KR102170895B1 - flexible substrate assembly with stretchable electrodes and fabrication method of it - Google Patents

Abstract

A method of manufacturing a stretchable electrode according to an aspect of the present invention includes: forming a first flexible substrate; Increasing and fixing the first flexible substrate in a direction of a tensile force applied during use of the finished product; Performing pre-deposition treatment on the stretched and fixed first flexible substrate; Depositing a metal electrode on the stretched and fixed first flexible substrate; Forming a second flexible substrate; Increasing and fixing the second flexible substrate in the direction of a tensile force applied during use of the finished product; Performing a pre-deposition treatment on the stretched and fixed second flexible substrate; Depositing a metal electrode on the stretched and fixed second flexible substrate; And combining the first flexible substrate and the second flexible substrate while the metal electrode of the first flexible substrate and the metal electrode of the second flexible substrate are aligned and contacted with each other.

Description

Flexible substrate assembly with stretchable electrodes and fabrication method of it}

The present invention relates to a stretchable electrode having a low resistance, and in particular, by using a metal nanowire spraying technology, a stretchable metal electrode is formed on a stretchable polymer substrate, and the metal electrode formed of the same polymer material is covered ( It relates to a flexible substrate assembly in which a stretchable metal electrode manufactured in a covering) method is formed.

In the case of a general electronic device, a structural solution is required for this because the physical/mechanical properties are easily lost even by a small external deformation. In the case of a flexible electronic device and a foldable electronic device, the external deformation is usually less than 1%. When a larger strain is applied, it is necessary to develop a device that does not lose its properties even with an external strain of several tens of percent. In this case, a flexible substrate or the like is used instead of a general plastic substrate.

Unlike general electronic devices that are fabricated on hard glass or silicon substrates, flexible and foldable devices are fabricated on plastic substrates such as polyimide. However, in the case of a stretchable electronic device, it is manufactured on a polymer substrate having a very low Young's modulus such as polydimethylsiloxane (PDMS), and in this case, various contamination problems occur due to the properties of the polymer material.

PDMS (PolyDiMethylSiloane) is a material that is expected to be widely applied in the manufacture of flexible substrates, flexible electrodes, and flexible electronics.

In addition, since PDMS (PolyDiMethylSiloane) is a material with excellent biocompatibility, it is used to make fluid channels used for diagnosis using human blood or to cultivate cells, and flexible electrodes for nerve signal stimulation and flexible electronics ( flexible electronics) can be used universally.

When fabricating a stretchable circuit, a large external tensile force is applied to the external wiring when a typical design is applied. Accordingly, when fabricating a stretchable electrode, it is required to optimize the structure of an external wiring capable of resisting the external tensile force.

In addition, in order to use the insulating material PDMS as a flexible electrode, an electrode must be formed on the PDMS. However, it has been difficult to stably apply a metal electrode to the PDMS substrate due to the high coefficient of thermal expansion and high elasticity of PDMS with the method introduced so far.

On the other hand, in the case of fabricating a stretchable electrode using a single metal electrode or a single nanowire electrode, there is also a problem in that the resistance change according to the tensile factor is large.

Korean Patent Publication No. 10-0875711

An object of the present invention is to provide a flexible substrate assembly including a flexible electrode having a stretchable property and a small resistance change according to tension, and a method of manufacturing the same.

A method of manufacturing a stretchable electrode according to an aspect of the present invention comprises: forming a flexible substrate; Increasing and fixing the flexible substrate in the direction of a tensile force applied during use of the finished product; Performing a pre-processing of forming an electrode on the stretched and fixed flexible substrate; Depositing a metal electrode on the stretched and fixed flexible substrate; Attaching a metal nanowire on the flexible substrate; And covering the flexible substrate from which the stretched state has been removed.

Here, the cover material is a cover substrate of the same material as the flexible substrate,

In the step of covering the cover material, the flexible substrate and the cover substrate may be bonded to each other by pressing the flexible substrate and the cover substrate while facing each other.

