Flexible strain sensor with very low temperature effect and method of making the same

Abstract

The present application relates to a flexible strain sensor with extremely low temperature effect, comprising: a metal composite flexible substrate comprising polymer and metal microstructures arranged alternately; and a strain sensitive grid resistor arranged above the metal composite flexible substrate, wherein the grid bar direction of the strain sensitive grid resistor is consistent with the arrangement direction of the metal microstructures in the metal composite flexible substrate. The present application also relates to a preparation method of the flexible strain sensor with extremely low temperature effect. The strain direction detected by the flexible strain sensor is consistent with the direction in which the metal composite flexible substrate has a low thermal expansion coefficient, and the thermal deformation rate of the metal composite flexible substrate in this direction is low, thereby reducing the influence of the temperature effect of the substrate in the strain direction on the strain measurement.

Description

Technical Field

[0001] This invention relates to the field of strain sensor technology, and in particular to a flexible strain sensor with an extremely low temperature effect on the substrate and its fabrication method. Background Technology

[0002] Most flexible strain sensors use isotropic polymer substrates. The strain applied to the device is absorbed by the deformation of the resistive sensing structure. However, the flexible substrate expands and contracts with ambient temperature, causing deformation, which is then transmitted to the resistive sensing structure, resulting in additional deformation and inaccurate resistance changes. Specifically, flexible strain sensors are susceptible to ambient temperature effects during use, primarily in two ways: first, the temperature effect of the resistive sensing structure, where changes in ambient temperature cause variations in the structure, leading to measurement errors; second, the temperature effect of the substrate, where temperature changes cause thermal expansion and contraction of the flexible polymer substrate. When the substrate transmits the strain from the object's surface to the upper resistive sensing structure, it introduces additional strain due to temperature-induced substrate deformation. These temperature-induced resistance changes are unrelated to the strain of the object being measured; they are purely due to additional strain caused by temperature changes. Therefore, to address the errors caused by the substrate's temperature effect, a strain sensor with a substrate exhibiting low temperature effect is needed. Summary of the Invention

[0003] The objective of this invention is to provide a flexible strain sensor with an extremely low temperature effect on the substrate and a method for fabricating the same. The strain direction detected by the flexible strain sensor is consistent with the direction in which the thermal expansion coefficient of the metal composite flexible substrate is low. The thermal deformation rate of the metal composite flexible substrate is low in this direction, thereby reducing the influence of the substrate temperature effect on the strain measurement in the strain direction.

[0004] In a first aspect, addressing the problems existing in the prior art, the present invention provides a flexible strain sensor with an extremely low temperature effect on the substrate, comprising:

[0005] A flexible metal composite substrate comprising alternating polymer and metal microstructures; and

[0006] A strain-sensitive gate resistor is disposed above the metal composite flexible substrate, wherein the gate direction of the strain-sensitive gate resistor is consistent with the arrangement direction of the metal microstructures in the metal composite flexible substrate.

[0007] In one embodiment of the present invention, a protective layer and a passivation layer are further provided between the strain-sensitive gate resistor and the metal composite flexible substrate, wherein the protective layer is disposed on the metal composite flexible substrate and the passivation layer is disposed on the protective layer.

[0008] In one embodiment of the present invention, the strain-sensitive gate resistor includes a first seed layer and a sensitive metal layer; and / or

[0009] The metal microstructure comprises, in sequence, a first metal, a third seed layer, and a second seed layer.

[0010] In one embodiment of the invention, the polymer has a width of 100–3000 micrometers and a thickness of 20–200 micrometers; and / or

[0011] The width of the metal microstructure is 10–300 micrometers, and the thickness is 20–200 micrometers; and / or

[0012] The ratio of the width of the polymer to the width of the metal microstructure is 1:10; and / or

[0013] The sensitive metal layer is a thin NiCrFeAlMn metal layer.

[0014] In one embodiment of the invention, an external resistance test wiring connected to the strain-sensitive gate resistor is also included.

