A method for measuring the in-plane thermal conductivity of a self-supporting film

Abstract

The present invention provides a method for measuring the in-plane thermal conductivity of a self-supporting film, the measuring method comprising the following steps: (1) determining the size of the film to be measured and the frequency range of the heating current according to the key physical property parameters of the film to be measured; (2) selecting a film to be measured of a specific size according to the size obtained in step (1), and preparing a film-frame complex using the film to be measured and a supporting frame; (3) depositing two mutually parallel conductive strips on a side surface of the film to be measured in the film-frame complex obtained in step (2), the strips being a first conductive strip and a second conductive strip; (4) according to the frequency range of the heating current obtained in step (1), utilizing the conductive strips obtained in step (3), and based on a data processing method of a one-dimensional heat conduction model, measuring the in-plane thermal conductivity of the film to be measured. The measuring method provided by the present invention simplifies the sample preparation process, reduces measurement cost, improves test efficiency, and broadens the range of sample characterization.

Description

Technical Field

[0001] The invention belongs to the technical field of thermal property measurement, and relates to a method for measuring the thermal conductivity of a thin film, in particular to a method for measuring the in-plane thermal conductivity of a self-supporting thin film. Background Art

[0002] Measuring thermal conductivity is a crucial step in the development of functional thin film materials. Accurately measuring thermal conductivity is challenging even for macroscopic samples due to factors such as radiative heat loss and contact thermal resistance. Characterizing thin film materials, especially those at the micron or nanometer scale, presents even greater challenges.

[0003] Since many thin film materials have structural anisotropy, their normal thermal conductivity (κ ⊥ ) and in-plane thermal conductivity (κ || ) are generally not equal and need to be measured separately. In terms of the characterization of the in-plane thermal conductivity of thin films, most of the current methods use steady-state and AC measurement techniques based on the one-dimensional heat conduction model. Infrared imaging thermometry can be used as a typical example of steady-state measurement (A. Greppmair, B. Stoib, N. Saxena, C. Gerstberger, P. Muller-Buschbaum, M. Stutzmann, MS Brandt, Measurement of the in-plane thermal conductivity by steady-state infrared thermography, Rev. Sci. Instrum. 2017, 88: 044903.). Although the sample preparation of this method is relatively simple, it requires the sample to have a relatively large light absorption and thermal radiation coefficient, and the measurement equipment needs to be calibrated more cumbersomely. When measuring at high temperatures, the thermal radiation of the sample surface may also bring relatively large errors, so its application range is subject to certain limitations. Hatta et al. proposed an AC calorimetric technique based on light heating, which can be used to measure the in-plane thermal diffusivity of thin films tens of microns thick, but cannot directly give the in-plane thermal conductivity of the film (I. Hatta, Y. Sasuga, R. Kato, and A. Maesono, Thermal diffusivity measurement of thin films by means of an ac calorimetric method, Rev. Sci. Instrum. 1985, 56: 1643.).

[0004] CN111458369A discloses an AC measurement method based on an ultrathin dielectric film. The method can directly obtain the in-plane thermal conductivity of the film, but the width of the conductive strip used does not exceed 5 microns. Electrodes of this width need to be made using standard micromachining methods such as ultraviolet lithography, which is costly. This method also requires that the film to be measured can be deposited on the surface of the ultrathin dielectric film, and is therefore not suitable for the characterization of self-supporting films. At the same time, in order to correctly use this AC measurement method, it is necessary to constrain the experimental conditions (such as the range of the heating current, the sample size, etc.) to a certain extent, but the invention does not clearly provide a solution for selecting the experimental conditions.

[0005] It can be seen that how to provide a method for measuring the in-plane thermal conductivity of thin films, simplify the sample preparation process, reduce measurement costs, improve test efficiency, and at the same time broaden the range of samples that can be characterized has become an urgent problem that technical personnel in this field need to solve. Summary of the Invention

[0006] The present invention aims to provide a method for measuring the in-plane thermal conductivity of a self-supporting film, which simplifies the sample preparation process, reduces measurement costs, improves test efficiency, and broadens the range of samples that can be characterized.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for measuring the in-plane thermal conductivity of a self-supporting film, the method comprising the following steps:

[0009] (1) Determine the size of the film to be tested and the frequency range of the heating current based on the key physical properties of the film to be tested;

[0010] (2) selecting a film to be tested of a specific size according to the size of the film to be tested obtained in step (1), and preparing a film-frame composite using the film to be tested of the specific size and a supporting frame;

[0011] (3) depositing two mutually parallel conductive strips on one side of the surface of the film to be tested in the film-frame composite obtained in step (2), namely, a first conductive strip and a second conductive strip;

[0012] (4) According to the frequency range of the heating current obtained in step (1), using the conductive strip obtained in step (3), and based on the data processing method of the one-dimensional heat conduction model, the in-plane thermal conductivity of the film to be measured is measured.

[0013] Among them, the key physical properties of the film to be tested in step (1) include the thickness, thermal conductivity magnitude and thermal diffusivity magnitude of the film to be tested; in step (3), the widths of the first conductive strip and the second conductive strip are respectively 30-40 μm, for example, can be 30 μm, 31 μm, 32 μm, 33 μm, 34 μm, 35 μm, 36 μm, 37 μm, 38 μm, 39 μm or 40 μm, but are not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0014] The present invention uses a simple hollow mask technology to deposit two parallel conductive strips on the surface of a micron-scale self-supporting film, and relaxes the width of the conductive strips to 30-40 μm without significantly affecting the measurement accuracy, thereby simplifying the sample preparation process, avoiding expensive and complex micromachining steps, reducing measurement costs, improving test efficiency, and broadening the range of sample characterization. The in-plane thermal conductivity of the film can be at least 0.1-100 Wm -1 K -1 varies within a wide range.

[0015] In addition, the measurement method provided by the present invention adopts a parallel double conductive strip configuration and a data processing method based on a one-dimensional heat conduction model. The errors caused by factors such as the heat capacity of the conductive strip itself, the thermal radiation loss on the film surface, the current / voltage wire and the lateral thermal conductivity of the part of the film to which it is attached are automatically offset to a certain extent, thereby further ensuring the accuracy of the measurement.

[0016] Preferably, the process of determining the size of the film to be measured and the frequency range of the heating current in step (1) is based on the following conditions:

[0017] (1.1) Ensure the thermal penetration depth δ of the film to be tested in the thickness direction ⊥ At least 5 times the thickness d of the film to be tested M , which is:

[0018]

[0019] The corresponding heating current frequency f1 is:

[0020]

[0021] Among them, α ⊥ It is the order of magnitude of the thermal diffusivity of the film to be tested in the thickness direction.

