JP2015115329A - Image pickup device and image pickup apparatus including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: In a polarization imaging apparatus provided with a polarizer, the light use efficiency is 50% in principle, and it is not possible to sufficiently cope with high-accuracy polarization information acquisition. An imaging device including a plurality of pixel structures having at least two photoelectric conversion regions arranged side by side, wherein the pixel structures are formed on a wavefront of incident light according to a polarization state of incident light. A wavefront adjusting element that varies the amount of phase applied is provided on the light incident side of the photoelectric conversion region, and the wavefront adjusting element varies the amount of phase applied to the wavefront in a direction in which the two photoelectric conversion regions are juxtaposed. An imaging device that calculates polarization information of the light based on signals read from the two photoelectric conversion regions. [Selection] Figure 3

Description

  The present invention relates to an imaging element and an imaging apparatus including the imaging element.

  In an imaging apparatus such as a digital camera or a digital video camera, a solid-state imaging apparatus that can detect polarization information of a subject by disposing pixels (hereinafter referred to as polarization detection pixels) that detect polarization information in some or all of the pixels of the image sensor. Proposed.

  Patent Document 1 proposes a polarization imaging apparatus that detects a light having a different polarization state by installing a polarizer in a light incident portion of an image sensor.

  A polarization imaging apparatus having a polarizer array that is divided into three or more polarizer regions each having a different transmission axis, a light receiving element array that independently receives light transmitted through each region, and an image processing unit is described.

  The light transmitted through the polarizer array has only a specific polarization component. The light is detected by the light receiving element array, and the signal from the light receiving element array is calculated by the image processing unit, so that the polarization information of the subject is obtained. Can be obtained.

Japanese Patent No. 4974543

  The device described in Patent Document 1 uses a polarizer to select a polarization component of incident light, and has a problem that the amount of light after passing through the polarizer is 50%. The remaining 50% is a loss due to reflection / absorption by the polarizer and cannot be used, and there is a concern that it cannot sufficiently cope with highly accurate acquisition of polarization information of the subject.

  In view of the above problems, an object of the present invention is to provide an imaging element that can acquire polarization information of incident light with high accuracy and has improved light utilization efficiency, and an imaging apparatus including the imaging element.

An imaging device provided by the present invention is an imaging device including a plurality of pixel structures having at least two photoelectric conversion regions juxtaposed,
The pixel structure includes a wavefront adjusting element that varies a phase amount given to a wavefront of incident light according to a polarization state of incident light on a light incident side from the photoelectric conversion region,
The wavefront adjusting element is configured to vary a phase amount given to the wavefront in a direction in which the two photoelectric conversion regions are juxtaposed.
The polarization information of the light is calculated based on signals read from the two photoelectric conversion regions.

  In the imaging device of the present invention, a wavefront adjusting element that varies the amount of phase applied to the wavefront according to the polarization state of incident light is provided on the light incident side of the photoelectric conversion region. The wavefront adjusting element is to vary the phase amount given to the wavefront in the direction in which the two photoelectric conversion regions are juxtaposed, and the light waves of the wavefronts having different phase amounts are biased in the two photoelectric conversion regions. Incident. In addition, polarization information of incident light is calculated based on signals read from the two photoelectric conversion regions.

  In the present invention, the polarization information is calculated by reading the signals from the two photoelectric conversion regions where the light is polarized and incident through the wavefront adjusting element, thereby obtaining highly accurate polarization information, which corresponds to high light utilization efficiency. An effect is produced.

Schematic diagram for explaining a pixel structure having a wavefront adjusting element Schematic diagram for explaining the behavior of light passing through the wavefront tuning element Schematic diagram for explaining the behavior of light passing through the wavefront tuning element A graph showing the relationship between the phase amount given by the wavefront adjusting element and the position A graph showing the relationship between the phase amount given by the wavefront adjusting element and the position Schematic diagram for explaining the behavior of light passing through the wavefront tuning element Schematic diagram for explaining a pixel structure according to the first embodiment. Schematic diagram for explaining a wavefront tuning element configured using a metal structure Schematic diagram for explaining the metal structure constituting the wavefront tuning element Graph showing relationship between metal structure and phase amount Schematic diagram showing a structural example of a metal structure Schematic diagram of a pixel structure in which a wavefront tuning element is constructed using a metal structure A graph showing the relationship between the phase amount given by the wavefront adjusting element and the position A graph showing the relationship between the phase amount given by the wavefront adjusting element and the position A graph showing the relationship between the phase amount given by the wavefront adjusting element and the position Schematic diagram for explaining structural birefringence material Graph showing the relationship between the refractive index and the filling factor in a wavefront tuning element constructed using a structural birefringent material Schematic diagram for explaining a wavefront tuning element composed of a structural birefringent material Schematic diagram showing an image sensor configured by arranging a plurality of pixel structures in a matrix. Schematic diagram showing an image sensor configured by arranging a plurality of pixel structures in a matrix. Schematic diagram showing an example of a pixel structure Schematic diagram showing an example of a pixel structure Schematic diagram showing an example of a pixel structure Schematic diagram showing an example of a pixel structure Schematic diagram showing an example of a pixel structure Schematic diagram showing an example of a pixel structure Schematic diagram showing an example of a digital camera

  In the imaging device of the present invention, a wavefront adjusting element that varies the amount of phase applied to the wavefront of incident light according to the polarization state of incident light is provided on the light incident side of the photoelectric conversion region.