[0015] In a second aspect, addressing the problems existing in the prior art, the present invention provides a method for fabricating a flexible strain sensor with an extremely low temperature effect on the substrate, comprising:

[0016] A protective layer and a passivation layer are sequentially arranged on a metal composite flexible substrate, wherein the metal composite flexible substrate comprises alternating polymer and metal microstructures;

[0017] Photoresist was applied to the passivation layer and then dried.

[0018] A grid pattern is formed on photoresist using photolithography.

[0019] A strain-sensitive gate resistor is formed by sequentially arranging a first seed layer and a sensitive metal layer in a gate strip pattern using magnetron sputtering, wherein the gate strip direction of the strain-sensitive gate resistor is consistent with the arrangement direction of the metal microstructure in the metal composite flexible substrate; and

[0020] The photoresist and the first seed layer and sensitive metal layer on it are removed to obtain a flexible strain sensor.

[0021] In one embodiment of the present invention, the preparation of a metal composite flexible substrate further includes:

[0022] The polymer is deposited on the substrate by spin coating and then dried.

[0023] Photoresist was applied to the polymer using a spin coating method and then dried.

[0024] A trench pattern is formed on a photoresist using photolithography, and a microstructure trench is formed on a polymer based on the trench pattern.

[0025] A second and third seed layer were sequentially arranged in the microstructure trench using magnetron sputtering.

[0026] Remove the photoresist and the second and third seed layers on it;

[0027] A metallic microstructure is formed by filling the microstructure trenches with a first metal using an electroplating method; and

[0028] The substrate is removed to obtain a metal composite flexible substrate.

[0029] In one embodiment of the present invention, a protective layer is deposited on a metal composite flexible substrate by spin coating and dried to semi-cured. Then, a passivation layer is deposited on the protective layer by spin coating and dried to full curing.

[0030] In one embodiment of the present invention, forming a grid pattern on photoresist using photolithography includes:

[0031] First, the photomask is placed on the dried photoresist and exposed under ultraviolet light. Then, it is immersed in the developer to pattern it. After drying, a grid pattern is obtained, wherein the direction of the grid pattern is consistent with the arrangement direction of the metal microstructure in the metal composite flexible substrate.

[0032] In one embodiment of the invention, the polymer has a width of 100–3000 micrometers and a thickness of 20–200 micrometers; and / or

[0033] The width of the metal microstructure is 10–300 micrometers, and the thickness is 20–200 micrometers; and / or

[0034] The ratio of the width of the polymer to the width of the metal microstructure is 1:10; and / or

[0035] The sensitive metal layer is a thin NiCrFeAlMn metal layer.

[0036] The present invention has at least the following beneficial effects: The flexible strain sensor with an extremely low temperature effect on the substrate disclosed in the present invention and its fabrication method include a process for fabricating the flexible strain sensor by arranging strain-sensitive gate resistors on a metal composite flexible substrate, such that the arrangement direction of the metal microstructures of the metal composite flexible substrate is consistent with the direction of the gate strips of the strain-sensitive gate resistors, thereby making the strain direction detected by the strain sensor parallel to the direction with a lower thermal expansion coefficient of the metal composite flexible substrate, that is, the thermal deformation rate of the metal composite flexible substrate in this direction is low, thereby reducing the influence of the substrate temperature effect in the strain direction on the accuracy of the strain-sensitive gate resistor (i.e., strain measurement). Attached Figure Description

[0037] To further illustrate the above and other advantages and features of the various embodiments of the present invention, a more specific description of the embodiments of the invention will be presented with reference to the accompanying drawings. It is to be understood that these drawings depict only typical embodiments of the invention and are therefore not intended to limit its scope. In the drawings, identical or corresponding parts will be indicated by identical or similar reference numerals for clarity.

[0038] Figure 1 A schematic diagram of a flexible strain sensor with an extremely low temperature effect on a substrate according to an embodiment of the present invention is shown.

[0039] Figure 2 A schematic diagram of a metal composite flexible substrate with extremely low temperature effect according to an embodiment of the present invention is shown;

[0040] Figure 3 A comparison diagram of a metal microstructure according to an embodiment of the present invention and a metal composite flexible substrate with the same and different strain directions is shown;

[0041] Figure 4 The diagram shows the expansion test results of a metal composite flexible substrate with extremely low temperature effect in the non-strain direction X according to an embodiment of the present invention.

