JPH07281021A - Near infrared ray absorbing glass, solid image pickup element protective filter using this glass and sold image pickup element using this filter - Google Patents

Abstract

PURPOSE:To provide near infrared ray absorbing glass by which the occurrence of a soft error of a solid image pickup element can be restrained even if it is used as solid image pickup element protective cover glass and image quality can be improved and to which a sensitivity correcting function can be applied, a solid image pickup element protective near infrared ray absorbing filter and a low pass filter using this glass, and a solid image pickup element using these filters. CONSTITUTION:In near infrared ray absorbing glass which is mainly composed of P2O5 and contains CuO, the near infrared ray absorbing glass has the respective U and Th contents not more than 5ppb as well as not more than 20ppb. In a solid image pickup element protective filter 13 composed of this near infrared ray absorbing glass, diffration gratings 14 are formed at least on one surface of a board, and the board is a solid image pickup element protective low pass filter 13 composed of the near infrared ray absorbing glass. In a sold image pickup element 12 having a protective light transmissive member, the protective light transmissive member is the solid image pickup element 12 being a protective filter or a protective low pass filter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a near-infrared absorbing glass useful as a light-transmitting material for protecting a solid-state image pickup device used in a video camera or the like, and more particularly to reducing soft error of the solid-state image pickup device. The present invention relates to a near-infrared absorbing glass effective for. Furthermore, the present invention relates to a protection filter and a protection low-pass filter for a solid-state image sensor using this near-infrared absorbing glass, and a solid-state image sensor using these filters.

[0002]

2. Description of the Related Art As shown in FIG. 1, an optical system of a color VTR camera includes a lens system 1 for forming an image, crystal plates 2 and 3 acting as a low pass filter, and a near infrared absorption filter having a sensitivity correcting action. It is composed of a device 5 and a solid-state image sensor 6 in which 4 are bonded together. In the solid-state image pickup device 6, a CCD chip 7 having a three-color mosaic filter formed on its light-receiving surface is set in an alumina ceramic package 8, and a cover glass 9 as a protective light transmitting member is adhered thereon with an epoxy resin or the like. It is structured. The sensitivity region of CCD extends from the visible light region to the near infrared region. Therefore, it is necessary to cut the near-infrared part of the incident light using a near-infrared absorption filter and approximate the sensitivity obtained as a whole to the visual sensitivity to improve the color reproducibility. Therefore, the near-infrared absorption filter is required to have good visible light transmittance and near-infrared light cutting property.

Further, from the viewpoint of reducing the size and weight of the product and reducing the cost, efforts are made to reduce the size of the solid-state image pickup device by increasing the pixel density, the size of the optical system accordingly, and the reduction of the number of lenses by using the aspherical lens. Is constantly being done. One of them is that by adding a sensitivity correction function to the cover glass by using a near infrared absorption glass, the near infrared absorption filter becomes unnecessary. It has been proposed that a quartz plate can be eliminated by forming a diffraction grating to provide a low-pass filter function [JP-A-4-110903].
issue〕.

[0004]

However, when the near-infrared absorbing glass is used as the cover glass for protecting the solid-state image pickup device as described above, there is a problem that the soft error of the solid-state image pickup device increases. Further, in recent years, noises and soft errors due to α rays have become major obstacles to image quality improvement with the advancement of solid-state image pickup devices, and their reduction is strongly desired. Then, the present inventor measured the α-ray emission amount of a commercially available near-infrared absorption filter, and as a result, it reached 0.01 to 0.05 c / sec · cm ^2, and it was found that it cannot be used for such purpose. 1 /
In order to suppress the soft error of the high-density solid-state imaging device that exceeds 500,000 pixels in 2 inches, the α-ray emission amount of the cover glass is usually required to be 0.001 c / sec · cm ² or less. Therefore, a first object of the present invention is to suppress the occurrence of soft errors in the solid-state image sensor even when used as a cover glass for protecting the solid-state image sensor, contribute to the improvement of image quality, and provide a sensitivity correction function. Another object is to provide a near-infrared absorbing glass.

