Metal-dielectric optical filter, sensor device, and fabrication method
An optical filter, a sensor device including the optical filter, and a method of fabricating the optical filter are provided. The optical filter includes one or more dielectric layers and one or more metal layers stacked in alternation. The metal layers are intrinsically protected by the dielectric layers. In particular, the metal layers have tapered edges that are protectively covered by one or more of the dielectric layers.
1. An optical filter, disposed on a substrate, comprising:
a plurality of dielectric layers; and
a plurality of metal layers,
wherein each metal layer of the plurality of metal layers is stacked in alternation with at least two of the plurality of dielectric layers and is surrounded by at least two of the plurality of dielectric layers,
wherein each metal layer of the plurality of metal layers has a first tapered edge and a second tapered edge that are protectively covered by at least one of the plurality of dielectric layers,
wherein the first tapered edge is located at a first periphery of the optical filter and the second tapered edge is located at a second periphery of the optical filter, and
wherein the plurality of metal layers are not adjacent, with respect to a length of the substrate, to any other metal layer.
2. The optical filter of claim 1 ,
wherein the optical filter has a substantially flat top and sloped sides, and
wherein the sloped sides of the optical filter are sloped at an angle of less than about 45° from horizontal.
3. The optical filter of claim 2 , wherein the sloped sides of the optical filter are sloped at an angle of less than about 20° from horizontal.
4. The optical filter of claim 1 , wherein the optical filter has a filter height of less than about 1 μm.
5. The optical filter of claim 1 , wherein each metal layer of the plurality of metal layers is substantially uniform in thickness throughout a central portion of the optical filter.
6. The optical filter of claim 1 , wherein the first tapered edge and the second tapered edge of each metal layer of the plurality of metal layers extend along the first periphery and the second periphery, respectively, of the metal layer and are protectively covered by at least one of the plurality of dielectric layers along the first periphery and the second periphery.
7. The optical filter of claim 1 , wherein each of the plurality of metal layers is composed of silver, a silver alloy, or aluminum.
8. The optical filter of claim 1 , wherein the optical filter is a color filter, a photopic filter, an infrared-blocking filter, or an ultraviolet filter.
9. The optical filter of claim 1 , wherein the plurality of dielectric layers include a top dielectric layer that protectively covers the first tapered edge and the second tapered edge of each metal layer of the plurality of metal layers.
10. The optical filter of claim 9 , wherein the top dielectric layer has a physical thickness of greater than about 40 nm.
11. The optical filter of claim 1 , wherein a first quantity of the plurality of metal layers is less than a second quantity of the plurality of dielectric layers.
12. A sensor device comprising:
one or more first sensor elements; and
one or more first optical filters disposed over the one or more first sensor elements,
wherein each of the one or more first optical filters includes:
a plurality of dielectric layers; and
a plurality of metal layers,
wherein each metal layer of the plurality of metal layers is stacked in alternation with at least two of the plurality of dielectric layers and is surrounded by at least two of the plurality of dielectric layers,
wherein each metal layer of the plurality of metal layers has a first tapered edge and a second tapered edge that are protectively covered by at least one of the plurality of dielectric layers,
wherein the first tapered edge is located at a first periphery of each first optical filter, of the of the one or more first optical filters, and the second tapered edge is located at a second periphery of each first optical filter of the one or more first optical filters, and
wherein the plurality of metal layers are not adjacent, with respect to a length of a substrate, to any other metal layer.
13. The sensor device of claim 12 , wherein the one or more first optical filters are disposed on a passivation layer of the one or more first sensor elements.
14. The sensor device of claim 12 , further comprising:
an encapsulation layer disposed over the one or more first optical filters and the one or more first sensor elements.
15. The sensor device of claim 12 , wherein the sensor device is an image sensor, an ambient light sensor, a proximity sensor, a hue sensor, an ultraviolet sensor, or a combination thereof.
16. The sensor device of claim 12 , further comprising:
one or more second sensor elements; and
one or more second optical filters disposed over the one or more second sensor elements,
wherein the one or more second optical filters are more environmentally durable than the one or more first optical filters, and
wherein the one or more second optical filters partially overlap with the one or more first optical filters to protectively cover the first periphery and the second periphery.
17. The sensor device of claim 16 ,
wherein the one or more first optical filters have substantially flat tops and sloped sides, and
wherein the one or more second optical filters extend over the sloped sides of the one or more first optical filters.
18. The sensor device of claim 16 , wherein the one or more second optical filters are one or more all-dielectric optical filters, one or more aluminum-dielectric optical filters, one or more silicon-dielectric optical filters, one or more hydrogenated-silicon-dielectric optical filters, or a combination thereof.
19. The sensor device of claim 16 , wherein the one or more second optical filters are one or more ultraviolet filters, one or more near-infrared filters, or a combination thereof.
20. The sensor device of claim 12 , wherein each metal layer of the plurality of metal layers is composed of silver or a silver alloy.
21. The sensor device of claim 12 , wherein the one or more first optical filters are one or more color filters, one or more photopic filters, one or more infrared-blocking filters, or a combination thereof.
22. The sensor device of claim 12 , wherein a first quantity of the plurality of metal layers is less than a second quantity of the plurality of dielectric layers.
23. A method of fabricating an optical filter, the method comprising:
providing a substrate;
applying a photoresist layer onto the substrate;
patterning the photoresist layer to uncover a filter region of the substrate, whereby an overhang is formed in the patterned photoresist layer surrounding the filter region;
depositing a multilayer stack, including a plurality of metal layers stacked in alternation with a plurality of dielectric layers, onto the patterned photoresist layer and the filter region of the substrate,
wherein each metal layer of the plurality of metal layers is stacked in alternation with at least two of the plurality of dielectric layers and is surrounded by at least two of the plurality of dielectric layers; and
removing the patterned photoresist layer and a first portion of the multilayer stack on the patterned photoresist layer so that a second portion of the multilayer stack remaining on the filter region of the substrate forms the optical filter,
wherein each metal layer of the plurality of metal layers in the optical filter has a first tapered edge and a second tapered edge that are protectively covered by at least one of the plurality of dielectric layers in the optical filter,
wherein the first tapered edge is located at a first periphery of the optical filter and the second tapered edge is located at a second periphery of the optical filter, and
wherein the plurality of metal layers are not adjacent, with respect to a length of the substrate, to any other metal layer.
24. The method of claim 23 , wherein the substrate is a sensor element.
25. The method of claim 23 , wherein the overhang is at least 2 μm.
26. The method of claim 23 , wherein the overhang is at least 4 μm.
27. The method of claim 23 , wherein the photoresist layer includes a bottom release layer and a top photosensitive layer.
28. The method of claim 27 , wherein the multilayer stack is deposited to a thickness of less than about 70% of a thickness of the bottom release layer.
29. The method of claim 27 , wherein the multilayer stack is deposited to a thickness of less than about 30% of a thickness of the bottom release layer.
30. The method of claim 23 , further comprising:
forming another optical filter that is more environmentally durable than the optical filter on the substrate so that the other optical filter partially overlaps with the optical filter to protectively cover the first periphery and the second periphery.
31. The method of claim 23 , wherein a first quantity of the plurality of metal layers is less than a second quantity of the plurality of dielectric layers.