A wavelength conversion device

Abstract

The utility model discloses a wavelength conversion device, which includes a fluorescent glass layer, a high thermal conductivity intermediate layer, a dielectric reflective film, a bonding layer and a heat sink substrate which are stacked in sequence, wherein the high thermal conductivity intermediate layer is a thermal conductive layer with a thermal conductivity of ≥100w / mk, and the dielectric reflective film is a composite layer of tantalum oxide, titanium oxide and silicon oxide with a thickness of 2‑10μm. The utility model adopts a fluorescent glass layer with a low sintering temperature, which can facilitate the addition of other fluorescent materials that improve the color rendering index, and provides the possibility of adaptively adjusting the color rendering index or obtaining a luminous effect with a high color rendering index; the high thermal conductivity intermediate layer can significantly improve the extreme light power resistance, aging performance and reliability of the wavelength conversion device, and the dielectric reflective film can effectively provide the reflectivity and luminous efficiency of the wavelength conversion device. The wavelength conversion device has high luminous efficiency and can meet the needs of static lighting.

Description

Technical Field

[0001] The utility model relates to the field of light emitting devices, and more specifically, to a wavelength conversion device. Background Art

[0002] In some mobile lighting applications, the laser light source is required to contain no moving components, while the traditional color wheel type wavelength conversion device relies on a rotating turntable to dissipate heat. If the turntable is removed, the heat dissipation is limited, the heat accumulates, and the wavelength conversion layer is easily burned. Therefore, it is necessary to develop a static wavelength conversion device that is heat-resistant and has better heat dissipation. In addition, in some laser lighting applications, there are certain requirements for the color rendering index of the laser, and if the wavelength conversion structure uses fluorescent ceramics, it is impossible to achieve certain color rendering index requirements, because the sintering temperature of fluorescent ceramics is very high. In most cases, only a single yellow powder or a single green powder can be used for preparation, and other fluorescent materials that can improve the color rendering index cannot be added because these fluorescent materials that can be used to improve the color rendering index are not resistant to high temperatures. Therefore, it is also necessary to develop a static wavelength conversion device that is easy to adjust or improve the color rendering index. Utility Model Content

[0003] The utility model aims to overcome at least one defect of the above-mentioned prior art and provide a wavelength conversion device. The wavelength conversion device has good heat dissipation efficiency, high temperature resistance, and aging resistance, can meet the needs of static lighting, and has high wavelength conversion efficiency. It can also provide the possibility of realizing adaptive adjustment of the color rendering index or obtaining a luminous effect with a high color rendering index.

[0004] The technical solution adopted by the utility model is:

[0005] A wavelength conversion device comprises a fluorescent glass layer, a high thermal conductivity intermediate layer, a dielectric reflective film, a bonding layer and a heat sink substrate which are stacked in sequence. The high thermal conductivity intermediate layer is a thermal conductive layer with a thermal conductivity of ≥100w / mk, and the dielectric reflective film is a composite layer of tantalum oxide, titanium oxide and silicon oxide with a thickness of 2-10μm.

[0006] In one embodiment, the fluorescent glass layer has a thickness of 20-80 μm.

[0007] In one embodiment, the fluorescent glass layer includes fluorescent powder particles and glass powder particles, and the fluorescent powder particles are any two or three of green powder, yellow powder, and red powder. Preferably, in the medium display system, the fluorescent powder particles are a mixture of green powder and yellow powder, and the mass ratio of green powder to yellow powder is (1-5):1; in the high display system, the fluorescent powder particles are a mixture of green powder and red powder, and the mass ratio of green powder to red powder is (4-30):1. The glass powder has a softening temperature of 450-750℃ and a room temperature thermal expansion coefficient of ≤6*10 -6 / ℃ glass powder.

[0008] In one embodiment, the fluorescent glass layer further comprises metal oxide particles with a particle size of 0.01-2 μm. More specifically, the metal oxide particles are one or a combination of aluminum oxide, titanium oxide, magnesium oxide, zinc oxide, and zirconium oxide.

[0009] In one embodiment, the high thermal conductivity intermediate layer is a single crystal silicon substrate, a single crystal / polycrystalline diamond substrate, or a single crystal / polycrystalline silicon carbide substrate, and has a thickness of 0.1-3 mm.

