Inorganic flexible electronic devices based on grid substrates and their integration methods

Abstract

This application provides an inorganic flexible electronic device based on a grid substrate and its integration method. The inorganic flexible electronic device includes: a wire, which includes a conductive portion and an encapsulation portion encapsulated outside the conductive portion; and a grid substrate, on which the wire is disposed. The integration method provided in this application includes: obtaining a top grid substrate, a bottom grid substrate, a first flexible block, a second flexible block, a third flexible block, and a wire; disposing the bottom grid substrate on the first flexible block; attaching the wire to be assembled to the second flexible block; aligning the second flexible block containing the wire and the first flexible block containing the bottom grid substrate under a microscope, removing the wire, and soldering the wire to the bottom grid substrate; supporting the top grid substrate on the third flexible block, aligning the top grid substrate and the bottom grid substrate, with the wire located between the two grid substrates, then removing the third flexible block, and soldering the top grid substrate to the wire.

Description

Technical Field

[0001] This application belongs to the field of flexible electronics technology, and in particular relates to inorganic flexible electronic devices based on grid substrates and their integration methods. Background Technology

[0002] In recent years, flexible electronic devices have become a hot topic in industry and academia. Since 2008, the emergence of new flexible devices such as electronic skin and electronic eye cameras has ushered in the era of flexible electronic devices. From a technological perspective, flexible electronic devices are mainly divided into two categories: organic flexible electronic devices and inorganic flexible electronic devices. Organic flexible electronic devices utilize intrinsically stretchable conductive materials (mainly conductive polymer materials) to achieve device stretchability, but their low carrier density leads to poor performance. Inorganic flexible electronic devices utilize brittle materials from traditional microelectronics technology, such as silicon and metal thin films, through mechanical structural design to achieve an overall stretchable structure, resulting in better performance.

[0003] Flexible electronics, with their low elastic modulus and properties allowing for stretching / compression, bending, and twisting, have revolutionized the form and usage of traditional electronic devices, greatly expanding the application scope of microelectronics. With increasing emphasis on healthcare, the continuous monitoring of human physiological signals using flexible electronic devices is an effective approach for early warning of major diseases and prevention and control of chronic diseases. Functionally, flexible electronic devices can be integrated with different parts of the body to detect basic physiological parameters such as body temperature, respiration, heart rate, blood oxygen, blood pressure, and pulse; electrophysiological signals such as electrocardiogram, electromyography, and electroencephalography; biochemical parameters such as sweat and blood glucose; and environmental temperature, humidity, and ultraviolet light measurements, as well as functions such as treatment, energy harvesting, body surface display, and tactile sensing. Flexible electronic devices provide precise and effective monitoring feedback and clinical guidance for chronic diseases such as hyperglycemia and cardiovascular diseases.

[0004] Improving the system elongation and integration of inorganic flexible electronic devices, based on their stretchable mechanical and circuit functional properties, is an essential path for the industrialization of flexible electronic devices.

[0005] 1. Elongation

[0006] Currently, the main mechanical design structures for flexible conductors include: corrugated structures, Euler buckling island bridge structures, serpentine conductor island bridge structures, segmented conductor island bridge structures, three-dimensional spiral conductor structures, planar spiral conductor structures, and paper-cut / origami structures. Among these, the serpentine conductor island bridge structure is a commonly used structure in flexible electronics. It separates the device from the conductor, uses "islands" to attach functional components, and utilizes the deformation of the structured "bridge" to improve the overall elongation. Under tension and compression, the curved beam of the serpentine bridge structure undergoes both in-plane deformation and out-of-plane buckling, resulting in an elongation greater than that of a straight bridge. Based on the serpentine bridge structure, serpentine conductors have been developed and have become a commonly used conductor form.

[0007] Serpentine conductors and their derivative structures possess significant theoretical elongation. However, in practical applications, especially after structured conductors are encapsulated (a common encapsulation method is solid encapsulation using PDMS casting, where the entire structured conductor is embedded within cured PMDS), serpentine conductors attached to or cast and sealed to the substrate exhibit restricted out-of-plane buckling deformation upon stretching, accompanied by significant stress concentration, making them prone to failure. This reduces the stretchability of the serpentine conductors and results in poor device ductility.

