Graphene multi-intercalation SiC light guide microwave device and preparation method thereof

Abstract

The invention discloses a graphene multi-intercalation silicon carbide light guide microwave device and a preparation method thereof, and solves the technical problems of surface flashover breakdown, overlarge substrate current density and short service life of a traditional light guide switch. According to the invention, the substrate is designed by alternately stacking multiple layers of silicon carbide and graphene, every two silicon carbide semi-insulating material layers and a graphene intercalation layer in the substrate form a silicon ink layer, a plurality of silicon ink layers are arranged in a laminated manner, and silicon carbide is extended on the upper surface of the silicon ink layers to form the device substrate. The preparation method comprises the steps of device design, cleaning, hydrogen etching, graphene intercalation preparation, epitaxial growth of silicon carbide, multi-lamination structure preparation and ohmic contact electrode preparation. According to the invention, the preparation of graphene by thermal cracking of silicon carbide and the epitaxial growth technology are combined, the process of graphene transfer is omitted, current distribution is optimized and concentrated in the device, surface flashover breakdown is reduced, the current-carrying and power output capabilities of the device are improved, the voltage resistance and heat dissipation capabilities of the device are improved, and the device is used in the fields of high-power microwave systems and the like.

Description

Technical Field

[0001] The present invention belongs to the field of microelectronics technology, mainly relates to photoconductive microwave devices, and specifically relates to a graphene multi-intercalated SiC photoconductive microwave device and a preparation method thereof, which can be used as high-power microwave electronic devices and are widely applied to the field of optoelectronic technology. Background Art

[0002] A photoconductive switch, also known as a photoconductive semiconductor switch (PCSS), is a solid-state switch that uses a laser pulse to trigger a photoconductive semiconductor. Since 1970, with the development of optoelectronic technology and semiconductor materials, photoconductive switches have gradually shown their unique advantages and broad application prospects. A photoconductive switch generates photo-generated carriers (electron-hole pairs) inside a semiconductor material through a laser pulse, thereby changing the conductivity of the material and realizing the on and off of the switch. Its working principle is essentially that when light irradiates on a semiconductor material, the material absorbs photon energy and excites photo-electrons to form a current. Photoconductive switches have application prospects in pulsed power technology, high-power microwave systems, radar detection systems, laser fusion systems, high-precision satellite positioning and tracking systems, electronic countermeasures and electronic warfare systems, etc. Compared with traditional switches, photoconductive switches have the advantages of fast response speed, small trigger jitter, large power capacity, strong anti-electromagnetic interference ability, small size, light weight, and easy integration.

[0003] The third-generation semiconductor silicon carbide (SiC) has the advantages of a wide bandgap, a high carrier saturation drift velocity (2×10 5 m / s), a high breakdown electric field strength (300 kV / mm), a high thermal conductivity (500 W·m -1 ·K -1 ), and fast response. Since the 1990s, with the continuous improvement of the SiC crystal growth process, photoconductive switches based on semi-insulating SiC crystals have also developed rapidly at home and abroad. According to the different relative positions of the electrodes, silicon carbide photoconductive switches can be divided into two categories. When both electrodes are on the same surface, it is called a planar photoconductive switch; when the two electrodes are located on the opposite sides of the substrate, it is called a vertical photoconductive switch. Among them, the preparation and packaging processes of planar photoconductive switches are relatively simple, which is beneficial to maintaining the stability and reliability of the device; and planar photoconductive switches can realize the regulation of optical signals through different triggering methods, such as front incident triggering, non-intrinsic backlight triggering, etc., increasing the flexibility of their application in different application scenarios, being more easily integrated with other devices, and making the system have better performance.

[0004] Graphene materials are a new type of two-dimensional material with unique physical and chemical properties. Since their first discovery in 2004, they have rapidly become a research hotspot in the fields of materials science, physics, and engineering. Graphene is a single-layer carbon material with a two-dimensional honeycomb lattice structure formed by carbon atoms in sp 2 hybrid orbitals. It is a single-atom layer arrangement of carbon atoms exfoliated from graphite, with a thickness of only the diameter of a single carbon atom, approximately 0.335 nanometers. The basic chemical properties of graphene are similar to those of graphite, but its single-layer hexagonal honeycomb structure, as well as boundary groups and planar defects, endow it with unique chemical properties. For example, graphene can adsorb and desorb various atoms and molecules. When these adsorbates act as donors or acceptors, they can change the carrier concentration of graphene, while graphene itself can maintain good electrical conductivity. In addition, graphene also has advantages such as high carrier mobility, high electrical conductivity, and high thermal conductivity. With the continuous in-depth research on graphene, it has been found that graphene has excellent electrical, thermal, mechanical, and optical properties, and thus has broad application prospects in the fields of electronic devices, energy storage, sensors, etc. However, traditional graphene preparation methods such as mechanical exfoliation and chemical vapor deposition have problems such as high cost, low yield, and difficult quality control. Therefore, many new graphene preparation methods need to be explored. Among them, the technology of preparing graphene by thermal decomposition of silicon carbide has been widely used in industry due to its advantages such as low cost, strong controllability, and compatibility with semiconductor material devices.

[0005] The thermal decomposition of SiC to prepare graphene can be traced back to the late 1990s to the early 2000s, proposed by a research group led by Professor Walter de Heer at the Georgia Institute of Technology. This technology is based on the principle that silicon atoms will sublime at high temperatures in silicon carbide, while carbon atoms will rearrange on the surface to form graphene. The technology of preparing graphene by thermal decomposition of silicon carbide has the advantages of high quality, large area, no need for transfer, and low cost.

[0006] The patent with the application number 202410074886.8 discloses a vertical GaN photoconductive switch and its manufacturing method. Its structure includes electrodes, a heavily doped epitaxial layer, a substrate, a heavily doped epitaxial layer, and electrodes designed with vertical stacking. And on one side of the substrate, an incident surface is provided with a first light-trapping structure, which is used to reflect, refract, and scatter incident light so that the incident light is dispersed throughout the interior of the substrate; on the other side of the substrate, an exit surface is provided with a second light-trapping structure, which is used to reflect, refract, and scatter the exit light so that the exit light is dispersed throughout the interior of the substrate. The first light-trapping structure includes a plurality of nano-protrusions arranged on the incident surface, and the nano-protrusions extend from the incident surface in a direction away from the exit surface; the second light-trapping structure includes a plurality of nano-grooves arranged on the exit surface, and the nano-grooves extend from the exit surface in a direction towards the incident surface. The above treatment of the light-trapping structure can reduce the reflection loss of light, improve the utilization rate of light energy, and thus enhance the photoelectric conversion efficiency of the device. The disadvantage of this manufacturing method is that it may introduce defects such as an uneven surface, cracks, and impurities on the device surface. These defects will hinder the movement of electrons, increase the reflection and scattering of electrons during their movement inside the device, thereby reducing the performance and lifespan of the device. And excessive light-trapping treatment will cause the device surface to absorb too much light energy, resulting in the number of photo-generated carriers exceeding the processing capacity of the device and increasing the thermal load of the device.

[0007] The patent with the application number 202011364521.7 discloses a photoconductive switch device. At least two mutually isolated parallel channels are arranged on any one side of its substrate. Ohmic contact regions with different doping concentrations of different conductive types are arranged at both ends of each parallel channel. Metal electrodes are arranged on the ohmic contact regions, and a passivation layer is arranged in the region except the metal electrodes. Current shunting is achieved through multiple parallel channels arranged on the substrate, reducing the current density of a single current filament, making the current distribute more evenly in the device, increasing the total power of the photoconductive switch device, and improving the switch lifespan. The disadvantage of this design is that the process of setting the trench parallel channels is relatively difficult, and implementing current shunting by arranging multiple parallel channels on the substrate will reduce the number of carriers in the device in the conducting state, resulting in a decrease in the peak value of the photocurrent, thereby reducing the power of the device in the conducting state.