A cover glass for protecting the solid-state image pickup device is sealed in an alumina ceramic package. Therefore, the coefficient of thermal expansion of the alumina ceramic that constitutes the alumina ceramic package (60 to 75 × 10 ⁻⁷ K ⁻¹ )
There is also a problem in that the sealing will be hindered if it is significantly different from. Therefore, a second object of the present invention is to achieve good sealing with the alumina ceramic package, and even when used as a cover glass for protecting the solid-state image sensor, it is possible to suppress the occurrence of soft errors in the solid-state image sensor and improve the image quality. Another object of the present invention is to provide a near-infrared absorbing glass that can contribute to the above, and can also have a sensitivity correction function.

A third object of the present invention is to use the above-mentioned near infrared absorbing glass to suppress the occurrence of soft errors in the solid-state image pickup device, contribute to the improvement of image quality, and have a sensitivity correction function. It is to provide a filter for protecting the solid-state image sensor having the same.

A fourth object of the present invention is to suppress the occurrence of soft error in the solid-state image pickup device by using the near infrared absorbing glass as described above, thereby contributing to the improvement of image quality, and the sensitivity correction function and It is to provide a low-pass filter for protecting a solid-state image sensor having a low-pass filtering function.

A fifth object of the present invention is to reduce the size and weight, reduce the cost, suppress the occurrence of soft errors, and improve the image quality. An object is to provide an image sensor.

[0009]

The present invention is a near-infrared absorbing glass containing P ₂ O ₅ as a main component and containing CuO, in which the contents of U and Th are 5 ppb or less and 20 ppb or less, respectively. The present invention relates to a near infrared absorbing glass.

Further, a preferred embodiment of the near infrared absorbing glass of the present invention is the above near infrared absorbing glass, wherein the weight% is
Indicated by 50 to 85% of P ₂ O ₅ and 4 of Al ₂ O ₃
~ 20%, the total content of both is 63% or more, Cu
O is contained in 0.1 to 10%, and the thermal expansion coefficient is 45 to 7
It relates to a near-infrared absorbing glass which is 5 × 10 ⁻⁷ K ⁻¹ .

The present invention also relates to a filter for protecting a solid-state image pickup device, which is made of the near-infrared absorbing glass of the present invention. Furthermore, the present invention relates to a low-pass filter for protecting a solid-state image pickup device, characterized in that a diffraction grating is formed on at least one surface of a substrate, and the substrate is made of the near-infrared absorbing glass of the present invention.

In addition, the present invention is a solid-state image pickup device comprising a protective light transmitting member, wherein the protective light transmitting member comprises:
The present invention relates to a solid-state image pickup device, which is the protective filter of the present invention or the protective low-pass filter of the present invention. The present invention will be further described below.

The near infrared absorbing glass of the present invention is made of P ₂ O ₅
Is a glass containing CuO as a main component. When CuO is added as a near infrared absorbing component, P ₂ O ₅
The glass containing as a main component is a glass that has a high transmittance of visible light and a good cuttability of near infrared light and is suitable for sensitivity correction. Further, the glass of the present invention has U and Th contents of 5 ppb or less and 20 ppb or less, respectively. Preferably, the U content is 3 ppb or less and the Th content is 10 ppb or less. By setting the contents of U and Th, which are α-ray sources, to 5 ppb and 20 ppb or less, respectively, it is possible to effectively suppress the occurrence of soft errors in the solid-state imaging device and improve the image quality. The content of U and Th in the glass can be reduced by using a high-purity raw material having a low content of U and Th and preventing the incorporation of these elements in the glass manufacturing process. In particular, ZrO ₂
It is desirable not to include a large amount of components such as TiO ₂ and TiO _{2 which} are difficult to separate and purify radioactive elements.

