阅读说明：本技术 一种基于hemt的环形开口太赫兹幅度调制器和制作方法 (Ring-shaped opening terahertz amplitude modulator based on HEMT and manufacturing method ) 是由 马勇 潘武 杨力豪 杨龙亮 何金橙 肖惠云 于 2020-08-04 设计创作，主要内容包括：本发明公开了一种基于HEMT的环形开口太赫兹幅度调制器及其制作方法,包括：半导体衬底、位于半导体衬底表面的外延层,外延层上设置有调制阵列、肖特基电极和欧姆电极；所述调制阵列由M×N个调制阵元周期排列组成,调制阵元由4个开口圆环形的结构单元构成,结构单元开口处匹配一个高电子迁移率晶体管,高电子迁移率晶体管的栅极通过栅极馈线与肖特基电极连接后连接电源负极,高电子迁移率晶体管的源极和漏极分别连接结构单元开口的两侧,结构单元通过源漏馈线与欧姆电极连接后连接电源正极。通过外加偏置电压控制高电子迁移率晶体管来进行超表面谐振模式的转换,实现对自由空间传播的太赫兹波的快速调幅,结构单元不同模式相互转换以达到多个频点的调制。(The invention discloses an annular opening terahertz amplitude modulator based on HEMT and a manufacturing method thereof, wherein the method comprises the following steps: the semiconductor device comprises a semiconductor substrate and an epitaxial layer positioned on the surface of the semiconductor substrate, wherein a modulation array, a Schottky electrode and an ohmic electrode are arranged on the epitaxial layer; the modulation array is formed by arranging M multiplied by N modulation array elements periodically, each modulation array element is formed by 4 annular structure units with openings, a high electron mobility transistor is matched at the opening of each structure unit, a grid electrode of the high electron mobility transistor is connected with a Schottky electrode through a grid electrode feeder and then connected with a power supply cathode, a source electrode and a drain electrode of the high electron mobility transistor are respectively connected with two sides of the opening of each structure unit, and the structure units are connected with ohmic electrodes through source drain feeders and then connected with a power supply anode. The high electron mobility transistor is controlled by an external bias voltage to convert a super-surface resonance mode, so that the rapid amplitude modulation of terahertz waves transmitted in free space is realized, and different modes of the structural unit are mutually converted to achieve the modulation of multiple frequency points.)

1. An annular opening terahertz amplitude modulator based on HEMT is characterized by comprising: the device comprises a semiconductor substrate (1) and an epitaxial layer (2) positioned on the surface of the semiconductor substrate, wherein a modulation array (3), a Schottky electrode (4) and an ohmic electrode (5) are arranged on the epitaxial layer;

the modulation array (3) is formed by M multiplied by N modulation array elements (31) in periodic arrangement, wherein M is the longitudinal arrangement period number of the modulation array elements (31), and N is the transverse arrangement period number of the modulation array elements (31);

each modulation array element (31) is composed of 4 structural units (311) with openings in circular ring shapes, a high electron mobility transistor (6) is matched at the opening of each structural unit (311), the grid electrode of the high electron mobility transistor (6) is connected with a Schottky electrode (4) through a grid electrode feeder line (7), the source electrode and the drain electrode of the high electron mobility transistor (6) are respectively connected with two sides of the opening of the structural unit (311), and the structural unit (311) is connected with an ohmic electrode (5) through a source drain feeder line (8); the Schottky electrode (4) is connected with the negative electrode of a power supply, and the ohmic electrode (5) is connected with the positive electrode of the power supply.

2. The HEMT-based annular opening terahertz amplitude modulator according to claim 1, characterized in that 4 structural units (311) in the modulation array element (31) are arranged in a square shape, and the circle center distance between two adjacent structural units is: 115-125 μm;

the outer radius of the structural unit (311) is: 45-55 μm, and the ring width of the structural unit (311) is as follows: 10-25 μm, the thickness of the structural unit (311) is: 0.2-1 μm;

an opening is arranged at the position of the structural unit (311) closest to the center of the modulation array element, and the width of the opening is as follows: 2-6 μm; the opening position in each modulation array element is in central symmetry.

3. The HEMT-based ring-open terahertz amplitude modulator of claim 1, wherein said gate feed line (7) comprises: the grid electrodes of all the structure units (311) in the modulation array element (31) are connected through the first grid electrode feeder line (71); each row of modulation array elements shares one second grid electrode feeder line (72), and the second grid electrode feeder lines (72) in each row are connected to the same Schottky electrode (4).

