JPS6062281A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To constitute a stop system semielectronically and obtain a constant image pickup output regardless of the intensity of incident light by using a charge transfer element which has a longitudinal overflow drain as an image pickup element, and controlling the potential applied to a semiconductor substrate on the basis of the level of the image pickup output. CONSTITUTION:The charge transfer element CCD10 which has the longitudinal overflow drain is used as the image pickup element to be used for a solid-state image pickup device. The optical image of an object 11 is projected upon this CCD10 through an optical system 12. The image pickup output converted into an electric signal by this CCD10 is applied to an encoder 14 including a processor, exponent converting circuit, etc., through a preamplifier 14. The mean level VA of the image pickup output of the amplifier 13 is detected by a mean level detecting circuit 17 and compared with a reference level V0 by a comparing circuit 18, which is applied the comparison output VD to a control circuit 19. The circuit 19 outputs a substrate potential VB to the semiconductor substrate of the CCD10 to output the constant image pickup output regardless of the intensity of incident light.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a solid-state imaging device using a charge transfer element such as a CCD having a vertical overflow P-rain, and particularly to an automatic aperture system thereof.

Background technology and its problems For example, in a solid-state imaging device that uses COD as an imaging element, in order to always obtain a constant imaging output regardless of the input light intensity, like other imaging devices, an aperture device is provided in the optical system and the imaging device is This aperture device is controlled according to the output level.

Therefore, in such conventional solid-state imaging devices, it is necessary to provide a mechanical aperture device, and a motor and drive circuit for automatically adjusting this aperture device are also required. The overall size and weight increased, and there were problems with durability. Furthermore, changing the aperture changes the depth of focus of the subject, and there is a drawback that the depth of focus cannot be adjusted independently of the aperture.

OBJECT OF THE INVENTION Therefore, in the present invention, the aperture p system is constructed purely electronically to eliminate the above-mentioned drawbacks.

Summary of the Invention Therefore, in this invention, a COD with a vertical overflow drain region is used as an image sensor, and by controlling the substrate potential supplied to the COD, the potential is always constant regardless of the input light intensity. The system is designed to provide an imaging output of

EXAMPLE Next, an example of the present invention will be explained in detail with reference to FIG. 1 and subsequent figures.

The CCD with a vertical overflow drain region used in this invention has an overflow drain that suppresses blooping not in a two-dimensional arrangement but in a three-dimensional arrangement.
That is, they are arranged in the depth direction of the substrate.

FIG. 1 shows an example of this, and is a cross-sectional view of a normal interline transfer type solid-state image sensor 00 along a plane perpendicular to signal transfer. In this figure, a bulk channel (
An N type region (2) for forming a buried channel) and a P+ type region (3) for forming a channel stopper C8 are formed, and a region (2) is formed between these regions (2) and (3).
An N+ area 4) which is in contact with 3) and becomes a sensor area S/EMS is formed. This region (4) and the substrate (1) form a PN junction J8 for the sensor.

A transfer electrode (7) for a vertical shift register VR is formed on the upper surface of the substrate (1) via an insulating layer (6) such as StO□. Note that the area between areas (2) and (4) is used as a control dart CG area for reading.

An N-type region (8) of a conductivity type different from that of the substrate (1) is formed on the lower surface of the P-type substrate (1).
) and the region (8) to control the overflow train OFD at the PN junction J
) area is formed. Therefore, this PN junction J. A predetermined reverse bias is applied from the outside. VB is its bias voltage (substrate voltage). According to this configuration, the optical signal charge based on the optical signal incident on the sensor region 5ENS is applied to the PN junction J. If the amount of charge exceeds the potential barrier formed by this, the excess optical signal charge is emitted into the N-type region (8) and the blue-pink color is suppressed.

Therefore, the substrate potential VB is generally constant. This invention actively varies the substrate potential VB according to the input light intensity so that the average level of the imaging output obtained from COD (I) remains constant regardless of the input light intensity. It is.

FIG. 2 shows the potential when one sensor region 5ENS is depleted.

In this figure, the horizontal direction is the depth direction of the substrate (1). Curve t is the potential when the substrate potential VB is 75KVB, and by increasing this substrate potential VB by more than VBl, VB
2, the potential in the depleted state changes as shown by curve t2. Difference between the lowest potential and the highest, II) tensile (potential barrier)
Since ΔPB is smaller for curve t than for curve t2, it is the amount of accumulated charge Q just before overflow at curve t.
. F: The amount of accumulated charge Q immediately before overflow when the curve t2 is shown. F2 has less. Therefore, the amount of accumulated charge when the substrate potential is VBl is Q. If the substrate potential is raised to VB2 in the case of F, the amount of accumulated charge at that time is Q. Since it decreases to F2, the imaging output decreases in response to the change in substrate potential.