  The wavefront adjusting element is to vary the phase amount given to the wavefront in the direction in which the two photoelectric conversion regions are juxtaposed, and the light waves of the wavefronts having different phase amounts are biased in the two photoelectric conversion regions. Incident.

  In addition, polarization information of incident light is calculated based on signals read from the two photoelectric conversion regions.

  In the present invention, the polarization information is calculated by reading the signals from the two photoelectric conversion regions where the light is polarized and incident through the wavefront adjusting element, thereby obtaining highly accurate polarization information, which corresponds to high light utilization efficiency. An effect is produced.

  First, the pixel structure constituting the imaging device of the present invention will be described.

  FIG. 1 is a schematic diagram (cross-sectional view) for explaining a pixel structure including a wavefront adjusting element.

  In FIG. 1, the pixel structure 100 has two photoelectric conversion regions 101 and 102 juxtaposed, and a wavefront adjusting element 103 is disposed on the light incident side with respect to the two photoelectric conversion regions 101 and 102. ing.

  In FIG. 1, components such as a metal wiring, a gate electrode, a memory, a passivation film, a microlens, and a color filter included in a general pixel structure are omitted.

  The behavior of light passing through the wavefront adjusting element will be described with reference to FIGS.

  Here, the wavefront adjusting element 103 does not modulate the transmission phase with respect to the polarization component parallel to the x direction, and modulates the transmission phase only with respect to the polarization component parallel to the y direction.

  Incident light (x-polarized light) 204 having a polarization parallel to the x direction does not change the wavefront before and after being transmitted through the wavefront adjusting element 103, as indicated by a wavefront 205 (shown by a dotted line) after passing through the wavefront adjusting element 103. Then, it enters the photoelectric conversion regions 101 and 102 as they are.

  On the other hand, as shown in FIG. 3, incident light (y-polarized light) 304 having polarization parallel to the y direction has a wavefront that changes before and after passing through the wavefront adjusting element 103, and the wavefront 305 (dotted line) after passing through the wavefront adjusting element The wavefront is bent in the direction of the photoelectric conversion region 101 as shown in FIG. Then, the light is incident on the photoelectric conversion region 101 with a bias.

  As described above, the wavefront adjusting element 103 has optical characteristics that vary the amount of phase applied to the wavefront of incident light according to the polarization state of the incident light. The wavefront adjusting element 103 varies the amount of phase applied to the wavefront in the direction in which the two photoelectric conversion regions are juxtaposed. Next, the phase amount given to the x-polarized light and the y-polarized light by the wavefront adjusting element 103 will be described. The graph of FIG. 4 shows the x-coordinate on the horizontal axis and the phase amount given to the incident light by the wavefront adjusting element on the vertical axis.

  The x-coordinate coincides with the x-axis direction in FIGS. 2 and 3, and coincides with the direction in which the two photoelectric conversion regions are juxtaposed.

  The point O in the graph corresponds to the x coordinate that divides the photoelectric conversion regions 101 and 102.

  A line segment 401 in the graph indicates a phase amount given to the x-polarized light by the wavefront adjusting element 103, and a line segment 402 shows a phase amount given to the y-polarized light by the wavefront adjusting element 103, respectively.

  A line segment 401 shows the same phase amount regardless of the x coordinate of the pixel structure. Therefore, the incident x-polarized light propagates while maintaining the wavefront after passing through the wavefront adjusting element 103.

  On the other hand, the phase amount of the line segment 402 changes with respect to the x coordinate of the pixel structure. Therefore, the incident y-polarized light is transmitted through the wavefront adjusting element 103 and then propagated with the wavefront being bent according to the phase amount.

  Here, the phase amount (line segment 402) given to the y-polarized light will be described.

  In the region where the x coordinate is relatively far from the point O, the phase amount given by the wavefront adjusting element 103 is small (the phase delay is small), and in the vicinity of the point O, the phase amount given by the wavefront adjusting element 103 is large (the phase delay amount). There are many).

  The phase amount to be given is a value that is asymmetrical with respect to the x coordinate (point O) that divides the photoelectric conversion regions 101 and 102. In this case, when the phase amount in the plus region relatively far from the point O is compared with the phase amount in the minus region, the phase amount in the plus region is smaller.

  The y-polarized light transmitted through the wavefront adjusting element 103 behaves like a wavefront 305 (denoted by a broken line) shown in FIG. Since light propagates in the wavefront normal direction, the y-polarized light that has passed through the wavefront adjusting element 103 propagates while being biased toward the photoelectric conversion region 101.

  The wavefront adjusting element 103 has an optical characteristic that varies the amount of phase applied to the wavefront of the incident light according to the polarization state of the incident light.

  The wavefront adjusting element 103 varies the amount of phase applied to the wavefront in the direction in which the two photoelectric conversion regions are juxtaposed. This can also be understood as asymmetric distribution of the phase amount given to the wavefront of light incident on one and the other of the photoelectric conversion regions with reference to the boundary between the two photoelectric conversion regions.

  The phase amount given to the incident light wavefront by the wavefront adjusting element 103 can take various values.

  An example is shown in FIGS. 5 (a) to 5 (d).

  5, the horizontal axis indicates the same direction as the x-axis direction described in FIGS. 2 and 3, and the direction in which the two photoelectric conversion regions are juxtaposed (in the direction in which the photoelectric conversion regions are divided). It corresponds to the x coordinate which is a direction parallel to the same).

  The point O is an x coordinate that divides the two photoelectric conversion regions 101 and 102.

  The vertical axis represents the phase amount φ (corresponding to the phase delay amount) given to the incident light wavefront by the wavefront adjusting element, and W represents the width of the pixel structure.