[0022] (1.2) Ensure the thermal penetration depth δ of the film to be tested in the in-plane direction || At least 5 times the half width of the conductive strip That is:

[0023]

[0024] The corresponding heating current frequency f2 is:

[0025] f2=α || / (25πw h 2 ) (4)

[0026] Among them, α || is the order of magnitude of the thermal diffusivity of the film to be tested in the in-plane direction.

[0027] (1.3) Assume that the in-plane thermal conductivity κ of the film to be tested is || It is isotropic, ensuring that the thermal conductivity G of the film adjacent to the first conductive strip is the same as that of the first conductive strip in the direction of thermal conductivity measurement. M The thermal conductivity of the current conductor and the portion of the film to which it is attached and the voltage conductor and the portion of the film to which it is attached is at least 10 times that of the first conductive strip. b , which is:

[0028]

[0029] and,

[0030]

[0031] Among them, L h is the length of the first conductive strip; is the average thermal conductivity of the composite structure consisting of the current / voltage conductor and the part of the film to which it is attached; κ h is the thermal conductivity of the electrode layer; d h is the thickness of the electrode layer; w i is the width of the current conductor; w v is the width of the voltage conductor; L i is the length of the current conductor; L v is the length of the voltage conductor.

[0032] In the present invention, it is assumed that the in-plane thermal conductivity κ of the film to be measured is || If it is anisotropic, then κ in formula (6) || The order of magnitude of the maximum component of the in-plane thermal conductivity of the film to be tested is used instead.

[0033] The corresponding heating current frequency f3 is:

[0034]

[0035] (1.4) Ensure the thermal penetration depth δ of the film to be tested in the in-plane direction || At most 1 / 5 times the half width of the suspended part of the film to be tested That is:

[0036]

[0037] The corresponding heating current frequency f4 is:

[0038] f4=25α || / (πl 2 ) (10)

[0039] Preferably, the thickness of the film to be tested in step (1) is 1-100 μm, for example, it can be 1 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm or 100 μm, but is not limited to the listed values, and other unlisted values within this numerical range are also applicable.

[0040] Preferably, the size of the film to be tested and the frequency range of the heating current in step (1) are determined based on f1, f2, f3 and f4 obtained in steps (1.1) to (1.4). The specific determination process is: the upper limit of the frequency of the heating current f max The lower limit of the frequency of the heating current is determined by the smaller value of f1 and f2. min Determined by the larger value of f3 and f4; at the same time, use any one or a combination of at least two of the following methods to ensure that f1 and f2 are both greater than f3 and f4, and increase f max and f min The width of the frequency window between:

[0041] (A) By reducing the width w of the conductive strip h To increase f2;

[0042] (B) By reducing the thermal conductivity κ of the electrode layer h and / or the thickness d of the electrode layer h To lower f3;

[0043] (C) By increasing the length L of the current conductor i and / or the length L of the voltage conductor v To lower f3;

[0044] (D) Reduce f4 by increasing the width l of the overhanging portion of the film to be tested.

[0045] Among them, method (C) is accompanied by increasing the longitudinal dimension of the film to be measured, and method (D) is accompanied by increasing the transverse dimension of the film to be measured, that is, to determine the size of the film to be measured.

[0046] Preferably, the shape of the film to be tested of the specific size in step (2) is square or rectangular.

[0047] Preferably, the support frame in step (2) is a metal frame with a hollow window in the center.

[0048] Preferably, the shape of the hollow window is square or rectangular.

[0049] Preferably, the metal frame is made of copper.

[0050] In step (2), the film to be measured is fixed at both ends to a support frame to form a film-frame complex, so that the film to be measured is suspended in the air to measure the in-plane thermal conductivity of the portion of the film between the two fixed ends. Good thermal contact exists between the film to be measured and the support frame, and the portion of the film to be measured that is in thermal contact with the support frame serves as a heat sink.

[0051] Preferably, in step (3), the distance D between the first conductive strip and the second conductive strip is δ ||,min As a benchmark, δ ||,min corresponds to f min The thermal penetration depth of the film under test in the in-plane direction.

[0052] Preferably, D is δ ||,min 0.2-1.2 times, for example, it can be 0.2 times, 0.3 times, 0.4 times, 0.5 times, 0.6 times, 0.7 times, 0.8 times, 0.9 times, 1 times, 1.1 times or 1.2 times, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0053] Preferably, in step (3), the first conductive strip and the second conductive strip are parallel to the frame of the support frame along the length direction and perpendicular to the thermal conductivity measurement direction.

[0054] Preferably, in step (3), the first conductive strip coincides with a central symmetry axis of the film to be tested along its length direction.

[0055] Preferably, in step (3), the first conductive strip and the second conductive strip are respectively connected to two current terminals via current conductors, and are connected to two voltage terminals via voltage conductors.

[0056] Preferably, the current conducting wire is located on an extension line of the connected conductive strip along the length direction.

[0057] Preferably, the voltage conductor is located on a side of the connected conductive strip, that is, a side away from an unconnected conductive strip.

[0058] Preferably, in step (3), the first conductive strip and the second conductive strip are made of metal or conductive compound, more preferably any one of gold, platinum or niobium nitride.

[0059] Preferably, the method for measuring the in-plane thermal conductivity of the film to be measured in step (4) adopts 3ω and 2ω voltage measurement technology, which specifically includes the following steps:

[0060] (4.1) Based on the frequency range of the heating current obtained in step (1), an alternating current I0sin(ωt) with an amplitude of I0 and an angular frequency of ω is passed through the first conductive strip, and the amplitude |ΔT(2ω)1| and phase Φ(2ω)1 of the temperature fluctuation of the first conductive strip and the phase Φ(2ω)2 of the temperature fluctuation of the second conductive strip are measured;

[0061] (4.2) is calculated value; wherein, N(2ω)=[Φ(2ω)1-Φ(2ω)2] / D, M(2ω)=N(2ω) / tan(3π / 2-Φ(2ω)1), and D is the spacing between the first conductive strip and the second conductive strip;

[0062] (4.3) Plot |ΔT(2ω)1| and calculate the in-plane thermal conductivity κ of the film to be tested based on the slope S1 of the fitted line. || =P L S1 / (2d M ); where P L is the AC heating power amplitude per unit length of the first conductive strip;

[0063] (4.4) Calculate the value of M(2ω)·N(2ω), plot ω against M(2ω)·N(2ω), fit the test data with a straight line passing through the origin, and calculate the in-plane thermal diffusivity α of the film to be tested based on the slope S2 of the fitted line. || =S2;

[0064] (4.5) According to step (4.3), the in-plane thermal conductivity κ || and the in-plane thermal diffusivity α obtained in step (4.4) || The volume heat capacity C of the film to be tested is calculated v =κ || / α || .

