US20150077851A1 - Multi-layer absorptive wire grid polarizer - Google Patents
Multi-layer absorptive wire grid polarizer Download PDFInfo
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- US20150077851A1 US20150077851A1 US14/314,814 US201414314814A US2015077851A1 US 20150077851 A1 US20150077851 A1 US 20150077851A1 US 201414314814 A US201414314814 A US 201414314814A US 2015077851 A1 US2015077851 A1 US 2015077851A1
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/30—Polarising elements
- G02B5/3025—Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state
- G02B5/3058—Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state comprising electrically conductive elements, e.g. wire grids, conductive particles
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/30—Polarising elements
- G02B5/3025—Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state
- G02B5/3075—Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state for use in the UV
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/20—Filters
- G02B5/22—Absorbing filters
Definitions
- the present application is related generally to wire grid polarizers.
- Wire grid polarizers may be used for polarizing light, by allowing one polarization to pass through the polarizer, and reflecting or absorbing the opposite polarization.
- the polarization that primarily passes through will be referred to as p-polarized light and the polarization that primarily reflects or absorbs will be referred to as s-polarized light.
- absorption of s-polarized light is preferred, such as for example if the reflection can disrupt the image or other intended use.
- reflected light may go back into the LCD imager causing damage or image degradation, or stray light can reach the screen, degrading contrast.
- An ideal selectively absorptive wire grid polarizer will transmit all p-polarized light and selectively absorb all s-polarized light. In reality, some s-polarized light is transmitted and some reflected; some p-polarized light is absorbed and some reflected.
- wire grid polarizers for infrared, visible, and ultraviolet light to have small wires with small pitch, such as nanometer or micrometer size and pitch, for effective polarization.
- small pitch such as nanometer or micrometer size and pitch
- a pitch of less than half of the wavelength of light to be polarized is needed for effective polarization.
- Smaller pitches may improve the contrast.
- small pitch can be an important feature of wire grid polarizers. Manufacture of wire grid polarizers with sufficiently small pitch is challenging, and is a goal of research in this field.
- Small wires can be damaged by handling and by environmental conditions. Protection of the wires can be important in wire grid polarizers.
- the present invention is directed to wire grid polarizers, and methods of making wire grid polarizers, that satisfy these needs.
- Each of the various embodiments may satisfy one, some, or all of these needs.
- the wire grid polarizer can comprise an array of parallel, elongated first rib groups disposed over a transmissive substrate, each first rib group can comprise a central first transmissive rib and a pair of first wires including a first wire disposed along each side of the first transmissive rib.
- a first dielectric material can substantially fill first gaps between each first rib group and an adjacent first rib group.
- An array of parallel, elongated second wires can be disposed over the first rib groups and the first dielectric material.
- the first wires or the second wires can be absorptive and the other can be reflective.
- a FIRST METHOD of making a wire grid polarizer can comprise:
- a SECOND METHOD of making a wire grid polarizer can comprise steps 1-4 of the FIRST METHOD plus the following additional steps:
- FIG. 1 is a schematic cross-sectional side view of a wire grid polarizer 10 with an array of parallel, elongated first rib groups 14 , first dielectric material 16 substantially filling first gaps 117 (see FIGS. 11-13 ) between the first rib groups 14 to form first dielectric ribs 16 a, the first dielectric material 16 further extending from the first gaps 117 above and over tops of the first rib groups 14 forming a first dielectric upper layer 16 b, and an array of parallel, elongated second wires 15 disposed over the first rib groups 14 , the first dielectric ribs 16 a, and the first dielectric upper layer 16 b, in accordance with an embodiment of the present invention;
- FIG. 2 is a schematic cross-sectional side view of a wire grid polarizer 20 with an array of parallel, elongated first rib groups 14 , first dielectric material 16 substantially filling first gaps 117 (see FIGS. 11-13 ) between the first rib groups 14 to form first dielectric ribs 16 a, and an array of parallel, elongated second wires 15 disposed over the first rib groups 14 and the first dielectric ribs 16 a, in accordance with an embodiment of the present invention;
- FIG. 3 is a schematic cross-sectional side view of a wire grid polarizer 30 with an array of parallel, elongated first rib groups 14 , first dielectric material 16 substantially filling first gaps 117 (see FIGS. 11-13 ) between the first rib groups 14 to form first dielectric ribs 16 a, the first dielectric material 16 further extending from the first gaps 117 above and over tops of the first rib groups 14 forming a transmissive dielectric layer 16 c, the first dielectric material 16 of the dielectric ribs 16 a comprising a different material than the first dielectric material 16 of the transmissive dielectric layer 16 c, and an array of parallel, elongated second wires 15 disposed over the first rib groups 14 and on a top-surface 16 t of the transmissive dielectric layer 16 c, in accordance with an embodiment of the present invention;
- FIG. 4 is a schematic cross-sectional side view of a wire grid polarizer 40 similar to one of the wire grid polarizers shown in FIGS. 1-3 and 6 - 10 , wherein the first wires 13 are absorptive wires 43 and the second wires 15 are reflective wires 45 , in accordance with an embodiment of the present invention;
- FIG. 5 is a schematic cross-sectional side view of a wire grid polarizer 50 similar to one of the wire grid polarizers shown in FIGS. 1-3 and 6 - 10 , wherein the first wires 13 are reflective wires 45 and the second wires 15 are absorptive wires 43 , in accordance with an embodiment of the present invention;
- FIG. 6 is a schematic cross-sectional side view of a wire grid polarizer 60 similar to one of the embodiments of FIGS. 1-5 , further comprising second dielectric material 66 substantially filling second gaps 17 (see FIGS. 1-5 ) between the second wires 15 to form second dielectric ribs 66 a, the second dielectric material 66 further extending from the second gaps 17 above and over tops of the second wires 15 forming a second dielectric upper layer 66 b, in accordance with an embodiment of the present invention;
- FIG. 6 is also a schematic cross-sectional side view of an eighth step of the FIRST METHOD for making a wire grid polarizer—backfilling the second gaps 17 and above the second wires 15 with second dielectric material 66 —in accordance with an embodiment of the present invention
- FIG. 7 is a schematic cross-sectional side view of a wire grid polarizer 70 , similar to one of the embodiments of FIGS. 1-5 , further comprising second dielectric material 66 substantially filling second gaps 17 (see FIGS. 1-5 ) between the second wires 15 to form second dielectric ribs 66 a, in accordance with an embodiment of the present invention;
- FIG. 7 is also a schematic cross-sectional side view of a ninth step of the FIRST METHOD for making a wire grid polarizer—etching the second dielectric material 66 and forming separate second dielectric ribs 66 a —in accordance with an embodiment of the present invention
- FIG. 8 is a schematic cross-sectional side view of a wire grid polarizer 80 similar to one of the embodiments shown in FIGS. 1-5 , except that the second wires 15 are part of an array of parallel, elongated second rib groups 84 each comprising a central second transmissive rib 82 and a second wire 15 disposed along each side of the second transmissive rib 82 , in accordance with an embodiment of the present invention;
- FIG. 9 is a schematic cross-sectional side view of a wire grid polarizer 90 , similar to wire grid polarizer 80 , further comprising a second dielectric material 66 substantially filling second gaps 17 (see FIG. 8 ) between the second rib groups 84 to form second dielectric ribs 66 a, the second dielectric material 66 further extending from the second gaps 17 above and over tops of the second rib groups 84 forming a second dielectric upper layer 66 b, in accordance with an embodiment of the present invention;
- FIG. 10 is a schematic cross-sectional side view of a wire grid polarizer 100 , similar to wire grid polarizer 80 , further comprising a second dielectric material 66 substantially filling second gaps 17 (see FIG. 8 ) between the second rib groups 84 to form second dielectric ribs 66 a, in accordance with an embodiment of the present invention;
- FIG. 11 is a schematic cross-sectional side view of a first step applicable to a FIRST METHOD or to a SECOND METHOD for making a wire grid polarizer—providing a transmissive substrate 11 having an array of parallel, elongated first transmissive ribs 12 disposed over the substrate 11 —in accordance with an embodiment of the present invention;
- FIG. 12 is a schematic cross-sectional side view of a second step applicable to the FIRST METHOD or to the SECOND METHOD for making a wire grid polarizer—conformal coating the substrate 11 and the first transmissive ribs 12 with a first coating 123 while maintaining solid-material-free first gaps 117 between the first transmissive ribs 12 —in accordance with an embodiment of the present invention;
- FIG. 13 is a schematic cross-sectional side view of a third step applicable to the FIRST METHOD or to the SECOND METHOD for making a wire grid polarizer—etching the first coating 123 to remove horizontal segments 121 and leaving vertical first wires 13 along sides 12 s of the first transmissive ribs 12 , forming first rib groups 14 each comprising a pair of first wires 13 which sandwich a first transmissive rib 12 —in accordance with an embodiment of the present invention;
