Force sensor module

Abstract

To reduce the possibility that a metasurface pattern might be damaged by electrostatic discharge.SOLUTION: A force sensor module (10) includes: a first substrate (11) having light transparency; a metasurface pattern (14) provided on a first principal surface (111); a second substrate (12) provided so that the second substrate (12) faces the first substrate (11) and including a second principal surface (121) facing the first principal surface (111); a reflective layer (16) provided on the second principal surface (121); a spacer layer (13) provided on the first principal surface (111) and made of an electrically-conductive material; a joining layer (18) for joining the second principal surface (121) and the spacer layer (13); and a grounding wire (22) connected to the spacer layer (13).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a force sensing sensor module.

Background Art

[0002] There is known a force sensing sensor module including a metasurface pattern provided on a first substrate made of glass, a reflective layer provided on a second substrate so as to face the metasurface pattern, and a spacer that defines the distance between the first substrate and the second substrate (for example, Patent Document 1). In such a force sensing sensor module, light is made incident on the metasurface pattern, and while passing through the metasurface pattern, the light reflected by the reflective layer is used to obtain information regarding the distance between the metasurface pattern and the reflective layer. Since the distance is determined according to the magnitude of the force acting on the second substrate, the force sensing sensor module can detect the magnitude of the force acting on the second substrate by using an optical method.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When manufacturing a force sensing sensor module as described in Patent Document 1, the first substrate provided with the metasurface pattern, the second substrate provided with the reflective layer, and the spacer are manufactured separately, and then the first substrate, the spacer, and the second substrate are stacked and joined in this order.

[0005] Figure 27 and paragraph 0040 of Patent Document 1 describe forming a spacer made of photoresist resin along the outer edge of the second substrate on the surface of the reflective layer provided on the second substrate (see Figure 27(1-b)), and joining the first substrate and the second substrate using this spacer (see Figure 27(3)).

[0006] In a force sensor module configured in this way, since the first substrate on which the metasurface pattern is provided is made of glass, there is a possibility that the metasurface pattern may be electrostatically damaged if the first substrate becomes charged for any reason.

[0007] A force sensor module according to one aspect of the present invention has been made in view of the above-mentioned problems, and its purpose is to reduce the possibility of electrostatic discharge damage to the metasurface pattern even when the first substrate is charged. [Means for solving the problem]

[0008] To solve the above problems, a force sensor module according to one aspect of the present invention comprises a first substrate, a metasurface pattern, a second substrate, a reflective layer, a spacer layer, a bonding layer, and ground wiring. The first substrate is translucent. The metasurface pattern is provided on the first main surface of the first substrate. The second substrate is provided facing the first substrate and includes a second main surface facing the first main surface. The reflective layer is provided on the second main surface. The spacer layer is made of a conductive material and is provided on the first main surface. The bonding layer bonds the second main surface and the spacer layer. The ground wiring is connected to the spacer layer. The spacer layer is made of indium titanium tin. The bonding layer is made of silicon. [Effects of the Invention]

[0009] According to one aspect of the present invention, the possibility of electrostatic discharge damage to the metasurface pattern can be reduced. [Brief explanation of the drawing]

[0010] [Figure 1]This is a schematic diagram of a force sensor system including a force sensor module according to one embodiment of the present invention. Figure 1 includes a cross-sectional view of the force sensor module. [Figure 2] (a) and (b) are plan views of the first and second substrates that constitute the force sensor module shown in Figure 1, respectively. [Modes for carrying out the invention]

[0011] A force sensor module 10 and a force sensor system 1 equipped with the force sensor module 10 according to one embodiment of the present invention will be described with reference to Figure 1. The force sensor module 10 will also be described with reference to Figure 2. Figure 1 is a schematic diagram of the force sensor system 1 including the force sensor module 10. Figure 1 includes a cross-sectional view of the force sensor module 10. Figures 2(a) and 2(b) are plan views of the first substrate 11 and the second substrate 12 constituting the force sensor module 10, respectively.