Further, the near infrared absorbing glass of the present invention is
50% to 85% of P ₂ O ₅ and Al ₂ O expressed by weight%
It is preferable that the content of ₃ is 4 to 20%, and the total amount of both is 63% or more. P ₂ O ₅ is an essential component because it has a high visible light transmittance as described above and can obtain a glass suitable for sensitivity correction, which has a good cut-off property for near infrared light.
However, if it exceeds 85%, the viscosity of the glass tends to be too high, volatilization becomes intense, and melting becomes difficult, so the upper limit is 85%, preferably 80%. On the other hand, when P ₂ O ₅ is less than 50%, the coefficient of thermal expansion tends to be too large, so the lower limit is 50%, preferably 55%. Al ₂ O ₃ is a particularly effective component for improving chemical durability. However, if it is less than 4%, the effect is not sufficient, and if it exceeds 20%, the devitrification resistance tends to deteriorate. Therefore, the lower limit is 4%, preferably 7
%, And the upper limit is 20%, preferably 15%.

The content of CuO is 0.1 to 10%, preferably 0.1 to 6%. CuO is effective in cutting near-infrared light, but less than 0.1% is less effective.
If it exceeds 0%, the devitrification resistance and the visible light transmittance tend to deteriorate. Further, the glass of the present invention has a coefficient of thermal expansion of 45 to 75 × 10 ⁻⁷ K ⁻¹ , preferably 45 to 70 × 10.
A range of ^-7 K ^-1 is suitable. Since the coefficient of thermal expansion of alumina ceramic is 60 to 75 × 10 ^-7 K ^-1, it is preferable to have a coefficient of thermal expansion in the above range which is equal to or slightly smaller than that of the alumina ceramic package. It is preferable from the viewpoint that it can be worn.

Further, a preferred embodiment of the near infrared ray absorbing glass of the present invention is such that the content of B ₂ O ₃ is 0, expressed in% by weight.
Is 15%, the content of SiO ₂ is 0 to 25%, the content of one or more of the group consisting of MgO, CaO, SrO, BaO and ZnO is 0 to 25%,
B ₂ O ₃ , SiO ₂ , MgO, CaO, SrO, BaO
And the content of one or more of the group consisting of ZnO and 5 is 5
˜37% and P ₂ O ₅ , Al ₂ O ₃ , B
It is a glass in which the total content of the group consisting of ₂ O ₃ , SiO ₂ , MgO, CaO, SrO, BaO and ZnO is 85% or more.

SiO ₂ and B ₂ O ₃ are effective for improving the devitrification resistance and lowering the coefficient of thermal expansion. But Si
O ₂ becomes less soluble than 25%, B ₂ O ₃ is 15%
If it exceeds, the devitrification resistance tends to be deteriorated. MgO,
CaO, SrO, BaO and ZnO are effective in improving the meltability and the devitrification resistance. However, if the total amount exceeds 25%, the thermal expansion coefficient becomes too large, and it becomes difficult to obtain a desired thermal expansion coefficient. Furthermore, B ₂ O ₃ , SiO ₂ ,
The total content of the components of the group consisting of MgO, CaO, SrO, BaO and ZnO is 5 to 37%, preferably 6 to 30 from the viewpoint of meltability, devitrification resistance, thermal expansion coefficient and permeability.
It is appropriate to set it in the range of%. Also, P ₂ O ₅ , A
l ₂ O ₃ , B ₂ O ₃ , SiO ₂ , MgO, CaO, Sr
For the same reason, the total content of the group consisting of O, BaO and ZnO is 85% or more, preferably 90% or more.

In addition to the above components, the glass of the present invention has a content of 15% or less, preferably 10% or less for the purpose of improving weather resistance, melting property, devitrification resistance and adjusting the coefficient of thermal expansion. , Sb ₂ O ₃ , Nb ₂ O ₅ , PbO, La ₂ O ₃ , alkali metal oxides and the like may be contained.

The raw material for forming the glass having the above composition may be in any form such as an aqueous solution, a carbonate, a nitrate, a hydroxide or an oxide. However, U mixed as an impurity
A raw material containing as little Th and Th as possible is selected. Finally, the content of U is 5 ppb or less and the content of Th is 2
In order to obtain a near infrared absorbing glass of 0 ppb or less, it is preferable to use a raw material having a U content of 3 ppb or less and a Th content of 15 ppb or less.

Next, the solid-state image sensor protection filter of the present invention, the solid-state image sensor protection low-pass filter, and the solid-state image sensor of the present invention using these filters will be described. The solid-state image sensor protection filter of the present invention is composed of the near-infrared absorbing glass of the present invention, and the shape and size thereof are not particularly limited. The shape and size can be appropriately determined according to the solid-state image sensor to be protected. Further, the thickness of the filter can be appropriately determined according to desired optical characteristics in consideration of the absorption characteristics of glass.
The protective filter of the present invention can be obtained by polishing the near-infrared absorbing glass of the present invention into a predetermined shape by a conventional method. Furthermore, the solid-state image sensor 10 of the present invention is
As shown in FIG. 2, a protective light transmitting member is sealed in an alumina package 8 containing a CCD chip 7, and the protective light transmitting member is the protective filter 11 of the present invention. Compared with the conventional optical system of FIG. 1, in the optical system using the protective filter of the present invention, the protective filter has the functions of a cover glass and a near-infrared absorption filter, so that the system can be made smaller and lighter. It is possible.

The low-pass filter for protecting a solid-state image pickup device of the present invention comprises a substrate having a diffraction grating formed on at least one surface thereof, and the substrate comprises the near-infrared absorbing glass of the present invention. The shape and the like of the diffraction grating can be appropriately determined according to desired characteristics. It should be noted that the diffraction grating can obtain a low-pass filtering function if it is provided on one surface of the substrate, but it also has an advantage that molding can be facilitated by distributing vertical and horizontal irregularities on both sides. The low-pass filter of the present invention can be prepared by softening the lump of the near-infrared absorbing glass of the present invention by a conventional method and pressing it with a mold having a surface shape of a diffraction grating. That is, a diffraction grating is press-molded on one or both surfaces of a glass plate polished into a predetermined shape by a molding technique. The protective low-pass filter of the present invention can also be obtained by forming a diffraction grating using a photolithography technique. Further, as shown in FIG. 3, the solid-state imaging device 12 of the present invention comprises an alumina package 8 containing a CCD chip 7 and a protective light-transmitting member sealed to the alumina package 8. It is the low pass filter 13 for protection of the invention. A diffraction grating 14 is formed on the surface of the protective low-pass filter 13. Compared with the conventional optical system of FIG. 1, in the optical system using the protective filter of the present invention, the protective filter has the functions of a cover glass, a near-infrared absorption filter, and a low-pass filter, so the system is small and lightweight. Is possible. FIG. 4 shows an example of the diffraction grating of the low-pass filter. However, the shape is not limited to this, and can be appropriately determined depending on the desired characteristics of the low-pass filter.

The solid-state image pickup device of the present invention can be manufactured by sealing the filter of the present invention to an alumina ceramic package containing a CCD chip with an adhesive such as an epoxy resin. In the solid-state imaging device of the present invention, there are no particular restrictions on the CCD chip, the adhesive, the alumina ceramic package, and the like.

The near-infrared absorbing glass of the present invention is used in addition to the above-mentioned use as a filter for protecting a solid-state image pickup device, for example, by laminating it on a normal cover glass and sealing the near-infrared absorbing glass. Can be applied to an ordinary cover glass. For example, as shown in FIG. 5, a low-pass filter 16 (17 is a diffraction grating) made of the near-infrared absorbing glass of the present invention can be provided inside the cover glass 9 to provide the solid-state imaging device 15. Although an example of the low-pass filter is shown in FIG. 5, a near-infrared absorption filter having no diffraction grating may be used. Further, as shown in FIG. 6, a low-pass filter 16 (17 is a diffraction grating) made of the near-infrared absorbing glass of the present invention may be provided on the front surface of the CCD chip 7 to provide the solid-state imaging device 18. Although FIG. 6 shows an example of the low-pass filter, a near-infrared absorption filter having no diffraction grating may be used.

[0024]

EXAMPLES The present invention will now be described in more detail with reference to examples. Example 1 No. in Table 1 Raw material batches were prepared using various high-purity raw materials so that the composition became 1. The glass composition in Table 1 is expressed in weight percent. This raw material batch 12kg
Was melt-purified in an electric furnace at 1330 ° C. using a platinum crucible having a capacity of 5 liters. Then, it was cast into an iron metal frame and subjected to predetermined annealing to obtain a glass block. The transmittance of this glass at a thickness of 2 mm is shown in FIG. Table 1 shows the coefficient of thermal expansion of the obtained glass, which is a value measured by a TMA analyzer. The coefficient of thermal expansion of this glass is 67 × 10
^{It is -7} K ^-1 , and it can be seen that it has a thermal expansion coefficient suitable for sealing with the alumina ceramic. Also, the amount of α-ray emission measured by Sumika Analytical Center's α-ray measurement device LACS and U and Th measured by Yokogawa Electric's ICP-MASS.
The content is shown in Table 2.

