Multispectral and hyperspectral filters, methods of forming and uses thereof

Abstract

The disclosure relates to systems and methods for forming multispectral and hyperspectral optical filters. Specifically, the disclosure is directed to methods of forming thin film optical filters with increased selectivity, using microreactor direct atomic layer processing (μDALP).

Description

MULTISPECTRAL AND HYPERSPECTRAL FILTERS, METHODS OF FORMING AND USES THEREOFBACKGROUND

[0001] The disclosure is directed to systems and methods for forming multispectral and hyperspectral optical filters. Specifically, the disclosure is directed to methods of forming optical filters with increased selectivity, using microreactor direct atomic layer processing (μDALP).

[0002] Hyperspectral imaging systems have made significant strides in recent years, with current state-of-the-art technologies offering high spectral resolution across hundreds of narrow bands. Advanced systems can now operate from the visible to the long-wave infrared regions, with some capable of sub-nanometer spectral resolution. Miniaturization efforts have led to more compact and portable hyperspectral cameras, while improvements in sensor technology have increased sensitivity and reduced noise. Data-driven reconstruction methods are also enhancing the ability to extract hyperspectral information from simpler RGB images.

[0003] Despite these advances, several challenges hinder the widespread adoption of hyperspectral imaging technology. The high cost of hyperspectral sensors remains a significant barrier, particularly for consumer applications. Manufacturing complexities, especially for systems with many spectral bands, contribute to this cost issue. For instance, Fabry-Perot based filters require multiple processing and lithography steps for each spectral band, increasing production time and expenses. Data management and processing present another hurdle.

[0004] Hyperspectral imaging generates vast amounts of data, necessitating substantial computational resources for storage, processing, and analysis. Real-time processing of hyperspectral data is particularly challenging, limiting its use in time-sensitive applications. The development of more efficient algorithms for data compression and analysis is an ongoing area of research. The lack of standardization in hyperspectral imaging systems is also a concern.

[0005] Different manufacturers use varying approaches to spectral filtering and sensor design, making it difficult to compare and integrate systems from different sources. This fragmentation in the market can lead to compatibility issues and hinder the development of universal analysis tools and software. Spectral reconstruction accuracy remains an area for improvement, particularly in challenging lighting conditions or when dealing with complex, heterogeneous scenes. While data- driven methods show promise, they often require large, diverse datasets for training, which are notalways available. The development of more robust and generalizable reconstruction algorithms is necessary to expand the applicability of hyperspectral imaging across different domains.

[0006] The proposed methods and system aim to address these challenges.SUMMARY

[0007] Disclosed, in various exemplary implementations, are systems and methods for forming optical filters with increased selectivity, using microreactor direct atomic layer processing (μDALP), potentially with other technologies.

[0008] In an exemplary implementation provided herein is a method of forming an optical filter, implemented with a microreactor direct atomic layer deposition (μDALP) system, the method comprising using the μDALP system, depositing a plurality of alternating layers of a material having a predetermined refractive index, wherein the optical thickness of the deposited layer of each material is proportional to a fraction of a target wavelength sought to be filtered, the plurality of alternating layers of the material having a predetermined refractive index arc configured to create constructive or destructive interference at the target wavelength for an incident light.

[0009] In another exemplary implementation, provided herein is a method of increasing selectivity of an optical filter to a predetermined wavelength, implemented with a microreactor direct atomic layer deposition (μDALP) system, the method comprising using the μDALP system: depositing a plurality of alternating layers comprised of a first layer material having a first refractive index and a second layer material having a second refractive index, the first layer material, and the second layer material each having an increasing optical thickness along a deposition direction; and depositing a suppressor layer, adapted, sized, and configured to suppress or transmit the predetermined wavelength, wherein the suppressor layer has an optical thickness that increases along the deposition direction, thereby forming an optical filter with increased selectivity to the predetermined wavelength.

[0010] In yet another exemplary implementation, the optical filters are arranged in an array configured to operate as a multispectral, or hyperspectral sensors.

[0011] These and other features of the methods of forming optical filters with increased selectivity, using microreactor direct atomic layer processing (μDALP), will become apparent from the following detailed description when read in conjunction with the figures and examples, which are exemplary, not limiting.BRIEF DESCRIPTION OF THE FIGURES

[0012] For a better understanding of the methods of forming optical filters with increased selectivity, using microreactor direct atomic layer processing (μDALP), with regard to the exemplary implementations thereof, reference is made to the accompanying examples and color figures, in which:

[0013] FIG. 1, is a schematic illustrating a typical distributed Bragg reflector (DBR), in comparison to a DBR cavity providing suppressor layers;

[0014] FIG. 2A, illustrates a schematic of a typical DBR with 3 alternating TiO2 / MgFi layers showing the effect of the optical thickness on the filtered wavelength, with FIG. 2B showing the effect of the optical thickness and the refractive index of the higher of the alternating material (left), the refractive index of the lower of the alternating material (right), on the wavelength reflected (A), and the resulting normalized filtering profile (B);

[0015] FIG. 3A, illustrates a schematic of a DBR cavity according to an exemplary implementation of the methods described, with 6 alternating TiO2 / AhCh layers showing the effect of the optical thickness of the layers and the suppressor layers (spacer) on the filtered wavelength, with FIG. 3B showing the effect of the alternating layer material in a cavity according to an exemplary implementation of the methods described, with 6 alternating TiCWMgFo layers with FIG. 3C showing the effect of the optical thickness and the refractive index of the higher of the alternating material (left), the refractive index of the lower of the alternating material (right), on the wavelength reflected (A), and the resulting normalized filtering profile (B);

[0016] FIG. 4A, illustrates a schematic of a DBR cavity with increased optical thickness according to an exemplary implementation of the methods described, with 4 alternating layers separated by a suppressor layer with increasing optical thickness, showing the effect of the optical thickness of the layers and the suppressor layers (spacer) on the filtered wavelength, with FIG. 4B showing the effect of the optical thickness and the refractive index of the higher of the alternating material (left), the refractive index of the lower of the alternating material (right), on the wavelength reflected;

