A single stable micro-mirror capable of one-way deflection

Abstract

The present application belongs to the field of micro-mirror devices, and relates to a one-way deflection single-stable micro-mirror, a micro-mirror storage unit, a micro-mirror array and an image projection system. The storage unit is arranged in a substrate layer, and the output end of the storage unit is connected with only one addressing electrode. The upper addressing electrodes on the two sides of a torsional beam are arranged on the upper end of a bias electrode and the upper end of the addressing electrode, respectively. The elastic body is electrically connected with the bias electrode. The electrostatic driving of the micro-mirror can only occur between the addressing electrode and the upper addressing electrode above the addressing electrode. Therefore, the deflectable mirror can be driven to deflect only in one direction, forming a single-stable working mode. The possibility of the micro-mirror being stuck in the bright state when the micro-mirror fails is eliminated. The technical problems that the fixed bright spots appear in the projected image and the contrast is reduced due to the bright state failure when the existing bistable micro-mirror is arranged in the dark area are solved. It is ensured that even if the micro-mirror fails, it can only be in the dark state or the non-deflection state, avoiding the failure of the dark area function.

Description

Technical Field

[0001] This invention belongs to the field of micromirror devices and relates to a monostable micromirror that can be deflected in one direction, a micromirror storage unit, a micromirror array and an image projection system. Background Technology

[0002] Micromechanical devices (MEMS) are typical miniature structures, typically fabricated on semiconductor wafers using processes developed in integrated circuit manufacturing, such as photolithography, doping, metal deposition, oxide deposition, and plasma etching. Micromirrors are a type of MEMS. Other MEMS include accelerometers, pressure and flow sensors, etc. Most of these have already achieved commercial applications.

[0003] Micromirror devices are primarily used in optical display systems. In these systems, micromirrors act as light modulators, operating in both analog and digital modes. They are typically arranged in arrays, modulating light beams based on image data. By selectively reflecting the beams, bright and dark pixels are formed, creating an image on the display screen. Among various micromirror light modulators, bistable micromirror arrays operating in digital mode are the core components of mainstream digital full-color projection display systems.

[0004] The micromirror array is supported by a ceramic substrate and encapsulated with a glass window. A metal aperture is located around the perimeter of the glass enclosure to block externally reflected light beams from the micromirror array and to define the projection area. The brightness of the light reflected by the metal aperture is lower than that of the bright pixels in the projected image but higher than that of the dark pixels, creating a bright edge around the image. To prevent the metal aperture from affecting the contrast of the projected image, a dark area is created at the edge of the micromirror array, separating the effective projection area from the bright edge of the metal aperture. The effective projection area and dark area of ​​the micromirror array typically contain millions of independent units, each operating independently, and the micromirrors in the effective projection area and the dark area operate differently.

[0005] Existing bistable micromirrors operate in two states: a bright state and a dark state. When a bistable micromirror fails, it may be in one of these two states. For a micromirror positioned in the dark region, failure in the bright state will result in the failure of its dark region function.

[0006] Therefore, the dark area of ​​a micromirror array needs a new type of monostable micromirror that is simple to design, suitable for existing control circuits, and that even if it fails, it will occur in the dark state without affecting the function of the dark area. Summary of the Invention

[0007] The purpose of this invention is to solve the problem in the prior art that when a bistable micromirror is working, if the micromirror arranged in the dark area fails in the bright state, the dark area function will fail, which will lead to fixed bright spots or reduced image contrast in the projected image. The invention provides a monostable micromirror that can be deflected in one direction.

[0008] To achieve the above objectives, the present invention employs the following technical solution: A monostable micromirror capable of unidirectional deflection includes a substrate layer and an isolation layer arranged sequentially from bottom to top, wherein a storage unit is disposed within the substrate layer; An addressing electrode and a bias electrode are provided on the isolation layer. A torsion beam is provided at the upper end of the bias electrode. Upper addressing electrodes are provided on both sides of the torsion beam. One upper addressing electrode is located at the upper end of the bias electrode, and the other is located at the upper end of the addressing electrode. The torsion beam is connected to elastic bodies at both ends, and the elastic bodies are electrically connected to bias electrodes. A mirror is provided at the upper end of the torsion beam. The output terminal of the storage unit is connected to the addressing electrode.

[0009] A further improvement of the present invention is that: The lower end of the elastomer is provided with a torsion beam support column, the upper end of which is connected to the elastomer and the lower end of which is connected to a bias electrode.

[0010] The lower end of the upper addressing electrode is provided with an addressing electrode support post, through which a bias electrode or an addressing electrode is connected.

