JPS58221576A - Solid state image pickup device - Google Patents

Abstract

PURPOSE:To improve the matching performance between a scanning part and a photoelectric film, by providing plural signal storing diodes, scanning lines to deliver the electric charge to outside from these diodes, and electric shielding electrodes between coupled parts of diodes and scanning lines respectively on a semiconductor substrate. CONSTITUTION:A photoelectric film 2 is laminated on a semiconductor substrate 1, and plural optical signal storing diodes containing N<+> layers 3 arrayed 2-dimensionally are formed to the film 2. In addition, a polycrystal silicon buffer layer 4 which reduces the level difference and a metallic electrode 5 connected to the layer 4 are coupled to the film 2. This coupled metallic surface is used as a collector in which an optical signal is absorbed. Then an optical signal transfer electrode 6 is provided on the substrate 1 via an insulated layer. The shielding electrodes 15 are inserted among the layer 4 and electrodes 5 and 6 to keep the substrate potential. Thus the parasitic capacity is reduced between an electrode 7 for bias of film 2 and the electrode 6. This improves the matching performance between a scanning part and the film 2.

Description

[Detailed description of the invention] The present invention relates to a solid-state imaging device.

2. Description of the Related Art Conventionally, solid-state imaging devices with high sensitivity, long life, and high reliability have been proposed in which a photoelectric film is laminated on a scanning portion of a semiconductor substrate. This device stores optical signal charges generated in a highly sensitive photoelectric film in an optical signal storage diode on a semiconductor substrate, and sequentially transfers and outputs the optical signal charges by signal scanning. This device has high sensitivity due to the characteristics of the photoelectric film, and because it does not have a vacuum tube section that must be handled carefully like the image pickup tube scanning section, it can be expected to have high reliability and long life. The bias required for the photoelectric film to contact the semiconductor scanning section is subject to fluctuations due to parasitic capacitance between the photoelectric film and the scanning circuit, resulting in unstable characteristics.

In view of this serious problem, the present invention aims to improve the matching between the photoelectric film characteristics and the scanning section due to the presence of this parasitic capacitance. Hereinafter, the causes of parasitic capacitance, the characteristics of the photoelectric film, and the compatibility between the scanning section and the photoelectric film will be described.

FIG. 1 shows a cross-sectional view of a unit pixel of a conventional solid-state imaging device. In the drawing, a photoelectric film 2 is laminated on a semiconductor substrate 1 made of P-type silicon, an n+ layer 3 forms an optical signal storage diode with a two-dimensional arrangement, and a polycrystalline silicon buffer layer 4 is formed to reduce the level difference. A metal electrode 5 connected to this is bonded to the photoelectric film 2, and since this bonded metal surface becomes a collector that absorbs the optical signal, it is sufficient that there is no electrical connection with adjacent picture elements. need to be made larger. Reference numeral 6 denotes an electrode for optical signal transfer installed on the silicon substrate 1 via the insulating layer 1a, a region A shown in the figure is a charge transfer region, and an electrode for biasing the interlayer is provided on the photoelectric film 2. An electrode 7 is provided.

Clearly from the same cross-sectional structure! Diffusion part 3 and transfer electrode 6 have parasitic capacitance Cp via intermediate insulating layer 1a. This parasitic capacitance poses a major problem in matching the photoelectric film characteristics and the semiconductor scanning section.

Next, the characteristics of the photoelectric film will be described. Usually, a sufficient bias vfB is applied to the photoelectric film 2, and signal charges generated by light are extracted to the outside by a sufficient drift electric field. Second
A solid line 8 in the figure represents the relationship between the bias VfB (horizontal axis) applied to the photoelectric film at a certain illuminance and the photocurrent ph (vertical axis) of the photoelectric film. As can be seen from the figure, when the bias vfB is lower than the bias voltage v1, all the generated signals are taken out and do not become optical signals, and in this state, an image defect called burn-in occurs. That is, the pressure VfB applied to the photoelectric film is required to be as high as (1). In addition, what is indicated by the dashed line 9 in the same figure is the leakage current of the photoelectric film in the dark state, and it is
If the photoelectric film bias VfB becomes larger than 2, the ratio of optical signal current to leakage current (ie, S/N) becomes poor, making it impossible to project a clear image.

- Therefore, in order to fully utilize the photoelectric film characteristics to obtain high sensitivity and high S/N image quality, it is necessary to satisfy the following condition that the photoelectric film bias VfB is always in the region B in the figure.

V <V <v (1)
-fB-2 Now that the photoelectric film characteristics have been clarified, the driving state when a photoelectric film having the above characteristics is laminated on a semiconductor scanning substrate will be discussed.

