JPS58182267A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To obtain a device of high photosensitivity wherefrom color image bright even by a room light is obtained by a method wherein a fluorescent film which is transparent in the range of specific wavelengths, and emits a light in the range of said specific wavelengths by absorbing the light in the range of wavelengths different therefrom is provided on a photosensor of the picture element part of a solid-state image pickup element. CONSTITUTION:The crystalline fluorescent film 12 constituted of sulfides, silicates, phosphates, etc. is formed on the photo diode B corresponded to e.g. a blue filter on the solid-state image pickup element wherein the picture element part 2 consisting of a drive circuit 3, a transfer part, and a photo diode part are previously formed. Now, when Ag doped ZnS-CdS is used as the fluorescent film, wavelengths of emitting fluorescence can be controlled as the curve shown in the figure. When the density of CdS in the figure is 40%, the wavelength of emission becomes 0.55mum; when a ZnSe-Zn1-xCdxTe film is used as the photo diode, the wavelength can be made to coincide with the maximum range of wavelength 0.55mum, and the sensitivity becomes twice or more compared with the case when the blue light is used as it is. Besides, the same treatment is applied also to green and red.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solid-state imaging device, and in particular provides a color solid-state imaging device that can improve photosensitivity and obtain vivid color images even in indoor light.

For example, in general, color solid-state imaging devices are shown in Figure 1 (,).
As shown in the top view and the x-x' cross-sectional view in 0)), in the center of the base substrate (hereinafter referred to as the substrate) 1 is a photodiode that senses an optical image, and an electrical signal converted by the photodiode. A pixel section 2 consisting of a charge transfer element COD or the like is provided, and around this pixel section 2 is a drive section 3 such as a shift register or COD that drives the pixel section.
is provided. Note that here, 4 is a metal wiring that connects between the driving parts, and 6 is an electrode that connects to an external lead (
pad), 6 is the Zetsun membrane.

On the other hand, in order to manufacture a single-plate color solid-state image sensor, it is necessary to further mount a mosaic or striped color filter 7 on the front surface of the photodiode. In FIGS. 1(a) and 1(b), a case is shown in which a color filter layer 9 is formed on a glass plate 8 in advance and is adhered via an adhesive 10. It may be formed directly.

However, the spectral transmittance of these color filters is as shown in Figure 2, for example in the case of a three-color system, and the light that actually reaches the photodiode and is used as photocurrent is only in the shaded area in Figure 2. It is. In other words, when converting to color, the sensitivity inevitably deteriorates significantly compared to when converting to black and white.

Therefore, in order to improve the optical sensitivity, it is necessary to improve the sensitivity of the photodiode, increase the transfer rate, or reduce noise in the transfer section and drive section to increase the amplification factor. However, there is a limit to reducing the noise in the transfer section and the drive section as long as the current semiconductor device manufacturing process (solid-state image sensor manufacturing process) is used. On the other hand, methods for improving the blue sensitivity of a photodiode include reducing the diffusion depth of the silicon photodiode, and instead of using a silicon photodiode, a photoconductive film such as that shown in FIG.
Zn1. , -ICd! Methods using To (= ubicon film), amorphous silicon, etc. have been proposed.

However, even if these methods are used, the spectral sensitivity shown in Figure 3 is currently obtained, and the blue sensitivity (400 to 480 n
m area), the limit was 40 to 60%. In other words, the photocurrent that can be extracted as an actual color signal has a very small blue component, resulting in a decrease in overall sensitivity.

In view of the above drawbacks, the present invention improves the photosensitivity of a color solid-state image sensor by increasing the photocurrent of the blue component and improving the overall color signal balance. That is, in the present invention, for example, the light that has passed through a blue filter is focused on the sensitive long wavelength side of the photodiode using a thin film made of a fluorescent material.
The present invention provides a solid-state imaging device characterized by increasing the blue light current and improving the overall sensitivity of the imaging device.

Hereinafter, the present invention will be described in detail using Examples. As shown in FIG. For example, a crystalline phosphor film 12 made of sulfide, silicate, phosphate, etc. is formed on a photodiode (indicated by B in the figure) corresponding to a blue filter. In addition, the fourth
In the figure, the same parts as in FIG. 1 are given the same numbers.

l is light. For example, if a silver-doped phosphor such as zinc sulfide-cadmium sulfide is used as the phosphor film, the fluorescence emission wavelength can be controlled as shown in FIG. In the figure, if the CdS concentration is 40%, the emission wavelength is 0.56 μm, and if a New Bicon film is used as a photodiode, the wavelength range (O, SS μm) where the New Bicon film has the highest sensitivity
It is possible to improve the sensitivity by about twice as much as when using blue light. Furthermore, if the photodiode is a silicon diode, the amount will be approximately three times larger. Note that at this time, the light that could not be converted remains as it is.
A mosaic color filter can be directly formed on the 0th order, which passes through the fluorescent film and reaches the photodiode, so there is no waste, or it can be glued as shown in Figure 4 to create a highly sensitive color solid-state image sensor. shall be.

As described above, with the configuration of the present invention, the light that has passed through the color filter can be converted into a wavelength range to which the photodiode is sensitive, so that the sensitivity can be greatly improved.

In addition, in the above embodiment, the case was described in which the light passing through the blue filter is converted to a wavelength in the green region to improve sensitivity, but in the case of a photodiode or silicon, it is more likely that the blue light is converted to a wavelength in the blue region. It is clear that it is more efficient to do so. It is also clear that even when used as a black and white device, sensitivity can be improved by forming a phosphor film over the entire surface. For example, if the photodiode is made of silicon and cas (9o%) is used as the phosphor, light in the visible light range can be converted to light with a wavelength of 600 nm, and the sensitivity can be greatly improved.

[Brief explanation of the drawing]

Figure 1 (,) is a top view of a conventional color solid-state image sensor.
Figure 2 is a diagram showing the spectral characteristics of the color filter used for colorization.
Figure 3 is a diagram showing the spectral sensitivity characteristics of various photosensors, Figure 4
The figure is a cross-sectional structural diagram of a color solid-state imaging device according to an embodiment of the present invention, and FIG. 6 is a diagram showing the relationship between the CdS concentration of CdS doped with silver and the conversion wavelength. 2... Pixel section, 70... Color filter,
8...Glass plate, 11...Photoconductive film,
12... Fluorescent film. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
figure? 3 Fig. 2 Deputy length (nrn) Fig. 3 Loss of length Cnrn) @ 5 Fig. dS, r, s + cas xfoo (%J

Claims (1)

[Claims] A phosphor film that is transparent in a specific wavelength range and absorbs light in another wavelength range different from the specific wavelength range and emits light in the specific wavelength range, on the photo sensor of the pixel part of the solid-state image sensor. A solid-state imaging device characterized by forming: