JPS60165878A - Solid-state image pickup element - Google Patents

Abstract

PURPOSE:To suppress smear noise completely by forming a unit picture element switching gate and a read-out drain on an insulating material. CONSTITUTION:A charge generated from an incident light is stored for a certain period in PN junction capacity. A thin film MOS transistor whose N type silicon films 7 and 9 connected to N type area 4 have functions as a source and drain, performs a switching operation at a poly-crystal silicon gate 6 and reads out a signal charge through a P type silicon filter 8. Because the drain 9 leading to an output line is completely separated from a silicon substrate 1, a part of the charges never shift through the substrate or never directly flow into the drain, thereby enabling complete control of smear noise.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a solid-state imaging device used in video cameras and the like.

Conventional Structures and Problems There has been a remarkable improvement in the performance of solid-state imaging devices in recent years, and they have already reached the stage of practical use, especially in the miniaturization of home video cameras and the like.

Hereinafter, a conventional solid-state image sensor as described above will be explained with reference to the drawings.

FIG. 1 shows a schematic cross-sectional view of a unit pixel in a conventional solid-state image sensor. In FIG. 1, 1 is a p-type silicon substrate, 2 and 3 are silicon dioxide films, 4 is an N shadow region forming a PN junction photodiode, 6 is an N shadow region forming a drain part connected to an output line, and 6 is an N shadow region forming a drain part connected to an output line. This is polycrystalline silicon that forms the switching gate for signal readout. Note that the circles in the figure indicate charges generated by incident light, and the arrows indicate the movement of charges within the substrate.

The operation of the unit pixel configured as described above will be described below. First, light incident on the P-type substrate 1 through the N shadow region 4 forming the PN junction generates charges, most of which move as indicated by the arrows and are accumulated in the PM junction capacitor. After being accumulated for a certain period of time, it is read out to the drain section 6 by the switching gate 6 and becomes a signal current.

However, the above structure has a major drawback of generating smear noise.

The smear noise is generated because the charge of -4 V directly flows into the drain section 6 as shown by arrow B, and becomes a false signal that significantly deteriorates the image quality.

OBJECTS OF THE INVENTION In view of the above drawbacks, the present invention provides a solid-state imaging device that can completely suppress the occurrence of smear noise.

Structure of the Invention In order to achieve this object, the solid-state image sensor of the present invention has the following features:
It has a unit pixel with a silicon thin film transistor structure in which a switching gate and an output drain are formed on an insulator.

This configuration prevents a portion of the charge generated within the substrate from directly flowing into the output drain, making it possible to significantly reduce smear noise.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 2 is a schematic cross-sectional view of a unit pixel of a solid-state image sensor according to an embodiment of the present invention.

In FIG. 2, 7 is an N-type silicon film in contact with the do-type region 4 forming the photodiode, 8 is a P-type silicon film, and 9 is an N-type silicon film. Further, 1 is a P-type silicon substrate, 2 and 3 are silicon dioxide films, and 6 is polycrystalline silicon, which is the same as the structure shown in FIG.

The operation of the unit pixel configured as described above will be described below.

First, charges generated by incident light are accumulated in the PN junction capacitor for a certain period of time. Then, the N-type silicon films 7 and 9 that are not connected to the N shadow region 4 are exposed.

The thin film MO3) run sister that acts as a drain is
A switching operation is performed by the polycrystalline silicon gate 6, and signal charges are read out to the drain 9 through the P-type silicon film 8.

As described above, according to this embodiment, the drain part 9 connected to the output line is completely separated from the silicon substrate 1, so that part of the charge moves within the substrate and flows directly into the drain part. smear noise can be completely suppressed.

A thin film MO8) run sister made of a silicon film can be easily formed using conventional techniques such as chemical vapor deposition, heat treatment, and ion implantation using silane gas as a raw material.

In this embodiment, the silicon substrate is of P type, but the same effect can be obtained even if it is of N type. Although the photodiode is a PH junction formed in a silicon substrate, similar effects can be obtained with a PN junction structure made of amorphous silicon or a compound semiconductor.

Effects of the Invention As described above, in the present invention, since the switching gate and readout drain of a unit pixel are formed on an insulator, smear noise is completely suppressed, and its practical effects are great. .

[Brief explanation of the drawing]

Figure 1 is a schematic cross-sectional diagram of a unit pixel of a conventional solid-state image sensor.
FIG. 2 is a schematic cross-sectional view of a unit pixel in an embodiment of the present invention. 1... Semiconductor substrate, 2, 3... Silicon dioxide film, 6. Completed, 9...H-type silicon region, 8...P-type silicon film.

Claims (1)

[Claims] A solid-state image sensor having a unit pixel consisting of a PN junction photodiode formed on a main surface of a semiconductor substrate, and a switching gate and a readout drain formed on an insulating film formed on the main surface.