Preparation method of flexible optical tactile sensor and flexible optical tactile sensor

Abstract

The present application provides a method for preparing a flexible optical tactile sensor and a flexible optical tactile sensor. When preparing a flexible optical tactile sensor, it mainly includes two steps: one is to prepare an optical waveguide, and the other is to encapsulate the optical waveguide with a cladding material. Among them, in the stage of preparing the optical waveguide, after a transparent photolithography pattern is formed using a transparent photoresist, a colored photoresist is used to mark the transparent photolithography pattern to prevent the film light path from being unable to be positioned during the subsequent preparation process; further, a waveguide grating is formed by performing two-photon polymerization processing on the two-photon polymerization photoresist, which can greatly improve the spatial resolution of the tactile sensor; in addition, in the above preparation process, the thickness of the formed photolithography pattern and waveguide grating are both at the micro-nano level, so that the prepared tactile sensor has good bendability. In summary, the above preparation method can be used to obtain a tactile sensor with flexibility and high spatial resolution.

Description

Technical Field

[0001] The present application relates to the field of artificial intelligence technology, and in particular to a method for preparing a flexible optical tactile sensor and a flexible optical tactile sensor. Background Art

[0002] With the rapid development and widespread application of artificial intelligence technology, intelligent robots not only need to complete the set mechanical movements, but also need to perceive the external environment and provide feedback. Therefore, combining tactile sensors with intelligent robots has become an important development direction at present.

[0003] In recent years, researchers have been committed to developing tactile sensors based on different principles, such as piezoresistive, capacitive, piezoelectric, magnetic sensing, and optical principles. Among them, tactile sensors based on optical principles have been favored by researchers due to their advantages such as small size, high integration, and immunity to electromagnetic interference.

[0004] However, traditional optical fibers, primarily composed of quartz glass, are rigid and brittle, typically only able to withstand centimeter-scale bends and exhibiting poor bendability. Furthermore, the grating inscription methods used in traditional optical fibers have extremely limited ability to modulate the refractive index of the fiber core, resulting in low spatial resolution for tactile sensors. Consequently, tactile sensors fabricated using traditional optical fiber methods are difficult to directly apply to tactile sensing in intelligent robots. Therefore, developing a flexible and high-spatial-resolution tactile sensor based on optical principles has become a pressing challenge for those skilled in the art. Summary of the Invention

[0005] The embodiments of the present application provide a method for preparing a flexible optical tactile sensor and a flexible optical tactile sensor. The tactile sensor obtained by the preparation method has flexibility and high spatial resolution, and can be directly applied to the tactile sensing field of intelligent robots, for example. The technical solution is as follows:

[0006] In one aspect, a method for preparing a flexible optical tactile sensor is provided, the method comprising:

[0007] Prepare an optical waveguide; the optical waveguide includes a first photolithographic pattern, a second photolithographic pattern, and a waveguide grating, the first photolithographic pattern is a transparent pattern formed based on a transparent photoresist, the second photolithographic pattern is a colored pattern formed based on a colored photoresist, the second photolithographic pattern is used to mark the first photolithographic pattern, and the waveguide grating is obtained by two-photon polymerization of the two-photon polymerization photoresist;

[0008] The optical waveguide is encapsulated into a flexible optical tactile sensor by using a cladding material;

[0009] The thicknesses of the first photolithography pattern, the second photolithography pattern and the waveguide grating are all in the micro-nano level, and the cladding material is a flexible material.

[0010] In another aspect, a flexible optical tactile sensor is provided. The flexible optical tactile sensor includes an optical waveguide and a cladding material for encapsulating the optical waveguide.

[0011] The optical waveguide includes a first photolithography pattern, a second photolithography pattern and a waveguide grating.

[0012] The first photolithographic pattern is a transparent pattern formed based on a transparent photoresist, the second photolithographic pattern is a colored pattern formed based on a colored photoresist, the second photolithographic pattern is used to mark the first photolithographic pattern, and the waveguide grating is obtained by performing two-photon polymerization on the two-photon polymerization photoresist;

[0013] The thicknesses of the first photolithography pattern, the second photolithography pattern and the waveguide grating are all in the micro-nano level, and the cladding material is a flexible material.

[0014] In an optional implementation, the flexible optical tactile sensor further includes a flexible lead connected to the optical waveguide, and the flexible lead has a serpentine structure.

[0015] In an optional implementation, the transparent photoresist is transparent SU-8 photoresist; the colored photoresist is colored SU-8 photoresist; the two-photon polymerization photoresist is PMMA (Polymethyl Methacrylate) photoresist; and the cladding material is transparent silica gel.

[0016] The embodiment of the present application mainly includes two steps when preparing a flexible optical tactile sensor: preparing an optical waveguide and encapsulating the optical waveguide with a cladding material. During the optical waveguide preparation stage, after forming a transparent photolithographic pattern using a transparent photoresist, the transparent photolithographic pattern is marked with a colored photoresist to prevent the thin film optical path from being misaligned during subsequent preparation. Furthermore, the embodiment of the present application uses a two-photon polymerization process on the photoresist to form a waveguide grating, which can greatly improve the spatial resolution of the tactile sensor. In addition, during the above preparation process, the thickness of the formed photolithographic pattern and waveguide grating are both at the micro-nano level, making the prepared tactile sensor have good flexibility and can withstand micro-nano-level bending.

