Plasma-assisted insulating surface fluid ejection method and applications

Abstract

The application belongs to the technical field of flexible electronic micro-nano manufacturing, and discloses a plasma-assisted insulating surface electrohydrodynamic jetting method and application, which comprises the following steps: modifying the surface of an insulating substrate by using plasma to inject active groups into the surface of the insulating substrate to improve the surface conductivity and bulk conductivity of the insulating substrate, and then performing electrohydrodynamic jetting; wherein the surface of the insulating substrate treated by plasma forms a coral-like structure. The plasma modification treatment changes the micro-nano structure of the surface of the insulating substrate, injects active groups into the surface of the insulating substrate, changes the charge trap energy level distribution of the surface of the insulating substrate, improves the surface conductivity and bulk conductivity of the insulating substrate, these changes inhibit the accumulation of charges on the insulating surface and accelerate the dissipation of charges, eliminate the distortion of the electric field, and thus optimize the electrohydrodynamic jetting effect on the surface of the insulating substrate.

Description

Technical Field

[0001] This invention belongs to the technical field of flexible electronic micro-nano manufacturing, and more specifically, relates to a plasma-assisted electrohydraulic inkjet printing method for insulating surfaces and its application. Background Technology

[0002] With the rapid development of flexible electronics technology, there is a greater demand for the portability, multi-scenario applicability, and wearability of devices. The flexibility, curvature, and stretchability of electronic devices have become inevitable trends. Flexible substrates, as a key component of flexible electronics, mainly include polyethylene naphthalate (PEN), polyimide (PI), polytetrafluoroethylene (PTFE), polymethyl methacrylate (PMMA), polyetherimide (PEI), polyethylene terephthalate (PET), and polyphenylene sulfide (PPS). These materials possess excellent deformability, insulation, flexibility, and strength requirements.

[0003] Electrofluidic inkjet printing, as a new printing technology, uses the electric field between the nozzle and the substrate to print functional materials in a "pulling" manner. It has many advantages, such as achieving submicron resolution, good ink compatibility, and a wider range of material applications. For many fields, such as curved electronics and aircraft skin, the substrate is mostly an insulating material. Electrofluidic inkjet printing of fine structures on insulating material substrates faces two major challenges: (1) The formation of a stable conical jet in electrofluidic inkjet printing requires reaching a critical field strength threshold. However, large insulating substrates have high cross-sections, making it difficult to build a sufficient electric field strength. The deposition of ink on the surface of materials with high dielectric constant will generate charge Coulomb repulsion, affecting the flight direction of the charged jet; (2) The tip discharge generated by the nozzle will cause charge accumulation on the substrate surface, and residual charge will also exist in the printed structure. Both of these will cause spatial electric field distortion and affect the electrofluidic printing process.

[0004] To achieve high-precision, high-resolution printing on insulating substrates, current main methods involve modifying the structure of the electrofluid printing device or controlling the voltage during the printing process. To address these issues, Lee et al. at North Carolina State University integrated a ring electrode below the nozzle, using a high-voltage electric field between the nozzle and the ring-shaped ground electrode to print the jet onto the substrate through the ring electrode. However, in the electric field between the nozzle and the ring-shaped ground electrode, the ejected electrofluid is easily printed onto the ring electrode. Leo Tse at Sungkyunkwan University introduced a method for printing by adding an auxiliary airflow between the printhead and the ground electrode. Yuan-Shin Lee's group at North Carolina State University printed a 20 μm microelectrode structure on a flexible insulating substrate using alternating current (AC) modulation. Yong'an Huang's group at Huazhong University of Science and Technology fabricated an airflow-assisted electrostatic focusing electrofluid printhead, using an outer sheath gas to focus the electrofluid jet, achieving precise printing on curved flexible substrates.

[0005] The above methods have achieved printing on insulating substrates to a certain extent, but their complex control and limited printing materials restrict the further promotion of insulating substrate printing technology. Summary of the Invention

[0006] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a plasma-assisted electrofluid printing method and application for insulating surfaces. By treating the surface of an insulating substrate with plasma, the electrical properties of the substrate surface are improved, increasing the dissipation rate of surface charge and volume charge on the insulating surface, reducing charge accumulation on the insulating surface, and enabling the construction of a stable electric field between the insulating surface and the electrofluid nozzle. This solves the problem of printing complex micro- and nano-structures on insulating substrates.

