JPS624362A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To prevent remained charges from being created at the photoelectric converting section and to prevent a residual image phenomenon from occuring, by increasing gradually the width of the transfer gate as it proceeds toward the vertical transfer section from the photoelectric converting section. CONSTITUTION:After a P-type wafer 12 is formed on an N-type semiconductor substrate 11, a photolithography technique forms a photoelectric converting section 8, a vertical transfer section 9 and a transfer gate 10. The photoelectric converting section 8 consists of a photo diode with a PN junction, which does photoelectric-converting according to light from an image-pickup body to create charges serving a an image pickup signal and to store the charges temporarily. The vertical transfer section 9 consists of a CCD, transferring the image pickup signal charges to the horizontal transfer section. The transfer gate 10 is formed into a trapezoidal shape which has the width being larger gradually L1-L2 from the photoelectric converting section 8 to the vertical transfer section 9.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a solid-state image sensing device, and more particularly to a solid-state one-image device capable of suppressing afterimage phenomena.

2. Description of the Related Art Recently, solid-state image pickup devices have begun to be used in household single-chip color cameras instead of image pickup tubes. Solid-state single image elements have many advantages over image pickup tubes, such as no burn-in and long life. Various structures have been proposed for this solid-state image sensor, one of which is a charge-coupled device (Charge) that has both a light weight conversion function and a self-scanning function.
There is a solid-state image sensor called an e-coupled device (hereinafter abbreviated as CCD). Imaging methods using COD include a frame transfer method and an interline method, and the interline method will be described here. The interline system has a configuration in which a photoelectric conversion section and a transfer section that performs signal scanning are spatially separated.

This interline method uses multiple lights arranged vertically! The structure consists of a conversion section and a vertical transfer section arranged to extend vertically next to the photoelectric conversion section, and each photoelectric conversion section and vertical transfer section are connected to a transfer gate. has been done. The imaging signal photoelectrically converted in the photoelectric conversion section is transferred to the vertical transfer section via the transfer gate. As shown in FIG. 7, a conventional interline transfer type solid-state image sensor 1
In the above, the shape of the transfer gate 1-4 connecting the photoelectric conversion unit 2 and the vertical transfer 8I13 was rectangular.

Problems to be Solved by the Invention Here, in the solid-state imaging probe 1 in which the transfer gate 4 has a rectangular shape as in the past, one photoelectric conversion unit 2
A potential diagram of the transfer gate 4° vertical transfer section 3 corresponding to the above is shown in FIG.

Note that in the same figure, the photoelectric conversion unit 2. The potentials corresponding to the vertical transfer unit 3° transfer 7 games 1 to 4 are shown with raJ appended to each symbol. Also, in the diagram, 5 is Goo 1~
The diagonal a of the electrode for applying a voltage indicates a signal charge, and the figure shows a state in which no gate voltage is applied. When a gate voltage is applied to the electrode 5, the transfer gate 4 is connected to the channel 4-1 as shown in FIG.
is formed, and the imaging signal charge 6 photoelectrically converted in the photoelectric conversion section 2 is transferred to the vertical transfer section 3 through the channel 4-1.

However, in the conventional solid-state imaging probe 1 described in F, the shape of the transfer gate 4 is rectangular, so that the potential 4a of the transfer gate 4 when a gate voltage is applied to the electrode 5 is on the photoelectric conversion unit 2 side. From there, the potential becomes flat toward the vertical transfer section 3 side. As the transfer progresses, the amount of charge to be transferred decreases, and the potential of the photoelectric conversion unit 2 approaches as much as 1 to the potential of the transfer gate 4. As a result, diffusion-based transfer becomes dominant, resulting in very poor transfer efficiency. Therefore, the moment the application of the gate voltage is stopped, charges that are not transferred to the photoelectric conversion section 2 remain. There is a problem in that this residual charge is superimposed on the charge of the next frame, resulting in a so-called afterimage phenomenon.

Therefore, in the present invention, the above-mentioned problem is solved by configuring the 1-transfer gate to have a potential gradient that increases from the photoelectric conversion section side to the vertical transfer section side when the 1-transfer gate voltage is applied. The purpose is to provide a solid-state imaging probe that solves the problem.

