High bonding force flexible conductive film and preparation method thereof

Abstract

The application discloses a high-bonding flexible conductive film in the field of flexible electronics and a preparation method thereof, wherein the conductive film comprises, from one end close to the substrate, an oxidation layer, a transition layer and a conductive layer arranged in sequence, the transition layer is fused after covering the oxidation layer and is transitioned to the conductive layer, the transition layer is composed of an amorphous silicon layer and a silicon nitride layer, and the amorphous silicon layer is close to one end of the oxidation layer. On the surface of a flexible polymer base, the oxidation layer for enhancing the hydrophilicity and compatibility of the base, the transition layer for enhancing the bonding force between the base and the copper film and the conductive layer for enhancing the conductivity of the base are sequentially added from inside to outside, so that the flexible conductive film with high bonding force is formed. The transition layer composed of the amorphous silicon layer and the silicon nitride layer is prepared through the corresponding preparation method, and the transition layer exhibits extremely high bonding strength at the bonding interfaces of the polymer base and the conductive layer, so that the problem that a single transition layer cannot simultaneously bond the base and the conductive film is solved, and the bonding force of the flexible conductive film is enhanced.

Description

Technical Field

[0001] This invention relates to the field of flexible electronics technology, specifically to a flexible conductive film with high bonding strength and its preparation method. Background Technology

[0002] As smart wearable electronics, medical sensors, and energy storage devices rapidly develop towards foldability, lightweight design, and portability, flexible conductive films, as an indispensable component for electrical connections, have received high attention due to their significant advantages such as high conductivity, light weight, and good flexibility.

[0003] Commonly used flexible conductive films are made by bonding a metal conductive film to a flexible polymer substrate using adhesives. This often leads to problems such as high dielectric loss, high porosity, and poor thermal stability. Adhesive-free flexible conductive films prepared using chemical plating, low-temperature sintering, and laser writing methods are more susceptible to pinholes, high temperatures, and stress, resulting in a decrease in film bonding strength.

[0004] Currently, flexible conductive films can be prepared in two ways, which will be explained below through Comparative Example 1 and Comparative Example 2.

[0005] Comparative Example 1:

[0006] like Figure 4-5 As shown, substrate 6 is a 50μm thick polyimide film, and the equipment used is an arc discharge assisted ionization device. The polyimide film is ultrasonically cleaned with ethanol, dried, placed in a vacuum chamber, fixed on a workpiece holder, and evacuated to below 5×10-3 Pa before the following operations are performed:

[0007] (1) Preparation of oxide layer 7: Gas plasma oxidation is performed on the surface of polymer substrate 6.

[0008] In a vacuum state, inert gas and oxygen are introduced to perform gas plasma oxidation on the surface of the polyimide film. AEGD (arc-enhanced glow discharge) gas plasma oxidation technology is adopted. Argon and oxygen are introduced into the vacuum chamber until the vacuum pressure reaches 0.8 Pa. The arc target current is set to 80 A and the anode current is set to 30 A. The gas ion oxidation time is 20 min.

[0009] (2) Deposit conductive layer 8: Sputter conductive layer 8 on the surface of flexible polymer substrate 6.

[0010] Argon gas is introduced into the vacuum chamber and the pressure is maintained at 0.3-0.5 Pa. A copper target is selected as the magnetron sputtering source and the current is set to 5 A. A polycrystalline copper layer is sputtered and deposited on the surface of oxide layer 7. This polycrystalline copper layer is the conductive layer 8. The sputtering time is 5 min, and the thickness of the conductive layer 8 is 500 nm.

[0011] (3) Deposit thickening layer 9: Electroplat the thickening layer 9 on the surface of the conductive layer 8.

[0012] Electroplating was performed in an electroplating bath containing copper sulfate and sulfuric acid, depositing a 2μm thickened layer 9 on the surface of the conductive layer 8.