[0010] In one embodiment, a surface of the high thermal conductivity intermediate layer close to the dielectric reflective film is a polished surface with a surface roughness Ra≤0.02 μm.

[0011] In one embodiment, the dielectric reflective film is an alternating film layer of tantalum oxide, titanium oxide, and silicon oxide.

[0012] In one embodiment, the film system of the dielectric reflective film is designed as follows: 430-465nm band: average reflectivity ≥93%, minimum reflectivity ≥92%; 485-700nm band: average reflectivity ≥92%, minimum reflectivity ≥91.5%; film system laser power damage threshold ≥80w / mm 2 .

[0013] In one embodiment, the bonding layer includes a soldering layer I, a welding layer, and a soldering layer II stacked in sequence, wherein the soldering layer I and the soldering layer II are gold layers, platinum layers, nickel layers, or alloy layers of any two of them or alloy layers of the three, and the welding layer is an AuSn layer, a SnAgCu layer, or a SnBiAg layer.

[0014] In one embodiment, the thickness of the soldering layer I and the soldering layer II is 0.3-3 μm, and the thickness of the welding layer is 10-40 μm.

[0015] In one embodiment, the heat sink substrate is red copper, pure copper, oxygen-free copper, copper-clad aluminum nitride, diamond aluminum or tungsten copper substrate, and has a thickness of 1-5 mm.

[0016] Compared with the prior art, the beneficial effects of the utility model are as follows: the wavelength conversion layer of the technical solution adopts a fluorescent glass layer with a low sintering temperature, which can facilitate the addition of other fluorescent materials that improve the color rendering index, thereby providing the possibility of adaptively adjusting the color rendering index or obtaining a high color rendering index luminous effect; the high thermal conductivity intermediate layer of the technical solution can improve the wavelength conversion device's resistance to extreme light power, aging performance and reliability, and the dielectric reflective film can effectively provide the reflectivity of the wavelength conversion device, thereby improving the luminous efficiency; the wavelength conversion device described in the technical solution has good heat dissipation efficiency, high temperature resistance, aging resistance, and high luminous efficiency, and can meet static lighting needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a simplified structural diagram of the wavelength conversion device of the present invention. DETAILED DESCRIPTION

[0018] In order to allow those skilled in the art to better understand this solution, the solution is further described in detail below in conjunction with specific examples. The process methods used in the examples are all conventional methods unless otherwise specified; the materials used are all commercially available unless otherwise specified.

[0019] The present invention provides a wavelength conversion device and a preparation method thereof. The wavelength conversion device proposed in the present invention comprises a fluorescent glass layer, a high thermal conductivity intermediate layer, a dielectric reflective film, a soldering layer I, a welding layer, a soldering layer II and a heat sink substrate which are stacked in sequence.

[0020] In the technical solution, the fluorescent glass layer is used as a wavelength conversion layer to convert the wavelength of the light incident to the wavelength conversion device, and convert at least part of the laser into the converted light. Specifically, the fluorescent glass layer includes fluorescent powder particles and glass powder particles. In the prior art, fluorescent ceramics with high thermal conductivity, excellent heat resistance and heat dissipation performance are used as wavelength conversion materials. However, in some laser lighting supplementary light scenes with high requirements for color rendering index, such as endoscopes, studio supplementary lights, or museum exhibition room lighting, in order to restore the true color of the object, the lighting supplementary light source needs to have a color rendering index requirement of 80 or even higher. The fluorescent ceramic wavelength conversion material prepared by a single yellow powder or a single green powder usually has a color rendering index below 72, and it is difficult to meet the color rendering index requirement of more than 80; and although a single red powder can meet the high color rendering index requirement, it is usually used as an additive powder for yellow powder and green powder in the wavelength conversion material to improve the color rendering index, but the red powder has poor heat resistance and blue light power resistance, and the luminous efficiency is very low, so it is difficult to use it alone as a wavelength conversion material. Fluorescent ceramic materials are usually sintered into fluorescent particles, but yellow powder is different from green powder, red powder and other systems, and the sintering temperature is different. It is difficult to achieve fluorescent ceramic wavelength conversion materials that are compounded with yellow powder, green powder and red powder. Therefore, to achieve a high CRI effect, it is not suitable to use fluorescent ceramics as a wavelength conversion layer. This technical solution uses a fluorescent glass layer as a wavelength conversion layer to provide the possibility of achieving high CRI, medium CRI and CRI adjustment.

