MEMS tensioning structure and manufacturing method thereof

Abstract

A micro-electro-mechanical (MEM) device may include a first platform including a first platform reflective surface; a first frame pivotally coupled to the first platform; a second frame coupled to the first frame; and one or more of: a second frame flexible structure on the first frame and the second frame or a first platform flexible structure on the first platform, and a tensioning structure. The tensioning structure may be coupled to the first frame for creating a tension in one or more of the second frame flexible structure and the first platform flexible structure to prevent buckling of one or more of the second frame flexible structure and the first platform flexible structure.

Description

[0001] Citations of Related Applications

[0002] This application claims priority to U.S. patent application No. 18 / 468,687, filed on September 16, 2023, which claims the benefit of U.S. Provisional Application No. 63 / 376,335, filed on September 20, 2022 (invention title: "MEMS tensioning structure and manufacturing method thereof"), the entire contents of which are incorporated herein by reference. Background Art

[0003] Micro-electromechanical systems (MEMS) devices are miniature mechanical structures with circuits and are manufactured using various integrated circuit (IC) manufacturing methods. One type of MEMS device is a MEMS micromirror device. A voltage can be applied between two electrodes in a micromirror device to control the state. Adjusting the state of the micromirror device can control the intensity and direction of light. Micromirror devices have a variety of applications in video projection, microscopy, and optics. Summary of the invention

[0004] Disclosed are a micro-electromechanical system (MEMS) micro-mirror device configured to have various tensioning structures and a method of manufacturing the MEMS micro-mirror device.

[0005] A microelectromechanical (MEM) device may include: a first platform including a first platform reflective surface; a first frame pivotally coupled to the first platform; a second frame coupled to the first frame; and one or more of the following: a second frame flexible structure located on the first frame and the second frame or a first platform flexible structure located on the first platform, and a tensioning structure. The tensioning structure may be coupled to the first frame to generate a tension in one or more of the second frame flexible structure and the first platform flexible structure to prevent buckling of one or more of the second frame flexible structure and the first platform flexible structure. The tensioning structure may include a material having a different thermal expansion coefficient than one or more of the first platform or the first frame. The tensioning structure may be partially embedded or fully embedded in the first frame. The tensioning structure may be partially or fully embedded in an edge portion of the first frame adjacent to the first platform.

[0006] The tensioning structure may include a first portion located on a first edge portion of the first frame and a second portion located on a second edge portion of the first frame. The first distance between the first platform and one or more of the first portion and the second portion may be greater than the second distance between the third portion and the first platform. The first frame may include one or more of one or more holes configured to generate a tension and one or more of one or more width reduction portions. The tensioning structure may include a plurality of sections that may be partially embedded or fully embedded in the first frame. The tensioning structure may be substantially perpendicular to the edge of the first frame. The tensioning structure may include a plurality of sections spaced apart by a predetermined distance, which may be substantially consistent. The tensioning structure may include one or more of a zigzag pattern and a sine wave pattern. The first portion of the tensioning structure may be substantially parallel to the second portion of the tensioning structure. The tensioning structure may be substantially parallel to the edge portion of the first frame. The first length of the first portion of the tensioning structure may be substantially the same as the second length of the second portion of the tensioning structure.

[0007] A method for generating tension in a microelectromechanical (MEM) device may include: coupling a movable frame to a platform having a reflective surface and to a stationary frame; and embedding one or more tensioning structures in the movable frame to generate a tension in one or more flexible structures to prevent buckling of the one or more flexible structures. The method may include: embedding a plurality of segments in the movable frame. The one or more tensioning structures may include one or more of a zigzag pattern and a sine wave pattern. The movable frame may include one or more of one or more holes configured to generate a tension and one or more reduced width portions. The one or more tensioning structures may be partially embedded or fully embedded in an edge portion of the movable frame adjacent to the platform. The one or more tensioning structures may include a first portion and a second portion. The first portion may be located at an edge portion of the movable frame and a distance from the platform that is less than a first distance, and the second portion may be located at an edge portion of the movable frame and a distance from the platform that is greater than the first distance.

[0008] A method for fabricating a tensioning structure in a microelectromechanical (MEM) device may include one or more of the following: forming a dielectric material layer on a first side of a substrate; forming one or more vertical isolation trenches containing the dielectric material on the first side of the substrate; patterning a mask layer on a second side of the substrate opposite the first side of the substrate; forming a through hole on the first side of the substrate; metallizing the first side of the substrate; depositing a second metal layer on the first side of the substrate to form a reflective surface; forming a second trench on the first side of the substrate to define a structure; deep etching the second side of the substrate to form a narrow blade; after forming the narrow blade, bonding a base wafer to the second side of the substrate; and etching through the second trench on the first side of the substrate to release the structure and provide electrical isolation.

[0009] The MEM device may include: a first platform including a first platform reflective surface; a first frame pivotally coupled to the first platform; a second frame coupled to the first frame; and a tensioning structure. The tensioning structure may be coupled to the first frame to generate a tension in one or more of the second frame flexible structure and the first platform flexible structure to prevent buckling of one or more of the second frame flexible structure and the first platform flexible structure. The substrate may include a silicon wafer, and the dielectric material may be silicon dioxide.

[0010] Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosed implementations, as claimed.

[0011] Incorporation by Reference

[0012] All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference.

[0013] US 5,501,893 A issued to Laermer et al. on March 26, 1996,

[0014] US 6,355,554 B1 issued to Choi et al. on March 12, 2002;

[0015] US 6,396,711 B1 issued to Degani et al. on May 28, 2002;

[0016] US 7,261,826 B2 issued to Adams et al. on August 28, 2007;

[0017] US 2002 / 0011759 A1 to Adams et al., published January 31, 2002;

[0018] US 2002 / 0146200 A1 by Kudrle et al., published October 10, 2002;

[0019] US 2004 / 0061579 A1 to Nelson, published April 1, 2004;

[0020] US 2005 / 0045727 A1 to Fu, published on March 3, 2005;

[0021] US 2005 / 0184003 A1 to Rodgers et al., published August 25, 2005;

[0022] US 2006 / 0203326 A1 to Fu, published September 14, 2006;

[0023] US 2008 / 0164542 A1 by Yang et al., published on July 10, 2008;

[0024] US 2011 / 0241137 A1 by Huang et al., published on October 6, 2011;

[0025] US 2012 / 0235725 A1 by Elmallah et al., published on September 20, 2012;

[0026] US 2013 / 0250532 A1 by Bryzek et al., published on September 26, 2013;

[0027] US 2013 / 0270660 A1 by Bryzek et al., published on October 17, 2013;

[0028] US 2020 / 0252716 A1 by Pedersen et al., published on August 6, 2020; and

[0029] US 2021 / 0396852 A1 by Wang et al., published on December 23, 2021. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The novel features of the present invention are particularly set forth in the appended claims. The features and advantages of the present invention will be better understood by referring to the following detailed description and the accompanying drawings, which set forth illustrative embodiments utilizing the principles of the present invention, and in the accompanying drawings:

[0031] Figure 1 shows a top view of a portion of a MEMS array including a plurality of MEMS micromirror devices according to some implementations of the present disclosure;

[0032] Figure 2 Some implementations of the present disclosure are shown along Figure 1 A partial cross section of the MEMS mirror array taken along line 2-2;

[0033] Figure 3A and Figure 3B shows a first tensioning structure and a second tensioning structure embedded in a movable frame according to some implementations of the present disclosure;

[0034] Figure 3C and Figure 3D shows a third tensioning structure and a fourth tensioning structure embedded in a movable frame according to some implementations of the present disclosure;

[0035] Figure 4A A movable frame according to some implementations of the present disclosure is shown;

[0036] Figure 4B A movable frame according to some implementations of the present disclosure is shown;

[0037] Figure 5A shows a fifth tensioning structure embedded in a movable frame according to some implementations of the present disclosure;

[0038] Figure 5B shows a sixth tensioning structure embedded in a movable frame according to some implementations of the present disclosure;