[0011] A micromirror storage unit for the monostable micromirror, comprising: A PMOS transistor, wherein the input terminal of the PMOS transistor is connected to a first input-output node and the output terminal is connected to a second input-output node; An NMOS transistor, wherein the input terminal of the NMOS transistor is connected to a second input-output node, and the output terminal is connected to a first input-output node; Bit line write transistor, the bit line write transistor being used to input write data into a first input / output node or a second input / output node; The first input / output node is connected to the addressing electrode.

[0012] A micromirror array, comprising: Multiple micromirror units, the multiple micromirror units being arranged in an array; The array includes an effective projection area and a dark area, with the dark area located outside the effective projection area; The micromirror units in the effective projection area are bistable micromirrors, and the micromirror units in the dark area are monostable micromirrors.

[0013] The dark area is located between the effective projection area and the metal aperture used to encapsulate the micromirror array.

[0014] An image projection system, comprising: A light source, used to provide a light beam along the first optical path; A micromirror array, wherein the micromirror array is located in the first optical path, and the micromirror array is the micromirror array as described in claim 5; The controller is used to provide image data signals and control signals to the micromirror array; A projection lens, located in the second optical path, is used to focus the reflected light beam from the received micromirror array onto the image plane; Light traps are used to absorb light reflected from micromirrors in dark areas.

[0015] A group of mirrors is arranged in the first optical path, and the group of mirrors is located between the light source and the micromirror array.

[0016] The controller is used to write image data signals into the storage units corresponding to each micromirror in the micromirror array. The micromirrors in the effective projection area rotate to the bright state or dark state according to the image data signals, and the monostable micromirrors in the dark area are all deflected to the dark state according to the image data signals.

[0017] The projection lens is positioned on the reflected light path of the micromirrors in the effective projection area of ​​the micromirror array, where the micromirrors are in a bright state. The light trap is positioned on the reflected light path of a micromirror that is in a dark state in the dark area.

[0018] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a monostable micromirror capable of unidirectional deflection. By setting a storage unit within the substrate layer and connecting the output of the storage unit to only one addressing electrode, and simultaneously placing the upper addressing electrodes on both sides of the torsion beam at the upper ends of the bias electrode and the addressing electrode respectively, and electrically connecting the elastic body to the bias electrode, the electrostatic force driving of the micromirror can only occur between the addressing electrode and the upper addressing electrode above it. Therefore, the deflectable mirror can only be driven to deflect in one direction, forming a monostable working mode. This eliminates the possibility of the micromirror being stuck in the bright state when it fails, and solves the technical problem of existing bistable micromirrors causing fixed bright spots and reduced contrast in the projected image when placed in the dark area due to bright state failure. It ensures that even if the micromirror fails, it can only be in the dark state or the undeflected state, avoiding the failure of the dark area function.

[0019] This invention discloses a micromirror memory cell, which includes a three-transistor structure containing only a PMOS transistor, an NMOS transistor, and a bit-line write transistor. The first input-output node is connected to the address electrode, so that the memory cell can reliably output a single control signal to drive the monostable micromirror to deflect in one direction. The circuit structure is simple and simplifies the control of the dark area micromirror.

[0020] This invention discloses a micromirror array that divides the array into an effective projection area and a dark area. In the dark area, monostable micromirrors are used, so that the micromirrors in the dark area can only be deflected in one direction to the dark state or the undeflected state, and there will be no bright state failure. This solves the technical problem in the prior art that the use of bistable micromirrors in the dark area may cause fixed bright spots at the edge of the projected image and reduce the contrast due to bright state failure.

[0021] Furthermore, the present invention defines the dark area between the effective projection area and the metal aperture used to encapsulate the micromirror array, so that the dark area micromirrors can block the stray light reflected by the metal aperture, forming a clear dark border around the projected image. This can effectively separate the projection area from the bright edge of the metal aperture, and prevent the bright edge of the metal aperture from affecting the contrast of the projected image.

[0022] This invention discloses an image projection system in which a light trap is set to absorb light reflected by micromirrors in the dark area and a projection lens receives light reflected by the effective projection area, so that the micromirrors in the dark area always reflect light to the light trap and not into the projection lens, thus avoiding the failure of the dark area function. Attached Figure Description

[0023] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is an exploded view of the monostable micromirror disclosed in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of a three-transistor static random access memory cell disclosed in Embodiment 2 of the present invention; Figure 3 This is a diagram showing the working state of a monostable micromirror in the dark region of a micromirror array in a display system disclosed in this invention. Figure 4 This is a top view of the micromirror device in the projection display system disclosed in Embodiment 3 of the present invention. The figure shows the glass encapsulation window, the metal aperture, the effective projection area of ​​the micromirror array, and the dark area. Figure 5 In this invention Figure 4 AA section Figure 1 ; Figure 6 This is a schematic diagram of the display system disclosed in Embodiment 4 of the present invention; Figure 7 In this invention Figure 4 AA section Figure 2 ; Figure 8In this invention Figure 4 AA section Figure 3 .

