KR20170089613A - Terahertz device - Google Patents

Abstract

The present invention provides a terahertz device capable of being manufactured in a small size and improving detection efficiency and performance. The terahertz device according to an embodiment of the present invention includes first and second electrodes, first and second waveguides respectively connected to the first and second electrodes, a gap region between the first and second waveguides. The present invention includes a filter line of a meander structure which is inserted into either or both between the first electrode and the first wave guide, and between the second electrode and the second wave guide.

Description

Terahertz device {TERAHERTZ DEVICE}

The present invention relates to a terahertz device which can be used for the generation and detection of terahertz waves.

Generally, a region of 0.1 to 10 THz (1THz is 10 ¹² Hz) in the electromagnetic wave spectrum band is defined as a terahertz wave. In particular, the 0.1 to 3 THz region is the region where the rotational and resonant frequencies of a wide variety of molecules are present. By acquiring these molecular fingerprints using non-destructive, unspared, and non-contact methods using terahertz waves, we can provide new core technologies for the future in medical, medical, agricultural food, environmental measurement, biotechnology, communications, have. As a result, there is intense competition in the development of related core technologies.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a terahertz device which can be manufactured in a small size and has improved detection efficiency and performance.

A terahertz device according to an embodiment of the present invention includes first and second electrodes, first and second waveguides connected to the first and second electrodes, respectively, and a second waveguide connected between the first and second waveguides, And a meander structure filter line inserted in at least one of the second electrode and the second waveguide between the first electrode and the first waveguide, .

According to an embodiment, the filter line may be a planar filter line formed on a plane in which the first and second electrodes and the first and second waveguides are formed.

According to an embodiment, the first electrode is formed at both ends of the first waveguide, and the filter line may be inserted between both ends of the first waveguide and the first electrode.

According to an embodiment, the second electrode is formed to be opposite to the first electrode at both ends of the second waveguide, and the filter line is also inserted between both ends of the second waveguide and the second electrode .

According to an embodiment, the filter line may be formed with a meander structure having a period of several to several tens of micrometers ([mu] m).

The present invention provides a terahertz device in which a filter line of a meander structure is inserted between an electrode and a waveguide.

According to the present invention, it is possible to provide a high-efficiency terahertz device which can be miniaturized and reduced in cost, while reducing multiple reflection in the city area, that is, resonance phenomenon in the frequency domain to improve performance. Thus, the application range of the terahertz device can be extended.

1 is a view showing the structure and operation principle of a terahertz photoconductive antenna.
Fig. 2 is a diagram showing the structure of a terahertz spectral region spectroscopic image system.
3 is a diagram showing the structure and operation principle of a terahertz photomixer.
4 is a diagram showing the structure of a frequency domain terahertz spectroscopy system.
FIG. 5 is a view showing an example of a terahertz photoconductive antenna structure in detail and particularly showing multiple reflection and resonance phenomena that may occur in a terahertz photoconductive antenna of such a structure.
FIG. 6 is a diagram showing a signal and frequency spectrum of the terrestrial photoconductive antenna according to multiple reflection.
7 is a view showing a terahertz device according to an embodiment of the present invention.
8 is a drawing showing the effect of the present invention, particularly showing the effect of the meander structure of various cycles.

Hereinafter, embodiments of the present invention and other matters necessary for those skilled in the art to understand the present invention will be described in detail. The embodiments to be described below and related arts have been specifically described for the purpose of understanding the present invention and are illustrative only, regardless of their representations. That is, the present invention is not limited to the embodiments described below, but may be modified into various forms.

In the time band, 1 terahertz (THz) means 10 ¹² vibrations per second and has a short oscillation period of 1 picosecond (10 ^-12 seconds). Therefore, in order to generate and detect the THz wave, it is necessary to design the element and design it so that the operation can be performed at a very high speed while selecting the material.

However, generation and detection of THz waves are not easy with common semiconductor materials whose charge lifetime is several nanoseconds (10 ^-10 seconds). Thus, techniques have been developed that artificially reduce the lifetime of a charge within a semiconductor to below a few picoseconds, for example below a picosecond.

In this regard, a technique has been developed in which a crystal growth is performed at a lower temperature than a general growth condition by a molecular beam deposition method to artificially generate crystal defects, and the excessive charge is absorbed through such crystal defects to lower the lifetime of the charge.

