KR102140669B1 - Passive radiating cooling structure - Google Patents

Abstract

A passive cooling radiation structure is disclosed. The passive cooling radiation structure according to an embodiment of the present invention includes a lower metal layer connected to a system targeted for radiative cooling, a dielectric layer provided on the lower metal layer for coloring chromatic color through resonance, and an upper metal layer provided on the dielectric It includes a MIM layer, and a thermal radiation layer provided on the upper metal layer and exhibiting passive radiation characteristics.

Description

PASSIVE RADIATING COOLING STRUCTURE

The present invention relates to a passive radiation cooling structure capable of performing passive radiation cooling while developing chromatic colors of various colors.

Along with the radical demand for the development of alternative energy for the next generation due to fossil fuel depletion, efforts are being made worldwide to utilize energy efficiently. The passive radiant cooling structure is a device for lowering the temperature of the invention product or building/plant without external power supply, and is attracting attention as an ultra power saving/environmental technology because it can lower the temperature by minimizing power consumption.

The passive radiant cooling structure is a technology distinctly distinguished from the conduction and convection methods that induce thermal equilibrium. In particular, research on passive radiant cooling structures that can be used not only at night but also during the day has been actively conducted in developed countries.

The passive radiation cooling structure for daytime use strongly reflects sunlight, and internal heat must be effectively emitted to the external space in the form of electromagnetic waves. Therefore, the ideal radiative cooling structure should 1) reflect light of 280 ~ 4000nm wavelength as much as possible, and 2) emit electromagnetic waves of 8 ~ 13μm area, the window area of the atmosphere, as much as possible. Since the optical design including both the visible/near-infrared band and the long-infrared band is very complex, the development of night cooling systems, excluding the effect of sunlight, has been the main focus.

Recently, as metamaterial research has been actively conducted, it is possible to develop a daytime cooling system based on a photonic structure. However, the structures of the previous research group are composed of a very complex dielectric/metal multilayer thin film structure or a mixed structure with a nano structure, so that the production cost is high, and there are limitations on large area achievement.

On the other hand, since the passive radiation cooling structure is mainly mounted on the exterior wall of a building or the exterior of a heating product, aesthetic factors must be considered for practical application, and therefore, it is required to implement various colors rather than simply white or silver-based colors. However, there has been no invented case for a structure having a color development function and showing passive cooling characteristics at the same time.

An object of the present invention is to provide a passive radiation cooling structure capable of performing passive radiation cooling while developing chromatic colors of various colors.

The passive cooling radiation structure according to an embodiment of the present invention includes a lower metal layer connected to a system targeted for radiative cooling, a dielectric layer provided on the lower metal layer for coloring chromatic color through resonance, and an upper metal layer provided on the dielectric It includes a MIM layer, and a thermal radiation layer provided on the upper metal layer and exhibiting passive radiation characteristics.

The passive cooling radiation structure proposed in the present invention has the advantage of improving aesthetics and increasing the utilization range because it can develop chromatic colors of various colors while maintaining a temperature similar to or lower than room temperature under sunlight during the daytime. have.

In addition, since the passive cooling radiation structure proposed in the present invention is a stacked structure and has a simple structure, patterning in various patterns and colors is possible, and it is easy to manufacture in a flexible device form.

1 shows a passive radiation cooling structure according to an embodiment of the present invention.
Figure 2 shows an example of a color-type passive cooling structure according to an embodiment of the present invention.
3 shows reflection characteristics according to thickness when SiO 2 is used as the dielectric.
4 shows reflectance and absorption according to the thickness of the upper Ag layer.
5 shows reflectance, absorption and transmittance according to the thickness of the lower Ag layer.
6 shows a passive radiation characteristic according to thickness when PDMS is used as a heat radiation layer.
FIG. 7 shows color coordinates (a) and cooling characteristics (b) depending on the thickness of the upper metal (Ag) layer.
FIG. 8 shows sample pictures (a) before and after PDMS coating of a color-type passive cooling radiation structure according to an embodiment of the present invention and optics (b) in visible light.
9A to 9D are diagrams for explaining the structure and features of CPRC.
10A to 10D are results of simulation (calculation) of the correlation between temperature and color in CPRC.
11A to 11D relate to measurement data of a sample actually produced according to a simulation (calculation) of the correlation between temperature and color in CPRC.
FIG. 12 is a diagram illustrating a flexible passive cooling radiation structure and test results.

Hereinafter, specific embodiments of the present invention will be described in detail with reference to the drawings. However, the spirit of the present invention is not limited to the following embodiments, and those skilled in the art to understand the spirit of the present invention can easily implement other embodiments included within the scope of the same spirit by adding, changing, deleting, and adding components. It can be suggested, but it will be said that this is also included within the scope of the present invention.

