KR102170894B1 - 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 low resistance and is stretchable, and in particular, to a flexible substrate assembly having a stretchable electrode having high stretchability and excellent stability that can be fabricated using a PDMS (polydimethylsiloxane) substrate bonding technology.

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.

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.

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.

Korean Patent Publication No. 10-0875711

The present invention is to provide a flexible substrate assembly having a stretchable electrode having stretchable properties and a method of manufacturing the same.

An object of the present invention is to provide a flexible substrate assembly having a flexible electrode having a small resistance change even in an extended state, and a method of manufacturing the same.

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.

Here, the first and second flexible substrates may be made of PDMS, and the metal electrode may be made of silver.

Here, prior to the step of combining the first and second flexible substrates, it may further include performing oxygen plasma treatment on the first and second flexible substrates.

Here, in the step of bonding the first flexible substrate and the second flexible substrate, the oxygen plasma-treated surfaces may be bonded by pressing them while facing each other.

Here, in the step of increasing and fixing the first flexible substrate and the step of increasing and fixing the second flexible substrate, the first flexible substrate or the second flexible substrate is increased by 20% to 100% in the length direction of the metal electrode. Can be fixed.

Here, after the step of depositing a metal electrode on the first flexible substrate, further comprising the step of patterning the metal electrode deposited on the first flexible substrate, and depositing a metal electrode on the second flexible substrate Thereafter, a step of patterning the metal electrode deposited on the second flexible substrate may be further included.

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

Here, in the step of forming the first flexible substrate and the step of forming the second flexible substrate, a base and a crosslinking agent are mixed in a ratio of 10: 1 and baked at 130 to 170° C. on a hot plate to form a PDMS substrate. I can.

A flexible substrate assembly having a stretchable electrode according to another aspect of the present invention comprises: a first PDMS substrate formed by mixing a base and a crosslinking agent in a ratio of 10:1; A first metal electrode deposited on the first PDMS substrate to a thickness of 80 nm to 900 nm; A second PDMS substrate formed by mixing a base and a crosslinking agent in a ratio of 10:1, and mechanically press-bonded with the first PDMS substrate; And a second metal electrode deposited on the second PDMS substrate to a thickness of 80 nm to 900 nm, and aligned with the first electrode and in close contact with each other, and the first metal electrode and the second metal electrode are stretched A reduced structure can be formed.

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 manufacturing method thereof is implemented, sufficient stretching is possible, and a stretchable electrode having a small resistance change even in the stretched state 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.

1 is a flow chart showing a method of manufacturing a stretchable electrode according to an embodiment of the present invention.
2A to 2E are conceptual diagrams showing a PDMS substrate and an electrode assembly during a manufacturing process according to the manufacturing method of FIG. 1.
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 2E.
4 is a photographic image of a stretchable electrode having various thickness and strain conditions in the range of 0 to 30%.
5A to 5C are graphs showing changes in sheet resistance for one cycle (extension and relaxation) when the maximum strain is 7%, 23%, and 38%, respectively.
5D to 5F are graphs showing the change in R/R ₀ for one cycle (stretching and relaxing) when the maximum strain is 7%, 23%, and 38%, respectively.
6A-6C are photographic images of stretchable silver (Ag) electrodes in different strains ranging from 0 to 38%.
7A and 7B are graphs showing R and R/R ₀ changes over the number of cycles between 1 cycle and 1000 cycles, respectively.
7C and 7D are graphs showing R/R ₀ change for the number of cycles 1 to 5 cycles, 995 to 1000 cycles (strain 15% and 0.5 mm/sec).
8A and 8B are circuit diagrams showing resistance circuit models of simple parallel and percolation connections, respectively.
9 is a graph showing R _relative experimental results consistent with Equation 6 below in 400+400nm samples.

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 forming a low-resistance stretchable metal electrode on a polymer substrate using a polymer (polymer) substrate bonding technology, more specifically a method of manufacturing a low-resistance stretchable Ag electrode on a PDMS substrate using a PDMS-PDMS bonding technology Suggest.

1 shows a method of manufacturing a stretchable electrode according to an embodiment of the present invention. 2A to 2E illustrate a PDMS substrate and an electrode assembly during a manufacturing process according to the manufacturing method of FIG. 1.

