WO2023010034A1

WO2023010034A1 - Broadband optical filter

Info

Publication number: WO2023010034A1
Application number: PCT/US2022/074184
Authority: WO
Inventors: Liping Ma
Original assignee: Nitto Denko Corporation
Priority date: 2021-07-29
Filing date: 2022-07-27
Publication date: 2023-02-02

Abstract

The present disclosure relates to broadband light filtering elements including a stacked architecture of a reflective layer, a first transparent layer, a light absorbing layer, and a second transparent layer, to provide enhancement of broadband light absorption.

Description

BROADBAND OPTICAL FILTER

Inventor: Liping Ma

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No. 63/227,273, filed July 29, 2021 , which is incorporated by reference in its entirety.

BACKGROUND

Unless otherwise indicated in the present disclosure, the materials described in the present disclosure are not prior art to the claims in the present application and are not admitted to be prior art by inclusion in this section.

Modulation of light transport through various media and devices is an active area of research, and have useful applications in our everyday life. Light absorption, reflection and transmission modulation have been found in many applications, including, for instance, (1) solar cells, which transfer solar light energy into electricity by absorbing photons through a light absorber thereby generating electric charges and producing electricity; (2) eye glasses with an anti-reflection coating, that may reduce reflection light and provide clearer vision; (3) televisions, smartphones, and other electronic display devices wherein the display may be utilized as a mirror when turned off. Dielectric reflective (or mirror) devices may play an important role in such applications, wherein such devices may comprise plural layers including a high refractive index layer and low refractive index layer. Light reflection and transmission may be modulated, and the dielectric layer is generally optically transparent and itself has no light absorption. In order to realize broadband light modulation, the dielectric reflective mirror consists of many such high-n low-n layers, making it expensive, where dielectric mirror does not consist of light absorber materials, it only modulates the light transmittance and reflectance. Microelectromechanical systems (MEMS) and devices may include structures having sizes ranging from about a micron to hundreds of microns or more. Nano electromechanical systems (NEMS) and devices may include structures having sizes smaller than a micron including, for example, sizes smaller than several hundred nanometers. Electromechanical elements may be created using deposition, etching, lithography, and/or other micromachining processes that etch away parts of Substrates and/or deposited material layers, or that add layers to form electrical and electromechanical devices.

One type of an electromechanical system device is called an interferometric modulator (IMOD). As used herein, the term interferometric modulator or interferometric light modulator refers to a device that selectively absorbs and/or reflects light using the principles of optical interference.

Light absorption is realized by light absorbing materials, wherein photon energy is higher than the energy band gap of the semiconductor, and light may be absorbed.

There remains a need for constructs, materials, elements and/or devices that may absorb more broadband incident light, e.g., over 90%, comprising an ultra-thin light absorber layer.

SUMMARY

The present disclosure generally relates a novel approach to achieving high light absorption comprising an ultra-thin light absorber layer.

A broadband light absorber element may comprise: a substrate; a reflective layer disposed above the substrate; a first transparent layer, disposed above the reflective layer; a light absorber layer, disposed above the first transparent layer; and a second transparent layer, disposed above the light absorber layer; wherein incident light passes through the second transparent layer into the light absorber layer. In these elements, at least a portion of the light passing through the light absorber layer and the first transparent layer is reflected back by the reflective layer, achieving interference cancellation and enhancing light absorption in the light absorber layer. In some embodiments, the reflective layer may comprise a highly reflective surface. In some embodiments, the reflective may comprise a metal or metal alloy. In some embodiments, the metal or metal alloy may comprise aluminum, silver, nickel, chromium, or a combination thereof. In some embodiments, the first transparent layer may comprise a transparent insulating layer. In some embodiments, the first transparent layer may comprise an oxide, nitride, or halide. In some embodiments, the light absorber layer comprises a metal, a partially oxidized metal, a semiconductor, or a combination thereof. In some embodiments, the second transparent layer may comprise a transparent insulating layer.

In some embodiments, the reflective layer comprises a highly reflective surface, having reflectance higher than 80%.

In some embodiments, the first transparent layer comprises silicon dioxide (S1O2), silicon nitride (S13N4), aluminum oxide (AI2O3), tungsten oxide (WO3), or molybdenum oxide (M0O3).

In some embodiments, the broadband light absorber layer comprises tungsten (W), nickel (Ni), chromium (Cr), molybdenum (Mo), aluminum (Al), manganese (Mn), or a combination thereof.