[0017] FIG. 5A, illustrates a schematic of a DBR cavity with 3 layers with increased optical thickness according to an exemplary implementation of the methods described, and 5 layers in FIG. 5B;

[0018] FIG. 6A, illustrating a schematic of another exemplary implementation of the DBR formed using a combination of mirrors and suppressor layers, with FIG. 6B showing the effect of the optical thickness and the refractive index of the higher of the alternating material (left), the refractive index of the lower of the alternating material (right), on the wavelength reflected (A), and the resulting normalized filtering profile (B) at a specific thickness;

[0019] FIG. 7, is a graph illustrating the agreement between expected and actual transmittance for a thin film fabricated using the methods disclosed; and

[0020] FIG. 8, depicting a sample showing lines of TiO2 formed using the methods disclosed, used for a refractive index study illustrated in FIG. 7, and an optical filter highlighted in the inset.DETAILED DESCRIPTION

[0021] Provided herein are exemplary implementations of methods of forming optical filters with increased selectivity, using microrcactor direct atomic layer processing (p DALP), as well as potentially other deposition technologies.

[0022] Microreactor Direct Atomic Layer Processing (μDALP) refers in an exemplary implementation to a precise thin film deposition technique enabling the growth of uniform and conformal films at the atomic scale.

[0023] The disclosure addresses fundamental challenges in the fabrication of optical filters for multispectral and hyperspectral imaging applications, particularly the need for cost-effective manufacturing of filters with precise spectral selectivity across multiple wavelength bands. Traditional approaches to hyperspectral filter fabrication, such as Fabry-Perot based systems, require multiple processing and lithography steps for each spectral band, resulting in substantial production time and expense that limit widespread adoption. The methods and systems disclosed overcomes these limitations by employing microreactor direct atomic layer deposition (μDALP) technology to fabricate distributed Bragg reflector (DBR) and other thin film filters’ structures with precision and efficiency. By enabling layer-by-layer growth at the atomic scale in a controlled, self-limiting fashion, the method permits formation of multiple optical filters with varying spectral characteristics in a single processing operation, substantially reducing manufacturing complexity while maintaining or even exceeding the spectral resolution capabilities of conventional approaches.

[0024] An example is shown in FIG. 2A, illustrating a schematic of a typical DBR with 3 alternating TiCb / MgFi layers showing the effect of the optical thickness on the filtered wavelength, with FIG. 2B showing the effect of the optical thickness and the refractive index of the higher of the alternating material (left), the refractive index of the lower of the alternating material (right), on the wavelength reflected (A), and the resulting normalized filtering profile (B).

[0025] In the case of film deposition, using μDALP, film growth is done in a controlled, layer- by-layer fashion beginning with modifying the substrate surface that is chemically prepared, typically cleaned to remove any contaminants or oxides. The deposition starts with a precursor, being introduced into a (micro) reaction chamber (e.g., for micro DALP, or μDALP). The precursor is selected based on the desired film composition, properties, and the expected etching methodology used. The precursor can be a vapor or gas-phase fluid that can react with, or preferentially adhere to the modified substrate surface, which in the case of optical filters, can be transparent. The precursors’ flows are precisely timed and controlled to ensure interaction with the modified substrate surface for a defined period. During this exposure, a self-limiting reaction occurs configured to terminate once a full monolayer is formed at the surface, resulting in the formation of a monolayer or sub-monolayer of the desired material. Excess precursor, unreacted byproducts, and any adsorbed impurities can then purged from the chamber using an inert gas such as, for example, nitrogen or argon. The cycle of precursor deposition, purge, reactant deposition and purge is then repeated, alternating between initial precursor exposure and final purge steps, thereby gradually building up the film layer by layer. The number of cycles is carefully controlled to achieve the desired film thickness, which can range from a few nanometers to several micrometers. The layer-by-layer growth using (microreactor) DALP ensures uniformity, even on complex 3D structures such as trenches, pores, or high aspect ratio (»1) features. The resulting film can be configured to exhibit uniform or variable thickness and width with excellent control over composition and properties. FIG. 5A, illustrates a schematic of a DBR cavity with 3 layers with increased optical thickness, and 5 layers in FIG. 5B clearly demonstrate the effect of the number and thickness of the alternating layers on the transmittance performance of the filter.

[0026] The plurality of alternating layers comprises at least two distinct materials selected to provide contrasting refractive indices, with the refractive index being the ratio of the speed of light in vacuum to the speed of light in the material and determining the degree to which light is refracted when passing between media. In exemplary implementations, the alternating layer pairs comprise a high refractive index material such as titanium dioxide (TiO?) with refractive index betweenapproximately 2.3 and 2.7 in the visible spectrum, tantalum pentoxide (Ta2O5) with refractive index between approximately 2.0 and 2.2, or niobium pentoxide (Nb2O5), alternating with a low refractive index material such as silicon dioxide (SiO2) with refractive index between approximately 1.45 and 1.55, aluminum oxide (AI2O3) with refractive index of approximately 1.6 at 623 nanometers, or magnesium fluoride (MgF2) with refractive index between approximately 1.38 and 1.45. The predetermined refractive index for each material is achieved through careful control of deposition parameters including precursor chemistry, reactant selection, deposition temperature, and postdeposition treatment, with the μDALP process enabling reproducible refractive index values with tolerances typically within plus or minus 0.02 across the deposited area.

[0027] For example, in an exemplary implementation, the precursor is Trimethylaluminum (TMA), and the reactant is Ozone, forming a layer of aluminum oxide (AI2O3) having a refractive index of about 1.6 at wavelength (λ) of 623 nm, while releasing methane (CPU) on purge, allowing for example the formation of thin films of varying optical thickness (referring to a value obtained by multiplying the actual deposited film thickness of the material layer by the refractive index of the material layer with respect to the wavelength of light emitted from the light emitting source, see e.g., FIG. 8).