The method of manufacturing a stretchable electrode according to an exemplary embodiment of the present invention may include forming a first flexible substrate 120 (S122); Pre-stretching and fixing the first flexible substrate 120 in the direction of a tensile force applied during use of the finished product (S124); Performing a pre-deposition treatment on the stretched and fixed first flexible substrate 120 (S126); Depositing a metal electrode 128 on the stretched and fixed first flexible substrate 120 (S128); Forming a second flexible substrate (S142); Pre-stretching and fixing the second flexible substrate 140 in the direction of a tensile force applied during use of the finished product (S144); Performing a pre-deposition treatment on the stretched and fixed second flexible substrate 140 (S146); Depositing a metal electrode 148 on the stretched and fixed second flexible substrate 140 (S148); Performing oxygen plasma treatment on the first flexible substrate 120 and the second flexible substrate 140 (S150); In a state in which the metal electrode 128 of the first flexible substrate 120 and the metal electrode 148 of the second flexible substrate 140 are aligned and in contact with each other, the first flexible substrate 120 and the second flexible substrate It includes a step (S160) of combining (140).

The method of manufacturing the stretchable electrode shown is a method of manufacturing an Ag electrode through a pre-stretching method.

As shown in FIG. 2A, first/second flexible substrates 120 and 140 that can be stretched such as PDMS or ecoflex are manufactured (S122, S142), and as shown in FIG. 2B, the first/second flexible substrate ( Plasma treatment is performed on the surface in the state of stretching 120 and 140 in advance (S124 and S144) (S126 and S146).

In the steps (S122, S142) of fabricating the first/second flexible substrates 120 and 140, for example, a base and a crosslinking agent are mixed in a ratio of 10:1 and 130 to 170°C, preferably 150°C, on a hot plate. By baking in, it can be carried out in a manner of fabricating two PDMS substrates.

In the step of pre-stretching the first and second flexible substrates 120 and 140 (S124 and S144), the first and second flexible substrates 120 and 140 are used with a clamping device having a wide predetermined width. It may be performed in a manner of fixing the sides facing each other and fixing the position of the clamping device in a state in which a tensile force is applied by pulling away from each other.

In the step of pre-stretching the first and second flexible substrates (S124, S144), for example, the second substrates 120 and 140 are preliminary up to 20% to 100%, preferably 40% in the length direction. Can be stretched.

Depending on the implementation, in steps S124 and S144, 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 increases in advance in the longitudinal direction may be applied.

Depending on the implementation, in steps S124 and S144, when the finished product has a shape close to a square, a tensile force that increases in advance in the longitudinal 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, S146) 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 80 W of power, pressure: 1.4 torr, and time: 15 s, oxygen plasma treatment may be performed on the pre-stretched first/second substrates.

In FIG. 2B, after the plasma treatment (S126 and S146), the result of depositing a metal electrode or the like through a shadow mask or photolithography (S128, S148) and patterning (S129, S149) is shown.

That is, similar to a general semiconductor manufacturing process, after the step of depositing a metal electrode on the first flexible substrate (S128), a step of patterning the metal electrode deposited on the first flexible substrate (S129) is performed. .

Likewise, after the step of depositing a metal electrode on the second flexible substrate (S148), a step (S149) of patterning the metal electrode deposited on the second flexible substrate is performed.

In the steps of depositing the metal electrode (S128, S148), for example, 20% to 100% through a shadow mask using a thermal evaporation method (atmospheric pressure <5 × 10 ^-5 torr, deposition rate: 1 ÅA/s), preferably Alternatively, a metal (preferably Ag) electrode may be deposited on a 40% pre-stretched first/second flexible (PDMS) substrate. According to the idea of the present invention, electrodes (half electrodes) formed on each of the first/second flexible (PDMS) substrates 120 and 140 may have a thickness of 80 nm to 900 nm, respectively, 100, 200, and 400. And 800 nm samples were prepared, and each sample had somewhat superiority and inferiority, but desired properties.

Next, as shown in FIG. 2C, plasma is again formed on the first/second flexible (PDMS) substrates 120 and 140 on which the metal electrodes 128 and 148 are deposited in the state where the tensile force for the pre-stretched state is removed. The processing is performed (S150). For example, oxygen plasma treatment may be performed, and the oxygen plasma treatment is to increase surface adhesion activity to adhere the two substrates 120 and 140.

