CN105610410B - A kind of Terahertz multiband modulator based on HEMT - Google Patents

Abstract

The invention discloses a terahertz multi-band modulator based on a high electron mobility transistor, which belongs to the technical field of electromagnetic functional devices and focuses on fast dynamic functional devices in the terahertz band. Combining HEMT with the optimized design of Metamaterials containing a variety of complex resonance modes, using the high-speed dynamic characteristics of HEMT and the precise control ability of Metamaterials on electromagnetic waves, the distribution of two-dimensional electron gas in HEMT is controlled by the applied voltage, and then the artificial The resonance mode conversion of the electromagnetic medium enables the HEMT terahertz modulator to have large modulation depth and high modulation efficiency in the four amplitude modulation frequency bands, and the phase modulation depth in the phase modulation frequency band can reach more than 90 degrees.

Description

A Terahertz Multiband Modulator Based on High Electron Mobility Transistors

technical field

The invention belongs to the technical field of electromagnetic functional devices, focusing on fast dynamic functional devices in the terahertz band.

Background technique

As one of the most important application directions in the field of terahertz, terahertz wireless communication has attracted the attention of countries all over the world. Compared with microwave communication, optical fiber communication and optical wireless communication, terahertz communication system has unique advantages. For example, compared with microwave communication, the application of THz can provide larger bandwidth and higher transmission speed. In addition, the size of the antenna will be significantly reduced, which is suitable for inter-satellite communication; THz can provide multiple data transmission. The range of action is greater than the line-of-sight infrared transmission; compared with optical communication, the loss of optical communication comes from the scattering and absorption of clouds, rain, dust, etc., the higher the frequency, the stronger the scattering, and compared with light waves, THz particle scattering is smaller Therefore, THz communication can be used as a backup system for optical communication links, and it can still maintain short-distance broadband communication in dense smoke and dust environments. Terahertz wireless communication technology has always been highly valued by Western powers, such as intersatellite communication, short-range atmospheric communication, short-range terrestrial wireless local area network, etc.

As one of the most critical core technologies in terahertz communication systems, terahertz wave dynamic functional devices—terahertz external modulators have become the focus of terahertz science and technology research. Since the size required for functional devices in the terahertz band is on the order of microns or even nanometers, communication devices in the microwave band cannot be directly applied to the terahertz band. Since 2004, a number of articles on terahertz wave external modulators have been published in top international natural science journals such as Nature and Science, including materials based on doped silicon, gallium arsenide, phase change materials and graphene. Combined with artificial electromagnetic media (Metamaterials), the modulation of terahertz waves is realized by using excitation methods such as external temperature, light, and electric fields.

In recent years, with the development of semiconductor materials and technologies, High Electron Mobility Transistor (HEMT) has shown outstanding performance and has been successfully applied to detectors, amplifiers and other fields. Dynamic devices provide new development ideas. A high electron mobility transistor (High Electron Mobility Transistor, HEMT) is a new type of field-effect transistor that utilizes the two-dimensional electron gas (2-DEG) existing in a modulated doped heterojunction to work. In 1978, R. Dingle first observed high electron mobility in modulation-doped GaAs/AlGaAs superlattice grown by MBE (molecular beam epitaxy). In 1980, Mimura of Fujitsu Corporation of Japan developed HEMT, which was successfully applied to microwave low-noise amplification. The third-generation wide-bandgap semiconductor material GaN not only has a wide band gap, but also has the characteristics of high thermal conductivity, high electron saturation rate, strong breakdown field and good thermal stability. Therefore, HEMTs based on GaN materials have great advantages in the preparation of high-speed functional devices.

Contents of the invention

The technical problem to be solved by the present invention is to design an external high-speed modulator in terahertz space that can work in multiple frequency bands through external voltage control, and has amplitude modulation effects of large modulation depth and high modulation efficiency in each modulation frequency band, At the same time, the modulator also has a certain phase modulation capability.

