KR102666357B1 - Large caliber array type terahertz photoconductive antenna - Google Patents

Abstract

A large-diameter array-type terahertz photoconductive antenna is disclosed. A large-diameter array-type terahertz photoconductive antenna according to one aspect of the present invention includes a substrate, an antenna pattern having different first and second electrodes formed on the upper surface of the substrate, a thin film layer formed on the upper surface of the antenna pattern, and an upper surface of the thin film layer. It is formed as a diffraction grating structure and includes a diffraction grating pattern that rotates a beam in the reverse voltage region of the antenna pattern to the forward voltage region.

Description

Large diameter array type terahertz photoconductive antenna {LARGE CALIBER ARRAY TYPE TERAHERTZ PHOTOCONDUCTIVE ANTENNA}

The present invention relates to a large-diameter array-type terahertz photoconductive antenna, and more specifically, to a large-diameter array-type terahertz photoconductive antenna that can increase the generation efficiency of terahertz waves.

The terahertz frequency band, which lies between the micro-frequency band and the optical frequency band, is of great importance in the fields of molecular optics, biophysics, medicine, spectroscopy, imaging or security. It is a frequency band. In other words, electromagnetic waves in the terahertz frequency band have different absorption characteristics depending on the material characteristics and have both the straight path of light and the transparency of radio waves. By utilizing these characteristics, they can be applied to material analysis, security, or medical scanning fields.

Photoconductive antenna (PCA) can be used for terahertz (or millimeter wave) electromagnetic wave oscillation and detection. For example, a terahertz photoconductive antenna may have a structure in which a dipole antenna pattern is formed on a group III-V semiconductor substrate such as GaAs. For example, when ultrashort pulse laser light is incident on this dipole antenna pattern, transporters such as electrons are excited in the dipole antenna pattern portion, and the electrons are moved by the electric field between the dipoles. At this time, electrons created by ultrashort pulses are generated at a very high speed and then disappear from the electrode, and this phenomenon mainly occurs in the frequency range of 0.3 to 3 THz. The generated electromagnetic waves pass vertically through the semiconductor substrate and propagate into the air.

Here, according to the photoconduction principle, when laser light with an energy greater than the bandgap energy of the semiconductor substrate is incident, electrons are excited into the conduction band and the electrons return to a stable state. In particular, the energy difference at this time is millimeter wave. The electromagnetic wave energy in the terahertz band is called the terahertz photoconduction phenomenon.

In a general photoconductive antenna, electromagnetic waves generated from the antenna pattern may propagate as surface waves, causing loss, and electromagnetic waves reflected from the surface opposite to the surface on which the antenna pattern is formed are refracted on the surface on which the antenna pattern is formed and are transmitted to the outside. It may be released and cause damage.

As described above, in the photoconductive antenna, light-generated carriers are generated by an external optical pump beam, and a current flows in the antenna according to an electric field formed by a voltage applied to the electrode, generating terahertz.

Hereinafter, we will look at a conventional large-diameter array-type terahertz photoconductive antenna with reference to the drawings.

Figure 1 is a diagram showing a conventional large-diameter array-type terahertz photoconductive antenna. Referring to FIG. 1, a conventional large-diameter array-type terahertz photoconductive antenna 10 has a structure in which an anode 31 and a cathode 32 are periodically alternately formed on the upper surface of a photoconductive substrate 20.

As shown in Figure 1 (b), since the electric field is repeatedly formed in the left and right directions, the current flowing into the antenna is canceled out and becomes very small or disappears. Therefore, one of the two directions must be viewed as the forward direction and the other as the reverse direction, and the optical pump beam on one side must be blocked to generate terahertz.

Accordingly, there is a demand for technology development for large-diameter array-type terahertz photoconductive antennas that can increase the generation efficiency of terahertz waves.

Prior art related to the present invention includes Republic of Korea Patent Publication No. 10-1453472 (announced on October 21, 2014, title of invention: Terahertz wave device).

The present invention was made to improve the above problems, and the purpose of the present invention is to provide a large-diameter array-type terahertz photoconductive antenna that can increase the generation efficiency of terahertz waves.

The problem to be solved by the present invention is not limited to the problem(s) mentioned above, and other problem(s) not mentioned will be clearly understood by those skilled in the art from the description below.

A large-diameter array-type terahertz photoconductive antenna according to one aspect of the present invention includes a substrate, an antenna pattern having different first and second electrodes formed on the upper surface of the substrate, a thin film layer formed on the upper surface of the antenna pattern, and an upper surface of the thin film layer. It is formed as a diffraction grating structure and includes a diffraction grating pattern that rotates a beam in the reverse voltage region of the antenna pattern to the forward voltage region.

