JP2019174552A - Metamaterial optical element and method for manufacturing the same - Google Patents

Abstract

To provide a metamaterial optical element capable of obtaining excellent optical properties in a terahertz band, and a method for manufacturing the same.SOLUTION: A metamaterial optical element 1 having a first surface 2s and a second surface 2r on the opposite side of the first surface 2s comprises: a thin film part 2 including silicon; a first metal pattern 3 formed on the first surface 2s and having a periodic structure; a second metal pattern 4 formed on the second surface 2r so as to overlap with the first metal pattern 3 when viewed from a direction intersecting the first surface 2s and having a periodic structure; and a frame part 5 provided in an edge portion of the first surface 2s or the second surface 2r and supporting the thin film part 2.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a metamaterial optical element and a method for producing a metamaterial optical element.

  Currently, by using terahertz band electromagnetic waves, it is expected to realize a so-called non-destructive and non-contact imaging technique that is higher resolution than millimeter waves and less invasive than X-rays. However, in general, the types of optical elements (for example, lenses and polarizers) that can be used in the terahertz band are fewer than the types of optical elements for visible light and infrared light. This is because the optical materials that can be used in the terahertz band are limited.

  On the other hand, as an optical element that can be used in the terahertz band, an element using a metamaterial can be considered. Metamaterial is a technology that produces a structure smaller than the wavelength and controls its dielectric constant and permeability. According to the metamaterial, it is possible to control the refractive index without being restricted by the material characteristics specific to the substance. Therefore, by using a metamaterial, an optical element that can be used in the terahertz band without being restricted by the optical material can be provided. As an optical element using such a metamaterial, an optical element having a structure in which metal patterns are arranged on both surfaces of a dielectric substrate is known (for example, Patent Document 1).

JP 2017-34584 A

  In Patent Document 1, a flexible cycloolefin polymer film having a thickness of about 23 μm to 50 μm is cited as a dielectric substrate. However, when the thickness of the dielectric substrate is about 23 μm to 50 μm as a metamaterial parameter, good optical characteristics may not be obtained in a high frequency region of about 1.5 THz to 3 THz, for example. On the other hand, if the thickness of the dielectric substrate is reduced to about several μm, it is considered that good optical characteristics can be obtained even in the high frequency region, but considering that the cycloolefin polymer film is produced by extrusion molding. Then, it is difficult to make the dielectric substrate thin to about several μm.

  The present invention has been made in view of such circumstances, and provides a metamaterial optical element capable of obtaining good optical characteristics in the terahertz band, and a method for manufacturing the metamaterial optical element. Objective.

  The metamaterial optical element according to the present invention has a first surface and a second surface opposite to the first surface, a thin film portion containing silicon, and a first metal formed on the first surface and having a periodic structure. The pattern is formed on the second surface so as to overlap the first metal pattern when viewed from the direction intersecting the first surface, and the second metal pattern having a periodic structure and the edge of the first surface or the second surface And a frame portion that supports the thin film portion.

  In this metamaterial optical element, a first metal pattern and a second metal pattern having a periodic structure are formed on each of the first surface and the second surface of the thin film portion. In particular, in this metamaterial optical element, the thin film portion contains silicon. For this reason, the thickness of the thin film portion can be controlled to about several μm by, for example, polishing and grinding using a semiconductor process. Furthermore, a frame portion that supports the thin film portion is provided on the first surface or the second surface of the thin film portion. For this reason, thinning of a thin film part is reliably realizable, hold | maintaining intensity | strength by a frame part. Therefore, according to this metamaterial optical element, it is possible to obtain good optical characteristics in the terahertz band including the high frequency region.

  In the metamaterial optical element according to the present invention, the frame portion is configured separately from the thin film portion, and may be bonded to the first surface or the second surface. In this case, the first and second metal patterns can be easily formed in a state where the frame portion is not joined to the thin film portion.

  In the metamaterial optical element according to the present invention, the frame portion may be configured integrally with the thin film portion. In this case, it is possible to simultaneously form the thin film portion and the frame portion.

  In the metamaterial optical element according to the present invention, the frame portion may include silicon. In this case, the frame portion can be easily formed with high accuracy by using, for example, a semiconductor process.

  In the metamaterial optical element according to the present invention, the first surface and the second surface are divided into a plurality of regions arranged concentrically, and the first metal pattern and the second metal pattern are regions on the center side. It may be configured as a spherical lens for light of the target wavelength by having a periodic structure in which the refractive index increases or decreases toward the outer region from.

  Alternatively, in the metamaterial optical element according to the present invention, the first surface and the second surface are divided into a plurality of regions arranged in the first direction, and the first metal pattern and the second metal pattern are It may be configured as a cylindrical lens for light of the target wavelength by having a periodic structure in which the refractive index increases or decreases from one region in one direction toward the other region.

  As described above, the metamaterial optical element may be configured as a distributed index (GRIN) lens in which a refractive index distribution is formed over a plurality of regions of the first surface and the second surface of the thin film portion. In this case, if the number of divided regions is small, the degree of freedom in lens design is low, and good characteristics may not be exhibited. The upper limit of the number of divisions of the region becomes lower as the target wavelength becomes higher when the thickness of the thin film portion is constant. In order to increase the upper limit of the number of divisions of the region while keeping the target wavelength constant, it is one idea to thin the thin film portion.