[0008] In summary, for traditional planar photoconductive microwave devices, carriers are mainly concentrated on the surface of the substrate, prone to surface flashover breakdown, resulting in a reduced lifespan of the device, and it is difficult to take advantage of the high breakdown electric field strength of SiC. Also, due to complex processes, the performance and lifespan of the device are reduced. The presence of the light-trapping structure will also cause the number of photo-generated carriers to exceed the processing capacity of the device, increasing the thermal load of the device, and the trench design of the parallel channels will lead to a decrease in the current peak. Summary of the Invention

[0009] The object of the present invention is to propose a graphene multi-intercalated SiC photoconductive microwave device and a preparation method thereof, which optimize the internal current distribution of the device, have good heat dissipation performance, and realize heterogeneous van der Waals epitaxy, aiming at the deficiencies of the existing technology.

[0010] The present invention relates to a graphene multi-intercalated silicon carbide photoconductive microwave device, which includes a substrate and a metal electrode from bottom to top. The material of the substrate contains silicon carbide material, or gallium nitride material, or diamond material. It is characterized in that the substrate is a multi-layer structure based on a silicon ink layer. The silicon ink layer is a composite layer structure with a silicon carbide semi-insulating material layer as the substrate and graphene intercalation prepared by thermal cracking on the upper surface of the substrate. The stacked composite structures of multiple silicon ink layers form the multi-layer structure of the substrate. In the multi-layer structure of the substrate, a single graphene intercalation is sandwiched between two silicon carbide semi-insulating material layers. The bottom layer and the top layer of the substrate are both silicon carbide semi-insulating material layers. The electrode is arranged on the upper surface of the top layer of the substrate.

[0011] The present invention also relates to a preparation method of a graphene multi-intercalated silicon carbide photoconductive microwave device for preparing the graphene multi-intercalated silicon carbide photoconductive microwave device according to any one of claims 1-4. It is characterized in that a silicon ink layer base structure is prepared by thermal cracking of a silicon carbide semi-insulating material to generate graphene intercalation on it, and the silicon ink layer base structures are stacked to form a device substrate, and an ohmic contact electrode is prepared on the upper surface of the substrate, including the following steps:

[0012] Step 1: Design a graphene multi-intercalated silicon carbide photoconductive microwave device: The graphene multi-intercalated silicon carbide photoconductive microwave device includes a substrate and a metal electrode from bottom to top. The material of the substrate contains silicon carbide material, or gallium nitride material, or diamond material. The substrate is a multi-layer structure based on a silicon ink layer. The silicon ink layer is a composite layer structure with a silicon carbide semi-insulating material layer as the substrate and graphene intercalation prepared by thermal cracking on the upper surface of the substrate. The stacked composite structures of multiple silicon ink layers form the multi-layer structure of the substrate. In the multi-layer structure of the substrate, a single graphene intercalation is sandwiched between two silicon carbide semi-insulating material layers. The bottom layer and the top layer of the substrate are both silicon carbide semi-insulating material layers. The electrode is arranged on the upper surface of the top layer of the substrate.

[0013] Step 2: Clean the silicon carbide semi-insulating material substrate: First, ultrasonically clean the silicon carbide semi-insulating material substrate with an organic solvent; then use a Piranha solution to remove organic pollutants on the surface of the material substrate; then soak the material substrate in hydrofluoric acid to remove the oxide layer; then soak the material substrate in an SC-2 solution to remove metal ions; finally, soak the material substrate in a diluted hydrofluoric acid solution to gently remove the oxide. Before and after each solution cleaning, rinse with deionized water and blow dry the material substrate with a nitrogen gun. After the cleaning is completed, take out the silicon carbide semi-insulating material substrate.

[0014] Step 3: Hydrogen etching of the upper surface of the semi-insulating silicon carbide material substrate: Place the cleaned semi-insulating silicon carbide material substrate into an etching furnace, rapidly heat up and hold the temperature, then continue to heat up and hold the temperature again. After that, introduce hydrogen, heat up to the etching temperature, and conduct hydrogen etching. Then, naturally cool down under hydrogen protection to make the upper surface of the substrate have a surface morphology with atomic-level flatness. After cooling to room temperature, complete the hydrogen etching of the upper surface of the substrate;

[0015] Step 4: Preparation of the grown graphene interlayer: Graphitize the upper surface of the semi-insulating silicon carbide material substrate to prepare the grown graphene interlayer. Place the semi-insulating silicon carbide material substrate after hydrogen etching into the reaction chamber of a high-temperature furnace, and conduct the first heating and temperature holding; further increase the temperature for the second heating and temperature holding; rise to the graphitization temperature and pyrolyze to generate the graphene interlayer on the semi-insulating silicon carbide material substrate. The Si-C bonds break, Si atoms sublime, and C atoms enrich and undergo reconstruction to form epitaxial graphene; cool down to complete the preparation of the graphene interlayer in the silicon ink layer; complete the preparation of the first silicon ink layer;

[0016] Step 5: Epitaxial growth of silicon carbide: Continuously grow a semi-insulating silicon carbide material layer on the silicon ink layer by chemical vapor deposition (CVD) method. First, clean the reaction chamber and place the material, heat up to the growth temperature in a hydrogen atmosphere, then introduce hydrogen for in-situ etching, introduce silicon source and carbon source gases to start epitaxial growth. After growth is completed, anneal in an inert gas and cool down to room temperature to complete the epitaxial growth of silicon carbide;

[0017] Step 6: Preparation of the multi-stack structure: Use the semi-insulating silicon carbide on the above-prepared silicon ink layer as a new material substrate, repeat the above Steps 2 - 5, and repeat 2 - 3 times according to the number of graphene interlayers in the substrate to complete the preparation of the substrate with a multi-stack structure;

[0018] Step 7: Preparation of ohmic contact electrodes on the device substrate: First, clean the device substrate to remove contaminants, make the surface flat by polishing or etching, spin-coat photoresist and expose to define the electrode pattern. Then, sputter-deposit a metal thin film, anneal in an inert gas to form an ohmic contact, and then remove the excess metal and clean the sample to complete the electrode preparation and obtain the entire photoconductive microwave device.

[0019] The present invention adopts a graphene multi-interlayer structure to make the carrier distribution inside the device more uniform, solving the problems of flashover breakdown caused by the concentration of carriers on the surface of the planar photoconductive microwave device, excessive device heat load, and reduced device life.

[0020] Compared with the prior art, the technical advantages of the present invention:

[0021] Homogenized current improves device lifespan: The present invention adopts a silicon carbide photoconductive microwave device structure with graphene multi-intercalations, which increases the conduction path, enhances the carrier current and power output capabilities of the device, reduces the surface current density of the device, makes the carrier distribution more uniform, significantly improves the service life of the photoconductive switch, and effectively reduces the surface flashover breakdown of the device.

[0022] Van der Waals epitaxial growth of graphene avoids transfer, pollution and damage: The present invention uses a method of preparing graphene by thermal pyrolysis of silicon carbide. Graphene intercalations are directly formed on the silicon carbide material substrate through the steps of cleaning, etching, and graphitization to achieve heterogeneous Van der Waals epitaxy. Due to the action of Van der Waals forces, the interface between the grown thin film and the substrate is relatively flat and clean, with a low defect density. Moreover, the pollution introduced during the graphene transfer process is avoided, and a silicon carbide photoconductive microwave device structure with graphene multi-intercalations is obtained through stacked epitaxial growth.

