TECHNICAL FIELD

The present disclosure generally pertains to a metalens portion, an electronic device and a method.

TECHNICAL BACKGROUND

Metasurfaces have attracted interest in recent years, since may enable precise control of optical wavefronts and are easy to fabricate with conventional microfabrication technology in a flat, thin, and light weight form factor. Various conventional devices such as gratings and lenses have been demonstrated using metasurfaces. These optical elements are typically composed of large numbers of scatterers, or meta-atoms placed on a two-dimensional lattice to locally shape optical wavefronts. A metalens design is basically a nanostructure applied to a substrate that allows controlling the wave- front to derive the lens function.

Generally, metalenses are known and used for providing a (micro)lens on, e.g., image sensors.

Metalenses may include refractive indexes which are smaller than one and they may be based on a plurality of nanopillars which are imprinted on a substrate. The nanopillars may include TiCh is ma- terial with an exemplary pillar diameter ranging from 50 to 340 nm and a pillar height of 600 nm. However, due to the structure of the nanopillars (small and thin), known metalenses typically may have a low mechanical stability.

Although there exist techniques for manufacturing metalenses, it is generally desirable to provide a metalens portion, an electronic device and a method, e.g., for providing metalenses with a high me- chanical stability.

SUMMARY

According to a first aspect the disclosure provides a metalens portion comprising a plurality of holes in a first substrate, wherein at least two holes of the plurality of holes differ in size, and wherein a refractive index of the metalens portion is defined by at least one of shape of the holes and an ar- rangement pattern of the holes, thereby providing a metalens.

According to a second aspect the disclosure provides an electronic device, comprising a second sub- strate; and a metalens portion including a plurality of holes in a substrate, wherein at least two holes of the plurality of holes differ in size, and wherein a refractive index of the metalens portion is de- fined by at least one of shape of the holes and an arrangement pattern of the holes, thereby provid- ing a metalens. According to a third aspect the disclosure provides a method for manufacturing a metalens portion, comprising: providing a plurality of holes in a first substrate, wherein at least two holes of the plural- ity of holes differ in size, and wherein a refractive index of the metalens portion is defined by at least one of shape of the holes and an arrangement pattern of the holes, thereby providing a metalens function.

Further aspects are set forth in the dependent claims, the following description and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are explained by way of example with respect to the accompanying drawings, in which:

Fig. 1 shows a metalens as it is generally known;

Fig. 2 shows a metalens according to the present disclosure;

Fig. 3 shows an electronic device according to the present disclosure;

Fig. 4 shows a method according to the present disclosure;

Fig. 5 shows a camera device according to the present disclosure; and

Fig. 6 is flowchart of a method for providing a plurality of holes as nanopores.

DETAILED DESCRIPTION OF EMBODIMENTS

Before a detailed description of the embodiments under reference of Fig. 1 is given, general explana- tions are made.

As mentioned in the outset, metalenses are generally known. It has been recognized that known metalenses have a low mechanical stability.

Therefore, some embodiments pertain to a metalens portion including a plurality of holes in a first substrate, wherein at least two holes of the plurality of holes differ in size, and wherein a refractive index of the metalens portion is defined by at least one of shape of the holes and an arrangement pattern of the holes, thereby providing a metalens.

As mentioned, a metalens may include a structured arrangement on a nanometer or micrometer scale (which may also be referred to as meta-material) and the metalens may have a refractive index, due to their structure, which is smaller than one. In principle, the metalens may provide a lens func- tion, as generally known. In more detail, in some embodiments, metasurfaces, which may be used for providing a metalens function, are typically thin optical components that rely on a different ap- proach for light control: A dense arrangement of subwavelength resonators is designed to modify the optical response of the interface. The resonant nature of the scatterers introduces an abrupt phase shift in the incident wavefront, making it possible to mold the scattered wavefront at will and enabling a new class of planar photonics components -flat optics. The metasurface approach may be distinct in that it provides continuous control of the phase profile (i.e., from 0 to 2p) with a binary structure (only two levels of thickness), circumventing the fundamental limitation of multiple dif- fraction orders while maintaining the size, weight, and ease-of-fabrication advantages of planar dif- fractive optics. However, metasurface-based optical devices demonstrated so far may be affected by chromatic aberrations, but research efforts have also shown that relatively broadband optical metasurfaces can be achieved.

