JPS59117377A - Solid-state image pickup element - Google Patents

Abstract

PURPOSE:To improve the dynamic range and the sensitivity by connecting a photoconductive film to a gate of a vertical switch MOS transistor (TR) and providing an MOS TR resetting a voltage of the former MOS TR. CONSTITUTION:A transparent electrode 13 and a photoconductive film 14 are conected in series with a gate section of the vertical MOS TR3 constituting each picture element 4 and an MOS TR16 is connected. Further, an MOS TR17 reading a signal charge outputted from the picture element 4 to a vertical signal line 290a corresponding to an output pulse of a vertical shift register 6 is connected to a drain section of the MOS TR3. When a vertical gate line 6a is at H level and a horizontal switch MOS TR9 is at H level, a saturated current flows from a video bias 7 via a load resistor 8 by positive holes stored on the photoconductive film 14 and a signal is detected at a point A.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a solid-state image sensor, and particularly to a photodiode-type MO8 type solid-state image sensor that expands the dynamic range of the photodiode generated by the intensity of incident light. It is.

[Prior art]

FIG. 1 is a circuit diagram of a main part of an example of a conventionally used MOS type solid-state imaging device. In the figure, a solid-state image sensor 1 has a plurality of pixels 4 arranged in the row and column directions, each composed of a photodiode 2 and a vertical switch MO8) transistor 3, selected by a horizontal shift register 5 and a vertical shift register 6. Load resistor 8. A charging current flows through the horizontal switch MO8) transistor 9, and the voltage drop due to the load resistor 8 is detected as an optical signal.
Amplified by video amplifier 11 via capacitor 1o,
A signal current is output from the output terminal 12.

Is Figure 2 the basic configuration of Figure 1? 1 is a diagram showing a cross-sectional structure of a solid-state image sensor using photoconductive i on a solid-state image sensor.

In the same figure, on a P-type silicon substrate 21 KU, ') - source ("n+ diffusion/W) 22. gate 28 and drain (
n+ diffusion layers) 24 are respectively formed to constitute a vertical switch MO8) transistor 25 corresponding to the vertical switch MO8) transistor 3 shown in FIG. 1st
A photodiode 26 corresponding to the photodiode 2 shown in the figure is configured. In addition, 27 is an oxide film for pixel isolation, 28 is an interlayer insulating film, 29 is a vertical signal line, and 30 is an At
31 is a photoconductive film, and 32 is a transparent electrode. In this case, the MO8 transistor 25 is the photodiode 2.
It is used as a switch to read out the signal charges accumulated in the vertical signal line 29 to the outside via the vertical signal line 29.

In a pixel configured in this manner, when external light is incident from above the transparent electrode 32, the video bias voltage vv is applied to the Al electrode 30 immediately after scanning, so that the Al electrode 30 will not respond in response to the amount of incident external light. Electron-hole pairs are generated in the photoconductive film 31, and the voltage VT applied to the transparent electrode 32 and the video bias voltage 7 of the Al-electrode 30 are
Due to the electric field (when vT>VV), electrons are transferred to the transparent electrode 32
The holes move toward the At electrode 30 side. At this time, since the At electrode 30 is in a floating state,
Due to the number of holes, the voltage of the At electrode 30 rises to a potential v7' higher than the video bias voltage 7. Then, when this vv' rises to the withstand voltage VB of the p-n junction of the photodiode 26, the p-n junction of the photodiode 26 breaks down and no more holes can be stored.

In other words, when breakdown occurs, a large amount of current flows through the p -n +'fR of the photodiode 26, and a portion of it generates a pseudo signal called pluming to the drain 24, significantly degrading the image quality. That is,
The optical signal charge is obtained only for the voltage change from the potential Vv' of the At electrode 30 to the potential VB of the photodiode 26, and therefore the problem with C1 is that the dynamic range is small and the sensitivity is low. [Object of the Invention] Therefore, the present invention has been made in view of the above-mentioned problems, and it is an object of the present invention to provide a solid-state image sensor that simultaneously improves the dynamic range and sensitivity.

[Summary of the invention]

In order to achieve such an object, the present invention connects a photoconductive film to the gate of a vertical switch MOS transistor, and also provides a MOS transistor for resetting the voltage of this vertical switch MOS transistor. The withstand voltage potential is improved to a level higher than the withstand voltage, and the amount of change in signal current with respect to minute light is further expanded.

[Embodiments of the invention]

Next, embodiments of the present invention will be described in detail using the drawings.