[0065] Preferably, the measurement method further comprises verifying the in-plane thermal conductivity of the film to be measured by using three-dimensional finite element simulation.

[0066] Compared with the prior art, the present invention has the following beneficial effects:

[0067] (1) The present invention uses a simple hollow mask technology to deposit two parallel conductive strips on the surface of a micron-scale self-supporting film, and relaxes the width of the conductive strips to 30-40 μm without significantly affecting the measurement accuracy, thereby simplifying the sample preparation process, avoiding expensive and complex micromachining steps, reducing measurement costs, improving test efficiency, and broadening the range of sample characterization. The thermal conductivity of the film surface can be at least 0.1-100 Wm -1 K -1 varies within a wide range;

[0068] (2) The measurement method provided by the present invention adopts a configuration of parallel double conductive strips and a data processing method based on a one-dimensional heat conduction model. The errors caused by factors such as the heat capacity of the conductive strips themselves, the thermal radiation loss of the film surface, the current / voltage wires and the lateral thermal conductivity of the part of the film to which they are attached are automatically offset to a certain extent, thereby further ensuring the accuracy of the measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 is a top view of the film-frame complex in the measurement method provided by the present invention;

[0070] Figure 2 is a side view of the film-frame complex in the measurement method provided by the present invention;

[0071] Figure 3 The lateral thermal conductivity G in the measurement method provided by the present invention b1 and the thermal conductivity G of the film to be measured M Schematic diagram;

[0072] Figure 4 The lateral thermal conductivity G in the measurement method provided by the present invention b2 and the thermal conductivity G of the film to be measured M Schematic diagram;

[0073] Figure 5 is a three-dimensional finite element simulation result diagram of the temperature fluctuation amplitude of the first conductive strip varying with frequency in Example 1;

[0074] Figure 6 3D finite element simulation result diagram of the temperature fluctuation phase of the first conductive strip and the second conductive strip varying with frequency in Example 1;

[0075] Figure 7 In Example 1 3D finite element simulation results as the first conductive strip temperature fluctuation amplitude |ΔT(2ω)1| changes;

[0076] Figure 8 is a three-dimensional finite element simulation result diagram of the temperature fluctuation amplitude of the first conductive strip varying with frequency in Example 2;

[0077] Figure 9 3D finite element simulation results of the temperature fluctuation phase of the first conductive strip and the second conductive strip varying with frequency in Example 2;

[0078] Figure 10 In Example 2 3D finite element simulation results as the first conductive strip temperature fluctuation amplitude |ΔT(2ω)1| changes;

[0079] Figure 11 3D finite element simulation results of ω varying with M(2ω)·N(2ω) in Example 2;

[0080] Figure 12 is a schematic structural diagram of the measurement circuit unit in Example 3;

[0081] Figure 13 3 is a graph showing the measurement results of the temperature fluctuation amplitude of the first conductive strip and the temperature fluctuation phase of the first conductive strip and the second conductive strip as a function of the heating current frequency in Example 3;

[0082] Figure 14 In Example 3 Actual measurement results of the first conductive strip as its temperature fluctuation amplitude |ΔT(2ω)1| changes;

[0083] Figure 15 This is a graph showing the actual measurement results of the in-plane thermal conductivity of the PTFE film changing with temperature in Example 3.

[0084] Among them: 1-film to be tested; 2-support frame; 3-first conductive strip; 4-second conductive strip; 5-current wire; 6-current terminal; 7-voltage wire; 8-voltage terminal; 9-computer; 10-AC current source; 11-variable resistor; 12-first differential amplifier; 13-second differential amplifier; 14-digital-to-analog conversion chip; 15-amplifier; 16-phase-locked amplifier; 17-DC current source; 18-matrix switch. DETAILED DESCRIPTION

[0085] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0086] The present invention provides a method for measuring the in-plane thermal conductivity of a self-supporting film, the method comprising the following steps:

[0087] (1) Figure 1 and Figure 2As shown, the size of the film 1 to be tested and the frequency range of the heating current are determined according to the thickness, thermal conductivity and thermal diffusivity of the film 1 to be tested. The specific determination process is based on the following conditions:

[0088] (1.1) Ensure the thermal penetration depth δ of the film 1 to be tested in the thickness direction ⊥ At least 5 times the thickness d of the film to be tested 1 M , which is:

[0089]

[0090] The corresponding heating current frequency f1 is:

[0091]

[0092] Among them, α ⊥ It is the order of magnitude of the thermal diffusivity of the film 1 to be tested in the thickness direction.

[0093] (1.2) Ensure the thermal penetration depth δ of the film 1 to be tested in the in-plane direction || At least 5 times the half width of the conductive strip That is:

[0094]

[0095] The corresponding heating current frequency f2 is:

[0096] f2=α || / (25πw h 2 ) (4)

[0097] Among them, α || It is the order of magnitude of the thermal diffusivity of the film 1 to be tested in the in-plane direction.

[0098] (1.3) Assume that the in-plane thermal conductivity κ of the film 1 to be tested is || It is isotropic, ensuring that the thermal conductivity G of the film adjacent to the first conductive strip 3 is the same as that of the first conductive strip 3 in the direction of thermal conductivity measurement. M The thermal conductivity G of the current conductor 5 and the part of the film attached thereto and the voltage conductor 7 and the part of the film attached thereto is at least 10 times that of the first conductive strip 3. b , which is:

[0099]

[0100] and,

[0101]

[0102] Among them, L h is the length of the first conductive strip 3; is the average thermal conductivity of the composite structure consisting of the current conductor 5 / voltage conductor 7 and the portion of the film to which they are attached; h is the thermal conductivity of the electrode layer; d h is the thickness of the electrode layer; w i is the width of the current conductor 5; w v is the width of the voltage conductor 7; L i is the length of the current conductor 5; L v is the length of the voltage wire 7.