[0013] Comparative Example 2:

[0014] like Figure 6-7 As shown, substrate 10 is a 50μm thick polyimide film, and the equipment used is an arc discharge assisted ionization device. The polyimide film is ultrasonically cleaned with ethanol, dried, placed in a vacuum chamber, fixed on a workpiece holder, and evacuated to below 5×10-3 Pa before the following operations are performed:

[0015] (1) Preparation of oxide layer 11: Gas plasma oxidation is performed on the surface of polymer substrate 10.

[0016] In a vacuum state, inert gas and oxygen are introduced to perform gas plasma oxidation on the surface of the polyimide film. AEGD (arc-enhanced glow discharge) gas plasma oxidation technology is adopted. Argon and oxygen are introduced into the vacuum chamber until the vacuum pressure reaches 0.8 Pa. The arc target current is set to 80 A and the anode current is set to 30 A. The gas ion oxidation time is 20 min.

[0017] (2) Deposit a metallic chromium transition layer 12: Sputter a metallic chromium transition layer 12 onto the surface of the oxide layer 11.

[0018] Argon gas was introduced into the vacuum chamber and the pressure was maintained at 0.3-0.5 Pa. A chromium target was selected as the magnetron sputtering source and the current was set to 5 A. A metallic chromium transition layer 12 was sputtered and deposited on the surface of the oxide layer 11. The sputtering time was 1 min, and the thickness of the metallic chromium transition layer 12 was 50 nm.

[0019] (3) Deposit conductive layer 13: Sputter conductive layer 13 on the surface of metallic chromium transition layer 12.

[0020] Maintaining the gas pressure at 0.3-0.5 Pa, a copper target is selected as the magnetron sputtering source, and the current is set to 5 A. A polycrystalline copper layer is sputtered and deposited on the surface of the chromium transition layer 12. This polycrystalline copper layer is the conductive layer 13. The sputtering time is 5 min, and the thickness of the conductive layer 13 is 500 nm.

[0021] (4) Deposit thickening layer 14: Electroplat the thickening layer 14 on the surface of the conductive layer 13.

[0022] Electroplating is performed in an electroplating bath containing copper sulfate and sulfuric acid to deposit a 2 μm thickened layer 14 on the surface of the conductive layer 13.

[0023] For Comparative Example 1 and Comparative Example 2, after the nano-scratch test, the critical load of the surface color value test of Comparative Example 1 was 29.5 mN, while the critical load of the surface color value test of Comparative Example 2 was 40.4 mN.

[0024] Therefore, a flexible conductive film with higher adhesion is needed to coat the polymer substrate. Physical vapor deposition (PVD) can deposit metal conductive films on flexible polymer substrates at low temperatures by controlling the energy of the deposited ions, offering advantages such as low substrate temperature, high conductivity, and no environmental pollution. However, due to the poor wettability of the polymer substrate to the metal film, metal atoms tend to bond with each other rather than with the polymer substrate atoms during deposition, severely weakening the interfacial chemical bond between the polymer substrate and the metal film. Therefore, poor adhesion still exists between the metal conductive film and the flexible polymer substrate, leading to the failure of the flexible conductive film during bending, twisting, and stretching. Summary of the Invention

[0025] The purpose of this invention is to overcome the above-mentioned defects and provide a flexible conductive film with high bonding strength. By adding a transition layer composed of an amorphous silicon layer and a silicon nitride layer to the inner layer of the conductive film, the high bonding strength inside the flexible conductive film is improved, thus solving the technical problems of poor stability and insufficient bonding strength of conductive films in the prior art.

[0026] The objective of this invention is achieved through the following means:

[0027] A flexible conductive film with high adhesion includes a film body for coating a substrate surface. The film body includes an oxide layer, a transition layer and a conductive layer sequentially disposed from one end near the substrate. The transition layer covers the oxide layer and is fused together, transitioning towards the conductive layer. The transition layer is composed of an amorphous silicon layer and a silicon nitride layer, with the amorphous silicon layer near the oxide layer.

[0028] Furthermore, the conductive layer is composed of a single metal, which is either Al or Cu.