In particular, such defect-controlled materials are essential for THz detectors. However, defect-controlled materials are very expensive due to the nature of the manufacturing process. Therefore, it is important to lower the unit cost in order to actually apply the technique of lowering the lifetime of the charge for the generation and detection of the THz wave.

There is a way to reduce the size of a semiconductor chip unit by lowering the unit price. If the number of chips that can be produced by processing a substrate having the same area is large, the unit cost is reduced, which is important for practical applications.

However, when the size of the chip is reduced as described above, the metal structures including the bias lines inside the chip act as antennas, and unwanted frequency characteristics are exhibited in the broadband detection. This is particularly fatal in spectral applications.

Accordingly, the present invention provides a method of reducing the size of a THz element and a module by reducing and ultimately eliminating unwanted frequency characteristics.

As the THz element to which the present invention can be applied, a THz photoelectric antenna (hereinafter referred to as THz-PCA) or a THz photo-mixer (hereinafter referred to as THz-PM) used for generation and / have. Specific embodiments of the THz device according to the present invention will be described later.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: FIG. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

1 is a diagram showing the structure and operation principle of a THz-PCA as an example of a THz element.

Referring to FIG. 1, the PCA for THz generation generates a transient current having a very short duration (e.g., a duration of less than 1 picosecond), thereby generating a THz pulse 107.

More specifically, a positive electrode 102 and a negative electrode 103 are formed on a substrate 101 made of a semiconductor or other material having a photoconductive property for generating a transient current, and the positive electrode 102 and the negative electrode 103 (That is, a gap region 104 is formed between the anode 102 and the cathode 103). A predetermined voltage 105 is applied between the anode 102 and the cathode 103 to form an electric field in the gap region 104.

When a light pulse 106 having a very short duration is applied to the gap region 104, a transient current flows instantaneously between the anode 102 and the cathode 103 due to the photoconductive property of the substrate 101 . This transient current emits a THz pulse 107 having an electric field magnitude proportional to the time derivative of the current in accordance with electromagnetic law.

In order to improve the emission efficiency, the shapes of the anode 102 and the cathode 103 may be formed in a planar antenna structure.

Also, a lens 108 having a hyper-hemispherical structure may be used for improving the emission efficiency. The lens 108 may be disposed in the direction in which the THz pulse 107 is emitted for the directivity of the THz wave.

Fig. 2 is a diagram showing the structure of a THz inverse spectroscopy and image system. More specifically, FIG. 2 shows a THz-time-domain spectroscopy (THz-TDS) using THz-PCA as shown in FIG.

Referring to FIG. 2, a pulse laser 201 having a duration of 200 femtoseconds (fs) or less is applied as a pulse light source for generation and detection of a THz wave, and THz-PCA shown in FIG. As shown in FIG. This THz wave is generated in the PCA 202 for generation on the transmission end side and detected on the detection PCA 203 on the reception end side.

In order to increase the efficiency, the laser for generation and measurement converges through a lens or the like in the gap region 104 of the THz-PCA as shown in FIG. 1, and the generated THz wave is transmitted through the THz lens 204 to the sample 205 And the PCA 203 for detection.

The characteristics of the THz wave can be acquired through the data acquisition device 207. [ More specifically, the data acquisition device 207 acquires the time-domain characteristics 207a of the THz wave transmitted through the specimen 205 by scanning an optical delay line (DL) 206 and performs Fourier transform (E.g., FFT) to obtain the spectral characteristics 207b of the THz wave. It is also possible to perform the THz spectroscopic measurement through the THz-TDS and to obtain the spectroscopic image by raster-scanning the specimen 205 on a two-dimensional plane.

Symbols M and BS, which are not described in FIG. 2, refer to a mirror and a beam-splitter, respectively, and these mirrors M and beam-splitter BS are used to control the path of light .

3 is a view showing the structure and operation principle of a THz photo-mixer. More specifically, FIG. 3 shows the structure and operation principle of the THz-PM for generating the continuous wave THz signal.

Referring to FIG. 3, the PM for generating THz generates a transient current whose magnitude is modulated at a very high rate of the THz frequency, thereby generating a THz continuous wave 307.