[0008] 2. Integration level

[0009] The structured design of conductors increases their length, width, and bending span, enhancing their ductility. However, it also reduces the design space and area ratio of electronic components, decreasing the functional efficiency and integration density of flexible electronic devices.

[0010] Utilizing vertical space to spatially arrange functional components is the most direct method to improve the integration density of flexible electronic devices. Folding or stacking can be used to increase device integration. However, current technologies use encapsulation materials such as silicone rubber to completely encapsulate the flexible electronic devices. Even after the wires are stretched and deformed, the actual elongation is still much lower than the elongation of the wires before encapsulation.

[0011] Therefore, in existing technologies, improving device scalability and increasing integration are often mutually exclusive, and current packaging and integration technologies struggle to achieve a balance between the two.

[0012] In addition, in practical applications, the mismatch between inorganic flexible electronic devices and skin mechanics introduces large measurement errors and increases the discomfort experienced by users during long-term wear. Summary of the Invention

[0013] To improve or solve at least one of the problems mentioned in the background art, this application proposes an inorganic flexible electronic device based on a grid substrate and its integration method.

[0014] This inorganic flexible electronic device based on a grid substrate includes:

[0015] A wire, comprising a conductive portion and an encapsulation portion encapsulated outside the conductive portion; and

[0016] A grid base, on which the wires are disposed.

[0017] In at least one embodiment, the material of the conductive portion includes at least one of copper and gold; and / or the material of the encapsulation portion is polyimide.

[0018] In at least one embodiment, the grid base includes an array of repeating base units, the grid shape of which is composed of U-shaped edges.

[0019] In at least one embodiment, pads are provided on both the conductor and the mesh substrate, and the conductor is soldered to the mesh substrate through the pads.

[0020] In at least one embodiment, the inorganic flexible electronic device includes two grid substrates, with the wires disposed between the two opposing grid substrates.

[0021] In at least one embodiment, the inorganic flexible electronic device includes multiple layers of the grid substrate and multiple layers of the wires, wherein the grid substrate and the wires constitute a multilayer structure of first layer grid substrate - first layer wires ... nth layer grid substrate - nth layer wires - n+1th layer grid substrate, where n > 1.

[0022] In at least one embodiment, the inorganic flexible electronic device based on a grid substrate further includes an electronic element connected to the conductive portion of the wire in the i-th layer, and the grid substrate in the (i+1)-th layer or the grid substrate in the i-th layer is provided with an opening capable of accommodating the electronic element.

[0023] In at least one embodiment, the inorganic flexible electronic device based on a grid substrate further includes a connector, through which the spacing between the wires and the grid substrate is controlled.

[0024] The inorganic flexible electronic device in the integration method of the grid-based inorganic flexible electronic device is the inorganic flexible electronic device as described above, and the integration method includes:

[0025] Obtain the top-level mesh base, the bottom-level mesh base, the first flexible block, the second flexible block, the third flexible block, and the wires;

[0026] The underlying mesh substrate is placed on the first flexible block;

[0027] The wires to be assembled are attached to the second flexible block;

[0028] Align the second flexible block containing the wire with the first flexible block containing the bottom mesh substrate under a microscope, remove the wire, and weld the wire to the bottom mesh substrate;

[0029] The top mesh substrate is supported on the third flexible block, the top mesh substrate and the bottom mesh substrate are aligned, the wire is located between the two mesh substrates, then the third flexible block is removed, and the top mesh substrate is welded to the wire.

[0030] In at least one embodiment, it further includes:

[0031] The inorganic flexible electronic device includes a plurality of the wires, which are welded and fixed together.

[0032] The inorganic flexible electronic device and integration method provided in this application increase the elongation of the flexible electronic device while ensuring a relatively large integration degree. Attached Figure Description

[0033] Figure 1A A schematic diagram of the structure of an inorganic flexible electronic device wire based on a grid substrate according to an embodiment of this application is shown.