[0012] [Configuration of the force sensor module] As shown in Figure 1, the force sensor module 10 comprises a first substrate 11, a second substrate 12, a spacer layer 13, a metasurface pattern 14, a protective layer 15, a reflective layer 16, a hard coat layer 17, a bonding layer 18, an anisotropic conductive film 21, and ground wiring 22.

[0013] The force sensor module 10 detects a point load F when it is applied to the second substrate 12 of the first substrate 11.

[0014] <First substrate> The first substrate 11 is a translucent plate-like member. In this embodiment, alkali-free glass is used as the material constituting the first substrate 11. Because alkali-free glass does not contain alkaline components, its surface is less susceptible to corrosion by chemicals and water, and it has excellent electrical insulation properties. However, the material constituting the first substrate 11 can be any solid material that is translucent in the wavelength band of light L1, as described later, and can be appropriately selected from materials available on the market. Other examples of materials constituting the first substrate 11 include quartz and polycarbonate resin. As will be described later, in this embodiment, the wavelength band of light L1 is set to 1400 nm or more and 1600 nm or less.

[0015] In this embodiment, the shape of the first substrate 11 when viewed from above (see Figure 2(a)) is a square with sides of 4 cm. Also in this embodiment, the thickness of the first substrate 11 is 500 μm. The shape and thickness of the first substrate 11 are not limited to the above example and can be determined as appropriate. A preferred thickness of the first substrate 11 is 500 μm or more and 2000 μm or less.

[0016] The first substrate 11 includes a pair of opposing main surfaces, namely main surface 111 and main surface 112. In the state shown in Figure 1, the first substrate 11 is arranged such that main surface 111 is on the upper side and main surface 112 is on the lower side. Main surface 111 is an example of a first main surface.

[0017] In the force sensor module 10, a point load F is applied to the second substrate 12 as described above. The force sensor module 10 then detects the point load F by utilizing the deflection of the second substrate 12 caused by the point load F. Therefore, it is preferable that the first substrate 11 is configured so that it does not deflect when the point load F is applied to the second substrate 12, or so that it deflects only to an extent that is negligible compared to the deflection of the second substrate 12.

[0018] (Metasurface pattern) As shown in (a) of FIGS. 1 and 2, a metasurface pattern 14 is provided on the main surface 111 of the first substrate 11. In (a) of FIG. 2, since the metasurface pattern 14 is covered with the protective layer 15, it is illustrated by a dashed line.

[0019] The metasurface pattern 14 is composed of a plurality (25 in (a) of FIG. 2) of sub-patterns 141 arranged periodically. In the present embodiment, the sub-patterns 141 are arranged in a 5-row and 5-column matrix. However, (a) of FIG. 2 is a schematic diagram for clearly showing the sub-patterns 141. The actual metasurface pattern 14 is composed of more (for example, 10,000 in the case of a 100-row and 100-column arrangement) sub-patterns 141.

[0020] In the present embodiment, each sub-pattern 141 (that is, the metasurface pattern 14) is made of metal (aluminum in the present embodiment). The metasurface pattern 14 as shown in (a) of FIG. 2 can be obtained, for example, by forming an aluminum solid film on the main surface 111 and then using lithography technology. Aluminum has good corrosion resistance and is cheaper than gold. However, the metasurface pattern 14 is not limited to aluminum and may be made of other metals (for example, gold, silver, copper). Gold is easy to process and corrosion-resistant but expensive. Also, in the present embodiment, the aluminum forming the sub-pattern 141 is pure aluminum that is not an alloy. Even pure aluminum with a high purity of aluminum contains a small amount of impurities. Here, the performance of the metasurface pattern 14 varies depending on the purity of aluminum. This is because the optical constants (refractive index, extinction coefficient) change depending on the purity of aluminum, so the purity of aluminum affects the optical characteristics.

