Glass substrate for high frequency device, liquid crystal antenna and high frequency device

Abstract

To provide a glass substrate which has a low dielectric dissipation factor in high-frequency ranges, has high glass homogeneity, making it less apt to opacification, and offers excellent acid resistance.SOLUTION: The present invention pertains to a glass substrate containing, in mol percent on an oxide base: 0.1-13% of alkaline earth metal oxides in total; 1-40% of Al2O3 and B2O3 in total, where the molar ratio Al2O3 / (Al2O3+B2O3) is 0-0.45; and 0.1-1.0% of one or more selected from the group consisting of TiO2, Y2O3, and ZrO2 in total, where ZrO2 is 0.1% or less. The main component of the glass substrate is SiO2. The glass substrate has a dielectric loss tangent of 0.007 or less at 35 GHz.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a glass substrate for a high-frequency device, and a liquid crystal antenna and a high-frequency device each having the glass substrate. [Background technology]

[0002] In electronic devices such as communication devices like mobile phones, smartphones, personal digital assistants, and Wi-Fi devices, as well as surface acoustic wave (SAW) devices, radar components, and antenna components, signal frequencies are becoming higher in order to increase communication capacity and speed. Insulating substrates such as resin substrates, ceramic substrates, and glass substrates are generally used for circuit boards used in such high-frequency electronic devices. Insulating substrates used in high-frequency devices are required to reduce transmission loss due to dielectric loss, conductor loss, etc., in order to ensure characteristics such as the quality and strength of high-frequency signals.

[0003] Of these insulating substrates, resin substrates have low rigidity due to their characteristics. Therefore, resin substrates are difficult to use when rigidity (strength) is required for semiconductor package products. Ceramic substrates have the drawback of being difficult to smooth, which can lead to large conductor losses due to the conductors formed on the substrate surface. On the other hand, glass substrates have high rigidity, making it easy to make packages smaller and thinner, and they also have excellent surface smoothness, and the substrate itself can easily be made larger.

[0004] However, while conventional alkali-free glass substrates are effective in reducing dielectric loss and the resulting transmission loss up to about 20 GHz, they have limitations in reducing dielectric loss beyond that, for example, in frequencies above 30 GHz. Therefore, circuit boards using conventional alkali-free glass substrates have difficulty maintaining characteristics such as the quality and strength of high-frequency signals above 30 GHz. On the other hand, while quartz glass substrates can maintain low dielectric loss even in frequencies above 30 GHz, their thermal expansion coefficients are too small, resulting in excessive differences in the thermal expansion coefficients of other components when constructing electronic devices. This reduces the practical utility of electronic devices.

[0005] Patent Document 1 discloses lead-free glass having a relative permittivity of 4.3 or less and a dielectric loss of 0.0035 or less at 35 GHz. In the lead-free glass described in Patent Document 1, B2O3 is said to be an essential component that reduces the permittivity ε and the dielectric loss tangent tanδ. Therefore, it is thought that increasing the B2O3 content will reduce the dielectric loss in the high frequency range above 30 GHz. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2014-244271 Summary of the Invention [Problem to be solved by the invention]

[0007] However, increasing the B2O3 content reduces the acid resistance of the glass. In the manufacturing process of circuit boards for liquid crystal antennas, high-frequency devices, and other applications, acid cleaning is performed as a pretreatment before forming a wiring layer on the glass substrate. If the glass has low acid resistance, the substrate surface may dissolve during acid cleaning, impairing the smoothness of the substrate surface and potentially reducing the adhesion of the film formed on the substrate surface. Furthermore, there is a risk that eluted material may adhere to the substrate surface. This may result in increased conductor loss due to the conductor formed on the substrate surface.

[0008] Furthermore, glass substrates used in high-frequency devices require high glass uniformity. If the glass uniformity is low, localized irregularities will occur on the substrate surface when the glass substrate is washed with acid, impairing the smoothness of the substrate surface. This will increase conductor loss due to the conductor formed on the substrate surface.

[0009] An object of the present invention is to provide a glass substrate for high frequency devices which has a low dielectric loss tangent in the high frequency range, is highly uniform in the glass, and is therefore less likely to become cloudy, and has excellent acid resistance. [Means for solving the problem]

[0010] As a result of extensive investigation, the present inventors have found that the above object can be achieved by employing the following configuration. (1) A glass substrate for high-frequency devices, containing, in mole percentages on an oxide basis, alkaline earth metal oxides in a total content of 0.1 to 13%, Al2O3 and B2O3 in a total content of 1 to 40%, the molar ratio of the contents expressed as Al2O3 / (Al2O3 + B2O3) being 0 to 0.45, and containing at least one element selected from the group consisting of Sc2O3, TiO2, ZnO2, Ga2O3, GeO2, Y2O3, ZrO2, Nb2O5, In2O3, TeO2, HfO2, Ta2O5, WO3, Bi2O3, La2O3, Gd2O3, Yb2O3, and Lu2O3 in a total content of 0.1 to 1.0%, and containing SiO2 as a main component, and having a dielectric loss tangent at 35 GHz of 0.007 or less. (2) The glass substrate for a high frequency device according to (1), which contains 0.25 to 1.0% ZrO2 in terms of mole percentage based on oxides. (3) The glass substrate for a high frequency device according to (1) or (2), which contains 0.1 to 0.5% Y2O3 in terms of mole percentage based on oxides. (4) A glass substrate for high-frequency devices, which contains, in mole percentage on an oxide basis, alkaline earth metal oxides in a total content of 0.1 to 13%, Al2O3 and B2O3 in a total content of 1 to 40%, the molar ratio of the contents expressed as Al2O3 / (Al2O3 + B2O3) being 0 to 0.45, and at least one of ZnO2 and ZrO2 in a total content of 1.5 to 4.0%, and which is composed mainly of SiO2, and which has a dielectric loss tangent at 35 GHz of 0.007 or less. (5) The glass substrate for a high-frequency device according to any one of (1) to (4) above, wherein the surface roughness of at least one main surface of the glass substrate is 1.5 nm or less in terms of arithmetic mean roughness Ra. (6) The glass substrate for high-frequency devices according to any one of (1) to (5) above, wherein the total content of alkali metal oxides is in the range of 0.001 to 5% in terms of molar percentage based on oxides, and the molar ratio of the content of the alkali metal oxides expressed as NaO / (NaO+KO) is 0.01 to 0.99. (7) The glass substrate for a high frequency device according to any one of (1) to (6) above, which contains 0.005 to 0.12% Fe calculated as Fe2O3. (8) The glass substrate for a high frequency device according to any one of (1) to (7) above, which contains 0.25% or less of Sn calculated as SnO2. (9) The glass substrate for a high frequency device according to any one of (1) to (8) above, which has a devitrification temperature of 1400° C. or lower. (10) Glass viscosity is 10 2 The glass substrate for a high frequency device according to any one of (1) to (9) above, wherein the temperature T2 at which the glass becomes dPa·s is 1700° C. or lower. (11) A liquid crystal antenna having the glass substrate according to any one of (1) to (10) above. (12) A high-frequency device having the glass substrate according to any one of (1) to (10) above. [Effects of the Invention]

