Stretchable electrical interconnects, flexible electronic systems, and methods of making same

Abstract

A stretchable electrical interconnect includes a curved wall longitudinally stretchable toward two ends of the curved wall, where the curved wall has a height extending perpendicular to a plane in which the two ends of the curved wall extend, and where the two ends of the curved wall are configured to be connectable to one or more electronic devices.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 593,235 filed on October 25, 2023. Technical Field

[0003] The present application relates broadly, but not exclusively, to stretchable electrical interconnects, flexible electronic systems, and methods of making the same. Background Art

[0004] Bent electronics (also referred to herein as flexible electronic systems) are rapidly developing due to their ability to conform to non-flat surfaces, providing flexibility and durability that rigid electronics cannot offer. These qualities make them ideal for a variety of applications such as wearable devices, smart lenses, flexible displays, and soft robotics.

[0005] Two main fabrication approaches have emerged: direct fabrication on curved surfaces using techniques like inkjet printing and 3D printing, and converting 2D devices into curved forms. The latter, although more complex, can result in better performance and stretchability, which is critical for complex surfaces with non-zero Gaussian curvature.

[0006] Stretchability can be achieved by using inherently stretchable materials or by incorporating stretchable structures. The first approach usually results in lower conductivity, while the second involves structural designs such as wavy or serpentine shapes that provide flexibility but can introduce mechanical stress. Despite advances, existing approaches still face limitations in long-term performance and industrial scalability.

[0007] After fabrication, converting planar devices into curved forms remains a challenge. Techniques like pre-stretching elastomers or using conformal additive stamping have been proposed, but suffer from drawbacks such as material fatigue or positional distortion. Origami-based approaches offer another solution by folding 2D tessellations into 3D shapes, but this approach can result in undesirable angles and limited application scenarios.

[0008] Therefore, there is a need to provide material and / or structural solutions and manufacturing methods for curved electronic devices that seek to overcome or at least minimize the above-mentioned problems related to stretchability, durability, scalability and long-term performance in order to fully realize the potential of curved electronic devices in different applications. Summary of the invention

[0009] According to one aspect of the present disclosure, a stretchable electrical interconnect is provided. The stretchable electrical interconnect comprises a curved wall that can be longitudinally stretched toward two ends of the curved wall, wherein the curved wall has a height extending perpendicular to a plane, the two ends of the curved wall extend in the plane, and wherein the two ends of the curved wall are configured to be connectable to the one or more electronic devices.

[0010] According to another aspect of the present disclosure, a flexible electronic system is provided. The flexible electronic system includes one or more electronic devices, and one or more stretchable electrical interconnects connecting the one or more electronic devices, wherein each of the one or more stretchable electrical interconnects includes a curved wall that can be longitudinally stretched toward two ends of the curved wall, wherein the curved wall has a height extending perpendicular to a plane, the two ends of the curved wall extend in the plane, and wherein the two ends of the curved wall are connected to the one or more electronic devices.

[0011] According to another aspect of the present disclosure, a method for manufacturing a flexible electronic system is provided, the method comprising: providing a silicon wafer, wherein a top oxide layer is formed on the top surface of the silicon wafer, and wherein a bottom oxide layer is formed on the bottom surface of the silicon wafer; depositing two electrode metal layers on the top oxide layer of the silicon wafer, with an insulating layer between the two electrode metal layers to form one or more electrodes; patterning and etching the two electrode metal layers, the insulating layer between the two electrode metal layers, the top oxide layer and the silicon wafer to form one or more grooves in the silicon wafer; sequentially depositing a first polymer layer, a metal layer, and a second polymer layer to fill the one or more grooves to form one or more stretchable electrical interconnects; and bonding one or more electronic devices to the one or more electrodes to form a flexible electronic system in a planar form, wherein each of the stretchable electrical interconnects is a curved wall that can be longitudinally stretched toward two ends of the curved wall, wherein the curved wall has a height extending perpendicular to a plane, two ends of the curved wall extend in the plane, and wherein the two ends of the curved wall are connected to the one or more electronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The embodiments and implementations are provided by way of example only and will be better understood and apparent to those of ordinary skill in the art from the following written description read in conjunction with the accompanying drawings, in which:

[0013] Figure 1 Illustrated is a schematic diagram 100 depicting an embodiment of a stretchable electrical interconnect 102 according to the present application. Figure 1Also shown is an embodiment of a flexible electronic system 104 incorporating a stretchable electrical interconnect 102 in accordance with the present application. For simplicity, the flexible electronic system 104 is interchangeably referred to as a "flexible electronic device" in this disclosure.

