JPS5827711B2 - Kotai Satsuzou Sochi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solid-state imaging device using a charge coupled device.

A charge-coupled device (hereinafter referred to as CCD) is a common name these days, and it is a charge-coupled device (hereinafter referred to as CCD), which is a charge-coupled device (hereinafter referred to as CCD), which is a charge-coupled device. device that stores and transfers electrical charge in a medium (medium).

One method for generating charges in a storage medium for the CCD is to generate electron-hole pairs in the storage medium by photon absorption.

In this case, the amount of charge accumulated changes depending on the intensity of the incident light.
By placing , a charge image corresponding to the optical image can be obtained, and by transferring and reading out this charge image, the optical image can be taken out as an electrical signal.

In other words, a solid-state imaging device using a CCD is realized.

When a solid-state imaging device as described above is composed of only one electrode array, charge storage and transfer must be performed alternately.

Therefore, since it is impossible to prevent light from hitting the CCD during the transfer period, the resolution deteriorates due to the light incident during the transfer period.

In order to solve this problem, it has been proposed to configure a solid-state imaging device with two electrode arrays, and is currently being put into practical use.

In a solid-state imaging device with such a structure, one electrode array functions as a photoelectric conversion element array (hereinafter referred to as a sensor array), and the other serves as an accumulation button and readout electrode array (hereinafter referred to as a shift register). .

In such a device, an entire frame of charge accumulated under the sensor array is rapidly transferred from under the sensor array to under the shift register.

The charge is then transferred under the shift register and read out while the charge for the next frame is stored under the sensor array.

When repeating this operation, if the shift register is shielded from light in some way, there will be no degradation in resolution due to photon absorption during readout.

FIG. 1 is an example of a conventional solid-state imaging device in which the sensor array and shift register as described above are constructed from separate electrode arrays.

In the figure, 1 is a sensor array composed of n potential wells spatially separated by channel stoppers, 2 is a transfer gate for transferring signal charges from the sensor array to the shift register, Reference numeral 3 designates a shift register constituted by a two-phase CCD, 4 an input circuit for manual bias charging, and 5 an output circuit for reading signal charges.

Further, Φ1 and Φ2 represent clock lines for driving the shift register, and Φ and r represent clock lines for the transfer gate.

In such a device, in order to prevent deterioration of resolution due to the mixing of signal charges with charges generated by absorption of photons in parts other than the sensor array during transfer or accumulation of signal charges, it is necessary to Parts must be shaded in some way.

As a means of illumination, sensors and
Generally, a method is used in which only the array portion is irradiated with light, or a method is used in which a portion of the device itself other than the light receiving portion is covered with an opaque thin film such as A1.

When considering the latter method, that is, covering the device itself, in order to obtain the effect of preventing resolution deterioration with this method, the charge generated by absorption of photons in areas other than the sensor array must be absorbed by the sensor array or the device itself. should not reach the channel area of the shift register.

Therefore, the area to be covered with the Al thin film must extend from the periphery of the sensor array button and the channel region of the shift register by at least 1 or more than the charge diffusion length.

For example, when the storage medium is silicon Si and the accumulated charges are electrons, the diffusion length is 100 μ or more.

Considering applying a coating that satisfies the above conditions to the conventional device shown in FIG. (The shaded area in the diagram)
Coating can be done relatively easily.

On the other hand, there is a demand for simplifying the manufacturing process by using the same material as the wiring, such as Al, for the coating.

When the covering and wiring are made of the same material, the covering between the left and right sides of the figure, that is, from both ends of the sensor array 1 to the input section 4 and the output section 5 is (from the relationship with the wiring of the input/output section)
This is not possible unless measures such as increasing the distance between both ends of the sensor array 1 and the input/output sections 4 and 5 or increasing the number of layers of multilayer wiring are taken.

For example, the output section has a structure as shown in FIG. 3 as an example.

That is, the upper and lower two channel shift registers 1 and 2 each have a timing gate 3.4 and a P-N junction 5.4 adjacent to the final stage transfer electrode. A reset gate 6.7 and reset drains 8, 9 are provided, and a MOS-Trlo is connected to the PN junction for the purpose of amplifying the potential change of the junction.

As is generally known, the operation of this output section is such that the charge transferred from the reset drain to the P-N junction, which is reverse biased to voltage VR through the reset gate, is transferred through the shift register through the timing gate. The change in potential of the P-N junction that occurs when the current flows in 1 to 1 is amplified by the MOS-Tr and read.

Therefore, in order to prevent reading errors caused by structural imbalance between the output section and the upper and lower shift registers, it is desirable that the structure of the output section be symmetrical with respect to the upper and lower shift registers. The MOS-Tr connection must be made at the center of the PN junction.

For example, each electrode of the output section having a structure as described in 1 to 1 above is
If wiring is done at the same time as a light shielding film made of a metal such as L, it is extremely difficult to shield the right end of the sensor array closest to the output section.

Therefore, in conventional solid-state imaging devices, the sensor array is coated only in the upper and lower directions, as shown by diagonal lines in FIG.

