Multi-layer functional composition film with gradient thickness change as well as preparation method and application of multi-layer functional composition film

Abstract

The invention relates to a multi-layer functional composition film with gradient thickness change and a preparation method and application thereof.The multi-layer functional composition film comprises one or more functional layers, each functional layer comprises a plurality of film layers, and at least two of the film layers are made of different materials; the thickness of at least one material in the plurality of film layers varies in the longitudinal direction in different film layers in the plurality of film layers. Compared with the prior art, the preparation condition is controllable, the film is low in modulatable heat conductivity, the thermoelectric power factor can be adjusted, and the preparation method is expected to have huge application prospects in the aspects of microelectronic device precision heat management, aircraft heat protection ultrathin layer and invisibility, efficient solid-state refrigeration, waste heat recovery and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of thermal functional protective materials and relates to a multilayer functional composition film with a thickness gradient and a coating containing the same. Background Art

[0002] With the continuous advancement of science and technology, thermal management technologies are increasingly being applied in fields such as microelectronics, aerospace, and energy conversion. For example, thermal protection for high-temperature aerospace components and extreme-environment aircraft require coating materials with ultra-low thermal conductivity to reduce substrate temperatures, extend service life, and, to a certain extent, achieve stealth. Nuclear power, gas turbines, and solar thermal power generation systems rely on high-efficiency thermal barrier coatings to reduce heat loss and improve energy conversion efficiency. In microelectronic devices, overheating or undercooling can affect the operating state of components or electronic devices. Therefore, coating materials with adjustable ultra-low thermal conductivity are required for precise thermal management and to address thermal interference. In these applications, the thermal conductivity of a material is a critical parameter, directly affecting heat transfer efficiency and device performance. In the field of microelectronics, in particular, with the increasing integration density and power density, thermal management issues are becoming increasingly prominent, and the demand for low thermal conductivity materials is becoming increasingly urgent.

[0003] At present, low thermal conductivity materials mainly include porous structure materials, superlattice materials and composite materials. Porous structure materials such as aerogels reduce thermal conductivity by introducing a large number of pores, but such materials are usually large in size and difficult to apply to space-constrained occasions such as microelectronic devices. Superlattice materials are composite structures formed by periodically and uniformly arranging thin film layers of different materials, which can effectively scatter phonons and reduce thermal conductivity. For example, CN104538542A discloses a process for preparing multilayer thermoelectric materials using a physical vapor deposition method. This process can prepare multilayer thermoelectric materials with uniform thickness and obvious layered structure and high precision. However, the thermal conductivity of existing superlattice periodic uniform material coatings is close to the theoretical limit and is difficult to reduce further.

[0004] In the field of thermoelectric conversion, the thermal conductivity and electrical conductivity of materials are two conflicting parameters. CN104538542A mentions that ideal thermoelectric materials should have high electrical conductivity and low thermal conductivity, but these two parameters are often interrelated and difficult to optimize simultaneously. Furthermore, while traditional compression refrigeration technology is highly efficient, it relies on greenhouse gas working fluids, which poses environmental concerns.

[0005] With the development of microelectronics technology, the requirements for thermal management are getting higher and higher. CN118465881A discloses a temperature-regulating nano-composite film, which is formed by coating a composite nano-film containing nano-metal, metal oxide, and silicon compound on the surface of a transparent substrate. It has the advantages of heat insulation, anti-infrared, anti-ultraviolet, and high visible light transmittance. However, this composite film is mainly used for heat insulation and protection, and cannot achieve precise control of thermal conductivity. In terms of multi-layer film structure design, CN118377076A discloses an RGB color-blocking narrow-band composite film, which includes 7 sub-composite layers, namely a first metal oxide layer, a first matching layer, a first functional layer, a metal film layer, a second functional layer, a second matching layer, and a second metal oxide layer. CN103151399A discloses a flexible thin-film solar cell with a periodic light-trapping structure, which includes a flexible metal substrate, an Al film with a periodic light-trapping structure, and a thin-film battery layer. Although these multi-layer film structures perform well in optical or electrical properties, there are few studies on their application in thermal management.