[0028] The effect of the number of the number of alternating layers is illustrated in FIGs. 3A, illustrating a schematic of a DBR cavity according to an exemplary implementation of the methods described, with 6 alternating TiO2 / Al2O3layers showing the effect of the optical thickness of the layers and the suppressor layers (spacer) on the filtered wavelength, with FIG. 3B showing the effect of the alternating layer material in a cavity according to an exemplary implementation of the methods described, with 6 alternating TiO2 / MgF2layers with FIG. 3C showing the effect of the optical thickness and the refractive index of the higher of the alternating material (left), the refractive index of the lower of the alternating material (right), on the wavelength reflected (A), and the resulting normalized filtering profile (B).

[0029] In another exemplary implementation, the precursor is Tetrakis(dimethylamino)titanium (TDMAT) and the reactant can be Oxygen plasma (or again Ozone (O3), hydrogen peroxide (H2O2), or water vapor), forming Titanium Oxide ( TiO2) films having a wavelength dependent refractive index (RI) of between about 3.71-1.28 between wavelength range of 400-800 nm. Other reactants that can be used are Hydrazine (N2H4), Ammonia (NH4), or Nitrogen Fluoride (NF4).

[0030] Likewise, to form Magnesium Fluoride (MgF2) using the p DALP systems disclosed, magnesium precursors such as Magnesium Bis(ethylcyclopentadienyl) (Mg(EtCp)2) or Magnesium Acetylacetonate (Mg(acac)2) can be used, and fluorine reactants like Hydrogen Fluoride (HF), Carbon Tetrafluoride (CF4), or Hexafluoroacety lacetone (HFAA) can be utilized. The resulting film can have a refractive index of between about 1.38 (e.g., at 588nm) and about 1.45, depending on deposition parameters and film thickness. It is noted, that throughout the disclosure, the specific precursors and / or reactants can be different.

[0031] Additionally and in another exemplary implementation, Silicone dioxide (SiCL), can. having a refractive index of between about 1.45 and about 1.55. Likewise, Tantalum pentoxide (Ta2O5) films can be formed using tantalum chloride (TaCls) or tantalum ethoxide (Ta(OEt)5) as the tantalum precursor, with ozone (O3) or water (H2O) as the reactant materials. Once deposited, the Ta2O5film can be configured to exhibit a refractive index in the range of approximately 2.0 to 2.2, depending on the specific deposition conditions and the film's stoichiometry.

[0032] The optical thickness of each deposited layer, defined as the product of the physical thickness and the refractive index of the material at the target wavelength, is precisely controlled to be proportional to a specific fraction of the target wavelength sought to be filtered. For example, each layer possesses an optical thickness equal to one quarter of the target wavelength, such that a filter designed for a target wavelength of 550 nanometers would comprise alternating layers with optical thicknesses of approximately 137.5 nanometers, achieved through appropriate combinations of physical thickness and refractive index for each material. For a titanium dioxide layer with refractive index of 2.4 at 550 nanometers, the physical thickness would be approximately 57.3 nanometers, while a silicon dioxide layer with refractive index of 1.46 would require a physical thickness of approximately 94.2 nanometers to achieve the same optical thickness. Alternative implementations may employ optical thicknesses corresponding to one-half the target wavelength, which introduce a full 360-degree phase shift in reflected light and effectively act as transparent layers at the design wavelength, enabling more complex filter designs including resonant cavity structures (see e.g., FIG. 1, illustrating a typical distributed Bragg reflector (DBR), in comparison to a DBR cavity providing suppressor layers).

[0033] The fractional relationship between optical thickness and target wavelength remains consistent across all layer pairs in basic DBR implementations, though variations in this relationship across different layers within a single structure permit creation of filters with tailored spectralcharacteristics including broadened reflection bands or multiple discrete reflection peaks. The μDALP system's atomic-scale precision enables optical thickness control with tolerances typically better than plus or minus 1 nanometer, translating to wavelength precision of approximately plus or minus 2 to 4 nanometers for quarter- wave designs in the visible spectrum.

[0034] Accordingly and in an exemplary implementation, provided herein is a method of forming an optical filter, implemented with a microreactor direct atomic layer deposition (μDALP) system, the method comprising using the μDALP system, depositing and growing a plurality of alternating layers of a single pair (or 60 pairs) of materials having a predetermined refractive index (one high RI, and one low RI) on a substrate that can be opaque or transparent, depending on the specific filter application, wherein the optical thickness of the deposited layer of each material is proportional to a fraction of a target wavelength sought to be filtered, the plurality of alternating layers of the material having a predetermined refractive index are configured to create constructive or destructive interference at the target wavelength for an incident light.

[0035] To reiterate, the substrate is sized adapted and configured to provide mechanical stability and may be either transparent or opaque depending on the intended application. For transmission filters, substrates such as sapphire, fused silica, or gallium arsenide can be employed to maintain optical transparency at the relevant spectral range. For reflective configurations or integration with semiconductor devices, silicon substrates can be used. The initial interface between the substrate and the first deposited layer is configured to enhance reflectivity or transmission by leveraging the refractive index contrast, thereby reducing the number of layer pairs required to achieve the desired optical response. Manufacturing tolerances at the substrate interface typically require control within ±0.5 nm of thickness uniformity to maintain consistent spectral alignment across large- scale filter arrays. An example of transmission between the measured and expected (by simulation) transmission of the thin-film filters disclosed herein is further shown in FIG. 7).

[0036] The plurality of alternating layers are sized adapted and configured to interact to create constructive interference at the target wavelength while suppressing adjacent spectral bands. This interaction is governed by the periodicity of the optical path length and the refractive index contrast between layers. By carefully engineering these parameters, the methods disclosed enable formation of narrowband or broadband filters as required.

[0037] As indicated, the alternating layers are configured with predetermined refractive indices and optical thicknesses function collectively to create constructive interference or transmissionat the target wavelength through coherent addition of reflected or transmitted light waves from the multiple interfaces. When incident light strikes the filter structure, partial reflections occur at each interface between materials of different refractive indices, with the amplitude of reflection at each interface determined by the Fresnel equations and proportional to the refractive index contrast. For layers with quarter-wave optical thickness at the target wavelength, reflections from successive interfaces experience phase shifts such that they arrive in phase and interfere constructively, building up high reflectivity at the target wavelength while allowing other wavelengths to pass through with minimal reflection. The number of alternating layer pairs, which may range from a single pair to sixty pairs or more depending on the desired reflectivity and spectral bandwidth, determines the peak reflectance and sharpness of the spectral response, with each additional pair incrementally increasing reflectivity according to well-established thin-film optical theory.