[0014] Figure 2 A series of images representing an embodiment of a stretchable electrical interconnect 102 under varying stretch conditions ranging from 0% to 4000% are presented. The images demonstrate that the stretchable electrical interconnect 102 maintains its structural integrity under significant elongation.

[0015] Figure 3 A graph 300 is provided that depicts the change in relative resistance when increasing strain from 0% to 4000% is applied to two embodiments of the stretchable electrical interconnect 102. The graph 300 indicates that the stretchable electrical interconnect 102 maintains its electrical properties under considerable strain.

[0016] Figure 4 A graph 400 illustrating the relative resistance change of the stretchable electrical interconnect 102 during cyclic stretching between ε=0% and ε=3000% over 20,000 cycles is shown. The graph 400 demonstrates the long-term repeatability and durability of the stretchable electrical interconnect 102.

[0017] Figure 5A A flow chart 500 illustrating a method of manufacturing the flexible electronic system 104 according to an embodiment is shown.

[0018] Figure 5B A flow chart 550 illustrating a method of manufacturing the flexible electronic system 104 according to another embodiment is shown.

[0019] Fig. 6A Structural and material details of an embodiment of a flexible electronic system 600 are illustrated, wherein one or more electronic devices include an 8×8 array of LED chips.

[0020] Figure 6B A 3D schematic diagram 650 of an embodiment of a flexible electronic system 600 is depicted.

[0021] Fig. 7A A photograph of a flexible electronic system 700 is shown, where the flexible electronic system 700 is an 8×8 LED array connected by stretchable electrical interconnects 102 .

[0022] Figure 7B is a scanning electron microscope (SEM) image showing the stretchable electrical interconnects 102 between functional island nodes (in this embodiment, LED chips) in the flexible electronic system 700.

[0023] Figure 7C Provided by Figure 7BA magnified image of a portion of the stretchable electrical interconnect 102.

[0024] Fig.7D A photograph of a flexible electronic system 700 wrapped around a finger is shown.

[0025] Fig. 7E and Figure 7F It is shown that due to the stretchable electrical interconnect 102, the flexible electronic system 700 bends in different directions while maintaining its structural integrity and electrical properties.

[0026] Figure 8 An embodiment of a conformal vacuum transfer printing (CVTP) method 800 for transferring a flexible electronic system onto a curved surface is shown. Figure 5A Once the illustrated method 500 has manufactured the flexible electronic system 104 in a planar form, the method 800 may be performed.

[0027] Fig.9A Shown according to Figure 5A , Figure 5B and / or Figure 8 An embodiment of a flexible electronic system 900 conforming to a hemispherical surface is fabricated using the method illustrated in FIG. 1 . In this embodiment, the flexible electronic system 900 is an 8×8 LED array connected by stretchable electrical interconnects 102 . Fig.9D FIG. 9 shows a partial enlarged view of the flexible electronic system 900 , and FIG. Figure 9G The system is shown with all LEDs lit.

[0028] Fig. 9B Shown according to Figure 5A , Figure 5B and / or Figure 8 An embodiment of a flexible electronic system 910 conforming to a saddle-shaped surface manufactured by the method illustrated in FIG. The flexible electronic system 910 is also an 8×8 LED array connected by stretchable electrical interconnects 102 . Fig.9E An enlarged partial view of flexible electronic system 910 is shown.

[0029] Fig. 9C Shown according to Figure 5A , Figure 5B and / or Figure 8 An embodiment of a flexible electronic system 920 that conforms to an irregular curved surface is fabricated using the method illustrated in FIG. 9A . In this embodiment, the flexible electronic system 920 is an 8×8 LED array connected by stretchable electrical interconnects 102 . Fig.9F An enlarged partial view of flexible electronic system 920 is shown.

[0030] Figure 9H , Fig.9I , Figure 9J , Figure 9K and Figure 9L An embodiment of a flexible electronic system is presented in which the LED chips form the letters H, K, U, S and T respectively.

[0031] Fig. 10A and Fig. 10B Finite element analysis (FEA) simulation results 1000a and 1000b depicting the stress distribution of the flexible electronic system 900 when conforming to a hemispherical surface are shown.

[0032] Fig. 10C and Fig. 10D FEA simulation results 1000c and 1000d depicting stress distribution in the flexible electronic system 910 when conforming to a saddle-shaped surface are shown.

