JPS58106965A - Solid-state image pickup device - Google Patents

Abstract

PURPOSE:To remove surely an excess charge without requiring an extra area, by forming a clip diode on a semiconductor substrate of a unit picture element by lamination. CONSTITUTION:A diffusion layer 1 is a junction diode part which has a conductive type opposite to that of a semiconductor substrate 2 and is connected electrically to a photoconductor film 5 through a conductive electrode 3 and a metallic electrode 4. A conductive electrode 6 having a conductive type opposite to that of the electrode 3 forms a junction diode 7 which is operated as a clip diode between electrodes 6 and 3, and an optional voltage is biased from the external. The potential of the diode 1 rises in accordance with the strength of a signal light. However, if the clip potential of the storage diode 1 is set to a value equal to the transfer capacity of a CCD of a transfer line 9 at this time, all of the excess signal charge larger than the transfer capacity is swept away to the diode 7 side. When the clip potential of the diode 1 is selected properly, the signal charge is prevented from overflowing to the transfer line even if a strong light is incident.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solid-state imaging device using a photoconductor film as a light-receiving element, and more particularly to a solid-state imaging device having a function of removing surplus signal charges from a light-receiving section.

In recent years, in two-dimensional surface imaging devices, there is a strong tendency for optical systems to become smaller, such as 1", 213'+, and X, due to the demand for smaller television cameras and lower power consumption. In order to increase this, there is a tendency to use solid-state imaging devices in which a photoconductor film is laminated on a semiconductor substrate.Therefore, in solid-state imaging devices that use a charge transfer element (for example, CAN) as a scanning circuit in the image section, A phenomenon occurs in which the capacity of the light receiving section becomes larger than the transfer capacity of the scanning circuit.

For this reason, the following problems occur and have an adverse effect on the imaging screen.

(1) When reading the entire signal amount of the light receiving section into the scanning circuit, when the signal amount of the light receiving section becomes larger than the transfer capacity of the scanning circuit due to strong light incidence, the total signal amount of the light receiving section read into the scanning circuit is overflowing with scanning circuits. Therefore, a vertical white line appears on the image capture screen. A so-called blooming phenomenon occurs.

(2) When reading the signal amount of the light receiving section by the transfer capacity of the scanning circuit, when the signal amount of the light receiving section becomes larger than the transfer capacity of the scanning circuit due to strong light incidence, one reading will cover the transfer capacity of the scanning circuit. Since only a few signals are read, signal charges are left unloaded. For this reason, an afterimage occurs on the image capture screen.

In view of such conventional problems, the present invention eliminates the influence of excess signal charge in the light receiving section on the imaging screen in a solid-state imaging device in which a plurality of picture elements using a photoconductor film are arranged two-dimensionally as the light receiving element. The aim is to provide a solid-state imaging device that can be used. That is, in the present invention, a circuit for clipping the potential of a signal charge storage diode of a light receiving section is formed by stacking it on a scanning circuit provided on a semiconductor substrate.

One embodiment of the present invention is shown in FIG. 1, and its operation will be explained in FIG.
This will be explained using FIG.

FIG. 1 shows a sectional view of an image section of a solid-state imaging device using a photoconductor film as a light receiving element and an embedded COD as a scanning circuit of the image section. In the figure, reference numeral 1 denotes a diffusion layer having a conductivity type opposite to that of the semiconductor substrate 2, and a junction diode portion electrically contacted with a photoconductor film 6 via a semiconductor conductive electrode 3 and a metal electrode 4. It is. The semiconductor conductive electrode 3 has the same conductivity type as the junction diode section 1 . 6 is a semiconductor conductive electrode having a conductivity type opposite to that of the 4-conductive electrode 3;
A junction diode 7 is formed between the two and can be externally biased with any voltage.

8 is a gate section that reads the signal charge accumulated in the junction diode section 18 to the transfer line side, and 9 is a buried type C
A vertical transfer line formed by OD is shown. 10 is a transfer electrode of the CCI forming the vertical transfer line 9, and also serves as the gate electrode of the gate section 8.

11 is a field oxide film, 12 is a channel stopper, 13 is an oxide film, and 14 is a transparent electrode film that supplies bias charges to the photoconductor film 5.

Next, the operation of the solid-state imaging device according to the present invention shown in FIG. 1 will be explained using FIGS. 2 and 3. FIG. 2 shows a vertical scanning drive pulse. In the same figure (&), φ1R is a reading pulse, φ71. is the transfer pulse, R is the amplitude of the read pulse φVIH, and T is the read pulse φ7. ! Tf is the amplitude of one frame period (s s m sea
), Tv is 1 field period (1e, esmssec
) is shown. In the same figure (b), φY2R is the read pulse, φY2R is the transfer pulse, R is the amplitude of the read pulse φM2R, T is the amplitude of the transfer pulse φM2, and T is the vertical blanking period. shows. Here, the drive pulse φma1. of the vertical scanning circuit is used. In φ machine 2, a read/read mi pulse is raised every 1 frame (3 emgec) in each pulse system, and 1 pulse is generated between φv1 and φ machine 2.
They stand alternately every field (1e, 5m5ea) (interlaced scanning). The transfer pulses of φma 1 and φma 2 are still inverted in phase (two-phase drive).