[0011] The glass substrate for high-frequency devices of the present invention can reduce the dielectric loss of high-frequency signals. A circuit board using such a glass substrate can reduce the transmission loss of high-frequency signals, and can provide a practical high-frequency device such as an electronic device. The glass substrate for high-frequency devices of the present invention has excellent acid resistance. Therefore, when the glass substrate is subjected to acid washing in the manufacturing process of circuit boards for liquid crystal antennas, high-frequency devices, etc., there is no risk of the substrate surface dissolving, impairing the smoothness of the substrate surface, or of eluted materials adhering to the substrate surface. Therefore, a decrease in adhesion of a film formed on the substrate surface can be prevented. Furthermore, an increase in conductor loss can be prevented. Furthermore, the glass substrate for a high-frequency device of the present invention has high glass uniformity. Therefore, when the glass substrate is subjected to acid cleaning, localized irregularities are prevented from occurring on the substrate surface. This also reduces the transmission loss of high-frequency signals. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view showing an example of the configuration of a high-frequency circuit, illustrating the configuration of a circuit board according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described. In the following description, numerical ranges indicated using "to" indicate ranges that include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. The content of each component in the glass substrate is expressed as a mole percentage (mol%) based on the oxide, unless otherwise specified. In this specification, "high frequency" refers to 10 GHz or higher, preferably greater than 30 GHz, and more preferably greater than 35 GHz.

[0014] FIG. 1 shows a circuit board for a high-frequency device according to an embodiment of the present invention. The circuit board 1 shown in FIG. 1 includes an insulating glass substrate 2, a first wiring layer 3 formed on a first main surface 2a of the glass substrate 2, and a second wiring layer 4 formed on a second main surface 2b of the glass substrate 2. The first and second wiring layers 3 and 4 form a microstrip line as an example of a transmission line. The first wiring layer 3 forms a signal line, and the second wiring layer 4 forms a ground line. However, the structure of the first and second wiring layers 3 and 4 is not limited to this, and the wiring layers may be formed on only one main surface of the glass substrate 2.

[0015] The first and second wiring layers 3 and 4 are layers formed of a conductor, and their thickness is usually about 0.1 to 50 μm. The conductor forming the first and second wiring layers 3 and 4 is not particularly limited, and examples thereof include metals such as steel, gold, silver, aluminum, titanium, chromium, molybdenum, tungsten, platinum, nickel, and copper, as well as alloys and metal compounds containing at least one of these metals. The structure of the first and second wiring layers 3 and 4 is not limited to a single-layer structure, and may also be a multi-layer structure, such as a laminate structure of a titanium layer and a copper layer. The method for forming the first and second wiring layers 3 and 4 is not particularly limited, and various known formation methods can be used, such as printing using a conductor paste, dipping, plating, vapor deposition, and sputtering.

[0016] The glass substrate 2 is made of a glass substrate for high-frequency devices according to an embodiment of the present invention, and has a dielectric loss tangent (tanδ) of 0.007 or less at 35 GHz. The relative dielectric constant of the glass substrate 2 at 35 GHz is preferably 10 or less. When the dielectric loss tangent of the glass substrate 2 at 35 GHz is 0.007 or less, dielectric loss in the high-frequency range exceeding 30 GHz can be reduced. When the relative dielectric constant of the glass substrate 2 at 35 GHz is 10 or less, dielectric loss in the high-frequency range can also be reduced. The dielectric loss tangent of the glass substrate 2 at 35 GHz is more preferably 0.005 or less, and even more preferably 0.003 or less. The relative dielectric constant of the glass substrate 2 at 35 GHz is more preferably 7 or less, further preferably 6 or less, and particularly preferably 5 or less.

[0017] Furthermore, the surface roughness of the main surfaces 2a and 2b of the glass substrate 2 on which the first and second wiring layers 3 and 4 are formed is preferably 1.5 nm or less in arithmetic mean roughness Ra. By having the arithmetic mean roughness Ra of the main surfaces 2a and 2b of the glass substrate 2 on which the first and second wiring layers 3 and 4 are formed be 1.5 nm or less, the skin resistance of the first and second wiring layers 3 and 4 can be reduced, thereby reducing conductor loss, even when a skin effect occurs in the first and second wiring layers 3 and 4 in the high frequency range exceeding 30 GHz. The arithmetic mean roughness Ra of the main surfaces 2a and 2b of the glass substrate 2 is more preferably 1.0 nm or less, and even more preferably 0.5 nm or less. The main surfaces of the glass substrate 2 refer to the surfaces on which wiring layers are formed. When a wiring layer is formed on one main surface, it is sufficient that the arithmetic mean roughness Ra of the main surface on which the wiring layer is formed is 1.5 nm or less. In this specification, the surface roughness Ra refers to a value obtained in accordance with JIS B0601 (2001).

[0018] The surface roughness of the main surfaces 2a and 2b of the glass substrate 2 can be achieved, as needed, by polishing the surface of the glass substrate 2. Examples of polishing methods that can be used include polishing using an abrasive primarily composed of cerium oxide or colloidal silica and a polishing pad; polishing using a polishing slurry containing an abrasive and an acidic or alkaline dispersion medium and a polishing pad; and polishing using an acidic or alkaline etching solution. These polishing methods are applied depending on the surface roughness of the raw glass substrate 2. For example, preliminary polishing and finish polishing may be combined. Furthermore, the edges of the glass substrate 2 are preferably chamfered to prevent breakage, cracks, or chipping of the glass substrate 2 during processing. The chamfering may be in the form of a C-chamfer, an R-chamfer, a light chamfer, or the like.