In the present invention, the first electrode includes a first line pattern extending in a first direction, a plurality of second line patterns connected to the first line pattern and extending in a second direction crossing the first direction, and a plurality of third line patterns connected to the first line pattern, extending in the second direction, positioned between the plurality of second line patterns, and having a longer length than the second line patterns, The second electrode includes a fourth line pattern extended in the first direction, a plurality of fifth line patterns connected to the fourth line pattern and extended in the second direction, and connected to the fourth line pattern and a plurality of sixth line patterns extending in a second direction, positioned between the plurality of fifth line patterns and having a longer length than the fifth line patterns, and disposed facing the first electrode. It can be characterized.

In the present invention, the antenna pattern is configured such that the first electrode and the second electrode are comprised of one unit grid, a plurality of unit grids constitute a plurality of rows, and a reverse voltage region or forward voltage is formed between the plurality of rows. It may be characterized by the location of the area.

In the present invention, the antenna pattern is characterized in that the first electrode and the second electrode are alternately formed at regular intervals at a predetermined distance apart, and a reverse voltage area or a forward voltage area is located between the first electrode and the second electrode. You can do this.

In the present invention, the thin film layer may be formed of polymer or dielectric.

In the present invention, the thickness of the thin film layer may be determined based on the angle of incidence of the diffraction grating pattern and the period of the antenna pattern.

In the present invention, the diffraction grating pattern may be formed of a dielectric.

In the present invention, the diffraction grating pattern may be formed on the upper surface of the thin film layer at a position corresponding to the reverse voltage region.

In the present invention, the incident angle of the diffraction grating pattern may be determined based on the wavelength of the beam and the period of the grating structure.

According to the present invention, by depositing a thin film layer on a substrate on which an antenna pattern is formed and arranging a diffraction grating pattern on the upper part of the reverse voltage region, the optical pump beam incident on the reverse voltage region can be diffracted into the forward voltage region, thereby The optical pump beam incident on the forward voltage region can be improved by up to two times.

In addition, according to the present invention, by arranging a diffraction grating pattern on the upper part of the reverse voltage area, the reflected optical pump beam can be significantly lowered, thereby suppressing diffuse reflection inside the system and improving the signal-to-noise ratio. .

Meanwhile, the effects of the present invention are not limited to the effects mentioned above, and various effects may be included within the range apparent to those skilled in the art from the contents described below.

Figure 1 is a diagram showing a conventional large-diameter array-type terahertz photoconductive antenna.
Figure 2 is a diagram schematically showing a large-diameter array-type terahertz photoconductive antenna according to an embodiment of the present invention.
Figure 3 is a diagram for explaining a method of determining the thickness of a thin film layer according to an embodiment of the present invention.
Figure 4 is a diagram for explaining the operation of a diffraction grating pattern according to an embodiment of the present invention.
Figure 5 is an exemplary diagram for explaining the results of computational simulation of a diffraction grating according to an embodiment of the present invention.
Figure 6 is a graph illustrating the transmitted power for each traveling angle according to an embodiment of the present invention.
Figure 7 is a diagram showing an antenna pattern of an SNG structure according to an embodiment of the present invention.
Figure 8 is a diagram comparing the NG structure, NE structure, and SNG structure according to an embodiment of the present invention.
Figure 9 is a diagram showing the unit row structure of a large-diameter array-type terahertz photoconductive antenna according to an embodiment of the present invention.
Figure 10 is a diagram showing the structure of a large-diameter terahertz photoconductive antenna configured by arranging a plurality of rows according to an embodiment of the present invention.

Hereinafter, a large-diameter array-type terahertz photoconductive antenna according to an embodiment of the present invention will be described with reference to the attached drawings. In this process, the thickness of lines or sizes of components shown in the drawings may be exaggerated for clarity and convenience of explanation.

In addition, the terms described below are terms defined in consideration of functions in the present invention, and may vary depending on the intention or custom of the user or operator. Therefore, definitions of these terms should be made based on the content throughout this specification.

FIG. 2 is a diagram schematically showing a large-diameter array-type terahertz photoconductive antenna according to an embodiment of the present invention, and FIG. 3 is a diagram illustrating a method of determining the thickness of a thin film layer according to an embodiment of the present invention. 4 is a diagram illustrating the operation of a diffraction grating pattern according to an embodiment of the present invention, FIG. 5 is an exemplary diagram illustrating the results of computational simulation of a diffraction grating according to an embodiment of the present invention, and FIG. 6 is a diagram illustrating the operation of a diffraction grating pattern according to an embodiment of the present invention. This is a graph to explain the transmitted power for each traveling angle according to one embodiment of .