[0103] The corresponding heating current frequency f3 is:

[0104]

[0105] (1.4) Ensure the thermal penetration depth δ of the film 1 to be tested in the in-plane direction || At most 1 / 5 times the half width of the suspended portion of the film to be tested 1 That is:

[0106]

[0107] The corresponding heating current frequency f4 is:

[0108] f4=25α || / (πl 2 ) (10)

[0109] Wherein, the thickness of the film 1 to be tested is 1-100 μm.

[0110] Based on f1, f2, f3 and f4 obtained in steps (1.1)-(1.4), the specific determination process of the size of the film 1 to be tested and the frequency range of the heating current is as follows: the upper limit of the frequency of the heating current f max The lower limit of the frequency of the heating current is determined by the smaller value of f1 and f2. min Determined by the larger value of f3 and f4; at the same time, use any one or a combination of at least two of the following methods to ensure that f1 and f2 are both greater than f3 and f4, and increase f max and f min The width of the frequency window between:

[0111] (A) By reducing the width w of the conductive strip h To increase f2;

[0112] (B) By reducing the thermal conductivity κ of the electrode layer h and / or the thickness d of the electrode layer h To lower f3;

[0113] (C) By increasing the length L of the current conductor 5 i and / or the length L of the voltage conductor 7v To lower f3;

[0114] (D) Reduce f4 by increasing the width l of the overhanging portion of the film 1 to be tested.

[0115] Among them, method (C) is accompanied by increasing the longitudinal dimension of the film 1 to be tested, and method (D) is accompanied by increasing the transverse dimension of the film 1 to be tested, that is, to determine the size of the film 1 to be tested.

[0116] (2) selecting a square or rectangular film 1 of a specific size according to the size of the film 1 to be tested obtained in step (1), and preparing a film-frame composite using the film 1 to be tested and a support frame 2; the support frame 2 is a metal frame with a square or rectangular hollow window provided in the center, and the material of the metal frame includes copper; Figure 1 and Figure 2 Shown are a top view and a side view of the film 1 to be tested fixed on the support frame 2 .

[0117] (3) Two parallel conductive strips with a thickness of 30-40 μm are deposited on one side of the film-frame composite obtained in step (2), namely, a first conductive strip 3 and a second conductive strip 4; the spacing D between the first conductive strip 3 and the second conductive strip 4 is δ ||,min As a benchmark, δ ||,min corresponds to f min The thermal penetration depth of the film 1 to be tested in the in-plane direction, and D is δ ||,min 0.2-1.2 times of the first conductive strip 3 and the second conductive strip 4 are parallel to the frame of the support frame 2 along the length direction and are parallel to the thermal conductivity measurement direction ( Figure 3 The first conductive strip 3 coincides with a central symmetry axis of the film 1 to be tested along its length direction; the first conductive strip 3 and the second conductive strip 4 are respectively connected to two current terminals 6 through current wires 5, and are connected to two voltage terminals 8 through voltage wires 7, and the current wires 5 are located on the extension lines of the connected conductive strips along their length directions, and the voltage wires 7 are located on one side of the connected conductive strips, that is, the side away from the unconnected conductive strips; the first conductive strips 3 and the second conductive strips 4 are respectively made of any one of gold, platinum or niobium nitride.

[0118] like Figure 3 and Figure 4 As shown, when the first conductive strip 3 is energized and heated, part of the heat generated is transferred to the film adjacent to the first conductive strip 3 and flows along the x and -x directions, and another part of the heat flows along the current conductor 5 and the film attached thereto (see FIG. Figure 3 sectional view in FIG) and the voltage conductor 7 and the portion of the film to which it adheres (see FIG). Figure 4In order to ensure the reliability of the measurement, the thermal conductivity of the film adjacent to the first conductive strip 3 in the x (or -x) direction is G M Need to be much larger than the lateral thermal conductivity G b Thermal conductivity G M The thermal conductivity κ of the film 1 to be tested || and thickness d M , in-plane heat diffusion depth δ || and the length L of the first conductive strip 3 h Determined by the lateral thermal conductivity G b It can be roughly divided into two parts. One part is mainly composed of the current conductor 5 and the part of the film it adheres to ( Figure 3 The shaded area contributes to (G b1 ), the other part is mainly composed of the voltage wire 7 and the part of the film it adheres to ( Figure 4 The shaded area contributes to (G b2 ). G b The size of the current conductor 5 and the voltage conductor 7, the film thickness d M and the average thermal conductivity of the wire / film composite structure Make an estimate.

[0119] (4) Using 3ω and 2ω voltage measurement techniques to measure the in-plane thermal conductivity of the film 1 to be tested, specifically comprising the following steps:

[0120] (4.1) Based on the frequency range of the heating current obtained in step (1), an alternating current I0sin(ωt) with an amplitude of I0 and an angular frequency of ω is passed through the first conductive strip 3, and the amplitude |ΔT(2ω)1| and phase Φ(2ω)1 of the temperature fluctuation of the first conductive strip 3 and the phase Φ(2ω)2 of the temperature fluctuation of the second conductive strip 4 are measured;

[0121] (4.2) is calculated value; wherein, N(2ω)=[Φ(2ω)1-Φ(2ω)2] / D, M(2ω)=N(2ω) / tan(3π / 2-Φ(2ω)1), and D is the distance between the first conductive strip 3 and the second conductive strip 4;

[0122] (4.3) The in-plane thermal conductivity κ of the film 1 to be tested is calculated based on the slope S1 of the fitted straight line. || =P L S1 / (2d M ); where P L is the AC heating power amplitude per unit length of the first conductive strip 3;

[0123] (4.4) Calculate the value of M(2ω)·N(2ω), plot ω against M(2ω)·N(2ω), fit the test data with a straight line passing through the origin, and calculate the in-plane thermal diffusivity α of the film to be tested based on the slope S2 of the fitted line. || =S2;

[0124] (4.5) According to step (4.3), the in-plane thermal conductivity κ || and the in-plane thermal diffusivity α obtained in step (4.4) || The volume heat capacity C of the film to be tested is calculated v =κ || / α || .

[0125] (5) The in-plane thermal conductivity of the obtained film 1 to be tested was verified using three-dimensional finite element simulation.