In the accompanying drawings, in order to easily understand the spirit of the invention, in describing the overall structure, the minute parts may not be specifically expressed, and in describing the minute parts, the overall structure may not be specifically reflected. In addition, even if specific parts, such as installation positions, are different, if the action is the same, the same name is given to enhance the convenience of understanding. In addition, when there are a plurality of identical configurations, only one of the configurations will be described, and the same description will be applied to other configurations, and the description will be omitted.

1 shows a passive radiation cooling structure according to an embodiment of the present invention.

1, the passive radiation cooling structure according to an embodiment of the present invention is formed by stacking a plurality of layers in sequence.

Passive radiation cooling structure according to an embodiment of the present invention may include a MIM layer and a heat radiation layer.

Here, the MIM layer (metal-dielectric-metal layer) is an abbreviation of metal-insulator-metal, and increases the absorption of wavelengths in a specific band by using a Fabry-Perot interference in the visible light band to obtain various colors. You can develop chromatic colors. That is, the chromatic color described in the present invention may refer to colors developed by the MIM layer (metal-dielectric-metal layer) through reflection resonance characteristics, not the natural color of the upper metal layer or the lower metal layer.

The MIM layer may include a lower metal layer 1 connected to a system targeted for radiative cooling, a dielectric layer 2 provided on the lower metal layer for coloring chromatic color through resonance, and an upper metal layer 3 provided on the dielectric.

In addition, the MIM layer may develop different colors as the thickness of at least one of the upper metal layer, the lower metal layer, and the dielectric layer is changed.

The lower metal layer 1 may be connected to a system targeted for radiative cooling, for example, ground or buildings, clothes, vehicles, wearable devices, satellites, photocells, infrared detectors, power plants, and other devices requiring cooling.

The lower metal layer may be formed of any one of gold (Au), copper (Cu), silver (Ag), and platinum (Pt).

In addition, the thickness of the lower metal layer may be 40 nm or more and 1 um or less.

Then, a dielectric layer 2 is provided on the lower metal layer. The dielectric layer 2 may be provided between the lower metal layer 1 and the upper metal layer 3 to separate the lower metal layer 1 and the upper metal layer 3.

The dielectric layer 2 may include a single layer composed of any one of SiO 2, TiO 2, Al 2 O 3, Ta 2 O 3, SiC, HfO 2 or SiNx.

For example, the dielectric layer 2 may be made of SiO2 having a thickness of 2 um or more. For another example, the dielectric layer 2 may be formed of Si3N4 having a thickness of 2 um or more.

However, the present invention is not limited thereto, and the dielectric layer 2 may be formed of a combination of two or more of SiO2, TiO2, Al2O3, Ta2O3, SiC, HfO2 or SiNx.

Specifically, the dielectric layer 2 may include a plurality of layers in which two or more dielectrics of SiO2, TiO2, Al2O3, Ta2O3, SiC, HfO2, or SiNx each constitute one layer.

For example, the dielectric layer 2 may be composed of a plurality of layers including one layer composed of SiO2 and one layer composed of Si3N4, by depositing SiO2 and Si3N4 to a thickness of 600 nm and 900 nm, respectively.

In addition, the dielectric layer is composed of any one of SiO2, TiO2, Al2O3, Ta2O3, SiNx, PDMS, Polyimide, PVDF, PMMA, or SU8, or a combination of two or more (a plurality of layers in which two or more dielectrics each constitute one layer). Can.

In this case, SiO2, TiO2, Al2O3, Ta2O3, SiNx, PDMS, Polyimide, PVDF, PMMA or SU8 may be transparent dielectric materials in the visible light band. That is, by configuring the dielectric layer with a transparent material in the visible light band, it is possible to improve the predictability of the color to be developed without affecting the color to be developed by the resonant structure.

The upper metal layer 3 is provided on the dielectric layer 2. The upper metal layer 3 can reflect solar radiation. The upper metal layer 3 may be formed of any one of gold (Au), copper (Cu), silver (Ag), aluminum (Al), titanium (Ti), or platinum (Pt).

Meanwhile, the material of the upper metal layer and the material of the lower metal layer may be the same or different.

For example, the material of the upper metal layer and the material of the lower metal layer may be both silver (Ag), but are not limited thereto, and different materials of the upper metal layer and the lower metal layer are also possible.

In addition, a heat radiation layer 4 is provided on the upper metal layer 3. The heat radiation layer 4 is a layer for passive radiation and may exhibit passive radiation characteristics. The thermal radiation layer 4 may be composed of any one of polydimethylsiloxane (PDMS), polymethylpentene (TPX), polyimide, polyvinylidene difluoride (PVDF), or PET.

Here, when the thermal emission layer is composed of polydimethylsiloxane (PDMS), polymethylpentene (TPX), polyimide, polyvinylidene difluoride (PVDF), or PET, the thermal emission layer may have a polymer layer having a high emissivity in a long infrared band.

Hereinafter, the dielectric layer is SiO2, and the upper metal layer and the lower metal layer are exemplified as silver (Ag).

In addition, hereinafter, the heat radiation layer 4 will be described as an example consisting of a polydimethylsiloxane (PDMS).