[0023] Enhances the heat dissipation capacity of the device: The present invention adopts a graphene intercalation structure and utilizes the good thermal conductivity of graphene material to effectively transfer the heat inside the photoconductive device, avoid excessive concentration, and improve the performance and lifespan of the device. Brief Description of the Drawings

[0024] Figure 1 is a schematic cross-sectional view of the graphene multi-intercalated SiC photoconductive microwave device structure of the present invention;

[0025] Figure 2 is a flow block diagram of the preparation method of the present invention;

[0026] Figure 3 is a flow block diagram of cleaning the silicon carbide semi-insulating material substrate in the preparation method of the present invention;

[0027] Figure 4 is a flow block diagram of hydrogen etching of the silicon carbide semi-insulating material substrate in the preparation method of the present invention;

[0028] Figure 5 is a flow block diagram of preparing and growing graphene intercalations on the silicon carbide substrate in the preparation method of the present invention;

[0029] Figure 6 is a flow block diagram of epitaxial growth of silicon carbide in the preparation method of the present invention;

[0030] Figure 7 is a flow block diagram of preparing ohmic contact electrodes on the upper surface of the device substrate in the preparation method of the present invention;

[0031] Figure 8 is a simulation diagram of the on-state current density on the device surface of the present invention. Detailed Embodiments

[0032] The technical solutions in the present invention will be described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0033] Embodiment 1

[0034] With the development of optoelectronic technology and semiconductor materials, photoconductive switches have gradually demonstrated their unique advantages and broad application prospects. Photoconductive switches have application prospects in pulsed power technology, high-power microwave systems, radar detection systems, laser fusion systems, high-precision satellite positioning and tracking systems, electronic countermeasures and electronic warfare systems, etc. However, existing photoconductive switches have problems such as insufficient conduction photocurrent, excessive current density in the device substrate, and insufficient device lifespan. The present invention proposes a design and preparation method for a graphene multi-intercalated SiC photoconductive microwave device, providing more novel and practical ideas for the design technology of such optoelectronic devices and greatly improving the device lifespan opportunity.

[0035] The present invention is a graphene multi-intercalated silicon carbide photoconductive microwave device, which includes a substrate and a metal electrode from bottom to top. The material of the substrate contains silicon carbide material, or gallium nitride material, or diamond material. Refer to Figure 1 , Figure 1 which is a schematic cross-sectional view of the structure of the graphene multi-intercalated SiC photoconductive microwave device of the present invention. The substrate of the graphene multi-intercalated silicon carbide photoconductive microwave device of the present invention is a multi-layer structure based on a silicon ink layer. The silicon ink layer is a composite layer structure with a silicon carbide semi-insulating material layer as the substrate and graphene intercalation prepared by thermal cracking on the upper surface of the substrate. The stacked arrangement of the composite structures of multiple silicon ink layers forms the multi-layer structure of the substrate. In the multi-layer structure of the substrate, a single graphene intercalation is sandwiched between two silicon carbide semi-insulating material layers. The bottom layer and the top layer of the substrate are both silicon carbide semi-insulating material layers. The electrode is arranged on the upper surface of the top layer of the substrate.

[0036] The substrate structure of the present invention adopts a multi-layer design based on a silicon ink layer. The silicon ink layer is a composite layer structure with a silicon carbide semi-insulating material layer as the substrate and graphene intercalation prepared by a thermal cracking process on its upper surface. The formation process of the silicon ink layer includes generating graphene intercalation by thermal cracking on the silicon carbide semi-insulating material layer, and then epitaxially growing another layer of silicon carbide semi-insulating material layer on the upper surface of the graphene intercalation, thus completing the stacking of one silicon ink layer. By repeating this process, the composite structures of multiple silicon ink layers are stacked together to form the multi-layer structure of the substrate. In the multi-layer structure of the substrate, a single graphene intercalation is sandwiched between two silicon carbide semi-insulating material layers, forming a "sandwich" structure. The structural feature of the entire substrate of the present invention is that the silicon carbide semi-insulating material layer and the graphene intercalation are stacked in sequence from bottom to top, and both the bottom layer and the top layer of the substrate are silicon carbide semi-insulating material layers. This design not only enhances the mechanical strength and thermal stability of the substrate, but also optimizes its electrical properties. The electrode is arranged on the upper surface of the top layer of the substrate for easy connection with the external circuit.

[0037] Aiming at the problems of surface flashover breakdown, excessive thermal load and reduced device life existing in the existing photoconductive microwave devices, the present invention proposes a design of a high-power SiC photoconductive microwave device with graphene intercalation. It enables a more uniform carrier distribution in the SiC photoconductive switch in the on state, reduces its surface flashover, increases the photocurrent of the photoconductive switch in the on state, and makes better use of the material advantages of SiC by virtue of the low-cost controllability of preparing graphene by SiC thermal cracking.

[0038] The graphene multi-intercalated silicon carbide photoconductive microwave device proposed by the present invention is a new device structure. The substrate structure of the device is a silicon carbide material substrate with graphene multi-intercalation. The existence of the graphene intercalation makes the current conduction concentrated inside the device, thus homogenizing the current, improving the device breakdown voltage and reliability, reducing the device surface flashover, and at the same time, making use of the good thermal conductivity of graphene to enhance the heat dissipation capacity of the device, further improving the device performance and life.

[0039] Example 2

[0040] The graphene multi-intercalated silicon carbide photoconductive microwave device is the same as that in Example 1. In this example, the thickness of the substrate is 0.3 mm - 1 mm, and the side lengths of the substrate are 5 mm - 10 mm respectively. The thickness of each silicon ink layer is 100 μm - 200 μm, and the side lengths are 5 mm - 10 mm respectively. The substrate of the photoconductive microwave device of the present invention can change the thickness and size according to actual applications.

[0041] In this example, the thickness of the entire substrate of an optical waveguide microwave device is 0.35 mm, the width is 5 mm, and the length is 8 mm. The substrate contains 7 material layers, that is, three silicon ink layers and a semi-insulating silicon carbide material layer on the top are stacked in sequence from bottom to top to form the entire substrate. The thickness of each silicon ink layer is 100 μm. The upper and lower surfaces of the substrate are both semi-insulating silicon carbide material layers. The materials of the two ohmic contact electrodes on the upper surface of the substrate are Ti / Pt / Au composite metal layers, which are symmetrically arranged on the upper surface of the substrate; the thickness of the electrodes is 1 μm, and the size is 2 mm × 2 mm. The overall size of the optical waveguide microwave device in this example is small, which is convenient for integration and has low production costs.

[0042] The optical waveguide microwave device in the present invention can also be such that the thickness of the entire substrate is 0.77 mm and the size is 10 mm × 10 mm. The substrate contains 11 material layers, that is, five silicon ink layers and a semi-insulating silicon carbide material layer on the top are stacked in sequence from bottom to top to form the entire substrate. The thickness of each silicon ink layer is 140 μm. The upper and lower surfaces of the substrate are both semi-insulating silicon carbide material layers. The materials of the two ohmic contact electrodes on the upper surface of the substrate are Wu / Ti / Au composite metal layers, which are symmetrically arranged on the upper surface of the substrate; the thickness of the electrodes is 3 μm, and the size is 2 mm × 2 mm. The overall size of the optical waveguide microwave device in this example is larger, so the overall heat dissipation area is larger, the heat dissipation effect is better, it is more suitable for high-power scenarios, and the manufacturing process is simple and the yield is higher.

[0043] Example 3

[0044] The graphene multi-intercalated silicon carbide optical waveguide microwave device is the same as in Examples 1-2. In this example, the thickness of the semi-insulating silicon carbide material layer in each silicon ink layer in the substrate is 50 μm - 100 μm, and the side lengths are 5 mm - 10 mm; the number of semi-insulating silicon carbide material layers in the substrate is 4 - 6, and the number of layers can be added or the size and thickness can be changed according to actual needs.