[0039] Figure 6 shows a seventh tensioning structure embedded in a movable frame according to some implementations of the present disclosure;

[0040] Fig. 7A shows an eighth tensioning structure embedded in a movable frame according to some implementations of the present disclosure;

[0041] Figure 7B shows a ninth tensioning structure embedded in a movable frame according to some implementations of the present disclosure;

[0042] Figure 8 shows a process flow for generating tension in a MEMs device according to some implementations of the present disclosure; and

[0043] FIG. 9A to FIG. 9K A process of manufacturing a tensioning structure according to some implementations of the present disclosure is shown. DETAILED DESCRIPTION

[0044] The micro-MEMS mirror device may include a stationary frame having a cavity and a mirror component in the cavity. The mirror component may include a movable frame (which may be suspended on the stationary frame by a first stationary frame flexible structure and a second stationary frame flexible structure) and a central platform (which may be suspended on the movable frame by a first central platform flexible structure and a second central platform flexible structure). The central platform may include a reflective surface / mirror surface. The movable frame may pivot about a first axis. The first axis may extend from the first stationary frame flexible structure to the second stationary frame flexible structure. The central platform may pivot about a second axis. The second axis may extend from the first central platform flexible structure and the second central platform flexible structure. The movable frame and the central platform may be pivotable due to electrostatic actuation. Electrostatic actuation may generate an electric field that may cause the mirror component (e.g., movable frame, central platform) to pivot.

[0045] When the flexible structures (e.g., the stationary frame flexible structures and / or the central platform flexible structures) are not properly tensioned, the flexible structures may buckle and / or deform due to compressive forces that may be generated when the mirror components pivot in undesirable directions due to thermal stress or packaging stress. Placing the flexible structures under increased tension may reduce the compressive forces and buckling and / or deformation of the flexible structures, but may increase bending stiffness, and thus may increase undesirable modes, and increase the stiffness of certain undesirable modes, which may move the resonance of the undesirable modes away from the desired mode.

[0046] Therefore, a MEMS micromirror device configured with a tensioning structure that can reduce the compressive force on the flexible structure while allowing appropriate tension may be useful. In addition, a method of manufacturing a MEMS micromirror device may be useful.

[0047] A microelectromechanical (MEM) device may include a first platform including a first platform reflective surface; a first frame pivotally coupled to the first platform; and one or more of a first frame flexible structure on the first frame and a first platform flexible structure on the first platform. A tensioning structure may be coupled to the first frame for generating a tension in one or more of the first frame flexible structure and the first platform flexible structure to prevent one or more of the first frame flexible structure and the first platform flexible structure from buckling.

[0048] I. Micro-Electro-Mechanical (MEM) Arrays

[0049] Figure 1A top view of a portion of a MEMS mirror array 100 according to some implementations of the present disclosure is shown, which may include one or more MEMS micromirror devices 101a, 101b, 101c. As shown in the figure, the MEMS mirror array 100 may include a mirror cavity 112 for the MEMS micromirror device 101a.

[0050] The MEMS mirror array 100 may have a plurality of MEMS micromirror devices 101a, 101b, 101c. The MEMS micromirror device 101a in the MEMS mirror array 100 may include a central platform 130, a movable frame 132, and a stationary frame 134. As shown in the accompanying drawings, the stationary frame 134 may form a mirror cavity 112, in which the central platform 130 and the movable frame 132 may be arranged. A reflective element or surface (e.g., a mirror) may be provided, which may be one or more of the following: (i) coupled to the central platform 130 or (ii) suspended on the movable frame 132 by a first central platform flexible structure 136A (which may be referred to as a first horizontal spring) and a second central platform flexible structure 136B (which may be referred to as a second horizontal spring). The reflective element or surface (e.g., a mirror) may be used to redirect a light beam along an optical path different from the optical path of the received light beam. The MEMS micromirror device 101 a may include a mirror (not shown) located on a central platform 130 , also referred to as a “mirror unit” or a “MEMS actuator with a mirror”.

[0051] The rotation of the central platform 130 can be independent of the rotation of the movable frame 132. The MEMS micromirror device 101a is capable of decoupled motion. For example, the central platform 130 can rotate relative to the stationary frame 134, while the movable frame 132 can remain parallel and stationary relative to the stationary frame 134. In addition, the movable frame 132 can rotate relative to the stationary frame 134, while the central platform can remain parallel and stationary relative to the movable frame 132. The movable frame 132 can engage the stationary frame 134 via a first stationary frame flexible structure 140A (which can be referred to as a first vertical double spring) and a second stationary frame flexible structure 140B (which can be referred to as a second vertical double spring). In addition, the central platform 130 and the movable frame 132 can, for example, rotate simultaneously and independently of each other. The central platform 130, the movable frame 132, and the stationary frame 134 can be non-parallel to each other and decoupled from each other during actuation.

[0052] The MEMS micromirror device 101a may include a tensioning structure. Various shapes of tensioning structures may be provided, and these tensioning structures may be embedded in the movable frame 132 to generate tensioning force, such as FIG. 3A to FIG. 3D , FIG. 5A to FIG. 5B , Figure 6 and 7A to Figure 7B 134. The tensioning structure (e.g., which may be embedded in the movable frame 132) may be used to generate tension by having a structure that may expand in an amount or at a rate that is different from the expansion amount or rate of one or more of the movable frame 132, the central platform 130, and the stationary frame 134. The tensioning structure (e.g., which may be embedded in the movable frame 132) may include a material (e.g., SiO2) that may have different expansion characteristics, which may generate a force on the movable frame 132 (e.g., which may be made of Si), thereby applying tension to the first stationary frame flexible structure 140A and the second stationary frame flexible structure 140B (e.g., by increasing the displacement at the ends of the first stationary frame flexible structure 140A and the ends of the second stationary frame flexible structure 140B, so that the first stationary frame flexible structure 140A and the second stationary frame flexible structure 140B are in a tensioned state). In addition, the tensioning structure (for example, which can be embedded in the movable frame 132) can exert a force on the movable frame 132, thereby applying a tensioning force to the first central platform flexible structure 136A and the second central platform flexible structure 136B (for example, by increasing the displacement at the end of the first central platform flexible structure 136A and the end of the second central platform flexible structure 136B, so that the first central platform flexible structure 136A and the second central platform flexible structure 136B are in a tensioned state).

[0053] Various shapes (e.g., Figure 4A The hole 402 in the movable frame 132 shown in FIG. 1 , or Figure 4B The reduced width portion 430 shown in FIG. 4 is used to change the shape (and / or structure) of the movable frame 132 to generate tension, such as FIG. 4A to FIG. 4B The movable frame 132 may utilize modifications and / or holes 402 to make it less rigid than a movable frame 132 without the modifications and / or holes 402. The movable frame 132 may utilize modifications (e.g., Figure 4B) to make it less stiff than a movable frame 132 having a full width. The movable frame 132 can utilize modifications to make it less stiff than a movable frame 132 without the modifications. Thus, the tensioning structure in the movable frame 132 (e.g., a movable frame with less stiffness) can increase the displacement at the ends of the vertical dual springs (e.g., the first stationary frame flexible structure 140A and the second stationary frame flexible structure 140B), thereby increasing the tension in the vertical dual springs. The tensioning structure in the movable frame 132 (e.g., a movable frame with less stiffness) can increase the displacement at the ends of the horizontal springs (e.g., the first central platform flexible structure 136A and the second central platform flexible structure 136B), thereby increasing the tension in the horizontal springs.

[0054] The tensioning structure can be used to generate tensioning forces to minimize or reduce the possibility of positional deformation caused by buckling of the flexible structures (e.g., the first central platform flexible structure 136A, the second central platform flexible structure 136B, the first stationary frame flexible structure 140A, and the second stationary frame flexible structure 140B) when compressive forces are applied.

