Optical element array, photoelectric conversion apparatus, and image pickup system

An optical element array includes a first optical element and a second optical element that is further away from a center of an array region than the first optical element. Orthogonal projections of the first and second optical elements include first and second ends and third and fourth ends, respectively, and vertices thereof are at first and second positions. An interval between the third end and the second position is smaller than that between the first end and the first position and that between the fourth end and that second position. The first and second optical elements respectively include first and second outer edges extending from the vertices thereof to the second and fourth ends. A radius of curvature, or a median value of the radius of curvature, of the second outer edge is in the range of 80% to 120% of that of the first outer edge.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical element array, a photoelectric conversion apparatus including the optical element array, and an image pickup system.

2. Description of the Related Art

Photoelectric conversion apparatuses include optical element arrays, such as microlens arrays. Japanese Patent Laid-Open No. 2006-049721 discloses a photoelectric conversion apparatus in which the maximum curvature of convex surfaces of microlenses in an outer (peripheral) region of the photoelectric conversion apparatus is greater than that of convex surfaces of microlenses in a central region of the photoelectric conversion apparatus, so that light that is obliquely incident on the photoelectric conversion apparatus can be efficiently collected.

SUMMARY OF THE INVENTION

An optical element array includes a plurality of optical elements including at least a first optical element and a second optical element located on a same plane. The first optical element is located at a center of an array region, which is a region on the same plane in which the optical elements are arranged. The second optical element is further from the center of the array region than the first optical element. An orthogonal projection of the first optical element on the plane includes a first end and a second end located closer to the second optical element than the first end and located on a first straight line that passes through the first end and the center of the array region. An orthogonal projection of a vertex of the first optical element on the plane is equally spaced from the first end and the second end and located at a first position on the first straight line. An orthogonal projection of the second optical element on the plane includes a third end that is located on the first straight line and a fourth end that is located on the first straight line and that is further from the center of the array region than the third end is. An orthogonal projection of a vertex of the second optical element on the plane is located at a second position on the first straight line. An interval between the third end and the second position is smaller than an interval between the first end and the first position, and is also smaller than an interval between the fourth end and the second position. In a cross section of the first optical element, the cross section being perpendicular to the plane and including the first straight line, the first optical element includes a first outer edge that extends from the vertex of the first optical element to the second end. In a cross section of the second optical element, the cross section being perpendicular to the plane and including the first straight line, the second optical element includes a second outer edge that extends from the vertex of the second optical element to the fourth end. A radius of curvature of the second outer edge or a median value of the radius of curvature of the second outer edge is greater than or equal to 80% and less than or equal to 120% of a radius of curvature of the first outer edge or a median value of the radius of curvature of the first outer edge.

An optical element array includes a plurality of optical elements including at least a first optical element and a second optical element located on a same plane. The second optical element is further from a center of an array region, which is a region on the same plane in which the optical elements are arranged, than the first optical element. An orthogonal projection of the first optical element on the plane includes a first end and a second end located further from the center of the array region than the first end is and located on a first straight line that passes through the first end and the center of the array region. An orthogonal projection of a vertex of the first optical element on the plane is located at a first position on the first straight line. An orthogonal projection of the second optical element on the plane includes a third end that is located on the first straight line and a fourth end that is located on the first straight line and that is further from the center of the array region than the third end is. An orthogonal projection of a vertex of the second optical element on the plane is located at a second position on the first straight line. An interval between the third end and the second position is smaller than an interval between the first end and the first position, and is also smaller than an interval between the fourth end and the second position. In a cross section of the first optical element, the cross section being perpendicular to the plane and including the first straight line, the first optical element includes a first outer edge that extends from the vertex of the first optical element to the second end. In a cross section of the second optical element, the cross section being perpendicular to the plane and including the first straight line, the second optical element includes a second outer edge that extends from the vertex of the second optical element to the fourth end. A radius of curvature of the second outer edge or a median value of the radius of curvature of the second outer edge is greater than or equal to 80% and less than or equal to 120% of a radius of curvature of the first outer edge or greater than or equal to 80% and less than or equal to 120% of a median value of the radius of curvature of the first outer edge.

DESCRIPTION OF THE EMBODIMENTS

With the microlenses described in Japanese Patent Laid-Open No. 2006-049721, although the maximum curvature of the convex surfaces of the microlenses is taken into consideration, the curvatures of end portions of the microlenses are not taken into consideration. The relationship between the curvatures of the end portions of the microlenses and the positions of the microlenses is also not taken into consideration.

When end portions of optical elements have different curvatures depending on the positions of the optical elements in an array region of the optical element array, there is a possibility that the light collecting performance of the optical elements will be reduced at the periphery of the array region. The reduction in the light collecting performance of the optical elements at the periphery of the array region may cause shading of an image in a photoelectric conversion apparatus.

Accordingly, the present disclosure provides an optical element array with which the reduction in light collecting performance of optical elements at the periphery of the array region can be suppressed.

The structures of optical element arrays according to embodiments of the present disclosure will be described. The embodiments may be modified or combined as appropriate. Optical element arrays according to the present disclosure may be included in a photoelectric conversion apparatus, a display device, an image pickup system including the photoelectric conversion apparatus, or a display system including the display device.

