JPH02181470A - Solid-state image pick-up element - Google Patents

Abstract

PURPOSE:To restrain a brooming from occurring by a method wherein a reset transistor is made conductive during the accumulation of a photo signal charge excluding the reset time. CONSTITUTION:With the exception of a reset time, electrons generated by incident light are collected in an aluminum electrode layer 3 conforming to the potential gradient in a photoconductive film 1 while holes are to be collected in a transparent electrode 2 side. Accordingly, any excess charge generated by intensive light from a high brightness light source is to be overflowed into a wiring 17 through the intermediary of the layer 3, a conductive region 18, a gate electrode 7 and a source region 4, a drain region 5 of a reset transistor. Normally, when the film 1 is not impressed with any voltage at all, the potential in the film 1 is leveled to cause a brooming. However, in this solid-state image pick-up element, the reset transistor is made conductive to provide the film 1 with potential gradient so that the brooming may be restrained from occurring.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an internal amplification type solid-state image pickup device in which each pixel is provided with a transistor having an amplification function and a reset transistor, and in particular, the present invention relates to an internal amplification type solid-state image sensor in which each pixel is provided with a transistor having an amplification function and a reset transistor. The present invention relates to a solid-state image element provided with a solid-state image element.

[Summary of the invention]

The present invention provides an internal amplification type solid-state image sensor in which a photoconductive film is formed on the entire surface, in which a reset transistor is made conductive during a period other than the reset time, and a pixel is connected from a transparent electrode on the photoconductive film and a source electrode of the reset transistor. The blooming characteristic is improved by applying a predetermined potential between the electrodes extending in each direction.

[Conventional technology]

Internal amplification type solid-state image sensors, which have an amplification function for each pixel, are attracting attention as devices that aim to increase sensitivity and resolution. AMI) Ya.

Various elements are known, such as a static induction transistor type imager (so-called SIT) in which each pixel is constituted by a static induction phototransistor, and a charge modulation device (so-called CMD) in which each pixel is constituted by a MOS phototransistor.

Regarding such technology, there is a technology for an amplified solid-state image sensor described in "Journal of the Televisier Society J, VOl, 411 N1111.1987, pages 1075 to 1082; Each pixel is an amplification transistor and a switch transistor.

It consists of a total of three transistors (reset transistor) and a diode.

[Problem to be solved by the invention]

Such amplified solid-state image sensing devices are required to have higher resolution, and the resolution is improved by arranging each pixel at a higher density. However, simply increasing the density of each pixel lowers the aperture ratio and makes it impossible to obtain sufficient sensitivity.

On the other hand, by providing a photoconductive film over the entire surface of each pixel, the aperture ratio can be increased, but for example, when strong light is incident, the photoconductive film in the portion corresponding to the pixel is charged. This causes a phenomenon (blooming) in which charges overflow and spread to surrounding pixels.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a solid-state image sensor that suppresses the blooming phenomenon in which charges spread to surrounding pixels.

[Means to solve the problem]

In order to achieve the above object, the solid-state image sensor of the present invention includes a transistor having an amplification function and a reset transistor in each pixel arranged in a matrix, and a photoconductive film formed on the entire surface thereof. In a solid-state imaging device consisting of It is characterized in that a predetermined potential is applied between the divided electric potentials.

Here, the impedance of the conductive state of the reset transistor other than during reset can be higher than that of the conductive state of the reset transistor during reset.

[Effect]

By bringing the reset transistor into conduction during accumulation of optical signal charges other than during reset, a predetermined potential is applied between the photoconductive film and the electrodes extending from the source electrode of the reset transistor and divided for each pixel. As a result, a potential difference is generated inside the photoconductive film, and holes and electrons are collected into the transparent electrode and the extended electrode, respectively.

As a result, charges that spread to surrounding pixels are also reduced, and blooming is suppressed.

〔Example〕

Preferred embodiments of the present invention will be described with reference to the drawings.

This example is an example of a solid-state imaging device in which a pixel is formed by a transistor having an amplification function and a reset transistor, and a solid-state imaging device in which a photoconductive film made of an a-3i (amorphous silicon) film is formed on the entire surface. This is an example of an element.