Figure 2 shows an example of a color-type passive cooling structure according to an embodiment of the present invention.

In one embodiment of the present invention, the passive radiant cooling structure may simultaneously implement 1) various visible light color expressions and 2) passive radiant cooling functions. 2, the passive radiation cooling structure according to an embodiment of the present invention, Ag/SiO2/Ag structure is placed under the PDMS layer, for example, having a thickness of several tens of micrometers to achieve the above two functions. Can have Specifically, in the visible region, it is possible to develop color with minimal absorption by the resonance structure, and in the infrared region, a passive radiation cooling structure having high reflectance is proposed.

If only one metal layer (for example, an Ag layer) is disposed under the thermal radiation layer represented by PDMS, the metal layer not only receives the sunlight (8~13 μm) region but also the sunlight in a wide wavelength band. It reflects and has only simple cooling characteristics. On the other hand, the structure of the metal/dielectric/metal represented by Ag/SiO2/Ag, as shown in Fig. 2, is only capable of absorbing the minimum amount of sunlight required to realize color in the visible light region, and thus, color-type passive cooling The structure can be implemented.

The MIM layer may develop various colors of chromatic colors, and one of the main materials for the MIM layer to produce various colors may be SiO2 disposed between Ag and Ag.

3 shows reflection characteristics according to thickness when SiO 2 is used as the dielectric.

The MIM layer may develop different colors as the thickness of the dielectric layer changes.

Specifically, as illustrated in FIG. 3, the thickness of the dielectric layer composed of SiO 2 is changed from 60 nm to 150 nm, and may be implemented from yellow to purple to blue and green.

If the upper metal layer is Au, the dielectric layer made of SiO2 may have a thickness between 60 nm and 180 nm.

4 shows reflectance and absorption according to the thickness of the upper Ag layer.

5 shows reflectance, absorption and transmittance according to the thickness of the lower Ag layer.

In order for the passive cooling radiation structure of the present invention to exhibit color development characteristics, the upper and lower metal layers each have an optimal thickness.

In a preferred embodiment, the thickness of the lower metal layer composed of Ag should be about 40-60 nm, and the thickness of the upper metal layer should be 50 nm or less. If the thickness of the upper metal layer becomes thicker, the natural color of Ag develops and the reflection resonance characteristic disappears as shown in FIG. 4.

In addition, as illustrated in FIG. 5, the thicker the lower metal layer is, the stronger the reflection resonance is, thereby increasing the purity of the color. However, as the absorption rate of sunlight in the band between 280 nm and 400 nm increases, the sun increases. There is also a disadvantage that the heating phenomenon caused by light increases. On the other hand, if the thickness of the lower metal layer is made too thin, the amount of transmitted light may be large, and the system connected to the color-type passive cooling radiation structure may be exposed to sunlight.

In conclusion, in a preferred embodiment of the present invention, for example, Ag as a metal layer, the upper metal layer may have a thickness between 20 nm and 40 nm. When the thickness of the upper metal layer is less than 20 nm, a vivid color cannot be realized, and when it is 50 nm or more, the color developed in the upper metal layer starts to change to a metallic color (Ag color).

In addition, taking Ag as an example, in a preferred embodiment, the lower metal layer may have a thickness between 40 nm and 60 nm. When the lower metal layer is less than 40 nm, there is a problem of color loss and increase in transmittance, and when it is 60 nm or more, there is a problem that the absorption rate of the lower metal layer converges to the maximum.

In the case of Ag/SiO2/Ag structure, other materials described above can be substituted.

Specifically, the upper metal layer and the lower metal layer may be made of a material having high reflectance such as gold (Au), aluminum (Al), platinum (Pt), and the dielectric layer may be made of another dielectric material such as TiO2, Al2O3 or SiNx.

On the other hand, when the materials constituting the upper metal layer, the lower metal layer and the dielectric layer are different, different thicknesses should be set according to the complex refractive index information of each material so that a desired color can be developed.

6 shows a passive radiation characteristic according to thickness when PDMS is used as a heat radiation layer.

In a preferred embodiment, when PDMS is used as the thermal radiation layer, it must have a thickness of at least 20 μm in order to have a passive radiation characteristic, and when a thermal radiation layer is made thinner than this, manual radiation may not be obtained due to insufficient emissivity in the window area of the atmosphere. There is a problem that cannot be achieved. PDMS can be replaced with other transparent polymer materials having high emissivity as described above.

In addition, the emissivity may be increased by doping a micro dielectric in the heat radiation layer. Here, the micro dielectric doped on the heat radiation layer may be any one of SiO 2, TiO 2 or SiC.

FIG. 7 shows color coordinates (a) and cooling characteristics (b) depending on the thickness of the upper metal (Ag) layer.

