Flexible electronic device with Kirgami structure

Abstract

The invention belongs to the technical field of flexible electronic devices, and particularly discloses a flexible electronic device of a Kirgami structure. The flexible electronic device comprises a rigid electronic element and a flexible PCB (printed circuit board) of a Kirgami structure, a polyimide film serves as a substrate of the flexible PCB of the Kirgami structure, the flexible PCB of the Kirgami structure comprises a double-helix Kirgami geometric structure formed by connecting double-helix connecting lines and an electrode circuit on the double-helix Kirgami geometric structure, and the double-helix Kirgami geometric structure is formed by connecting four geometric units through the double-helix connecting lines. Compared with the prior art, the device has the advantages that the double-helix connecting lines are used as the connecting lines among the geometric units, so that the device has high stretch rate in the three-dimensional direction, better fatigue resistance is provided, the service life of the device is prolonged, and the device has high fill factors; and due to the negative Poisson's ratio caused by the double-helix connecting line, the structure does not shrink in the vertical direction after the device is stretched, and distortion and deformation can be resisted.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible electronic devices, and particularly relates to a flexible electronic device with a Kirigami structure. Background Art

[0002] In recent years, wearable devices have been increasingly applied in fields such as health monitoring and human-computer interaction, occupying a huge market share. Most of the currently commercial functional electronic components are of rigid structures and cannot change with the dynamic changes of the skin. Therefore, there will be discomfort problems when wearing them. In addition, from the perspective of bioelectrical signal acquisition, if the changing curved surface cannot be fitted in real time, problems such as inaccurate signal acquisition and signal delay will occur. Therefore, the research on stretchable electronic devices is of great significance.

[0003] There are many studies on the structural design of stretchable electronic devices at home and abroad. Currently, there are mainly two design methods: the wrinkled structure (such as CN110393507B) and the island-bridge structure (such as CN116981331A). The wrinkled structure is to fix a two-dimensional structure on a pre-stretched elastic substrate. When the prestress of the substrate is released, the elastic substrate will contract, and the two-dimensional structure will bend out of the plane to form a stretchable wrinkled shape. However, limited by the processing technology and the substrate, the wrinkled structure cannot be prepared in large sizes, and there are also limitations in the stretching direction. The island-bridge structure is to place functional elements on rigid island structures as functional areas for actual electronic functions, and the stretchable bridge structure is used as a connection area to achieve stretchable performance. The island-bridge structure is not limited by size, and the stretching direction is more flexible, so it has a wider application. However, there are also many problems, such as low stretching rate, low filling factor (i.e., the area ratio of the island structure), inability to achieve large-scale out-of-plane stretching, and most materials and structures have a positive Poisson's ratio. After axial stretching, radial contraction will occur, and the structure will be distorted.

[0004] With the high integration of the product functions of wearable devices, how to improve the stretching rate, filling factor in three dimensions (including in-plane and out-of-plane), and the anti-twisting performance of the structure during stretching of stretchable electronic devices, so as to improve the accuracy and extend the service life of the device, has become an important content in the research of stretchable electronic devices. Summary of the Invention

[0005] Aiming at the problems existing in the prior art, the invention purpose of the present invention is to provide a flexible electronic device with a high fill factor, a high elongation rate, and three-dimensional stretchability. The flexible electronic device is based on a Kirigami structure, with a polyimide film as the substrate, achieving excellent stretchability in three dimensions, having a high elongation rate in both the in-plane and out-of-plane directions, providing better fatigue resistance than existing flexible screens, extending the service life of the device, and enabling the device to have a high fill factor. Due to the negative Poisson's ratio brought by the double-helix connecting wires, after the device is stretched, the structure does not shrink in the vertical direction and can resist torsional deformation.

[0006] To achieve the above purpose, the technical solution of the present invention is as follows:

[0007] A flexible electronic device with a Kirigami structure includes a flexible PCB board with a Kirigami structure using a polyimide film as the substrate and rigid electronic components soldered on top of it. The flexible PCB board with a Kirigami structure includes a double-helix kirigami geometric structure formed by connecting double-helix connecting wires and an electrode circuit thereon. Taking one double-helix kirigami geometric structure as a unit, it extends infinitely in the horizontal and vertical directions to form the Kirigami structure. One double-helix kirigami geometric structure is formed by connecting four geometric units with double-helix connecting wires, and each geometric unit includes at least one independent module circuit.

[0008] Furthermore, the preparation process of the flexible PCB board with a Kirigami structure is as follows: First, determine the size, shape of the flexible PCB board and the electrode circuit, and the shape of the Kirigami structure through software KiCAD design; then, using a polyimide film as the substrate, prepare the required electrodes on the polyimide film, and the electrode circuit is as shown in the attached Figure 3 specification; next, through laser cutting, prepare a Kirigami structure that meets the design conditions. Preferably, the size of each geometric unit included in the flexible PCB board with a Kirigami structure is 13mm×13mm, and the spacing between adjacent geometric units is 0.2mm (as shown in Figure 4 A).