First, FIG. 3 shows an electrical equivalent circuit of the solid-state imaging device of FIG. 1. Parasitic capacitance 1 between the transfer electrode 6 and the n+ diffusion part 10
2 is Cp, and the photoelectric film 2 is a capacitance Cf, then the storage diode 3 can be expressed as a diode with a junction capacitance of C. In addition, the electric potential in the semiconductor under the transfer electrode 6 is in a state as shown by the solid line d during optical signal storage and as shown by the broken line a when reading the signal charge, and the potentials ψD and ψ of 12 and 13 are as follows.
0 is the read/input partition potential of each state. FIG. 4 is an example of a pulse timing chart at the time of signal reading of the voltage φITO applied to the second electrode 7 of the photoelectric film and the pulse φV applied to the transfer electrode 6, where t=T1 when reading the signal and t='r2 when the photosensitive calyx is accumulated. FIG. 6 shows the driving state. When t='r1, the potential of the n+ diffusion part is set to ψD13, and at this time, the accumulated charge 14 is read into the potential pocket under the transfer electrode 6 and transferred and output. At this time, the photoelectric film bias ■f B (R1 is determined by the difference between the electrode 7 and the n+ diffusion part 1o Vf B(R)-ψD-φITO""""' (2)
becomes. Next, at t-T2, when the signal reading pulse φV is removed and the optical signal accumulation state occurs, the parasitic capacitance! fCp1
1, the potential of the n+ diffusion portion 10 is lowered by ΔψD from ψD, and the photoelectric film bias fB(1) becomes as follows.

v7B(I) = ψD−φITO−Δ9′p −(3
) - In order to fully exhibit the force tip electrical film characteristics, the condition of formula (2) must be satisfied as described above. That is, Vl”vfB(I)<vfB(R)≦v2 +++++
++ (4), but the parasitic capacitance C
p11 is large and ΔψD cannot be made small enough to satisfy the above equation (4).

In order to reduce this parasitic capacitance Cp11, the present invention provides a polycrystalline silicon buffer layer 4 for step reduction and an electric shield between the metal electrode 6 and the transfer electrode 6, as shown in the embodiment of the present invention in FIG. By inserting the electrode 15 and maintaining the substrate potential, the parasitic capacitance Cp is reduced. At this time, when the pulse shown in FIG. 4 is applied to the electrode 7 on the photoelectric film and the transfer electrode, The potential and the potential of the n+ diffusion portion 1o are shown in FIG.

When reading the signal at t-T1, the potential of the n+ diffusion section 10 is set to ψD, and the photoelectric film via "'/B (
R1 is Vf B(R) −ψD−φITO””””' (
6). Next, at t=T2, when the read pulse φ■ is removed and the optical signal accumulation state is reached, the parasitic capacitance between the transfer electrode 6 and the n+ diffusion region 1o is negligibly small, so the fluctuation due to the read pulse φ■ R4-diffusion part 1
I don't accept o. Therefore, with the potential of ψD unchanged, the photoelectric film bias Vf B (I) becomes vfB (■) - ψD - φITO, as in equation (5). At this time, it is easy to satisfy the following conditions: (1) 1$vfB(I)-fB(R)-For example, the value of φITO may be set appropriately.

As explained above, the electrical shield structure of the present invention improves the matching with the scanning section, and has high industrial utility value.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a unit picture element of a conventional photoelectric film layered solid-state imaging device, Figure 2 is a diagram showing the characteristic curve of the photoelectric film, and Figure 3 is an equivalent circuit diagram of the unit picture element shown in Figure 1. , FIG. 4 is a diagram showing drive pulses, FIG. 6 is an internal potential diagram of a unit pixel during signal reading and optical signal accumulation in the solid-state imaging device of FIG. 1, and FIG. 6 is an example of the present invention. 7 is an internal potential diagram of the unit pixel at the time of signal reading and optical signal accumulation in the solid-state imaging device of FIG. 6. FIG. 1... Semiconductor substrate, 1a... Insulating layer,
2...Photoelectric film, 3...n'' single layer, 4...
... Polycrystalline silicon buffer layer, 5 ... Gold loincloth, oligopolar electrode, 6 ... Transfer electrode, 7 ...
Electrode for photoelectric film bias, 16... Electrode for shielding. Name of agent: Patent attorney Toshio Nakao and 1 other person! @
1 Figure 2 of Figure J B1 A person's advance pressure Vh! @Figure 3 Figure 4 t=T, b=L

Claims (1)

[Claims] A semiconductor substrate includes a plurality of signal storage diodes, a scanning line for scanning and outputting signal charges from the signal storage diodes to the outside, and a photoelectric film coupled to at least a portion of one end of the signal storage diodes. , an electric shielding electrode is interposed between the signal storage diode and photoelectric film coupling part and the signal scanning line, and the shielding potential is kept at a constant potential to reduce the influence of the signal scanning line on the photoelectric film coupling part. A solid-state imaging device characterized by: