KR101677840B1 - Apparatus and method for assessment of flexible multi-layered thin film - Google Patents
Apparatus and method for assessment of flexible multi-layered thin film Download PDFInfo
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Abstract
The method of evaluating the durability of a flexible multilayer film according to embodiments of the present invention includes the steps of obtaining a load-depth curve according to a nano-indentation test on thin films constituting the multilayered film, Calculating the elastic modulus of each of the thin films from the thickness of the multilayer thin film, deriving the relation between the neutral axis position and the elastic modulus ratio on the thickness of the multilayer thin film, calculating the relationship between the derived neutral axis position-elastic modulus ratio and the elastic moduli of the thin films constituting the multilayer thin film And determining the neutral axis position according to the obtained elastic modulus ratio measurement value. The elastic modulus ratio can be defined as the ratio of the elastic modulus of the upper thin film to the elastic modulus of the lower thin film among the multilayer thin films.
Description
The present invention relates to thin film testing techniques, and more particularly, to thin film durability testing techniques.
Multilayer thin film based electronic devices such as thin film transistors, thin film batteries, thin film solar cells, and thin film displays are essential elements for realizing a flexible or foldable device. Flexible devices must have resistance and durability to bending that was not needed in existing electronic devices.
Typically, various electronic devices implemented as a multilayer structure on a fired substrate not only degrade mechanical properties such as cracks in the device layer after hundreds of thousands of bending cycles, but also voltage-current characteristics may vary. In addition, peeling occurs between the thin films and the multilayer thin film itself is damaged.
In order to evaluate the durability of the flexible multilayer film, the ability to withstand mechanical damage such as cracking or peeling should be evaluated. Conventionally, in order to measure the durability of the flexible multilayer thin film, it has been inevitable to evaluate the surface damage and the electrical performance deterioration that have occurred after performing the bending cycle of several hundred to several thousand times.
When the multilayer thin film is bent, stresses of different magnitudes are applied to the bonded films. Since the stress is applied in different directions by the compressive stress in the inner thin film and tensile stress in the outer thin film, there is a stress-free side in the middle of the multilayer thin film, and this plane is referred to as a neutral plane, neutral axis. Using this point, it is known to determine the thickness of the layers constituting the multilayered film such that the neutral plane lies in the middle of the thin film corresponding to the element layer.
If the neutral plane is formed in the middle of the element layer thin film and flexible and stretchable materials having conductivity are used, it is possible to reduce the degradation of mechanical and electrical performance due to cracks.
SUMMARY OF THE INVENTION The present invention has been made in an effort to provide an apparatus and a method for evaluating the durability of a flexible multilayer film.
An object of the present invention is to provide an apparatus and a method for evaluating the durability of a flexible multilayer thin film based on the mechanical properties of individual thin films instead of evaluating durability with a bending test which is time- In order to solve the problem.
SUMMARY OF THE INVENTION It is an object of the present invention to provide a flexible multilayer thin film durability evaluation apparatus and method capable of deriving an optimum thin film structure based on mechanical properties.
The solution to the problem of the present invention is not limited to those mentioned above, and other solutions not mentioned can be clearly understood by those skilled in the art from the following description.
A flexible multilayer thin film durability evaluation method performed in a computer according to an aspect of the present invention is characterized in that the computer obtains a load-depth curve according to a nano-indentation test on the thin films constituting the multilayer thin film step; Calculating elastic moduli of the respective thin films from the shape of the load-depth curve; Deriving a neutral axis position-elastic modulus ratio relationship on the thickness of the multilayered film; Determining a neutral axis position according to the relationship of the derived neutral axis position-elastic modulus ratio and the measured elastic modulus ratio values obtained from the elastic modulus values of the thin films constituting the multilayered thin film, It can be defined as the ratio of the elastic modulus of the upper thin film to the elastic modulus of the lower thin film in the thin film.
According to one embodiment, the modulus of elasticity of each of the thin films is calculated by the following equation
, Where < RTI ID = 0.0 >
According to one embodiment, the neutral axis position is calculated by the following equation
, Where h is the neutral axis position, i is the order of the thin film, y ci is the centroid height of the i th thin film, and A i is the effective sectional area of the i th thin film.