Referring to FIG. 2, the large-diameter array-type terahertz photoconductive antenna 100 according to an embodiment of the present invention includes a substrate 110, an antenna pattern 120 formed on the upper surface of the substrate 110, and an antenna pattern 120. It includes a thin film layer 130 formed on the top, and a diffraction grating pattern 140 formed on the upper surface of the thin film layer 130.

The substrate 110 may be a semi-insulating GaAs substrate or an InGaAs substrate to minimize the amount of terahertz waves absorbed by charges present on the semiconductor substrate.

The antenna pattern 120 is formed on the upper surface of the substrate 110 by having different first electrodes 121 and second electrodes 122 spaced a predetermined distance apart from each other. At this time, when the first electrode 121 is an anode, the second electrode 122 may be a cathode, or vice versa.

Since the antenna pattern 120 is formed by alternating the first electrode 121 and the second electrode 122 at regular intervals with a predetermined distance apart, the electric field may be repeatedly formed in the left and right directions as described in FIG. 1. At this time, if one of the two directions is defined as the forward direction and the other direction is defined as the reverse direction, a reverse voltage area (A) or a forward voltage area (B) may be located between the first electrode 121 and the second electrode 122. there is.

Additionally, the antenna pattern 120 may include the first electrode 121 and the second electrode 122 as one unit grid, and a plurality of unit grids may form a plurality of rows. At this time, a reverse voltage area or a forward voltage area may be located between a plurality of rows.

This antenna pattern 120 may have at least one of a shifted nano-gap (SNG) structure, a nano-gap (NG) structure, and a nano-electrode (NE) structure. For a detailed description of the antenna pattern 120, refer to FIGS. 3 to 5.

A thin film layer 130 may be deposited on the antenna pattern 120 as described above.

The thin film layer 130 may be formed of a material such as polymer or dielectric. For example, the thin film layer 130 may be formed of polydimethylsiloxane (PDMS).

The thickness of the thin film layer 130 needs to be adjusted in order to direct the optical pump beam incident on the reverse voltage area of the antenna pattern 120 to the forward voltage area. Referring to FIG. 3 for the thickness of the thin film layer 130, the thickness (t) of the thin film layer 130 may be determined based on the incident angle of the diffraction grating pattern 140 and the period of the antenna pattern 120. That is, the thickness (t) of the thin film layer 130 can be determined through Equation 1 below, as shown in FIG. 3.

[Equation 1]

Here, b may mean the period of the antenna pattern 120, and θ may mean the incident angle of the diffraction grating pattern 140.

For example, the thin film layer 130 may be formed to have a thickness (t) of 10 to 200 μm.

The diffraction grating pattern 140 is formed as a diffraction grating structure on the upper surface of the thin film layer 130, and rotates the beam in the reverse voltage area (A) of the antenna pattern 120 to the forward voltage area (B). At this time, the diffraction grating pattern 140 may be formed on the upper surface of the thin film layer 130 at a position corresponding to the reverse voltage area A of the antenna pattern 120. For example, the diffraction grating pattern 140 may be formed on the reverse voltage area A located between a plurality of rows of the antenna pattern 120.

This diffraction grating pattern 140 may be formed of a dielectric. For example, the diffraction grating pattern 140 is Si ₃ N ₄ , It may be formed of a material such as SiO ₂ . Additionally, in the diffraction grating pattern 140, each grating may have a structure having, for example, a thickness of 0.1 to 2 μm, a period (a) of 0.4 to 1.6 μm, and a duty ratio of 0 to 1.

For reference, a diffraction grating is one in which numerous slits are made at regular intervals. Therefore, when an optical pump beam is incident on a diffraction grating, the transmitted or reflected light can be divided by wavelength to obtain a spectrum. Optical pump beams incident in parallel to this diffraction grating are absorbed or scattered anywhere other than the slit, and light entering the slit passes through. However, the beam that passes does not go straight, but is diffracted according to Huygens' principle, spreads out in the form of a circular pillar, and is transmitted to a specific direction where constructive interference occurs.

The incident angle of the first constructive interference point generated by the lattice structure is affected by the period (a) of the lattice structure, the wavelength (λ) of the incident optical pump beam, and the refractive index depending on the material, as shown in the equation shown in FIG. You can. Accordingly, the angle of incidence of the diffraction grating pattern 140 may be determined based on the wavelength of the optical pump beam and the period of the grating structure. That is, the incident angle of the diffraction grating pattern 140 can be determined through Equation 2 below.