- FIG. 14 is a schematic cross-sectional side view related to a fourth and/or fifth step in the FIRST METHOD or the SECOND METHOD for making a wire grid polarizer—backfilling the first gaps 117 and above the first rib groups 14 with first dielectric material 16 and forming a substantially flat, planar top-surface 16 t above the first rib groups 14 —in accordance with an embodiment of the present invention;
- FIG. 15 is a schematic cross-sectional side view related to a fourth and/or fifth step in the FIRST METHOD or the SECOND METHOD for making a wire grid polarizer—etching the first dielectric material 16 and forming separate first dielectric ribs 16 a, with a first dielectric rib 16 a in one first gap 117 separate from a first dielectric rib in an adjacent first gap 117 , and forming the substantially flat, planar top-surface 16 t above the first rib groups 14 and the first dielectric ribs—in accordance with an embodiment of the present invention;
- FIG. 16 is a schematic cross-sectional side view related to a fourth and/or fifth step applicable to the FIRST METHOD or to the SECOND METHOD for making a wire grid polarizer—applying a transmissive dielectric layer 16 c over the first rib groups 14 and the first dielectric ribs 16 a to form the substantially flat, planar top-surface 16 t with material of the transmissive dielectric layer 16 c —in accordance with an embodiment of the present invention;
- FIG. 17 is a schematic cross-sectional side view of a sixth step of the FIRST METHOD for making a wire grid polarizer—applying a continuous thin film of upper-material 175 over the top-surface 16 t of the first dielectric material 16 —in accordance with an embodiment of the present invention
- FIG. 18 is a schematic cross-sectional side view of a seventh step of the FIRST METHOD for making a wire grid polarizer—etching the thin film of upper-material 175 to form an array of parallel, elongated second wires 15 disposed over the top-surface 16 t —in accordance with an embodiment of the present invention
- FIG. 19 is a schematic cross-sectional side view of a sixth step of the SECOND METHOD for making a wire grid polarizer—etching the top-surface 16 t to form an array of parallel, elongated second transmissive ribs 82 —in accordance with an embodiment of the present invention
- FIG. 20 is a schematic cross-sectional side view of a seventh step of the SECOND METHOD for making a wire grid polarizer—conformal coating the second transmissive ribs 82 with a second coating 203 while maintaining solid-material-free second gaps 17 between the second transmissive ribs 82 —in accordance with an embodiment of the present invention;
- FIG. 21 is a schematic cross-sectional side view of a eighth step of the SECOND METHOD for making a wire grid polarizer—etching the second coating 203 to remove horizontal segments 201 and leaving vertical second wires 15 along sides 82 s of the second transmissive ribs 82 , forming second rib groups 84 each comprising a pair of second wires 15 which sandwich a second transmissive rib 82 —in accordance with an embodiment of the present invention;
- FIG. 22 is a schematic cross-sectional side view of a ninth step of the SECOND METHOD for making a wire grid polarizer—backfilling the second gaps 17 and extending above the second rib groups 84 with second dielectric material 66 —in accordance with an embodiment of the present invention.
- FIG. 23 is a schematic cross-sectional side view of a tenth step of the SECOND METHOD for making a wire grid polarizer—etching the second dielectric material 66 and forming separate second dielectric ribs 66 a, with a second dielectric rib 66 a in one second gap 17 separate from a second dielectric rib 66 a in an adjacent second gap 17 —in accordance with an embodiment of the present invention.
- a wire grid polarizer 10 comprising a transmissive substrate 11 with an array of parallel, elongated first rib groups 14 disposed over the substrate 11 .
- Each first rib group 14 can comprise a central first transmissive rib 12 and a pair of first wires 13 including a first wire 13 disposed along each side of the first transmissive rib 12 .
- Each pair of first wires 13 can directly touch the central first transmissive rib 12 sandwiched there between; or there may be another material disposed between each pair of first wires 13 and the central first transmissive rib 12 .
- a first dielectric material 16 can substantially fill first gaps 117 (see FIGS. 11-13 ) between each first rib group 14 and an adjacent first rib group 14 . All or portions of the first dielectric material 16 can be transmissive.
- An array of parallel, elongated second wires 15 can be disposed over the first rib groups 14 and the first dielectric material 16 .
- the second gaps 17 can be disposed on each side 15 s of the second wires 15 .
- the second gaps 17 can separate a second wire 15 from adjacent second wires 15 on each side 15 s.
- the second gaps 17 can be solid-material-free and can be filled with air or vacuum. Alternatively, another material can fill the second gaps 17 , as will be discussed below in reference to wire grid polarizers 60 and 70 in FIGS. 6-7 .
- the first transmissive ribs 12 can be integral with, and formed of the same material as, the substrate 11 by etching into the substrate 11 to form the first transmissive ribs 12 .
- the first transmissive ribs 12 can be formed on top of the substrate 11 , such as for example, by depositing a transmissive layer on the substrate 11 then etching to form the first transmissive ribs 12 .
- the first transmissive ribs 12 can be formed by standard lithography techniques, such as patterning a resist and etching for example.
- pitch P 13 or distance between adjacent first wires 13 It can be beneficial to have a very small pitch P 13 or distance between adjacent first wires 13 .
- the pitch P 12 of the first transmissive ribs 12 may be limited by present lithography technology, the present invention teaches how to make two first wires 13 for every first transmissive rib 12 ; effectively cutting the pitch P 13 of the first wires approximately in half in comparison to the pitch P 12 of the first transmissive ribs 12 .
- a pitch P 12 of the first transmissive ribs 12 can be, for example, less than 200 nanometers in one aspect, less than 150 nanometers in another aspect, or less than 110 nanometers in another aspect; but the pitch P 13 of the first wires 13 can be approximately half these numbers.
- the wire grid polarizers described herein can be made with a relatively high first wire 13 aspect ratio (first wire thickness Th 1 divided by first wire width W 13 ). Modeling has shown good polarization characteristics with first wire 13 aspect ratios between 8 and 60. Modeling has shown good polarization characteristics in the visible spectrum with first wire 13 width W of between 5 nm and 20 nm and a thickness Th 1 of between 150 nm and 300 nm.
- the first wires 13 can extend along each side 12 s of the transmissive ribs substantially from a bottom of the transmissive ribs to a top of the transmissive ribs.
- the second wires 15 can be disposed over or directly on a top-surface 16 t .
- the top-surface 16 t can be first dielectric material 16 only, as shown in FIGS. 1 & 3 or the top-surface 16 t can be tops of the first rib groups 14 and tops of first dielectric ribs 16 a of the first dielectric material 16 as shown in FIG. 2 .
- the first dielectric material 16 can extend from the first gaps 117 above and over tops of the first rib groups 14 .
- the first dielectric material 16 can include first dielectric ribs 16 a between first rib groups 14 and a first dielectric upper layer 16 b above the first rib groups 14 .
- the first dielectric material 16 can have a substantially flat, planar top-surface 16 t.
- the second wires 15 can be disposed on the top-surface 16 t.
- the first dielectric upper layer 16 b can be etched, prior to forming the second wires 15 , and can be etched down to tops of the first rib groups 14 .
- the second wires 15 can then be formed on a top-surface 16 t comprising tops of the first rib groups 14 and tops of first dielectric ribs 16 a.
- the first dielectric material 16 can form separate first dielectric ribs 16 a, with a first dielectric rib 16 a in one first gap 117 being separate from a first dielectric rib 16 a in an adjacent first gap 117 . “Separate” meaning that each first dielectric rib 16 a is not connected by the same material to an adjacent first dielectric rib 16 a.
- First dielectric ribs 16 a are also separate from each other on wire grid polarizer 30 in FIG. 3 , with a first dielectric rib 16 a in one first gap 117 being separate from a first dielectric rib 16 a in an adjacent first gap.
- a difference between wire grid polarizer 20 and 30 is that on polarizer 30 , a transmissive dielectric layer 16 c is disposed between (i) tops of the first rib groups 14 and tops of the first dielectric ribs 16 a and (ii) bottoms of the second wires 15 .
- the transmissive dielectric layer 16 c can have a substantially flat, planar, top-surface 16 t.
- the first dielectric upper layer 16 b can be etched, prior to forming the second wires 15 , and can be etched down to tops of the first rib groups 14 .
- the transmissive dielectric layer 16 c can then be applied, such as for example by chemical vapor deposition, physical vapor deposition, or spin on.
- the second wires 15 can then be formed on a top-surface 16 t of the transmissive dielectric layer 16 c.
- the transmissive dielectric layer 16 c may be desired in some designs for modifying optical characteristics or for increased structural strength. A thickness of the transmissive dielectric layer 16 c can be adjusted for optimal optical properties.
- a choice of polarizer 10 , 20 , or 30 can be made based on overall performance requirements, such as for example a required Tp, Ts, Rs, for the wavelength range, materials used, durability requirements, and manufacturing cost.
- Polarizer 10 can have an advantage of less manufacturing steps than required to make polarizers 20 and 30 .
- Polarizers 20 and 30 can have the advantage of having the first dielectric ribs 16 a separate from each other. With such separation of the first dielectric ribs 16 a, these ribs can affect polarization.
