Micromirror array based on electrically-controlled deformable micro-nano structure and preparation method thereof

Abstract

According to the micro-mirror array based on the electric control deformable micro-nano structure provided by the invention, the micro-mirror array with remarkable size advantage and cost benefit can be manufactured by innovatively fusing the electric control deformable suspended nano structure and the mirror surface design of the supporting column body; the suspended nano-structure can generate surface shape deformation through potential regulation and control so as to drive the mirror surface array to generate displacement, so that optical phase regulation and control or optical display are carried out through the mirror surface array, and the key technical bottlenecks of complex manufacturing process, low duty ratio, insufficient dynamic performance and the like of existing market products are effectively solved; performance limitation of a traditional micro-mirror device is broken through, and meanwhile localization breakthrough of a core device is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical fields of three-dimensional micro-nano manufacturing and micro-optical electromechanical systems, and particularly relates to a micro-mirror array based on an electrically controllable deformable micro-nano structure and a preparation method thereof. Background Art

[0002] As an important branch of modern on-chip microsystem technology, micro-optical electromechanical systems have achieved a deep integration of optical technology and micro-electromechanical systems. Its core lies in integrating optical components such as optical waveguides, micro-mirrors, and gratings with micron-scale mechanical actuators (electrostatic drive, piezoelectric drive, etc.) and control circuits on a single chip to form a miniaturized intelligent system with sensing, execution, and regulation functions, so as to achieve precise manipulation and dynamic adjustment of optical signals. In recent years, with the development of advanced micro-nano processing technologies, micro-optical electromechanical devices have made remarkable breakthroughs in terms of structural complexity, integration, and performance stability. These technological advancements not only enable them to maintain good compatibility with traditional semiconductor processes but also drive the system towards higher precision (nanoscale displacement control), lower power consumption (microwatt-level drive), and more functions (reconfigurable optical processing).

[0003] Currently, micro-optical electromechanical systems have been applied on a large scale in fields such as optical communication, consumer electronics, and biomedicine. Among them, the digital micro-mirror device of Texas Instruments in the United States, as a landmark commercial product, is widely used in high-end projection displays. As the core component of digital light processing projection technology, the digital micro-mirror system consists of millions of independently controllable micro-mirrors. Each micro-mirror serves as a pixel point and can form three modes (-12 degrees, 0 degrees, +12 degrees) in the diagonal direction to regulate incident light and achieve the required projection imaging function.

[0004] Although the micro-mirror array, as a core device in fields such as beam control, optical communication, and three-dimensional imaging, has been industrially applied, it still faces multiple key technical bottlenecks. First, the existing manufacturing system relies on high-precision lithography and wafer bonding technologies. The complex process flow results in a low yield rate and high production costs. The exorbitant pricing of high-resolution commercial models has become a key obstacle restricting the popularization of its industrial applications. Second, limited by the inherent defects of micron-scale structural gaps, the actual duty cycle of the device is significantly reduced, which not only causes light energy loss and diffraction effects but also leads to the deterioration of the signal-to-noise ratio of the imaging system. Moreover, it is difficult to fundamentally break through this technical limitation within the existing framework. Third, even for the current digital micro-mirror device with the best performance, its electro-controlled hinge drive architecture has a principle limitation, resulting in the maximum deflection angle being difficult to break through the design threshold and unable to meet the technical requirements of multi-modal continuous regulation in high-dynamic response scenarios. Summary of the Invention

[0005] To solve the above problems, the present invention provides a micromirror array based on an electrically controllable deformable micro-nano structure and a preparation method thereof. The combination of a micrometer-level mirror surface and a suspended nano-structure generates displacement coupling. The suspended nano-structure can be deformed in surface shape by potential regulation, thereby driving the mirror array to generate displacement, and then optical phase regulation or optical display can be performed through the mirror array, achieving a breakthrough in size.

[0006] A micromirror array based on an electrically controllable deformable micro-nano structure, which successively includes a base layer, a bottom conductive layer, a dielectric layer, a top conductive layer, and a mirror surface layer from bottom to top;

[0007] The bottom conductive layer deposited on the base layer is an array structure composed of a plurality of bottom conductive units, and each bottom conductive unit is composed of a bottom conductive electrode, a bottom conductive plate, and a bottom conductive wire connecting the two;

[0008] The dielectric layer deposited on the bottom conductive layer includes a plurality of dielectric columns;

[0009] The top conductive layer deposited on the dielectric layer is an array structure composed of a plurality of top conductive units, and each top conductive unit is composed of a top conductive electrode, a top conductive plate, and a top conductive wire connecting the two; at the same time, the arrangement directions of each bottom conductive plate and each top conductive plate are perpendicular to each other, and a suspended nano-structure is formed in the overlapping area of each bottom conductive plate and each top conductive plate;

[0010] A dielectric column is distributed at each of the four corners of each suspended nano-structure, and a hollow pattern is distributed on the top conductive plate in the overlapping area;

[0011] The mirror surface layer deposited on the top conductive layer is an array structure composed of a number of mirror surfaces equal to the number of suspended nano-structures; at the same time, each mirror surface is respectively connected to the top conductive plate part of the corresponding suspended nano-structure through a column.