[0019] Use of such a glass substrate 2 reduces the transmission loss of the circuit board 1 at 35 GHz, preferably to 1 dB / cm or less. Therefore, the characteristics of high-frequency signals, particularly high-frequency signals above 30 GHz, and even high-frequency signals above 35 GHz, such as quality and strength, are maintained, providing a glass substrate 2 and circuit board 1 suitable for high-frequency devices that handle such high-frequency signals. In other words, the characteristics and quality of high-frequency devices that handle such high-frequency signals can be improved. The transmission loss of the circuit board 1 at 35 GHz is more preferably 0.5 dB / cm or less.

[0020] A glass substrate 2 having the dielectric properties such as the dielectric loss tangent and excellent acid resistance described above can be realized by a glass substrate containing SiO2 as a network former, which satisfies the following conditions (1), (2), and (3). Here, the glass substrate 2 is formed by melting and hardening a raw material composition. The method for manufacturing the glass substrate 2 is not particularly limited, and a method can be applied in which molten glass is formed into a predetermined plate thickness by a float method, and after annealing, the glass is cut into the desired shape to obtain a plate glass.

[0021] Here, glass in this specification is, by definition, amorphous and refers to a solid that exhibits glass transition. It does not include sintered glass, which is a mixture of glass and crystal, or glass sintered bodies containing crystalline fillers. Amorphous glass can be identified, for example, by X-ray diffraction measurement, if no clear diffraction peaks are observed.

[0022] In addition, in this specification, "SiO2 as the main component" means that the content of SiO2 is the largest in terms of the proportion of components in mole percent based on oxides.

[0023] Condition (1): The glass substrate 2 contains alkaline earth metal oxides in a total content of 0.1 to 13%.

[0024] In condition (1), examples of alkaline earth metal oxides include MgO, CaO, SrO, and BaO, all of which function as components that enhance the dissolution reactivity of glass. If the total content of such alkaline earth metal oxides is 13% or less, the dielectric loss of the glass substrate 2 can be reduced. The total content of alkaline earth metal oxides is more preferably 11% or less, even more preferably 10% or less, particularly preferably 8% or less, and most preferably 6% or less. Furthermore, if the total content of alkaline earth metal oxides is 0.1% or more, the dissolution properties of the glass can be maintained well. The total content of alkaline earth metal oxides is more preferably 1% or more, even more preferably 3% or more, particularly preferably 4% or more, and most preferably 5% or more.

[0025] MgO is a component that increases Young's modulus without increasing specific gravity. In other words, MgO increases the specific modulus, thereby reducing deflection problems and improving fracture toughness and glass strength. MgO also improves solubility. While MgO is not an essential component, when MgO is included, its content is preferably 0.1% or more, more preferably 1% or more, and even more preferably 3% or more. A MgO content of 0.1% or more fully achieves the effects of MgO inclusion and prevents the thermal expansion coefficient from becoming too low. The MgO content is preferably 13% or less, more preferably 12% or less, even more preferably 11% or less, even more preferably 10% or less, especially preferably 9% or less, even more preferably 8% or less, and particularly preferably 7% or less. A MgO content of 13% or less prevents an increase in the devitrification temperature.

[0026] Among alkaline earth metals, CaO is the second most important component after MgO in increasing the specific modulus without excessively lowering the strain point. Similarly to MgO, CaO also improves solubility. Furthermore, compared to MgO, CaO is less likely to increase the devitrification temperature. While CaO is not an essential component, when CaO is present, its content is preferably 0.1% or more, more preferably 1% or more, and even more preferably 3% or more. When CaO is 0.1% or more, the effects of CaO inclusion are fully achieved. Furthermore, the CaO content is preferably 13% or less, more preferably 10% or less, even more preferably 8% or less, even more preferably 7% or less, particularly preferably 6% or less, particularly preferably 5.5% or less, and most preferably 5% or less. When the CaO content is 13% or less, the average thermal expansion coefficient does not become too high, and the increase in the devitrification temperature is suppressed, thereby preventing devitrification during glass production.

[0027] SrO is a component that improves the meltability without increasing the devitrification temperature of glass. Although SrO is not an essential component, when SrO is contained, the content is preferably 0.1% or more, more preferably 0.5% or more, even more preferably 1.0% or more, even more preferably 1.5% or more, and particularly preferably 2% or more. When the SrO content is 0.1% or more, the effect of containing SrO is sufficiently obtained. Furthermore, the SrO content is preferably 13% or less, more preferably 10% or less, even more preferably 7% or less, and particularly preferably 5% or less. When the SrO content is 13% or less, the specific gravity is not made too high, and the average thermal expansion coefficient is also prevented from becoming too high.

[0028] Although BaO is not an essential component, it does not increase the devitrification temperature of the glass and improves its melting point. However, a large amount of BaO tends to increase the specific gravity, decrease the Young's modulus, increase the dielectric constant, and increase the average thermal expansion coefficient too much. Therefore, the BaO content is preferably 10% or less, more preferably 8% or less, more preferably 5% or less, and even more preferably 3% or less, and it is particularly preferable that the BaO content is substantially zero.

[0029] In this specification, "substantially not containing" means that BaO is not contained except as an inevitable impurity mixed in from raw materials, etc., that is, BaO is not intentionally contained. In the present invention, "substantially not containing BaO" means, for example, 0.3% or less.

[0030] Condition (2): The glass substrate 2 contains Al2O3 and B2O3 in a total content of 1 to 40%, and the molar ratio of the contents expressed as Al2O3 / (Al2O3+B2O3) is 0 to 0.45.

[0031] In condition (2), Al2O3 is not essential, but is a component that is effective in improving weather resistance, suppressing phase separation of glass, and reducing the thermal expansion coefficient. When Al2O3 is contained, its content is preferably 1% or more, more preferably 3% or more, even more preferably 5% or more, even more preferably 6% or more, particularly preferably 7% or more, and particularly preferably 8% or more. Furthermore, its content is preferably 15% or less, more preferably 13% or less, even more preferably 11% or less, and particularly preferably 10% or more. B2O3 is a component that is effective in improving the melting reactivity of glass and lowering the devitrification temperature. Its content is preferably 1% or more, more preferably 3% or more, even more preferably 5% or more, even more preferably 7% or more, particularly preferably 9% or more, even more preferably 11% or more, even more preferably 13% or more, even more preferably 15% or more, still more preferably 17% or more, even more preferably 17.5% or more, particularly preferably 18% or more, more particularly preferably 18.5% or more, even more particularly preferably 19% or more, particularly preferably 19.5% or more, and most preferably 20% or more. The B2O3 content is preferably 30% or less, more preferably 28% or less, even more preferably 26% or less, and particularly preferably 24% or less.

