JP2007037015A - Frequency selective element and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a frequency selective element in a novel structure, and a manufacturing method thereof. <P>SOLUTION: The present invention relates to a frequency selective element for transmitting electromagnetic waves in a specific frequency domain, the frequency selective element comprising a substrate 501 and a roll part 503 formed by spirally rolling a laminate film 502 formed on the substrate 501. The laminate film 502 includes a multilayered film including at least two semiconductor layers of which lattice constants differ from each other. The laminate film 502 is spirally rolled by a force generated by the difference of the lattice constants and within the laminate film of the roll part 503, a periodic conductor pattern is formed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a frequency selective element and a manufacturing method thereof.

  A frequency selective surface (FSS: Frequency Selective Surfaces) is known as an element that selects or reflects an electromagnetic wave having a specific frequency among incident electromagnetic waves (for example, Patent Document 1). Faraday cages and photonic band gap crystals are also known as elements for selecting the wavelength.

  The FSS can be formed of a single layer, but the characteristics can be improved by forming the FSS with a laminated film. An example of a three-dimensional FSS composed of a laminated film is schematically shown in FIGS. 6 (a) and 6 (b).

The element shown in FIG. 6A has a structure in which a plurality of dielectric films 10 and lattice-like metal films 11 are alternately stacked. The element shown in FIG. 6B has a structure in which a plurality of dielectric films 10 each having a rectangular metal film 12 arranged in a matrix are stacked. Thus, when forming a three-dimensional FSS, it was necessary to laminate a plurality of conductive layers and dielectric layers having a periodic structure.
Japanese Patent Application Laid-Open No. 11-307989

  However, it is not easy to form a laminated structure as shown in FIG.

  Under such circumstances, it is an object of the present invention to provide a frequency-selective element having a novel structure and a manufacturing method thereof.

  In order to achieve the above object, a frequency selective element of the present invention is a frequency selective element that transmits electromagnetic waves in a specific frequency range, and spirally winds a substrate and a laminated film formed on the substrate. The laminated film includes a multilayer film including at least two semiconductor layers having different lattice constants, and the laminated film is spirally formed by a force generated by the difference in the lattice constants. A periodic conductor pattern is formed in the laminated film of the roll portion.

  In addition, the method of the present invention for manufacturing a frequency selective element includes (i) a step of forming a sacrificial layer on a substrate, and (ii) at least two semiconductor layers having different lattice constants. Forming a laminated film on which the body pattern is formed on the sacrificial layer; (iii) forming a groove reaching the sacrificial layer in three directions around the conductor pattern; and (iv) Removing the sacrificial layer present in the region surrounded by the groove, and winding the laminated film surrounded by the groove in a spiral shape.

  Hereinafter, the frequency selective element of the present invention and the manufacturing method thereof will be described.

<Frequency selective element>
The frequency selective element of the present invention is an element that transmits electromagnetic waves in a specific frequency range. This element includes a substrate and a roll portion formed by winding a laminated film formed on the substrate in a spiral shape. The laminated film includes a multilayer film including at least two semiconductor layers having different lattice constants. The laminated film is spirally wound by the force generated by the difference in the lattice constant. A periodic conductor pattern is formed in the laminated film of the roll part.

The substrate is selected according to the semiconductor layer formed thereon. As the substrate, for example, a GaAs substrate, InP substrate, Al ₂ O ₃ substrate, SiC substrate, Si substrate, or the like is used.

  A sacrificial layer is disposed between the substrate and the laminated film. The sacrificial layer is a layer that is selectively removed when the roll film is formed by bending the laminated film. Therefore, the sacrificial layer is formed of a material that is easily removed selectively. As the sacrificial layer, for example, a film in which a plurality of AlGaAs layers and AlAs layers are alternately stacked can be used.