[0009] Furthermore, the connection method between the geometric units included in the flexible PCB board with a Kirigami structure: Two horizontally adjacent geometric units and two vertically adjacent geometric units form a double-helix kirigami geometric structure of a 2×2 array. Taking one double-helix kirigami geometric structure as a unit, it extends infinitely in the horizontal and vertical directions to form the Kirigami structure;

[0010] Furthermore, the connection relationships among the four geometric units within each double-helix kirigami geometric structure are as follows: the lower left corner of the upper left geometric unit and the upper left corner of the lower left geometric unit are connected by a double-helix connecting line; the lower right corner of the upper left geometric unit and the lower left corner of the upper right geometric unit are connected by a double-helix connecting line; the lower right corner of the upper right geometric unit and the upper right corner of the lower right geometric unit are connected by a double-helix connecting line; the upper left corner of the lower right geometric unit and the upper right corner of the lower left geometric unit are connected by a double-helix connecting line. The connection relationships between each double-helix kirigami geometric structure and the double-helix kirigami geometric structures in the four positions above, below, to the left, and to the right of it are as follows: the upper right corner of the upper left geometric unit within the double-helix kirigami geometric structure at the center and the lower right corner of the lower left geometric unit within the double-helix kirigami geometric structure in the upper position are connected by a double-helix connecting line; the upper left corner of the upper left geometric unit within the double-helix kirigami geometric structure at the center and the upper right corner of the upper right geometric unit within the double-helix kirigami geometric structure in the left position are connected by a double-helix connecting line; the upper left corner of the upper right geometric unit within the double-helix kirigami geometric structure at the center and the lower left corner of the lower right geometric unit within the double-helix kirigami geometric structure in the upper position are connected by a double-helix connecting line; the upper right corner of the upper right geometric unit within the double-helix kirigami geometric structure at the center and the upper left corner of the upper left geometric unit within the double-helix kirigami geometric structure in the right position are connected by a double-helix connecting line; the lower right corner of the lower right geometric unit within the double-helix kirigami geometric structure at the center and the lower left corner of the lower left geometric unit within the double-helix kirigami geometric structure in the right position are connected by a double-helix connecting line; the lower left corner of the lower right geometric unit within the kirigami geometric structure at the center and the upper left corner of the upper right geometric unit within the kirigami geometric structure in the lower position are connected by a double-helix connecting line; the lower right corner of the lower left geometric unit within the kirigami geometric structure at the center and the upper right corner of the upper left geometric unit within the kirigami geometric structure in the lower position are connected by a double-helix connecting line; the lower left corner of the lower left geometric unit within the kirigami geometric structure at the center and the lower right corner of the lower right geometric unit within the kirigami geometric structure in the left position are connected by a double-helix connecting line.

[0011] Preferably, a rigid electronic component is soldered onto the module circuit of each geometric unit to form a series structure; the micro-control unit independently controls the electrical signals within each geometric unit.

[0012] Preferably, the process parameters of the double-helix connecting line are obtained from the following formula:

[0013]

[0014] The minimum width of the given connecting line is d min (which is jointly determined by the processing technology, materials, geometric dimensions, and maximum elongation rate), then the maximum rotation angle θ of the double helix max can be calculated by the following formula:

[0015]

[0016] wherein, the side length of a geometric unit connected by the double helix connecting line is L, the initial radius of the helix is a, the rotation radius is R, the rotation angle corresponding to R is θ, and R max is the maximum rotation radius of the helix, and R max corresponds to the maximum rotation angle θ max , the distance between two centrosymmetric helices is D; L is determined by the size of the functional element, and a and D are jointly determined by the minimum cutting distance of the processing accuracy and the width and number of electrodes. Connect the centers of the initial circles of the two helices, and the acute angle between the connecting line and the horizontal direction is β. R1 and R2 are the rotation radii corresponding to the two helices at the center connecting line respectively.

[0017] Preferably, the value range of the number of turns of the double helix connecting line is 0.75 ≤ n ≤ 2, more preferably 1 ≤ n ≤ 2, and most preferably 1.25.

[0018] The present invention also provides a preparation method for the flexible electronic device with the above-mentioned Kirigami structure, including the following steps:

[0019] (1) The preparation process of the flexible PCB board with the Kirigami structure is as follows: First, determine the size, shape of the flexible PCB board and the electrode circuit, and the shape of the Kirigami structure through software KiCAD design; then, use the polyimide film as the substrate, and prepare the required electrode circuit on the polyimide film; then, through laser cutting, prepare the Kirigami structure that meets the design conditions;

[0020] (2) Solder the rigid electronic components to the module circuit of each geometric unit.