[0006] CN108140784A discloses an improved porous membrane or substrate, diaphragm, separator, composite material, and electrochemical device. This technology is primarily used in the battery field to improve battery performance by optimizing the membrane structure. However, while this porous structure can reduce thermal conductivity, it is difficult to achieve precise control of thermal conductivity.

[0007] In terms of refrigeration, traditional compression refrigeration technology relies on greenhouse gas working fluids, which poses environmental problems. Thermoelectric refrigeration does not require moving parts and can achieve precise temperature control (such as cooling of lasers, medical equipment, and electronic chips), high power factor (PF=S 2 σ , where S is the Seebeck coefficient, σ Conductivity (PF) directly determines cooling efficiency (maximum cooling power density is proportional to PF). Consumer electronics (such as mobile phones and wearable devices) require micro-cooling modules, requiring materials with high PF under small temperature gradients for rapid heat dissipation. Industrial waste heat or automobile exhaust recovery requires materials to maintain high PF in high-temperature areas to improve thermoelectric conversion efficiency. Extreme environments such as aerospace and deep-sea applications require liquid-free cooling solutions, and high PF materials can reduce reliance on temperature gradients. Therefore, there is an urgent need for high power factor materials.

[0008] In summary, existing low thermal conductivity materials face the following challenges: 1) Low thermal conductivity materials with porous structures are large, making them difficult to apply to space-constrained applications such as microelectronic devices; 2) The thermal conductivity of periodically uniform superlattice material coatings is already close to the theoretical limit and is difficult to reduce further; 3) Traditional compression refrigeration technology relies on greenhouse gas working fluids, which poses environmental concerns; 4) There is a lack of materials with adjustable ultra-low thermal conductivity for precise thermal management and addressing thermal interference; and 5) There is a lack of materials with high power factors under small temperature gradients to achieve efficient thermoelectric conversion. Therefore, the development of a new composite membrane that can precisely control thermal conductivity and achieve efficient thermoelectric conversion under small temperature gradients has important theoretical and practical value. Summary of the Invention

[0009] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a multilayer functional composite film with a thickness gradient change and its preparation method and application, accurately control the thermal conductivity, and achieve efficient thermoelectric conversion under small temperature differences, and improve the thermoelectric power factor.

[0010] The objectives of the present invention can be achieved through the following technical solutions: a composite film comprising one or more functional layers, each functional layer comprising multiple film layers, at least two of the multiple film layers using different materials, and at least one material in the multiple film layers having thicknesses varying longitudinally between different film layers in the multiple film layers.

[0011] Furthermore, the thickness of different film layers of at least one material in the multiple film layers increases or decreases in sequence along the longitudinal direction, or decreases first and then increases, or increases first and then decreases, but the same material must have at least two unequal thicknesses.

[0012] Furthermore, the thickness of the multiple film layers formed of the same material in the same functional layer increases, decreases, decreases first and then increases, or increases first and then decreases in the longitudinal direction. That is, the same functional layer has at least two film layers formed of the same material, and the thickness of each layer in the longitudinal direction is different.

[0013] At least one material in the plurality of film layers has a thickness that varies in a longitudinal direction for at least 2 times.

[0014] Furthermore, the multiple functional layers are formed by multiple film layers periodically arranged along the longitudinal direction.

[0015] The composite film is formed by stacking at least two materials alternately along the longitudinal direction.

[0016] Furthermore, the plurality of functional layers are periodically arranged in the longitudinal direction, and the stacking period is at least one period.

[0017] Furthermore, the thickness of each film layer is not less than 0.1 nm and not more than 0.1 mm.

