Solid-state imaging element, solid-state imaging device, and method for fabricating the same
A solid state-imaging element including photoelectric conversion element and an optical element such as a photonic crystal is disclosed. The optical element is formed on the photoelectric conversion element, and has a refractive index periodic structure made up of stacked layers of materials with different refractive indices. The refractive index periodic structure is defined by multiple layers along a stacking direction and by a group of concentric similar shapes along an in-plane direction. The optical element may be fabricated via lithography and etching, or an autocloning technique. A solid state-imaging device including an arrangement of several solid-state imaging elements is also disclosed.
1. A solid-state imaging element comprising a photoelectric conversion element and an optical element which is formed on said photoelectric conversion element, wherein;
a center of said optical element is aligned with a center of said photoelectric conversion element, and
said optical element has a refractive index periodic structure for a predetermined refractive index, said refractive index periodic structure being made up of at least two types of light-transparent materials with different refractive indices which are stacked in layers, and
said refractive index periodic structure has a periodic structure along a stacking direction of the layers of light-transparent materials and a periodic structure, along an in-plane direction, defined by concentric similar shapes, wherein;
said concentric similar shapes are disposed in a horizontal plane, and
said optical element has a tube-shape which is formed by extending said concentric similar shapes in a direction vertical to the in-plane direction, wherein:
said optical element has a central opening and one or more concentric similar-shaped openings disposed in the horizontal plane, the opening being defined by said concentric similar shapes, and
said optical element has a central cavity and one or more concentric cavities around the central cavity, which are formed by extending said central opening and said one or more concentric similar-shaped openings in a direction vertical to the in-plane direction.
2. The solid-state imaging element according to claim 1 , wherein a ratio of a width of an opening to a pitch increases as the opening is more distant from a center of said concentric similar shapes, the pitch being a distance between the opening and an adjacent outer opening.
3. The solid-state imaging element according to claim 2 , wherein the pitch is constant and the width of the opening increases as the opening is more distant from the center of said concentric similar shapes.
4. The solid-state imaging element according to claim 2 , wherein the width is constant and the pitch decreases as the opening is more distant from the center of said concentric similar shapes.
5. The solid-state imaging element according to claim 2 , wherein the pitch decreases as the opening is more distant from the center of said concentric similar shapes, and the width of the opening increases as said opening is more distant from the center of said concentric similar shapes.
6. A method for fabricating a solid-state imaging device comprising a plurality of solid-state imaging elements which are arranged in a two-dimensional plane, wherein each of the solid-state imaging elements comprises a photoelectric conversion element and an optical element which is formed on the photoelectric conversion element, wherein:
a center of the optical element is aligned with a center of the photoelectric conversion element, and
the optical element has a refractive index periodic structure for a predetermined refractive index, the refractive index periodic structure being made up of at least two types of light-transparent materials with different refractive indices which are stacked in layers, and
the refractive index periodic structure has a periodic structure along a stacking direction of the layers of light-transparent materials and a periodic structures along an in-plane direction, defined by concentric similar shapes,
said method comprising:
forming the optical element in a tube shape by creating, using lithography and etching, a central cavity and one or more concentric cavities around the central cavity inside the optical element by extending, in a direction vertical to the in-plane direction, a central opening and one or more concentric similar-shaped openings, the openings being defined by the concentric similar shapes and disposed in a horizontal plane; and
aligning the center of the optical element with the center of the photoelectric conversion element.
7. The method for fabricating a solid-state imaging device according to claim 6 , wherein the optical element is a photonic crystal.