[0055] Figure 2 Shown along Figure 1 2-2 in FIG. 1 , a partial cross-section of a MEMS mirror array 100 having a top side 10 and a bottom side 20, wherein each layer within the MEMS mirror array 100 may have a top surface of the layer oriented toward the top side 10 and a bottom surface oriented toward the bottom side 20. The array may have: a silicon wafer 210, which may be a substrate wafer for the MEMS mirror array 100; a device wafer 220, at which the MEMS mirror array 100 may be manufactured; and a cover wafer 250, which may be used as a protective layer. The silicon wafer 210 may be bonded to the device wafer 220 using, for example, glass frit bonding, eutectic bonding, thermocompression bonding, fusion bonding, or anodic bonding. During the bonding process, a pair of bonding elements 212, 212' may contact silicon members 238, 238' surrounding the MEMS mirror array 100. A second pair of bonding elements 222 , 222 ′, such as frit glass seals, may be provided at both ends of the cap wafer 250 to bond the device wafer 220 to the cap wafer 250 .

[0056] The structure release can be accomplished at the upper surface (eg, top side 10) of the device wafer 220 using dry etching. The dry etching can penetrate the plurality of trenches 226 to allow the movable elements (eg, Figure 1 The central platform 130 in the embodiment of the present invention) and the movable elements of the frame 230 (e.g., Figure 1236 ′) suspended from the mirror cavity 232. An isolation joint 228 may be formed by etching the front until the etch approaches or just reaches the mirror cavity 232. In addition, the release etch may aid in electrical isolation by separating, for example, the silicon of the frame 230 from the silicon of the surrounding members 238, 238′. The vias 224 may connect the silicon regions to the metal interconnects 240. To seal the mirror from the external environment, a cover wafer 250 may be bonded to the device wafer 220, for example, by a second pair of bonding elements 222, 222′, which may be frit glass seals. The cover wafer 250 may be glass to allow incident light to be transmitted with low loss in the mirror cavity 242 above the mirror, reflected from the upper surface of the mirror 236, and transmitted out of the mirror cavity 242.

[0057] II. Structural changes to generate tension

[0058] The microelectromechanical (MEM) device 101 may include a first platform (e.g., central platform 130), which may include a first platform reflective surface (e.g., a micromirror). The MEM device 101 may include a first frame (e.g., movable frame 132), which may be pivotally coupled to the first platform (e.g., central platform 130). The MEM device 101 may include one or more of the following: (i) one or more second frame flexible structures (e.g., first stationary frame flexible structure 140A and second stationary frame flexible structure 140B), which may be located on the second frame (e.g., stationary frame 134) and the first frame (e.g., movable frame 132); (ii) one or more first platform flexible structures (e.g., first central platform flexible structure 136A and second central platform flexible structure 136B), which are located on the first platform and the first frame (e.g., movable frame 132).

[0059] The MEM device 101 may include a tensioning structure that may be coupled to the first frame (e.g., the movable frame 132) for generating a tension in one or more of the second frame flexible structure (e.g., the first stationary frame flexible structure 140A and the second stationary frame flexible structure 140B) and the first platform flexible structure (e.g., the first central platform flexible structure 136A and the second central platform flexible structure 136B) to prevent buckling of one or more of the second frame flexible structure (e.g., the first stationary frame flexible structure 140A and the second stationary frame flexible structure 140B) and the first platform flexible structure (e.g., the first central platform flexible structure 136A and the second central platform flexible structure 136B).

[0060] The tensioning structure may include a material having a thermal expansion coefficient that is different from the thermal expansion coefficient of one or more of the first platform (e.g., central platform 130), the first frame (e.g., movable frame 132), and the second frame (e.g., stationary frame 134). The tensioning structure may be partially or completely embedded in the first frame (e.g., movable frame 132).

[0061] The tensioning structure may be partially or completely embedded in an edge portion of the first frame (eg, movable frame 132) adjacent to the first platform (eg, central platform 130), for example, may be embedded in the inner edge portion 132A (eg, FIG. 3A to FIG. 3D , 5A to Figure 5B , Figure 6 and FIG. 7A to FIG. 7B ) or in the outer edge portion (e.g. Figure 3C 304A or Figure 3D 305A or Figure 3C 304B or Figure 3D 305B shown in FIG. Figure 3A and Figure 3B A first tensioning structure 302A (which may be referred to as a SiO2 layer in grooves of a “sun hat” shape pattern) for an upper portion UP of the movable frame 132 and a second tensioning structure 302B (which may be referred to as a SiO2 layer in grooves of an “inverted sun hat” shape pattern) for a lower portion LP of the movable frame 132 are shown, which may be embedded in the movable frame 132 according to some implementations of the present disclosure. The first tensioning structure 302A and / or the second tensioning structure 302B may be completely embedded in the movable frame 132. The first tensioning structure 302A and / or the second tensioning structure 302B may be partially embedded in the movable frame 132. The first tensioning structure 302A and / or the second tensioning structure 302B may include SiO2 or include a suitable material whose expansion amount may be different from that of the movable frame 132 (e.g., which may be made of Si).

[0062] like Figure 3A and Figure 3B As shown in FIG. 1 , the first tensioning structure 302A and the second tensioning structure 302B may be embedded in an inner edge portion 132A of the movable frame 132 adjacent to the central platform 130 .

[0063] The first tensioning structure 302A (which may be fully or partially embedded) and the second tensioning structure 302B (which may be fully or partially embedded) may include a material (e.g., SiO2) whose expansion characteristics may be different from the expansion characteristics of the movable frame 132, thereby generating a force on the movable frame 132, thereby applying a tensioning force to the first stationary frame flexible structure 140A and the second stationary frame flexible structure 140B. Additionally or alternatively, the first tensioning structure 302A (which may be fully or partially embedded) and the second tensioning structure 302B (which may be fully or partially embedded) may include a material (e.g., SiO2) whose expansion characteristics may be different from the expansion characteristics of the movable frame 132, thereby generating a force on the movable frame 132, thereby applying a tensioning force to the first central platform flexible structure 136A and the second central platform flexible structure 136B.

[0064] The tensioning structure (eg, third tensioning structure 304) may include one or more of the following: (i) a first portion (eg, Figure 3C 304A as shown in or Figure 3D 305A, (ii) the second part (e.g., Figure 3C 304B as shown in Figure 3D 305B), and (iii) the third part (e.g., Figure 3C 304C as shown in Figure 3D 305C shown in ). Figure 3C A third tensioning structure 304 is shown, which may include a first portion 304A (which may be referred to as a SiO2 layer filled in a straight-line-shaped groove), a second portion 304B (which may be referred to as a SiO2 layer filled in a straight-line-shaped groove), and a third portion 304C (which may be referred to as a SiO2 layer in a dome-shaped groove) for an upper portion UP of the movable frame 132. Figure 3D A fourth tensioning structure 305 is shown that can be embedded (e.g., completely or partially) in the movable frame 132, which includes a first portion 305A (which can be referred to as a SiO2 layer filled in a straight-line-shaped groove), a second portion 305B (which can be referred to as a SiO2 layer filled in a straight-line-shaped groove), and a third portion 305C (which can be referred to as a SiO2 layer in an inverted dome-shaped groove) for a lower portion LP of the movable frame 132.

[0065] As shown in the drawings, third tensioning structure 304 and fourth tensioning structure 305 may be completely embedded in movable frame 132. Alternatively or additionally, third tensioning structure 304 and fourth tensioning structure 305 may be partially embedded in movable frame 132. Third tensioning structure 304 and fourth tensioning structure 305 may include SiO2 or include a suitable material whose expansion amount may be different from that of movable frame 132 (e.g., which may be made of Si).

[0066] The embedded third tensioning structure 304 and the fourth tensioning structure 305 (whose expansion amount may be different from the expansion amount of one or more of the movable frame 132, the central platform 130, and the stationary frame 134) may apply tensioning force to the first stationary frame flexible structure 140A and the second stationary frame flexible structure 140B (e.g., by increasing the displacement at the end of the first stationary frame flexible structure 140A and the end of the second stationary frame flexible structure 140B, so that the first stationary frame flexible structure 140A and the second stationary frame flexible structure 140B are in tension). Alternatively or additionally, the embedded third tensioning structure 304 and the fourth tensioning structure 305 may apply tensioning force to the first central platform flexible structure 136A and the second central platform flexible structure 136B (e.g., by increasing the displacement at the end of the first central platform flexible structure 136A and the end of the second central platform flexible structure 136B, so that the first central platform flexible structure 136A and the second central platform flexible structure 136B are in tension).