[0018] Furthermore, the materials of each film layer include n types (n≥1), and the materials include organic and inorganic substances, covering metals, semi-metals, conductors, semiconductors, and insulators, preferably Pt / Bi2Te3 or Ag / Bi2Te3.

[0019] The present invention also provides a method for preparing the composition film, wherein the composition film is sequentially arranged by physical vapor deposition, chemical vapor deposition, electrochemical deposition or spin coating, that is, the film layer can be prepared by physical vapor deposition (including sputtering, evaporation, molecular beam epitaxy, etc.), chemical vapor deposition (atomic layer deposition, organometallic chemical vapor deposition, chemical vapor deposition), electrochemical deposition, spin coating, etc.

[0020] Furthermore, the composition film is disposed on a substrate, which includes a SiO2 / Si wafer, a quartz sheet, or a metal alloy. A bonding layer, such as a Cr layer, a Ni layer, or a Ti layer, may be disposed between the substrate and the composition.

[0021] The present invention also provides an application of the composition film, wherein the composition film is applied to the surface of a microelectronic device or various thermal management components.

[0022] Compared with the prior art, the present invention has the following beneficial effects: Heat propagates in the material in the form of phonons. Different materials have different distributions of their own phonon wavelength ranges. The thermal conductivity can be reduced to a certain extent by using periodic material combination films. However, there are significant differences in the scattering behavior of phonons on characteristic size interfaces. A single repeating period and interface cannot completely cover the phonon wavelength range of the film used. Therefore, the present invention designs a combination film. On the basis of utilizing the differences in the intrinsic properties of different materials, a thickness variation design is further introduced to make the designed thickness variation cover the range of phonon wavelength scattering of the materials in the combination film, so as to achieve full scattering of the phonon spectrum as much as possible, thereby achieving the effect of maximizing the reduction of thermal conductivity along the thickness variation direction. At the same time, the thickness variation design optimization also directly affects the carrier and phonon transport behavior parallel to the thickness variation direction. The modulation of this coupling effect allows the thermoelectric power factor to be further improved.

[0023] Compared to existing technologies, the variable thickness film introduced in this invention can further reduce thermal conductivity while maintaining the same material, further reducing the volume of the thermal protection material and making it easier to apply to the surfaces of microelectronic devices and thermal management components. Furthermore, this variable thickness design significantly improves the thermoelectric power factor along the plane of the composite film, making it suitable for the fabrication of planar thermoelectric devices. This has important application prospects in waste heat energy recovery for power generation, self-powered electronic devices, and efficient localized cooling of microdevices. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of n periodic functional layers, wherein the functional layer includes 3 film layers.

[0025] Figure 2 2A is a schematic diagram of the composition film in Example 1. Figure 2 B is the cross-sectional SEM image of Pt / Bi2Te3 in this embodiment. Figure 2 C is the SEM image of Comparative Example 1-1.

[0026] Figure 3 Schematic diagram of the structure of the composite film of Example 2. In a single cycle, there are three film layer materials (301 and 304, 302 and 305, 303 and 306), and each material has two decreasing thicknesses t (t 301 >t 304 , t 302 >t 305 , t 303 >t 306 ).

[0027] Figure 4 Schematic diagram of the structure of the composite film of Example 3. In a single cycle, there are two film layer materials (401, 403 and 405; 402, 404 and 406), and each material has three thicknesses. The thickness decreases first and then increases (t 401 >t 403 <t 305 ;t 402 >t 404 <t 406 ); Figure 5 Schematic diagram of the structure of the composite film of Example 4. In a single cycle, there are two film layers with two materials (501 and 503; 502), one of which has two decreasing thicknesses (t 501 >t 503 ). DETAILED DESCRIPTION

[0028] The following describes the embodiments of the present application through specific examples, and those skilled in the art can easily understand other advantages and effects of the present application from the contents disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The present application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present application. It should be noted that, in the absence of conflict, the features in the following embodiments and embodiments can be combined with each other. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of this application.

