JPH0414549B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an imaging device using a charge transfer device.

Imaging devices using charge transfer devices include those in which photoelectric conversion element groups are arranged one-dimensionally and those in which photoelectric conversion element groups are arranged two-dimensionally. In particular, one-dimensional arrays are used in facsimile devices, OCR (optical character reading devices), image input devices, etc. Main scanning is performed by the scanning function of the imaging device itself, and sub-scanning is performed by the mechanical scanning of the document. The two-dimensional image is read using a feeding mechanism.

Since an image pickup device using a conventional charge transfer device does not have a reset function, the signal cannot be read out again unless all the photoelectrically converted signals are read out and output to the outside. Therefore, when reading originals of various sizes using the same device, such as OCR, the reading speed remains the same even if the original sizes (especially in the width direction) are different.
When the originals were small, we were unable to meet the demand for faster reading speed.

SUMMARY OF THE INVENTION In order to eliminate such drawbacks, it is an object of the present invention to provide an imaging device that can be reset while reading signals from an imaging device using a charge transfer device, and a method for driving the same.

According to the present invention, the first and second bonding regions are formed on the main surface of a semiconductor substrate and have a conductivity type opposite to that of the substrate, and the bonding depth of the first bonding region is a predetermined first bonding region. The junction depth of the second junction region is formed at a predetermined second depth shallower than the first depth, and the photoelectric conversion element group is formed on the main surface of the first junction region. There is obtained a solid-state imaging device characterized in that a device for reading signals from the photoelectric conversion element group is formed on the main surface of the second bonding region.

Further, according to the present invention, a reverse bias is applied to sweep out signal charges remaining in a device for reading out signals from the photoelectric conversion element group on the main surface of the second junction region in the depth direction of the semiconductor substrate. A solid-state imaging device characterized in that a voltage is applied between the first junction region and the second junction region and the semiconductor substrate for a predetermined period within one cycle of reading signal charges from the photoelectric conversion element group. A driving method is obtained.

This will be explained in detail below with reference to the drawings.

FIG. 1 is a block diagram of a one-dimensional imaging device using a general charge transfer device. The signal charge accumulated in the photoelectric conversion element 1 is sent to the charge transfer device 4 for reading out the signal by the bias voltage applied to the transfer electrode 2, and the signal is sent to the input terminals 5, 5'.
With the pulse signal applied to the output gate electrode 6
The signal is sent to the charge detection section 8 through the charge detection section 8, and a signal is obtained from the output terminal 9.

FIG. 2 schematically shows a cross section taken along line A-A' in FIG. 1. A charge transfer electrode 13 of a shift register is provided on the main surface of the semiconductor substrate 11 via an insulating layer 12, a transfer gate electrode 14 for controlling signal charge transfer from the photoelectric conversion section to the shift register, and a layer 15 of a conductivity type different from that of the substrate semiconductor ( A photoelectric conversion section consisting of a pn junction (pn junction) is formed, and the photoelectric conversion section is separated from an adjacent shift register by, for example, a channel stop region 17 having an impurity layer higher than the substrate impurity concentration. Furthermore, parts other than the photoelectric conversion part are shielded from light by, for example, a metal layer 18.
In such a one-dimensional imaging device, the photoelectric conversion unit 1 accumulates signal charges according to the amount of incident light, and transfers the signal charges to the corresponding shift registers 4 via the transfer gates 2. After the signal charges are transferred to the shift register, the transfer gate is closed, and the photoelectric conversion section 1 accumulates the signal charges for the next cycle. On the other hand, the signal charge transferred to the shift register 4 is transferred in the direction of the arrow 10, and is taken out as a signal from the charge detection section 8 to the outside.

In order to transfer signal charges in this manner, a pulse signal as shown in FIG. 3 may be applied to each electrode. That is, the pulse signal applied to the transfer gate 2 is as shown in FIG. 3a, and is applied to the input terminal 3. The pulse signal applied to the charge transfer electrode 13 is the third
As shown in Figure b, it is applied to input terminal 5. Third
In the figure, the period T _e represents one period in which all photoelectrically converted signal charges are read out, and the number of pulses n ₀ represents the number of pulses required when all of the photoelectric conversion elements 1 are read out to the outside.

In this way, in the image pickup device shown in FIG. 2, the next cycle cannot be read unless all the signal charges accumulated in all the photoelectric conversion sections 1 are taken out from the charge detection section 8. Therefore, even when the paper width of the original varies, as in OCR, it is necessary to read out all the photoelectrically converted signals, and even if the paper width of the original is narrow, the readout time is the same as that of a wide paper. Is required. This is disadvantageous when high-speed reading is desired.

Next, embodiments of the present invention will be described using the drawings. Hereinafter, in order to simplify the explanation, an N-channel semiconductor device will be described.