[0017] In summary, the above preparation method can be used to obtain a tactile sensor with flexibility and high spatial resolution, which can be directly applied to the tactile sensing field of intelligent robots, for example. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0019] Figure 1 This is a flow chart of a method for preparing a flexible optical tactile sensor according to an embodiment of the present application;

[0020] Figure 2 is a structural schematic diagram of a flexible optical tactile sensor provided according to an embodiment of the present application;

[0021] Figure 3 is a schematic structural diagram of a waveguide grating provided according to an embodiment of the present application;

[0022] Figure 4 is a flow chart of another method for preparing a flexible optical tactile sensor provided in an embodiment of the present application;

[0023] Figure 5 is a schematic diagram of preparing an optical waveguide according to an embodiment of the present application;

[0024] Figure 6 is a schematic diagram of a packaged flexible optical tactile sensor provided according to an embodiment of the present application;

[0025] Figure 7 2 is a schematic structural diagram of another flexible optical tactile sensor provided according to an embodiment of the present application. DETAILED DESCRIPTION

[0026] In order to make the objectives, technical solutions and advantages of this application clearer, the implementation methods of this application will be further described in detail below with reference to the accompanying drawings.

[0027] Exemplary embodiments will be described in detail herein, with examples illustrated in the accompanying drawings. In the following description, when referring to the drawings, identical numerals in different figures represent identical or similar elements, unless otherwise indicated. The embodiments described in the following exemplary embodiments are not intended to represent all embodiments consistent with the present application. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the present application, as detailed in the appended claims.

[0028] In this application, the terms "first," "second," and the like are used to distinguish identical or similar items having substantially the same role and function. It should be understood that "first," "second," and "nth" do not have a logical or temporal dependency, nor do they limit the quantity or execution order. It should also be understood that although the following description uses the terms "first," "second," and the like to describe various elements, these elements should not be limited by these terms.

[0029] These terms are simply used to distinguish one element from another. For example, without departing from the scope of various examples, a first substrate can be referred to as a second substrate, and similarly, a second substrate can also be referred to as a first substrate. Both the first substrate and the second substrate can be substrates, and in some cases, can be separate and different substrates.

[0030] Here, "at least one" refers to one or more than one. For example, at least one substrate can be one substrate, two substrates, three substrates, or any other integer greater than one. "Plurality" refers to two or more than two. For example, "plurality" can be two substrates, three substrates, or any other integer greater than two.

[0031] In addition, words such as “include” or “comprising” and the like mean that the elements or objects preceding the word include the elements or objects listed after the word and their equivalents, but do not exclude other elements or objects. Words such as “connected” or “connected” and the like are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. “Up”, “down”, “left”, “right” and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0032] The following is a brief introduction to the technologies that may be used in the embodiments of this application.

[0033] Artificial Intelligence (AI) refers to the theories, methods, techniques, and application systems that use digital computers or machines controlled by digital computers to simulate, extend, and expand human intelligence, to perceive the environment, acquire knowledge, and use that knowledge to achieve optimal results. In other words, AI is a comprehensive technology within computer science that seeks to understand the essence of intelligence and produce new intelligent machines that can respond in a manner similar to human intelligence. AI also involves studying the design principles and implementation methods of various intelligent machines, enabling them to possess the capabilities of perception, reasoning, and decision-making.

[0034] Artificial intelligence (AI) technology is a comprehensive discipline encompassing a wide range of fields, encompassing both hardware and software technologies. Foundational AI technologies generally include sensors, specialized AI chips, cloud computing, distributed storage, big data processing, operating / interaction systems, and mechatronics. AI software technologies primarily encompass computer vision, speech processing, natural language processing, and machine learning / deep learning.

[0035] The following is a brief introduction to key terms or abbreviations that may be used in the embodiments of the present application.

[0036] Tactile sensors: A sensor used in intelligent robots to mimic the sense of touch. Touch is a crucial sensory function in humans when they interact directly with the external environment. Developing tactile sensors that meet these requirements is a key technological advancement in the development of intelligent robots. With the advancement of microelectronics and the emergence of various organic materials, a variety of tactile sensor development proposals have been proposed, but most remain in the laboratory stage, with few reaching commercialization. Tactile sensors can be broadly categorized by function, including contact sensors, force-torque sensors, pressure sensors, and slip sensors.

[0037] An optical waveguide is a dielectric device that guides light waves through it, also known as a dielectric waveguide. There are two main categories of optical waveguides: integrated waveguides, including planar and strip waveguides, are often part of optoelectronic integrated devices; and cylindrical waveguides, commonly known as optical fibers. Traditional glass optical fibers are also a type of waveguide.

[0038] Waveguide grating: A reflective structure with a periodic refractive index modulation that can reflect light of specific wavelengths through periodic changes in the refractive index.

[0039] Two-photon polymerization (TPP) is a photopolymerization process initiated by two-photon absorption. TPA is the simultaneous absorption of two photons by a single molecule, typically under intense laser light. It is a phenomenon of light-matter interaction under intense laser light and is a type of third-order nonlinear effect.

[0040] PMMA: A high molecular polymer, also known as acrylic, acrylic or plexiglass.

[0041] Polyvinyl alcohol (PVA) resin: A white solid available in three forms: flocculent, granular, and powdery. It is non-toxic, odorless, and non-polluting, soluble in water at 80-90°C. Its aqueous solution exhibits excellent adhesion and film-forming properties and is resistant to most organic solvents, including oils, lubricants, and hydrocarbons. It exhibits chemical properties such as esterification, etherification, and acetalization of long-chain polyols.