  However, as described above, when the thin film portion is a cycloolefin polymer film, it is difficult to reduce the thickness to about several μm. As a result, the number of divisions of the region is limited by the lower limit of the thickness of the thin film portion, and it is difficult to ensure the degree of freedom in lens design. On the other hand, according to this metamaterial optical element, since the thin film portion can be reliably thinned as described above, the upper limit of the division number of the region can be sufficiently ensured. Therefore, when this metamaterial optical element is configured as a lens, the degree of freedom in lens design and good optical characteristics are sufficiently secured, which is particularly effective.

  Here, the manufacturing method of the metamaterial optical element according to the present invention includes a thin film portion having a first surface and containing silicon, a support layer laminated on the thin film portion on the opposite side of the first surface, and a first surface. A first step of preparing a base including a first metal pattern having a periodic structure, a second step of joining the base to the support member from the first surface side after the first step, and a second step After the step, a third step of exposing the second surface opposite to the first surface in the thin film portion by removing the support layer, and the first step as viewed from the direction intersecting the first surface after the third step. A fourth step of forming a second metal pattern having a periodic structure on the second surface so as to overlap with the metal pattern, and a frame portion that supports the thin film portion on the edge of the second surface after the fourth step. A fifth step of joining.

  According to this manufacturing method, a metamaterial optical element capable of obtaining good optical characteristics in the terahertz band as described above can be preferably manufactured. In particular, in this manufacturing method, the second metal pattern is formed in the fourth step on the second surface of the thin film portion exposed in the third step. And a frame part is joined to the edge of the 2nd surface in the 5th process. Thus, in this manufacturing method, in a state where the frame portion is not joined to the second surface and in a state where the thin film portion is supported by the support member on the first surface side, the second metal pattern Is formed. For this reason, a 2nd metal pattern can be formed easily, suppressing the failure | damage of a thin film part.

  Moreover, the manufacturing method of the metamaterial optical element which concerns on this invention has a 1st surface, and the thin film part which contains a silicon | silicone, the support layer laminated | stacked on the thin film part on the opposite side of the 1st surface, On the 1st surface A first step of preparing a base including a first metal pattern formed and having a periodic structure, a second step of joining the base to the support member from the first surface side after the first step, and a second step After the third step, the support layer is removed to expose the second surface opposite to the first surface in the thin film portion, and after the third step, the first metal as viewed from the direction intersecting the first surface. A fourth step of forming a second metal pattern having a periodic structure on the second surface so as to overlap with the pattern, and the support member includes a frame portion. In the second step, The thin film portion is supported on the edge portion of the first surface by bonding the portion to the edge portion. Providing a frame portion.

  According to this manufacturing method, a metamaterial optical element capable of obtaining good optical characteristics in the terahertz band as described above can be preferably manufactured. In particular, in this manufacturing method, the second metal pattern is formed in the fourth step on the second surface of the thin film portion exposed in the third step. On the other hand, in the second step, the frame portion as the support member is joined to the first surface. Thus, in this manufacturing method, the second metal pattern is formed in a state where the frame portion is not bonded to the second surface. For this reason, a 2nd metal pattern can be formed easily. Moreover, since it is not necessary to prepare and join a frame part separately from the support member, a metamaterial optical element can be manufactured in a short time and at a low cost.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the metamaterial optical element which makes it possible to acquire a favorable optical characteristic in a terahertz band, and a metamaterial optical element can be provided.

It is a figure which shows the metamaterial optical element which concerns on this embodiment. It is a figure for demonstrating the principle of operation of the metamaterial optical element shown by FIG. It is a figure for demonstrating the principle of operation of the metamaterial optical element shown by FIG. It is a top view which shows an example of the metal pattern in the metamaterial optical element shown by FIG. It is a top view for illustrating a metal pattern. It is sectional drawing which shows the 1st example of the manufacturing method of the metamaterial optical element shown by FIG. It is sectional drawing which shows the 1st example of the manufacturing method of the metamaterial optical element shown by FIG. It is sectional drawing which shows the 1st example of the manufacturing method of the metamaterial optical element shown by FIG. It is sectional drawing which shows the 2nd example of the manufacturing method of the metamaterial optical element shown by FIG. It is sectional drawing which shows the 1st modification of the manufacturing method of a metamaterial optical element. It is sectional drawing which shows the 2nd modification of the manufacturing method of a metamaterial optical element. It is a figure which shows the 3rd modification of the manufacturing method of a metamaterial optical element. It is a figure which shows the 3rd modification of the manufacturing method of a metamaterial optical element. It is a figure which shows the 3rd modification of the manufacturing method of a metamaterial optical element. It is sectional drawing of the example which comprised the metamaterial optical element shown by FIG. 1 as a band pass filter. It is a figure which shows the optical apparatus using the metamaterial optical element shown by FIG.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In each figure, the same elements or corresponding elements may be denoted by the same reference numerals, and redundant description may be omitted.