[Equation 2]

θ = sin ^-1 λ/a (rad)

Here, λ may mean the wavelength of the optical pump beam, and a may mean the period of the lattice structure.

If this diffraction grating pattern 140 is simulated using a 700 nm thick grid structure made of Si ₃ N ₄ (period 1 μm, duty ratio 1), the results shown in FIG. 5 can be confirmed. In this case, as shown in Figure 6, the transmitted power by traveling angle can be confirmed that 40% of the light is transmitted at an angle of 33 degrees on both the left and right, and less than 10% of the light traveling straight is transmitted.

The large-diameter array-type terahertz photoconductive antenna 100 constructed as described above deposits a thin film layer 130 on the substrate 110 on which the antenna pattern 120 is formed, and forms a diffraction grating pattern 140 on the upper part of the reverse voltage area. By arranging, the optical pump beam incident on the reverse voltage region can be diffracted into the forward voltage region.

Figure 7 is a diagram showing an antenna pattern of the SNG structure according to an embodiment of the present invention.

Referring to FIG. 7, the antenna pattern 120 according to an embodiment of the present invention has a Shifted Nano-Gap (SNG) structure. At this time, the antenna pattern 120 includes a pair of electrodes 121 and 122, one of which may be an anode and the other may be a cathode.

The first electrode 121 has a first line pattern 121A extending in the first direction (I-I') and a second direction (II-II') crossing the first direction (I-I'). and a plurality of second and third line patterns 121B and 121C. Here, one end of the plurality of second and third line patterns 121B and 121C is connected to the first line pattern 121A. Accordingly, the first electrode has a finger shape or a comb shape. Additionally, the second line patterns 121B and the third line patterns 121C may be arranged alternately, and the third line patterns 121C may have a longer length than the second line patterns 121B. You can.

The second electrode 122 includes a fourth line pattern 122A extending in the first direction (II-I') and a plurality of fifth and sixth line patterns extending in the second direction (II-II') ( 122B, 122C). Here, one end of the plurality of fifth and sixth line patterns 122B and 122C is connected to the fourth line pattern 122A. Accordingly, the second electrode 122 has a finger shape or a comb shape.

Additionally, the fifth line patterns 122B and the sixth line patterns 122C may be arranged alternately, and the sixth line patterns 122C may have a longer length than the fifth line patterns 122B. You can.

The first line pattern 121A of the first electrode 121 and the fourth line pattern 122A of the second electrode 122 are arranged to face each other, and the first line pattern 121A and the fourth line pattern 122A are A plurality of second line patterns 121B, a plurality of third line patterns 121C, a plurality of fifth line patterns 122B, and a plurality of sixth line patterns 122C may be arranged between the there is.

Additionally, the plurality of second line patterns 121B and the plurality of sixth line patterns 122C are positioned to correspond to each other, and the plurality of third line patterns 121C and the plurality of fifth line patterns 122B ) can be positioned to correspond to each other. According to this structure, the third line patterns 121C of the first electrode 121 and the sixth line patterns 122C of the second electrode 122 partially overlap.

Figure 8 is a diagram comparing the NG structure, NE structure, and SNG structure according to an embodiment of the present invention.

Referring to FIG. 8, the antenna pattern 120 according to an embodiment of the present invention may have a nano-gap (NG) structure (120C), a nano-electrode (NE) structure (120B), or an SNG structure (120A). there is.

Here, the NG structure 120C has a structure similar to the SNG, but the plurality of second line patterns 121B and the plurality of third line patterns 121C have the same length, and the plurality of fifth line patterns ( 122B) and the plurality of sixth line patterns 122C have the same length. In addition, the NE structure (120B) has a similar structure to the NG structure (120C), but the spacing (121, 122) between the anode and the cathode is different.

For example, the NG structure 120C consists of an array of nanoelectrodes with a period 126 of 200 nm. Additionally, it may include a pair of anodes and cathodes, and the gap 123 between them may be about 200 nm. The NE structure (120B) has a similar shape to the NG structure (120C), and the gap 124 between the anode and the cathode is about 3 um. As previously described with reference to FIG. 3, the SNG structure 120A has a region 125 where both electrodes intersect each other. The width of the intersection area 125 may be approximately 1 um.

Figure 9 is a diagram showing the unit row structure of a large-diameter array-type terahertz photoconductive antenna according to an embodiment of the present invention.