[0029] Furthermore, the conductive layer is composed of an alloy target material, which is one of CuAl, CuNi, CuZn, AlSi, and AlMg.

[0030] Furthermore, the conductive layer is composed of a single metal and an alloy target, wherein the single metal is one of Al and Cu, and the alloy target is one of CuAl, CuNi, CuZn, AlSi, and AlMg.

[0031] Furthermore, the oxide layer has a thickness of 10-50 nm, the transition layer has a thickness of 100-500 nm, and the conductive layer has a thickness of 100-1000 nm.

[0032] Furthermore, the membrane also includes a conductive thickening layer, which is deposited on the outer surface of the conductive layer and has a thickness of 2-5 μm.

[0033] In addition, the present invention also provides a method for preparing a flexible conductive film with high bonding strength, which is used to prepare the above-mentioned flexible conductive film with high bonding strength. Through the process, the bonding strength of the internal structure of the flexible conductive film can be strengthened, which can also solve the technical problems of poor stability and insufficient bonding strength of conductive films in the background art.

[0034] The objective of this invention is achieved through the following means:

[0035] A method for preparing a flexible conductive film with high bonding strength includes the following steps:

[0036] Step S1, Preparation of oxide layer: The substrate is ultrasonically cleaned with alcohol or deionized water. After cleaning, it is placed in a vacuum state and oxygen and inert gas are introduced. The substrate is oxidized by gas plasma, and an oxide layer of hydrocarbons and elemental carbon is formed on the surface.

[0037] Step S2, Deposit an amorphous silicon layer: In an inert gas environment, an amorphous silicon layer covering an oxide layer is sputtered and deposited on the substrate surface in a vacuum chamber using a high-power pulsed magnetron sputtering source. An interfacial chemical bond, including Si-C bonds and Si-O bonds, is formed between the amorphous silicon layer and the substrate.

[0038] Step S3, depositing a silicon nitride layer: In an inert gas environment, nitrogen gas is refilled into the vacuum chamber to ionize nitrogen or carbon ions, which are then sputtered and deposited on the surface of the amorphous silicon layer by a high-power pulsed magnetron sputtering source to form a silicon nitride layer fused with the amorphous silicon layer.

[0039] Step S4, Deposit conductive layer: In an inert gas environment, nitrogen gas is stopped being introduced into the vacuum chamber, and a conductive layer is formed by sputtering and depositing on the surface of the silicon nitride layer using a high-power pulsed magnetron sputtering source;

[0040] Step S5, Deposit thickening layer: A thickening layer is deposited on the surface of the conductive layer by electroplating or welding. The thickening layer is bonded to the conductive layer by metallic bonds and has conductive function.

[0041] Further, in step S1, gas plasma oxidation is one of plasma source ion oxidation, bias-assisted glow discharge ion oxidation, and AEDG arc discharge enhanced ionization ion oxidation.

[0042] Furthermore, the inert gas is one of argon, helium, neon, krypton, and xenon.

[0043] Compared with the prior art, the beneficial effects of the present invention are:

[0044] (1) This invention forms a flexible conductive film with high bonding strength by sequentially adding an oxide layer to enhance the hydrophilicity and compatibility of the substrate, a transition layer to improve the bonding force between the substrate and the copper film, and a conductive layer to enhance the conductivity of the substrate on the surface of a flexible polymer substrate. At the same time, the transition layer, composed of an amorphous silicon layer and a silicon nitride layer, exhibits extremely high bonding strength at the interface with the polymer substrate and the conductive layer, thereby enhancing the bonding force.