More specifically, a positive electrode 302 and a negative electrode 303 are formed on a substrate 301 made of a semiconductor or other material having a photoconductive property for generating a transient current, and the positive electrode 302 and the negative electrode 303 are formed between the positive electrode 302 and the negative electrode 303 A metal electrode is formed so as to have a gap region 304 including a finger structure or the like. A voltage 305 is applied between the anode 302 and the cathode 303 so that an electric field is formed in the gap region 304.

When a light source 306 vibrating at a THz frequency is incident on this gap region 304, a current oscillating continuously between the anode 302 and the cathode 303 is generated by the photoconductive property of the substrate 301, This current emits a THz continuous wave 307 according to the electromagnetic law.

In order to obtain a light source oscillating at the THz frequency, a method of generating a beating light source 306 that vibrates in the city area by spatially overlapping two different wavelengths of laser may be used.

In order to improve the emission efficiency, the anode 302 and the cathode 303 may be formed in a planar antenna structure. Also, a lens 308 having a primary spherical structure can be used for improving the emission efficiency.

4 is a diagram showing the structure of a frequency domain THz spectroscopy system. More specifically, FIG. 4 shows an example of a THz frequency-domain spectrometer (THz-FDS) using PM.

4, a first semiconductor laser 401 having a first wavelength (frequency)? 1 and a second semiconductor laser 401 having a second wavelength (frequency)? 2) for generating a beating light source 403, 402 through an optical system to generate a beating light source 403 that vibrates at a frequency corresponding to the difference between the first frequency and the second frequency (? 1 -? 2). The generated beating light source 403 is separated by the beam-splitter BS and is incident on the PM 404 for generating THz and the PM 405 for detection, respectively.

For control of the phase difference, a phaser 406 may be inserted on one of the optical paths of generation or detection.

Although not shown in the drawings, a lens for focusing the light source in the gap region (304 in FIG. 3) of the PMs 404 and 405 for generating / detecting can be used for increasing the light efficiency.

Like THz-TDS, THz-FDS can also be applied to spectroscopy and imaging. Particularly, in the spectroscopy, the frequency of the THz continuous wave (307 in FIG. 3) can be controlled by controlling the frequency of the beating light source 403 by adjusting the frequencies of the first and / or second semiconductor lasers 401 and 402 have.

FIG. 5 is a view showing an example of a THz-PCA structure in detail, and particularly shows multiple reflection and resonance phenomena that may occur in a THz-PCA having such a structure.

Referring to FIG. 5, a metal film of a THz-PCA structure as shown in FIG. 5 is formed on a substrate (for example, 101 in FIG. 1) having a very short charge lifetime having photoconductive properties. The metal film may include a first electrode 501 and a second electrode 502, a first waveguide 503a and a second waveguide 503b connected to the first electrode 501 and the second electrode 502, and the like.

The first electrode 501 and the second electrode 502 are electrodes to which different voltages are applied. For example, the first electrode 501 may be set as an anode, and the second electrode 502 may be set as a cathode. In an embodiment, a predetermined bias voltage may be applied to the first electrode 501, and a ground voltage may be applied to the second electrode 502.

The waveguide structure 503 is constituted by the first and second waveguides 503a and 503b. These first and second waveguides 503a and 503b are formed so as to sandwich a gap region 504 serving as a photoconductive switch to guide the THz electromagnetic wave excited to the photoconductive switch. 5, the total length of each of the first and second waveguides 503a and 503b is defined as L. In Fig.

In the THz-PCA of this structure, optical switching (sampling) of the THz wave can be achieved by injecting a pulsed laser into the gap region 504. An instantaneous light charge is generated by the optical sampling instant pulse laser and the generated light charge is separated by an electric field formed between the first electrode 501 and the second electrode 502 of the gap region 504 by the THz wave . Accordingly, a current flows through an external detector (not shown) connected to the first electrode 501 and the second electrode 502, thereby measuring the electric field strength of the THz wave. Also, by adjusting the time difference between the THz pulse and the light pulse, the intensity of the electric field can be measured in the municipal area.