In the following description, an X-axis direction (first direction), a Y-axis direction (second direction), and a Z-axis direction (third direction), which pass through a certain center O, are used as references. However, the references are not limited to this. For example, a direction131that is inclined by an angle θ1with respect to the X-axis direction illustrated inFIG. 1may be defined as the first direction, and a direction perpendicular to the direction131may be defined as the second direction. In other words, any direction that radially extends from the center of a region in which optical elements are arranged (array region) toward the outer periphery of the region may be defined as the first direction, and a direction perpendicular to the first direction may be defined as the second direction. In the following description, it is assumed that the optical element array extends along a plane including the first direction and the second direction.

First Embodiment

An optical element array according to a first embodiment will be described with reference toFIGS. 1,2A, and2B.FIG. 1is a schematic plan view illustrating an optical element array100. The schematic plan view shows a projection image (orthogonal projection image) in which each element is projected onto a plane including an X-axis and a Y-axis, which is perpendicular to the X-axis.

The optical element array100includes a plurality of optical elements110on the same plane. The optical elements110are arranged in an array region120. An orthogonal projection of the array region120has a center (hereinafter referred to as center O). The center O of the array region120is the center of a region in which the optical elements110, which function optically, are arranged in at least one direction. Here, optical elements that do not function optically include, for example, optical elements arranged in a light shielding region including an optical black region, a peripheral circuit region, etc., of a photoelectric conversion apparatus. The optical elements110are arranged such that the centers of orthogonal projection images of the optical elements110are on a straight line that extends in a single direction.

In the present embodiment, the optical elements110are arranged on a plane including an X-axis and a Y-axis, which is perpendicular to the X-axis. More specifically, the optical elements110are arranged in a matrix pattern (two-dimensional pattern) including n columns (n is a natural number) that are arranged in a direction along the X-axis (hereinafter referred to as an X-axis direction) and m rows (m is a natural number) that are arranged in a direction along the Y-axis (hereinafter referred to as a Y-axis direction). The one direction is defined as the X-axis direction (straight line). InFIG. 1, the coordinates of each optical element110are defined as (m, n). In the following description, an optical element111(first optical element) and an optical element112(second optical element) will be described as examples. As illustrated inFIG. 1, in the present embodiment, the optical element111is at the center O of the array region120, and the optical element112is separated from the optical element111by a length141in the X-axis direction. Here, it is assumed that the bottom surfaces of the optical elements110are included in the above-described plane.

FIG. 2Ais a schematic diagram for describing the cross-sectional shapes of the optical element111and the optical element112along a plane that extends in the X-axis direction and a direction along a Z-axis (hereinafter referred to as a Z-axis direction). The Z-axis is perpendicular to both the X-axis and the Y-axis. In the following description, dimensions of each optical element in the X-axis direction, the Y-axis direction, and the Z-axis direction are defined as length, width, and height, respectively. The shapes of the optical element111and the optical element112will now be described in detail. In drawings illustrating cross-sectional shapes of optical elements, such asFIG. 2A, the cross-sectional shapes may be referred to as cross sections.

The optical element111has a semispherical shape, and has a vertex on the Z-axis in the plane extending in the X-axis direction and the Z-axis direction. Referring toFIG. 2A, in a cross section211of the optical element111, the optical element111includes a first end201and a second end202that are arranged in the first direction. Each end may either be a dot or a line. In the following description, the ends are dots arranged in the first direction (straight line). As shown in the cross section211, the optical element111has a bottom surface243that extends along the X-axis at the position where Z=0. The first end201of the optical element111is separated from the center O in the direction opposite to the X-axis direction, and the second end202of the optical element111is separated from the center O in the X-axis direction. The length between the first end201and the second end202in the X-axis direction is a length220. The length between the first end201and the second end202may be the largest length of the optical element111in the X-axis direction. Here, a length between two positions may mean an interval or a distance.

As illustrated inFIG. 2A, the optical element111has a first vertex205that is located at a first position207in the X-axis direction in the orthogonal projection image. The optical element111has a rotationally symmetrical shape with respect to the normal to the bottom surface243that passes through the vertex205. Here, the vertex is a highest portion of the optical element. The optical element may have a flat top surface. In such a case, the height of any point on the flat surface is defined as the height of the vertex. Also in the following description, the vertex has the same meaning. The first vertex205is located at a position separated from the bottom surface243by a length230in the Z-axis direction. In other words, the height of the optical element111is the length230. In addition, in the orthogonal projection image, the length between the first position207and the first end201is equal to the length between the first position207and the second end202. When it is assumed that the optical element111is provided in a unit cell that is a rectangular region having the length220, it can be said that the first vertex205is at a center C1of the unit cell. In the present embodiment, the first position207is located at the center O of the array region120inFIG. 1.

The optical element112has an aspherical shape. When a cross section212is set as a reference, the optical element112is symmetric (line symmetric). However, the optical element112does not have a rotationally symmetrical shape with respect to the normal to a bottom surface244that passes through a second vertex206. The optical element112may, for example, have a planar shape illustrated inFIGS. 8A to 8C, which will be described below, or a shape called a teardrop shape.