According to one embodiment, the flexible multi-layer thin film durability evaluation method is characterized in that, in accordance with the distribution of the internal stress due to the change of the elastic modulus ratio and the elastic modulus ratio measured value obtained from the elastic moduli of the thin films constituting the multilayered thin film, And estimating an internal stress at a boundary surface position of the thin films constituting the multilayer thin film.
According to one embodiment, the relationship between the modulus of elasticity modulus and the internal stress is given by the following equation
, Where < RTI ID = 0.0 >
According to one embodiment, the flexible multi-layer thin film durability evaluation method is characterized in that the flexible multilayer thin film durability evaluation method is a method of evaluating the durability of a flexible multilayer thin film according to a distribution of a strain energy density according to a change in elastic modulus ratio and a measurement value of elastic modulus ratio obtained from elastic moduli And estimating a strain energy density at a boundary surface position of the thin films constituting the multilayer thin film.
According to one embodiment, the relationship between the modulus of elasticity modulus and the strain energy density is given by the following equation
, Where < RTI ID = 0.0 >
According to one embodiment, the flexible multilayer thin film durability evaluation method may further include the step of quantifying the durability based on the interface position of the thin films constituting the multilayer thin film and the neutral axis position.
According to another aspect of the present invention, there is provided an apparatus for evaluating durability of a flexible multilayer film, comprising: a nanoindentation test processing unit for obtaining a load-depth curve according to a nanoindentation test on thin films constituting a multilayered film; An elastic modulus calculating unit for calculating elastic moduli of the respective thin films from the shape of the load-depth curve; And the relationship of the neutral axis position-elastic modulus ratio on the thickness of the multilayer thin film is derived, and the relationship of the derived neutral axis position-elastic modulus ratio and the elastic modulus ratio obtained from the elastic modulus of the thin films constituting the multilayer thin film The elastic modulus ratio may be defined as a ratio of the elastic modulus of the upper thin film to the elastic modulus of the lower thin film among the multilayer thin films.
According to one embodiment, the durability evaluator may calculate the durability of the multilayered thin film according to the distribution of the internal stress due to the change of the elastic modulus ratio and the elastic modulus ratio obtained from the elastic moduli of the thin films constituting the multilayered film, Lt; RTI ID = 0.0 > interfacial < / RTI > position of the constituting thin films.
According to one embodiment, the durability evaluating section may calculate the durability of the multilayer thin film according to the distribution of the strain energy density corresponding to the change of the elastic modulus ratio and the elastic modulus ratio obtained from the elastic moduli of the thin films constituting the multilayer thin film, To estimate the strain energy density at the interface position of the thin films constituting the thin film.
According to one embodiment, the durability evaluator may operate to quantify durability based on the interface position of the thin films constituting the multilayered film and the neutral axis position.
According to the flexible multilayer thin film durability evaluation apparatus and method of the present invention, instead of evaluating the durability by a bending test which is time-consuming and difficult to qualitatively evaluate, the flexible multilayer thin film is evaluated for durability of the flexible multilayer thin film based on the mechanical properties of the individual thin film Can be evaluated.
INDUSTRIAL APPLICABILITY According to the flexible multilayer thin film durability evaluation device and method of the present invention, an optimum thin film structure can be derived based on mechanical property values.
The effects of the present invention are not limited to those mentioned above, and other effects not mentioned can be clearly understood by those skilled in the art from the following description.
1 is a flowchart illustrating a method of evaluating a durability of a flexible multilayer thin film according to an embodiment of the present invention.
2 is a schematic view illustrating a structure of a multilayer thin film to which a flexible multilayer thin film durability evaluation method according to an embodiment of the present invention is applied.
3 is a graph illustrating a load-depth curve measured according to a nanoindentation test in the structure of a multilayer thin film to which a flexible multilayer thin film durability evaluation method according to an embodiment of the present invention is applied.
FIG. 4 is a schematic diagram illustrating the conversion of a multilayer thin film for calculating a neutral axis using a modulus of elasticity in a multilayer thin film structure to which a flexible multilayer thin film durability evaluation method according to an embodiment of the present invention is applied.
5 is a graph illustrating the relationship between the modulus of elasticity and the neutral axis in the structure of the multilayer thin film to which the flexible multilayer thin film durability evaluation method according to an embodiment of the present invention is applied.
6 is a graph illustrating the relationship between the elastic modulus ratio and the normalized stress in the multilayer thin film structure to which the flexible multilayer thin film durability evaluation method according to an embodiment of the present invention is applied.
FIG. 7 is a graph illustrating the relationship between elastic modulus ratio and strain energy density in a multilayer thin film structure to which a flexible multilayer thin film durability evaluation method according to an embodiment of the present invention is applied.
8 is a block diagram illustrating a flexible multilayer film durability evaluation apparatus according to an embodiment of the present invention.
For the embodiments of the invention disclosed herein, specific structural and functional descriptions are set forth for the purpose of describing an embodiment of the invention only, and it is to be understood that the embodiments of the invention may be practiced in various forms, The present invention should not be construed as limited to the embodiments described in Figs.
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The same reference numerals are used for the same constituent elements in the drawings and redundant explanations for the same constituent elements are omitted.
1 is a flowchart illustrating a method of evaluating a durability of a flexible multilayer thin film according to an embodiment of the present invention.
1, a flexible multi-layer thin film durability evaluation method performed by a computer includes the steps of: calculating a load-depth curve according to a nano-indentation test on a thin film constituting a multilayer thin film in step S11; (Force-Depth Curve).
In order to measure the mechanical properties of the thin film and to analyze the interface characteristics between the thin film and the base substrate, the nano indentation test was carried out by pressing the tip made of a diamond material onto the thin film surface while measuring the applied load and the depth Compression test (uniaxial compression test).
Such a nanoindentation test can be performed individually for each of the plurality of thin films constituting the multilayer thin film as shown in FIG.
In FIG. 2, the thickness of the multilayer thin film is 400 nm, and the thicknesses of the two thin films constituting the multilayer thin film are 100 nm and 300 nm, respectively. The upper thin film is a flexible organic semiconductor QQT (CN) 4 thin film and the lower thin film is a ferroelectric polymer PVDF-TrFE thin film.
With reference to the basal plane of the multilayer film, the interface is at a position of 300 nm, and the geometrical center plane is at a position of 200 nm.
The neutral axis position where the internal stress or elastic energy (or strain energy density) is minimum when such multilayer thin film is bent will be located somewhere on the longitudinal axis (thickness) in the multilayer thin film. It is possible to know the difference between the ideal neutral axis position and the actual interface position due to the physical properties of the thin films obtained through the nanoindentation test, and the strength stress or elastic energy level according to the physical properties of the thin films can be known at the actual interface position.
Accordingly, the durability of the individual multilayer thin films can be quantified, or the durability among various multilayer thin films can be relatively compared.
FIG. 3 is a graph illustrating a load-depth curve measured according to a nanoindentation test in the structure of a multilayer thin film to which a flexible multilayer thin film durability evaluation method according to an embodiment of the present invention is applied.
In Figure 3, the load-depth curve begins at the origin corresponding to the load-depth relationship at the point at which the Berkovich tip begins to apply the load, for example, as the tip penetrates into the thin film, The load is also increasing.
When the indentation depth reaches a predetermined final indentation depth, a change in the indentation depth is measured while gradually removing the load.
The final indentation depth may be determined, for example, in accordance with the ISO-14577 standard, which is recommended to be within 10 to 15% of the thickness of the film or to ensure that the average roughness is within 5% of the final indentation depth.
As the load is removed, the thin film is partially recovered from the pressed shape depending on the physical properties. From the degree of recovery, the elasticity and plasticity characteristics of the material can be deduced.
Referring again to FIG. 1, in step S12, the computer can calculate the elastic moduli of the respective films from the shape of the load-depth curve.
The elastic modulus of the thin film can be calculated according to the following equation (1).
here,
Meanwhile,
In step S13, the computer can derive the neutral axis position-elastic modulus ratio relationship on the thickness of the multilayered film.
