and the upper portions of which are disposed in the vicinity of the micro-mirror (51) so that distances between the micro-mirror (51) and the auxiliary electrodes (40) can remain narrow even when the micro-mirror (51) is inclined by electrostatic attraction forces in one direction, and the micro-mirror (51) can be restored by electrostatic attraction forces of the auxiliary electrodes when restored.

Description: The present invention relates to a micro-mirror device adapted so as to change a reflection path of an incident light beam by pivoting a micro-mirror using electrostatic attraction forces, and more particularly, to a micro-mirror device in which a structure for restoring the micro-mirror skewed by electrostatic attraction forces to its original position is improved. 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 reflect incident light beams at different reflection angles depending on pivoting angles or directions. Micro-mirror device arrays are applied to 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 a number of required pixels are arrayed in a two-dimensional plane, as shown in Figure 1. The micro-mirrors 1 arrayed 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. Patent No. 5,331,454 entitled "LOW RESET VOLTAGE PROCESS FOR DMD" issued Jul. 19, 1994 and allowed to Texas Instruments Incorporated, and U.S. Patent No. 5,535,047 entitled "ACTIVE YOKE HIDDEN HINGE DIGITAL MICROMIRROR DEVICE" issued Jul. 9, 1996 and allowed to Texas Instruments Incorporated. EP 769 713 discloses a micro-mirror controlled by a first set of electrodes and elevated auxiliary electrodes. US 5,444,566 discloses a micro-mirror controlled by main and auxiliary electrodes. When the disclosed micro-mirror devices are briefly reviewed, as shown in Figure 2, each device 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. Here, 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 horizontally positioned state by an elastic restoring force. Since 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 a side having a 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 horizontally positioned state. That is, as shown in Figure 3, when voltages V1 and V2 applied to the first and second address electrodes 13 and 14, and voltage V3 applied to the micro-mirror 15 all are zero (0), the micro-mirror 15 is maintained in a horizontally positioned state. Therefore, distance r1 between the first electrode 13 and the micro-mirror 15 and distance r2 between the second electrode 14 and the micro-mirror 15 are the same. On the other hand, when voltages V1, V2, and V3 applied to the first and second address electrodes 13 and 14 and the micro-mirror 15, respectively, have the relationship of V1 < V2 < V3, an electrostatic force F1 acting between the first address electrode 13 and the micro-mirror 15 is greater than an electrostatic force F2 acting between the second address electrode 14 and the micro-mirror 15, as shown in Figure 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 F1 is balanced with the sum of the electrostatic force F2 and a restoring force of the hinge or post, and the condition of r1 < r2 can be satisfied. Subsequently, when the position of the micro-mirror is changed from the position shown in Figure 4 to the position shown in Figure 3, or to a position where the micro-mirror is inclined to a direction opposite to the position shown in Figure 4, the operation of the micro-mirror device will be described as follows. First, when voltages V1, V2, and V3 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 Figure 3 by the restoring force of the hinge or post which tends to maintain the micro-mirror in a horizontally positioned state. In this case, since the dimensions of the hinge or post are on the order of µm, the strength of the hinge is relatively weak with respect to a torque, and the restoring force of the hinge is very weak. Therefore, a time required to change the position of the micro-mirror is longer than a desired time for driving the micro-mirror device, and there is a problem in that the micro-mirror device cannot be driven at high speed. Next, when voltages V1, V2, and V3 which have the relationship of V2 < V1 < V3 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 F1 and F2 are compared to each other, the fact the difference between voltages V2 and V3 is greater than the difference between voltages V2 and V3 does not always mean that the electrostatic force F2 is greater than the electrostatic force F1. The reason is that the electrostatic forces F1 and F2 are inversely proportional to respective squares of distances r1 and r2 between the first and second address electrodes 13 and 14 and the micro-mirror 15. Therefore, in this case, until distances r1 and r2 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, and the driving speed of the micro-mirrors is limited. With a view to solve or reduce the above problem, it is an aim of embodiments of the present invention to provide a micro-mirror device in which structures of electrodes are improved 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. According to a first aspect of the present invention, there is provided a micro-mirror device including a substrate, address electrodes provided on the substrate, and a micro-mirror disposed to face the substrate and to be spaced a predetermined distance from