Direct-bonded lamination for improved image clarity in optical devices
Direct-bonded lamination for improved image clarity in optical devices is provided. An example process planarizes and plasma-activates optical surfaces to be laminated together, then forms direct bonds between the two surfaces without an adhesive or adhesive layer. This process provides improved optics with higher image brightness, less light scattering, better resolution, and higher image fidelity. The direct bonds also provide a refractory interface tolerant of much higher temperatures than conventional optical adhesives. The example process can be used to produce many types of improved optical components, such as improved laminated lenses, mirrors, beam splitters, collimators, prism systems, optical conduits, and mirrored waveguides for smartglasses and head-up displays (HUDs), which provide better image quality and elimination of the dark visual lines that are apparent to a human viewer when conventional adhesives are used in conventional lamination.
1. A method of forming a mirrored optical waveguide, the method comprising:
depositing one or more reflective coatings on at least a first optically transparent substrate, wherein the one or more reflective coatings is at least partially reflective;
providing an inorganic dielectric layer over the one or more reflective coatings, the inorganic dielectric layer forming a first surface of the first optically transparent substrate;
providing a second optically transparent substrate having a second surface;
placing the first surface and the second surface together to form a stack;
forming a refractory interface via a direct bond between the first surface and the second surface at room temperature, wherein the refractory interface has a same coefficient of thermal expansion as a coefficient of thermal expansion of at least one of the first surface or the second surface; and
dicing the stack at an oblique angle to a perpendicular of the one or more reflective coatings.
2. The method of claim 1 , wherein:
the first optically transparent substrate comprises one of a glass, a fused silica, a quartz, a sapphire, a borosilicate, a plastic, or a ceramic; and
the second optically transparent substrate comprises one of a glass, a fused silica, a quartz, a sapphire, a borosilicate, a plastic, or a ceramic.
3. The method of claim 1 , wherein the first surface and the second surface are placed together at an ambient room temperature to form spontaneous chemical bonds between the first surface and the second surface.
4. The method of claim 3 , further comprising:
after forming the spontaneous chemical bonds, heating the first optically transparent substrate and the second optically transparent substrate to a temperature of approximately 150° C. to strengthen the spontaneous chemical bonds; and
cooling the first optically transparent substrate and the second optically transparent substrate to a room temperature.
5. The method of claim 1 , further comprising forming the direct bond at room temperature.
6. The method of claim 1 , further comprising annealing the direct bond at a temperature greater than the boiling point temperature of water.
7. A method of forming a mirrored optical waveguide, the method comprising:
depositing one or more reflective coatings on at least one of (i) a first optically transparent substrate or (ii) a second optically transparent substrate, wherein the one or more reflective coatings is at least partially reflective, wherein the one or more reflective coatings at least partially defines at least one of a first surface of the first optically transparent substrate or a second surface of the second optically transparent substrate;
forming a refractory interface via a direct oxide bond between the first surface and the second surface at a room temperature, wherein the refractory interface has a same coefficient of thermal expansion as a coefficient of thermal expansion of at least one of the first surface or the second surface; and
dicing the stack at an oblique angle to a perpendicular of the one or more reflective coatings.
8. The method of claim 7 , wherein the plasma process comprises one of (i) a nitrogen-based etch process or (ii) a reactive ion etch process.
9. The method of claim 1 , wherein at least one of the one or more reflective coatings is fully reflective.
10. The method of claim 1 , wherein the one or more reflective coatings comprises one or more of aluminum, silver, gold, platinum, mercury, magnesium fluoride, titanium dioxide, silicon dioxide, zinc sulphide, tantalum pentoxide, a reflective dielectric, or a Bragg mirror.
11. The method of claim 1 , further comprising:
covering the one or more reflective coatings with one or more layers of a silicon oxide, silicon nitride, silicon carbonitride or silicon oxynitride; and
forming spontaneous chemical bonds between respective layers of the silicon oxide, silicon nitride, silicon carbonitride or silicon oxynitride on the first optically transparent substrate and the second optically transparent substrate.
12. The method of claim 7 , further comprising:
covering the one or more reflective coatings with one or more layers of one or more optically transparent dielectrics.
