Near infrared optical interference filters with improved transmission

• US 9,989,684 B2
• Filed: 01/22/2016
• Issued: 06/05/2018
• Est. Priority Date: 01/23/2015
• Status: Active Grant

• Current Assignee: Materion Corporation
• Original Assignee: Materion Corporation
• Inventors: Sprague, Robert
• Primary Examiner(s): Won, Bumsuk
• Assistant Examiner(s): Washington, Tamara Y
• Application Number:
  US15/004,754
• Publication Number:
  US 20160216419A1
• Time in Patent Office: 865 Days
• CPC Class Codes: B29D 11/00634 Production of filters
• CPC Class Codes: C23C 14/0652 Silicon nitride
• CPC Class Codes: C23C 14/10 Glass or silica
• CPC Class Codes: C23C 14/165 by cathodic sputtering
• CPC Class Codes: C23C 14/34 Sputtering
• CPC Class Codes: C23C 14/3414 Metallurgical or chemical aspects of target preparation, e.g. casting, powder metallurgy
• CPC Class Codes: G02B 5/207 comprising semiconducting materials
• CPC Class Codes: G02B 5/208 for use with infrared or ultraviolet radiation, e.g. for separating visible light from infrared and/or ultraviolet radiation
• CPC Class Codes: G02B 5/281 designed for the infrared light

Abstract

An interference filter includes a layers stack comprising a plurality of layers of at least: layers of amorphous hydrogenated silicon with added nitrogen (a-Si:H,N) and layers of one or more dielectric materials, such as SiO₂, SiO_x, SiO_xN_y, a dielectric material with a higher refractive index in the range 1.9 to 2.7 inclusive, or so forth. The interference filter is designed to have a passband center wavelength in the range 750-1000 nm inclusive. Layers of a dielectric material with a higher refractive index in the range 1.9 to 2.7 inclusive provide a smaller angle shift compared with a similar interference filter using SiO₂ as the low index layers.

Claims

1. An optical filter comprising:

a transparent substrate;

an interference filter comprising a layers stack comprising a plurality of layers of at least;

layers of amorphous hydrogenated silicon; and

layers of one or more dielectric materials having a refractive index lower than the refractive index of the amorphous hydrogenated silicon wherein the layers of one or more dielectric materials include layers of a dielectric material having a refractive index in the range 1.9 to 2.7 inclusive;

the layers stack including repeating units of two or more layers configured to have a passband with properties defined by the repeating units including at least a passband center wavelength,

wherein the layers stack includes a first layers stack on one side of transparent substrate and a second layers stack on the opposite side of the transparent substrate.

2. The optical filter of claim 1, wherein the layers of a dielectric material having a refractive index in the range 1.9 to 2.7 inclusive include one or more layers consisting of:

Si₃N₄, SiO_xN_y with y large enough to provide a refractive index of 1.9 or higher, Ta₂O₅, Nb₂O₅, or TiO₂.

3. The optical filter of claim 2, wherein the layers of one or more dielectric materials further include SiO₂ layers.

4. The optical filter of claim 1 wherein the layers stack is configured to have the passband wavelength range of 800-1100 nm inclusive.

5. The optical filter of claim 1 wherein the layers stack is configured to have the passband wavelength range of 750-1100 nm inclusive.

6. The optical filter of claim 1, wherein the transparent substrate comprises a glass substrate.

7. The optical filter of claim 1, wherein the first layers defines a low pass filter with a low pass cutoff wavelength, the second layers stack defines a high pass filter with a high pass cutoff wavelength, and the interference filter has the passband defined between the high pass cutoff wavelength and the low pass cutoff wavelength.

8. A method comprising:

fabricating an optical filter as set forth in claim 1 by operations including depositing the layers stack on the transparent substrate.

9. The method of claim 8 wherein the depositing comprises sputtering using at least a silicon-based sputtering target.

10. The optical filter of claim 1 wherein the repeating unit includes at least one layer of amorphous hydrogenated silicon and at least one layer of the dielectric material having a refractive index in the range 1.9 to 2.7 inclusive.

11. The optical filter of claim 1 wherein the repeating units of two or more layers are configured to have the passband with properties defined by the repeating units further including FWHM full width at half maximum of the passband.

12. An optical filter comprising:

an interference filter comprising a layers stack comprising a plurality of layers of at least;

layers of amorphous hydrogenated silicon and

layers of one or more dielectric materials having a refractive index lower than the refractive index of the amorphous hydrogenated silicon including layers of a dielectric material having a refractive index in the range 1.9 to 2.7 inclusive,

wherein the layers stack is configured to have a passband wavelength range of 750-1100 nm inclusive.

13. The optical filter of claim 12 wherein the layers of a dielectric material having a refractive index in the range 1.9 to 2.7 inclusive include one or more layers consisting of:

Si₃N₄, SiO_xN_y with y large enough to provide a refractive index of 1.9 or higher, Ta₂O₅, Nb₂O₅, or TiO₂.

14. The optical filter of claim 12 wherein the layers of one or more dielectric materials further include SiO₂ layers.

15. The optical filter of claim 14 wherein the layers stack includes at least one SiO₂ layer immediately adjacent a layer of a dielectric material having a refractive index in the range 1.9 to 2.7 inclusive with no intervening layer of amorphous hydrogenated silicon.

16. An optical filter comprising:

an interference filter comprising a layers stack comprising a plurality of layers of at least;

layers of amorphous hydrogenated silicon and

layers of one or more dielectric materials having a refractive index lower than the refractive index of the amorphous hydrogenated silicon including layers of a dielectric material having a refractive index in the range 1.9 to 2.7 inclusive,

wherein the one or more dielectric materials consisting of;

Si₃N₄, SiO_xN_y with y large enough to provide a refractive index of 1.9 or higher, Ta₂O₅, Nb₂O₅, or TiO₂;

wherein layers of the one or more dielectric materials are disposed between layers of amorphous hydrogenated silicon.