  FIG. 1 is a diagram showing a metamaterial optical element according to the present embodiment. 1A is a perspective view, and FIG. 1B is a schematic cross-sectional view taken along line Ib-Ib in FIG. 1A. As shown in FIG. 1, the metamaterial optical element 1 includes a thin film portion 2, a first metal pattern 3, a second metal pattern 4, and a frame portion 5. The thin film portion 2 includes a first surface 2s and a second surface 2r opposite to the first surface 2s. The thin film portion 2, the first surface 2s, and the second surface 2r are rectangular.

  The thickness of the thin film portion 2 (the distance between the first surface 2s and the second surface 2r) is, for example, about several μm (for example, 1 μm to 10 μm). The thin film portion 2 is made of a dielectric material that does not absorb the terahertz band. The thin film part 2 contains silicon. The thin film portion 2 is, for example, a silicon layer (high resistance Si layer) in an SOI substrate.

  The first metal pattern 3 is formed on the first surface 2s. The first metal pattern 3 has a plurality of first metal portions 3p. The first metal portions 3p are each formed in a rectangular parallelepiped shape having a short side direction and a long side direction. The first metal parts 3p are two-dimensionally arranged along the short side direction and the long side direction. The first metal portion 3p can be made of any metal having high electrical conductivity and low light loss, but is made of, for example, Au, Ag, Cu, or Al. The first metal pattern 3 has a periodic structure corresponding to the size and arrangement of the first metal portions 3p.

  The second metal pattern 4 is formed on the second surface 2r. The second metal pattern 4 overlaps the first metal pattern 3 when viewed from the direction intersecting (orthogonal) with the first surface 2s and the second surface 2r. More specifically, the second metal pattern 4 has a plurality of second metal portions 4p arranged two-dimensionally on the second surface 2r. Each of the second metal parts 4p faces the first metal part 3p with the thin film part 2 interposed therebetween. The shape and position of the second metal part 4p are the same shape and position as the opposing first metal part 3p. Thereby, the 1st metal pattern 3 and the 2nd metal pattern 4 overlap mutually. The first metal pattern 3 and the second metal pattern 4 are formed in a region R (here circular) of the first surface 2s and the second surface 2r. The second metal part 4p can be made of the same material as the first metal part 3p, for example.

  The frame part 5 is provided at the edge of the thin film part 2. More specifically, the frame 5 is formed in a rectangular ring shape, and is provided at the edge of the second surface 2r so that the second metal pattern 4 is exposed from the opening 5h. The frame part 5 may be configured separately from the thin film part 2 or may be configured integrally with the thin film part 2. When the frame part 5 is configured separately from the thin film part 2, the frame part 5 is bonded to the second surface 2r by bonding using an adhesive, anodic bonding, direct bonding, or the like. As the adhesive, for example, in addition to an adhesive such as an epoxy resin, an organic resin such as BCB (Benzo-Cyclobutene), an inorganic material such as water glass, and a metal such as solder can be used. . In this case, the material of the frame part 5 is not limited, but the frame part 5 contains silicon as an example.

  If the material of the frame part 5 is a material having a thermal expansion coefficient close to that of the thin film part 2, the difference in thermal expansion coefficient at the joint between the frame part 5 and the thin film part 2 is reduced. For this reason, joining at high temperature becomes possible, and joining strength improves. On the other hand, when the frame portion 5 is configured integrally with the thin film portion 2, it can be formed together with the formation of the thin film portion 2 by etching of the SOI substrate, for example. Also in this case, the frame portion 5 contains silicon (which is a Si support substrate of an SOI substrate).

  2 and 3 are diagrams for explaining the operation principle of the metamaterial optical element shown in FIG. 2A is a perspective view of a unit cell of the metamaterial optical element, and FIG. 2B is a cross-sectional view of the unit cell. FIG. 3A is a schematic diagram for explaining a change in dielectric constant, and FIG. 3B is a schematic diagram for explaining a change in magnetic permeability. As shown in FIGS. 2 and 3, the unit cell C includes a pair of first metal part 3p and second metal part 4p facing each other, and a first metal part 3p and a second metal part 4p in the thin film part 2. And a portion 2p located therebetween.

  When light enters the metamaterial optical element 1, a current I is generated in the first metal part 3p on the same surface (for example, on the first surface 2s) due to the interaction with the electric field E of the incident light. As a result, a charge bias occurs in the first metal part 3p, and the electric flux density changes. As a result, the intrinsic dielectric constant of the substance changes. Further, when light enters the metamaterial optical element 1, an annular current I is generated in the first metal part 3p and the second metal part 4p of the unit cell C due to the interaction with the magnetic field H of the incident light. As a result, magnetic flux is generated, and the magnetic permeability inherent to the substance changes. Accordingly, the refractive index can be controlled without being restricted by the material characteristics specific to the substance, and for example, it can be used in a terahertz band including a high frequency region (1.5 THz to 3 THz).

  FIG. 4 is a plan view showing an example of a metal pattern in the metamaterial optical element shown in FIG. As shown in FIG. 4, here, the metamaterial optical element 1 is configured as a distributed index (GRIN) lens. This will be described more specifically. The region R in which the first metal pattern 3 and the second metal pattern 4 are formed on the first surface 2s and the second surface 2r of the thin film portion 2 is a plurality of (here, nine) regions R1 to R1 arranged concentrically. It is divided into R9. As an example, the number of divisions of the region R is 5 or more, more preferably 7 or more. The region R1 is a circular region disposed at the center of the region R, and the other regions R2 to R9 are concentric annular regions.

