JP7486908B1 - Wavelength-selective infrared radiation control member - Google Patents

Abstract

[Problem] To provide a selective infrared radiation control member with a high overall emissivity by making the metal coating formed on the cavity surface thinner than a specific thickness, combining the effects of optical interference between adjacent cavities and the high emissivity of the substrate itself. [Solution] A wavelength-selective infrared radiation control member that selectively emits infrared rays in a preset wavelength range, in which a large number of cavities having a preset opening shape and opening depth are arranged two-dimensionally in a preset configuration on one surface of a substrate made of a semiconductor material or a dielectric material, and the cavities and the surface on which the cavities are formed are formed with a metal coating having a lower emissivity in the infrared region than the substrate, the metal coating formed on the surface on which the cavities are formed has a thickness equal to or greater than the skin depth and equal to or less than 3.5 times the skin depth, and the metal coating formed on the cavities has a thickness equal to or less than the thickness of the metal coating formed on the surface on which the cavities are formed. [Selected Figure] Figure 1

Description

The present invention relates to a wavelength-selective infrared radiation control member that can increase the radiation intensity of a specific infrared wavelength range in a resin member having a specific infrared transmission wavelength range.

Many semiconductor elements are used in electronic devices such as personal computers and smartphones, and their processing speeds are improving year by year. There is a demand for semiconductor elements such as CPUs to be both compact and highly functional, and the amount of heat generated per unit volume is increasing significantly. However, since semiconductor elements are often sealed with resin, it is difficult to efficiently cool the heat generated by the semiconductor elements to the outside. In addition, there is a strong demand for miniaturization and weight reduction not only in semiconductor elements but also in various electronic devices, and there is a trend toward structures in which they are directly sealed with resin from the metal casing.

Generally, heat transfer occurs through thermal conduction, convection, and thermal radiation. In many cases, resin-encapsulated semiconductor elements are cooled by placing a highly thermally conductive sheet tightly between the semiconductor element and a heat sink, and cooling is achieved using thermal conduction. However, as the demand for smaller devices increases, it is becoming more difficult to provide space for placing a heat sink. As a result, in recent years, cooling methods that use thermal radiation have been attracting attention.

Thermal radiation is the phenomenon in which an object releases energy in the form of electromagnetic waves; in the low temperature range of around 0 to 100°C, electromagnetic waves are mostly emitted in the infrared region. The amount of heat dissipated by thermal radiation is proportional to the heat dissipation area and emissivity, and increases as the temperature difference with the ambient temperature increases. Various radiating materials have also been developed to dissipate heat by thermal radiation.

For example, in an electronic device in which a heat source is covered with a resin member having a specific infrared transmission wavelength range, a wavelength-selective heat radiation material having a heat radiation surface on which a large number of microcavities forming a periodic surface micro-convex pattern are arranged two-dimensionally is placed between the heat source and the resin member so as to cover the heat source, thermal energy from the heat source is input to the wavelength-selective heat radiation material by heat transfer or thermal radiation, and thermal radiation light corresponding to the infrared transmission wavelength range of the resin member is selectively emitted from the heat radiation surface of the wavelength-selective heat radiation material toward the resin member, thereby improving the heat dissipation efficiency of the electronic device, and a wavelength-selective heat radiation material for this purpose has been disclosed (see, for example, Patent Document 1).

Also disclosed is a method for producing a wavelength-selective heat emitting or absorbing material, which comprises the steps of: preparing an alloy substrate capable of being separated into two phases by spinodal decomposition when a supersaturated solid solution is aged in a two-phase coexistence region; aging the alloy substrate in a two-phase coexistence region to cause spinodal decomposition to form a regularly arranged first phase and a second phase arranged between the first phase; selectively dissolving and removing the second phase to a predetermined depth to lift up the first phase; physically removing the first phase lifted up by dissolving and removing the second phase with ultrasonic waves; and physically removing the first phase with ultrasonic waves and then selectively dissolving and removing the first phase on the surface. (See, for example, Patent Document 2.)

Furthermore, a wavelength-selective thermal radiation material that selectively emits thermal radiation light corresponding to the infrared transmission wavelength range of a resin member has been disclosed, the wavelength-selective thermal radiation material having a thermal radiation surface on which a large number of microcavities having rectangular openings that are periodically repeated and two-dimensionally arranged in a lattice pattern are formed, the microcavities having an opening ratio a/Λ (a: opening diameter, Λ: opening period) in the range of 0.5 to 0.9, and the surface roughness Rz of the upper part of the cavity wall that defines the microcavity being 1 μm or less (see, for example, Patent Document 3).

Furthermore, a wavelength-selective thermal emission material has been disclosed that is used to efficiently heat radiative gas molecules having a specific light absorption band, and is characterized by having a large number of microcavities arranged substantially two-dimensionally so as to form a periodically repeated fine uneven pattern on a plane, and a thermal emission surface that has a coating layer that covers the microcavities and selectively emits thermal radiation electromagnetic waves that correspond to the wavelength region of the specific light absorption band of the radiative gas molecules (see, for example, Patent Document 4).

JP 2010-27831 A JP 2013-32570 A WO2015/190163 JP 2004-238230 A

The invention described in Patent Document 1 is a wavelength-selective heat radiation material used to improve the heat dissipation efficiency of a heat source in an electronic device in which the heat source is covered with a resin member having a specific infrared transmission wavelength range, and it is disclosed that elemental semiconductors such as silicon and germanium, and high-melting point metals such as tungsten and tantalum are used as the base material, and a metal film with excellent electrical conductivity such as platinum, gold, silver, copper or aluminum is formed as the surface material of the microcavity as a coating layer. However, while the numerical analysis and examples disclose the formation of a platinum film as the coating layer, there is no disclosure of its thickness.

