Wire grid polarizers are frequently used for polarizing infrared, visible, and ultraviolet light. Wire grid polarizers can be comprised of a transparent substrate with an array of substantially parallel, discrete wires. A pitch, comprising a width of a wire and a distance between wires, is normally less than about half of the wavelength of incoming light, for efficient polarization.
Improved polarization has been shown by etching into the substrate between the wires, thus forming substrate ribs beneath the wires. For example, see U.S. Pat. No. 6,122,103.
Due to the small size of the wires on top of the substrate, wire grid polarizers can be easily damaged, such as by handling. The damage can be toppling of wires, thus causing the wire grid polarizer to lose polarization ability in damaged areas. It would be desirable to have a more durable wire grid polarizer that could be handled more easily.
Wires can also topple during manufacturing if an aspect ratio, defined as wire height divided by width of either the wire or the gap between the wires, is too high. A high aspect ratio is desirable to minimize undesirable transmission of the polarization Ts that the polarizer is designed to reflect. Transmission of desirable polarization is often called Tp. It is desirable in a polarizer to have high contrast, defined as Tp/Ts. Contrast is an indication of the effectiveness of transmitting the desirable polarization Tp while preventing polarization of undesirable polarization Ts. Thus a polarizer with a higher aspect ratio can provide for better contrast.
Wires can also corrode because three sides of wires can be exposed to a corrosive environment. Various methods, such as coating the wires with a corrosion protective coating, have been proposed. For example, see U.S. Pat. No. 6,785,050.
Other related wire grid polarizer publications include U.S. Pat. Nos. 5,412,502, 7,158,302, and 7,692,860; and U.S. patent publication numbers 20070242187, 20090041971, 20090046362, and 20090053655.
It has been recognized that it would be advantageous to have a more durable wire grid polarizer with higher contrast. It has also been recognized that it would be advantageous to have a polarizer that is less susceptible to damage by corrosion. The present invention is directed to a wire grid polarizer that satisfies the needs for less susceptibility to damage by corrosion, increased durability, and/or higher contrast.
The device comprises a substrate with an array of substantially parallel channels extending into the substrate from a top of the substrate. An array of substantially parallel ribs is defined between the array of channels and is integral with and extends from the substrate. The channels can contain at least one material forming an array of substantially parallel wires. The wires can be made of a material that will aid in polarization of incoming light. The ribs can separate the wires into separate and discrete wires.
In one embodiment, wires terminate below a top surface of the substrate ribs. In another embodiment, some of the channels can be deeper than other channels.
The above design can allow for a more durable wire grid polarizer because substrate ribs can support the wires. Channel walls can partially protect the wires from corrosion.
Reference will now be made to the exemplary embodiments illustrated in the drawings, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Alterations and further modifications of the inventive features illustrated herein, and additional applications of the principles of the inventions as illustrated herein, which would occur to one skilled in the relevant art and having possession of this disclosure, are to be considered within the scope of the invention.
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An array of substantially parallel ribs 12 is defined between the array of channels 13 and is integral with and extends from the substrate 11. Because the array of ribs 12 is integral with and extends from the substrate 11, there can be a continuous transition from substrate 11 to ribs 12 with no boundary region between substrate 11 and ribs 12. If ribs are formed on top of the substrate, even if made of the same material as the substrate, there may be a boundary region or disconnect between the ribs and substrate. Such a boundary region can result in weakening of the rib to substrate bond and also can adversely affect polarizer performance, thus it can be advantageous to etch channels in the substrate such that ribs are integral with the substrate.
The channels 13 can contain at least one material forming an array of substantially parallel wires 14. The wires 14 can be made of a material that will aid in polarization of incoming light. For example, the material of the wires 14 can be conductive, such as aluminum, silver or gold. The ribs 12 can separate the wires 14 into separate and discrete wires. Thus, the wire in one channel does not contact an adjacent wire in an adjacent channel. In one aspect, the material of the wires can be flush with the top of the substrate. In another aspect, the material of the wires can be recessed below the top of the substrate. In another aspect, the material of the wires can extend above the top of the substrate, while not extending laterally to contact another wire or channel. This design can allow for a more durable polarizer because substrate ribs 12 can support the wires 14.