Here, the cooling characteristic means the difference between the ambient temperature and the sample temperature. The color coordinates were calculated based on the reflectance characteristics in the visible light band of the designed structure. The cooling characteristics are based on the thermal equilibrium state, and calculated based on the vertical incidence of AM1.5G sunlight. The variable h on the x-axis of the cooling characteristic graph is a non-radiative heat exchange coefficient, and is a coefficient indicating the amount of heat transfer due to convection and conduction. Since the pure passive cooling radiation capability is evaluated at hc = 0, the cooling capability was evaluated based on this point. The bottom Ag layer thickness of the designed structure is 40 nm, and the PDMS thickness is 20 μm.

As shown in FIG. 7, the structure without PDMS (no PDMS) is maintained at about 300 degrees higher than the ambient temperature when convection is exposed to sunlight in the absence of conduction at midday. When PDMS is introduced on the color-developing structure, the temperature of the color-type passive cooling radiation structure can be maintained about 5 degrees higher than the ambient temperature or about 20 degrees lower depending on the thickness of the upper Ag layer.

As described above, the thicker the thickness of the upper metal layer, the lower the purity of the color, but in terms of cooling characteristics, when the thickness is thin to 20 nm, the widest color range is wide and various colors can be produced. On the other hand, there are some that are maintained about 5 degrees higher than the ambient temperature.

Therefore, it is preferable that the thickness of the upper Ag layer is 30 nm to 40 nm in order to realize a passive cooling radiation function that is lower than the ambient temperature while maintaining various colors. If the aim is to achieve a passive cooling radiation level similar to the ambient temperature, it is better in terms of color to deposit the upper Ag layer as thin as 20 nm.

Figure 8 shows a sample photo (a) before and after PDMS coating of the color-type passive cooling radiation structure according to an embodiment of the present invention and optical (b) in visible light.

As shown in FIG. 8, it can be seen that the color-type passive cooling radiation structure according to an embodiment of the present invention shows various colors according to the thickness of SiO 2, and it is also seen that it is constant in reflective properties regardless of whether or not PDMS is coated. have.

On the other hand, in the previous embodiment, it was described that the heat radiation layer is composed of polydimethylsiloxane (PDMS).

Meanwhile, polydimethylsiloxane (PDMS) has high emissivity in a very wide band. And because emissivity is high, it means that absorptance is also high, so polydimethylsiloxane (PDMS) can absorb electromagnetic waves in a very wide band, which can adversely affect passive cooling.

Therefore, hereinafter, it is proposed a structure capable of increasing chromatic colors of various colors through the MIM structure, while increasing the absorption rate only in the band required for passive cooling and color development. The thermal radiation layer for realizing this may be referred to as an optional thermal radiation layer.

9 is a view for explaining the structure and features of the CPRC.

9A is a diagram showing a passive radiative cooling structure having a chromatic region of various colors on a silver background to add aesthetics.

9B is a structural schematic diagram of the passive radiation cooling structure in the silver region (top left), a scanning electron microscope (SEM) image in the silver region (bottom left), and a schematic structural diagram of the passive radiation cooling structure in the chromatic region (top right). , A diagram showing a scanning electron microscope (SEM) image (bottom right) in a chromatic region.

9C shows the reflectivity, absorption (emissivity) characteristics of the passive radiation cooling structure (left structure in FIG. 9B) in the silver region (top graph), metal-insulator without thermal radiation layer? Reflectance, absorption (emissivity) characteristics of the passive radiative cooling structure in which only the MIM layer composed of metal is present (interruption graph), metal-insulator It is a diagram showing reflectance and absorption (emissivity) characteristics (bottom graph) when a selective heat-emitting layer is provided on a MIM layer made of metal.

FIG. 9D is a diagram for showing the color difference when only the MIM layer is present without the selective heat emission layer and when the selective heat emission layer is provided on the MIM layer.

9E is a diagram showing a passive radiation cooling structure used for decoration.

Hereinafter, a passive radiation structure capable of developing chromatic colors of various colors through the MIM structure while increasing absorption in the band required for passive cooling and color development may be referred to as a colored passive radiative cooler (CPRC). .

In addition, the CPRC may include a MIM layer and a thermal emission layer (optional thermal emission layer) provided on the MIM layer.

9A and 9B, a thermal radiation layer composed of a double layer is provided on the MIM layer composed of Ag-SiO2-Ag.

Meanwhile, the heat radiation layer may include a plurality of layers in which two or more of SiO2, HfO2, TiO2, SiC, Ta2O3, and Si3N4 each constitute one layer. In this case, each of the plurality of layers may have a thickness of several nm to several hundred nm, respectively.

In this case, SiO2, HfO2, TiO2, SiC, Ta2O3 and Si3N4 may be transparent materials in the visible light band. That is, by configuring the heat-emitting layer as a transparent material in the visible light band, the heat-emitting layer can improve the predictability of the color to be developed without affecting the natural color developed in the MIM layer.

When an example of Si3N4 and SiO2 among a plurality of materials capable of forming a heat radiation layer is described, the heat radiation layer is provided on the MIM layer, and the first layer is composed of Si3N4 and the first layer is composed of SiO2. It may include a second layer.

In addition, since the Si3N4 / SiO2 bilayer has a higher absorption rate (emissivity) in a selected band than an absorption rate (emissivity) in another band, it can serve as a high-efficiency heat emitter. The heat radiation layer configured as described above may be referred to as an optional heat radiation layer.

The selective heat radiation layer may be a selective emitter comprising a double layer of SiO2 (650 nm) and Si3N4 (910 nm).

In addition, the thickness of SiO2 (650 nm) and Si3N4 (910 nm) can be determined by numerical optimization in consideration of the color expression by reflection resonance of the MIM layer and emissivity of CPRC.

9B is a structure in which the MIM layer is composed of one metal (Ag) without a dielectric, and in the right view of FIG. 9B, the MIM layer is a metal-dielectric? It is made of metal.

When an insulator is present in the MIM layer, the color to be developed can be determined by adjusting the thickness of the insulator layer. Specifically, when the insulator layer becomes thin, the yellow color may be developed while the thin film interference resonance occurs at a short wavelength, and when the insulator layer becomes thick, the Cyan color may develop as the thin film interference resonance occurs at a long wavelength.

The MIM structure has a narrow band with a high absorption rate compared to other filters, and thus can minimize the loss of reflectance.

In addition, since the CPRC in which the MIM layer and the selective heat radiation layer are combined has a structure in which a thin film is stacked, patterning is easy. That is, CPRC can be used in a flexible device due to its thin and simple structure.

The upper graph of FIG. 9C shows reflectance and absorption (emissivity) characteristics of the passive radiant cooling structure (left structure in FIG. 9B) in the daytime and silver regions.

Referring to the upper graph of FIG. 9C, it can be seen that the passive radiation cooling structure in the silver region shows a high absorption (emissivity) compared to the surrounding band in the window of the atmosphere, and a high solar reflectance in the other band.

That is, referring to the upper graph of FIG. 9C, as the MIM layer is composed of silver (Ag), a metallic silver color is developed, but as the thermal radiation layer increases the absorption (emissivity) in the window region of the atmosphere, passive radiative cooling It can be seen that the structure exhibits a high absorption rate (emissivity) in the window of the atmosphere. In addition, it can be seen that it exhibits high reflectance in the infrared band and is advantageous for cooling.

The interruption graph in FIG. 9C shows day-time, metal-dielectric without a heat-radiating layer. Reflectance and absorption (emissivity) characteristics of the passive radiative cooling structure in which only the MIM layer made of metal is present.

Referring to the interruption graph in FIG. 9C, metal-insulator? It can be seen that the MIM layer made of metal exhibits a low reflectance and a high absorption rate in the visible light band compared to the surrounding band. In this case, in the MIM layer, the reflectance of the infrared band may be higher than that of the visible light band.

Ie metal-insulator? The MIM layer made of metal may increase absorption of sunlight in the visible light band and develop chromatic color through a resonance structure. Also, by adjusting the thickness of the insulator, the color of the chromatic color to be developed can be determined.

Specifically, the MIM layer may selectively increase the absorption rate of a wavelength required for chromatic color development in the visible light band.

More specifically, when the MIM layer develops a specific color, the MIM layer can selectively increase the absorption rate of a wavelength required to develop a specific color. For example, when the MIM layer develops yellow, the thickness of a plurality of layers included in the MIM layer may be determined in order to develop yellow. In this case, the MIM layer increases the absorption rate of the wavelength required to develop yellow than that of the surrounding wavelengths (wavelengths of other colors except yellow).

The bottom graph of FIG. 9C shows daytime, metal-insulator? Reflectance and absorption (emissivity) characteristics when a selective heat-emitting layer is provided on a MIM layer made of metal.

Referring back to the interruption graph in FIG. 9C, metal-dielectric? It can be seen that the MIM layer made of metal blocks the infrared wavelength.

And the MIM layer provides isolation properties that create independence between the MIM structure and the selective heat radiation layer.

That is, referring to FIG. 9D, since the MIOM layer and the selective heat-radiating layer do not inhibit each other's properties, a metal-dielectric? When an optional heat radiation layer is provided on the MIM layer made of metal, the color developed by the MIM layer can be maintained.

Also, since the MIOM layer and the selective heat-radiating layer do not interfere with each other, the metal-insulator? When the selective heat radiation layer is provided on the MIM layer made of metal, the passive radiation characteristics of the selective heat radiation layer can be maintained.

That is, CPRC may have both the color development property of the MIM layer and the passive radiation property of the selective heat emission layer.

Accordingly, when an optional thermal radiation layer including a first layer composed of Si3N4 and a second layer composed of SiO2 provided on the first layer is provided on the MIM layer, a thermal radiation layer composed of polydimethylsiloxane (PDMS) is provided. The emissivity in the window area of the atmosphere may be greater than that provided on the MIM layer.

In FIG. 9D, images in the case where only the MIM layer is present without the selective heat radiation layer are shown on the left, and images in the case where the optional heat radiation layer is provided on the MIM layer are shown on the right.

Referring to FIG. 9D, it can be seen that even at an oblique angle of incidence (AOI), the color between the MIM layer and the CPRC is very similar.

10A to 10D are results of simulation (calculation) of the correlation between temperature and color in CPRC.

According to FIG. 10A, the color of the CPRC may be changed according to at least one of the thickness of the upper metal layer (Ag) and the thickness of the dielectric layer (SiO2).

And the color comes out clearly at a certain thickness, and accordingly, the absorption of sunlight increases, and the temperature of CPRC is higher or lower than that of the atmosphere.

For example, referring to the graph below in FIG. 10A and FIG. 10B, under strong sunlight (1000 W/m2), the thickness of the upper metal layer is 20 nm. Here, C, M, Y may mean Cyan, Magenta, and Yellow, which are three primary colors that can be expressed by a reflective color filter.

On the other hand, referring to the above graph of FIG. 10A and FIG. 10B, when the upper metal layer is 20 nm, it exhibits the most vivid color, but in this case, the temperature is higher than room temperature at the thickness of almost all dielectric layers. That is, CPRC operates as a heater.

However, since CPRC's temperature is about 6K higher than room temperature, it can be said that CPRC exhibits a temperature characteristic similar to that of the atmosphere in the middle of the day.

On the other hand, referring to Figure 10b, the inside of the red dotted line is the region that can develop the most vivid chromatic color. However, in the area inside the red dotted line, the temperature of CPRC is slightly higher than the atmosphere.

And when the color sharpness is slightly sacrificed, for example, when the thickness of the upper metal layer is 20 nm or more, the CPRC may operate as a cooler while the temperature of the CPRC falls below room temperature.

On the other hand, in the region outside the gray dotted line, the color that the CRPC develops becomes a metallic color (silver), so the chromatic color development characteristics of the MIM are lost.

Therefore, the present invention, by designing the thickness of the upper metal layer and the thickness of the dielectric layer to correspond to the area inside the red dotted line, maintains the temperature characteristics of CPRC similar to the atmosphere (a level higher than room temperature by about 6K) and provides the most vivid chromatic color. Can be implemented.

In addition, by designing the thickness of the upper metal layer and the thickness of the dielectric layer to correspond to areas outside the red dotted line and inside the gray dotted line, the CPRC can be operated as a cooler instead of sacrificing the clarity of chromatic color.

In addition, by designing the thickness of the upper metal layer and the thickness of the dielectric layer to correspond to an area outside the gray dotted line, the color to be developed can be saturated with a metallic color (silver).

In addition, when the thickness of the upper metal layer is 10 nm to 40 nm, CPRC may develop a chromatic color while maintaining a temperature characteristic similar to that of the atmosphere (a level about 6K higher than room temperature) or operating as a cooler.

10C is calculation data showing temperature characteristics of a MIM layer and CPRC according to a non-radiative heat exchange coefficient, hc.

hc is a coefficient of how much convection and conduction are considered, and when hc is 0, it is assumed that there is no convection and conduction.

Referring to FIG. 10C, while the MIM layer always shows a temperature higher than room temperature, the CPRC including the MIM layer and the selective heat emitting layer can maintain a temperature similar to or lower than normal temperature regardless of hc.

10D is a diagram showing the color difference between the MIM layer and the CPRC for each thickness of the lower metal layer.

Referring to FIG. 10D, the color difference between the MIM layer and the CPRC is very small at all thicknesses of the lower metal layer. That is, it can be seen that even if the selective heat radiation layer is disposed on the MIM layer, the selective heat radiation layer has little effect on the color development of the MIM layer.

In addition, referring to FIG. 10D, it can be seen that despite the thickness change of the lower metal layer, the color is almost the same at 50 nm or more. That is, when the thickness of the lower metal layer is 50 nm or more, a change in reflectance is hardly found.

11A to 11D relate to measurement data of a sample actually produced according to a result of simulation (calculation) of the correlation between temperature and color in CPRC.

In FIG. 11A, measured values for the actually manufactured CPRC are shown. The selective heat emission layer is composed of SiO2 (650 nm) and Si3N4 (910 nm), and in this case, it can be seen that CPRC exhibits a very high emissivity in the window region of the atmosphere.

11B is a MIM layer composed of a metal-dielectric-metal, and three samples embodying the colors of Magenta, Cyan, and Yellow (bottom), and three samples embodying the colors of Magenta, Cyan, and Yellow by CPRC (top). It is a diagram showing one sample (top rightmost) and a broadband emitter (bottom rightmost) that implements a metallic color with a MIM layer composed of metal and an optional heat emitting layer.

11C is a graph showing temperature characteristics during the daytime.

In the case of the MIM structure, the color average temperature is about 3-4 degrees higher than that of the atmosphere (orange line), whereas CPRC shows that the color average temperature is almost the same as that of the atmosphere, which is in good agreement with the previous calculation results.