The invention described in Patent Document 2 has the problem that when forming a microcavity of a certain shape, the process is complicated and costs increase when using the commonly used combination method of photolithography and etching processes. To solve this problem, the key point is to form a microcavity by simply etching an alloy material with a regular structure. This alloy material has low electrical conductivity and low reflection in the infrared region, so it is covered with a metal film with higher electrical conductivity than the alloy material. It is said that the material should be a precious metal such as platinum, or a metal such as tungsten or tantalum, and that the thickness must be at least the penetration depth of the electromagnetic waves. In the embodiment, it is disclosed that platinum was formed to a thickness of 100 nm. In addition, there is also the problem that it is difficult to stably manufacture the regular structure required for a wavelength-selective infrared radiator at a mass production level using this alloy material.

The invention described in Patent Document 3 is characterized by the use of a metal foil of aluminum or an aluminum alloy, in which the area occupancy rate of the (100) crystal plane is 93% or more, as the substrate, and the use of anisotropic etching to easily fabricate microcavities oriented perpendicular to the heat radiation surface. Because aluminum is used as the substrate, no coating layer is formed.

The invention described in Patent Document 4 is characterized by increasing the emissivity in the light absorber wavelength range of the target gas by forming the period to be substantially the same as or 1 μm shorter than the specific light absorber wavelength of the radiative gas molecules in order to efficiently heat the radiative gas. Since a silicon wafer is used as the substrate, the coating layer is formed by forming a 40 nm titanium thin film, followed by a 100 nm platinum thin film to improve adhesion, but the required thickness of the coating layer is not disclosed.

The present invention aims to provide a wavelength-selective infrared radiation control component that has a high overall emissivity by combining the effects of optical interference between adjacent cavities and the high emissivity of the substrate itself, by forming a metal coating on the cavity surface thinner than a specific thickness in order to improve the emissivity in a specific infrared wavelength range.

In order to solve the above-mentioned problems of the prior art, the wavelength-selective infrared radiation control member of the present invention is a wavelength-selective infrared radiation control member that selectively emits infrared radiation in a preset wavelength range, and is characterized in that a large number of cavities having a preset opening shape and opening depth are arranged two-dimensionally in a preset configuration on one side of a substrate made of a semiconductor material or a dielectric material, the cavities and the surface on which the cavities are formed are formed with a metal coating having an emissivity in the infrared region lower than that of the substrate, the metal coating formed on the surface on which the cavities are formed has a thickness equal to or greater than the skin depth and equal to or less than 3.5 times the skin depth, and the metal coating formed on the cavities has a thickness equal to or less than the thickness of the metal coating formed on the surface on which the cavities are formed.

By using this type of configuration, the infrared shielding ability of the metal coating on the surface is reduced, and the optical interference with adjacent cavities and the large emissivity of the substrate are utilized. As a result, a large emissivity can be achieved by synergizing not only the emissivity from the cavity, but also the emissivity of the optical interference and the emissivity of the substrate.

Emissivity is a measure of the efficiency of radiation (and absorption) of an object, and takes values between 0 and 1, the value for a black body. The ratio for all wavelengths is called total emissivity, and the ratio for a specific wavelength is called spectral emissivity. The emissivity referred to in this invention is spectral emissivity. It is also known that emissivity varies depending on the material of the object, the surface condition (oxidation, dirt, etc.), the surface shape (roughness, unevenness), and the temperature. Furthermore, skin depth refers to the distance at which an electromagnetic field incident on a certain material attenuates to 1/ e . Since metals are negative dielectrics, the skin depth can be calculated using the following formula.

In the present invention, the wavelength-selective infrared radiation control member is mainly for efficiently radiating infrared rays in the transmission wavelength band of the sealing resin member, which is about 3.5 to 5.6 μm. Therefore, when the wavelength is set to 5 μm and aluminum (Al) is used as the material of the metal coating, the skin depth is 17.2 nm. When the thickness of the skin depth is formed, the energy of the electromagnetic wave is attenuated by 1/ε, that is, -8.7 dB. As a guideline for electromagnetic wave shielding performance, it is more preferable to set it to -30 dB, so in this case, the thickness is 3.5 times the skin depth, that is, 60.4 nm for Al. If the thickness is formed more than this, the electromagnetic wave shielding performance will be even greater, but in the present invention, by slightly reducing the electromagnetic wave shielding performance, it is intended to achieve a large emissivity by synergizing not only the emissivity from the cavity but also the emissivity of the light interference and the emissivity of the base material. For this reason, it is preferable that the thickness of the metal coating is at least 3.5 times the skin depth. On the other hand, if the metal coating is thin, the wavelength selectivity decreases. To avoid this, it is preferable to set it at least equal to or greater than the skin depth. For Al, it is preferable to set it to equal to or greater than the skin depth of 17.2 nm and equal to or less than the skin depth of 60.4 nm.

In the above configuration, the cavity may have an aspect ratio, which is the ratio between the opening shape and the opening depth, of at least 1, and may be arranged such that the center-to-center distance between the cavity and a plurality of other cavities adjacent to the cavity differs by at least one.

The cavity is considered to act as a resonator of the electromagnetic field. Under resonance conditions, the absorption rate of the incident electromagnetic wave increases, resulting in increased radiation. Therefore, an aspect ratio smaller than 1 is not preferable because it is difficult to function as a resonator. A larger aspect ratio is better, but since the target value of the aperture diameter of the aperture shape is about 3 μm, if the aspect ratio is attempted to be larger than 2, side etching will become large during the etching process to form the cavity, and the accuracy of the aperture diameter of the aperture shape will decrease. Therefore, the aspect ratio is preferably 1 or more and 2 or less. However, it may be larger than 2 if side etching can be prevented from occurring during the etching process. The aperture diameter of the aperture shape refers to the width in the case of a square, and the diameter in the case of a circle. In the following, the aperture diameter may be referred to as the aperture shape.