[0045] (2) The present invention uses a method for preparing a flexible conductive film to gradually deposit an amorphous silicon layer and a silicon nitride layer between the oxide layer and the conductive layer by high-power pulse sputtering. This can solve the problem that a single transition layer cannot simultaneously bond the substrate and the conductive film, and effectively enhance the bonding force of the internal structure of the flexible conductive film. Attached Figure Description

[0046] Figure 1 This is a schematic diagram of the membrane structure according to an embodiment of the present invention;

[0047] Figure 2 This is a flowchart of the preparation method according to an embodiment of the present invention;

[0048] Figure 3 This is a diagram showing the nano-scratch test results of an embodiment of the present invention;

[0049] Figure 4 This is a schematic diagram of the membrane structure of Comparative Example 1 in the background art of the present invention;

[0050] Figure 5 This is a diagram showing the nano-scratch test results of Comparative Example 1 in the background art of this invention;

[0051] Figure 6 This is a schematic diagram of the membrane structure of Comparative Example 2 in the background art of the present invention;

[0052] Figure 7 This is a diagram showing the nano-scratch test results of Comparative Example 2 in the background art of this invention;

[0053] Numbering on the map:

[0054] Figure 1 middle:

[0055] 1-Substrate, 2-Oxide layer, 3-Transition layer, 4-Conductive layer, 5-Thickening layer;

[0056] 301 - Amorphous silicon layer, 302 - Silicon nitride layer;

[0057] Figure 4 middle:

[0058] 6-Substrate, 7-Oxide layer, 8-Conductive layer, 9-Thickening layer;

[0059] Figure 6 middle:

[0060] 10-Substrate, 11-Oxide layer, 12-Chromium transition layer, 13-Conductive layer, 14-Thickening layer. Detailed Implementation

[0061] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0062] Example:

[0063] like Figure 1 As shown, this embodiment of the invention provides a flexible conductive film with high bonding strength, which is used in conjunction with a substrate 1 on the surface of which is provided with a flexible polymer. It is a film that covers the surface of the substrate.

[0064] The film consists of an oxide layer 2, a transition layer 3, a conductive layer 4, and a thickening layer 5, arranged sequentially starting from the end closest to the substrate 1. The transition layer 3 covers the oxide layer 2 and fuses with it, transitioning towards the conductive layer 4. The thickening layer 5, disposed on the outer surface of the conductive layer 4, is a metal thickening layer 5, which has conductive properties after being deposited on the outer surface of the conductive layer 4.

[0065] Among them, the oxide layer 2 is formed directly on the surface of the substrate 1 after oxidation treatment.

[0066] The transition layer 3 is composed of an amorphous silicon layer 301 and a silicon nitride layer 302. The amorphous silicon layer 301 is close to one end of the oxide layer 2, and the corresponding silicon nitride layer 302 is close to one end of the conductive layer 4. The transition layer 3 transitions from the amorphous silicon layer 301 to the silicon nitride layer 302.

[0067] The conductive layer 4 can be composed of a single metal or an alloy target, or a combination of both. The single metal is selected from Al and Cu, while the alloy target is selected from CuAl, CuNi, CuZn, AlSi, and AlMg.

[0068] In addition, such as Figure 2 As shown, this embodiment of the invention also provides a method for preparing the highly adhesive flexible conductive film. During preparation, a 50 μm thick polyimide film is selected as the substrate 1, and an arc discharge assisted ionization device is used. The entire preparation process includes the following steps:

[0069] Step S1, Preparation of oxide layer 2: Gas plasma oxidation is performed on the surface of polymer substrate 1 to form oxide layer 2.

[0070] The polyimide film was ultrasonically cleaned with ethanol. After cleaning and drying, it was placed in a vacuum chamber, fixed on a workpiece holder, and evacuated to below 5×10-3 Pa.

[0071] An inert gas and oxygen are introduced into a vacuum state. The inert gas is selected from argon, helium, neon, krypton, and xenon. Then, gas plasma oxidation is performed on the surface of the polyimide film. This method uses AEGD (arc-enhanced glow discharge) gas plasma oxidation technology. Argon and oxygen are introduced into the vacuum chamber until the vacuum pressure reaches 0.8 Pa. The arc target current is set to 80 A and the anode current to 30 A. The gas ion oxidation time is 20 min. After the substrate 1 is oxidized by gas plasma, an oxide layer 2 of hydrocarbons (~CxHy) and elemental carbon (~CC) is formed on the surface of the polyimide film. The thickness of the oxide layer 2 is between 10-50 nm.