- the first dielectric ribs 16 a can be absorptive and can be used to selectively absorb one polarization of light.
- the first wires 13 or the second wires 15 can be absorptive (absorptive wires 43 ) and the other of the first wires 13 or the second wires 15 can be reflective (reflective wires 45 ).
- the reflective wires 45 can cause polarization of incident light and the absorptive wires can cause absorption, rather than reflection, of one polarization (thus selectively absorptive) of the incident light.
- the first wires 13 can be absorptive wires 43 and the second wires 15 can be reflective wires 45 .
- the first wires 13 can be reflective wires 45 and the second wires 15 can be absorptive wires 43 .
- Whether the first wires 13 or the second wires 15 are the reflective wires 45 or absorptive wires 43 can depend on factors such as desired pitch of reflective wires 45 and absorptive wires 43 , direction of incident light, and overall materials of construction.
- a second dielectric material 66 can substantially fill gaps 17 (see FIGS. 1-5 ) between the second wires 15 , forming second dielectric ribs 66 a.
- the second dielectric material 66 can extend from the second gaps 17 above and over tops of the second wires 15 .
- the second dielectric material 66 can include second dielectric ribs 66 a and a second dielectric upper layer 66 b above the second wires 15 .
- the second dielectric material 66 can be etched down to tops of the second wires 15 , thus forming separate second dielectric ribs 66 a, with a second dielectric rib 66 a filling one gap 17 being separate from a second dielectric rib 66 a filling an adjacent gap 17 .
- a choice of polarizer 60 or 70 can depend on manufacturing cost considerations, durability, and whether there is a need to separate one second dielectric rib 66 a from another.
- the second wires 15 are fully embedded, which can be beneficial if there is a concern of corrosion of the second wires 15 .
- the second dielectric ribs 66 a are separate from each other, with can be beneficial if the second dielectric ribs 66 a are used for separation of the different polarization states, or for absorption of one polarization state.
- one of the second wires 15 or the second dielectric ribs 66 a can be reflecting structures and the other can be absorptive structures.
- the second wires 15 can be part of an array of parallel, elongated second rib groups 84 .
- Each second rib group 84 can comprise a central second transmissive rib 82 and a pair of the second wires 15 .
- a second wire 15 can be disposed along each side of the second transmissive rib 82 .
- the second wires 15 can extend along each side of the second transmissive ribs 82 substantially from a bottom of the second transmissive ribs 82 to a top of the second transmissive ribs 82 .
- the second transmissive ribs 82 can be formed in the top-surface 16 t by by etching the first dielectric material 16 , or by etching a thin film disposed over the first dielectric material 16 .
- the first dielectric material 16 can be a single layer, or multiple layers, similar to the description of the first dielectric material 16 above for polarizers 10 , 20 , and 30 .
- the first wires 13 or the second wires 15 can be absorptive and the other can be reflective.
- the description of polarizers 40 and 50 is applicable to polarizers 80 , 90 , and 100 .
- a second dielectric material 66 can substantially fill the second gaps 17 (see FIG. 8 ) between each second rib group 84 and an adjacent second rib group 84 . As shown on wire grid polarizer 90 of FIG. 9 , the second dielectric material 66 can extend from the second gaps 17 above and over tops of the second rib groups 84 . Thus, the second dielectric material 66 can include second dielectric ribs 66 a between second rib groups 84 and a second dielectric upper layer 66 b above the second rib groups 84 .
- the second dielectric material 66 can be a single layer and can be a single material; or the second dielectric material 66 can be multiple layers and can be layers of different materials.
- the second dielectric upper layer 66 b can be etched down to tops of the second rib groups 84 .
- the second dielectric material 66 can form separate second dielectric ribs 66 a, with a second dielectric rib 66 a in one second gap 17 being separate from a second dielectric rib 66 a in an adjacent second gap 17 .
- “Separate” meaning that each second dielectric rib 66 a is not connected by the same material to an adjacent second dielectric rib 66 a. Having separate second dielectric ribs 66 a can allow such ribs to have a polarizing function.
- the second dielectric ribs 66 a can separate light into different polarization states if it is reflective, can selectively absorb one polarization state if absorptive, or can act as a birefringent transmissive thin film if made of transmissive material.
- Polarizer 80 has the benefits of (1) at least one less manufacturing step than polarizers 90 and 100 , and (2) air in the second gaps 17 can improve Tp in some designs.
- Polarizers 90 and 100 can have better durability over polarizer 80 .
- the second wires 15 are fully embedded, which can be beneficial if there is a concern of corrosion of the second wires 15 .
- the second wires 15 are mostly embedded, which may be sufficient corrosion protection if the environment is not too corrosive.
- the second dielectric ribs 66 a are separate from each other, with can be beneficial if the second dielectric ribs 66 a are used for separation of the different polarization states, or for absorption of one polarization state.
- one of the second wires 15 or the second dielectric ribs 66 a can be reflective and the other can be absorptive.
- the second transmissive ribs 82 can be formed by standard lithography techniques, such as patterning a resist and etching for example. It can be beneficial to have a very small pitch P 15 or distance between adjacent second wires 15 . Although the pitch P 82 of the second transmissive ribs 82 may be limited by present technology, the present invention teaches how to make two second wires 15 for every second transmissive rib 82 ; effectively cutting the pitch P 15 of the second wires in half in comparison to the pitch P 82 of the second transmissive ribs 82 .
- a pitch P 82 of the second transmissive ribs 82 can be, for example, less than 200 nanometers in one aspect, less than 150 nanometers in another aspect, or less than 110 nanometers in another aspect; but the pitch P 15 of the second wires 15 can be approximately half these numbers.
- the wire grid polarizers 80 , 90 , 100 can be made with a relatively high second wire 15 aspect ratio (second wire thickness Th 2 divided by second wire width W 15 ). Modeling has shown good polarization characteristics with second wire 15 aspect ratios between 8 and 60. Modeling has shown good polarization characteristics in the visible spectrum with second wire 15 width W of between 5 nm and 20 nm and a thickness Th 1 of between 150 nm and 300 nm.
- a first method of making a wire grid polarizer can comprise some or all of the following steps. The steps can be performed in the order shown.
- a second method of making a wire grid polarizer can comprise some or all of the following steps. The steps can be performed in the order shown. Steps 1-4 from the first method above.
- the first wires 13 and the second wires 15 are partially or fully embedded in some of the embodiments described herein.
- embedding wires of a wire grid polarizer can increase wire grid polarizer durability
- embedding the wires in some polarize designs can also adversely affect wire grid polarizer performance, especially by decreasing transmission of p-polarized light (decrease Tp). Therefore, embedded wire grid polarizers have often not been implemented in practice for applications requiring high polarizer performance, such as for example in computer projectors or semiconductor analysis equipment. Modeling has shown that the specific designs shown herein, although wires are partially or completely embedded, especially combined with proper aspect ratio, can provide good wire grid polarizer performance.
- polarizer performance examples include:
Abstract
A wire grid polarizer comprising an array of parallel, elongated first rib groups disposed over a substrate. Each first rib group can comprise a central first transmissive rib and a pair of first wires including a first wire disposed along each side of the first transmissive rib. A first dielectric material can substantially fill first gaps between each rib group and an adjacent rib group. An array of parallel, elongated second wires can be disposed over the rib groups and the first dielectric material. The first wires or the second wires can be absorptive and the other of the first wires or the second wires can be reflective.
Description
- This is a continuation-in-part of U.S. patent application Ser. No. 13/326,566, filed on Dec. 15, 2011, which claims priority to U.S. Patent Application Ser. No. 61/428,555, filed Dec. 30, 2010; all of which are hereby incorporated herein by reference in their entirety. This claims priority to U.S. Provisional Patent Application No. 61/863,298, filed on Aug. 7, 2013, which is hereby incorporated herein by reference in its entirety.
- The present application is related generally to wire grid polarizers.
- Wire grid polarizers may be used for polarizing light, by allowing one polarization to pass through the polarizer, and reflecting or absorbing the opposite polarization. For simplicity, the polarization that primarily passes through will be referred to as p-polarized light and the polarization that primarily reflects or absorbs will be referred to as s-polarized light. For some applications, absorption of s-polarized light is preferred, such as for example if the reflection can disrupt the image or other intended use. In a transmissive panel system, reflected light may go back into the LCD imager causing damage or image degradation, or stray light can reach the screen, degrading contrast. An ideal selectively absorptive wire grid polarizer will transmit all p-polarized light and selectively absorb all s-polarized light. In reality, some s-polarized light is transmitted and some reflected; some p-polarized light is absorbed and some reflected.
- The effectiveness of a selectively absorptive wire grid polarizer can be quantified by high transmission of p-polarized light, high absorption of s-polarized light, and high contrast. Contrast is equal to a percent of p-polarized light transmitted (Tp) divided by a percent of s-polarized light transmitted (Ts): Contrast=Tp/Ts.