the substrate; and adapted so that the slope of the micro-mirror can be adjusted by electrostatic attraction forces between the address electrodes and the micro-mirror, wherein the micro-mirror device includes auxiliary electrodes which are formed on and projected from the substrate, and wherein the upper portions of the auxiliary electrodes are disposed in the vicinity of the micro-mirror and are located outside a perimeter 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, characterized in that side walls of the auxiliary electrodes extend substantially vertically from the substrate to the vicinity of the micro-mirror. Preferably, the address electrodes include first and second address electrodes provided on the substrate and spaced a predetermined distance from each other; the auxiliary electrodes include first and second auxiliary electrodes provided in the vicinity of the first and second address electrodes, respectively, and formed to project beyond the micro-mirror; and when the micro-mirror is restored after being inclined by an electrostatic attraction force between the first address electrode and the micro-mirror, the restoring speed of the mirror can be enhanced by an electrostatic attraction force between the second auxiliary electrode and the micro-mirror. Preferably, the first and second auxiliary electrodes are shaped like vertically erected plates, cylinders, or polygonal pillars. Preferably, when the position of the micro-mirror is changed, the same voltage is applied to the first address electrode and the first auxiliary electrode. Preferably, the first address electrode and the first auxiliary electrode are integrally formed. Preferably, wherein when the position of the micro-mirror is changed, the same voltage is applied to the second address electrode and the second auxiliary electrode. Preferably, the second address electrode and the second auxiliary electrode are integrally formed. For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which: Figure 1 is a schematic plan view illustrating a conventional micro-mirror device array for an image displaying apparatus; Figure 2 is a schematic perspective view illustrating a conventional micro-mirror device; Figures 3 and 4 are schematic side views for describing the operation of the conventional micro-mirror device; Figure 5 is a schematic perspective view illustrating a micro-mirror device of an image displaying apparatus according to an embodiment of the present invention; Figures 6 and 7 are schematic side views for describing the operation of the micro-mirror device shown in Figure 5; and Figure 8 is an exploded perspective view illustrating a micro-mirror device of an image displaying apparatus according to another embodiment of the present invention. Referring to Figure 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 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 supported to be 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 has a corner shape. In this case, since distances between the first and second auxiliary electrodes 41 and 45 and the micro-mirror are narrow and 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 is 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 narrow. 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 more 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 Figures 6 and 7 as follows. Figure 6 shows that the micro-mirror 51 is maintained in a horizontally positioned state. In Figure 6, voltages V11 and V21 applied to the first and second address electrodes 31 and 35, respectively, voltages V12 and V22 applied to the first and second auxiliary electrodes 41 and 45, respectively, and voltage V4 applied to the micro-mirror all are zero (0), and, therefore, the micro-mirror 51 is maintained in a horizontal state by the strength of the hinge or post. Therefore, distances r11 and r21 between the first and second address electrodes 31 and 35 and the micro-mirror 51 are the same. Also, distances r12 and r22 between the first and second auxiliary electrodes 41 and 45 and the micro-mirror 51 are the same. Here, the distances r12 and r22 are much smaller than the distances r11 and r21 when the micro-mirror 51 is in a horizontal state, and even when the micro-mirror 51 is inclined, the distances r12 and r22 remain smaller than the distances r11 and r21. On the other hand, when voltages V11, V21, and V4 applied to the first and second address electrodes 31 and 35 and the micro-mirror 51 have the relationship, V11 < V21 < V4, an electrostatic force F11 acting between the first address electrode 31 and the micro-mirror 51 is greater than an electrostatic force F21 acting between the second address electrode 35 and the micro-mirror 51, as shown in Figure 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 F11 is balanced with the sum of the electrostatic force F21 and the restoring force of the hinge or post, and the condition of r11 < r21 is satisfied. Here, voltages V12 and V22 are applied to the first and second auxiliary electrodes 41 and 45 and voltage V4 is applied to the micro-mirror 51 so that voltages V12, V22, and V4 have the relationship V12 < V22 < V4. When voltages V12 and V22 are applied as above, the voltages V12 and V22 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 V11, V21, and V4 applied to the first and second address electrodes 