JPS63306657A - Solid-state image sensing device - Google Patents

Abstract

PURPOSE:To reduce harmful high range components of space frequency components of a solid state image sensing device by a method wherein a lens array is provided on the light detecting surface side of an image sensor and a phase lattice unit is provided between the lens array and an image sensing object and adjacent two parts among the image sensor, the lens array and the phase lattice unit are unified. CONSTITUTION:A lens array 2 composed of a group of minute lenses 2A which condense the lights from an image sensing object and apply the condensed lights to respective photodetectors 5 constituting an image sensor 1 is provided on the light detecting surface side of the image sensor 1 constituted by the photodetectors 5 arranged in a plane and a phase lattice unit 3 is provided between the lens array 2 and the image sensing object. At least two adjacent parts among the image sensor 1, the lens array 2 and the phase lattice unit 3 are unified. With this constitution, the light which is applied between the photodetectors of the image sensor and is rot utilized as an image light in the conventional image sensing device can be condensed and applied to the photodetector by the minute lense so that the utilization efficiency of the incident light can be improved. Moreover, as the lights are divided into a plurality of light beams, high range components of space frequency components on the image sensing surface can be reduced.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a solid-state imaging device.

[Conventional technology]

In recent years, with advances in semiconductor integration technology, solid-state image sensors are increasingly being used in place of image pickup tubes.

However, the ratio of transistors, electrodes, and wiring on the surface of the image sensor is high, and therefore the ratio of the area of the photoelectric conversion section is usually as low as about 30%.

That is, there was a drawback that the efficiency of utilizing incident light was poor.

On the other hand, the spatial frequency response of a solid-state image sensor is determined by the array pitch of the elements, so if an image with a higher spatial layer wavenumber is formed on the imaging surface, after photoelectric conversion by the image sensor, The drawback was that unnecessary moiré appeared in the image enhancement.

Conventionally, in order to suppress this moire, the birefringence of the crystal plate is used to form double images whose positions are slightly shifted on the imaging plane, thereby suppressing the high-frequency components of the spatial frequency of the image itself. It was getting worse.

[The key point that the invention is trying to solve]

As mentioned above, conventional solid-state imaging devices have a problem in that the efficiency of using incident light in the sensor element is low, and the crystal plate used to prevent moiré is expensive, making the entire device expensive. Ta.

[Means for solving problems]

A lens array consisting of a group of microlenses that converges subject light onto each of the photodetecting elements is arranged on the light-receiving surface side of an image sensor in which photodetecting elements are arranged in a planar manner. A phase grating body was placed between them, and at least λ of the image pickup element, lens array, and phase grating body that were in contact with each other with a gap were integrated.

[For production]

According to the above configuration, light that was conventionally irradiated between the photodetecting elements of an image sensor and not used as image light is now condensed and incident on the photodetecting element by each microlens of the lens array. Light usage efficiency improves by approximately 30%. In addition, the phase grating arranged in front of the lens array divides the light beam from the subject toward the photodetector element into a plurality of light beams that differ slightly in the direction of travel, thereby increasing the spatial frequency of the image on the imaging surface. The ingredients are reduced and unnecessary moiré can be suppressed.

Furthermore, since at least λ of the image sensor, lens array, and phase grating are integrally manufactured, the number of parts can be reduced and the positioning accuracy can be improved.

〔Example〕

The present invention will be described in detail below based on embodiments shown in the drawings.

FIG. 1 shows a cross section of the main parts of an imaging device, where / is an image sensor, C is a lens array, and 3 is a phase grating.

The image sensor is constructed by arranging a large number of photodetecting elements j at intervals on a plane in a line or matrix on a semiconductor substrate. The lens array 2 and the phase grating 3 are integrally formed within the thickness of a parallel plane transparent substrate 7 made of glass, synthetic resin, etc., which is placed at a distance m+ from the surface of the image sensor, as described below. It is set in.

That is, the lens array 2 is constructed by arranging a large number of microlenses 2A in a plane at the same pitch as the photodetecting elements, and as shown in FIG. 2, each lens has a hemispherical shape. One flat lens surface coincides with the surface 7A of the substrate 7 facing the photodetecting element, and the spherical lens surface faces into the matrix. It is formed of a refractive index distribution region in which the refractive index gradually increases in the radial direction from the outer periphery toward the center, and each equirefractive index line forms a concentric circle in the cross section, as shown by the broken line in the figure.

The lens array λ consisting of a large number of independent refractive index distribution regions as described above is obtained by, for example, covering one milliliter of a flat glass plate with an ion permeation prevention mask material, and providing a narrow aperture on this mask material at a predetermined lens pitch. It can be produced by diffusing monovalent cations such as T1, which have a large effect of increasing the refractive index of the substrate glass, through this opening by exchanging with ions in the glass.