The elastic modulus ratio is the ratio of the elastic modulus of the upper thin film to the elastic modulus of the lower thin film among the multilayer thin films.
In order to analyze the stress when the multilayer thin film is bent, this multilayer thin film can be converted into thin films made of the same material as shown in Fig. FIG. 4 is a schematic diagram illustrating the conversion of a multilayer thin film for calculating a neutral axis using a modulus of elasticity in a multilayer thin film structure to which a flexible multilayer thin film durability evaluation method according to an embodiment of the present invention is applied.
In Fig. 4, Fig. 4 (a) is an original multilayer thin film, in which thin films of width W and different materials are stacked.
At this time, if the elastic modulus (E QQT (CN) 4 ) of the upper thin film is n times the elastic modulus (E PVDF-TrFE ) of the lower thin film, that is, if the elastic modulus ratio is n, then the effective sectional area of the upper thin film is n times.
Accordingly, as shown in FIG. 4 (b), the original multi-layer thin films having different physical properties but having the same width have different widths (n times longer), but the physical properties can be converted into multi- have.
In such a multi-layered film, the position of the neutral axis with respect to the bottom surface of the multi-layered film can be calculated by the following equation (2).
Here, h is the neutral axis position, i is the order of the thin film, y ci is the centroid height of the i th thin film, and A i is the effective sectional area of the i th thin film. At this time, the elastic modulus ratio n is included in the effective sectional area A i of each thin film.
For example, in the case of a multilayer thin film composed of two thin films as shown in FIG. 2 and each thin film having a thickness of 300 nm and 100 nm, the center plane height of each thin film is 150 nm and 350 nm, The neutral axis position can be expressed as a function of the ratio of the modulus of elasticity to the height of the thin film center plane (which depends on the film thickness).
The neutral axis position according to Equation (3) is the same as in Fig. 5 is a graph illustrating the relationship between the modulus of elasticity and the neutral axis in the structure of the multilayer thin film to which the flexible multilayer thin film durability evaluation method according to an embodiment of the present invention is applied.
In FIG. 5, the actual boundary surface position of the multilayer thin film is 300 nm, and the geometric center surface position is 200 nm. When the modulus of elasticity modulus n is decreased, the neutral axis position of the multilayered film becomes close to 150 nm when the modulus of elasticity ratio n is small. When the modulus of elasticity ratio n is large, the modulus of elasticity modulus n approaches 350 nm. function.
According to the graph of FIG. 5, when the elastic modulus ratio n is 10 in the present multilayered film structure, the neutral axis position is located at approximately 300 nm, and the interface and the neutral axis position are substantially aligned, The applied stress is very small and is therefore expected to be the most stable.
If the elastic modulus ratio n is 1, the neutral axis position is approximately 200 nm, and is somewhat distant from the interface, so that some stress appears at the interface when bent.
In the experimental results obtained with the actual organic semiconductor QQT (CN) 4 thin film and the ferroelectric polymer PVDF-TrFE thin film, the elastic modulus ratio n was about 1.6, in which case the neutral axis position is calculated as 221 nm.
Since the neutral axis position can be expressed as a function of the elastic modulus ratio, the position of the neutral axis can be determined from the relationship between the neutral axis position-elastic modulus ratio and the actual elastic modulus ratio.
Using this relationship, returning to FIG. 1, in step S14, the computer calculates the elastic modulus obtained from the elastic modulus of the thin films constituting the multilayer thin film and the relationship between the neutral axis position- Depending on the non-measured value, the neutral axis position can be determined.
Meanwhile, the method of evaluating the durability of the flexible multilayer thin film according to an embodiment of the present invention can further analyze the internal stress according to the change of the modulus of elasticity.
Specifically, in step S15, the computer calculates the elastic modulus ratio obtained from the distribution of the internal stress due to the change in the elastic modulus ratio and the elastic modulus ratio obtained from the elastic moduli of the thin films constituting the multilayered thin film, The internal stress can be estimated at the interface position of the thin films.
