JPH06252375A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To improve the resolution without increasing the number of picture elements by meandering the charge transfer paths of vertical CCD resistors in the shape of sine waves, and arranging the charge transfer paths of two vertical CCD resistors between photoelectric elements adjacent to each other in horizontal direction. CONSTITUTION:The signal charge of photodiodes 132 and 139 is shifted to a vertical CCD resistor 123. The signal charge shifted to the vertical CCD resistor is shifted to a horizontal CCD resistor separately for each line along the channel of the vertical CCD resistor, and is outputted to outside as a signal. Here, the horizontal spatial sampling pitch becomes XP/2, defining that the pitch of horizontal picture elements is XP. Accordingly, as compared with a conventional image pickup device the same in the number of picture elements, the horizontal resolution improves to double. Moreover, the signal of the picture elements adjacent in vertical direction can be transferred independently without being mixed, so there is no vertical resolution deterioration, either.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device, and more particularly to a solid-state image pickup device capable of handling high resolution image signals.

[0002]

2. Description of the Related Art FIG. 5 shows a conventional solid-state image pickup device structure described in Proceedings pp33 to 34 of the 1991 Annual Conference of the Television Society. The signal charge accumulated in the photodiode 1 during one field period is transferred to the vertical CCD register 3 via the photogate 2. Vertical CCD register 3
The signal charge transferred to the vertical clock input terminal 40,
Each vertical clock gate line 10, 11, 12, 13 is driven by an external pulse applied to 41, 42, 43 to be sent to the horizontal CCD register 5 every horizontal scanning period, and output via the output amplifier 6. Output to the outside.

FIG. 6 shows a plane pattern of a photodiode and a vertical CCD register. Where 1
0 and 12 are polysilicon gate electrodes of the first layer, 1
Reference numerals 1 and 13 denote second-layer polysilicon gate electrodes, which correspond to 10 to 13 in FIG. 5, respectively. 14 ~
Reference numeral 19 denotes an area which is not covered with the light shielding film made of aluminum or the like formed on the polysilicon gate electrode and is called an opening area.

In FIG. 6, a sectional view taken along the line AA 'is shown in FIG. 7, and a sectional view taken along the line BB' is shown in FIG. In FIG. 7, 22,122 P-type wells of higher concentration are formed in 21 P-type wells formed in 20 N-type semiconductor substrates, and CCD channels are formed therein 23,1.
23 N-type impurity regions are provided. Further, 24 is an N-type impurity region which becomes a photodiode, and 25 P + -type impurity region formed on the upper surface thereof is provided to suppress a dark current generated on the semiconductor surface. 23,
26 and 126 P-type impurity regions provided on one side of 123 are for separating the vertical CCD register and the photodiode. 27,127 on the CCD channel
Is formed through an insulating film 29 such as an oxide film. Further, 28,128 light-shielding aluminum is arranged on the upper surface thereof. The potential of the opposing portion of 23 and 24 is controlled by the gate 27, and the portion functions as a selection gate of the photodiode.

FIG. 8 is a sectional view taken along line BB 'in FIG. Here, each element of 10 to 29 is the same as each element of FIG. 7. Further, aluminum and the like formed on the upper surface thereof are omitted here.

FIG. 9 schematically shows the time variation of the channel potential of the vertical CDD register shown in FIG.
First, at time t = ta, a high level voltage is applied to the polysilicon gate of the second layer, and the signal charges Qa, Qb, Qc ... From each photodiode are transferred to the vertical CCD register. Then, at time t = tb, each signal charge is Qa
Two pixel signals such as + Qb, Qc + Qd ... Are mixed and held under the two transfer gate electrodes having the intermediate level voltage. Then, at time t = tc, each signal charge is held under the three transfer gate electrodes at the next gate as an intermediate level voltage. Subsequently, at time t = td, each signal charge is held at the lower level of the two transfer gate electrodes by returning the previous gate to the low level voltage. In this way, the signal charge read by the vertical CCD register when the high level voltage is applied to the transfer gate is mixed with two pixel signals, and the transfer gate is fed with a four-phase clock signal of an intermediate level voltage and a low level voltage. The pulses are alternately applied and transferred to the horizontal CCD register.

