JPH03171883A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To prevent burning or flicker from being generated by increasing the potential of a channel area higher than a block potential between a source area under the gate electrode of an MOSFET and a circuit element. CONSTITUTION:A control pulse is impressed to a gate electrode 13. The polarity of this pulse is reverse to the polarities of transfer and read pulses and the block potential of a read part for a signal charge positioning just under the gate electrode 13 is made higher than that of the other part on a substrate, namely, higher than the block potential just under a source area 11. Therefore, the excess charge flowing out to a substrate 10 in a regular bias state is not read into the area 12 in a transfer step and an unnecessary pseudo signal is not outputted. Thus, the output of the unnecessary pseudo signal caused by the excess charge and latent image are prevented form being generated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solid-state imaging device, in which a circuit element having a charge scanning function and a source region (hereinafter referred to as a blank space) that accumulates signal charges generated by incident light are provided on a semiconductor substrate. In a solid-state image sensor in the form of an engraving (no change in content), only the excess charge in the source region is reliably drained to the semiconductor substrate side,
The object of the present invention is to provide a solid-state imaging device that is free from charge overflow and afterimage in a scanning circuit section.

Conventionally, there are various types of solid-state image pickup plates having a charge scanning function, but circuit elements with a self-scanning function such as CCD-i or BBD have been proposed as those having a charge transfer function with particularly low noise. (Japanese Unexamined Patent Publication No. 61-95721
(see issue).

However, in some cases as described above, if the amount of charge handled by the charge transfer stage composed of COD or BBD is smaller than the amount of charge generated by incident light and accumulated in the source region, strong incident light The excess charge caused by overflow caused by overflow in the scanning circuit section caused the voltage applied to the photoelectric conversion section to be restricted, causing burnout and flickering.

The present invention provides a circuit element in which a source region for accumulating signal charges is provided on a semiconductor substrate, a diode is formed by the substrate and the source region, and this diode has a charge transfer function. When a signal charge larger than the amount of charge to be handled is generated, the diode is put into a forward bias state while preventing the charge in the source region from being read into the circuit elements, and the excess charge generated in the photoelectric conversion section is transferred to the bottom of the non-nu region. It is an object of the present invention to provide a solid-state imaging device that does not generate false signals or afterimages due to unnecessary signals leaking to a transfer section due to overflow.

A solid-state imaging device according to an embodiment of the present invention will be described below with reference to the drawings. The scanning circuit will be explained using a charge transfer type which has less noise. COD or BBD as a charge transfer type differs in whether charge is accumulated in a depletion layer or an impurity region, but
The operation is essentially the same. Therefore, this will be explained in the future on BBD.

Figure 1 shows a BBD formed on a Si substrate and its transfer stage connected to the drain. This figure shows one unit of a solid-state imaging device in which a photoconductor and an electrode are provided on these regions.

An n+ type region 11 serving as a source region is formed in a p-type semiconductor substrate 10.
A diode is provided to prevent this. 12 is a potential well in the n+A (no change in content) type region of nJ and becomes a bSt charge transfer circuit element.

13 is a gate electrode and has an overlapping portion with the n+ type region 11. 14 is a semiconductor substrate 10 and a gate electrode 1
This is an insulator film between the gate electrode 3 and the gate oxide film. 16 is
First t-pole 16, semiconductor substrate 10 and gate electrode 1i13
and N. This is an insulating layer for gas separation. Reference numeral 16 denotes a first electrode, which is an electrode of a diode electrically connected to the n+ type region 11 and also serves as an electrode of the hole blocking layer 17. 18 is (Zn1, Cd, To)1-y(I
n2To3), (where o(x(1, o(y≦0.3)
A transparent electrode (second electrode) 19 is formed on the photoconductor, and incident light is irradiated from the side of the transparent electrode 19.

First, the optical information reading operation when the present invention is not used will be explained.

Pressing the button in the configuration shown in FIG. 1 above, a drive pulse as shown in FIG. 2 (.) is applied to the gate [m13]. At time t7, the button is pressed and the electrode 16 is turned on (vcH-
vT). Here, vT is the threshold voltage of a MOS field effect transistor (FET) constructed of n+IIB* (no change in content) regions 11, 12 and gate tFM13. Now, when there is incident light 21, electron-hole pairs are generated in the photoconductor 18, and each electric current Wi1 6
j 1 9, signal charges are accumulated in the source region 10, and the potential of the electrode 16 decreases.

Furthermore, when vcH is applied to gate electrode 13 at time t2, signal charges are transferred from n+ region 11 to n+ region 12. As a result, the potential of n+ region 11 rises again to (vCH-vT). The signal charge transferred to the n+ region 12 is then transferred to the output section in accordance with the transfer pulse v0 shown in FIG. 2(a).

The above is the optical information reading operation when the present invention is not used, and the voltage applied to the photoconductor is when the second electrode 19 is kept at the ground potential (vcH-vT).

However, the transfer circuit element CCD-1 or BB
If the amount of charge handled by the charge transfer stage constituted by D is less than the maximum charge specification generated by the photoconductor which is the photoelectric conversion unit (no change in content), the voltage to be applied to the photoconductor. There is no choice but to make it smaller, but doing so will result in burnt-out, flicker, etc. On the other hand, if a sufficient voltage is applied to the photoconductor, the signal cannot be read in one reading operation, and the generated excess charge (overflow charge) leaks into the transfer stage.
Unnecessary signals are output and afterimages also occur.