Means for Solving the Problems In order to solve the above problems, the present invention employs interline transfer in which the carrier signal photoelectrically converted in the photoelectric conversion section is transferred to the vertical transfer section via the transfer game 1. In the solid-state imaging probe of this type, the potential of the transfer gate during transfer of the image signal from the photoelectric conversion section to the vertical transfer section is set so that the potential gradient increases from the photoelectric conversion section side to the vertical transfer section side. The width of the transfer gate was formed to increase from the photoelectric conversion section side toward the vertical transfer section side.

Embodiment FIGS. 1 and 2 show an embodiment of the solid-state imaging cable according to the present invention. Both figures show an interline type COD solid state 11 [141] using the present invention shown in FIG. 3 is an enlarged view showing the vicinity of the vertical transfer section 9. FIG. Moreover, FIG. 2 shows the AA cross section in FIG. 1. The solid-state spa element 7 shown in FIGS. 1 and 2 has approximately a photoelectric conversion section 8. °Vertical transfer section 9. Transfer gate 1
It is composed of 0, etc. L light distribution electric conversion section 8. Vertical transfer section 9. The transfer gate 10, as shown in FIG.
First, a P well 12 is formed on an n-type semiconductor substrate 11, and then a photolithography technique is used. Note that 13 is a 5fOz film for insulation (not shown with a satin finish in FIG. 1. Note that the 5iO2B film on the photoelectric conversion section 8, vertical transfer section 9, and transformer 77 gate 10 has a matte finish.); 14 is a gate electrode.

The photoelectric conversion unit 8 is a pn junction photodiode, which performs photoelectric conversion in response to light from the image pickup body, generates a charge that becomes an image pickup signal, and temporarily converts this Ti charge into M. The vertical transfer section 9 is composed of a CCD, and transfers the image signal charge transferred from each photoelectric conversion section 8 to the horizontal transfer section 15 (shown in FIG. 3). As shown in FIG. 1, the transfer gate 10 has a trapezoidal shape whose width gradually increases from the photoelectric conversion section 8 side toward the vertical transfer section 9 side. The width dimension (indicated by arrow L+ in FIG. 1) of the transfer gate 10 on the side of the photoelectric conversion section 8 is selected to be small enough to produce a narrow channel effect.

Also, the goo on the vertical transfer section 9 side of the transfer gate 10]
- The width dimension (indicated by arrow L2 in FIG. 1) is selected to be larger than Ll.

Here, consider the potential when the transfer gate width is changed in the solid-state image transfer element 7 as shown in FIG. FIG. 4 shows the change in the potential of the signal 'mA when the transfer gate I width is changed. As shown in the figure, when the transfer gate width is equal to or larger than a certain dimension (indicated by L3 in the figure), the potential shows a certain high value. However, as the transfer gate width becomes narrower than in the above M method 1-3, the potential becomes smaller and a narrow channel effect occurs.

In view of the above points, the charge potential state of the l-transfer gate 10 having the shape shown in FIG. 1 will be described below. As described above, the gate width dimension L1 of the transfer gate 10 on the photoelectric conversion section 8 side is selected to be a small dimension that causes a narrow channel effect, and the gate width dimension L1 of the transfer gate 10 on the vertical transfer section 9 side is selected to be a small dimension that causes a narrow channel effect. L2 is the gate width dimension and is selected to be larger than 1. Therefore,
When a gate voltage is applied to the gate electrode 14, the potential state of the transfer gate 10 becomes as shown in the potential diagram shown in FIG. As the potential on the photoelectric conversion section 8 side becomes smaller and the potential on the vertical transfer section 9 side increases, the potential between the photoelectric conversion section 8 and the vertical transfer section 9 corresponds to the width dimension of the transfer gate 10. A potential state with a potential gradient is created in which the potential iz becomes extremely large toward the vertical transfer section 9. Note that since the signal charges (11 children) 16 are pulled toward the direction having a larger potential, the transfer speed of the signal charges 16 becomes faster in the 1-transfer 1-10 having a potential gradient. Note that in the same figure, the photoelectric conversion section 8. Vertical transfer section 9.1 to transfer gate 10
The potentials corresponding to each are shown with raJ appended to each code.

The procedure for transferring the m-image signal in the solid-state image carrier 7 having the above configuration will be described below. When light from the imaging body enters the photoelectric conversion unit 8, the energy of this light excites signal charges 16 that become carrier signals and accumulates them in the photoelectric conversion unit 8 (as shown in FIG. 6). Next, when a gate voltage of 1.degree.