In addition, in the same figure (0), φ(IL indicates the clip potential applied to the diode electrodes, which is a constant potential OL here. Also, in the same figure (IL), from t1 to
t5 indicates the phase at an arbitrary time.

FIG. 3 shows the potential state of the unit pixel portion during reading and optical integration in the solid-state imaging device of the present invention when the drive pulse system shown in FIG. 2 is used. In FIG. 3(a), I)at is an equivalent circuit diagram of the junction diode 7, and φCL is a clip voltage applied to the diode DCL. C and R are equivalent circuits of the photoconductor film 5, and φB is the transparent electrode 14 on this photoconductor film 6.
is the bias potential applied via the . φv1 is a vertical scanning drive Noculus. Figures 3(b) to (a) are the third
It shows the potential state of the portion corresponding to the figure (IL), and the operation will be explained below using this. Figure 3(b)
In ~(d), ψOFF is the potential of the read gate section 8 when φv1-0, \ψ is the potential x when φv1:φv+T.
ψR is the potential when a read pulse is applied when φy+=ψvut. ψCL is the clip potential φ (the clip potential of the storage diode 1 when IL is applied). Qs is the signal charge and QS' is the surplus signal charge.

Here, to Qs-, (ψR-ψCL) ......(1)C
0: Total capacity electrically connected to storage diode 1.

The relationship holds true.

Next, FIG. 3(t)) and (C
).

A step-by-step explanation will be given using (d).

As shown in FIG. 3(b), the potential of the diode 1 rises from the reset level ψR of the read pulse φvan in accordance with the intensity of the signal light. However, if the click potential ψCL of the storage diode 1 is set to be the same as the transfer capacitance Qsac of the transfer line COD, Qs
” All the surplus signal charge Qs' above Q8HO is swept out to the clip diode 7 side, that is, to the φCL side.The clipping voltage ψCL of the storage diode 1 is still larger than ψte, that is, ψ!〈ψc L --(2) If set, no matter how strong the light is incident during the optical integration period, the signal charges will not exceed 9 and overflow to the transfer line.

Next, as shown in FIG. 3(C), 1=1. ~t4, that is, the read pulse φv+i is applied, and the signal charge Q
s is read into the transfer line side.

As shown in Figure 3 ((1), after t-15, the light receiving section enters the optical integration period again, while on the transfer line side, the previously read signal charge Q8 is vertically transferred by applying a transfer pulse. , and is taken out as a signal to an external circuit via a horizontal scanning circuit.

As described above, the present invention forms the clip diode in a stacked manner above the semiconductor substrate of the unit picture element, thereby achieving
Overcrowding often reduces the area occupied by other components (storage diodes, transfer circuits) in the pixel.
Drain function can be realized. Also, compared to the conventional method, the planar pattern area required for one pixel, which is necessary to realize the over/crow/drain function, is no longer required, and the number of primes to be supplied can be increased in density. Therefore, even when the pixel size is reduced due to the miniaturization of the TV right camera optical system, by realizing the over, claw, and drain functions, an image sensor with sufficient pluming suppression and imaging characteristics (sensitivity, dynamic range) can be realized. can.

Although this embodiment shows an example in which the clip diodes are separated one picture element at a time, similar effects can be expected even in the case of the entire image area. Although an example of mixed pulse drive has been described here, similar effects can also be expected in a system in which reading and transfer are performed using independent gate electrodes and drive pulses. Furthermore, as a scanning circuit, MO
S) Similar effects can be expected with systems using transistors and systems using BBD.

As described above, according to the present invention, surplus charge in a solid-state imaging device can be reliably removed without requiring an extra area, and therefore its industrial value is extremely high.

[Brief explanation of drawings]

Waveform diagrams of the vertical scanning driving nodal and clipping voltages that drive the gymnastics imaging device; FIGS. 1...junction diode, 3...conductive electrode, 6...--conductive electrode of opposite conductivity type to electrode 3,
7... Diode consisting of electrode 3.6, 8...
...Gate section, 9...Vertical transfer line, 1
0...Transfer electrode. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure v

Claims (1)

[Claims] a photoconductor film that converts optical signals into electrical signals; a diode that stores signal charges generated in the photoconductor film; and a diode of one conductivity type that electrically connects the diode and the photoconductor film. 1 electrode, a second electrode of the other conductivity type integrally formed with the first electrode, and a transfer circuit that transfers the signal accumulated in the diode, and the second electrode A solid-state imaging device characterized in that it is biased to a predetermined voltage.