[0126] Example 1

[0127] This embodiment provides a low thermal conductivity film (0.1-1Wm -1 K -1 ) The estimation method and 3D simulation verification of the in-plane thermal conductivity measurement conditions are as follows:

[0128] Assuming that the thermal conductivity of the film 1 to be tested is isotropic, the in-plane thermal conductivity κ || and thermal conductivity κ in the thickness direction ⊥ The order of magnitude is 0.5Wm -1 K -1 (i.e., κ || =κ ⊥ ≈0.5Wm -1 K -1 ), in-plane thermal diffusivity α || and thermal diffusivity α in the thickness direction ⊥ The order of magnitude is 10 -6 m 2 s -1 (i.e. α || =α ⊥ ≈10 -6 m 2 s -1 ). Measuring electrode pattern as Figure 1 As shown, the width l (along the x direction) and thickness d of the suspended part of the film 1 to be tested are M 8 mm and 10 μm respectively, and the longitudinal dimension (along the y direction) is 9.2 mm; correspondingly, the lengths of the current wire 5 and the voltage wire 7 are L i =2.7mm and L v =6.1mm; thermal conductivity of electrode layer κ h and thickness d h240Wm -1 K -1 and 80nm; the length L of the first conductive strip 3 h and width w h The length and width of the second conductive strip 4 are 0.6 mm and 35 μm respectively; the width of the current conductor 5 and the voltage conductor 7 is w i =w v =35μm.

[0129] According to formula (6), the average in-plane thermal conductivity of the composite structure composed of the current conductor 5 / voltage conductor 7 and the part of the film to which they are attached is 2.4Wm -1 K -1 Substituting the above parameters into formula (2), formula (4), formula (8) and formula (10), the calculated f1, f2, f3 and f4 are 31.8Hz, 10.4Hz, 0.10Hz and 0.12Hz respectively. According to the size of f1 and f2, the upper limit of the frequency of the heating current f max Determined to be 10.4Hz; according to the size of f3 and f4, the lower limit of the frequency of the heating current f min Determined to be 0.12Hz. According to formula (3), corresponding to f min = 0.12Hz in-plane heat penetration depth is δ ||,min =814 μm, and the distance D between the first conductive strip 3 and the second conductive strip 4 is set to δ ||,min About 0.2 times of D, that is, D = 160μm.

[0130] In order to verify the feasibility of measuring the in-plane thermal conductivity of a micron-thick, low-thermal-conductivity film using a 35μm-wide heating strip, this embodiment uses a three-dimensional finite element simulation to simulate the measurement process in a vacuum, taking into account the surface thermal radiation loss of the film and the measuring electrode. The simulated geometric configuration is as follows: Figure 1 As shown, the two ends of the film 1 to be tested are fixed on a copper frame. The film 1 to be tested is isotropic and has a thickness of d. M The length of the electrode layer is 10 μm, the width of the suspended portion is 8 mm, and the vertical width is 9.2 mm. The electrode layer is made of gold with a thickness of 80 nm. The spacing D between the first conductive strip 3 and the second conductive strip 4 is 160 μm. Table 1 lists the physical properties of the film 1 to be tested, the gold measuring electrode, and the copper frame set in the simulation, including thermal conductivity κ, volume heat capacity C, and the like. V , thermal radiation coefficient ε and electrical conductivity σ, assuming that the physical properties parameters in Table 1 do not change with temperature during the simulation process.

[0131] Table 1

[0132] Physical properties Gold measuring electrodes Copper frame Film to be tested <![CDATA[κ(Wm -1 K -1 )]]> 240.00 400.00 0.26 <![CDATA[C V (Jm. -3 K -1 )]]> <![CDATA[1.60×10 6 ]]> <![CDATA[3.44×10 6 ]]> <![CDATA[2.22×10 6 ]]> ε 0.03 0.5 0.9 <![CDATA[σ(Sm -1 )]]> <![CDATA[1.34×10 7 ]]> / /

[0133] The initial temperature of the film-copper frame complex is set at 300K, and the temperature of the bottom of the copper frame is also kept constant at 300K during the simulation. A sinusoidal alternating current I(t)=I0sin(ωt) is applied to the first conductive strip 3 to periodically heat the film (I0=3mA). Figure 5 and Figure 6 As shown in FIG1 , the data of the temperature fluctuation amplitude |ΔT(2ω)1| and phase Φ(2ω)1 of the first conductive strip 3 and the temperature fluctuation phase Φ(2ω)2 of the second conductive strip 4 as a function of the heating current frequency f (f=ω / 2π) can be obtained from the simulation results. min and f max ,In the simulation experiment, the frequency of the heating current ranges from 1 to 5 Hz.

[0134] Will Figure 5 and Figure 6 The temperature fluctuation information in is used as the observation quantity to calculate value, where, N(2ω)=[Φ(2ω)1-Φ(2ω)2] / D, M(2ω)=N(2ω) / tan(3π / 2-Φ(2ω)1). like Figure 7 As shown, Plotting |ΔT(2ω)1|, we can get a straight line. Using the slope S of the straight line obtained by linear fitting and the formula κ || =P L S / (2d M )(P L is the AC heating power amplitude per unit length of the first conductive strip 3) and the in-plane thermal conductivity of the film is 0.259 Wm -1 K -1 , which is consistent with the simulation setting value (0.26Wm -1 K -1 ) is less than 0.5%; the same method is used to obtain simulation results at different measurement temperatures, and the results are summarized in Table 2. It can be seen that even when the measurement temperature reaches 410K, the relative error between the simulation measurement results and the simulation set values is still less than 1%. This shows that for low thermal conductivity films, when the heating line width is between 35-40μm, even if the measurement temperature reaches 410K, the influence of surface thermal radiation loss on the in-plane thermal conductivity measurement results can still be ignored.

[0135] Table 2

[0136] <![CDATA[Measure the temperature T0 (K)]]> 300 360 410 <![CDATA[Simulation result κ || (Wm -1 K -1 )]]> 0.259 0.261 0.262 Relative error -0.38％ 0.38％ 0.77％

[0137] Example 2

[0138] This embodiment provides a high thermal conductivity film (50-100Wm -1 K -1) The estimation method and 3D simulation verification of the in-plane thermal conductivity measurement conditions are as follows:

[0139] Assuming that the thermal conductivity of the film 1 to be tested is isotropic, the in-plane thermal conductivity κ || and thermal conductivity κ in the thickness direction ⊥ The order of magnitude is 100Wm -1 K -1 (i.e., κ || =κ ⊥ ≈100Wm -1 K -1 ), the volumetric heat capacity is on the order of 10 6 Jm -3 K -1 , in-plane thermal diffusivity α || and thermal diffusivity α in the thickness direction ⊥ The order of magnitude is 10 -4 m 2 s -1 (i.e. α || =α ⊥ ≈10 -4 m 2 s -1 ). Measuring electrode pattern as Figure 1 As shown, the width l (along the x direction) and thickness d of the suspended part of the film 1 to be tested are M are 20 mm and 5 μm respectively, and the longitudinal dimension (along the y direction) is 20 mm; correspondingly, the lengths of the current wire 5 and the voltage wire 7 are L i =7.9mm and L v =11.4mm; thermal conductivity of electrode layer κ h and thickness d h 240Wm -1 K -1 and 80nm; the length L of the first conductive strip 3 h and width w h The length and width of the second conductive strip 4 are 0.8 mm and 35 μm respectively; the width of the current conductor 5 and the voltage conductor 7 is w i =w v =35μm.