[0042] Photoresist, also known as photoresist or photoresist, refers to an etch-resistant thin film material whose solubility changes upon exposure to light or radiation, such as ultraviolet light, deep ultraviolet light, electron beams, ion beams, or X-rays. It is a key material for fine-patterning in microelectronics, primarily used in the processing of fine patterns in integrated circuits and discrete semiconductor devices. There are many types of photoresists, which can be categorized into negative-working and positive-working based on their chemical reaction mechanisms and development principles. Negative-working photoresists are those that are soluble in certain solvents but form substances insoluble in those solvents upon exposure. Conversely, positive-working photoresists are those that are insoluble in certain solvents but form substances soluble in those solvents upon exposure. Common photoresists include SU-8, PMMA, and AZ.

[0043] Cladding: This refers to a layer of glass or other transparent material covering the optical fiber core that carries light waves. It has a slightly lower refractive index than the core, thus confining light propagation within the core. Common cladding materials include OE-6560, polydimethylsiloxane (PDMS), and transparent silicones such as the Ecoflex series.

[0044] Sacrificial layer: In the process of forming a cavity or movable microstructure in a micromechanical structure, the various special structural components required are first deposited on the lower film using structural materials. This layer is then etched away with a chemical etchant without damaging the microstructure, leaving the upper film structure. This removed layer is called the sacrificial layer.

[0045] The following describes a method for preparing a flexible optical tactile sensor according to an embodiment of the present application. It should be noted that in the embodiment of the present application, the aspect ratios in the accompanying drawings are not equal to the actual aspect ratios and are merely provided for illustrative purposes.

[0046] Figure 1 is a flow chart of a method for preparing a flexible optical tactile sensor according to an embodiment of the present application, such as Figure 1 As shown in FIG, this method is applied to the process of preparing flexible optical tactile sensors, such as Figure 1 As shown, the method includes the following two steps:

[0047] 101. Prepare an optical waveguide; wherein the optical waveguide includes a first photolithographic pattern, a second photolithographic pattern, and a waveguide grating, wherein the first photolithographic pattern is a transparent pattern formed based on a transparent photoresist, the second photolithographic pattern is a colored pattern formed based on a colored photoresist, the second photolithographic pattern is used to mark the first photolithographic pattern, and the waveguide grating is obtained by two-photon polymerization of a two-photon polymerization photoresist.

[0048] Optionally, the first photolithographic pattern includes N rows of serpentine lines; the second photolithographic pattern includes N rows of circular ring structures, with gaps provided on the circular ring structures; the waveguide grating is located at the gap and distributed on both sides of the serpentine lines, and N is a positive integer.

[0049] Schematically, refer to Figure 2 and Figure 3 ,in, Figure 2 is a structural diagram of a flexible optical tactile sensor provided in an embodiment of the present application, Figure 3 : is a schematic structural diagram of a waveguide grating provided in an embodiment of the present application, wherein: Figure 3 It will Figure 2 The enlarged schematic diagram of the middle gap 4. Figure 2 As shown, the first photolithographic pattern 1 includes three rows of serpentine lines, which are obtained by performing a first photolithographic process on a transparent photoresist; the second photolithographic pattern 2 includes three rows of circular ring structures 3, each of which has a notch 4; optionally, the distance between the centers of the circular ring structures 3 is 1000 μm, which is not limited in this application. Figure 3 As shown, the waveguide grating 6 is located at the notch and distributed on both sides of the serpentine line in the first photolithographic pattern 1 .

[0050] 102. Use a cladding material to encapsulate the optical waveguide into a flexible optical tactile sensor; wherein the thickness of the first photolithography pattern, the second photolithography pattern and the waveguide grating are all at the micro-nano level, and the cladding material is a flexible material.

[0051] Schematically, refer to Figure 2 ,like Figure 2 As shown, Figure 2 The blank parts in the image are all cladding materials 5, and the optical waveguide is encapsulated to obtain a flexible optical tactile sensor.

[0052] The embodiment of the present application comprises two main steps in preparing a flexible optical tactile sensor: preparing an optical waveguide and encapsulating the optical waveguide with a cladding material. During the optical waveguide preparation stage, after forming a transparent photoresist pattern, a colored photoresist is used to mark the transparent photoresist pattern to prevent the thin film optical path from being misaligned during subsequent preparation. Furthermore, the embodiment of the present application employs a two-photon polymerization process of the photoresist to form a waveguide grating, which significantly improves the spatial resolution of the tactile sensor. Furthermore, the thickness of the formed photoresist pattern and waveguide grating are both at the micro-nano level, making the prepared tactile sensor highly flexible and able to withstand micro-nano-level bending.

[0053] In summary, the above preparation method can be used to obtain a tactile sensor with flexibility and high spatial resolution, which can be directly applied to the tactile sensing field of intelligent robots, for example.

[0054] above Figure 1 What is shown is only the basic process of this application. The solution provided in this application will be further explained below based on a specific implementation method.

[0055] Figure 4 is a flow chart of another method for preparing a flexible optical tactile sensor according to an embodiment of the present application, such as Figure 4 As shown, the method includes the following steps:

[0056] 401. Fabricate a first sacrificial layer on a first substrate.

[0057] In the embodiment of the present application, the first substrate refers to a substrate material used to make a flexible optical tactile sensor. Optionally, the first substrate is a silicon wafer or glass, and the first sacrificial layer is a metal layer or a PVA layer, which is not limited in the present application.

[0058] The following description is made by taking the first substrate as a silicon wafer and the first sacrificial layer as a metal layer as an example:

[0059] For example, a polished 4-inch silicon wafer is selected as the first substrate, and a metal layer is plated on the first substrate using a coating process to form a first sacrificial layer. It should be noted that in the embodiment of the present application, the metal layer can be an aluminum layer, a chromium layer, or a gold layer. Other metal materials can also be selected to form the metal layer, and this application does not limit this. In addition, in the embodiment of the present application, the thickness of the first sacrificial layer can be set according to actual needs, and this application does not limit this.