[0038] Moreover, filters designed for transmission at the target wavelength employ the same principles but can further incorporate defect or cavity layers with optical thickness equal to one-half the target wavelength positioned between DBR stacks, creating a narrow transmission window within a broader reflection band. The substrate material selection influences the overall filter performance through its refractive index contrast with the first deposited layer, with high-index substrates such as silicon effectively functioning as an additional high- index layer and reducing the number of deposited pairs required to achieve a specified reflectance. The resulting optical filter structure exhibits spectral selectivity with full- width-half-maximum bandwidths ranging from approximately 10 to 100 nanometers depending on the number of layer pairs and refractive index contrast, enabling discrimination between closely spaced spectral features, which is highly beneficial for hyperspectral imaging applications.

[0039] In the context of the disclosure, the predetermined refractive index (RI), in the context of a distributed Bragg reflector (DBR), such as those formed in a single pass using the μDALP systems described, (see e.g., FIG. 1, left), is an optical property that quantifies how light propagates through the deposited material layer. The Predetermined RI is defined as the ratio of the speed of light in vacuum to the speed of light in the deposited material layer, determining the degree to which light is bent, or refracted, when passing from one medium to another. As illustrated in FIG. 1, forming a distributed Bragg reflector (DBR) using the systems provided, alternating layers of materials with different refractive indices (e.g., one high, and one low) are used to create constructive interference of reflected light waves, resulting in high reflectivity at specific wavelengths (see e.g., FIG. 1. Thecontrast between the refractive indices of adjacent layers directly influences the reflector's performance, with greater differences typically leading to higher reflectivity and broader reflection bands. The refractive index of each layer also affects the optical thickness, which is used for achieving the desired phase conditions for maximum reflection in the distributed Bragg reflector structure.

[0040] In certain exemplary implementation, the optic filter formed using the μDALP systems disclosed is a DBR cavity. The distributed Bragg reflector (DBR) cavity (see e.g., FIG. 1, right) differs from the regular Bragg mirror forming an exemplary implementation of the optic filters formed using the systems and methods disclosed. While a regular Bragg mirror consists of alternating layers of high and low refractive index materials designed to reflect specific wavelengths (see e.g., FIG. 3C), the DBR cavity incorporates an additional layer or defect within the mirror structure. This defect layer, typically half the thickness of the predetermined wavelength sought to be filtered, creates a resonant cavity between two DBR structures, which can be the same or different in the number of layer pairs.

[0041] FIG. 6A illustrating a schematic of DBR formed using a combination of mirrors and suppressor layers, with FIG. 6B showing the effect of the optical thickness and the refractive index of the higher of the alternating material (left), the refractive index of the lower of the alternating material (right), on the wavelength reflected (A), and the resulting normalized filtering profile (B) at a specific thickness. As illustrated, there is a sharp transmittance profile at a given thickness.

[0042] The (disruptor) cavity allows the wavelengths of light sought to be filtered (either in or out) to be trapped and amplified within the structure, resulting in a narrow transmission peak (see e.g., FIG. 3C (B)) within the reflection band of the DBR. This configuration enables the DBR cavity to act as a highly selective filter (in other words, reflecting certain wavelengths) or resonator (in other words, transmitting certain wavelengths), making it useful for applications such as vertical-cavity surface-emitting lasers (VCSELs), optical filters, and sensors. The presence of the cavity layer in a DBR cavity allows in certain implementations, for precise fine tuning and control over the optical properties of the device, including its resonant frequency and quality factor (Q-factor).

[0043] In certain exemplary implementations, the optical thickness of each material in the optical filters formed using the systems and methods disclosed, whether a DBR, or a DBR with a defect (disruptor) layer as disclosed herein, is one quarter of the wavelength sought to be filtered, while, in another exemplary implementation, the optical thickness is one half (1 / 2) the wavelength. Incorporating layers with an optical thickness of half the wavelength, rather than quarter wavelength, when integrated into the DBR structure, can be configured to introduce a full 360-degree phase shiftin the reflected light, effectively acting as a transparent layer at the design wavelength, which allows for the creation of resonant cavities within the DBR stack without disrupting the overall reflectance characteristics.

[0044] In an exemplary implementation, placing half-wave layers, the spectral response of the DBR is tuned, enabling the design of more complex optical filters with tailored transmission and reflection bands. For example, these layers can be used to separate distinct quarter- wave stacks within the DBR, facilitating the combination of multiple reflection bands or the broadening of existing ones (see e.g., FIG. 6). The inclusion of half-wave layers in DBRs enhances the flexibility and precision of optical filter design, allowing for the creation of sophisticated structures such as multi-cavity filters, wide-band reflectors, and filters with customized spectral shapes, all while maintaining the high reflectivity characteristic of DBRs.

[0045] In certain implementations of the methods and systems disclosed, once the plurality of alternating high- and low-refractive index layers have been deposited, a suppressor layer may be further formed to provide enhanced spectral selectivity. The suppressor layer is adapted, sized, and configured to either suppress or amplify reflection at a central frequency, thereby tuning the spectral response of the optical filter beyond that achievable with a standard distributed Bragg reflector stack. The suppressor layer functions by disrupting the periodicity of the alternating structure and introducing a localized optical resonance within the stop band of the reflector. This produces a sharp transmission or rejection band centered at the target wavelength.

[0046] Accordingly and in another exemplary implementation, the methods disclosed, using the systems described further comprise depositing a layer, adapted, sized, and configured to suppress a wavelength reflection at a central frequency, thereby forming a suppressor, or a defect layer. The defect layer is configured to have an optical thickness represented by the formula:wherein: to , is the optical thickness of the suppressor layer in nanometer (nm); target , is the target wavelength sough to be suppressed or transmitted; and nhigh, is the refractive index of the first layer, or second layer having a higher refractive index.