First, regarding its structure, as shown in FIG. 1, a field oxide film 12 is formed on a p-type silicon substrate 11 by selective oxidation, and a channel stopper region 13 is formed under the field oxide film 12. ing. Note that the p-type silicon substrate 11 is a p-type silicon substrate.
The source 6N+! of the reset transistor is formed on the surface of the silicon substrate 11, which may have a type well region formed therein. ! N-type high-concentration impurity diffusion regions are formed apart from each other so that the source region 4 and the drain region 5 are composed of MO3I transistors, and a A gate electrode 6 of a reset transistor is formed. A wiring 17 for sweeping out unnecessary charges is connected to the drain region 5 of the reset transistor.

A gate electrode 7 of a MOS transistor having an amplification function is connected to the source region 4 of the reset transistor, and the source region 4 is connected to a conductive region formed in the glabella insulating film 15 via the gate electrode 7. 18, it is connected to the aluminum electrode layer 3 which is divided into sections for each pixel.

This aluminum electrode layer 3 is provided over one pixel area on the glabellar insulating film 15, and a photoconductive film 1 made of an amorphous silicon film is formed on the aluminum electrode N3 to a required thickness. . By forming the photoconductive film 1 in this manner, its aperture ratio can be increased, and optical signal charges are generated in the photoconductive film 1. A transparent electrode 2 is formed on this photoconductive film 1, and a ground voltage GND (for example, Ov) is applied to this transparent electrode 2.

The gate electrode 7 of the amplification MOS transistor connected to the source region 4 extends within the same pixel region, and this MOS transistor having an amplification function is connected in series with, for example, a vertical switch transistor (not shown) within the same pixel. Ru.

FIG. 2 is a diagram schematically showing the circuit configuration of the solid-state image sensing device of this embodiment, in which each pixel is arranged in a matrix, and each pixel is a MOS transistor (2), a reset transistor (22), and a reset transistor (22), each having an amplification function. Vertical switch transistor 23
and a light receiving section 20 made of the photoconductive film 1. The light receiving section 20 of each pixel is connected to the source electrode of the reset transistor 22 and also to the gate of the amplification MO5) transistor 21. The gate of the reset transistor 22 is controlled by a signal from the vertical scanning circuit 31, and the reset transistor 22 is made conductive even at times other than reset. To read a signal, one column formed by the vertical scanning circuit 31 is selected, and the vertical switch transistor 23 of the selected column is turned on. As a result, the potential of the vertical signal line changes depending on the optical signal charge. and,
The horizontal switch transistors 33 are sequentially selected by the horizontal scanning circuit 32, and the signal appearing on the video line 34 is outputted via the amplifier 35.

The solid-state imaging device of this example having such a configuration has potential distributions as shown in FIGS. 3 and 4.

First, FIG. 3 shows the potential in the direction of the film thickness of the photoconductive film, and the potential of the transparent electrode 2 is constantly set to Ov.

The potential of the aluminum electrode layer 3 facing this transparent electrode 2 across the photoconductive n'A I changes depending on the conduction state of the reset transistor, and becomes the potential Φ2 at the time of reset, and becomes the potential at the time of accumulation other than the time of reset. Φ. Potential Φ
, the same potential as the beam set drain, and the potential Φ1 is o
The potential is slightly higher than v. Such a change in potential is caused by the fact that the aluminum electrode Ji3 is connected to the gate f17 of the amplifying MOS transistor and is also connected to the source region (electrode) 4 of the reset transistor, as will be described later.
This is done because the impedance of the reset transistor changes.

First, at the time of reset, the potential of the aluminum electrode N3 becomes the potential Φ, so that electrons are collected toward the aluminum electrode layer 3 side, and unnecessary electrons are further swept out to the wiring 17 via the reset transistor. - On the other hand, the holes are on the transparent electrode 2 on the surface.
They are gathered to the side and reset.