[0021] Furthermore, the thickness of the fluorescent glass layer is 20-80 μm. Compared with fluorescent ceramics, the sintering temperature of the fluorescent glass molding process is lower, which is convenient for adding other fluorescent materials that improve the color rendering index, and provides the possibility of adaptively adjusting the color rendering index or obtaining a high color rendering index luminous effect. Compared with fluorescent glue, fluorescent glass has better high temperature resistance and aging resistance, and is suitable for use as a wavelength conversion layer for high-power laser lighting.

[0022] Furthermore, the fluorescent glass layer includes fluorescent powder particles and glass powder particles, and the fluorescent powder particles are any two or three of green powder, yellow powder, and red powder. For example, in the medium display system, the fluorescent powder particles include green powder and yellow powder, and the mass ratio of green powder to yellow powder is (1-5):1; in the high display system, the fluorescent powder particles include green powder and red powder, and the mass ratio of green powder to red powder is (4-30):1, preferably (15-30):1, and more preferably (15-20):1. It is worth mentioning that in the high display system, due to the presence of red powder, the extreme blue light power resistance of the wavelength conversion device will be reduced, but the high display system of the present technical solution can still be better than the extreme blue light power resistance of the wavelength conversion device on the market.

[0023] Furthermore, the glass powder has a softening temperature of 450-750°C and a room temperature thermal expansion coefficient of ≤6*10 -6 / ℃ glass powder.

[0024] Furthermore, the fluorescent glass layer further comprises metal oxide particles, and the particle size is preferably 0.01-2 μm. More specifically, the metal oxide particles are one or a combination of aluminum oxide, titanium oxide, magnesium oxide, zinc oxide, and zirconium oxide.

[0025] In the technical solution, the high thermal conductivity intermediate layer is used to improve the extreme optical power resistance and reflectivity of the wavelength conversion device. The fluorescent glass used as the wavelength conversion layer is usually 0.08-0.2mm thick. However, the fluorescent glass is usually not densely sintered and has a large number of pores inside. During grinding and polishing, the surface roughness is difficult to meet the coating requirements of the optical mirror. If the fluorescent glass is directly used as the substrate for the reflective film, there are still many microscopic concave-convex structures on the polished surface of the fluorescent glass. When the laser is incident on the coating part of these concave-convex structures, it will cause the energy of the laser to concentrate. The laser power density in this area is abnormally high. Long-term use can easily cause damage to the film system. Therefore, the wavelength conversion device is insufficient in its extreme optical power resistance. In addition, the presence of the porous structure of the fluorescent glass when sintered is not dense will also make its mechanical properties poor, making it unsuitable as a coating substrate. In addition, when the mirror effect of the wavelength conversion layer is not good, the reflectivity will not be high enough. The utility model sets a high thermal conductivity intermediate layer with a thermal conductivity of ≥100w / mk between the fluorescent glass layer and the dielectric reflective film, which can solve the above problems well. Specifically, the high thermal conductivity intermediate layer is a single crystal silicon substrate, a single crystal / polycrystalline diamond substrate, or a single crystal / polycrystalline silicon carbide substrate, with a thickness of 0.1-3 mm. Furthermore, the high thermal conductivity intermediate layer has a polished surface close to the dielectric reflective film, with a surface roughness Ra≤0.02 μm.

[0026] The dielectric reflective film of the present technical solution serves as a reflective layer, so that the excited converted laser light and the unconverted laser light are emitted in the opposite direction of the incident laser light. Specifically, the dielectric reflective film is a composite layer of tantalum oxide, titanium oxide, and silicon oxide, more specifically, an alternating film layer of tantalum oxide, titanium oxide, and silicon oxide, with a thickness of 2-10μm. Furthermore, the film system of the dielectric reflective film is designed as follows: 430-465nm band: average reflectivity ≥93%, minimum reflectivity ≥92%; 485-700nm band: average reflectivity ≥92%, minimum reflectivity ≥91.5%; film system laser power damage threshold ≥80w / mm 2 .