[0021] Preferably, the process parameters of the double helix connecting line are obtained by the following formula:

[0022]

[0023] Given that the minimum width of the double helix connecting line is d min , then the maximum rotation angle θ of the double helix connecting line max is calculated by the following formula:

[0024]

[0025] Among them, the side length of a geometric unit connected by a double - helix connecting line is L, the initial radius of the helix is a, the rotation radius is R, the rotation angle corresponding to R is θ, and R max is the maximum rotation radius of the helix, and R max corresponds to the maximum rotation angle of θ max , the distance between two centrosymmetric helices is D; L is determined by the size of the functional element, and a and D are jointly determined by the minimum cutting distance of the processing accuracy and the width and number of electrodes. Connect the centers of the initial circles of the two helices, and the acute - angle between the connecting line and the horizontal direction is β. R1 and R2 are the rotation radii corresponding to the two helices at the connecting line of the centers of the circles respectively.

[0026] Preferably, the value range of the number of turns of the double - helix connecting line is 0.75 ≤ n ≤ 2, more preferably 1 ≤ n ≤ 2, and most preferably 1.25. Correspondingly, the value range of θ is [1.5π, 4π], more preferably [π, 4π], and most preferably 2.5π.

[0027] Compared with the prior art, the beneficial effects and advantages of the present invention are as follows:

[0028] 1. Stretchability in three - dimensional directions, and high stretch ratios in both in - plane and out - of - plane directions;

[0029] 2. Excellent fatigue resistance. By introducing a helical structure, stress concentration in the structure is avoided, thereby prolonging the service life of the device;

[0030] 3. High filling factor, and a high proportion of the area of the rigid island structure;

[0031] 4. Negative Poisson's ratio. After stretching, the structure does not shrink in the vertical direction and can resist torsional deformation;

[0032] 5. Stretchability can be regulated, and the stretchability can be adjusted by adjusting the key parameters of the double - helix. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic assembly structure diagram of a flexible electronic device with a Kirigami structure in Example 1.

[0034] Figure 2 It is a schematic diagram of a kirigami geometric structure formed by straight connecting lines in CN116761491B, the double - helix connecting line of the present invention, and the double - helix kirigami geometric structure formed by the double - helix connecting line in Example 1 of the present invention.

[0035] Figure 3In it, the left figure is a schematic diagram of the electrode circuit on the flexible PCB board with a Kirigami structure in Embodiment 1 of the present invention (the red color is the front side for soldering rigid electronic components, and the blue color is the back side), and the right figure is a schematic diagram of the electrode circuit at the double - helix connecting line in Embodiment 1 of the present invention.

[0036] Figure 4 In it, A is the flexible PCB board with a Kirigami structure in Embodiment 1, and B is the flexible PCB board with a Kirigami structure soldered with rigid electronic component 1.

[0037] Figure 5 In it, A is in the prior art 1 Figure 1 d; B is a schematic diagram of the in - plane stretching state of the flexible electronic device with a Kirigami structure in Embodiment 1 of the present invention in the energized state.

[0038] Figure 6 In it, A and B are schematic diagrams of the fitting state with the step when the flexible thermoelectric device with a Kirigami structure in CN116761491B is subjected to out - of - plane stretching; C and D are schematic diagrams of the fitting state with the step when the flexible electronic device with a Kirigami structure in Embodiment 1 of the present invention is subjected to out - of - plane stretching in the energized state.

[0039] Figure 7 In it, A, B, and C are respectively schematic diagrams of the stress distribution of the finite - element simulation analysis in the step - fitting state when the geometric structures formed by connecting a straight connecting line (Kirigami geometric structure in CN116761491B), a serpentine connecting line (2 * 1.25 turns), and the double - helix connecting line (2 * 1.25 turns) of the present invention are subjected to out - of - plane stretching; among them, the maximum stresses in the states shown in Figures A, B, and C are 516 MPa, 355 MPa, and 101 MPa in sequence.

[0040] Figure 8 In it, A, B, and C are respectively schematic diagrams of the stress distribution of the finite - element simulation analysis when the geometric structures formed by connecting a straight connecting line (Kirigami geometric structure in CN116761491B), a serpentine connecting line (2 * 1.25 turns), and the double - helix connecting line (2 * 1.25 turns) of the present invention are subjected to in - plane stretching; among them, the maximum stresses in the states shown in Figures A, B, and C are 493.4 MPa, 182.2 MPa, and 40.5 MPa in sequence.

[0041] Figure 9 It is a schematic diagram of the geometric relationship of the double - helix connecting line.