[0021] Each sub-pattern 141 has a square shape with a side length of 300 nm. Also, the thickness of each sub-pattern 141 (i.e., the thickness of the meta-surface pattern 14) is 30 nm. The preferred thickness of each sub-pattern 141 is 20 nm or more and 60 nm or less. The performance of the meta-surface pattern 14 changes according to the thickness of each sub-pattern 141. The standard for the lower limit value in the thickness of each sub-pattern 141 is the skin depth. The skin depth is the depth of the skin determined by the skin effect, and is the depth of the region where the electromagnetic field density increases when an electromagnetic wave having a certain frequency is irradiated onto a metal. When the thickness of each sub-pattern 141 approaches the skin depth, the optical characteristics deteriorate, for example, light is not sufficiently reflected. On the other hand, when the thickness of each sub-pattern 141 is thick, another resonance mode occurs or the resonance wavelength shifts. Also, when the thickness of each sub-pattern 141 is thick, the difficulty of manufacturing increases.

[0022] However, the periodic arrangement in the meta-surface pattern 14, the material constituting the meta-surface pattern 14, the shape of each sub-pattern 141, the size of each sub-pattern 141, and the thickness of each sub-pattern 141 are not limited to those described above, and can be appropriately determined by referring to existing technologies.

[0023] Note that the force sensing module 10 includes a protective layer 15 described later for the purpose of reducing or preventing oxidation of the meta-surface pattern 14 during cleaning. In order to suppress oxidation of the meta-surface pattern 14 without using the protective layer 15, it is also conceivable to adopt a material that is difficult to oxidize, such as gold and platinum, as the material constituting the meta-surface pattern 14.

[0024] (Protective layer) As shown in (a) of FIG. 2, a protective layer 15 that completely covers each sub-pattern 141 constituting the meta-surface pattern 14 is provided on the main surface 111 of the first substrate 11. The protective layer 15 has light-transmitting properties, similar to the first substrate 11. In this embodiment, the protective layer 15 is a solid film made of quartz glass (SiO2). In this embodiment, the thickness of the protective layer 15 is 35 nm. The thickness of the protective layer 15 is not limited to the example described above and can be determined as appropriate. A preferred thickness of the protective layer 15 is 35 nm or more and 60 nm or less.

[0025] By providing the protective layer 15, oxidation of the metasurface pattern 14 (especially oxidation on its surface) that may occur due to the metasurface pattern 14 being directly exposed to a cleaning solution (e.g., pure water) during the cleaning process of the first substrate 11 on which the metasurface pattern 14 is provided can be reduced or prevented. Therefore, it is preferable that the protective layer 15 is not only translucent but also composed of a dense film that does not allow the cleaning solution to pass through.

[0026] The protective layer 15 only needs to be capable of reducing or preventing the oxidation of the metasurface pattern 14 described above. By suppressing the oxidation of the metasurface pattern 14, the desired response characteristics defined during the design phase can be obtained over a long period of time. The materials that make up the protective layer 15, its deposition method, and its thickness can be determined as appropriate.

[0027] <Second board> The second substrate 12 is a plate-shaped member configured to bend when a point load F is applied. As shown in Figure 1, the second substrate 12 is provided facing the first substrate 11. In this embodiment, polycarbonate resin is used as the material constituting the second substrate 12. However, the material constituting the second substrate 12 can be any solid material that bends when a point load F is applied, and can be appropriately selected from materials available on the market. Other examples of materials constituting the second substrate 12 include resin materials such as acrylic resin, polystyrene resin, AS resin, and silicone resin, and metal materials such as aluminum, copper, and stainless steel.

[0028] In this embodiment, the shape of the second substrate 12 when viewed from above (see Figure 2(b)) is a square with sides of 4 cm, the same as the first substrate 11. Also in this embodiment, the thickness of the second substrate 12 is 300 μm. The shape and thickness of the second substrate 12 are not limited to the above example, as long as they are configured to bend by an appropriate amount when a point load F is applied. A preferred thickness of the second substrate 12 is 300 μm or more and 400 μm or less.

[0029] The second substrate 12 includes a pair of opposing main surfaces, main surface 121 and main surface 122. Main surface 121, an example of the second main surface, faces the main surface 111 of the first substrate 11. In the state shown in Figure 1, the second substrate 12 is arranged such that main surface 121 is on the lower side and main surface 122 is on the upper side.