The technical solution adopted by the present invention to solve the above-mentioned problems is to combine HEMT with optimized designed Metamaterials containing multiple complex resonance modes, utilize the high-speed dynamic characteristics of HEMT and the precise control ability of Metamaterials to electromagnetic waves, and control the HEMT through an applied voltage The distribution of the two-dimensional electron gas in the medium changes, and then controls the resonance mode conversion of the artificial electromagnetic medium, so that the HEMT terahertz wave modulator has the modulation effect of large modulation depth and high modulation efficiency in the four frequency bands, and the phase modulation depth can be adjusted. Up to 90 degrees or more.

Therefore, the present invention is a multi-band modulator based on a high electron mobility transistor, which includes: a semiconductor substrate, an epitaxial layer disposed on the semiconductor substrate, and a modulation unit array disposed on the epitaxial layer; the modulation unit Each modulation unit of the array includes: a source resonator, a drain resonator, a gate connection line, and a semiconductor-doped heterostructure; wherein the source resonator and the drain resonator are "E"-shaped structures with the same shape and size , symmetrically arranged on both sides of the gate connecting line with openings facing each other; the "E"-shaped structure includes a short branch, long branches located on both sides of the short branch and metal feeders connecting each branch; wherein the semiconductor is doped with heterogeneous The structure connects the source resonator and the drain resonator to the opposite "E"-shaped structure long branch, and the semiconductor doped heterostructure is arranged at the end of the "E"-shaped structure long branch of the source resonator and the drain resonator and located below the gate connection line; each row of modulation units in the modulation unit array shares the same gate connection line, and the gate connection line of each row is connected to the same negative electrode; the source of each row of modulation units The pole resonator and the drain resonator are respectively communicated with and connected to the positive electrode through a metal feeder.

Further, the ends of the long branches in the "E"-shaped structure of the source resonator and the drain resonator are connected to the doped heterojunction structure through metal electrodes.

Further, the end of the long branch in the "E" shaped structure of the source resonator and the drain resonator is provided with a short branch perpendicular to the end and extending inward, forming an "L" shaped structure; the source resonator A short branch perpendicular to the end is arranged at the end of the short branch in the "E" shape structure of the drain resonator to form a "T" shape structure.

Further, the part of the gate connection line located in the semiconductor-doped heterostructure is narrower than other parts.

Further, the modulation unit array is an M*N array composed of a plurality of modulation units, where M>3 and N>3.

The metal electrode material is Ti, Al, Ni or Au.

The material of the semiconductor substrate is sapphire, high resistance silicon or silicon carbide.

The material of the semiconductor-doped heterostructure is AlGaN/GaN, InGaN/GaN, AlGaAs/GaAs, AlGaAs/InGaAs or AlGaAs/InGaAs/InP, wherein the slash indicates the combination of the two materials.

The material of the source resonator, drain resonator, gate connection line and metal feeder line is Au, Ag, Cu or Al.

The beneficial effects of the present invention are: (1), each modulation unit of the HEMT terahertz multi-band modulator contains two high electron mobility transistors, compared with the design concept of only one transistor, the double transistor design is greatly enhanced The ability of HEMT to regulate the artificial electromagnetic resonance structure is improved, the utilization efficiency of the resonance mode is effectively improved, and the foundation for the multi-band modulation capability is laid. (2) The HEMT modulator combines the artificial electromagnetic resonance structure obtained after optimization design with the HEMT efficiently, so that the modulator has four different resonance frequency points in the two states of HEMT on and off, so that the modulator has Four amplitude modulation frequency bands; at each resonance frequency point, the resonance structure has different and complex resonance modes. Modulation depth and modulation efficiency. (3) The modulator not only has multi-band amplitude modulation capability, but also has good phase modulation capability. It has three phase modulation frequency bands, and the phase modulation depth in two frequency bands can reach more than 90 degrees. (4) The modulator uses a high electron mobility transistor as its control device. The high mobility characteristics of the two-dimensional electron gas in the HEMT allow the modulator to quickly switch between different resonance modes, so the modulator has a very high modulation rate. (5) In the present invention, the modulation unit array formed by Metamaterials design is a two-dimensional planar structure, which can be realized by means of micro-fabrication, mature technology, easy to manufacture, and avoids the difficult processing brought by the design scheme of complex three-dimensional structure . (6) The present invention designs a transmissive terahertz wave modulator, which is simpler to operate and more convenient to use than a reflective modulator, and can play a role more effectively in terahertz point-to-point communication. (7), the modulator designed by the present invention has excellent amplitude modulation and phase modulation capabilities for terahertz waves, and the device can work under normal temperature, normal pressure, and non-vacuum conditions, without waveguide loading, and is easy to package, which makes The modulator has good development and application prospects.