[0033] It will be appreciated by those skilled in the art that the elements in the drawings are illustrated for simplicity and clarity and are not necessarily depicted to scale. For example, the dimensions of some of the elements in the diagrams, block diagrams, or flow charts may be exaggerated relative to other elements to help improve understanding of the present embodiment. DETAILED DESCRIPTION

[0034] Embodiments of the present invention will be described by way of example only with reference to the accompanying drawings. Like reference numerals and characters used in the drawings correspond to like elements or equivalents throughout.

[0035] The present disclosure provides stretchable electrical interconnects and flexible electronic systems incorporating flexible and stretchable interconnects that maintain structural integrity and electrical performance on curved surfaces, under varying elongation, bending, and conformational conditions. The disclosed embodiments enable the development of flexible electronic systems (interchangeably referred to as "flexible electronic systems") for flexible applications such as wearable electronics, soft robotics, and flexible displays.

[0036] Figure 1 A schematic diagram 100 of an embodiment of a stretchable electrical interconnect 102 is illustrated. This figure also depicts an embodiment of a flexible electronic system 104 incorporating the stretchable electrical interconnect 102.

[0037] In this embodiment, the stretchable electrical interconnect 102 includes a curved wall W that can be stretched longitudinally L toward its two ends. Figure 1 , the curved wall W has a height H extending perpendicularly from a plane P defined by two ends of the wall. These ends are configured to be connected to one or more electronic devices 106. The stretchable nature of the curved wall W allows it to conform to non-planar geometries, which is beneficial in applications requiring adaptation to dynamic or complex surfaces.

[0038] The vertical height H of the curved wall W enables 3D bending, both out-of-plane bending and in-plane bending relative to the plane P. Such three-dimensional flexibility enhances the versatility of the stretchable electrical interconnect 102, allowing the stretchable electrical interconnect 102 to adapt to various surface topologies (such as convex or concave surfaces) while maintaining electrical and mechanical performance.

[0039] The height H imparts a 3D geometry to the curved wall W. In some embodiments, the 3D geometry is serpentine, providing enhanced stretchability by evenly distributing mechanical strain across the entire structure. This design minimizes stress concentration at the arcuate region during deformation, thereby improving the mechanical and electrical performance of the interconnect compared to in-plane serpentine structures known in the art. It will be appreciated by those skilled in the art that the curved wall W is not limited to a serpentine geometry; any 3D structure incorporating curved regions to achieve flexibility and stretchability is contemplated.

[0040] When the stretchable electrical interconnect 102 is applied on a flat surface, the plane P is horizontal and the vertical curved walls W are arranged vertically, resulting in a vertical serpentine geometry. The vertical serpentine structure allows the height H of the wall to extend vertically relative to the plane p. In such embodiments, the interconnect 102 can be referred to as a vertical serpentine conductor (VSC), and the associated flexible electronic system 104 can be referred to as a VSC interconnected functional device.

[0041] Those skilled in the art will appreciate that, when applied to curved surfaces, plane P may not be horizontal and the vertical arrangement of curved walls W may not be strictly vertical.

[0042] The curved wall W has a thickness including a conductive metal layer sandwiched between two insulating polymer layers. Preferably, the polymer layer made of polyparaxylene (e.g., polyparaxylene C) provides flexibility, durability, and uniformity. The metal layer is strategically positioned near the mechanical neutral plane to minimize strain during mechanical deformation, thereby improving durability and reducing material fatigue.

[0043] In certain embodiments, the vertical serpentine geometry of the interconnect 102 has a bend radius of 30 micrometers (μm) in the arc region, with a height H of 50 μm. This configuration balances mechanical flexibility and conductivity, ensuring that the interconnect 102 can withstand repeated mechanical stresses without degradation of performance. It will be appreciated by those skilled in the art that variations in radius or height may be achieved to meet specific application requirements without sacrificing flexibility or conductivity.

[0044] The stretchable electrical interconnect 102 is integrated with the flexible electronic system 104. Figure 1, system 104 includes one or more electronic devices 106 connected by interconnects 102. Each interconnect features a curved wall structure, allowing the system to conform to various curved surfaces while maintaining electrical connections. This is particularly advantageous for applications like wearable electronics where the system must adapt to the contours of a user's body or other dynamic surfaces.

