An actively electrically controlled terahertz metamaterial filter based on negative differential resistance effect

Abstract

The present invention discloses an active electrically controlled terahertz metamaterial filter based on the negative differential resistance effect, consisting of a top metamaterial layer, a metal electrode, a substrate layer, and a bottom metamaterial layer. The invention belongs to the field of terahertz technology. The top metamaterial layer is composed of a periodic metal array structure, the substrate layer is gallium arsenide, a III-V semiconductor material with a negative differential resistance effect, and the bottom metamaterial layer on the lower surface of the substrate is composed of a periodic metal array structure. Two metal electrodes are fabricated on the upper surface of a heavily doped substrate. A high bias voltage is applied to the semiconductor substrate through the two metal electrodes, generating a strong transverse electric field within the semiconductor substrate, which induces a negative differential resistance effect in the semiconductor material. This changes the material properties of the semiconductor substrate, thereby affecting the resonant frequency and transmittance of the device, thereby forming an active electrically controlled terahertz metamaterial filter device.

Description

Technical Field

[0001] The present invention belongs to the field of terahertz technology, and in particular relates to an active electrically controlled terahertz metamaterial filter based on negative differential resistance effect. Background Art

[0002] Terahertz (THz) waves are electromagnetic waves with a frequency of 0.1THz-10THz and a wavelength range of 0.03-3mm. They are located between the microwave and infrared bands on the electromagnetic spectrum. This band is in the frequency band where macroscopic electronics transitions to microscopic optoelectronics. Terahertz waves have lower energy and stronger penetrating power, as well as transparency to most dielectric materials. This makes terahertz waves widely used, such as in radar, non-destructive testing, transmission imaging, etc. One of the difficulties in the research of terahertz functional devices is that most natural materials cannot produce a more obvious electromagnetic response to terahertz waves. Metamaterials composed of periodic or non-periodic metal arrays can achieve flexible and diverse control of the amplitude, phase, polarization and propagation of terahertz waves, thereby providing an effective way to realize terahertz functional devices.

[0003] Research on actively tunable terahertz metamaterial devices has become a hot topic among researchers both domestically and internationally. There are five approaches to implementing these devices. The first involves temperature-adjustable materials whose phase-change properties change with temperature as the device's resonant or dielectric layer. The second involves laser-adjustable materials whose electrical properties change with light intensity, embedded in the openings or gaps of the unit structure. The third involves using electrically controlled Fermi-level-adjustable materials, whose Fermi level changes with voltage, as structural membranes. The fourth involves piezoelectric-deformable metamaterials, where voltage is used to alter the metamaterial's structure. The fifth involves integrating nonlinear elements or materials, such as varactor diodes, into the unit structure's openings.

[0004] There are various ways to realize actively tunable terahertz metamaterial devices, but the invention of using the negative differential resistance effect of III-V semiconductors (such as GaAs, GaN, InP, etc.) to achieve active electrical control of the electromagnetic properties of metamaterial devices has not yet appeared.

[0005] Among the existing modulation methods for terahertz metamaterial devices, the experimental environment for optical modulation is harsh; the temperature-sensitive materials used in temperature modulation require strict control of ambient temperature and oxygen content during processing; MEMS modulation has high requirements for the device preparation process; and devices with integrated electronic components in electrical modulation mostly operate in the microwave range due to their large area. Summary of the Invention

[0006] The present invention aims to provide an active electrically tunable terahertz metamaterial filter based on the negative differential resistance effect. By applying a high bias lateral voltage to a III-V semiconductor substrate, the heavily doped layers at both ends and the intermediate semiconductor substrate form a Gunn diode, generating a negative differential resistance effect within the semiconductor. This causes changes in the distribution of carrier concentration, mobility, and effective mass within the substrate, thereby changing the resonant characteristics of the device, thereby forming an electrically tunable active terahertz metamaterial filter.

[0007] In order to solve the above technical problems, the specific technical solutions of the present invention are as follows:

[0008] An active electrically controlled terahertz metamaterial filter based on negative differential resistance effect consists of a top metamaterial layer, a top metal electrode, a substrate layer and a bottom metamaterial layer.

[0009] Furthermore, the top metamaterial layer is a periodic array structure;

[0010] Furthermore, the bottom metamaterial layer is a periodic array structure;

[0011] Further, a top metamaterial layer is fabricated on the upper surface of the semiconductor substrate;

[0012] Furthermore, the bottom metamaterial layer is fabricated on the lower surface of the semiconductor substrate;

[0013] Furthermore, the structural unit of the top metamaterial layer can adopt a cross structure, a square ring structure, an open resonant ring, a ring structure, etc.