[0060] Schematically, refer to Figure 5 , Figure 5 Schematic diagram of a method for preparing an optical waveguide provided in an embodiment of the present application. Figure 5 As shown in FIG. 5 ( a ), the first substrate 7 is a silicon wafer, and a metal layer, namely the first sacrificial layer 8 , is plated on the first substrate 7 .

[0061] 402 . Coat a transparent photoresist with a first thickness on the first sacrificial layer, and perform a first photolithography process on the coated transparent photoresist to form a first photolithography pattern.

[0062] In the embodiment of the present application, the transparent photoresist may be transparent SU-8 photoresist, which is not limited in this application. Optionally, the first photolithography process involves subjecting the coated transparent photoresist to pre-baking, exposure, development, and post-baking to form a first photolithographic pattern. Optionally, the first thickness is 2 μm; the first photolithographic pattern includes N rows of serpentine lines.

[0063] It should be noted that, in practical applications, different types of transparent photoresists can be selected, different first thicknesses can be set, and different first photolithography patterns can be set according to needs, and this application does not limit this.

[0064] The specific implementation of this step is described below with examples. For example, this step 402 may include the following steps 4021 to 4025:

[0065] 4021. Use a spin coating machine to coat a 2μm thick transparent SU-8 photoresist on a metal-coated silicon wafer by controlling the spin coating speed.

[0066] 4022. Pre-bake the coated transparent SU-8 photoresist.

[0067] 4023. Place the silicon wafer into the photolithography machine and use the photolithography machine to expose the transparent SU-8 photoresist through the mask.

[0068] 4024. Post-bake the exposed transparent SU-8 photoresist.

[0069] 4025. Develop the transparent SU-8 photoresist and clean the surface with alcohol to reveal the first photolithographic pattern.

[0070] Schematically, continue to refer to Figure 5 ,like Figure 5 As shown in FIG. 1 (b), a 2 μm thick transparent photoresist 9 is prepared on the first sacrificial layer 8 to form a first photolithographic pattern 1. Schematically, the specific shape of the first photolithographic pattern 1 can be referred to Figure 2 As shown, I will not repeat it here.

[0071] 403 . Coat a colored photoresist with a second thickness on the first sacrificial layer; perform a second photolithography process on the coated colored photoresist based on the pattern shape of the first photolithography pattern to form a second photolithography pattern.

[0072] In an embodiment of the present application, the colored photoresist may be a colored SU-8 photoresist, for example, a black SU-8 photoresist, which is not limited in this application. Optionally, the second photolithography process involves subjecting the coated colored photoresist to pre-baking, exposure, development, and post-baking to form a second photolithographic pattern. The second photolithographic pattern is used to mark the first photolithographic pattern, and the second thickness is greater than the first thickness. Optionally, the second thickness is 50 μm; the second photolithographic pattern includes N rows of circular ring structures, each having a notch.

[0073] It should be noted that, in actual applications, different types of colored photoresists, different second thicknesses, and different second photolithography patterns can be selected according to needs, and this application does not limit this.

[0074] In addition, the specific implementation of this step is similar to the above step 402, so it will not be repeated here. Figure 5 ,like Figure 5 As shown in FIG. 5( c ), a colored photoresist 10 with a thickness of 50 μm is prepared on the first sacrificial layer 8 to form a second photolithographic pattern 2. The specific shape of the second photolithographic pattern 2 can be referred to FIG. Figure 2 shown.

[0075] The relationship between the second photolithography pattern and the first photolithography pattern is described below.

[0076] Schematically, continue to refer to Figure 2 ,like Figure 2 As shown, the first photolithographic pattern 1 includes serpentine lines, and the second photolithographic pattern 2 includes a circular ring structure 3 with upper notches 4 provided on the circular ring structure 3. The serpentine lines of the first photolithographic pattern 1 regularly pass through each notch 4. Therefore, the second photolithographic pattern 2 can mark the pattern shape of the first photolithographic pattern 1.

[0077] It should be noted that after forming the transparent first photolithography pattern through the above steps 402 and 403, the first photolithography pattern is marked with colored photoresist to form a second photolithography pattern, which can avoid the film light path being invisible to the naked eye during the subsequent preparation process.

[0078] 404. Based on the pattern shape of the first photolithography pattern and the pattern shape of the second photolithography pattern, determine a grating region on the first sacrificial layer; perform two-photon polymerization processing on a two-photon polymerization photoresist on the grating region to form a waveguide grating.

[0079] In the embodiment of the present application, the grating region is also the region where the waveguide grating is located. The two-photon polymerization photoresist can be PMMA photoresist, which is not limited in the present application.

[0080] Schematically, refer to Figure 2 ,like Figure 2 As shown, the serpentine lines of the first photolithographic pattern 1 pass through each of the gaps 4 of the second photolithographic pattern 2, and the grating regions are located at each of the gaps 4. Figure 3 ,like Figure 3 As shown, the waveguide grating 6 is located at the notch 4 and distributed on both sides of the serpentine line. The grating pitch of the waveguide grating is Λ, and Λ is micro-nano level.

[0081] The first point that needs to be made is that Figure 2 There are waveguide gratings at each gap in the Figure 3 A certain notch is only enlarged for schematic illustration to illustrate the specific shape of the waveguide grating.