The metalens portion may provide a lens function of an optical device, wherein the lens function is achieved by a nanostructuring or a microstructuring of a substrate material, which is suitable to transmit light of specific wavelengths (e.g. red , green, infrared, 430 nm) or a range of wavelengths (e.g. visible light, microwaves, 450 nm to 500 nm). The lens may transmit all the incident light (i.e. transmission of 100 %), or only a fraction of the incident light (e.g. 50 %).

The first substrate may include a metal, such as silicon, titanium, aluminum, or the like, which is known to be processed to have desired metalens properties (e.g. transmissibility of tight, processable to be nano- or microstructured, and the tike), for example by oxidation, nitration, arsenation, or the tike.

The metalens portion may include a single metalens or a plurality of metalenses arranged side-by- side in order to enlarge a light incident area and/ or arranged in series, as it is known from (common) lenses.

The plurality of holes may refer to any number of holes, which is suitable for providing a metalens function (e.g. 100 without limiting the present disclosure in that regard), wherein a hole refers to a through hole, a pit, a cavity, or the tike, in the first substrate material, as described above. In this context, the nanostructuring or the microstructuring refers to providing the plurality of holes.

At least two holes may differ in size. In general, every hole may differ in size or at least one subset may have a first common size, whereas another subset may have a second common size, or the tike.

A size may refer to at least one of shape of the holes, such as diameter, height, depth, geometry, or the like, and by providing different sizes of the holes, different optical properties may be locally achieved, such as a locally differing refractive index. Also, the (locally differing) refractive index of the lens may be defined by an arrangement pattern of the plurality of holes, e.g. a ring like arrangement, circular arrangement, triangular arrangement, rec- tangular arrangement, or the like.

Thereby, lens errors, such as aberrations, distortions, or the like may be compensated for.

For example, the plurality of holes may be through holes which have a cylindrical shape and are ar- ranged on concentric rings around a center of the metalens, wherein the radius of the holes is the same for the holes on each ring, but among the rings the radius may differ. Thereby each concentric ring has another refractive index.

In some embodiments, the first substrate includes an oxide, as described above, wherein the oxide may include at least one of titanium and aluminum, as described herein.

In some embodiments, the arrangement pattern includes concentric rings, as described herein.

In some embodiments, the shape of the holes is defined by at least one of height and diameter, as described herein. Moreover, depending on the geometry of the holes, the holes may have more than one height or diameter or other parameters may be used in order to characterize the holes, such as curvature, or the like.

In some embodiments, the metalens portion further includes a plurality of refractive indexes on the metalens portion, wherein the refractive indexes increase from a middle of the metalens portion to a predetermined distance from the middle of the metalens.

For example, the metalens portion may include three different refractive indexes, the first (smallest) refractive index in the middle, a second smallest refractive index on a first ring around the middle, a largest refractive index on a second ring around the middle, wherein the radius of the second ring is larger than the radius of the first ring. On a third ring with the largest radius, the first (smallest) re- fractive index may, however, be found again, since the holes have the same shape and size as in the middle.

Some embodiments pertain to an electronic device (e.g. an image sensor, camera, mobile phone, or any other type of electronic device), including a second substrate; and a metalens portion including a plurality of holes in a first substrate, wherein at least two holes of the plurality of holes differ in size, and wherein a refractive index of the metalens portion is defined by at least one of shape of the holes and an arrangement pattern of the holes, thereby providing a metalens, as described herein.

The second substrate may be another metalens portion, an optical device, such as an image sensor, or the like. The second substrate may be the same substrate as the first substrate, but in other em- bodiments, the second substrate is different from the first substrate. In some embodiments, the second substrate and the metalens portion (which may each may also be a wafer) are mounted onto each other. The mounting may be achieved with known techniques, for example bonding between a device or substrate including the metalens portion and the second sub- strate, wherein the bonding may be one of the following: plasma activated bonding, direct bonding, adhesive bonding, anodic bonding, eutectic bonding, glass frit bonding, thermocompression bond- ing, transient liquid phase diffusion bonding, surface activated bonding, or the like.

In some embodiments, the electronic device includes circuitry configured to process a photoelectric signal generated in the electronic device, such as a photodiode, an photoconversion unit, transistors, floating diffusions, and the like, suitable for processing a signal which may be generated in response to light, which is transmitted through the transparent optical portion. Thereby, a function of an im- aging device or a part of an imaging device may be achieved.