Next, using the obtained glass, a filter having a predetermined shape (15.5 × 17.7 × 2.0 mm) also serving as a cover glass was prepared. This filter was sealed in an alumina ceramic package containing a CCD chip with an effective pixel count of 580,000 pixels using epoxy resin to fabricate the solid-state image sensor of the present invention shown in FIG. The presence or absence of soft error was investigated. For comparison, the same experiment was performed using a commercially available near infrared absorption filter and glasses (A) and (B). . Glass (A) was fluorophosphate glass and glass (B) was phosphate glass. The thermal expansion coefficients of these glasses are shown in Table 1, respectively. Glass (A) has a large coefficient of thermal expansion of 158 × 10 ⁻⁷ K ^−1, and cracks occurred during sealing with the alumina ceramic package, and a solid-state image sensor could not be obtained. On the other hand, the glass (B) could be sealed with the alumina ceramic package without cracking. Therefore, with respect to the obtained solid-state imaging device, the presence or absence of a soft error was investigated as in the above. The results are shown in Table 2. From the results of Table 2, the solid-state imaging device using the glass of Example 1 had few soft errors, whereas the solid-state imaging device using comparative glass (B) had remarkably many soft errors. For comparison, Table 2 also shows the α-ray emission amount and U and Th contents of the comparative glass (B).

Example 2 No. 1 in Table 1 Raw material batches were prepared using various high-purity raw materials so as to have the composition of 2. This raw material batch 16k
g was roughly melted with a 7 liter capacity SiO ₂ crucible to prepare a cullet, and 12 kg of the cullet was used to melt-refin in a 5 liter capacity crucible made of platinum in an electric furnace at 1230 ° C. Then, it was cast into an iron metal frame and subjected to predetermined annealing to obtain a glass block. The transmittance of this 2 mm thick glass is shown in FIG. Table 1 shows the thermal expansion coefficient, which is the value measured by the TMA analyzer. It can be seen that this glass has a coefficient of thermal expansion suitable for sealing with the alumina ceramic. Table 2 shows the α-ray emission amount and the U and Th analysis values.

A non-defective portion was selected from this glass block, and a preform polished into a desired shape (15.5 × 17.7 × 2.0 mm) was produced. Then, a well-shaped diffraction grating was formed on one surface of the preform by a conventional molding technique using a mold made of quartz glass having a predetermined grating shape and a sputtered carbon film. 13.5 x 14.5 mm width with diffraction grating, thickness 2.0 mm
To obtain a near infrared absorption filter. This diffraction grating is shown in FIG.
It has a trapezoidal cross-sectional shape as shown in Fig.
The pitch was 5.2 μm. Next, the near-infrared absorption filter is sealed in an alumina ceramic package containing a CCD chip having 580,000 effective pixels so that the diffraction grating surface faces inside, and the present invention shown in FIG. The solid-state image sensor of was produced. The presence or absence of soft error was investigated for the obtained solid-state imaging device. The results are shown in Table 2. This solid-state image sensor had few soft errors like the solid-state image sensor of Example 1.

On the other hand, in order to evaluate whether or not the diffraction grating has a function of a low-pass filter, a case where a pasting element of a conventional quartz plate and a near-infrared absorption filter and a solid-state image pickup element are combined, and The image quality of video images was compared when a solid-state image sensor in which a near-infrared absorption filter having a diffraction grating was sealed as a cover glass was used.
As a result, it was confirmed that both have almost the same image quality, and that the filter of this embodiment has a function as a low-pass filter and a sensitivity correction function.