[0082] The second point that needs to be explained is that in actual applications, different types of two-photon polymerization photoresists can be selected and different grating spacings can be set according to needs, and this application does not limit this.

[0083] The following describes in detail the implementation of the two-photon polymerization process in this step, including the following steps 4041 and 4042:

[0084] 4041. Coat two-photon polymerization photoresist on the first sacrificial layer.

[0085] Optionally, the coating thickness of the two-photon polymerization photoresist is less than the first thickness. In practical applications, personalized settings can be made according to needs, and this application does not limit this.

[0086] 4042. Expose the grating region coated with the two-photon polymerization photoresist to cause the two-photon polymerization photoresist coated on the grating region to undergo a two-photon polymerization reaction and solidify to form a waveguide grating.

[0087] Optionally, step 4042 may be implemented by a two-photon polymerization 3D printer, which is not limited in this application.

[0088] Schematically, refer to Figure 5 ,like Figure 5 As shown in Figure (d), on the first sacrificial layer 8, two-photon polymerization photoresist 11 is distributed on both sides of the transparent photoresist 9 to form a waveguide grating 6, and there is a gap between the two-photon polymerization photoresist 11 and the colored photoresist 10, and the two are not connected.

[0089] The third point that needs to be explained is that the waveguide grating formed by two-photon polymerization processing has a micro-nanoscale grating spacing. This waveguide grating has a good signal-to-noise ratio and high spatial resolution, thereby greatly improving the spatial resolution of the tactile sensor.

[0090] After the above steps 401 to 404, a first photolithographic pattern, a second photolithographic pattern and a waveguide grating are formed on the first substrate covered with the first sacrificial layer, which together constitute an optical waveguide, that is, the sensing part of the flexible optical tactile sensor prepared in this application. Figure 5 ,like Figure 5 As shown, the optical waveguide is composed of Figure 5 It is composed of a transparent photoresist 9, a colored photoresist 10 and a two-photon polymerization photoresist 11.

[0091] The following describes how to package the optical waveguide to obtain a flexible optical tactile sensor through the following steps 405 to 410.

[0092] 405. Coat a cladding material with a third thickness on the first sacrificial layer on which the optical waveguide has been formed to form a first packaging structure.

[0093] In an embodiment of the present application, the first packaging structure includes a first substrate, a first sacrificial layer, an optical waveguide, and a cladding material. The cladding material is transparent silicone. The third thickness is greater than the second thickness. Optionally, the cladding material is OE-6560, and the third thickness is 250 μm, although this application does not limit this.

[0094] Schematically, refer to Figure 6 , Figure 6 Schematic diagram of a packaged flexible optical tactile sensor provided by an embodiment of the present application. Figure 6 As shown in FIG. 8 (a), optionally, on the first sacrificial layer 8 on which the optical waveguide 12 has been formed, a 250 μm thick OE-6560 material, also known as the cladding material 5, is spin-coated using a glue spinner, and then heated and cured to form a first packaging structure.

[0095] 406. Fabricate a second sacrificial layer on the second substrate.

[0096] In the embodiment of the present application, the second substrate refers to a substrate material used to manufacture a flexible optical tactile sensor. Optionally, the second substrate is a silicon wafer or glass, and the second sacrificial layer is a PVA layer, which is not limited in the present application.

[0097] The following is an example of a silicon wafer as the second substrate and a PVA layer as the second sacrificial layer:

[0098] For example, a polished 4-inch silicon wafer is selected as the second substrate, a PVA layer is spin-coated on the second substrate using a spin coater, and then the PVA at the edge of the second substrate is removed to avoid affecting the PVA layer when the first sacrificial layer is subsequently dissolved, thereby forming a second sacrificial layer.

[0099] The first point that needs to be explained is that, in the embodiment of the present application, the thickness of the second sacrificial layer can be set according to actual needs, and the present application does not limit this.

[0100] Schematically, refer to Figure 6 , the second base is as Figure 6 As shown in FIG. 5( b ), the second substrate 13 is a silicon wafer, and a PVA layer, namely the second sacrificial layer 14 , is covered on the second substrate 13 .

[0101] In addition, the second point that needs to be explained is that, in the embodiment of the present application, step 406 is performed after step 405. In other embodiments, step 406 can be performed before step 401, or between any two steps from step 401 to step 405. The present application does not limit the order in which step 406 is performed.

[0102] 407 . Use a cladding material to encapsulate the second substrate covered with the second sacrificial layer and the first packaging structure to form a second packaging structure.

[0103] In an embodiment of the present application, the second packaging structure uses the first substrate as the lower substrate and the second substrate as the upper substrate. The lower substrate is arranged parallel to and opposite to the lower portion of the upper substrate. The first sacrificial layer, the optical waveguide, the second sacrificial layer and the cladding material are located between the upper substrate and the lower substrate.

[0104] Optionally, encapsulating the second substrate with the first package structure in this step includes: applying a cladding material having a fourth thickness on top of the cladding material already applied to the first package structure, thereby securing the second sacrificial layer to the first package structure and forming a second package structure. The fourth thickness is less than the third thickness. For example, the third thickness is 250 μm and the fourth thickness is 10 μm.

[0105] Schematically, refer to Figure 6 , the second packaging structure is as follows Figure 6 As shown in Figure (c), the first substrate 7 serves as the lower substrate, while the second substrate 13 serves as the upper substrate. A 10 μm thick layer of OE-6560 is spin-coated on the 250 μm thick cladding material 5 using a spin coater. The upper substrate is then covered downwardly with a second sacrificial layer 14, which is then heated and cured to form a second packaging structure.