[0045] In one device substrate in this example, the thickness of the semi-insulating silicon carbide material layer in each silicon ink layer is 50 μm, the width is 5 mm, the length is 8 mm, and the number of semi-insulating silicon carbide material layers in the entire device substrate is 4. In the device substrate of this embodiment, the semi-insulating silicon carbide material layer in each silicon ink layer is designed with a smaller thickness size and number of layers, and the parasitic capacitance and inductance introduced by the device are relatively smaller, which is better for high-frequency applications, the cost is relatively small, and it is conducive to integration.

[0046] In the photoconductive microwave device of the present invention, the thickness of the semi-insulating silicon carbide material layer in each silicon ink layer in the substrate can also be 70 μm, the size is 10 mm × 10 mm, and the number of layers of the semi-insulating silicon carbide material layer in the entire device substrate is 6. In this embodiment, the semi-insulating silicon carbide material layer in each silicon ink layer in the device substrate is designed with a relatively large thickness and number of layers. By increasing the heat conduction path, the heat dissipation is improved and the heat dissipation efficiency is enhanced. It has a relatively better current-carrying capacity and is more suitable for high-power applications.

[0047] Example 4

[0048] The graphene multi-intercalated silicon carbide photoconductive microwave device is the same as in Examples 1-3. In this example, the thickness of the graphene intercalation in each silicon ink layer in the substrate is 50 μm - 100 μm, and the side lengths are 5 mm - 10 mm respectively; the number of graphene intercalations in the entire device substrate is 3 - 5. According to the actual application scenario, the number of graphene intercalations in the substrate or the size and thickness of the graphene intercalation can be selected.

[0049] In a photoconductive microwave device in this example, the thickness of the graphene intercalation in each silicon ink layer in the substrate is 50 μm, the width is 5 mm, and the length is 8 mm. The number of graphene intercalations in the entire device substrate is 3; in this embodiment, the graphene intercalation in each silicon ink layer in the device substrate is designed with a relatively small thickness and number of layers, having a relatively high carrier mobility, introducing smaller parasitic parameters, and having good high-frequency characteristics.

[0050] In the photoconductive microwave device of the present invention, the thickness of the graphene intercalation in each silicon ink layer in the substrate can also be 70 μm, the size is 10 mm × 10 mm, and the number of layers is 5; in this embodiment, the graphene intercalation in each silicon ink layer in the device substrate is designed with a relatively large thickness and number of layers. Utilizing the good thermal conductivity of graphene, it has a large heat dissipation area, relatively better heat dissipation performance, and better power-carrying capacity.

[0051] The present invention adopts a structure of a graphene multi-intercalated silicon carbide photoconductive microwave device, which increases the conduction path, improves the current-carrying and power output capabilities of the device, reduces the surface current density of the device, makes the carrier distribution more uniform, significantly improves the service life of the photoconductive switch, and effectively reduces the surface flashover breakdown of the device.

[0052] Example 5

[0053] For the graphene multi-intercalated silicon carbide photoconductive microwave device in the same embodiments as Embodiments 1-4, the substrate of the photoconductive microwave device of the present invention can be changed in thickness and size according to actual applications. In order to obtain better heat dissipation effect and current-carrying capacity, the thickness of each silicon ink layer in the substrate can be set to 200 μm, where the thickness of both the silicon carbide semi-insulating material layer and the graphene intercalation layer is 100 μm, and the size is set to 10 mm × 10 mm. The sizes of the silicon carbide semi-insulating material layer and the graphene intercalation layer in the silicon ink layer in the substrate are consistent with the overall size of the device. In addition, silicon carbide semi-insulating material layers and graphene intercalation layers with different thicknesses are alternately stacked to form substrates with different thicknesses. Thinner substrate thicknesses are suitable for flexible or special applications, while thicker substrate thicknesses are suitable for high-power or high-mechanical-strength requirements.

[0054] Embodiment 6

[0055] The present invention is also a method for fabricating a graphene multi-intercalated silicon carbide photoconductive microwave device. To fabricate the above-mentioned graphene multi-intercalated silicon carbide photoconductive microwave device, refer to Figure 2 , Figure 2 , which is a flowchart of the fabrication method of the present invention. The present invention prepares a silicon ink layer base structure by thermally cracking a silicon carbide semi-insulating material to generate graphene intercalations thereon, stacks the silicon ink layer base structures to form a device substrate, and fabricates ohmic contact electrodes on the upper surface of the substrate, including the following steps:

[0056] Step 1: Design the graphene multi-intercalated silicon carbide photoconductive microwave device: The substrate structure of the present invention adopts a multi-layer stack design based on silicon ink layers, where the silicon ink layer is a composite layer structure with a silicon carbide semi-insulating material layer as the substrate and graphene intercalations prepared by a thermal cracking process on its upper surface. The formation process of the silicon ink layer includes generating graphene intercalations by thermal cracking on the silicon carbide semi-insulating material layer, and then continuously epitaxially growing another layer of silicon carbide semi-insulating material layer on the upper surface of the graphene intercalation, thereby completing the stack setting of one silicon ink layer. By repeating this process, multiple composite structures of silicon ink layers are stacked together to form the multi-layer stack structure of the substrate. In the multi-layer stack structure of the substrate, a single graphene intercalation is sandwiched between two silicon carbide semi-insulating material layers, forming a "sandwich" structure. The structural feature of the entire substrate of the present invention is that the silicon carbide semi-insulating material layers and the graphene intercalation layers are sequentially and repeatedly stacked from bottom to top, and both the bottom layer and the top layer of the substrate are silicon carbide semi-insulating material layers. This design not only enhances the mechanical strength and thermal stability of the substrate but also optimizes its electrical properties. The electrodes are arranged on the upper surface of the top layer of the substrate for easy connection to an external circuit.

[0057] Step 2: Clean the silicon carbide semi-insulating material substrate: First, ultrasonically clean the silicon carbide semi-insulating material substrate with an organic solvent. Then, use Piranha solution to remove organic contaminants on the surface of the material substrate. Next, soak the material substrate in hydrofluoric acid to remove the oxide layer. After that, soak the material substrate in SC-2 solution to remove metal ions. Finally, soak the material substrate in diluted hydrofluoric acid solution to gently remove the oxide. Before and after each solution cleaning, rinse with deionized water and blow dry the material substrate with a nitrogen gun. After the cleaning is completed, take out the silicon carbide semi-insulating material substrate.

[0058] Step 3: Hydrogen etching of the upper surface of the silicon carbide semi-insulating material substrate: In order to remove scratches on the surface of the silicon carbide semi-insulating material substrate and form a surface topography with atomic-level flatness, put the cleaned silicon carbide semi-insulating material substrate into an etching furnace, quickly raise the temperature and hold it, then continue to raise the temperature and hold it again. After that, introduce hydrogen, raise the temperature to the etching temperature, carry out hydrogen etching, and then naturally cool down under hydrogen protection, so that the upper surface of the substrate has a surface topography with atomic-level flatness. After cooling to room temperature, the hydrogen etching of the upper surface of the substrate is completed.

[0059] Step 4: Prepare the growth of graphene interlayers: Graphitize the silicon carbide semi-insulating material substrate to prepare the growth of graphene interlayers. Put the etched silicon carbide semi-insulating material substrate into the reaction chamber of a high-temperature furnace, and carry out the first temperature rise and holding. Further increase the temperature for the second temperature rise and holding. When the temperature rises to the graphitization temperature, thermally crack on the silicon carbide semi-insulating material substrate to generate graphene interlayers. The Si-C bonds break, Si atoms sublimate, and C atoms enrich and reconstruct to form epitaxial graphene. After cooling, the preparation of the graphene interlayers in the silicon ink layer is completed, and the first silicon ink layer is obtained. The generated graphene interlayers can be directly attached to the upper surface of the silicon carbide material, saving the transfer step, reducing costs and avoiding contamination and damage.