Here, the cover material may be a thin film in a form in which the same material as the flexible substrate is applied on the flexible substrate and sintered.

Here, the metal nanowires may be attached to the flexible substrate by spraying them using spray coating.

Here, in the step of depositing the metal electrode on the flexible substrate, the electrode may be deposited to a thickness of 80 nm to 900 nm through a shadow mask using a thermal evaporation method.

Here, the metal electrode to be deposited is made of at least one material selected from gold, silver, and copper,

The metal nanowire may be made of at least one material selected from silver and copper.

A flexible substrate assembly having a stretchable electrode according to another aspect of the present invention includes a PDMS substrate formed by mixing a base and a crosslinking agent in a ratio of 10:1; A deposited metal electrode layer deposited on the PDMS substrate to a thickness of 80 nm to 900 nm; A metal nanowire layer attached in the form of spray coating on the deposited metal electrode layer; And a cover material made of a PDMS material to cover an upper portion of the metal nanowire layer and the PDMS substrate.

Here, the evaporated metal electrode layer may have a structure that is stretched and then reduced.

Here, the deposited metal electrode layer is made of at least one material selected from gold, silver, and copper,

The metal nanowire layer may be made of at least one material selected from silver and copper.

If a flexible substrate assembly having a stretchable stretchable electrode according to the spirit of the present invention having the above-described configuration or a method of manufacturing the same is performed, sufficient stretching is possible and a stretchable electrode having a small change in resistance depending on the degree of tension can be achieved. There is this.

The stretchable electrode of the present invention described above has the advantage of being easily applied to a flexible display, a wearable device, or a medical device.

The effect of the stretchable electrode of the present invention will be described in detail, by using a hybrid electrode structure of a metal electrode and a metal nanowire, to enhance the stretch characteristics of the wiring structure. Accordingly, it is possible to minimize the change in resistance of the electrode even for a large external deformation, and due to the stability of the nanowire structure, the change in resistance of the electrode is small even under long-term stress. As a result, the stretching performance is significantly improved compared to the stretchable electrode manufactured using only the existing metal electrode.

1 is a flow chart showing a method of manufacturing a stretchable electrode according to an embodiment of the present invention.
2A to 2D are cross-sectional views illustrating a PDMS substrate and an electrode assembly during a process of being manufactured according to the manufacturing method of FIG. 1.
FIG. 3 is a cross-sectional view illustrating an electrode assembly having a stretchable metal electrode formed on a PDMS substrate manufactured according to the manufacturing method of FIG. 1.
4A to 4C are electron micrographs according to the tensile force of the copper nanowires applied on the top of the deposited metal electrode layer made of copper.
5A is a graph showing changes in tensile modulus and resistance according to a tensile speed in a PDMS substrate electrode assembly in which only copper-deposited metal electrodes are formed.
5B is a graph showing changes in tensile modulus and resistance according to a tensile speed in a PDMS substrate electrode assembly in which a double electrode of a metal layer and a metal nanowire is formed of copper.

Hereinafter, a specific embodiment for carrying out the present invention will be described with reference to the accompanying drawings.

In describing the present invention, terms such as first and second may be used to describe various elements, but the elements may not be limited by terms. The terms are only for the purpose of distinguishing one component from other components. For example, without departing from the scope of the present invention, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element.

When a component is connected to or is referred to as being connected to another component, it can be understood that it may be directly connected or connected to the other component, but other components may exist in the middle. .

The terms used in the present specification are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions may include plural expressions unless the context clearly indicates otherwise.

In the present specification, terms such as include or include are intended to designate the existence of features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and one or more other features or numbers, It may be understood that the presence or addition of steps, operations, components, parts, or combinations thereof, does not preclude the possibility of preliminary exclusion.

In addition, shapes and sizes of elements in the drawings may be exaggerated for clearer explanation.