The phase grating 3 is provided near the object-side surface 7B of the transparent substrate 7, and is made up of a refractive index distribution region like the lens 2A, and its thickness changes periodically in a direction parallel to the substrate surface.

The operation of the imaging device having the above configuration will be explained below.

FIG. 3 shows how the optical path length changes at each position of the phase grating 3, and the optical path length fluctuation of the incident light beam, that is, the distribution of the phase depth of the phase grating 3 has a period P.

A sinusoidal variation expressed by amplitude Δl is obtained. The phase grating 3 divides the incident light beam into diffracted lights having a diffraction angle corresponding to the pitch of the phase grating 3.

By making the optical path length change sinusoidal and appropriately setting the amplitude Δl, most of the power of the diffracted light can be effectively concentrated in the 0th and 10th order diffracted lights.

Figure ≠ is a diagram showing the state of diffraction by the phase grating 3, in which the phase grating 30 cycles 1 the thickness of the substrate 7 are 1 and the refractive index n
is appropriately selected so that the image of the subject is shifted by a distance Δ smaller than the arrangement pitch of the lenses 2A on the surface of the lens array λ.

The point spread function (PSF) of the imaging lens system is f (, rl
If the phase grating 3 separates the diffraction images into ±/order diffraction images shifted by a distance Δ, then the PSF at this time is...
...(1) In the formula, * represents convolution.

Therefore, the spatial frequency response (MTF) of the imaging lens system including the phase grating 3 is given by the 7-Lier transform of equation (1), and is expressed as follows.

F(ν) cos (△ν)...
(2) F(ν) is the 7-lier transform of f(to), that is, the MTF of the original imaging lens system. It can be seen that the MTF is reduced by Δν). At this point, by appropriately selecting the positional shift amount Δ, it is possible to reduce the high frequency components of one image and suppress unnecessary moiré (the same applies to the two-dimensional case).

The object light that has passed through the phase grating 3 is incident on each of the two lenses forming the lens array as shown in Figure 3, and the incident light t is directed closer to the center axis of the lens with the larger refractive index due to the refractive index distribution of the two lenses. The photodetector element on the image sensor is bent!
The light is focused on the light receiving surface.

Therefore, by closely arranging the lenses JA..., the light that conventionally irradiated the non-detection area between the photodetector and the photodetector j will be received by the photodetector j. The increased amount improves detection sensitivity compared to conventional methods.

Although the present invention has been described above based on the embodiments shown in the drawings, it goes without saying that the invention can be modified in ways other than those shown in the drawings.

For example, instead of forming the lens array 2 or the phase grating 3 as a refractive index distribution region in a flat base material, it may be formed as a protruding small spherical surface or as a sinusoidal uneven surface. In addition, a transparent plate material is interposed between the light receiving surface of the image pickup element l and the lens array 2 instead of an empty space mA, and the image pickup element l and the lens array substrate 7 are integrally bonded via the transparent plate. You can also do that. Further, the direction and period of the phase grating 3 are appropriately determined according to the value of the frequency component (two-dimensional spatial frequency component) to be reduced, and a plurality of phase gratings may be combined.

Furthermore, to simplify the explanation, only the diffraction order is described as 2/2, but even when high-order diffracted lights overlap, the same effect can be obtained by appropriately setting the period and the intensity of each diffracted light. be able to.

〔Effect of the invention〕

According to the present invention, it is possible to reduce harmful high-frequency components of the spatial frequency components of a solid-state imaging device, and furthermore, the incident light beam is effectively focused on each photodetecting element by the lens array,
The efficiency of using incident light can be improved.

According to the present invention, the phase grating for reducing high spatial frequency components can be easily formed together with the lens array on the same substrate using well-known technology, and the solid-state imaging device has excellent sensitivity and image quality. can be manufactured at low cost.

[Brief explanation of the drawing]

The drawings show embodiments of the present invention; FIG. 7 is a cross-sectional view of a main part of a solid-state imaging device, FIG. 2 is a cross-sectional view showing an enlarged lens portion of the device shown in FIG. 1, and FIG. A diagram showing how the optical path length changes in the phase grating section, and Fig. ψ is a schematic diagram showing the operation of the phase grating.

Claims (2)

[Claims] (1) A lens array consisting of a group of microlenses that converges subject light on each of the photodetecting elements is arranged on the light-receiving surface side of an image sensor in which photodetecting elements are arranged in a planar manner, and the lens array and Place a phase grating between the subject and
A solid-state imaging device characterized in that at least two adjacent ones of the imaging element, lens array, and phase grating are integrated. (2) A solid-state imaging device according to claim 1, wherein the lens array and the phase grating are formed by a refractive index distribution region within a common transparent substrate.