  The multilayer film including a plurality of stacked semiconductor layers includes at least two semiconductor layers having different lattice constants. Inside, an internal stress resulting from a difference in lattice constant is generated. Using the distortion based on the difference in lattice constant, the laminated film is bent to form a roll portion. The multilayer film is formed of, for example, a compound semiconductor (for example, a III-V group compound semiconductor), Si, or a semiconductor containing Si. Examples of combinations of materials having different lattice constants (materials having a small lattice constant / materials having a large lattice constant) include combinations such as GaAs / InGaAs, GaN / InGaN, and Si / SiGe. The curvature radius of the multilayer film can be adjusted by changing the composition ratio and thickness of these semiconductor layers.

  The multilayer film that generates internal stress may be two layers or three layers. For example, a multilayer film in which a layer A having a large lattice constant and a layer B having a small lattice constant are laminated as thick layer A / layer B / thin layer A may be used. In this case, since the stress exerted on the layer B by the thick layer A is greater than the stress exerted on the layer B by the thin layer A, a total stress that tends to bend on the thin layer A side is generated. Similarly, in the laminated film of thick layer B / layer A / thin layer B, a stress that tends to bend toward the thick layer B is generated in total. By utilizing such a relationship, the multilayer film can be bent in a predetermined direction.

  The conductor pattern may be formed on the multilayer film (semiconductor multilayer film). In this case, the semiconductor multilayer film and the conductor pattern are integrally wound in a spiral shape. Further, the conductor pattern may be formed by etching a part of the semiconductor layer constituting the semiconductor multilayer film.

  The conductor pattern has a periodic structure. The shape and size of the periodic structure are determined according to the purpose of the element (particularly, the frequency range in which light is selectively transmitted). In one example, the conductor pattern may have a lattice shape (grid shape). Further, rectangular conductors may be arranged in a matrix. The conductor pattern can be formed of a metal such as Au or Al, or a semiconductor doped with a dopant.

  Note that the laminated film may include layers other than the above-described layers as necessary.

<Method of manufacturing frequency selective element>
Hereinafter, the method of the present invention for manufacturing a frequency selective element will be described. According to this manufacturing method, the frequency selective element of the present invention can be manufactured. Since the substrate, the sacrificial layer, the semiconductor multilayer film, and the conductor pattern are the same as those described above, a duplicate description is omitted.

  The method of the present invention for manufacturing a frequency selective element includes the step (i) of forming a sacrificial layer on a substrate. Usually, a buffer layer is formed before forming the sacrificial layer in order to increase the crystallinity of the sacrificial layer or the laminated film.

  Next, a laminated film including at least two semiconductor layers having different lattice constants and having a periodic conductor pattern is formed on the sacrificial layer (step (ii)). The sacrificial layer and the semiconductor multilayer film included in the stacked film can be formed by a known method, for example, a molecular beam epitaxial growth method (MBE method) or a metal organic chemical vapor deposition method (MOCVD method). Moreover, when a conductor pattern consists of a metal film, it can form with a vapor deposition method or sputtering method.

  The periodic conductor pattern can be formed, for example, by etching a metal film or a doped semiconductor film in a photolithography etching process.

  Next, grooves reaching the sacrificial layer are formed in three directions around the conductor pattern (step (iii)). This groove penetrates the laminated film and reaches the sacrificial layer, and can be formed by a known dry etching method or photolithography / etching method.

  Next, by removing the sacrificial layer present in the region surrounded by the groove, the laminated film surrounded by the groove is spirally wound (step (iv)). When the sacrificial layer is removed, the laminated film present on the removed sacrificial layer is bent by the force generated by the strain present in the semiconductor multilayer film and wound into a roll shape to form a roll portion. At this time, the conductor pattern is also spirally wound at the same time. In this way, a conductor pattern wound in a spiral shape is formed.

  Hereinafter, examples of specific embodiments will be described with reference to the drawings. In order to facilitate understanding, some of the drawings shown below are simplified.

<Embodiment 1>
In Embodiment 1, an example in which the frequency selective element of the present invention is formed will be described. The manufacturing process is shown in FIGS. 1 (a), (c) and (e) are top views, and cross-sectional views thereof are shown in FIGS. 1 (b), (d) and (f).

First, as shown in FIG. 1A, a buffer layer 102 (thickness 300 nm), a sacrificial layer 103, a first semiconductor layer 104a and a second semiconductor are formed on a substrate 101 which is a GaAs (100) substrate. The multilayer film 104 including the layer 104b is epitaxially grown. The sacrificial layer 103 has a structure (total thickness of 64 nm) in which 80 pairs of Al _0.58 Ga _0.42 As (thickness 0.4 nm) / AlAs (thickness 0.4 nm) are stacked. The buffer layer 102 and the sacrificial layer 103 are non-doped layers formed by an epitaxial growth method.

The first semiconductor layer 104a is a non-doped In _0.22 Ga _0.78 As layer (thickness 10 nm), and the second semiconductor layer 104b is a GaAs layer (thickness 100 nm) doped with Si. Since the first semiconductor layer 104a has a lattice constant larger than that of the second semiconductor layer 104b, internal stress that tends to bend toward the second semiconductor layer 104b exists in the multilayer film 104.

  Next, the second semiconductor layer 104b is processed into a grid shape by a normal photolithography / etching process. The second semiconductor layer 104b can be selectively etched by adjusting an etching time or an etching method.

  By etching the second semiconductor layer 104b, a periodic conductor pattern 104p (a grid-like portion of the second semiconductor layer 104b) is formed as shown in FIG. When a mask having a line width of 60 nm and a grid pitch of 110 nm is used, a part of the second semiconductor layer 104b is etched to form a grid-like shape in which a square through hole 104h having a side of 50 nm is formed. It can be shaped. By forming a conductor pattern of such a size, it is possible to form a roll part that transmits light outside the blue region.

  Next, as shown in FIG. 1E, a periodic conductor pattern 104p, that is, a sacrificial layer 103 penetrating the multilayer film 104 in three directions around the grid-like second semiconductor layer 104b. A reaching groove 105 is formed. The groove 105 can be formed by a known photolithography / etching process. As shown in FIG. 1E, the groove 105 is preferably formed so that two sides of the groove 105 are parallel to the [110] direction of the substrate.

Next, the sacrificial layer 103 present in the region surrounded by the groove 105 is removed by wet etching. The etching solution reaches the sacrificial layer 103 through the groove 105. As the etching solution, for example, a mixed solution of HF: H ₂ O = 1: 10 can be used.

  When the sacrificial layer 103 is etched, the multilayer film 104 existing in the region surrounded by the groove 105 is separated from the substrate 101. The state at this time is schematically shown in FIGS. The multilayer film 104 separated from the substrate 101 is wound up to the second semiconductor layer 104b side by internal stress existing in the multilayer film 104, and a roll portion 106 is formed.

<Embodiment 2>
In the second embodiment, another example of the element of the present invention will be described with reference to FIG. 3 (a) and 3 (c) are top views, and cross-sectional views thereof are shown in FIGS. 3 (b) and 3 (d).

  First, as shown in FIGS. 3A and 3B, on a substrate 101 which is a GaAs (100) substrate, a buffer layer 102 (thickness 300 nm), a sacrificial layer 103, a first semiconductor layer 104a, The multilayer film 104 including the second semiconductor layer 104c is epitaxially grown. In this embodiment, the second semiconductor layer 104c (thickness 100 nm) made of non-doped GaAs is used in place of the second semiconductor layer 104b (thickness 100 nm) made of doped GaAs. This is the same as the process described in 1.

  Next, as shown in FIGS. 3C and 3D, a grid-like metal pattern 301 is formed in a predetermined region on the second semiconductor layer 104c. The multilayer film 104 and the metal pattern 301 constitute a laminated film 302. Thereafter, as in the first embodiment, the groove 105 is formed around the metal pattern 301, and the sacrificial layer 103 in the region surrounded by the groove 105 is removed. As a result, the laminated film 302 (multilayer film 104 and metal pattern 301) surrounded by the groove 105 is wound up to form a roll part.