[0067] The first platform (e.g., central platform 130) and the first portion (e.g., Figure 3C 304A as shown in or Figure 3D 305A shown in FIG. 305A and a second portion (e.g., as shown in FIG. Figure 3C 304B as shown in Figure 3D The first distance between one or more of the portions (e.g., 305B) may be greater than the third portion (e.g., Figure 3C 304C as shown in Figure 3D 305C) and a second distance between the first platform (e.g., the central platform 130). Figure 3C and Figure 3D As shown in FIG. 1 , the third portions 304C, 305C of the third tensioning structure 304 and the fourth tensioning structure 305 may be embedded in the inner edge portion 132A of the movable frame 132 adjacent to the central platform 130. The first portions 304A, 305A and / or the second portions 304B, 305B of the third tensioning structure 304 and / or the fourth tensioning structure 305 may be embedded in the outer edge portion (e.g., Figure 3C 304A shown in, or Figure 3D 305A shown in, or Figure 3C 304B as shown in, or Figure 3D 305B shown in the figure), the outer edge portion can be away from the inner edge portion 132A of the movable frame 132 adjacent to the central platform 130. However, the first portion 304A, 305A and / or the second portion 304B, 305B can be embedded in or closer to the inner edge portion 132A of the movable frame 132 adjacent to the central platform 130 to increase the tension in the first central platform flexible structure 136A and the second central platform flexible structure 136B (for example, by increasing the displacement at the end of the first central platform flexible structure 136A and the end of the second central platform flexible structure 136B, so that the first central platform flexible structure 136A and the second central platform flexible structure 136B are in a tensioned state), and reduce the tension in the first stationary frame flexible structure 140A and the second stationary frame flexible structure 140B (by reducing the displacement at the end of the first stationary frame flexible structure 140A and the end of the second stationary frame flexible structure 140B). When the first portion 304A, 305A and / or the second portion 304B, 305B is located farther from the central platform 130, the tension in the first stationary frame flexible structure 140A and the second stationary frame flexible structure 140B may increase (e.g., from 2.2 μN to 4.0 μN), while the tension in the first central platform flexible structure 136A and the second central platform flexible structure 136B may decrease (e.g., from 7.8 μN to 1.4 μN). Therefore, the length and position of the first portion 304A, 305A and / or the second portion 304B, 305B can be selected or adjusted to fine-tune the tension applied to the flexible structures (e.g., the first central platform flexible structure 136A and the second central platform flexible structure 136B, the first stationary frame flexible structure 140A and the second stationary frame flexible structure 140B).

[0068] The movable frame 132 may include one or more of the following: (i) one or more holes (e.g., Figure 4A 402A or 402B) and (ii) one or more reduced width portions (e.g., Figure 4B The reduced width portion 430 shown in FIG. Figure 4A The movable frame 132 is shown including modifications (e.g., holes 402 in the movable frame 132) that can reduce the stiffness of the movable frame 132 according to some implementations of the present disclosure. For example, the upper portion UP of the movable frame 132 (e.g., as FIG. 3A to FIG. 3C ) (eg, upper right portion UR, upper left portion UL) and a lower portion LP of the movable frame 132 (eg, as shown in Figure 3A and Figure 3D) (eg, lower right portion LR, lower left portion LL) may include a plurality of holes 402 (eg, square or rectangular openings). Figure 4A As shown in , the movable frame 132 may include holes 402A, which may be spaced apart from each other by a predetermined distance (for example, the predetermined distance may be a predetermined distance of about 2 microns to about 5 microns (such as 3 microns), which may be an average predetermined distance between each hole 402A). Alternatively or in addition, the movable frame 132 may include holes 402B (these holes may be arranged in an alternating manner), which may be spaced apart from each other by a predetermined distance (for example, spaced apart by a predetermined distance of about 2 microns to about 5 microns (such as 3 microns), which may be an average predetermined distance between each hole 402A). The holes may be square or triangular in shape. As shown in the drawings, the movable frame 132 may include a suitable truss structure having holes 402 (for example, holes 402A, 402B).

[0069] The movable frame 132 may be configured to have a hole 402, and the stiffness of the movable frame may be less than the stiffness of the movable frame 132 without the hole 402. Therefore, the hole 402 in the movable frame 132 may be used to increase the displacement at the end of the vertical double spring (e.g., the first stationary frame flexible structure 140A and the second stationary frame flexible structure 140B) (e.g., from 3.75 nm to 4.09 nm), thereby increasing the tension generated in the vertical double spring (e.g., a 10% increase in displacement may be used to increase the tension by 10%). Similarly, the hole 402 in the movable frame 132 may be used to increase the displacement at the end of the horizontal spring (e.g., the first central platform flexible structure 136A and the second central platform flexible structure 136B) (e.g., from 5.65 nm to 7.47 nm), thereby increasing the tension generated in the horizontal spring (e.g., the first central platform flexible structure 136A and the second central platform flexible structure 136B) (e.g., a 30% increase in displacement may be used to increase the tension by 30%).

[0070] Figure 4A It is shown that the hole 402 can have various shapes, including but not limited to square, rectangular and triangular. Other shapes, such as circular, octagonal, hexagonal, and diamond shapes, can also be used without departing from the scope of the present disclosure.

[0071] Figure 4B 4 shows a movable frame 132 that can be configured to have a reduced width portion 430. For example, the upper portion UP of the movable frame 132 (e.g., FIG. 3A to FIG. 3C ) (eg, the upper right portion UR, the upper left portion UL) and the lower portion LP of the movable frame 132 (eg, Figure 3A and Figure 3D ) (e.g., lower right portion LR, lower left portion LL) includes a reduced width portion 430. The width W of the reduced width portion 430 may be about 15 microns to about 30 microns. Alternatively or additionally, the width W of the reduced width portion 430 may be about 5 microns to about 15 microns.

[0072] The movable frame 132 may be configured to have the reduced width portion 430 so that it has lower stiffness than the movable frame 132 without the reduced width portion 430. Therefore, the reduced width portion 430 may increase the displacement (e.g., from 3.75 nm to 4.27 nm) at the ends of the vertical double springs (e.g., the first stationary frame flexible structure 140A and the second stationary frame flexible structure 140B), thereby increasing the tension generated in the vertical double springs (e.g., the first stationary frame flexible structure 140A and the second stationary frame flexible structure 140B) (e.g., a 10% increase in displacement may be used to increase the tension by 10%). Alternatively or additionally, the reduced width portion 430 in the movable frame 132 can increase the displacement at the ends of the horizontal springs (e.g., the first central platform flexible structure 136A and the second central platform flexible structure 136B) (e.g., from 5.65 nm to 6.27 nm), which can be used to increase the tension generated in the horizontal springs (e.g., the first central platform flexible structure 136A and the second central platform flexible structure 136B) (e.g., a 10% increase in displacement can be used to increase the tension by 10%).

[0073] like Figure 5A As shown in , the tensioning structure (e.g., the fifth tensioning structure 502) can include a plurality of segments (e.g., short segments 504) that can be partially embedded in a first frame (e.g., movable frame 132). The plurality of segments (e.g., short segments 504) can be spaced apart at a substantially average predetermined distance. The predetermined distance can be substantially average when the spacing between each adjacent segment in the plurality of segments differs from the average spacing between each adjacent segment by less than one or more of 10%, 5%, 3%, 2%, or 1%.