[0045] In some embodiments, the flexible electronic system 104 is designed to be applied on a curved surface (such as a spherical or saddle-shaped substrate). The system can stretch, bend, and conform without affecting electrical performance, making it well suited for a variety of applications, including wearable electronics, soft robotics, flexible displays, and energy harvesting devices. Due to these properties, flexible electronic systems are also referred to as bendable or bendable electronic systems. FIG. 9A to FIG. 9L An example of such an application is depicted. That is, when applied to a curved surface, the flexible electronic system 104 conforms to the curvature of the surface, thereby becoming a curved system. It will be appreciated by those skilled in the art that when applied to a flat surface, the flexible electronic system 104 may not exhibit any curvature and may remain flat.

[0046] Figure 2 A series of images depicting a stretchable electrical interconnect 102 under various stretching conditions ranging from 0% to 4000% elongation are illustrated. The images demonstrate that, even under significant elongation, the interconnect 102 maintains its structural integrity.

[0047] In this embodiment, the stretchable electrical interconnect 102 has an initial length of 5 millimeters (mm) and exhibits excellent stretchability, maintaining its structural integrity at elongation levels of 800%, 1600%, 2400%, 3200%, and up to 4000% of its original length. Such a degree of stretchability is particularly advantageous for applications that require the interconnect to withstand large mechanical deformations, such as wearable electronics, where both flexibility and durability are critical for reliable operation.

[0048] Figure 3 A graph 300 is provided that illustrates the relative change in resistance of two embodiments of the stretchable electrical interconnect 102 when subjected to increasing strain from 0% to 4000%.

[0049] In the graph 300, two interconnects are labeled as conductor 1 and conductor 2. Their relative resistance changes under applied strains of 0%, 200%, 1000%, 1500%, 2000%, 2500%, 3000%, 3500%, and 4000% are represented by square and circle marks, respectively. The results indicate that the stretchable electrical interconnect 102 can maintain its electrical properties even under significant strain.

[0050] Figure 4A graph 400 illustrating the relative resistance change of the stretchable electrical interconnect 102 during cyclic stretching between 0% and 3000% strain over 20,000 cycles is depicted. The graph demonstrates the long term durability and repeatability of the interconnect 102.

[0051] The flexible electronic system 104 can be manufactured using various methods. For example, Figure 5A A flow chart of a method 500 for manufacturing the system 104 according to one embodiment is illustrated. The method 500 employs a silicon-based micro-electromechanical system (MEMS) manufacturing process.

[0052] Step 502 of method 500 includes providing a silicon wafer, wherein a top oxide layer is formed on a top surface of the silicon wafer, and wherein a bottom oxide layer is formed on a bottom surface of the silicon wafer.

[0053] Step 504 involves depositing two electrode metal layers on the top oxide layer of the silicon wafer with an insulating layer between the two electrode metal layers to form one or more electrodes.

[0054] Step 506 involves patterning and etching the two electrode metal layers, the insulating layer between the two electrode metal layers, the top oxide layer, and the silicon wafer to form one or more grooves in the silicon wafer.

[0055] In step 508, method 500 involves sequentially depositing a first polymer layer, a metal layer, and a second polymer layer to fill one or more grooves to form one or more stretchable electrical interconnects. As described above, each interconnect includes a longitudinally stretchable curved wall, wherein the height of the interconnect extends perpendicular to the plane of two ends of the wall. The two ends are configured to be connected to an electronic device.

[0056] Step 510 involves bonding one or more electronic devices to one or more electrodes to form a flexible electronic system in a planar form.

[0057] In some embodiments, prior to step 504 , method 500 may include a step of patterning the bottom oxide layer to configure one or more regions of the bottom surface of the silicon wafer.

[0058] In some embodiments, the method 500 further comprises:

[0059] Obtaining a flexible electronic system using a thin polymer film, wherein the edges of the thin polymer film are fixed by an acrylic ring; and

[0060] The flexible electronic system is printed onto a curved surface within a vacuum chamber, wherein an edge of the thin polymer film is brought into close contact with the vacuum chamber and the remaining portion of the thin polymer film is stretched to transfer the flexible electronic system onto the curved surface.

[0061] As described above, method 500 begins with preparing a silicon wafer that is processed to form oxide layers on both surfaces. In some embodiments, the bottom oxide layer is patterned to act as a mask for a subsequent etching process. A metal electrode layer is deposited on the top oxide layer with an insulating layer between the two metal electrode layers to form an electrode.

[0062] The electrodes, insulating layer, top oxide layer and silicon wafer are patterned and etched to form grooves. These grooves are filled by sequentially depositing a first polymer layer, a metal layer and a second polymer layer to form stretchable interconnects. The final step involves bonding the electronics to the electrodes, resulting in a planar flexible electronic system with stretchable interconnects.