[0025] Wherein: 502 - substrate; 504 - bistable micromirror array; 506 - glass cover plate; 508 - metal aperture; 510 - monostable micromirror array; 602 - Mirror surface; 604 - Substrate layer; 606 - Isolation layer; 608 - Addressing electrode; 610 - Bias electrode; 612 - Torsion beam support column; 614 - Upper addressing electrode support column; 616 - Torsion beam; 618 - Upper addressing electrode; 620 - Mirror support column; 622 - Elastomer; 700 - Micromirror memory cell; 702 - Bit line write transistor; 704 - PMOS transistor; 706 - NMOS transistor; 708 - First input / output node; 710 - Second input / output node; 712 - Input word line; 900 - Image projection system; 902 - Micromirror array; 904 - Light source; 906 - Mirror group; 908 - Controller; 910 - Light trap; 912 - Projection lens; 914 - Screen; 916 - Image; 918 - Edge. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0027] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0028] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0029] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper," "lower," "horizontal," or "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, terms such as "first" and "second" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0030] Furthermore, the use of the term "horizontal" does not imply that the component must be absolutely horizontal, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0031] In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0032] The present invention will now be described in further detail with reference to the accompanying drawings: See Figure 1 This invention discloses a monostable micromirror that can be deflected in one direction. The micromirror is located in the dark area and is used to divide the effective projection area from the bright edge of the metal aperture.

[0033] Example 1 This invention discloses a monostable micromirror capable of unidirectional deflection, see details below. Figure 1 This is an exploded perspective view of the monostable micromirror 600. The first metal layer of the upper structure is asymmetrical, retaining only one side of the addressing electrode, allowing the micromirror to operate in only one direction. Although the mirror surface can rotate freely in any direction about the axis of the torsion beam, the only mechanism capable of generating electrostatic force is designed to drive the micromirror to deflect in only one direction. The control circuitry of the micromirror typically includes, but is not limited to, a memory cell corresponding to each micromirror and located below it, and digital logic circuitry for controlling the transmission of digital image data to the memory cell below. The substrate 604 is a silicon substrate. The circuit metal layer in the substrate 604 is electrically connected to the upper structure of the micromirror through an isolation layer 606, on which the upper structure of the micromirror is fabricated. Through-holes are formed in the isolation layer 606 to achieve electrical connection between the upper structure of the micromirror and the circuitry within the substrate 604. The specific structure is as follows: The device includes a substrate layer 604 and an isolation layer 606 arranged sequentially from bottom to top. A memory cell is disposed within the substrate layer 604. An addressing electrode 608 and a bias electrode 610 are disposed on the isolation layer 606. A torsion beam 616 is disposed at the upper end of the bias electrode 610. Upper addressing electrodes 618 are disposed on both sides of the torsion beam 616, wherein one upper addressing electrode 618 is located above the bias electrode 610 and the other is located above the addressing electrode 608. An elastic body 622 is connected to both ends of the torsion beam 616, and the elastic body 622 is electrically connected to the bias electrode 610. The output terminal of the memory cell is connected to the addressing electrode 608.

[0034] Furthermore, in this embodiment, the storage unit refers to the SRAM circuit in which each micromirror independently controls the deflection direction, excluding external signal circuits.

[0035] Furthermore, in this embodiment, the first layer on top of the isolation layer 606 is a metal layer used for interconnection with the substrate circuit. This metal layer is patterned to form addressing electrodes 608 and bias electrodes 610, which are respectively connected to the SRAM circuit and the external signal circuit.

[0036] Furthermore, in this embodiment, a first support structure is fabricated on the addressing electrode 608 and the bias electrode 610, including a torsion beam support column 612 and an upper addressing electrode support column 614. In terms of process, an oxide sacrificial layer is first deposited and holes are photolithographically formed, then filled with metal and planarized, leaving only the torsion beam support column 612 and the upper addressing electrode support column 614 in the holes.