By configuring in this way, periodic disturbances occur in some areas, resulting in the emergence of multiple radiation waves with different wavelengths and emissivity, which are superimposed to increase the integral emissivity in the required infrared wavelength range of 3.5 to 5.6 μm. In this invention, the integral emissivity refers to the integrated value of the emissivity in the wavelength range of 3.5 to 5.6 μm, i.e., the emissivity area in the range of 3.5 to 5.6 μm.

In the above configuration, the aspect ratio of the cavity, which is the ratio between the opening shape and the opening depth, is at least 1, and the cavities may be arranged at the same period. By using such an arrangement, a large number of cavities are arranged two-dimensionally at a constant period, so that the radiation peak intensity of a specific wavelength can be increased.

In the above configuration, the semiconductor material may be a single crystal, polycrystalline, or amorphous material selected from silicon, germanium, silicon carbide, and gallium arsenide. The semiconductor material may also be a film formed on a substrate having a smooth surface to a thickness at least equal to or greater than the opening depth.

Since semiconductor materials such as silicon and germanium have high emissivity, by making the metal coating of the present invention thin, radiation from the base material can also be effectively utilized. When the wavelength is 0.9 μm, the emissivity of silicon is 0.69 to 0.71, the emissivity of germanium is 0.6, the emissivity of silicon carbide is 0.80 to 0.83, and the emissivity of gallium arsenide is 0.68. However, emissivity is greatly affected by the surface condition, so these values are for reference only.

The semiconductor material may be single crystal, polycrystalline, or amorphous. In the case of single crystal, a wafer used in integrated circuit manufacturing may be used. In the case of polycrystal, a wafer used in solar cells may be used, or the film may be formed on a glass substrate or a quartz substrate with a thickness at least equal to the opening depth. In film formation, it is not necessary to make the film polycrystallized, and the film may be amorphous or may be a mixture of amorphous and polycrystalline. The film may be formed by existing film formation methods such as sputtering or CVD. The substrate is not limited to a glass substrate or a quartz substrate, and may be formed on a polyimide sheet having a smooth surface, for example.

By using such materials, it is possible to easily obtain a large, smooth substrate with high emissivity, and the photolithography and etching processes for cavity formation can be carried out reliably.

When forming a film of semiconductor material, it is preferable to make the thickness equal to or greater than the opening depth of the cavity. With such a thickness, when the cavity is formed by etching, it is formed only within the semiconductor material. Therefore, it is possible to obtain the same characteristics as when a single crystal semiconductor material is used. On the other hand, if a semiconductor material is formed on a glass substrate or a quartz substrate, it can be made less expensive than single crystal semiconductor material.

In the above configuration, the dielectric material may be a resin material or a ceramic material. The resin material may be formed on a substrate having a smooth surface to a thickness at least equal to or greater than the opening depth of the cavity.

Resin materials are selective emitters, and their transmission and absorption (radiation) change significantly at specific wavelengths. When measured at wavelengths where absorption (radiation) is high, the emissivity is high. Examples of resin materials that can be used include polyethylene terephthalate resin, polycarbonate resin, ABS resin, acrylic resin, polyvinyl chloride resin, and polyester resin. Examples of ceramic materials that can be used include sintered materials such as alumina (emissivity: 0.9), magnesia (emissivity: 0.91), and silicon nitride (emissivity: 0.89), as well as film-formed materials or bulk materials formed by CVD, etc.

In the case of resin materials, if a resin material is formed on a substrate having a smooth surface such as a glass substrate, a quartz substrate, or an aluminum foil to a thickness at least equal to the opening depth of the cavity, the cavity can be formed only from the resin material, which makes etching easy. Note that forming the resin material to a predetermined thickness can be easily performed by using, for example, a roll coater.
In the above configuration, the cavity may be polygonal or circular, or may be a combination of a polygonal shape and a circular shape.

One of the objectives of the present invention is to increase the integral value of radiation intensity in the wavelength range of 3.5 to 5.6 μm, i.e., the integral emissivity. By combining polygons of different sizes, combining circles of different sizes, or combining a polygon and a circle, the peak value of the radiation intensity differs depending on each shape, so the integrated integrated emissivity of these can be increased. Note that a single polygonal shape or a single circular shape may also be used.

The above configuration may be used in an electronic device in which an electronic circuit section having a heat source is sealed with a sealing resin member having an area with high transmittance in a specific infrared wavelength range, and the cavity shape and configuration may be set so that the cavity is disposed between the electronic circuit section and the sealing resin member and selectively radiates the specific infrared transmission wavelength range of the sealing resin member.

For example, as the functionality of CPUs and other devices increases, the amount of heat generated per unit volume increases. Because these packages are usually sealed with resin, it is difficult to dissipate heat by thermal conduction through the sealing resin material. By placing the wavelength-selective infrared radiation control member of the present invention between such an electronic circuit section and the sealing resin material, it is possible to increase the radiation to the outside from the highly transmittance areas of the sealing resin material, thereby improving the heat dissipation effect by radiation.

The electronic device of the present invention is an electronic device in which an electronic circuit section having a heat source is sealed with a sealing resin member having an area with high transmittance in a specific infrared wavelength range, and includes a wavelength-selective infrared radiation sheet that is disposed between the electronic circuit section and the sealing resin member and selectively radiates the specific infrared transmission wavelength range of the sealing resin member, and is characterized in that the wavelength-selective infrared radiation sheet is the wavelength-selective infrared radiation control member described above.