  FIG. 5A is an example in which the phase amount of the wavefront adjusting element 103 is different between the plus side and the minus side of the x coordinate and the phase amount in the plus side region and the minus side region is constant. is there.

  FIG. 5B is an example in which the phase amount of the wavefront adjusting element 103 is different between the plus side and the minus side of the x coordinate and the phase amount is changed in a stepped manner.

  In FIG. 5C, the phase amount of the wavefront adjusting element 103 is different between the plus side and the minus side of the x-coordinate, and the phase amount changes with a linear function (changes linearly). It is an example.

  In FIG. 5D, the phase amount of the wavefront adjusting element 103 is different between the plus side and the minus side of the x coordinate, and the phase amount is changed by a high-order function (changes in a curve). It is an example.

  As described above, by providing the wavefront adjusting element 103 with various phase amounts, the wavefront can be controlled according to the polarization state of incident light.

  With reference to FIG. 6, Table 1, Table 2, etc., it will be explained that according to the present invention, light detection is possible with high accuracy.

  In FIG. 6, the pixel structure 100 includes photoelectric conversion regions 101 and 102 and a wavefront adjusting element 103.

  The polarization state of incident light includes a mixture of incident light (x-polarized light) 604 having a polarization component parallel to the x direction and incident light (y-polarized light) 605 having a polarization component parallel to the y direction. The intensity ratio of polarized light is 1: 1.

  The wavefront after passing through the wavefront adjusting element 103 will be described.

  For the x-polarized light 604, the wavefront does not change before and after transmission through the wavefront adjusting element 103, and is transmitted as it is like the x-polarized transmitted wavefront 606.

  For the y-polarized light 605, the wavefront changes before and after transmission through the wavefront adjusting element 103, and the wavefront is bent like the y-polarized transmitted wavefront 607.

  As an example, a case will be described in which the wavefront adjusting element 103 acts on the x-polarized light 604 and the y-polarized light 605 with 100% efficiency.

  When the amount of incident light is 100, the amount of incident light of x-polarized light 504 can be expressed as 50, and the amount of incident light of y-polarized light 505 can be expressed as 50.

  After the x-polarized light 504 passes through the wavefront adjusting element 103, the amounts of light detected by the photoelectric conversion regions 101 and 102 are 25 and 25, respectively.

  Similarly, after the y-polarized light 505 passes through the wavefront adjusting element 103, the amounts of light detected by the photoelectric conversion regions 101 and 102 are 50 and 0, respectively.

  From the above results, the total light amounts detected in the photoelectric conversion regions 101 and 102 are 75 and 25, respectively.

  The total amount of light detected by the pixel structure is the total amount of light detected by the photoelectric conversion regions 101 and 102 and becomes 100.

  As described above, the total light amount detected by the pixel structure is 100 with respect to the light amount 100 of incident light, and here, light detection can be performed with high light utilization efficiency without light loss.

  Next, a method for calculating polarization information based on signals read from two photoelectric conversion regions, which is an important feature of the present invention, will be described.

  As a first example, a case where the incident light amounts of x-polarized light and y-polarized light are 50 and 50, respectively, will be described.

  As described above, the signal intensities read and detected in the photoelectric conversion regions 101 and 102 are 75 and 25, respectively.

  Here, the difference between the signal intensities detected in the photoelectric conversion regions 101 and 102 is 50.

  As a second example, when the incident light amounts of x-polarized light and y-polarized light are 100 and 0, respectively, the signal intensities read and detected in the photoelectric conversion regions 101 and 102 are 50 and 50, respectively.

  Here, the difference between the signal intensities detected in the photoelectric conversion regions 101 and 102 is 0.

  As a third example, when the incident light amounts of x-polarized light and y-polarized light are 0 and 100, respectively, the signal intensities read and detected in the photoelectric conversion regions 101 and 102 are 100 and 0, respectively.

  Here, the difference between the signal intensities detected in the photoelectric conversion regions 101 and 102 is 100.

  Table 1 summarizes these conditions.

  In Table 1, the incident polarization state represents the amount of light of each of the x-polarized light 604 and the y-polarized light 605 when the total amount of incident light is 100.

  The detection signal value represents a detection signal value corresponding to the amount of light received by the photoelectric conversion regions 101 and 102.

  The calculated value represents a value obtained by subtracting the detection signal value of the photoelectric conversion region 102 from the detection signal value of the photoelectric conversion region 101.

  From Table 1, it is understood that the polarization state of the incident light has a one-to-one relationship with the calculated value, and the polarization state of the incident light can be determined from the calculated value.

  A case where an image signal obtained by photographing a subject based on the detection signal values of the photoelectric conversion regions 101 and 102 will be described.

  Since the total amount of light incident on the pixels corresponds to the image signal, the image signal of the subject can be generated by adding the detection signal values of the photoelectric conversion regions 101 and 102.

  In an actual wavefront adjusting element, the transmittance may not be 100% due to the influence of manufacturing errors and absorption loss due to materials.

  As an example, Table 2 shows a case where a loss of 10% occurs when passing through the wavefront adjusting element when the total amount of incident light is 100.

  In Table 2, the light amounts of the x-polarized light 604 and the y-polarized light 605 are shown. This corresponds to the case where the transmittance of the wavefront adjusting element is 90%.

  For example, when the incident polarization state is x-polarized light and y-polarized light are 100 and 0, respectively, the detection signal values transmitted through the wavefront adjusting element and detected by the photoelectric conversion regions 101 and 102 are 45 and 45, respectively.