Referring toFIG. 2A, the cross section212of the optical element112includes a third end203and a fourth end204. As shown in the cross section212, the optical element112has the bottom surface244that extends along the X-axis at the position where Z=0. The third end203of the optical element112is closer to the center O, and the fourth end204of the optical element112is further from the center O. The length between the third end203and the fourth end204in the X-axis direction is a length221. The length between the third end203and the fourth end204may be the largest length of the optical element112in the X-axis direction.

As illustrated inFIG. 2A, the optical element112has the second vertex206that is located at a second position208in the X-axis direction. The second vertex206is at a position separated from the bottom surface244by the length230in the Z-axis direction. In other words, the height of the optical element112is the length230, which is the same as the height of the optical element111. In the orthogonal projection image, the length between the second position208and the third end203is smaller than the length between the second position208and the fourth end204. When it is assumed that the optical element112is provided in a unit cell that is a rectangular region having the length220, it can be said that the second vertex206is closer to the center O than a center C2of the unit cell by a length223.

When the optical element111and the optical element112are compared with each other, in the X-axis direction, the length between the first end201and the first position207is greater than the length between the third end203and the second position208. In other words, unlike the positional relationship between the first vertex205and the center of the optical element111, the second vertex206is shifted toward the center O from the center of the optical element112. In addition, the length221, which is the length between the third end203and the fourth end204, is smaller than the length220, which is the length between the first end201and the second end202, by a length222.

Each of the optical element111and the optical element112has a plurality of outer edges which will be described below. The optical element111has an outer edge241(first outer edge) that extends from the first vertex205to the second end202. Similarly, the optical element112has an outer edge242(second outer edge) that extends from the second vertex206to the fourth end204. The radius of curvature of the outer edge242is the same as the radius of curvature of the outer edge241. When the optical elements have such a shape, in the case where the vertices of the optical elements are shifted, reduction in the light collecting performance of the optical elements can be suppressed even at positions separated from the center O in the X-axis direction. In the case where the outer edge241and/or the outer edge242have/has a nonuniform radius of curvature, the median value of the radius of curvature of the outer edge241and/or the median value of the radius of curvature of the outer edge242may be determined. The effects of the present embodiment can be achieved as long as the radii of curvature, or the median values of the radii of curvature, are in the range of 80% or more and 120% or less. In other words, the effects can be achieved as long as the difference between the radii of curvature, or the median values of the radii of curvature, is within ±20%.

Next, a case in which the optical element array according to the present embodiment is included in a photoelectric conversion apparatus will be described with reference toFIG. 2B.FIG. 2Bis a schematic sectional view of a part of a photoelectric conversion apparatus including the optical element array corresponding toFIG. 2A. A multilayer wiring structure252including a plurality of wiring layers and a plurality of insulating layers, a color filter layer253including a plurality of color filters, and a planarization layer254are provided on a semiconductor substrate250including a plurality of photoelectric conversion elements251. The optical element array100is provided on the planarization layer254. The semiconductor substrate is, for example, an N-type semiconductor substrate, and includes an epitaxial layer and P-type semiconductor regions that serve as wells. The photoelectric conversion elements are, for example, photodiodes. InFIG. 2B, N-type semiconductor regions that serve as the photoelectric conversion elements are illustrated. Here, pixels are rectangular regions, and are also regarded as unit cells. Each pixel includes at least one photoelectric conversion element. In the present embodiment, a single pixel is provided for each of the optical elements included in the optical element array100. In other words, the optical element array100is arranged in accordance with an image pickup region, in which a plurality of pixels of the photoelectric conversion apparatus are arranged. Here, the image pickup region is a region in which the pixels for acquiring image signals are arranged, and the center of the image pickup region is the center of the region in which the pixels for acquiring optical signals are arranged. The region in which the pixels for acquiring the optical signals are arranged does not include optical black pixels or circuit regions.FIG. 2Billustrates three optical elements111and three optical elements112. Three photoelectric conversion elements (first photoelectric conversion elements) are provided for the three optical elements111, and three photoelectric conversion elements (second photoelectric conversion elements) are provided for the three optical elements112. The three optical elements111are arranged without gaps therebetween, and are in contact with each other. Here, gaps refer to flat regions between the optical elements. The three optical elements112are arranged with gaps G1therebetween. The behavior of light in the above-described photoelectric conversion apparatus will now be described.

In general, an imaging lens (not shown) is disposed above the image pickup region of the photoelectric conversion apparatus. The imaging lens is arranged such that an optical axis thereof corresponds to the center of the image pickup region, and focuses light from an object on the plane of the image pickup region. At this time, the incident angle of the chief ray is small at the center of the image pickup region, and the incident angle of the chief ray is large at the periphery of the image pickup region. Here, the incident angle is, for example, an angle between a direction perpendicular to the top surface of the photoelectric conversion apparatus and the chief ray. To increase the sensitivity at the periphery of the image pickup region, it is necessary to collect the incident light and make the direction in which light is incident on the light receiving surface of each photoelectric conversion element of the photoelectric conversion apparatus close to the direction perpendicular to the light receiving surface.