[0072] Step S2, depositing an amorphous silicon layer 301: an amorphous silicon layer 301 is formed by sputtering on the surface of oxide layer 2.

[0073] Under inert gas conditions, argon gas is introduced into the vacuum chamber to maintain the internal pressure at 0.3-0.5 Pa. A silicon target is selected as the magnetron sputtering source, and the current is set to 5 A. A high-power pulse is used to sputter an amorphous silicon layer 301 covering the oxide layer 2 on the surface of the polyimide film. The sputtering time is 2 min, and the thickness of the amorphous silicon layer 301 is 50 nm.

[0074] The amorphous silicon layer 301 prepared by magnetron sputtering forms obvious interfacial chemical bonds with the substrate 1 it covers, including Si-C bonds and Si-O bonds, which enhances the bonding force between the transition layer 3 and the substrate 1.

[0075] Step S3, depositing silicon nitride layer 302: forming silicon nitride layer 302 by sputtering on the surface of amorphous silicon layer 301.

[0076] Under inert gas conditions, nitrogen gas is refilled into the vacuum chamber to ionize nitrogen or carbon ions, and the flow rate of nitrogen gas is gradually increased to maintain the internal pressure at 0.5-0.8 Pa. Finally, the flow rate ratio of argon gas to nitrogen gas gradually increases from 1:0 to 5:1. A silicon nitride layer 302 fused with the amorphous silicon layer 301 is formed by sputtering and depositing on the surface of the amorphous silicon layer 301 using a high-power pulsed magnetron sputtering source. The sputtering time is 3 min, and the thickness of the silicon nitride layer 302 is 70 nm.

[0077] The silicon nitride layer 302 exhibits excellent diffusion-blocking properties against moisture and oxygen diffusion. The deep-level acceptor provided by oxygen in the band gap lowers the Fermi level, leading to effective ionization of neutral metal atoms in the oxide. Therefore, the silicon nitride layer 302 possesses excellent diffusion-blocking capabilities. Furthermore, the silicon nitride layer 302 is prepared by introducing nitrogen gas during magnetron sputtering of the silicon target, which improves the transition between it and the amorphous silicon layer 301.

[0078] Step S4, Deposit conductive layer 4: Form conductive layer 4 by sputtering on the surface of silicon nitride layer 302.

[0079] Under inert gas conditions, nitrogen filling into the vacuum chamber is stopped, and the internal pressure is maintained at 0.3-0.5 Pa. A copper target is selected as the magnetron sputtering source, and the current is set to 5 A. A polycrystalline copper layer is formed by sputtering and depositing on the surface of the silicon nitride layer 302 through a high-power pulsed magnetron sputtering source. This polycrystalline copper layer is the conductive layer 4. The sputtering time is 5 min, and the thickness of the conductive layer 4 is 500 nm.

[0080] The conductive layer 4 is a metal or alloy layer coated on the surface of the silicon nitride layer 302. When bonded to the silicon nitride layer 302, the silicon nitride layer 302 can prevent bonding failure caused by interfacial diffusion of the conductive layer 4 and enhance the bonding force between the two layers.

[0081] Step S5, Deposit thickened layer 5: Electroplat the thickened layer 5 on the surface of the conductive layer 4.

[0082] Electroplating is performed in an electroplating bath containing copper sulfate and sulfuric acid to deposit a 2μm thickening layer 5 on the surface of the conductive layer 4. The thickening layer 5 is bonded to the conductive layer 4 by metallic bonds and has excellent bonding force and conductivity.

[0083] For this embodiment, the sample was tested, and the test results are as follows: Figure 3 As shown, the critical load of the sample in this embodiment during the nano-scratch test is 43.5 mN. Compared with the test results of Comparative Examples 1 and 2 in the background art, the critical load of this embodiment increases by 14 mN and 3.1 mN, respectively.