[0042] Figure 5 The diagram shows the expansion test results of a metal composite flexible substrate with extremely low temperature effect in the strain direction Y according to an embodiment of the present invention.

[0043] Figure 6 A fabrication process roadmap for a flexible strain sensor with an extremely low temperature effect on a substrate according to an embodiment of the present invention is shown; and

[0044] Figure 7 A fabrication process route for a metal composite flexible substrate with extremely low temperature effect according to an embodiment of the present invention is shown. Detailed Implementation

[0045] It should be noted that the components in the accompanying drawings may be shown exaggerated for illustrative purposes and may not be to scale.

[0046] In this invention, the various embodiments are merely intended to illustrate the solutions of the invention and should not be construed as limiting.

[0047] In this invention, unless otherwise specified, the quantifiers “a” and “one” do not exclude scenarios involving multiple elements.

[0048] It should also be noted that, in the embodiments of the present invention, only a portion of the parts or components may be shown for clarity and simplicity. However, those skilled in the art will understand that, under the teachings of the present invention, the required parts or components can be added as needed for specific scenarios.

[0049] It should also be noted that within the scope of this invention, the terms "same", "equal", and "equal to" do not mean that the two values ​​are absolutely equal, but allow for a certain reasonable error. In other words, the terms also cover "substantially the same", "substantially equal", and "substantially equal to".

[0050] It should also be noted that in the description of this invention, the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not explicitly or implicitly suggest that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0051] Furthermore, the embodiments of the present invention describe the process steps in a specific order. However, this is only for the convenience of distinguishing each step, and is not a limitation on the order of each step. In different embodiments of the present invention, the order of each step can be adjusted according to the process.

[0052] Figure 1 A schematic diagram of a flexible strain sensor with an extremely low temperature effect on a substrate is shown according to an embodiment of the present invention.

[0053] like Figure 1 As shown, a flexible strain sensor with an extremely low temperature effect includes a metal composite flexible substrate 101, a strain-sensitive gate resistor 102, a protective layer 103, and a passivation layer 104.

[0054] A protective layer 103 is disposed on a metal composite flexible substrate 101. A passivation layer 104 is disposed on the protective layer 103. A strain-sensitive gate resistor 102 is disposed on the passivation layer 104.

[0055] The sensitive direction of the flexible strain sensor is aligned with the direction of minimal thermal deformation of the metal composite flexible substrate 101. The strain-sensitive gate resistor 102 includes a first seed layer and a sensitive metal layer. In one embodiment of the invention, the first seed layer is a thin chromium metal layer. In another embodiment of the invention, the sensitive metal layer is a thin NiCrFeAlMn metal layer.

[0056] Those skilled in the art should understand that the materials used in the strain-sensitive gate resistors in the above embodiments are merely exemplary and not limiting; therefore, the materials of the strain-sensitive gate resistors can be selected according to actual needs.

[0057] exist Figure 1 In the illustration, for clarity, the strain-sensitive gate resistor and passivation layer are shifted upwards, separating the strain-sensitive gate resistor metal, passivation layer, composite flexible substrate, and protective layer by a specific distance for clear observation. Those skilled in the art should understand that this does not represent the actual flexible strain sensor where the strain-sensitive gate resistor metal, passivation layer, composite flexible substrate, and protective layer are separated.

[0058] In other embodiments of the invention, a flexible strain sensor with an extremely low temperature effect on the substrate further includes an external resistance test wiring connected to a strain-sensitive gate resistor.

[0059] Figure 2 A schematic diagram of a metal composite flexible substrate with extremely low temperature effect according to an embodiment of the present invention is shown.

[0060] like Figure 2 As shown, the metal composite flexible substrate 200 with extremely low temperature effect includes alternating polymers 201 and metal microstructures 202. The metal microstructures 202 are metal strips. The metal microstructures 202 include, from top to bottom, a first metal, a third seed layer, and a second seed layer. In one embodiment of the invention, the first metal can be copper, the third seed layer can be a thin copper metal layer, and the second seed layer can be a thin chromium metal layer. In one embodiment of the invention, the polymer can be an organic material such as polyimide.