[0032] In condition (2), when the molar ratio of the content expressed by Al2O3 / (Al2O3+B2O3) is 0.45 or less, the dielectric loss of the glass substrate 2 can be reduced. The molar ratio of the content expressed by Al2O3 / (Al2O3+B2O3) may be 0. The molar ratio of the content expressed by Al2O3 / (Al2O3+B2O3) is more preferably 0.4 or less, even more preferably 0.3 or less, even more preferably 0.28 or less, especially preferably 0.25 or less, even more preferably 0.23 or less, and particularly preferably 0.2 or less. The molar ratio of the content represented by Al2O3 / (Al2O3+B2O3) is preferably 0.01 or more, more preferably 0.01 or more, more preferably 0.02 or more, even more preferably 0.03 or more, even more preferably 0.04 or more, especially preferably 0.05 or more, still more preferably 0.06 or more, even more preferably 0.07 or more, even more preferably 0.08 or more, and particularly preferably 0.09 or more.

[0033] A combined Al2O3 and B2O3 content of 1% or more (including when the Al2O3 content is zero) improves the meltability of the glass. The combined Al2O3 and B2O3 content is preferably 3% or more, more preferably 5% or more, even more preferably 7% or more, particularly preferably 9% or more, even more preferably 11% or more, even more preferably 13% or more, even more preferably 15% or more, even more preferably 17% or more, still more preferably 19% or more, especially preferably 21% or more, more especially preferably 23% or more, even especially preferably 25% or more, even especially preferably 26% or more, even even more especially preferably 27% or more, particularly preferably 28% or more, and most preferably 29% or more. Furthermore, a combined Al2O3 and B2O3 content of 40% or less (including when the Al2O3 content is zero) reduces the dielectric loss of the glass substrate 2 while maintaining the meltability of the glass. The total content of Al2O3 and B2O3 is more preferably 37% or less, further preferably 35% or less, and particularly preferably 33% or less.

[0034] If the Al2O3 content is 15% or less, the melting property of the glass is good. The Al2O3 content is more preferably 14% or less. The Al2O3 content is more preferably 0.5% or more. A B2O3 content of 30% or less can improve the strain point. The B2O3 content is preferably 28% or less, more preferably 26% or less, even more preferably 24% or less, particularly preferably 23% or less, even more preferably 21% or less, even more preferably 19% or less, particularly preferably 18% or less, and most preferably 17% or less. Furthermore, a B2O3 content of 9% or more improves the solubility. The B2O3 content is more preferably 13% or more, and even more preferably 15% or more.

[0035] If the conditions (1) and (2) are satisfied, the dielectric loss tangent of the glass substrate 2 at 35 GHz can be set to 0.007 or less. However, if the B2O3 content is high, the acid resistance of the glass decreases. When the glass substrate 2 satisfies the condition (3A) or the condition (3B) as the condition (3), the acid resistance of the glass is improved.

[0036] Condition (3A): The glass substrate 2 contains at least one component (hereinafter sometimes referred to as a "trace component") selected from the group consisting of Sc2O3, TiO2, ZnO2, Ga2O3, GeO2, Y2O3, ZrO2, Nb2O5, In2O3, TeO2, HfO2, Ta2O5, WO3, Bi2O3, La2O3, Gd2O3, Yb2O3, and Lu2O3 in a total content of 0.1 to 1.0%.

[0037] In condition (3A), the acid resistance of the glass is improved by including trace elements in a total content of 0.1% or more. However, if the content of trace elements is too high, the uniformity of the glass decreases and phase separation becomes more likely to occur. Therefore, the total content of trace elements is set to 1.0% or less.

[0038] In condition (3A), only one or more of the above-mentioned trace components may be contained. In condition (3A), any of the above-mentioned trace components may be contained, but it is preferable to contain at least one selected from the group consisting of TiO2, ZnO2, Y2O3, ZrO2, and La2O3, and it is more preferable to contain at least one of Y2O3 and ZrO2. The preferred ranges for the contents of the above trace elements vary. For example, the content of ZrO2 is preferably 0.25 to 1.0%, more preferably 0.3 to 1.0%. The content of Y2O3 is preferably 0.1 to 0.5%.

[0039] Among the above trace components, when only ZnO2 and ZrO2 are contained, that is, when only ZnO2, ZrO2, or ZnO2 and ZrO2 are contained as the trace components, the content can be higher than 1.0% as shown in the following condition (3B). Condition (3B): The glass substrate 2 contains at least one of ZnO2 and ZrO2 in a total content of 1.5 to 4.0%.

[0040] In condition (3B), the acid resistance of the glass is improved by including at least one of ZnO2 and ZrO2 in a total content of 1.5% or more. However, if the total content of at least one of ZnO2 and ZrO2 is too high, the uniformity of the glass decreases and phase separation becomes more likely to occur, so the total content is set to 4.0% or less.

[0041] In the condition (3B), either ZnO2 or ZrO2 may be contained, or both may be contained.

[0042] It is preferable that the glass substrate 2 further satisfies the condition (4) in order to reduce dielectric loss in a high frequency range exceeding 30 GHz.

[0043] Condition (4): The glass substrate 2 contains alkali metal oxides in a total content of 0.001 to 5%, and the molar ratio of the alkali metal oxide content expressed as Na2O / (Na2O+K2O) is 0.01 to 0.99.

[0044] Regarding condition (4), by ensuring that the total alkali metal oxide content of the SiO2-based glass substrate 2 is 5% or less, the dielectric loss of the glass substrate 2 can be reduced. Furthermore, by ensuring that the total alkali metal oxide content is 0.001% or more, practical glass meltability and productivity of the glass substrate 2 can be achieved without the need for excessive raw material refinement, and the thermal expansion coefficient of the glass substrate 2 can be adjusted. Examples of alkali metal oxides contained in the glass substrate 2 include Li2O, Na2O, K2O, Rb2O, and Cs2O. Na2O and K2O are particularly important, so the total content of Na2O and K2O is preferably 0.001 to 5%. The total alkali metal oxide content is preferably 3% or less, more preferably 2.5% or less, even more preferably 2% or less, even more preferably 1.5% or less, even more preferably 1% or less, even more preferably 0.5% or less, even more preferably 0.2% or less, even more preferably 0.1% or less, and particularly preferably 0.05% or less. The total content of alkali metal oxides is more preferably 0.002% or more, further preferably 0.003% or more, and particularly preferably 0.005% or more.