Referring toFIG. 2B, light261is a chief ray that is incident on the optical element array100at the center of the image pickup region, which is also the center of the optical element array100, and is incident on a surface255of the semiconductor substrate250in a direction substantially perpendicular to the surface255. Light262is a chief ray that is incident on the optical element array100at a position separated from the center of the image pickup region, that is, from the center of the optical element array100, and is obliquely incident on the surface255of the semiconductor substrate250. Each optical element112is capable of reducing the incident angle at which the light262is incident on the light receiving surface of the corresponding photoelectric conversion element. In addition, high light collecting performance can be achieved even at the periphery of the image pickup region. As a result, the sensitivity can be increased at the periphery of the image pickup region.

Next, the effects achieved by the optical elements according to the present embodiment will be described with reference toFIGS. 3A and 3B.FIGS. 3A and 3Billustrate a case in which an optical element array300including optical elements312having a shape that differs from the shape of the optical elements inFIGS. 2A and 2Bis used.FIG. 3Ais a schematic diagram corresponding toFIG. 2A, and illustrates the cross sectional shapes of each optical element111and each optical element312.FIG. 3Bis a schematic sectional view corresponding toFIG. 2B, and illustrates a photoelectric conversion apparatus including the optical elements111and the optical elements312. In the structure illustrated inFIGS. 3A and 3B, the optical elements111are the same as the optical elements111illustrated inFIGS. 2A and 2B, and explanations thereof are thus omitted.

The cross section of the optical element312illustrated inFIG. 3Aincludes an end303of the optical element312that is closer to the center O, and an end304of the optical element312that is further from the center O of the optical element312, and is taken along the X-axis. As illustrated in the cross section, the optical element312has a bottom surface that extends along the X-axis at the position where Z=0. The end303of the optical element312is closer to the center O, and the end304of the optical element312is further from the center O. The length between the end303and the end304in the X-axis direction is the length220. The length between the end303and the end304is the largest length of the optical element312in the X-axis direction.

Referring toFIG. 3A, the optical element312has a vertex306at a position308in the X-axis direction. The vertex306is at a position separated from the bottom surface by the length230in the Z-axis direction. In other words, the height of the optical element312is the length230, which is the same as the height of the optical element111. The length between the position308and the end303is smaller than the length between the position308and the end304. When it is assumed that the optical element312is provided in a unit cell that is a rectangular region having the length220, it can be said that the vertex306is closer to the center O than a center C3of the unit cell by a length223.

Similar to the optical element111, the cross section of the optical element312illustrated inFIG. 3Ahas an outer edge342that extends from the vertex306to the end304. The differences between the optical element312and the optical element112illustrated inFIGS. 2A and 2Bare the length in the X-axis direction and the radius of curvature of the outer edge. The radius of curvature of the outer edge342differs from that of the outer edge242of the optical element112illustrated inFIGS. 2A and 2B. In other words, the radius of curvature of the outer edge342differs from that of the outer edge241of the optical element111. The radius of curvature, or the median value of the radius of curvature, of the outer edge342is not in the range of 80% or more and 120% or less (i.e. greater than or equal to 80% and less than or equal to 120%) of the radius of curvature, or the median value of the radius of curvature, of the outer edge241. More specifically, the radius of curvature of the outer edge342is above the range of 80% or more and 120% or less (i.e. greater than or equal to 80% and less than or equal to 120%) of the radius of curvature of the outer edge241.

FIG. 3Billustrates a case in which light262is incident in a manner similar to that inFIG. 2Bon a photoelectric conversion apparatus including optical elements312having the above-described structure. The light collecting performance of the optical elements312is smaller than that of the optical elements112illustrated inFIG. 2B, and the light262is incident on a wiring layer instead of the corresponding photoelectric conversion elements251.

The radius of curvature of the optical elements112illustrated inFIG. 2Bis the same as that of the optical elements111. With this type of optical element array, the reduction in light collecting performance of the optical elements at the periphery of the array region can be suppressed. In the photoelectric conversion apparatus including the optical element array, the reduction in sensitivity at the periphery of the image pickup region can be suppressed.

The optical element array according to the present embodiment can be formed by the following method. For example, the color filter layer253is formed on the multilayer wiring structure of the photoelectric conversion apparatus. Then, a film of photosensitive resist for forming the optical elements is formed. The photosensitive resist is, for example, a positive type resist, and can be applied by spin-coating. The photosensitive resist is subjected to exposure by using a photo mask formed on the basis of the shape of the above-described optical element array, and is then developed. Thus, the optical elements are formed. A half-tone mask or an area gradation mask may be used as the photo mask. The area gradation mask is a photo mask whose transmittance is controlled by adjusting the density and area of small light-shielding elements. The optical element array may be formed by other methods. In the case where the optical elements have heights and shapes different from the design due to variations in manufacturing, the effect of suppressing the reduction in sensitivity at the periphery can be achieved when the differences are within the following range. That is, the heights of the optical elements at the periphery need to be in the range of 80% or more and 120% or less (i.e. greater than or equal to 80% and less than or equal to 120%) of those of the optical elements at the center of the image pickup region, and the radii of curvature of the outer edges of the optical elements at the periphery need to be in the range of 80% or more and 120% or less (i.e. greater than or equal to 80% and less than or equal to 120%) of those of the optical elements at the center of the image pickup region. The range for the heights may be 90% or more and 110% or less (i.e. greater than or equal to 90% and less than or equal to 110%), and the range for the radii of curvature of the outer edges may be 90% or more and 110% or less (i.e. greater than or equal to 90% and less than or equal to 110%).