Polarization and device durability can be improved by having wires 14 recessed below the top of the substrate 17, such that channel depth d can be greater tha wire height h, and the wires 14 extend all the way to the bottom 16 of the channels 13. Thus, wires 14 can be fully disposed in the channels 13 and can have a top surface that terminates below a top surface 17 of the substrate ribs 12. In one embodiment, the top surface 17 of the substrate ribs 12 can be free of wires 14.
Channel depth d minus wire height h can be greater than 5 nanometers in one embodiment, greater than 10 nanometers in another embodiment, greater than 25 nanometers in another embodiment, greater than 50 nanometers in another embodiment, or greater than 100 nanometers in another embodiment. Channel depth d minus wire height h can be greater between 5-20 nanometers in one embodiment, between 19-50 nanometers in another embodiment, or between 49-100 nanometers in another embodiment.
In one embodiment, the polarizer can have a low aspect ratio. Aspect ratio is defined as channel depth d divided by channel width wc. For example, channel depth d can be at least 30 nm, channel width wc can be less than 1000 nm, and ribs width wr can be less than 1000 nm. In another embodiment, the polarizer can have a very high aspect ratio, such as greater than 5, greater than 10, greater than 15, or greater than 20, thus allowing for better contrast. For example, channel depth d can be greater than 1000 nanometers or greater than 2000 nanometers, the channel width wc can be less than 100 nm, less than 50 nm, or less than 30 nm, and the rib width wr can be less than about 100 nm, less than 50 nm, or less than 30 nm. A higher aspect ratio, without wire toppling during manufacturing or during handling, can be achieved due to support that the ribs provide to the wires. This higher aspect ratio can result in improved contrast.
In one embodiment of the present invention, channels 13 of the wire grid polarizers described herein can have a depth d of at least about 200 nm. In another embodiment of the present invention, channels 13 of the wire grid polarizers described herein can have a depth d of at least about 500 nm. In another embodiment of the present invention, channels 13 of the wire grid polarizers described herein can have a depth d of at least about 1000 nm. In another embodiment of the present invention, channels 13 of the wire grid polarizers described herein can have a width wc of less than about 100 nanometers. In another embodiment of the present invention, ribs 12 of the wire grid polarizers described herein can have a width wr of less than about 100 nanometers.
In one embodiment of the present invention, channels 13 can have a depth d of at least about 500 nm and a width wc of less than about 100 nanometers, and ribs can have width wr of less than about 100 nanometers.
The embodiment shown in
In one embodiment of the present invention, wires 14 of the wire grid polarizer can substantially fill the channels 13. The wires 14 can fill the channels up to a top surface 18 of the wires. In another embodiment, wires 14 of the wire grid polarizer do not fill the channels 13.
In one embodiment, wires 14 can comprise multiple layers of different materials, with one layer disposed on top of the other. For example, wires 14 can comprise two layers. In another embodiment, shown in
In one embodiment, wires 14 can comprise multiple layers of different materials, with sub-channels in lower layers and with one layer disposed on top of the sub-channel of the lower layer. For example, wires 14 can comprise two layers. In another embodiment, shown in
In the multilayer embodiments described above, each layer can serve a different purpose. For example, one layer can optimize polarization, and another can absorb one polarization. In another example, one layer can be optimized for one wavelength or group of wavelengths, and another layer can be optimized for another wavelength or group of wavelengths. For example, one layer can be optimized for infrared, another for visible, and another for ultraviolet light, thus allowing creation of a very broadband wire grid polarizer, such as a broadband polarizer. The layers of material can alternate between different conductive materials, or can alternate between conductive and dielectric materials.