[0045] Furthermore, by allowing Na2O and K2O to coexist in the glass substrate 2, which is primarily composed of SiO2, in other words, by ensuring that the molar ratio of the content expressed as Na2O / (Na2O + K2O) is 0.01 to 0.99, the migration of alkali components is suppressed, thereby reducing the dielectric loss of the glass substrate 2. The molar ratio of the content expressed as Na2O / (Na2O + K2O) is more preferably 0.98 or less, even more preferably 0.95 or less, and particularly preferably 0.9 or less. The molar ratio of the content expressed as Na2O / (Na2O + K2O) is more preferably 0.02 or more, even more preferably 0.05 or more, even more preferably 0.1 or more, especially preferably 0.2 or more, even more preferably 0.3 or more, even more preferably 0.4 or more, even more preferably 0.5 or more, even more preferably 0.6 or more, even more preferably 0.7 or more, even more preferably 0.75 or more, and particularly preferably 0.8 or more.

[0046] Among the constituent components of the glass substrate 2, the content of SiO2 as a network former, which is the main component, is preferably 40 to 75%. If the SiO2 content is 40% or more, the glass-forming ability and weather resistance can be improved, and devitrification can be suppressed. The SiO2 content is more preferably 45% or more, even more preferably 50% or more, and particularly preferably 55% or more. Furthermore, if the SiO2 content is 75% or less, the meltability of the glass can be improved. The SiO2 content is more preferably 74% or less, even more preferably 73% or less, and particularly preferably 72% or less.

[0047] The glass substrate 2 may contain Fe2O3 and SnO2 as optional components in addition to the components described above.

[0048] Fe2O3 is a component that controls the light absorption performance, such as infrared absorption performance and ultraviolet absorption performance, of the glass substrate 2, and may contain up to 0.12% Fe as calculated as Fe2O3, as needed. If the Fe content is 0.12% or less, the dielectric loss of the glass substrate 2 can be reduced and ultraviolet transmittance can be maintained, which is preferable. To improve UV transmittance (e.g., wavelength 300 nm or 350 nm), the Fe content is more preferably 0.03% or less, even more preferably 0.02% or less, even more preferably 0.015% or less, especially preferably 0.013% or less, even more preferably 0.012% or less, even more preferably 0.011% or less, even more preferably 0.009% or less, even more preferably 0.008% or less, even more preferably 0.007% or less, especially preferably 0.006% or less, even especially preferably 0.005% or less, even more preferably 0.004% or less, and especially preferably 0.002% or less. Increasing the UV transmittance of the glass substrate 2 allows the use of UV-curable materials in lamination processes and the like in the manufacturing process of high-frequency devices, improving the manufacturability of high-frequency devices. In this specification, ultraviolet light referred to as ultraviolet light absorption performance, ultraviolet light transmittance, ultraviolet light shielding ability, etc. means, for example, absorption performance, transmittance, shielding ability, etc. of a wavelength of 300 nm or 350 nm.

[0049] Furthermore, the glass substrate 2 preferably contains 0.005% or more Fe in terms of Fe2O3, as needed, because this increases the UV-shielding ability. When increasing the UV-shielding ability of the glass, the Fe content is more preferably 0.01% or more, and even more preferably 0.05% or more. By increasing the UV-shielding ability of the glass substrate 2, the glass substrate 2 can function as a protective material when a resin that deteriorates under UV rays is used as a component. The "content of Fe in terms of Fe2O3" means the content of Fe when all of the Fe present in the glass substrate is assumed to be in the form of Fe2O3.

[0050] SnO2 can be contained in the glass because it is used as a fining agent in the fining step of the manufacturing method of the glass substrate described later. The content of tin compounds in the glass is calculated as an SnO2 equivalent value relative to 100% of the total amount of the matrix composition of the glass, i.e., the Sn content calculated as SnO2, is preferably 0.25% or less, more preferably 0.2% or less, and particularly preferably 0.15% or less.

[0051] The glass substrate 2 has a thermal expansion coefficient suitable for electronic devices depending on the content of alkali metal oxides and alkaline earth metal oxides, etc. Specifically, the average thermal expansion coefficient at 50 to 350°C is 3 to 15 ppm / °C. When a glass substrate 2 having such a thermal expansion coefficient is used to construct a semiconductor package or the like as a high-frequency device, the difference in thermal expansion coefficient with other components can be more appropriately adjusted.

[0052] Furthermore, the glass substrate 2 preferably has a Young's modulus of 40 GPa or more. A glass substrate 2 with such a Young's modulus reduces the amount of strain when the glass substrate 2 is flowed during the manufacturing process (wafer process) of high-frequency devices, thereby preventing manufacturing defects in high-frequency devices. The Young's modulus of the glass substrate 2 is more preferably 50 GPa or more, and even more preferably 55 GPa or more. The glass substrate 2 also preferably has a porosity of 0.1% or less. This prevents noise generation during the manufacture of high-frequency devices. The porosity of the glass substrate 2 is more preferably 0.01% or less, and even more preferably 0.001% or less.

[0053] The glass substrate 2 preferably has a transmittance of 60% or more at a wavelength of 600 nm. If the transmittance satisfies this condition, the glass has high uniformity, which prevents localized irregularities from occurring on the substrate surface when the glass substrate is acid-washed. This reduces the transmission loss of high-frequency signals.

[0054] The transmittance of the glass substrate 2 at a wavelength of 600 nm is more preferably 70% or more, even more preferably 75% or more, even more preferably 80% or more, and particularly preferably 85% or more.

[0055] The haze value of the glass substrate 2 is preferably 35% or less. If the haze value of the glass substrate 2 is 35% or less, the uniformity of the glass is high, and therefore, when the glass substrate is acid-washed, localized irregularities are prevented from occurring on the substrate surface. This reduces the transmission loss of high-frequency signals. The haze value of the glass substrate 2 is more preferably 30% or less, even more preferably 20% or less, even more preferably 10% or less, particularly preferably 5% or less, and most preferably 1% or less.

