JPS58106966A - Solid-state image pickup device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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 excess signal charge from a light-receiving portion.

In recent years, in two-dimensional solid-state imaging devices, the optical system has become smaller than 1" due to the demand for smaller TV right cameras and lower power consumption.
On the other hand, in order to increase photosensitivity, there is a tendency to use solid-state imaging devices in which a photoconductor film is laminated on a semiconductor substrate. as a charge transfer device (e.g. C0D)
In a solid-state imaging device using a semiconductor device, 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, vertical white lines appear on the image capture screen.

(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 is larger than the transfer capacity of the scanning circuit due to strong light incidence, the transfer capacity of the scanning circuit can be read in one read. Since only a portion of the signal charge is read, there is an unloaded signal charge. For this reason, an afterimage occurs on the image capture screen.

In view of these conventional problems, the present invention eliminates the influence of surplus signal charges in the light receiving section on the imaging screen of 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 purpose of this invention is to provide a solid-state image sensor structure that is possible. That is, in the present invention, a MOS transistor for clipping the potential is newly connected to the signal charge storage diode of the light receiving section.

An embodiment of the present invention is shown in FIGS. 1, 2, and 3, and its operation will be explained using FIGS. 4 and 6.

FIG. 1 is a schematic plan view of an interline transfer type two-dimensional solid-state imaging device that has a photoconductor film as a light-receiving element and uses COD with two-layer polysilicon electrodes as a vertical scanning circuit. It is. This solid-state imaging device is driven with two-phase vertical transfer drive pulses that are a mixture of read drive pulses and transfer drive pulses. In the figure, al.

a2. ..., aa-+, ILn is a photoconductor film and a light receiving element array consisting of a signal charge storage diode that stores signal charges generated in this photoconductor film, bl, b2
．． .......

bn, , bn are vertical scanning circuits composed of COD, and light receiving element arrays a5 . a2. ......,&n-1,"n reads the optical signal charge and vertically transfers it in the direction of the arrow bone PT. C is a vertical scanning circuit consisting of a CCD, b2.
...2 for driving l bn '+bn
These are vertical transfer lock pulses φvt and φv2 of the phase, and the vertical transfer lock pulses φv+ and φv2 contain transfer driving pulses as well as light receiving element rows! L,, a2.・
..., an-+, vertical scanning circuit from an, b
, , . . . , also includes reading drive pulses for reading optical signal charges into bn-1 and bn. d is a horizontal scanning circuit made of COD, and a vertical scanning circuit.

b2. . . . The vertical optical signal charges sent from bn-1 and bn are horizontally transferred in the direction of the arrow bone PII, and taken out as a signal output f to an external circuit. e is a horizontal transfer lock pulse φ for driving the horizontal scanning circuit d
IN, φH2. g, h are light receiving element rows IJ, a
2. .......

This is an electrode for clipping the potential of the an-+ and an signal charge storage diodes to an arbitrary value.

FIG. 2 is a plan view schematically showing the structure of the image portion of FIG. 1. FIG. Figure 3 (&) schematically shows the cross section taken along the line ■-■ in Figure 2, and Figure 3 (b) schematically shows the cross section taken along the line ■-■ in Figure 2. It is something. For ease of explanation, common components are given the same number. Figures 2 and 3 (a).