[0014] Furthermore, the structural unit of the bottom metamaterial layer can adopt a cross structure, a square ring structure, an open resonant ring, a ring structure, etc.

[0015] Furthermore, the material of the top metamaterial layer, the metal electrode and the bottom metamaterial layer is one of gold, silver, copper and aluminum;

[0016] Furthermore, the substrate layer is a III-V semiconductor having a negative differential resistance effect;

[0017] Furthermore, a metal electrode is formed on the upper surface of the semiconductor substrate;

[0018] Furthermore, the III-V semiconductor material is one of gallium arsenide, gallium nitride, and indium phosphide. When a high bias voltage is applied to the substrate (the electrode and the substrate are equivalent to forming a Gunn diode), the high bias voltage causes a negative differential resistance effect within the substrate layer, thereby affecting the substrate's material properties such as carrier concentration, mobility, and effective mass distribution;

[0019] Furthermore, the Gunn diode operates in one of an ideal mode, a dipole domain transit time mode, an electron accumulation domain mode, a confined space charge accumulation mode, and a quenched dipole layer mode;

[0020] The present invention's active electrically controlled terahertz metamaterial filter based on the negative differential resistance effect has the following advantages: By utilizing the negative differential resistance of III-V semiconductors to alter the device's transmission characteristics, the invention provides a novel approach to realizing active terahertz metamaterial devices. Compared to dynamic control using optical, thermal, or magnetic methods, voltage-based control is much easier to implement, requiring no complex equipment or experimental conditions, and is therefore more convenient to use. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A three-dimensional schematic diagram of the top of the active electrically controlled terahertz metamaterial filter structure based on the negative differential resistance effect of the present invention;

[0022] Figure 2 This is a three-dimensional schematic diagram of the bottom of the active electrically controlled terahertz metamaterial filter structure based on the negative differential resistance effect of the present invention;

[0023] Figure 3 2. It is a top two-dimensional schematic diagram of the active electrically controlled terahertz metamaterial filter based on negative differential resistance effect of the present invention;

[0024] Figure 4 This is a two-dimensional bottom schematic diagram of the active electrically controlled terahertz metamaterial filter based on the negative differential resistance effect of the present invention;

[0025] Figure 5 A comparison diagram of transmission characteristic curves of the device when voltage is applied and when no voltage is applied under the ideal mode of the present invention;

[0026] Explanation of the marks in the figure: 1. First metamaterial layer; 2. Substrate layer; 3. Anode; 4. Anode highly doped semiconductor layer; 5. Cathode highly doped semiconductor layer; 6. Cathode; 7. Second metamaterial layer. DETAILED DESCRIPTION

[0027] In order to better understand the purpose, structure and function of the present invention, the following is a further detailed description of an active electrically controlled terahertz metamaterial filter based on negative differential resistance effect of the present invention in conjunction with the accompanying drawings.

[0028] like Figure 1 As shown in FIG, the active electrically controlled terahertz metamaterial filter based on the negative differential resistance effect of the present invention is composed of a first metamaterial layer 1, an anode 3, a cathode 6, a substrate layer 2, and a second metamaterial layer 7. Figure 3 、 Figure 4As shown, the first metamaterial layer 1 is composed of periodically arranged cross-shaped metal structural units. Figure 2 As shown, the second metamaterial layer 7 is composed of periodically arranged square ring metal structural units. Figure 1 , Figure 3 As shown, the anode 3 and cathode 6 are made on the upper surface of the substrate layer 2. The substrate layer 2 is a semiconductor material with a negative differential resistance effect. Figure 1 As shown in the stripe pattern area, there is an anode highly doped semiconductor layer 4 under the pattern corresponding to the anode 3, and a cathode highly doped semiconductor layer 5 under the pattern corresponding to the cathode 6, so that the two electrodes form ohmic contact with the substrate layer.

[0029] The structural unit of the first metamaterial layer 1 can adopt a cross structure, a square ring structure, an open resonant ring, a ring structure, etc. In this embodiment, the cross structure is selected.

[0030] The structural unit of the second metamaterial layer 7 can adopt a cross structure, a square ring structure, an open resonant ring, a ring structure, etc. In this embodiment, the square ring structure is selected.

[0031] The materials of the first metamaterial layer 1 , the anode 3 , the cathode 6 , and the second metamaterial layer 7 can be gold, silver, copper, aluminum, etc. In this embodiment, gold is selected.