In some embodiments, the second substrate is a semiconductor substrate, such as silicon, silicon compounds, or other semiconductor substrates known in the art, whereby known methods may be utilized, wherein the circuitry may be formed on the second substrate, such that the first substrate (metalens portion) and the second substrate may be manufactured independently from each other.

Some embodiments pertain to a method for manufacturing a metalens portion, comprising:

providing a plurality of holes in a first substrate, wherein at least two holes of the plurality of holes differ in size, and wherein a refractive index of the metalens portion is defined by at least one of shape of the holes and an arrangement pattern of the holes, thereby providing a metalens function, as described herein.

In some embodiments the providing of the plurality of holes includes a molding of the plurality of holes, wherein the plurality of holes are molded in a mold.

The molding may be performed by any known molding technique, such as casting, cold defor- mation, hot deformation, spray cast, injection molding, or the like. The mold may be a negative of the metalens portion, wherein the first substrate may be casted around a plurality of protrusions (e.g. nanopillars), or the like.

Therefore, in some embodiments the mold includes a plurality of protrusions and the plurality of holes is molded based on the plurality of protrusions. Thereby, known techniques of providing na- nopillars may be the basis of the mold.

The providing of the plurality of holes may further be based on chemical etching methods, na- nopore generation, electrochemical anodization, and the like. Hence, some embodiments, provide the same wavefront construction efficiency as in“normal” pil- lar based metasurfaces, discussed above, the mechanical stability may be improved due to a continu- ous material surface, which is only interrupted by wholes, and/ or the fabrication by

photolithography and chemical etching methods may reduce costs and manufacturing complexity, since such methods are well-established.

Returning to Fig. 1, there is shown a metalens 1, as it is generally known. The metalens 1 includes a plurality of nanopillars 2 including titanium oxide. The nanopillars 2 differ in their sizes, thereby providing different refractive indexes on the metalens, as it is shown in another representation 1’ of the metalens 1. The metalens 1' depicts the distribution of refractive indexes n ₁ , n ₂ , n ₃ , n ₄ , wherein the refractive indexes are based on the size of the corresponding nanopillars, such that the refractive index m is found in the middle of the metalens and on the outer ring of the metalens. Moreover, in the metalens 1', the refractive index becomes smaller from the middle of the lens to the outside (ex- cept for the outer ring), which is depicted with a corresponding density of the respective hachures of the rings, i.e. n ₁ > n ₂ > n ₃ > n ₄ . Furthermore, the refractive index of air is bigger than m.

Fig. 2 depicts a metalens 3 according to an embodiment of the present disclosure. The metalens in- cludes a substrate 4 including titanium oxide and a plurality of through holes, which are manufac- tured with electrochemical anodization. The substrate has a thickness of 600 nanometers. Moreover, the through holes differ in their respective sizes, thereby providing different refractive indexes on the metalens, as it is shown in the representation 3’ of the metalens 3. The metalens 3’ depicts a dis- tribution of refractive indexes n ₁ ’, n ₂ ’, n ₃ ’, n ₄ ’, similar to the distribution of refractive indexes of Fig.

1. However, the refractive indexes become larger from the middle to the outside, with exception of the outer ring, i.e. n ₁ ’ < n ₂ ’ < n ₃ ’ < n ₄ ’.

Fig. 3 shows a cross section of an electronic device 10 according to the present disclosure. The elec- tronic device 10 includes a metalens portion 11, which in turn includes a plurality of holes 12 through a first substrate 13 including titanium oxide.

The metalens portion 11 is mounted to a semiconductor device 14 (second substrate), as it is gener- ally known, including silicon and further including circuitry (not depicted) to process a photoelectric signal. The mounting may involve a bonding process, for example, between a device including the metalens portion 11 and the semiconductor device.

Fig. 4 shows a method 20 for providing a plurality of holes for the production of a metalens portion according to the present disclosure.

In 21, a mold is formed by a photolithographic imprinting of nanopillars, as it is generally known. In 22, the imprinted nanopillars are coated in order to have a low adhesion with the substrate, which is casted on the mold in 23. In this embodiment, the substrate includes titanium oxide, wherein the substrate is melted before it is casted.

In 24, the substrate is equilibrated, i.e. in this case, cooled down, such that it is in a state where it can be removed from the mold.

In 25, the substrate is removed and thereby the metalens is provided.