[0056] The shape of the glass substrate 2 is not particularly limited, but the thickness is preferably 0.05 to 1 mm, and the area of ​​one main surface of the glass substrate 2 is preferably 225 to 10,000 cm. 2 is preferable. When the thickness of the glass substrate 2 is 1 mm or less, it is possible to make high-frequency devices thinner and more compact, and to improve production efficiency. In addition, UV transmittance is improved, and manufacturability can be improved by using UV-curable materials in the device manufacturing process. The thickness of the glass substrate 2 is more preferably 0.5 mm or less. Furthermore, if the thickness of the glass substrate 2 is 0.05 mm or more, the strength of the glass substrate 2 can be maintained when it flows. Furthermore, UV-shielding ability is improved, and it is possible to protect resins that deteriorate under UV rays. The thickness of the glass substrate 2 is more preferably 0.1 mm or more, and even more preferably more than 0.2 mm. Furthermore, according to the glass substrate 2 of the embodiment, it is possible to make a glass substrate having an area of ​​10,000 cm with the above-mentioned thickness. 2 The glass substrate 2 has an area of ​​3600 cm. 2 The following is more preferred:

[0057] The glass substrate 2 preferably has a devitrification temperature of 1400°C or lower. A devitrification temperature of 1400°C or lower allows the temperature of components in the forming equipment to be lowered when forming the glass, extending the component life. The devitrification temperature is more preferably 1350°C or lower, even more preferably 1330°C or lower, and particularly preferably 1300°C or lower. The devitrification temperature of glass is determined by placing crushed glass particles in a platinum dish, heat-treating them for 17 hours in an electric furnace controlled at a constant temperature, and observing the heat-treated sample with an optical microscope between the maximum temperature at which crystals precipitate on the surface and inside of the glass and the minimum temperature at which crystals do not precipitate.

[0058] The glass substrate 2 has a glass viscosity of 10 2 The temperature T2 at which the viscosity becomes dPa·s is preferably 1700°C or lower. T2 is the temperature that indicates the melting property of glass, and it is preferable for melting glass that T2 is 1700°C or lower. It is more preferably 1690°C or lower, even more preferably 1680°C or lower, particularly preferably 1670°C or lower, and most preferably 1660°C or lower.

[0059] The glass substrate 2 has a low temperature T2 and is therefore excellent in meltability. The glass substrate 2 has a low devitrification temperature and is therefore excellent in formability by the float method.

[0060] Next, a method for manufacturing a glass substrate of an embodiment will be described. When manufacturing a glass substrate of an embodiment, a melting process for heating glass raw materials to obtain molten glass, a fining process for removing bubbles from the molten glass, a forming process for forming the molten glass into a plate shape to obtain a glass ribbon, and an annealing process for annealing the glass ribbon to room temperature are performed. Alternatively, a glass substrate may be manufactured by forming the molten glass into a block shape, annealing it, and then cutting and polishing it.

[0061] In the melting step, raw materials are prepared to have the desired composition of the glass substrate, and the raw materials are continuously charged into a melting furnace and heated preferably to about 1450°C to 1750°C to obtain molten glass.

[0062] Halides such as oxides, carbonates, nitrates, hydroxides, and chlorides can also be used as raw materials. If the molten glass comes into contact with platinum during the melting or refining process, minute platinum particles may dissolve into the molten glass and become contaminated as foreign matter in the resulting glass substrate. However, the use of a nitrate raw material has the effect of preventing the generation of platinum foreign matter.

[0063] As the nitrate, strontium nitrate, barium nitrate, magnesium nitrate, calcium nitrate, etc. can be used. The use of strontium nitrate is more preferable. The particle size of the raw material can be appropriately selected from raw materials with a large particle size of several hundred μm so that no undissolved residue remains, to raw materials with a small particle size of about several μm so that no scattering occurs during raw material transportation and no aggregation occurs as secondary particles. Granules can also be used. The moisture content of the raw material can also be appropriately adjusted to prevent scattering of the raw material. The oxidation-reduction degree of β-OH and Fe (redox [Fe 2+ / (Fe 2+ +Fe 3+ )]) can also be appropriately adjusted.

[0064] The next fining step is a step of removing bubbles from the molten glass obtained in the melting step. The fining step may be performed by degassing under reduced pressure, or by heating to a temperature higher than the melting temperature of the raw materials. Furthermore, in the manufacturing process of the glass substrate according to the embodiment, SO3 or SnO2 can be used as a fining agent. The SO3 source is preferably a sulfate of at least one element selected from Al, Na, K, Mg, Ca, Sr, and Ba, more preferably an alkaline earth metal sulfate. Among these, CaSO4·2H2O, SrSO4, and BaSO4 are particularly preferred because of their remarkable bubble-enhancing effect.

[0065] The use of halogens such as Cl or F as a fining agent in the reduced pressure degassing method is preferred. The Cl source is preferably a chloride of at least one element selected from Al, Mg, Ca, Sr, and Ba, more preferably an alkaline earth metal chloride. Among these, SrCl2·6H2O and BaCl2·2H2O are particularly preferred due to their significant bubble-enhancing effect and low deliquescence. The F source is preferably a fluoride of at least one element selected from Al, Na, K, Mg, Ca, Sr, and Ba, more preferably an alkaline earth metal fluoride. Among these, CaF2 is more preferred due to its significant effect of increasing the solubility of the glass raw materials.

[0066] Tin compounds, such as SnO2, generate O2 gas in molten glass. In molten glass, SnO2 is reduced to SnO at temperatures of 1450°C or higher, generating O2 gas and promoting bubble growth. In the production of the glass substrate 2 of this embodiment, glass raw materials are heated to approximately 1450 to 1750°C for melting, which effectively increases the bubble size in the molten glass. When SnO2 is used as a clarifier, the raw materials are preferably prepared so that the tin compound is contained in an amount of 0.01% or more, calculated as SnO2, relative to the total amount of the matrix composition (100%). An SnO2 content of 0.01% or more provides a clarification effect during the melting of the glass raw materials, and is preferably 0.05% or more, and even more preferably 0.10% or more. An SnO2 content of 0.3% or less is preferred because it suppresses the occurrence of coloration and devitrification of the glass. The content of the tin compound in the glass is more preferably 0.25% or less, further preferably 0.2% or less, and particularly preferably 0.15% or less, calculated as SnO2 relative to 100% of the total amount of the glass matrix composition.

[0067] The next forming step is a step of forming the molten glass from which bubbles have been removed in the fining step into a sheet to obtain a glass ribbon. As the forming step, a known method for forming glass into a sheet can be applied, such as a float method in which molten glass is poured onto a molten metal such as tin to form a sheet to obtain a glass ribbon, an overflow downdraw method (fusion method) in which molten glass is made to flow downward from a trough-shaped member, or a slit downdraw method in which molten glass is made to flow down from a slit.