  As shown by the calculated values in Table 2, each polarization state can be detected by taking the difference between the detection signals of the photoelectric conversion regions 101 and 102.

  Even if the efficiency of the wavefront adjusting element is not 100%, each polarization state can be detected.

  Here, the efficiency indicates the ratio of giving a phase change by the wavefront adjusting element when light in a specific polarization state is incident.

  For example, in a wavefront adjusting element that gives a phase change to y-polarized light, if the efficiency is 100%, the phase change is given to all (100%) of incident y-polarized light. As a result, for 100% of the y-polarized light, the wavefront changes (bends) by the given phase amount.

  When the efficiency is 90%, a phase change is given to 90% of the incident y-polarized light, and no phase change is given to the remaining 10%.

  As a result, for 90% of the y-polarized light, the wavefront changes by the given phase amount, and the remaining 10% propagates without phase change.

  Table 3 shows the case where the efficiency of the wavefront adjusting element is 90%.

  Similar to the description of Tables 1 and 2, the polarization state of the incident light can be determined by calculating based on the detection signal values of the photoelectric conversion regions 101 and 102.

  In Table 3, the polarization state is determined by taking the difference between the output signal values of the photoelectric conversion regions 101 and 102.

  As another calculation method, as shown in Table 4, it is also possible to determine the incident polarization state by taking the ratio of the output signal values of the photoelectric conversion regions 101 and 102.

  As described above, even when the efficiency of the wavefront adjusting element is not 100%, it is possible to reliably determine the incident light polarization state, and various calculation methods can be applied to increase the polarization state of the incident light. It can be detected with accuracy.

  In the present invention, signals are read from the photoelectric conversion region by a CMOS sensor (a sensor using a complementary metal oxide semiconductor) or a CCD sensor (a sensor using a charge coupled device), which is a general image sensor. It can be carried out by applying a method adopted.

  Next, the wavefront adjusting element in the present invention will be described.

  The wavefront adjusting element in the present invention is largely divided into a configuration in which a plurality of fine metal structures smaller than the wavelength of incident light are arranged and a configuration in which a material that generates birefringence is used. Can be separated.

  In a configuration in which a plurality of metal structures are arranged, the metal structure can be made of a material that can generate plasmon resonance upon receiving light.

  Here, plasmon is a collective oscillation of free electrons on a metal surface excited by an external electric field such as light. Since electrons are charged, polarization due to the density distribution of free electrons occurs when the electrons vibrate. The phenomenon in which the polarization and the electromagnetic field are combined is called plasmon resonance.

  In particular, the phenomenon of resonance between light and plasma vibration of free electrons generated on the surface of a metal fine particle or a fine metal structure is called localized plasmon resonance.

  In other words, collective vibrations of free electrons on the surface of fine particles and fine metal structures are excited by an external electric field such as light, and the vibration causes electron density distribution and accompanying polarization. A localized electromagnetic field is generated.

  In the wavefront adjusting element of the present invention, the amount of phase applied to the incident wavefront is controlled by controlling the shape and size of the minute metal structure to control the direction of the electromagnetic wave radiated by localized plasmon resonance.

  When localized plasmon resonance occurs, electromagnetic waves are placed in a state close to retention due to resonance, so that a difference occurs in the propagation speed of light and a phase difference can be generated.

  In the present invention, examples of the metal constituting the metal structure include gold, silver, platinum, and aluminum, or alloys containing any of these.

  A fine metal structure can be produced by forming a resist pattern using lithography or the like, then performing a metal thin film deposition process such as vapor deposition or sputtering deposition, and performing a lift-off process. In addition, a metal may be deposited on the drawing beam using a focused ion beam (FIB) or the like.

  In a form configured using a material that generates birefringence, a structural birefringent material can be cited as a suitable material. In the present specification, the structural birefringent material is also expressed as a structural birefringent material.

  A periodic structure having a pitch shorter than the incident wavelength (or a structure having a period that changes) has an effective refractive index that differs in a direction having a period (or a direction in which the period changes) and a direction having no period. It behaves as if it is a refractive index material. This is a structural birefringent material.

  Due to the difference in effective refractive index, a difference occurs in the propagation speed of light in the polarization direction, thereby causing a phase difference in the passing light.

  The principle of operation of the wavefront adjusting element using the structural birefringent material is based on effective refractive index (dielectric constant) control by a periodic structure having a wavelength equal to or less than the wavelength of incident light.

  That is, by changing the periodic structure (or changing the filling factor), the effective refractive index is moderately modulated. Therefore, it is more effective for applications in which a wavefront adjusting element operating in a wide wavelength region is used. Become.

  The structural birefringent material can form a periodic fine structure by forming a resist pattern by lithography or the like and then performing a dry etching or wet etching process using the resist pattern as a mask.

In addition to the structural birefringent material, the wavelength control element can be configured using various birefringent materials such as crystals such as quartz, LiNbO ₃ , calcite, liquid crystal materials, and polymer materials. For example, polarized light other than linearly polarized light such as circularly polarized light and elliptically polarized light can be detected by using a material having a helical structure such as nematic liquid crystal.

  The present invention will be described in more detail in the following examples, including a specific configuration example of the wavefront adjusting element.

  FIG. 7 shows a schematic diagram (cross-sectional view) of a main part of the pixel structure of this embodiment.