In the present invention, a method of manufacturing a stretchable metal electrode in which a stretchable metal electrode is formed on a stretchable polymer substrate using a metal nanowire spraying technology, and a metal electrode formed of the same polymer material is covered. , We propose a method of manufacturing a flexible metal electrode with a small resistance change due to tension on a substrate made of PDMS or ecoflex, which is used as a flexible electronic device.

1 shows a method of manufacturing a stretchable electrode according to an embodiment of the present invention. 2A to 2D illustrate a PDMS substrate and an electrode assembly during a manufacturing process according to the manufacturing method of FIG. 1. FIG. 3 shows an electrode assembly provided with a stretchable metal electrode formed on a PDMS substrate manufactured according to the manufacturing method of FIG. 1.

The method of manufacturing a stretchable electrode according to an embodiment of the present invention illustrated includes the steps of forming a flexible substrate (S122); Increasing and fixing the flexible substrate in the direction of a tensile force applied during use of the finished product (S124); Performing a pre-processing of forming an electrode on the stretched and fixed flexible substrate (S126); Depositing a metal electrode on the stretched and fixed flexible substrate (S127); Attaching (spraying) metal nanowires on the flexible substrate (S128); And covering the flexible substrate from which the stretched state has been removed (S130).

The illustrated method of manufacturing a stretchable electrode proposes a method of manufacturing a relatively inexpensive copper (Cu) electrode through a pre-stretching method.

As shown in FIG. 2A, a stretchable flexible substrate 120 such as PDMS or ecoflex is manufactured, and the manufactured flexible substrate 120 is stretched in the direction of the tensile force applied during use of the finished product (pre-stretching) and fixed ( S124), a shadow mask layer 129 (or photolithography layer) is formed on the stretched flexible substrate 120, and plasma treatment is performed on the open surface through the shadow mask (S126).

In the step (S122) of fabricating the flexible substrate 120, for example, a base and a crosslinking agent are mixed in a ratio of 10:1 and baked at 130 to 170°C (preferably 150°C) on a hot plate, so that the PDMS substrate is It can be done in a way of making.

In the step of pre-stretching the flexible substrate 120 (S124), the sides facing each other of the flexible substrate 120 are fixed with a clamping device having a wide width and pulled away from each other to apply a tensile force. In a state, it may be performed by fixing the position of the clamping device.

In the step of pre-stretching the flexible substrate (S124), for example, the PDMS substrate 120 may be pre-stretched to 40% in the direction of a tensile force applied during use of the finished product.

Depending on the implementation, in step S124, when the finished product has a rectangular shape, it is highly possible that a large tensile force is applied in the longitudinal direction, and thus a tensile force that is pre-stretched in the longitudinal direction may be applied.

Depending on the implementation, in the step S124, when the finished product has a shape close to a square, a tensile force that increases in advance in the length direction of the electrode may be applied rather than in the direction of the finished product. This takes into account that the tensile force applied in the longitudinal direction of the electrode gives a strong stress to the electrode.

In other implementations, it can be fixed by applying tension in all plane directions.

The plasma treatment (S126) may be performed in a variety of known methods for the purpose of removing impurities from the surface of the substrate and/or enhancing the bonding strength between the substrate and the deposited metal. For example, under the conditions of power 80W, pressure: 1.4torr, time: 15s, helium or oxygen plasma treatment may be performed on the pre-stretched first/second substrates.

In the step of depositing the metal electrode (S127), for example, 40% pre-stretched flexibility (PDMS) through a shadow mask using a thermal evaporation method (atmospheric pressure <5 × 10 ^-5 torr, deposition rate: 1 ÅA/s) A metal (preferably Cu) electrode may be deposited on the substrate. An electrode (which is an unfinished half electrode) formed on the flexible (PDMS) substrate 120 according to the idea of the present invention may have a thickness of 80 nm to 900 nm.