[0140] According to formula (6), the average in-plane thermal conductivity of the composite structure composed of the current conductor 5 / voltage conductor 7 and the part of the film to which they are attached is 102.2Wm -1 K -1 Substituting the above parameters into formula (2), formula (4), formula (8) and formula (10), the calculated f1, f2, f3 and f4 are 1.27×10 4 Hz, 1.04×103 Hz, 0.05Hz and 2.0Hz. According to the size of f1 and f2, the upper limit of the frequency of the heating current f max Determined to be 1.04×10 3 Hz; According to the size of f3 and f4, the lower limit of the frequency of the heating current is f min Determined to be 2.0Hz. According to formula (3), corresponding to f min =The in-plane heat penetration depth at 2.0 Hz is δ ||,min =2×10 3 μm, and the distance D between the first conductive strip 3 and the second conductive strip 4 is set to δ ||,min 0.5 times of , that is, D = 1000μm.

[0141] In order to verify the feasibility of measuring the in-plane thermal conductivity of a micron-thick high thermal conductivity film using a 35μm wide heating strip, this embodiment uses a three-dimensional finite element simulation to simulate the measurement process in a vacuum, taking into account the surface thermal radiation loss of the film and the measuring electrode. The simulated geometric configuration is as follows: Figure 1 As shown, the two ends of the film 1 to be tested are fixed on a copper frame. The film 1 to be tested is isotropic and has a thickness of d. M The length of the electrode layer is 5 μm, the width of the suspended portion is 20 mm, and the vertical width is 20 mm. The electrode layer is made of gold with a thickness of 80 nm. The spacing D between the first conductive strip 3 and the second conductive strip 4 is 1000 μm. Table 3 lists the physical properties of the film 1 to be tested, the gold measuring electrode, and the copper frame set in the simulation, including thermal conductivity κ, volume heat capacity C V , thermal radiation coefficient ε and electrical conductivity σ, assuming that the physical properties parameters in Table 3 do not change with temperature during the simulation process.

[0142] Table 3

[0143] Physical properties Gold measuring electrodes Copper frame Film to be tested <![CDATA[κ(Wm -1 K -1 )]]> 240.00 400.00 80 <![CDATA[C V (Jm. -3 K -1 )]]> <![CDATA[1.60×10 6 ]]> <![CDATA[3.44×10 6 ]]> <![CDATA[7.75×10 5 ]]> ε 0.03 0.5 0.9 <![CDATA[σ(Sm -1 )]]> <![CDATA[1.34×10 7 ]]> / /

[0144] The initial temperature of the film-copper frame complex was set at 300K, and the temperature of the bottom of the copper frame was also kept constant at 300K during the simulation. A sinusoidal alternating current I(t) = I0sin(ωt) was applied to the first conductive strip 3 to periodically heat the film (I0 = 8 mA). Figure 8 and Figure 9 As shown in FIG1 , the data of the temperature fluctuation amplitude |ΔT(2ω)1| and phase Φ(2ω)1 of the first conductive strip 3 and the temperature fluctuation phase Φ(2ω)2 of the second conductive strip 4 as a function of the heating current frequency f (f=ω / 2π) can be obtained from the simulation results. min and f max ,In the simulation experiment, the frequency of the heating current ranges from 10 to 50 Hz.

[0145] Will Figure 8 and Figure 9 The temperature fluctuation information in is used as the observation quantity to calculate value, where, N(2ω)=[Φ(2ω)1-Φ(2ω)2] / D, M(2ω)=N(2ω) / tan(3π / 2-Φ(2ω)1). like Figure 10 As shown, Plotting |ΔT(2ω)1|, we can get a straight line. Using the linear fitting slope S1 and the formula κ || =P L S1 / (2d M )(P L is the AC heating power amplitude per unit length of the first conductive strip 3) and the in-plane thermal conductivity of the film is 80.8 Wm -1 K -1 , which is consistent with the simulation setting value (80Wm -1 K -1 ) is only 1%. The value of M(2ω)·N(2ω) is calculated as follows: Figure 11 As shown, plot ω against M(2ω)·N(2ω), fit the test data with a straight line passing through the origin, and calculate the slope S2 of the fitted straight line and the formula α || = S2, the in-plane thermal diffusivity of the film is 1.02×10 -4 m 2 s -1 , which is consistent with the simulation setting value (1.03×10 -4 m 2 s -1 ) is less than 1%. According to the above-mentioned in-plane thermal conductivity κ || and the in-plane thermal diffusivity α || and Formula C v =κ || / α || The volume heat capacity of the film can be obtained to be 7.92×10 5 Jm -3 K -1 , which is consistent with the simulation setting value (7.75×10 5 Jm -3 K -1 ) is only 2.2%.

[0146] It can be seen that for high thermal conductivity films, when the heating line width is between 35-40 μm, it is still possible to obtain high measurement accuracy of in-plane thermal conductivity, in-plane thermal diffusivity and volumetric heat capacity.

[0147] Example 3

[0148] This embodiment provides a low thermal conductivity film (0.1-1Wm-1 K -1 ) is an experimental method for measuring the in-plane thermal conductivity of a 10.8 μm thick polytetrafluoroethylene (PTFE) film. Figure 1 As shown in the figure, the two ends of the PTFE film are fixed to a copper frame with silver glue. The overhang width l between the two ends of the film is 8mm, and the longitudinal dimension along the y direction is 10mm. A gold electrode pattern is thermally evaporated on the surface of the PTFE film using a hollow mask. The shape of the electrode pattern is similar to Figure 1 The electrode patterns shown have the same shape, the thickness of the electrode layer is 80 nm, and the length and width of the first conductive strip 3 are 0.77 mm and 35 μm, respectively.