[0032] In this embodiment, the period of the artificial unit structure of the first metamaterial layer 1 on the upper surface of the substrate layer 2 is preferably 38 μm, the cross length is 34 μm, the width of the wider metal strip is 16 μm, the width of the narrower metal strip is 8 μm, and the thickness is 150 nm. The thickness of the substrate layer 2 is preferably 8 μm, and the substrate doping concentration is 1×10 16 cm -3 Preferably, the artificial unit structure period of the second metamaterial layer 7 on the lower surface of the substrate layer 2 is 38 μm, the side length of the square ring is 34 μm, the width of the square ring is 2 μm, and the thickness is 150 nm.

[0033] The dynamic control of the electromagnetic response of the metamaterial is achieved by tuning the material properties of the semiconductor substrate layer 2. In this embodiment, the substrate layer 2 is made of a group III-V semiconductor. Based on the negative differential resistance effect, the material properties of the semiconductor are modulated. The semiconductor material is one of gallium arsenide, gallium nitride, and indium phosphide. In this embodiment, gallium arsenide is preferably used. A high bias voltage is applied to the gallium arsenide substrate through two electrodes. At this time, the two electrodes and the gallium arsenide substrate form a Gunn diode. The Gunn diode based on the negative differential resistance effect has five working modes: ideal mode, dipole domain transit time mode, electron accumulation domain mode, limited space charge accumulation mode, and quenched dipole layer mode. In this embodiment, it is assumed that there are no defects and inhomogeneities inside the semiconductor. At this time, the Gunn diode operates in the ideal mode. In the ideal mode, the high electric field is evenly distributed throughout the semiconductor. Therefore, it can be considered that the movement of carriers everywhere inside the semiconductor is the same, and the material properties everywhere inside the semiconductor are also the same, and no oscillating current will be generated. In the ideal mode, the electrons in the central valley inside the semiconductor obtain enough energy to jump to the satellite valley, resulting in a decrease in the electron mobility of the semiconductor material, an increase in the effective mass of electrons, and an increase in the real part of the dielectric constant, thereby causing a redshift in the resonance frequency of the device. The enhancement of the resonance intensity is due to the influence of impedance matching. The material properties of the semiconductor change with the voltage, which will affect the equivalent impedance of the device.

[0034] As Figure 5 shown are the transmission characteristic curves of the device with (without) voltage applied. Among them, V0 = 0 < V1, V0 is the voltage not applied, V1 is the voltage applied, and V1 can excite all electrons to the high-energy valley, causing the negative differential resistance effect in the substrate layer (2). It can be seen from the curve that after the voltage is applied, the resonance frequency of the device decreases and the transmission intensity increases.

[0035] Therefore, in the ideal mode, by applying different magnitudes of transverse voltages, the time-invariant control of the resonance frequency and resonance amplitude of the metamaterial device can be achieved. However, this mode has very high requirements for the contact between the semiconductor material and the electrodes, so it is very difficult to achieve. In practice, this device is more likely to generate the dipole domain transit time mode.

[0036] Embodiment 2:

[0037] The following changes are made in this embodiment compared with Embodiment 1:

[0038] In reality, there are always various defects and impurities inside the semiconductor substrate. These impurities and defects can lead to the generation of space charge regions, and charge domains are generated near the cathode due to changes in carrier concentration and other reasons. The device described in the present invention is more likely to generate a dipole domain transit time mode. In the dipole domain transit time mode, a dipole domain consisting of an electron accumulation layer and an electron depletion layer is generated near the cathode. After the dipole domain is generated from the cathode, it continues to grow as it moves toward the anode, and is eventually absorbed by the anode. Then, new dipole domains continue to be generated at the cathode, and this cycle repeats, generating an oscillating current.

[0039] A dipole domain consists of an electron accumulation layer and an electron depletion layer. When a dipole domain is first generated at the cathode, the electron concentration in the electron accumulation layer increases, the mobility decreases, and its width is relatively small, so its influence can be ignored. The electron concentration in the electron depletion layer decreases, the mobility decreases, and its width is relatively small, so its influence can be ignored. In the region between the cathode and the electron accumulation layer, the electron concentration and mobility are the same everywhere, the electric field is small, and the mobility is high. In the region between the electron accumulation layer and the electron depletion layer, the electron concentration and mobility are the same everywhere, the electric field is high, and the mobility is low. In the region between the electron depletion layer and the anode, the electron concentration and mobility are the same everywhere, the electric field is small, and the mobility is high. Therefore, compared to semiconductor materials without an electric field, the overall electron mobility of semiconductors with a high bias voltage decreases, and the effective mass increases. This increases the real part of the dielectric constant, which affects the resonant frequency of metamaterial devices and causes them to redshift.