[0027] The soldering layer I plays a role in welding modification. The welding effect between the welding layer and the dielectric reflective film is not good enough. The provision of the soldering layer I can increase the bonding strength between the dielectric reflective film and the soldering layer. Specifically, the soldering layer I is a gold layer, a platinum layer, a nickel layer, or an alloy layer of any two of them or an alloy layer of the three. Such a metal layer can form a bond with the dielectric reflective film, improve the wettability of the dielectric reflective film and the soldering layer, and enhance the bonding strength between the dielectric reflective film and the soldering layer. Furthermore, the thickness of the soldering layer I is 0.3-3 μm.

[0028] The welding layer serves to connect the high thermal conductivity intermediate layer and the heat sink substrate. The high thermal conductivity intermediate layer with the fluorescent glass layer on the surface is connected to the heat sink substrate through the welding layer, and the fluorescent glass layer and other structures and the heat sink substrate are welded and packaged together. The large amount of heat generated when the fluorescent glass layer performs wavelength conversion can be transferred to the heat sink substrate through the welding layer. Specifically, the welding layer is an AuSn layer, a SnAgCu layer or a SnBiAg layer. Furthermore, the thickness of the welding layer is 10-40μm.

[0029] The soldering layer II also plays a role in welding modification. The welding effect between the soldering layer and the heat sink substrate is not good enough. Setting the soldering layer II can increase the bonding strength between the soldering layer and the heat sink substrate. Specifically, the soldering layer II is also a gold layer, a platinum layer, a nickel layer, or an alloy layer of any two of them or an alloy layer of the three. The soldering layer is easy to form a bond with the solder, improving the welding bonding effect. Furthermore, the thickness of the soldering layer II is also 0.3-3μm.

[0030] The heat sink substrate mainly plays a role of heat conduction, quickly dissipating the heat of the fluorescent glass layer. Specifically, the heat sink substrate is red copper, pure copper, oxygen-free copper, copper-clad aluminum nitride, diamond aluminum or tungsten copper substrate. Preferably, it is a tungsten copper alloy, copper-clad aluminum nitride or diamond aluminum substrate. Furthermore, the shape of the heat deposition plate is circular. The thickness of the heat sink substrate is preferably 1-5 mm.

[0031] The preparation method of the wavelength conversion device described in this technical solution is as follows:

[0032] S1. Preparation of glass fluorescent slurry: Add fluorescent powder particles and glass powder particles into an organic solvent according to a set ratio, and stir and disperse for 10-30 minutes to make the two types of particles evenly dispersed.

[0033] S2. Polishing of high thermal conductivity intermediate layer: polishing the high thermal conductivity intermediate layer to achieve a mirror effect; more specifically, polishing to a surface roughness Ra ≤ 0.02 μm to achieve a mirror effect.

[0034] S3, dielectric reflective film plating: the dielectric reflective film is plated on the polished surface of the high thermal conductivity intermediate layer by evaporation. The dielectric reflective film is an alternating film layer of tantalum oxide, titanium oxide, and silicon oxide with a thickness of 2-10μm. The film system is designed as follows: 430-465nm band: average transmittance ≥93%, minimum transmittance ≥92%; 485-700nm band: average reflectivity ≥92%, minimum reflectivity ≥91.5%.

[0035] S4. The glass fluorescent slurry is attached to the high thermal conductivity middle layer: the glass fluorescent slurry is applied to one side of the high thermal conductivity middle layer plated with the dielectric reflective film by screen printing, dispensing or scraping technology; the high thermal conductivity middle layer coated with the fluorescent glass layer is placed in an oven for pre-drying treatment, and then placed in a sintering furnace for high temperature sintering at 600-900℃ for 0.5-1.5h.

[0036] S5. Plating solder layer I on the other side of the high thermal conductivity intermediate layer: Plating solder layer I on the other side of the high thermal conductivity intermediate layer by sputtering, evaporation or electroplating. The solder layer I is a gold layer, a platinum layer, a nickel layer, or an alloy layer of any two of them or an alloy layer of the three, with a thickness of 0.3-3 μm.

[0037] S6. Plating solder layer II on the surface of the heat sink substrate: Plating solder layer II on the surface of the heat sink substrate by sputtering, evaporation or electroplating. The solder layer II is also a gold layer, a platinum layer, a nickel layer, or an alloy layer of any two or all three, with a thickness of 0.3-3 μm.