[0042] Figure 10Among them, A is the shape of the double - helix kirigami geometric structure of the present invention when the number of turns is 0.5, 0.75, 1, 1.25, 1.5, 1.75, and 2 respectively; B is the relationship diagram of the filling factor and the elongation rate corresponding to the structure formed by connecting the double - helix connecting lines of each number of turns in A.

[0043] Figure 11 Among them, A is in the prior art 1 Figure 1 a; B is a schematic diagram of the state when the flexible electronic device with the Kirigami structure of Embodiment 1 of the present invention is uniaxially stretched in - plane corresponding to A.

[0044] In the figure, 1 - rigid electronic component, 2 - flexible PCB board with Kirigami structure, 3 - kirigami geometric structure, 4 - double - helix connecting line, 5 - double - helix kirigami geometric structure;

[0045] The above - mentioned prior art 1 is: Auxetic Meta - Display: Stretchable Display without Image Distortion, Adv. Funct. Mater. 2022, 32, 2113299. Detailed implementation manners

[0046] The present invention will be further described below in conjunction with the specification drawings and embodiments. The present invention is not limited by the following embodiments, and the specific implementation manners can be determined according to the technical solutions of the present invention and the actual situation.

[0047] The object of the present invention is: A flexible thermoelectric device with a Kirigami structure disclosed in CN116761491B is the prior research of our research group. In our group's practice, the Kirigami structure included in this flexible thermoelectric device has many limitations, which affect the practical application: First, when the stretching in the Z - axis direction is large, the fitting degree of the device substrate drops sharply, and the substrate is distorted; Second, when stretching in the plane where the device substrate is located, the stretching degree is limited; Third, due to the excessive stress of the connecting lines between the geometric units in the Kirigami structure during stretching, the fatigue resistance of the substrate is reduced under cyclic stretching, resulting in a shortened service life of the device. Therefore, by using a double - helix line as the connecting line between the geometric units in the flexible substrate of the Kirigami structure, while endowing the device with greater ductility, the fatigue resistance of the device is improved, and the fitting ability of the substrate during Z - axis direction stretching is improved. Figure 1-2Among them, there are a rigid electronic component 1, a flexible PCB board 2 with a Kirigami structure on a polyimide substrate, a kirigami geometric structure 3 formed by connecting straight connecting lines in CN116761491B, a double - helix connecting line 4, and a double - helix kirigami geometric structure 5 formed by connecting the double - helix connecting lines. Two geometric units adjacent horizontally and two geometric units adjacent vertically form a kirigami geometric structure of a 2×2 array.

[0048] The plane where the flexible electronic device is located before stretching is the XY plane. It can be stretched in the X - axis and Y - axis directions, and can also be stretched in other directions. The stretching in the X - axis and Y - axis directions is in - plane stretching. The direction perpendicular to the XY plane is the Z - axis direction, and the flexible electronic device can be stretched in the Z - axis direction, which is also called out - of - plane stretching.

[0049] Example 1

[0050] A flexible electronic device with a Kirigami structure includes a flexible PCB board 2 with a Kirigami structure using a polyimide film as a substrate and a rigid electronic component 1 welded on top of it.

[0051] Figure 2 Among them, the flexible PCB board 2 with a Kirigami structure includes a double - helix kirigami geometric structure 5 formed by connecting double - helix connecting lines 4 and the electrode circuit thereon. Taking the double - helix kirigami geometric structure 5 as a unit, it extends infinitely in the horizontal and vertical directions to form the Kirigami structure. Among them, the number of turns of each helix in the double - helix connecting line 4 is 1.25, the distance D between the helices is 1.1 mm, and the initial radius of the helix is 0.25 mm.

[0052] The preparation process of the flexible PCB board 2 with a Kirigami structure is as follows: First, determine the size, shape of the flexible PCB board and the electrode circuit, and the shape of the Kirigami structure through software KiCAD design. Then, using a polyimide film as a substrate, prepare the required electrode circuit on the polyimide film, and the electrode circuit is as Figure 3 shown. Then, through laser cutting, prepare a Kirigami structure that meets the design conditions. Among them, the flexible PCB board 2 with a Kirigami structure includes 25 geometric units, the size of each geometric unit is 13 mm×13 mm, and the distance between adjacent geometric units is 0.2 mm( Figure 4 A).