[0047] In practice, the suppressor layer may be formed from the same class of materials used in the alternating layers, such as titanium dioxide, aluminum oxide, silicon dioxide, or magnesium fluoride, provided the chosen material allows accurate control of the refractive index and is compatible with μDALP precursors. The μDALP process allows precise tailoring of the thickness to within ±0.5 nm of the target specification, since small deviations can shift the resonant peak significantly. The resulting structure enables a narrowband transmission peak within the stop band of the reflector when configured for amplification, or conversely, a notch filter when configured for suppression (see e.g., FIG.s 2B(B), 3C(B)).

[0048] FIG. 4A, illustrates a DBR cavity with increased optical thickness, with 4 alternating layers separated by a suppressor layer with increasing optical thickness, the effect of the optical thickness of the layers and the suppressor layers (spacer) on the filtered wavelength, with FIG. 4B showing the effect of the optical thickness and the refractive index of the higher of the alternating material (left), the refractive index of the lower of the alternating material (right), on the wavelength reflected.

[0049] In another exemplary implementation, the plurality of alternating layers of the first and second materials may be deposited in a configuration such that the completed optical filter exhibits a top plan view in the shape of a circle or in the form of a polygon having between three and six facets. The geometry of the deposited filter influences both manufacturing integration and optical performance. A circular footprint can be advantageous for applications requiring rotational symmetry, such as imaging systems where uniformity of filtering is sought and strictly required across all incident angles, and can be formed by μDALP deposition using circular microreactor. Alternatively, polygonal geometries such as triangular, square, pentagonal, or hexagonal shapes can be produced by controlling the deposition area either through using a microreactor having a periphery defining the required polygon, lithographic patterning, precision etching, or selective masking prior to or after μDALP deposition. These polygonal designs are beneficial for tiled filter arrays, where close packing arrays with minimal dead space is required to optimize active area utilization. The geometry implementation allows adaptation to system-level architectures, such as hyperspectral mosaics, and does not affect the optical interference principle of alternating layers but rather enhances scalability and manufacturability in compact device layouts. Tolerances for defining polygonal edges or circular perimeters are maintained for example, within ±1 pm to prevent edge scattering losses or spectral distortion, ensuring the filter maintains its designed wavelength selectivity.

[0050] Therefore using the pDALP systems disclosed herein is operable to form several optical filters arranged in a predetermined topology, allowing for a multispectral or hyperspectral filtering by forming metasurfaces with plurality of filters, whether with cavities or a regular DBR, all in a single operation. It is noted, that other technologies can be used in conjunction with the μDALP systems disclosed. The filters can be used, for example as color filters for various applications.

[0051] Accordingly, a plurality of optical filters may be deposited on a common substrate, each filter being operable to transmit or reflect a different target wavelength. This arrangement enables the construction of multispectral or hyperspectral arrays where each element is tuned to a distinct spectral band by adjusting the optical thickness of its alternating layer stack, the refractive index contrast of its material pair, or the inclusion of defect or suppressor layers. Implementation can be achieved by sequentially depositing patterned stacks with varying thicknesses in a step-and-repeat fashion, or by employing spatially selective μDALP deposition where the precursor dosing is varied across regions of the substrate. The ability to deposit multiple filters of different spectral response in a single integrated process provides substantial manufacturing advantages over current technology that relies on discrete filter components mechanically assembled into arrays. Alternative embodiments can be, for example fabricating filters with partially overlapping spectral ranges to broaden detection bandwidth or tailoring arrays with regularly spaced narrowband filters for hyperspectral imaging.

[0052] Performance uniformity across the array can be achieved by maintaining deposition thickness precision within ±0.5 nm, ensuring that each filter achieves its designed passband without spectral cross-talk. The scalability of this approach permits integration with solid-state imaging sensors, enabling wafer-level production of compact multispectral and hyperspectral devices with reduced cost and improved reproducibility.

[0053] In another exemplary implementation, the selectivity of an optical filter to a predetermined wavelength is enhanced by employing a microreactor direct atomic layer deposition ( μDALP) system to form a multilayer structure with controlled variation in optical thickness along the deposition direction. Using μDALP, alternating layers of a first material having a first refractive index and a second material having a second refractive index are deposited on a substrate. Unlike conventional distributed Bragg reflector structures in which each layer has a constant optical thickness, here each successive layer is formed with an increasing (or decreasing) optical thickness relative to the preceding layer, achieved by precisely extending the number of μDALP cycles (or etching cycles) in each deposition step. This progressive variation modifies the phase matching condition within themultilayer stack, thereby sharpening the spectral discrimination at the target wavelength by suppressing sideband transmission or reflection. The materials selected for the alternating stack, such as titanium dioxide and silicon dioxide or magnesium fluoride and aluminum oxide, are chosen to maximize refractive index contrast while maintaining thermal and mechanical stability during sequential deposition.

[0054] Following deposition of the alternating layers, a suppressor layer is introduced within the multilayer structure to further refine the filter’ s spectral selectivity. The suppressor layer is adapted and sized to disrupt periodicity in a controlled manner, creating a localized defect mode within the reflector bandgap. For example, the suppressor layer is deposited with an optical thickness that itself increases along the deposition direction, enabling tunability of the resonance condition across the filter’s depth and thereby enhances rejection of unwanted wavelengths adjacent to the target. This increasing thickness may be implemented by sequentially depositing sub-layers of the same material with stepwise variations in thickness, or by continuously modulating deposition cycles during μDALP growth. The suppressor layer may be composed of materials compatible with the alternating stack, such as silicon dioxide or aluminum oxide, to ensure conformal adhesion and minimal lattice mismatch. By integrating the suppressor layer with the variable-thickness alternating stack, the method yields an optical filter with sharply defined transmission or reflection peaks, reduced spectral leakage, and improved quality factor relative to conventional uniform-thickness multilayer designs. The approach is inherently scalable to wafer-level processing, allowing the fabrication of large-area or arrayed filters with reproducible performance suitable for multispectral and hyperspectral architectures.