Depending on the implementation, in the step of performing the plasma treatment on the first/second flexible substrate (S150), first, in a state where the metal (Ag) electrodes 128 and 148 are covered using a shadow mask, the first / An oxygen plasma treatment may be performed on the surfaces of the second flexible substrates 120 and 140 on which the metal electrodes 128 and 148 are formed. At this time, 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.

Next, in order to measure the resistance change, an external electrode was connected to the pad using a paste (not shown), which is to examine the manufacturing result, and this process may be removed during mass production.

Next, as shown in FIG. 2D, the two substrates 120 and 140 subjected to oxygen plasma treatment are compressed (S160). That is, the first flexible substrate 120 and the second flexible substrate 140 are bonded by pressing the surfaces treated with oxygen plasma in step S150 in a state of facing each other.

When a substrate such as PDMS uses an oxygen plasma method, the two substrates 120 and 140 are strongly fused, as shown in FIG. 2E, without the need for an adhesive. At this time, the electrode portions are well aligned, and the two electrodes 128 and 148 are fused to form a conductive close contact (contact). That is, the two PDMS substrates are attached by applying mechanical pressure to the first/second flexible substrates in a state in which the surfaces on which the electrodes are formed are brought into contact with each other as shown.

When the two electrodes 128 and 148 are in contact, the performance of the stretchable electrode is significantly improved, rather than connecting a single electrode in parallel. That is, it is possible to manufacture an electrode with little resistance change due to external deformation.

In the above-described implementation, the pre-stretching state was removed from the step S150, but in another implementation, the pre-stretching state may be removed from the step S160, and in another implementation, It can be performed while maintaining a pre-stretching state until step S160.

FIG. 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 2E.

The flexible substrate assembly having the illustrated stretchable electrode includes: a first PDMS substrate 120 formed by mixing a base and a crosslinking agent in a ratio of 10:1; First electrodes 128-1 to 128-3 deposited on the first PDMS substrate 120 to a thickness of 80 nm to 900 nm; A second PDMS substrate 140 formed by mixing a base and a crosslinking agent in a ratio of 10:1, and mechanically press-bonded with the first PDMS substrate 120; The second electrodes 148-1 to 148-3 are deposited on the second PDMS substrate 140 to a thickness of 80 nm to 900 nm, and are aligned with and in close contact with the first electrodes 128-1 to 128-3. Including, the first electrodes 128-1 to 128-3 and the second electrodes 148-1 to 148-3 have a structure that is stretched and then reduced.

An experiment to determine the stretched and then reduced structure and the preferred thickness of the first and second electrodes are as follows.

4 shows photographic images of a stretchable electrode having various thickness and strain conditions in the range of 0 to 30%. As a metal, it can be seen that a wavy pattern is observed as the film thickness of the silver (Ag) electrode increases. That is, the wavy pattern is a structure that was stretched and then reduced, and is due to the fact that the electrode was deposited while the flexible substrate was stretched during the manufacturing process and then reduced again.

Of the samples shown, the 800 nm sample shows many surface cracks that can be observed with the naked eye. This is because the film stress between the silver (Ag) electrode and the PDMS substrate increases as the film thickness increases, so that when it approaches 1000 nm, the silver (Ag) film is deformed to the extent that the silver (Ag) film is peeled off. Optimization of the silver (Ag) electrode thin film thickness is important to lower the resistance of the stretchable Ag electrode. Other samples show relatively clean surfaces with few cracks from zero to large deformation conditions. Although there is a slight risk of problems with strength or resistance, the minimum thickness of the silver (Ag) electrode that can be formed on the PDMS substrate according to the idea of the present invention can be seen as 80 nm, and the maximum thickness can be seen as 900 nm. have. The relationship between surface morphology and performance can be studied by measuring the resistance change as a function of deformation.

Meanwhile, an experiment for an optimum thickness of a silver (Ag) electrode as the first electrode and the second electrode according to the present invention will be described as follows.

5A to 5C show changes in sheet resistance for one cycle (extension and relaxation) when the maximum strain is 7%, 23%, and 38%, respectively. 6A to 6C are photographic images of stretchable silver (Ag) electrodes in different strains ranging from 0 to 38%.

