JPH04125963A - Photoelectric conversion device - Google Patents

Abstract

PURPOSE:To make equal the signal charge storage times in photodiodes between all pixels by a method wherein switching of reset switches and transfer switches are controlled equally in respect to all the pixels. CONSTITUTION:A plurality of pixels are respectively constituted of each of photodiodes PD1 to PDn on a P-type substrate and moreover, each of capacitors C1 to Cn, each of transfer switches ST1 to STn and each of reset switches SDR1 to SRDn are provided in every pixel of the plurality of the pixels. The reset switches SRD1 to SDRn and the transfer switches ST1 to STn are controlled in such a way that they can be simultaneously switched in respect to the plurality of the pixels.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a photoelectric conversion device that sequentially reads out signal charges photoexcited by photodiodes for each pixel.

[Conventional technology]

The signal charges of the photodiodes that make up multiple pixels are
As a typical example of a conventional device that sequentially reads out each pixel, the third
There are those shown in the figure. As shown in FIG. 2(a), an n-type light-receiving region 2 is formed on a p-type substrate 1 made of silicon or the like to constitute a photodiode. , n-type accumulation region 3 is formed. Then, the n-type light receiving region 2 and the n-type accumulation region 3
A read gate electrode 4 is provided on the p-type substrate 1 between the two through an insulating film (not shown). If this is shown as an equivalent circuit, it will be as shown in FIG. 3(b).

That is, the photodiode PD composed of a p-type substrate 1 and an n-type light receiving region 2 is a readout switch S having an FET structure composed of an n-type light receiving region 2, an n-type accumulation region 3, and a readout gate electrode 4. is connected to the video line VL via.

According to the above device, the photodiode PD for each pixel
The signal charge is transferred to a readout switch S that is opened and closed for each pixel.

is output to the video line VL. The amount of signal charge that can be stored, that is, the amount of saturated charge, is determined by the area of the photodiode PD.

[Problem to be solved by the invention]

However, in the conventional device described above, since the successive switch So is sequentially opened and closed for each pixel, the accumulation time of the signal charge by the signal light IN differs from pixel to pixel. Furthermore, if the photodiode PD is made larger in order to increase the amount of saturated charge, the pn junction area becomes larger and dark current increases.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a photoelectric conversion device that can make the accumulation time of signal charges the same for each pixel and can increase the amount of saturation charge without increasing dark current.

[Means to solve the problem]

A photoelectric conversion device according to the present invention is a device in which a plurality of pixels are each constituted by a photodiode on a single semiconductor substrate, and signal charges caused by photoexcitation of the photodiodes are sequentially read out via a readout switch and output as a video signal. , a capacitor configured by forming a wiring layer on a semiconductor substrate via an insulating film so as to be connected in parallel with a photodiode, a transfer switch connected between the photodiode and the capacitor, and a capacitor connected to the photodiode in parallel. A connected reset switch is provided for each pixel, and the reset switch is opened and closed simultaneously for multiple pixels when the photodiode starts to accumulate signal charges, and the transfer switch is opened and closed for multiple pixels simultaneously when the accumulation of signal charges ends. It is characterized by being able to be opened and closed.

[Effect]

According to the present invention, by controlling the opening and closing of the reset switch and the transfer switch in the same manner for all pixels, it is possible to make the signal charge accumulation time in the photodiode the same for all pixels.

In addition, the signal charge sent from the photodiode via the transfer switch can be stored in a capacitor constructed by forming a wiring layer on the semiconductor substrate, so the amount of saturation charge can be increased without increasing the size of the photodiode. .

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows the configuration of a photoelectric conversion device according to an embodiment, with FIG. 1(a) being a sectional view and FIG. 1(b) being an equivalent circuit diagram thereof.

As shown in FIG. 5A, an n-type region 5 doped with impurities is formed near the n-type light-receiving region 2 formed on the p-type substrate 1, and between the n-type light-receiving region 2 and the n-type region 5. A transfer gate 6 is formed on the p-type substrate 1 via an insulating film (not shown), and this FET structure constitutes a transfer switch sT. The n-type light receiving region 2 is connected to a reset power supply terminal via a light receiving region reset switch SRD. Note that this light-receiving region reset switch SRD is formed of, for example, a MOSFET on a p-type substrate. n-type region 5
is connected to an n-type drain 8 forming an output FET via a wiring 7 made of polysilicon, aluminum, or the like.

This FET includes the n-type drain 8, the n-type source 9 and the gate electrode 10, thereby causing a subsequent switch S.

is configured. Here, since the wiring 7 is formed on the p-type substrate 1 via an insulating film (not shown) or is formed of two layers of polysilicon sandwiching the insulating film, the capacitor C (dotted line in the figure) is generated.

As a prior art similar to this embodiment, for example, Japanese Patent Laid-Open No. 63
−． 157581 is known, but in this example, a device consisting of a photodiode, a switch, a scanning circuit, etc. is configured on a single semiconductor substrate, and a capacitor C is connected in parallel to the photodiode. It is characterized in that it is formed by wiring 7 made of polysilicon or the like.