In the step of attaching (spraying) the metal nanowires (S128), the metal nanowires are coated using a printed electronic technology such as spray coating. Metallic nanowires are silver nanowire, copper nanowire, and gold nanowire, and the nanowires connect to the cracked part, thereby minimizing the change in resistance due to stretching, and improving the stretching characteristics. In other words, the long nanowire serves as a path for current connecting the crack of the metal electrode and the crack portion. In Figure 2d, a nanowire made of Cu was applied. The preferred thickness of the nanowire layer is 50 to 500 nm.

In FIG. 2C, after the step of depositing the metal electrode (S127), the shadow mask layer 129 remaining on the flexible substrate 120 is removed, and the tensile force applied to the flexible substrate 120 is released, The flexible substrate 120 shows a reduced state similar to the original value. In another embodiment, from the step of depositing the metal electrode (S127) to the step of attaching the metal nanowire (S128), the tensile force is increased in the direction of the tensile force applied during use of the finished product and is fixed, and after performing the step S128, the tensile force You can also turn off.

Meanwhile, similar to a general semiconductor manufacturing process, after the step of depositing a metal electrode on the flexible substrate (S127) or attaching a metal nanowire (S128), the metal electrode deposited on the first flexible substrate is patterned. The step (not shown) may be further performed.

In the above description, although it has been embodied and described as a preferred Cu electrode in terms of price, a method of manufacturing almost the same as described above through a method of pre-stretching Ag, Au electrodes or alloy electrodes of Ag, Cu, and Au is also the scope of the present invention. Of course it belongs to.

In the above description, although it has been embodied and described as Cu nanowires, which are preferable in terms of price, a method of fabricating the Ag nanowires in the same manner as described above through a pre-stretching method also falls within the scope of the present invention. Gold (Au) nanowires are technically applicable, but in the case of fairly expensive gold, a certain degree of quality is expressed with only the deposition electrode, so the practical benefit of adding an expensive gold nanowire attachment process is small.

In the step of covering the cover material on the flexible substrate 120 (S130), the cover material is preferably made of the same material as the flexible substrate 120.

For example, the step of covering the cover material on the flexible substrate 120 (S130) is performed by applying a sintered material (PDMS or ecoflex) of the same material as the flexible substrate to the flexible substrate 120 and then sintering it. Can be. Sintering is baked at 130 to 170°C (preferably 150°C).

Alternatively, the step of covering the cover material on the flexible substrate 120 (S130) may be performed by applying pressure to a cover substrate prepared in advance as a cover material to the flexible substrate 120.

In this case, the step of covering the cover material on the flexible substrate 120 (S130) comprises: manufacturing a cover substrate of the same material (PDMS or ecoflex) as the flexible substrate; And bonding the flexible substrate 120 and the cover substrate by pressing the flexible substrate 120 and the cover substrate while facing each other.

Depending on the implementation, prior to bonding the flexible substrate 120 and the cover substrate, it may further include performing a pretreatment for increasing the surface adhesion activity of the flexible substrate 120 and/or the cover substrate. .

The pretreatment may be performed in a helium or oxygen plasma treatment method similar to that performed in the plasma treatment step S126. For example, the oxygen plasma treatment conditions may be a power of 0 W, a pressure of 1.4 torr, a flow rate of oxygen gas of 100 sccm, and a treatment time of 60 seconds.

In the step of combining the flexible substrate and the cover substrate, the flexible substrate 120 and the cover substrate are compressed. In the case of performing the pre-treatment, the flexible substrate 120 and the cover substrate are bonded by pressing the pre-treated surfaces in a state of facing each other.

When a substrate such as PDMS uses an oxygen/helium plasma method, the two substrates are strongly fused without the need for an adhesive.

3 is a cross-sectional view illustrating a flexible substrate assembly having stretchable and stretchable electrodes formed on a flexible substrate manufactured by the manufacturing method described in FIGS. 1 and 2A to 2D.

The flexible substrate assembly having the illustrated stretchable electrode includes: a PDMS substrate 120 formed by mixing a base and a crosslinking agent in a ratio of 10:1; A deposited metal electrode layer 152 deposited on the PDMS substrate 120 to a thickness of 80 nm to 900 nm; A metal nanowire layer 156 attached on the deposited metal electrode layer 152 in a spray-coated form; And a cover material 160 made of a PDMS material in a form covering an upper portion of the metal nanowire layer 156 and the PDMS substrate 120, wherein the deposited metal electrode layer 152 has a structure that is stretched and then reduced. Is formed.