Here, the metamaterial optical element 1 has a periodic structure in which the first metal pattern 3 and the second metal pattern 4 have a refractive index that decreases from the central region R1 toward the outer region R2. This will be described more specifically. The width of the first metal portion 3p and W _n, the gap of the first metal portion 3p adjacent to each other along the longitudinal direction of the first metal portion 3p and gx _k, along the widthwise direction of the first metal portion 3p The gap between the first metal portions 3p adjacent to each other is defined as a gap gy _p, and the length of the first metal portion 3p is defined as l _q (in the drawing, n, k, p, q = 1 to 3, and 1 to 1 as a whole). 9).

Here, in the region R1~ area R9, while a constant width _{W n} and gap gy _p, by changing the length _{l q} and gap gx _k, adjusting the refractive index and transmittance. In this case, the effective refractive index is largely changed by the change in the gap gx _k. Change in length l _q is used for fine adjustment. Qualitatively, the gap gx _k is the refractive index is increased if small, there is a tendency in which the refractive index is lower the greater the gx _k. Therefore, when the metamaterial optical element 1 is configured as a convex spherical lens (convex lens), the refractive index n _m (m = 1 to 9) decreases from the central region R1 toward the outer region R9. to manner, to form a periodic structure by placing a first metal portion 3p as gap gx _k increases. The same applies to the second metal portion 4p (the same applies to the following description).

FIG. 5 is a plan view for illustrating a metal pattern. FIG. 5 shows an example in which the region R is divided into four regions R1 to R4 for the sake of simplicity. (A) of FIG. 5 is an example in the case of configuring the metamaterial optical element 1 as a convex spherical lens as described above. When configuring the convex lens, as the center of the region R1 toward the outside of the region R4, placing a first metal portion 3p as gap gx _k increases. As a result, the respective refractive indexes are changed from the maximum n ₁ to the minimum n ₄ (so as to decrease) from the central region R 1 toward the outer region R ₄ .

The example of (b) of FIG. 5 is an example in the case where the metamaterial optical element 1 is configured as a concave spherical lens (concave lens). In this case, as the center of the region R1 toward the outside of the region R4, placing a first metal portion 3p as gap gx _k decreases. As a result, the refractive index is changed from the minimum n ₄ to the maximum n ₁ (increase) from the central region R 1 toward the outer region R ₄ .

The example of (c) of FIG. 5 is an example in the case where the metamaterial optical element 1 is configured as a cylindrical lens. In this case, the region R is formed in a rectangular shape, and is divided into a plurality of rectangular regions R1 to R4 arranged along the longitudinal direction (first direction) of the first metal portion 3p. . Here, only one side of the center line of the region R is shown, but the other side is the same. Then, as the center of the region R1 toward the outside of the region R4, placing a first metal portion 3p as gap gx _k increases. As a result, the respective refractive indexes are changed from the maximum n ₁ to the minimum n ₄ (so as to decrease) from the central region R 1 toward the outer region R ₄ .

Then, the 1st example of the manufacturing method of the metamaterial optical element 1 is demonstrated. FIGS. 6-8 is sectional drawing which shows the 1st example of the manufacturing method of the metamaterial optical element shown by FIG. As shown in FIG. 6A, in the first example, first, the base 10 is prepared (first step). The base 10 includes a thin film portion 2, a support layer 11 laminated on the thin film portion 2 on the second surface 2 r side (the opposite side of the first surface) of the thin film portion 2, and between the thin film portion 2 and the support layer 11. And an intermediate layer 12 interposed. The substrate 10 is an SOI substrate as an example. In this case, the supporting layer 11 is a Si support substrate, the intermediate layer 12 is an insulating layer such as SiO ₂ (etching stop layer), thin-film portion 2 is a high-resistance Si layer. The thickness of the thin film portion 2 (high resistance Si layer) is several μm.

  Subsequently, as shown in FIG. 6B, the first metal pattern 3 is formed on the first surface 2s of the thin film portion 2 (first process). As a result, the thin film portion 2, the support layer 11 laminated on the thin film portion 2 on the opposite side of the first surface 2s of the thin film portion 2, and the first metal pattern 3 formed on the first surface 2s and having a periodic structure. Are prepared (first step).

  Subsequently, as shown in FIG. 7A, a support member M is prepared (second step). Here, the support member M is a transparent substrate for temporary bonding having a bonding surface Ms wider than the first surface 2s. Subsequently, the base body 20 is joined to the support member M from the first surface 2s side (second step). Here, the top of the first metal pattern 3 on the first surface 2s is bonded to the bonding surface Ms. In addition, here, as an example, the first metal pattern 3 and the bonding surface Ms are pasted with wax (temporary bonding).

Subsequently, as shown in FIG. 7B, the support layer 11 and the intermediate layer 12 are removed from the substrate 20 by etching (third step). Supporting layer 11 is a Si support substrate, if the intermediate layer 12 is etch stop layer such as SiO ₂ (insulating layer), by appropriate selection of the gas or solution used for etching, the support layer 11 and the intermediate The etching selectivity in the layer 12 can be controlled. For this reason, the thin film portion 2 (high resistance Si layer) having a thickness of several μm can be easily and reliably left and formed. By this step, the second surface 2r in the thin film portion 2 is exposed (third step).