[0149] The dimensions of the PTFE film and the electrodes in this embodiment are similar to those of the film 1 to be measured and the electrodes in Example 1. The thermal conductivity and thermal diffusivity of the PTFE film are also on the same order of magnitude as the corresponding physical quantities of the film 1 to be measured in Example 1. Therefore, the heating current frequency range (0.1-10 Hz) obtained in Example 1 can be directly adopted in this embodiment. In actual measurements, the frequency range of the heating current in this embodiment is limited to between 0.5-4 Hz. The measuring device for the thermal conductivity of the film is similar to the measuring device provided in Example 1 in CN111458369A, so it will not be described in detail here.

[0150] The measurement method provided in this embodiment specifically includes the following steps:

[0151] (1) The film-frame composite is placed in a vacuum sample chamber, and the resistance temperature coefficient β of the first conductive strip 3 is calibrated.

[0152] (2) The film-frame composite is balanced to a certain temperature, and a sinusoidal heating current I(ω)=I0sin(ωt) (where I0 is the amplitude of the heating current and ω=2πf is the angular frequency of the heating current) is passed through the first conductive strip 3. The amplitude of the 3ω voltage signal of the first conductive strip 3 is measured using the 3ω voltage measurement technique. 3ω | and phase Φ 3ω The relationship between the change of current frequency and the change of β and |V 3ω |Calculate the amplitude of the temperature fluctuation of the first conductive strip 3 |ΔT(2ω)1|(|ΔT(2ω)|1=(2|V 3ω |) / (|V ω |β), where |V ω | is the voltage signal amplitude of 1ω at both ends of the first conductive strip 3) and the phase Φ(2ω)1(Φ(2ω)1=Φ 3ω+π / 2). A direct current is passed through the second conductive strip 4, and the relationship between the phase Φ(2ω)2 of the temperature fluctuation of the second conductive strip 4 and the current frequency is obtained using the 2ω voltage measurement technique. The parameters N(2ω) = (Φ(2ω)1 - Φ(2ω)2) / D and M(2ω) = N(2ω) / tan(3π / 2 - Φ(2ω)1) corresponding to each heating current frequency are calculated, where the spacing D between the first conductive strip 3 and the second conductive strip 4 is 162 μm.

[0153] (3) Figure 12 As shown, the voltage signal measurement circuit of this embodiment is similar to CN111458369A, and a computer 9 is used to control the measurement process and data acquisition. The measurement circuit includes a 3ω voltage measurement circuit for measuring the 3ω voltage signal of the first conductive strip 3 to obtain the amplitude and phase of its temperature fluctuation. The measurement circuit includes an AC current source 10, a variable resistor 11, two differential amplifiers (12 and 13), a digital-to-analog converter chip (DAC) 14, an amplifier 15, and a lock-in amplifier 16. The AC current amplitude injected by the AC current source 10 into the first conductive strip 3 is 2.1mA (RMS value). The measurement circuit also includes a 2ω voltage measurement circuit for measuring the 2ω voltage signal of the second conductive strip 4 to obtain the phase of its temperature fluctuation. The measurement circuit also includes a DC current source 17 and a lock-in amplifier 16, and the DC current amplitude injected by the DC current source 17 into the second conductive strip 4 is 1.5mA. Unlike CN111458369A, the 3ω voltage measurement circuit and the 2ω voltage measurement circuit in this embodiment share a lock-in amplifier 16. For each fixed heating current frequency, the computer 9 controls the matrix switch 18 to connect the lock-in amplifier 16 to the 3ω voltage measurement circuit and the 2ω voltage measurement circuit in turn to measure the 3ω and 2ω voltage signals, respectively.

[0154] Figure 13 Shown are the trends of |ΔT(2ω)1|, Φ(2ω)1, and Φ(2ω)2 signals of the PTFE film measured at room temperature as a function of the heating current frequency.

[0155] (4) Starting from the measured values |ΔT(2ω)1|, Φ(2ω)1 and Φ(2ω)2, calculate the corresponding frequency of each heating current value, where, N(2ω)=[Φ(2ω)1-Φ(2ω)2] / D, M(2ω)=N(2ω) / tan(3π / 2-Φ(2ω)1). like Figure 14 As shown, Plotting |ΔT(2ω)1|, we can get a straight line. Using the slope S of the straight line obtained by linear fitting and the formula κ || =P L S / (2d M )(P Lis the AC heating power amplitude per unit length of the first conductive strip) and the in-plane thermal conductivity of the PTFE film at room temperature is 0.30±0.02Wm -1 K -1 .

[0156] (5) The temperature of the film-frame composite was changed, and the trend of the in-plane thermal conductivity of the PTFE film changing with temperature was measured.

[0157] Figure 15 The results show that the in-plane thermal conductivity of PTFE film varies with temperature in the temperature range of 300-410K. This result is basically consistent with the size of the thermal conductivity of PTFE bulk material and its trend of variation with temperature reported in the literature (J.Blumm, A.Lindemann, M.Meyer, C.Strasser, Characterization of PTFE Using Advanced Thermal Analysis Techniques, Int.J.Thermophys., 31(10)(2008)1919-1927.).

[0158] It can be seen that the present invention uses a simple hollow mask technology to deposit two parallel conductive strips on the surface of a micron-level self-supporting film, and relaxes the width of the conductive strips to 30-40 μm without significantly affecting the measurement accuracy, thereby simplifying the sample preparation process, avoiding expensive and complex micromachining steps, reducing measurement costs, improving test efficiency, and broadening the range of sample characterization. The in-plane thermal conductivity of the film can be at least 0.1-100 Wm -1 K -1 varies within a wide range.

[0159] In addition, the measurement method provided by the present invention adopts a parallel double conductive strip configuration and a data processing method based on a one-dimensional heat conduction model. The errors caused by factors such as the heat capacity of the conductive strip itself, the thermal radiation loss on the film surface, the current / voltage wire and the lateral thermal conductivity of the part of the film to which it is attached are automatically offset to a certain extent, thereby further ensuring the accuracy of the measurement.