[0063] After fabrication of a planar system, it can be transferred to a curved surface using conformal vacuum transfer printing (CVTP). Figure 8 An exemplary CVTP method 800 for transferring a flexible system onto a curved surface via a polymer film stretched within a vacuum chamber is depicted in FIG.

[0064] Figure 5B A flow chart is depicted of another MEMS manufacturing method 550 for producing a flexible electronic system 104 using a double-side polished silicon wafer with 3 micron thick thermal oxide on both sides.

[0065] In step 552, a silicon wafer with oxide layers on both surfaces is prepared, and step 554 uses photolithography to pattern the oxide layer on the reverse side, which serves as a mask for the subsequent etching process. The photolithography process involves deposition of adhesion promoter, spin coating of photoresist, UV exposure, development, and hard baking.

[0066] Thereafter, the reverse silicon oxide layer is etched using a dry etching process. An O2 plasma is applied to remove any remaining photoresist.

[0067] Step 556 includes depositing and patterning a bottom electrode metal layer on the front side of the silicon wafer. The deposition is performed at a high sputtering rate, followed by patterning via photolithography and wet etching.

[0068] In step 558, a thin insulating layer of silicon dioxide is deposited between the metal layers using a high deposition rate plasma enhanced chemical vapor deposition (PECVD) process.

[0069] In step 560, a second electrode metal layer is deposited on top of the insulating layer and patterned.

[0070] In step 562, three-dimensional deep trenches are etched in the silicon wafer to form stretchable interconnects. Photolithography, dry etching, and deep reactive ion etching (DRIE) processes are used to form the grooves with highly anisotropic profiles.

[0071] Step 564 involves depositing a first Parylene-C layer onto the front side of the wafer. The surface treatment process improves the adhesion between the silicon wafer and the Parylene-C layer to ensure uniform deposition.

[0072] In step 566, the sprayed photoresist layer is applied as a mask layer for subsequent metal layer openings, followed by exposure, development, and etching processes.

[0073] Step 568 involves depositing additional metal layers to interconnect the island nodes 576. In step 570, a second Parylene-C layer is deposited and patterned in step 572 to encapsulate and protect the internal functional layers. In silicon-based MEMS manufacturing, "islands" refer to discrete, isolated areas of material that are structurally independent of the surrounding substrate. These islands, also referred to as island nodes 576 in this application, serve as electrically functional areas for bonding and encapsulating electronic devices (such as LED chips) in the flexible electronic system 104.

[0074] Thereafter, in step 574, the silicon wafer is dry etched from the back side. The oxide layer patterned in step 554 is used as a mask during this etching. Both a deep reactive ion etching (DRIE) system and a reactive ion etching (RIE) system are used in this step to release the stretchable electrical interconnect 102 and the interconnected island nodes 576. During this period, the silicon substrate is also thinned to enhance the flexibility of the system. The DRIE process is performed with alternating passivation and etching cycles, which provides a highly anisotropic etch to ensure the structural integrity of the interconnect while minimizing lateral undercuts.

[0075] Despite Figure 5B Not shown, a manual flip chip bonding tool (such as a FINEPLACER 96 "Lambda") can be used to pick up the LED chip (30 mil x 30 mil) and place it on the island node 576. During this time, a low temperature solder paste is used to maintain the mechanical properties of the Parylene-C layer while ensuring proper electrical connection.

[0076] Fig. 6A A detailed illustration of the structural composition of the flexible electronic system 600 is provided, showing an 8×8 array of LED chips interconnected by stretchable electrical interconnects 652. Figure 6B A 3D schematic 650 of a flexible electronic system 600 is shown, demonstrating how a stretchable electrical interconnect 652 enables the system to conform to curved surfaces while maintaining electrical performance.

[0077] like Fig. 6AAs shown in FIG. 6 , the flexible electronic system 600 is composed of functional silicon island nodes interconnected by stretchable electrical interconnects 652. These island nodes serve as bonding points for 8×8 LED chips to form an LED array display device. The interconnects 652 provide mechanical flexibility and are designed to maintain conductivity even under mechanical stress. Fig. 6A The material composition and structural layering of the 8×8 LED array device are also highlighted, illustrating the functional elements that enable its bendability and reliability.

[0078] As described in step 556 and Figure 5B As depicted in , the manufacturing process involves forming silicon islands 576, 656 that serve as functional carriers to house electronic devices. These islands or island nodes may also be referred to as silicon-based functional carriers. Photolithography and etching processes are used to define an oxide layer as a mask on the back side of the wafer. The passive matrix configuration of the LED array allows individual control of the LEDs, where three metal layers form the electrical interconnects between the anode, cathode, and island nodes.