FIG. 4 shows one embodiment of the present invention, and similarly to FIG. 2 described in the conventional example, it schematically shows the A-A' cross section of the charge transfer imaging device shown in FIG.
In FIG. 4, areas having the same functions as those in FIG. 2 are indicated by the same symbols. The difference between the embodiment shown in FIG. 4 and the conventional example shown in FIG.
A first P-type region 19 that forms a p-n junction with 1 and has a deep junction depth, and a second P-type region 20 that has a shallow junction depth compared to the first P-type region 19. It lies in the fact that it is being formed.

Next, the operation of the embodiment of the present invention will be explained.
Since the basic operation as an imaging device is the same as that of the conventional imaging device shown in FIG. 2, the P-type region 19, which is an important element of the present invention shown in FIG.
The operation of 20 will be explained.

FIG. 5 shows a pulse signal waveform applied to each electrode of the imaging device of the embodiment shown in FIG. FIG. 5a shows a pulse signal applied to the transfer gate 14 and is applied to the terminal 3 shown in FIG. Figure 5b and c are charge transfer electrodes 1
With the pulse signal applied to terminal 3, terminal 5 shown in FIG.
and 5'. FIG. 5d shows a pulse signal applied to the semiconductor substrate 21. FIG. Terminals to semiconductor substrate 21 are not shown in FIG.

The number of pulses n ₁ shown in Fig. 5 b, c is the first
A driving method is shown in which only signals obtained by n ₁ signals counted from the side closest to the charge detection section 8 of the photoelectric conversion section 1 shown in the figure are read out. Therefore, if the number of photoelectric conversion units 1 included in this imaging device is n ₀ , driving is possible when signals are read only from n ₁ photoelectric conversion units, which is smaller than n 0 . As shown in FIGS. 5b and 5c, if the number of pulses is n ₁ , all signal charges have not yet been extracted to the outside. The signal charges that have not been taken out remain within the charge transfer section 4 shown in FIG.
The remaining signal charges are ejected toward the semiconductor substrate ₂₁ at timing t1 shown in FIG. 5, and a state immediately before reading out a signal from the photoelectric conversion section 1 can be achieved.

Figure 6 shows the potential distribution in the depth direction of the cross section B-B' of the photoelectric conversion section shown in Figure 4 at timing _t0 shown in Figure 5, and Figure 7 shows the potential distribution at the same timing.
Cross section C of the charge transfer device shown in Figure 4 at t ₀
The potential distribution in the depth direction of −C′ is shown. 6th
In both FIGS. 7 and 7, the horizontal axis represents distance in the depth direction, and the vertical axis represents potential. This is the case where the junction depth of the P-type region 19 is deep and the junction depth of the P-type region 20 is shallow. Now, the channel top area 17 shown in FIG.
Let the potential of be the reference potential (in this case 0 volts),
The N-type photoelectric conversion unit 15 has the potential of the transfer gate 14.
When V _TG is the transfer gate threshold voltage V _T , it is set at a potential of V _TG − V _T . The potential distribution between the P-type region 19 and the substrate 21 is as shown by a curve 22. Further, a curve 23 is a potential distribution in a state where the pulse applied to the charge transfer electrode 13 is at a high level and there is no signal charge in the charge transfer device. Similarly, a curve 24 is a potential distribution when the applied pulse is at a low level. In such a state, the signal charge still remains within the charge transfer device 4.

Next, the potential distribution in the depth direction of the cross section B-B' at timing t1 shown in FIG. ₅ is shown as a curve 25 in FIG. 8. That is, it is desirable to form the P-type region 16 to a thickness such that it will not be completely depleted even if a reverse bias voltage is applied between the P-type region 19 and the substrate semiconductor 21 at timing _t1 in FIG. , even if depleted, the N-type region 15 and the P-type region 19 and the P-type region 19 and the substrate semiconductor 2
The thickness and impurity concentration of the P-type region 19 must be such that each of the P-type regions 19 is not in the forward direction.

FIG. 9 shows the potential distribution in the depth direction of the cross section C-C' from the buried channel 16 directly under the charge transfer electrode 13 to the P-type region 20 and the substrate semiconductor ₂₁ at timing t1. That is, when a deep reverse bias voltage is applied between the P-type region 20 and the substrate semiconductor 21, the P-type region 20 is depleted, and the direction between the buried channel 16 and the P-type region 20 becomes forward, and the buried channel directly under the transfer electrode 13 is depleted. All the signal charges in the semiconductor substrate 16 are discharged in the direction of the substrate semiconductor 21. In this way, while the signal charges are being transferred, all remaining signal charges can be discharged to the substrate semiconductor and the signal can be reset.

This means that a one-dimensional charge transfer imaging device having n ₀ bits is operated as if it were a one-dimensional charge transfer imaging device having n ₁ bits (n ₀ > n ₁ ). The disadvantages of the example can be overcome and the number of bits to be read can be freely set. That is, even if the paper width of a document such as OCR varies, it is possible to switch the number of bits of the photoelectric conversion unit to be read according to the paper width, and high-speed character reading can be achieved.

Although the embodiment shown in FIG. 4 does not show an overflow drain region for discharging the excess charge generated in the photoelectric conversion section 15 to the outside before it overflows to the charge transfer section 16, of course,
It goes without saying that the present invention is also applicable to the charge transfer imaging device 12 having such a function.

