JPS647543B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor imaging device, and more particularly to a solid-state imaging device in which a plurality of photodetecting elements are arranged in one dimension.

Research on solid-state imaging devices has been conducted for some time, but as research into CCDs (charge-coupled devices) has progressed in recent years, the development of CCD imaging devices has progressed significantly and its applications have been actively pursued. Among these, one-dimensional imaging devices are becoming indispensable for the widespread use and speeding up of facsimile machines. However, CCD
Currently, facsimile using an imaging device has the following problems. Below, we will clarify this problem by explaining the concept of CCD imaging devices and the concept of facsimile.

As shown in FIG. 1, a one-dimensional light-detecting CCD imaging device has a large number of light-transmissive gate electrodes 3 made of a polycrystalline silicon thin film or the like on the surface of a semiconductor substrate 1 with a light-transparent insulating film 2 such as a silicon oxide film interposed therebetween. , 3 . Specifically, the photodetector section 4 and the CCD transfer section 5 are electrically connected via transfer gates 6, 6, . . . of signal transfer means.

In such a configuration, by applying a detection voltage (V _O ) to the gate electrodes 3, 3, . . . of the photodetecting section 4, inversion layers 7, 7, .
is generated, and the charges generated by the light irradiated at that time are accumulated in the inversion layers 7, 7..., and the charges are transferred to the CCD 5 by the transfer gates 6, 6...
An imaging output signal is obtained at the output terminal of CCD5.

On the other hand, in facsimile using a one-dimensional imaging device, a second
As shown in the figure, one line of an object 12 such as a drawing illuminated by a fluorescent lamp 11 is imaged using an optical system 13, and image signals are extracted for each line. When the signal for one line extracted in this way is observed with a synchroscope, the output level corresponds to a dark area of the object 12, for example, a black area with letters or lines in a drawing, as shown in Figure 3. is low, and conversely, the output level of white areas (bright areas) is high. Such an output signal is compared with a predetermined threshold voltage (V _T ) to determine whether the image is black or white.

However, if the object (drawing) is large, the brightness at the periphery of the object will be darker than the center due to problems with the optical system, and the output signal will be lower than the overall output level at the periphery, as shown in Figure 3. A decline is seen. Moreover, depending on the case, the output level corresponding to bright areas (white areas) in the periphery may be the threshold voltage [V _T ].
It may become lower. Of course, lowering the threshold voltage (V _T ) at that time will solve this problem in the peripheral areas, but it will no longer be possible to distinguish between black and white in the central area.

The present invention has been made in view of these problems, and its configuration is shown in FIG. 4.

In the figure, numerals 3, 4, 5, and 6 respectively indicate a light-transmissive gate electrode, a light detection section, a CCD transfer section, and a transfer gate as in FIG. , 6... The main feature lies in the signal transfer level applied to the signals. That is, as is clear from FIG. 4, the transfer gates 6, 6, . . . are cascade-connected via resistors 8, 8, . The gates 62, 62 at both ends are connected together and connected to a transfer voltage source 10 that sets a signal transfer level when transferring a signal from the photodetector 4 to the CCD transfer section 6.

Let us now consider the transfer operation in the signal transfer means. As shown in FIG. 5, a charge q corresponding to the amount of irradiated light is accumulated in the inversion layer 7 directly under the light-transmissive gate electrode 3 of the photodetecting section, and this charge q
By applying a transfer signal to the transfer gate 6,
It is transferred to the gate area of the CCD transfer unit 5, and when there is a large amount of charge q as shown in A of the same figure, and when there is only a small amount of charge q as shown in B of the figure, the same happens to the transfer gates 6, 6, etc. As previously explained, when the signal transfer level is set, the amount of transferred charge differs, causing the inconvenience shown in FIG. 3. Therefore, in the present invention, as shown in FIG. 5, the transfer level (E _T ) at a location (a) where a large amount of accumulated charge q is present is set higher than the transfer level (E _T ′) at a location (b) where a small amount of charge is present. Depending on the situation, the amount of charge transferred to the CCD transfer unit 5 is made uniform.

