Optical sensor assembly
An optical sensor assembly is provided in which a dark mirror coating is used to suppress stray light in the form of both unwanted reflections from non-optically active regions of the sensor assembly surface and unwanted transmission of light into the surface region of the sensor assembly. The sensor assembly includes an image sensor positioned in a substrate adjacent to substrate surface areas that are not optically active. A dark mirror coating covering those surface areas significantly reduces reflections from non-optically active surface regions and improves image sensor performance in terms of signal-to-noise ratio and reduction in the appearance of “ghost” images, in turn enhancing the accuracy and precision of the sensor. The dark mirror coating may in the alternative, or in addition, be positioned underneath an optical filter, depending on the structure, material, and requirements of a particular sensor assembly.
1. An optical sensor assembly comprising:
a substrate having a surface;
an optical image sensor positioned in the surface of the substrate;
an optical thin film filter covering the optical image sensor, wherein the optical thin film filter includes terminal tapering regions covering a portion of the surface of the substrate that extends beyond either side of the optical image sensor; and
a dark mirror coating covering a portion of the surface of the substrate and a portion of the optical thin film filter.
2. The optical sensor assembly of claim 1 , wherein the dark mirror coating covers a portion of the terminal tapering region of the optical thin film filter.
3. The optical sensor assembly of claim 1 , further comprising a bond pad positioned in the surface of the substrate, wherein the dark mirror coating covers a terminal tapering region of the optical thin film filter, and a portion of the surface of the substrate to each bond pad.
4. The optical sensor assembly of claim 3 , wherein the dark mirror coating extends a distance from an edge of the optical image sensor to the bond pad.
5. The optical sensor assembly of claim 4 , wherein the distance is from about 30 μm to about 100 μm.
6. The optical sensor assembly of claim 1 , further comprising electronic circuitry positioned within the substrate.
7. The optical sensor assembly of claim 1 , wherein dark mirror coating covers a first terminal tapering region of a first optical thin film filter, a portion of the substrate surface, and a second terminal tapering region of a second optical thin film filter.
8. The optical sensor assembly of claim 1 , wherein the dark mirror coating includes an absorbing layer and an outwardly facing dielectric layer.
9. The optical sensor assembly of claim 8 , wherein the outwardly facing dielectric layer has a low refractive index.
10. The optical sensor assembly of claim 1 , wherein the dark mirror coating includes a first substantially non-absorbing layer, a first absorbing layer, and an outwardly facing dielectric layer.
11. The optical sensor assembly of claim 1 , wherein the dark mirror coating is a multilayer structure including an outwardly facing dielectric layer and alternating layers of absorbing layers and non-absorbing layers.
12. An optical sensor assembly comprising:
a substrate having a surface;
an optical image sensor positioned in the surface of the substrate;
a dark mirror coating covering a portion of the surface of the substrate, wherein the dark mirror coating includes at least one absorbing layer of a gray metal or metal alloy and an outwardly facing dielectric layer, wherein the dark mirror coating includes at least one substantially non-absorbing layer comprised of two or more substantially non-absorbing sublayers; and
an optical thin film filter covering the optical image sensor and the dark mirror coating.
13. The optical sensor assembly of claim 12 , wherein the optical image sensor is positioned centrally in the surface of the substrate.
14. The optical sensor assembly of claim 12 , wherein the dark mirror coating and the optical thin film filter coterminate at a first end of the optical sensor assembly.
15. The optical sensor assembly of claim 12 , wherein a portion of the dark mirror coating extends beyond the optical thin film filter leaving an exposed surface portion of the dark mirror coating.
16. The optical sensor assembly of claim 12 , wherein the at least one absorbing layer is comprised of two or more absorbing sublayers.
17. The optical sensor assembly of claim 12 , wherein the at least one substantially non-absorbing layer is comprised of a dielectric material.