- It can be important in wire grid polarizers for infrared, visible, and ultraviolet light to have small wires with small pitch, such as nanometer or micrometer size and pitch, for effective polarization. Typically, a pitch of less than half of the wavelength of light to be polarized is needed for effective polarization. Smaller pitches may improve the contrast. Thus, small pitch can be an important feature of wire grid polarizers. Manufacture of wire grid polarizers with sufficiently small pitch is challenging, and is a goal of research in this field.
- Small wires can be damaged by handling and by environmental conditions. Protection of the wires can be important in wire grid polarizers.
- Durability of wire grid polarizers is thus another important feature. For example, see U.S. Pat. No. 5,991,075, U.S. Pat. No. 6,288,840, U.S. Pat. No. 6,665,119, U.S. Pat. No. 7,630,133, U.S. Pat. No. 7,692,860, U.S. Pat. No. 7,800,823, U.S. Pat. No. 7,961,393, and U.S. Pat. No. 8,426,121; U.S. Patent Publication Numbers US 2008/0055723, US 2009/0041971, and US 2009/0053655; U.S. patent application Ser. No. 13/326,566, filed on Dec. 15, 2011; “Application of 100 Å linewidth structures fabricated by shadowing techniques” by D. C. Flanders in J. Vac. Sci. Technol., 19(4), November/December 1981; and “Submicron periodicity gratings as artificial anisotropic dielectrics” by Dale C. Flanders in Appl. Phys. Lett. 42 (6), 15 Mar. 1983, pp. 492-494.
- It has been recognized that it would be advantageous to provide a durable, selectively-absorptive, wire-grid polarizer with high transmission of one polarization, high absorption of an opposite polarization, high contrast, and small pitch. The present invention is directed to wire grid polarizers, and methods of making wire grid polarizers, that satisfy these needs. Each of the various embodiments may satisfy one, some, or all of these needs.
- The wire grid polarizer can comprise an array of parallel, elongated first rib groups disposed over a transmissive substrate, each first rib group can comprise a central first transmissive rib and a pair of first wires including a first wire disposed along each side of the first transmissive rib. A first dielectric material can substantially fill first gaps between each first rib group and an adjacent first rib group. An array of parallel, elongated second wires can be disposed over the first rib groups and the first dielectric material. The first wires or the second wires can be absorptive and the other can be reflective.
- A FIRST METHOD of making a wire grid polarizer can comprise:
- 1. providing a transmissive substrate having an array of parallel, elongated first transmissive ribs disposed over the substrate;
- 2. conformal coating the substrate and the first transmissive ribs with a first coating while maintaining solid-material-free first gaps between the first transmissive ribs;
- 3. etching the first coating to remove horizontal segments and leaving vertical first wires along sides of the first transmissive ribs, forming first rib groups each comprising a pair of first wires which sandwich a first transmissive rib;
- 4. backfilling the first gaps with first dielectric material;
- 5. forming a substantially flat, planar top-surface above the first rib groups;
- 6. applying a continuous thin film of upper-material over the top-surface; and
- 7. etching the thin film of upper-material to form an array of parallel, elongated second wires disposed over the top-surface, and wherein the first wires or the second wires are absorptive and the other are reflective of the incident light.
- A SECOND METHOD of making a wire grid polarizer can comprise steps 1-4 of the FIRST METHOD plus the following additional steps:
- 5. forming a substantially flat, planar top-surface above the first rib groups;
- 6. etching the top-surface to form an array of parallel, elongated second transmissive ribs;
- 7. conformal coating the second transmissive ribs with a second coating while maintaining solid-material-free second gaps between the second transmissive ribs; and
- 8. etching the second coating to remove horizontal segments and leaving vertical second wires along sides of the second transmissive ribs, forming second rib groups each comprising a pair of second wires which sandwich a second transmissive rib, and wherein the first wires or the second wires comprise are absorptive and the other are reflective of the incident light.
-
FIG. 1 is a schematic cross-sectional side view of awire grid polarizer 10 with an array of parallel, elongatedfirst rib groups 14, firstdielectric material 16 substantially filling first gaps 117 (seeFIGS. 11-13 ) between thefirst rib groups 14 to form firstdielectric ribs 16 a, the firstdielectric material 16 further extending from thefirst gaps 117 above and over tops of thefirst rib groups 14 forming a first dielectricupper layer 16 b, and an array of parallel, elongatedsecond wires 15 disposed over thefirst rib groups 14, the firstdielectric ribs 16 a, and the first dielectricupper layer 16 b, in accordance with an embodiment of the present invention; -
FIG. 2 is a schematic cross-sectional side view of awire grid polarizer 20 with an array of parallel, elongatedfirst rib groups 14, firstdielectric material 16 substantially filling first gaps 117 (seeFIGS. 11-13 ) between thefirst rib groups 14 to form firstdielectric ribs 16 a, and an array of parallel, elongatedsecond wires 15 disposed over thefirst rib groups 14 and the firstdielectric ribs 16 a, in accordance with an embodiment of the present invention; -
FIG. 3 is a schematic cross-sectional side view of awire grid polarizer 30 with an array of parallel, elongatedfirst rib groups 14, firstdielectric material 16 substantially filling first gaps 117 (seeFIGS. 11-13 ) between thefirst rib groups 14 to form firstdielectric ribs 16 a, the firstdielectric material 16 further extending from thefirst gaps 117 above and over tops of thefirst rib groups 14 forming atransmissive dielectric layer 16 c, the firstdielectric material 16 of thedielectric ribs 16 a comprising a different material than the firstdielectric material 16 of thetransmissive dielectric layer 16 c, and an array of parallel, elongatedsecond wires 15 disposed over thefirst rib groups 14 and on a top-surface 16 t of thetransmissive dielectric layer 16 c, in accordance with an embodiment of the present invention; -
FIG. 4 is a schematic cross-sectional side view of awire grid polarizer 40 similar to one of the wire grid polarizers shown inFIGS. 1-3 and 6-10, wherein thefirst wires 13 areabsorptive wires 43 and thesecond wires 15 arereflective wires 45, in accordance with an embodiment of the present invention; -
FIG. 5 is a schematic cross-sectional side view of awire grid polarizer 50 similar to one of the wire grid polarizers shown inFIGS. 1-3 and 6-10, wherein thefirst wires 13 arereflective wires 45 and thesecond wires 15 areabsorptive wires 43, in accordance with an embodiment of the present invention; -
FIG. 6 is a schematic cross-sectional side view of awire grid polarizer 60 similar to one of the embodiments ofFIGS. 1-5 , further comprising seconddielectric material 66 substantially filling second gaps 17 (seeFIGS. 1-5 ) between thesecond wires 15 to form seconddielectric ribs 66 a, the seconddielectric material 66 further extending from thesecond gaps 17 above and over tops of thesecond wires 15 forming a second dielectricupper layer 66 b, in accordance with an embodiment of the present invention; -
FIG. 6 is also a schematic cross-sectional side view of an eighth step of the FIRST METHOD for making a wire grid polarizer—backfilling thesecond gaps 17 and above thesecond wires 15 with seconddielectric material 66—in accordance with an embodiment of the present invention; -
FIG. 7 is a schematic cross-sectional side view of awire grid polarizer 70, similar to one of the embodiments ofFIGS. 1-5 , further comprising seconddielectric material 66 substantially filling second gaps 17 (seeFIGS. 1-5 ) between thesecond wires 15 to form seconddielectric ribs 66 a, in accordance with an embodiment of the present invention; -
FIG. 7 is also a schematic cross-sectional side view of a ninth step of the FIRST METHOD for making a wire grid polarizer—etching the seconddielectric material 66 and forming separate seconddielectric ribs 66 a—in accordance with an embodiment of the present invention; -
FIG. 8 is a schematic cross-sectional side view of awire grid polarizer 80 similar to one of the embodiments shown inFIGS. 1-5 , except that thesecond wires 15 are part of an array of parallel, elongatedsecond rib groups 84 each comprising a central secondtransmissive rib 82 and asecond wire 15 disposed along each side of thesecond transmissive rib 82, in accordance with an embodiment of the present invention; -
FIG. 9 is a schematic cross-sectional side view of awire grid polarizer 90, similar towire grid polarizer 80, further comprising a seconddielectric material 66 substantially filling second gaps 17 (seeFIG. 8 ) between thesecond rib groups 84 to form seconddielectric ribs 66 a, the seconddielectric material 66 further extending from thesecond gaps 17 above and over tops of thesecond rib groups 84 forming a second dielectricupper layer 66 b, in accordance with an embodiment of the present invention; -
FIG. 10 is a schematic cross-sectional side view of awire grid polarizer 100, similar towire grid polarizer 80, further comprising a seconddielectric material 66 substantially filling second gaps 17 (seeFIG. 8 ) between thesecond rib groups 84 to form seconddielectric ribs 66 a, in accordance with an embodiment of the present invention; -