[0030] (reflective layer) As shown in Figures 1 and 2(b), a reflective layer 16 is provided on the main surface 121 of the second substrate 12. The reflective layer 16 is a metal film that generates reflected light L2 by reflecting light L1. In this embodiment, aluminum is used as the material constituting the reflective layer 16. However, the material constituting the reflective layer 16 can be any solid material that reflects light L1, and can be appropriately selected from metals available on the market. Other examples of materials constituting the reflective layer 16 include gold and silver. Here, it is advantageous in terms of process simplification and cost if the material of the reflective layer 16 is the same as the metal of the metasurface. Furthermore, the second substrate 12 does not simply need to be a metal with high reflectivity. In the force sensor module 10, the second substrate 12 and the metasurface pattern 14 are integrated via surface plasmon polaritons to form an optical resonator. Therefore, it is thought that changing the metal of the second substrate 12 will affect the optical properties.

[0031] In this embodiment, the thickness of the reflective layer 16 is 50 nm. The thickness of the reflective layer 16 is not limited to the example described above and can be determined as appropriate. A preferred thickness of the reflective layer 16 is 50 nm or more and 100 nm or less.

[0032] However, the materials that make up the reflective layer 16, the method of forming the film, and its thickness can be determined as appropriate.

[0033] (Hard coat layer) As shown in Figure 1, a hard coat layer 17 is provided on the main surface 122. In this embodiment, the hard coat layer 17 is provided so as to cover the entire second substrate 12. Preferably, the hard coat layer 17 covers as wide an area as possible of the surface of the second substrate 12 that is exposed to the outside of the force sensor module 10. The hard coat layer 17 may also be provided so as to further cover the side surfaces of the second substrate 12.

[0034] The hard coat layer 17 is a coating layer configured similarly to the coating layers provided on the surface of smartphones and display panels. In this embodiment, silicone resin is used as the material constituting the hard coat layer 17. However, the material constituting the hard coat layer 17 is not limited to this. Other examples of materials constituting the hard coat layer 17 include acrylic resin and fluororesin.

[0035] The hard coat layer 17 is harder than the material constituting the second substrate 12 (polycarbonate in this embodiment), making it less susceptible to scratches. Furthermore, the hard coat layer 17 has the property of being less permeable to gases.

[0036] <Spacer layer> As shown in Figure 1, the spacer layer 13 is a component made of a conductive material provided on the main surface 111. The spacer layer 13 is a component that defines the distance between the first substrate 11 and the second substrate 12 (distance when unloaded). In this embodiment, the spacer layer 13 is sandwiched between the first substrate 11 and the second substrate 12. The first substrate 11 and the spacer layer 13 are joined to each other, and the second substrate 12 and the spacer layer 13 are joined to each other by a bonding layer 18, which will be described later.

[0037] The spacer layer 13 is made of indium titanium tin. However, the spacer layer 13 can be made of any conductive material, and can be appropriately selected from materials available on the market.

[0038] <Joining layer> The bonding layer 18 is a component that joins the main surface 121 and the spacer layer 13. In this embodiment, the bonding layer 18 is a component formed by joining a first bonding layer 181 provided on the first substrate 11 side and a second bonding layer 182 provided on the second substrate 12 side using room-temperature bonding technology. The first bonding layer 181 and the second bonding layer 182 constituting the bonding layer 18 are made of silicon. However, the materials constituting each of the first bonding layer 181 and the second bonding layer 182 can be any material that exhibits good adhesion when formed on the main surface 121 and the spacer layer 13, respectively, and that can be joined to each other using room-temperature bonding technology, and can be appropriately selected from materials available on the market. Silicon exhibits good adhesion to both the indium titanium tin constituting the spacer layer 13 and the polycarbonate resin constituting the second substrate 12, and can be joined using room-temperature bonding technology. Examples of materials other than silicon that constitute the first bonding layer 181 and the second bonding layer 182 include silicon oxide, copper, and titanium.

[0039] As described above, because the spacer layer 13 is made of indium titanium tin and the bonding layer 18 is made of silicon, the first substrate 11 on which the spacer layer 13 is provided and the second substrate 12 can be bonded using room-temperature bonding technology. Therefore, the force sensor module 10 can be manufactured with precise control over the distance between the main surface 111 and the main surface 121.

