JPH065727B2 - Solid-state imaging device - Google Patents

Description

The present invention relates to a solid-state image pickup device using a photoconductor film as a light receiving element, and more particularly to a solid-state image pickup device having a function of removing surplus signal charges in a light receiving portion.

In recent years, in a two-dimensional solid-state imaging device, an optical system has been required to meet the demand for miniaturization and low power consumption of a television camera.
There is a strong tendency to reduce the size to 1 ", 2/3", and 1/2 ". On the other hand, in order to increase photosensitivity, there is a tendency to use a solid-state imaging device in which a photoconductor film is laminated on a semiconductor substrate. for that reason,
A charge transfer element (for example, CC
In the solid-state imaging device using D), a phenomenon occurs in which the capacity of the light receiving unit becomes larger than the transfer capacity of the scanning circuit.

For this reason, the following problems occur and the image pickup screen is adversely affected.

(1) When all the signal amount of the light receiving unit is read into the scanning circuit, when the signal amount of the light receiving unit becomes larger than the transfer capacity of the scanning circuit due to strong light incidence, the total signal amount of the light receiving unit read by the scanning circuit Overflows in the scanning circuit. Therefore, a white line is vertically generated on the imaging screen. A so-called blooming phenomenon occurs.

(2) When the signal amount of the light receiving part is read by the transfer capacity of the scanning circuit, when the signal amount of the light receiving part becomes larger than the transfer capacity of the scanning circuit due to strong light incidence, the reading capacity of the scanning circuit is equal to the reading capacity of one time Since only the signal charges are read, the signal charges are left behind. Therefore, an afterimage is generated on the image pickup screen.

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

An embodiment of the present invention is shown in FIG.
This will be described with reference to FIGS.

FIG. 1 is a sectional view of an image portion of a solid-state image pickup device using a photoconductor film as a light receiving element and an embedded CCD as a scanning circuit of the image portion. In the figure, reference numeral 1 is a diffusion layer having a conductivity type opposite to that of the semiconductor substrate 2, and a junction diode portion electrically contacted with the photoconductor film 5 through the semiconductor conductive electrode 3 and the metal electrode 4. Is. The semiconductor conductive electrode 3 has the same conductivity type as the junction diode unit 1. Reference numeral 6 denotes a semiconductor conductive electrode having a conductivity type opposite to that of the conductive electrode 3.
A junction diode 7 can be formed between and to bias an arbitrary voltage from the outside. Reference numeral 8 is a gate portion for reading the signal charges accumulated in the junction diode portion 1 to the transfer line side, and 9 is a vertical transfer line formed by an embedded CCD. 10 is a CC forming the vertical transfer line 9
The transfer electrode of D also functions as the gate electrode of the gate portion 8.
Reference numeral 11 is a field oxide film, 12 is a channel stopper, 13 is an oxide film, and 14 is a transparent electrode film for supplying a bias charge 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 described with reference to FIGS. 2 and 3. FIG. 2 shows a drive pulse for vertical scanning. Phi _V1R In FIG (a) reads the pulse, φ _V1T transfer pulse, R represents read pulse phi _V1R
, T is the amplitude of the transfer pulse φ _V1T , and T _f is 1
The frame period (33 msec) and T _V indicate one field period (16.5 msec). In the figure (b), φ
_V2R reads pulse, phi _V2T transfer pulse, R represents the amplitude of the read pulse phi _V2R, T represents the amplitude of the transfer pulse φ _V2T, T _B indicates a vertical blanking period. Here, with respect to the drive pulses φ _V1 and φ _V2 of the vertical scanning circuit, a read pulse is generated for each frame (33 msec) in each pulse system, and for each field (16.5 msec) between φ _V1 and φ _V2. Alternate (interlaced scan). The phases of the transfer pulses of φ _V1 and φ _V2 are inverted (two-phase drive). Further, in FIG. 6C, φ _CL represents a clipping potential applied to the diode electrode 6, and here it is a constant potential CL. Further, in FIG. 3A, t _{1 to} t ₅ indicate phases at arbitrary times.

