JPS6139569A - solid state photodetection device - Google Patents

Abstract

PURPOSE:To widen sufficiently the dynamic range of the imaging cell by a method wherein the capacity of the capacitor, wherein parts of optical carriers are stored, is formed of the dielectric layer and the electrode layer, which are formed in order in such a manner as to cover a region, where a p-n junction is formed between the semiconductor substrate and the photo diode. CONSTITUTION:The p-n junction between a p type silicon substrate 12 and the photo diode is formed at the n<+> type region 14 of the substrate 12. An IGFET is constituted using the n<+> type region 14 as its source, using an n<+> type region 16 as its drain and using an electrode layer 20 of a silicon oxide layer 18 between the n<+> type regions 14 and 16 as its gate electrode. A capacitor is formed between an electrode layer 26 and the n<+> type region 14, which is used as the cathode of the photo diode, holding a dielectric layer 24 between them. When light is irradiated on the photo diode region, parts of optical carriers excited at the p-n junction region are stored in the capacitor, the dynamic range of an imaging cell 10 becomes wider by the amount of a component equivalent to the capacity of the capacitor.

Description

DETAILED DESCRIPTION OF THE INVENTION 1. Summary of the Invention The present invention relates to a photodetection device, particularly a solid state photodetection device.

11. For example, for a solid-state imaging device that has an imaging cell array in which imaging cells with a photodiode structure are arranged in one or two dimensions, an important issue is how to improve the photoelectric conversion efficiency, that is, the sensitivity of generating optical carriers to incident light. It is one of the Therefore, conventionally, various methods have been taken to improve the optical aperture ratio of each imaging cell to the incident light and to reduce the loss of the incident light.

For example, there is a photodetection device in which a pn junction photodiode is formed on a silicon substrate, the sword or node of which forms the source region of an rGFET that constitutes an optical carrier readout circuit. Photocarriers generated in the photodiode region by the incident light are temporarily accumulated near the pn junction, and are outputted as a signal current according to the incident light through the IGFET. However, in this configuration, there is a limit to the capacity of the pn junction, so it becomes saturated with a relatively small amount of photocarriers generated by the incident light.
The amount of light at which the capacity is saturated is small, and therefore a sufficient dynamic range cannot be obtained as an imaging device.

Public-J In view of such demands, an object of the present invention is to provide a solid-state photodetection device with a sufficiently wide dynamic range.

A solid-state photodetection device has a region of the other conductivity type forming a pn junction, and a readout means for reading out photocarriers excited in the pn junction by light incident on one principal surface,
a dielectric layer formed on a main surface to cover at least a region of the other conductivity type, and an electrode layer formed to cover the dielectric layer; The electrode layer forms a capacitor that stores some of the photocarriers.

Embodiments of the solid-state photodetection device according to the present invention will now be described in detail with reference to the accompanying drawings.

Referring to FIG. 1, one imaging cell 1 of a solid-state imaging device in an embodiment of a solid-state photodetection device according to the present invention.
0 is shown in cross section, and a plurality of these imaging cells 10 are arranged one-dimensionally or two-dimensionally to form an imaging cell array.

In this embodiment, the imaging cell 10 has two n-type regions 14 and 1θ formed on one main surface of a p-type silicon substrate 12. One n medium region 14 forms a pn junction of the photodiode together with the p type substrate 12.

Between the two n medium regions 14 and 16 on the same main surface is a silicon oxide layer! 8 is formed, and an electrode layer 2o is further formed thereon. These constitute an IGFET in which the n medium region 14 serves as a source, the n÷ region 16 serves as a drain, and the electrode layer 2° serves as a gate electrode. drain area 1
An aluminum electrode N22 is formed at E of B.

On the other hand, a dielectric layer 24 is formed on the source region 14 as shown in FIG. 1, and an electrode layer 2B further covers the dielectric layer 24. The dielectric layer 24 is preferably made of a non-photosensitive material, that is, a material whose carriers are not excited by incident light;
For example, nitride films such as Si3N4, oxide films such as S+02, etc. are advantageously used.