[0040] <Ground Wiring> The ground wire 22 is connected to the spacer layer 13. As shown in Figure 1, the ground wire 22 is connected to the spacer layer 13 via an anisotropic conductive film 21. With this configuration, the ground wire 22 can be easily and reliably connected to the spacer layer 13 in a conductive state.

[0041] In this embodiment, the thicknesses of the spacer layer 13 and the bonding layer 18 are determined so that the gap G between the protective layer 15 and the reflective layer 16 is 190 nm. Furthermore, the amount of deflection of the second substrate 12 when a point load F is applied near the center of the second substrate 12 is defined as the deflection amount ΔG. When a point load F is applied, the second substrate 12 deflects by the amount of deflection amount ΔG, so the gap G becomes narrower by the deflection amount ΔG than the gap G in the unloaded case.

[0042] In this way, the spacing between the first substrate 11 and the second substrate 12 is fixed by interposing the spacer layer 13 and the bonding layer 18 between them. Specifically, an annular frame with both its outer and inner edges being square is used as the spacer layer 13 and the bonding layer 18. In this embodiment, the spacer layer 13 and the bonding layer 18 have an outer edge with a side length of 4 cm, and their contour shapes are the same as those of the first substrate 11 and the second substrate 12. However, the shape of the outer edges of the spacer layer 13 and the bonding layer 18 is not limited to this and can be determined as appropriate. Also, the spacer layer 13 and the bonding layer 18 are not limited to a closed frame, and may have a part of them cut out. Furthermore, the spacer layer 13 may be composed of one member or of multiple members. In the latter case, each of the multiple members may be a columnar member or a cylindrical member that functions as a column.

[0043] The thickness of the spacer layer 13 is constant. Therefore, the first substrate 11 and the second substrate 12 can be fixed so that the main surfaces 111 and 121 sandwiching the spacer layer 13 are parallel to each other.

[0044] <Effects> Here, the effects of the force sensor module 10 will be explained. Figure 15 of Patent Document 1 describes a force sensor module that uses a chromium (Cr) spacer as a spacer to define the distance between the first substrate and the second substrate. However, it is not possible to directly bond a chromium spacer to the first substrate, which is made of glass.

[0045] Therefore, in the force sensor module shown in Figure 15, a chromium spacer and the first substrate are joined using some kind of bonding means. In fact, as described in Patent Document 1 in Figure 21 and paragraph 0035, polyimide tape is used as the bonding means. The method of using polyimide tape as a bonding means is effective for applications such as confirming the optical properties of the metasurface pattern in a prototype force sensor module. However, since the polyimide tape only temporarily bonds the spacer and the first substrate, it cannot be used in a production version of the force sensor module.

[0046] One example of a bonding method for long-term bonding between a chromium spacer and a first substrate is a resin-based adhesive, such as an ultraviolet-curing resin. However, such adhesives have the problem that it is difficult to precisely control the distance between the first and second substrates.

[0047] In one aspect of the present invention, a force sensor module 10 is used, for example, by using an interlayer made of silicon to form a spacer layer 13 and a 2 Circuit board 1 2 To join them, the distance between the first substrate 11 and the second substrate 12 can be precisely controlled.

[0048] Furthermore, in the force sensor module 10, the first substrate 11 is grounded via the spacer layer 13 made of conductive material and the ground wiring 22 by grounding the ground wiring 22. Therefore, the force sensor module 10 can suppress the charging of the first substrate 11, thereby reducing the possibility of electrostatic discharge damage to the metasurface pattern 14.

[0049] [Configuration of the force sensor system] As shown in Figure 1, the force sensor system 1 comprises the force sensor module 10 described above and a measurement unit 30. Here, the measurement unit 30 will be briefly described.

[0050] The measuring unit 30 includes a light source 31, an optical fiber 32, a circulator 33, an optical fiber 34, a collimating lens 35, an optical fiber 36, and a light detection unit 37.