That is, as shown in FIG. 6, each transfer gate 6, 6...
The potential of is resistance 8, 8... and ground resistance 9
As shown by ( _E It increases at the end and decreases at both ends, so
These two signals are superimposed, and as a result, as shown in FIG. 7, the output signal does not vary depending on the location and can be made substantially uniform.

In this way, each time charges are accumulated in the inversion layers 7, 7 below each of the transparent gate electrodes 3, 3 in the photodetector 4, they are flattened by the transfer gates 6, 6... The charge is transferred to the CCD 5, and is taken out from the output terminal of the CCD 5 as an imaging output signal, but each time this one line of imaging output signal is taken out, it is transferred at each transfer gate 6, 6, etc. Each transparent gate electrode 3, 3... corresponds to the level.
The charges remaining in the lower inversion layers 7, 7, . . . are immediately erased. That is, a method for erasing such residual charges is to temporarily increase the voltage of the transfer voltage source 10 of the transfer gate 6 immediately before starting photoelectric conversion in the photodetector 4, and transfer all the remaining charges to the CCD 5. However, a method is adopted in which the CCD 5 is driven at high speed to immediately flush out the remaining charges to the outside. In addition, a transfer gate for residual charge and a drain for absorbing residual charge are provided adjacent to the transparent gate electrodes 3, 3, . A transfer signal is applied to the transfer gate for residual charge to transfer each transparent gate electrode 3, 3...
The gate electrodes 3, 3... can be drained by draining all the remaining charges below to the drain for absorbing the remaining charges, or by simply setting the detection voltage (V _O ) to the gate electrode to zero or inverting it to the opposite polarity. A method may be adopted in which the lower anti-transfer is eliminated and the remaining charges are recombined in the semiconductor substrate 1.

Note that a resistor 8, which is provided between each transfer gate 6, 6...
8 are incorporated into the IC of the imaging device, but the ground resistor 9 is connected as an external component. Therefore, by changing this resistance value, the voltage division ratio of the transfer voltage source 10 to each electrode 6, 6... can be changed, so the degree of potential displacement, that is, the slope, to the transfer gate electrodes 6, 6... can be controlled. This makes it possible to always obtain the imaging function in the best condition.

As is clear from the above description, the present invention changes the transfer level during signal transfer by the charge transfer means between the center and both ends, so that the imaging output signal level is flattened and imaging with stable characteristics is achieved. You can get the equipment.

[Brief explanation of drawings]

Fig. 1 is a plan view and a longitudinal and cross-sectional view showing the structure of a conventional device, Fig. 2 is an optical system diagram showing the concept of facsimile, Fig. 3 is a waveform diagram showing the output signal of the conventional device, and Fig. 4 is an imaging method according to the present invention. FIG. 5 is a plan view showing the structure of the device; FIGS. 5A and 5B are sectional views of essential parts for explaining the charge transfer situation; FIG. The figure is a waveform diagram showing the output signal of the device of the present invention.
5 indicates a light-transmissive gate electrode, 5 indicates a CCD transfer section, 6 indicates a transfer gate, 7 indicates an inversion layer, 8 indicates a resistor, and 9 indicates a grounding resistor.

Claims (1)

[Scope of Claims] 1. A photodetecting section consisting of a plurality of photodetecting elements arranged one-dimensionally, and a CCD signal transfer section arranged in parallel to the photodetecting section to transfer detection signals obtained from the photodetecting section. 1. A solid-state imaging device using a CCD, comprising: a transfer means for transmitting a signal, and a transfer level during signal transfer of the transfer means is changed between a central portion and both ends thereof. 2 The above transfer means is connected to each gate region of the photodetecting element.
It is composed of a plurality of transfer gates spanning each gate region of the CCD, and these transfer gates are continuously connected via a resistor, and a transfer means is connected between the central part and both ends of the collective connection. A solid-state imaging device using a CCD according to claim 1, characterized in that a transfer voltage for setting a signal transfer level is applied.