That is, the experimental data in FIG. 11C shows that CPRC can maintain a temperature similar to or lower than the ambient temperature even while developing various colors.

In addition, the CPRC of the present invention is a selective thermal radiation layer combined with the MIM structure, and the experimental data of FIG. 11C shows that the CPRC can maintain a lower temperature than a broadband radiator (black line).

11D is a graph showing the temperature characteristics of MIM and CPRC designed to pattern various chromatic colors on an achromatic background.

The graph of FIG. 11D shows that the temperature of CPRC is lower than that of the atmosphere to operate as a cooler, and the temperature of CPRC is lower than that of MIM.

In addition, when the chromatic color of various colors is designed to be patterned on the achromatic background, according to the high reflectance of the background color (for example, silver color), the cooling efficiency may be higher than when the CPRF is designed with only the chromatic color.

12 is a diagram illustrating a passive cooling radiation structure and test results in a flexible form.

The flexible passive radiative cooling structure may be referred to as flexible radiative cooling material (fRCM).

The flexible passive cooling radiation structure in FIG. 12A includes a MIM layer of Ag-SiO2-Ag structure and a selective heat radiation layer. In addition, the PDMS film was coated for protection for the selective heat radiation layer, and the lower metal layer was made of aluminum foil for flexible properties.

Also shown is a flexible heater made for testing.

12B is a measurement result of shooting a Bare heater, an Al layer coated with PDMS, and a flexible radiative cooling material (fRCM) through a thermal imaging camera.

FIG. 12C is a graph showing the result of measurement over time after attaching a thermocouple to the back side.

(i) Bare heater, (ii) PDMS coated Al layer, (iii) flexible radiative cooling material (fRCM) temperature graph.

12B and 12C, it can be seen that heat radiation is most excellent in a flexible radiative cooling material (fRCM).

12D is a result of observing a flexible radiative cooling material (fRCM) on a bare heater and observing it with a thermal imaging camera while irradiating artificial sunlight.

In the case of flexible radiative cooling material (fRCM) that develops a chromatic color, sunlight is absorbed for coloring. Therefore, not only the heat of operation of the device (the temperature of the bar heater), but also sunlight can act as a heat source.

Referring to the first image and the second image of FIG. 12D, it can be seen that the flexible radiative cooling material (fRCM) spreads heat generated in the device well.

In addition, referring to the third image of FIG. 12D, it can be seen that even under artificial sunlight, a difference in temperature between a region where chromatic color develops and a region having a metallic color (or achromatic color) is insignificant.

12E is a result of applying a flexible radiative cooling material (fRCM) to a wearable device.

Specifically, a part of the watch band of the smart watch was covered with flexible radiative cooling material (fRCM). In addition, an experiment was conducted by attaching one thermocouple to a watch band covered with flexible radiative cooling material (fRCM) and a watch band not covered with flexible radiative cooling material (fRCM).

12F is a result of taking a smart watch with a thermal imaging camera (990W/m2) at midday.

Referring to FIG. 12F, it can be seen that a region covered with flexible radiative cooling material (fRCM) represents a low temperature and a high temperature in a bare device without flexible radiative cooling material (fRCM).

12G is a result of measuring while turning the wrist at an interval of 1 minute so that the covered area and the uncovered area of flexible radiative cooling material (fRCM) can be completely exposed to sunlight while wearing a smart watch.

The area where the flexible radiative cooling material (fRCM) is not covered has a very large temperature rise (about 36-48 degrees) when exposed directly to sunlight, while the area covered by flexible radiative cooling material (fRCM) It can be observed that the silver stays at about 30 to 36 degrees.

Next, the CPRC manufacturing method will be described with reference to FIG. 9A again.

It has been previously described that the MIM layer includes a lower metal layer, a dielectric layer provided on the lower metal layer, and an upper metal layer provided on the dielectric layer.

In the state in which the lower metal layer is formed, a dielectric layer may be deposited on the lower metal layer. In this case, some regions of the lower metal layer are not masked, and other regions of the lower metal layer are masked, and then a dielectric layer may be deposited.

Then, when the upper metal layer is deposited, the MIM layer is completed, and when the selective heat radiation layer including the Si3N4 layer and the SiO2 layer is grown on the MIM layer, CPRC can be produced.

When looking at the CPRC manufactured in this way, some regions of the MIM layer may include both the lower metal layer, the dielectric layer and the upper metal layer. However, some other regions of the MIM layer may include a lower metal layer and an upper metal layer, except for the dielectric layer.

Accordingly, chromatic colors are developed in some regions and metallic colors (or achromatic colors) are developed in other regions, and various pattern patterns may be generated by appropriately adjusting the partial regions and the other partial regions.

Meanwhile, a dielectric layer having various thicknesses may be generated in a process of depositing the dielectric layer.

Specifically, some regions of the MIM layer including both the lower metal layer, the dielectric layer, and the upper metal layer may include a first region and a second region.