  In FIG. 7, a pixel structure 900, photoelectric conversion regions 901 and 902, and a wavefront adjusting element 903 are shown. The wiring structure included in other general pixel structures is omitted. FIG. 8 shows the configuration of the wavefront adjusting element used in this example. The wavefront adjusting element 1000 is configured using a plurality of fine metal structures 1001 to 1008 having different shapes. A fine metal structure means that the size of the metal structure is smaller than the wavelength of incident light (on the order of submicrons).

  The structural parameters of the metal structure are as shown in FIG. 9. In addition to the rod structure width 1101, the rod structure length 1102, the angle 1103 between the rods, the rod thickness, the metal material constituting the rod, and the rod As a parameter, a substrate material on which the substrate is disposed can be adopted.

  The phase amounts for the metal structures 1001 to 1008 are shown in FIG.

  In this example, by changing the structural parameters from the metal structures 1001 to 1008, the phase amount is controlled between 0 and 2π while maintaining substantially linearity.

  A design example of the metal structure is shown in FIG.

  The metal material constituting the metal structure is gold, the substrate material on which the rod is disposed is quartz, and the thickness of the rod structure is 60 nm.

  The rod structure 1001 has a rod width 1101 of 180 nm, a rod length 1102 of 50 nm, and a rod angle 1103 of 79 degrees.

  The rod structures 1002 to 1008 are also as described in FIG.

  The rod structure 1005 is a structure obtained by rotating the rod structure 1001 180 degrees. The rod structures 1006 to 1008 also have a structure in which 1002, 1003, and 1004 are rotated 180 degrees, respectively.

  In this way, the phase amount can be controlled by controlling the structural parameters of the metal microstructure.

  An example in which this fine metal structure is arranged in a pixel structure to constitute a wavefront adjusting element will be described with reference to FIG.

  In FIG. 12, the pixel structure 900 includes two photoelectric conversion regions 901 and 902 that are juxtaposed, and includes a wavefront adjusting element 903 on the light incident side of the photoelectric conversion region. Although only one pixel structure is shown in FIG. 12, an actual image sensor is configured by arranging a plurality of pixel structures such as a matrix (two-dimensional array).

  Here, for explanation, the pitch of the pixel structure is P, the interval between the wavefront adjusting element 903 and the photoelectric conversion region is H, the center coordinates in the photoelectric conversion region 901 are parallel to the x coordinate direction in the A, and A to z directions. Let B be the intersection of the straight line segment and the wavefront adjusting element. Further, the intersections between the wavefront adjusting element and the end face of the pixel structure are C and D, respectively, and the angle between the line segment AB and the line segment AC is θ.

  Then, the phase amount given by the wavefront adjusting element 903 is set to zero for the wavefront traveling on the line segment AB, and this is used as a reference for the phase amount.

The phase amount φAC with respect to the wavefront traveling on the line segment AC is calculated by Equation 1.
φAC = 2π / λ × ΔL (Formula 1)

  Here, λ is the wavelength of incident light, and ΔL is the difference between the line segment AC and the line segment AB.

  From FIG. 12, since the length of the line segment AB is H and the length of the line segment AC is H / cos θ, ΔL is H / cos θ-H.

Assuming that the length of the line segment BC is W, θ can be written as arctan (W / H), so φAC can be described as in Equation 2.
φAC = 2π / λ × (H / cos (arctan (W / H)) − H) (Formula 2)

  For example, when λ = 530 nm, H = 4000 nm, and W = 500 nm, φAC = 0.369035.

Similarly, the phase amount φ at an arbitrary point N on the wavefront adjusting element can be described by Expression 3.
φ = 2π / λ × (H / cos (arctan (Wn / H)) − H) (Formula 3)

  Thus, by using Expression 3, it is possible to calculate a design value for concentrating only a specific incident polarization component on the photoelectric conversion unit 901 at an arbitrary position of the pixel structure.

  FIG. 13 is a graph showing a design example of the phase amount given by the wavefront adjusting element. This wavefront adjusting element gives a phase amount only to y-polarized light.

  As structural parameters of the pixel structure, the incident wavelength λ is 530 nm, the pixel pitch P is 2000 nm, the length H between the photoelectric conversion region and the wavefront adjusting element is 1850 nm, and y-polarized light is concentrated in the photoelectric conversion region 901. Designed.

  The horizontal axis of the graph will be described. B in FIG. 12 corresponds to 0 of the x coordinate on the wavefront adjusting element in the graph of FIG.

  The vertical axis indicates the phase amount, and indicates a value normalized as π = 1.

  Specific phase amounts are shown in FIG. Here, the phase amount at the point where the x coordinate is zero is set to approximately 2π.

  Based on Equation 3 described above, the phase amount at the x coordinate on each wavefront adjusting element was calculated. Here, the maximum phase amount is designed to be approximately 2π.

  The wavefront adjusting element can be designed by arranging a fine metal structure corresponding to the calculated phase amount at the x coordinate on the wavefront adjusting element.

  The wavefront adjusting element may set the maximum phase amount to an integer multiple of 2π such as 4π or 6π according to the design requirements, and control the phase amount given by the wavefront adjusting element to be larger.

  In addition, the design value of each structural parameter may be adjusted in consideration of robustness such as manufacturing error.

  FIG. 14 shows another design example related to a wavefront tuning element using a fine metal structure.

  The horizontal axis of the graph indicates the x coordinate on the wavefront adjusting element, and B, C, and D correspond to the coordinates shown in FIG.

  The vertical axis represents the phase amount. The phase amount given by the wavefront adjusting element is given by a linear expression passing through the coordinate B.