[0068] Next, the annealing step is a step of cooling the glass ribbon obtained in the forming step to room temperature under controlled cooling conditions. In the annealing step, the glass ribbon is cooled to form a glass ribbon, and then annealed to room temperature under predetermined conditions. The annealed glass ribbon is cut to obtain a glass substrate.

[0069] If the cooling rate R in the slow cooling step is too high, distortion is likely to remain in the cooled glass. Furthermore, the equivalent cooling rate, which is a parameter reflecting the fictive temperature, becomes too high, resulting in an inability to reduce dielectric loss. Therefore, it is preferable to set R so that the equivalent cooling rate is 800°C / min or less. The equivalent cooling rate is more preferably 400°C / min or less, even more preferably 100°C / min or less, and particularly preferably 50°C / min or less. On the other hand, if the cooling rate is too low, the required process time becomes too long, resulting in low productivity. Therefore, it is preferable to set R to 0.1°C / min or more, more preferably 0.5°C / min or more, and even more preferably 1°C / min or more.

[0070] The definition and evaluation method of the equivalent cooling rate are as follows: Glass of the target composition is processed into a rectangular parallelepiped of 10 mm x 10 mm x 0.3 to 2.0 mm, and is held at strain point +1700°C for 5 minutes in an infrared heating electric furnace, after which the glass is cooled to room temperature (25°C). At this time, multiple glass samples are prepared by varying the cooling rate in the range of 10°C / min to 1000°C / min.

[0071] Using a precision refractive index measuring device (e.g., Shimadzu Devices KPR2000), the refractive index n of multiple glass samples at the d line (wavelength 587.6 nm) was measured. d The V-block method or the minimum deviation method may be used for the measurement. d By plotting against the logarithm of the cooling rate, n d Obtain a calibration curve.

[0072] Next, we compared the n of glasses with the same composition that were actually manufactured through processes such as melting, molding, and cooling. d is measured by the above-mentioned measurement method. d The corresponding cooling rate (referred to as an equivalent cooling rate in this embodiment) is determined from the calibration curve.

[0073] The present invention is not limited to the above-described embodiments. Modifications and improvements are permitted within the scope of achieving the object of the present invention. For example, when manufacturing the glass substrate of the present invention, glass may be formed into a plate shape by a press molding method in which molten glass is directly formed into a plate shape.

[0074] Furthermore, when producing the glass substrate of the present invention, in addition to the production method using a refractory melting tank, a crucible made of platinum or an alloy containing platinum as a main component (hereinafter referred to as a platinum crucible) may be used as the melting tank or refining tank. When a platinum crucible is used, the melting step involves preparing raw materials so as to obtain the composition of the glass substrate to be obtained, and heating the platinum crucible containing the raw materials in an electric furnace, preferably to about 1450°C to 1750°C. A platinum stirrer is inserted and the mixture is stirred for 1 to 3 hours to obtain molten glass.

[0075] In the forming process of glass plate manufacturing using a platinum crucible, molten glass is poured onto, for example, a carbon plate or a mold and formed into a plate or block. The slow cooling process typically involves maintaining the glass at a temperature of about Tg + 50°C, then cooling it to near the strain point at a rate of about 1 to 10°C / min, and then cooling it to room temperature at a cooling rate that does not leave any residual strain. After cutting and polishing into a predetermined shape, a glass substrate is obtained. Alternatively, the glass substrate obtained by cutting may be heated to, for example, about Tg + 50°C, and then slowly cooled to room temperature at a predetermined cooling rate. This allows the equivalent cooling temperature of the glass to be adjusted.

[0076] The circuit board 1 using the glass substrate 2 of the embodiment described above is suitable for high-frequency devices that handle high-frequency signals, particularly high-frequency signals exceeding 30 GHz, and even high-frequency signals of 35 GHz or higher, and can reduce transmission loss of such high-frequency signals and improve their characteristics, such as quality and strength. The glass substrate 2 and circuit board 1 of the embodiment are suitable for high-frequency devices (electronic devices) such as semiconductor devices used in communication devices such as mobile phones, smartphones, personal digital assistants, and Wi-Fi devices, surface acoustic wave (SAW) devices, radar components such as radar transceivers, and antenna components such as liquid crystal antennas. [Example]

[0077] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Examples 1 to 18 are working examples, and Examples 19 to 24 are comparative examples.

[0078] [Examples 1-24] Glass substrates were prepared with the compositions shown in Tables 1 to 5 (in mole percent based on oxides), a thickness of 1.0 mm, dimensions of 50 × 50 mm, and an arithmetic mean roughness Ra of 1.0 nm on the main surface. The glass substrates were fabricated by a melting method using a platinum crucible. Raw materials such as silica sand were mixed to prepare 1 kg batches of glass having the compositions shown in Tables 1 to 5. The raw materials were placed in a platinum crucible and heated in an electric furnace at 1650°C for 3 hours to melt the materials into molten glass. A platinum stirrer was inserted into the platinum crucible and the glass was stirred for 1 hour to homogenize the glass. The molten glass was poured onto a carbon plate and formed into a plate. The plate was then placed in an electric furnace at a temperature of approximately Tg + 50°C and held there for 1 hour. After that, the electric furnace was cooled to Tg - 100°C at a cooling rate of 1°C / min. The glass was then allowed to cool to room temperature. Thereafter, the glass was cut and polished to form a plate. In Table 1, "total RO content" means the sum of MgO, CaO, SrO, and BaO as the total content of alkaline earth metal oxides, and "total R2O content" means the sum of Na2O and KO as the total content of alkali metal oxides.

[0079] For the glass substrates of Examples 1 to 24, the Young's modulus, average thermal expansion coefficient at 50 to 350°C, relative dielectric constants and their ratios at 10 GHz and 35 GHz, dielectric loss tangents and their ratios at 10 GHz and 35 GHz, density, specific elastic modulus, T2, devitrification temperature, acid resistance, haze value, and transmittance at a wavelength of 600 nm are shown in Tables 6 to 10. The haze value and transmittance at a wavelength of 600 nm are indicators of the uniformity of the glass.