In some embodiments, the broadband light absorber layer comprises a partially oxidized metal such as tungsten (W), nickel (Ni), chromium (Cr), molybdenum (Mo), aluminum (Al), or manganese (Mn).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of one embodiment of broadband light absorber structure.

FIG. 2 is a graphic illustration showing the light absorbance percentage (A%) as a function of wavelength (nm) of the device of an embodiment with and without the bottom mirror or reflective layer. The light absorber layer is tungsten (W).

FIG. 3 is a graphic illustration showing the light absorbance percentage (A%) as a function of wavelength (nm) of the device of an embodiment with and without the bottom reflective layer. The light absorber layer is tungsten (Mo).

DETAILED DESCRIPTION The embodiments herein relate to optical systems, such as interferometric modulator elements for the absorption of light.

It is to be understood that the embodiments disclosed herein do not thereby limit the scope of the disclosure; modifications and further applications of the disclosed principles as described herein are contemplated.

The term “transparent” as used herein describes a device, element, material, or layer that has a minimal amount of light absorption. A transparent device, element, material or layer transmits or allows the passage of light of about 80% to about 100%.

The term “broadband” as used herein includes plural wavelength light, e.g., light having a spectrum of about 400 nm to about 800 nm.

The term “ultrathin” as used herein refers to a thickness on the order of nanometers.

The present disclosure generally relates to broadband light absorber elements, which include materials having one or more optical properties that may provide optical absorption, transmittance and reflectance. Particularly, but not exclusively, the present disclosure relates to broadband light absorber elements comprising ultrathin light absorber layers exhibiting enhanced broadband light absorption.

The some embodiments, the broadband light absorber element may comprise: a substrate; a mirror or reflective layer disposed above the substrate; a first transparent layer disposed above the reflective layer; a light absorber layer disposed above the first transparent layer; a second transparent layer disposed above the light absorber layer; and combinations of the described layers. In some embodiments, incident light passes through the second transparent layer into the light absorber layer, and at least a portion of the light may pass through the light absorber layer and the first transparent layer and be reflected back by the reflective layer. Incident light, meeting with reflected light with an opposite phase caused by interference from the reflective mirror layer decreases the reflected light so as to enhance light absorption. In some embodiments, the reflective layer may comprise a highly reflective surface. In some embodiments, the reflective layer may comprise a metal or metal alloy. In some embodiments, the metal or metal alloy may comprise silver, chromium or aluminum. In some embodiments, the first transparent layer may comprise a transparent insulating layer. In some embodiments, the first transparent layer may comprise an oxide, nitride, or halide. In some embodiments, the light absorber layer comprises a metal, a partially oxidized metal, a semiconductor, or a combination thereof. In some embodiments, the second transparent layer may comprise a transparent insulating layer.

A schematic illustration of a broadband light absorber element/device described herein, such as element 10, is shown in FIG. 1. In some embodiments, the broadband light absorber element may comprise a substrate, such as substrate 12. In some embodiments, the broadband light absorber element may comprise a reflective or mirror layer or element, such as layer 14, having a reflective surface, such as surface 16. In some embodiments, the broadband light absorber element may comprise a first transparent layer, such as layer 18. In some embodiments, the broadband light absorber element may comprise a light absorbing layer, such as layer 20. In some embodiments, the broadband light absorber element may comprise a second transparent layer, such as layer 22. It is believed that incident, ambient or external light, indicated by first arrow 24, passes through the second transparent layer and then interacts with the absorbing layer, and at least some portion of that light strikes the reflective surface of the absorbing layer, as indicated by arrow 26, may be reflected back towards the exterior and combine with the incoming incident light to effect an interference, reducing the reflectance and enhancing the apparent light absorption.

In some embodiments, the broadband light absorber described herein has a total light apparent absorption (A%) of greater than 50%, greater than 55%, greater than 60%, greater than 65%, greater than 70%, greater than 75%, greater than 80%, greater than 85%, greater than 90%, greater than 95%, or greater than 99%.

In some embodiments, the broadband light absorber described herein provides a light absorption over a broad spectrum with a roughly flat absorption spectrum over a wide wavelength range, such as about 400 nm to about 800 nm, about 400-500 nm, about 500-600 nm, about 600-700 nm, about 700-800 nm, about 400-600 nm, about 500-700 nm, about 600-800 nm, or about any wavelength in a range bounded by any of these values.