Further, it is formed to be sufficiently thin so that light 30 incident on the main surface of the substrate 12 from above can reach the pn junction region below.

A transparent electrode material is advantageously used for the electrode layer 2B.

Alternatively, at least the portion corresponding to the source region 14 is desirably formed so that the incident light 30 is substantially transmitted.

One imaging cell 10 includes an insulating layer 32 made of silicon oxide or the like.
and 34, and such cells 1O are arranged one-dimensionally or two-dimensionally on the main surface of the substrate 12 to form an imaging cell array.

In this way, a capacitor is formed between the electrode layer 2B and the n♦ region 14 with the dielectric layer 24 in between. As can be seen from the figure, the n◆ region 14 has three functions: the cathode of the photodiode, the source region of the IGFET, and one electrode of the capacitor, and these are commonly connected. Become. Therefore, the circuit of this image pickup cell 10 is as shown in FIG.

As can be seen from the figure, the cathode of the photodiode D, the source of the IGFET Q, and one electrode of the capacitor C are commonly connected in the region 14, and the rGFET
The drain I6 of the ET Q forms the output terminal for the signal current as the drain electrode 22. In this embodiment, ground voltage or a positive reference voltage of a predetermined value is applied to the other electrode 2B of the capacitor C, and a read gate pulse is applied to the gate 20. Therefore, as shown in the figure, by connecting the power source E to the output terminal 22 via the resistor R, the signal voltage Vout can be obtained at the output terminal 22.

As shown by the arrow 30 in FIG. 1, when the photodiode region is irradiated with light, some of the photocarriers excited in the pn junction region of the photodiode D are accumulated there,
The remainder is stored in capacitor C. As can be seen from FIG. 2, the capacitor C is connected in parallel with the pn junction capacitance of the photodiode D in terms of circuit. therefore,
The total capacity that can store optical carriers is the sum of the capacitance of the capacitor C and the capacitance of the pn junction.

In the configuration of the solid-state photodetection device according to the prior art, the capacitor C as in the present embodiment was not provided.
The device of this embodiment has a charge storage capacity larger than that of the conventional device by the capacitance of the capacitor C. That is, the intensity of the incident light 30 required to feed the entire capacity of the imaging cell 10 is that much higher. Therefore, the imaging cell l
The dynamic range of O is wider than the conventional one by an amount equivalent to the capacitance of capacitor C.

Although an embodiment in which the solid-state photodetection device according to the present invention is applied to a one-dimensional or two-dimensional imaging cell has been described, it goes without saying that the present invention can also be advantageously applied to a single-cell photodetection device.

As described above, the solid-state photodetection device according to the present invention has a large storage capacity for generated photocarriers.

A sufficiently wide dynamic range is achieved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view schematically showing the structure of an embodiment of a solid-state photodetection device according to the present invention, and FIG. 2 is a circuit diagram showing a schematic equivalent circuit of the solid-state photodetection device shown in FIG. 1. ,'-'+1 10,,,Imaging cell 14,,,N+ region 4,,,Dielectric layer 26t,,,Electrode layer C01,Capacitor patent applicant Fuji Photo Film Co., Ltd. Agent Takao Katori i! ′, ゛: i sail I tumo 2

Claims (1)

[Claims] 1. A semiconductor substrate of one conductivity type, a region of the other conductivity type formed on one main surface of the substrate and forming a pn junction with the substrate, and readout means for reading out photocarriers excited in the pn junction by light incident on the main surface, the solid-state photodetection device comprising It has a dielectric layer formed on a surface, and an electrode layer formed to cover the dielectric layer, and a part of the optical carrier is controlled by the region of the other conductivity type, the dielectric layer, and the electrode layer. A solid-state photodetection device characterized in that it forms a capacitor that accumulates. 2. The solid-state photodetection device according to claim 1, wherein the electrode layer includes a material transparent to light.