In (b), 1 is connected to the photoconductor film 3 via the metal electrode 2.
This is a junction diode portion electrically connected to the photoconductor film 3 for accumulating optical signal charges generated in the photoconductor film 3, and is formed of a diffusion layer having a conductivity type opposite to that of the semiconductor substrate 4. Reference numeral 6 indicates a read gate section formed by a depletion type MOS (MOS) transistor that reads the signal charges accumulated in the junction diode section 1 to the transfer line side, and 6 indicates a vertical transfer line formed from a buried type COD. The area of the metal electrode 2 that electrically connects the photoconductor film 3 and the junction diode section 1 becomes the light-receiving area of one picture element. 6a is an accumulation region for accumulating signal charges which forms a part of the vertical transfer line 6, and 6b is an accumulation region 6.
This is a transition region for transferring signal charges of a. 7 and 8 are the polysilicon transfer electrodes of the CCD forming the vertical transfer line 6, and the gate electrodes of the read gate section 6 formed by transistors are MOS transistors that read signal charges from the junction diode section 1 to the vertical transfer line/6. Also serves as 9 is a field oxide film, 10 is a channel stopper, 11 is an oxide film for insulating and separating between the polysilicon transfer electrodes 7 and 8 and the metal electrode 2, and 12 is a transparent electrode that supplies bias charges to the photoconductor film 3. The film 13 indicates a portion where the metal electrode 2 in contact with the photoconductor film 3 makes electrical contact with the junction diode portion 1 formed on the semiconductor substrate 4, and 14 is a gate oxide film. 16 is a diffusion layer having a conductivity type opposite to that of the semiconductor substrate 4; 16 is a polysilicon gate electrode;
17 is a gate oxide film. Here, a MOS transistor is formed by the diffusion layer 1.16 and the polysilicon electrode 16, and the polysilicon electrode 16.degree. diffusion layer 16 is independently biased to an arbitrary voltage from the outside. 18 indicates a gate channel section.

Next, using Figures 4 and 5, convert Figure 2 to Figure 3 (IL).
, O)) The operation of the solid-state imaging device according to the present invention shown in (O)) will be explained. FIG. 4 shows a vertical scanning drive pulse. In the same figure (a), φ1R is the read pulse, φv1 is the transfer pulse, R is the amplitude of the read pulse φY+1, T is the amplitude of the read pulse φ1, and T( is one frame period (33 m). 5ec), Ty indicates one field period (16,5tn 5ec). In the same figure (b), φma 2R is a read pulse, φma 2 is a transfer pulse,
R is the amplitude of the read pulse φma2R, T is the transfer pulse φ
Indicates the amplitude of v2, and TB indicates the vertical blanking period.

Here, the drive pulse φma1. of the vertical scanning circuit is used. In the φ machine 2, each pulse system has one frame (33ms
A read pulse is generated every time ec), and φv1 and φma2
In the dark, the images alternate every field (16.5m 5ec) (interlaced scanning). Also, φv1 and φ
The phase of the transfer pulse of the main unit 2 is inverted (two-phase drive). Further, in FIG. 4, t1 to t1 indicate phases at arbitrary times.

FIG. 6 shows the potential state of the unit pixel portion during reading and light integration in the solid-state imaging device of the present invention when the drive pulse system shown in FIG. 4 is used. In FIG. 6(a), vDD and φB() respectively indicate the drain terminal and gate terminal of the MOS transistor (TRI). C,
R is an equivalent circuit diagram of the photoconductor film 3, and φB is a bias potential applied to the photoconductor film 3 via the transparent electrode 12.

φv1 is a vertical scanning drive pulse. Figure 5<b)~
(d) shows the potential state of the portion corresponding to FIG. 5 (+L), and the operation will be explained using this.

In Fig. 6(b) to (d), ψOFF is φv1=O
When vO, ψd is 1 when φv1:φYfT φB is φma1
This is the potential when the read pulse is applied when =φmaIR. vDD is the drain terminal v of the transistor TRI
The potential of the drain when an arbitrary voltage is applied to nn is shown, and vDD is the potential of the gate channel section when an arbitrary voltage is applied to the gate terminal φDG. Further, yi is a signal charge, and Qs' is a surplus signal charge.

Here・Qs= 00・(ψR−ψOa)...
(1) Co: Total capacitance electrically connected to storage diode 1.

The relationship holds true.

Next, FIG. 6(b) shows how the surplus signal charge Qs' is swept out by the sweeping MOS transistor TRI.
CC)s (d) will be used to explain step by step.