Referring to FIG. 9, a nanostructure can be applied to the antenna pattern 120 that constitutes one row of the large-diameter photoconductive antenna 100. For example, the SNG structure is applied to the facing first electrode 121 and the second electrode 122, and the first electrode 121 and the second electrode 122 are electrically controlled by the bias power supply 150. do. Here, the width 125 and period 126 of the intersection area can be adjusted in various ways. In addition, not only the SNG structure, but also the NG structure and NE structure can be applied.

Figure 10 is a diagram showing the structure of a large-diameter terahertz photoconductive antenna configured by arranging a plurality of rows according to an embodiment of the present invention.

Referring to FIG. 10, a reverse voltage area 1010 may be located between a plurality of rows, and a diffraction grating pattern 140 may be formed on the reverse voltage area 1010. In this way, by forming the diffraction grating pattern 140 in the reverse voltage area, it is possible to prevent terahertz generation efficiency from being reduced. Additionally, the size of the entire area (1000) may be determined in various ways, for example, may be 100 um x 100 um or more.

As described above, the large-diameter array-type terahertz photoconductive antenna according to an embodiment of the present invention deposits a thin film layer on a substrate on which an antenna pattern is formed and arranges a diffraction grating pattern on the upper part of the reverse voltage area, The incident optical pump beam can be diffracted into the forward voltage region, thereby improving the optical pump beam incident on the forward voltage region by up to two times.

In addition, the large-diameter array-type terahertz photoconductive antenna according to an embodiment of the present invention can significantly lower the reflected optical pump beam by arranging a diffraction grating pattern on the upper part of the reverse voltage area, thereby reducing diffuse reflection inside the system. It can be suppressed and the signal-to-noise ratio can be improved.

The present invention has been described with reference to the embodiments shown in the drawings, but these are merely exemplary, and those skilled in the art will recognize that various modifications and other equivalent embodiments are possible therefrom. You will understand.

Therefore, the true technical protection scope of the present invention should be determined by the scope of the patent claims below.

100: Large-diameter array-type terahertz photoconductive antenna
110: substrate
120: antenna pattern
121: first electrode
122: second electrode
130: thin film layer
140: diffraction grating pattern

Claims (9)

Board;
an antenna pattern in which different first and second electrodes are formed on the upper surface of the substrate;
a thin film layer formed on the antenna pattern; and
It includes a diffraction grating pattern formed in a diffraction grating structure on the upper surface of the thin film layer to diffract the beam in the reverse voltage region of the antenna pattern into the forward voltage region,
The thickness of the thin film layer is determined based on the angle of incidence of the diffraction grating pattern and the period of the antenna pattern,
The diffraction grating pattern is formed on the upper surface of the thin film layer at a position corresponding to the reverse voltage region,
In the antenna pattern, the first electrode and the second electrode are composed of one unit grid, and a plurality of unit grids constitute a plurality of rows,
A reverse voltage area or a forward voltage area is located between the plurality of rows,
The antenna pattern has at least one of a Shifted Nano-Gap (SNG) structure, a Nano-Gap (NG) structure, and a Nano-Electrode (NE) structure,
A large-diameter array-type terahertz photoconductive antenna, wherein the diffraction grating pattern is formed on an upper portion of a reverse voltage area located between a plurality of rows of the antenna pattern.
According to paragraph 1,
The first electrode includes a first line pattern extending in a first direction, a plurality of second line patterns connected to the first line pattern and extending in a second direction crossing the first direction, and the first line pattern extending in a first direction. a plurality of third line patterns connected to a line pattern, extending in the second direction, positioned between the plurality of second line patterns, and having a longer length than the second line patterns;
The second electrode includes a fourth line pattern extended in the first direction, a plurality of fifth line patterns connected to the fourth line pattern and extended in the second direction, and connected to the fourth line pattern, extending in the second direction, comprising a plurality of sixth line patterns located between the plurality of fifth line patterns and having a longer length than the fifth line patterns, and disposed facing the first electrode. A large-diameter array-type terahertz photoconductive antenna, characterized in that.
delete According to paragraph 1,
The antenna pattern is formed by alternating the first electrode and the second electrode at regular intervals with a predetermined distance apart,
A large-diameter array-type terahertz photoconductive antenna, characterized in that a reverse voltage area or a forward voltage area is located between the first electrode and the second electrode.
According to paragraph 1,
A large-diameter array-type terahertz photoconductive antenna, wherein the thin film layer is formed of polymer or dielectric.
delete According to paragraph 1,
A large-diameter array-type terahertz photoconductive antenna, wherein the diffraction grating pattern is formed of a dielectric.
delete According to paragraph 1,
A large-diameter array-type terahertz photoconductive antenna, characterized in that the angle of incidence of the diffraction grating pattern is determined based on the wavelength of the beam and the period of the grating structure.

Images