For example, as the functionality of CPUs and the like increases, the amount of heat generated per unit volume increases, and heat dissipation measures are required for electronic devices that include such electronic circuitry. These electronic devices are usually sealed with resin, making it difficult to dissipate heat by thermal conduction through the sealing resin material. By placing the wavelength-selective infrared radiation control member of the present invention between such electronic circuitry and the sealing resin, it is possible to increase the radiation to the outside from the highly transmittance areas of the sealing resin material, thereby realizing electronic devices with improved heat dissipation effects through radiation.

The wavelength-selective infrared radiation control member of the present invention can dissipate heat from a heat source of an electronic device that has an electronic circuit section with a heat generating section by radiating it through the infrared transmission band of the sealing resin, thereby cooling it, and is highly effective in the field of semiconductor devices.

1A and 1B are diagrams showing a schematic configuration of a wavelength-selective infrared radiation control member according to a first embodiment of the present invention, in which (a) is a plan view and (b) is a sectional view taken along line XX of (a). FIG. 11 is a diagram comparing the emissivity characteristics of a wavelength-selective infrared radiation control member according to the first embodiment, which has a circular opening shape and is arranged so that at least one of the center-to-center distances between a cavity and a plurality of other cavities adjacent to the cavity is different, and a wavelength-selective infrared radiation control member which is arranged at a constant period. 3A to 3C are diagrams showing the arrangement states of a periodic array, a random array A, and a random array B for a wavelength-selective infrared radiation control member according to the first embodiment. The graph shows the results of investigating the emissivity characteristics of the wavelength-selective infrared radiation control member according to the first embodiment by changing the thickness of the metal film on the surface forming the cavity in the periodic array configuration of FIG. The wavelength-selective infrared radiation control member according to the first embodiment has a random arrangement B configuration as shown in FIG. 3. The thickness of the metal film on the surface forming the cavity is changed, and the emissivity characteristics are examined. 13 shows the results of investigating the emissivity characteristics as a function of the Al film thickness when the wavelength-selective infrared radiation control member according to the first embodiment has rectangular openings arranged periodically with a period of 5 μm. The wavelength-selective infrared radiation control member according to the first embodiment has circular openings with a period of 5 μm between the imaginary circles, and is arranged periodically. The results show the emissivity characteristics as a function of the Al film thickness. 8 is a SEM image showing the shape of an opening of the sample used in FIG. 6 and FIG. 7 for the wavelength-selective infrared radiation control member according to the first embodiment. FIG. 11 is a schematic cross-sectional view of a wavelength-selective infrared radiation control member according to a second embodiment. 13A to 13C are schematic cross-sectional views for explaining a manufacturing process for a wavelength-selective infrared radiation control member according to a third embodiment. 1 is a schematic cross-sectional view showing a structure of an electronic device of the present invention.

(First embodiment)

The wavelength-selective infrared radiation control member according to the first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of a wavelength-selective infrared radiation control member 1 according to the present invention, where (a) is a plan view and (b) is a cross-sectional view taken along line X-X in (a). Note that FIG. 1 is a schematic view, and the plan view and the cross-sectional view are not necessarily drawn to exactly match each other.

The wavelength-selective infrared radiation control member 1 of the present invention is a wavelength-selective infrared radiation control member that selectively emits infrared rays in a preset wavelength range, and has a number of cavities 4a, 4b, 4c, 4d, 4e, 4f having a set opening shape W and opening depth D arranged two-dimensionally in a set arrangement configuration on one surface of a substrate 2 made of a semiconductor material or a dielectric material. Metal coatings 3a, 3b having a lower emissivity in the infrared region than the substrate are formed on the cavities 4a, 4b, 4c, 4d, 4e, 4f and the surfaces 5a, 5b, 5c, 5d, 5e on which the cavities 4a, 4b, 4c, 4d, 4e, 4f are formed. The metal coating 3a formed on the surfaces 5a, 5b, 5c, 5d, 5e on which the cavities 4a, 4b, 4c, 4d, 4e, 4f are formed has a thickness that is equal to or greater than the skin depth and is 3.5 times the skin depth or less. On the other hand, the metal coating 3b formed on the cavities 4a, 4b, 4c, 4d, 4e, and 4f is made to be equal to or less in thickness than the metal coating formed on the surfaces 5a, 5b, 5c, 5d, and 5e on which the cavities 4a, 4b, 4c, 4d, 4e, and 4f are formed.

In the above explanation, only the cavities shown in the cross-sectional view along line X-X, the surface on which the cavities are formed, and the metal coating formed thereon are described, but as can be seen from Figure 1(a), numerous cavities are arranged over the entire surface.

In this embodiment, the cavity has an aspect ratio, which is the ratio between the opening shape W and the opening depth D, of at least 1, and is arranged such that at least one of the center-to-center distances between the cavity and a plurality of other cavities adjacent to the cavity is different. For example, when focusing on cavity 4g in Fig. 1(a), among cavities 4h, 4i, 4j, 4k, 4l, and 4m adjacent to cavity 4g, the center-to-center distance between cavity 4m and cavity 4g is set to be smaller than the center-to-center distance between the other cavities. When focusing on the other cavities, at least one of the adjacent cavities is arranged such that the center-to-center distance is different.
In this embodiment, a silicon substrate, which is a semiconductor material, is used as the base material 2. The procedure for fabricating the shape shown in FIG.

Photoresist is applied to the surface of the silicon substrate. Spin coating is generally used to apply photoresist. Spin coating was also used in this embodiment.

