JP7525287B2 - Photoelectric conversion layer stacked type solid-state imaging device - Google Patents

Description

The present invention relates to a photoelectric conversion film stacked solid-state imaging element in which a photoelectric conversion film is stacked on a signal readout circuit board, and in particular to a photoelectric conversion film stacked solid-state imaging element having an electrode structure that applies a lateral electric field to the photoelectric conversion film parallel to a support substrate (circuit board).

In recent years, as a result of the rapid increase in the number of pixels and the increase in frame rate of solid-state imaging devices, the amount of incident light per pixel has decreased, and the sensitivity of the device has decreased. As a technology to solve this problem, a photoelectric conversion film stacked type solid-state imaging device in which a photoelectric conversion film is stacked on a signal readout circuit is known (see, for example, Non-Patent Documents 1 and 2 below). In a photoelectric conversion film stacked type solid-state imaging device in which a photoelectric conversion film is stacked, in order to apply an external electric field to the photoelectric conversion film, a voltage is applied between a transparent common electrode formed on the outermost surface and a pixel electrode, and an external electric field is applied in the stacking direction of the photoelectric conversion film to read out the charges photoelectrically converted in the film. However, in this structure, a high voltage corresponding to the thickness of the photoelectric conversion film must be applied between both electrodes, and there is a limit to the electric field strength that can be applied in relation to the withstand voltage of the solid-state imaging device.
On the other hand, if the thickness of the photoelectric conversion film is made too thin, the incident light is not sufficiently absorbed and passes through, making it difficult to obtain good sensitivity.

Therefore, in the technology described in Non-Patent Document 3 below, a comb-shaped opposing electrode is formed on a substrate, and an external electric field is applied in the surface direction of the photoelectric conversion film, which is perpendicular to the stacking direction of the photoelectric conversion film, and the charges generated in the photoelectric conversion film are caused to travel laterally, making it possible to apply a high electric field to the photoelectric conversion film without reducing the thickness of the photoelectric conversion film.

On the other hand, the applicant of the present application has disclosed the technology of Patent Document 1 below. This technology relates to an imaging element using a metal-semiconductor-metal type light receiving element (MSM), in which a photoelectric conversion film having sensitivity in a predetermined wavelength range is laminated on a circuit board, pixels are formed in an array, and each pixel is provided with a common electrode formed along the pixel boundary area and a readout electrode formed at the center position of each pixel, thereby achieving the effect of improving the efficiency of manufacturing with a high electric field in a type in which an external electric field is applied in the lateral direction (parallel to the surface of the substrate element).

JP 2019-24057 A

Institute of Image Information and Television Engineers Annual Conference 12-3, pp.166-167, 1998 Institute of Image Information and Television Engineers Annual Conference 14-4, 2002 IEEE. Trans. Electron Devices, vol. 57, no. 8, p. 1953, 2010

However, while the techniques of Non-Patent Document 3 and Patent Document 1 mentioned above can obtain a certain degree of high electric field strength, in today's world where there is a demand for even higher sensitivity of elements, there is a demand for a method of applying a highly uniform and even higher electric field strength to the photoelectric conversion film while keeping the applied voltage within the withstand voltage of the solid-state imaging element.
The present invention has been made in consideration of the above circumstances, and aims to provide a photoelectric conversion film-stacked solid-state imaging element that can suppress the applied voltage between both electrodes within the withstand voltage of the solid-state imaging element, maintain high uniformity of the electric field strength in the surface direction of the photoelectric conversion film, and generate a high electric field strength between both electrodes by utilizing the avalanche multiplication phenomenon within the photoelectric conversion film.

In order to achieve the above object, a photoelectric conversion film stacked solid-state imaging device according to the present invention has the following configuration.
That is, the photoelectric conversion film stacked type solid-state imaging device of the present invention has
a photoelectric conversion film having sensitivity in a predetermined wavelength range is laminated on a circuit board, pixel elements are arranged in an array on a plane parallel to a surface of the circuit board, and electrodes constituting anodes and cathodes are alternately arranged in at least one direction of the arrangement of the pixel elements;
One or a group of adjacent pixel elements constitutes one pixel;
At least one electrode constituting the anode and one electrode constituting the cathode are disposed in each of the pixel elements, and the electrode width in the one direction of at least one of the two electrodes constituting the cathode and the interval in the one direction between the electrodes constituting the anode and the cathode are both set to 10 nm or less;
The shape of the corners of each of the electrodes constituting the anode and the cathode in a cross-sectional view is characterized in that it satisfies the following formula:
0.6≦radius of curvature of the corner portion of the electrode/thickness of the electrode≦1.0

Here, "alternately" means that the anodes and cathodes are arranged in an alternating order, but when the same type of electrodes are arranged adjacent to each other with no gap between them, they are treated as one electrode.

As a first aspect of the photoelectric conversion film stacked solid-state imaging device,
a common electrode constituting the anode and formed along the boundary area of the pixel elements, and a readout electrode constituting the cathode and formed at the center position of each of the pixel elements;
It is preferable that the electrode width of the anode is 0.5 to 2 times the electrode width of the cathode.