FIG. 3 is a cross-sectional view of a main part of a pixel portion of a solid-state image sensing device according to the present invention, which corresponds to FIG. In FIG. 3, an AL IK circuit 30 is connected to the gate 23 of the vertical switch MOS transistor 25, but not connected to the source 22. In FIG.

In such a configuration, typically the vertical switch MO8)
When the current ID flowing between the drain 24 and the source 22 of the transistor 25 is in a saturated state, β is a constant, and VG
is the gate voltage, and Vth is the threshold voltage.

and depends on VG, V c >> V th
When , β ID=VG” (2). Therefore, holes generated in the photoconductive film 31 due to the incidence of external light enter the gate 23 via the At electrode 30. The voltage of the gate 23 is increased, and the square of the change is read out as a change in current.Therefore, even a small amount of external light can be detected as a large signal change.1, for pixel division Since the breakdown voltage of the oxide film 27 is about 50 V or more, by optimally designing the area of the gate 23, the breakdown voltage can be improved more than the breakdown voltage in the pn junction direction.

Actually, the circuit configuration shown in FIG. 4 may be used.

Here, the same symbols as in FIG. 1 are the same elements, so their explanation will be omitted. In other words, in FIG. The electrode 13 and the photoconductive film 14 are connected in series, and this vertical switch MO8) transistor 3
A MOS transistor 16 is connected to the gate of the vertical shift register 6 to reset the vertical swing transistor 3 with an external reset bias 15 in response to the output current of the vertical shift register 6.
A MoS) transistor 17 is connected to the drain portion of the O8) transistor 3, which reads the signal charges outputted from the pixel 4 to the vertical signal line 29m in correspondence with the output pulse of the vertical shift register 6.

In the solid-state imaging device configured in this manner, when the vertical gate helix 6a of the vertical shift register 6 goes to H level and the horizontal switch MO8) transistor 9 goes to H level, the holes stored in the photoconductive film 14 cause Since the saturation current shown in the above equation (1) flows from the video node (IAS T through the load resistor 8), it is sufficient to detect the voltage drop at point A as a signal.Next, the vertical gate line 6b is ■
(level, turn on the MoS transistor 16, and vertical switch MO8) reset the gate of the transistor 3 (A in FIG. 3 is common with the electrode 30) to the reset bias 15.
to reset and accumulate signal charges again.

Is this behavior below? All you have to do is manipulate it back.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to obtain a large change in signal current with respect to very small amounts of light, so it is possible to achieve high sensitivity, and it is also possible to improve the withstand voltage due to holes of photoelectrons, so dynamic An extremely excellent effect can be obtained in that the range can be significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram of an essential part of an example of a conventional solid-state image sensor, FIG. 2 is a sectional view of an essential part of an all-in-one image sensor using a photoconductive film, and FIG. 3 is a diagram of a solid-state image sensor according to the present invention. FIG. 4 is a sectional view of a main part showing a pixel portion, and a circuit configuration diagram of a main part showing an example of a solid-state image sensor according to the present invention. 2. Fist: Photodiode, 3: Vertical switch MO8) transistor, 4: Pixel, 5: Horizontal shift register, 6: Vertical shift register, 61
r 6b...Vertical gate line, 7.Φ...Video bias, 8.Fist...Load resistance, 9...Horizontal switch MO8) transistor, 1゜...Capacitor, 11.
...Video amplifier, 12...Output terminal, 13...
...Transparent electrode, 14...Photoconductive film, 15...Reset bias, 16.17-...MoS transistor, 21...P-type silicon substrate, 22...Source (n+ diffusion layer), 23...gate, 24...
・Drain (n+ diffusion layer), 25...vertical switch MO8) transistor, 26...photodiode,
27... Oxide film for pixel isolation, 28... Interlayer insulating film, 29, 29a... Vertical signal line, 30...
- At electrode, 31... photoconductive film, 32... transparent electrode. 1st Ward DoD Guan 3 ψ ψ

Claims (1)

[Claims] A large number of pixels formed by a transparent electrode provided on the light receiving surface side, a photoconductive film, a photodiode for accumulating optical signals, and a vertical switch MO8) transistor are arranged in the row and column directions, and the pixels are connected to a horizontal shift register and a vertical shift register. 8) In a solid-state imaging device configured to take out a signal current to the outside by a transistor selected by a shift register, the photoconductive film is connected to the vertical switch M.
O8) A MOS connected to the gate of the transistor and the vertical switch MO8) MOS that resets the voltage of the transistor.
A solid-state image sensor characterized by being provided with a transistor.