[0007] To achieve the above objectives, according to one aspect of the present invention, a plasma-assisted electrohydraulic inkjet printing method for insulating surfaces is provided, the method comprising the following steps:

[0008] Plasma is used to modify the surface of the insulating substrate to inject active groups into the surface of the insulating substrate to improve the surface conductivity and bulk conductivity of the insulating substrate, thereby enabling electrofluid printing.

[0009] The surface of the insulating substrate, after plasma treatment, forms a coral-like structure.

[0010] Furthermore, after plasma treatment, irregular nano-sized particles appear on the surface of the insulating substrate to form the coral-like structure on the surface of the insulating substrate.

[0011] Furthermore, the active group is a hydroxyl group.

[0012] Furthermore, the insulating substrate is an insulating ceramic substrate, and the insulating substrate is treated with oxygen plasma for 60 seconds at a power of 150W.

[0013] Furthermore, a nano-silver paste with a viscosity of 100cp was used as the printing ink, a glass needle with an outer diameter of 50μm was used as the printing needle, the printing height was 50μm, and the ink was connected to a 700V DC voltage.

[0014] Furthermore, the process includes a cleaning step of the insulating substrate prior to plasma treatment.

[0015] The present invention also provides a flexible electronic device, which is prepared by the plasma-assisted insulating surface electrofluid printing method described above.

[0016] In summary, compared with the prior art, the plasma-assisted electrohydraulic inkjet printing method and application for insulating surfaces provided by the present invention have the following advantages:

[0017] 1. Plasma modification treatment alters the micro-nano structure of the insulating substrate surface, injects active groups into the surface of the insulating substrate, changes the charge trap energy level distribution on the surface of the insulating substrate, and improves the surface conductivity and bulk conductivity of the insulating substrate. These changes suppress charge accumulation on the insulating surface and accelerate charge dissipation, eliminate electric field distortion, and thus optimize the electrofluid printing effect on the surface of the insulating substrate. The duration of the plasma modification treatment improving the electrofluid printing effect on the surface of the insulating substrate is approximately 24 hours. During this time, electrofluid printing can achieve good printing results.

[0018] 2. The plasma modification treatment is applied only to the surface of the insulating substrate, and the treatment area is only tens of nanometers deep on the material surface. Therefore, it will not affect the performance of the bulk material or significantly alter the properties of the material matrix.

[0019] 3. Plasma treatment is a widely used and effective method for modifying the surface properties of dielectric materials. It has low energy consumption, no chemical pollution, and does not involve chemical treatment or liquid immersion treatment during the process. It can be widely used for surface modification treatment of various insulating substrates.

[0020] 4. Plasma modification treatment can increase the surface energy of the substrate and increase the hydrophilicity of the substrate, making the outline of the pattern prepared by electrohydraulic inkjet printing more uniform after drying. The adhesion between the plasma-treated surface and the dried and cured ink will also be improved. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the apparatus for plasma modification of the surface of an insulating substrate according to the present invention;

[0022] Figure 2 This is a schematic diagram illustrating the principle of improving charge dissipation rate before and after plasma modification of the surface of an insulating substrate according to the present invention.

[0023] Figure 3 These are SEM images of the microstructure of the insulating substrate surface before and after plasma treatment, showing the original PI surface and the surface after O2 plasma treatment, respectively.

[0024] Figure 4 This is a schematic diagram of the charge decay curve and surface charge trap distribution curve on the surface of the insulating substrate before and after plasma treatment.

[0025] Figure 5 This is a schematic diagram showing the electrofluid printing effect before and after plasma modification of the insulating substrate surface according to the present invention.

[0026] Figure 6 This is a comparison image of the electrofluid printing effect before and after plasma modification of the insulating ceramic surface according to the present invention.