[0037] Furthermore, a metal layer is deposited on top of the sacrificial layer, and etched to form a torsion beam 616 and an upper addressing electrode 618. An oxide sacrificial layer is deposited again, and holes for the mirror support pillars are etched out. The holes are filled with metal and planarized, while retaining the mirror support pillars 620 in the holes. Another metal layer is deposited and etched to form a mirror 602.

[0038] Furthermore, after the two sacrificial layers are removed, the mirror 602 can be freely deflected. The electrostatic attraction generated by the addressing electrode 608 and the upper addressing electrode 618 is used to drive the mirror deflection. The elastomer 622 is electrically connected to the bias electrode 610 to limit the deflection of the mirror 602 and prevent it from contacting the addressing electrode 608 with a potential difference, which could lead to device failure.

[0039] Example 2 This embodiment discloses a micromirror storage unit. The micromirror storage unit in this embodiment is used in the monostable micromirror described in the embodiment. See [link to documentation]. Figure 2 This is a schematic diagram of the micromirror memory cell 700. This memory cell contains 3 transistors: A PMOS transistor 704 has its input terminal electrically connected to the first input / output node 708 and its output terminal electrically connected to the second input / output node 710. An NMOS transistor 706 has its input terminal electrically connected to the second input / output node 710 and its output terminal electrically connected to the first input / output node 708, forming a coupled latch.

[0040] When input word line 712 is at logic low and bit line write transistor 702 is enabled, a low-level signal reaches node 708. Transistor 704 is enabled, presenting a logic high level at node 710. The high level at node 710 causes the transistor to output a low level at node 708, ensuring that data within the cell is retained after write transistor 702 is turned off. When part of a micromirror cell, output node 708 is connected to address electrode 608, allowing data in the memory cell to control the deflection of the micromirror in one direction.

[0041] See Figure 3 To illustrate the working principle of dark-area micromirrors, the light source is also arranged at an angle equal to twice the deflection angle of the micromirrors. When a micromirror deflects away from the light source, it reflects the light away from the projection lens, keeping the corresponding dark-area micromirror in a dark state. The micromirror array as a whole adopts a row-group segmented reset design. The bias electrodes of the micromirrors in the dark area and the effective projection area of ​​each group are connected to the same external signal circuit, eliminating the need for a separate control circuit for the dark-area micromirrors.

[0042] Example 3 In existing technologies, micromirrors in the dark area and those in the effective projection area employ almost identical designs, the only difference being that micromirrors in the dark area only need to rotate in a single direction. The dark area constitutes a significant proportion of the total number of micromirrors in the array. For example, in a 1948×1108 array, the dark area uses 84,784 micromirrors, while the effective area uses 2,073,600 micromirrors. The more micromirrors used in the dark area, the higher the probability of at least one defective micromirror appearing. Since the dark area is always in a dark state, any micromirror failure in a bright state will create a highly noticeable image flaw. Therefore, it is essential to minimize the probability of bright-state failure of micromirrors.

[0043] In view of this, see Figure 4 and Figure 5This embodiment discloses a plan view of a micromirror array 500. A substrate 502 supports an effective projection area composed of a bistable micromirror array 504 and a dark area composed of a monostable micromirror array 510. The bistable micromirror array 504 and the monostable micromirror array 510 are encapsulated by the substrate 502 and a glass cover plate 506 fixed thereon to form a sealed structure. A metal aperture 508 is deposited inside the encapsulation cover, blocking light outside the metal aperture 508. When the micromirror display system is working, the brightness of the metal aperture 508 is much higher than that of the dark-state micromirrors, forming a bright edge around the image. To form a clear dark border around the effective projection area of ​​the array, monostable micromirrors are used in this embodiment. Approximately 15 monostable micromirrors are arranged around the micromirrors in the effective projection area to form a dark area. The micromirrors in this area are always in the off state. Figure 4 In the diagram, the dark area extends from the edge of the bistable micromirror array 504, which is blocked by the aperture stop, to the position of the monostable micromirror array 510 inside the aperture stop. As long as the light source beam illuminates the aperture stop, the dark area outside the effective region forms a dark edge band, avoiding the influence of the bright edge of the metal aperture stop. Example 4 See Figure 6 This embodiment discloses an image projection system 900, in which... Figure 6 In the image, light emitted from light source 904 is focused onto micromirror array 902 by lens group 906. Controller 908 writes image data and control signals into storage units below each micromirror. The data in the storage units causes the micromirrors in the effective projection area to rotate to a bright or dark state; while the micromirrors in the dark area are all deflected to a dark state. The dark-state micromirrors reflect light to light trap 910; the bright-state micromirrors reflect light to projection lens 912. Projection lens 912 focuses the light modulated by micromirror device 902 onto image plane or screen 914, where the screen contains image 916 projected by the effective area micromirror array and edges 918 defined by the dark area micromirror array.