[0080] The methods for measuring each physical property are shown below. (Young's modulus) Measurements were taken using the ultrasonic pulse method for glass with a thickness of 0.5 to 10 mm in accordance with the method specified in JIS Z2280 (1993). The unit of measurement was GPa. (average thermal expansion coefficient) Measurements were made using a differential thermal dilatometer in accordance with the method specified in JIS R3102 (1995). The measurement temperature range was 50 to 350°C, and the unit was expressed as ppm / °C. (relative permittivity, dielectric loss tangent) Measurements were made using a cavity resonator and a vector network analyzer according to the method specified in JIS R1641 (2007). The measurement frequency was 10 GHz or 35 GHz, which is the resonant frequency of the air in the cavity resonator. (density) The density of a glass block weighing approximately 20 g and containing no bubbles was measured by the Archimedes method. The unit is g / cm. 3 It was expressed as: (specific elastic modulus) The specific elastic modulus is calculated using the density and Young's modulus measurements, and is expressed in GPa cm. 3 Expressed as / g. (T2) The viscosity of the glass was measured using a rotational viscometer, and the viscosity was 10 2 The temperature T2 (unit: °C) at which the viscosity becomes dPa·s was determined. (devitrification temperature) Crushed glass particles were placed in a platinum dish and heat-treated for 17 hours in an electric furnace controlled at a constant temperature of 1100°C to 1400°C. After heat treatment, the sample was observed under an optical microscope to determine the average value of the maximum temperature at which crystals precipitated inside the glass and the minimum temperature at which crystals did not precipitate. (acid resistance) The glass sample was immersed in an acid solution (6 wt% HNO3 + 5 wt% H2SO4, 45°C) for 170 seconds, and the amount of glass components dissolved per unit surface area (mg / cm 2 The amount of eluted glass components was 0.02 mg / cm 2 If it is below this, the acid resistance is good. (Haze value) The haze value of the glass was measured using a haze meter (manufacturer: Suga Test Instruments Co., Ltd., model: HZ-V3 Hazemeter). The glass to be evaluated was a glass plate with a thickness of 1.0 mm and mirror polished on both sides. A haze value of 35% or less was considered to be a good product. (transmittance) The transmittance of the glass at a wavelength of 600 nm was measured using a visible-ultraviolet spectrophotometer (manufacturer: Hitachi, model: U-4100 Spectrophotometer). The transmittance was expressed as external transmittance, including loss due to reflection. The glass used for evaluation was a glass plate with a thickness of 1.0 mm, mirror-polished on both sides. A product was considered to be good if its transmittance at a wavelength of 600 nm was 60% or higher.

[0081] [Table 1]

[0082] [Table 2]

[0083] [Table 3]

[0084] [Table 4]

[0085] [Table 5]

[0086] [Table 6]

[0087] [Table 7]

[0088] [Table 8]

[0089] [Table 9]

[0090] [Table 10]

[0091] The glass substrates of Examples 1 to 18 all had a dielectric loss tangent at 35 GHz of 0.007 or less, and exhibited good acid resistance, as well as good haze and transmittance at a wavelength of 600 nm, which are indicators of glass uniformity. Examples 19 and 20, which did not contain trace components, exhibited poor acid resistance. Example 21 did not contain trace components, had a molar ratio expressed as Al2O3 / (Al2O3 + B2O3) greater than 0.45, and a low B2O3 content, resulting in a dielectric loss tangent at 35 GHz greater than 0.007, making it impossible to reduce dielectric loss in the high-frequency range. Examples 22 and 23, which contained trace components in a total content of more than 1.0% under condition (3A), exhibited poor acid resistance and poor haze and transmittance, which are indicators of glass uniformity. Example 24, in which the total content of ZnO2 and ZrO2 under condition (3B) was more than 4.0%, had good acid resistance, but was poor in haze value, which is an index of glass uniformity, and transmittance at a wavelength of 600 nm.

[0092] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2018-213526) filed on November 14, 2018, the contents of which are incorporated herein by reference. [Industrial Applicability]

[0093] The glass substrate for high-frequency devices of the present invention can reduce the dielectric loss of high-frequency signals, and is useful for high-frequency electronic devices in general that handle high-frequency signals of 10 GHz or higher, particularly high-frequency signals exceeding 30 GHz, and even high-frequency signals of 35 GHz or higher, such as glass substrates for communication equipment, frequency filter components such as SAW devices and FBARs, bandpass filters such as waveguides, SIW (Substrate Integrated waveguide) components, radar components, and antenna components (particularly liquid crystal antennas that are considered optimal for satellite communications). [Explanation of symbols]

[0094] 1: Circuit board 2: Glass substrate 2a, 2b: Main surface 3,4: Wiring layer

Claims

1. The total content of alkaline earth metal oxides is 0.1 to 13% in terms of mole percentage based on oxides, and Al ２ O ３ and B ２ O ３ The total content of Al is 1 to 40%. ２ O ３ / (Al ２ O ３ +B ２ O ３ ) is 0 to 0.45, and TiO ２ , Y ２ O ３ , and ZrO ２ and ZrO ２ The content of SiO is 0.1% or less, ２ The glass substrate is a glass substrate mainly composed of the above-mentioned compound, and has a dielectric loss tangent at 35 GHz of 0.007 or less.

2. In terms of mole percentage based on oxide, Y ２ O ３ 2. The glass substrate according to claim 1, wherein the content is 0.1 to 0.5%.

3. 3. The glass substrate according to claim 1, wherein at least one of the main surfaces of the glass substrate has a surface roughness in terms of arithmetic mean roughness Ra of 1.5 nm or less.

4. The total content of alkali metal oxides is 0.001 to 5% in terms of mole percentage based on oxides, and among the alkali metal oxides, Na ２ O / (Na ２ O+K ２ 4. The glass substrate according to claim 1, wherein the molar ratio of the content represented by the formula (I) to the content represented by the formula (I) is 0.01 to 0.

99.

5. Fe ２ O ３ The glass substrate according to any one of claims 1 to 4, containing 0.005 to 0.12% Fe in terms of carbon content.

6. SnO ２ The glass substrate according to any one of claims 1 to 5, containing 0.25% or less Sn in terms of Sn content.

7. The glass substrate according to any one of claims 1 to 6, which has a devitrification temperature of 1400°C or lower.

8. Glass viscosity is 10 ２ Temperature T at which viscosity becomes dPa s ２ The glass substrate according to any one of claims 1 to 7, wherein the glass substrate has a melting point of 1700°C or less.

9. A liquid crystal antenna comprising the glass substrate according to any one of claims 1 to 8.

10. A high frequency device comprising the glass substrate according to any one of claims 1 to 8.

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