  Subsequently, as shown in FIG. 8A, a second metal pattern 4 is formed on the exposed second surface 2r of the thin film portion 2 (fourth step). At this time, the second metal pattern 4 is formed so as to overlap the first metal pattern 3 when viewed from the direction intersecting (orthogonal) with the first surface 2s and the second surface 2r (fourth step). Then, as shown in FIG. 8B, the thin film portion 2 so that the second metal pattern 4 is exposed from the opening 5h at the edge of the second surface 2r on which the second metal pattern 4 is formed. The frame portion 5 that supports the frame is joined (fifth step). The frame portion 5 may be joined by using an adhesive, anodic joining, or the like. Thus, the metamaterial optical element 1 is manufactured. Thereafter, the metamaterial optical element 1 is removed from the support member M.

  Then, the 2nd example of the manufacturing method of the metamaterial optical element 1 is demonstrated. FIG. 9 is a cross-sectional view showing another example of the method for manufacturing the metamaterial optical element shown in FIG. Also in the second example, the first step is the same as the first example described above. That is, first, after preparing the base 10 as shown in FIG. 6A, the first metal pattern 3 is formed on the first surface 2s of the thin film portion 2 as shown in FIG. 6B. The base 20 is prepared (first step).

  Subsequently, in this example, as shown in FIG. 9A, a support member N is prepared (second step). The support member N is the frame part 5 here. An opening 5 h is formed in the frame portion 5. That is, the support member N includes an opening 5h and a frame 5 that defines the opening 5h. Subsequently, the base body 20 is joined to the support member N from the first surface 2s side (second step). More specifically, the edge portion of the first surface 2s is joined by joining the frame portion 5 (support member N) to the edge portion of the first surface 2s so that the first metal pattern 3 is exposed from the opening 5h. Is provided with a frame portion 5 for supporting the thin film portion 2 (second step).

  Subsequently, as shown in FIG. 9B, the support layer 11 and the intermediate layer 12 are removed from the substrate 20 by etching (third step). Thus, the second surface 2r opposite to the first surface 2s in the thin film portion 2 is exposed (third process). And the 2nd metal pattern 4 is formed in the exposed 2nd surface 2r in the thin film part 2 (4th process). At this time, the second metal pattern 4 is formed so as to overlap the first metal pattern 3 when viewed from the direction intersecting (orthogonal) with the first surface 2s and the second surface 2r (fourth step). Thus, the metamaterial optical element 1 is manufactured.

  As described above, in the metamaterial optical element 1, the first metal pattern 3 and the second metal pattern 4 having a periodic structure are provided on the first surface 2s and the second surface 2r of the thin film portion 2, respectively. Is formed. In particular, in the metamaterial optical element 1, the thin film part 2 contains silicon. For this reason, the thickness of the thin film portion 2 can be controlled to about several μm by, for example, polishing and grinding using a semiconductor process. Furthermore, a frame portion 5 that supports the thin film portion 2 is provided on the first surface 2 s or the second surface 2 r of the thin film portion 2. For this reason, thinning of the thin film part 2 is reliably realizable, hold | maintaining intensity | strength with the frame part 5. FIG. Therefore, according to the metamaterial optical element 1, it is possible to obtain good optical characteristics in the terahertz band including the high frequency region.

  Moreover, in the metamaterial optical element 1, the frame part 5 is comprised separately from the thin film part 2, and may be joined to the 1st surface 2s or the 2nd surface 2r. In this case, the first metal pattern 3 and the second metal pattern 4 can be easily formed in a state where the frame portion 5 is not joined to the thin film portion 2.

  Alternatively, in the metamaterial optical element 1, the frame portion 5 may be configured integrally with the thin film portion 2. In this case, formation of the thin film portion 2 and formation of the frame portion 5 can be performed simultaneously.

  Moreover, in the metamaterial optical element 1, the frame part 5 may contain silicon. In this case, the frame portion 5 can be easily formed with high accuracy using, for example, a semiconductor process.

In the metamaterial optical element 1, the first surface 2s and the second surface 2r are divided into a plurality of regions R1 to R9 arranged concentrically, and the first metal pattern 3 and the second metal pattern 4 are divided. However, it may be configured as a spherical lens for light of the target wavelength by having a periodic structure in which the refractive index _nm increases or decreases from the central region R1 toward the outer region R9.

Alternatively, in the metamaterial optical element 1, the first surface 2s and the second surface 2r are divided into a plurality of regions R1 to R4 arranged in the first direction, and the first metal pattern 3 and the second metal pattern 4 has a periodic structure in which the refractive index _nm increases or decreases from the region R1 on one side to the region R4 on the other side in the first direction, so that it is configured as a cylindrical lens for light of the target wavelength. May be.