1. It is known that the following relationship exists between the O-G flow and the amount of accumulated charge when the same substrate potential (1)8 is applied.

That is, if the curve q in Figure 3 is the potential at the start of overflow, the potential at an input light intensity stronger than the input light intensity at this time is the curve q2 t 1
13, the amount of charge newly stored in the potential well formed in the N+ region 4) is greater than the amount of charge that overflows, and therefore the input light intensity exceeds the input light intensity that has already overflowed. Even the light intensity
The imaging output level increases corresponding to the input light intensity.

Therefore, the input light intensity (corresponding to the imaging output) at the horizontal line where the subject is currently projected on the CCDαO is the fourth
In the case of curve ta in the figure, even if it is assumed that the input light intensity at horizontal position T (a) originally overflows, if the input light intensity is stronger than this input light intensity (for example, horizontal position ff ?Hb), an imaging output corresponding to this input light intensity is obtained.In this state, if the substrate potential VB is increased, the amount of accumulated charge immediately before overflow decreases over the entire projection area, and As is clear from Fig. 3, the amount of accumulated charge 1d decreases depending on the intensity of input light incident on each sensor region INs, so even if the substrate potential is raised, the amount of accumulated charge 1d will be lower in areas where the input light intensity is stronger than in areas where it is weaker. There is no change in the fact that there is a large amount of accumulated charge, and the imaging output level differs accordingly.For this reason, when the substrate potential is increased, the imaging output level at that time will be on the lower level side as a whole, as shown by curve tb. The shape is shifted to .

Therefore, for example, the straight line t in FIG. is set as the reference level (average level) vo of the imaging output, and if the average level is higher than this, the substrate potential is increased, and when it is lower than this, the substrate potential is conversely lowered. It is possible to always maintain a constant imaging output (average level) regardless of the situation.

To this end, the design may be such that the amount of electric charge relative to the input light intensity I of C0D (In), and therefore the imaging output, overflows earlier than in the normal case.

For example, as shown in FIG. 5, when operating with a fixed substrate potential VB, the input light intensity layer overflows,
. It is also designed to already overflow at a much lower input light intensity IPO' (for example, the intensity when using an indoor light source), and the reference level V of the imaging output. This can be achieved by positioning as shown in the figure. Such input/output characteristics depend on the diffusion concentration of N-type impurity and the ratio of diffusion depth (x
:x+y) (see Figure 2) can be obtained relatively easily by appropriately selecting.

FIG. 6 shows an example of a solid-state imaging device according to the present invention using a COD α0 having the input/output characteristics as described above, in which an optical image of a subject α° C.
The imaging output projected onto the CCD 60 and converted into an electric signal by the CCD (], C) is supplied to an encoder α→ including a processor, an index conversion circuit, etc. via a Norianzo θ encoder. Therefore, a well-known, for example, color video signal is output to the terminal 05. The reason why the index conversion circuit is provided in the encoder α4 is to convert the characteristic shown in FIG. 5 into a linear characteristic.

The imaging output of the preamplifier α) is further processed by the average value detection circuit 0.
The average level of the imaging output over the entire screen where the original signal is converted into an electrical signal by being supplied to η is determined, and this detection output ■
□ is supplied to the level comparison circuit α→ and is the reference level V. compared to And this comparison output v9 is the voltage control circuit θ
The substrate potential VB supplied to the silicon and the N-type region (8) is controlled. As described above, the substrate potential V is controlled to be high when vA>Vo and low when vA<vo.

Note that the conductivity type of C0D (10) described above is only an example.

As described in detail, according to the present invention, by controlling the substrate potential VB by the input source intensity, a constant imaging output is always obtained regardless of the input light intensity. can be configured.

Therefore, the disadvantages of mechanical drawing devices, namely the large size of the device, maintenance and inspection problems, and durability problems can be eliminated, and
The weight of the entire device can be reduced.

In addition, the shutter itself may be damaged due to other reasons (C due to direct sunlight).
It should be added to prevent damage to CDs, etc.).

Unfortunately, the input source strength itself is not controlled at all, so
The depth of focus can always be kept constant even when the automatic aperture is in operation.

[Brief explanation of drawings]

Figure 1 shows the kl type overflow drain.
FIGS. 2 to 5 are cross-sectional views showing an example of an OD, FIGS. 2 to 5 are diagrams for explaining the operation of a COD applied to the present invention, and FIG. 6 is a system diagram showing an example of a solid-state imaging device according to the present invention. α1 is a CCD, αη is an average level detection circuit, (181
is a level comparison circuit, (one is a control circuit for substrate potential (voltage) VB. Fig. 1 J. Fig. 5 Fig. 2 ↓ B Fig. 3

Claims (1)

[Claims] A solid-state imaging device that uses a charge transfer element having a vertical overflow drain as an imaging element, and controls a substrate potential applied to a semiconductor substrate thereof according to an imaging output level.