Next, a photomask is prepared in which the center distance of at least one of the adjacent cavities is made different. Exposure is performed using this photomask. Since the target opening shape W is 3 μm, a stepper is used. Note that in this embodiment, wavelength-selective infrared radiation control members having circular and rectangular opening shapes, as well as opening shapes of various sizes, were produced. For this purpose, photomasks of various shapes were also produced.

After exposure for a predetermined time, a development process is performed to develop predetermined locations of the photoresist, exposing the surface of the silicon substrate. The silicon substrate thus prepared is subjected to anisotropic dry etching using a dry etching device. This results in a structure in which a large number of cavities having a predetermined opening shape W and a predetermined depth are arranged. The photoresist is then removed, and after cleaning, the substrate is placed in a sputtering device to form, for example, Al to a predetermined thickness. In this way, a wavelength-selective infrared radiation component 1 is obtained in which a large number of cavities having a predetermined opening shape W and a predetermined depth D are arranged.

In addition, when the film is formed by sputtering, the thickness of the metal film formed on the cavity can be in the range of about 0.5 to 1 with respect to the thickness of the metal film formed on the surface on which the cavity is formed. Furthermore, strictly speaking, the opening shape W and the depth D are the shapes after the metal film is formed, but the cavity opened by etching is about 3 μm and the metal film is about 50 nm, so the thickness of the metal film can be almost negligible. The film formation method is not limited to sputtering, and may be, for example, an MOCVD method or an electroless plating method. In these methods, the thickness of the metal film formed on the cavity can be almost the same as or slightly smaller than the thickness of the metal film formed on the surface on which the cavity is formed. That is, it can be in the range of about 0.8 to 1.
Next, the emissivity characteristics of wavelength-selective infrared radiation control members fabricated using Al as the metal coating and varying the film thickness and opening shape will be described.

2 is a diagram comparing the emissivity of a wavelength-selective infrared radiation control member having a circular opening shape W, arranged so that at least one of the center distances between a cavity and a plurality of other adjacent cavities is different, and a wavelength-selective infrared radiation control member arranged at a constant period. The configuration in which the cavities are arranged differently will be referred to as a random arrangement below.
FIG. 3 is a diagram showing the arrangement states of a periodic array, a random array A, and a random array B.

The periodic array was made with a circular opening shape W of 3 μm and a center-to-center distance of 5 μm. This array was obtained by arranging imaginary circles with a diameter of 5 μm in a dense state, and then arranging circular opening shapes of 3 μm concentrically with the imaginary circles.

In the random array A, the circular opening shape is also 3 μm. The array method is to arrange imaginary circles with a diameter of 5 μm in a dense state, and then arrange a second imaginary circle with a diameter of 4 μm concentrically within this imaginary circle, and arrange the circular opening shape eccentrically relative to this second imaginary circle within a range that does not protrude from the second imaginary circle.

In random array B, the circular opening shape is also 3 μm. The arrangement method is to arrange imaginary circles with a diameter of 5 μm in a dense state, and arrange the circular opening shapes off-center with respect to the imaginary circles, but within a range that does not extend beyond the imaginary circles. As can be seen from Figure 3, random array B is an arrangement with a higher degree of randomness than random array A.

As can be seen from the explanation of the arrangement method, they are all the same in that 5 μm imaginary circles are densely arranged with 3 μm circular opening shapes arranged within them. Therefore, the number of cavities in the same area is all the same.

Looking at the emissivity characteristics in Figure 2, the periodic array has a peak wavelength of 4.9 μm and a peak intensity of 69.1. Meanwhile, the random array A has a peak wavelength of 4.9 μm and a peak intensity of 67.0. The random array B also has a peak wavelength of 4.9 μm and a peak intensity of 61.4. Looking at the peak intensity, it was found that the periodic array has the largest emissivity. However, when the integrated emissivity was calculated for the range of 3.5 to 5.6 μm, which is the infrared transmission wavelength band of the sealing resin material, the periodic array had an integrated emissivity of 3365, the random array A had an integrated emissivity of 3390, and the random array B had an integrated emissivity of 3598. Looking at these results, it was found that the random array B has a better cooling effect by emitting infrared rays. This is because the peak intensity is smaller in the case of the random array B, but the emissivity is higher than the others in a wide range of wavelengths from 3.5 to 5.6 μm.

Figure 4 shows the results of investigating the emissivity characteristics by changing the thickness of the metal film on the surface forming the cavity in the periodic array configuration of Figure 3. The metal film was formed by sputtering using Al. The opening shape W was 3 μm, the opening depth D was 3.3 μm, and the period of the periodic array was 5 μm. As can be seen from the figure, no clear peak was obtained when no Al film was formed and when an Al film was formed to a thickness of 12 nm, and it was found that it cannot be used as a wavelength-selective infrared radiation control member. When the Al film thickness was 25 nm and 50 nm, the peak wavelength was the same 4.9 μm, and the integrated emissivity was also large, 4307 at 25 nm and 5096 at 50 nm. On the other hand, when the Al film thickness was 100 nm, the peak wavelength was almost the same, but the peak intensity was smaller. Furthermore, the integrated emissivity was 3365, which was smaller than the results obtained for 25 nm and 50 nm.

In the case of Al, the skin depth is 17.2 nm, so even if Al is formed to a thickness of 12 nm, no shielding effect is obtained, and radiation is emitted even in the long wavelength band of 5.6 μm or more, and the effect of the wavelength-selective infrared radiation control member is not obtained. In order to reliably obtain the shielding effect, it is necessary to make it -30 dB, but for that, a thickness of 3.5 times the skin depth is required. 3.5 times the skin depth of Al is 60.4 nm. When the Al film thickness is 100 nm, the shielding effect works sufficiently. As a result, a steep peak is obtained at a wavelength of 4.9 μm, and the emissivity is very small at other wavelengths. If a steep peak is desired, it is an extremely excellent characteristic. However, as a wavelength-selective infrared radiation control member, it is preferable to increase the integral emissivity in the range of 3.5 to 5.6 μm. When the film thickness is 100 nm, a steep peak is obtained, but the integral emissivity is small, so the characteristics as a wavelength-selective infrared radiation control member cannot be said to be sufficient.