Thus, the metamaterial optical element 1 may be configured as a GRIN lens. In this case, if the number of divisions of the region R is small, the degree of freedom in lens design is low, and good characteristics may not be exhibited. When designing a GRIN lens using a metamaterial, the maximum lens radius r is the difference between the focal length f _{0 of the} lens, the maximum refractive index n _max obtained using the metamaterial, and the minimum refractive index n _min. Using Δn and the thickness d of the metamaterial, it is determined as in the following formula (1).
r ² = (Δn · d) ² + 2f ₀ · Δn · d (1)

For example, in Patent Document 1 (Japanese Patent Laid-Open No. 2017-34584), in a design where the thickness d of the dielectric substrate in the 0.3 THz band is 50 μm, the maximum refractive index n _max is about 9 and the minimum refractive index n _min is It is about 2. Setting the focal length f ₀ of the lens 10 times the operating wavelength, the lens radius r according to Equation (1) is 2.7 times the wavelength. The number of area divisions at this time is 4-5. In the design where the thickness d of the dielectric substrate is 23 μm in the same frequency band, the maximum refractive index n _max is about 16 and the minimum refractive index n _min is about 4. Then, setting the focal length f ₀ of the lens Similarly, the lens radius r becomes 2.4 times the wavelength, the region division number is about 7. Furthermore, in a design in which the thickness d of the dielectric substrate is 23 μm in the 3 THz band, the lens radius r becomes 3.8 times the wavelength and the number of area divisions is about 4 when the same focal length is set.

  From these facts, when the frequency d is constant and the thickness d of the dielectric substrate is reduced, the number of divided regions increases. When the thickness d of the dielectric substrate is constant and the frequency is increased, the number of divided regions is decreased. Understood. Further, when the number of area divisions is increased, a refractive index distribution corresponding to the desired lens performance can be formed. That is, the degree of freedom in lens design and good optical characteristics can be ensured. Therefore, in order to increase the number of area divisions, it is one idea to thin the dielectric substrate.

  However, when the dielectric substrate is a cycloolefin polymer film, it is difficult to reduce the thickness to about several μm. As a result, the number of area divisions is limited by the lower limit of the thickness of the dielectric substrate, and it is difficult to ensure the degree of freedom in lens design. On the other hand, according to the metamaterial optical element 1, as described above, the thin film portion 2 can be reliably thinned, so that the upper limit of the division number of the region R can be sufficiently secured. Therefore, when the metamaterial optical element 1 is configured as a lens, the degree of freedom in lens design and good optical characteristics are sufficiently secured, which is particularly effective.

  Moreover, according to the manufacturing method of the metamaterial optical element 1 which concerns on this embodiment, the metamaterial optical element 1 which can obtain a favorable optical characteristic in a terahertz band as mentioned above can be manufactured suitably. In particular, in the first example of the manufacturing method, the second metal pattern 4 is formed in the fourth step on the second surface 2r of the thin film portion 2 exposed in the third step. And the frame part 5 is joined to the edge part of the 2nd surface 2r in a 5th process. Thus, in a state where the frame portion 5 is not joined to the second surface 2r, and in a state where the thin film portion 2 is supported by the support member M on the first surface 2s side, the second metal pattern 4 is provided. Is formed. For this reason, it is possible to easily form the second metal pattern 4 while suppressing damage to the thin film portion 2.

  On the other hand, in the second example of the manufacturing method, the second metal pattern 4 is formed in the fourth step on the second surface 2r of the thin film portion 2 exposed in the third step. On the other hand, in the second step, the frame portion 5 as the support member N is joined to the first surface 2s. As described above, the second metal pattern 4 is formed in a state where the frame portion 5 is not bonded to the second surface 2r. For this reason, the second metal pattern 4 can be easily formed. Moreover, since it is not necessary to prepare and join the frame part 5 separately from the support member N, the metamaterial optical element 1 can be manufactured in a short time and at a low cost.

  The above embodiments describe an example of the metamaterial optical element and the method for manufacturing the metamaterial optical element according to the present invention. Therefore, the metamaterial optical element and the method for manufacturing the metamaterial optical element according to the present invention are not limited to the above-described examples, and can be arbitrary modified examples. Subsequently, modified examples will be described.

  FIG. 10 is a cross-sectional view illustrating a first modification of the method for manufacturing a metamaterial optical element. Also in this first modified example, the first step is the same as the first example of the above embodiment. That is, first, after preparing the base 10 as shown in FIG. 6A, the first metal pattern 3 is formed on the first surface 2s of the thin film portion 2 as shown in FIG. 6B. The base 20 is prepared (first step).

  Subsequently, as shown in FIG. 10A, the central portion of the base layer 20 is etched from the support layer 11 side to remove the central portions of the support layer 11 and the intermediate layer 12. As a result, only the thin film portion 2 remains in the central portion of the base body 20. Thereby, the annular outer portions of the support layer 11 and the intermediate layer 12 are formed as the frame portion 5. Further, the central portion of the second surface 2r of the thin film portion 2 is exposed from the opening 5h of the frame portion. When the etching here is wet etching, the first surface 2s of the thin film portion 2 and the first metal pattern 3 are protected with a resist or the like.

  Subsequently, as illustrated in FIG. 10B, the second metal pattern 4 is formed on the second surface 2 r exposed from the opening 5 h of the frame portion 5. At this time, the second metal pattern 4 is formed so as to overlap the first metal pattern 3 when viewed from the direction intersecting (orthogonal) with the first surface 2s and the second surface 2r. Thus, the metamaterial optical element 1 is manufactured. According to the first modification, the frame portion 5 integral with the thin film portion 2 can be formed using the support layer 11 and the intermediate layer 12.