[0060] Step 5: Epitaxial growth of silicon carbide: Use chemical vapor deposition (CVD) method to continue the epitaxial growth of the silicon carbide semi-insulating material layer on the silicon ink layer. First, clean the reaction chamber and put in the material. Raise the temperature to the growth temperature in a hydrogen atmosphere, and then introduce hydrogen for in-situ etching. Introduce silicon source and carbon source gases to start epitaxial growth. After the growth is completed, anneal in an inert gas and cool down to room temperature to complete the epitaxial growth of silicon carbide.

[0061] Step 6: Preparation of multi-stack structure: Take the silicon carbide semi-insulating material on the already prepared silicon ink layer as the new material substrate, and repeat Steps 2 - 5 according to the designed number of graphene interlayers in the substrate. Finally, complete the preparation of the substrate containing different numbers of graphene interlayers.

[0062] Step 7: Fabricate ohmic contact electrodes on the device substrate: First, clean the device substrate to remove contaminants, flatten the surface by polishing or etching, spin-coat photoresist and expose to define the electrode pattern. Then, sputter-deposit a metal thin film, anneal in an inert gas to form an ohmic contact, and then remove the excess metal and clean the sample to complete the electrode fabrication and obtain the entire photoconductive microwave device.

[0063] The preparation method of the graphene multi-intercalated SiC photoconductive microwave device of the present invention solves the problems of flashover breakdown caused by the concentration of carriers on the surface of the planar photoconductive microwave device, excessive device thermal load, and reduced device life by introducing graphene intercalation into the SiC photoconductive microwave device, realizes uniform current distribution, improves the voltage resistance and reliability of the device, and increases the conduction path, thereby improving the current-carrying capacity and power output capacity of the device. Through preparation methods such as cleaning, hydrogen etching, graphitization treatment, and epitaxial growth technology, a multi-layer structured SiC photoconductive microwave device is finally formed. The method of directly growing graphene on the SiC material substrate avoids the possible contamination and damage introduced during the traditional transfer process and improves the crystal quality of graphene. This technology can be widely applied to high-power microwave systems, radar detection systems, laser fusion systems, high-precision satellite positioning and tracking systems, electronic countermeasures, and electronic warfare systems, etc., and has the advantages of fast response speed, large power capacity, and strong anti-electromagnetic interference ability.

[0064] Example 7

[0065] The graphene multi-intercalated silicon carbide photoconductive microwave device and its preparation method are the same as those in Examples 1-6, see Figure 3 , Figure 3 is the flow chart of cleaning the silicon carbide semi-insulating material substrate in the preparation method of the present invention. The cleaning of the silicon carbide semi-insulating material substrate described in Step 2 includes the following steps:

[0066] 2.1. Ultrasonic cleaning of the substrate: The silicon carbide semi-insulating material substrate with a silicon ink layer is sequentially placed in acetone CH3COCH3 and isopropyl alcohol (CH3)2CH(OH) for ultrasonic cleaning for 5 minutes. Using the above two organic solvents can effectively dissolve and remove the grease, organic residues, and other organic pollutants on the substrate surface. The cavitation effect of ultrasonic waves can also enhance the cleaning effect and help remove the fine particles and pollutants attached to the substrate surface. Among them, acetone and isopropyl alcohol are volatile, and the operation needs to be carried out in a well-ventilated environment, and the ultrasonic cleaning time should not be too long to avoid damaging the substrate surface.

[0067] 2.2. Removal of organic pollutants by Piranha solution: Immerse it in a mixed solution of concentrated sulfuric acid H2SO4: hydrogen peroxide H2O2 = 4:1 at 180 °C for 10 min. This solution has extremely strong oxidizing properties and can completely decompose and remove organic pollutants on the substrate surface. Concentrated sulfuric acid can dissolve some metal impurities, while hydrogen peroxide further removes metal pollutants through oxidation.

[0068] 2.3. Removal of oxide layer: Then immerse it in hydrofluoric acid HF at room temperature for 5 min. Hydrofluoric acid can dissolve the natural oxide layer SiO on the surface of silicon carbide, making the substrate surface cleaner. And the surface after HF treatment can form a hydrogen-terminated surface, reducing the surface state density and improving the electrical properties. The immersion time should not be too long to avoid over-corroding the substrate surface.

[0069] 2.4. Removal of metal ions: Immerse it in a mixed solution of deionized water H2O: hydrogen peroxide H2O2: hydrochloric acid HCl = 4:1:1 at 80 °C for 10 min. Hydrochloric acid can effectively remove metal ion pollutants on the substrate surface. Hydrogen peroxide further cleans the surface through oxidation and removes residual organic pollutants. And this solution can keep the substrate surface hydrophilic, facilitating subsequent processes.

[0070] 2.5. Gentle removal of oxide: Immerse it in a mixed solution of deionized water H2O: hydrofluoric acid HF = 5:1 at room temperature for 5 min to form a hydrogen-terminated surface on the substrate surface, reducing the surface state density. And diluted hydrofluoric acid can gently remove the thin oxide layer that may reform on the substrate surface.

[0071] 2.6. Rinse with deionized water and dry with a nitrogen gun: In the above cleaning process, rinse with deionized water for 5 min before and after each cleaning with the solution, and dry with a nitrogen gun. After each chemical solution treatment, rinsing with deionized water can completely remove the chemical substances remaining on the substrate surface and avoid cross-contamination. Drying with nitrogen can quickly remove the moisture on the substrate surface and prevent water marks and secondary contamination. When drying with nitrogen, high-purity nitrogen should be used to avoid introducing new pollutants. After the cleaning is completed, take out the semi-insulating silicon carbide material substrate to obtain the cleaned semi-insulating silicon carbide material substrate.

[0072] Through multi-step chemical treatment and physical cleaning, the present invention gradually removes organic pollutants, oxides, and metal ions on the surface of the semi-insulating silicon carbide material substrate, ensuring a highly clean substrate surface. This not only improves the electrical properties of the material but also provides a good foundation for subsequent processing and applications.

[0073] Example 8

[0074] The graphene multi-intercalated silicon carbide photoconductive microwave device and its preparation method are the same as those in Examples 1-7, see Figure 4 ,Figure 4 This is a flowchart of the hydrogen etching process for the silicon carbide semi-insulating material substrate in the preparation method of the present invention. The hydrogen etching of the upper surface of the silicon carbide semi-insulating material substrate described in step 3 includes the following steps:

[0075] 3.1. Place the substrate in the etching furnace, rapidly heat up and hold the temperature: In order to remove the scratches on the surface of the silicon carbide semi-insulating material substrate and form a surface topography with atomic-level flatness, the upper surface of the silicon carbide semi-insulating material substrate is subjected to hydrogen etching. The cleaned silicon carbide semi-insulating material substrate is placed in the reaction chamber of the etching furnace, and the temperature is raised from room temperature to 800 °C within 90 s and held for 90 s. The temperature is raised slowly to avoid excessive thermal stress on the substrate caused by sudden temperature changes, preventing the substrate from cracking or deforming. And holding at 800 °C can remove the moisture, gas and other volatile contaminants adsorbed on the substrate surface.

[0076] 3.2. Continue to heat up and hold the temperature again, and introduce hydrogen: The temperature in the reaction chamber is raised from 800 °C to 1150 °C within 30 s and held for 30 s. After the holding ends, high-purity hydrogen with a pressure of 0.7 - 0.9 atmospheres is introduced. Holding at 1150 °C can enhance the surface activity of the substrate, facilitating the reaction between hydrogen and the surface. The relatively high temperature can initially remove the shallow scratches and defects on the surface. High-purity hydrogen is the medium for the etching reaction, which reacts chemically with the silicon carbide surface to remove surface defects. As a reducing gas, hydrogen can prevent the oxidation of the substrate surface at high temperatures.