The initial resistances (R0) of the 100, 200, 400 and 400+400 nm samples are about 819, 444, 353 and 242 mΩ/square, respectively. It can be seen that the initial resistance does not decrease linearly as the film thickness increases. In particular, when the film thickness is thicker than 200 nm, the resistance slightly decreases.

This is due to the film stress between the silver (Ag) electrode and the PDMS substrate, and is due to the occurrence of large initial cracks as seen in the electron microscope image of FIG. 6. This simply increases the thickness to reduce the resistance of the stretchable silver (Ag) electrode, and the effect is weak when the thickness of the thin film is thicker than 200 nm. Conversely, the 400+400nm sample shows a very low sheet resistance, which is about 32% reduction compared to the 400nm sample. This sheet resistance is the lowest value among data found in literature using metal electrodes.

In addition, all samples, including 400 + 400nm samples, show excellent stretch performance up to 38%. For the 7% and 23% strains, only slight changes in resistance values were observed for all samples shown in Figures 5A and 5B. In particular, even when the strain is increased to 38%, the 400+400nm sample maintains a sheet resistance of less than 440mΩ/square as shown in FIG. 5C. This is the lowest value among all samples. Therefore, comparing the absolute resistance values, it can be said that the 400+400nm sample has the best performance with the minimum sheet resistance change.

To further evaluate the bonding effect of the 400+400nm sample, it is important to look at the R/R ₀ change with strain. 5D-5F show the R/R ₀ change as a function of strain calculated from 5C in FIGS. 5A. As the strain increased to 7%, all samples exhibited good stretchability at R/R ₀ of 1.04 or less. As the strain increases to 23%, the 100, 200 and 400+400 nm samples still exhibit good stretch at R/R ₀ below 1.06. In this case, the 400 nm sample shows that the R/R ₀ value increases to 1.27. However, as the strain further increases to 38% similar to the ratio before stretching in the manufacturing process of the PDMS substrate, it tends to have a value depending on the thickness of the thin film. It can be seen that the stretching ability follows the order of 100nm> 200nm ≥ 400+400nm> 400nm. It is reasonable to judge that the thin film shows the smallest film stress and superior performance compared to the thick film. However, the 400+400nm sample shows better performance than the 400nm sample when comparing R and R/R ₀ values.

6A shows an optical micrograph of a sample having a strain in the range of 0 to 38%. In the case of a 100 nm sample, as the strain increases, the wavy pattern becomes flat, and new vertical cracks occur due to Poisson contraction in the vertical direction of FIG. 6A. Other samples have a much larger wavy structure as the film thickness increases, so a small change in the wavy pattern can be observed. This can be confirmed by measuring the amplitude and period of the wavy structure. 6B shows confocal microscopy images for different samples when strain = 0%. Theoretically, the period and amplitude of the wavy pattern can be obtained by Equation 1 below.

Here, E _PDMS and E _Ag , and νP _DMS and ν _Ag are Young's Moduli and Poisson ratios of the PDMS substrate and the silver (Ag) electrode layer, respectively, and ε _c is the critical strain directly calculated by Equation 1 above. . The values of λ ₀ and A ₀ obtained from the theory using parameters of E _PDMS = 2.0 MPa, E _Ag = 69 GPa, ν _PDMS = 0.48, ν _Ag = 0.37 and t = 100-400 nm are summarized in Table 1 below. Images from a confocal microscope are also summarized in Table 1. The theory and experimental values of amplitude and period were found to have good consistency. This indicates that the Ag thin film on the PDMS substrate exhibits almost bulk characteristics with good film quality, and the effect of the PDMS substrate containing a large amount of oxygen and carbon impurities is sufficiently reduced.

According to the experimental results described above, it can be seen that the optimum thickness of the metal (Ag) electrode according to the idea of the present invention is a state in which the first electrode made of 400 nm and the second electrode made of 400 nm are conductively coupled to each other. Therefore, considering the margin in the process, the optimum thickness range of the first electrode and the second electrode can be viewed as 360nm to 440nm.

In addition, the relationship between the elasticity and thickness of the silver (Ag) electrode will be examined. A very low sheet resistance of 242 mΩ/square was obtained using a 400 nm thick silver (Ag) electrode and PDMS-PDMS bonding technology. The electrical properties of flexible silver (Ag) electrodes are studied under single and multi-cycle strain conditions.