In the THz-PCA having the structure as shown in FIG. 5, the incident THz pulse excites the mode of the waveguide structure 503. The excited mode propagates along the waveguide structure 503, causing reflection and transmission when it encounters structural discontinuities. As a result, the performance of the THz-PCA deteriorates, such as multiple reflections in the results of the municipal station measurement and resonance at specific frequency components.

There is a way to increase the length L of the waveguide structure 503 in order to improve the performance degradation caused by multiple reflection or resonance phenomenon. For example, in the case of a detector for precise spectroscopy, the length L of the waveguide structure 503 is designed to be 1 cm or more.

However, when the length L of the waveguide structure 503 becomes longer, the number of elements that can be manufactured on one substrate is limited. Therefore, a measure must be taken to reduce the size of the device, particularly the length L of the waveguide structure 503, while preventing distortion in the broadband spectrum and in the backwind waveform due to multiple reflections and resonance phenomena as described above.

FIG. 6 is a diagram showing a time domain signal and a frequency spectrum of THz-PCA due to multiple reflection. In particular, FIG. 6 shows the result of THz-pulse measurement using the inverse spectroscopy technique using THz-PCA of the structure shown in FIG. 5 as a detector.

Referring to FIG. 6A, after the main THz pulse 601, it can be seen that multiple pulses 602 appear.

As a result of the Fourier transform (e.g., FFT), it is confirmed that multiple peaks 603 appear due to multiple reflections in the spectrum in the low frequency region, as shown in FIG. 6B. This is a factor that makes spectroscopic applications difficult, and needs to be minimized.

7 is a view showing a THz element according to an embodiment of the present invention. THz-PCA or THz-PM may be used as the THz element to which the embodiment structure shown in FIG. 7 can be applied. For the sake of convenience, in the description of the embodiment of FIG. 7, detailed description of components similar to or the same as those of FIG. 5 will be omitted.

Referring to FIG. 7, a THz device according to an embodiment of the present invention includes a filter line 705 implemented using an electrode connection line of a meander structure meander structure.

More specifically, the THz element according to the embodiment of the present invention includes a first electrode 701 and a second electrode 702 formed on a substrate (for example, 101 in FIG. 1) having a photoconductive property, A waveguide structure 703 including a first waveguide 703a connected to the first electrode 701 and a second waveguide 703b connected to the second electrode 702, And a gap region 704 formed between the two waveguides 703b.

The first electrode 701 and the second electrode 702 may be integrated with a first electrode pad to which a first voltage is applied and a second electrode pad to which a second voltage is applied, respectively. In this case, the first and second electrodes 701 and 702 may be regarded as first and second electrode pads, respectively.

It should be noted that the THz element according to the embodiment of the present invention has at least one of the first electrode 701 and the first waveguide 703a and the second electrode 702 and the second waveguide 703b And a filter line (electrode connection line for filtering function) 705 having a meander structure inserted into the electrode line 705. Thus, the influence of multiple reflections can be minimized.

For example, the meander-shaped filter line 705 is formed between the first electrode 701 and the first waveguide 703a and between the second electrode 702 and the second waveguide 703b, respectively .

The first electrode 701 is formed on both ends of the first waveguide 703a and the second electrode 702 is formed on both ends of the second waveguide 703b by the first electrode 701 For example, be symmetrical. In this structure, a filter line 705 is inserted between both ends of the first waveguide 703a and the first electrode 701, and both ends of the second waveguide 703b and the second electrode 702 The filter line 705 can be inserted between the filter lines 705 and 705, respectively.

This filter line 705 is formed on the photoconductive substrate such that it is disposed on a plane substantially coincident with the plane where the first and second electrodes 701 and 702 and the first and second waveguides 703a and 703b are formed . That is, the filter line 705 according to the present embodiment can be implemented as a two-dimensional planar filter line.

In addition, the filter line 705 is connected to the first or second electrodes 701, 702 and the first or second waveguide 703a, 703b electrically connected thereto, as shown in Fig. 7 And may have a meander structure having a predetermined period (P).