[0160] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for measuring the in-plane thermal conductivity of a self-supporting film, characterized in that: The measuring method comprises the following steps: (1) Determine the size of the film to be tested and the frequency range of the heating current based on the key physical properties of the film to be tested; (2) selecting a film to be tested of a specific size according to the size of the film to be tested obtained in step (1), and preparing a film-frame composite using the film to be tested of the specific size and a supporting frame; (3) depositing two mutually parallel conductive strips on one side of the surface of the film to be tested in the film-frame composite obtained in step (2), namely, a first conductive strip and a second conductive strip, wherein the widths of the first conductive strip and the second conductive strip are 30-40 μm respectively; (4) measuring the in-plane thermal conductivity of the film to be measured using the conductive strips obtained in step (3) according to the frequency range of the heating current obtained in step (1) and a data processing method based on a one-dimensional heat conduction model; The key physical properties of the film to be tested in step (1) include the thickness, thermal conductivity magnitude, and thermal diffusivity magnitude of the film to be tested, and the size of the film to be tested and the frequency range of the heating current are determined based on the following conditions: (1.1) Ensure the thermal penetration depth δ of the film to be tested in the thickness direction ⊥ 5 times the thickness of the film to be tested d M , which is: The corresponding heating current frequency f1 is: Among them, α ⊥ is the magnitude of the thermal diffusivity of the film to be tested in the thickness direction; (1.2) Ensure the thermal penetration depth δ of the film to be tested in the in-plane direction || 5 times the half width of the conductive strip That is: The corresponding heating current frequency f2 is: f2=a || / (25πw h 2 ) (4) Among them, α || is the magnitude of the thermal diffusivity of the film to be tested in the in-plane direction; (1.3) Assume that the in-plane thermal conductivity κ of the film to be tested is || It is isotropic, ensuring that the thermal conductivity G of the film adjacent to the first conductive strip is the same as that of the first conductive strip in the direction of thermal conductivity measurement. M The thermal conductivity G of the current conductor and the part of the film it adheres to, and the voltage conductor and the part of the film it adheres to, which is 10 times that of the first conductive strip b , which is: and, Among them, L h is the length of the first conductive strip; is the average thermal conductivity of the composite structure consisting of the current / voltage conductor and the part of the film to which it is attached; κ h is the thermal conductivity of the electrode layer; d h is the thickness of the electrode layer; w i is the width of the current conductor; w v is the width of the voltage conductor; L i is the length of the current conductor; L v is the length of the voltage conductor; The corresponding heating current frequency f3 is: (1.4) Ensure the thermal penetration depth δ of the film to be tested in the in-plane direction || 1 / 5 times the half width of the suspended part of the film to be tested That is: The corresponding heating current frequency f4 is: f4＝25α || / (πl 2 ) (10) The determination process is as follows: the upper frequency limit f of the heating current max The lower limit of the frequency of the heating current is determined by the smaller value of f1 and f2. min Determined by the larger value of f3 and f4; at the same time, use any one or a combination of at least two of the following methods to ensure that f1 and f2 are both greater than f3 and f4, and increase f max and f min The width of the frequency window between: (A) By reducing the width w of the conductive strip h To increase f2; (B) By reducing the thermal conductivity κ of the electrode layer h and / or the thickness d of the electrode layer h To lower f3; (C) By increasing the length L of the current conductor i and / or the length L of the voltage conductor v To lower f3; (D) Reduce f4 by increasing the width l of the overhanging portion of the film to be tested; Among them, method (C) is accompanied by increasing the longitudinal dimension of the film to be measured, and method (D) is accompanied by increasing the transverse dimension of the film to be measured, that is, determining the size of the film to be measured.

2. The measuring method according to claim 1, wherein The thickness of the film to be tested in step (1) is 1-100 μm.

3. The measuring method according to claim 1, wherein The shape of the film to be tested of the specific size in step (2) is square or rectangular.

4. The measuring method according to claim 1, wherein The support frame in step (2) is a metal frame with a hollow window in the center.

5. The measuring method according to claim 4, characterized in that The shape of the hollow window is square or rectangular.

6. The measuring method according to claim 4, characterized in that The material of the metal frame includes copper.

7. The measuring method according to claim 1, characterized in that Step (3) The distance D between the first conductive strip and the second conductive strip is δ ||,min 0.2-1.2 times of ||,min corresponds to f min The thermal penetration depth of the film under test in the in-plane direction.

8. The measurement method according to claim 1, characterized in that In step (3), the first conductive strip and the second conductive strip are parallel to the frame of the support frame along the length direction and perpendicular to the thermal conductivity measurement direction.

9. The measuring method according to claim 1, wherein: Step (3) The first conductive strip coincides with a central symmetry axis of the film to be tested along its length direction.

10. The measurement method according to claim 1, characterized in that Step (3) The first conductive strip and the second conductive strip are respectively connected to two current terminals through current conductors, and are connected to two voltage terminals through voltage conductors.

11. The measuring method according to claim 10, characterized in that: The current conducting wire is located on an extension line of the connected conductive strip along the length direction.

12. The measuring method according to claim 10, characterized in that: The voltage conductor is located on a side of the connected conductive strip, that is, a side away from the unconnected conductive strip.

13. The measuring method according to claim 1, characterized in that Step (3) The first conductive strip and the second conductive strip are made of metal or conductive compound respectively.

14. The measuring method according to claim 13, characterized in that: Step (3) The first conductive strip and the second conductive strip are made of any one of gold, platinum or niobium nitride.

15. The measurement method according to claim 1, characterized in that The method for measuring the in-plane thermal conductivity of the film to be measured in step (4) adopts 3ω and 2ω voltage measurement technology, and specifically includes the following steps: (4.1) Based on the frequency range of the heating current obtained in step (1), an alternating current I0sin(ωt) with an amplitude of I0 and an angular frequency of ω is passed through the first conductive strip, and the amplitude |ΔT(2ω)1| and phase Φ(2ω)1 of the temperature fluctuation of the first conductive strip and the phase Φ(2ω)2 of the temperature fluctuation of the second conductive strip are measured; (4.2) is calculated value; wherein, N(2ω)=[Φ(2ω)1-Φ(2ω)2] / D, M(2ω)=N(2ω) / tan(3π / 2-Φ(2ω)1), and D is the spacing between the first conductive strip and the second conductive strip; (4.3) Plot |ΔT(2ω)1| and calculate the in-plane thermal conductivity κ of the film to be tested based on the slope S1 of the fitted line. || =P L S1 / (2d M ); where P L is the AC heating power amplitude per unit length of the first conductive strip.

16. The measurement method according to claim 1, characterized in that The measurement method further comprises verifying the in-plane thermal conductivity of the film to be measured by using three-dimensional finite element simulation.

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