[0012] Further, the hollow pattern is distributed along the circumference of the top conductive plate in the overlapping area and is composed of a plurality of arc-shaped grooves arranged in a spiral pattern with respect to each other.

[0013] Further, the bottom conductive electrodes in each bottom conductive unit are grounded, and the top conductive electrodes in each top conductive unit are connected to independent external voltage sources;

[0014] By turning on different external voltage sources, a potential difference is generated between the bottom conductive plate and the top conductive plate in different suspended nano-structures. Then, due to the potential difference, the top conductive plate with the hollow pattern generates displacement deformation, and at the same time, the mirror unit is driven to move vertically through the support column, realizing the phase regulation of the light beam incident on the mirror unit.

[0015] Further, the bottom conductive electrodes in each bottom conductive unit are connected to independent external voltage sources, and the top conductive electrodes in each top conductive unit are grounded;

[0016] By turning on different external voltage sources, a potential difference is generated between the bottom conductive plate and the top conductive plate in different suspended nanostructures. Then, due to the potential difference, the top conductive plate with a hollow pattern undergoes displacement deformation, and at the same time, the mirror unit is driven by the support column to move vertically, realizing the phase modulation of the light beam incident on the mirror unit.

[0017] Further, the materials of the bottom conductive layer and the top conductive layer are both metal or doped silicon materials.

[0018] Further, the material of the dielectric layer is silicon oxide or silicon nitride.

[0019] Further, a method for fabricating a micromirror array based on an electro-controlled deformable micro-nano structure includes the following steps:

[0020] Step 1: Fabricate a voltage-driven functional substrate with micron-level independent addressing capabilities;

[0021] Step 2: Fabricate a suspended nanostructure based on the principle of electro-deformation;

[0022] Step 3: Fabricate a reflective mirror array that realizes mechanical coupling through support columns.

[0023] Further, the method for fabricating a voltage-driven functional substrate with micron-level independent addressing capabilities is as follows:

[0024] Step ①: Select silicon dioxide as the base layer;

[0025] Step ②: Use electron beam evaporation coating technology to sequentially deposit a 5-nanometer platinum adhesion layer and a 25-nanometer gold conductive layer on the base layer to form a bottom electrode structure;

[0026] Step ③: First, perform an adhesion treatment on the bottom electrode structure, and then spin-coat a 1.2-micron-thick S1805 photoresist. After pre-baking at 100 °C for 60 seconds, use a step-type ultraviolet lithography system to expose the S1805 photoresist layer with a minimum line width of 0.7 microns; after developing the S1805 photoresist with 2.38% TMAH, fixing with deionized water, and hardening the film, complete the pattern transfer from the S1805 photoresist to the bottom electrode structure by ion beam etching the gold conductive layer in the bottom electrode structure. Finally, remove the residual S1805 photoresist on the bottom electrode structure after pattern transfer by dissolving in an organic solution and cleaning with oxygen plasma to obtain a patterned bottom conductive layer;

[0027] Step ④: Use plasma-enhanced chemical vapor deposition technology to prepare silica with a thickness of 300 - 600 nm on the bottom conductive layer as the dielectric layer, and precisely control the polishing to a thickness of 300 ± 20 nm through chemical mechanical polishing;

[0028] Step ⑤: Adopt electron beam evaporation coating process to deposit a 5 nm platinum adhesion layer and a 70 nm gold conductive layer on the dielectric layer to form the top electrode structure;

[0029] Step ⑥: First, perform an adhesion treatment on the top electrode structure, and then spin-coat AZ5214 photoresist with a thickness of 1.5 μm. After pre-baking at 100 °C for 60 seconds, use a contact ultraviolet lithography system to expose the AZ5214 photoresist layer with a minimum line width of 2 μm; after developing the AZ5214 photoresist with 2.38% TMAH, fixing with deionized water, and hardening the film, complete the pattern transfer from the AZ5214 photoresist to the top electrode structure by ion beam etching the gold conductive layer in the top electrode structure. Finally, remove the residual AZ5214 photoresist on the top electrode structure after pattern transfer through dissolution in an organic solution and oxygen plasma cleaning to obtain a patterned top conductive layer.