Figure 5 shows the results of investigating the emissivity characteristics by changing the thickness of the metal film on the surface forming the cavity in the configuration of random arrangement B in Figure 3. The metal film was formed by sputtering using Al. The opening shape W was 3 μm, the opening depth D was 3.3 μm, and the diameter of the virtual circle was 5 μm. As can be seen from the figure, when the Al film thickness was 25 nm, the emissivity was high on the longer wavelength side than 5.6 μm, but the integrated emissivity in the wavelength range of 3.5 to 5.6 μm was also 4503, which was a large result. When the Al film thickness was 50 nm, the peak intensity was the largest and the integrated emissivity was 4329, but this was slightly smaller than when the Al film thickness was 25 nm. On the other hand, when the Al film thickness was 100 nm, not only was the peak intensity slightly smaller, but the integrated emissivity was also smaller.

In the case of Al, the skin depth is 17.2 nm, and 3.5 times the skin depth is 60.4 nm. If the Al film thickness is set to 100 nm, the shielding effect is sufficient, but as a result, the integrated emissivity in the range of 3.5 to 5.6 μm becomes small, and the characteristics as a wavelength-selective infrared radiation control member are not fully obtained.

Figure 6 shows the results of investigating the emissivity characteristics as a function of Al film thickness when the opening shape is rectangular, the period is 5 μm, and they are periodically arranged. Figure 7 shows the results of investigating the emissivity characteristics as a function of Al film thickness when the opening shape is circular, the period of the virtual circles is 5 μm, and they are periodically arranged. Figure 8 is an SEM image showing the opening shape of the sample used in Figures 6 and 7. The photomask shows a regular square, but the corners are rounded due to the effects of exposure and dry etching, and the shape is not strictly square. The circular sample is almost exactly circular.

As can be seen from Figure 6, when the Al film thickness is 50 nm, the peak intensity exceeds 90, whereas when the Al film thickness is 100 nm or 500 nm, the peak intensity is smaller. The integral emissivity in the wavelength range of 3.5 to 5.6 μm is 14045 when the Al film thickness is 50 nm, 10410 when it is 100 nm, and 9542 when it is 500 nm. From this result, it was found that the integral emissivity is smaller when the thickness is greater than 3.5 times the skin depth of Al. In addition, a peak is also seen on the long wavelength side of the peak wavelength in the emissivity characteristics. It is presumed that this is due to the fact that the rectangular shape is not accurately obtained, as shown in Figure 8.

Figure 7 shows the case where the opening shape is circular and the imaginary circle is arranged periodically at 5 μm. Even in this case, the peak intensity is greatest for an Al film thickness of 50 nm, and the peak value tends to decrease for both 100 nm and 500 nm. Looking at the integrated emissivity, it is 12792 for an Al film thickness of 50 nm, 11742 for 100 nm, and 9452 for 500 nm, and it was found that the integrated emissivity decreases when the Al film thickness is made larger than 3.5 times the skin depth, just as in the case of a square shape.

In this embodiment, a silicon substrate is used as the semiconductor material, but germanium, silicon carbide, gallium arsenide, etc. may be used. Silicon carbide may be a single crystal material or a polycrystalline material. Also, alumina, zirconia, etc. may be used as the ceramic material.
Second Embodiment

9 is a schematic cross-sectional view of a wavelength-selective infrared radiation control member 10 according to a second embodiment of the present invention. The wavelength-selective infrared radiation control member 10 according to this embodiment is fabricated by forming a semiconductor material film on a substrate 11 having a smooth surface to a thickness at least equal to or greater than the opening depth of the cavities 14a, 14b, 14c, 14d, 14e, and 14f, forming the cavities 14a, 14b, 14c, 14d, 14e, and 14f in the semiconductor material using a photolithography process and an etching process, and then forming the metal coatings 13a and 13b.
A method for manufacturing the wavelength-selective infrared radiation control member 10 according to this embodiment will be described below.

In this embodiment, a glass substrate was used as the substrate 11. Glass substrates are thin and have very smooth surfaces, and are mass-produced for use in liquid crystal displays, making them an easy-to-use material. An amorphous silicon film was formed on the glass substrate 11 to a thickness of 4 μm using a plasma CVD device. Then, using the same manufacturing method as described in the first embodiment, a wavelength-selective infrared radiation control member 11 with a circular opening shape and random arrangement B was manufactured. Dry etching for forming the cavities 14a, 14b, 14c, 14d, 14e, and 14f was possible under the same conditions as for single-crystal silicon, but since it is an amorphous material, etching was easier than with single crystals.

The metal coating was formed by sputtering Al. The thickness of the Al metal coating 13a formed on the surfaces 15a, 15b, 15c, 15d, and 15e on which the cavities were formed was set to be equal to or greater than the skin depth and equal to or less than 3.5 times the skin depth, and the thickness of the Al metal coating 13b formed on the cavities 14a, 14b, 14c, 14d, 14e, and 14f was set to be equal to or less than the thickness of the Al metal coating 13a formed on the surfaces 15a, 15b, 15c, 15d, and 15e on which the cavities 14a, 14b, 14c, 14d, 14e, and 14f were formed. Specifically, the thickness of the metal coating 13a formed on the surfaces 15a, 15b, 15c, 15d, and 15e on which the cavities 14a, 14b, 14c, 14d, 14e, and 14f was set to 50 nm. Since the film was formed by sputtering, the Al metal coating 13b formed in the cavities 14a, 14b, 14c, 14d, 14e, and 14f had a thickness of at least 50 nm.
The wavelength-selective infrared radiation control member 10 thus fabricated had emissivity characteristics that were substantially the same as those in the case of the Al thickness of 50 nm shown in FIG.