In some embodiments, the substrate of the broadband light absorber element may comprise a transparent material. In some embodiments, the substrate may be flexible. In some embodiments, the substrate may be inflexible or rigid. In some embodiments, the substrate may comprise a non-conductive material, e.g., glass, plastic (for example PET) and metal foils. In some embodiments, the transparent layer may comprise a transparent oxide. In some embodiments the reflective or mirror layer may comprise a metal or metal alloy. In some embodiments, the metal may be aluminum, silver, chromium, or any combination thereof. In some embodiments, the reflective layer may have a measure of reflectance of at least 50% of the impinging light, at least 75% of the impinging light, at least 90% of the impinging light, or up to 99% of the impinging light In some embodiments, the first transparent layer may be an oxide, a nitride or a halide. The first transparent layer may comprise a first transparent material having a first refractive index. In some embodiments, the transparent layer material may have a refractive index (n) of from about 1-3; or may have a refractive index within a range of about +/- 20% or about +/- 10% of the following values: about 1.3 (a range of about +/- 20% for 1.3 would be 1.04-1.56, or about 1-1.6), about 1.4, about 1.45, about 1.55, about 1.6, about 1.8, about 2.0, about 2.5, about 2.75. about 3.0; or any value in a range defined by any of the above values.

In some embodiments, the transparent materials may be S1O2, S13N4, AI2O3, AIN, WO3, and or M0O3. Suitable, but not limiting, transparent materials are shown in Table 1 below:

Table-1

In some embodiments, the first transparent layer may have a thicknes between about 1-200 nm, about 1-2 nm, about 2-5 nm, about 5-10 nm, about 10-20 nm, about 20-50 nm, about 50-70 nm, about 40-60 nm, about 70-100 nm, about 100-150 nm, about 150-200 nm, or about any thickness in a range bounded by any of these values.

In some embodiments, the second transparent layer may have thicknesses between about 1-200 nm, about 1-2 nm, about 2-5 nm, about 5-10 nm, about 10-20 nm, about 20-50 nm, about 50-70 nm, about 60-80 nm, about 70-100 nm, about 100- 150 nm, about 150-200 nm, or about any thickness in a range bounded by any of these values.

In some embodiments, the second transparent layer may comprise the same material and/or materials having similar refractive indices as the first transparent layer. In some embodiments, when the first and second transparent layers comprise the same material, or may comprise different materials. The refractive index and layer thickness are arranged in a way that reflection light will be significantly canceled by interference and a majority of the incident light will be absorbed in the ultra-thin light absorber layer. In some embodiments, when the transparent layers have the same or a similar refractive index, the layer more proximal to the exterior impinging light and/or more distal from the reflective surface, e.g., the second transparent layer, may be thicker to provide a layer that has a greater refractive index value, e.g., a greater value of thickness of transparent layer times the thickness of the respective layer. For example, where the first and second transparent layers comprise silica dioxide, the first transparent layer, that more proximal to the reflective layer and/or more distal to the impinging incident light, may be between 40 and 70 nm thick, e.g., 54 nm thick and the second transparent layer, that more distal to the reflective layer and / or proximal to the impinging incident light may be between 65 and 95 nm thick may be thicker, e.g., 80 nm thick. In some embodiments, the first and second dielectric layers may comprise different dielectric materials, e.g., one having a higher refractive index. In some embodiments, the first and second transparent layers may have the same thickness, but materials having different refractive indices.

In some embodiments, the absorbing layer may comprise light absorbing materials. In some embodiments, the light absorbing material may comprise metals, for example, tungsten (W), nickel (Ni), chromium (Cr), silver (Ag), aluminum (Al), manganese (Mn) and/ or molybdenum (Mo). In some embodiments, the light absorbing material may be a partially oxidized metal. In some embodiments, the partially oxidized metal may be WOx, wherein x is less than 3, e.g., WO2. It is believed these materials share the characteristic of absorbing light by electron oscillations, for example, the free electrons in metals or locally-free electrons in some semiconductors such as WO3. In some embodiments, the light absorber material may comprise semiconductors, organic or inorganic semiconductors.

The light absorber element may be arranged in such a way that incident light from the top surface of the second transparent layer interferes with the reflected light from the reflective layer, causing destructive interference at the top surface of the second transparent layer, resulting in significant reduced incident light reflection from the top surface of the second transparent layer. In this way, light confinement in the light absorber layer results in significantly enhanced light absorption in the ultra-thin light absorber layer. This is described as light cancellation by interference. In some embodiments, a method for preparing a light absorber element may be described. In some embodiments, the method may comprise providing a substrate. In some embodiments the method may comprise providing a reflective layer having a reflective surface. In some embodiments, the method may comprise providing a first transparent layer wherein the first transparent layer may comprise a transparent material and in optical communication with the first transparent layer. In some embodiments, the method may comprise providing a light absorbing layer. In some embodiments, the method may comprise providing a second transparent layer. In some embodiments, the aforementioned layers may be disposed atop one another in the aforementioned order or stack.

EMBODIMENTS

Embodiment 1. A broadband light absorber element comprising: a. a substrate; b. a reflective layer disposed above the substrate; c. a first transparent layer, disposed above the reflective layer; d. a light absorber layer, disposed above the first transparent layer; and e. a second transparent layer; wherein incident light passes through the second dielectric layer into the light absorber layer and at least a portion of the light is reflected back by the reflective layer, providing interference cancellation which enhances light absorption in the light absorber layer.

Embodiment 2. The light absorber of embodiment 1 , wherein the reflective layer comprises a highly reflective surface, having reflectance higher than 80%.

Embodiment 3. The light absorber of embodiment 2, wherein the reflective layer can comprise a metal or metal alloy.

Embodiment 4. The light absorber of embodiment 3, wherein the metal or metal alloy comprises aluminum, silver, nickel, chromium or alloys thereof.

Embodiment 5. The light absorber of embodiment 3, the first transparent layer comprises an oxide, nitride, or halide.

Embodiment 6. The light absorber of embodiment 1 , wherein the first transparent layer comprises silicon dioxide (S1O2), silicon nitride (S13N4), aluminum oxide (AI2O3), Tungsten oxide (WO3), or M0O3 (molybdenum oxide).

Embodiment 7. The light absorber of embodiment 1 , wherein the light absorber layer comprises metals or semiconductors.

Embodiment 8. The light absorber of embodiment 1 , wherein the light absorber layer comprises tungsten (W), Nickel (Ni), chromium (Cr), Molybdenum (Mo), aluminum (Al), or Manganese (Mn).

Embodiment 9. The light absorber of embodiment 1 , wherein the light absorber layer comprises a partially oxidized metal tungsten (W), nickel (Ni), chromium (Cr), molybdenum (Mo), aluminum (Al), or manganese (Mn).

Embodiment 10. The light absorber of embodiment 1 , wherein the second transparent layer comprises a transparent insulating layer.

EXAMPLES

It should be appreciated that the following Examples are for illustration purposes and are not intended to be construed as limiting the subject matter disclosed in this document to only the embodiments disclosed in these examples. Preparing broadband light absorber element

Glass substrates and glass substrates with pre-deposited mirror layers were loaded onto a home-made sputtering system. The base vacuum was less than 2x 10 ⁶ torr. First, the first transparent layer (50 nm) of silicon oxide (S1O2) was reactively deposited from a Si sputtering target under a processing gas of argon (Ar) and oxygen (O2), the gases controlled separately by mass flow controllers, the Ar flow rate was 10 Standard Cubic Centimeters per Minute (SCCM), the O2 rate was 2 SCCM, the deposition rate was about 2A/sec. Next an absorbing layer of either 10 nm thick tungsten or 11 nm thick Mo layer was deposited from either a tungsten (W) target or

a molybdenum (Mo) target, respectively, at a deposition rate of about 2-3 A/s. Next, a second transparent layer of silicon oxide (S1O2, 70 nm) was deposited in a similar manner as the first transparent layer. The reference samples of Examples without mirror layers, CE-1 or CE-2 samples are fabricated with the broadband light absorber samples AB1 or AB2 as indicated in TABLE 2 below.

TABLE 2 Measurement of the light transmittance (T%). reflectance (R%) and absorbance (A%1 Filmetrics system, model number F10-RT-UV was used for the measurement.

The light source is the combination of Halogen lamp and D2 lamp. Incident angle was 2 degree, spectral reflectance percentage (R%) and transmittance percentage (T%) was measured by photo diode, for samples without scattering or haze, the light absorbance A% was obtained from A%=1-T% +R%. the testing incident light direction was from the top surface of the second transparent layer.