FIG. 11 is a schematic cross-sectional side view of a first step applicable to a FIRST METHOD or to a SECOND METHOD for making a wire grid polarizer—providing atransmissive substrate 11 having an array of parallel, elongated firsttransmissive ribs 12 disposed over thesubstrate 11—in accordance with an embodiment of the present invention; -
FIG. 12 is a schematic cross-sectional side view of a second step applicable to the FIRST METHOD or to the SECOND METHOD for making a wire grid polarizer—conformal coating thesubstrate 11 and the firsttransmissive ribs 12 with afirst coating 123 while maintaining solid-material-freefirst gaps 117 between the firsttransmissive ribs 12—in accordance with an embodiment of the present invention; -
FIG. 13 is a schematic cross-sectional side view of a third step applicable to the FIRST METHOD or to the SECOND METHOD for making a wire grid polarizer—etching thefirst coating 123 to removehorizontal segments 121 and leaving verticalfirst wires 13 alongsides 12 s of the firsttransmissive ribs 12, formingfirst rib groups 14 each comprising a pair offirst wires 13 which sandwich a firsttransmissive rib 12—in accordance with an embodiment of the present invention; -
FIG. 14 is a schematic cross-sectional side view related to a fourth and/or fifth step in the FIRST METHOD or the SECOND METHOD for making a wire grid polarizer—backfilling thefirst gaps 117 and above thefirst rib groups 14 with firstdielectric material 16 and forming a substantially flat, planar top-surface 16 t above thefirst rib groups 14—in accordance with an embodiment of the present invention; -
FIG. 15 is a schematic cross-sectional side view related to a fourth and/or fifth step in the FIRST METHOD or the SECOND METHOD for making a wire grid polarizer—etching the firstdielectric material 16 and forming separate firstdielectric ribs 16 a, with a firstdielectric rib 16 a in onefirst gap 117 separate from a first dielectric rib in an adjacentfirst gap 117, and forming the substantially flat, planar top-surface 16 t above thefirst rib groups 14 and the first dielectric ribs—in accordance with an embodiment of the present invention; -
FIG. 16 is a schematic cross-sectional side view related to a fourth and/or fifth step applicable to the FIRST METHOD or to the SECOND METHOD for making a wire grid polarizer—applying atransmissive dielectric layer 16 c over thefirst rib groups 14 and the firstdielectric ribs 16 a to form the substantially flat, planar top-surface 16 t with material of thetransmissive dielectric layer 16 c—in accordance with an embodiment of the present invention; -
FIG. 17 is a schematic cross-sectional side view of a sixth step of the FIRST METHOD for making a wire grid polarizer—applying a continuous thin film of upper-material 175 over the top-surface 16 t of the firstdielectric material 16—in accordance with an embodiment of the present invention; -
FIG. 18 is a schematic cross-sectional side view of a seventh step of the FIRST METHOD for making a wire grid polarizer—etching the thin film of upper-material 175 to form an array of parallel, elongatedsecond wires 15 disposed over the top-surface 16 t—in accordance with an embodiment of the present invention; -
FIG. 19 is a schematic cross-sectional side view of a sixth step of the SECOND METHOD for making a wire grid polarizer—etching the top-surface 16 t to form an array of parallel, elongated secondtransmissive ribs 82—in accordance with an embodiment of the present invention; -
FIG. 20 is a schematic cross-sectional side view of a seventh step of the SECOND METHOD for making a wire grid polarizer—conformal coating thesecond transmissive ribs 82 with asecond coating 203 while maintaining solid-material-freesecond gaps 17 between thesecond transmissive ribs 82—in accordance with an embodiment of the present invention; -
FIG. 21 is a schematic cross-sectional side view of a eighth step of the SECOND METHOD for making a wire grid polarizer—etching thesecond coating 203 to removehorizontal segments 201 and leaving verticalsecond wires 15 alongsides 82 s of thesecond transmissive ribs 82, formingsecond rib groups 84 each comprising a pair ofsecond wires 15 which sandwich asecond transmissive rib 82—in accordance with an embodiment of the present invention; -
FIG. 22 is a schematic cross-sectional side view of a ninth step of the SECOND METHOD for making a wire grid polarizer—backfilling thesecond gaps 17 and extending above thesecond rib groups 84 with seconddielectric material 66—in accordance with an embodiment of the present invention; and -
FIG. 23 is a schematic cross-sectional side view of a tenth step of the SECOND METHOD for making a wire grid polarizer—etching the seconddielectric material 66 and forming separate seconddielectric ribs 66 a, with a seconddielectric rib 66 a in onesecond gap 17 separate from a seconddielectric rib 66 a in an adjacentsecond gap 17—in accordance with an embodiment of the present invention. -
- 11 Substrate
- 12 First transmissive rib
- 12 s Sides of the first transmissive rib
- 13 First wire
- 14 First rib group
- 15 Second wire
- 16 First dielectric material
- 16 a First dielectric rib
- 16 b First dielectric upper layer
- 16 c Transmissive dielectric layer
- 16 t Top-surface
- 17 Second gap
- 43 Absorptive wire
- 45 Reflective wire
- 66 Second dielectric material
- 66 a Second dielectric rib
- 66 b Second dielectric upper layer
- 82 Second transmissive rib
- 82 s Sides of the second transmissive rib
- 84 Second rib group
- 117 First gap
- 121 Horizontal segments of the first coating
- 123 First coating
- 175 Upper-material
- 201 Horizontal segments of the second coating
- 203 Second coating
- P12 First transmissive rib pitch
- P13 First wire pitch
- P15 Second wire pitch
- P82 Second transmissive rib pitch
- Th1 Thickness of the first wire
- Th2 Thickness of the second wire
- W13 Width of the first wire
- W15 Width of the second wire
- W123 Width of the first coating
- W203 Width of the second coating
- Many materials used in optical structures absorb some amount of light, reflect some amount of light, and transmit some amount of light. The following definitions are intended to distinguish between materials or structures that are primarily absorptive, primarily reflective, or primarily transmissive.
- 1. As used herein, the term “absorptive” means substantially absorptive of light in the wavelength of interest.
- a. Whether a material is “absorptive” is relative to other materials used in the polarizer. Thus, an absorptive structure will absorb substantially more than a reflective or a transmissive structure.
- b. Whether a material is “absorptive” is dependent on the wavelength of interest. A material can be absorptive in one wavelength range but not in another.
- c. In one aspect, an absorptive structure can absorb greater than 40% and reflect less than 60% of light in the wavelength of interest (assuming the absorptive structure is an optically thick film—i.e. greater than the skin depth thickness).
- 2. As used herein, the term “reflective” means substantially reflective of light in the wavelength of interest.
- a. Whether a material is “reflective” is relative to other materials used in the polarizer. Thus, a reflective structure will reflect substantially more than an absorptive or a transmissive structure.
- b. Whether a material is “reflective” is dependent on the wavelength of interest. A material can be reflective in one wavelength range but not in another. Some wavelength ranges can effectively utilize highly reflective materials. At other wavelength ranges, especially lower wavelengths where material degradation is more likely to occur, the choice of materials may be more limited and an optical designer may need to accept materials with a lower reflectance than desired.
- c. In one aspect, a reflective structure can reflect greater than 80% and absorb less than 20% of light in the wavelength of interest (assuming the reflective structure is an optically thick film—i.e. greater than the skin depth thickness).
- 3. As used herein, the term “transmissive” means substantially transmissive to light in the wavelength of interest.
- a. Whether a material is “transmissive” is relative to other materials used in the polarizer. Thus, a transmissive structure will transmit substantially more than an absorptive or a reflective structure.
- b. Whether a material is “transmissive” is dependent on the wavelength of interest. A material can be transmissive in one wavelength range but not in another.
- c. In one aspect, a transmissive structure can transmit greater than 90% and absorb less than 10% of light in the wavelength of interest.
- 4. As used in these definitions, the term “material” refers to the overall material of a particular structure. Thus, a structure that is “absorptive” is made of a material that as a whole is substantially absorptive, even though the material may include some reflective or transmissive components. Thus for example, a rib made of a sufficient amount of absorptive material so that it substantially absorbs light is an absorptive rib even though the rib may include some reflective or transmissive material embedded therein.
- 5. As used herein, the term “light” can mean light or electromagnetic radiation in the x-ray, ultraviolet, visible, and/or infrared, or other regions of the electromagnetic spectrum.