[0030] Furthermore, the method for preparing a suspended nanostructure based on the electro-deformation principle is as follows:

[0031] Step ①: Implement a PMMA photoresist spin-coating process with a thickness of 270 nm on the top conductive layer. After pre-baking at 180 °C for 60 seconds, uniformly coat a conductive adhesive layer on the surface of the PMMA photoresist and perform a second pre-baking at 90 °C for 60 seconds; use an electron beam lithography system to expose the double-layer resist composed of PMMA photoresist and conductive adhesive layer with a minimum line width of 70 nm, and expose a hollow pattern array with a unit period of 4.8 μm × 4.8 μm; after removing the conductive adhesive from the double-layer resist, developing the PMMA photoresist with a developer, and fixing the PMMA photoresist with isopropyl alcohol, complete the nano-scale pattern transfer from the PMMA photoresist to the top conductive layer by ion beam etching the top conductive layer. Finally, use oxygen plasma cleaning to completely remove the PMMA photoresist residue to obtain a hollow pattern;

[0032] Step ②: Use a diluted hydrofluoric acid solution to perform isotropic wet etching on the product of Step ① to remove the silica dielectric layer under the gold conductive layer in the top conductive layer. At the same time, according to the experimentally measured etching rate, control the etching degree of the silica so that the silica directly below the suspended nanostructure is etched away while retaining the four support pillars at the corners of each suspended nanostructure.

[0033] Furthermore, the method for preparing a reflective mirror array that realizes mechanical coupling through support pillars is as follows:

[0034] Step ①: Implement a spin coating process of S1813 photoresist with a thickness of 1 micron on the suspended nanostructure. After pre-baking at 110 °C for 60 seconds, use a laser direct writing system to perform pattern exposure on this layer of S1813 photoresist with the ultimate resolution. After developing and fixing the S1813 photoresist, a mask structure in the shape of a double square frame is formed.

[0035] Step ②: Use magnetron sputtering technology to deposit a 1.2-micron high-reflectivity aluminum layer on the whole product of Step ①, synchronously constructing the mirror body and support columns. The bottom end of the support column is connected to the suspended nanostructure to form a mechanical coupling structure of the mirror-substrate.

[0036] Step ③: Implement a spin coating process of AR-P 6200 photoresist with a thickness of 300 nanometers; use electron beam lithography to perform pattern exposure on this layer of AR-P 6200 photoresist, and over-etch to expose a mirror array with a unit period of 4.8 microns × 4.8 microns; after developing and fixing the AR-P 6200 photoresist, use inductively coupled plasma etching of the high-reflectivity aluminum layer to achieve pattern transfer from the AR-P 6200 photoresist to the high-reflectivity aluminum layer.

[0037] Step ④: Use an organic solution to remove the AR-P 6200 photoresist above the mirror surface in Step ③ and the sacrificial layer below the high-reflectivity aluminum layer in Step ①, achieving the suspended release of the mirror body area, and finally forming an aluminum mirror array with a vertical displacement degree of freedom.

[0038] Beneficial effects:

[0039] 1. The present invention provides a micromirror array based on an electro-controlled deformable micro-nano structure. By innovatively integrating an electro-controlled deformable suspended nanostructure and a support column mirror design, a micromirror array with significant size advantages and cost-effectiveness can be fabricated. The suspended nanostructure can be deformed in-plane by potential regulation, thereby driving the mirror array to generate displacement, so as to perform optical phase regulation or optical display through the mirror array, effectively solving the key technical bottlenecks such as complex manufacturing processes, low duty ratios, and insufficient dynamic performance of existing market products, breaking through the performance limitations of traditional micromirror devices, and at the same time achieving a breakthrough in the localization of core devices.

[0040] 2. The present invention provides a micromirror array based on an electro-controlled deformable micro-nano structure, which can achieve continuously adjustable displacement control from 0 to 500 nanometers through voltage drive, rather than only switching between several modes, and has significant advantages in application scenarios such as holographic display that require continuous phase modulation.

[0041] 3. The present invention provides a method for fabricating a micromirror array based on an electrically controllable deformable micro-nano structure. Through innovative process flow optimization, the entire device can be fabricated with only 5 key lithography steps. By streamlining the process steps, the process complexity is significantly reduced, the device reliability is improved, and the production cost is reduced simultaneously, providing a more feasible manufacturing solution for the industrial application of large-scale micromirror arrays. Description of the Drawings

[0042] Figure 1 It is a process diagram for fabricating a voltage-functional driving substrate provided by the present invention;

[0043] Figure 2 It is a side view and a top view of a voltage-functional driving substrate provided by the present invention;

[0044] Figure 3 It is a process diagram for fabricating a suspended nano-structure provided by the present invention;

[0045] Figure 4 It is a process diagram for fabricating a reflecting mirror surface unit provided by the present invention;

[0046] Figure 5 It is a reflecting mirror surface unit that realizes mechanical coupling through a support column structure and a suspended nano-structure provided by the present invention;

[0047] Figure 6 It is a demonstration of the deformation effect of a single reflecting mirror surface unit provided by the present invention;

[0048] Figure 7 It is an effect diagram of a micromirror array provided by the present invention. Detailed Embodiments

[0049] In order to enable those skilled in the art to better understand the solution of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application.