In the present embodiment, the vertex of an optical element111is located at the center O of the array region120in the orthogonal projection image. However, in the orthogonal projection image, the positional relationship between the center O of the array region120and the optical elements is not limited to this. For example, the center O may be located between two optical elements. Alternatively, the center O may be offset from the vertex of an optical element111.

When the shapes of the optical element arrays according to the present embodiments are measured, it can be confirmed that the optical element arrays have the following structure. That is, the vertices of the optical elements arranged in a direction away from the center of the array region have substantially the same height. Also, the vertices of the optical elements that are far from the center of the array region are closer to the center of the array region in the optical elements than the vertices of the optical elements that are close to the center of the array regions are in the optical elements. In addition, the width of the gaps between the optical elements increases as the distance from the center of the array region increases. When the optical elements have the above-described shape, the structures described in the present embodiment can be obtained.

Second Embodiment

An optical element array according to a second embodiment will be described with reference toFIGS. 4A and 4B. An optical element array400according to the present embodiment includes an optical element113(third optical element).FIG. 4Ais a schematic diagram illustrating the cross sectional shapes of optical elements, andFIG. 4Bis a schematic sectional view of a photoelectric conversion apparatus. InFIGS. 4A and 4B, an optical element112is the same as that inFIGS. 2A and 2B, and descriptions thereof are thus omitted.

Referring toFIG. 1, the optical element113illustrated inFIGS. 4A and 4Bis further from the center O in the X-axis direction than the optical element112is, and is separated from the center O by a length142in the X-axis direction. The optical element113is shaped so as to be symmetric when a cross section413is set as a reference and asymmetric when the normal to a bottom surface445that passes through a third vertex407is set as a reference.

Referring toFIG. 4A, the cross section413of the optical element113includes a fifth end405and a sixth end406. As shown in the cross section413, the optical element113has the bottom surface445that extends along the X-axis at the position where Z=0. The fifth end405of the optical element113is closer to the center O, and the sixth end406of the optical element113is further from the center O. The length between the fifth end405and the sixth end406in the X-axis direction is a length421. The length between the fifth end405and the sixth end406is the largest length of the optical element113in the X-axis direction.

As illustrated inFIG. 4A, the optical element113has the third vertex407at a third position409in the X-axis direction. The third vertex407is at a position separated from the bottom surface445by the length230in the Z-axis direction. In other words, the height of the optical element113is the same as the height of the optical element112. The length between the third position409and the fifth end405is smaller than the length between the third position409and the sixth end406. When it is assumed that the optical element113is provided in a unit cell that is a rectangular region having the length220, it can be said that the third vertex407is closer to the center O than a center C4of the unit cell by a length423.

When the optical element112and the optical element113are compared with each other, in the X-axis direction, the length between the third end203and the second position208is greater than the length between the fifth end405and the third position409. In other words, compared to the positional relationship between the second vertex206and the center of the optical element112, the third vertex407is shifted further toward the center O from the center of the optical element113. In addition, the length421, which is the length between the fifth end405and the sixth end406, is smaller than the length220, and is also smaller than the length221, which is the length between the third end203and the fourth end204. In other words, a length422is smaller than the length222.

The optical element113has an outer edge442(third outer edge) that extends from the third vertex407to the sixth end406in the cross section413. The radius of curvature of the outer edge442is the same as that of the outer edge242of the optical element112in the cross section212. Since the optical element113has such a shape, reduction in the light collecting performance of the optical elements can be suppressed also at a position further from the center O in the X-axis direction than the optical element112is. Similar to the first embodiment, also with the outer edge242and the outer edge442, the median values of the radii of curvature can be determined. The effects of the present embodiment can be achieved when these values are within the range of 80% or more and 120% or less (i.e. greater than or equal to 80% and less than or equal to 120%).

A gap G2having the length422is provided between the optical element113and an optical element that is adjacent to the optical element113in the X-axis direction. A gap G1, which has the length222smaller than the length422, is provided between the optical element112and an optical element that is adjacent to the optical element112in the X-axis direction. Thus, the gap between the optical elements increases as the distance from the center O of the optical element array increases. The length of an interval between the optical element111and an optical element that is adjacent to the optical element111in the X-axis direction is smaller than the length222. Alternatively, the adjacent optical elements may be in contact with each other (not shown). With the optical element array including the above-described optical elements, the reduction in light collecting performance of the optical elements can be suppressed even at positions separated from the center O. In addition, in the case where the optical element array is included in a photoelectric conversion apparatus as illustrated inFIG. 4B, the reduction in light collecting performance of the optical elements at positions separated from the center O can be further suppressed.

InFIG. 4B, the unit cells of the optical elements of the optical element array400are arranged such that the centers thereof coincide with the centers of the corresponding pixels of the photoelectric conversion apparatus. However, when the incident angle of light is large at the periphery of the array region120, the unit cells of the optical elements may be shifted toward the center O of the array region120. This will be described in detail with reference toFIG. 5.