[0055] In addition, as indicated the substrate can be either transparent, or opaques, depending on whether the filter is configured for reflection or transmission of the predetermined wavelength sought to be modulated. The transparency or opacity of the substrate depends in certain implementations, on several factors and design considerations. In applications where light transmission through the entire structure is required, such as in vertical-cavity surface-emitting lasers (VCSELs) or certain optical filters, a transparent substrate is used. Common transparent substrate materials comprise, for example, sapphire, glass, or semiconductor materials like gallium arsenide (GaAs) or indium phosphide (InP) when the operating wavelength is longer than their bandgap (referring to the intrinsic energy difference between the valence and conduction bands). Thesetransparent substrates allow light to pass through the entire filter structure, enabling the design of devices that utilize both reflected and transmitted light.

[0056] Conversely, and in another exemplary implementation, opaque substrates are employed when light transmission through the entire structure is not necessary, or when the substrate serves additional functions beyond optical properties. In certain implementation, Silicon provided for example not by being formed using the μDALP systems disclosed, is the opaque substrate, for example, in applications where integration with electronic components is desired for example, when forming optical multiplexers. Opaque substrates are used also in applications where light absorption below the filter is desired, such as in certain types of photodetectors or solar cells. In these use cases, the opaque substrate is used to prevent unwanted reflections or interference from the backside of the device.

[0057] Furthermore, and in yet another exemplary implementation, the choice of substrate can be further manipulated depending on the wavelength range of interest. A substrate that is transparent at one wavelength may become opaque at shorter wavelengths due to absorption. For instance, silicon is transparent in the infrared region but opaque in the visible spectrum, as is Galim Arsenide (GaAs). The intended operating wavelength range of the filters formed using the methods disclosed will affect the substrate material to ensure proper functionality of the device.

[0058] Additionally, the refractive index contrast between the substrate layer and the first layer of the filter formed using the system and methods disclosed, is used to amplify the reflectivity of the structure, effectively reducing the number of layers required to achieve a desired reflectance, taking into consideration design flexibility and bandwidth of the filter. For example, a fdter designed for use in the visible spectrum, centered around 550 nm (green light), is formed using using alternating layers of titanium dioxide (TiO2, n ~ 2.4) and silicon dioxide (SiO2, n ~ 1.45) as high and low refractive index materials, respectively. Silicon substrate (n « 3.5 at 550 nm) is used to take advantage of the high refractive index contrast between silicon and the first SiO2layer. In this configuration, the silicon substrate effectively acts as an additional high-index layer in the structure, with the first interface (Si / SiO2) contributing significantly to the overall reflectivity due to the large index contrast (An ~ 2.05). This initial high reflection, combined with the subsequent TiO2 / SiO2layers (optionally with cavity layers), can achieve the same reflectivity with fewer layer pairs compared to a filter on a glass substrate. For example, a 5-pair TiO2 / SiO2on silicon is configured to achieve the same reflectivity as a 7-pair filter on glass, potentially simplifying fabrication and reducing costs.

[0059] Accordingly and in an exemplary implementation, the first layer, or the second layer is comprised of Titanium oxide ( TiO2), Magnesium Fluoride (MgF2), Aluminum sequioxide (AI2O3), Silicon Dioxide (SiO2), Tantalum pentoxide (Ta2O5), Niobium pentoxide (Nb2O5), Zirconium dioxide (ZrO2), Hafnium dioxide (HfO2), Yttrium oxide (Y2O3), Silicon nitride (Si3N4), Zinc sulfide (ZnS), cryolite (Na3AIF6), Cerium fluoride (CeF3), Indium tin oxide (ITO), or Aluminum nitride (AIN), while the the suppressor layer is formed of Silicon dioxide (SiO2), Poly(methylmethacrylate) (PMMA), Air, Silicon nitride (Si3N4), Magnesium fluoride (MgF2), Aluminum oxide (AI2O3), Titanium dioxide (TiO2), cryolite (Na3AIF6), or a Low-index fluoride material.

[0060] In an exemplary implementation and as illustrated in FIGs 5A-5B illustrating a schematic of a filter with cavity layer with increased optical thickness according to an exemplary implementation of the methods described, with 3 layers, and 5 layers in FIG. 5B where a method of increasing selectivity of an optical filter to a predetermined wavelength is provided, the method implemented with a microreactor direct atomic layer deposition (μDALP) system as well as potentially other technologies, the method comprising using the μDALP system: on a substrate (opaque or transparent), depositing a plurality of alternating layers comprised of a first layer material having a first refractive index and a second layer material having a second refractive index, the first layer material, and the second layer material each having an increasing optical thickness along a deposition direction in the Z-dierction; and depositing a suppressor layer, adapted, sized, and configured to suppress (reflect) or transmit the predetermined wavelength, wherein the suppressor layer (in other words, the cavity) has an optical thickness that increases along the deposition direction (for example, between X / 4 to X / 2 of the predetermined wavelength sough to be modulated, thereby forming an optical filter with increased selectivity to the predetermined wavelength.Definitions:

[0061] In an exemplary implementation, the term “refractive index” (RI), refers to the real part and / or the imaginary part thereof, such that a change in the refractive index of the modulating medium or material can result in a change in the phase and / or intensity of light passing therethrough.

[0062] In the context of the disclosure, the term "feature" refers to an individual element or component of a pattern that is being transferred onto the substrate. These features can include various shapes, such as lines, spaces, dots, or any other geometric structures, and they collectively form theoverall pattern that defines the layout or design on the substrate. Features are typically characterized by their critical dimensions, which may include their width, spacing, and shape.

[0063] In the context of the disclosure, the term “stop band” refers to specific range of light frequencies that are effectively blocked and reflected by a periodic optical structure, and the "suppressor layer" is adapted, sized and configured to disrupt this periodicity to create a narrow, localized resonance, namely an exception where a specific frequency within that blocked range is allowed to exist.

