Electromagnetic shield

Abstract

There is provided an inexpensive electromagnetic shield that can achieve exceptional shielding and display visibility characteristics, and provide high environmental resistance as necessary. In an electromagnetic shield (1), an intermediate layer (3) is formed on a glass substrate (2) comprising soda lime glass, an electroconductive layer (4) of Al is formed thereon, and openings (5) are formed by wet etching on the intermediate layer (3) and the electroconductive layer (4) after these layers have been formed by sputtering or vacuum deposition. Furthermore, an ITO layer (6) is formed on the entire glass surface including the intermediate layer (3) and the electroconductive layer (4) after the openings (5) are formed. In this configuration, the intermediate layer (3) comprises a mixture of at least one metal selected from chromium, molybdenum, and tungsten, and at least one oxide selected from oxides of silicon, oxides of aluminum, and oxides of titanium.

Claims

1. An electromagnetic shield in which an intermediate layer is formed on a glass substrate and an electroconductive layer of Al is formed on the intermediate layer, wherein the electromagnetic shield is characterized in that: after the intermediate layer and the electroconductive layer are formed by sputtering or vacuum deposition, openings in said intermediate layer and said electroconductive layer are formed by wet etching; the intermediate layer is a layer that is black when seen from a side of the glass substrate; the intermediate layer consists of a mixture of molybdenum and Al.sub.2O.sub.3, the glass substrate is a soda lime glass substrate and a layer of indium tin oxide is formed on glass surfaces at said openings formed by wet etching and on surfaces of the electroconductive layer and the intermediate layer after said openings are formed by wet etching; and when the electromagnetic shield is left to stand for 1000 hours at a temperature of 60 C. and a relative humidity of 95%, there will be no clouding in the glass surface.

2. The electromagnetic shield of claim 1, characterized in that the thickness of the intermediate layer is 5-500 nm, and the thickness of the electroconductive layer is 500-5000 nm.

3. The electromagnetic shield of claim 1, characterized in that the amount of the Al.sub.2O.sub.3 contained relative to the total amount of the mixture is 2-16 wt. %.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic cross-sectional view showing an example of the electromagnetic shield of the present invention;

(2) FIG. 2 is an enlarged view of the surface on which the electroconductive layer is formed;

(3) FIG. 3 is a schematic cross-sectional view showing another example of the electromagnetic shield of the present invention;

(4) FIG. 4 is a graph showing the effect that including or withholding the intermediate layer has on the spectral characteristics of reflectance;

(5) FIG. 5 is a graph showing the effect that the mixture composition ratio of the intermediate layer has on reflectance; and

(6) FIG. 6 is a view of electron microscope images showing the glass surface after testing at high temperature and high humidity.

MODE FOR CARRYING OUT THE INVENTION

(7) An example of the electromagnetic shield of the present invention is described on the basis of FIGS. 1 and 2. FIG. 1 is a schematic cross-sectional view showing an example of the electromagnetic shield, the illustration exaggerating the thickness of each of the layers more than the actual thickness for the sake of the description. FIG. 2 is an enlarged view of the surface on which the electroconductive layer is formed. In the electromagnetic shield 1 of this embodiment, an intermediate layer 3 is formed on a glass substrate 2, and an electroconductive layer 4 of Al is formed thereon, as shown in FIG. 1. After the intermediate layer 3 and the electroconductive layer 4 are formed by sputtering or vacuum deposition, openings 5 are formed by wet etching.

(8) The glass substrate 2 is a translucent insulating substrate, for which soda lime glass, quartz glass, borosilicate glass, non-alkali glass containing no alkali components, or the like can be employed. In the present invention, soda lime glass is preferably used due to its high transmittance and extremely low cost when used in window glass of common building materials. The thickness of the glass substrate 2 is approximately 0.2-1.8 mm, and preferably approximately 0.5-1.2 mm.

(9) The intermediate layer 3 is a layer comprising a mixture of (1) at least one metal selected from Cr, Mo, and W, and (2) at least one oxide selected from oxides of Si, oxides of Al, and oxides of Ti. SiO.sub.2 is an example of an oxide of Si, TiO.sub.2 is an example of an oxide of Ti, and Al.sub.2O.sub.2 is an example of an oxide of Al. The intermediate layer 3 is formed on the surface of the glass substrate 2 by sputtering or vacuum deposition, which is a vacuum process, using a solid target (a vapor deposit) of the mixture described above. Particularly, it is preferable to form the film by sputtering because a uniform film can be formed and it is easy to ensure stable shielding and visibility characteristics. Sputtering involves bombarding the solid target with accelerated argon ions, and causing the atoms or molecules scattered from the target surface to adhere to the glass substrate to form a film.