  In addition, illustrated embodiment is an example of this invention and this invention is not limited to said example. For example, in Embodiment 1, a thin etching stopper film may be provided between the first semiconductor layer 104a and the second semiconductor layer 104b to etch only the second semiconductor layer 104b. Alternatively, the first semiconductor layer 104a may be etched together with the second semiconductor layer 104b to form a grid shape. In the second embodiment, the multilayer film 104 may be etched to form a grid shape in the same manner as the metal pattern 301. In these cases, the roll part is formed of a grid-like film.

  The periodic conductor pattern is not limited to the grid shape, and may be formed by arranging a plurality of rectangular conductors in a matrix shape. Part of such an example process is shown in the perspective views of FIGS. 4 (a) and 4 (b). In the example of FIG. 4, a plurality of rectangular metal films 401 are arranged in a matrix on the multilayer film 104. Also in this case, as shown in FIG. 4B, the roll portion is formed by the internal stress of the multilayer film 104.

  An example of the function of the element of the present invention is shown in FIG. In the frequency selective element 500 of FIG. 5, the laminated film 502 formed on the substrate 501 is wound up to form a roll portion 503. When electromagnetic waves (for example, laser light) are incident along the central axis of the roll unit 503, only electromagnetic waves in a specific frequency range pass through the roll unit, and electromagnetic waves in other frequency ranges are absorbed or reflected. The frequency range that passes through the roll part can be controlled by the material constituting the roll part, the period of the periodic structure of the conductor pattern, and the like.

  The embodiments of the present invention have been described above by way of examples, but the present invention is not limited to the above-described embodiments, and can be applied to other embodiments based on the technical idea of the present invention.

  According to the present invention, a frequency selective element that selectively transmits electromagnetic waves in a specific frequency range can be obtained. This element can be used in various fields such as the photonics field, for example, fields such as a microwave filter, a polarizer, a Faraday cage, a photonic band gap crystal, an optical waveguide, a holey fiber, and a gas sensor.

It is a figure which shows typically an example of the manufacturing method of the frequency selective element of this invention. It is a figure which shows typically the process of the continuation of the process of FIG. It is a figure which shows typically another example of the manufacturing method of the frequency selective element of this invention. It is a figure which shows typically another example of the manufacturing method of the frequency selective element of this invention. It is a figure which shows typically the function of the frequency selective element of this invention. It is a perspective view which shows the example of the conventional frequency selective element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Substrate 102 Buffer layer 103 Sacrificial layer 104 Multilayer film 104a First semiconductor layer 104b Second semiconductor layer (conductor pattern)
104c Second semiconductor layer 105 Groove 106, 503 Roll part 301 Metal pattern (conductor pattern)
302, 502 Multilayer film 500 Frequency selective element 501 Substrate

Claims (4)

A frequency selective element that transmits electromagnetic waves in a specific frequency range,
A substrate, and a roll portion formed by spirally winding a laminated film formed on the substrate,
The laminated film includes a multilayer film including at least two semiconductor layers having different lattice constants,
The laminated film is spirally wound by the force generated by the difference in the lattice constant,
A frequency selective element in which a periodic conductor pattern is formed in the laminated film of the roll part.   The frequency selective element according to claim 1, wherein the conductor pattern is formed on the multilayer film, and the multilayer film and the conductor pattern are integrally wound in a spiral shape.   The frequency selective element according to claim 1, wherein the conductor pattern has a lattice shape. (I) forming a sacrificial layer on the substrate;
(Ii) forming a laminated film including at least two semiconductor layers having different lattice constants and having a periodic conductor pattern formed on the sacrificial layer;
(Iii) forming a groove reaching the sacrificial layer in three directions around the conductor pattern;
(Iv) A method of manufacturing a frequency selective element, including a step of spirally winding the laminated film surrounded by the groove by removing the sacrificial layer present in the region surrounded by the groove.