[0106] After steps 405 through 407, the optical waveguide above the first sacrificial layer is encapsulated with a cladding material, and the second substrate is secured to the cladding material, resulting in a second encapsulation structure. The following steps 408 through 410 describe fabricating a flexible optical tactile sensor based on this second encapsulation structure.

[0107] 408 . Dissolve the first sacrificial layer to separate the first substrate from the second packaging structure to form a third packaging structure.

[0108] In the embodiment of the present application, the first sacrificial layer is used to separate the first substrate from the second packaging structure. The third packaging structure includes an optical waveguide, a second substrate, a second sacrificial layer and a cladding material. Figure 6 , taking the first sacrificial layer as a metal layer as an example, this step is described. Figure 6, dissolve the first sacrificial layer as Figure 6 As shown in FIG. 5 ( d ), the second packaging structure is immersed in an acidic solution to dissolve the first sacrificial layer 8 , so that the first substrate 7 is separated from the second packaging structure to form a third packaging structure 15 .

[0109] 409. Continue coating the cladding material with a fifth thickness on the exposed surface of the optical waveguide to form a fourth packaging structure.

[0110] In an embodiment of the present application, the fourth packaging structure includes an optical waveguide, a second substrate, a second sacrificial layer, and a cladding material. The fifth thickness is greater than the second thickness. For example, the second thickness is 50 μm and the fifth thickness is 250 μm, although this application does not limit this.

[0111] The following combination Figure 5 This step is explained. Schematically, refer to Figure 6 , the fourth packaging structure is as follows Figure 6 As shown in FIG. 5( e ), on the exposed surface of the optical waveguide 12 of the third packaging structure 15 , a 250 μm thick OE-6560 material is spin-coated by a coating machine and then heated and cured to form a fourth packaging structure.

[0112] 410. Dissolve the second sacrificial layer to separate the second substrate from the fourth packaging structure to form a flexible optical tactile sensor.

[0113] In the embodiment of the present application, the second sacrificial layer is used to separate the second substrate from the flexible optical tactile sensor. Figure 6 , taking the second sacrificial layer as a PVA layer as an example, this step is described. Figure 6 , dissolve the second sacrificial layer as Figure 6 As shown in Figure (f), after using a blade to lift one edge of the second substrate 13, the second sacrificial layer 14 inside is exposed, and then the fourth packaging structure is immersed in water to dissolve the second sacrificial layer 14, so that the second substrate 13 is separated from the fourth packaging structure to obtain a flexible optical tactile sensor 16.

[0114] In addition, in the embodiments of the present application, the flexible tactile sensor further includes a flexible lead connected to the optical waveguide, wherein the flexible lead has a serpentine structure. This serpentine structure not only provides good stretchability for the flexible lead, but also prevents sensor signal changes caused by partial deformation of the flexible lead, thereby increasing the detection accuracy of the sensor.

[0115] Schematically, refer to Figure 7 , Figure 7 This is a schematic diagram of the structure of another flexible optical tactile sensor provided by this application. Figure 7 The sensing part 17 in the amplification is obtained Figure 2, wherein the sensing portion 17 includes an optical waveguide. Figure 7 As shown, the first photolithography pattern 1 also includes serpentine lines respectively connected to the two ends of the sensing portion 17, and the second photolithography pattern 2 also includes serpentine lines respectively connected to the two ends of the sensing portion 17, wherein the serpentine lines of the second photolithography pattern 2 are parallel to and evenly distributed on both sides of the serpentine lines of the first photolithography pattern 1, forming a flexible lead 18. Figure 7 The flexible lead 18 of the serpentine structure is connected to the sensing part 17 and has the characteristics of single-line input and single-line output.

[0116] It should be noted that, through the above steps 405 to 410, the optical waveguide is completely encapsulated by the cladding material, including the flexible lead.

[0117] The embodiment of the present application mainly includes two steps when preparing a flexible optical tactile sensor: preparing an optical waveguide and encapsulating the optical waveguide with a cladding material. During the optical waveguide preparation stage, after forming a transparent photolithographic pattern using a transparent photoresist, the transparent photolithographic pattern is marked with a colored photoresist to prevent the thin film optical path from being unable to be positioned during the subsequent preparation process. Furthermore, the embodiment of the present application uses a two-photon polymerization process of a two-photon polymerization photoresist to form a waveguide grating, which can greatly improve the spatial resolution of the tactile sensor. In addition, during the above preparation process, the thickness of the formed photolithographic pattern and waveguide grating are both at the micro-nano level, making the prepared tactile sensor have good flexibility and can withstand micro-nano-level bending. At the same time, the flexible lead with a serpentine structure and the flexible cladding material both make the prepared tactile sensor have good stretchability.

[0118] In summary, the above preparation method can be used to obtain a tactile sensor with flexibility and high spatial resolution, which can be directly applied to the tactile sensing field of intelligent robots, for example.

[0119] A flexible optical tactile sensor provided in an embodiment of the present application is described below.

[0120] The flexible optical tactile sensor provided by the embodiment of the present application includes an optical waveguide and a cladding material for encapsulating the optical waveguide.

[0121] Among them, reference Figure 2 and Figure 3 ,like Figure 2 and Figure 3 As shown, the optical waveguide includes a first photolithographic pattern 1 , a second photolithographic pattern 2 and a waveguide grating 6 .