[0050] As Figure 5 shown, a micromirror array based on an electrically controllable deformable micro-nano structure includes, from bottom to top, a base layer, a bottom conductive layer, a dielectric layer, a top conductive layer, and a reflecting mirror layer;

[0051] The bottom conductive layer deposited on the base layer is an array structure formed by arranging a plurality of bottom conductive units, and each bottom conductive unit is composed of a bottom conductive electrode, a bottom conductive plate, and a bottom conductive wire connecting the two;

[0052] The dielectric layer deposited on the bottom conductive layer includes a plurality of dielectric columns;

[0053] The top conductive layer deposited on the dielectric layer is an array structure composed of multiple top conductive units, and each top conductive unit is composed of a top conductive electrode, a top conductive plate, and a top conductive wire connecting the two; at the same time, the arrangement directions of the bottom conductive plates and the top conductive plates are perpendicular to each other, and a suspended nanostructure is formed in the overlapping area of each bottom conductive plate and each top conductive plate;

[0054] A dielectric column is distributed at each of the four corners of each suspended nanostructure, and the top conductive plates in the overlapping area are all distributed with hollow patterns; the hollow patterns are distributed along the circumferential direction of the top conductive plates in the overlapping area and are composed of multiple arc-shaped grooves arranged in a spiral pattern;

[0055] The mirror layer deposited on the top conductive layer is an array structure composed of a number of mirror surfaces equal to the number of suspended nanostructures; at the same time, each mirror surface is respectively connected to the top conductive plate part in the corresponding suspended nanostructure through a column.

[0056] Furthermore, the bottom conductive electrodes in each bottom conductive unit are connected to independent external voltage sources, and the top conductive electrodes in each top conductive unit are grounded; or, the bottom conductive electrodes in each bottom conductive unit are grounded, and the top conductive electrodes in each top conductive unit are connected to independent external voltage sources;

[0057] By turning on different external voltage sources, a potential difference is generated between the bottom conductive plate and the top conductive plate in different suspended nanostructures. Furthermore, due to the potential difference, the top conductive plate with the hollow pattern generates a displacement deformation, and at the same time, the mirror unit is driven by the support column to generate a vertical movement, realizing the phase control of the light beam incident on the mirror unit.

[0058] That is to say, the present invention realizes the pixel-level independent addressing function through the nano-precision deformation control of the micro-scale structural units, and can accurately reconstruct the target optical display effect. The core architecture of the present invention includes three functional levels: 1) a voltage-driven functional substrate with micro-scale independent addressing ability; 2) a suspended nanostructure response unit based on the principle of electro-deformation; 3) a mirror array realized by mechanical coupling through a support column structure.

[0059] The voltage-driven functional substrate adopts a three-layer architecture of a conductive layer / dielectric layer / conductive layer on a quartz substrate. This structure is formed by a multi-layer thin film deposition process. The conductive layer can be metal or doped silicon material, the dielectric layer can be silicon oxide, silicon nitride and other materials with insulation ability, and the top and bottom conductive layers are formed into an interdigital electrode array with independent addressing function through micro-nano processing to realize precise electric field distribution control.

[0060] The suspended nanostructure response unit adopts a topology-optimized structure with a period of 2-5 microns, which is formed by high-precision lithography and isotropic wet etching processes. Its hollow structure is precisely suspended above the interdigital electrodes. This unit realizes out-of-plane displacement deformation based on the electrostatic force mechanism, and can generate a deformation displacement of 0-500 nanometers through the regulation of the potential difference between the upper and lower conductive layers, breaking through the size limitation and deformation limitation of the existing micromirror surface.

[0061] The mechanically coupled mirror array forms a three-dimensional interconnected structure with the suspended nanostructure unit through support columns and is constructed by a sacrificial layer release process. Each mirror unit realizes displacement transfer with the corresponding suspended nano-response unit through the support column. When the suspended nanostructure generates an out-of-plane displacement, the support column drives the mirror to move vertically synchronously, thereby achieving precise regulation of the optical phase and promising to realize the effect of miniaturized three-dimensional holographic display. This architecture effectively solves the problem of dynamic response mismatch between the traditional reflecting mirror and the driving unit through mechanical coupling design.

[0062] Furthermore, in terms of the manufacturing process, the present invention creatively integrates key process modules such as electron beam lithography, sacrificial layer suspended coating, wet etching, and critical point drying, significantly simplifying the process complexity while ensuring reliability.