TABLE 3

Based on these results, it can be seen from Table 3 that the R% for the samples CE-1 and CE-2 is high (9.5% and 8.0%), when a mirror layer is added sample AB-1 and AB-2, the reflectance is reduced tremendously (4.5% and 0.79%), the reduced light reflectance is believed from interference cancelation, for example the mirror layer should be effective in reflecting light and blocking light transmission, (T%=0% for AB- 1 and 0.06% for AB-2). The light absorbance A% is tremendously enhanced from 43.1% to 95.5% for AB-1 sample and from 51.6% to 99.2% for AB-2 sample, such enhancement could not be explained by double optical distance by the mirror layer.

For the processes and/or methods disclosed, the functions performed in the processes and methods may be implemented in differing order, as may be indicated by context. Furthermore, the outlined steps and operations are only provided as examples, and some of the steps and operations may be optional, combined into fewer steps and operations, or expanded into additional steps and operations.

This disclosure may sometimes illustrate different components contained within, or connected with, different other components. Such depicted architectures are merely examples, and many other architectures may be implemented which achieve the same or similar functionality.

The terms used in this disclosure, and in the appended embodiments, are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including, but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes, but is not limited to,” etc.). In addition, if a specific number of elements is introduced, this may be interpreted to include at least the recited number, as may be indicated by context (e.g., the bare recitation of "two recitations," without other modifiers, includes at least two recitations, or two or more recitations). As used in this disclosure, any disjunctive word and/or phrase presenting two or more alternative terms should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B" or “A and B.”

The terms and words used are not limited to the bibliographical meanings but are merely used to enable a clear and consistent understanding of the disclosure. It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a component surface" includes reference to one or more of such surfaces.

By the term "substantially" it is meant that the recited characteristic, parameter, or value need not be achieved exactly, but that deviations or variations, including for example, tolerances, measurement error, measurement accuracy limitations and other factors known to those skilled in the art, may occur in amounts that do not preclude the effect the characteristic was intended to provide.

Aspects of the present disclosure may be embodied in other forms without departing from its spirit or essential characteristics. The described aspects are to be considered in all respects illustrative and not restrictive. The embodied subject matter is indicated by the appended embodiments rather than by the foregoing description. All changes, which come within the meaning and range of equivalency of the embodiments, are to be embraced within their scope.

In closing, it is to be understood that the embodiments disclosed herein are illustrative of the principles of the claims. Other modifications that may be employed are within the scope of the claims. Thus, by way of example, but not of limitation, alternative embodiments may be utilized in accordance with the teachings herein. Accordingly, the claims are not limited to embodiments precisely as shown and described.

Claims

1. A broadband light absorber element comprising: a substrate; a reflective layer disposed upon and in optical communication with the substrate; a first transparent layer, disposed upon and in optical communication with the reflective layer; a light absorber layer, disposed upon and in optical communication with the first transparent layer; and a second transparent layer, disposed upon and in optical communication with the light absorber layer; wherein incident light passes through the second transparent layer into the light absorber layer and at least a portion of the light is reflected back by the reflective layer, providing interference cancellation and enhancing light absorption in the light absorber layer.

2. The broadband light absorber element of claim 1 , wherein the reflective layer has a reflectance higher than 80%.

3. The broadband light absorber element of claim 2, wherein the reflective layer comprises a metal or metal alloy.

4. The broadband light absorber element of claim 3, wherein the metal or metal alloy comprises aluminum, silver, nickel, chromium, or a combination thereof.

5. The broadband light absorber element of claim 3, the first transparent layer comprises an oxide, nitride, or halide.

6. The broadband light absorber element of claim 1 , wherein the first transparent layer comprises silicon dioxide (S1O2), silicon nitride (S13N4), aluminum oxide (AI2O3), tungsten oxide (WO3), or molybdenum oxide (M0O3).

7. The broadband light absorber element of claim 1 , wherein the light absorber layer comprises a metal or a semiconductor.

8. The broadband light absorber element of claim 1 , wherein the light absorber layer comprises tungsten (W), nickel (Ni), chromium (Cr), molybdenum (Mo), aluminum (Al), or manganese (Mn).

9. The broadband light absorber element of claim 1 , wherein the light absorber layer comprises a partially oxidized metal, wherein the metal comprises tungsten (W), nickel (Ni), chromium (Cr), molybdenum (Mo), aluminum (Al), or manganese (Mn).

10. The broadband light absorber element of claim 1 , wherein the second transparent layer comprises a transparent insulating layer.