[0077] 3.3. Raise the temperature to the etching temperature and conduct hydrogen etching: The temperature in the reaction chamber is raised from 1150 °C to the etching temperature within 90 s. The hydrogen etching of silicon carbide needs to be carried out at extremely high temperatures, and the etching temperature is usually 1450 °C to 1650 °C. At high temperatures, hydrogen reacts with the silicon atoms and carbon atoms on the silicon carbide surface to generate volatile gases such as SiH and CH, thereby removing the surface material. After the temperature increase process is completed, hydrogen etching starts, and the duration is 10 min to 30 min. Hydrogen reacts with the silicon carbide surface to remove scratches, unevenness and other surface defects. Hydrogen etching can form a hydrogen-terminated structure on the surface, reduce the surface state density, and improve the electrical properties.

[0078] 3.4. Naturally cool down under hydrogen protection: After the etching is completed, to prevent oxidation, the entire cooling process is carried out under hydrogen protection. Due to the carbon felt insulation layer, it takes about 3 h to naturally cool down to room temperature. Maintaining a hydrogen atmosphere during the cooling process can prevent the substrate surface from contacting with oxygen at high temperatures and oxidizing. The long-term natural cooling can avoid the thermal stress caused by rapid cooling and prevent the substrate from cracking or deforming. Hydrogen protection can ensure that the surface is not contaminated during the cooling process.

[0079] 3.5. After cooling to room temperature, take out the substrate: After the cooling is completed, take out the semi-insulating silicon carbide material substrate to obtain the etched semi-insulating silicon carbide material substrate.

[0080] Through multi-step temperature control and hydrogen reaction, the present invention gradually removes scratches, unevenness and other defects on the surface of the semi-insulating silicon carbide material substrate, forming a surface topography with atomic-level flatness. This not only improves the surface quality of the material, but also improves its electrical properties, providing a good foundation for subsequent processing and applications. Hydrogen protection prevents surface oxidation and contamination throughout the process, ensuring the high quality of the substrate.

[0081] Example 9

[0082] The graphene multi-intercalated silicon carbide photoconductive microwave device and its preparation method are the same as those in Examples 1-8, see Figure 5 , Figure 5 is the flow chart of preparing and growing graphene intercalation on the silicon carbide substrate in the preparation method of the present invention. The preparation of generating graphene intercalation described in step 4 includes the following steps:

[0083] 4.1. Place the substrate in the high-temperature furnace and heat up for the first time and keep the temperature constant: Carefully place the semi-insulating silicon carbide material substrate inside the high-temperature furnace. Start the temperature-raising program of the high-temperature furnace to ensure that the temperature rapidly rises from room temperature to 800 °C within a short time of 90 seconds and remains stable at 800 °C for 90 seconds. The silicon carbide substrate has a certain stability in material properties, but when the temperature is gradually increased, the activity of its internal atoms begins to increase. In this stage, rapidly heating up to 800 °C is to initially activate the atoms in the silicon carbide lattice, causing subtle changes in the forces between atoms and preparing for the reaction at higher temperatures later. Keeping the temperature constant for 90 seconds can allow the substrate to fully reach the thermal equilibrium state at this temperature, ensuring that the atomic activities of all parts inside the substrate tend to be consistent and providing stable and uniform basic conditions for further temperature-raising reactions later.

[0084] 4.2. Second heating and insulation: After the first heating and insulation is completed, the heating program is started again, and the temperature in the high-temperature furnace is increased from 800°C to 1150°C within 90 seconds. After reaching 1150°C, continue to keep warm for 90 seconds. After the insulation operation is completed, argon gas with a pressure maintained at 0.8-0.9 atmospheres is quickly introduced into the high-temperature furnace. Raising the temperature to 1150°C can further intensify the atomic vibration in the silicon carbide lattice and further weaken the bonding force between atoms. The insulation process ensures that the entire substrate reacts fully at this temperature, making the internal structure change more fully. The introduction of argon is mainly based on the fact that argon has stable chemical properties and is an inert gas. In the subsequent higher temperature reaction process, argon can form an inert protective atmosphere around the substrate, effectively isolating possible oxidizing substances such as oxygen from the outside world, avoiding oxidation of the silicon carbide substrate and the intermediate products generated by subsequent reactions, and providing a safe and stable reaction environment for the next key graphitization reaction.

[0085] 4.3. Raise to graphitization temperature: Under the continuous protection of the introduced argon gas, start the heating program, requiring the temperature in the high-temperature furnace to be quickly raised from 1150℃ to the graphitization temperature range of 1500℃-1650℃ within 60 seconds. In this high temperature range, the reaction lasts for 10 to 50 minutes. In this process, the Si-C bond in silicon carbide breaks due to high temperature, Si atoms leave the lattice due to sublimation, and C atoms are enriched in the lattice and begin to rearrange and gradually form epitaxial graphene. When the temperature reaches the graphitization temperature range, the bond energy of the Si-C bond cannot withstand such high energy, so it breaks. Si atoms obtain enough energy at high temperature to overcome the lattice constraints and escape from the silicon carbide structure in the form of sublimation. After losing the constraints of Si atoms, C atoms begin to rearrange due to their own chemical activity and the influence of the high temperature environment. This arrangement follows the bonding characteristics of carbon atoms themselves, and gradually forms a graphene layered structure with a six-membered ring structure. The reaction lasts for a period of time, which can ensure that a sufficient number of C atoms complete the reconstruction, thereby growing epitaxial graphene with a certain thickness and quality. By controlling the reaction time from 10 minutes to 50 minutes, the growth thickness, crystal quality and other characteristics of graphene can be regulated to meet the requirements of graphene performance in different application scenarios.

[0086] 4.4 Cooling to room temperature: After the graphitization reaction is completed, turn off the heating device of the high-temperature furnace. During the entire cooling process, continuously introduce argon gas to ensure that the inside of the furnace is always in an argon protection atmosphere. This cooling process lasts for about 3 hours. After the high-temperature furnace naturally cools down to room temperature, open the furnace door and carefully take out the prepared silicon carbide substrate with epitaxial graphene, thus completing the preparation of the first silicon ink layer. The graphene generated at high temperature has relatively high chemical activity. If it comes into contact with oxidizing substances such as oxygen during the cooling process, it is very easy to undergo an oxidation reaction, resulting in serious damage to the structure and performance of the graphene. Therefore, slowly cooling under argon protection can enable the graphene to gradually cool in a relatively stable environment and avoid contact with external oxidizing substances. At the same time, the process of slow cooling also helps the atoms inside the graphene to further adjust and optimize their arrangement structure, making the prepared graphene have better crystallinity and stability. After about 3 hours of cooling, the temperature inside the high-temperature furnace is close to room temperature. At this time, the graphene on the taken-out substrate is in a relatively stable state and can be used for subsequent research, analysis, or further processing.

[0087] In the present invention, graphene intercalation is directly generated on a silicon carbide material substrate through the steps of cleaning, etching, and graphitization to achieve hetero-van der Waals epitaxy. Due to the action of van der Waals forces, the interface between the grown thin film and the substrate is relatively flat and clean, and the defect density is low. And it avoids the pollution introduced during the graphene transfer process, and a silicon carbide photoconductive microwave device structure with multiple graphene intercalations is obtained through stacked epitaxial growth.