In this embodiment, a silicon film is formed on a glass substrate, but a germanium or silicon carbide film may be formed on the glass substrate. Silicon carbide is a preferred material because it has a high emissivity, is used in a variety of fields, and has an established etching technology.
Third Embodiment

10A and 10B are schematic cross-sectional views for explaining the manufacturing process of a wavelength-selective infrared radiation control member 24 according to a third embodiment of the present invention. Fig. 10A is a diagram showing a state in which a resin sheet 23 to be the wavelength-selective infrared radiation control member 24 is bonded to a substrate 21 via an adhesive member 22. Fig. 10B is a diagram showing a state in which, after bonding, predetermined locations of the resin sheet 23 are etched to form cavities 25, and then a metal coating 26 is formed to produce the wavelength-selective infrared radiation control member 24. Fig. 10C is a diagram showing a state in which only the wavelength-selective infrared radiation control member 24 remains after peeling from the substrate 21.
A method for manufacturing the wavelength-selective infrared radiation control member 24 according to this embodiment will be described below.

In this embodiment, a glass substrate was used as the substrate 21, as in the second embodiment. After the adhesive member 22 was uniformly applied onto the glass substrate 21, a polyimide sheet having a thickness of 18 μm was attached as the resin sheet 23. Hereinafter, the resin sheet 23 may be referred to as the polyimide sheet 23. Care must be taken not to generate air bubbles between the adhesive member 22 and the polyimide sheet 23 when attaching them.

Then, using the same manufacturing method as described in the first embodiment, the cavity was etched to form a random arrangement B with a circular opening. The etching for forming the cavity utilized polyimide etching processing technology used in the semiconductor field. Specifically, reactive ion etching (RIE) was used for processing. After the cavity was formed, a 50 nm thick Al film was formed as a metal coating 26 on the entire surface. This forms a wavelength-selective infrared radiation control member 24. This state is shown in Figure 10 (b).

Next, the adhesive member 22 and the wavelength-selective infrared radiation control member 24 are peeled off. The peeling may be performed mechanically, or a liquid that dissolves the adhesive member 22 may be poured in to cause it to lose its adhesiveness and peel off. This is shown in Figure 10 (c). In this way, a wavelength-selective infrared radiation control member 24 made of a polyimide sheet 23 with a total thickness of 18 μm was obtained.

The emissivity characteristics of this wavelength-selective infrared radiation control member 24 were investigated. Since polyimide has a lower thermal conductivity than silicon, it takes time for the heat from the heat-generating member to be transmitted to the cavity 25. However, when the cavity 25 is heated, it is possible to obtain characteristics that are almost the same as those obtained when the Al film in Figure 5 is 50 nm thick.

In this embodiment, a polyimide sheet having a thickness of 18 μm is used as the resin sheet 23, but the present invention is not limited to this. The thickness may be set arbitrarily, and the resin sheet may be made of thermoplastic resins such as polyester, polycarbonate, polystyrene, polypropylene, polyphenylene sulfide, polyethylene terephthalate, or thermosetting resins such as epoxy resin.

In addition, in the present embodiment, the resin sheet 23 is etched by dry etching polyimide, but wet etching may also be used, and the cavity may be formed by an imprinting method instead of etching.

The wavelength-selective infrared radiation control member 1 according to the first embodiment, the wavelength-selective infrared radiation control member 10 according to the second embodiment, and the wavelength-selective infrared radiation control member 24 according to the third embodiment may be used in an electronic device in which an electronic circuit unit having a heat source is sealed with a sealing resin member having a region with high transmittance in a specific infrared wavelength range. In this case, the wavelength-selective infrared radiation control member may be disposed between the electronic circuit unit and the sealing resin member, and the cavity shape and arrangement may be set so as to selectively radiate a specific infrared transmission wavelength range of the sealing resin member. Specifically, the region with high infrared transmittance of the sealing resin is in the wavelength range of 3.5 to 5.6 μm. Therefore, a wavelength-selective infrared radiation control member with a large integral emissivity in this range has good heat dissipation characteristics.
(Fourth embodiment)

Next, the electronic device 30 of the present invention will be described. FIG. 11 is a schematic cross-sectional view showing the structure of the electronic device 30 of the present invention. The electronic device 30 includes an electronic circuit section 31 having a heat source sealed with a sealing resin member 33 having a region with high transmittance in a specific infrared wavelength range, and includes a wavelength-selective infrared radiation sheet 35 that is disposed between the electronic circuit section 31 and the sealing resin member 33 and selectively radiates a specific infrared transmission wavelength range of the sealing resin member 33, and the wavelength-selective infrared radiation sheet 35 is a wavelength-selective infrared radiation control member of the above configuration. In the present embodiment, the electronic device 30 is mounted not only with the electronic circuit section 31 having a heat source on the substrate 34, but also with the electronic circuit section 32 having no heat source, and is sealed with the sealing resin member 33 including these. Epoxy resin is often used as the sealing resin member 33, and epoxy resin is also used for the electronic device 30 of the present embodiment. From the infrared absorption characteristic data of epoxy resin, it has a characteristic of specifically transmitting infrared rays in the wavelength range of 3.5 to 5.6 μm. Therefore, when the wavelength-selective infrared radiation control member of the present invention is placed on a heat source, the wavelength-selective infrared radiation control member has a large integral emissivity in the specific wavelength range described above, so that infrared rays pass through the sealing resin member 33 and are emitted to the outside, as shown by the arrows in Figure 11, thereby increasing the cooling efficiency by radiation.