[0051] The light source 31 is configured to emit light L1 with a wavelength range of 1400 nm to 1600 nm. In this embodiment, a light-emitting diode (LED) that emits near-infrared light is used as the light source 31. However, the light source 31 is not limited to an LED and can be appropriately selected from light sources available on the market. Furthermore, the light source 31 is a filter provided downstream of the LED, which limits the wavelength range of light L1 to 1400 nm to 1600 nm.

[0052] The circulator 33 is an optical element having three ports P1, P2, and P3. The circulator 33 is configured to emit light incident on port P1 from port P2, emit light incident on port P2 from port P3, and emit light incident on port P3 from port P1.

[0053] One end of the optical fiber 32 is connected to the light source 31, and the other end is connected to port P1 of the circulator 33. Therefore, the optical fiber 32 receives the light L1 emitted from the light source 31 into port P1 of the circulator 33.

[0054] One end of the optical fiber 34 is connected to the collimating lens 35, and the other end is connected to port P2 of the circulator 33. Therefore, the optical fiber 34 emits light L1 from port P2 of the circulator 33 to the collimating lens 35, and also emits light L2 that enters port P2 from the collimating lens 35.

[0055] The collimating lens 35 converts light L1 emitted from one end of the optical fiber 34 into collimated light. The collimated light L1 is then reflected by the reflective layer 16 and converted into light L2, which propagates in the reverse direction along the same path. Light L2 enters the other end of the optical fiber 34 via the collimating lens 35. Here, the collimating lens 35 efficiently couples light L2, which is collimated light just like light L1, to the other end of the optical fiber 24.

[0056] One end of the optical fiber 36 is connected to the photodetector 37, and the other end is connected to port P3 of the circulator 33. Therefore, the optical fiber 36 emits the light L2 emitted from port P3 of the circulator 33 to the photodetector 37.

[0057] The photodetector 37 is configured to measure the spectrum of light L2 (in this embodiment, the reflectance spectrum). In this embodiment, the photodetector 37 includes a spectrometer that spectrally analyzes light L2, and a photodiode that converts the spectrally analyzed light L2 into electrical signals.

[0058] The inset in Figure 1 is a schematic graph showing the spectra of light L1, which is the input light of the force sensor module 10, and light L2, which is the output light of the force sensor module 10. In the inset, the spectrum of light L1 is shown with a solid line, and the spectrum of light L2 is shown with a dashed line.

[0059] As can be seen from the inset, the spectrum of light L2 is shifted to the longer wavelength side by a shift amount Δλ when the center wavelengths of the spectrum of light L1 are compared. The shift amount Δλ is a quantity determined by the interval G shown in Figure 1. The interval G is a quantity determined by the amount of deflection ΔG of the second substrate 12 when a point load F is applied near the center of the second substrate 12. Therefore, in the force sensor module 10, the shift amount Δλ is a quantity determined by the magnitude of the point load F. In the force sensor system 1, the point load F can be detected by pre-acquiring or calculating the correlation between the point load F and the shift amount Δλ in the force sensor module 10.

[0060] [Additional Notes] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Explanation of Symbols]

[0061] 1. Force Sensor System 10 Force Sensor Module 11. First circuit board 12 Second board 13 Spacer layer 14 Metasurface Patterns 15 Protective layer 16 Reflective layer 17. Hard court layer 18 Bonding layer 22 Ground Wiring 30 Measuring part

Claims

1. A first substrate having light-transmitting properties, A metasurface pattern provided on the first main surface of the first substrate, A second substrate provided so as to face the first substrate, the second substrate including a second main surface facing the first main surface, A reflective layer provided on the second main surface, A spacer layer made of a conductive material is provided on the first main surface, A bonding layer that joins the second main surface and the spacer layer, The spacer layer is connected to a ground wire, The spacer layer is made of indium titanium tin, The bonding layer is made of silicon. A force sensor module characterized by the following features.

2. The ground wiring is connected to the spacer layer via an anisotropic conductive film. The force sensor module according to feature 1.

3. It is translucent and further comprises a protective layer that covers the metasurface pattern. The force sensor module according to claim 1 or 2.

Images