FIG. 3 shows the potential state of the unit pixel portion during reading and light integration of the solid-state imaging device of the present invention when the drive pulse system of FIG. 2 is used. In FIG. 3 (a), D _CL is an equivalent circuit of the junction diode 7, φ _CL is a clipping voltage applied to the diode D _CL , and C and R are equivalent circuits of the photoconductor film 5. Φ _B is a bias potential applied to the photoconductor film 5 through the transparent electrode 14. φ _V1 is a vertical scanning drive pulse. FIGS. 3 (b) to 3 (d) show the potential state of the portion corresponding to FIG. 3 (a), and the operation will be described below using this. In Fig. 3 (b) to (d), _OFF is φ _V1
= When the potential of the read gate portion 8 when the ov, _T is a transfer pulse phi _V1T vertical scan drive pulses phi _V1 ON, the i.e. φ _V1 = φ _V1T = T reading gate portion 8 when the (V)
Similarly, _R is the potential when the vertical scanning drive pulse φ _V1 read pulse φ _V1R is ON, that is, φ _V1 = φ _V1R = R
This is the potential of the read gate unit 8 at the time of (V). _CL is the clipping potential of the storage diode 1 when the clipping voltage φ _CL is applied to the semiconductor electrode 6. Q _S is the signal charge
Q _S'is the surplus signal charge.

Here, Q _S = C ₀ · ( _R − _CL ) ... (1) C ₀ : Total capacitance electrically connected to the storage diode 1.

The relationship is established.

Next, the excess signal charge Q by the clip diode D _CL
The manner _{in which S 'is} swept FIG. 3 (b), (c), will be described in order with reference to (d).

As shown in FIG. 3 (b), the potential of the diode 1 rises from the reset level _R of the read pulse φ _V1R according to the intensity of the signal light. However, at this time, if the clipping potential _CL of the storage diode 1 is set to be the same as the transfer capacitance Q _SHC of the CCD of the transfer line, all the excess signal charges Q _S ′ above Q _S = Q _SHC will be clipped. Diode 7
Side, that is, to the φ _CL side. Further, if the clipping potential _CL of the storage diode 1 is set to be larger than _T , that is, _T < _CL (2), no matter how strong the light enters during the light integration period, the signal charge will be _T. It does not cross over and overflow the transfer line.

Next, as shown in FIG. 3 (c), when t = t _{3 to} t ₄ , that is, the read pulse φ _V1R is applied, the signal charge Q
_S is read into the transfer line side.

Then, as shown in FIG. 3 (d), after t = t ₅ , the light receiving portion again enters the light integration period, while on the transfer line side, the signal charge Q _S read previously is vertically transferred by applying a transfer pulse. Then, it is taken out as a signal to an external circuit through the horizontal scanning circuit.

As described above, according to the present invention, by forming the clip diode in a stacked type above the semiconductor substrate of the unit pixel,
Overflow without reducing the area of other components (storage diode, transfer circuit) in double-layered painting.
The drain function can be realized. Further, as compared with the prior art, the planar pattern area occupied by one picture element for realizing the overflow / drain function is not required, and the number of picture elements can be increased by that amount. Therefore, even when the picture element size is reduced due to the miniaturization of the optical system of the TV camera, the overflow drain function is realized to realize an image sensor with sufficient blooming suppression and imaging characteristics (sensitivity, dynamic range). it can.

Incidentally, in the present embodiment, an example in which the clip diodes are separated for each picture element is shown, but the same effect can be expected in the case of the entire image portion. Although the example of the mixed pallet driving has been described here, the same effect can be expected in a system in which reading and transfer are performed by independent gate electrodes and driving pulses. Furthermore, as the scanning circuit, MO
The same effect can be expected in the system using the S transistor and the system using the BBD.

As described above, according to the present invention, the excess charge in the solid-state imaging device can be surely removed without requiring an extra area, so that the industrial value thereof is extremely high.

[Brief description of drawings]

FIG. 1 is a sectional view of a solid-state imaging device according to an embodiment of the present invention, and FIGS. 2A to 2C are vertical scanning drive pulses and clips for driving the solid-state imaging device according to the embodiment of the present invention. Voltage waveform diagrams and FIGS. 3A to 3D are potential state diagrams in each period of the solid-state imaging device according to the embodiment of the present invention. 1 ... Junction diode, 3 ... Conductive electrode, 6 ... Conductive electrode of opposite conductivity type to electrode 3, 7 ... Diode composed of electrodes 3 and 6, 8 ... Gate part, 9 ... Vertical transfer line ,
10 ... Transfer electrode.

Claims (1)

[Claims] 1. A photoconductor film for converting an optical signal into an electric signal, a diode for accumulating signal charges generated in the photoconductor film, and the diode and the photoconductor film are electrically connected. A first semiconductor electrode of one conductivity type and the same conductivity type as the diode, a second semiconductor electrode of the other conductivity type connected to the first semiconductor electrode, and a signal stored in the diode are transferred. A transfer circuit and a read gate unit for reading signal charges from the storage diode to the transfer circuit, wherein the second semiconductor electrode has a potential of the read gate unit and a read pulse when a transfer pulse is applied. A solid-state image pickup device, wherein the solid-state image pickup device is biased to a predetermined voltage between the potential of the read gate portion when applied.