At the same time, the potential of the vertical transfer section 9, which is also arranged in a part of the goo 1-electrode 14r, increases, and the signal charge 16 accumulated in the photoelectric conversion section 8 passes through the channel 10-1 and passes through the vertical transfer section. Transferred to 9.

When the signal charge 16 is transferred from the photoelectric conversion section 8 to the vertical transfer section 9, the potential of the transfer gate 10 has a potential gradient that increases from the photoelectric conversion section 8 side to the vertical transfer section 9 side. The transfer speed of the signal charges 16 is accelerated within the channel 10-1, and the transfer of the signal charges 16 is performed at extremely high speed. Therefore, even if the gate voltage is applied and stopped to the gate electrode 14, the channel 10-1
Since the signal charge 16 does not remain in the photoelectric conversion section 9 and the signal charge 16 is transferred at extremely high speed as described above, so-called incomplete transfer occurs in which the signal charge 16 remains in the photoelectric conversion section 9. It is possible to realize a good image carrying screen without any afterimage phenomenon.

Note that the configuration in which the transfer speed of charges transferred within the channel is increased by appropriately selecting the transfer gate width by utilizing the narrow tI channel effect as described above is similar to the solid-state image device 7 described above. MOS (met
al oxide sc+5iconductor)
The device is also considered to have 14 applications. In other words, the channel width of the transfer gate in a MOS t-transistor is set so that the source side is narrow enough to cause the 1-channel effect, and the train side is set to a larger width, thereby increasing the charge velocity in the channel. Therefore, the switching speed can be improved.

Effects of the Invention As described above, according to the solid-state image device of the present invention, the potential of the transfer gate when transferring the image signal from the photoelectric conversion section to the vertical transfer section is changed from the photoelectric conversion section side to the vertical transfer section side. By forming the width of the transfer gate in such a shape that it becomes larger from the photoelectric conversion section side toward the vertical transfer section side, the width of the transfer gate becomes larger toward the vertical transfer section so that the gradient of the potential becomes larger towards the right side. The signal charge is gradually accelerated as it passes through the transfer gate, and the signal charge can be transferred from the photoelectric conversion section to the vertical transfer section at extremely high speed. Even if the signal charges accumulated in the photoelectric conversion section are almost all transferred to the vertical transfer section, and
No signal charge remains in the transfer gate 1- when the application of the i-pressure is stopped, and therefore a good image carrying screen with less occurrence of afterimage phenomenon can be realized.

[Brief explanation of the drawing]

FIG. 1 is a plan view (not shown in an enlarged manner) of a portion near the transfer gate of an embodiment of the solid-state image sensor according to the present invention, FIG. 2 is a cross-sectional view taken along line A-A in FIG. 1, and FIG. A diagram showing the overall configuration of the solid-state Iff image element according to the present invention, Figure 4 is a diagram for explaining the narrow channel effect, and Figure 5 is a diagram showing the potential when a gate voltage is applied in the solid-state single image element according to the present invention. Figure 6 is a diagram to explain the potential state when the application of gate voltage is stopped in Figure 5. Figure 7 is a diagram showing the vicinity of the transfer gate of an example of a conventional solid-state image sensor. A diagram showing an enlarged view of
Figure 8 is a diagram for explaining the potential state when no gate voltage is applied in a conventional solid-state image sensor, and Figure 9 is a diagram for explaining the potential state in Figure 8 when the gate voltage is applied. This is a diagram for 7... Solid-state ll image element, 8... Photoelectric conversion section, 9...
・Vertical transfer section, 10...Transnor gate, 10-
1... Channel. Characteristics Applicant: Victor Japan Co., Ltd. Figure 1 1 w! , 2 Figure W, 6 Figure 7

Claims (1)

[Claims] In an interline transfer type solid-state image sensor that transfers an image signal photoelectrically converted in a photoelectric conversion section to a vertical transfer section via a transfer gate, when the image signal is transferred from the photoelectric conversion section to the vertical transfer section. so that the potential of the transfer gate in has a potential gradient that increases from the photoelectric conversion section side to the vertical transfer section side,
1. A solid-state image pickup device, characterized in that the width of the transfer gate increases from the photoelectric conversion section side toward the vertical transfer section side.