JPH01320236A - Cover glass for solid-state image pickup element - Google Patents

Abstract

PURPOSE:To provide cover glass having a low refractive index, a high Abbe's number, a high UV transmissivity and a prescribed coefft. of linear expansion and giving a solid-state image pickup element not generating noise due to glass by incorporating SiO2, B2O3, Al2O3 and Fe2O3 in a specified weight ratio. CONSTITUTION:Glass contg., by weight, 50-70% SiO2, 5-20% B2O3, 0.2-16% Al2O3 and 50-200ppm Fe2O3 and having <=1.52 refractive index, >=55 Abbe's number, 35-65X10<-7>/ deg.C average coefft. of linear expansion and >=30% transmissivity at 300nm wavelength in case of 2mm thickness is produced and used as cover glass protecting a solid-state image pickup element for a video camera, etc. A solid-state image pickup element using the cover glass can be suppress the lowering of sensitivity due to the increase of image elements, so the glass is especially suitable for use as cover glass for a solid-state image pickup element having increased image elements.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a cover glass for protecting a solid-state image sensor used in a video camera or the like.

[Conventional technology]

In recent years, CCD-type and MOS-type solid-state image sensors have been increasingly replacing image pickup tubes as image sensors due to their characteristics such as small size, light weight, and low extinguishing power.

In particular, the dependence on solid-state image sensors is increasing as they are installed in camera-integrated VTRs.

A solid-state image sensor has an LSI chip, which is a light-receiving and light-receiving device, housed in an alumina ceramic package, and a color separation mosaic filter is layered on the light-receiving surface and wire bonded, and a cover glass is placed on top using epoxy resin or glass frit. It has a sealed structure. The cover glass used here is made of an optically homogeneous material with no internal defects, in order to not only connect the υL8ILSI chip to the alumina ceramic package by hermetically sealing it, but also to efficiently introduce optical signals to the light receiving surface. characteristics are required.

Conventionally, this type of cover glass has been made of polished soda lime-based white plate glass, or alkali-free barium or silicate glass.

[HIjl that the invention attempts to solve]

Solid-state imaging device chips are gradually increasing the number of pixels due to the need for higher resolution and density, and the optical system size is already 2.
A 3-inch model with an effective pixel count of 380,000 has been commercialized. If the number of pixels is increased without changing the chip size, the amount of light incident on each pixel υ will decrease, leading to a decrease in sensitivity.

On the other hand, the signal voltage 1- appearing at the output terminal of the solid-state image sensor
It is relatively large at 1.150 to 500771v. For this reason, in video cameras and the like, the S/N ratio of the entire camera is highly dependent on the performance of the solid-state image sensor. Therefore, if the noise generated in the solid-state image sensor can be reduced, by increasing the gain of the amplifier after photoelectric conversion, etc. Miniaturization without loss of sensitivity? gJ pixelization can be realized.

The inventors have discovered that the noise generated in a solid-state image pickup device includes not only noise caused by the device itself such as dark current bugs, but also noise caused by the optical customization of the cover glass. In other words, as a result of investigating the glass used in the coffins, it was found that in the unlikely event that glass that does not absorb ultraviolet radiation was used as the cover glass,
It has been found that the noise of the solid-state sensor 1j element is reduced.

Although the mechanism is not clear, when glass absorbs ultraviolet rays, it emits fluorescence having a peak at 400 to 500 nm, as shown in FIG. 2, and it is thought that this fluorescence becomes noise during dark signals. Further, since this fluorescent light has a large decay time constant, it becomes an afterglow and enters the solid-state image sensor, which is undesirable.

Conventionally used soda lime glass and barium silicate glass tend to absorb ultraviolet rays and generate noise as described above, making it difficult to use them as cover glasses for solid-state imaging devices with a high number of pixels.

In addition, if the light incident on the solid-state image sensor is refracted and dispersed by the cover glass, the image on the light-receiving surface will become unclear, so the cover glass of the solid-state image sensor should be made of glass with the lowest possible refractive index and small dispersion. It's so cool.

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a cover glass for a solid-state image sensor that does not generate noise in the solid-state image sensor due to glass.

Means and operation for solving problem C8] The present invention provides at least a weight percentage of 5I0250-7.
5%, B2O55-20%, A-ez03 0.2-1
Glass containing 6% rFa21s 50 to 200 ppm, with a refractive index (nd) of 1.52 or less, an Atsbe number (νd) of 55 or more, and an average linear expansion coefficient of 35 to 6.
Within the range of 5 x 10"/'C and wavelength 300
Transmittance at nm is 2I thick! The present invention is a cover glass for a solid-state image sensor, which is characterized by a film thickness of 30% or more.

In the optical properties of glass, dispersion refers to the variation in the refractive index depending on the wavelength of light, and this is closely related to the absorption of light caused by the transition of the outer shell electrons of single-bonded oxygen in the glass to an excited state. is related to. As the absorption in the ultraviolet region increases, the dispersion tends to increase as well.Glass with high ultraviolet transmittance is suitable for use as a cover glass for solid-state imaging devices from the viewpoints of suppressing fluorescence generation and controlling dispersion. In other words, the glass has a wall thickness of 2 dragons, and the wavelength is 300.
If the transmittance in nm is less than 30%, it is undesirable because fluorescence in the glass will be noticeable due to external incident light.

Regarding the dispersion, it is desirable that the Abbe number (vd) is 55 or more. When the Abbe number is less than 55, color separation occurs in the cover glass due to the difference in refractive index depending on the wavelength of light, which causes a decrease in resolution.