[0038] S7. Encapsulate the high thermal conductivity intermediate layer and the heat sink substrate by welding material: Use steel screen printing to print welding material on the side of the heat sink substrate coated with solder layer II and the side of the intermediate layer substrate coated with solder layer I, and then bond the two sides together and weld them to obtain a wavelength conversion device. The welding material is AuSn, SnAgCu or SnBiAg.

[0039] The following is an example in which the high thermal conductivity intermediate layer is a single crystal silicon substrate, the dielectric reflective film is an alternating film layer of tantalum oxide, titanium oxide, and silicon oxide, the soldering layer I and the soldering layer II are platinum metal layers, and the heat sink substrate is a tungsten copper alloy.

[0040] Example 1

[0041] like Figure 1As shown, a wavelength conversion device comprises a fluorescent glass layer 1, a high thermal conductivity intermediate layer 2, a dielectric reflective film 3, a soldering layer I4, a welding layer 5, a soldering layer II6 and a heat sink substrate 7 which are stacked in sequence. The high thermal conductivity intermediate layer 2 is a single crystal silicon substrate with a thermal conductivity of ≥100w / mk and a thickness of 0.1-3mm. The dielectric reflective film 3 is an alternating film layer of tantalum oxide, titanium oxide and silicon oxide with a thickness of 2-10μm. The soldering layer I4 and the soldering layer II6 are platinum metal layers with a thickness of 0.3-3μm. The welding layer 5 is a SnAgCu welding layer with a thickness of 10-40μm. The heat sink substrate 7 is a tungsten copper alloy with a thickness of 1-5mm. The fluorescent glass layer 1 is a fluorescent glass layer formed by compounding fluorescent powder particles and glass powder particles in a mass ratio of (5-10):1, with a thickness of 20-80μm, wherein the fluorescent powder particles are obtained by mixing green powder and yellow powder in a mass ratio of (1-5):1. The softening temperature of glass powder is 450-750℃, and the thermal expansion coefficient at room temperature is ≤6*10 -6 / ℃ alumina glass powder, particle size is 0.01-2μm.

[0042] Comparative Example 1

[0043] A wavelength conversion device has a structure substantially the same as that of Example 1, except that this comparative example 1 does not have a high thermal conductivity intermediate layer.

[0044] Comparative Example 2

[0045] A wavelength conversion device has a structure substantially the same as that of Example 1, except that this comparative example 2 does not have a first soldering layer and a second soldering layer.

[0046] Comparative Example 3

[0047] A wavelength conversion device, whose structure is substantially the same as that of Example 1, except that the thickness of the dielectric reflective film of this comparative example 3 is 12-15 μm.

[0048] The wavelength conversion devices of Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were tested for performance. The test method is as follows: The laser light source system uses a blue laser light source with a maximum blue light output power of 40W and a laser spot size of Φ0.9mm. The test items include: the blue light power limit value, the maximum luminous flux, and the color rendering index of the wavelength conversion device. The specific test method is as follows:

[0049] Blue light tolerance limit power value test: The wavelength conversion devices of the embodiment and the comparative example are installed in the light source system respectively. The power at which the luminous flux no longer increases or even decreases with the increase of blue light power is the limit value of the blue light tolerance power of the wavelength conversion device.

[0050] Limit luminous flux test: Light up the light source and align the light outlet of the light source with the entrance of the integrating sphere so that the light completely enters the integrating sphere. Test the luminous flux of the wavelength conversion device at the limit blue light power, which is the limit value of the luminous flux.

[0051] Color rendering index test: The wavelength conversion devices of the embodiment and the comparative example are installed in the light source system respectively. The light source is turned on, and the light outlet of the light source is aligned with the entrance of the integrating sphere so that the light completely enters the integrating sphere, and the color rendering index of the wavelength conversion device is tested.

[0052] The test results are shown in Table 1.