(10) The intermediate layer is a layer (a black layer) that absorbs incident light due to the interference of visible light, and appears black. The Al electroconductive layer is extremely reflective of visible light (wavelengths of approximately 400-700 nm) and is prone to glare, and the visibility characteristics of the display is therefore significantly reduced when only an Al electroconductive layer is formed on the glass substrate. In the present invention, the intermediate layer is interposed between the glass substrate and the Al electroconductive layer, thereby reducing reflectance of visible light.

(11) FIG. 4 shows an example of the spectral characteristics of reflectance depending on whether or not the intermediate layer is included. In FIG. 4, the term with intermediate layer indicates that a target of a mixture of Mo and Al.sub.2O.sub.3 (containing 10 wt. % of Al.sub.2O.sub.3) is used to form an intermediate layer (100 nm) by sputtering on a soda lime glass substrate (0.7 mm), and an Al electroconductive layer (1000 nm) of 99% purity is formed by sputtering on the intermediate layer. The term without intermediate layer indicates that in the configuration described above, an intermediate layer is not formed and only an Al electroconductive layer (1000 nm) is formed. Without the intermediate layer, reflectance is much higher than that of the glass substrate, and the visibility characteristics are poor, as shown in FIG. 4. It is therefore apparent that it is favorable to provide the intermediate layer, which makes reflectance much less than in the case of the glass substrate alone. It is also apparent that with all wavelengths, the spectral characteristics are mostly flat and there is no coloration.

(12) The mixture composition ratio of the intermediate layer has an effect on reflectance and the like. Consequently, to form a film having a desired composition ratio, it is preferable during the film forming to use a solid target of the mixture in which the metal and the oxide have been substantially uniformly mixed in advance in the desired composition ratio. In the present invention, metals constituting oxides and metals solely comprising a metal overlap in the intermediate layer, and a film of the composition described above therefore cannot be formed by a method of using a solid target of only metal and a mixed gas of argon and oxygen.

(13) In the mixture composition ratio of the intermediate layer, the oxide content relative to the total amount of the mixture (metal alone+oxide) is preferably 2-16 wt. %. When the oxide content is less than 2 wt. %, a metallic luster emerges and it might not be possible to reduce reflectance. When the oxide content exceeds 16%, cloudiness emerges and it might not be possible to reduce reflectance.

(14) FIG. 5 shows an example of the effect of the mixture composition ratio of the intermediate layer. In FIG. 5, a target of a mixture of Mo and Al.sub.2O.sub.3 is used to form an intermediate layer (100 nm) by sputtering on a soda lime glass substrate (0.7 mm), an Al electroconductive layer (1000 nm) of 99% purity is formed by sputtering thereon, and the change in visible light (wavelength 500 nm) reflectance is measured when the amount (wt. %) of Al.sub.2O.sub.3 in the mixture is changed. The mixture composition ratio has an optimal range, and when a mixture of Mo and Al.sub.2O.sub.3 is used in the intermediate layer, the Al.sub.2O.sub.3 content is preferably 2-16 wt. %, more preferably 5-15 wt. %, and even more preferably 8-12 wt. %, as shown in FIG. 5.

(15) An appropriate film thickness for the intermediate layer is 5-500 nm. When the film thickness is less than 5 nm, the layer might not be sufficiently black and reflectance might not be reduced. When the film thickness exceeds 500 nm, there may not be any reflectance-reducing effect from the effect of visible light interference. A more desirable film thickness is 50-200 nm. The film thickness is determined for each material in accordance with the refractive index of the intermediate layer material.

(16) The electroconductive layer 4 comprises Al, the layer 4 being formed on the intermediate layer 3 (on the side opposite the side in contact with the glass substrate). Similarly to the intermediate layer 3, the electroconductive layer 4 is formed by sputtering or vacuum deposition, which is a vacuum process, using a solid target (a vapor deposit) of Al. An appropriate film thickness for the electroconductive layer is 500-5000 nm. When the film thickness is less than 500 nm, it might not be possible to ensure the desired shielding characteristics. When the film thickness exceeds 5000 nm, the shielding characteristics will be exceptional, but there will be more steps and manufacturing costs will rise. A more preferable film thickness is 800-3500 nm.