Next, the depth of the P-type region 19 directly under the photoelectric conversion section 15 is made shallower, and
Excess charge generated in the photoelectric conversion unit 15 can be discharged to the substrate semiconductor 21 by performing the operation shown in No. 130517 solid-state imaging device and method for driving the same. That is, by making the P-type region 19 shallow to some extent in FIG. 4 and selecting the reverse bias voltage to be applied to the substrate semiconductor 21 with respect to the P-type region 19 at timing _t0 shown in FIG. 19 is depleted, and the generated excess charge is discharged toward the substrate semiconductor 21. Then, the substrate semiconductor 21 added at timing _t1 shown in FIG.
The depth of the P-type region 19 is selected so that the photoelectric conversion section 15 and the P-type region 19 and between the P-type region 19 and the substrate semiconductor 21 are not in the forward direction even when a higher reverse bias voltage is applied to the P-type region 19. .

Figure 10 shows a potential distribution diagram of cross section B-B',
A curve 29 shows the potential distribution at timing _t0 , and a curve 30 shows the potential distribution at timing _t1 . The excess electric charge generated in the photoelectric conversion unit 15 exceeds the potential peak 29' and is transferred to the substrate semiconductor 21.
It is pushed out towards.

FIG. 11 shows the potential distribution on the cross section C-C', and a curve 32 shows the potential distribution at timing _t0 , and charges 31 are stored in the buried channel 16 directly below the transfer electrode 14. When this charge 31 enters the state at timing t ₁ , the potential distribution becomes as shown by the curve 26 in FIGS. 9 and 11, and the charge 31 becomes the charge 27.
It moves in the direction of arrow 28 and is ejected in the direction of substrate semiconductor 21 .

In this way, blooming can be suppressed without providing a region such as an overflow drain, so the chip size can be reduced and an imaging device that is highly mass-producible can be obtained.

In order to obtain the potential distribution as shown in the curve 26 of FIGS. 9 and 11, the electrodes 5 and 5' are set in a more negative direction than the target potential at timing _t1 , as shown in FIGS. 5b and 5c. It may be desirable to apply a potential of .

Further, in the embodiment, an N-channel semiconductor has been described, but it goes without saying that the present invention can be applied to a P-channel semiconductor by reversing the conductivity type of each region.

Furthermore, it is clear that the present invention is not limited to a one-dimensional charge transfer imaging device, but can also be applied to an interline transfer type two-dimensional charge transfer imaging device.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a one-dimensional charge transfer imaging device, Fig. 2 is a schematic diagram of the cross section A-A' shown in Fig. 1 of a conventional charge transfer imaging device, and Fig. 3 a and b are a diagram of a conventional charge transfer imaging device. Driving pulse signals applied to the imaging device, FIG. 4 is a schematic diagram of the cross section A-A′ shown in FIG. 1 of the device showing one embodiment of the present invention, and FIG. a drive pulse signal applied to the charge transfer imaging device;
6, 8, and 10 are potential distribution diagrams in the depth direction of the cross section B-B' shown in FIG. 4 of the imaging device of the present invention, and FIG. 7, FIG. 9, and FIG. 4 shows a potential distribution diagram in the depth direction of the cross section C-C' shown in FIG. 4 of the imaging device of the invention. FIG. 15 is a photoelectric conversion element, 16 is a buried channel,
Reference numeral 19 indicates a region having a conductivity type opposite to that of the substrate and which does not lead to a forward direction in the junction region, and 20 indicates a region having a conductivity type opposite to that of the substrate and which can lead to a forward direction in the junction region.

Claims (1)

[Scope of Claims] 1. First and second bonding regions formed on the principal surface of a semiconductor substrate and having a conductivity type opposite to that of the substrate;
The bonding depth of the bonding region is formed to a predetermined first depth, the bonding depth of the second bonding region is formed to a predetermined second depth shallower than the first depth, and forming a photoelectric conversion element group on the main surface of the first bonding region;
A solid-state imaging device characterized in that a device for reading signals from the photoelectric conversion element group is formed on the main surface of the second bonding region. 2. At first and second bonding regions formed on the main surface of a semiconductor substrate and having a conductivity type opposite to that of the substrate,
The bonding depth of the bonding region is formed to a predetermined first depth, the bonding depth of the second bonding region is formed to a predetermined second depth shallower than the first depth, and forming a photoelectric conversion element group on the main surface of the first bonding region;
In the solid-state imaging device configured such that a device for reading out signals from the photoelectric conversion element group is formed on the main surface of the second bonding region, a device for reading signals from the photoelectric conversion element group on the main surface of the second bonding region is formed. A reverse bias voltage is applied between the first junction region and the second junction region and the semiconductor substrate to sweep out the signal charge remaining in the device for reading out the signal in the depth direction of the semiconductor substrate. A method for driving a solid-state imaging device, characterized in that signal charges from a group of elements are applied for a predetermined period within one reading period.