[0053] Table 1

[0054] Test items Endurance to extreme blue light power Limit luminous flux Color rendering index Example 1 32 5864 83 Comparative Example 1 8 1136 83 Comparative Example 2 14 2646 82 Comparative Example 3 21 3932 83

[0055] It can be seen from the above embodiment 1 that the wavelength conversion device of the present technical solution under the medium display system has a higher resistance to extreme blue light power and extreme luminous flux. It can be seen from the above embodiment 2 that the present technical solution can achieve a high color rendering index effect. Although the resistance to extreme blue light power and extreme luminous flux performance has decreased under the high display system, it is still better than other high-display wavelength conversion materials on the surface. From the comparison of embodiment 1 and comparative example 1, it can be seen that the high thermal conductivity intermediate layer has a great improvement effect on the resistance to extreme blue light power and extreme luminous flux of the wavelength conversion device. The reason is that the high thermal conductivity intermediate layer can solve the problem of the microscopic concave-convex structure on the surface of the fluorescent glass. From the comparison of embodiment 1 and comparative example 2, it can be seen that the presence of the solder layer can also improve the resistance to extreme blue light power and extreme luminous flux of the wavelength conversion device. The reason is that the solder is not firmly bonded to the intermediate layer substrate or the heat sink substrate, and the solder layer is easy to form a bond with the solder, improve the welding bonding effect, reduce the thermal resistance of the bonding interface, and improve the heat dissipation effect of the wavelength conversion device, thereby enhancing the device's resistance to blue light power. From the comparison between Example 1 and Comparative Example 3, it can be seen that the thickness of the dielectric reflective film also has a great influence on the ultimate blue light power and the ultimate luminous flux. The thicker the dielectric reflective film, although the reflectivity is higher and the luminous efficiency is higher, the ultimate blue light power is worse. The reason is that the thicker the dielectric reflective film, the greater the thermal resistance of the bonding interface between the dielectric reflective film and the heat sink substrate, and the worse the thermal conductivity and heat dissipation capacity of the wavelength conversion device, so the ultimate blue light power becomes worse.

[0056] Obviously, the above embodiments of the utility model are only examples for clearly explaining the technical solution of the utility model, and are not intended to limit the specific implementation methods of the utility model. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the claims of the utility model shall be included in the protection scope of the claims of the utility model.

Claims

1. A wavelength conversion device, characterized in that: It includes a fluorescent glass layer, a high thermal conductivity intermediate layer, a dielectric reflective film, a bonding layer and a heat sink substrate which are stacked in sequence. The high thermal conductivity intermediate layer is a thermal conductive layer with a thermal conductivity of ≥100w / mk, the dielectric reflective film is a composite layer of tantalum oxide, titanium oxide and silicon oxide, and the dielectric reflective film is an alternating film layer of tantalum oxide film layer, titanium oxide film layer and silicon oxide film layer with a thickness of 2-10μm.

2. The wavelength conversion device according to claim 1, characterized in that: The thickness of the fluorescent glass layer is 20-80 μm.

3. The wavelength conversion device according to claim 2, characterized in that: The fluorescent glass layer also includes metal oxide particles with a particle size of 0.01-2 μm.

4. The wavelength conversion device according to claim 1, characterized in that: The high thermal conductivity intermediate layer is a single crystal silicon substrate, a single crystal / polycrystalline diamond substrate, or a single crystal / polycrystalline silicon carbide substrate, and has a thickness of 0.1-3 mm.

5. The wavelength conversion device according to claim 1, characterized in that: The film system of the dielectric reflective film is designed as follows: 430-465nm band: average reflectivity ≥93%, minimum reflectivity ≥92%; 485-700nm band: average reflectivity ≥92%, minimum reflectivity ≥91.5%; film system laser power damage threshold ≥80w / mm 2 .

6. The wavelength conversion device according to claim 1, characterized in that: The bonding layer includes a soldering layer I, a welding layer, and a soldering layer II stacked in sequence, wherein the soldering layer I and the soldering layer II are gold layers, platinum layers, nickel layers, or alloy layers of any two of them or alloy layers of the three, and the welding layer is an AuSn layer, a SnAgCu layer, or a SnBiAg layer.

7. The wavelength conversion device according to claim 6, characterized in that: The thickness of the soldering layer I and the soldering layer II is 0.3-3 μm, and the thickness of the welding layer is 10-40 μm.

8. The wavelength conversion device according to any one of claims 1 to 7, characterized in that: The heat sink substrate is made of red copper, pure copper, oxygen-free copper, copper-clad aluminum nitride, diamond aluminum or tungsten copper substrate, and has a thickness of 1-5 mm.

Images