[0040] The dipole domain continues to move toward the anode, the area between the cathode and the electron accumulation layer is gradually getting longer, the area between the electron accumulation layer and the electron depletion layer is gradually getting shorter, and the area from the electron depletion layer to the anode remains basically unchanged. Therefore, the overall mobility of the material is constantly increasing, the effective mass is constantly decreasing, and the real part of the dielectric constant is constantly decreasing, causing the resonant frequency of the device to continue to blueshift.

[0041] When the dipole domain moves to the vicinity of the anode, the electron depletion layer begins to be absorbed by the anode, the area between the cathode and the electron accumulation layer gradually becomes longer, and the area between the electron accumulation layer and the electron depletion layer gradually becomes shorter. Therefore, the mobility of the material continues to increase, the effective mass continues to decrease, and the real part of the dielectric constant continues to decrease, causing the resonant frequency of the device to continue to blueshift.

[0042] As the dipole domains continue to move, the electron accumulation layer also begins to be absorbed by the anode. The electric field outside the domain gradually increases as the domain is absorbed by the anode. Therefore, the mobility in the region from the cathode to the electron accumulation layer continues to decrease. Therefore, the real part of the dielectric constant of the semiconductor gradually increases, and the resonant frequency continues to redshift.

[0043] Therefore, in the dipole domain transit time mode, moving dipole domains will be generated under high bias lateral voltage, making the voltage regulation of the resonant frequency of the metamaterial device time-varying.

[0044] It will be understood that the present invention is described by way of some embodiments, and it will be appreciated by those skilled in the art that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are intended to be protected by the present invention.

Claims

1. An active electrically controlled terahertz metamaterial filter based on negative differential resistance effect, characterized in that: The invention comprises a first metamaterial layer (1) composed of top artificial structural units, an anode (3), a cathode (6), a substrate layer (2), an anode highly doped semiconductor layer (4), a cathode highly doped semiconductor layer (5), and a second metamaterial layer (7) composed of bottom artificial structural units; the first metamaterial layer (1) is provided on the substrate layer (2), the anode highly doped semiconductor layer (4) is provided on one side of the substrate layer (2), and the cathode highly doped semiconductor layer (5) is provided on the other side of the substrate layer (2); the anode (3) is provided on the anode highly doped semiconductor layer (4), and the cathode (6) is provided on the cathode highly doped semiconductor layer (5); wherein the first metamaterial layer (1), the anode (3), and the cathode (6) are on the same plane; and the second metamaterial layer (7) composed of the artificial structural units is provided at the bottom of the substrate layer (2); The substrate layer (2) is a semiconductor material having a negative differential resistance effect; The semiconductor material of the substrate layer (2), the anode highly doped semiconductor layer (4) and the cathode highly doped semiconductor layer (5) is one of gallium arsenide, gallium nitride and indium phosphide. A high bias voltage is applied to the substrate layer (2) via the anode (3) and the cathode (6). At this time, the anode (3), the cathode (6) and the substrate layer (2) form a Gunn diode. The negative differential resistance effect generated inside the substrate layer (2) affects the distribution of carrier concentration, mobility and effective mass in the substrate layer (2), thereby changing the resonance characteristics of the filter.

2. The active electrically controlled terahertz metamaterial filter based on negative differential resistance effect according to claim 1, characterized in that: The first metamaterial layer (1) is composed of periodically arranged artificial structural units.

3. The active electrically controlled terahertz metamaterial filter based on negative differential resistance effect according to claim 1, characterized in that: The second metamaterial layer (7) is composed of periodically arranged artificial structural units.

4. The active electrically controlled terahertz metamaterial filter based on negative differential resistance effect according to claim 1, characterized in that: The structural units of the first metamaterial layer (1) and the second metamaterial layer (7) are one of a cross structure, a square ring structure, an open resonant ring, and a ring structure.

5. The active electrically controlled terahertz metamaterial filter based on negative differential resistance effect according to claim 1, characterized in that: The materials of the first metamaterial layer (1), the anode (3), the cathode (6) and the second metamaterial layer (7) are one of gold, silver, copper and aluminum.

6. The active electrically controlled terahertz metamaterial filter based on negative differential resistance effect according to claim 1, characterized in that: The anode (3) forms ohmic contact with the anode highly doped semiconductor layer (4), and the cathode (6) forms ohmic contact with the cathode highly doped semiconductor layer (5).

7. The active electrically controlled terahertz metamaterial filter based on negative differential resistance effect according to claim 1, characterized in that: The operating mode of the Gunn diode is one of an ideal mode, a dipole domain transit time mode, an electron accumulation domain mode, a confined space charge accumulation mode or a quenched dipole layer mode.

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