[0053] The connection mode between the geometric units included in the flexible PCB board 2 of the Kirigami structure: two geometric units adjacent horizontally and two geometric units adjacent vertically form a double-helix kirigami geometric structure 5 of a 2×2 array, and the double-helix kirigami geometric structure 5 is infinitely extended in the horizontal and vertical directions as a unit to form the Kirigami structure; among them, the connection relationship between the four geometric units in each double-helix kirigami geometric structure 5 is that the lower left corner of the upper left corner geometric unit and the upper left corner of the lower left corner geometric unit are connected by a double-helix connecting line 4, the lower right corner of the upper left corner geometric unit and the lower left corner of the upper right corner geometric unit are connected by a double-helix connecting line 4, the lower right corner of the upper right corner geometric unit and the upper right corner of the lower right corner geometric unit are connected by a double-helix connecting line 4, and the upper left corner of the lower right corner geometric unit and the upper right corner of the lower left corner geometric unit are connected by a double-helix connecting line 4;The connection relationship between each double - helix kirigami geometry 5 and the double - helix kirigami geometries 5 in the four positions above, below, left, and right of it is as follows: The upper - right corner of the upper - left geometric unit in the central double - helix kirigami geometry 5 and the lower - right corner of the lower - left geometric unit in the double - helix kirigami geometry 5 in the upper position are connected by a double - helix connecting line 4; the upper - left corner of the upper - left geometric unit in the central double - helix kirigami geometry 5 and the upper - right corner of the upper - right geometric unit in the double - helix kirigami geometry 5 in the left position are connected by a double - helix connecting line 4; the upper - left corner of the upper - right geometric unit in the central double - helix kirigami geometry 5 and the lower - left corner of the lower - right geometric unit in the double - helix kirigami geometry 5 in the upper position are connected by a double - helix connecting line 4; the upper - right corner of the upper - right geometric unit in the central double - helix kirigami geometry 5 and the upper - left corner of the upper - left geometric unit in the double - helix kirigami geometry 5 in the right position are connected by a double - helix connecting line 4; the lower - right corner of the lower - right geometric unit in the central double - helix kirigami geometry 5 and the lower - left corner of the lower - left geometric unit in the double - helix kirigami geometry 5 in the right position are connected by a double - helix connecting line 4; the lower - left corner of the lower - right geometric unit in the central double - helix kirigami geometry 5 and the upper - left corner of the upper - right geometric unit in the double - helix kirigami geometry 5 in the lower position are connected by a double - helix connecting line 4; the lower - right corner of the lower - left geometric unit in the central double - helix kirigami geometry 5 and the upper - right corner of the upper - left geometric unit in the double - helix kirigami geometry 5 in the lower position are connected by a double - helix connecting line 4; the lower - left corner of the lower - left geometric unit in the central double - helix kirigami geometry 5 and the lower - right corner of the lower - right geometric unit in the double - helix kirigami geometry 5 in the left position are connected by a double - helix connecting line 4.;

[0054] Solder is used to weld the rigid electronic components 1 onto the module circuits of each geometric unit to form a series structure, as Figure 4 shown in B; By independently controlling the electrical signals in each geometric unit through a micro - control unit, it can present Figure 9 the opening and closing states shown in B.

[0055] Figure 5In it, Figure A is in the text of the academic paper "Auxetic Meta-Display: Stretchable Display without Image Distortion" (Adv. Funct. Mater. 2022, 32, 2113299, DOI: 10.1002 / adfm.202113299). Figure 1 d (the Kirigami structure is the same as the Kirigami structure disclosed in CN116761491B), which reflects that the in-plane stretch ratio of the Kirigami structure with straight lines as the connecting lines of geometric units reaches 24.5%; Figure B shows the state of the flexible electronic device with the Kirigami structure in the above embodiment after in-plane stretching. The size before stretching is 65.8 mm, and it can reach 118 mm after stretching, with a stretch ratio reaching 80%. Comparing the two, the double-helix connecting line 4 enables the flexible electronic device to have better ductility.

[0056] Figure 6 In it, Figures A and B show that the stretching ability of the Kirigami structure in the Z-axis direction in CN116761491B is limited. After the flexible electronic device is stretched, the substrate of each geometric unit in the Kirigami structure cannot fit with the surface of the stepped surface; Figures C and D show that after the flexible electronic device in the above embodiment is stretched in the Z-axis direction, the substrate can fit perfectly with the stepped surface. According to our tests, the flexible electronic device in the above embodiment can achieve a maximum stretch of 12496.4% (nearly 125 times the thickness of the FPCB) in the Z-axis direction. Comparing the two, when facing discontinuous / parallel planes with height differences such as stepped surfaces, the double-helix connecting line of the present invention enables the flexible substrate of the Kirigami structure to have excellent out-of-plane stretching effects.