[0063] Based on this, the present invention provides a method for manufacturing a micromirror array of an electrically controllable deformable micro-nano structure, and the specific steps are as follows:

[0064] Step 1: Prepare a voltage-driven functional substrate with micron-level independent addressing ability, and the specific steps are as follows:

[0065] Step ①: Select silicon dioxide as the base layer; it should be noted that the base material is not limited to silicon dioxide, and any base material with insulating ability or an insulating layer can be used.

[0066] Step ②: Use electron beam evaporation coating technology to sequentially deposit a 5-nanometer platinum adhesion layer and a 25-nanometer gold conductive layer on the base layer to form the bottom electrode structure; the coating equipment is not limited to electron beam evaporation coating, and coating equipment such as magnetron sputtering can also be used;

[0067] Step ③: First, perform a tackifying treatment on the bottom electrode structure. Subsequently, spin-coat a layer of S1805 photoresist with a thickness of 1.2 microns. After pre-baking at 100 °C for 60 seconds, use a step-and-repeat ultraviolet lithography system to expose the S1805 photoresist layer with a minimum line width of 0.7 microns. After developing the S1805 photoresist with 2.38% TMAH, fixing with deionized water, and hardening the film, complete the pattern transfer from the S1805 photoresist to the bottom electrode structure by ion beam etching the gold conductive layer in the bottom electrode structure. Finally, remove the residual S1805 photoresist on the bottom electrode structure after pattern transfer by dissolving it in an organic solution and cleaning it with oxygen plasma to obtain a patterned bottom conductive layer;

[0068] Step ④: Use plasma-enhanced chemical vapor deposition technology to deposit silicon dioxide with a thickness of 300 - 600 nanometers on the bottom conductive layer as a dielectric layer, and precisely control the polishing to a thickness of 300 ± 20 nanometers by chemical mechanical polishing; the material of the dielectric layer can be selected from other materials with good support and insulation properties, and the polished thickness can be changed according to the situation.

[0069] Step ⑤: Use electron beam evaporation coating technology to deposit a 5nm platinum tackifying layer and a 70nm gold conductive layer on the dielectric layer to form a top electrode structure; the materials of the bottom and top electrode structures are not limited to platinum and gold, and other metals can also be used as alternative solutions;

[0070] Step ⑥: First, perform a tackifying treatment on the top electrode structure. Subsequently, spin-coat a layer of AZ5214 photoresist with a thickness of 1.5 microns. After pre-baking at 100 °C for 60 seconds, use a contact ultraviolet lithography system to expose the AZ5214 photoresist layer with a minimum line width of 2 microns. After developing the AZ5214 photoresist with 2.38% TMAH, fixing with deionized water, and hardening the film, complete the pattern transfer from the AZ5214 photoresist to the top electrode structure by ion beam etching the gold conductive layer in the top electrode structure. Finally, remove the residual AZ5214 photoresist on the top electrode structure after pattern transfer by dissolving it in an organic solution and cleaning it with oxygen plasma to obtain a patterned top conductive layer.

[0071] After completing the above processes, obtain Figure 2 the voltage-driven functional substrate shown Figure 2 The schematic structure of a 3×3 array is shown. The actual process supports the preparation of larger-scale arrays. This substrate forms 9 independent pixel units through a three-layer structure of conductive layer / dielectric layer / conductive layer, and each pixel can be precisely and independently regulated by the top and bottom electrode voltages. It should be noted that the selection of photoresist and the different exposure systems can also be used as alternative solutions. At the same time, the substrate with voltage-driven function is not limited to the interdigital electrode independent addressing type, and other structures with micron-level single-point voltage driving can also be used.

[0072] Step 2: Prepare a suspended nanostructure based on the principle of electro-deformation. The specific steps are as follows:

[0073] Step ①: Implement a spin-coating process of PMMA photoresist with a thickness of 270 nm on the top conductive layer. After pre-baking at 180 °C for 60 s, uniformly coat a conductive adhesive layer on the surface of the PMMA photoresist and perform a second pre-baking at 90 °C for 60 s. Use an electron beam lithography system to expose the double-layer resist composed of PMMA photoresist and the conductive adhesive layer with a minimum line width of 70 nm, and expose a hollow pattern array with a unit period of 4.8 μm × 4.8 μm. After removing the conductive adhesive from the double-layer resist, developing the PMMA photoresist with a developer, and fixing the PMMA photoresist with isopropanol, use an ion beam to etch the top conductive layer to achieve nano-scale pattern transfer from the PMMA photoresist to the top conductive layer. Finally, use oxygen plasma cleaning to completely remove the PMMA photoresist residue to obtain a hollow pattern.