Next, the operation of the present invention as an example of draining excess charge will be described. FIG. 3 shows a pulse applied to the second electrode 19 as an example of a method for forward biasing a diode formed by a semiconductor substrate and a source region and draining excess charge to the substrate without causing unnecessary charge loading. This shows a method of applying and controlling the gate wL pole and using pulses. At time T1, if excess charge (generated charge with a large amount of transferred charge) is generated due to the incident light and the diode potential becomes below Vc, the external voltage applied to the second voltage lfA19, that is, the negative pulse (-vc') As a result, the diode potential (potential of the source region 11) is pulled down to a negative value of Vc with respect to the substrate until it becomes the same potential as the substrate (ground potential). Charge flows out to the substrate.

At this time, a control pulse 30 shown in FIG. 3(.) is applied to the gate i[m13. This pulse 30 has a polarity opposite to that of the transfer button and the read pulse, and naturally the barrier potential of the signal charge reading portion located directly below the gate electrode 13 is higher than that of the other portion of the substrate, that is, the barrier potential directly below the source region 11. Shi will also be higher.

By such a means, the excess charge flowing into the substrate 1o in a forward bias state is read into the region 12 of the transfer stage.
Unnecessary pseudo signals are not output. After such outflow, when the pulse of the second electrode 19 returns to oV, the diode potential becomes
vc, and then Leetpa k,X Ic J:
A signal charge corresponding to the potential K is read into the transfer stage region 12. Time T1
When the diode potential is above Vc, that is, when the signal charge is less than the transfer handling charge amount, the second! The polar pulse does not go below OV and the diode is not forward biased. Therefore, when the diode potential is above Vc (no change in the content), optical information is proportional to the incident light intensity, but when it is below vc, that is, when the incident light intensity is very strong, the optical information is transferred. By draining the excess charge to the substrate without causing unnecessary reading in the stage, the optical information remains constant at a certain value (white clip). The above is an example of the optical information reading operation when the present invention is used.

The above is a photoconductor ("1-xCdx")1-y
("zT@3)y has been described, but the photoconductor may also be made of other materials, such as amorphous silicon. Furthermore, a semiconductor substrate and a source may be used as the photoelectric conversion section. It is also possible to use a diode formed in a region.Furthermore, a similar effect can be obtained by using an insulator for the photoconductor.

As described above, the solid-state imaging device of the present invention has a mechanism capable of forward biasing a diode formed of a semiconductor substrate and a source region that accumulates signal charges,
It also has means for increasing the barrier potential of the signal charge reading section, and if the present invention is used, COD or BB
Even if the amount of charge handled by the charge transfer stage consisting of D is smaller than the maximum amount of charge to be expected in the photoelectric conversion section, excess charge will not overflow to the charge transfer stage. This makes it possible to reliably flow out to the substrate without causing excess charge, eliminate the output of unnecessary spurious signals due to excess charge, prevent afterimages, and output signal charges that are faithful to the incident light. This will greatly contribute to the realization of high-performance solid-state imaging devices.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional structural diagram of one unit of a solid-state imaging device in which a photoconductor is provided on a circuit element having a charge transfer function, and Fig. 2 is a diagram for explaining the operation of the solid-state imaging device shown in Fig. 1. FIG. 3 is a waveform diagram showing the time relationship between clock pulses and the potential relationship of the photoconductor. FIG. 3 is a waveform diagram showing a state in which a diode formed in a semiconductor substrate and a source region in a solid-state imaging device according to an embodiment of the present invention is put into a forward bias state. FIG. 3 is a potential waveform diagram for explaining the operation of FIG. 10...P-type semiconductor substrate, 11...N+ type region which becomes a source region, 12...Engraving of a transfer specification which becomes a potential well (no changes are made to the contents) ) 11 Peno feeding n+ type region, 13... Gate electrode, 14...
...Insulator film, 15...Insulator layer.

Claims (2)

[Claims] (1) A semiconductor substrate of one conductivity type has the other conductivity type and accumulates signal charges generated by incident light, and the signal charges are transferred to a source region forming a diode and a portion of the substrate other than the source region. A circuit element to be transferred and a MOS for reading signal charges in the source region into the circuit element.
FET, barrier means for increasing the potential of the channel region of the MOSFET, and a photoconductor whose one electrode is electrically connected to the source region, and the barrier means increases the potential of the channel region to the above level. A solid-state imaging device in which the barrier potential is higher than the barrier potential between the source region under the gate electrode of the MOSFET and the circuit element, and the diode is placed in a forward bias state. (2) A semiconductor substrate having one conductivity type has the other conductivity type and accumulates signal charges generated by incident light, and the signal charges are transferred to a source region forming a diode and a portion of the substrate other than the source region. A circuit element to be transferred and a MOS for reading signal charges in the source region into the circuit element.
FET, barrier means for increasing the potential of the channel region of the MOSFET, and a photoconductor whose one electrode is electrically connected to the source region, and has an electric charge larger than the amount of charge handled by the circuit element. is accumulated in the source region, the barrier means makes the potential of the channel region higher than the barrier potential between the source region under the gate electrode of the MOSGET and the circuit element, thereby putting the diode in a forward bias state. Solid-state imaging device.