[0057] This research group noticed that there are also flexible devices with serpentine lines as connecting lines in the prior art. For example, serpentine lines are used as the connecting lines between units in CN109545450B, CN116981331A, CN117618080B, CN117765824A, and CN119413326A. Therefore, replacing the double-helix connecting line in the above embodiment with a serpentine connecting line, under the same other conditions, a simulation analysis is respectively carried out on the Kirigami geometric structures connected by straight connecting lines (the same as the Kirigami structure disclosed in CN116761491B), serpentine connecting lines, and double-helix connecting lines, and the stress distribution diagrams of the structures under the same stretching degree are obtained. The ease of tensile fracture of the structure and the fatigue resistance of the structure are judged by the numerical values and positions of the stresses. As Figure 7, through finite element simulation analysis, when the flexible device is stretched in the Z-axis direction, the maximum stress inside the structure reaches 516 MPa for the straight connecting line (a kirigami geometric structure in the Kirigami structure disclosed in CN116761491B). For the double-helix connecting line in the above embodiment, when the flexible device is stretched in the Z-axis direction, the maximum stress inside the structure is 101 MPa. For the serpentine connecting line with the same number of turns (2×1.25) as the double-helix connecting line in the above embodiment, when the flexible device is stretched in the Z-axis direction, the maximum stress inside the structure is 355 MPa. It can be seen from Figure 7 that there is obvious distortion of the base of the geometric unit in Figure A, there is a certain degree of deformation at the four corners of the base of the geometric unit in Figure B, and the base of the geometric unit in Figure C (in the Kirigami structure of the above embodiment) is basically undeformed. Thus, it can be known that when performing the same degree of stretching in the Z-axis direction (i.e., out-of-plane stretching), the maximum stresses borne by the structure for the straight connecting line and the serpentine connecting line are 5.1 times and 3.5 times respectively of the maximum stress borne by the structure for the helical connecting line. This shows that using the double-helix connecting line for connection can effectively reduce the stress concentration of the Kirigami geometric structure, making the flexible electronic device have better fatigue resistance. Therefore, compared with using the serpentine connecting line for connection, using the double-helix connecting line for connection can reduce the deformation of the structure. And because under the same deformation, the maximum stress inside the Kirigami geometric structure connected by the serpentine connecting line is 3.5 times that of the Kirigami geometric structure connected by the double-helix connecting line. When both are stretched in the Z-axis direction at the same time, the maximum stretching length of the Kirigami geometric structure connected by the double-helix connecting line in the Z-axis direction is significantly longer than that of the Kirigami geometric structure connected by the serpentine connecting line.

[0058] The above is the simulation analysis for out-of-plane stretching, Figure 8 and the following is the simulation analysis for in-plane stretching. Figure 8 The geometric structures of A, B, and C in Figure 7 are the same as those of A, B, and C in Figure 8 , except that in

[0059] in-plane stretching is performed. Through finite element simulation analysis, under the condition of the same degree of in-plane stretching, the maximum stresses for the corresponding cases of the straight connecting line (A), the serpentine connecting line (B), and the double-helix connecting line (C) are 493.4 MPa, 182.2 MPa, and 40.5 MPa respectively. This shows that using the double-helix connecting line for connection can greatly reduce the stress inside the structure during in-plane stretching, thus making the structure have better fatigue resistance.

[0059] In summary, using the double-helix connecting line can improve the fatigue resistance of the flexible electronic device of the Kirigami structure, thereby extending the service life of the device.

[0060] In the prior art CN116761491B, the width of the connecting line between the geometric units of the Kirigami structure needs to be minimized as much as possible to achieve the stretching of the structure. If the width is too large, the structure will be difficult to stretch, but if the width is too small, stress concentration will occur during stretching, making it prone to breakage. Therefore, the width of the connecting line must be within a certain size range.

[0061] The size of the double - helix connecting line affects the performance of the flexible device. For example, Figure 9 , the design of the radius, width, and number of turns of the double - helix connecting line is described as follows: We adjust the process parameters of the double - helix connecting line to adjust the filling factor and stretching rate of the double - helix kirigami geometric structure. For example, Figure 9 A, the side length of a geometric unit connected by the double - helix connecting line is L, the initial radius of the helix is a, the rotation radius is R, the rotation angle corresponding to R is θ, and the distance between two centrosymmetric helices is D. Among them, L is determined by the size of the functional element (Example 1 above), and a and D are jointly determined by the minimum cutting distance of the processing accuracy and the width and number of electrodes. Each parameter is obtained from the following formula:

[0062]

[0063] Given that the minimum width of the connecting line is d min (jointly determined by the processing technology, material, geometric size, and maximum stretching rate), then the maximum rotation angle θ of the double - helix max can be calculated by the following formula:

[0064]

[0065] Among them, the side length of a geometric unit connected by the double - helix connecting line is L, the initial radius of the helix is a, the rotation radius is R, the rotation angle corresponding to R is θ, and R max is the maximum rotation radius of the helix, and the maximum rotation angle corresponding to R max is θ max , the distance between two centrosymmetric helices is D; L is determined by the size of the functional element, a and D are jointly determined by the minimum cutting distance of the processing accuracy and the width and number of electrodes. Connect the initial circle centers of the two helices, and the acute - angle between the connecting line and the horizontal direction is β, and R1 and R2 are the rotation radii corresponding to the two helices at the center - connecting line.