When the thickness of the deposited metal electrode layer 152 exceeds 900 nm, the stress between the electrode and the substrate causing electrode peeling appears too strong, and when the thickness is less than 80 nm, the resistance change due to deformation becomes severe and the absolute resistance value is also A growing problem occurs.

4A to 4C are electron micrographs of copper nanowires applied on the top of the deposited metal electrode layer made of copper. FIG. 4A is a state in which a tensile force is not applied, FIG. 4B is a state in which a 6% tensile force is applied, and FIG. 4C is a state in which a 12% tensile force is applied.

In FIGS. 4A to 4C, the above photo is enlarged at 850 times, and the lower photo is enlarged at 1700 times. The copper nanowires applied on the top are applied on a number of cracks that are horizontally or vertically generated, and the applied conductive copper nanowires connect to each other in the metal electrode layer on the lower substrate broken by cracks, thereby acting as a bridge for current flow. Is done. With such a configuration, as shown in FIG. 5, when tensile is performed at a low speed, excellent properties with little change in resistance can be obtained.

5A is a graph showing changes in tensile modulus and resistance according to a tensile speed in a PDMS substrate electrode assembly in which only a metal electrode deposited with copper is formed,

5B is a graph showing changes in tensile modulus and resistance according to a tensile speed in a PDMS substrate electrode assembly in which a double electrode of a metal layer deposited with copper and a metal nanowire is formed.

It can be seen that the case in which the electrode is formed in the double of the deposited metal layer and the metal nanowire has less resistance change due to tension than the case where the electrode is formed only with the deposited metal. In particular, it can be seen that it is excellent by up to 40% depending on the tensile speed (at a low tensile speed).

It should be noted that the above-described embodiments are for the purpose of explanation and not limitation. In addition, those of ordinary skill in the technical field of the present invention will understand that various embodiments are possible within the scope of the technical idea of the present invention.

120: flexible substrate
129: shadow mask layer
152: vapor deposition metal electrode layer
156: metal nanowire layer
160: cover material

Claims (9)

Forming a flexible substrate;
Increasing and fixing the flexible substrate in the direction of a tensile force applied during use of the finished product;
Forming a shadow mask layer on the stretched flexible substrate;
Performing plasma treatment on a surface opened through the shadow mask layer;
Depositing a metal electrode on the stretched and fixed flexible substrate;
Removing the shadow mask layer;
Releasing the tensile force applied to the flexible substrate to remove the stretched state;
Attaching the metal nanowires by spraying them on the flexible substrate from which the stretched state has been removed using a spray coating; And
Including the step of covering the cover material on the flexible substrate,
The cover material is a cover substrate of the same material as the flexible substrate,
In the step of covering the cover material, a plasma treatment is performed on the surfaces of the flexible substrate and the cover substrate before bonding the flexible substrate and the cover substrate, and the flexible substrate and the cover substrate are pressed against each other, and the Combining the flexible substrate and the cover substrate,
In the step of depositing the metal electrode on the flexible substrate, the method of manufacturing a stretchable electrode, characterized in that the electrode is deposited to a thickness of 80 nm to 900 nm through a shadow mask by a thermal evaporation method.
delete The method of claim 1,
The cover material is a method of manufacturing a stretchable electrode in the form of a thin film in which the same material as the flexible substrate is applied on the flexible substrate and sintered.
delete delete The method of claim 1,
The metal electrode to be deposited is made of at least one material selected from gold, silver, and copper,
The metal nanowire is a method of manufacturing a stretchable electrode made of at least one material selected from silver and copper.
A flexible substrate assembly provided with a stretchable electrode manufactured by the method of any one of claims 1, 3 and 6.
delete delete

Images