In this embodiment, the sealing resin member 33 is provided in close contact with the electronic circuit units 31, 32 and the wavelength-selective infrared radiation control member 35, but the present invention is not limited to this structure. The sealing resin member 33 may be provided so that there is a space between the sealing resin member 33 and the electronic circuit units 31, 32 and the wavelength-selective infrared radiation member 35. In addition, the electronic circuit unit 32 that does not have a heat source is implemented, but the present invention is not limited to this. Both electronic circuit units may be electronic circuit units that have a heat source.

In the first to fourth embodiments, the cavity opening shape has been described as being rectangular or circular, but the present invention is not limited to this. The cavity may be polygonal or circular, or a combination of polygonal and circular shapes. For example, a combination of polygonal or circular shapes may be an arrangement of multiple polygonal or circular shapes of different sizes. Furthermore, a combination of polygonal and circular shapes may be arranged. If a combination of polygonal shapes of different sizes, a combination of circular shapes of different sizes, or a combination of polygonal and circular shapes is used, the peak value of the radiation intensity differs depending on the shape, and the integrated radiation intensity can be increased.

Although an Al film has been described as the metal coating of the wavelength-selective infrared radiation control member according to the first to fourth embodiments, the present invention is not limited to this. The metal coating must be a material with high conductivity and a lower emissivity in the infrared region than the base material. Copper (Cu), gold (Au), silver (Ag), etc. meet this condition, but because they have poor adhesion to silicon and resin, it is required to form titanium or the like and form the coating on top of it.

The wavelength-selective infrared radiation control member of the present invention can be used in electronic devices in which an electronic circuit section having a heat source is sealed with a sealing resin member to enable efficient cooling by radiation, and is therefore useful in the semiconductor equipment field.

1, 10, 24 Wavelength-selective infrared radiation control member 2 Base material 3a, 3b, 13a, 13b, 26 Metal coating 4a, 4b, 4c, 4d, 4e, 4f, 4g, 4h, 4i, 4j, 4k, 4l, 4m, 14a, 14b, 14c, 14d, 14e, 14f, 25 Cavity 5a, 5b, 5c, 5d, 5e, 15a, 15b, 15c, 15d, 15e Surface 11, 21, 34 Substrate 22 Adhesive member 23 Resin sheet (polyimide sheet)
30 Electronic device 31, 32 Electronic circuit section 33 Sealing resin member 35 Wavelength-selective infrared radiation sheet (wavelength-selective infrared radiation control member)
W Opening shape D Opening depth

Claims (8)

A wavelength-selective infrared radiation control member that selectively emits infrared rays in a wavelength range of 3.5 to 5.6 μm,
A number of rectangular or circular cavities having a set opening shape and opening depth are arranged two-dimensionally in a random arrangement on one surface of a substrate made of a semiconductor material or a dielectric material;
a metal coating having an infrared emissivity lower than that of the base material is formed on the cavity and the surface on which the cavity is formed;
The metal coating formed on the surface on which the cavity is formed has a thickness that is equal to or greater than a skin depth calculated by the following formula (Mathematical Formula 1 ) when the wavelength of the infrared ray is 5 μm, and is equal to or less than 3.5 times the skin depth,
the thickness of the metal coating formed on the cavity is equal to or less than the thickness of the metal coating formed on the surface on which the cavity is formed;
4. A wavelength-selective infrared radiation control member, wherein the metal coating is made of aluminum, copper, gold or silver .
2. The wavelength-selective infrared radiation control member according to claim 1, wherein the cavity has an aspect ratio, which is a ratio between the opening shape and the opening depth, of at least 1, and the randomly arranged arrangement is such that at least one of the center-to-center distances between the cavity and a plurality of other cavities adjacent to the cavity is different.
2. The wavelength-selective infrared radiation control member according to claim 1, wherein the semiconductor material is a single crystal, polycrystalline or amorphous material selected from the group consisting of silicon, germanium, silicon carbide and gallium arsenide.
4. The wavelength-selective infrared radiation control member according to claim 3 , wherein the semiconductor material is formed on a substrate having a smooth surface to a thickness at least equal to or greater than the depth of the opening.
2. The wavelength-selective infrared radiation control member according to claim 1, wherein the dielectric material is a resin material or a ceramic material.
6. The wavelength-selective infrared radiation control member according to claim 5 , wherein the resin material is formed on a substrate having a smooth surface to a thickness at least equal to or greater than the depth of the opening.
The present invention is used in an electronic device in which an electronic circuit portion having a heat source is sealed with a sealing resin member having a region with high transmittance in a specific infrared transmission wavelength region of 3.5 to 5.6 μm,
7. The wavelength-selective infrared radiation control component according to claim 1, wherein the wavelength-selective infrared radiation control component is disposed between the electronic circuit section and the sealing resin member, and the opening shape of the cavity and the arrangement configuration of the cavity are set so as to selectively radiate the specific infrared transmission wavelength range of the sealing resin member.
An electronic device in which an electronic circuit section having a heat source is sealed with a sealing resin member having a region with high transmittance in a specific infrared transmission wavelength range of 3.5 to 5.6 μm,
7. An electronic device comprising: a wavelength-selective infrared radiation sheet disposed between the electronic circuit section and the sealing resin member and selectively radiating the specific infrared transmission wavelength range of the sealing resin member, the wavelength-selective infrared radiation sheet being a wavelength-selective infrared radiation control member according to any one of claims 1 to 6 .