[0088] Example 10

[0089] The graphene multi-intercalated silicon carbide photoconductive microwave device and its preparation method are the same as those in Examples 1-9, see Figure 6 , Figure 6 which is the flow chart of epitaxial growth of silicon carbide in the preparation method of the present invention. The epitaxial growth of silicon carbide described in step 5 includes the following steps:

[0090] 5.1. Clean the reaction chamber and place the materials. Heat up to the growth temperature in a hydrogen atmosphere: Use chemical vapor deposition (CVD) method to continue epitaxially grow a semi-insulating silicon carbide material layer on the silicon ink layer. Introduce an inert gas such as argon into the reaction chamber for cleaning. The inert gas can purge the residual gases and particulate contaminants in the reaction chamber, ensuring a clean reaction chamber environment. And the inert gas can exclude oxygen and water vapor in the reaction chamber to prevent oxidation of the substrate and the growth layer at high temperatures. Place the materials in the reaction chamber and heat up the reaction chamber to the growth temperature of 1300 - 1600 °C in a hydrogen atmosphere, controlling the pressure at atmospheric pressure or low pressure of 100 - 500 Torr. Slowly heating up to the growth temperature can avoid cracking or deformation of the substrate caused by thermal stress. And the surface activity of the substrate is enhanced at high temperatures, facilitating subsequent etching and epitaxial growth. Hydrogen can also remove adsorbed moisture, oxides, and other contaminants on the substrate surface at high temperatures.

[0091] 5.2. Introduce hydrogen for in-situ etching: Introduce hydrogen to perform in-situ etching on the graphene surface to remove residual contaminants. Hydrogen etching can remove surface defects, obtain a flat surface morphology, provide an ideal basis for epitaxial growth, and can form a hydrogen-terminated structure on the surface, reducing the surface state density and improving the quality of the epitaxial layer.

[0092] 5.3. Introduce silicon source and carbon source gases to start epitaxial growth: Introduce silicon source silane SiH4 or silicon tetrachloride SiCl4 and carbon source propane C3H8 or methane CH4 gases to start the epitaxial growth of silicon carbide. The silicon source and carbon source gases decompose at high temperatures, providing silicon atoms and carbon atoms for the epitaxial growth of silicon carbide. At high temperatures, silicon atoms and carbon atoms are arranged orderly on the substrate surface to form high-quality silicon carbide crystals.

[0093] 5.4. Anneal in an inert gas after growth: After growth, anneal for several hours at 1400 - 1600 °C in an inert gas environment such as argon. Annealing can relieve the thermal stress and lattice stress in the epitaxial layer, improve the crystal quality, make the interface between the epitaxial layer and the substrate more flat, reduce interface defects, and can activate dopants to improve the electrical properties of the epitaxial layer.

[0094] 5.5. Cool down to room temperature: Cool down the temperature in the reaction chamber to room temperature to complete the epitaxial growth of the semi-insulating silicon carbide material layer on the silicon ink layer.

[0095] Through multi-step temperature control, gas reactions, and annealing treatments, the present invention gradually forms a high-quality semi-insulating silicon carbide material layer on the silicon ink layer. This not only improves the crystal quality and electrical properties of the material but also ensures a flat interface between the epitaxial layer and the substrate, reducing interface defects. The use of inert gas and hydrogen prevents oxidation and contamination throughout the process, ensuring the high quality of the epitaxial layer.

[0096] Example 11

[0097] The graphene multi-intercalated silicon carbide photoconductive microwave device and its preparation method are the same as those in Embodiment 1-10. Refer to Figure 7 , Figure 7 This is a flowchart of the process for fabricating ohmic contact electrodes on the upper surface of the device substrate in the preparation method of the present invention. The steps for fabricating ohmic contact electrodes on the device substrate described in Step 7 include the following steps:

[0098] 7.1. Clean the device substrate to remove contaminants: Use organic solvents such as acetone, isopropyl alcohol, and deionized water to clean the device substrate. Acetone and isopropyl alcohol can dissolve and remove surface grease, organic residue, and other organic contaminants, and deionized water rinsing can remove surface particulate contaminants.

[0099] 7.2. Make the surface flat by polishing or etching: Make the surface flat by chemical mechanical polishing (CMP) or dry etching such as reactive ion etching. CMP or dry etching can remove surface scratches, unevenness, and other defects. A flat surface helps the uniformity of subsequent photolithography and metal deposition processes, can improve the contact quality between the metal electrode and the substrate, and reduce the contact resistance.

[0100] 7.3. Spin-coat photoresist and expose to define the electrode pattern: Spin-coat photoresist on the surface of the device substrate, use a mask aligner to expose through a mask to define the electrode pattern, and use a developer to remove the photoresist in the exposed area to form the electrode pattern. After development, the photoresist in the unexposed area remains as a mask for subsequent metal deposition.

[0101] 7.4. Sputter-deposit a metal thin film: Deposit a metal thin film using Ti / Pt / Au metal, Ni / Ti / Pt / Au metal, or Wu / Ti / Au metal sputtering. Ti or Ni serves as an adhesion layer, which can improve the adhesion of the metal thin film to the substrate.

[0102] 7.5. Anneal in an inert gas to form an ohmic contact: Anneal in an inert gas such as nitrogen or argon at 800 °C to 1000 °C for 1 to 5 minutes to promote the reaction between the metal and the semi-insulating silicon carbide material on the upper surface of the device substrate to form a low-resistance ohmic contact. High-temperature annealing causes the metal to react with silicon carbide to form metal silicides such as TiSi and NiSi, reducing the contact resistance. Annealing can improve the interface quality between the metal and silicon carbide, reduce interface defects, and the annealed electrodes have more stable electrical properties and reliability.

[0103] 7.6. Remove the excess metal: Immerse the device in a photoresist stripper such as acetone. The stripper dissolves the photoresist in the unexposed area and simultaneously removes the excess metal covered thereon, retaining the defined electrode pattern to ensure the clarity and edge quality of the electrode pattern.

[0104] 7.7. Cleaning the sample: Rinse the sample with deionized water to thoroughly remove the photoresist stripper and metal residues, completing the fabrication of the entire device.

[0105] Through multiple steps of cleaning, planarization, photolithography, metal deposition, annealing, and cleaning, the present invention gradually forms high-quality ohmic contact electrodes on semi-insulating silicon carbide materials. This not only ensures low-resistance contact between the electrodes and the substrate but also improves the mechanical stability and electrical properties of the electrodes. Precise photolithography and metal deposition processes ensure the clarity and dimensional accuracy of the electrode pattern, and the annealing treatment improves the interface quality, reduces interface defects, and enhances the reliability and performance of the electrodes.

[0106] The technical effects of the present invention will be further illustrated through simulation experiments below.

[0107] Example 12

[0108] The simulation of the graphene multi-intercalated silicon carbide photoconductive microwave device of the present invention is the same as that in Examples 1-11. Refer to Figure 8 , Figure 8 which is the simulation result of the surface conduction state current density of the graphene multi-intercalated silicon carbide photoconductive microwave device of the present invention.

[0109] The simulation conditions are as follows: the vanadium concentration in semi-insulating 4H-SiC is 5e16 cm -3 , the nitrogen concentration is 1e16 cm -3 , the boron concentration is 2e15 cm -3 , the light energy is 2 mj, the bias voltage is 1 kV, the back incidence, and the spot area is 2 mm × 8 mm.

[0110] The simulation content is to construct two planar photoconductive switch device models with the same overall size and thickness. One is a common lateral SiC photoconductive switch, and the other is the SiC photoconductive microwave device with graphene multi-intercalation designed by the present invention. The output characteristics and surface current of the two devices with different structures are compared.

[0111] Simulation results: The simulation results are shown in Figure 8 , Figure 8 where the abscissa is the device surface position, the ordinate is the current density, the black curve is the current density of the planar device, and the red curve is the current density of the device with graphene multi-intercalation. The experimental results show that when the voltage across the device is 1 kV, the surface conduction state current density between the device electrodes is reduced by two orders of magnitude, and the current in the device is significantly concentrated inside the device rather than on the device surface, effectively reducing the surface flashover breakdown of the device.