4. The HEMT-based annular open terahertz amplitude modulator according to claim 3, characterized in that the first gate feed lines (71) in the modulation array elements are arranged in a cross shape, and the second gate feed lines (72) are connected to the cross points of the cross shape.

5. The HEMT-based annular opening terahertz amplitude modulator according to claim 2, characterized in that a source-drain feeder is arranged above and below each row of modulation array elements, the source-drain feeder above the modulation array elements is connected with all upper-layer structural units, the source-drain feeder below the modulation array elements is connected with all lower-layer structural units, and the source-drain feeders (8) in each row are connected to the same ohmic electrode (5).

6. The HEMT-based ring-open terahertz amplitude modulator of claim 1, characterized in that the modulation array elements (31) are one period 240 μm wide.

7. The HEMT-based ring-open terahertz amplitude modulator according to claim 1,

the semiconductor substrate (1) is made of silicon carbide, and the thickness of the semiconductor substrate (1) is as follows: 200-270 μm;

the epitaxial layer (2) is made of gallium nitride.

8. The HEMT-based ring-open terahertz amplitude modulator according to claim 1,

the line width of the grid feeder line (8) is as follows: 1-2 μm, thickness: 0.2-1 μm;

the line width of the source-drain feeder (9) is as follows: 1-2 μm, thickness: 0.2-1 μm.

9. A manufacturing method of an annular opening terahertz amplitude modulator based on a HEMT is characterized by comprising the following steps:

s1, cleaning a SiC semiconductor substrate;

s2, preparing a heterostructure film of AlGaN and GaN on the cleaned SiC semiconductor substrate;

s3, sequentially depositing composite metal layers at two ends of an active table structure of the high-electron-mobility transistor to serve as a source electrode and a drain electrode of the high-electron-mobility transistor;

s4, performing rapid thermal annealing treatment on the source electrode and the drain electrode of the high-electron-mobility transistor in a nitrogen environment, rapidly reducing the temperature in an annealing furnace from 900 ℃ to 25 ℃ within 140 seconds, and enabling the source electrode and the drain electrode of the high-electron-mobility transistor to form ohmic contact with the two-dimensional electron gas channel;

and S5, manufacturing a modulation array, a Schottky electrode and an ohmic electrode on the heterostructure thin film through photoetching, electron beam evaporation and stripping processes.

10. A manufacturing method of an annular opening terahertz amplitude modulator based on a HEMT is characterized in that S2 comprises the following steps:

s21: spin-coating a photoresist on the SiC substrate, and determining an HEMT active region by using the photoresist after photoetching and developing by using a mask;

s22: and (3) excessively etching the heterostructure film outside the active region by using Cl2-BCl3 mixed gas for inductively coupled plasma etching in dry etching, and removing the residual photoresist on the substrate after etching is finished to obtain the active mesa structure of the high-electron-mobility transistor with the thickness of 35 nm.

Technical Field

The invention relates to the technical field of terahertz wave amplitude modulation, in particular to an annular opening terahertz amplitude modulator based on a HEMT (high Electron mobility transistor) and applied to a 6G communication system and a manufacturing method thereof.

Background

With the continuous improvement of the demand of space high-speed networks, the existing spectrum resources are difficult to meet the social demand, so new spectrum resources need to be developed. The terahertz frequency band (0.1-10THz) is extremely rich in frequency spectrum resources, and compared with microwave communication, terahertz communication has the characteristics of wide bandwidth and high carrier frequency, and provides possibility for meeting social requirements. Currently, terahertz communication systems are developing towards high-speed and long-distance directions, but the development is hindered due to the lack of high-performance key devices. The terahertz modulator is one of the most critical devices, and is the key point in the field of terahertz scientific and technical research in recent years. Since 2004, successive articles about terahertz external modulators were published in numerous international top-level journal of science, and the contents of the articles include the combination of doped semiconductor substrates, phase-change materials, graphene and the like with super-surfaces, and the modulation of terahertz waves propagating in free space is realized by using excitation modes such as external temperature, illumination, electric fields and the like.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: at present, the terahertz modulator is influenced by the structure and the material of a device, has higher parasitic effect, causes the modulation depth and the modulation rate of the modulator to be lower, and is not easy to integrate.