Description of drawings:

FIG. 1 is a schematic diagram of an overall design scheme of a HEMT multi-band modulator.

FIG. 2 is a perspective schematic diagram of a modulation unit of a HEMT multi-band modulator.

Fig. 3 is a schematic diagram of electric field and surface current distribution of the resonant unit in the state of voltage application.

Fig. 4 is a model diagram of electric field and surface current distribution of the resonant unit in the state of no voltage applied.

Fig. 5 is a simulation diagram of transmission curves of a HEMT multi-band modulator under different voltages.

Fig. 6 is a simulation diagram of the phase change of the HEMT multi-band modulator under different voltages.

In the figure: 1. Semiconductor substrate, 2. Epitaxial layer, 3. Positive voltage loading electrode, 4. Negative voltage loading electrode, 5. Modulation cell array, 5-1. Long branch end in "E" shape structure, 5- 2. Metal electrodes.

Detailed ways

The modulation functional area of the HEMT terahertz wave space external multi-band modulator in the present invention is a triode array structure in which HEMT and Metamaterials are ingeniously and effectively combined. Through the optimized design of the resonance structure and the efficient combination with dual transistors, the modulator has There are four amplitude modulation frequency bands and three phase modulation frequency bands, and the amplitude modulation efficiency in the amplitude modulation frequency band can reach more than 90%, and the phase modulation depth in the phase modulation frequency band can reach more than 90 degrees. The modulator controls the concentration change of the two-dimensional electron gas in the HEMT through an applied voltage, and the high mobility characteristics of the two-dimensional electron gas in the HEMT allow the modulator to quickly switch between different resonance modes, enabling it to obtain a fairly high amplitude modulation, Phasing rate. The simulation calculation shows that this is a multi-band, high-efficiency, fast terahertz wave amplitude modulation and phase modulation device with great development potential and practical value.

The invention comprises a semiconductor substrate (1), an epitaxial layer (2), a modulation unit array (5), a positive voltage loading electrode (3) and a negative voltage loading electrode (4). The positive voltage loading electrode (3), the negative voltage loading electrode (4) and the modulation unit array (5) constitute a metal structure layer, and an epitaxial layer (2) and a semiconductor material substrate (1) are sequentially arranged under the metal structure layer. The modulation unit group is an array of M*N composed of a plurality of modulation units, wherein M>3, N>3; the modulation unit includes a high electron mobility transistor and an artificial metal electromagnetic resonance structure, and each transistor gate is connected to Negative voltage applied electrode (5), source and drain connected to positive voltage applied electrode (3).

Each modulation unit contains two symmetrical and identical transistors. Each transistor is composed of source, gate, drain and modulation doped heterogeneous materials. The transistors are located on the upper side of the "L" structure and the lower side Between the "L"-shaped structures and short metal horizontal bars in the "L"-shaped structures are overlaid on the source or drain of each transistor.