As shown in Fig. 61, when t=t1 to t2, that is, during the optical integration period, the potential of the storage diode 1 rises from the reset level ψR of the read pulse φ1R according to the intensity of the signal light. . However, at this time, if the gate potential ψDG of the sweep-out MOS transistor TRI is set so that the signal charge amount Q8 of the light receiving section is the same as the transfer capacitance Qc of the transfer lines C and CD, even if strong light Even if Qg = Qan or more, all the surplus signal charge amount is T
It is swept out to the drain 16 side of the RI. At this time, in order to be swept out to the drain 16 side of TRI, 2 ・・・・・・・・・@)vDD −
vDD relationship must be established. Also, the gate potential ψDG of the sweep transistor TRI is read and transferred to the gate part of the storage diode 1, and the potential ψ when <Rus φv+'r is applied! Larger, that is, ψna>ψ!
If you set (3), the signal charge will be ψ! no matter how strong the light is incident during the optical integration period. It will not overflow onto the transfer line.

Next, as shown in FIG. 5C, a read pulse φIR is applied from t-15 to t4, and the signal charge Qs is read from the storage diode 1 to the transfer line side.

As shown in FIG. 6(d), after t = ts, the light-receiving section enters the optical integration period again, while on the transfer line side, the previously read signal charge Qs is vertically transferred by the application of the transfer noculus, and is transferred horizontally. The signal is taken out as a signal to an external circuit via a scanning circuit.

As described above, in the present invention, a sweep transistor is provided, and the gate potential and drain potential are set so that the total signal charge amount Qs of the light receiving section is equal to the transfer capacitance amount Qsac of the COD transfer line. Excess signal charge exceeding the transfer capacity can be swept out to the drain side of the transistor. In addition, by setting the gate potential and drain potential of the sweep transistor during optical integration higher than the potential of the read gate section when the transfer pulse is applied, no matter how strong the light is incident, it is possible to It is possible to prevent optical signal charges from overflowing to the transfer line side. Therefore, no matter how strong the incident light is, it is possible to eliminate afterimages, blooming, and smear on the imaging screen. Furthermore, since a bias voltage can be applied to the photoconductor film independently of the gate terminal and drain terminal of the sweep transistor, it is possible to suppress afterimage 2 blooming and smear while taking into consideration the knee point and breakdown voltage of the photoconductor film. This makes it possible to set the optimum bias for the photoconductor film.

In the above embodiments, the gate terminal and drain terminal of the sweep-out transistor are made independent, but the same effect can be expected even if the gate terminal and drain terminal are electrically connected. or,
Although the example of mixed pulse drive has been described, similar effects can also be expected in a system in which reading and transfer are performed using independent gate electrode drive pulses. Further, as described above, according to the present invention, surplus charges in a solid-state imaging device can be reliably removed, and its industrial value is extremely high.

[Brief explanation of drawings]

Fig. 1 is an overall view of a two-dimensional object imaging device using an interline transfer method, Fig. 2 is a plan view of an image portion of a solid-state imaging device according to an embodiment of the present invention, and Fig. 3 (IL) is a diagram of Fig. 2. (7) II-I [Cross-sectional view, Figure 3(b) is
■A sectional view, FIG. 4 is a vertical scanning drive pulse waveform diagram for driving a solid-state imaging device in an embodiment of the present invention, and FIG.
a) to (d) show potential state diagrams showing the operation of a solid-state imaging device in an embodiment of the present invention. 16... Drain diffusion layer of the sweep transistor, 16... Gate electrode of the sweep transistor, 18... Channel portion of the sweep transistor. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 (Figure 3 Figure 4

Claims (1)

[Claims] A photoconductor film that converts optical signals into electrical signals, a diode that accumulates optical signal charges generated in the photoconductor film, a signal transfer circuit that transfers the signal charges of the diode, and a signal transfer circuit that is connected to the diode. A solid-state imaging device characterized by having an MO8) transistor for discharging excess charge.