The invention provides an open ring-shaped super-surface structure with high resonance strength, wherein a High Electron Mobility Transistor (HEMT) with high-speed dynamic characteristics is designed at an opening of the super-surface structure, the concentration of two-dimensional electron gas in a channel of the HEMT is adjusted in a voltage applying mode, the resonance mode of the super-surface structure is changed, and further the regulation and control on terahertz waves are achieved, so that the modulator can rapidly and efficiently perform amplitude modulation on the terahertz waves transmitted in a free space, and the modulation depth can reach more than 90%.

The invention is realized by the following technical scheme:

an annular opening terahertz amplitude modulator based on a HEMT, comprising: the semiconductor device comprises a semiconductor substrate and an epitaxial layer positioned on the surface of the semiconductor substrate, wherein a modulation array, a Schottky electrode and an ohmic electrode are arranged on the epitaxial layer;

the modulation array is formed by M multiplied by N modulation array elements in periodic arrangement, wherein M is the number of the longitudinal arrangement periods of the modulation array elements, and N is the number of the transverse arrangement periods of the modulation array elements;

each modulation array element is composed of 4 open ring-shaped structural units, and a High Electron Mobility Transistor (HEMT) is matched at the opening of each structural unit; the grid electrode of the high electron mobility transistor is connected with the Schottky electrode through a grid electrode feeder line, the source electrode and the drain electrode of the high electron mobility transistor are respectively connected with two sides of the opening of the structural unit, and the structural unit is connected with the ohmic electrode through a source drain feeder line; the Schottky electrode is connected with the negative electrode of the power supply, and the ohmic electrode is connected with the positive electrode of the power supply.

The further optimization scheme is that 4 structural units in the modulation array element are arranged in a square shape, and the circle center distance between two adjacent structural units is as follows: 115-125 μm;

the outer radius of the structural unit is: 45-55 μm, and the ring width of the structural unit is as follows: 10-25 μm, the thickness of the structural unit is: 0.2-1 μm;

an opening is arranged at the position of the structural unit closest to the center of the modulation array element, and the width of the opening is as follows: 2-6 μm; the opening position in each modulation array element is in central symmetry.

Further optimization scheme is that the gate feeder comprises: the grid electrodes of all the structural units in the modulation array element are connected through the first grid electrode feeder line; each row of modulation array elements share one second grid electrode feeder line, and the second grid electrode feeder lines in each row are connected to the same Schottky electrode.

The further optimization scheme is that first grid feeder lines in the modulation array elements are arranged in an oblique cross shape, and second grid feeder lines are connected to the cross points of the oblique cross.

The further optimization scheme is that a source-drain feeder is arranged above and below each row of modulation array elements, the source-drain feeders above the modulation array elements are connected with all upper-layer structural units, the source-drain feeders below the modulation array elements are connected with all lower-layer structural units, and the source-drain feeders of each row are connected to the same ohmic electrode.

The further optimization scheme is that the modulation array elements are one period with the width of 240 mu m.

The further optimization scheme is that the semiconductor substrate is made of silicon carbide, and the thickness of the semiconductor substrate is 200-270 mu m; the epitaxial layer is made of gallium nitride.

The further optimization scheme is that the line width of the grid feeder line is as follows: 1-2 μm, thickness: 0.2-1 μm;

the source drain feeder line width is: 1-2 μm, thickness: 0.2-1 μm;

a manufacturing method of an annular opening terahertz amplitude modulator based on a HEMT comprises the following steps:

s1, firstly, placing a SiC semiconductor substrate in an acetone and ethanol solution to clean organic matters on the surface, then treating metal ions on the surface of the SiC semiconductor substrate by using a hot acid solution, and finally washing the SiC semiconductor substrate by using a large amount of deionized water;

s2, preparing a heterostructure film of AlGaN and GaN on the SiC semiconductor substrate obtained in the step S1 by using a metal organic phase chemical deposition method;

spin-coating a photoresist with the thickness of 1.5 mu m on a SiC substrate, and determining an HEMT active region by using the photoresist after photoetching and developing by using a mask; and then, carrying out over etching on the heterostructure film outside the active region by using Cl2-BCl3 mixed gas for inductively coupled plasma etching in dry etching, and removing the residual photoresist on the substrate after the etching is finished so as to obtain the active mesa structure of the high electron mobility transistor with the thickness of 35 nm.