In addition, the thickness of the dielectric layer in the first region and the thickness of the dielectric layer in the second region may be different from each other.

In this case, the first region of the MIM layer may develop a chromatic color of the first color, and the second region of the MIM layer may develop a chromatic color (different from the first color) of the second color.

In this case, as illustrated in FIG. 9A, the CPRC may have various pattern patterns and various pattern colors on an achromatic (or metallic) background.

The existing passive cooling device has a structure for reducing solar absorption to enable cooling even during the daytime, but has a silver or white surface color, thereby deteriorating aesthetics. Therefore, there is a problem that the installation location is limited and difficult to use for various exterior materials.

However, since the passive cooling radiation structure proposed in the present invention can develop chromatic colors of various colors while maintaining a temperature similar to or lower than room temperature under sunlight during the daytime, the aesthetics are improved and the utilization range is very high. There is this.

In addition, since the passive cooling radiation structure proposed in the present invention is a stacked structure and has a simple structure, patterning in various patterns and colors is possible, and it is easy to manufacture in a flexible device form.

The above detailed description should not be construed as limiting in all respects, but should be considered illustrative. The scope of the invention should be determined by rational interpretation of the appended claims, and all changes within the equivalent scope of the invention are included in the scope of the invention.

1: lower metal layer 2: dielectric layer
3: upper metal layer 4: heat radiation layer

Claims (15)

A MIM layer including a lower metal layer connected to a system targeted for radiative cooling, a dielectric layer provided on the lower metal layer for coloring chromatic color through resonance, and an upper metal layer provided on the dielectric; And
A heat radiation layer provided on the upper metal layer and exhibiting passive radiation characteristics
Manual cooling radiation structure. According to claim 1,
The upper metal layer is made of any one of gold (Au), copper (Cu), silver (Ag), aluminum (Al), titanium (Ti), or platinum (Pt),
The lower metal layer is made of any one of gold (Au), copper (Cu), silver (Ag), or platinum (Pt),
The material of the upper metal layer and the material of the lower metal layer are the same or different
Manual cooling radiation structure. According to claim 1,
The dielectric layer,
Comprises a single layer consisting of SiO2, TiO2, Al2O3, Ta2O3, SiC, HfO2 or SiNx, or
The SiO2, TiO2, Al2O3, Ta2O3, SiC, HfO2, or two or more dielectrics of SiNx each include a plurality of layers constituting one layer
Manual cooling radiation structure. According to claim 1,
The heat radiation layer is composed of any one of polydimethylsiloxane (PDMS), polymethylpentene (TPX), polyimide, polyvinylidene difluoride (PVDF) or PET
Manual cooling radiation structure. According to claim 1,
The MIM layer,
In the visible light band, to selectively increase the absorption rate of the wavelength required for the chromatic color development
Manual cooling radiation structure. According to claim 1,
The MIM layer,
Different colors are developed as the thickness of at least one of the upper metal layer, the lower metal layer, and the dielectric layer is changed.
Manual cooling radiation structure. According to claim 1,
The dielectric layer,
SiO2, TiO2, Al2O3, Ta2O3, SiNx, PDMS, Polyimide, PVDF, PMMA or SU8, or a combination of two or more,
The SiO2, TiO2, Al2O3, Ta2O3, SiNx, PDMS, Polyimide, PVDF, PMMA or SU8,
Transparent dielectric material in the visible light band
Manual cooling radiation structure. According to claim 1,
The thickness of the upper metal layer,
10 nm to 40 nm
Manual cooling radiation structure. According to claim 1,
The thickness of the lower metal layer,
40 nm to 1 um
Manual cooling radiation structure. According to claim 1,
The heat radiation layer increases the emissivity in the window region of the atmosphere,
Two or more of SiO2, HfO2, TiO2, SiC, Ta2O3 and Si3N4 each include a plurality of layers constituting one layer
Manual cooling radiation structure. The method of claim 10,
The heat radiation layer,
A first layer formed on the MIM layer and composed of Si3N4; And
It is provided on the first layer and comprises a second layer composed of SiO2
Manual cooling radiation structure. According to claim 1,
When the heat radiation layer including the first layer made of Si3N4 and the second layer made of SiO2 and provided on the first layer is provided on the MIM layer, the heat radiation layer made of polydimethylsiloxane (PDMS) is The emissivity in the window area of the atmosphere is greater than that provided on the MIM layer.
Manual cooling radiation structure. According to claim 1,
The MIM layer,
The reflectance of the infrared band is higher than that of the visible light band.
Manual cooling radiation structure. According to claim 1,
Some regions of the MIM layer include all of the lower metal layer, the dielectric layer, and the upper metal layer,
Some other regions of the MIM layer include the lower metal layer and the upper metal layer, except for the dielectric agent layer.
Manual cooling radiation structure. The method of claim 14,
Some regions of the MIM layer include a first region and a second region,
The thickness of the dielectric layer in the first region and the thickness of the dielectric layer in the second region are different from each other.
Manual cooling radiation structure.

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