- As illustrated in
FIG. 1 , awire grid polarizer 10 is shown comprising atransmissive substrate 11 with an array of parallel, elongatedfirst rib groups 14 disposed over thesubstrate 11. Eachfirst rib group 14 can comprise a central firsttransmissive rib 12 and a pair offirst wires 13 including afirst wire 13 disposed along each side of the firsttransmissive rib 12. Each pair offirst wires 13 can directly touch the central firsttransmissive rib 12 sandwiched there between; or there may be another material disposed between each pair offirst wires 13 and the central firsttransmissive rib 12. - A first
dielectric material 16 can substantially fill first gaps 117 (seeFIGS. 11-13 ) between eachfirst rib group 14 and an adjacentfirst rib group 14. All or portions of the firstdielectric material 16 can be transmissive. An array of parallel, elongatedsecond wires 15 can be disposed over thefirst rib groups 14 and the firstdielectric material 16. There can be parallel, elongatedsecond gaps 17 between thesecond wires 15. Thesecond gaps 17 can be disposed on each side 15 s of thesecond wires 15. Thesecond gaps 17 can separate asecond wire 15 from adjacentsecond wires 15 on each side 15 s. Thesecond gaps 17 can be solid-material-free and can be filled with air or vacuum. Alternatively, another material can fill thesecond gaps 17, as will be discussed below in reference towire grid polarizers FIGS. 6-7 . - The first
transmissive ribs 12 can be integral with, and formed of the same material as, thesubstrate 11 by etching into thesubstrate 11 to form the firsttransmissive ribs 12. Alternatively, the firsttransmissive ribs 12 can be formed on top of thesubstrate 11, such as for example, by depositing a transmissive layer on thesubstrate 11 then etching to form the firsttransmissive ribs 12. In either case, the firsttransmissive ribs 12 can be formed by standard lithography techniques, such as patterning a resist and etching for example. - It can be beneficial to have a very small pitch P13 or distance between adjacent
first wires 13. Although the pitch P12 of the firsttransmissive ribs 12 may be limited by present lithography technology, the present invention teaches how to make twofirst wires 13 for every firsttransmissive rib 12; effectively cutting the pitch P13 of the first wires approximately in half in comparison to the pitch P12 of the firsttransmissive ribs 12. A pitch P12 of the firsttransmissive ribs 12 can be, for example, less than 200 nanometers in one aspect, less than 150 nanometers in another aspect, or less than 110 nanometers in another aspect; but the pitch P13 of thefirst wires 13 can be approximately half these numbers. - The wire grid polarizers described herein can be made with a relatively high
first wire 13 aspect ratio (first wire thickness Th1 divided by first wire width W13). Modeling has shown good polarization characteristics withfirst wire 13 aspect ratios between 8 and 60. Modeling has shown good polarization characteristics in the visible spectrum withfirst wire 13 width W of between 5 nm and 20 nm and a thickness Th1 of between 150 nm and 300 nm. Thefirst wires 13 can extend along eachside 12 s of the transmissive ribs substantially from a bottom of the transmissive ribs to a top of the transmissive ribs. - The
second wires 15 can be disposed over or directly on a top-surface 16 t. The top-surface 16 t can be firstdielectric material 16 only, as shown inFIGS. 1 & 3 or the top-surface 16 t can be tops of thefirst rib groups 14 and tops of firstdielectric ribs 16 a of the firstdielectric material 16 as shown inFIG. 2 . - As shown on
wire grid polarizer 10 ofFIG. 1 , the firstdielectric material 16 can extend from thefirst gaps 117 above and over tops of the first rib groups 14. Thus, the firstdielectric material 16 can include firstdielectric ribs 16 a betweenfirst rib groups 14 and a first dielectricupper layer 16 b above the first rib groups 14. The firstdielectric material 16 can have a substantially flat, planar top-surface 16 t. Thesecond wires 15 can be disposed on the top-surface 16 t. - The first dielectric
upper layer 16 b can be etched, prior to forming thesecond wires 15, and can be etched down to tops of the first rib groups 14. Thesecond wires 15 can then be formed on a top-surface 16 t comprising tops of thefirst rib groups 14 and tops of firstdielectric ribs 16 a. Thus, as shown onwire grid polarizer 20 inFIG. 2 , the firstdielectric material 16 can form separate firstdielectric ribs 16 a, with a firstdielectric rib 16 a in onefirst gap 117 being separate from a firstdielectric rib 16 a in an adjacentfirst gap 117. “Separate” meaning that each firstdielectric rib 16 a is not connected by the same material to an adjacent firstdielectric rib 16 a. - First
dielectric ribs 16 a are also separate from each other onwire grid polarizer 30 inFIG. 3 , with a firstdielectric rib 16 a in onefirst gap 117 being separate from a firstdielectric rib 16 a in an adjacent first gap. A difference betweenwire grid polarizer polarizer 30, atransmissive dielectric layer 16 c is disposed between (i) tops of thefirst rib groups 14 and tops of the firstdielectric ribs 16 a and (ii) bottoms of thesecond wires 15. Thetransmissive dielectric layer 16 c can have a substantially flat, planar, top-surface 16 t. - To make
wire grid polarizer 30, the first dielectricupper layer 16 b can be etched, prior to forming thesecond wires 15, and can be etched down to tops of the first rib groups 14. Thetransmissive dielectric layer 16 c can then be applied, such as for example by chemical vapor deposition, physical vapor deposition, or spin on. Thesecond wires 15 can then be formed on a top-surface 16 t of thetransmissive dielectric layer 16 c. - The
transmissive dielectric layer 16 c may be desired in some designs for modifying optical characteristics or for increased structural strength. A thickness of thetransmissive dielectric layer 16 c can be adjusted for optimal optical properties. - A choice of
polarizer Polarizer 10 can have an advantage of less manufacturing steps than required to makepolarizers dielectric ribs 16 a separate from each other. With such separation of the firstdielectric ribs 16 a, these ribs can affect polarization. For example, the firstdielectric ribs 16 a can be absorptive and can be used to selectively absorb one polarization of light. - The
first wires 13 or thesecond wires 15 can be absorptive (absorptive wires 43) and the other of thefirst wires 13 or thesecond wires 15 can be reflective (reflective wires 45). Thereflective wires 45 can cause polarization of incident light and the absorptive wires can cause absorption, rather than reflection, of one polarization (thus selectively absorptive) of the incident light. - As shown on
wire grid polarizer 40 inFIG. 4 , thefirst wires 13 can beabsorptive wires 43 and thesecond wires 15 can bereflective wires 45. As shown onwire grid polarizer 50 inFIG. 5 , thefirst wires 13 can bereflective wires 45 and thesecond wires 15 can beabsorptive wires 43. Whether thefirst wires 13 or thesecond wires 15 are thereflective wires 45 orabsorptive wires 43 can depend on factors such as desired pitch ofreflective wires 45 andabsorptive wires 43, direction of incident light, and overall materials of construction. - As shown on
wire grid polarizer 60 inFIG. 6 , a seconddielectric material 66 can substantially fill gaps 17 (seeFIGS. 1-5 ) between thesecond wires 15, forming seconddielectric ribs 66 a. The seconddielectric material 66 can extend from thesecond gaps 17 above and over tops of thesecond wires 15. Thus, the seconddielectric material 66 can include seconddielectric ribs 66 a and a second dielectricupper layer 66 b above thesecond wires 15. As shown onwire grid polarizer 70 inFIG. 7 , the seconddielectric material 66 can be etched down to tops of thesecond wires 15, thus forming separate seconddielectric ribs 66 a, with a seconddielectric rib 66 a filling onegap 17 being separate from a seconddielectric rib 66 a filling anadjacent gap 17. - A choice of
polarizer dielectric rib 66 a from another. Onpolarizer 60, thesecond wires 15 are fully embedded, which can be beneficial if there is a concern of corrosion of thesecond wires 15. Onpolarizer 70, the seconddielectric ribs 66 a are separate from each other, with can be beneficial if the seconddielectric ribs 66 a are used for separation of the different polarization states, or for absorption of one polarization state. For example, one of thesecond wires 15 or the seconddielectric ribs 66 a can be reflecting structures and the other can be absorptive structures. - As shown on
polarizers FIGS. 8-10 , thesecond wires 15 can be part of an array of parallel, elongated second rib groups 84. Eachsecond rib group 84 can comprise a central secondtransmissive rib 82 and a pair of thesecond wires 15. Asecond wire 15 can be disposed along each side of thesecond transmissive rib 82. There can besecond gaps 17 between eachsecond rib group 84 and an adjacentsecond rib group 84. Thesecond wires 15 can extend along each side of thesecond transmissive ribs 82 substantially from a bottom of thesecond transmissive ribs 82 to a top of thesecond transmissive ribs 82. Thesecond transmissive ribs 82 can be formed in the top-surface 16 t by by etching the firstdielectric material 16, or by etching a thin film disposed over the firstdielectric material 16. Onpolarizers dielectric material 16 can be a single layer, or multiple layers, similar to the description of the firstdielectric material 16 above forpolarizers - On
polarizers first wires 13 or thesecond wires 15 can be absorptive and the other can be reflective. Thus, the description ofpolarizers - As shown in
FIGS. 9-10 , a seconddielectric material 66 can substantially fill the second gaps 17 (seeFIG. 8 ) between eachsecond rib group 84 and an adjacentsecond rib group 84. As shown onwire grid polarizer 90 ofFIG. 9 , the seconddielectric material 66 can extend from thesecond gaps 17 above and over tops of the second rib groups 84. Thus, the seconddielectric material 66 can include seconddielectric ribs 66 a betweensecond rib groups 84 and a second dielectricupper layer 66 b above the second rib groups 84. The seconddielectric material 66 can be a single layer and can be a single material; or the seconddielectric material 66 can be multiple layers and can be layers of different materials. - The second dielectric
upper layer 66 b can be etched down to tops of the second rib groups 84. Thus, as shown onwire grid polarizer 100 inFIG. 10 , the seconddielectric material 66 can form separate seconddielectric ribs 66 a, with a seconddielectric rib 66 a in onesecond gap 17 being separate from a seconddielectric rib 66 a in an adjacentsecond gap 17. “Separate” meaning that each seconddielectric rib 66 a is not connected by the same material to an adjacent seconddielectric rib 66 a. Having separate seconddielectric ribs 66 a can allow such ribs to have a polarizing function. For example, the seconddielectric ribs 66 a can separate light into different polarization states if it is reflective, can selectively absorb one polarization state if absorptive, or can act as a birefringent transmissive thin film if made of transmissive material. - A choice of
polarizer dielectric rib 66 a from another.Polarizer 80 has the benefits of (1) at least one less manufacturing step than polarizers 90 and 100, and (2) air in thesecond gaps 17 can improve Tp in some designs. Polarizers 90 and 100 can have better durability overpolarizer 80. Onpolarizer 90, thesecond wires 15 are fully embedded, which can be beneficial if there is a concern of corrosion of thesecond wires 15. Onpolarizer 100, thesecond wires 15 are mostly embedded, which may be sufficient corrosion protection if the environment is not too corrosive. Onpolarizer 100, the seconddielectric ribs 66 a are separate from each other, with can be beneficial if the seconddielectric ribs 66 a are used for separation of the different polarization states, or for absorption of one polarization state. For example, one of thesecond wires 15 or the seconddielectric ribs 66 a can be reflective and the other can be absorptive. - The
second transmissive ribs 82 can be formed by standard lithography techniques, such as patterning a resist and etching for example. It can be beneficial to have a very small pitch P15 or distance between adjacentsecond wires 15. Although the pitch P82 of thesecond transmissive ribs 82 may be limited by present technology, the present invention teaches how to make twosecond wires 15 for every secondtransmissive rib 82; effectively cutting the pitch P15 of the second wires in half in comparison to the pitch P82 of thesecond transmissive ribs 82. A pitch P82 of thesecond transmissive ribs 82 can be, for example, less than 200 nanometers in one aspect, less than 150 nanometers in another aspect, or less than 110 nanometers in another aspect; but the pitch P15 of thesecond wires 15 can be approximately half these numbers. - The
wire grid polarizers second wire 15 aspect ratio (second wire thickness Th2 divided by second wire width W15). Modeling has shown good polarization characteristics withsecond wire 15 aspect ratios between 8 and 60. Modeling has shown good polarization characteristics in the visible spectrum withsecond wire 15 width W of between 5 nm and 20 nm and a thickness Th1 of between 150 nm and 300 nm. - A first method of making a wire grid polarizer can comprise some or all of the following steps. The steps can be performed in the order shown.