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In one embodiment, deep channels 13a include at least two different wire materials 14p and 14o. In one embodiment, a wire material 14o at a bottom of deep channels 13a can be different from any wire material in shallow channels 13b and a wire material at a top of deep channels 13a can be the same as wire material in shallow channels 13b. In one embodiment, deep channels 13a and shallow channels 13b can alternate.
This embodiment can be useful by allowing one material 14o at a bottom of deeper channels to have a different pitch than other material 14p in shallower channels. This can be useful to use one material for polarization and another material for another purpose, such as for a diffraction grating.
A difference in depth between deeper channels and shallow channels (d3-d2) can be at least 20 nm in one embodiment, at least 50 nm in another embodiment, or at least 100 nm in another embodiment.
The substrate can comprise a single, integral material in one embodiment. The substrate 11 can be comprised of multiple layers of different materials in another embodiment. If the layers are sufficiently thin and in a location where the substrate is etched, then the ribs 12 can also be comprised of multiple layers of different materials. For example, the wire grid polarizer 70 shown in
Although the wire grid polarizers shown in
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In the variously described channel shapes, light can react differently, or different wavelengths of light can react differently, in the different portions due to the different characteristics. Also, some shapes may be preferable due to ease of manufacturing.
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Wire grid polarizer 170 shown in
A wire grid polarizer having an index of refraction of wires nw that is greater than an index of refraction of gaps ng between wires (nw>ng) can allow for polarization of light. Alternatively, a wire grid polarizer having an index of refraction of wires nw that is less than an index of refraction of ribs nr between wires (nw<nr) can allow for polarization of light. Thus, in the various embodiments described herein, an index of refraction of the wires nw can be greater than an index of refraction of the ribs nr or an index of refraction of the wires nw can be less than an index of refraction of the ribs nr. In one embodiment, a difference between the index of refraction of the wires nw and an index of refraction of the ribs nr can be greater than 0.5 (nw−nr>0.5 or nr−nw>0.5). In another embodiment, a difference between the index of refraction of the wires nw and an index of refraction of the ribs nr can be greater than 2 (nw−nr>2 or nr−nw>2). The difference in index of refraction can be controlled by the type of material selected for the ribs 12 and the type of material selected for the wires 14.
Channels 13 of the wire grid polarizer 10 of
Wires 14 in the channels 13 can be formed by a conformal deposition process such as chemical vapor deposition or atomic layer deposition. The deposition can be aided by rapid thermal anneal. An etch can remove wire 14 material on ribs 12 at the substrate surface 12a while leaving wire material in the channels 13. Wire 14 material can remain in the channels 13 during removal of wire 14 material on the ribs 12 because of the greater depth of material in channels 13 than on top of ribs 12.
Tops of the wires 18 can be lowered below a top surface 17 of the substrate ribs 12 by selective etching the wires. For example, a chemical etch in dilute base such as potassium hydroxide may be used. Another example is reactive ion etching and adjusting the etch chemistries to bias the selectivity of the metal to the oxide.
Wire grid polarizers 20 and 30 of
Wire grid polarizer 40 of
Wire grid polarizer 50 of
Wire grid polarizer 60 of
Wire grid polarizer 70 of
Wire grid polarizer 80 of
Wire grid polarizer 90 of
Wire grid polarizer 100 of
Wire grid polarizer 110 of
Wire grid polarizers 120 of
Wire grid polarizer 140 of
Wire grid polarizer 150 of
The wires 14 and/or the elements 104 can be conductive. The wires 14 and/or the elements 104 can comprise a metal. The wires 14 and/or the elements 104 can comprise aluminum, silver, gold or copper. The wires can also be a metal alloy. The wires can be a dielectric or a plasmon resonance material.