[0034] Figure 1B It shows Figure 1A Side view of the center conductor.

[0035] Figure 2A A schematic diagram of the structure of a grid substrate for an inorganic flexible electronic device based on a grid substrate according to an embodiment of this application is shown.

[0036] Figure 2B It shows Figure 2A A repeating cell in the grid base.

[0037] Figure 2C Stress-strain diagrams of an inorganic flexible electronic device based on a grid substrate according to an embodiment of this application are shown.

[0038] Figure 3 A schematic diagram of the structure of an inorganic flexible electronic device based on a grid substrate according to an embodiment of this application is shown.

[0039] Figure 4A , 4B Figures 4C, 4D, 4E, 4F, 4G, and 4H show an integration flowchart of an inorganic flexible electronic device based on a grid substrate according to an embodiment of this application.

[0040] Figure 5 The diagram illustrates the relationship between the number of stretching cycles and the change in wire conductivity for an inorganic flexible electronic device based on a grid substrate according to an embodiment of this application and a conventional packaging form.

[0041] Figure 6A , Figure 6B A schematic diagram of a multilayer structure of an inorganic flexible electronic device based on a grid substrate according to an embodiment of this application is shown.

[0042] Figure 7A , Figure 7B A schematic diagram of the internal structure of an inorganic flexible electronic device based on a grid substrate according to an embodiment of this application is shown. Detailed Implementation

[0043] Exemplary embodiments of this application are described below with reference to the accompanying drawings. It should be understood that these specific descriptions are for teaching those skilled in the art how to implement this application only, and are not intended to exhaustively describe all possible methods of this application, nor to limit the scope of this application.

[0044] This application provides an inorganic flexible electronic device (hereinafter, sometimes referred to as "flexible electronic device") based on a grid substrate, which includes a wire 1 and a grid substrate 2.

[0045] See Figure 1A The extension direction of conductor 1 can be serpentine. For example, the line width W of conductor 1... S The span T of conductor 1 can be 60μm. S The length L of the straight segment in conductor 1 can be 0.52 mm. S It can be 0.26mm.

[0046] The wire 1 includes a conductive portion 11 and an encapsulation portion 12 encapsulated on the outside of the conductive portion 11. Exemplarily, the conductive portion 11 may be made of copper, gold, or the like, but copper is preferred. The encapsulation portion 12 may be made of polyimide (PI) or the like.

[0047] See Figure 1B In one embodiment of this application, the wire 1 can be a sandwich structure of encapsulation portion 12-conductive portion 11-encapsulation portion 12. Exemplarily, the thickness t of the top or bottom encapsulation portion 12... 12 The thickness t of the conductive part 11 can be 25 μm. 11 It can be 0.7μm. This is understandable, given the linewidth W of conductor 1. S In the direction, the width of the conductive part 11 is smaller than the line width W of the conductor 1. S To prevent the conductive part 11 from being exposed to the outside world.

[0048] For example, taking copper as the material of the conductive part 11 and polyimide as the material of the encapsulation part 12, this application provides a method for manufacturing a wire 1, which includes:

[0049] (1) First, a sacrificial layer is spin-coated onto the silicon wafer;

[0050] (2) After the sacrificial layer has cured, a layer of PI (polyimide) precursor solution is spin-coated and the PI is cured into a film by heat baking, thereby forming the bottom layer PI in the sandwich structure. Its thickness can generally be from a few micrometers to tens of micrometers.

[0051] (3) Using metal thin film growth equipment, such as electron beam evaporation equipment, a copper Cu (copper) thin film is grown on the underlying PI, and its thickness can generally be several hundred nanometers.

[0052] (4) Using a common photolithography process, the metal thin film is patterned to create the designed serpentine wire shape;

[0053] (5) Spin-coat another layer of PI precursor solution and cure it into a thin film by hot baking. This layer of PI is the top layer of the three-layer wire, and its thickness is generally the same as that of the bottom layer of PI.