[0029] Embodiments of the present invention will be described in detail below. Throughout this specification, as used herein, the terms "substantially," "substantially," and "approximately" are used to describe and illustrate small variations. When used in conjunction with an event or situation, the term may refer to an example where the event or situation precisely occurs and an example where the event or situation very approximately occurs. For example, when used in conjunction with a numerical value, the term may refer to a range of variation less than or equal to ±10% of the numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. For example, two values may be considered "substantially" the same if the difference between them is less than or equal to ±10% of the mean of the values (e.g., less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%).

[0030] In this specification, amounts, ratios, and other numerical values are sometimes presented herein in a range format. It should be understood that such a range format is used for convenience and brevity and should be interpreted flexibly to include not only the values explicitly specified as limits of the range, but also all individual values or sub-ranges within the range, as if each value and sub-range were explicitly specified.

[0031] To address the technical challenges of existing low thermal conductivity materials, such as the large size of porous structure designs, the difficulty in further reducing the thermal conductivity of superlattice coatings, the environmental concerns of traditional compression refrigeration technology that relies on greenhouse gas working fluids, the need for adjustable ultra-low thermal conductivity materials for precise thermal management, and the need for materials with high power factors under small temperature differences to achieve efficient thermoelectric conversion, the present invention provides a composite membrane that, through a special material combination and thickness variation design, achieves full scattering of the phonon spectrum, maximizes the reduction of thermal conductivity along the thickness variation direction, further reduces the volume of the thermal protection material, and improves the thermoelectric power factor. Specifically: like Figure 1 As shown, a composite film 100 includes one or more functional layers 110, and the functional layer 110 includes multiple film layers. In one embodiment, the multiple film layers include a first film layer 101, a second film layer 102 and a third film layer 103, at least two of the multiple film layers are made of different materials, and the thickness of at least one material in the multiple film layers varies along the longitudinal direction d1 in different film layers.

[0032] For example, Figure 1The first film layer 101 and the second film layer 102 located above the first film layer 101 can be made of different materials. The third film layer 103 located above the second film layer 102 can be made of the same material as the first film layer 101, both made of the first material. The second film layer 102 can be made of the second material. The thickness of the first film layer 101 is t1, and the thickness of the third film layer 103 is t3, where t1 is greater than t3.

[0033] In other embodiments of the present application, t1 may also be smaller than t3. The composite film 100 may also include n functional layers 110. For example, the n functional layers are formed by periodically arranging a plurality of film layers along the longitudinal direction to form the composite film.

[0034] In other embodiments of the present application, the thickness of the first material in different film layers in the multiple film layers may decrease successively, or increase successively, or decrease first and then increase, or increase first and then decrease successively along the longitudinal direction d1.

[0035] The preparation methods for the film layer include: physical vapor deposition (including sputtering, evaporation, molecular beam epitaxy, etc.), chemical vapor deposition (atomic layer deposition, metal organic chemical vapor deposition, chemical vapor deposition), electrochemical deposition, spin coating, etc. Any material can be used to form the required film layer.

[0036] In some embodiments of the present application, the composite film may further include a substrate, and the functional layer may be located on the substrate. The composite film may be prepared on various substrates. For example, the substrate may be a SiO2 / Si wafer, a quartz wafer, a metal alloy, such as a CrMo alloy.

[0037] In some embodiments of the present application, in order to make the composition film fit better with the substrate, an adhesion layer such as a Cr layer, a Ni layer, a Ti layer, etc. may be prepared between the substrate and the film layer. A suitable adhesion layer may be selected according to the material of the specific film layer and the material of the substrate.

[0038] In some embodiments of the present application, the materials used in the multiple film layers include Pt / Bi2Te3, Ag / Bi2Te3, as described in the following embodiments. Unless otherwise specified, the equipment and materials used in the examples are conventional equipment and materials in the art obtained from commercial channels.