[0074] The hollow pattern of the suspended nanostructure is not limited to Figure 3 the pattern shown. Any pattern with topological optimization and capable of surface deformation under voltage drive can be used as an alternative. This step of making the nanostructure pattern suspended can choose other methods according to the different dielectric layers.

[0075] Step ②: Use a diluted hydrofluoric acid solution to perform isotropic wet etching on the product of Step ① to remove the silica dielectric layer under the gold conductive layer in the top conductive layer. At the same time, according to the experimentally measured etching rate, control the etching degree of the silica so that the silica directly below the suspended nanostructure is etched away while retaining the four support pillars at the corners of each suspended nanostructure.

[0076] Step 3: Prepare a reflective mirror array that realizes mechanical coupling through support pillars, as Figure 4 shown. The specific steps are as follows:

[0077] Step ①: Implement a spin-coating process of S1813 photoresist with a thickness of 1 μm on the suspended nanostructure. After pre-baking at 110 °C for 60 s, use a laser direct writing system to perform pattern exposure on this layer of S1813 photoresist with the ultimate resolution. After developing and fixing the S1813 photoresist, a mask structure in the shape of a Chinese character "hui" is formed.

[0078] Step ②: Use magnetron sputtering technology to deposit a 1.2-μm high-reflectivity aluminum layer on the entire product of Step ①, synchronously constructing the mirror body and the support pillars. The bottom end of the support pillar is connected to the suspended nanostructure to form a mechanical coupling structure of the mirror-substrate.

[0079] It should be noted that the present invention can also obtain a smoother aluminum mirror surface by polishing after deposition.

[0080] Step ③: Implement the spin coating process of AR-P 6200 photoresist with a thickness of 300 nm; use electron beam lithography to perform pattern exposure on this layer of AR-P 6200 photoresist, and overlay expose a mirror array with a unit period of 4.8 μm × 4.8 μm; after developing and fixing the AR-P 6200 photoresist, use inductively coupled plasma etching of the high-reflection aluminum layer to achieve pattern transfer from the AR-P 6200 photoresist to the high-reflection aluminum layer;

[0081] Step ④: Use an organic solution to remove the AR-P 6200 photoresist above the mirror surface in Step ③ and the sacrificial layer below the high-reflection aluminum layer in Step ①, achieving the suspended release of the mirror main body area, and finally forming an aluminum mirror array with vertical displacement freedom.

[0082] After completing the above processes, the Figure 5 shown mirror unit is obtained, and its dynamic working mode is as Figure 6 shown: The suspended nanostructure unit generates a surface shape deformation under voltage drive, and realizes mechanical displacement transmission through the support column, driving the mirror to achieve nanoscale longitudinal displacement regulation.

[0083] This architecture supports large-scale array expansion, such as the Figure 7 shown 3×3 array verification model, and actually can achieve a higher order of pixel integration. The height of each pixel mirror can be continuously adjusted through independent potential regulation, breaking through the discreteness limitation of traditional digital switch regulation.

[0084] In summary, compared with the traditional micromirror array, the present invention has the following advantages:

[0085] 1. The present invention achieves a breakthrough in size compared with the traditional micromirror array

[0086] The micromirror array of the present invention realizes high integration, and the size period of its metal micromirror is jointly determined by the parameters of the suspended nanostructure and the ultimate processing ability of the support column. Theoretically, the smaller the size of the suspended nanostructure unit, the smaller the size of the single micromirror surface that can be fabricated on it, and the size ratio of the two is about 1:1. However, due to the fact that the suspended nanostructure cannot obtain a large displacement at a small size, and the yield of the too-small support column is poor and cannot support the weight of the mirror, the three restrict each other, and an optimal solution needs to be obtained through long-term experiments. Based on the current experimental experience accumulation, a periodic array with a period less than 5 μm × 5 μm can be achieved, and the optimal can reach 2.5 μm × 2.5 μm (the typical value of traditional commercial devices is 8-15 μm), and the unit density is increased to more than 6 times.

[0087] 2. The present invention realizes significant process optimization

[0088] Traditional microelectromechanical systems rely on the stacking of multi-layer semiconductor processes, and complex processes such as multiple precision lithographies, three-dimensional micro-structure fabrication, and wafer bonding are required to implement the mirror driving structure. In contrast, the solution of the present invention optimizes the process flow through innovation, and only 5 key lithography steps are required to complete the fabrication of the entire device; by streamlining the process steps, the process complexity is significantly reduced, the device reliability is improved, and the production cost is reduced at the same time, providing a more feasible manufacturing solution for the industrial application of large-scale micro-mirror arrays.

[0089] 3. The mirrors described in the present invention can achieve a higher duty cycle

[0090] Due to the simpler processing method, the present invention can significantly compress the gap between the micro-mirror array units, improve the duty cycle of the reflective mirror, enhance the light energy utilization efficiency, and reduce the diffraction effect caused by the gap in existing related products.