The structure of the artificial metal electromagnetic resonance unit is composed of a source resonator, a drain resonator, and a gate connecting line. The E"-shaped structure is the source resonator, and the lower "E"-shaped structure is the drain resonator. Each "E"-shaped structure contains two symmetrical "L"-shaped structures and a "T"-shaped structure, " A long metal bar in the E" structure connects the three structures above at one end. Among them, the "T"-shaped structure is located in the middle of the "L"-shaped structure, and is also located in the middle of the long metal horizontal bar. The upper and lower "E" structures are mirror images of each other with respect to the gate connection line located in the middle of the resonant structure. The gate connection line is located between the source and drain resonators. There are three sections of gate connection lines in each resonance structure unit. The middle section is connected to the gates of the two transistors in the modulation unit, and the left and right sections are respectively connected to the left, The gate connection wires of the resonant units on the right side.

The space terahertz wave multi-band modulator based on the high electron mobility transistor of the present invention is a composite metal-semiconductor structure formed by combining an artificial electromagnetic medium resonance structure and a HEMT. In the above technical solution, the substrate (1) is Semiconductor materials such as sapphire, high-resistance silicon, and silicon carbide; the HEMT epitaxial layer (2) is a semiconductor material that can form a heterojunction, such as AlGaN/GaN, InGaN/GaN, AlGaAs/GaAs, etc. Generally, Ti, Al, Ni, Au, etc. are used to form metal electrodes (17), (18), and metal materials such as Au, Ag, Cu, Al are used to form socket circuits (3), (4). The metal materials listed above can also be replaced by other metals with similar properties.

As shown in Figure 5, the modulator has four resonant frequency points: frequency point ① is around 0.2THz, frequency point ② is around 0.34THz, frequency point ③ is around 0.54THz, and frequency point ④ is around 0.6THz. Frequency points ① and ③ correspond to the state when the HEMT is connected, and frequency points ② and ④ correspond to the state when the HEMT is disconnected. Mode 1 to Mode 4 in Figure 3 and Figure 4 represent the electric field distribution and surface current distribution from frequency point ① to frequency point ④ respectively. As shown in Figure 3, when the HEMT is in the pinch-off state, the source resonator and the drain resonator are in a disconnected state and work independently of each other, and the electric field is mainly concentrated on the upper "L"-shaped structure and the lower " Between L"-shaped structures; as shown in Figure 4, when the HEMT is in the connected state, the source resonator and the drain resonator are connected to form a whole through the HEMT, and the electric field is mainly concentrated on the upper and lower long metal bars and the "T" shape On one end of the short metal horizontal bar in the structure. In Figure 3 and Figure 4, arrow lines indicate the flow direction of the surface current of the resonant structure in different modes, where the same arrow line represents a continuous and independent current, and the solid line, dotted line, dotted line, and dotted line represent each other respectively Discontinuous surface current. The figure only shows the schematic diagram of the surface current distribution on the left side of the resonant unit. Since the resonant unit is a left-right symmetrical structure, the current distribution on the right side is symmetrical to the left side. The modulator uses HEMT to carry out the specific process of amplitude modulation and phase modulation as follows. In the modulator, the negative voltage loading electrode 4 connected to the gate in the modulator is applied with a negative voltage, and the positive voltage loading electrode 3 connected to the source and drain is applied with a positive voltage. When the positive and negative voltage difference When the value is 0, the HEMT is in the conduction state, as shown in Figure 4, there are resonance frequency points ① and ③ at this time; as the difference between positive and negative voltages gradually increases, the two-dimensional electron gas in the HEMT between the source and drain The concentration gradually decreases until it is exhausted, and the HEMT gradually changes from connected to pinched off. The resonance frequency point ① shifts to frequency point ②, and the resonance frequency point ③ shifts to frequency point ④. Figure 5 and Figure 6 show the three-dimensional simulation results of the amplitude and phase transmission curves of the modulator in the on and off states of the HEMT, respectively. It can be seen from Fig. 5 that the modulator has four amplitude modulation frequency bands. When the HEMT changes from connected to pinched off, the transmittance at frequency point ① increases from 3.5% to 83.7%, and the modulation efficiency is 95.8%. The transmittance at frequency point ② decreases from 82.5% to 7.7%, and the modulation efficiency is 90.7%; the transmittance at frequency point ③ increases from 5% to 65.4%, and the modulation efficiency is 92.4%; at frequency point ④ The transmittance is reduced from 72.3% to 4%, and the modulation efficiency is 94.5%. The amplitude modulation efficiencies in the four frequency bands are all above 90%. It can be seen from Fig. 6 that the modulator has three phase modulation frequency bands: 0.21-0.33THz, 0.55-0.6THz, and 0.67-0.69THz. Among them, the phase modulation depth in the two frequency bands of 0.55-0.6THz and 0.67-0.69THz can reach more than 90 degrees.