[0044] Combination Figure 7 and Figure 8 To further explain the dark area disclosed in this embodiment, if no dark area is set, the brightness of the dark pixels at the projection edge will be less than the brightness of the metal aperture area, which will result in poor projection image quality. It should also be noted that although the brightness of the dark area pixels is still less than the brightness of the metal aperture area, it will not affect the imaging quality of the effective projection area.

[0045] The main advantages of the monostable micromirror disclosed in this embodiment are that it is arranged in the dark area of ​​the micromirror array and operates in a monostable mode, which can divide the effective projection area and the metal aperture, thereby enhancing the contrast of the projected image; the new micromirror design is simple, the entire storage unit only requires 3 transistors, and no process flow adjustment is required; the new micromirror is suitable for existing micromirror array control methods, without the need to add additional control circuits; the failure of the new micromirror will not cause the dark area function to fail.

[0046] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A monostable micromirror capable of unidirectional deflection, characterized in that, It includes a substrate layer (604) and an isolation layer (606) arranged sequentially from bottom to top, and a memory cell is disposed within the substrate layer (604); An addressing electrode (608) and a bias electrode (610) are provided on the isolation layer (606). A torsion beam (616) is provided at the upper end of the bias electrode (610). An upper addressing electrode (618) is provided on both sides of the torsion beam (616). One upper addressing electrode (618) is located at the upper end of the bias electrode (610), and the other is located at the upper end of the addressing electrode (608). The torsion beam (616) is connected to two ends of an elastic body (622), the elastic body (622) is electrically connected to a bias electrode (610), and a mirror (602) is provided at the upper end of the torsion beam (616). The output terminal of the storage unit is connected to the addressing electrode (608).

2. A monostable micromirror capable of unidirectional deflection according to claim 1, characterized in that, The lower end of the elastomer (622) is provided with a torsion beam support column (612), the upper end of the torsion beam support column (612) is connected to the elastomer (622), and the lower end is connected to the bias electrode (610).

3. A monostable micromirror capable of unidirectional deflection according to claim 1, characterized in that, The upper addressing electrode (618) is provided with an addressing electrode support post (614) at its lower end, and the bias electrode (610) or the addressing electrode (608) is connected through the addressing electrode support post (614).

4. A micromirror storage unit for the monostable micromirror of claim 1, characterized in that, include: PMOS transistor (704), the input terminal of which is connected to the first input-output node (708) and the output terminal is connected to the second input-output node (710). NMOS transistor (706), the input terminal of which is connected to the second input-output node (710) and the output terminal is connected to the first input-output node (708). Bit line write transistor (702) is used to input write data to a first input / output node (708) or a second input / output node (710). The first input / output node (708) is connected to the addressing electrode (608).

5. A micromirror array, characterized in that, include: Multiple micromirror units, the multiple micromirror units being arranged in an array; The array includes an effective projection area and a dark area, with the dark area located outside the effective projection area; The micromirror units in the effective projection area are bistable micromirrors, and the micromirror units in the dark area are monostable micromirrors as described in claim 1.

6. A micromirror array according to claim 5, characterized in that, The dark area is located between the effective projection area and the metal aperture used to encapsulate the micromirror array.

7. An image projection system, characterized in that, include: Light source (904) is used to provide a light beam along the first optical path; A micromirror array (902) is located in the first optical path, and the micromirror array (902) is the micromirror array as described in claim 5; The controller (908) is used to provide image data signals and control signals to the micromirror array (902); A projection lens (912) is located in the second optical path and is used to focus the reflected beam of the received micromirror array (902) onto the image plane (914). Light trap (910) is used to absorb light reflected by micromirrors in dark areas.

8. An image projection system according to claim 7, characterized in that, A mirror group (906) is provided on the first optical path, and the mirror group (906) is located between the light source (904) and the micromirror array (902).

9. An image projection system according to claim 7, characterized in that, The controller (908) is used to write image data signals into the storage units corresponding to each micromirror in the micromirror array (902). The micromirrors in the effective projection area rotate to the bright state or the dark state according to the image data signals, and the monostable micromirrors in the dark area are all deflected to the dark state according to the image data signals.

10. An image projection system according to claim 7, characterized in that, The projection lens (912) is positioned on the reflected light path of the micromirrors in the bright state within the effective projection area of ​​the micromirror array (902); The light trap (910) is set on the reflected light path of the micromirror in the dark region.

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