Even if each thin film is not broken at the time of bending, the multilayer thin film can no longer function when peeling occurs, which is a phenomenon in which thin films are separated at the interface. Therefore, the durability of the multilayer thin film can be evaluated by the possibility of peeling at the interface position. The method for evaluating the durability of the flexible multilayer thin film according to the embodiment of the present invention can analyze the internal stress according to the elastic modulus ratio at the interface position as shown in the following Equation (4).
here,
The distribution of the internal stress according to the change of the modulus of elasticity ratio calculated according to Equation (4) is shown in FIG. 6 is a graph illustrating the relationship between the modulus of elasticity and the normalized internal stress in the structure of the multilayer thin film to which the flexible multilayer thin film durability evaluation method according to an embodiment of the present invention is applied.
In Fig. 6, the elastic modulus ratio n is represented by a logarithmic scale, and the internal stress is expressed by a logarithm while being normalized to denominator when n = 1.
In the case of the elastic modulus ratio n = 1.6 in the actual experimental example, it can be seen that there is almost no difference between the internal stresses at the interface positions based on the elastic modulus ratio n = 1. When the elastic modulus ratio n increases to 9, the internal stress sharply decreases. However, when the modulus of elasticity ratio n exceeds 9, the internal stress rapidly increases again.
Accordingly, it can be seen that, in the case of the multilayer thin film designed to have the thickness as shown in FIG. 2, it is possible to obtain a desired durability if the elastic modulus ratio of the thin films can be designed so as to be closer to 9 than to 9.
In the case of the multilayer thin film having the thickness as shown in FIG. 2, the multilayer thin films composed of the thin films having the elastic modulus ratio of about 0.1 to 3 have no difference in terms of the internal stress at the interface, that is, It can be seen that it will be similar.
Referring back to FIG. 1, the method of evaluating the durability of a flexible multilayer thin film according to an embodiment of the present invention can further analyze the strain energy density according to the change of elastic modulus ratio.
Specifically, in step S16, the computer is configured to construct the multilayer thin film according to the distribution of the strain energy density according to the change in the elastic modulus ratio and the elastic modulus ratio obtained from the elastic modulus of the thin films constituting the multilayer thin film It is possible to estimate the strain energy density at the interface of the thin films.
The flexible multilayer thin film durability evaluation method according to the embodiment of the present invention can analyze the strain energy density according to the elastic modulus ratio at the interface position as shown in the following Equation (5).
here,
The distribution of the strain energy density according to the change of the modulus of elasticity ratio calculated according to the equation (5) is shown in FIG. FIG. 7 is a graph illustrating the relationship between elastic modulus ratio and strain energy density in a multilayer thin film structure to which a flexible multilayer thin film durability evaluation method according to an embodiment of the present invention is applied.
7, the elastic modulus ratio n is represented by a logarithmic scale, and the strain energy density is represented by a logarithmic scale while being normalized to denominator when n = 1.
In the case of the elastic modulus ratio n = 1.6 in the actual experimental example, it can be seen that the strain energy density at the interface position has almost no difference based on the elastic modulus ratio n = 1. As the elastic modulus ratio n increases, the strain energy density decreases sharply when it approaches 9, but sharply increases again when the elastic modulus ratio n exceeds 9.
Accordingly, it can be seen that, in the case of the multilayer thin film designed to have the thickness as shown in FIG. 2, it is possible to obtain a desired durability if the elastic modulus ratio of the thin films can be designed so as to be closer to 9 than to 9.
In the case of the multilayer thin film designed to have the thickness shown in FIG. 2, the multilayer thin films composed of the thin films having the elastic modulus ratio of the thin films have no difference in terms of the strain energy density at the interface, that is, Can be seen to be similar.
Referring again to FIG. 1, in an optional step S17, the computer can quantify durability based on the interface position and the neutral axis position of the thin films constituting the multilayered film. Accordingly, the durability may be quantified with absolute reference based on experimental data, or may be relatively compared among the control groups.
8 is a block diagram illustrating a flexible multilayer film durability evaluation apparatus according to an embodiment of the present invention.
8, the flexible multilayer film durability evaluation apparatus 80 according to an embodiment of the present invention may include a nanoindentation test processing unit 81, an elastic modulus calculating unit 82, and a durability evaluating unit 83 have.