[0079] After defining the electrode pads for the LEDs on the silicon islands, grooves approximately 10 μm wide and 40 μm to 50 μm deep are patterned using DRIE to form stretchable electrical interconnects 102, 652 between the island nodes 576, 656. The grooves are filled by depositing successive layers of parylene-C, metal, and parylene-C. The first parylene-C layer is deposited at the bottom, while the metal layer is positioned near the neutral mechanical plane to improve mechanical robustness. A second parylene-C layer is then deposited to encapsulate the metal and protect the interconnects. Photolithography and reactive ion etching (RIE) are used to define and pattern both the parylene-C and oxide layers.

[0080] The silicon is then etched from the back side of the wafer using DRIE and RIE in sequence, releasing the stretchable electrical interconnects 102, 652 and the interconnected silicon-based functional carrier 656.

[0081] Once the interconnect 652 has been released, the LED chip 654 is bonded to the electrode pads on the island node 656 using pick and place techniques to ensure precise alignment and connectivity.

[0082] Figure 6B A 3D schematic diagram 650 of a silicon-based functional carrier (island node) 656 bonded to each LED chip 654 is shown. Multiple stretchable electrical interconnects 652 are used to connect the island nodes 656. In this embodiment, the interconnects 652 are designed to be redundant to improve system reliability. In future applications, these interconnects can also serve as data connections for more complex circuits.

[0083] Fig. 7AA photograph is provided of a flexible electronic system 700 featuring a 22 mm x 22 mm display including an 8 x 8 LED array connected by stretchable electrical interconnects 102 .

[0084] Figure 7B is a scanning electron microscope (SEM) image showing the stretchable electrical interconnect 102 between functional island nodes in the flexible electronic system 700, with an LED chip (Bridgelux BXDA, 40 mil×40 mil) bonded thereto. Figure 7C An enlarged view of the stretchable interconnect 102 is provided. Fig.7D A photograph of a flexible electronic system 700 wrapped around a finger is shown. Fig. 7E and Figure 7F The system is illustrated being bent in various directions, demonstrating its ability to maintain structural integrity and electrical properties during significant deformation.

[0085] like 7A to 7F As depicted, the flexible electronic system 700 is capable of operating on a variety of curved surfaces. The stretchable electrical interconnects ensure that electrical performance is maintained even under considerable bending and stretching. For example, Fig.7D The adaptability of the system when wrapped around a finger is demonstrated, highlighting its applicability to irregular surfaces while remaining fully functional.

[0086] The flexible electronic system 700 enabled by the stretchable electrical interconnects 102 and 652 provides a robust and flexible solution for applications where electronics need to conform to dynamic and complex surfaces. This is particularly beneficial for wearable devices and other applications that require durability and flexibility to maintain performance during continuous movement and deformation.

[0087] Figure 8 An embodiment of a conformal vacuum transfer printing (CVTP) method 800 for transferring a flexible electronic system onto a curved surface is illustrated. Figure 5A and Figure 5B ), the method is applied after the flexible electronic system 104, 700 has been manufactured in a planar form. In this embodiment, the flexible electronic system 104, 700 is referred to as a functional device.

[0088] In some embodiments, a thin polymer film is used to pick up the flexible electronic system 104, 700 (step 8b) and transfer it to a curved substrate within a vacuum chamber (step 8d). The polymer film is stretched during transfer to ensure accurate placement of the flexible electronic system 104, 700 on the curved surface to minimize distortion or misalignment.

[0089] In the illustrated CVTP method 800, the flexible electronic system 104, 700 is picked up from a planar substrate using a thin polymer film whose edges are fixed by an acrylic ring. As shown in step 8a, the process begins after manufacturing the flexible electronic system 104, 700, which can be manufactured using silicon-based MEMS manufacturing technology, as depicted in methods 500 and 550.

[0090] During picking up as depicted in step 8b, the thin polymer film is fastened to a ring holder, allowing controlled movement. The film is gently lowered until it is in full contact with the flexible electronic system 104, 700, enabling the system to be picked up from the substrate.

[0091] In step 8d, the flexible electronic system 104, 700 is transferred onto the curved surface inside the custom vacuum chamber. Air channels integrated into the chamber allow uniform stretching of the polymer film to ensure that the flexible electronic system is accurately and smoothly placed on the curved mold. Once the system is in full contact with the curved surface, the vacuum chamber is vented, causing the flexible electronic system to remain on the curved surface by means of adhesion to the processing surface (e.g., using uncured polydimethylsiloxane (PDMS)).