Originally, it is desirable that the signals of the image pickup device read the signals of each pixel independently from the viewpoint of resolution. It didn't bring out enough.

FIG. 10 shows an example of another conventional image pickup apparatus disclosed in Japanese Unexamined Patent Publication No. 58-175372. 5 here
Reference numeral 1 is a photodiode, and 52 is a vertical CCD register. Signal charges from two pairs of photodiodes are transferred to one vertical CCD register, and the signal charges transferred to the vertical CCD register are output to the outside through a horizontal CCD register 53 and an output amplifier 54. Is. The reading of the signal charges from the two pairs of photodiodes into the vertical CCD register is staggered as shown by the arrows in the figure.

Since signal charges from two pairs of photodiodes are transferred per four-phase transfer electrode of the vertical CCD register, the above-mentioned conventional example has no choice but to mix pixels in the transfer of the vertical CCD register. However, in this conventional example, since the pixels can be made independent, an improvement in vertical resolution can be expected. Further, since the signal charges from the pair of two photodiodes are used, the charge amount of one photodiode may be halved, and the area of the photodiode can be reduced. As a result, the pixel pitch in the horizontal direction can be reduced, so that the horizontal resolution can be improved to some extent.

However, since two photodiodes generate one signal charge, spatial sampling points are separated, and there is a problem that improvement of MTF (Modulation Transfer Function; spatial modulation degree characteristic of resolution) cannot be expected. there were. In order to improve the resolution of such a solid-state imaging device, it is necessary to increase the number of pixels, but a finer processing technique is inevitably required.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide a high resolution solid-state image pickup device without increasing the number of pixels.

[0012]

The above object is to provide a vertical CCD.
This is achieved by causing the charge transfer paths of the registers to meander in a sinusoidal shape and disposing the charge transfer paths of the two vertical CCD registers between the photoelectric conversion elements adjacent in the horizontal direction.

[0013]

By making the charge transfer path of the vertical CCD register meander like a sine wave, the arrangement of the photoelectric conversion element groups can be shifted by a half pitch for each row. As a result, the pixels are complemented in the horizontal direction, so that the horizontal resolution is doubled. Further, by arranging the charge transfer paths of two vertical CCD registers between the photoelectric conversion elements adjacent in the horizontal direction, the signal charges of the pixels adjacent in the vertical direction can be independently read out, so that the vertical resolution is also increased. improves. Thus, the resolution can be improved without increasing the number of pixels of the image pickup device.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. This figure shows a plan view of the image pickup apparatus of the present invention, and the difference can be seen clearly when compared with FIG. 6 which is a plan view of the conventional image pickup apparatus. 121, 122, 12 in the figure
Reference numeral 3124 denotes a charge transfer path of the vertical CCD register, that is, a channel. Moreover, 131-142 have shown the photodiode which is a photoelectric conversion element. 110
Reference numerals 116 to 116 denote transfer gates of the vertical CCD register, in which even numbers such as 110 and 112 are polysilicon gates of the first layer, and odd numbers such as 111 and 113 are polysilicon gates of the second layer. Indicates.

A high level voltage is applied to the second gate polysilicon gate of the signal charges accumulated in each photodiode, and the signal charges from each photodiode are independently transferred to the vertical CCD register. For example, the signal charges of the photodiodes 132 and 139 are transferred to 123 vertical CCD registers. The signal charges transferred to the vertical CCD registers are transferred to the horizontal CCD registers row by row along the channels of the vertical CCD registers and output as signals to the outside.

Here, the spatial sampling pitch in the horizontal direction is XP /, where XP is the pixel pitch in the horizontal direction.
It becomes 2. Therefore, it can be seen that the horizontal resolution is doubled as compared with the conventional image pickup device having the same number of horizontal pixels. Also, the spatial sampling pitch in the vertical direction is the same as that of the conventional image pickup device having the same number of vertical pixels, but in the conventional device, signals of pixels adjacent in the vertical direction have to be mixed, so that the vertical resolution is increased. However, in the present image pickup apparatus, since signals of pixels vertically adjacent to each other can be independently transferred without being mixed, vertical resolution is not deteriorated. In this way, the resolution can be improved without increasing the number of pixels of the image pickup device.