  In this case, the wavefront transmitted through the wavefront adjusting element is bent as if it was transmitted through the prism and reaches the photoelectric conversion region 901 in FIG. An example of the arrangement of fine metal structures at this time is shown in 1601.

  Similarly, FIG. 15 shows a case where a phase amount is given to a part of the wavefront adjusting element. In FIG. 15, the region between the coordinates B and C is given by a linear expression passing through the coordinates B. In the region between coordinates B and C, the phase amount is the same value as point B.

  As shown in FIG. 15, even when a phase amount is given to a partial region on the wavefront adjusting element, the wavefront transmitted through the wavefront adjusting element is bent and reaches the photoelectric conversion region 901 in a biased manner. An example of the arrangement of fine metal structures at this time is shown in 1701.

  In the second embodiment, the case where the phase change amount is given by a linear expression has been described, but a function of an arbitrary order may be applied. By applying a higher-order function, the wavefront can be controlled more precisely and the polarization detection accuracy can be increased.

  The principle of operation of the wavefront tuning element with a fine metal structure is based on an anisotropic localized plasmon resonance phenomenon. Therefore, it is more effective in applications that selectively act on a specific operating band.

  Further, by using a fine metal microstructure, a very thin wavefront adjusting element having an element thickness of about 100 nm or less can be realized.

  In Example 3, an example in which the wavefront adjusting element is formed using a birefringent material will be described.

  What is described here is an example using a structural birefringent material.

  Structural birefringence is a phenomenon in which, when light passes through a structure having a period equal to or shorter than the wavelength of incident light, the refractive index (effective refractive index) felt by the light changes according to the polarization state. . Here, a material that exhibits structural birefringence is called a structural birefringent material (structural birefringent material).

  FIG. 16 shows a schematic diagram of a structural birefringent material.

  The structural birefringent material 1800 is composed of materials M1 and M2. M <b> 1 and M <b> 2 are periodically arranged, and a structure in which the periodic interval is P, the width of the refractive index M <b> 1 is W, and the length in the z-axis direction is H.

Here, when the periodic interval P is sufficiently smaller than the incident wavelength λ (generally, when P is a fraction of λ to 1/10 or less), the x-polarized light 1801 is a structural birefringent material. The effective refractive index nx felt by the x-polarized light 1801 and the effective refractive index ny felt by the y-polarized light 1802 when the x-polarized light 1801 is a structural birefringent material can be expressed by the following equations.
(Nx) ² = F × (n1) ² + (1−F) × (n2) ² (Expression 4)
1 / (ny) ² = F × 1 / (n1) ² + (1−F) × 1 / (n2) ² (Equation 5)

  Here, F is the filling factor W / P, n1 is the refractive index of the material M1, and n2 is the refractive index of the material M2.

  FIG. 17 shows effective refractive indexes nx and ny calculated by setting n1 = 2.0 and n2 = 1.0 and using the filling factor F as a variable. It can be seen that the values of nx and ny are changed by changing the filling rate.

  When the effective refractive index changes, a difference occurs in the propagation speed of light in the polarization direction, and different phase amounts can be given to x-polarized light and y-polarized light.

  By utilizing this, a wavefront adjusting element can be configured by arranging a structural birefringent material (structural birefringent material) in a plane while changing the filling factor.

  An example of the design is shown in FIG.

  In FIG. 18, the wavefront adjusting element 2000 has structural birefringent materials 2001, 2002, 2003, 2004, 2005 having different filling factors on a substrate material 2006.

  The refractive index n1 of the materials constituting the structural birefringent materials 2001 to 2005 and the substrate material 2006 is 2.0, and the refractive index of the low refractive index material (air) n2 is 1.0.

  The filling rates of the structural birefringence materials 2001 to 2005 are 0.5, 0.6, 0.7, 0.8, and 1.0, respectively.

  Table 5 shows effective refractive indexes nx and ny for the respective structural birefringent materials.

  Here, it is assumed that the wavefront adjusting element controls the phase amount only for y-polarized light.

  The height H of each structural birefringent material is designed so that the phase amount with respect to x-polarized light after passing through each structural birefringent material becomes the same.

  Here, the height H is designed so that the phase amount φnx after the x-polarized light is transmitted becomes 1.0.

  The heights H of the structural birefringent materials 2001 to 2005 were 1.0000, 0.9449, 0.8980, 0.8575, and 0.7906, respectively. The value of the height H is a value normalized by the height of the structural birefringent material 2001.

  At this time, the phase amounts φny after the y-polarized light was transmitted were 0.8000, 0.8058, 0.8241, 0.8575, and 1.0000, respectively.

  According to the designed wavefront adjusting element, when x-polarized light is incident, the in-plane distribution of the phase amount is not given and the wavefront advances as it is. On the other hand, when y-polarized light is incident, an in-plane distribution of the phase amount is given, and the wavefront is bent according to the phase amount.

  As described above, a desired wavefront adjusting element can be designed by controlling the filling rate and height of the structural birefringent material.

  In the fourth embodiment, a configuration example of a pixel structure will be described.

  In an imaging apparatus such as a digital camera or a video camera, when light that has passed through an imaging optical system forms an image on the imaging device, a light amount difference may occur between the central region and the peripheral region of the imaging device. This is particularly noticeable in wide-angle imaging optical systems.

  In an image shot under such shooting conditions, the amount of light decreases from the center toward the periphery, and the peripheral region becomes a dark image.

  FIG. 19 shows an image sensor 2200 configured by arranging a plurality of pixel structures 2201 in a two-dimensional array.