31 and 35 and the micro-mirror 51 respectively, have the relationship of V11 > V21 > V4, the result as shown in Figure 7 can also be obtained. Subsequently, when the position of the micro-mirror 51 is changed from the position shown in Figure 7 to the position shown in Figure 6, or to a position where the micro-mirror 51 is inclined in a direction opposite to the position shown in Figure 7, the operation of the micro-mirror device will be described as follows. Voltages V12, V22, and V4 which have the relationship of V22 < V12 < V4 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 electrostatic forces. In this case, since distances r12 and r22. between the first and second auxiliary electrodes 41 and 45 and the micro-mirror 51 are very short, and the difference between V22 and V4 is greater than the difference between V12 and V4, electrostatic force F22 is greater than electrostatic force F12. The time required to change the position of the micro-mirror 51 by the electrostatic attraction force between the first and second auxiliary electrodes 41 and 45 and the micro-mirror 51 as above can be reduced. In addition, when the slope of the micro-mirror 51 is to be changed, desired voltages, i.e., voltages V11 and V21 which have the relationship V21 < V11 < V4 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 Figure 7. In this case, since electrostatic attraction forces between the first and second auxiliary electrodes 41 and 45 and the micro-mirror 51 act in addition to 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 reduced more. 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 be the same. In addition, when the micro-mirror 51 is operated and restored, it is possible that voltages may be sequentially applied to the first and second auxiliary electrodes 41 and 45 and the first and second address electrodes 31 and 35. Referring to Figure 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. Here, 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, since 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 Figures 5 through 7, detailed descriptions thereof are omitted. This embodiment is different 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 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.

Claims: A micro-mirror device including a substrate (21), address electrodes (30) provided on the substrate, and a micro-mirror (51) disposed to face the substrate and to be spaced a predetermined distance from the substrate; and adapted so that the slope of the micro-mirror can be adjusted by electrostatic attraction forces between the address electrodes (30) and the micro-mirror (51), wherein the micro-mirror device includes auxiliary electrodes (40) which are formed on and projected from the substrate (21), and wherein the upper portions of the auxiliary electrodes are disposed in the vicinity of the micro-mirror (51) and are located outside a perimeter of the micro-mirror so that restoring force and restoring speed can be enhanced by electrostatic forces of the auxiliary electrodes (40) when an inclined micro-mirror (51) is restored, characterized in that the side walls of the auxiliary electrodes (40) extend substantially vertically from the substrate (21) to the vicinity of the micro-mirror (51). The micro-mirror device as claimed in claim 1, wherein the address electrodes (30) include first and second address electrodes (31, 35) provided on the substrate (21) and spaced a predetermined distance from each other; the auxiliary electrodes (40) include first and second auxiliary electrodes (41, 45) provided in the vicinity of the first and second address electrodes (31, 35), respectively, and formed to project beyond the micro-mirror (51); and when the micro-mirror (51) is restored after being inclined by an electrostatic attraction force between the first address electrode (31) and the micro-mirror (51), the restoring speed of the mirror can be enhanced by an electrostatic attraction force between the second auxiliary electrode (45) and the micro-mirror (51). The micro-mirror device as claimed in claim 2, wherein the first and second auxiliary electrodes (41, 45) are shaped like vertically erected plates, cylinders, or polygonal pillars. The micro-mirror device as claimed in claim 2 or 3, wherein when the position of the micro-mirror (51) is changed, the same voltage is applied to the first address electrode (31) and the first auxiliary electrode (41). The micro-mirror device as claimed in any of claims 2 to 4, wherein the first address electrode (31) and the first auxiliary electrode (41) are integrally formed. The micro-mirror device as claimed in any one of claims 2 through 5, wherein when the position of the micro-mirror (51) is changed, the same voltage is applied to the second address electrode (35) and the second auxiliary electrode (45). The micro-mirror device as claimed in any of claims 2 through 6, wherein the second address electrode (35) and the second auxiliary electrode (45) are integrally formed.

Inventors: CHIN DAE-JE, LEE SANG-HUN, SHIN HYUNG-JAE, CHIN, DAE-JE, LEE, SANG-HUN, SHIN, HYUNG-JAE, Chin, Dae-je, 1501 Samsung Borameomni Apt., Shin, Hyung-jae, 125-703 Sibeom Hanshin Apt.
Applicants: SAMSUNG ELECTRONICS CO LTD, SAMSUNG ELECTRONICS CO., LTD.
Application year: 2000
Main classification: G02B26
IPC codes: G02B26, H04N5, B81B3