[0039] Example 1 A composite film is prepared by the following method: (1) The substrate is a double-sided polished SiO2 / Si wafer with an upper oxide layer thickness of 300 nm. The oxide layer is oxidized by wet oxygen, cleaned with acetone and alcohol in sequence, and dried with argon.

[0040] The substrate was placed in a magnetron sputtering thin film deposition system to deposit a composite film on the SiO2 surface. The targets used were 99.99% pure Pt and Bi2Te3, purchased from Zhongnuo New Materials (Beijing) Technology Co., Ltd.

[0041] (2) Considering the adhesion between the film layer and the SiO2 on the substrate surface, a bonding layer can be deposited. A 20 nm thick Cr metal is used for the bonding layer. Multiple film layers are then deposited sequentially. In this embodiment, two materials are selected to stack multiple film layers to form a functional layer. The first material is Pt, and the second material is Bi2Te3. Multiple functional layers are then periodically prepared to form a composite film.

[0042] (3) Figure 2 A is a schematic diagram of the composition film in Example 1.

[0043] like Figure 2 As shown in A, a 15 nm thick first material is first deposited on the surface of the bonding layer obtained in step (2) to form a first film layer 201, a 15 nm thick second material is deposited to form a second film layer 202, and then a 10 nm thick first material is deposited to form a third film layer 203, a 15 nm thick second material is deposited to form a fourth film layer 204, and then a 5 nm thick first material is deposited to form a fifth film layer 205, and a 15 nm thick second material is deposited to form a sixth film layer 206, thereby realizing a functional layer 210 having multiple film layers of the first material and the second material alternately stacked, wherein the thickness of the film layer where the first material is located has three different values, which decrease along the longitudinal direction d1, namely 15 nm, 10 nm, and 5 nm, respectively, while the thickness of the film layer where the second material is located does not change, and is 15 nm, that is, the total thickness of one functional layer is 75 nm, and the total thickness of the composition containing four periodic functional layers is 300 nm.

[0044] (4) The above thin film deposition process was repeated 4 times to obtain a composite film formed by 4 cycles of functional layers. The cross-sectional SEM image of the obtained composite film is shown in FIG. Figure 2 As shown in B. Figure 2 In A, only one periodic functional layer 210 is shown, and the substrate and the adhesion layer are not shown.

[0045] Comparative Example 1-1 As a comparative example, comparative example 1-1 adopts the same method to prepare a composite film formed by 4 periods of functional layers, which are composed of 3 periods of 10 nm thick first material and 15 nm thick second material film layers, ensuring that the total thickness of the composite film is consistently 300 nm, and the total thickness of the film layer formed by the first material Pt is 120 nm, and the total thickness of the film layer formed by the second material Bi2Te3 is 180 nm. Figure 2 C is the SEM picture of comparative example 1-1, Figure 2 B- Figure 2 As can be seen from Figure 2B, the multilayer structure exhibits obvious thickness variations, while the multilayer structure in Figure 2C is uniform.

[0046] Comparative Example 1-2 Comparative Examples 1-2 employed a composition film made of the second material with a thickness of 300 nm.

[0047] Comparative Examples 1-3 Comparative Examples 1-3 adopt the bulk structure of the first material.

[0048] Table 1 shows the parameters and thermal conductivity test results of the composite film in Example 1 and the materials in the comparative example. Comparative Example 1-1 is a periodic thin film with unchanged thickness in the prior art. Both Example 1 and Comparative Example 1-1 were prepared using the same equipment and conditions. The thermal conductivity test was measured using femtosecond laser time-domain thermal reflectance (TDTR), which demonstrated that the composite film of the present application has very low thermal conductivity (W·m -1 ‧K -1 ).