First, a cycling stress test is applied to all samples to confirm stability under long-term strain conditions.

Figures 7a and 7b show the change of R and R/R ₀ for the number of cycles between 1 cycle and 1000 cycles, respectively, and Figures 7c and 7d show the number of cycles 1 to 5 cycles, 995 to 1000 cycles (strain 15% and 0.5 mm/sec) to R/R ₀ change. An additional condition of fast strain rate was applied to the sample compared to the one cycle test. When comparing the absolute values of R, the 400+400 nm sample shows the lowest sheet resistance in the entire cycle range shown in FIG. 7A. The highest sheet resistance of the 400+400nm sample is less than 310 mΩ/square even after 1000 cycles. However, when comparing R/R ₀ , the 100 nm sample shows the best performance with a very small change in R/R ₀ shown in Fig. 7 (b). Other samples show similar performance as the R/R ₀ value increases below 1.4. The 400+400nm sample has much better stability than the 400nm sample shown in Figs. 7c and 7d Based on the R/R ₀ value, the stability of the stretchable silver (Ag) electrode is 100nm> 400+400nm sample Depends on the film thickness in the order of> 200 nm> 400 nm This is an almost identical sequence to the cycle test shown in Figures 5d-5f.

The 400+400nm sample shows good performance in the slow 1 cycling and fast multi cycling tests. This sample shows excellent performance not only for the absolute value of R, but also for the relative value of R/R ₀ . This is because when the PDMS-PDMS bonding technique is adopted for bonding the first and second flexible substrates, the first and second electrodes are in close contact with each other to affect the conductive path. The bonding effect of the first/second electrode by applying the resistance network model, and more specifically, the effect of the conductive close contact of the first electrode and the second electrode (also referred to as percolation of the current path) is as follows. same.

8A and 8B show resistance circuit models of simple parallel and percolation connections, respectively. The 400nm sample can be modeled with a simple series resistance connection between the normal and strained regions. If a strained region is in the electrode, the resistance of the region increases. Therefore, the total resistance of the 400nm sample can be modeled using the following equations 2 and 3.

Here, R _{400_0} and R ₄₀₀ are the resistances in the case of no strain and in the case of strain for each 400 nm sample, a is the number of normal regions, b is a + b = n (constant). The number of strained regions, r is the length of the resistance normal region per unit, and r _s is the resistance per unit length of the strained region.

In the case of the 400+400nm sample, if the two electrodes (the first electrode at the top and the second electrode at the bottom) are simply connected without being connected to the middle of the electrode as shown in Fig. 8a, the R/R ₀ change is the resistance of the upper and lower electrodes. Since this increases at the same rate, the resistivity of the 400 nm sample can be expressed by the following equation.

Here, || denotes a parallel connection of two resistors, and R _para0 and R _para are resistances with and without strain of a 400 + 400 nm sample assuming a simple parallel connection shown in FIG. 8A. Therefore, R/R ₀ calculated from Equation 4 is the same as in Equation 3. This means that the _{R 400 / R 400_0 = R para} / R para0.

If the two electrodes are connected to the center of the electrode as shown in FIG. 8B, a new percolation path is created due to the parallel connection of r and r _s , so that the total resistance is lowered compared to the simple parallel connection of 8a, and the current increases the contact area (r _p ). Flows through In this case, due to the distribution of the strained regions, r in the uppermost layer can be connected to r _s in the lower layer with very low probability. In resistance modeling, the following constraints were assumed.

(1) The number of normal regions is larger than the number of deformed regions with a> b and the regions are distributed, so the percolation between the resistance values of r and r _s in the 400+400 nm sample is dominant.

(2) r _p is negligible due to metal-metal contact (r _p = 0).

Therefore, the total resistance can be modeled by Equation 5 below using FIG. 8B.

Here, the strained regions of the upper and lower electrodes are considered. Due to the strained regions of the upper and lower electrodes 2b, the number of electrodes 2b in the normal region is from a to ab Is reduced to In Equations 4 and 5, the relative resistance drop rate due to R _relative indicating how much current flows between the upper electrode and the lower electrode may be defined as in Equation 6 below.