Example 3 No. 1 in Table 1 For the glasses having compositions of 3 to 7, U and Th were used in the same manner as in Example 1 except that high-purity raw materials were used.
The near-infrared absorbing glass having a content of 5 ppb or less and a content of 20 ppb or less was prepared. Table 1 shows the thermal expansion coefficient of the obtained glass. Furthermore, using the obtained glass,
A low-pass filter having a near-infrared absorption filter and a diffraction grating was prepared in the same manner as in Examples 1 and 2, and a solid-state imaging device was prepared using these near-infrared absorption filter and low-pass filter. As a result of investigating the presence or absence of soft errors in the obtained solid-state image pickup devices, there were few soft errors in any of the solid-state image pickup devices.
It was also confirmed that the low-pass filter having the diffraction grating has a function as a low-pass filter.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

As described above, since the near-infrared absorbing glass of the present invention has a remarkably low content of U and Th, it is less likely to cause a soft error even if it is placed in the vicinity of the CCD chip, and the cover is covered. It is possible to provide a protective filter and a protective low-pass filter that combine the functions of glass, a near-infrared absorption filter, and a low-pass filter. Furthermore, the solid-state imaging device using these filters has few soft errors, can be made small and lightweight, and can be expected to reduce costs.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of an optical system of a conventional VTR camera.

FIG. 2 is an explanatory diagram showing a configuration of an optical system of a VTR camera using the protective filter of the present invention.

FIG. 3 is a graph showing V using the low pass filter for protection of the present invention.
It is explanatory drawing which shows the structure of the optical system of TR camera.

FIG. 4 is a local bird's-eye view of an example of a diffraction grating formed on the surface of the protective low-pass filter of the present invention.

FIG. 5 is an explanatory view showing a solid-state imaging device using the low-pass filter of the present invention laminated on a cover glass.

FIG. 6 is an explanatory diagram showing a solid-state image sensor in which the low-pass filter of the present invention is provided on the front surface of a CCD chip.

FIG. 7 shows a spectral transmittance curve of the near-infrared absorbing glass of the present invention.

[Explanation of symbols]

 1 Lens system 2, 3 Quartz plate 4 Near infrared absorption filter 6, 10, 12, 15, 18 Solid-state image sensor 7 CCD chip 8 Alumina ceramic package 9 Cover glass 11 Protective filter 13 Protective low-pass filter 14, 17 Diffraction grating 16 low pass filter

Claims (7)

[Claims] 1. A near infrared absorption glass containing P ₂ O ₅ as a main component and containing CuO, wherein the contents of U and Th are 5 ppb or less and 20 ppb or less, respectively. Glass. 2. The P ₂ O ₅ content in terms of weight% is 50 to 85.
% And Al ₂ O ₃ of 4 to 20%, and the total amount of both is 6
The near-infrared absorbing glass according to claim ^1, which is 3% or more, contains 0.1 to 10% of CuO, and has a thermal expansion coefficient of 45 to 75 × 10 ^-7 K ^-1 . 3. Expressed in% by weight, the content of B ₂ O ₃ is 0 to 15%, the content of SiO ₂ is 0 to 25%, and MgO, CaO, SrO, BaO and ZnO are used. The content of one or more of the group consisting of 0 to 25%,
B ₂ O ₃ , SiO ₂ , MgO, CaO, SrO, BaO
And the content of one or more of the group consisting of ZnO and 5 is 5
˜37% and P ₂ O ₅ , Al ₂ O ₃ , B
The near-infrared absorbing glass according to claim 1 or 2, wherein the total content of the group consisting of ₂ O ₃ , SiO ₂ , MgO, CaO, SrO, BaO and ZnO is 85% or more. 4. A filter for protecting a solid-state image sensor, comprising the near-infrared absorbing glass according to any one of claims 1 to 3. 5. A diffraction grating is formed on at least one surface of a substrate, and the substrate is any one of claims 1 to 3.
A low-pass filter for protecting a solid-state imaging device, which is made of the near-infrared absorbing glass according to the item. 6. A solid-state image sensor including a protective light-transmitting member, wherein the protective light-transmitting member is the protective filter according to claim 4. 7. A solid-state image sensor including a protective light-transmitting member, wherein the protective light-transmitting member is the low-pass filter according to claim 5.