(17) The openings 5 of the intermediate layer 3 and the electroconductive layer 4, shown in FIGS. 1 and 2, are formed by wet etching. As an example, the openings are obtained by using a resist to form a mask layer having an etching pattern by screen printing or the like, and using a predetermined etching liquid to remove the portions corresponding to the openings by wet etching. Manufacturing efficiency is exceptional when a liquid that can simultaneously etch the materials of the intermediate layer and the electroconductive layer is selected as the etching liquid. For example, a phosphate etching liquid is suitable. In FIG. 2, the shape of the openings 5, i.e., the etching pattern is a grid, but is not limited as such. When the pattern is a grid, normally 5-50 m is chosen as the line width W and 50-500 m is chosen as the line pitch P. If the opening ratio is reduced, the shielding characteristics improves but the display transmittance is poor; therefore, the opening ratio is decided in accordance with the required characteristics.

(18) Another example of the electromagnetic shield of the present invention is described with reference to FIG. 3. FIG. 3 is a schematic cross-sectional view showing another example of an electromagnetic shield, and similarly to FIG. 1, the illustration exaggerates the thickness of each layer more than reality for the sake of the description. In the electromagnetic shield 1 of this embodiment, an intermediate layer 3 is formed on a glass substrate 2 comprising soda lime glass, an electroconductive layer 4 comprising AL is formed thereon, and openings 5 are formed by wet etching in the intermediate layer 3 and the electroconductive layer 4 after these layers have been formed by sputtering or vacuum deposition, as shown in FIG. 3. In this embodiment, an ITO layer 6 is also formed on the glass surface including the intermediate layer 3 and the electroconductive layer 4 after the openings 5 are formed. The ITO layer is preferably formed on the surface in the glass substrate on which at least an electroconductive layer or the like is formed (see FIG. 3), but the ITO layer may also be formed on another surface.

(19) The ITO layer 6 is formed by sputtering or vacuum deposition, which is a vacuum process, similarly to the intermediate layer 3 and the electroconductive layer 4. A mixture of In.sub.2O.sub.3:SnO.sub.2=95:5 (wt. %) can be used for the ITO, but the composition is not particularly limited. An appropriate film thickness for the ITO layer is 5-500 nm. When the film thickness is less than 5 nm, there is a risk that it will not be possible to sufficiently ensure environmental resistance. If the film thickness exceeds 500 nm, there is a risk that transmittance will be reduced by the colored ITO layer.

(20) Due to the coating of an ITO layer, the soda lime glass surface does not come into direct contact with water vapor in the atmosphere, and the Na in the soda glass does not convert to NaOH. Because the combined front surfaces of the Al electroconductive layer and the intermediate layer are covered by the ITO layer, there is no reaction between the Al, the Ca in the glass, and the NaOH. As a result, clouding of the glass can be prevented. This makes it possible to significantly confirm the effects by performing high-temperature, high-humidity testing at 60 C. in a relative humidity of 95%. FIG. 6 shows electron photomicrographs of the glass surface after testing for 1000 hours at 60 C. in a relative humidity of 95%. The upper photograph in FIG. 6 shows a case in which no ITO layer is formed (equivalent to Example 1 described hereinafter), and the lower photograph shows a case in which an ITO layer is formed (equivalent to Example 2 described hereinafter). In the case with no ITO layer, there is much clouding of the glass surface, but the case provided with an ITO layer exhibits mostly no change and is favorable. In the case with no ITO layer, it was confirmed that some of the Mo in the intermediate layer had moved to the opening portions and crystallized.

(21) The electromagnetic shield of the present invention is primarily utilized as a shield window disposed on a PDP, a CRT, a VFD, an LCD, or another type of display.

EXAMPLES

Example 1

(22) An intermediate layer was formed by sputtering on a soda lime glass substrate 0.7 mm in thickness, using a target made of a mixture of Mo and Al.sub.2O.sub.3 (the Al.sub.2O.sub.3 content being 10 wt. %). The film thickness of the intermediate layer was 100 nm. Next, an Al electroconductive layer of 99% purity was formed by sputtering. The film thickness of the electroconductive layer was 1000 nm. A grid pattern 10 m in line width and 300 m in line pitch was then formed by wet simultaneous etching, using a phosphate etching liquid. The opening ratio was 93%.

Example 2

(23) An ITO layer was formed by sputtering on the entire surface on which the pattern was formed in Example 1. The film thickness of the ITO layer was 100 nm.