[0049] Table 1

[0050] Table 1 shows that compared to pure Bi2Te3 (Comparative Examples 1-2) and Pt (Comparative Examples 1-3), the thermal conductivity of the composite film of the present invention is reduced by 93.6% and 99.8%, respectively. Furthermore, compared to the periodic Pt (120 nm) and Bi2Te3 (180 nm) films of the same thickness used in Comparative Example 1-1, the thermal conductivity of the composite film of the present invention is still reduced by 51.7%, demonstrating the lower thermal conductivity advantage of the composite film of the present invention compared to the prior art. Furthermore, while achieving the same thermal insulation effect, the composite film can further reduce material usage.

[0051] Table 2 shows the test results of the thermoelectric power factor performance of the composition film in Example 1 and the comparative example in Table 1. The test adopts the display along the in-plane performance d2 direction.

[0052] Table 2 <![CDATA[Seebeck coefficient (μV‧K -1 ).]]> <![CDATA[Conductivity (S‧cm -1 )]]> <![CDATA[Power factor (μW‧cm -1 ‧K -2 )]]> Example 1 230.4 3320.3 176.2 Comparative Example 1-1 154.4 1259.1 30.0 Comparative Example 1-2 61.5 533.4 2.0 Comparative Examples 1-3 5.5 96600 2.9 As shown in Table 2, compared to the pure Bi2Te3 in Comparative Example 1-2, the thermoelectric power factor of Example 1 is enhanced by 87 times. Compared to Comparative Example 1-1 using the same material, the thermoelectric power factor of Example 1 is still enhanced by about 5 times. The above comparison shows that after introducing thickness variation in the composition of the present invention, in addition to reducing the thermal conductivity in the d1 direction, it also directly optimizes electron transport in the d2 direction, resulting in a significant increase in the thermoelectric power factor, achieving a record high of 176.2 μW‧cm for the Bi2Te3 system. -1 ‧K-2 Thermoelectric power factor.

[0053] Example 2 The substrate selection, treatment and thin film deposition method are the same as those in Example 1, except that the first material Pt is replaced by Ag, the thickness and period parameters remain unchanged, and the comparative example is also set. Figure 3 As shown in the figure, it is a schematic diagram of the structure of the composite film of this embodiment. The composite film 300 is formed by stacking multiple functional layers 310. Each functional layer 310 is formed by sequentially setting a first material with a thickness of 15 nm to form a first film layer 301, a second material with a thickness of 15 nm to form a second film layer 302, a first material with a thickness of 10 nm to form a third film layer 303, a second material with a thickness of 15 nm to form a fourth film layer 304, a first material with a thickness of 5 nm to form a fifth film layer 305, and a second material with a thickness of 15 nm to form a sixth film layer 306. The thickness of the film layer where the first material is located has three different values, which decrease along the longitudinal direction d1, namely 15 nm, 10 nm, and 5 nm, respectively, while the thickness of the film layer where the second material is located does not change, and is 15 nm.

[0054] Comparative Example 2-1 As a comparative example, Comparative Example 2-1 adopts the same method to prepare a composite film formed by 4 periods of functional layers, which are composed of 3 periods of 10 nm thick first material and 15 nm thick second material film layers, ensuring that the total thickness of the composite film is consistently 300 nm, and the total thickness of the film layer formed by the first material Ag is 120 nm, and the total thickness of the film layer formed by the second material Bi2Te3 is 180 nm.

[0055] Comparative Example 2-2 Comparative Example 2-2 uses a composition film prepared from the second material with a thickness of 300 nm.

[0056] Comparative Examples 2-3 Comparative Example 2-3 adopts the block structure of the first material.

[0057] Table 3 shows the parameters and performance test results of the composite film of Example 2 and the materials in the comparative example, which proves that the composite film of the present application has a better performance in ultra-low thermal conductivity (W·m -1 ‧K -1 ) has significant advantages.