FIG. 5is a schematic plan view of a photoelectric conversion apparatus500including the optical element array100. The photoelectric conversion apparatus500includes an image pickup region520in which a plurality of pixels510of the photoelectric conversion apparatus500are arranged. InFIG. 5, the array region120and the image pickup region520are drawn so as to overlap, and rectangular unit cells including the pixels510and rectangular unit cells including the respective optical elements110are schematically drawn so as to overlap. The center O of the array region120coincides with the center of the image pickup region520. The center of each optical element110is shifted from the center of the corresponding pixel510by a certain length toward the center O. Even when light is obliquely incident on pixels near the outer periphery of the image pickup region520at a large incident angle, the optical elements are located on the optical paths. Therefore, the reduction in light collecting performance can be suppressed. The positions of the optical elements and the pixels may be adjusted in this manner. Another method for shifting the centers of the pixels with respect to the centers of the respective optical elements is to make the size (area) of the unit cells including the optical elements110smaller than the size (area) of the unit cells including the pixels510. Another method for shifting the centers of the pixels with respect to the centers of the optical elements is to change the size of the gap illustrated inFIG. 2B.

In the optical element array illustrated inFIG. 5, the amount of shift increases as the length from the center of the image pickup region increases. The amount of shift will be described with reference toFIG. 6A. InFIG. 6A, the horizontal axis represents the length from the center of the image pickup region in a direction from the center of the image pickup region toward the outside of the image pickup region, and the vertical axis represents the amount of shift of the vertex of each optical element.FIG. 6Ashows three examples of the manner in which the amount of shift is changed. Line A shows an example in which the amount of shift increases in direct proportion to the length from the center of the image pickup region. Line B shows an example in which the amount of shift increases non-linearly along a parabola with respect to the length from the center of the image pickup region. Line C shows an example in which the amount of shift starts to increase from a position that is separated from the center of the image pickup region by a certain length. Thus, the amount of shift can be changed in any way. The amount of shift can be determined on the basis of, for example, design data such as the opening ratio of the photoelectric conversion apparatus, the height from the photoelectric conversion elements to the optical elements, the refractive index of each material, and the incident angle of light.

As illustrated inFIG. 2B, to maintain the radius of curvature of the outer edge of each optical element at the periphery of the image pickup region, a gap, which is a flat region, is provided between each optical element112and an optical element adjacent thereto. The length of the gaps will be described with reference toFIG. 6B. InFIG. 6B, the horizontal axis represents the length from the center of the image pickup region in a direction from the center of the image pickup region toward the outside of the image pickup region, and the vertical axis represents the gap length.FIG. 6Bshows three examples of the manner in which the gap length is changed. Line A shows an example in which the gap length increases in direct proportion to the length from the center of the image pickup region. Line B shows an example in which the gap length increases non-linearly along a parabola with respect to the length from the center of the image pickup region. Line C shows an example in which the gap length starts to increase from a position that is separated from the center of the image pickup region by a certain length. Similar to the amount of shift, the gap length can be changed in any way. In the case where the amount of shift is changed along Line B, the gap length may also be changed along Line B to facilitate the design of the radius of curvature of the outer edge of each optical element.

In the present embodiment, the optical element111, the optical element112, and the optical element113illustrated inFIG. 1are described as first, second, and third optical elements, respectively. However, the above-described relationships of the amount of shift of the vertex and the gap length also apply to, for example, three optical elements including the optical element112, the optical element113, and an optical element114illustrated inFIG. 1. As illustrated inFIG. 1, the optical element114is further away from the center O in the X-axis direction than the optical element113is, and has the height230, similar to the optical element112and the optical element113. In this case, the amount of shift of the vertex and the gap length of the optical element114may be designed so as to satisfy the above-described relationships.

In the optical element array, the number of each of the first to third optical elements may, for example, be one. Alternatively, different numbers of first to third optical elements may be provided. Thus, any numbers of first to third optical elements may be provided. For example, each of the first to third optical elements may be provided in a plurality in the optical element array. In this case, the optical element array may include a first region in which the first optical elements are arranged, a second region in which the second optical elements are arranged, and a third region in which the third optical elements are arranged.

Third Embodiment

FIGS. 7A and 7Bare schematic sectional views illustrating photoelectric conversion apparatuses according to a third embodiment.FIG. 7Ais a schematic sectional view that corresponds toFIG. 2B. An optical element array700includes optical elements711and optical elements712. The optical elements711differ from the optical elements111illustrated inFIG. 2Bin that the boundaries between the adjacent optical elements are higher than those between the optical elements111by a height721, and the optical elements711are shaped such that a member having the height721and the optical elements111are combined together. The optical elements712differ from the optical elements112illustrated inFIG. 2Bin that there are no gaps between the adjacent optical elements. Similar toFIG. 2B, the height of the optical elements711and the height of the optical elements712are both equal to a length722. Similar toFIG. 2B, the vertices of the optical elements712are shifted further toward the center of the image pickup region than the vertices of the optical elements711are in the respective unit cells. Also when the optical elements711and712have the above-described shapes, the height of the optical elements711can be made the same as the height of the optical elements712and the radius of curvature of the outer edge between the vertex and an end of each optical element711can be made the same as the radius of curvature of the outer edge between the vertex and an end of each optical element712. In this optical element array, since there are no gaps in a region corresponding to the periphery of the image pickup region, compared to the first embodiment, the amount of incident light that can be collected can be increased at the periphery of the image pickup region. As a result, the reduction in sensitivity at the periphery of the image pickup region can be further suppressed.