For example, the filter line 705 may be formed with a meander structure having a period P of several to several tens of micrometers (or less, um). This is a numerical value proposed in the embodiment in consideration of ease of fabrication and expected effect of the meander structure. For example, when a minute meander structure is applied to a degree P of less than 1 탆, it may be difficult to mass- In the case of a meander structure having a period P of 100 μm or more, it is considered that the filtering effect expected in the present invention can be relatively reduced. However, it should be understood that the present invention is not limited thereto, and that the period P of the filter line 705 may be variously changed according to the manufacturing environment of the THz device or the desired characteristic value.

In addition, the shape P of the meander structure that can be applied to the filter line 705, as well as the shape thereof, may be variously changed. For example, it is apparent that a line having a more complicated bending structure than the meander structure as shown in Fig. 7 can also fall within the scope of the present invention.

8 is a drawing showing the effect of the present invention, particularly showing the effect of the meander structure of various cycles.

8, three types of meander-shaped THz devices having a period (P) of 36 mu m, 24 mu m, and 6 mu m are fabricated, and a reference structure having no meander structure (e.g., (REF) of the THz element of the structure shown in FIG.

Figure 8 (A) shows the municipal signal measured with THz-PCA with various meander structures. As shown in FIG. 8 (A), it can be seen that as the period decreases, the effect of multiple reflections after the main peak and the resonance phenomenon are significantly reduced compared to the measurement result (REF) in the reference structure.

As a result, the peaks of the frequency spectrum are also decreased as shown in FIG. 8 (B).

In order to more clearly show the effect of the meander structure according to the embodiment of the present invention, in FIG. 8C, the vertical axis is set as a logarithmic scale interval, and compared with the measurement result (REF) The effect of the under structure was shown.

As can be seen from FIG. 8, through the meander structure proposed in the embodiment of the present invention, the performance of the THz element, for example, the receiving THz-PCA can be improved.

As described above, an embodiment of the present invention discloses a THz device in which a planar filter structure, e.g., a planar meander structure, filter line 705 is inserted.

More specifically, according to an embodiment of the present invention, a bias line (e.g., a first electrode) of a THz element such as THz-PCA or THz-PM (e.g., first electrode 701) and / (Electrode connection line) is inserted into the line (filter line, 705) which can serve as a filter. This reduces multiple reflections in the city area, that is, resonance in the frequency domain.

In other words, the present invention provides a planar filter structure capable of controlling or eliminating frequency characteristics due to a bias electrode or an electrode structure for detection in a THz generating and / or detecting element.

According to the embodiments of the present invention, it is possible to provide a THz element that can prevent emission and detection of unwanted electromagnetic waves due to resonance in a specific frequency range. Accordingly, the THz element according to the present invention has more suitable performance for spectroscopic measurement.

In addition, by preventing the energy loss to the resonance frequency, the effect of increasing the measurement efficiency of the THz element can also be expected.

The concept of the present invention can be broadly interpreted as a function of inserting a filter capable of blocking electromagnetic waves in the low frequency region between the detection unit and the electrode unit to enhance the detection efficiency and performance of the THz device.

Thereby, it is possible to provide a THz device capable of reducing the unit cost and downsizing while securing a desired characteristic value. Thus, the application range of the THz element can be extended.

It is to be noted that the technical idea of the present invention has been specifically described in accordance with the above-mentioned embodiments, but it should be noted that the above embodiments are intended to be illustrative and not restrictive. It will be apparent to those skilled in the art that various modifications may be made without departing from the scope of the present invention.

701: first electrode 702: second electrode
703: waveguide structure 703a: first waveguide
703b: second waveguide 704: gap region
705: Filter line

Claims (5)

First and second electrodes,
First and second waveguides respectively connected to the first and second electrodes,
A gap region between the first and second waveguides,
A meander structure filter line is inserted into at least one of the first electrode and the first waveguide and between the second electrode and the second waveguide. The method according to claim 1,
Wherein the filter line is a planar filter line formed on a plane in which the first and second electrodes and the first and second waveguides are formed. The method according to claim 1,
The first electrode is formed at both ends of the first waveguide,
Wherein the filter line is inserted between both ends of the first waveguide and the first electrode. The method of claim 3,
Wherein the second electrode is formed at both ends of the second waveguide so as to face the first electrode,
And the filter line is inserted between both ends of the second waveguide and the second electrode. The method according to claim 1,
Wherein the filter line is formed with a meander structure having a period of several to several tens of micrometers (占 퐉).

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