Example 3

(24) An intermediate layer was formed by sputtering on a soda lime glass substrate 0.7 mm in thickness, using a target of a mixture of W and SiO.sub.2 (the SiO.sub.2 content being 10 wt. %). The film thickness of the intermediate layer was 150 nm. Next, an Al electroconductive layer of 99% purity was formed by sputtering. The film thickness of the electroconductive layer was 3000 nm. A grid pattern 10 m in line width and 100 m in line pitch was then formed by wet simultaneous etching, using a phosphate etching liquid. The opening ratio was 74%. An ITO layer was also formed by sputtering on the entire surface on which the pattern was formed. The film thickness of the ITO layer was 100 nm.

Comparative Example 1

(25) An Al electroconductive layer of 99% purity was formed by sputtering on a soda lime glass substrate 0.7 mm in thickness. The film thickness of the electroconductive layer was 1000 nm. A grid pattern 10 m in line width and 300 m in line pitch was then formed by wet simultaneous etching, using a phosphate etching liquid. The opening ratio was 93%.

(26) The shielding characteristics of the samples in Examples 1 to 3 and Comparative Example 1 were measured by KEC, and the shielding characteristics at the typical frequency of 30 MHz are shown in Table 1. The reflectance of visible light (500 nm) was also measured, and the effect of the intermediate layer was confirmed. Furthermore, to confirm the effect of the ITO layer, a high-temperature, high-humidity test was performed in which the samples were left for 1000 hours in conditions with a temperature of 60 C. and a relative humidity of 95%, and visual confirmation was made as to whether or not there was clouding of the glass surface. These results are shown collectively in Table 1.

(27) TABLE-US-00001 TABLE 1 Al Elec. Hi- Int. Layer Pattern ITO Shielding temp/humid. Layer Thickness (m) Layer Char. Reflect. test Ex. 1 Mo + Al.sub.2O.sub.3 1000 nm w10 p300 no 40 dB 8% clouding Ex. 2 Mo + Al.sub.2O.sub.3 1000 nm w10 p300 yes 40 dB 8% no change Ex. 3 W + SiO.sub.2 3000 nm w10 p100 yes 60 dB 10% no change C. Ex. 1 no 1000 nm w10 p300 no 40 dB 22% clouding

(28) It follows from Table 1 that the Examples had low visible light reflectance, exceptional visibility characteristics, and exceptional shielding characteristics. In particular, in Examples 2 and 3 in which the ITO layer was formed, no clouding of the glass surface was observed even in the high-temperature, high-humidity test, and it is clear that these Examples had exceptional environmental resistance as well.

(29) Next, a comparison was made between the electromagnetic shield of the present invention, and a shield member in which a metal Cu foil was bonded to a polymeric film used in conventional practice and patterned by etching.

Comparative Example 2

(30) Polycarbonate was used as the base material, a 15-m Cu foil was bonded thereto, a pattern 10 m in line thickness and 300 m in line pitch was formed by etching, and a shield member was obtained. Table 2 below shows the numerical values of transmittance, reflectance, and shielding characteristics required for the shield member in this Comparative Example 2 and in Example 1. The term base material in the table indicates an evaluation of the base material alone, and the term product indicates an evaluation of the base material with an electroconductive layer or the like formed thereon.

(31) TABLE-US-00002 TABLE 2 Transmittance Base Reflect. Shielding Base Material Material Product Product char. Ex. 1 soda lime 94% 85% 8% 40 dB glass (0.7 mm) C. Ex. 2 polycarbonate 87% 77% 12% 40 dB (0.2 mm)

(32) As shown in Table 2, Example 1 exhibits more favorable product transmittance than Comparative Example 2 because of the exceptional glass transmittance. Example 1 had low reflectance of visible light due to the effect of the intermediate layer, and the shielding characteristics were similar to conventional practice. Furthermore, because glass was used in Example 1, there was no curling, folding, or the like, and ease of handling was exceptional compared with Comparative Example 2.

INDUSTRIAL APPLICABILITY

(33) The electromagnetic shield of the present invention is inexpensive, has exceptional shielding and display visibility characteristics, and can provide high environmental resistance as necessary; therefore, this electromagnetic shield can be used in desired locations where electromagnetic waves must be blocked, and in particular, the plate can be suitably utilized in the application of being installed on the front surface of a PDP, a CRT, a VFD, an LCD, or another display.

EXPLANATION OF REFERENCE NUMERALS AND SYMBOLS

(34) 1 Electromagnetic shield 2 Glass substrate 3 Intermediate layer 4 Electroconductive layer 5 Opening 6 ITO layer