Therefore, for a conventional solid-state imaging device, the potential wells of the photosensitive element near both ends of the sensor array 1 are generated due to photon absorption in the vicinity of the sensor array 1 and the human output parts 4 and 5. Or, because it flows into the potential wells near both ends of the upper and lower shift registers and mixes with the signal charges,
There was a drawback that the resolution at both ends of the sensor play was significantly reduced.

Furthermore, when coating both ends of the sensor array using the above method, the former method increases the resistance and capacitance of the electrodes, and also increases the chip area, while the latter method complicates the manufacturing process. There was a disadvantage of doing so.

An object of the present invention is to improve the drawbacks of these conventional solid-state imaging devices and to provide a solid-state imaging device that does not suffer from deterioration in resolution due to charges generated by photon absorption in areas other than the sensor array. It is in.

According to the present invention, at least one photoelectric conversion element is provided at both ends of an effective sensor array that operates as a light receiving part for a solid-state imaging device, and a measure for transferring the charges accumulated in the photoelectric conversion element is provided. A solid-state imaging device is obtained, which is characterized by a structure in which a transfer gate and a shift register are provided, and the photoelectric conversion element and the opposing shift register are illuminated.

The present invention will be explained below with reference to the drawings.

FIG. 2 is a schematic structural diagram of a solid-state imaging device showing one embodiment of the present invention.

This figure is shown by a configuration diagram similar to the above-mentioned FIG. - Indicates an array, 7 indicates a transfer gate, and 8 indicates a shift register including transfer electrodes corresponding to the 42 photoelectric conversion elements 1 to . 9 indicates an input circuit, and 10 indicates an output circuit.

In the figure, the shaded area indicates the area covered with the light film.

As is clear from the figure, the opening of the photoelectric conversion element according to the present invention is completely covered.

To explain the basic operation of this device, first, an appropriate voltage is applied to the sensor array 6 to create a potential well in the semiconductor substrate.

When an optical image is formed on the sensor array in this state, minority carriers are accumulated in the potential well in proportion to the potential strength (accumulation period).

Next, by applying a predetermined voltage to a predetermined electrode of the transfer gate 7 and the shift register 8, a channel is formed under the transfer gate and at the same time a potential well is formed under the shift register.

In the case of the present invention, a potential is applied to 7 to form a channel under the transfer gate, a pulse is applied to Φ2 to form a large surface potential, and a pulse to Φ1 is applied to create a small surface potential. do.

Next, the voltages of the sensor array and transfer gate are sequentially decreased to transfer all the charges in the sensor array to the bottom of the shift register, and then a clock pulse is applied to the shift register to transfer the charges from the output section of 10. Reads signal charges.

Due to the above operation, in conventional devices, during the accumulation period, charges generated by light incident on parts other than the sensor array near the input/output section are diffused and flow into the photoelectric conversion elements at both ends of the sensor array. However, according to the present invention, the charge generated by the incident light on the area other than the sensor play near the human output section is located at both ends of the sensor array, and Since the incident light flows into the potential well of the photoelectric conversion element (A, opening in Figure 2) that is illuminated by the incident light, it has no effect on the n-type photoelectric conversion elements that make up the sensor array. It doesn't even give.

It is clear that the effect will be more pronounced if two or more pairs of photoelectric conversion elements and shift registers coated with these opaque films are provided at both ends.

Therefore, it is possible to obtain a solid-state imaging device without any deterioration in resolution at both ends of the sensor array as seen in conventional devices.

In explaining the present invention, the specific material structure driving method of a solid-state imaging device using a charge-coupled device has been described above, but the main purpose of the present invention is the structure of the end portion of the sensor array, and the above description is It is clear that this is not intended to limit the invention in any way.

[Brief explanation of the drawing]

FIG. 1 shows a configuration diagram of a solid-state imaging device using a conventional charge-coupled device, and FIG. 2 is a schematic configuration diagram showing an embodiment of the present invention. In the figure, 1 and 6 are sensor arrays, 2 and 7 are transfer gates, 3 and 8 are shift registers, 4 and 9 are input circuits, and 5
, 10 indicates an output circuit. In the button diagram, ``A'' and ``Open'' indicate photoelectric conversion elements according to the present invention. Additionally, Φ1 and Φ2 represent the clock lines of the shift register, Φ3 represents the clock line of the transfer gate, and the shaded area indicates that a light shield is provided. FIG. 3 shows a schematic diagram of an example of an output section of a solid-state imaging device using a charge-coupled device. In the figure, 12 is a shift register, 3 and 4 are timing gates, 5 is a P-N junction, 6,
7 is the reset gate, 8°9 is the reset drain, 10
indicates a MOS-Tr.

Claims (1)

[Claims] 1. For a solid-state imaging device composed of a photoelectric conversion element array, a charge transfer gate, a shift register, and a charge detection element formed on the same semiconductor substrate, effective photoelectric conversion element rows constituting the photoelectric conversion element array are At least one dummy photoelectric conversion element and a shift register facing the element for taking out the charge in the photoelectric conversion element are arranged at both ends, and the photoelectric conversion element and the opposing shift register are covered with an opaque thin film. A solid-state imaging device characterized by being shielded from light by a covering.