- 1. Providing a
transmissive substrate 11 having an array of parallel, elongated firsttransmissive ribs 12 disposed over thesubstrate 11. There can be an array of parallel, elongated solid-material-freefirst gaps 117 between the firsttransmissive ribs 12. SeeFIG. 11 . - 2. Conformal coating the
substrate 11 and the firsttransmissive ribs 12 with afirst coating 123 while maintaining the solid-material-freefirst gaps 117 between the firsttransmissive ribs 12. The conformal coating can be done by atomic layer deposition or other conformal coating method. A width W123 of thefirst coating 123 can be approximately equal to a width W13 of thefirst wires 13. SeeFIGS. 1 & 12 . - 3. Etching the
first coating 123 to removehorizontal segments 121 and leaving verticalfirst wires 13 along sides of the firsttransmissive ribs 12, formingfirst rib groups 14 each comprising a pair offirst wires 13 which sandwich a firsttransmissive rib 12. The etch can be an anisotropic etch to preferentially removehorizontal segments 121 while leaving verticalfirst wires 13. SeeFIGS. 12-13 . - 4. Backfilling the
first gaps 117 and above thefirst rib groups 14 with the firstdielectric material 16. The backfilling can be done by various methods including spinning on a liquid material (e.g. spin-on glass), then baking to drive out volatile chemicals and harden. The backfilling can be done by atomic lay deposition. SeeFIG. 14 . - 5. Forming a substantially flat, planar top-
surface 16 t above the first rib groups 14. Formation of this top-surface 16 t may be done by various methods, including the following:- a. The first
dielectric material 16 can form the substantially flat, planar top-surface 16 t as shown inFIG. 14 . Thus, this formation is a completion of the process of step 4. - b. An additional layer of material can be added on top of the first dielectric material, and a top-surface of this additional layer can form the top-
surface 16 t. - c. Etching the first
dielectric material 16 and forming separate firstdielectric ribs 16 a. The substantially flat, planar top-surface 16 t can comprise tops of therib groups 14 and tops of the firstdielectric ribs 16 a. SeeFIG. 15 . - d. Etching the first
dielectric material 16 and forming separate firstdielectric ribs 16 a. Applying atransmissive dielectric layer 16 c, substantially transmissive to incident light, over thefirst rib groups 14 and the firstdielectric ribs 12 to form the substantially flat, planar top-surface 16 t with material of thetransmissive dielectric layer 16 c. SeeFIG. 16 .
- a. The first
- 6. Applying a continuous thin film of upper-
material 175 over the top-surface 16 t. SeeFIG. 17 . - 7. Etching the thin film of upper-
material 175 to form an array of parallel, elongatedsecond wires 15 disposed over the top-surface 16 t of the firstdielectric material 16 and solid-material-freesecond gaps 17 between thesecond wires 15. SeeFIG. 18 . - 8. Backfilling the
second gaps 17 and above thesecond wires 15 with seconddielectric material 66. Backfilling may be done as described above in step 4. SeeFIG. 6 . - 9. Etching the second
dielectric material 66 and forming separate seconddielectric ribs 66 a. SeeFIG. 7 .
Thefirst coating 123 and thefirst wires 13 or the thin film of upper-material 175 and thesecond wires 15 can be absorptive and the other can be reflective. - A second method of making a wire grid polarizer can comprise some or all of the following steps. The steps can be performed in the order shown. Steps 1-4 from the first method above.
- 5. Forming a substantially flat, planar top-
surface 16 t above the first rib groups 14. Formation of this top-surface 16 t may be done by various methods, including the following:- a. The first
dielectric material 16 can form the substantially flat, planar top-surface 16 t as shown inFIG. 14 . Thus, this formation is a completion of the process of step 4. - b. An additional layer of material can be added on top of the first
dielectric material 16. A top-surface of this additional layer can form the top-surface 16 t. - c. Etching the first
dielectric material 16 and forming separate firstdielectric ribs 16 a. Applying atransmissive dielectric layer 16 c, substantially transmissive to incident light, over thefirst rib groups 14 and the firstdielectric ribs 12 to form the substantially flat, planar top-surface 16 t with material of thetransmissive dielectric layer 16 c. SeeFIG. 16 .
- a. The first
- 6. Etching the top-
surface 16 t to form an array of parallel, elongated secondtransmissive ribs 82. Thesecond transmissive ribs 82 can be substantially transmissive to incident light. SeeFIG. 19 . Note thatFIGS. 19-23 show formation of thesecond transmissive ribs 82 in the firstdielectric material 16, but as noted in step 5, thesecond transmissive ribs 82 might be formed in another material above the firstdielectric material 16. - 7. Conformal coating the
second transmissive ribs 82 with asecond coating 203 while maintaining solid-material-freesecond gaps 17 between thesecond transmissive ribs 82. A width W203 of thesecond coating 203 can be approximately equal to a width W15 of thesecond wires 15. SeeFIGS. 8 & 20 . - 8. Etching the
second coating 203 to removehorizontal segments 201 and leaving verticalsecond wires 15 along sides of thesecond transmissive ribs 82, formingsecond rib groups 84 each comprising a pair ofsecond wires 15 which sandwich asecond transmissive rib 82. SeeFIGS. 20-21 . - 9. Backfilling the
second gaps 17 with seconddielectric material 66 substantially filling thesecond gaps 17 and extending above the second rib groups 84. SeeFIG. 22 . - 10. Etching the second
dielectric material 66 and forming separate seconddielectric ribs 66 a, with a seconddielectric rib 66 a in onesecond gap 17 separate from a seconddielectric rib 66 a in an adjacentsecond gap 17. SeeFIG. 23 .
Thefirst coating 123 and thefirst wires 13 or thesecond coating 203 and thesecond wires 15 can be absorptive and the other can be reflective. - U.S. patent application Ser. No. 13/326,566, filed on Dec. 15, 2011; and U.S. Pat. No. 7,570,424 and U.S. Pat. No. 7,961,393; incorporated herein by reference in their entirety, provide examples of
possible substrate 11 materials, dielectric materials, absorptive materials, and materials for polarization (i.e. reflective materials) for the various polarizer structures and methods described herein. For example, aluminum could be used as a material for thereflective wires 45 to polarize visible light and silicon could be used as a material forabsorptive wires 43 to selectively absorb one polarization of visible light. The choice of material is dependent on the wavelength range of desired polarization, the overall polarizer structure, durability requirements, and performance requirements. - Note that a material's interaction with light (i.e. whether the material is primarily absorptive, reflective, or transmissive) is not solely dependent on elements in the material, but also on crystal structure and stoichiometry. These characteristics of different materials for use in polarizers are discussed extensively in U.S. Pat. No. 7,570,424 and U.S. Pat. No. 7,961,393.