S3, depositing a titanium layer with the thickness of 20nm, an aluminum layer with the thickness of 120nm, a nickel layer with the thickness of 70nm and a gold layer with the thickness of 100nm on two ends of the active table structure in sequence through photoetching, electron beam evaporation, stripping and other processes to serve as a source electrode and a drain electrode of the high electron mobility transistor;

s4, performing rapid thermal annealing treatment on the source electrode and the drain electrode of the high-electron-mobility transistor in a nitrogen environment, rapidly reducing the temperature in an annealing furnace from 900 ℃ to 25 ℃ within 140 seconds, and enabling the source electrode and the drain electrode of the high-electron-mobility transistor to form ohmic contact with the two-dimensional electron gas channel;

and S5, manufacturing a modulation array, a Schottky electrode and an ohmic electrode on the heterostructure thin film through photoetching, electron beam evaporation and stripping processes.

The principle of the technical scheme is as follows: under the condition that incident terahertz waves vertically enter a modulator and polarization direction source drain feeder lines of the incident terahertz waves sag, when bias voltage is not applied to a grid electrode, the opening of a metal ring of a structural unit is short-circuited due to the fact that high-concentration two-dimensional electron gas concentration exists in a High Electron Mobility Transistor (HEMT) channel, at the moment, 4 metal rings of a modulation array element cannot generate LC resonance, the whole formed by a first grid feeder line in an oblique cross shape and the metal rings generates dipole resonance, and at the moment, electromagnetic waves can penetrate through the modulator. With the increase of grid voltage, the concentration of two-dimensional electron gas in a channel of a High Electron Mobility Transistor (HEMT) is gradually reduced, when the voltage reaches a certain value, the two-dimensional electron gas in the channel of the HEMT is completely exhausted, 4 metal opening rings can generate strong LC resonance, an electric field is strongly restricted at the opening of the metal ring, at the moment, electromagnetic waves are difficult to penetrate through a modulator, and therefore the control of the amplitude of the electromagnetic waves is achieved. The modulator is driven by an external voltage, integration is easy, and a transmission type terahertz modulator is designed, so that compared with a reflection type modulator, the terahertz modulator is simple to operate and more convenient to use.

Compared with the prior art, the invention has the following advantages and beneficial effects:

1. according to the ring-shaped opening terahertz amplitude modulator based on the HEMT and the manufacturing method, 4 highly symmetrical opening ring-shaped super-surface structures are adopted, each opening ring is matched with one HEMT, the resonance strength of the super-surface structure is greatly enhanced, and a foundation is laid for realizing a modulator with high modulation depth and high modulation rate; the two-dimensional electron gas concentration in the HEMT channel is controlled by an external bias voltage to carry out conversion of a super-surface resonance mode, so that rapid amplitude modulation of terahertz waves transmitted in free space is realized. The super-surface structure is in different resonance modes or is mutually converted between different modes under the on-off state of the HEMT, so that the modulation of a plurality of frequency points is achieved.

2. According to the ring-shaped opening terahertz amplitude modulator based on the HEMT and the manufacturing method thereof, the modulation array element of the two-dimensional plane structure can be realized through a micro-nano processing technology, and the processing difficulty caused by a complicated three-dimensional structure design scheme is avoided; the structural plasticity is strong: the whole structure of the modulation array element is kept unchanged, and the position of the modulation frequency point and the modulation bandwidth can be effectively adjusted by changing the parameters (such as the width of an opening ring) of the super-surface structure unit.

Drawings

The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention.

In the drawings:

FIG. 1 is a schematic diagram of a modulator according to the present invention;

FIG. 2 is a schematic diagram of a modulation array element structure;

FIG. 3 is a partial cross-sectional view of a HEMT structure;

FIG. 4 is a spectrum of transmission coefficients of the modulator at different plasma frequencies;

FIG. 5 is a graph of the surface current and electric field distribution of the modulator for the HEMT on state;

FIG. 6 is a plot of the surface current and electric field of the modulator in the HEMT off state.

In the drawings:

1-semiconductor substrate, 2-epitaxial layer, 3-modulation array, 31-modulation array element, 311-structural unit, 4-Schottky electrode, 5-ohmic electrode, 6-high electron mobility transistor, 7-grid feeder line, 71-first grid feeder line, 72-second grid feeder line, 8-source drain feeder line, 9-grid, 10-drain, 11-source.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.