On the other hand, as a second aspect,
In the row of the array of pixel elements, each electrode constituting the anode and the cathode is formed in a comb shape, and one is configured so that the comb teeth are inserted between the comb teeth of the other,
It is preferable that the electrode width of the anode is two to three times the electrode width of the cathode.
Furthermore, in the first and second aspects, it is preferable that the distance between the electrodes constituting the anode and cathode is equal to or less than the electrode width of the cathode.

In the photoelectric conversion film stacked solid-state imaging element according to the present invention, pixel elements that constitute each pixel and have an anode and a cathode are formed in an array on a circuit board for signal readout, and of the two electrodes, an anode and a cathode, arranged in each pixel element, at least the electrode width in one direction of the electrode that constitutes the cathode and the distance between these two electrodes are set to 10 nm or less.

This configuration was discovered through the research of the present inventors. That is, in a solid-state imaging element having a stacked photoelectric conversion film, it is conceivable that the avalanche multiplication phenomenon in the photoelectric conversion film can be utilized to dramatically increase the multiplication factor of the charge photoelectrically converted in the film. However, in general, a high voltage must be applied to generate avalanche multiplication, and applying such a high voltage exceeds the withstand voltage of the solid-state imaging element.

Therefore, in the photoelectric conversion film stacked solid-state imaging element of the present invention, when a voltage of 5 V is selected as the voltage applied between both electrodes that can be sufficiently kept within the withstand voltage of the solid-state imaging element in a solid-state imaging element that applies a lateral electric field, the conditions for generating avalanche multiplication are such that, of the two electrodes, a cathode and an anode, arranged in each pixel, at least the electrode width in one direction of the cathode and the distance between these two electrodes are set to 10 nm or less, and the shapes of the corners of each electrode constituting the anode and cathode are configured to satisfy the following formula.
0.6≦radius of curvature of corner of said electrode/thickness of said electrode≦1.0
This makes it possible to generate a high electric field strength between the two electrodes that can utilize the avalanche multiplication phenomenon within the photoelectric conversion film while keeping the voltage within the withstand voltage of the solid-state imaging element and maintaining a high uniformity of the electric field strength in the surface direction of the photoelectric conversion film.

1 is a schematic diagram showing a planar structure of a portion of a photoelectric conversion film stack type solid-state imaging element according to a first embodiment of the present invention; 1 is a schematic diagram showing a cross-sectional structure of a portion of a photoelectric conversion film stack type solid-state imaging element according to a first embodiment of the present invention. 1 is a graph showing the relationship between the applied electric field intensity and the output signal current when a constant amount of light is irradiated onto a photoelectric conversion film mainly composed of amorphous selenium. 1 is a schematic diagram showing an equivalent circuit configuration of one pixel of a photoelectric conversion film stack type solid-state imaging element according to a first embodiment of the present invention; 4 is a graph showing the relationship between the electrode spacing and the generated electric field strength of the photoelectric conversion film stack type solid-state imaging element according to the first embodiment of the present invention. 4 is a graph showing the relationship between the electrode width of the electrode A (cathode) of the photoelectric conversion film stack type solid-state imaging element according to the first embodiment of the present invention and the generated electric field strength. 1 is a graph showing the relationship between the value of (electrode width of electrode B (anode)/electrode width of electrode A (cathode)) and the electric field strength ratio in a photoelectric conversion film stack type solid-state imaging element according to Example 1 of the present invention. 8A to 8E are diagrams showing the state of electric field concentration at each position on the graph of FIG. 8B(F) in the photoelectric conversion film stack type solid-state imaging element according to the first embodiment of the present invention. In the photoelectric conversion film-stacked solid-state imaging element of Example 1 of the present invention, (F) is a graph showing the relationship between the value of (radius of curvature of electrode corner/thickness of electrode A (cathode)) and the electric field intensity ratio, and (G) is a schematic cross-sectional diagram showing the equipotential lines of the photoelectric conversion film-stacked solid-state imaging element of Example 1. FIG. 11 is a schematic diagram showing a planar structure of a portion of a photoelectric conversion film stack type solid-state imaging element according to a second embodiment of the present invention. 11 is a graph showing the relationship between the electrode width and electrode spacing of an electrode A (cathode) and the generated electric field strength in a photoelectric conversion film stack type solid-state imaging element according to Example 2 of the present invention. 11 is a graph showing the relationship between the value of (electrode width of electrode B (anode)/electrode width of electrode A (cathode)) and the electric field strength ratio in a photoelectric conversion film stack type solid-state imaging element according to Example 2 of the present invention.

Example 1
Fig. 1 shows the planar structure of a lateral electric field application type (MSM) photoelectric conversion film stacked type solid-state imaging element (hereinafter, simply referred to as a solid-state imaging element unless otherwise specified), and Fig. 2 shows the cross-sectional structure of the solid-state imaging element when a photoelectric conversion film is stacked on the electrodes of the solid-state imaging element.