Next, at times other than reset, the potential of the aluminum electrode layer 3 is set to the potential Φ1, and in the photoconductive film l, the one-dot chain line P,
The potential gradient shown is obtained. Therefore, the electrons generated by the incidence of light follow the gradient of the aluminum electrode layer 3.
Similarly, holes are also collected on the transparent electrode 2 side according to the gradient. Therefore, for example, excess charges generated by strong light from a high-intensity light source are transferred to the aluminum electrode layer 3. Conductive region 18. Gate electrode 7 and source region of the reset transistor 4. Through the drain region 5, the distribution!
17 will be overflowed. If no voltage is applied to the photoconductive film 1, the potential of the aluminum electrode layer 3 is the potential Φ. Therefore, the potential in the photoconductive film 1 becomes flat as shown by the broken line P in the figure. Therefore, excess charges generated by strong light from a high-intensity light source cannot be swept away in the thickness direction of the photoconductive film 1, and overflow to surrounding pixels, causing blooming.

However, in the solid-state imaging device of this example, the reset transistor is made conductive, the potential of the aluminum electrode N3 is set to the potential Φ1, and since there is a potential gradient in the photoconductive film 1, blooming is suppressed. become.

FIG. 4 shows the potential distribution of the reset transistor, where the drain region 5 is the reset drain,
A reset potential Φr is given as the potential.

A voltage is applied to the gate electrode 6 of the reset transistor, and the potential thereof is set to the potential Φ8 at the time of resetting, and the potential is set to the potential Φ at times other than the time of resetting. The potential Φ8 of the gate electrode 6 at the time of resetting is a level at which the impedance of the reset transistor becomes sufficiently low, and the charge on the reset source side is swept out to the drain side to perform resetting. Also, at this time, since the impedance of the reset transistor becomes sufficiently low, the potential of the aluminum electrode layer 3 becomes the potential Φ, as described above, and the photoconductor II
The electric charge of U1 is also collected. Next, the potential Φ of the gate electrode 6 other than during reset is the potential that makes the reset transistor conductive.
The potential is about the same as applying a voltage of about 5 to 2 volts.

Therefore, the impedance of the reset transistor is lower than when the gate voltage is Ov (although the potential barrier is higher than the gate potential at reset. A potential is formed on the aluminum electrode N3 side of the photoconductive film 1, and blooming is suppressed due to the overflow of excess charge.

In the above-described embodiment, the reset transistor is of horizontal type, but an n-type silicon substrate, a p-type well region,
nMO3) It may be a vertical type in which the element is configured with a transistor and discharges unnecessary charges to the substrate.Also, the aluminum electrode layer 3 may be made of other conductive materials. As a means of applying a potential difference to the membrane, instead of changing the potential of the aluminum electrode layer 3 as described above,
It is also possible to apply a required potential to the transparent electrode 2 side to cause excess charge to overflow.

Furthermore, the structure of the pixel having the amplification function can also be made into another structure.

〔Effect of the invention〕

In the solid-state imaging device of the present invention, since the photoconductive film is formed on the pixel, the aperture ratio is improved, and in combination with its internal amplification function, high sensitivity and high resolution can be achieved. Further, as described above, the reset transistor is kept in a conductive state even when not being reset, so that the transparent electrode on the photoconductive film and the electrode extending from the source electrode of the reset transistor and divided for each pixel are connected. Since a predetermined potential is applied between them, excess charge can overflow, making it possible to suppress blooming.

FIG. 3 is a potential distribution diagram in the thickness direction of a photoconductive film as an example, and FIG. 4 is a potential distribution diagram in a reset transistor as an example.

1... Photoconductive film 2...Transparent electrode 3...Aluminum electrode layer 4...Source area 5...Drain region 6.7...Gate electrode Patent applicant: Sony Corporation Representative patent attorney Akira Koba (and 2 others)

[Brief explanation of the drawing]

Claims (1)

[Scope of Claims] A solid-state image sensor comprising a transistor having an amplification function and a reset transistor arranged in each pixel arranged in a matrix, and a photoconductive film formed entirely on the pixel, By keeping the reset transistor in a conductive state even when not resetting, the transparent electrode on the photoconductive film and
A solid-state image pickup device, wherein a predetermined potential is applied between an electrode extending from the source electrode of the reset transistor and divided for each pixel.