  FIG. 11: is sectional drawing which shows the 2nd modification of the manufacturing method of a metamaterial optical element. In the second modification, the first step, the second step, and the third step are the same as the first example of the above embodiment. That is, first, after preparing the base 10 as shown in FIG. 6A, the first metal pattern 3 is formed on the first surface 2s of the thin film portion 2 as shown in FIG. 6B. A base 20 is prepared.

  Subsequently, as shown in FIG. 7A, the support member M is prepared, and the base body 20 is joined to the support member M from the first surface 2 s side. Subsequently, as shown in FIG. 7B, the support layer 11 and the intermediate layer 12 are removed from the substrate 20 by etching. Thereby, the 2nd surface 2r in the thin film part 2 is exposed. Thereby, the intermediate body 60 including the thin film portion 2, the first metal pattern 3, and the support member M is formed.

  Subsequently, as shown in FIG. 11A, a pair of intermediate bodies 60 is prepared, and the second surfaces 2r of the respective thin film portions 2 are joined to each other. Thereby, one thin film portion 2A composed of a pair of thin film portions 2 is formed. The thin film portion 2A includes a pair of first surfaces 2s and a first metal pattern 3 formed on each first surface 2s. And as FIG.11 (b) shows, the metamaterial optical element 1 is manufactured by joining the frame part 5 to the edge part of 1st surface 2s. In preparing the pair of intermediate bodies 60, the thin film portion 2 in which the first metal pattern 3 is formed on the first surface 2s is formed in a size larger than the final size and is divided. May be used.

12-14 is a figure which shows the 3rd modification of the manufacturing method of a metamaterial optical element.
The upper part of (a), (b) of FIGS. 12-14 is a top view, and a lower part is sectional drawing. In the third modification, a plurality of metamaterial optical elements 1 are formed in a wafer state, and the metamaterial optical elements 1 are separated into pieces by cutting the wafer. This will be described more specifically. First, as shown in FIG. 12A, a wafer 70 is prepared. The wafer 70 includes a support layer 71 for the support layer 11, an intermediate layer 72 for the intermediate layer 12 stacked on the support layer 71, and a thin film layer for the thin film portion 2 stacked on the intermediate layer 72. 73. Subsequently, a plurality of first metal patterns 3 are formed on the main surface 70 s of the wafer 70. The main surface 70 s of the wafer 70 is the surface of the thin film layer 73 opposite to the support layer 71.

  Subsequently, as shown in FIG. 12B, a support member M is prepared. Here, the support member M is a transparent substrate for temporary bonding having a bonding surface Ms wider than the main surface 70s. Subsequently, the wafer 70 is bonded to the support member M from the main surface 70s side. Here, the tops of the plurality of first metal patterns 3 on the main surface 70s are bonded to the bonding surface Ms. In addition, here, as an example, the first metal pattern 3 and the bonding surface Ms are pasted with wax (temporary bonding).

  Subsequently, as shown in FIG. 13A, the support layer 71 and the intermediate layer 72 are removed from the wafer 70 by etching. Thereby, the back surface 70r opposite to the main surface 70s in the thin film layer 73 is exposed. Subsequently, as shown in FIG. 13B, a plurality of second metal patterns 4 are formed on the back surface 70 r of the thin film layer 73.

  Subsequently, as illustrated in FIG. 14A, the support layer 75 including the plurality of openings 5 h and the plurality of frame portions 5 that define the openings 5 h is formed on the second metal pattern 4 in each of the openings 5 h. Are formed (bonded) to the back surface 70r so that each of the above is exposed. Thereby, the some metamaterial optical element 1 integrated mutually is obtained.

  Subsequently, as shown in FIG. 14B, the thin film layer 73 and the support layer 75 (wafer) along the line set in the frame portion 5 so as to pass between the adjacent metamaterial optical elements 1. ). Thereby, the some metamaterial optical element 1 is separated into pieces.

  For the cutting of the thin film layer 73 and the support layer 75 (wafer), any method such as blade dicing can be used. For example, a modified region is formed inside the thin film layer 73 by laser irradiation. In addition, it is possible to employ a cutting method in which a crack extending from the modified region is developed by external stress. According to this, the freedom degree of a chip shape is improved, the dead space of the wafer 70 is reduced, and more efficient manufacture is attained.

  In each example of the manufacturing method described above, the mode in which the thin film portion is formed by etching a substrate (for example, an SOI substrate) including a plurality of layers such as a support layer and an intermediate layer has been described. However, the thin film portion may be formed by thinning to a few μm by grinding, polishing, and etching a single layer (for example, a high resistance Si layer).

  Here, in the said embodiment, the example which comprises the metamaterial optical element 1 as a lens was demonstrated. However, the metamaterial optical element 1 may be configured as another optical element that can be used in the terahertz band. For example, as a property of the metamaterial optical element 1, the refractive index differs with respect to the light deflection direction, and a phase difference can be generated. Therefore, the metamaterial optical element 1 can be configured as a half-wave plate by setting the phase difference to π, and can be configured as a quarter-wave plate by setting the phase difference to 0.5π. Furthermore, for example, since the metamaterial optical element 1 has a characteristic of transmitting or reflecting a specific wavelength, it can be configured as a bandpass filter.