[0066] Meanwhile, when the helix angle θ ≤ π, the double - helix connecting line is approximately a straight - line connecting line, as shown in Figure 10As shown in the figure corresponding to 0.5 turns in A, the range of values of θ can thus be obtained. Through calculation, the range of values of θ is [π, 4π], that is, the number of turns of the double-helix connecting line is 0.5 turns to 2 turns (i.e., 0.5 ≤ n ≤ 2). If the number of turns continues to increase, adjacent spirals will overlap with each other and a geometric figure cannot be formed.

[0067] On the above basis, by adjusting the number of turns of the double-helix connecting line, the stress of the structure under in-plane stretching conditions is regulated. As Figure 10 shown in A, we designed corresponding double-helix Kirigami geometric structures according to the number of turns being 0.5, 0.75, 1, 1.25, 1.5, 1.75, and 2 respectively. Through finite element simulation analysis, as Figure 10 shown in B, it can be known that the filling factor and stretching rate of the geometric structure can be regulated by the number of turns of the double helix, that is, increasing the number of turns of the double helix will increase the stretching rate of the geometric structure. Similarly, increasing the radius and width of the double-helix connecting line will also increase the stretching rate of the device.

[0068] To sum up, we believe that the stretchability of the geometric structure can be adjusted by regulating the key parameters of the double-helix structure. At the same time, considering the fatigue resistance of flexible electronic devices, combined with Figure 7 C, Figure 8 the maximum stress of the structure shown in C, the range of values of the number of turns of the double-helix connecting line is 0.75 ≤ n ≤ 2, preferably 1 ≤ n ≤ 2, and optimally 1.25.

[0069] It should be noted that the above stretching rate is the stretching rate of a single geometric structure. In practice, the flexible PCB board of the Kirigami structure included in the device is an array formed by multiple geometric structures, and its stretching rate is greater than that of a single geometric structure.

[0070] Figure 11 Figure a in the academic paper "Auxetic Meta-Display: Stretchable Display without Image Distortion" (Adv. Funct. Mater. 2022, 32, 2113299, DOI: 10.1002 / adfm.202113299) Figure 1 When stretched, the image on the flexible display screen is distorted. Figure 11 Figure b in the above Embodiment 1 shows the flexible electronic device. When uniaxially axially stretched in the plane, it expands along the stretching direction and the substrate does not undergo distortion, indicating that it has the property of negative Poisson's ratio and can resist distortion.

[0071] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Those skilled in the art to which the present invention pertains may make various modifications or supplements to the described specific embodiments or use similar means for substitution, but will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

[0072] Although terms such as rigid electronic component 1, flexible PCB board 2 with Kirigami structure, Kirigami geometric structure 3, double - helix connecting line 4, double - helix Kirigami geometric structure 5, etc. are used herein, the possibility of using other terms is not excluded. These terms are used only to more conveniently describe and explain the essence of the present invention; interpreting them as any additional limitation is contrary to the spirit of the present invention. Moreover, due to the different processing precisions achievable by the processing technology, the achievable range of the number of turns of the double - helix connecting line in the present invention is also different from that in the above - mentioned embodiments; the range of the number of turns in the above - mentioned embodiments is the range achievable by FPCB processing, and using a processing technology or tool with higher processing precision can make the range of the number of turns larger. Therefore, the range of the number of turns in the above - mentioned embodiments cannot be used as a limitation on the technical path embodied by the present invention.

Claims

1. A flexible electronic device with a Kirigami structure, comprising a flexible PCB board with a Kirigami structure using a polyimide film as a substrate and rigid electronic components soldered on top of it, characterized in that, The flexible PCB board of the Kirigami structure includes a double - helix kirigami geometric structure formed by connecting double - helix connecting lines and an electrode circuit thereon. Taking one double - helix kirigami geometric structure as a unit, it extends infinitely in the horizontal and vertical directions to form the Kirigami structure. One double - helix kirigami geometric structure is formed by connecting four geometric units with double - helix connecting lines, and each geometric unit includes at least one independent module circuit.

2. The flexible electronic device with the Kirigami structure according to claim 1, characterized in that, The value range of the number of turns of the double - helix connecting line is 0.75 ≤ n ≤ 2.

3. The flexible electronic device with a Kirigami structure according to claim 1, characterized in that, The size of each geometric unit is 13 mm × 13 mm, and the distance between adjacent geometric units is 0.2 mm.