As shown in Fig. 1 and Fig. 2, in the photoelectric conversion film stacked type solid-state imaging element according to this embodiment, a common electrode (electrode B: anode) 2 is arranged in a lattice pattern on a signal readout circuit board 1, and a readout electrode (electrode A: cathode) 3 is arranged in the center of an area (a square area in Fig. 1) separated by the lattice (the layer in which the common electrode 2 and readout electrode 3 are arranged may be referred to as a metal wiring layer), and a photoelectric conversion layer 5 is laminated above it. In this case, one square area shown in Fig. 1 corresponds to the "pixel element" in claim 1, and one pixel may be composed of this one "pixel element" (see pattern 1 in Figs. 1 and 2).

In addition to the configuration in which one pixel is composed of one "pixel element" (Pattern 1), one pixel may be composed of a group of multiple square regions ("pixel elements"), such as four square regions ("pixel elements") (see Pattern 2 in Figures 1 and 2). In the cross-sectional view shown in Figure 2, the Pattern 2 configuration corresponds to a square region in which one pixel has two pitches of electrode B (2) on one side.

A predetermined voltage is applied between the common electrode 2 and the readout electrode 3 , and a lateral electric field is applied to the photoelectric conversion layer 5 due to the potential difference between these electrodes 2 , 3 .
In this manner, since the common electrode 2 and the readout electrode 3 are disposed in a direction perpendicular to the lamination direction, rather than in a vertical direction, the direction of the electric field is horizontal to the photoelectric conversion layer 5 .

In the conventional configuration (a configuration in which an electric field is applied to the lamination method using a transparent conductive film), the thickness of the photoelectric conversion layer needs to be thinned in order to increase the electric field strength without increasing the applied voltage, but if it is made too thin, the proportion of incident light that is not absorbed and is transmitted increases. Therefore, there is a limit to increasing the sensitivity by increasing the electric field strength. In contrast, in the configuration of the photoelectric conversion film stacked solid-state imaging element according to this embodiment, the electric field strength is increased by the above-mentioned configuration, so there is no need to thin the photoelectric conversion layer 5 as in the conventional case. This makes it possible to eliminate the limit when increasing the electric field strength (increasing sensitivity) without increasing the applied voltage.

In addition, a common electrode 2 is arranged along the boundary areas that divide the pixel regions into a grid pattern, and a readout electrode 3 is arranged in the center of each of the regions divided by the grid, forming a two-dimensional array-like configuration. One pixel is defined as one unit of pixel element formed by one readout electrode 3 surrounded by the common electrode 2, or multiple units of such pixel elements. This is an extremely simple configuration, making it easy to fabricate electrodes even for very small pixels.

For example, a photoelectric conversion film mainly composed of crystalline selenium or amorphous selenium is used for the photoelectric conversion layer 5. The photoelectric conversion film has a function of generating and storing electric charges according to the amount of incident light, and avalanche multiplication occurs when a strong electric field of about 1×10 ⁸ V/m is applied within the photoelectric conversion film.

As described above, the metal wiring shape in the metal wiring layer in which the common electrode 2 and readout electrode 3 are arranged is such that within the pixel, metal wiring forming a pair of electrodes, consisting of a cathode (electrode A) and an anode (electrode B) arranged to surround the periphery of electrode A, are arranged in an array.
As mentioned above, when multiple square regions are grouped into one pixel, as shown in Figure 4, electrodes of the same type (preferably electrode A) arranged in the same pixel are wired together and connected to the gate electrode of an amplification transistor (AMP) formed on circuit board 1.

In the photoelectric conversion film stacked solid-state imaging element of this embodiment (both Examples 1 and 2), it is desired to obtain a uniform and high electric field strength. However, as a result of the research of the present inventor, it has become clear that there is a limit to achieving both the uniformity of the electric field strength in the surface direction of the photoelectric conversion film and the high electric field strength required to utilize the avalanche multiplication phenomenon by simply shortening the distance between the electrodes in one pixel, and that it is necessary to strictly regulate other elements such as the electrode shape in one pixel in order to meet the above demand, as described below. Therefore, in the photoelectric conversion film stacked solid-state imaging element of this embodiment, the specified regulation contents are set to appropriate numerical values for each Example based on the data obtained from this research. The regulation contents that can meet the above demands are listed below in the form of numerical requirements.

<1> First, in this embodiment, the electrode width (α in FIG. 1) of the readout electrode (cathode: electrode A) 3 in at least one direction (horizontal and/or vertical directions in the figure) in each pixel is set to 10 nm or less. Also, the electrode spacing γ between the common electrode (anode: electrode B) 2 and the readout electrode (cathode: electrode A) 3 in each pixel is set to 10 nm or less.
Moreover, it is more preferable that the electrode width α of the read electrode 3 in at least one direction and the electrode interval γ between the common electrode 2 and the read electrode 3 are 1 nm or more in order to facilitate manufacturing.

<2> In addition to the requirement of <1> above, by setting the electrode width β of the common electrode (anode: electrode B) 2 in each pixel to be 0.5 to 2 times the electrode width α of the readout electrode (cathode: electrode A) 3, it is possible to further meet the above demands.

<3> Furthermore, when the electrode width α of the readout electrode (cathode: electrode A) 3 described in <1> above is set to 10 nm or less, the electrode spacing γ between the common electrode (anode: electrode B) 2 and the readout electrode (cathode: electrode A) 3 in each pixel can be set to a range of 1 nm or more and less than the electrode width α of the readout electrode (cathode: electrode A) 3, thereby making it possible to further meet the above demands.

The common electrode 2 and readout electrode 3 may be made of conductive materials such as ITO (indium tin oxide), IZO (indium zinc oxide), Au (gold), Al (aluminum), Cu (copper), Ni (nickel), niobium (Nb), Pt (platinum), Mo (molybdenum), W (tungsten), Ti (titanium), and TiN (titanium nitride).

The photoelectric conversion layer 5 may also have a laminated structure of crystalline selenium, a bonding film, and a semi-insulating metal oxide film. The semi-insulating metal oxide film is composed of one or more selected from the group consisting of zinc oxide, gallium oxide, zinc sulfide, cerium oxide, yttrium oxide, and indium oxide. The bonding film is composed of one selected from the group consisting of tellurium, bismuth, and antimony. By disposing the bonding film between the crystalline selenium and the semi-insulating metal oxide film, it has the function of improving the adhesive strength between the crystalline selenium and the semi-insulating metal oxide film. In the case of a laminated structure, the thickness of the semi-insulating metal oxide film is preferably 2 nm to 100 nm. The thickness of the crystalline selenium is preferably 100 nm or more. When the thickness of the crystalline selenium is 100 nm or more, it functions well as a photoelectric conversion layer. The thickness of the crystalline selenium is preferably 1 μm or less, and more preferably 500 nm or less. When the thickness of the crystalline selenium is 500 nm or less, incident light is more likely to reach the depletion layer formed at the interface between the semi-insulating oxide film and the crystalline selenium film.

If the thickness of the crystalline selenium is 0.1 μm or more, the crystalline selenium can be made to have a sufficient thickness, so that sufficient sensitivity can be obtained over the entire visible light range, resulting in good crystalline selenium as a photoelectric conversion layer. For this reason, it is more preferable to set the thickness to 0.3 μm or more. On the other hand, if the thickness is 5 μm or less, the crystalline selenium film can be formed efficiently, resulting in a photoelectric conversion film with excellent productivity. For this reason, it is preferable to set the upper limit to 2 μm or less.

Figure 4 is a circuit diagram showing the equivalent circuit of one pixel. As shown in Figure 4, each pixel has a photoelectric conversion layer 5 that generates charges according to incident light, a floating diffusion FD that converts the charges into an electric potential, a reset transistor RST that resets the electric potential of the floating diffusion FD, the aforementioned amplification transistor AMP as an amplifier that outputs a signal according to the electric potential of the floating diffusion FD, and a selection transistor SEL that selects the readout row.

1 is connected to the floating diffusion region FD, and the charge generated in the photoelectric conversion layer 5 is transferred to the floating diffusion region FD. The output of the selection transistor SEL is sent to a circuit section (not shown) via a vertical signal line.
The relationship between the applied electric field strength and the output signal current when a constant amount of light is irradiated onto a photoelectric conversion film whose main component is amorphous selenium is shown in Figure 3. As the applied electric field to the photoelectric conversion film is increased, the output signal current first saturates and then increases rapidly above 1 x ¹⁰⁸ V/m, suggesting that avalanche multiplication is occurring within the photoelectric conversion film.

<Verification of Example 1>
The above numerical requirements <1> and <2> for the photoelectric conversion film stack type solid-state imaging device of the first embodiment will be examined below.
(Verification of <1>)
FIG. 5 shows the results of a simulation analysis of the change in electric field strength applied to the photoelectric conversion layer 5 when the electrode width α of the readout electrode (cathode: electrode A) 3 is set to 100 nm, the electrode width β of the common electrode (anode: electrode B) 2 is set to infinity, and the electrode gap γ is changed from 50 nm to 10 nm.

According to Fig. 5, the electric field strength increases as the electrode gap γ decreases, and by setting the electrode gap to 30 nm or less, a strong electric field of 1 x 10 ⁸ V/m or more that can cause avalanche multiplication can be obtained at the electrode ends (see ● in Fig. 5). In contrast, as shown in Fig. 5, the change in electric field strength with respect to the electrode gap γ at the center of the electrode (see ◯ in Fig. 5) is more gradual than that at the electrode ends, and even if the electrode gap γ is reduced to 10 nm, a strong electric field of 1 x 10 ⁸ V/m or more cannot be obtained.

6 shows the results of a simulation analysis of the change in electric field strength applied to the photoelectric conversion layer 5 when the electrode gap γ is set to 10 nm, the electrode width β of the common electrode (anode: electrode B) 2 is set to infinity, and the electrode width α of the readout electrode (cathode: electrode A) 3 is changed from 50 nm to 10 nm. As the electrode width α of the readout electrode (cathode: electrode A) 3 is reduced, the electric field strength increases and the difference in electric field strength between the electrode center (see the circles in FIG. 6) and the electrode ends (see the black circles in FIG. 6) decreases. When the electrode width α of the readout electrode (cathode: electrode A) 3 is 10 nm, a strong electric field of 1×10 ⁸ V/m or more that can cause avalanche multiplication can be obtained, and at the same time, the electric field strength at the electrode center and the electrode ends can be made almost equal, as shown in FIG. 6.

As a result, when a certain amount of light is irradiated onto the photoelectric conversion film, the output signal current can be made to be nearly equal at the center of the electrode and at the end of the electrode, making it possible to achieve high sensitivity that is uniform in the surface direction of the photoelectric conversion film and utilizes the avalanche multiplication phenomenon.

On the other hand, when the electrode width α of the readout electrode (cathode: electrode A) 3 is 20 nm, both the center and end portions of the electrode can obtain a strong electric field of 1×10 ⁸ V/m or more that can cause avalanche multiplication, but the electric field strength at the end portions is about 1.3 times larger than that at the center portion. Based on FIG. 3, the output signal current ratio is calculated from the ratio of the applied electric field strengths at the center and end portions of the electrode, and when the electric field strength is 1.2×10 ⁸ V/m, the output signal current is about 15 times larger than when the electric field strength is 1×10 ⁸ V/m. In other words, when the electric field strength is 1.2 times larger, the output signal current is about 15 times larger. Therefore, since the electric field strength is about 1.3 times larger in the above example (although FIG. 3 does not show the output signal current value when the electric field strength is larger than 1.2×10 ⁸ V/m), it is clear that the output signal current is more than 15 times larger.

Therefore, when the electrode width α of the readout electrode (cathode: electrode A) 3 is 20 nm, the sensitivity (output signal) when a certain amount of light is irradiated onto the photoelectric conversion film is more than 15 times greater at the center of the electrode than at the end of the electrode, and uniformity in sensitivity cannot be obtained.

In contrast, by arranging a readout electrode (cathode: electrode A) 3 and a common electrode (anode: electrode B) 2 surrounding the readout electrode (cathode: electrode A) 3 within each pixel, and setting the electrode width α of the readout electrode (cathode: electrode A) 3 and the electrode spacing γ to 10 nm or less, it is clear that a uniform and large electric field strength (charge multiplication) can be obtained.

As described above, according to the photoelectric conversion film stacked type solid-state imaging element of Example 1, the output signal current when a certain amount of light is irradiated onto the photoelectric conversion film can be made to be approximately the same at the center of the electrode and the end of the electrode, thereby realizing uniform and high sensitivity by utilizing the avalanche multiplication phenomenon.

(Verification of <2>)
FIG. 7 shows the results of a simulation analysis of the change in the electric field strength ratio (the electric field strength when the electrode width β of the common electrode (anode: electrode B) 2 is infinite is taken as 100%) when the electrode spacing γ is fixed and the value of (electrode width β of the common electrode (anode: electrode B) 2/electrode width α of the readout electrode (cathode: electrode A) 3) is changed to 0.2, 0.5, 1, and 2.

According to FIG. 7, when the electrode width β of the common electrode (anode: electrode B) 2 is 0.2 times the electrode width α of the readout electrode (cathode: electrode A) 3, the electric field strength ratio applied to the photoelectric conversion film does not reach 90% due to the interaction of the electric fields formed by adjacent electrode pairs (pairs of electrodes A and B) and the insufficient supply of the electric field (electric lines of force) from electrode B. In contrast, when the electrode width β of the common electrode (anode: electrode B) 2 is 0.5 times or more the electrode width α of the readout electrode (cathode: electrode A) 3, the interaction of the electric fields formed by adjacent electrode pairs is suppressed and the insufficient supply of the electric field (electric lines of force) from electrode B is improved, resulting in an electric field strength ratio of 90% or more.

Therefore, by setting the electrode width β of the common electrode (anode: electrode B) 2 to 0.5 times or more the electrode width α of the readout electrode (cathode: electrode A) 3, the electric field strength applied to the photoelectric conversion film can be improved to 90% or more. On the other hand, if the electrode width of the common electrode is twice that of the readout electrode, an electric field strength ratio of approximately 98% is obtained, and the electric field interaction due to adjacent electrode pairs and the insufficient supply of the electric field (electric field lines) are improved to a level that can be ignored. Therefore, even if the electrode width of the common electrode is further increased beyond twice that of the readout electrode, the further increase in the electric field strength ratio is limited.

From the above results, the optimal electrode width β of the common electrode (anode: electrode B) 2 for efficiently applying an electric field to the photoelectric conversion film is between 0.5 and 2 times the electrode width α of the readout electrode (cathode: electrode A) 3. By setting both electrodes in this shape, a high electric field can be efficiently applied to the photoelectric conversion film, enabling efficient charge multiplication within the photoelectric conversion film.

Figure 8B (F) is a graph showing the relationship between the value of (radius of curvature of electrode corner/thickness of electrode A (cathode)) and the electric field intensity ratio, and Figure 8B (G) is a schematic cross-sectional view showing the equipotential lines of the photoelectric conversion film stacked solid-state imaging element of this embodiment (the equipotential lines are formed between both electrodes 2 and 3. The radius of curvature of the electrode corner and the thickness of electrode A (cathode) are defined in the figure).

On the other hand, Figure 8A shows the state of electric field concentration at each position (<A> to <E>) on the graph of Figure 8B (F) ((A) to (E) (corresponding to <A> to <E>, respectively)). When the value of (radius of curvature of electrode corner/thickness of electrode A (cathode)) is approximately 0, it is <A>, when it is approximately 0.2, when it is approximately 0.8, when it is approximately 1.2, when it is approximately 1.4, it is <D>, and when it is approximately 1.4, it is <E>.

The electric field strength is defined as 100% when the electric field is concentrated at the corner of the electrodes (electrode A (cathode) and electrode B (anode)) when the angle between the two adjacent faces in the cross section of the corner of this electrode is 90 degrees. As shown in Figure 8B (F), when the shape is changed so that the value of (radius of curvature of electrode corner/thickness of electrode A (cathode)) increases from 0.2 to 1.4 in increments of 0.2, the electric field strength due to the electric field concentration at the corner of this electrode changes so that it decreases halfway.

It is at a minimum when the radius of curvature of the electrode corner/thickness of electrode A (cathode) is 0.6≦(radius of curvature of the electrode corner/thickness of electrode A (cathode))≦1.0, and the electric field strength at this time drops to about 50%.
Furthermore, when the value of (radius of curvature of electrode corner / thickness of electrode A (cathode)) is increased, the electric field strength begins to increase, and when the value of (radius of curvature of electrode corner / thickness of electrode A (cathode)) is about 1.4, the electric field strength increases to about 90%.
In addition, in FIG. 8A, the electric field is concentrated at the corners in (A) and (B), but in FIG. 8A(C), it is clear that the electric field concentration at the corners is alleviated and dispersed over a wide range.

Therefore, by optimizing the value of (radius of curvature of electrode corner/thickness of electrode A (cathode)), it is possible to suppress electric field concentration at the electrode corner. In particular, when 0.6≦(radius of curvature of electrode corner/thickness of electrode A (cathode))≦1.0, the electric field strength due to electric field concentration can be halved.
Based on Figure 3, the effect of suppressing sensitivity variations when electric field concentration at the electrode corners is suppressed can be considered as follows. When an electric field strength of ^1x108 V/m, which is necessary to utilize the avalanche multiplication phenomenon, is applied within the photoelectric conversion film, and electric field concentration occurs at the electrode corners, and an electric field strength twice as high ( ^2x108 V/m) is applied, the output signal current at the electrode corners exceeds 15 times (see Figure 3). In other words, the sensitivity of the photoelectric conversion film at the electrode corners increases to more than 15 times that of other parts of the electrode, and uniformity in sensitivity cannot be obtained.

On the other hand, particularly in the range of 0.6≦(radius of curvature of electrode corner/thickness of electrode A (cathode))≦1.0, the electric field concentration at the electrode corner can be halved, and a sudden increase in the output signal current at the electrode corner can be suppressed. Therefore, it is possible to maintain the uniformity of the sensitivity of the photoelectric conversion film.
This improves the image quality of the captured image. In other words, excessive electric field concentration at the electrode corners can be suppressed, which makes it possible to avoid non-uniformity in the amplification factor and non-uniformity in brightness within the pixel, and to prevent deterioration of image quality.

Example 2
The photoelectric conversion film-stacked solid-state imaging element of this Example 2 differs from the photoelectric conversion film-stacked solid-state imaging element of Example 1 described above in terms of the electrode arrangement relationship, but is otherwise similar, so only the electrode shape and the differences in action and effect resulting from this difference in electrode shape will be described.

FIG. 9 shows the planar structure of a solid-state imaging device of the lateral magnetic field type (MSM).
9, one pixel area is formed by an area of two pitches of the electrode B (12), but it is also possible to form one pixel area by an area of any n pitches (n is a positive integer) of the electrode B (12). In this case, the area of one pitch of the electrode B (12) forms one pixel element in claim 1.

As shown in FIG. 9, each electrode (common electrode (anode: electrode B) 12 and readout electrode (cathode: electrode A) 13) is comb-shaped and configured so that the teeth of one comb can be inserted between the teeth of the other comb. The electrodes 12 and 13 can be interchanged as cathodes and anodes.

As described above, in the photoelectric conversion film stack type solid-state imaging element according to this embodiment, the specified prescribed contents are set to appropriate numerical values based on data obtained through research by the inventors of the present application. The prescribed contents are listed below in the form of numerical requirements.

<1> First, in this embodiment, the electrode width α' of the readout electrode (cathode: electrode A) 13 in each pixel (in FIG. 9, two comb teeth of electrode B are provided in one pixel, so the width of each of the two comb teeth of electrode B) is set to 10 nm or less. Also, the electrode spacing γ' between the common electrode (anode: electrode B) 12 and the readout electrode (cathode: electrode A) 13 in each pixel is set to 10 nm or less. Note that the electrode width β' of the common electrode (anode: electrode B) 12 in this embodiment (two comb teeth of electrode A are provided in one pixel, so the width of each of the comb teeth of the two electrode B) is also set to 10 nm or less.

Moreover, it is more preferable that the electrode width α' of the read electrode 13, the electrode width β' of the common electrode 12, and the electrode interval γ' between the common electrode 12 and the read electrode 13 are 1 nm or more to facilitate manufacturing.
In these respects, the numerical requirements are basically the same as those in the first embodiment.

<2> In addition to the requirement <1> above, by setting the electrode width 2β' of the common electrode (anode: electrode B) 12 in each pixel to at least twice, and more preferably twice, the electrode width 2α' of the readout electrode (cathode: electrode A) 13, it is possible to better meet the above demands.

<Verification of Example 2>
The above numerical requirements <1> and <2> for the photoelectric conversion film stack type solid-state imaging device according to the second embodiment will be examined below.
(Verification of <1>)
FIG. 10 shows the results of a simulation analysis of the change in electric field strength applied to the photoelectric conversion layer 5 when the electrode width 2α' and the electrode spacing γ'(2α' = γ') of the readout electrode (cathode: electrode A) 13 are changed from 100 nm to 10 nm.

According to Figure 10, when the electrode width 2α' and the electrode spacing γ' of the readout electrode (cathode: electrode A) 13 are set to 100 nm, the electric field strength does not reach 0.5 x 10 ⁸ V/m, and the electric field strength required to cause avalanche multiplication cannot be obtained.
The electric field strength increases as the electrode width 2α' and the electrode spacing γ' decrease. By setting the electrode spacing to 30 nm or less, a strong electric field of 1×10 ⁸ V/m or more, which can cause avalanche multiplication, can be obtained at the electrode ends.

On the other hand, however, the change in electric field strength in response to a change in the electrode spacing γ' at the center of the electrode is more gradual than that at the electrode ends. As shown in the explanation of Example 1, the difference in electric field strength between the electrode center and the electrode ends decreases as the electrode width 2α' and the electrode spacing γ' of the read electrode (cathode: electrode A) 13 are reduced, but the electric field strength at the electrode center and the electrode ends can be made almost equal by reducing the electrode width 2α' of the read electrode (cathode: electrode A) 13 to 10 nm.

Therefore, by disposing a comb-tooth shaped common electrode (anode: electrode B) 12 and a comb-tooth shaped readout electrode (cathode: electrode A) 13 in each pixel, and setting the electrode width 2α' and the electrode spacing γ' of the readout electrode (cathode: electrode A) 13 to lengths of 10 nm or less, it is possible to obtain a uniform and high electric field strength (charge multiplication).

(Verification of <2>)
FIG. 11 shows the results of a simulation analysis of the change in the electric field strength ratio (the electric field strength when the electrode width β' of the common electrode (anode: electrode B) 12 is infinite is taken as 100%) when the electrode spacing γ' is fixed and the value of (electrode width β' of the common electrode (anode: electrode B) 12/electrode width α' of the readout electrode (cathode: electrode A) 13) is changed to 1, 2, and 3.

According to FIG. 11, when the electrode width 2β' of the common electrode (anode: electrode B) 12 is equal to the electrode width 2α' of the readout electrode (cathode: electrode A) 13 (when the above value is 1), the electric field strength ratio applied to the photoelectric conversion film drops to 85%.

On the other hand, when the electrode width β' of the common electrode (anode: electrode B) 12 is twice the electrode width α' of the readout electrode (cathode: electrode A) 13 (when the above value is 2), the electric field intensity ratio applied to the photoelectric conversion film increases to 91%. This is because, by making the electrode width 2β' of the common electrode (anode: electrode B) 12 somewhat wider, the interaction of the electric fields formed by the adjacent electrode pairs (pairs of electrodes A and B) is suppressed, and the supply of the electric field (electric lines of force) from the common electrode (anode: electrode B) 12 can be made sufficient.
Furthermore, when the electrode width β' of the common electrode (anode: electrode B) 2 is three times the electrode width α' of the readout electrode (cathode: electrode A) 3 (when the above value is 3), the electric field strength ratio applied to the photoelectric conversion film is 91%.