[0027] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1-Oxygen source, 2-Upper electrode, 3-Vacuum cavity, 4-Insulating substrate, 5-Lower substrate liner, 6-Exhaust gas, 7-Neutral particle, 8-Ion, 9-Ground wire, 10-Excitation voltage, 11-Nitrogen, 12-Oxygen, 13-Surface charge, 14-Deep level trap, 15-Shallow level trap, 16-Hydroxy group, 17-Surface charge dissipation, 18-Bulk charge dissipation. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0029] This invention provides a plasma-assisted electrohydrodynamic printing method for insulating surfaces, the printing method mainly comprising the following steps:

[0030] (a1) Provide an insulating substrate, perform a pre-cleaning treatment on the insulating substrate to remove surface foreign matter and prevent it from affecting the uniformity of plasma processing.

[0031] (a2) The surface of the insulating substrate is modified by low-pressure plasma. Specifically, different power and time are selected for the treatment of insulating substrates of different materials and thicknesses.

[0032] (a3) Conductive functional ink is deposited onto the surface of an insulating substrate using electrohydraulic inkjet printing, and its conductivity is achieved through post-processing such as sintering and drying.

[0033] Plasma modification alters the micro- and nano-structure of the insulating substrate surface, injecting active groups and changing the charge trap energy level distribution. This improves the surface and bulk conductivity of the substrate, suppressing charge accumulation and accelerating charge dissipation, eliminating electric field distortion, and thus optimizing the electrohydraulic printing effect on the insulating substrate surface. The duration of the improved electrohydraulic printing effect from plasma modification is approximately 24 hours, during which good printing results can be obtained.

[0034] Plasma modification treatment alters the micro-nano structure of the insulating substrate surface: After plasma treatment, the micro-nano structure of the insulating substrate surface changes. For the original relatively smooth insulating substrate surface at the nanoscale, irregular nano-sized particles appear on the insulating substrate surface after plasma treatment, forming a coral-like structure on the insulating substrate surface.

[0035] Plasma modification introduces active groups, altering the trap density distribution and energy level depth. The coral-like structure provides numerous physical interfaces for the active groups. The coral-like nanoparticles, together with the active groups, cause changes in the distribution of charge trap energy levels. Through plasma treatment, the energy level depth on the surface of the insulating substrate decreases, deep traps decrease, and shallow traps increase. The ability of the insulating substrate surface to bind charges decreases, accelerating surface charge dissipation and reducing the amount of accumulated charge on the insulating substrate surface.

[0036] Furthermore, plasma modification alters the surface and bulk conductivity of the insulating substrate. Conductivity reflects changes in trap size; a decrease in deep traps and an increase in shallow traps indicates a reduced ability to bind charges, making them easier for charges to migrate. Plasma treatment can increase both surface and bulk conductivity by several orders of magnitude, thereby accelerating the dissipation of surface charges on the insulating substrate and reducing the impact of residual charges from the printed structure on the electrostatic printing electric field.

[0037] Plasma treatment suppresses charge accumulation on the surface of the insulating substrate during electrofluid printing, allowing residual charges of electrofluid droplets on the surface of the insulating substrate to be rapidly conducted away through surface and volume conduction. This eliminates electric field distortion, improves the stability of electrofluid printing on the surface of the insulating substrate to prepare printed circuits, and enhances the printing performance of electrofluid printing on the insulating substrate.

[0038] The present invention also provides a flexible electronic device, which is prepared by the plasma-assisted insulating surface electrofluid printing method described above.

[0039] The present invention will be further described in detail below with reference to examples.

[0040] Please see the appendix Figure 1 This device is a reactive ion etching apparatus, consisting of an upper electrode 2, a vacuum chamber 3, and a lower substrate liner 5. The upper electrode 2 and the vacuum chamber 3 are connected to a grounding wire 9, and the lower substrate liner 5 is connected to an excitation voltage 10. When plasma treating the insulating substrate 4, the insulating substrate 4 is placed on the lower substrate liner 5, the vacuum chamber 3 is evacuated, and then oxygen is introduced into the vacuum chamber through an oxygen source 1 while the excitation voltage is turned on to generate neutral particles 7 and ions 8. The ions 8 bombard the substrate surface, thereby achieving plasma modification treatment of the insulating substrate 4.

[0041] Please see the appendix Figure 2 Before plasma modification, the insulating substrate was surrounded by nitrogen 11 and oxygen 12. The surface charge 13 of the insulating substrate underwent weak surface charge dissipation 17 and bulk charge dissipation 18, and deep-level traps 14 and shallow-level traps 15 were present. After plasma treatment, the surface roughness of the insulating substrate bombarded by ions 8 increased. The coral-like particles formed on the surface of the insulating substrate provided a large number of physical interfaces for shallow traps, while introducing a large number of hydroxyl groups 16, reducing the accumulation of surface charge in deep traps and improving the ability of the insulating substrate surface to capture free charges. Secondly, after plasma treatment, the surface charge dissipation 17 and bulk charge dissipation 18 of the insulating substrate were significantly improved, both of which facilitated the dissipation of more surface charge 13 along the surface and through the bulk. After plasma treatment, the trap density distribution and energy level depth decreased, the deep-level traps 14 decreased, and the shallow-level traps 15 increased. These all helped to suppress the accumulation of surface charge and accelerate the dissipation of surface charge. Therefore, after plasma treatment, the charge dissipation rate of the insulating substrate was significantly improved.

[0042] Please see the appendix Figure 3 Comparing the images before (left) and after (right) plasma treatment, it can be seen that plasma modification alters the micro- and nano-structures of the insulating substrate surface. After plasma treatment, the micro- and nano-structures of the insulating substrate surface change. What was originally a relatively smooth surface at the nanoscale becomes covered with irregular nano-sized particles, forming a coral-like structure. These overlapping coral-like structures provide numerous physical interfaces for shallow traps, increasing the number of shallow traps on the substrate surface. This increased number of shallow traps reduces the substrate's ability to bind charges, thus reducing charge accumulation and allowing a stable electric field to be formed between the insulating substrate and the electrofluid nozzle.

[0043] Please see the appendix Figure 4 The left figure shows the potential decay curves, which depict the potential change over time on the surface of the insulating substrate after charging, before and after oxygen plasma treatment. The figure shows that the potential decreases faster over time on the oxygen plasma-treated substrate than on the untreated substrate, indicating that the charge dissipation rate is faster on the oxygen plasma-treated substrate. The right figure compares the trap distribution on the surface of the insulating substrate before and after oxygen plasma treatment. The figure shows that the energy level and density of charge traps on the surface of the insulating substrate decrease after oxygen plasma treatment, the number of deep traps decreases, and the number of shallow traps increases. This will affect the amount of charge accumulated on the insulating surface, reducing the surface's ability to bind the accumulated charge and thus decreasing the accumulation of charge on the insulating surface.

[0044] Please see the appendix Figure 5 Without plasma modification, the surface charge dissipates slowly on the insulating substrate, causing droplets deposited by electrohydraulic inkjet printing to carry the same charge as subsequent droplets. As droplets continue to deposit, the surface charge on the insulating substrate increases, creating an electric field that affects the deposition of subsequent electrohydraulic inkjet printing droplets, leading to a decrease in the accuracy and resolution of the printed circuit. Plasma modification, on the other hand, increases the charge dissipation rate on the insulating substrate surface. The charge on the droplets deposited by electrohydraulic inkjet printing is quickly neutralized through volumetric and surface dissipation, reducing the accumulation of surface charge.

[0045] The following describes the plasma-assisted electrofluid printing method for insulating surfaces using a plasma-modified electrofluid printing circuit for insulating ceramic surfaces as a specific embodiment.

[0046] Step S1: Provide an insulating ceramic substrate.

[0047] Step S2: Clean the insulating ceramic substrate by using anhydrous ethanol and lint-free paper to clean the surface of the ceramic substrate to ensure that the surface of the ceramic substrate is clean.

[0048] Step S3: Perform plasma modification treatment on the insulating ceramic substrate.

[0049] Specifically, turn on the power to the equipment and the cooling device, then fill the vacuum chamber with air to restore the air pressure inside to atmospheric pressure. Open the vacuum chamber, place the insulating ceramic substrate on the lower substrate liner, and close the vacuum chamber. Evacuate the vacuum chamber to reduce the pressure inside to 10... -3 Pa. Activate the plasma treatment program to perform plasma modification treatment on the insulating ceramic substrate. Treat the insulating ceramic substrate with oxygen plasma for 60 seconds at a power of 150W. After treatment, fill the vacuum chamber with air to restore the pressure inside the vacuum chamber to atmospheric pressure. Open the vacuum chamber and remove the plasma-modified insulating ceramic substrate. Close the vacuum chamber and apply vacuum protection. Turn off the power to the device and the cooling device.

[0050] Step S4: Electrohydraulic circuit printing is performed on the surface of the plasma-modified insulating ceramic substrate.

[0051] Specifically, an electrohydraulic inkjet printing platform is used to print circuits onto the surface of a plasma-modified insulating ceramic substrate. Please refer to the appendix. Figure 3A nano-silver paste with a viscosity of 100 cp was used as the printing ink, a glass needle with an outer diameter of 50 μm was used as the printing needle, the printing height was 50 μm, and the ink was connected to a 700V DC voltage. The printing circuit path was imported to complete the printing of the electrohydraulic inkjet circuit.

[0052] Please see the appendix Figure 6 It can be seen that when electrofluid printing is performed on the surface of insulating ceramics without plasma treatment, the electric field on the surface of the insulating ceramics is distorted as electrofluid droplets are deposited, and the lines printed by electrofluid printing become discontinuous. When electrofluid printing is performed on the surface of insulating ceramics after plasma treatment, since the surface of insulating ceramics after plasma treatment does not produce electric field distortion, stable electrofluid printing can be performed, and the lines printed by electrofluid printing are more uniform and continuous than those on the surface of insulating ceramics without treatment.

[0053] Step S5: Conductive sintering of printing ink.

[0054] Specifically, the printed circuit-insulating ceramic substrate is placed on a hot plate for conductive heat sintering at a temperature of 230°C for 40 minutes.

[0055] The method for plasma modification treatment of insulating ceramic surfaces to print electrical circuits using this embodiment modifies the insulating ceramic substrate by using a reactive ion etching device to generate oxygen plasma. This increases the surface charge dissipation rate of the modified insulating ceramic substrate, thereby improving the electrical circuit printing effect and obtaining a high-precision, continuous electrical circuit printed on the surface of the insulating substrate.

[0056] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A plasma-assisted electrohydraulic inkjet printing method for insulating surfaces, characterized in that, The method comprises the following steps: The surface of the insulating substrate is modified by plasma. When the insulating substrate is treated by plasma, the insulating substrate is placed behind the lower substrate pad, the vacuum cavity is vacuumized, then oxygen is introduced into the vacuum cavity through an oxygen source and an excitation voltage is turned on to generate neutral particles and ions, wherein the ions bombard the surface of the substrate to inject hydroxyl groups into the surface of the insulating substrate to improve the surface conductivity and bulk conductivity of the insulating substrate, and then electrofluidic jet printing is performed. After the plasma treatment, nano-sized irregular particles appear on the surface of the insulating substrate to form a coral-like structure on the surface of the insulating substrate.

2. The method of claim 1, wherein the method is a plasma- assisted insulating surface fluid ejection method, further comprising: The insulating substrate is an insulating ceramic substrate, and the insulating substrate is treated by oxygen plasma for 60 s with a power of 150 w.

3. The method of claim 2, wherein the plasma assisted insulating surface fluid ejection method further comprises: Nano-silver paste with a viscosity of 100 cp is used as printing ink, a glass needle with an outer diameter of 50 μm is used as a printing needle, the printing height is 50 μm, and the ink is connected to a 700 V direct current voltage.

4. The method of claim 3, wherein the plasma assisted insulating surface fluid ejection method further comprises: The method further comprises a step of cleaning the insulating substrate before the plasma treatment.

5. A flexible electronic device, characterized by: The flexible electronic device is prepared by the plasma-assisted insulating surface electrofluidic jet printing method according to any one of claims 1-4.

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