[0064] The terms “first,” “second,” and the like, when used herein do not denote any order, quantity, or importance, but rather are used to denote one element from another. The terms “a”, “an” and “the” herein do not denote a limitation of quantity and are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The suffix “(s)” as used herein is intended to include both the singular and the plural of the term that it modifies, thereby including one or more of that term (e.g., the film(s) includes one or more film). Reference throughout the specification to “one exemplary implementation”, “another exemplary implementation”, “an exemplary implementation”, and so forth, means that a particular element (e.g., feature, structure, and / or characteristic) described in connection with the exemplary implementation is included in at least one exemplary implementation described herein, and may or may not be present in other exemplary implementations. In addition, it is to be understood that the described elements may be combined in any suitable manner in the various exemplary implementations.

[0065] In addition, for the purposes of the present disclosure, directional or positional terms such as "top", “apical”, “basal”, “proximal”, “distal”, "bottom", "upper," "lower," "side," "front," "frontal," "forward," "rear," "rearward," "back," "trailing," "above," "below," "left," "right," "radial ," "vertical," "upward," "downward," "outer," "inner," "exterior," "interior," "intermediate," etc., are merely used for convenience in describing the various exemplary implementations of the present disclosure.

[0066] The term "comprising" and its derivatives, as used herein, are intended to be open ended terms that specify the presence of the stated features, elements, components, groups, integers, and / or steps, but do not exclude the presence of other unstated features, elements, components, groups, integers and / or steps. The foregoing also applies to words having similar meanings such as the terms, "including", "having" and their derivatives.

[0067] Accordingly and in an exemplary implementation, provided herein is a method of forming an optical filter, implemented with a microreactor direct atomic layer deposition (μDALP) system, the method comprising using the μDALP system, depositing a plurality of alternating layers of a material having a predetermined refractive index on a substrate, wherein the optical thickness of the deposited layer of each material is proportional to a fraction of a target wavelength sought to be filtered, the plurality of alternating layers of the material are each having a predetermined refractive index configured to create constructive interference or transmission at the target wavelength for an incident light, wherein (i) the optical thickness of each layer is a quarter of the targeted wavelength (A / 4), and / or (ii) half of the targeted wavelength (X / 2), wherein (iii) the plurality of alternating layers are comprised of a first layer having a first refractive index and a second layer having a second refractive index, wherein the first refractive index is different than the second refractive index, with (iv) total number of alternating layers being between 6 and 120, (v) the method further comprising a step of depositing a layer, adapted, sized, and configured to suppress or amplify a wavelength reflection at a central frequency, thereby forming a suppressor layer, (vi) the suppressor layer is configured to have an optical thickness represented by the formula: wherein: to , is theoptical thickness of the suppressor layer in nanometer (nm); / (target , is the target wavelength sough to be suppressed; and nhigh, is the refractive index of the first layer, or second layer having a higher refractive index, wherein (vii) the step of depositing the plurality of alternating layers of the first layer and the second layer is configured to form the optical filter with a top plan view in the shape of a circle, or a polygon having between 3 and 6 facets, (viii) the method further comprising depositing a plurality of the optical filters, wherein each optical filter is operable to filter a different target wavelength, wherein (ix) the first layer, or the second layer is comprised of Titanium oxide (TiO2), Magnesium Fluoride (MgFj), Aluminum sequioxide (AI2O3), Silicon Dioxide (SiO2), Tantalum pentoxide (Ta2O5). Niobium pentoxide (Nb2O5), Zirconium dioxide (ZrO2). Hafnium dioxide (HfO2), Yttrium oxide (Y2O3), Silicon nitride (Si3N4), Zinc sulfide (ZnS), cryolite (Na3AIF6), Cerium fluoride (CeF3), Indium tin oxide (ITO), or Aluminum nitride (AIN), (x) the suppressor layer is formed of Silicon dioxide (SiO2), Poly(methylmethacrylate) (PMMA), Air, Silicon nitride (Si3N4), Magnesium fluoride (MgF2), Aluminum oxide (AI2O3), Titanium dioxide (TiO2), cryolite (Na3AIF6), or a Low- index fluoride material, and (xi) wherein the substrate has a transparency that depends on the target wavelength.

[0068] In another exemplary implementation, provided herein is a method of increasing selectivity of an optical filter to a predetermined wavelength, implemented with a microreactor direct atomic layer deposition (μDALP) system, the method comprising using the μDALP system: on a substrate, depositing a plurality of alternating layers comprised of a first layer material having a first refractive index and a second layer material having a second refractive index, the first layer material, and the second layer material each having an increasing optical thickness along a deposition direction; and depositing a suppressor layer, adapted, sized, and configured to suppress the predetermined wavelength, wherein the suppressor layer has an optical thickness that increases along the deposition direction, thereby forming an optical filter with increased selectivity to the predetermined wavelength, wherein (xii) a maximum optical thickness of each of the first layer material, and the second layer material is a quarter (1 / 4) of the targeted wavelength, or (xiii) a half (1 / 2) of the targeted wavelength, wherein (xiv) a maximum optical thickness the suppressor layer is configured to have an optical thickness represented by the formula: wherein: to , is the maximum optical thickness ofthe suppressor layer in nanometer (nm); , is the target wavelength sough to be suppressed; andnhigh, is the refractive index of the first layer, or second layer having a higher refractive index, wherein (xv) the optical filter with increased selectivity to the predetermined wavelength is configured to form a top plan view in the shape of a circle, or a polygon having between 3 and 6 facets, the method further comprising (xvi) depositing a plurality of the optical filters, wherein each optical filter is operable to filter a different target wavelength, wherein (xvii) the first layer, or the second layer is comprised of Titanium oxide (TiO2), Magnesium Fluoride (MgFo), Aluminum sequioxide (AI2O3), Silicon Dioxide (SiO2), Tantalum pentoxide (Ta2O5), Niobium pentoxide (Nb2O5), Zirconium dioxide (ZrCL), Hafnium dioxide (HfCL), Yttrium oxide (Y2O3), Silicon nitride (Si3N4), Zinc sulfide (ZnS), cryolite (NasAIFe), Cerium fluoride (CcFq, Indium tin oxide (ITO), or Aluminum nitride (AIN), (xviii) the suppressor layer is formed of Silicon dioxide (SiO2), Poly(methylmethacrylate) (PMMA), Air, Silicon nitride (Si3N4), Magnesium fluoride (MgF2), Aluminum oxide (AI2O3), Titanium dioxide (TiO2), cryolite (Na3AIF6), or a Low-index fluoride material, and wherein (xix) the substrate has a transparency that depends on the target wavelength.