[0091] 4. The present invention can achieve continuously adjustable modes

[0092] Compared with the digital micromirror connected by hinges, the present invention can achieve continuously adjustable displacement control of 0-500 nanometers through voltage driving, rather than only switching between several modes, and has significant advantages in application scenarios such as holographic display that require continuous phase modulation.

[0093] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can certainly make various corresponding changes and deformations according to the present invention, but these corresponding changes and deformations should all fall within the protection scope of the appended claims of the present invention.

Claims

1. A micromirror array based on an electrically controllable deformable micro-nano structure, characterized in that From bottom to top are a base layer, a bottom conductive layer, a dielectric layer, a top conductive layer, and a mirror surface layer in sequence; The bottom conductive layer deposited on the base layer is an array structure formed by arranging a plurality of bottom conductive units, and each bottom conductive unit is composed of a bottom conductive electrode, a bottom conductive plate, and a bottom conductive wire connecting the two; The dielectric layer deposited on the bottom conductive layer includes a plurality of dielectric columns; The top conductive layer deposited on the dielectric layer is an array structure formed by arranging a plurality of top conductive units, and each top conductive unit is composed of a top conductive electrode, a top conductive plate, and a top conductive wire connecting the two; at the same time, the arrangement directions of each bottom conductive plate and each top conductive plate are perpendicular to each other, and a suspended nanostructure is formed in the overlapping area of each bottom conductive plate and each top conductive plate; A dielectric column is distributed at each of the four corners of each suspended nanostructure, and a hollowed-out pattern is distributed on the top conductive plate in the overlapping area; The mirror surface layer deposited on the top conductive layer is an array structure formed by arranging mirror surfaces with the same number as the number of suspended nanostructures; at the same time, each mirror surface is respectively connected to the top conductive plate part in the corresponding suspended nanostructure through a column.

2. The micromirror array based on an electrically controllable deformable micro-nano structure as claimed in claim 1, wherein The hollowed-out pattern is distributed along the circumferential direction of the top conductive plate in the overlapping area and is composed of a plurality of arc-shaped grooves arranged in a spiral pattern with respect to each other.

3. The micromirror array based on the electro-controlled deformable micro-nano structure according to claim 1, wherein Ground the bottom conductive electrodes in each bottom conductive unit, and connect the top conductive electrodes in each top conductive unit to independent external voltage sources; By turning on different external voltage sources, a potential difference is generated between the bottom conductive plate and the top conductive plate in different suspended nanostructures. Furthermore, due to the potential difference, the top conductive plate with the hollowed-out pattern generates a displacement deformation, and at the same time, the mirror unit is driven by the support column to generate a vertical movement, realizing the phase modulation of the light beam incident on the mirror unit.

4. The micromirror array based on an electrically controllable deformable micro-nano structure according to claim 1, wherein Connect the bottom conductive electrodes in each bottom conductive unit to independent external voltage sources, and ground the top conductive electrodes in each top conductive unit; By turning on different external voltage sources, a potential difference is generated between the bottom conductive plate and the top conductive plate in different suspended nanostructures. Furthermore, due to the potential difference, the top conductive plate with the hollowed-out pattern generates a displacement deformation, and at the same time, the mirror unit is driven by the support column to generate a vertical movement, realizing the phase modulation of the light beam incident on the mirror unit.

5. The micromirror array based on the electro-controlled deformable micro-nano structure according to claim 1, wherein, The materials of the bottom conductive layer and the top conductive layer are both metals or doped silicon materials.

6. The micromirror array based on an electrically controllable deformable micro-nano structure according to claim 1, wherein The material of the dielectric layer is silicon oxide or silicon nitride.

7. A preparation method of a micromirror array based on an electrically controllable deformable micro-nano structure, characterized in that, It includes the following steps: Step 1: Prepare a voltage-driven functional substrate with micron-level independent addressing ability; Step 2: Prepare a suspended nanostructure based on the principle of electro-deformation; Step 3: Prepare a mirror surface array that realizes mechanical coupling through support columns.