FIG. 2 shows a vertical CC on line CC 'of FIG.
It is a sectional view of a D register. Each element in the figure is essentially the same as the sectional view of the conventional vertical CCD register of FIG. Only the transfer gates of the vertical CCD register are combined with the numbers in FIG.

FIG. 3 schematically shows the time variation of the channel potential of the vertical CDD register shown in FIG.
First, at time t = ta, a high level voltage is applied to the polysilicon gate of the second layer, and the signal charges Qa, Qb, Qc ... From each photodiode are transferred to the vertical CCD register. Then, as can be seen from the states at time t = tb, time t = tc, and time t = td, each signal charge is transferred independently, transferred to the horizontal CCD register, and then output to the outside. To be done.

FIG. 4 shows a light-shielding pattern of aluminum or the like formed on the upper surface of the image pickup device. This drawing is drawn corresponding to FIG. 1, and 150 is a portion with a light shielding film such as aluminum and the like, and a portion without light shielding such as 151,
That is, the opening has a circular shape. Such a circular pattern is made possible by the fact that the photodiodes can be arranged in a zigzag manner as shown in FIG. 1, but the MTF (Modula)
From the viewpoint of the spatial transfer degree characteristic of the resolution), horizontal and vertical balance is also desirable. In recent years, it has become possible to improve sensitivity by forming a microlens for each pixel on the top surface of the device.
The circular pattern photodiode is also convenient for forming a microlens. In the figure, reference numeral 152 indicates the peripheral edge of the microlens. In the conventional rectangular photodiode, the microlenses have to be rectangular and it is difficult to form the shape of the lens with high accuracy. However, in the case of a circular pattern lens, there is also an advantage that only the diameter and thickness of the lens need to be controlled.

[0020]

According to the present invention, the resolution can be improved without increasing the number of pixels of the image pickup device.

[Brief description of drawings]

FIG. 1 is a plan view of an image pickup apparatus showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the element at the CC ′ portion in FIG.

FIG. 3 is a potential explanatory diagram for the signal charges in FIG.

FIG. 4 is a plan view of an image pickup apparatus showing an embodiment of the present invention.

FIG. 5 is a block diagram of a conventional imaging device.

FIG. 6 is a plan view of a conventional element.

7 is a cross-sectional view of the element taken along the line AA ′ in FIG.

FIG. 8 is a cross-sectional view of the element taken along the line BB ′ in FIG.

9 is a potential explanatory diagram for the signal charges in FIG. 8. FIG.

FIG. 10 is a plan view of another conventional device.

[Explanation of symbols]

121 ... Vertical CCD register charge transfer path, 131 ... Photoelectric conversion element, 110 ... Vertical CCD register transfer gate, 150 ... Aluminum, etc. light-shielding film, 151 ... Opening part.

Front page continuation (72) Inventor Katsutaka Kimura 1-280 Higashi Koigokubo, Kokubunji, Tokyo Inside Hitachi Central Research Laboratory

Claims (3)

[Claims] 1. A photoelectric conversion element group formed two-dimensionally on the same semiconductor substrate, a vertical CCD register group for vertically transferring signal charges from each photoelectric conversion element group, and the vertical CCD register group. Solid-state image pickup having a selection gate which is shared with the transfer gate of FIG. 2 and which transfers a signal from the photoelectric conversion element group to the vertical CCD register group, and a horizontal readout section which horizontally transfers the signal from each vertical CCD register group. In the device, the charge transfer paths of the two vertical CCD registers are provided between the photoelectric conversion elements that are adjacent in the horizontal direction, and the rows of the photoelectric conversion elements that are adjacent in the vertical direction correspond to 1/2 pixel in the horizontal direction. A solid-state imaging device characterized by being deviated. 2. The solid-state imaging device according to claim 1, wherein the charge transfer path of the vertical CCD register meanders in a sinusoidal shape. 3. The solid-state imaging device according to claim 1, wherein an opening of a film which shields a region other than the photoelectric conversion element group is circular.