[0069] While in the foregoing specification the devices, systems and methods of forming etch masks having fine features at the substrate level, using direct atomic layer processing (DALP), have been described in relation to certain preferred exemplary implementations, and many details are setforth for purpose of illustration, it will be apparent to those skilled in the art that the disclosure is susceptible to additional exemplary implementations and that certain of the details described in this specification and as are more fully delineated in the following claims can be varied considerably without departing from the basic principles of this disclosure.

Claims

What is Claimed:

1. A method of forming an optical filter, implemented with a microreactor direct atomic layer deposition (μDALP) system, the method comprising using the μDALP system, depositing a plurality of alternating layers of a material having a predetermined refractive index on a substrate, wherein the optical thickness of the deposited layer of each material is proportional to a fraction of a target wavelength sought to be filtered, the plurality of alternating layers of the material are each having a predetermined refractive index configured to create constructive interference or transmission at the target wavelength for an incident light.

2. The method of claim 1, wherein the optical thickness of each layer is a quarter of the targeted wavelength (X / 4).

3. The method of claim 1, wherein the optical thickness of each layer is a half of the targeted wavelength (X / 2).

4. The method of claim 1, wherein the plurality of alternating layers are comprised of a first layer having a first refractive index and a second layer having a second refractive index, wherein the first refractive index is different than the second refractive index.

5. The method of claim 4, wherein a total number of alternating layers is between 6 and 120.

6. The method of claim 5, further comprising a step of depositing a layer, adapted, sized, and configured to suppress or amplify a wavelength reflection at a central frequency, thereby forming a suppressor layer.

7. The method of claim 6, wherein the suppressor layer is configured to have an optical thickness represented by the formula:wherein: to , is the optical thickness of the suppressor layer in nanometer (nm); λtarget, is the target wavelength sough to be suppressed; and nhigh, is the refractive index of the first layer, or second layer having a higher refractive index.

8. The method of claim 4, wherein the step of depositing the plurality of alternating layers of the first layer and the second layer is configured to form the optical filter with a top plan view in the shape of a circle, or a polygon having between 3 and 6 facets.

9. The method of claim 8, further comprising depositing a plurality of the optical filters, wherein each optical filter is operable to filter a different target wavelength.

10. The method of claim 4, wherein the first layer, or the second layer is comprised of Titanium oxide (TiO2), Magnesium Fluoride (MgF2), Aluminum sequioxide (AI2O3), Silicon Dioxide (SiO2), Tantalum pentoxide (Ta2O5), Niobium pentoxide (Nb2O5), Zirconium dioxide (ZrO2), Hafnium dioxide (HfCL), Yttrium oxide (Y2O3), Silicon nitride (Si3N4), Zinc sulfide (ZnS), cryolite (Na3AIF6), Cerium fluoride (CcF.?). Indium tin oxide (ITO), or Aluminum nitride (AIN).

11. The method of claim 7, wherein the suppressor layer is formed of Silicon dioxide (SiO2), Poly(methylmethacrylate) (PMMA), Air, Silicon nitride (Si3N4), Magnesium fluoride (MgF2), Aluminum oxide (AI2O3), Titanium dioxide (TiO2), cryolite (Na3AIF6), or a Low-index fluoride material.

12. The method of claim 1, wherein the substrate has a transparency that depends on the target wavelength.

13. A method of increasing selectivity of an optical filter to a predetermined wavelength, implemented with a microreactor direct atomic layer deposition (μDALP) system, the method comprising using the μDALP system: a. on a substrate, depositing a plurality of alternating layers comprised of a first layer material having a first refractive index and a second layer material having a second refractive index, the first layer material, and the second layer material each having an increasing optical thickness along a deposition direction; and b. depositing a suppressor layer, adapted, sized, and configured to suppress the predetermined wavelength, wherein the suppressor layer has an optical thickness that increases along the deposition direction, thereby forming an optical filter with increased selectivity to the predetermined wavelength.

14. The method of claim 13, wherein a maximum optical thickness of each of the first layer material, and the second layer material is a quarter (1 / 4) of the targeted wavelength.

15. The method of claim 13, wherein a maximum optical thickness of each of the first layer material, and the second layer material is a half (1 / 2) of the targeted wavelength.

16. The method of claim 13, wherein a maximum optical thickness the suppressor layer is configured to have an optical thickness represented by the formula:wherein: to , is the maximum optical thickness of the suppressor layer in nanometer (nm);^target , is the target wavelength sough to be suppressed; and nhigh, is the refractive index of the first layer, or second layer having a higher refractive index.

17. The method of claim 13, wherein the optical filter with increased selectivity to the predetermined wavelength is configured to form a top plan view in the shape of a circle, or a polygon having between 3 and 6 facets.

18. The method of claim 17, further comprising depositing a plurality of the optical filters, wherein each optical filter is operable to filter a different target wavelength.

19. The method of claim 13, wherein the first layer, or the second layer is comprised of Titanium oxide (TiO2), Magnesium Fluoride (MgF2), Aluminum sequioxide (AI2O3), Silicon Dioxide (SiO2), Tantalum pentoxide (Ta2O5), Niobium pentoxide (Nb2O5), Zirconium dioxide (ZrCh), Hafnium dioxide (HfCh), Yttrium oxide (Y2O3), Silicon nitride (Si3N4), Zinc sulfide (ZnS), cryolite (Na3AIF6), Cerium fluoride (CeF3), Indium tin oxide (ITO), or Aluminum nitride (AIN).

20. The method of claim 19, wherein the suppressor layer is formed of Silicon dioxide (SiO2), Poly(methylmethacrylate) (PMMA), Air, Silicon nitride (Si3N4), Magnesium fluoride (MgF2), Aluminum oxide (AI2O3), Titanium dioxide (TiO2), cryolite (Na^AIFe), or a Low-index fluoride material.

21. The method of claim 13, wherein the substrate has a transparency that depends on the target wavelength.

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