JPH063454A - Internal amplification type solid-state image sensor - Google Patents

Abstract

PURPOSE:To enable the detection of various corpuscular beams two- dimensionally at a high sensitivity and with higher resolving power by arranging a thin film layer comprising material with high quantum efficiency on the surface of a metal electrode exposed to the surface of an element. CONSTITUTION:A thin film forming material is preferably high in absorption coefficient having an absorption end in an area of a wavelength shorter than the wavelength of light to be detected and a compound material such as CsI or MgF2 is ideal in an ultraviolet ray area. When the CsI is applied to the surface of an aluminum electrode 1, for instance, connected being exposed to a photodiode structure area 2 formed at a lower layer part at a thickness of about 350Angstrom . the quantum efficiency shows a high value of 20-30% in an ultraviolet area with the wavelength thereof shorter than about 1200Angstrom . The electrode 1 has the quantum efficiency of below about 1% in the wavelength area and the electrode 1 forming a CsI thin film layer improves the sensitivity by more than two order of magnitude. Thus, when a particle beam is applied, a large number of electrons can be released thereby increasing a current value to be read out with an increase in charge value to be accumulated in the area 2.

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 sensor used for detecting ultraviolet rays and soft X-rays (light having a wavelength of several Å to several hundred Å) and observing an object with soft X-rays, especially for each pixel. The present invention relates to an internal amplification type solid-state imaging device in which a metal connected to one side of a capacitive structure region is exposed on the surface.

[0002]

2. Description of the Related Art FIG. 2 shows an internal amplification type solid-state image sensor (AM).
The structure for one pixel of I) is shown. In the figure, reference numeral 1 denotes a metal electrode (mainly an aluminum electrode) exposed on the surface of the device, which is connected to a photodiode structure region 2 formed in a lower layer portion thereof. FIG. 3 is an equivalent circuit diagram of the above element, and the inside of a dotted line frame corresponds to one pixel. When a particle beam is incident on the surface of the electrode 1, electrons are emitted from the surface. At that time, the positive charge generated from the electrode is accumulated in the photodiode section D of the capacitor C _PD , and the accumulated charge amount is the incident particle. Corresponding to the number of. The potential due to this accumulated charge is applied to the gate of the amplification transistor Ta, and the amplified current is read out through the vertical scanning switch Ty and the horizontal scanning switch Tx. As described above, according to the internal amplification type solid-state imaging device, various particle beams can be two-dimensionally detected with high resolution.

[0003]

By the way, as is clear from FIG. 4 showing the characteristics of the quantum efficiency of aluminum, aluminum has a quantum efficiency in the ultraviolet to soft X-ray region (for one incident photon, the The number of generated electrons) is less than 20% at maximum, and is 1 especially in the ultraviolet region.
%, The sensitivity of the device as a detector was extremely low.

The present invention has been made in view of the above problems of the solid-state image pickup device of this type, and an object of the present invention is to provide internal amplification having high detection sensitivity in the ultraviolet to soft X-ray region. A solid-state image sensor is provided.

[0005]

In order to achieve the above object, in the internal amplification type solid-state image pickup device according to the present invention,
A thin film layer made of a substance having high quantum efficiency is provided on the surface of the metal electrode exposed on the device surface.

[0006]

This internal amplification type solid-state image pickup device can emit more electrons as compared with the conventional device due to the incidence of the particle beam, and therefore the amount of positive charges accumulated in the photodiode section also increases. , The read current value also increases.

It is desirable that the material forming the thin film layer has a high absorption coefficient having an absorption edge in a wavelength region shorter than the wavelength of light to be detected. In the ultraviolet region, compounds such as CsI and MgF ₂ are suitable as the thin film layer forming substance.

[0008]

EXAMPLE A conventional internal amplification type solid-state image pickup device was used, and 350 CsI was applied to the exposed surface of the aluminum electrode 1.
A thin film layer was formed by coating so as to have a thickness of 0Å. FIG. 1 shows the quantum efficiency at this time. According to this figure, the quantum efficiency is 20 in the UV region shorter than 1200 Å.
It can be seen that a very high value of -30% is exhibited. Although the aluminum electrode 1 has a quantum efficiency of 1% or less in this wavelength region, it can be seen that the sensitivity is improved by about two orders of magnitude according to the present embodiment.

[0009]

As described above, according to the present invention, it is possible to provide a solid-state image sensor capable of two-dimensionally detecting various particle beams with high sensitivity and high resolution.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing quantum efficiency of a thin film layer in an example of the present invention.

FIG. 2 is a diagram showing a structure of one pixel of an internal amplification type solid-state imaging device.

FIG. 3 is an equivalent circuit diagram of the device shown in FIG.

FIG. 4 is a characteristic diagram showing the quantum efficiency of aluminum.

[Explanation of symbols]

 1 metal electrode 2 photodiode structure area

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[Procedure amendment]

[Submission date] July 10, 1992

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[0002]

2. Description of the Related Art FIG. 2 shows an internal amplification type solid-state image sensor (AM).
The structure for one pixel of I) is shown. In the figure, reference numeral 1 denotes a metal electrode (mainly an aluminum electrode) exposed on the surface of the device, which is connected to a photodiode structure region 2 formed in a lower layer portion thereof. FIG. 3 is an equivalent circuit diagram of the above element, and the inside of a dotted line frame corresponds to one pixel. That is, AM
One pixel of I is composed of an n + p photodiode D as a photoelectric conversion unit, a reset transistor Trs, an amplification transistor Ta, and three n-channel MOSFETs for a vertical scanning switch Ty. The horizontal scanning switch Tx is provided for each vertical signal line. In principle, the photodiode is reverse-biased to be discharged by photocharge, and the potential thereof is current-amplified and taken out. The basic operation is as follows. In the reset period, the photodiode D is set to the initial value Vrs (positive potential) via the reset transistor Trs. In the storage period, of the electron-hole pairs excited by the irradiation of light, the electrons are stored in the capacitance C _{PD of the} photodiode D and the holes flow out to the substrate. Therefore, the potential of the photodiode D decreases according to the incident light. This potential is applied to the gate of the amplification transistor Ta, and the amplified current corresponding to the potential of the photodiode D is read out through the vertical scanning switch Ty and the horizontal scanning switch Tx. As described above, according to the internal amplification type solid-state imaging device, various particle beams can be two-dimensionally detected with high resolution.

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[0003]

By the way, as is clear from FIG. 4 showing the characteristics of the quantum efficiency of aluminum, aluminum has a quantum efficiency (incident wavelength) from the ultraviolet to the soft X-ray region (wavelength number Å to several thousand Å). The number of electrons generated from the surface for one photon) was less than 20% at the maximum, and was 1% or less particularly in the ultraviolet region, so the sensitivity of the detector element was extremely low. . ─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] January 26, 1993

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[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image sensor used for detecting ultraviolet rays and soft X-rays (light having a wavelength of several Å to several hundreds nm), observing an object with soft X-rays, and particularly for each pixel. The present invention relates to an internal amplification type solid-state imaging device in which a metal connected to one side of a capacitive structure region is exposed on the surface.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shoichiro Mochimaru 2-43-2 Hatagaya, Shibuya-ku, Tokyo Inside Olympus Optical Co., Ltd.

Claims (1)

[Claims] 1. An internal amplification type solid-state imaging device in which a metal electrode connected to a capacitive structure region of each pixel is exposed on the surface, and a thin film layer made of a substance having high quantum efficiency is provided on the surface of the metal electrode. A solid-state imaging device characterized by the above.