Further, in glass having a high refractive index, the reflection loss of light caused by the difference in refractive index with the atmosphere becomes large, and the amount of light incident on the light receiving element is attenuated, so the lower the refractive index is, the better. Glasses having the above basic composition and having a refractive index (7Jd) exceeding 1.52 are not preferred because their absorption in the ultraviolet region becomes high.

The average coefficient of linear expansion needs to be within the range of 35 to 65 x 10-'/C in order to maintain good sealing with the alumina ceramic package.

Next, the reason for limiting the basic composition of the glass to the above range will be fully explained.

If SiO2 is less than 50%, the average coefficient of linear expansion becomes large, causing problems in hermetic sealing with the alumina ceramic package, and if it exceeds 75%, the meltability of the glass deteriorates.

B20. If it is less than 5%, the melting properties will be poor, and if it exceeds 20%, the chemical durability will deteriorate, causing weathering on the surface during long-term use and making the image unclear. A no 20
If 3 is less than 10.5%, the glass will undergo phase separation, making it difficult to form, and if it exceeds 16%, striae will occur and a homogeneous glass will not be obtained.

For glasses containing the above-mentioned constituents, “201
If it exceeds 200 ppm, the ultraviolet transmittance decreases, the generation of fluorescence becomes noticeable and the generation of υ noise increases. Generally F
It is known that the lower the e2O content, the better the ultraviolet transmittance. However, it is extremely difficult to completely remove impurity components that have a large effect on the properties of glass even in trace amounts. Therefore, Fe2O3 is 50 pp
In order to obtain a glass with a high purity of less than m, it is not preferable because it causes a significant increase in the cost of raw materials and equipment.

〔Example〕

Examples of the present invention will be described below. In the following, we will show the composition and measurement results of each characteristic of an example of the cover glass for a solid-state image sensor according to the present invention and a conventional example made of alkali-free barium silicate glass.

The glass composition in the table is Fl! Weight % except 203, Fe
2O3 is given in ppm by weight. Note that R20 represents an alkali metal oxide, and RO represents an alkaline earth metal oxide. In addition, the ultraviolet transmittance is 1.011 nm and 2.
．． The spectral transmittance at a wavelength of 300 rlm of a glass plate polished to 0 m was measured, and the fluorescence intensity was measured using a light spectrophotometer.
The relative value of the amount of fluorescence generated when irradiated with ultraviolet light with a wavelength of 360 nm is displayed. Water resistance was expressed as a weight loss rate measured by the method for measuring chemical durability of optical glass specified by the Japan Optical Glass Industry Association.

Furthermore, as a measurement when actually used as a cover glass for a solid-state image sensor, each piece of glass polished to a wall thickness of 1 dragon was sealed on the front surface of a COD chip with an effective pixel count of 380,000, and the 8/N ratio of the solid-state image sensor was measured. We investigated changes in In the table, the width of modification of 8/N ratio when using conventional glass as standard is d.
Indicated by B.

As is clear from the table below and the spectral transmittance curve shown in Figure 1, the example glass of the present invention has lower ultraviolet transmittance than the conventional glass, and the fluorescence generation after ultraviolet irradiation is halved.
It is as small as ~/1o. Therefore, unnecessary signals caused by fluorescence of the cover glass can be reduced. In addition, the glass of this embodiment has a low refractive index and low dispersion, so that loss of light incident on the light receiving surface and color separation, which are problems especially in solid-state image sensors with a large number of pixels, are hardly a problem. Although such individual glass characteristics cannot be said to have a large influence on the solid-state image sensor, it is thought that their mutual effects are effective in reducing noise and improving the sensitivity of the solid-state image sensor.

As a result, the solid-state image sensor using the glass of this example was 8/8
The N ratio was improved by 3 to 8 dB compared to the conventional glass case.

In addition, in the glass of this example, the content of alkaline components is kept to the minimum necessary in consideration of the use of epoxy resin for sealing with the A/I/Mina ceramic package. This prevents the alkali components in the glass from deteriorating the epoxy resin and improves the chemical durability of the glass itself, making it possible to maintain the above-mentioned excellent properties for a long period of time.

〔Effect of the invention〕

As explained above, the cover glass for a solid-state image pickup device of the present invention has (1) high ultraviolet transmittance and less generation of fluorescence due to externally incident light;

■Low refractive index, so light reflection loss is small.

■Low dispersion, so color separation is less likely to occur.

It has the following characteristics.

For this reason, solid mf using the cover glass according to the present invention
The ffi element has effects such as generating less noise due to the cover glass and suppressing a decrease in sensitivity due to an increase in the number of pixels.

Therefore, the cover glass for a solid-state image sensor of the present invention is
It is extremely suitable as a cover glass for a solid-state imaging device with a high pixel count.

[Brief explanation of the drawing]

Fig. 1 is a curve diagram showing the spectral transmission characteristics in the ultraviolet region of the example glass of the present invention and the conventional glass, and Fig. 2 is a curve diagram showing the relationship between the ultraviolet rays irradiated to the conventional glass and the generated fluorescence. is. Figure 1 Wavelength (nm) 2nd blade wavelength <hm)

Claims (1)

[Claims] At least in weight percentage, SiO_2 50-70%B
_2O_3 5-20%, Al_2O_3 0.2-1
6%, Fe_2O_3 50 to 200 ppm, the refractive index (nd) is 1.52 or less, the Abbe number (νd) is 55 or more, and the average linear expansion coefficient is 35 to 65.
×10^-^7/℃ and wavelength 300n
A cover glass for a solid-state image sensor, characterized in that the transmittance at m is 30% or more at a wall thickness of 2 mm.