Therefore, by making the electrode width β' of the common electrode (anode: electrode B) 2 at least twice the electrode width α' of the readout electrode (cathode: electrode A) 3, the electric field strength ratio applied to the photoelectric conversion film can be increased to 90% or more. However, even if the electrode width β' of the common electrode (anode: electrode B) 2 is increased to three times the electrode width α' of the readout electrode (cathode: electrode A) 3, no further increase in the electric field strength ratio applied to the photoelectric conversion film is observed.

As a result, the electrode width β' of the common electrode (anode: electrode B) 2, which is optimal for efficiently applying an electric field to the photoelectric conversion film while increasing the density of the electrode arrangement, is twice the electrode width α' of the readout electrode (cathode: electrode A) 3. By forming the comb-tooth electrode, which is relatively easy to manufacture, into the shape described above, a high electric field can be efficiently applied to the photoelectric conversion film, enabling efficient charge multiplication within the photoelectric conversion film.

In this embodiment as well, similarly to the first embodiment, the value of (radius of curvature of electrode corner/thickness of electrode A (cathode)) is optimized, and the content to be optimized is similar to that described using FIGS. 8A and 8B.
That is, the shape of the corners of the electrodes (common electrode (anode: electrode B) 2 and readout electrode (cathode: electrode A) 3) is set to 0.6≦(radius of curvature of electrode corner/thickness of electrode A (cathode))≦1.0, in particular, to halve the electric field strength due to electric field concentration.

The photoelectric conversion film stack type solid-state imaging device of the present invention is not limited to the above-mentioned embodiment, and various other modifications are possible.
For example, in the above embodiment, each pixel has an electrode arrangement including a common electrode formed along the pixel boundary region and a readout electrode formed at the center of each pixel, or an electrode arrangement including a common electrode and a readout electrode, both of which are comb-shaped. However, it is also possible to configure the pixel group consisting of four adjacent pixels forming a square, as shown in FIG. 1 as a whole, as an enlarged unit pixel, which is regarded as one pixel.

In this case, electrical signals from the four actual pixels may be synthesized to produce an electrical signal that is output from the enlarged unit pixel.
Furthermore, even in the case of comb-tooth electrodes, the number of comb teeth of each electrode arranged within one pixel is not limited to two pairs as in the embodiment, but may be one pair or any other desired number (excluding 0).

For example, in the above embodiment 1, the read electrode located in the center of the pixel is rectangular in shape, but this shape may be circular or another shape such as hexagonal.

Furthermore, the layer structure of the photoelectric conversion film stack type solid-state imaging device is not limited to that in the above embodiment, and other layers may be sandwiched therebetween.
Moreover, various other aspects can be adopted for the configuration of the pixel circuit in FIG.

The photoelectric conversion film stacked solid-state imaging element of the present invention is generally sensitive to the entire visible light range, but it can also cover any other wavelength range, for example, it can be a solid-state imaging element sensitive only to the infrared range.

1. Signal readout circuit board (circuit board)
2, 12 Common electrode (electrode B)
3, 13 Read electrode (electrode A)
5 Photoelectric conversion layer FD Floating diffusion capacitance (Floating diffusion)
RST Reset transistor AMP Amplification transistor SEL Selection transistor

Claims (4)

a photoelectric conversion film having sensitivity in a predetermined wavelength range is laminated on a circuit board, pixel elements are arranged in an array on a plane parallel to a surface of the circuit board, and electrodes constituting anodes and cathodes are alternately arranged in at least one direction of the arrangement of the pixel elements;
One or a group of adjacent pixel elements constitutes one pixel;
At least one electrode constituting the anode and one electrode constituting the cathode are disposed in each of the pixel elements, and the electrode width in the one direction of at least one of the two electrodes constituting the cathode and the interval in the one direction between the electrodes constituting the anode and the cathode are both set to 10 nm or less;
1. A photoelectric conversion film stacked solid-state imaging device, wherein the shape of corners in a cross-sectional view of each of the electrodes constituting the anode and the cathode satisfies the following formula:
0.6≦radius of curvature of the corner portion of the electrode/thickness of the electrode≦1.0 a common electrode constituting the anode and formed along the boundary area of the pixel elements, and a readout electrode constituting the cathode and formed at the center position of each of the pixel elements;
2. The photoelectric conversion film stack type solid-state imaging device according to claim 1, wherein the electrode width of the anode is 0.5 to 2 times the electrode width of the cathode. In the row of the pixel elements in the array, each electrode constituting the anode and the cathode is formed in a comb shape, and one is configured so that the comb teeth are inserted between the comb teeth of the other,
2. The photoelectric conversion film stack type solid-state imaging device according to claim 1, wherein the electrode width of the anode is from two to three times the electrode width of the cathode. The photoelectric conversion film stacked solid-state imaging device according to claim 2 or 3, characterized in that the distance between the electrodes constituting the anode and the cathode is equal to or less than the electrode width of the cathode.

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