Since the capacitor C is formed by the wiring 7, the amount of saturation charge can be increased without increasing the dark current. Specifically, the dark current can be reduced by about three orders of magnitude compared to when the pn junction of the photodiode is made larger to increase the amount of saturation charge. In addition, the capacitance of this capacitor C is such that the insulating film between the wiring 7 and the p-type substrate 1 is thin < (200 to 500
By setting A), it is possible to easily increase the size of the photodiode, and the amount of saturated charge can be increased with less than half the occupied area compared to the case where the photodiode has a large area.

FIG. 2 shows the overall configuration of the photoelectric conversion device shown in FIG. As shown in the figure, this photoelectric conversion device has n pixels from 1st to nth, and the signal charges of these photodiodes PD1 to PDo are sequentially read out by the scanning circuit 20 and sent to the video line. It is designed to be output as a video signal to VL.

The operation of the embodiment will be explained with reference to FIG.

The device of this embodiment accumulates and detects signal charges by repeating the following four steps. First, in the first step, with the readout switches So1 to S5 of all pixels, the capacitor reset switches 5RD1 to CnS, and the light receiving area reset switches 5RD1 to CnS open, a transfer control signal is used to control the transfer switches of all Dn pixels. ST1~ST1 are closed, and the signal charges of the photodiodes PD, ~PD, of all pixels are sent to the respective capacitors C1~Cn.Next, in the second step, the transfer switches ST1~''Tn of all pixels are in the open state. Then, the light receiving area reset switches S-8 of all pixels are closed, and the photo diodes PD1 to PDn are simultaneously reset.

Next, the light receiving area reset switch S-8 for all pixels
opens all at once, and the photo-excited signal RDI RDn begins to accumulate charge. Next, in the third step, the readout switches S01 to Son are set to the first (S) for each pixel.
The capacitors C1 to Cn are sequentially closed, and the signal charges of the capacitors C1 to Cn are sequentially read out to the video line VL. During this time, photodiodes PD1~
In the PD, signal charges continue to accumulate. In the next fourth step, the successive switch S is activated. 1 to Soo is completed for all pixels, the capacitor reset switch S-8 is closed, and the capacitor R
CI RCn 01-co is reset for all pixels.

Note that signal charges continue to be accumulated in the photodiodes PD1 to PDn during this period. When this fourth step is completed, the process returns to the first step and the transfer switches ST1 to ST
n is closed for all pixels. Therefore, it becomes possible to sequentially read out signals while maintaining the simultaneity of signal charge accumulation time. In this case, since the signal charge is held in the capacitor C, even if there is a dark current in the photodiode, the time change in the charge when read out by the scanning circuit is extremely small.

〔Effect of the invention〕

As described above in detail, in the present invention, by controlling the opening and closing of the reset/soto switch and the transfer switch in the same manner for all pixels, it is possible to make the signal charge accumulation time in the photodiode the same. In addition, a capacitor constructed by forming a wiring layer on a semiconductor substrate,
Since the signal charge from the photodiode can be accumulated, the amount of saturation charge can be increased without increasing the size of the photodiode. Therefore, simultaneousness can be ensured by making the accumulation time of signal charges the same for each pixel, and moreover, the amount of saturated charges can be increased without increasing dark current.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of the main parts of the photoelectric conversion device according to the embodiment, and Fig. 2
The figure is an overall configuration diagram of a photoelectric conversion device according to an embodiment, and FIG. 3 is a diagram showing a photoelectric conversion device according to a conventional example. 1...p-type substrate, 2...n-type light receiving region, 3...n
Type storage region, 4... Readout gate electrode, 5... N-type region, 6... Transfer gate, 7... Wiring, 8... N-type drain, 9... N-type source, S ,S-S
... Cabaret RCRCI RCn Shita reset switch, S, S -5RD R
DI RDn"' Light receiving area reset switch, 5S-S...T'
TI Tn Transfer switch, S, S-S ... Successive switch, 0
01 0n pD, PD1~PDo...Photodiode, VL・
...Video line.

Claims (1)

[Scope of Claims] A photoelectric conversion device in which a plurality of pixels are each constituted by a photodiode on a single semiconductor substrate, and signal charges caused by photoexcitation of the photodiodes are sequentially read out via a readout switch and output as a video signal. A capacitor configured by forming a wiring layer on the semiconductor substrate via an insulating film so as to be connected in parallel with the photodiode, and a transfer switch connected between the photodiode and the capacitor. , a reset switch connected to the photodiode is provided for each of the plurality of pixels, the reset switch is opened and closed simultaneously for the plurality of pixels when the photodiode starts accumulating the signal charge, and the transfer switch is A photoelectric conversion device characterized in that the plurality of pixels are simultaneously opened and closed upon completion of accumulation of the signal charge.