In summary, the HEMT-based terahertz space external multi-band modulator is a fast dynamic device in the terahertz band with great development potential and practicability, which has both amplitude modulation and phase modulation functions.

Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limitations on the present invention. Under the premise of the principle of the invention, some improvements and modifications can also be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims (9)

1. A multi-band modulator based on a high electron mobility transistor, the modulator comprising: a semiconductor substrate, an epitaxial layer arranged on the semiconductor substrate, a modulation unit array arranged on the epitaxial layer; the modulation unit array Each modulation unit includes: a source resonator, a drain resonator, a gate connection line, and a semiconductor-doped heterostructure; wherein the source resonator and the drain resonator are "E"-shaped structures with the same shape and size, It is symmetrically arranged on both sides of the gate connection line and the openings are opposite; the "E"-shaped structure includes a short branch, long branches located on both sides of the short branch and metal feeders connecting each branch; wherein the heterostructure is doped by semiconductor Connecting the opposite "E"-shaped structure long branches of the source resonator and the drain resonator, the semiconductor doped heterostructure is arranged at the end of the "E"-shaped structure long branches of the source resonator and the drain resonator Below, and located below the gate connection line; each row of modulation units in the modulation unit array shares the same gate connection line, and the gate connection line of each row is connected to the same negative electrode; the source of each row of modulation units The resonator and the drain resonator are respectively communicated with and connected to the positive electrode through a metal feeder. 2. A terahertz multi-band modulator based on high electron mobility transistors as claimed in claim 1, characterized in that the long branch ends in the "E" shape structure of the source resonator and the drain resonator pass through Metal electrodes are connected to the semiconductor-doped heterostructure. 3. A terahertz multi-band modulator based on high electron mobility transistors according to claim 1 or 2, characterized in that the long branches in the "E" shape structure of the source resonator and drain resonator A short branch perpendicular to the end and extending inward is provided at the end to form an "L"-shaped structure; a short branch perpendicular to the end is provided at the end of the short branch in the "E"-shaped structure of the source resonator and the drain resonator, Form a "T" shape structure. 4 . The terahertz multi-band modulator based on high electron mobility transistors according to claim 1 , wherein the part of the gate connection line located on the doped heterostructure is narrower than other parts. 5. A terahertz multi-band modulator based on a high electron mobility transistor as claimed in claim 1, wherein the modulation unit array is an M*N array composed of a plurality of modulation units, wherein M>3 , N>3. 6. A terahertz multi-band modulator based on a high electron mobility transistor as claimed in claim 2, characterized in that said metal electrode material is Ti, Al, Ni or Au. 7. A terahertz multi-band modulator based on high electron mobility transistors according to claim 1, characterized in that the semiconductor substrate is made of sapphire, high-resistance silicon or silicon carbide. 8. A terahertz multi-band modulator based on a high electron mobility transistor as claimed in claim 1, wherein the material of the semiconductor-doped heterostructure is AlGaN/GaN, InGaN/GaN, AlGaAs/GaAs , AlGaAs/InGaAs or AlGaAs/InGaAs/InP, where the slash indicates the combination of the two materials. 9. A terahertz multi-band modulator based on a high electron mobility transistor as claimed in claim 1, wherein the material of the source resonator, the drain resonator, the gate connection line and the metal feeder is Au , Ag, Cu or Al.