Fig. 5 shows a camera device 30 according to the present disclosure including the electronic device 10 of Fig. 3, a processor 31 (circuitry) to process a photoelectric signal generated in the electronic device, and an optical stack to focus light which is then transmitted to the electronic device 10. The camera device 30 may further include other parts, such as a flash, a display, or the like, which may be apparent to a person skilled in the art.

Fig. 6 is a flowchart of another method 40 for providing a plurality of holes for the production of a metalens portion, wherein the plurality of holes are formed as nanopores.

At 41, a silicon substrate is provided.

At 42, poly(methylmethacrylate) (PMMA) is spin-coated on the silicon (Si) substrate.

At 43, an anodic aluminum oxide (AAO) membrane is provided as an etching mask on the PMMA layer. The etching mask is such configured that it includes the pattern of the to be formed plurality of holes.

At 44, a contact printing is performed for providing a conformal contact of the AAO membrane mask to the Si substrate.

At 45, a CF ₄ plasma etching is conducted for transferring nanopores onto the SI substrate through the PMMA layer, thereby generating the nanopores.

It should be recognized that the embodiments describe methods with an exemplary ordering of method steps. The specific ordering of method steps is however given for illustrative purposes only and should not be construed as binding. For example the ordering of 21 and 22 in the embodiment of Fig. 4 may be exchanged. Other changes of the ordering of method steps may be apparent to the skilled person.

Please note that the division of the camera device 30 into units 10, 31 and 32 is only made for illus- tration purposes and that the present disclosure is not limited to any specific division of functions in specific units. For instance, the camera device 30 could be implemented by a respective programmed processor, field programmable gate array (FPGA) and the like. AH units and entities described in this specification and claimed in the appended claims can, if not stated otherwise, be implemented as integrated circuit logic, for example on a chip, and functionality provided by such units and entities can, if not stated otherwise, be implemented by software.

Note that the present technology can also be configured as described below.

(1) A metalens portion comprising a plurality of holes in a first substrate, wherein

at least two holes of the plurality of holes differ in size, and wherein

a refractive index of the metalens portion is defined by at least one of shape of the holes and an arrangement pattern of the holes, thereby providing a metalens.

(2) The metalens portion of (1), wherein the first substrate includes an oxide.

(3) The metalens portion of anyone of (1) or (2), wherein the oxide includes at least one of tita- nium and aluminum.

(4) The metalens portion of anyone of (1) to (3), wherein the arrangement pattern includes con- centric rings.

(5) The metalens portion of anyone of (1) to (4), wherein the shape of the holes is defined by at least one of height and diameter.

(6) The metalens portion of anyone of (1) to (5), further comprising a plurality of refractive in- dexes on the metalens portion, wherein the refractive indexes increase from a middle of the metalens portion to a predetermined distance from the middle of the metalense.

(7) An electronic device, comprising:

a second substrate; and

a metalens portion including a plurality of holes in a substrate, wherein at least two holes of the plurality of holes differ in size, and wherein a refractive index of the metalens portion is defined by at least one of shape of the holes and an arrangement pattern of the holes, thereby providing a metalens.

(8) The electronic device of (7), wherein the second substrate and the metalens portion are mounted onto each other.

(9) The electronic device of anyone of (7) or (8), further comprising circuitry configured to pro- cess a photoelectric signal generated in the electronic device.

(10) The electronic device of anyone of (7) to (9), wherein the second substrate is a semiconduc- tor substrate.

(11) The electronic device of anyone of (7) to (10), wherein the second substrate includes silicon. (12) A method for manufacturing a metalens portion, comprising:

providing a plurality of holes in a Srst substrate, wherein at least two holes of the plurality of holes differ in size, and wherein a refractive index of the metalens portion is defined by at least one of shape of the holes and an arrangement pattern of the holes, thereby providing a metalens func- tion.

(13) The method of (12), wherein the providing of the plurality of holes includes a molding of the plurality of holes, wherein the plurality of holes are molded in a mold.

(14) The method of anyone of (12) or (13), wherein molding includes casting of the first sub- strate.

(15) The method of anyone of (12) to (14), wherein the mold includes a plurality of protrusions and the plurality of holes is molded based on the plurality of protrusions.

(16) The method of anyone of (12) to (15), wherein the providing of the plurality of holes in- cludes a chemical etching of the holes.

(17) The method of anyone of (12) to (16), wherein the providing of the plurality of holes in- eludes nanopore generation.

(18) The method of anyone of (12) to (17), wherein the providing of the plurality of holes in- cludes electrochemical anodization.