  FIG. 20 illustrates an image sensor 2300 that includes a plurality of pixel structures constituting the central region 2301 of the image sensor and a plurality of pixel structures constituting the peripheral region 2302 of the image sensor.

  FIG. 21 shows an example of a pixel structure arranged in the central region 2301.

  The pixel structure 2400 includes photoelectric conversion regions 2401 and 2402 arranged side by side, a wavefront adjusting element 2403, a microlens 2404, a wiring layer 2405, a wiring 2406, and an insulating layer 2407.

  In the central region 2301 of the image sensor, the angle at which light is incident on the image sensor is generally vertical or small, as indicated by an arrow 2408 (generally within about several degrees). Therefore, light can be received efficiently by making the center of the pixel structure 2400 substantially coincide with the center of the microlens 2404.

  FIG. 22 shows an example of a pixel structure arranged in the peripheral region 2302 of the image sensor.

  In FIG. 22, a part of the description of the parts constituting the pixel structure is omitted, but it is the same as that described in FIG.

  The pixel structure 2400 includes a wavefront adjusting element 2403, a microlens 2504, and the like. Here, the center of the pixel structure 2400 and the center of the microlens 2504 are not shifted as shown by an arrow 2505 but are shifted.

  In the peripheral region 2302, the angle at which light is incident on the image sensor is larger than the central region 2301 (approximately several degrees or more).

  Therefore, when the pixel structure shown in FIG. 21 is applied as it is, vignetting occurs due to the partition walls and wiring layers constituting the pixel structure, the amount of light reaching the photoelectric conversion region is reduced, and the light use efficiency is lowered. .

  In order to improve this, the center of the pixel structure 2400 and the center of the microlens 2504 are coordinate-shifted in a direction in which the component coincides with the light incident direction (the direction of the arrow 2505). As a result, light incident from an oblique direction can be efficiently guided to the photoelectric conversion region.

  As described above, it is possible to design a pixel with high light utilization efficiency by devising the arrangement position of the microlens.

  In addition to devising the arrangement position of the microlens, regarding the phase amount given to the transmitted light by the wavefront adjusting element, the phase amount given to the transmitted light by the wavefront adjusting element in the central region 2301 and the wavefront adjusting element in the peripheral region 2302 given to the transmitted light Even when the phase amount is designed to be different, the same effect can be obtained.

  For example, the wavefront of the incident light is bent more greatly by designing the phase amount given to the transmitted light by the wavefront adjusting element in the peripheral region 2302 larger than the phase amount given to the transmitted light by the wavefront adjusting element in the central region 2301. Therefore, it can be efficiently led to the photoelectric conversion region. Further, as in the pixel structure shown in FIG. 23, an in-layer microlens may be provided between the photoelectric conversion region and the wavefront adjusting element.

  The pixel structure 2400 includes a wavefront adjusting element 2403, a microlens 2602, an in-layer microlens 2602, and a photoelectric conversion region.

  By providing the in-layer microlens 2602, the light beam after passing through the wavefront adjusting element 2403 is further condensed by the in-layer microlens and more efficiently guided to the photoelectric conversion region. Therefore, it becomes possible to operate as a highly efficient polarization detection pixel.

  In addition, unlike the pixel structure 2400 illustrated in FIG. 24, a wavefront adjusting element 2403 and an in-layer microlens 2603 can be provided without providing a microlens at the top of the pixel structure.

  By appropriately designing the phase amount of the wavefront adjusting element, it is possible to control the wavefront and guide light appropriately without the uppermost microlens. It is possible to reduce the number of manufacturing steps and more easily.

  Further, as shown in FIG. 25, a color filter for selecting a wavelength band to be detected may be provided.

  A pixel structure 2400 in FIG. 5 includes a wavefront adjusting element 2403, a microlens 2404, a color filter 2801 having characteristics of transmitting light in a specific wavelength band, and the like.

  Here, the color filter 2801 is arranged between the microlens 2404 and the wavefront adjusting element 2403, but the arrangement position is not limited to this.

  In the case of an absorptive color filter, it can be composed of an organic material containing pigments or pigments, an inorganic material doped with metal ions, or the like.

  In the case of a reflective color filter, it can be composed of a metal thin film, a dielectric multilayer film structure, or the like.

  By providing the color filter, polarization information for each wavelength band can be acquired. For example, in the case of using an image sensor including a color filter that transmits blue, green, red, and each wavelength band, a child that acquires polarization information in the entire visible light wavelength band can be obtained.

  A configuration may be adopted in which only a specific wavelength band is detected, for example, a color filter having a single wavelength characteristic is provided.

  It is also possible to acquire polarization information with a narrower wavelength band by appropriately combining a wavefront adjusting element using a metal microstructure with a high wavelength selectivity and a color filter. By detecting a minute change in the polarization state, it is possible to acquire various subject information such as edge detection for a low-contrast subject.

  As described above, by providing a color filter in the polarization detection pixel, polarization information and captured images in various wavelength bands can be acquired.

  Next, a pixel structure having photoelectric conversion regions having different volumes will be described with reference to FIG.

  The pixel structure 2900 includes photoelectric conversion regions 2901 and 2902, a wavefront adjusting element 2903, a microlens 2904, and the like.

  Here, the volume of the photoelectric conversion region is larger in the photoelectric conversion region 2901 than in 2902.

  As described above with reference to FIG. 6, the x-polarized light and the y-polarized light transmitted through the wavefront adjusting element are received by the photoelectric conversion region, but in accordance with the polarization state, The amount of received light changes.