[0092] This CVTP method 800 provides an efficient and reliable way to transfer flexible electronics onto non-planar surfaces. It ensures that the system maintains functional integrity after the transfer process, making it ideal for high-precision applications such as biomedical devices where conformity to complex surfaces is critical.

[0093] According to some embodiments, by means of a CVTP method, such as 9A to 9C As shown, the flexible electronic systems 900 , 910 , and 920 can be applied to a variety of curved surfaces, including hemispherical surfaces, saddle-shaped surfaces, and irregular surfaces. FIG. 9D to FIG. 9F The detailed view in Figure 2 shows how the stretchable electrical interconnect allows the system to maintain its structural and electrical integrity when conforming to different surface geometries. Fig.9A As shown in FIG. 1 , the LED array is tightly wrapped around the curved surface, and Fig.9D The enlarged image in reveals the different deformations of the stretchable electrical interconnect 102 in the central area to better adapt to the curved surface.

[0094] exist Fig.9D, the stretchable electrical interconnect 102 in the middle region is in a stretched state, while the stretchable electrical interconnect 102 in the surrounding portion shows a compressed state. The stresses generated on these non-planar surfaces are mitigated by the 3D bending or dual bending capability imparted by the curved walls, which allows both out-of-plane bending (relative to the plane defined by the two ends of the wall) and in-plane bending. This dual bending capability enables the flexible electronic systems described in this application to conform to a variety of complex surface geometries. This adaptability makes the present invention particularly suitable for flexible displays, wearable electronic devices, and other applications where the device must conform to dynamic surfaces while maintaining consistent performance.

[0095] Also presented is a saddle display ( Fig. 9B and Fig.9E ) and irregular curved displays ( Fig. 9C and Fig.9F ) to demonstrate the consistency of flexible electronic systems and the feasibility of CVTP technology. The electronic devices (in this embodiment, LED arrays) can be configured with a passive matrix to drive each device / chip individually and display the designed pattern. Figure 9G shows the system in operation in which all LEDs on the hemispherical surface are illuminated, and Figure 9H , Fig.9I , Figure 9J , Figure 9K and Figure 9L Different configurations of LED arrays that form specific letters and patterns, such as H, K, U, S, and T, are depicted respectively.

[0096] like Fig.9A , Fig. 9B and Fig. 9C As illustrated in , three different concave curved molds can be manufactured by a 3D printer, including a hemispherical mold with a diameter of 2.5 cm, a saddle surface mold with a curvature diameter of 2.5 cm at the saddle point, and an irregular curved surface mold with a size of 2.5 cm×2.5 cm. The corresponding convex curved substrate can be manufactured using a demolding process.

[0097] Fig. 10A and Fig. 10B Finite element analysis (FEA) simulation results 1000a and 1000b depicting the stress distribution of the flexible electronic system 900 when conforming to a hemispherical surface are shown. These results demonstrate that the system can maintain mechanical and electrical properties under deformation.

[0098] Fig. 10C and Fig. 10D FEA simulation results 1000c and 1000d are presented for the flexible electronic system 910 when applied to a saddle-shaped surface. Stress distribution analysis confirms that the system can conform to the surface while maintaining its structural integrity.

[0099] The simulations indicate that the maximum stress occurs at the stretchable electrical interconnect in the central region of the hemispherical surface, with a value of 6.1 MPa ( Fig. 10B For the saddle surface, the maximum stress was observed at the edge, reaching 6.8 MPa ( Fig. 10D These stress values ​​are significantly lower than the tensile strength of copper (approximately 210 MPa), confirming that the stretchable interconnects effectively control stress concentration and enhance the overall reliability of flexible electronic systems under mechanical deformation.

[0100] The present invention provides a robust and flexible solution for stretchable and flexible electronic systems that combines mechanical adaptability with reliable electrical performance. The stretchable electrical interconnect technology described herein addresses the challenge of applying electronic devices to dynamic and irregular surfaces, paving the way for next-generation electronic devices in a variety of applications, including flexible displays, wearable devices, and soft robotics.

[0101] It will be appreciated by those skilled in the art that numerous variations and modifications may be made to the present invention without departing from the scope of the invention as broadly described. Therefore, the embodiments presented herein are illustrative rather than restrictive.

Claims

1. A stretchable electrical interconnect, comprising: a curved wall capable of being stretched longitudinally toward both ends of the curved wall, The curved wall has a height extending perpendicular to a plane, and two ends of the curved wall extend in the plane, and Wherein, the two ends of the curved wall are configured to be connected to one or more electronic devices.