[0061] Those skilled in the art should understand that the metal microstructures and polymer materials selected in the above embodiments are merely exemplary and not limiting; therefore, the metal microstructures and polymer materials can be selected according to actual needs.

[0062] In one embodiment of the present invention, the polymer 201 has a width of 100-3000 micrometers and a thickness of 20-200 micrometers; the metal microstructure 202 has a width of 10-300 micrometers and a thickness of 20-200 micrometers; the ratio of the width of the polymer 201 to the width of the metal microstructure 202 is 1:10.

[0063] Those skilled in the art should understand that the dimensions of the metal microstructures and polymers selected in the above embodiments are merely exemplary and not limiting, and therefore the dimensions of the metal microstructures and polymers can be adjusted according to actual needs.

[0064] Figure 3 A comparison diagram is shown of a metal microstructure according to an embodiment of the present invention and a metal composite flexible substrate with the same and different strain directions.

[0065] like Figure 3 As shown in the figure, the metal microstructures in the metal composite flexible substrate on the left are arranged in the strain direction Y, while the metal microstructures in the metal composite flexible substrate on the right are arranged in the non-strain direction X, with the metal microstructures being more densely distributed in the non-strain direction.

[0066] Figure 4 The diagram shows the expansion test results of a metal composite flexible substrate with extremely low temperature effect in the non-strain direction X according to an embodiment of the present invention. Figure 5 The diagram shows the expansion test results of a metal composite flexible substrate with extremely low temperature effect in the strain direction Y according to an embodiment of the present invention.

[0067] like Figure 4 and Figure 5 As shown, the metal composite flexible substrate with extremely low temperature effect exhibits smaller thermal deformation in the strain direction Y, which is also the strain measurement direction of the flexible strain sensor, while its thermal deformation is larger in the non-strain direction X. The arrangement direction of the metal microstructures in the metal composite flexible substrate with extremely low temperature effect is the strain direction Y. The control of the width and arrangement ratio of the metal microstructures and polymers in the metal composite flexible substrate will change the difference in thermal expansion deformation in the two directions of the substrate. The ratio of the thermal expansion coefficients in the two directions (thermal expansion coefficient in the X direction / thermal expansion coefficient in the Y direction) can be controlled within the range of 1 to 5.

[0068] Figure 6 A fabrication process roadmap for a flexible strain sensor with an extremely low temperature effect on a substrate, according to an embodiment of the present invention, is shown.

[0069] like Figure 6 As shown, the fabrication of a flexible strain sensor with an extremely low temperature effect on the substrate includes the following steps:

[0070] Step 1, providing a metal composite flexible substrate 300. The metal composite flexible substrate 300 includes alternating polymers 301 and metal microstructures 302.

[0071] Step 2: A protective layer 303 and a passivation layer 304 are sequentially deposited on the metal composite flexible substrate 300. The protective layer 303 is deposited on the metal composite flexible substrate 300 by spin coating and dried to semi-cured state. Then, the passivation layer 304 is deposited on the protective layer 303 by spin coating and dried to full curing state. Both the protective layer 303 and the passivation layer 304 can be organic materials such as polyimide.

[0072] Step 3: Apply photoresist 305 onto the passivation layer 304 by spin coating and then dry it.

[0073] Step 4: Form a grating pattern 306 on the photoresist 305 using photolithography. Specifically, first, place the mask on the dried photoresist 305, expose it under ultraviolet light, then immerse it in a developing solution for patterning, and finally dry it to obtain the grating pattern 306. The orientation of the grating pattern 306 is consistent with the arrangement direction of the metal microstructure in the metal composite flexible substrate 300.

[0074] Step 5: Using magnetron sputtering, a first seed layer 307 and a sensitive metal layer 308 are sequentially arranged in the gate strip pattern 306 to form a strain-sensitive gate resistor. The gate strip direction of the strain-sensitive gate resistor is consistent with the arrangement direction of the metal microstructure in the metal composite flexible substrate.