  In FIG. 26, the amount of light received by the juxtaposed photoelectric conversion regions 2901 and 2902 changes.

  In the description of FIG. 6, the amount of light received by the photoelectric conversion region 101 is 50 to 100, and the amount of light received by the photoelectric conversion region 102 is 0 to 50.

  This means that when the volumes of the photoelectric conversion regions 101 and 102 are the same, the photoelectric conversion region 101 is more easily saturated with a signal value.

  When signal value saturation occurs in the photoelectric conversion unit 101, there is a concern that polarization information cannot be detected correctly. In addition, overexposure occurs as a photographed image, and there is a concern that the image quality may deteriorate.

  In the pixel structure shown in FIG. 26, the volume of the photoelectric conversion region 2901 is made larger than that of the photoelectric conversion region 2902 so that signal value saturation in the photoelectric conversion portion 2901 hardly occurs.

  Such a device increases the robustness with respect to the shooting environment, and enables detection of polarization information and acquisition of a shot image under various shooting conditions.

  About the volume of each photoelectric conversion area | region, it can design suitably based on the signal value detected in each photoelectric conversion area | region.

  In the example described with reference to FIG. 6, the maximum detection signal values in the photoelectric conversion regions 101 and 102 are 100 and 50, respectively, so that the volume ratio of the photoelectric conversion region is designed to be about 100 to 50. do it.

  The wavefront adjusting element may be arranged in all the pixel structures constituting the imaging element, or may be arranged only in a part.

  When the polarization detection pixels are arranged in a part of the pixel structures constituting the image sensor, they may be arranged continuously along a vertical, horizontal, or diagonal line, or may be arranged discretely.

  In the fifth embodiment, an imaging apparatus including the imaging element described so far will be described.

  FIG. 27 is a schematic diagram showing a digital camera provided with an image sensor according to the present invention.

  The digital camera 3000 includes an imaging optical system 3001, an imaging device 3002 according to the present invention, and a signal processing unit 3003.

  The subject 3004 generates an image on the image sensor 3002 via the photographing optical system 3001. Reference numeral 3010 denotes an optical axis.

  The image sensor 3002 includes, for example, the pixel structure 100 described with reference to FIG. The amount of light is detected by the photoelectric conversion regions 101 and 102 according to the incident x-polarized light and y-polarized light.

  The signal processing unit 3003 generates polarization information and image information based on the signal values detected in the photoelectric conversion regions 101 and 102.

  The generation of polarization information can obtain intensity information of x-polarized light and y-polarized light by calculating a difference between signal values detected in the photoelectric conversion regions 101 and 102.

  Further, the generation of the image information related to the subject 3004 can be acquired by the sum of the signal values detected in the photoelectric conversion regions 101 and 102.

  This makes it possible to provide a digital camera that can acquire polarization information and image information.

  Moving picture information can also be acquired by executing subject photographing and signal processing continuously in time series. That is, it is possible to provide a video camera that can acquire polarization information and image information.

  In addition to consumer cameras, the digital cameras and video cameras shown in this example are medical cameras such as surveillance cameras, security cameras, machine vision cameras and endoscope cameras installed in industrial equipment, weather and space observations, objects It can be applied to various applications such as academic field applications such as surface state analysis and substance identification. The image sensor of the present invention can also be applied as an image sensor of a one-shot interferometer.

DESCRIPTION OF SYMBOLS 100 Pixel structure 101 Photoelectric conversion area | region 102 Photoelectric conversion area | region 103 Wavefront adjustment element 205 Wavefront

Claims (14)

An imaging device comprising a plurality of pixel structures having at least two photoelectric conversion regions juxtaposed,
The pixel structure includes a wavefront adjusting element that varies a phase amount given to a wavefront of incident light according to a polarization state of incident light on a light incident side from the photoelectric conversion region,
The wavefront adjusting element is configured to vary a phase amount given to the wavefront in a direction in which the two photoelectric conversion regions are juxtaposed.
An imaging element, wherein polarization information of the light is calculated based on signals read from the two photoelectric conversion regions.   The imaging device according to claim 1, wherein the wavefront adjusting element is configured by arranging a plurality of metal structures smaller than a wavelength of the incident light.   The imaging device according to claim 2, wherein the metal structure is made of a material that can generate plasmon resonance upon receiving light.   The imaging device according to claim 2 or 3, wherein the metal structure is made of any one of gold, silver, platinum, and aluminum, or an alloy containing any of these.   The image sensor according to claim 1, wherein the wavefront adjusting element is made of a material that causes birefringence.   The imaging element according to claim 5, wherein the material that causes the birefringence is a structural birefringent material.   The imaging element according to claim 1, wherein polarization information of the light is calculated based on a difference between signals read from the two photoelectric conversion regions.   The image sensor according to claim 1, wherein an image signal is generated based on a sum of signals read from the two photoelectric conversion regions.   9. The pixel structure according to claim 1, wherein the pixel structures are arranged in a matrix, and a phase amount given by the wavefront adjusting element is different depending on a position where the pixel structures are arranged. The imaging device described in 1.   The imaging device according to claim 9, wherein a phase amount given by the wavefront adjusting element is different between a central region and a peripheral region of the matrix.   The image pickup device according to claim 10, wherein a volume of the photoelectric conversion region is different depending on a position where the pixel structure is arranged.   The imaging device according to claim 1, wherein the pixel structure includes a microlens.   The image sensor according to claim 1, wherein the pixel structure includes a color filter.   An imaging apparatus comprising: an imaging optical system; a signal processing unit; and the imaging element according to claim 1.

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