[0074] Figure 5AA fifth tensioning structure 502 is shown that can be embedded in the movable frame 132. As shown in the figure, the fifth tensioning structure 502 can include a plurality of short segments 504. The short segments 504 can be completely embedded in the movable frame 132, or can be partially embedded in the movable frame 132. For example, the partially embedded short segments 504 can have about 2 / 3 of the short segments 504 embedded in the movable frame 132, and about 1 / 3 of the short segments 504 exposed. The short segments 504 can include SiO2 or include a suitable material whose expansion amount can be different from the expansion amount of one or more of the movable frame 132, the central platform 130, and the stationary frame 134. For example, the fifth tensioning structure 502 can be arranged at the upper portion UP of the movable frame 132 (for example, as shown in FIG. 1 ). FIG. 3A to FIG. 3C ) (eg, the upper right portion UR, the upper left portion UL) and the lower portion LP of the movable frame 132 (eg, as shown in Figure 3A and Figure 3D ) (eg, lower right portion LR, lower left portion LL).

[0075] like Figure 5A As shown in , the short segments 504 can be embedded in the inner edge portion (e.g., 132A) of the movable frame 132 adjacent to the central platform 130. The short segments 504 can be spaced apart from each other by a predetermined distance (e.g., a distance between 5 microns and 15 microns (such as 10 microns)), which can be an average distance between each short segment 504.

[0076] As discussed, an embedded tensioning structure (e.g., the fifth tensioning structure 502) (whose expansion amount may be different from the expansion amount of one or more of the movable frame 132, the central platform 130, and the stationary frame 134) may apply tensioning forces to the first stationary frame flexible structure 140A and the second stationary frame flexible structure 140B (e.g., by increasing the displacement at the ends of the first stationary frame flexible structure 140A and the ends of the second stationary frame flexible structure 140B). Similarly, an embedded tensioning structure (e.g., the short section 504) may apply tensioning forces to the first central platform flexible structure 136A and the second central platform flexible structure 136B (by increasing the displacement at the ends of the first central platform flexible structure 136A and the ends of the second central platform flexible structure 136B). The fifth tensioning structure 502 may cover a smaller portion of the movable frame 132 than the portion of the movable frame 132 covered by the sixth tensioning structure 506. The smaller portion covered by the fifth tensioning structure 502 allows the amount of the first tensioning structure 302A in the movable frame 132 to be reduced.

[0077] Figure 5BA sixth tensioning structure 506 is shown that can be embedded in the movable frame 132. The sixth tensioning structure 506 can cover a larger portion of the movable frame 132 than the portion of the movable frame 132 covered by the fifth tensioning structure 502. In one example, the sixth tensioning structure 506 can cover a majority of the arcuate portion and / or cover the entire arcuate portion of the first tensioning structure 302A. The sixth tensioning structure 506 can cover a majority of the arcuate portion of the first tensioning structure 302A when more than one or more of 95%, 96%, 97%, 98%, and 99% of the arcuate portion of the first tensioning structure 302A is covered by the sixth tensioning structure 506. Covering a larger portion by the sixth tensioning structure allows the first tensioning structure 302A in the movable frame 132 to be omitted.

[0078] The sixth tensioning structure 506 may include a plurality of short segments 504 that may be fully or partially embedded in the movable frame 132. Figure 5B As shown in , the short segment 504 may be partially embedded in the movable frame 132. For example, about 2 / 3 of the short segment 504 may be embedded in the movable frame 132, and about 1 / 3 of the short segment 504 may be exposed. The short segment 504 may include SiO2 or include a suitable material whose expansion amount may be different from that of the movable frame 132.

[0079] like Figure 5B As shown in , the short segments 504 can be embedded in an edge portion of the movable frame 132 that can be adjacent to the central platform 130. The short segments 504 can be spaced apart from each other by a predetermined distance (e.g., a distance between 5 microns and 15 microns (such as 10 microns)), which can be an average distance between each short segment 504.

[0080] The embedded sixth tensioning structure 506 (whose expansion amount may be different from the expansion amount of one or more of the movable frame 132, the central platform 130, and the stationary frame 134) may apply tensioning force to the first stationary frame flexible structure 140A and the second stationary frame flexible structure 140B (e.g., by increasing the displacement at the ends of the first stationary frame flexible structure 140A and the ends of the second stationary frame flexible structure 140B). The embedded sixth tensioning structure 506 may apply tensioning force to the first central platform flexible structure 136A and the second central platform flexible structure 136B (by increasing the displacement at the ends of the first central platform flexible structure 136A and the ends of the second central platform flexible structure 136B).

[0081] The movable frame 132 may be adjacent to an upper portion UP of the first stationary frame flexible structure 140A (eg, FIG. 3A to FIG. 3C) and a lower portion LP of the movable frame 132 that may be adjacent to the second stationary frame flexible structure 140B (e.g., as shown in Figure 3A and Figure 3D ), can be configured to include a short section 504.

[0082] The tensioning structure (eg, seventh tensioning structure 602) may have one or more of a zigzag pattern and a sine wave pattern. Figure 6 , the seventh tensioning structure 602 (also referred to as a zigzag tensioning structure with abrupt alternating right and left turns) can be fully or partially embedded in the movable frame 132. The seventh tensioning structure 602 can be configured as follows: Figure 6 The groove structure in the zigzag pattern shown in FIG. 6 includes a SiO2 layer. The seventh tensioning structure 602 can be completely embedded in the movable frame 132. The seventh tensioning structure 602 can be formed of a variety of materials, including SiO2 or a suitable material whose expansion amount can be different from the expansion amount of the movable frame 132 (for example, made of Si).

[0083] like Figure 6 As shown in , the seventh tensioning structure 602 can be embedded in the inner edge portion 132A of the movable frame 132 adjacent to the central platform 130. The seventh tensioning structure 602 (whose expansion amount can be different from the expansion amount of one or more of the movable frame 132, the central platform 130, and the stationary frame 134) can apply tensioning force to the first stationary frame flexible structure 140A and the second stationary frame flexible structure 140B (e.g., by increasing the displacement of the ends of the first stationary frame flexible structure 140A and the ends of the second stationary frame flexible structure 140B). Similarly, the seventh tensioning structure 602 can apply tensioning force to the first central platform flexible structure 136A and the second central platform flexible structure 136B (by increasing the displacement at the ends of the first central platform flexible structure 136A and the ends of the second central platform flexible structure 136B).

[0084] The upper portion UP of the movable frame 132 (eg, FIG. 3A to FIG. 3C ) (upper right portion UR, upper left portion UL) and the lower portion LP of the movable frame 132 (eg, as shown in Figure 3A and Figure 3D ) (shown in ) (lower right portion LR, lower left portion LL) may include a seventh tensioning structure 602.

[0085] Figure 6The seventh tensioning structure 602 in the embodiment may have a curved end (e.g., curved end 602A) at each abrupt alternating right and left turns. Additionally or alternatively, the seventh tensioning structure 602 may have a radius of curvature (e.g., at each alternating right and left turns). For example, the curvature of the seventh tensioning structure 602 may have a radius of curvature that may approach a sharp end based on manufacturing standards at the outer and inner curves at the alternating right and left turns. Additionally or alternatively, the seventh tensioning structure 602 may have a sine wave pattern.

[0086] The first portion 704 of the tensioning structure (e.g., the eighth tensioning structure 701) can be substantially parallel to the second portion 705 of the eighth tensioning structure 701. The first portion 704 and the second portion 705 can be substantially parallel to each other when the angle between the first portion 704 and the second portion 705 varies from a 0 degree angle between the two members to less than one or more of 10 degrees, 5 degrees, 3 degrees, 2 degrees, and 1 degree. Fig. 7A An eighth tensioning structure 701 (e.g., a SiO2 layer in a groove) is shown, which may include a first portion 704 and a second portion 705 that may be embedded in the movable frame 132. As shown in the figure, the first portion 704 of the eighth tensioning structure 701 and the second portion 705 of the eighth tensioning structure 701 may be completely embedded in the movable frame 132. Alternatively or additionally, the first portion 704 of the eighth tensioning structure 701 and the second portion 705 of the eighth tensioning structure 701 may be partially embedded in the movable frame 132. The first portion 704 of the eighth tensioning structure 701 and the second portion 705 of the eighth tensioning structure 701 may include SiO2 or include a suitable material whose expansion amount may be different from the expansion amount of the movable frame 132. Additionally or alternatively, the first portion 704 and the second portion 705 may be embedded in an inner edge portion 132A of the movable frame 132 adjacent to the central platform 130.