[0058] Table 3

[0059] Table 3 above shows that compared to pure Bi2Te3 (Comparative Example 2-2) and Ag (Comparative Example 2-3), the thermal conductivity of the composite film of the present invention is reduced by 73.2% and 99.9%, respectively. Compared to the periodic thin films of Ag (120 nm) and Bi2Te3 (180 nm) of the same thickness used in Comparative Example 2-1, the thermal conductivity of the composite film of the present invention is still reduced by 41%, demonstrating the low thermal conductivity advantage of the composite film of the present application compared to the prior art. While achieving the same thermal insulation effect, the material usage can be further reduced. Tables 1 and 3 also illustrate that different materials have different phonon distributions, and the same thickness design can result in different reductions in the thermal conductivity of the film. Therefore, targeted thickness variation design for different material components can further reduce thermal conductivity.

[0060] Table 4 <![CDATA[Seebeck coefficient (μV‧K -1 )]]> <![CDATA[Conductivity (S‧cm -1 )]]> <![CDATA[Power factor (μW‧cm -1 ‧K -2 ).]]> Example 2 60.99 4039.02 15.0 Comparative Example 2-1 54.33 2042.02 6.0 Comparative Example 2-2 61.5 533.38 2.0 Comparative Examples 2-3 1.5 630000 1.4 In Table 4, compared to the pure Bi2Te3 in Comparative Example 2-2, the thermoelectric power factor of Example 2 is enhanced by 6.5 times. Compared to Comparative Example 2-1 using the same material, the thermoelectric power factor of Example 2 is still enhanced by 1.5 times. The above comparison shows that after introducing thickness variation, the composition of the present invention not only reduces the thermal conductivity in the d1 direction, but also directly optimizes the electron transport in the d2 direction, resulting in an increase in the thermoelectric power factor. The enhancement of thermal conductivity and thermoelectric power factor is related to the composition of the material. At the same time, the corresponding thickness variation can be designed according to the phonon electrical transport characteristics of different composite materials.

[0061] Example 3 like Figure 4 As shown, in this embodiment, there are two film layer materials in a single cycle of the composite film. The first material is Pt and the second material is Bi2Te3. The thickness of the 10nm first film layer 401, the 5nm third film layer 403, and the 15nm fifth film layer 405 formed by the first material first decreases and then increases, that is, t 401 >t 403 <t 305 The second material layer is formed: the thickness of the second film layer 402 is 15nm, the fourth film layer 404 is 10nm, and the sixth film layer 406 is 20nm, which first decreases and then increases, ie, t 402 >t 404 <t 406 , The rest is the same as Example 1.

[0062] Example 4 like Figure 5 As shown, in this embodiment, there are two film layer materials in a single cycle of the composite film. The first material is Bi2Te3 and the second material is Ag. The first material forms a 15nm first film layer 501 and a 5nm third film layer 203. The first material has two decreasing film layers, namely t501 >t 502 , the film layer formed by the second material: a 15nm second film layer 502, and the rest is the same as in Example 1.

[0063] The performance of the film obtained in Examples 3-4 was tested using the same method as in Example 1. The results are as follows: Table 5 <![CDATA[Thermal conductivity (W‧m -1 ‧K -1 )]]> <![CDATA[Seebeck coefficient (μV‧K -1 ).]]> <![CDATA[Conductivity (S‧cm -1 )]]> <![CDATA[Power factor (μW‧cm -1 ‧K -2 )]]> Example 3 0.68 143.4 1972 40.6 Example 4 1.1 58.3 1706 5.8 The results in Table 5 show that after the combined film thickness is designed, the thermal conductivity of the combined film is reduced and the power factor is greatly improved compared to Bi2Te3. The degree of this reduction / increase is related to the periodicity of the functional layer and the thickness combination of the thin film layer. As the periodicity increases, the thermal conductivity can be further reduced.

[0064] The composite film proposed in the present invention adjusts the thermal conductivity by varying the thickness of different film layers of the same material, for example, reducing the thermal conductivity and improving the thermoelectric power factor, which can meet application requirements in many fields.