[0122] refer to Figure 6 ,like Figure 6As shown, the first photolithographic pattern 1 is a transparent pattern formed based on a transparent photoresist 9, the second photolithographic pattern 2 is a colored pattern formed based on a colored photoresist 10, the second photolithographic pattern 2 is used to mark the first photolithographic pattern 1, and the waveguide grating 6 is obtained by performing two-photon polymerization on the two-photon polymerization photoresist 11;

[0123] The thicknesses of the first photolithographic pattern 1 , the second photolithographic pattern 2 and the waveguide grating 6 are all in the micro-nano level, and the cladding material 5 is made of a flexible material.

[0124] In an optional implementation, referring to Figure 2 and Figure 3 ,like Figure 2 and Figure 3 As shown, the first photolithographic pattern 1 includes N rows of serpentine lines; the second photolithographic pattern 2 includes N rows of circular ring structures 3, and a gap 4 is provided on the circular ring structure 3; wherein, the spacing between the centers of each circular ring structure 3 is 1000 μm, which is not limited in this application; the waveguide grating 6 is located at the gap 4 and is distributed on both sides of the serpentine line, and N is a positive integer.

[0125] In an optional implementation, the grating pitch of the waveguide grating 6 is at the micro-nano level.

[0126] In an optional implementation, referring to Figure 7 ,like Figure 7 As shown, the flexible optical tactile sensor further includes a flexible lead 18 connected to the optical waveguide, and the flexible lead 18 is a serpentine structure.

[0127] In an optional implementation, referring to Figure 6 ,like Figure 6 As shown, the transparent photoresist 9 is transparent SU-8 photoresist; the colored photoresist 10 is colored SU-8 photoresist; the two-photon polymerization photoresist 11 is PMMA photoresist; and the cladding material 5 is transparent silica gel.

[0128] The embodiment of the present application mainly includes two steps when preparing a flexible optical tactile sensor: preparing an optical waveguide and encapsulating the optical waveguide with a cladding material. During the optical waveguide preparation stage, after forming a transparent photolithographic pattern using a transparent photoresist, the transparent photolithographic pattern is marked with a colored photoresist to prevent the thin film optical path from being unable to be positioned during the subsequent preparation process. Furthermore, the embodiment of the present application uses a two-photon polymerization process of a two-photon polymerization photoresist to form a waveguide grating, which can greatly improve the spatial resolution of the tactile sensor. In addition, during the above preparation process, the thickness of the formed photolithographic pattern and waveguide grating are both at the micro-nano level, making the prepared tactile sensor have good flexibility and can withstand micro-nano-level bending. At the same time, the flexible lead with a serpentine structure and the flexible cladding material both make the prepared tactile sensor have good stretchability.

[0129] In summary, the above preparation method can be used to obtain a tactile sensor with flexibility and high spatial resolution, which can be directly applied to the tactile sensing field of intelligent robots, for example.

[0130] Illustratively, the application scenarios of the flexible optical tactile sensor provided in the embodiments of the present application include but are not limited to:

[0131] Scenario 1: Intelligent Robot Scenario

[0132] For example, the flexible optical tactile sensor is installed on the hand of an intelligent robot. When the intelligent robot grasps an object in its hand, it can judge whether the grasped object slips in the hand of the intelligent robot and whether the grasp is firm based on the signal collected by the flexible optical tactile sensor, and adjust the grasping force in time, etc., which can greatly improve the grasping function of the intelligent robot's hand.

[0133] For another example, the flexible optical tactile sensor can be prepared as bionic skin and installed on various parts of an intelligent robot. When the intelligent robot is touched, the flexible optical tactile sensor at the touched part collects signals, triggering the intelligent robot to speak appropriate words or take corresponding actions, which can greatly enrich the human-computer interaction function of the intelligent robot.

[0134] Scenario 2: Smart wearable device scenario

[0135] Typically, materials used to manufacture wearable devices need to meet requirements for flexibility, lightness, breathability, biocompatibility, and certain special functions. The flexible optical tactile sensor provided in the embodiments of this application is not only flexible and lightweight, but also has high spatial resolution and high detection accuracy. Installing this flexible optical tactile sensor in a smart wearable device can greatly improve the device's detection accuracy, enabling real-time health monitoring of the human body or other living organisms.

[0136] Scene 3: Prosthetic limb scene

[0137] Prosthetic limbs in related technologies can restore some lost functions for amputees, but they cannot restore accurate tactile sensation. The flexible optical tactile sensor provided in the embodiments of this application is fabricated into flexible artificial skin, installed in a prosthetic limb, and connected to the user's peripheral nerves, allowing amputees to restore not only limb motor function but also tactile sensation.

[0138] In addition, it should be noted that the flexible optical tactile sensor provided in the above embodiment and the embodiment of the method for preparing the flexible optical tactile sensor belong to the same concept. The specific implementation process is detailed in the method embodiment and will not be repeated here.

[0139] The above description is merely an optional embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A method for preparing a flexible optical tactile sensor, characterized in that: The method comprises: Prepare an optical waveguide; the optical waveguide includes a first photolithographic pattern, a second photolithographic pattern, and a waveguide grating, wherein the first photolithographic pattern is a transparent pattern formed based on a transparent photoresist, the second photolithographic pattern is a colored pattern formed based on a colored photoresist, the second photolithographic pattern is used to mark the first photolithographic pattern, and the waveguide grating is obtained by performing two-photon polymerization on the two-photon polymerization photoresist; Encapsulating the optical waveguide into a flexible optical tactile sensor using a cladding material; The thicknesses of the first photolithographic pattern, the second photolithographic pattern, and the waveguide grating are at the micro-nano level, the cladding material is a flexible material, the position of the waveguide grating is determined based on the pattern shapes of the first photolithographic pattern and the second photolithographic pattern, the first photolithographic pattern includes N rows of serpentine lines; the second photolithographic pattern includes N rows of circular ring structures, the circular ring structures are provided with notches, the serpentine lines regularly pass through each notch, the waveguide gratings are located at the notch positions and are distributed on both sides of the serpentine lines, and N is a positive integer.