The wires 14 and/or the elements 104 can be formed of or can include a dielectric and/or absorptive material. The wires 14 and/or the elements 104 can be formed of: aluminum oxide; antimony trioxide; antimony sulphide; beryllium oxide; bismuth oxide; bismuth triflouride; cadmium sulphide; cadmium telluride; calcium fluoride; ceric oxide; chiolite; cryolite; germanium; hafnium dioxide; lanthanum fluoride; lanthanum oxide; lead chloride; lead fluoride; lead telluride; lithium fluoride; magnesium fluoride; magnesium oxide; neogymium fluoride; neodymium oxide;
praseodymium oxide; scandium oxide; silicon; silicon oxide; disilicon trioxide; silicon dioxide; sodium fluoride; tantalum pentoxide; tellurium; titanium dioxide; thallous chloride; yttrium oxide; zinc selenide; zinc sulphide; and zirconium dioxide, and combinations thereof.
The wires 14 and/or the elements 104 can be formed of or can include a carbide, chloride, fluoride, nitride, oxide, sulfide, etc.
It is believed that cadmium telluride, germanium, lead telluride, silicon oxide, tellurium, titanium dioxide, silicon, cadmium sulfide, zinc selenide, and zinc sulfide are appropriate for the ultra-violet range; cadmium telluride, germanium, lead telluride, silicon oxide, tellurium, titanium dioxide, and silicon are appropriate for the visible range; and magnesium fluoride, aluminum oxide, cadmium telluride, germanium are appropriate for the infrared range.
In another aspect, the wires 14 and/or the elements 104 can be formed of or can include a material or materials selected from: silicon nitride, titanium nitride, titanium carbide, silicon carbide, tantalum, cupric oxide, cuprous oxide, cupric chloride, cuprous chloride, cuprous sulfide, titanium, tungsten, niobium oxide, aluminum silicate, boron nitride, boron oxide, tantalum oxide, carbon and combinations thereof. In addition to the material listed herein, ionic states of the material can also be included, particularly for transition metal oxides, hydrides, nitrides, salts, etc.
Many of the materials mentioned above can be deposited using various deposition techniques such as sputtering, Chemical Vapor Deposition (CVD), or evaporation to produce a material of the wires or elements that are not stoichiometric. This can be used to produce dielectric wires or elements that have different optical properties than the common bulk stoichiometric material. For example, it is possible to produce a titanium oxide dielectric film by sputtering that is oxygen-starved, and therefore has much higher optical absorption than the standard film. Such a film can be used to produce a wire grid that strongly absorbs one polarization rather than strongly reflecting the same polarization using the present invention. In a similar manner, it is possible to do the same thing with other metal oxides such as zirconium oxide, magnesium oxide, silicon oxide, etc. Similar effects can also be accomplished with metal fluorides such as magnesium fluoride, with metal nitrides such as silicon nitride, and with metal sulphides, silicides, or selenides.
The substrate 11 can be transparent to incident light. The substrate 11 can be glass, quartz, or polymer. The substrate 11 can be flexible. Furthermore, the substrate 11 can have a refractive index (or index of refraction) ns. For example, a glass substrate (Bk7) has a refractive index ns of 1.52 (at 550 nm). (It will be appreciated that the refractive index varies slightly with wavelength.)
It is to be understood that the above-referenced arrangements are only illustrative of the application for the principles of the present invention. Numerous modifications and alternative arrangements can be devised without departing from the spirit and scope of the present invention. While the present invention has been shown in the drawings and fully described above with particularity and detail in connection with what is presently deemed to be the most practical and preferred embodiment(s) of the invention, it will be apparent to those of ordinary skill in the art that numerous modifications can be made without departing from the principles and concepts of the invention as set forth herein.
This claims priority to U.S. Patent Application Ser. No. 61/428,555, filed Dec. 30, 2010; which is hereby incorporated herein by reference in its entirety.
Number | Date | Country | |
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61428555 | Dec 2010 | US |