The shape of the optical element array is not limited to this, and the optical element array may instead have a shape illustrated inFIG. 7B.FIG. 7Bis a schematic sectional view that corresponds toFIG. 7A. An optical element array1700includes optical elements1711and optical elements1712. The optical elements1711are the same as the optical elements711illustrated inFIG. 7A. The optical elements1712differ from the optical elements712illustrated inFIG. 7Ain that the boundaries between the adjacent optical elements are higher than those between the optical elements712by a height723. Similar toFIG. 7A, the vertices of the optical elements1712are shifted further toward the center of the image pickup region than the vertices of the optical elements1711are in the respective unit cells. Also when the optical elements1711and1712have the above-described shapes, the height of the optical elements1711can be made the same as the height of the optical elements1712and the radius of curvature of the outer edge between the vertex and an end of each optical element1711can be made the same as the radius of curvature of the outer edge between the vertex and an end of each optical element1712.

Fourth Embodiment

In a fourth embodiment, an example of the shape of an optical element112according to other embodiments will be described.FIG. 8Ais a schematic diagram illustrating the planar shape of the optical element112.FIGS. 8B and 8Care schematic diagrams illustrating the cross sectional shapes of the optical element112.

FIG. 8Ais a schematic plan view illustrating a bottom surface800of the optical element112on a plane that extends in the X-axis direction and the Y-axis direction. The bottom surface800has the same shape as an image (orthogonal projection image) obtained by projecting the optical element112onto the plane that extends in the X-axis direction and the Y-axis direction. As is clear from the bottom surface800, the optical element112has a length L1in both the X-axis direction and the Y-axis direction. The bottom surface800(optical element) includes positions P1to P6arranged in the X-axis direction. The positions P3, P1, P6, P5, P2, and P4are arranged in that order from the position closest to the center O.

In the bottom surface800of the optical element112, an outer edge811of a region850, the outer edge811being closest to the center O and extending in the Y-axis direction, is disposed at the position P3. In addition, in the bottom surface800of the optical element112, an outer edge815of the region850, the outer edge815being farthest from the center O and extending in the Y-axis direction, is disposed at the position P4. The center of the bottom surface800of the optical element112is disposed at the position P5, which is at the middle point between the position P3and the position P4. In other words, the position P4is separated from the position P3by the length L1, and the position P5is separated from the position P3by half the length L1(L1/2). The position P6is the position of the vertex of the optical element112in the X-axis direction, as described below. The region850corresponds to a unit cell described in other embodiments, and corresponds to a single cell of a two-dimensional grid arranged in the array region120. A single optical element is disposed in each cell.

As illustrated inFIG. 8A, the bottom surface800is horizontally line symmetric about the X-axis, and includes outer edges811to818. The outer edge811is a straight line connecting a point801and a point808. The outer edge812is a curve connecting the point801and a point802. The outer edge813is a straight line connecting the point802and a point803. The outer edge814is a curve connecting the point803and a point804. The outer edge815is a straight line connecting the point804and a point805. The outer edge816is a curve connecting the point805and a point806. The outer edge817is a straight line connecting the point806and a point807. The outer edge818is a curve connecting the point807and the point808. The outer edges811and815are straight lines that extend in the Y-axis direction. The outer edges813and817are straight lines that extend in the X-axis direction. The outer edges812,814,816, and818have curvatures, and connect the straight lines.

The bottom surface800has a width W1(first width) in the Y-axis direction at the position P1(fourth position) in the X-axis direction. The bottom surface800has a width W2(second width) in the Y-axis direction at the position P2(fifth position) in the X-axis direction. In addition, the bottom surface800has widths W3and W4in the Y-axis direction at the positions P3and P4, respectively. These widths satisfy at least W1>W2. Furthermore, W1>W2>W3>W4may be satisfied. InFIG. 8A, W1=L1is satisfied.

The position P1is any position that is separated from the position P3by a length that is less than or equal to half the length L1, and the position P2is any position that is separated from the position P3by a length that is greater than half the length L1. In other words, the position P1is any position that is closer to the position P3than the position separated from the position P3by half the length L1, and the position P2is any position that is further from the position separated from the position P3by half the length L1. The positions P1and P2are arranged such that the distance between the position P2and the center O is greater than the distance between the position P1and the center O.

FIG. 8Bis a schematic diagram illustrating the cross sectional shape of the optical element112along the X-axis inFIG. 8A. A cross section820of the optical element112along the plane that extends in the Z-axis direction and the X-axis direction includes outer edges831to833. The outer edge831is a straight line that connects a point821and a point822. The outer edge832is a curve that connects the point822and a point823. The outer edge833is a curve that connects the point823and a point824. The optical element112has a height H1(first height) at the position P1, a height H2(second height) at the position P2, and a height H3at the position P6. The heights satisfy H3>H1>H2. Here, the height H3is the largest height of the optical element112. In other words, the point823at the position P6is the vertex of the optical element112. The vertex of the optical element112is at the position P6, which is closer to the center O than the position P5. Here, the vertex means the highest portion of the cross section. In the present embodiment, the optical element112has the vertex point. However, it is not necessary that the highest portion be a point, and the portion between the position P1and the position P5may, for example, have the height H3.