The nanoindentation test processing unit 81 can obtain a load-depth curve according to the nanoindentation test on the thin films constituting the multilayered film.
The elastic modulus calculating unit 82 can calculate the elastic modulus of each thin film from the shape of the load-depth curve.
The durability evaluation unit 83 derives the relationship between the neutral axis position and the elastic modulus ratio on the thickness of the multilayered film and calculates the elastic modulus ratio obtained from the elastic modulus ratios of the thin films constituting the multilayered film Depending on the measured value, the position of the neutral axis can be determined, for example, as shown in equations (1) and (2).
In this case, the elastic modulus ratio can be defined as the ratio of the elastic modulus of the upper thin film to the elastic modulus of the lower thin film among the multilayer thin films.
According to the embodiment, the durability evaluation unit 83 determines the durability of the multilayer thin film according to the distribution of the internal stress due to the change in the elastic modulus ratio and the elastic modulus ratio obtained from the elastic moduli of the thin films constituting the multilayer thin film The internal stress at the interface of the thin films can be estimated as shown in Equation (4).
According to the embodiment, the durability evaluating section 83 constructs the multilayer thin film according to the distribution of the strain energy density according to the change of the elastic modulus ratio and the elastic modulus ratio obtained from the elastic modulus of the thin films constituting the multilayer thin film Strain energy densities at the interface positions of the thin films can be estimated, for example, as shown in Equation (5).
According to the embodiment, the durability evaluation section 83 can quantify the durability based on the position of the interface and the position of the neutral axis of the thin films constituting the multilayered film.
It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. It will be understood that variations and specific embodiments which may occur to those skilled in the art are included within the scope of the present invention.
80 Flexible multilayer thin film durability evaluation device
81 nano indentation test processing section
82 elasticity modulus calculating section
83 Durability evaluation section
Claims (13)
The elastic modulus ratio is defined as the ratio of the elastic modulus of the upper thin film to the elastic modulus of the lower thin film among the multilayer thin films,
The strain energy densities at the interface positions of the thin films constituting the multilayer thin film were measured according to the distribution of the strain energy density according to the change of the elastic modulus ratio and the elastic modulus ratio measured values obtained from the elastic moduli of the thin films constituting the multilayer thin film And estimating the durability of the flexible multilayer film durability.
, Where < RTI ID = 0.0 >
, Where h is the neutral axis position, i is the order of the thin film, y ci is the centroid of the i th thin film, and A i is the effective cross sectional area of the i th thin film. Assessment Methods.
The internal stress is estimated at the interface positions of the thin films constituting the multilayer thin film according to the distribution of the internal stress due to the change of the elastic modulus ratio and the elastic modulus ratio measured values obtained from the elastic moduli of the thin films constituting the multilayer thin film Further comprising the step of evaluating the durability of the flexible multilayer film.
, Where < RTI ID = 0.0 >
, Where < RTI ID = 0.0 >
Further comprising the step of quantifying the durability based on the position of the interface of the thin films constituting the multilayered film and the position of the neutral axis.
The elastic modulus ratio is defined as the ratio of the elastic modulus of the upper thin film to the elastic modulus of the lower thin film among the multilayer thin films,
The durability evaluating unit may calculate the durability of the multilayer thin film based on the distribution of the strain energy density according to the change in the elastic modulus ratio and the elastic modulus ratio obtained from the elastic moduli of the thin films constituting the multilayer thin film, And estimating a strain energy density at a position of the thin film layer.
The internal stress is estimated at the interface positions of the thin films constituting the multilayer thin film according to the distribution of the internal stress due to the change of the elastic modulus ratio and the elastic modulus ratio measured values obtained from the elastic moduli of the thin films constituting the multilayer thin film Layer thin film durability evaluation device.
Layer thin film durability evaluating device is operable to quantify durability based on the position of the interface between the thin films constituting the multilayer thin film and the position of the neutral axis.
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| KR20230081482A (en) | 2021-11-30 | 2023-06-07 | 한국생산기술연구원 | Deformation measuring Method of Thin Flexible Material |
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