[0087] The eighth tensioning structure 701 (whose expansion amount may be different from the expansion amount of one or more of the movable frame 132, the central platform 130, and the stationary frame 134) may apply tensioning force to the first stationary frame flexible structure 140A and the second stationary frame flexible structure 140B (e.g., by increasing the displacement at the ends of the first stationary frame flexible structure 140A and the ends of the second stationary frame flexible structure 140B). Similarly, the eighth tensioning structure 701 may apply tensioning force to the first central platform flexible structure 136A and the second central platform flexible structure 136B (by increasing the displacement at the ends of the first central platform flexible structure 136A and the ends of the second central platform flexible structure 136B).

[0088] As shown in the drawings, the first portion 704 and the second portion 705 of the eighth tensioning structure 701 may extend from the right side UR of the movable frame 132 to the left side UL of the movable frame 132 (eg, FIG. 3A to FIG. 3C ), and the second portion 705 of the eighth tensioning structure 701 may be shorter than the first portion 704 of the eighth tensioning structure 701. As shown in the accompanying drawings, the distance between the first portion 704 of the eighth tensioning structure 701 and the central platform 130 may be smaller than the distance between the second portion 705 of the eighth tensioning structure 701 and the central platform 130.

[0089] The first length of the first portion 706 of the ninth tensioning structure 702 can be substantially the same as the second length of the second portion 707 of the ninth tensioning structure 702. Figure 7B , the ninth tensioning structure 702 (e.g., the SiO2 layer in the groove) may include a first portion 706 and a second portion 707, which may be embedded in the movable frame 132. As shown in the figure, the first portion 706 and the second portion 707 of the ninth tensioning structure 702 may be completely embedded in the movable frame 132. Alternatively or additionally, one or more of the first portion 706 and the second portion 707 of the eighth tensioning structure 701 may be partially embedded in the movable frame 132. For example, the first portion 706 of the ninth tensioning structure 702 may be completely embedded in the movable frame 132, and the second portion 707 of the ninth tensioning structure 702 may be partially embedded in the movable frame 132, or vice versa. The first portion 706 and the second portion 707 of the ninth tensioning structure 702 may include SiO2 or include a suitable material whose expansion amount may be different from the expansion amount of the movable frame 132.

[0090] like Figure 7B As shown in FIG. 7 , the first portion 706 and the second portion 707 of the ninth tensioning structure 702 may be embedded at a position closer to the inner edge portion 132A of the movable frame 132 adjacent to the central platform 130 .

[0091] The ninth tensioning structure 702 may expand in an amount different from the amount of expansion of one or more of the movable frame 132, the central platform 130, and the stationary frame 134, thereby applying tension to the first stationary frame flexible structure 140A and the second stationary frame flexible structure 140B (e.g., by increasing the displacement at the ends of the first stationary frame flexible structure 140A and the ends of the second stationary frame flexible structure 140B). Similarly, the embedded ninth tensioning structure 702 may apply tension to the first central platform flexible structure 136A and the second central platform flexible structure 136B (by increasing the displacement at the ends of the first central platform flexible structure 136A and the ends of the second central platform flexible structure 136B).

[0092] As shown in the drawings, the first portion 706 and the second portion 707 of the ninth tensioning structure 702 may extend from the right side UR of the movable frame 132 to the left side UL of the movable frame 132 (eg, FIG. 3A to FIG. 3C ). As shown, the length of the first portion 706 of the ninth tensioning structure 702 and the length of the second portion 707 of the ninth tensioning structure 702 can be substantially the same and can be positioned substantially parallel to each other. The lengths of the first portion 706 and the second portion 707 can be substantially the same when the total percentage difference in length between the first portion 706 and the second portion 707 is less than one or more of: 10%, 5%, 3%, 2%, and 1% of the greater portion of the first portion 706 and the second portion 707. The first portion 706 and the second portion 707 can be substantially parallel to each other when the angle between the first portion 706 and the second portion 707 varies from a 0 degree angle between the two members to less than one or more of 10 degrees, 5 degrees, 3 degrees, 2 degrees, and 1 degree.

[0093] Figure 8 A process flow of an exemplary method 800 according to at least one example described in the present disclosure, which can be used to generate a tension force in a MEMs device, is shown. The method 800 can be arranged according to at least one example described in the present disclosure.

[0094] Method 800 may begin at block 805 where the method may include coupling a movable frame to a platform having a reflective surface and to a stationary frame.

[0095] At block 810 , the method may include embedding one or more tensioning structures in the movable frame for generating a tensioning force in the one or more flexible structures to prevent buckling of the one or more flexible structures.

[0096] The method may include: embedding a plurality of segments in a movable frame. The tensioning structure may include one or more of a zigzag pattern and a sine wave pattern. The movable frame may include one or more of: one or more holes or one or more reduced width portions. The tensioning structure may be partially or completely embedded in an edge portion of the first frame adjacent to the first platform. The tensioning structure may include a first portion, a second portion, and a third portion.

[0097] Without departing from the scope of the present disclosure, modifications, additions, or omissions may be made to the method 800. For example, in some examples, the method 800 may include any number of other components that may not be explicitly shown or described.

[0098] III. Manufacturing Method

[0099] Fabrication of MEM arrays (e.g., Figure 1 The method of forming a MEMS mirror array 100 in the present invention may include: forming a dielectric material layer on a first side of a substrate; forming vertical isolation trenches containing the dielectric material on the first side of the substrate; patterning a mask layer on a second side of the substrate opposite to the first side of the substrate; forming a through hole on the first side of the substrate; metallizing the first side of the substrate; depositing a second metal layer on the first side of the substrate to form a reflective surface; forming a second trench on the first side of the substrate to define a structure; deep etching the second side of the substrate to form narrow blades; after forming the narrow blades, placing a base wafer (e.g., Figure 2 bonding a silicon wafer 210 in the substrate to a second side of the substrate; and etching a second trench through the first side of the substrate to release the structure and provide electrical isolation.

[0100] The MEM device may include one or more of the following: a first platform having a first platform reflective surface, a first frame pivotally coupled to the first platform, a second frame coupled to the first frame, and a tensioning structure coupled to the first frame. The tensioning structure may be coupled to the first frame to generate a tension in one or more of the second frame flexible structure and the first platform flexible structure to prevent buckling of one or more of the second frame flexible structure and the first platform flexible structure.

[0101] The substrate may comprise a silicon wafer. Alternatively or additionally, the dielectric material may be silicon dioxide. Alternatively or additionally, the method may comprise one or more of: forming a passivation dielectric layer on the first side of the substrate after metallizing the first side of the substrate; and attaching a cap wafer to the first side of the substrate. The cap wafer may be composed of glass.

[0102] The process flow of the manufacturing method will refer to FIG. 9A to FIG. 9K To elaborate.

[0103] Fig.9A A cross section of a silicon wafer 902 (e.g., silicon on a bonded wafer) is shown, the thickness of which is selected to be in the range of 300 micrometers (um)-600 micrometers (um). The silicon wafer 902 can have a top side 10 (or device side, or simply top) and a back side or bottom side 20. The layers made of the silicon wafer 902 within the MEMS mirror array 100 can have a top surface of the layer oriented toward the top side 10 and a bottom surface oriented toward the bottom side 20. The silicon wafer 902 is marked in the upper left portion of the drawing. The buried oxide layer 912 can have a thickness of 0.5 um-1 um and is located 10 um-50 um below the top side 10.

[0104] FIG. 9B to FIG. 9E A process of manufacturing a tensioning structure according to some implementations of the present disclosure is shown.

[0105] Although there are many variations in the manufacturing method, the process in this example is as follows FIG. 9B to FIG. 9E As shown in , as described in US 6,239,473. The tensioning structure can be manufactured using the same process that can be used to manufacture the isolation trench structure. The tensioning structure can be fully or partially embedded in the mechanical structure.