As illustrated inFIG. 8B, in the optical element112, the outer edge832includes a portion having a radius of curvature that is smaller than that of the outer edge833. The outer edge832may also include a portion having a radius of curvature that is greater than that of the outer edge833. The radius of curvature, or the median value of the radius of curvature, of the outer edge833is the same as that of the outer edge241of the optical element111. With this structure, high lens power can be achieved and the light incident on the outer edge833can be collected with higher light collecting performance compared to that in the structure of the related art. The radius of curvature can be determined from a tangent line at any point on the cross section of an optical element. For example, a tangent line of the outer edge833at the middle point of the outer edge833in the X-axis direction (middle point between the positions P6and P4) is determined. The radius of curvature can be determined from an inscribed circle that is in contact with the tangent line. The radius of curvature of each portion can be determined by other general methods for measuring the radius of curvature. Alternatively, similar to other embodiments, the median value of the radius of curvature of each outer edge can be determined.

FIG. 8Cis a schematic diagram illustrating the cross sectional shapes of the optical element112at the position P1and the position P2inFIG. 8A. A cross section841is a cross section of the optical element112taken along the Y-axis direction at the position P1inFIG. 8A. A cross section842is a cross section of the optical element112taken along the Y-axis direction at the position P2inFIG. 8A. In the cross section841, the optical element112has a width W1and a first height H1, which is the largest height of the cross section841, at the vertex of the cross section841. The outer edge of the cross section841has a radius of curvature R1(first radius of curvature). In the cross section842, the optical element112has a width W2and a height H2, which is the largest height of the cross section842, at the vertex of the cross section842. Although the cross sections of the optical element112have the vertex points in the present embodiment, as described above, it is not necessary that portions at which the optical element112have the heights H1and H2be points. The outer edge of the cross section842has a radius of curvature R2(second radius of curvature). The radii of curvature satisfies R1<R2. Although R1≧R2may be satisfied, the width W2will be reduced in such a case. Accordingly, there is a possibility that the area occupancy will be reduced. In such a case, the width W2of the optical element may form an outer edge inFIG. 8A. When the outer edge having the width W2is provided at the position farthest from the center O, the area occupancy can be increased and light can be received over a broader range.

As illustrated inFIGS. 8A to 8C, the optical element112has the width W1, the height H1, and the radius of curvature R1at the position P1, and has the width W2, the height H2, and the radius of curvature R2at the position P2. When W1>W2, H1>H2, and R1<R2are satisfied, the optical element112provides higher light collecting performance and higher area occupancy compared to those in the structure of the related art, and the light collection efficiency can be increased.

The optical elements of each embodiment can be formed by, for example, photolithography. In this case, desired optical elements can be obtained by subjecting photoresist to exposure in an exposure device by using an area gradation mask or a gray tone mask having a transmittance determined from the design data of the shape of the optical elements, and then performing development. In addition, heat treatment for deforming the shape of the photoresist can be additionally performed. An optical element array according to any of the above-described embodiments manufactured by the above-described method may have a shape that differs from the shape defined by the design data due to diffraction of light in the exposure process or the influence of the heat treatment.

The shape of an optical element array according to any of the embodiments that has been manufactured will be described with reference toFIG. 9.FIG. 9is a diagram illustrating a shape941that corresponds to the shape of the cross section211of the optical element111illustrated inFIG. 2A. InFIG. 9, components that are the same as those inFIG. 2Aare denoted by the same reference numerals, and explanations thereof are thus omitted. The manufactured optical element111may include extending portions901which are in contact with a bottom surface200and spread from the bottom surface200. The spreading of the portions that are in contact with the bottom surface200may occur in any of the optical elements in any region. When the widths and gaps are actually measured, a plane900that is parallel to the bottom surface200may be set at a position where the height is 1% of the largest height H4of any optical element111, and the shape of each optical element on the plane900may be measured. Also when the adjacent optical elements are in contact with each other and it is difficult to determine the shapes of thereof, distances, etc., on the plane900may be measured.

Examples of methods for measuring the shapes include a method of measuring the surface of the optical element array with an AFM or the like and a method for measuring a cross section of the optical element array with an SEM or the like.

The above-described embodiments may be applied to an image pickup system, such as a camera. The concept of the image pickup system is not limited to an apparatus which is used mainly to perform a shooting operation, and also includes an apparatus having a shooting function as an auxiliary function (for example, a personal computer or a mobile device). The image pickup system includes a photoelectric conversion apparatus according to any of the above-described embodiments of the present invention, and a signal processing unit for processing signals output from the photoelectric conversion apparatus. This signal processing unit includes, for example, an A/D converter and a processor for processing digital data output from the A/D converter.

This application claims the benefit of Japanese Patent Application No. 2013-212298 filed Oct. 9, 2013, which is hereby incorporated by reference herein in its entirety.