  FIG. 15 is a cross-sectional view of an example in which the metamaterial optical element shown in FIG. 1 is configured as a bandpass filter. As shown in FIG. 15, the bandpass filter 100 includes one metamaterial optical element 1 and an optical member 1 </ b> A obtained by removing the frame portion 5 from the metamaterial optical element 1. The optical member 1A is bonded to the frame portion 5 of the metamaterial optical element 1 at the edge of the first surface 2s. The first metal pattern 3 and the second metal pattern 4 of the metamaterial optical element 1 and the first metal pattern 3 and the second metal pattern 4 of the optical member 1A are disposed so as to overlap each other. Thus, even if it is single, it can narrow down more by using the metamaterial optical element 1 and the optical member 1A which function as a band pass filter.

  FIG. 16 is a diagram showing an optical device using the metamaterial optical element shown in FIG. As shown in FIG. 16, the optical device 200 includes a light emitting element 80 and the metamaterial optical element 1 configured as a lens. The light emitting element 80 includes, for example, a terahertz band such as a quantum cascade laser (DFG-QCL) that emits output light generated by difference-frequency generation (DFG) or a THz quantum cascade laser (THz-QCL). It is a light emitting element which outputs this light.

  In the example of FIG. 16A, the metamaterial optical element 1 is provided for the light emitting element 80 by bonding the frame portion 5 to the light emitting surface 80 s of the light emitting element 80. In the example of FIG. 16B, the metamaterial optical element 1 is provided for the light emitting element 80 by bonding the first metal pattern 3 to the light emitting surface 80s. In these cases, by setting the periodic structure of the first metal pattern 3 and the second metal pattern 4 to have a refractive index corresponding to the beam pattern of the emitted light from the light emitting element 80, the emitted light Can be efficiently collimated or condensed.

  In the example of FIG. 16A, the focal length is obtained simply by joining the frame 5 to the light emitting surface 80s by forming the thickness of the frame 5 (the length from the second surface 2r) at the focal length. Can be adjusted. On the other hand, in the example of FIG. 16B, since the first metal pattern 3 can be directly joined to the light emitting surface 80s, the NA of the lens can be improved.

  DESCRIPTION OF SYMBOLS 1 ... Metamaterial optical element, 2 ... Thin film part, 2s ... 1st surface, 2r ... 2nd surface, 3 ... 1st metal pattern, 4 ... 2nd metal pattern, 5 ... Frame part, 5h ... Opening part, R, R1, R2, R3, R4, R5, R6, R7, R8, R9... Region, 11 ... support layer, 20 ... base, M, N ... support member.

Claims (8)

A first surface and a second surface opposite to the first surface, the thin film portion including silicon;
A first metal pattern formed on the first surface and having a periodic structure;
A second metal pattern formed on the second surface so as to overlap the first metal pattern when viewed from a direction intersecting the first surface, and having the periodic structure;
A frame portion provided at an edge of the first surface or the second surface and supporting the thin film portion;
A metamaterial optical element comprising: The frame portion is configured separately from the thin film portion, and is joined to the first surface or the second surface.
The metamaterial optical element according to claim 1. The frame portion is configured integrally with the thin film portion,
The metamaterial optical element according to claim 1. The frame includes silicon;
The metamaterial optical element as described in any one of Claims 1-3. The first surface and the second surface are divided into a plurality of regions arranged concentrically,
The first metal pattern and the second metal pattern have the periodic structure in which the refractive index increases or decreases from the central region toward the outer region, so that a spherical lens with respect to light of a target wavelength is obtained. Configured as
The metamaterial optical element as described in any one of Claims 1-4. The first surface and the second surface are divided into a plurality of regions arranged in a first direction,
The first metal pattern and the second metal pattern have the periodic structure in which the refractive index increases or decreases from the one side region in the first direction toward the other side region. Configured as a cylindrical lens for light,
The metamaterial optical element as described in any one of Claims 1-4. A thin film portion having a first surface and containing silicon; a support layer laminated on the thin film portion on the opposite side of the first surface; and a first metal pattern formed on the first surface and having a periodic structure; A first step of preparing a substrate including:
After the first step, a second step of joining the base body to the support member from the first surface side;
After the second step, a third step of exposing the second surface of the thin film portion opposite to the first surface by removing the support layer;
After the third step, a fourth step of forming a second metal pattern having the periodic structure on the second surface so as to overlap the first metal pattern when viewed from the direction intersecting the first surface. ,
After the fourth step, a fifth step of joining a frame portion that supports the thin film portion to an edge portion of the second surface,
A method for producing a metamaterial optical element. A thin film portion having a first surface and containing silicon; a support layer laminated on the thin film portion on the opposite side of the first surface; and a first metal pattern formed on the first surface and having a periodic structure; A first step of preparing a substrate including:
After the first step, a second step of joining the base body to the support member from the first surface side;
After the second step, a third step of exposing the second surface of the thin film portion opposite to the first surface by removing the support layer;
After the third step, a fourth step of forming a second metal pattern having the periodic structure on the second surface so as to overlap the first metal pattern when viewed from the direction intersecting the first surface. With
The support member includes a frame portion,
In the second step, the frame portion that supports the thin film portion is provided on the edge portion of the first surface by joining the frame portion to the edge portion of the first surface.
A method for producing a metamaterial optical element.

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