[0054] (6) Another layer of metal is grown on the top PI layer and processed by photolithography. The shape is generally a pattern similar in size to the copper wires, which serves as a mask for etching.

[0055] (7) Using dry etching, such as reactive ion etching equipment, all PI in the three-layer wire except for the area covered by the top metal mask is removed. Then, a metal etching solution can be used to remove the metal above the top PI layer, thus obtaining a PI-Cu-PI three-layer wire structure; and

[0056] (8) Dissolve the sacrificial layer, and the completed PI-Cu-PI three-layer wire can be released from the silicon wafer and removed.

[0057] The grid base 2 serves as the supporting base for conductor 1. (See also...) Figure 2A The mesh in mesh base 2 can be horseshoe-shaped. See also Figure 2B The grid base 2 includes an array of repeating base units 23, which are horseshoe-shaped (U-shaped) edges. See also... Figure 2C When the base repeating unit 23 is stretched, it will first be stretched into a triangle. The stress-strain curve at this stage is relatively flat. After the base repeating unit 21 is further stretched, its structure itself is elongated. At this time, the stress-strain curve is relatively steep. That is, the stress-strain curve of its stretching process presents a "J" shape, which matches the mechanical properties of human skin.

[0058] The grid substrate 2 is the main load-bearing object. The thickness of the wire 1 set in the grid substrate 2 (the relative position and connection method of the wire 1 and the grid substrate 2 are described later) is less than 1 / 100 of the thickness of the grid substrate 2. The influence of the wire 1 on the stress-strain curve can be ignored, so that the mechanical properties exhibited by the flexible electronic device are consistent with those of the grid substrate 2.

[0059] Flexible electronic devices are biomechanically compatible with human skin, resulting in smaller measurement errors and higher wearing comfort. The material of the mesh substrate 2 can be, but is not limited to, polyimide. The mesh shape of the mesh substrate 2 is also not limited to horseshoe shape; for example, it can also be triangular, hexagonal, etc.

[0060] The mesh substrate 2, also known as the encapsulation substrate of the wire 1, may include a top mesh substrate 21 and a bottom mesh substrate 22, and the wire 1 may be encapsulated between the top mesh substrate 21 and the bottom mesh substrate 22.

[0061] Pads 3 can be provided at both ends of the conductor 1 and on the mesh substrate 2, and vias 31 can be provided in the pads 3. The flexible electronic device may include multiple conductors 1, and the conductors 1 can be physically and electrically connected by soldering to each other via the pads 3. The conductors 1 and the mesh substrate 2 can also be physically connected by soldering to each other via the pads 3. For example, the pads 3 can be fixed by solder paste or other solder paste injected into the vias 31. The pads 3 can be connected to the conductive portion 11 of the conductor 1, or they can be etched and manufactured together with the patterned conductive portion 11.

[0062] Exemplarily, this application provides an integrated assembly method for a wire 1 and a mesh substrate 2, comprising:

[0063] (S1) See also Figure 4A , Figure 4B The bottom grid substrate 22 is supported on a plane by a PDMS (polydimethylsiloxane) block 51 of appropriate size. Generally, the other side of the PDMS can be placed on a glass slide.

[0064] (S2) See also Figure 4C , Figure 4D Take another PDMS block 52 that is the same size as wire 1 as the transfer stamp, and attach the wire 1 to be assembled to this stamp.

[0065] (S3) See also Figure 4E , Figure 4FAlign the PDMS block 52 containing the conductor 1 with the PDMS block 51 of the mesh substrate 2 under a microscope. After alignment, press the two together and remove the PDMS block 52 from the conductor 1. At the same time, apply solder paste to the via 31 of the opposite pad 3 of the conductor 1 and the bottom mesh substrate 22, and heat and solder using a hot plate.