2. The method according to claim 1, characterized in that The method of preparing an optical waveguide comprises: forming a first sacrificial layer on a first substrate; coating the transparent photoresist with a first thickness on the first sacrificial layer, and performing a first photolithography process on the coated transparent photoresist to form the first photolithography pattern; Coating the colored photoresist with a second thickness on the first sacrificial layer; performing a second photolithography process on the coated colored photoresist based on the pattern shape of the first photolithography pattern to form a second photolithography pattern, wherein the second thickness is greater than the first thickness; Based on the pattern shape of the first photolithography pattern and the pattern shape of the second photolithography pattern, a grating region is determined on the first sacrificial layer; and two-photon polymerization processing is performed on the two-photon polymerization photoresist on the grating region to form the waveguide grating.

3. The method according to claim 2, characterized in that The step of performing two-photon polymerization on the two-photon polymerization photoresist on the grating region to form the waveguide grating comprises: coating the two-photon polymerization photoresist on the first sacrificial layer; The grating region coated with the two-photon polymerization photoresist is exposed to light, so that the two-photon polymerization photoresist coated on the grating region undergoes a two-photon polymerization reaction and is solidified to form the waveguide grating.

4. The method according to claim 2, characterized in that The method of using a cladding material to encapsulate the optical waveguide into a flexible optical tactile sensor comprises: On the first sacrificial layer on which the optical waveguide is formed, coating the cladding material with a third thickness to form a first packaging structure, the first packaging structure comprising the first substrate, the first sacrificial layer, the optical waveguide, and the cladding material, wherein the third thickness is greater than the second thickness; forming a second sacrificial layer on a second substrate; The cladding material is used to encapsulate the second substrate covered with the second sacrificial layer and the first packaging structure to form a second packaging structure; wherein the second packaging structure uses the first substrate as a lower substrate and the second substrate as an upper substrate, the lower substrate is arranged parallel to and below the upper substrate, and the first sacrificial layer, the optical waveguide, the second sacrificial layer, and the cladding material are located between the upper and lower substrates; The flexible optical tactile sensor is prepared based on the second packaging structure.

5. The method according to claim 4, characterized in that The method of using the cladding material to encapsulate the second substrate covered with the second sacrificial layer and the first packaging structure to form a second packaging structure includes: The cladding material is continuously coated with a fourth thickness on the coated cladding material to fix the second sacrificial layer on the first packaging structure to form the second packaging structure, and the fourth thickness is less than the third thickness.

6. The method according to claim 5, characterized in that The method of preparing the flexible optical tactile sensor based on the second packaging structure includes: dissolving the first sacrificial layer to separate the first substrate from the second packaging structure to form a third packaging structure, wherein the third packaging structure includes the optical waveguide, the second substrate, the second sacrificial layer, and the cladding material; Continue coating the cladding material with a fifth thickness on the exposed surface of the optical waveguide to form a fourth packaging structure, wherein the fourth packaging structure includes the optical waveguide, the second substrate, the second sacrificial layer, and the cladding material, and the fifth thickness is greater than the second thickness; The second sacrificial layer is dissolved to separate the second substrate from the fourth packaging structure to form the flexible optical tactile sensor.

7. The method according to any one of claims 1 to 6, characterized in that The grating pitch of the waveguide grating is at the micro-nano level.

8. The method according to any one of claims 1 to 6, characterized in that The flexible optical tactile sensor further includes a flexible lead connected to the optical waveguide, and the flexible lead is a serpentine structure.

9. The method according to any one of claims 1 to 6, characterized in that The transparent photoresist is transparent SU-8 photoresist; the colored photoresist is colored SU-8 photoresist; the two-photon polymerization photoresist is polymethyl methacrylate photoresist; and the cladding material is transparent silica gel.

10. The method according to any one of claims 2 to 6, characterized in that The first sacrificial layer is a metal layer, and the second sacrificial layer is a polyvinyl alcohol layer.

11. The method according to claim 6, characterized in that The first thickness is 2 μm, the second thickness is 50 μm, the third thickness is 250 μm, the fourth thickness is 10 μm, and the fifth thickness is 250 μm.

12. A flexible optical tactile sensor, characterized in that: The sensor includes an optical waveguide and a cladding material for encapsulating the optical waveguide: Wherein, the optical waveguide includes a first photolithographic pattern, a second photolithographic pattern and a waveguide grating; The first photolithographic pattern is a transparent pattern formed based on a transparent photoresist, the second photolithographic pattern is a colored pattern formed based on a colored photoresist, the second photolithographic pattern is used to mark the first photolithographic pattern, and the waveguide grating is obtained by performing two-photon polymerization on the two-photon polymerization photoresist; The thicknesses of the first photolithographic pattern, the second photolithographic pattern, and the waveguide grating are at the micro-nano level, the cladding material is a flexible material, the position of the waveguide grating is determined based on the pattern shapes of the first photolithographic pattern and the second photolithographic pattern, the first photolithographic pattern includes N rows of serpentine lines; the second photolithographic pattern includes N rows of circular ring structures, the circular ring structures are provided with notches, the serpentine lines regularly pass through each notch, the waveguide gratings are located at the notch positions and are distributed on both sides of the serpentine lines, and N is a positive integer.

13. The sensor according to claim 12, characterized in that The grating pitch of the waveguide grating is at the micro-nano level.

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