[0065] Application Examples The composition film is applied to the surface of a microelectronic device or a thermal management component. Taking the composition film in Example 1 as an example, it is applied to the surface of a microelectronic device and a thermal management component.

[0066] (1) Thermoelectric conversion device: The composite film is integrated into the thermoelectric conversion device as the core functional layer. Since the thickness of the Pt and Bi2Te3 materials in the composite film varies along the longitudinal direction, a gradient structure can be formed, effectively establishing a temperature gradient and improving the thermoelectric conversion efficiency. In practical applications, the composite film can be sandwiched between two electrodes. When there is a temperature difference between the two electrodes, the composite film can convert thermal energy into electrical energy, realizing the energy collection function. Tests have shown that the conversion efficiency of the thermoelectric conversion device using this composite film is 38% higher than that of traditional devices.

[0067] (2) Heat dissipation cooling film: The composite film is applied to the surface of high-power electronic equipment as a heat dissipation film. Due to the multi-layer structure and material combination of the composite film, it has a high thermoelectric power factor and high electronic thermal conductivity (matching the electrical conductivity) in the plane, which can achieve efficient power-on cooling function. In practical applications, one end of the composite film can be attached to the heat source surface of the electronic device. When the composite film is powered on for cooling (thermoelectric Peltier cooling effect), the composite film quickly transports heat to the other end of the heat source, reducing the temperature of the device. Tests have shown that the heat dissipation system using this composite film can reduce the device temperature by 16°C.

[0068] (3) Heat shielding material: The composite film is applied to areas requiring heat isolation as a heat shielding material. Due to the multi-layer structure and material combination of the composite film, effective heat isolation can be achieved to prevent heat transfer. In practical applications, the composite film can be attached to the surface of equipment requiring heat protection to prevent external heat from entering or internal heat from transferring out. Tests have shown that a heat shielding system using the composite film can reduce heat transfer efficiency by 73%.

[0069] Through the above applications, the excellent performance of the composite film can be fully utilized to solve various technical problems in the fields of microelectronic devices and thermal management, and promote the development of related technologies.

[0070] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. A composite film, characterized in that It comprises one or more functional layers, each functional layer comprises multiple film layers, at least two of the multiple film layers are made of different materials, and the thickness of different film layers of at least one material in the multiple film layers varies along the longitudinal direction.

2. A composite film according to claim 1, characterized in that: The thickness of at least one material in the multiple film layers in different film layers increases or decreases in sequence along the longitudinal direction, or decreases first and then increases, or increases first and then decreases.

3. A composite film according to claim 1, characterized in that The film layers formed by multiple materials used in the same functional layer have thicknesses of at least multiple film layers of the same material that increase, decrease, decrease first and then increase, or increase first and then decrease in sequence in the longitudinal direction.

4. A composite film according to claim 1, characterized in that: The multiple functional layers are formed by periodically arranging multiple film layers along the longitudinal direction.

5. A composite film according to claim 1, characterized in that: The multiple functional layers are periodically arranged along the longitudinal direction.

6. A composite film according to claim 1, characterized in that: The thickness of each film layer is not less than 0.1 nm and not more than 0.1 mm.

7. A composite film according to claim 1, characterized in that: The materials of each film layer include Pt / Bi2Te3 or Ag / Bi2Te3.

8. A method for preparing a composition film according to any one of claims 1 to 7, characterized in that: The composition film is sequentially formed by physical vapor deposition, chemical vapor deposition, electrochemical deposition or spin coating.

9. The method for preparing a composite film according to claim 8, characterized in that: The composition film is arranged on a substrate, and the substrate comprises a SiO2 / Si wafer, a quartz plate or a metal alloy.

10. An application of the composition film according to any one of claims 1 to 7, characterized in that: The composition film is applied to the surface of microelectronic devices or various thermal management components.

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