2. The stretchable electrical interconnect according to claim 1, wherein: The curved wall has a vertical serpentine geometry, and the height of the curved wall extends vertically relative to the plane in which both ends of the curved wall extend.

3. The stretchable electrical interconnect according to claim 1, wherein: The curved wall includes a thickness comprising a metal layer sandwiched between two polymer layers.

4. The stretchable electrical interconnect according to claim 3, characterized in that The two polymer layers include parylene.

5. The stretchable electrical interconnect according to claim 3, wherein: The metal layer is located near a mechanical neutral plane.

6. The stretchable electrical interconnect according to claim 1, wherein: When conforming to a curved surface, the curved surface wall is configured to be bendable out of the plane relative to the plane, with both ends of the curved wall extending in the plane.

7. The stretchable electrical interconnect according to claim 1, wherein: The curved wall is configured to be bendable within the plane relative to the plane, and both ends of the curved wall extend in the plane.

8. The stretchable electrical interconnect of claim 1, wherein: The curved wall is configured to stretch up to 4000% of its original length while maintaining structural integrity and electrical performance.

9. The stretchable electrical interconnect according to claim 2, wherein: The vertical serpentine geometry had a radius of 30 micrometers (μm) and a height of 50 micrometers (μm).

10. A flexible electronic system, comprising: one or more electronic devices, and one or more stretchable electrical interconnects connecting the one or more electronic devices, wherein each of the one or more stretchable electrical interconnects comprises: a curved wall capable of being stretched longitudinally toward both ends of the curved wall, The curved wall has a height extending perpendicular to a plane, and two ends of the curved wall extend in the plane, and Wherein, two ends of the curved wall are connected to the one or more electronic devices.

11. The flexible electronic system according to claim 10, characterized in that: The curved wall has a vertical serpentine geometry, and the height of the curved wall extends vertically relative to the plane in which both ends of the curved wall extend.

12. The flexible electronic system according to claim 10, characterized in that: The curved wall includes a thickness comprising a metal layer sandwiched between two polymer layers.

13. The flexible electronic system according to claim 12, characterized in that: The two polymer layers include parylene.

14. The flexible electronic system according to claim 12, characterized in that: The metal layer is located near a mechanical neutral plane.

15. The flexible electronic system according to claim 10, characterized in that: When the flexible electronic system conforms to a curved surface, the curved wall is configured to be able to bend out of a plane relative to the plane, and both ends of the curved wall extend in the plane.

16. The flexible electronic system according to claim 10, characterized in that: The curved wall is configured to be bendable within the plane relative to the plane, and both ends of the curved wall extend in the plane.

17. The flexible electronic system according to claim 10, characterized in that: The curved wall is configured to stretch up to 4000% of its original length while maintaining structural integrity and electrical performance.

18. The flexible electronic system according to claim 11, characterized in that: The vertical serpentine geometry had a radius of 30 micrometers (μm) and a height of 50 micrometers (μm).

19. A method for manufacturing a flexible electronic system, the method comprising: Providing a silicon wafer, wherein a top oxide layer is formed on a top surface of the silicon wafer, and wherein a bottom oxide layer is formed on a bottom surface of the silicon wafer; depositing two electrode metal layers on the top oxide layer of the silicon wafer with an insulating layer between the two electrode metal layers to form one or more electrodes; patterning and etching the two electrode metal layers, the insulating layer between the two electrode metal layers, the top oxide layer, and the silicon wafer to form one or more grooves in the silicon wafer; sequentially depositing a first polymer layer, a metal layer, and a second polymer layer to fill the one or more grooves to form one or more stretchable electrical interconnects; and bonding one or more electronic devices to the one or more electrodes to form the flexible electronic system in a planar form, wherein each of the stretchable electrical interconnects is a curved wall capable of being stretched longitudinally toward both ends of the curved wall, The curved wall has a height extending perpendicular to a plane, and two ends of the curved wall extend in the plane, and Wherein, two ends of the curved wall are connected to the one or more electronic devices.

20. The method according to claim 19, characterized in that Also includes: Obtaining the flexible electronic system using a thin polymer film, wherein the edges of the thin polymer film are fixed by an acrylic ring; and The flexible electronic system is printed onto a curved surface within a vacuum chamber, wherein an edge of the thin polymer film is in close contact with the vacuum chamber and a remaining portion of the thin polymer film is stretched to transfer the flexible electronic system onto the curved surface.

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