[0084] Experimental results show that by using AEGD (Arc Enhanced Glow Discharge) to sequentially add an oxide layer from the inside out on the surface of a flexible polymer substrate, enhancing the substrate's hydrophilicity and compatibility, a transition layer to improve the adhesion between the substrate and the copper film, and a conductive layer to enhance the substrate's conductivity, are deposited using high-power pulsed magnetron sputtering, forming a flexible conductive film with high film-substrate adhesion. The transition layer, composed of an amorphous silicon layer 301 and a silicon nitride layer 302, exhibits extremely high bonding strength at the interfaces with both the polymer substrate and the conductive layer. This solves the problem that a single transition layer cannot simultaneously bond to both the substrate and the conductive film, thereby enhancing the film-substrate adhesion of the flexible conductive film.

[0085] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A high-adhesion flexible conductive film, comprising a film body for coating a substrate surface, characterized in that, The film includes an oxide layer, a transition layer and a conductive layer arranged sequentially from one end near the substrate. The transition layer covers the oxide layer and is fused together, and then transitions to the conductive layer. The transition layer is composed of an amorphous silicon layer and a silicon nitride layer. The amorphous silicon layer is located near the oxide layer. The film also includes a thickening layer with conductive function, which is deposited on the outer surface of the conductive layer. The preparation method of a flexible conductive film with high adhesion includes the following steps: Step S1, Preparation of oxide layer: The substrate is ultrasonically cleaned with alcohol or deionized water. After cleaning, it is placed in a vacuum state and oxygen and inert gas are introduced. The substrate is oxidized by gas plasma, and an oxide layer of hydrocarbons and elemental carbon is formed on the surface. Step S2, Deposit an amorphous silicon layer: In an inert gas environment, an amorphous silicon layer covering an oxide layer is sputtered and deposited on the substrate surface in a vacuum chamber using a high-power pulsed magnetron sputtering source. An interfacial chemical bond, including Si-C bonds and Si-O bonds, is formed between the amorphous silicon layer and the substrate. Step S3, depositing a silicon nitride layer: In an inert gas environment, nitrogen gas is refilled into the vacuum chamber to ionize nitrogen or carbon ions, which are then sputtered and deposited on the surface of the amorphous silicon layer by a high-power pulsed magnetron sputtering source to form a silicon nitride layer fused with the amorphous silicon layer. Step S4, Deposit conductive layer: In an inert gas environment, nitrogen gas is stopped being introduced into the vacuum chamber, and a conductive layer is formed by sputtering and depositing on the surface of the silicon nitride layer using a high-power pulsed magnetron sputtering source; Step S5, Deposit thickening layer: A thickening layer is deposited on the surface of the conductive layer by electroplating or welding. The thickening layer is bonded to the conductive layer by metallic bonds and has conductive function.

2. The high-bonding-strength flexible conductive film according to claim 1, characterized in that, The conductive layer is composed of a single metal, which is either Al or Cu.

3. The high-bonding-strength flexible conductive film according to claim 1, characterized in that, The conductive layer is composed of an alloy target, which is one of CuAl, CuNi, CuZn, AlSi, and AlMg.

4. The high-bonding-strength flexible conductive film according to claim 1, characterized in that, The conductive layer is composed of a single metal and an alloy target. The single metal is either Al or Cu, and the alloy target is either CuAl, CuNi, CuZn, AlSi, or AlMg.

5. The high-bonding-strength flexible conductive film according to claim 1, characterized in that, The oxide layer has a thickness of 10-50 nm, the transition layer has a thickness of 100-500 nm, and the conductive layer has a thickness of 100-1000 nm.

6. A high-bonding-strength flexible conductive film according to any one of claims 1-5, characterized in that, The thickness of the thickening layer is 2-5 μm.

7. A flexible conductive film with high bonding strength according to any one of claims 1-5, characterized in that, In step S1, gas plasma oxidation is one of plasma source ion oxidation, bias-assisted glow discharge ion oxidation, and AEDG arc discharge enhanced ionization ion oxidation.

8. A high-bonding-strength flexible conductive film according to any one of claims 1-5, characterized in that, The inert gas is one of argon, helium, neon, krypton, and xenon.

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