[0075] In one embodiment of the present invention, the first seed layer is a thin layer of chromium metal. In one embodiment of the present invention, the sensitive metal layer is a thin layer of NiCrFeAlMn metal.

[0076] Step 6: Remove the photoresist and the first seed layer and sensitive metal layer thereon to obtain the flexible strain sensor 400. The strain-sensitive gate resistor of the flexible strain sensor 400 includes the first seed layer 307 and the sensitive metal layer 308.

[0077] The fabrication process of flexible strain sensors involves designing the arrangement of strain-sensitive gate resistors on a metal composite flexible substrate. By adjusting the direction of the gate strips of the strain-sensitive gate resistors to be consistent with the arrangement direction of the metal microstructures in the metal composite flexible substrate, the strain direction detected by the flexible strain sensor is parallel to the direction with a lower thermal expansion coefficient of the metal composite flexible substrate. That is, the thermal deformation rate of the substrate in this direction is low, thereby reducing the influence of substrate temperature effect on the accuracy of strain-sensitive gate resistors (i.e. strain measurement) in the strain direction.

[0078] Figure 7 A fabrication process route for a metal composite flexible substrate with extremely low temperature effect according to an embodiment of the present invention is shown.

[0079] like Figure 7 As shown, the fabrication of a metal composite flexible substrate with extremely low temperature effect includes the following steps:

[0080] Step 1: Apply polymer 501 to substrate 500 by spin coating and then dry.

[0081] Step 2: Apply photoresist 502 onto polymer 501 by spin coating and then dry it.

[0082] Step 3: A trench pattern 503 is formed on the photoresist 502 using photolithography, and a microstructure trench 504 is formed on the polymer 501 based on the trench pattern 503. Specifically, a mask is placed on the photoresist 502, exposed under ultraviolet light, immersed in a developing solution for patterning, and dried to obtain the microstructure trench 504.

[0083] Step 4: A second seed layer 505 and a third seed layer 506 are sequentially arranged in the microstructure trench 504 using magnetron sputtering. In one embodiment of the present invention, the second seed layer can be a thin layer of chromium metal, and the third seed layer can be a thin layer of copper metal.

[0084] Step 5: Remove the photoresist 502 and the second and third seed layers on it.

[0085] Step 6: Fill the microstructure trenches 504 with a first metal 507 using an electroplating method to form a metal microstructure. In one embodiment of the present invention, the first metal may be copper.

[0086] Step 7: Remove the substrate 500 to obtain the metal composite flexible substrate 600. Peel the flexible metal composite substrate 600 off the substrate.

[0087] The fabrication process of the aforementioned flexible strain sensor includes the arrangement design of strain-sensitive gate resistors on a metal composite flexible substrate. The arrangement direction of the metal microstructures of the metal composite flexible substrate is aligned with the gate direction of the strain-sensitive gate resistors. This results in the strain direction detected by the strain sensor being parallel to the direction with the lower thermal expansion coefficient of the metal composite flexible substrate. In other words, the thermal deformation rate of the metal composite flexible substrate in this direction is low, thereby reducing the impact of substrate temperature effects in the strain direction on the accuracy of the strain-sensitive gate resistors (i.e., strain measurement). The metal composite flexible substrate exhibits low temperature effects and is adjustable in the strain direction, allowing the resistive strain sensor to reduce the impact of additional substrate deformation caused by changes in ambient temperature, thus ensuring the accuracy of the resistive strain sensor in a specific direction.

[0088] While some embodiments of the present invention have been described in this application, those skilled in the art will understand that these embodiments are merely illustrative. Numerous variations, alternatives, and improvements will arise in those skilled in the art under the teachings of this invention without departing from its scope. The appended claims are intended to define the scope of the invention and thereby cover methods and structures within the scope of the claims themselves and their equivalents.