- The
first wires 13 and thesecond wires 15 are partially or fully embedded in some of the embodiments described herein. Although embedding wires of a wire grid polarizer can increase wire grid polarizer durability, embedding the wires in some polarize designs can also adversely affect wire grid polarizer performance, especially by decreasing transmission of p-polarized light (decrease Tp). Therefore, embedded wire grid polarizers have often not been implemented in practice for applications requiring high polarizer performance, such as for example in computer projectors or semiconductor analysis equipment. Modeling has shown that the specific designs shown herein, although wires are partially or completely embedded, especially combined with proper aspect ratio, can provide good wire grid polarizer performance. - Examples of polarizer performance that may be obtained with polarizers described herein, and polarizers made from methods described herein, include:
-
- 1. transmission of at least 90% of one polarization (e.g. p-polarized light) and absorption of at least 90% of an opposite polarization (e.g. s-polarized light) at a single wavelength of light; or
- 2. transmission of at least 90% of one polarization (e.g. p-polarized light) and absorption of at least 80% of an opposite polarization (e.g. s-polarized light) at all wavelengths from 400 nm through 700 nm.
Claims (20)
1. A wire grid polarizer comprising:
a. a transmissive substrate;
b. an array of parallel, elongated first rib groups disposed over the substrate, each first rib group comprising:
i. a central first transmissive rib; and
ii. a pair of first wires including a first wire disposed along each side of the first transmissive rib;
c. a first dielectric material substantially filling first gaps between each rib group and an adjacent rib group;
d. an array of parallel, elongated second wires disposed over the rib groups and the first dielectric material; and
e. the first wires or the second wires are absorptive and the other of the first wires or the second wires are reflective.
2. The polarizer of claim 1 , wherein the second wires are part of an array of parallel, elongated second rib groups, each second rib group comprising:
a. a central second transmissive rib;
b. a pair of the second wires including a second wire disposed along each side of the second transmissive rib; and
c. second gaps between each second rib group and an adjacent second rib group.
3. The polarizer of claim 2 , further comprising second dielectric material substantially filling the second gaps.
4. The polarizer of claim 3 , wherein the second dielectric material extends from the first gaps above and over tops of the second rib groups and the second dielectric material is substantially transmissive to the incident light.
5. The polarizer of claim 1 , wherein:
a. the first dielectric material extends from the gaps above and over tops of the rib groups and has a substantially flat, planar top-surface;
b. the first dielectric material is substantially transmissive to the incident light; and
c. the second wires are disposed on the top-surface of the first dielectric material.
6. The polarizer of claim 1 , wherein the first dielectric material forms separate first dielectric ribs, with a first dielectric rib in one first gap separate from a first dielectric rib in an adjacent first gap.
7. The polarizer of claim 6 , wherein:
a. the first wires are reflective and the second wires are absorptive;
b. the first dielectric ribs absorptive;
c. a substantially flat, planar, transmissive dielectric layer is disposed between (i) tops of the first rib groups and tops of the first dielectric ribs and (ii) bottoms of the second wires.
8. The polarizer of claim 1 , wherein the first wires are absorptive and the second wires are reflective.
9. The polarizer of claim 1 , wherein the first wires are reflective and the second wires are absorptive.
10. The polarizer of claim 1 , wherein a pitch of the transmissive ribs is less than 150 nanometers.
11. The polarizer of claim 1 , wherein the polarizer transmits at least 90% of one polarization and absorbs at least 90% of an opposite polarization at a single wavelength of light.
12. The polarizer of claim 1 , wherein the polarizer transmits at least 90% of one polarization and absorbs at least 80% of an opposite polarization at all light wavelengths from 400 nm through 700 nm.
13. A method of making a wire grid polarizer, the method comprising:
a. providing a transmissive substrate having an array of parallel, elongated first transmissive ribs disposed over the substrate;
b. conformal coating the substrate and the first transmissive ribs with a first coating while maintaining solid-material-free first gaps between the first transmissive ribs;
c. etching the first coating to remove horizontal segments and leaving vertical first wires along sides of the first transmissive ribs, forming first rib groups each comprising a pair of first wires which sandwich a first transmissive rib;
d. backfilling the first gaps with first dielectric material;
e. forming a substantially flat, planar, top-surface above the first rib groups;
d. applying a continuous thin film of upper-material over the top-surface; and
f. etching the thin film of upper-material to form an array of parallel, elongated second wires disposed over the top-surface of the first dielectric material and solid-material-free second gaps between the second wires, and wherein the first wires or the second wires are absorptive and the other of the first wires or the second wires care reflective.
14. The method of claim 13 , wherein backfilling the first gaps and forming a substantially flat, planar top-surface further includes:
a. backfilling above the first rib groups with the first dielectric material, the first dielectric material is substantially absorptive to the incident light and the first wires are reflective;
b. etching the first dielectric material and forming separate first dielectric ribs, with a first dielectric rib in one first gap separate from a first dielectric rib in an adjacent first gap; and
c. applying a transmissive dielectric layer over the first rib groups and the first dielectric ribs to form the substantially flat, planar top-surface with material of the transmissive dielectric layer.
15. The method of claim 13 , wherein backfilling the first gaps and forming a substantially flat, planar top-surface further includes backfilling above the first rib groups with the first dielectric material to form the substantially flat, planar top-surface with material of the first dielectric material.
16. The method of claim 13 , further comprising backfilling the second gaps with second dielectric material.
17. The method of claim 13 , wherein backfilling the second gaps further comprises backfilling above the second wires with second dielectric material.
18. A method of making a wire grid polarizer, the method comprising:
a. providing a transmissive substrate having an array of parallel, elongated first transmissive ribs disposed over the substrate;
b. conformal coating the substrate and the transmissive ribs with a first coating while maintaining solid-material-free first gaps between the first transmissive ribs;
c. etching the first coating to remove horizontal segments and leaving vertical first wires along sides of the first transmissive ribs, forming first rib groups each comprising a pair of first wires which sandwich a first transmissive rib;
d. backfilling the first gaps with first dielectric material;
e. forming a substantially flat, planar top-surface above the first rib groups;
f. etching the top-surface to form an array of parallel, elongated second transmissive ribs, the second transmissive ribs;
g. conformal coating the second transmissive ribs with a second coating while maintaining solid-material-free second gaps between the second transmissive ribs;
h. etching the second coating to remove horizontal segments and leaving vertical second wires along sides of the second transmissive ribs, forming second rib groups each comprising a pair of second wires which sandwich a second transmissive rib, and wherein the first wires or the second wires are absorptive and the other of the first wires or the second wires are reflective.
19. The method of claim 18 , further comprising backfilling the second gaps with second dielectric material substantially filling the second gaps and extending above the second rib groups.
20. The method of claim 18 , further comprising etching the second dielectric material and forming separate second dielectric ribs, with a second dielectric rib in one second gap separate from a second dielectric rib in an adjacent second gap.
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EP14833826.2A EP3030925A4 (en) | 2013-08-07 | 2014-07-02 | Multi-layer absorptive wire grid polarizer |
JP2016533299A JP2016528550A (en) | 2013-08-07 | 2014-07-02 | Multilayer Absorbing Wire Grid Polarizer |
CN201480044399.1A CN105452916A (en) | 2013-08-07 | 2014-07-02 | Multi-layer absorptive wire grid polarizer |
KR1020167002884A KR20160040548A (en) | 2013-08-07 | 2014-07-02 | Multi-Layer Absorptive Wire Grid Polarizer |
PCT/US2014/045287 WO2015020744A1 (en) | 2013-08-07 | 2014-07-02 | Multi-layer absorptive wire grid polarizer |
US15/248,846 US10114161B2 (en) | 2010-12-30 | 2016-08-26 | Multi-layer absorptive wire grid polarizer |
Applications Claiming Priority (4)
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US201061428555P | 2010-12-30 | 2010-12-30 | |
US13/326,566 US20140300964A1 (en) | 2010-12-30 | 2011-12-15 | Wire grid polarizer with substrate channels |
US201361863298P | 2013-08-07 | 2013-08-07 | |
US14/314,814 US20150077851A1 (en) | 2010-12-30 | 2014-06-25 | Multi-layer absorptive wire grid polarizer |
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Also Published As
Publication number | Publication date |
---|---|
EP3030925A4 (en) | 2017-03-08 |
US10114161B2 (en) | 2018-10-30 |
JP2016528550A (en) | 2016-09-15 |
CN105452916A (en) | 2016-03-30 |
WO2015020744A1 (en) | 2015-02-12 |
EP3030925A1 (en) | 2016-06-15 |
US20160363706A1 (en) | 2016-12-15 |
KR20160040548A (en) | 2016-04-14 |
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