Here, x = b/n represents the portion of the deformation region in the film, and r _ratio is defined as r _s /r. x can be obtained from the length deformed by the equation x = strain/(1 + strain). This is because x is equal to the ratio of the increased length to the total length. If R _relative is less than 1, current percolation exists between the upper electrode and the lower electrode, leading to a drop in resistance of the flexible electrode.

9 shows experimental results consistent with Equation 6 in the 400+400nm sample.

When the maximum strain is 7%, R _relative is almost 1, which means there is no percolation. In this case, since the strained area is very small, the percolation effect is negligible. However, when the maximum strain increases to 30 and 38%, R _relative decreases to 0.75 and 0.7, respectively, and the theoretical equation fits well with the experimental value except for the small strain condition. The fitting parameters obtained are r _c = (3.8 ± 0.03) r and (4.8 ± 0.08) r for 30 and 38% strain, respectively, indicating that a large strain of 1 cycle leads to an increase in resistance in the strained region. Show. When the strain increases, an increase in the resistance of the strained region leads to a decrease in R _relative by an increase in the percolation current for the same strain range shown in FIG. 9. Thus, using a simple resistive network model, the excellent performance of the 400 + 400nm sample from the percolation current path is well described.

According to the above-described experimental results, it is preferable that the first electrode and the second electrode, which are metal (Ag) electrodes according to the present invention, are in close conductive contact with each other to achieve a percolation effect on the current path. .

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: first flexible substrate
128, 128-1, 128-2, 128-3: first electrode
140: second flexible substrate
148, 148-1, 148-2, 148-3: second electrode

Claims (9)

Forming a first flexible substrate made of a stretchable PDMS material;
Performing a pre-stretched state in which the first flexible substrate is stretched and fixed by applying a tensile force in the longitudinal direction of the electrode;
Performing oxygen plasma treatment on the fixed first flexible substrate in the pre-stretched state;
Depositing a first silver electrode on the fixed first flexible substrate in a pre-stretched state;
Forming a second flexible substrate made of a stretchable PDMS material;
Performing a pre-stretched state in which the second flexible substrate is stretched and fixed by applying a tensile force in the longitudinal direction of the electrode;
Performing oxygen plasma treatment on the fixed second flexible substrate in the pre-stretched state;
Depositing a second silver electrode on the fixed two flexible substrates in the pre-stretched state;
Performing oxygen plasma treatment on the surface of the first flexible substrate on which the first silver electrode is deposited, while the tensile force for the pre-stretched state is removed;
Performing oxygen plasma treatment on the surface of the second flexible substrate on which the second silver electrode is deposited, while the tensile force for the pre-stretched state is removed; And
The surface on which the silver electrode of the first flexible substrate is deposited and the surface on which the silver electrode is deposited of the second flexible substrate are aligned with each other so that the first silver electrode and the second silver electrode are electrically coupled to each other. Including the step of combining the first flexible substrate and the second flexible substrate in a manner of pressing in a contact state,
In the step of depositing a first silver electrode on the first flexible substrate and depositing a second silver electrode on the second flexible substrate, the first silver electrode has a thickness of 360 nm to 440 nm through a shadow mask by a thermal evaporation method. And depositing a second silver electrode, respectively.
delete delete delete The method of claim 1,
In the step of increasing and fixing the first flexible substrate and the step of increasing and fixing the second flexible substrate,
A method of manufacturing a stretchable electrode, characterized in that the first flexible substrate or the second flexible substrate is fixed by increasing 20% to 100% in the length direction of the metal electrode.
The method of claim 1,
After depositing a metal electrode on the first flexible substrate,
Patterning a metal electrode deposited on the first flexible substrate
Including more,
After depositing a metal electrode on the second flexible substrate,
Patterning a metal electrode deposited on the second flexible substrate
The method of manufacturing a stretchable electrode further comprising a.
delete The method of claim 1,
In the step of forming the first flexible substrate and the step of forming the second flexible substrate,
A method of manufacturing a stretchable electrode, comprising mixing a base and a crosslinking agent in a ratio of 10: 1 and baking at 130 to 170° C. on a hot plate to form a PDMS substrate.
The flexible substrate assembly manufactured by the manufacturing method of any one of claims 1, 5, 6, and 8.

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