[0106] refer to Fig. 9B , the silicon wafer 902 may be provided with a mask layer 914. The mask layer 914 may be silicon dioxide (e.g., an oxide layer). The silicon wafer 902 may have any doping concentration, resistivity, and crystal orientation, as the process may rely on reactive ion etching to carve and form structures. The mask layer 914 may protect the upper surface of the silicon wafer 902 during the trench etching process and may serve as a mask layer. The mask layer 914 may be formed by a variety of techniques, including thermal oxidation of silicon or chemical vapor deposition (CVD). The thickness of the mask layer 914 may be 0.5 µm-1.0 µm. A photoresist layer 916 may be spun onto the silicon wafer 902 and exposed and developed using photolithography techniques to define a trench pattern 922. The photoresist pattern may be transferred to the mask layer 914 using reactive ion etching to expose the top surface of the silicon wafer 902. Typically, the silicon dioxide mask may be etched in a Freon gas mixture (e.g., CHF3 or CF4). High etch rates for silicon dioxide etching can be achieved using a high-density plasma reactor such as an inductively coupled plasma (ICP) chamber. These ICP chambers use a high-power RF source to maintain a high-density plasma and apply a low-power RF bias on the wafer to achieve high etch rates at low ion energies. For this hardware configuration, oxide etch rates of 200 nm / min and photoresist selectivities greater than 1:1 can be achieved.

[0107] like Fig. 9CAs shown in , a groove 922 can be formed in a silicon wafer 902 by deep reactive ion etching of silicon using a high etch rate, high selectivity etch. The groove can be etched in a high density plasma using a sulfur hexafluoride (SF6) gas mixture, as described in U.S. Pat. No. 5,501,893. Preferably, the etching can be controlled so that the profile of the groove 922 is concave or tapered, wherein the top of the groove 922 is narrower than the bottom of the groove 922. The tapering of the groove 922 can allow for proper electrical isolation in subsequent processing. The tapering of the profile can be achieved in reactive ion etching by adjusting the degree of passivation or changing the discharge parameters (power, gas flow, pressure) during the etching process. Since the groove 922 can be filled with a dielectric material, the width of the opening at the top of the groove 922 can be less than 2 μm. The depth of the groove 922 can be in the range of 10 μm-50 μm. The process of etching the trench 922 can be a process of alternating etching steps (SF6 and argon mixture) and passivation steps (Freon and argon) in an ICP plasma to achieve an etch rate in excess of 2 µm / min with high selectivity to photoresist (>50:1) and oxide (>100:1). The power and time of the etching cycle may be increased as the trench deepens to achieve a tapered profile. Although the geometry of the trench can be concave, the microstructure treatment can be adjusted to accommodate any trench profile. A variety of trench etching chemistries can be used to achieve suitable results. After etching the silicon trench, the photoresist layer 916 can be removed using wet chemical or dry ashing techniques, and the mask layer 914 can be removed using reactive ion etching ("RIE") or buffered hydrofluoric acid.

[0108] refer to Fig.9D , the trench 922 may be filled with an insulating dielectric material (e.g., silicon dioxide). The filling process may form a larger solid section (e.g., the SiO2 layer discussed above) in the trench 922, and a mask layer 914 of a dielectric material may be deposited on the top side (top surface) of the silicon wafer 902 and a dielectric layer may be deposited on the sidewalls 928 and bottom of the trench 922. The thickness of the deposited layer may exceed 1 µm. The filling may be achieved by oxidizing the silicon at a high temperature. During the thermal oxidation process, the wafer may be exposed to an oxygen-rich environment at a temperature of 900°C-1150°C. The oxidation process may consume the silicon surface to form silicon dioxide. The volume expansion generated in the process may cause the sidewalls of the trench to invade each other, ultimately closing the opening of the trench. The newly formed oxide and silicon may be relatively stress-free at high temperatures compared to room temperature. When the wafer returns to room temperature, the mismatch in thermal expansion coefficients between the silicon and silicon dioxide of the wafer may generate thermal stress. Since the oxide has a lower coefficient of thermal expansion, it may exert tension on the adjacent silicon, and if the silicon is not attached to the oxide, its size may be further reduced.

[0109] During the filling process of the trench 922, the profile of the trench may not be completely filled, which may result in the formation of an interface 932 and a void 930 in the trench 922. Local stress concentrations in the void 930 may cause electrical and mechanical failure of certain devices, but may not affect other micromechanical devices due to the closed geometry of the trench 922. The interface 932 and the void 930 can be eliminated by shaping the trench 922 so that the trench opening at the top of the trench 922 is wider than the trench opening at the bottom of the trench 922. However, proper electrical isolation can be achieved by making additional tapering adjustments to the microstructure trench etch in subsequent operations. Another product of the trench filling process may be a dent 926, which may be formed on the surface of the dielectric 914 centered on the trench 922. The dent may be used for various trench filling processes and may have a depth of up to 0.5 µm, depending on the deposition thickness. To remove the dent 926, the surface may be planarized to form a flat or substantially flat surface, such as Fig.9E , for subsequent lithography steps and deposition steps. Planarization can be achieved by chemical mechanical polishing (CMP); or depositing a viscous material (which can be a photoresist, spin-on glass, or polyimide) and flowing these materials to fill the indentations 926 into a smooth surface. During the etching back of the viscous material (which can be the second step of planarization), the surface (including the filled indentations) can be uniformly etched. Therefore, by removing part of the surface oxide layer, the indentations 926 can be removed to form a layer of uniform thickness. For example, when the mask layer 914 is initially 2 µm thick, removing the indentations 926 by planarization can leave a mask layer 914 with a final thickness of less than 1 µm. The top side 10 (upper surface) of the silicon wafer 902 can be almost defect-free and can be ready for further lithography and deposition.

[0110] Fig.9F A silicon wafer 902 with a mask layer 914 and isolation trenches 922 is shown. After the isolation trenches 922 are made, a mask layer for blades can be patterned on the bottom side 20 (back side) of the silicon wafer 902 by a photolithography process using a front-to-back alignment technique. Blade patterns 972 can be exposed and etched into the mask layer as isolation trenches 922. The mask layer 914 can be a layer composed of a combination of thermally grown silicon oxide and an oxide deposited by chemical vapor deposition. The mask layer can also be composed of a metal layer such as aluminum. The photolithographic pattern can be transferred to the mask layer by reactive ion etching, but the silicon blade etching may not be completed until later in the process. Before the blades are etched, the remaining device layers of the wafer can be easily processed. The blade pattern 972 on the back side can typically be aligned to the isolation trenches 922 on the top side within a few microns.

[0111] like Figure 9G As shown in , the top side 10 of the silicon wafer 902 can be metallized. In order to contact the underlying silicon wafer 902, through holes 950, 952 can be patterned and etched into the mask layer 914 using photolithography and reactive ion etching. In some areas, through holes 954 can be etched through the buried oxide layer 912 and the top silicon portion of the silicon wafer 902, and the through holes 954 can be filled with polysilicon to form polysilicon through holes. After the through holes 950, 952 are etched, a metallization layer can be deposited to form a metal layer 940 and patterned to form a metal interconnect 956 that is interconnected with the silicon wafer 902 through the through hole 952. As an example, the metal can be aluminum and can be patterned using wet etching techniques. In a mirror array with a high interconnection density, patterning the metal using dry etching or evaporation metal stripping techniques can achieve a finer line width. The metal layer 940 can be used to provide bonding pads and interconnects that can connect electrical signals from a control circuit to the mirror to control the drive of the mirror.

[0112] The deposition of the second metal layer 960 can provide a reflector surface. The metal can be adjusted to provide a higher mirror reflectivity at the wavelength of light of interest, and can be evaporated and patterned using lift-off techniques to allow a wider selection of metallization techniques. The metal layer can be composed of 500 nm of aluminum. However, additional metal stacks such as Cr / Pt / Au can be used to increase reflectivity in wavelength bands common in fiber optic communications. Since the metal may be deposited under stress and may affect the final mirror flatness, the thickness of the mask layer 914 in the mirror area can be reduced by dry etching the underlying dielectric before evaporation.