4. The flexible electronic device with a Kirigami structure according to claim 1, characterized in that, The connection method between the geometric units included in the flexible PCB board of the Kirigami structure: Two horizontally adjacent geometric units and two vertically adjacent geometric units form a double - helix kirigami geometric structure of a 2×2 array. Taking one double - helix kirigami geometric structure as a unit, it extends infinitely in the horizontal and vertical directions to form the Kirigami structure.

5. The flexible electronic device with a Kirigami structure according to claim 1, characterized in that, The connection relationships among the four geometric units within each double - helix kirigami geometric structure are as follows: the lower - left corner of the upper - left geometric unit and the upper - left corner of the lower - left geometric unit are connected by a double - helix connecting line; the lower - right corner of the upper - left geometric unit and the lower - left corner of the upper - right geometric unit are connected by a double - helix connecting line; the lower - right corner of the upper - right geometric unit and the upper - right corner of the lower - right geometric unit are connected by a double - helix connecting line; the upper - left corner of the lower - right geometric unit and the upper - right corner of the lower - left geometric unit are connected by a double - helix connecting line. The connection relationships between each double - helix kirigami geometric structure and the double - helix kirigami geometric structures at its upper, lower, left, and right positions are as follows: the upper - right corner of the upper - left geometric unit within the double - helix kirigami geometric structure at the center and the lower - right corner of the lower - left geometric unit within the double - helix kirigami geometric structure at the upper position are connected by a double - helix connecting line; the upper - left corner of the upper - left geometric unit within the double - helix kirigami geometric structure at the center and the upper - right corner of the upper - right geometric unit within the double - helix kirigami geometric structure at the left position are connected by a double - helix connecting line; the upper - left corner of the upper - right geometric unit within the double - helix kirigami geometric structure at the center and the lower - left corner of the lower - right geometric unit within the double - helix kirigami geometric structure at the upper position are connected by a double - helix connecting line; the upper - right corner of the upper - right geometric unit within the double - helix kirigami geometric structure at the center and the upper - left corner of the upper - left geometric unit within the double - helix kirigami geometric structure at the right position are connected by a double - helix connecting line; the lower - right corner of the lower - right geometric unit within the double - helix kirigami geometric structure at the center and the lower - left corner of the lower - left geometric unit within the double - helix kirigami geometric structure at the right position are connected by a double - helix connecting line; the lower - left corner of the lower - right geometric unit within the kirigami geometric structure at the center and the upper - left corner of the upper - right geometric unit within the kirigami geometric structure at the lower position are connected by a double - helix connecting line; the lower - right corner of the lower - left geometric unit within the kirigami geometric structure at the center and the upper - right corner of the upper - left geometric unit within the kirigami geometric structure at the lower position are connected by a double - helix connecting line; the lower - left corner of the lower - left geometric unit within the kirigami geometric structure at the center and the lower - right corner of the upper - right geometric unit within the kirigami geometric structure at the left position are connected by a double - helix connecting line.

6. The flexible electronic device with the Kirigami structure according to claim 1, characterized in that, The rigid electronic components are soldered onto the module circuits of each geometric unit to form a series structure; the micro - control unit independently controls the electrical signals within each geometric unit.

7. The flexible electronic device with a Kirigami structure according to claim 1, characterized in that, The value range of the number of turns of the double - helix connecting line is 1 ≤ n ≤ 2.

8. A preparation method for a flexible electronic device with a Kirigami structure as described in any one of claims 1 - 7, comprising the following steps: (1) The preparation process of the flexible PCB board with the Kirigami structure is as follows: First, determine the dimensions, shapes of the flexible PCB board and the electrode circuit, and the shape of the Kirigami structure through software KiCAD design; then, using a polyimide film as the substrate, prepare the required electrode circuit on the polyimide film; next, through laser cutting, prepare the Kirigami structure that meets the design conditions; (2) Solder rigid electronic components onto the module circuits of each geometric unit.

9. The preparation method according to claim 8, wherein, The process parameters of the double - helix connecting line are obtained from the following formula: The minimum width of the given double - helix connecting line is d min , then the maximum rotation angle θ of the double - helix connecting line max is calculated by the following formula: Among them, the side length of a geometric unit connected by a double - helix connection line is L, the initial radius of the helix is a, the rotation radius is R, the rotation angle corresponding to R is θ, and R max is the maximum rotation radius of the helix, and R max corresponds to the maximum rotation angle of θ max , the distance between two centrosymmetric helices is D; L is determined by the size of the functional element, and a and D are jointly determined by the minimum cutting distance of the processing accuracy and the width and number of electrodes. Connect the centers of the initial circles of the two helices, and the acute - angle between the connecting line and the horizontal direction is β. R1 and R2 are the rotation radii corresponding to the two helices at the connecting line of the centers respectively.

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