Claims

1. A flexible strain sensor with an extremely low temperature effect on its substrate, characterized in that, include: Metal composite flexible substrate comprising alternating polymer and metal microstructures; A strain-sensitive gate resistor is disposed above the metal composite flexible substrate, wherein the gate direction of the strain-sensitive gate resistor is consistent with the arrangement direction of the metal microstructures in the metal composite flexible substrate; as well as A protective layer and a passivation layer are located between the strain-sensitive gate resistor and the metal composite flexible substrate, wherein the protective layer is disposed on the metal composite flexible substrate and the passivation layer is disposed on the protective layer.

2. The flexible strain sensor with an extremely low temperature effect on the substrate according to claim 1, characterized in that, The strain-sensitive gate resistor includes a first seed layer and a sensitive metal layer; and / or The metal microstructure comprises, in sequence, a first metal, a third seed layer, and a second seed layer.

3. The flexible strain sensor with an extremely low temperature effect on the substrate according to claim 2, characterized in that, The polymer has a width of 100–3000 micrometers and a thickness of 20–200 micrometers; and / or The width of the metal microstructure is 10–300 micrometers, and the thickness is 20–200 micrometers; and / or The ratio of the width of the polymer to the width of the metal microstructure is 1:10; and / or The sensitive metal layer is a thin NiCrFeAlMn metal layer.

4. The flexible strain sensor with an extremely low temperature effect on the substrate according to claim 1, characterized in that, It also includes an external resistance test wiring connected to the strain-sensitive gate resistor.

5. A method for fabricating a flexible strain sensor with an extremely low temperature effect on the substrate, characterized in that, include: A protective layer and a passivation layer are sequentially arranged on a metal composite flexible substrate, wherein the metal composite flexible substrate comprises alternating polymer and metal microstructures; Photoresist was applied to the passivation layer and then dried. A grid pattern is formed on a photoresist using photolithography, wherein the orientation of the grid pattern is consistent with the arrangement direction of the metal microstructure in the metal composite flexible substrate. A strain-sensitive gate resistor is formed by sequentially arranging a first seed layer and a sensitive metal layer in a gate strip pattern using magnetron sputtering, wherein the gate strip direction of the strain-sensitive gate resistor is consistent with the arrangement direction of the metal microstructure in the metal composite flexible substrate. as well as The photoresist and the first seed layer and sensitive metal layer on it are removed to obtain a flexible strain sensor.

6. The method for fabricating a flexible strain sensor with an extremely low temperature effect on a substrate according to claim 5, characterized in that, It also includes the preparation of metal composite flexible substrates, including: The polymer is deposited on the substrate by spin coating and then dried. Photoresist was applied to the polymer using a spin coating method and then dried. A trench pattern is formed on a photoresist using photolithography, and a microstructure trench is formed on a polymer based on the trench pattern. A second and third seed layer were sequentially arranged in the microstructure trench using magnetron sputtering. Remove the photoresist and the second and third seed layers on it; A metallic microstructure is formed by filling the microstructure trenches with a first metal using an electroplating method; and The substrate is removed to obtain a metal composite flexible substrate.

7. The method for fabricating a flexible strain sensor with an extremely low temperature effect on a substrate according to claim 5, characterized in that, A protective layer is deposited on a metal composite flexible substrate by spin coating and dried to semi-cured. Then, a passivation layer is deposited on the protective layer by spin coating and dried to full curing.

8. The method for fabricating a flexible strain sensor with an extremely low temperature effect on a substrate according to claim 5, characterized in that, The process of forming a grid pattern on photoresist using photolithography includes: First, place the photomask on the dried photoresist, expose it under ultraviolet light, then immerse it in the developer to pattern it, and after drying, obtain the grid pattern.

9. The method for fabricating a flexible strain sensor with an extremely low temperature effect on a substrate according to claim 5, characterized in that, The polymer has a width of 100–3000 micrometers and a thickness of 20–200 micrometers; and / or The width of the metal microstructure is 10–300 micrometers, and the thickness is 20–200 micrometers; and / or The ratio of the width of the polymer to the width of the metal microstructure is 1:10; and / or The sensitive metal layer is a thin NiCrFeAlMn metal layer.

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