13. An apparatus, comprising:
a first optically transparent substrate comprising a first plasma-activated surface and a first inorganic dielectric layer at least partially defining the first surface of the first optically transparent substrate;
a second optically transparent substrate comprising a second plasma-activated surface, one or more reflective coatings on the second optically transparent substrate and a second inorganic dielectric layer on the one or more reflective coatings, the second inorganic dielectric layer at least partially defining the second surface of the second optically transparent substrate, wherein the one or more reflective coatings is at least partially reflective;
a direct bond between the first inorganic dielectric layer and the second inorganic dielectric layer; and
a refractory interface between the first plasma-activated surface and the second plasma-activated surface,
wherein the refractory interface has a same coefficient of thermal expansion as a coefficient of thermal expansion of at least one of the first plasma-activated surface or the second plasma-activated surface and
wherein the apparatus has a diced surface at an oblique angle with respect to a perpendicular of the one or more reflective coatings.
14. The apparatus of claim 13 , wherein:
the first plasma-activated surface and the second plasma-activated surface comprise a same material bonded to itself across the direct bond.
15. The apparatus of claim 13 , wherein the direct bond comprises a direct bond of one of silicon oxide, silicon nitride, silicon carbonitride or silicon oxynitride between the first plasma-activated surface and the second plasma-activated surface.
16. The apparatus of claim 13 , wherein:
the first optically transparent substrate comprises a glass, a fused silica, a quartz, a sapphire, a borosilicate, a plastic, or a ceramic; and the second optically transparent substrate comprises a glass, a fused silica, a quartz, a sapphire, a borosilicate, a plastic, or a ceramic.
17. The apparatus of claim 13 , wherein at least one of the one or more reflective coatings is fully reflective.
18. The apparatus of claim 13 , wherein the one or more reflective coatings comprises one or more of aluminum, silver, gold, platinum, mercury, magnesium fluoride, titanium dioxide, silicon dioxide, zinc sulphide, tantalum pentoxide, a reflective dielectric, and a Bragg mirror.
19. The apparatus of claim 13 , further comprising:
a layer of a silicon oxide, silicon nitride, silicon carbonitride or silicon oxynitride on the one or more reflective coatings.
20. The apparatus of claim 13 ,
wherein the inorganic dielectric layer comprises one or more optically transparent dielectric layers over the one or more reflective coatings.
21. The apparatus of claim 13 , wherein the first and second plasma-activated surfaces are sufficiently flat to allow a direct bond to be formed between the first plasma-activated surface and the second plasma-activated surface without an adhesive.
22. The apparatus of claim 13 , wherein the first and second plasma-activated surfaces are polished using chemical mechanical polishing prior to formation of the direct bond.
23. The apparatus of claim 13 , wherein the first plasma-activated surface comprises a nitrogen-based plasma-activated surface.
24. The apparatus of claim 13 , wherein the direct bond comprises a bond interface comprising nitrogen.
25. A method of forming a mirrored optical waveguide, the method comprising:
depositing one or more reflective coatings on (i) a first optically transparent substrate and (ii) a second optically transparent substrate, wherein the one or more reflective coatings is at least partially reflective;
covering the one or more reflective coatings on the first optically transparent substrate with a layer of a silicon oxide, silicon nitride, silicon carbonitride or silicon oxynitride, wherein the layer of the silicon oxide, silicon nitride, silicon carbonitride or silicon oxynitride comprises a first surface of the first optically transparent substrate;
covering the one or more reflective coatings on the second optically transparent substrate with a layer of a silicon oxide, silicon nitride, silicon carbonitride or silicon oxynitride, wherein the layer of the silicon oxide, silicon nitride, silicon carbonitride or silicon oxynitride comprises a second surface of the second optically transparent substrate;
placing the first surface and the second surface together to form a stack; forming spontaneous chemical bonds between respective layers of the silicon oxide, silicon nitride, silicon carbonitride or silicon oxynitride on the first optically transparent substrate and the second optically transparent substrate; and
dicing the stack at an oblique angle to a perpendicular of the one or more reflective coatings.
26. The method of claim 25 , further comprising:
after forming the spontaneous chemical bonds, heating the first optically transparent substrate and the second optically transparent substrate to a temperature of approximately 150° C. to strengthen the spontaneous chemical bonds; and
cooling the first optically transparent substrate and the second optically transparent substrate to a room temperature.
27. The method of claim 26 , further comprising:
prior to formation of the spontaneous chemical bonds, activating the first surface and the second surface with a plasma process.
28. The method of claim 27 , wherein the plasma process comprises one of (i) a nitrogen-based etch process or (ii) a reactive ion etch process.