[0066] (S4) Participate in Figure 4G , Figure 4H Repeat step (S1) to mount the top mesh substrate 21 onto another PDMS block. Using a method similar to step (3), align the top mesh substrate 21 with the conductor 1-bottom mesh substrate 22. Then, remove the PDMS block of the top mesh, apply solder paste, and heat and solder it using a hot plate. This completes the packaging system of top mesh substrate 21-conductor 1-bottom mesh substrate 22.

[0067] (S5) If there are multiple wires that need to be welded in a plane, repeat step (S2) after step (S2) until all wires that the grid base needs to support are welded and fixed, and then proceed to steps (S3) and (S4).

[0068] It is understandable that PDMS blocks can be replaced by other flexible blocks.

[0069] When conductor 1 is deformed under stress, its out-of-plane deformation can be accommodated by the mesh pores of the mesh substrate 2. Compared with the traditional solid encapsulation method of PDMS silicone rubber, this application reduces the restriction of the substrate on the deformation of the conductor, so that the elongation of the encapsulated conductor is close to the free elongation of the unencapsulated conductor, ultimately improving the elongation of the flexible electronic device.

[0070] See Figure 5 The elongation results obtained from finite element analysis show that the effective elongation of the wire 1 encapsulated in traditional PDMS solid-state packaging is 5%-5.5% (when the elongation is 5%, the number of tensile cycles exceeds 10,000; when the elongation is 5.5%, the number of tensile cycles reaches 9,000, which can be considered as an effective elongation of 5%-5.5%). However, the effective elongation of the wire 1 encapsulated using the mesh substrate 2 of this application is 47% (when the elongation is 50%, it breaks after 2,500 tensile cycles; when the elongation is 45%, the number of tensile cycles exceeds 10,000, which can be considered as an effective elongation of 45%-50%, for example, an elongation of 47% that can withstand 5,500 cycles). Therefore, this application demonstrates superior performance in improving elongation.

[0071] In addition, the mesh base 2 has good breathability, and when the integrated electronic component 4 (described later) detects human body temperature, humidity and other factors, the detection is more accurate and the wearing comfort is better.

[0072] In flexible electronic devices, the wire 1 can be distributed in a single layer or in multiple layers.

[0073] See Figure 3 For flexible electronic devices with a single-layer conductor, the general form is that a conductor 1 is encapsulated by two layers of mesh substrate 2.

[0074] When the conductors are multilayered, the structure can be a multilayer flexible electronic device consisting of a first-layer grid substrate 2 - a first-layer conductor 1 - a second-layer grid substrate 2 - a second-layer conductor 1... a nth-layer grid substrate 2 - a nth-layer conductor 1 - a (n+1)th-layer grid substrate 2. This layered design significantly improves the integration density of the flexible electronic device.

[0075] See Figure 6A , Figure 6B Taking a five-layer conductor 1 as an example, this application illustrates the distribution of the five layers of conductor 1. It is understood that the sixth layer, the mesh substrate 2, is not shown in the figure. Each layer of conductor 1 can undergo relatively free out-of-plane deformation, which is accommodated by the pores of the mesh substrate 2, thereby alleviating stress concentration in the conductor 1. This allows for increased device integration through multi-layer stacking without affecting device ductility, achieving a balance between device integration and ductility.

[0076] See Figure 7A Flexible electronic devices may also include surface-mount capacitors, surface-mount resistors, surface-mount inductors, or chips, etc., as electronic components 4. The thickness of electronic components 4 is generally in the millimeter range, commonly 0.3 mm. The thickness of the conductive wire 1 is generally in the micrometer range, for example, 50 μm-90 μm. That is, the thickness of electronic components 4 is much greater than the thickness of conductive wire 1 (conductive layer).

[0077] See Figure 7B In order to provide sufficient installation space for electronic component 4, small connectors 6 (such as small cylinders obtained by cutting silver wire with a diameter of 0.1 mm) can be used to connect and fix wires 1 and grid base 2 by welding.