[0113] exist Figure 9H , top side processing can be completed. First, a passivation dielectric layer (not shown) can be applied to protect the metal layer during subsequent processing. The passivation dielectric layer in the bonding pad area can be removed. Second, the mirror structure including the frame, mirror and support can be defined by multiple etches that define the grooves 921 separating the structural elements. The etching can be self-aligned and pass through the various metals, dielectrics and silicon wafer 902. A further capping deposition can be applied to the top side, which passivates the sidewalls of the grooves 921 and prepares the top side for mechanical release.

[0114] like Fig.9IAs shown in , the blade pattern 972 can be transferred to the substrate of the silicon wafer 902 by back silicon etching to obtain the blade 970. The etching can be performed using deep silicon etching techniques with high oxide selectivity, which are disclosed in U.S. Patent No. 5,501,893. The deep silicon etching achieves a nearly vertical profile in the blade 970, which can have a nominal width of 5 μm-20 μm and a depth of more than 300 μm. The etching stops on the buried oxide layer 912 to provide a uniform depth across the wafer without penetrating the top side 10 surface of the silicon wafer 902. Since the etching stops on the buried oxide layer 912, it is not necessary to use a slender member to eliminate etching depth variations across the device. Therefore, different patterns are possible. The blade 970 can be etched on the mirror element and the mirror array at the same time. The buried oxide layer 912 can also be etched at the same time.

[0115] refer to Figure 9J , since the device wafer is now ready for microstructure release, the device wafer 220 may be more susceptible to yield loss due to processing shock or airflow. To facilitate processing and help seal the mirror array in an airtight manner, the silicon wafer 902 (or substrate wafer) can be bonded to the device wafer 220 to protect the blades after release. As an example, bonding can be achieved by using a bonding element 211a (such as a frit glass material bonding element) that can be heated to its flow temperature and then cooled. In this way, the bonding element 211a at a temperature of 400°C produces an airtight seal around the mirror array. Using a bonding element 211a (such as a frit glass material bonding element) to separate the device wafer 220 and the silicon wafer 210 can allow the blades to swing unimpeded over a higher range of rotation angles. Typically, this spacing can be greater than 25 μm.

[0116] exist Figure 9K In the embodiment of the present invention, the final structure release is accomplished on the top side of the wafer using a combination of dry etches of silicon dioxide and silicon that penetrate trenches 921 to suspend the movable elements of mirror 236 and the movable elements of frame 230. In addition, the release etch facilitates electrical isolation by separating, for example, the silicon of frame 230 from the silicon of surrounding members 238a, 238b and the silicon of device wafer 220. The silicon regions are connected to metal interconnects 956 (e.g., vias 952) using vias 952. Figure 9G ). To seal the mirror from the external environment, for example, by bonding elements 222a and 222b (e.g., frit glass seals) (e.g., as shown in Figure 2 242) to bond the cover wafer 250 to the device wafer 220. The cover wafer 250 is typically glass, which allows incident light to be transmitted in the mirror cavity 242 with low loss (e.g., as Figure 2 ), reflected from the upper surface of mirror 236, and transmitted out of mirror cavity 242 (e.g., as shown in Figure 2 ).

[0117] Although embodiments of the present invention have been shown and described herein, it will be apparent to those skilled in the art that these embodiments are provided by way of example only. Various changes, modifications and substitutions will now occur to those skilled in the art without departing from the present invention. It should be understood that in practicing the present invention, various alternatives to the implementation of the present invention described herein may be adopted. Any claims proposed are intended to limit the scope of the present invention, and methods and structures within the scope of these claims and their equivalents are also encompassed.

Claims

1. A micro-electromechanical (MEM) device, comprising: a first platform including a first platform reflective surface; a first frame pivotally coupled to the first platform; a second frame coupled to the first frame; One or more of the following: a second frame flexible structure located on the first frame and the second frame or a first platform flexible structure located on the first platform; and A tensioning structure is coupled to the first frame for generating a tension in one or more of the second frame flexible structure and the first platform flexible structure to prevent buckling of one or more of the second frame flexible structure and the first platform flexible structure.

2. The MEM device according to claim 1, wherein: The tensioning structure includes a material having a different coefficient of thermal expansion than one or more of the first platform and the first frame.

3. The MEM device according to claim 1, wherein: The tensioning structure is partially embedded or completely embedded in the first frame.

4. The MEM device according to claim 1, wherein: The tensioning structure is partially or fully embedded in an edge portion of the first frame adjacent to the first platform.

5. The MEM device according to claim 1, wherein: The tensioning structure includes a first portion located on a first edge portion of the first frame and a second portion located on a second edge portion of the first frame.

6. The MEM device according to claim 5, wherein: A first distance between the first platform and one or more of the first portion and the second portion is greater than a second distance between the third portion and the first platform.

7. The MEM device according to claim 1, wherein: The first frame includes one or more of one or more holes and one or more reduced width portions configured to generate a tension force.

8. The MEM device according to claim 1, wherein: The tensioning structure includes a plurality of segments partially embedded or fully embedded in the first frame.

9. The MEM device according to claim 8, wherein: The tensioning structure is substantially perpendicular to an edge of the first frame.

10. The MEM device according to claim 1, wherein: The tensioning structure includes a plurality of segments spaced apart at substantially uniform predetermined distances.

11. The MEM device according to claim 1, wherein: The tensioning structure includes one or more of a zigzag pattern and a sine wave pattern.

12. The MEM device according to claim 1, wherein: The first portion of the tensioning structure is substantially parallel to the second portion of the tensioning structure.

13. The MEM device according to claim 1, wherein: The tensioning structure is substantially parallel to an edge portion of the first frame.

14. The MEM device according to claim 1, wherein: A first length of the first portion of the tensioning structure is substantially the same as a second length of the second portion of the tensioning structure.

15. A method for generating tension in a microelectromechanical (MEM) device, comprising: coupling the movable frame to the platform having the reflective surface and to the stationary frame; as well as One or more tensioning structures are embedded in the movable frame for generating a tension in the one or more flexible structures to prevent the one or more flexible structures from buckling.

16. The method according to claim 15, further comprising: A plurality of segments are embedded in the movable frame.

17. The method according to claim 15, wherein: The one or more tensioning structures include one or more of a zigzag pattern and a sine wave pattern.

18. The method according to claim 15, wherein: The movable frame includes one or more of one or more holes and one or more reduced width portions configured to generate a tension force.

19. The method according to claim 15, wherein: The one or more tensioning structures are partially embedded or fully embedded in an edge portion of the movable frame adjacent the platform.

20. The method according to claim 15, wherein: The one or more tensioning structures include a first portion and a second portion, wherein the first portion is located at an edge portion of the movable frame and a distance from the platform is less than a first distance, and the second portion is located at the edge portion of the movable frame and a distance from the platform is greater than the first distance.

21. A method of manufacturing a tensioning structure in a micro-electromechanical (MEM) device, comprising: forming a layer of dielectric material on a first side of the substrate; forming one or more vertical isolation trenches containing a dielectric material on the first side of the substrate; patterning a mask layer on a second side of the substrate opposite the first side of the substrate; forming a through hole on the first side of the substrate; metallizing the first side of the substrate; depositing a second metal layer on the first side of the substrate to form a reflective surface; forming a second trench on the first side of the substrate to define a structure; deep etching the second side of the substrate to form narrow blades; bonding a base wafer to the second side of the substrate after forming the narrow blades; as well as etching the second trench through the first side of the substrate to release the structure and provide electrical isolation, Wherein, the MEM device comprises: a first platform including a first platform reflective surface; and a first frame pivotally coupled to the first platform, a second frame coupled to the first frame; and A tensioning structure is coupled to the first frame for generating a tension in one or more of a second frame flexible structure and a first platform flexible structure to prevent buckling of one or more of the second frame flexible structure and the first platform flexible structure.

22. The method according to claim 21, wherein: The substrate comprises a silicon wafer, and the dielectric material is silicon dioxide.

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