8. The manufacturing method of a micromirror array based on an electrically controllable deformable micro-nano structure as described in claim 7, characterized in that, The method for preparing a voltage-driven functional substrate with micron-level independent addressing ability is: Step ①: Select silicon dioxide as the base layer; Step ②: Use electron beam evaporation coating technology to sequentially deposit a 5-nanometer platinum adhesion layer and a 25-nanometer gold conductive layer on the base layer to form a bottom electrode structure; Step ③: First, perform a tackifying treatment on the bottom electrode structure, and then spin-coat S1805 photoresist with a thickness of 1.2 microns. After pre-baking at 100 °C for 60 seconds, use a step-and-repeat ultraviolet lithography system to expose the S1805 photoresist layer with a minimum line width of 0.7 microns; after developing the S1805 photoresist with 2.38% TMAH, fixing with deionized water, and hardening the film, complete the pattern transfer from the S1805 photoresist to the bottom electrode structure by ion beam etching the gold conductive layer in the bottom electrode structure. Finally, remove the residual S1805 photoresist on the bottom electrode structure after pattern transfer by dissolving in an organic solution and cleaning with oxygen plasma to obtain a patterned bottom conductive layer; Step ④: Use plasma-enhanced chemical vapor deposition technology to deposit silicon dioxide with a thickness of 300 - 600 nm on the bottom conductive layer as a dielectric layer, and precisely control the polishing to a thickness of 300 ± 20 nm by chemical mechanical polishing; Step ⑤: Use electron beam evaporation coating technology to deposit a 5 nm platinum tackifying layer and a 70 nm gold conductive layer on the dielectric layer to form a top electrode structure; Step ⑥: First, perform a tackifying treatment on the top electrode structure, and then spin-coat AZ5214 photoresist with a thickness of 1.5 microns. After pre-baking at 100 °C for 60 seconds, use a contact ultraviolet lithography system to expose the AZ5214 photoresist layer with a minimum line width of 2 microns; after developing the AZ5214 photoresist with 2.38% TMAH, fixing with deionized water, and hardening the film, complete the pattern transfer from the AZ5214 photoresist to the top electrode structure by ion beam etching the gold conductive layer in the top electrode structure. Finally, remove the residual AZ5214 photoresist on the top electrode structure after pattern transfer by dissolving in an organic solution and cleaning with oxygen plasma to obtain a patterned top conductive layer.

9. The manufacturing method of a micromirror array based on an electrically controllable deformable micro-nano structure according to claim 7, characterized in that, The method for preparing a suspended nanostructure based on the electro-deformation principle is as follows: Step ①: Perform a spin-coating process of PMMA photoresist with a thickness of 270 nm on the top conductive layer. After pre-baking at 180 °C for 60 seconds, uniformly coat a conductive adhesive layer on the surface of the PMMA photoresist and perform a second pre-baking at 90 °C for 60 seconds; use an electron beam lithography system to expose the double-layer resist composed of PMMA photoresist and the conductive adhesive layer with a minimum line width of 70 nm, and expose a hollow pattern array with a unit period of 4.8 microns × 4.8 microns; After removing the conductive adhesive from the double-layer resist, developing the PMMA photoresist with a developer, and fixing the PMMA photoresist with isopropyl alcohol, complete the nano-scale pattern transfer from the PMMA photoresist to the top conductive layer by ion beam etching the top conductive layer. Finally, thoroughly remove the PMMA photoresist residue by oxygen plasma cleaning to obtain a hollow pattern; Step ②: Use the diluted hydrofluoric acid solution to perform isotropic wet etching on the product of Step ① to remove the silicon dioxide dielectric layer under the gold conductive layer in the top conductive layer. At the same time, according to the experimentally measured etching rate, control the etching degree of the silicon dioxide so that the silicon dioxide directly under the suspended nanostructure is etched away while retaining the four support pillars at the corners of each suspended nanostructure.

10. The preparation method of a micromirror array based on an electrically controllable deformable micro-nano structure according to claim 7, characterized in that The method for preparing a reflective mirror array with mechanical coupling achieved through support pillars is as follows: Step ①: Implement a 1-micron-thick S1813 photoresist spin-coating process on the suspended nanostructure. After pre-baking at 110 °C for 60 seconds, use a laser direct writing system to perform pattern exposure on this layer of S1813 photoresist with the ultimate resolution. After developing and fixing the S1813 photoresist, a meandering mask structure is formed. Step ②: Use magnetron sputtering technology to deposit a 1.2-micron-high reflectivity aluminum layer on the whole product of Step ①, synchronously constructing the mirror body and the support pillars. The bottom end of the support pillar is connected to the suspended nanostructure to form a mirror-substrate mechanical coupling structure. Step ③: Implement a 300-nanometer-thick AR-P 6200 photoresist spin-coating process; use electron beam lithography to perform pattern exposure on this layer of AR-P6200 photoresist, and over-etch to expose a reflective mirror array with a unit period of 4.8 microns × 4.8 microns. After developing and fixing the AR-P 6200 photoresist, use inductively coupled plasma etching to transfer the pattern of the AR-P6200 photoresist to the high reflectivity aluminum layer. Step ④: Use an organic solution to remove the AR-P 6200 photoresist above the mirror in Step ③ and the sacrificial layer under the high reflectivity aluminum layer in Step ① to achieve the suspended release of the mirror body area, and finally form an aluminum reflective mirror array with a vertical displacement degree of freedom.

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