[0078] For larger chips, such as microcontroller unit chips, the thickness is typically between 0.5 mm and 0.8 mm. To accommodate such a thick electronic component 4 arranged on the i-th layer of conductive lines 1, the electronic component 4 can be designed to be arranged either facing forward (e.g., upward) or backward (e.g., downward) on the i-th layer of structured conductive lines. Simultaneously, a hole of the same size as the electronic component 4 is formed in the (i+1)-th layer of mesh substrate or the i-th layer of mesh substrate, using this hole to accommodate the electronic component 4. The advantage of this design is that it can fully utilize the vertical space of flexible electronic devices, further improving the integration density of flexible electronic devices.

[0079] This application increases the elongation of flexible electronic devices while ensuring a relatively high degree of integration, achieving a mechanical fit between flexible electronic devices and skin.

[0080] The above description is the preferred embodiment of this application. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. An inorganic flexible electronic device based on a grid substrate, characterized in that, include: A conductor (1) includes a conductive portion (11) and an encapsulation portion (12) encapsulated outside the conductive portion (11). In the width direction of the conductor (1), the width of the conductive portion (11) is smaller than the line width of the conductor (1) to prevent the conductive portion (11) from being exposed to the outside. A grid base (2) is provided on the grid base (2). The wire (1) is disposed on the grid base (2). The inorganic flexible electronic device includes two grid substrates (2), and a wire (1) is disposed between the two opposing grid substrates (2) such that the wire (1) is encapsulated via the grid substrates (2), and the wire (1) is not encapsulated by a polydimethylsiloxane solid. The inorganic flexible electronic device includes multiple layers of the grid substrate (2) and multiple layers of the conductive wires (1), wherein the grid substrate (2) and the conductive wires (1) constitute a multilayer structure of first layer grid substrate - first layer conductive wire ... nth layer grid substrate - nth layer conductive wire - n+1th layer grid substrate, where n > 1. The inorganic flexible electronic device also includes a connector (6), the spacing between the conductor (1) and the grid substrate (2) is controlled by the connector (6), and the connector (6) is welded to the conductor (1) and the substrate (2).

2. The inorganic flexible electronic device based on a grid substrate according to claim 1, characterized in that, The material of the conductive part (11) includes at least one of copper and gold; and / or the material of the encapsulation part (12) is polyimide.

3. The inorganic flexible electronic device based on a grid substrate according to claim 1, characterized in that, The grid base (2) includes an array of base repeating units (23), the base repeating units (23) being U-shaped.

4. The inorganic flexible electronic device based on a grid substrate according to claim 1, characterized in that, Both the conductor (1) and the mesh substrate (2) are provided with pads (3), and the conductor (1) is soldered to the mesh substrate (2) through the pads (3).

5. The inorganic flexible electronic device based on a grid substrate according to claim 1, characterized in that, Includes electronic component (4), the electronic component (4) is connected to the conductive part (11) of the wire (1) of the i-th layer, and the grid substrate (2) of the i+1-th layer or the grid substrate (2) of the i-th layer is provided with an opening that can accommodate the electronic component (4).

6. An integration method for inorganic flexible electronic devices based on a grid substrate, characterized in that, The inorganic flexible electronic device is the inorganic flexible electronic device according to any one of claims 1 to 5, and the integration method includes: Obtain the top-level mesh base (21), the bottom-level mesh base (22), the first flexible block, the second flexible block, the third flexible block, and the wire (1); The bottom mesh base (22) is placed on the first flexible block; The wire (1) to be assembled is attached to the second flexible block; Align the second flexible block containing the wire (1) with the first flexible block containing the bottom mesh substrate (22) under a microscope, remove the wire (1), and weld the wire (1) to the bottom mesh substrate (22). The top mesh substrate (21) is supported on the third flexible block, the top mesh substrate (21) and the bottom mesh substrate (22) are aligned, the wire (1) is located between the two mesh substrates, then the third flexible block is removed, and the top mesh substrate (21) is welded to the wire (1).

7. The integration method for inorganic flexible electronic devices based on a grid substrate according to claim 6, characterized in that, Also includes: The inorganic flexible electronic device includes a plurality of the wires (1), which are welded and fixed together.

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