[0112] In summary, the present invention discloses a graphene multi-intercalated silicon carbide photoconductive microwave device and its preparation method, which solves the technical problems of surface flashover breakdown, excessive substrate current density and insufficient lifespan of traditional photoconductive switches. The substrate of the photoconductive microwave device of the present invention adopts a design of alternating stacking of multiple layers of silicon carbide and graphene. In the substrate, every two semi-insulating silicon carbide material layers and graphene intercalations form a silicon ink layer. Multiple silicon ink layers are stacked and a semi-insulating silicon carbide material layer is epitaxially grown on the upper surface to form the device substrate, and ohmic contact metal electrodes are prepared on the upper surface of the substrate. The preparation method of the present invention includes designing a graphene multi-intercalated silicon carbide photoconductive microwave device, cleaning the semi-insulating silicon carbide material substrate, hydrogen etching, preparing and growing graphene intercalations, epitaxial growth of silicon carbide, preparation of a multi-stack structure, and preparation of ohmic contact electrodes. The present invention combines the preparation of graphene by SiC pyrolysis and epitaxial growth technology to realize the fabrication of an integrated, multi-intercalated SiC optoelectronic device, eliminating the transfer process. By introducing graphene intercalations into the silicon carbide photoconductive microwave device, the current distribution is optimized, the conduction path is increased, the current is concentrated inside the device, effectively reducing surface flashover breakdown, improving the current-carrying capacity and power output capacity of the device, and enhancing the voltage resistance, reliability and heat dissipation capacity of the device. It can be used in fields such as high-power microwave systems, radar detection systems, laser fusion systems, high-precision satellite positioning and tracking systems, electronic countermeasures and electronic warfare systems, etc.

Claims

1. A graphene multi-intercalated silicon carbide photoconductive microwave device, which includes a substrate and a metal electrode from bottom to top. The material of the substrate contains silicon carbide material, or gallium nitride material, or diamond material. It is characterized in that, The substrate is a multi-layered structure based on a silicon ink layer. The silicon ink layer is a composite layer structure with a semi-insulating silicon carbide material layer as the substrate, and graphene intercalation is prepared by thermal cracking on the upper surface of the substrate. The stacked arrangement of the composite structures of multiple silicon ink layers forms the multi-layered structure of the substrate. In the multi-layered structure of the substrate, a single graphene intercalation is sandwiched between two semi-insulating silicon carbide material layers. Both the bottom layer and the top layer of the substrate are semi-insulating silicon carbide material layers. The electrode is disposed on the upper surface of the top layer of the substrate.

2. The graphene multi-intercalated silicon carbide photoconductive microwave device according to claim 1, wherein, The thickness of the substrate is 0.3 mm - 1 mm, and the side lengths of the substrate are 5 mm - 10 mm respectively; the thickness of each silicon ink layer is 100 μm - 200 μm, and the side lengths are 5 mm - 10 mm respectively.

3. The graphene multi-intercalated silicon carbide photoconductive microwave device according to claim 1, characterized in that, The thickness of the semi-insulating silicon carbide material layer in each silicon ink layer within the substrate is 50 μm - 100 μm, and the side lengths are 5 mm - 10 mm respectively; the number of semi-insulating silicon carbide material layers within the entire device substrate is 4 - 6.

4. The graphene multi-intercalated silicon carbide photoconductive microwave device according to claim 1, wherein The thickness of the graphene intercalation in each silicon ink layer within the substrate is 50 μm - 100 μm, and the side lengths are 5 mm - 10 mm respectively; the number of graphene intercalations within the entire device substrate is 3 - 5.

5. A preparation method of a graphene multi-intercalated silicon carbide photoconductive microwave device for preparing the graphene multi-intercalated silicon carbide photoconductive microwave device according to any one of claims 1-4, characterized in that, The silicon ink layer base structure is obtained by preparing graphene intercalation on it through thermal cracking of semi-insulating silicon carbide material. The device substrate is formed by stacking the silicon ink layer base structures. An ohmic contact electrode is prepared on the upper surface of the substrate, including the following steps: Step 1: Design a graphene multi-intercalated silicon carbide photoconductive microwave device: The graphene multi-intercalated silicon carbide photoconductive microwave device includes a substrate and a metal electrode from bottom to top. The material of the substrate includes or contains silicon carbide material, or contains gallium nitride material, or contains diamond material. The substrate is a multi-layered structure based on a silicon ink layer. The silicon ink layer is a composite layer structure with a semi-insulating silicon carbide material layer as the substrate, and graphene intercalation is prepared by thermal cracking on the upper surface of the substrate. The stacked arrangement of the composite structures of multiple silicon ink layers forms the multi-layered structure of the substrate. In the multi-layered structure of the substrate, a single graphene intercalation is sandwiched between two semi-insulating silicon carbide material layers. Both the bottom layer and the top layer of the substrate are semi-insulating silicon carbide material layers. The electrode is disposed on the upper surface of the top layer of the substrate. Step 2: Clean the semi-insulating silicon carbide material substrate: First, ultrasonically clean the semi-insulating silicon carbide material substrate with an organic solvent; then use Piranha solution to remove organic pollutants on the surface of the material substrate; then soak the material substrate in hydrofluoric acid to remove the oxide layer; then soak the material substrate in SC-2 solution to remove metal ions; finally, soak the material substrate in a diluted hydrofluoric acid solution to gently remove the oxide. Before and after each solution cleaning above, rinse with deionized water and blow dry the material substrate with a nitrogen gun. After the cleaning is completed, take out the semi-insulating silicon carbide material substrate. Step 3: Hydrogen etching of the upper surface of the silicon carbide semi-insulating material substrate: Place the cleaned silicon carbide semi-insulating material substrate into an etching furnace, rapidly heat up and hold the temperature, then continue to heat up and hold the temperature again. After that, introduce hydrogen, heat up to the etching temperature, conduct hydrogen etching, and then naturally cool down under hydrogen protection to make the upper surface of the substrate have an atomic-level flat surface morphology. After cooling to room temperature, complete the hydrogen etching of the upper surface of the substrate; Step 4: Preparation of the grown graphene interlayer: Graphitization is carried out on the upper surface of the silicon carbide semi-insulating material substrate to prepare the grown graphene interlayer. Place the silicon carbide semi-insulating material substrate after hydrogen etching into the reaction chamber of a high-temperature furnace, and conduct the first heating and temperature holding; further increase the temperature for the second heating and temperature holding; raise the temperature to the graphitization temperature to thermally crack and generate the graphene interlayer on the silicon carbide semi-insulating material substrate. The Si-C bonds are broken, Si atoms sublime, and C atoms are enriched and reconstructed to form epitaxial graphene; cool down to complete the preparation of the graphene interlayer in the silicon ink layer; complete the preparation of the first silicon ink layer; Step 5: Epitaxial growth of silicon carbide: Use chemical vapor deposition (CVD) method to continue epitaxially grow the silicon carbide semi-insulating material layer on the silicon ink layer. First, clean the reaction chamber and place the material, heat up to the growth temperature in a hydrogen atmosphere, then introduce hydrogen for in-situ etching, introduce silicon source and carbon source gases to start epitaxial growth. After growth is completed, anneal in an inert gas and cool down to room temperature to complete the epitaxial growth of silicon carbide; Step 6: Preparation of the multi-stack structure: Use the silicon carbide semi-insulating material on the already prepared silicon ink layer as a new material substrate, and repeat Steps 2 - 5 according to the designed number of graphene interlayers in the substrate to complete the preparation of the substrate with a multi-stack structure; Step 7: Preparation of ohmic contact electrodes on the device substrate: First, clean the device substrate to remove contaminants, make the surface flat by polishing or etching, spin-coat photoresist and expose to define the electrode pattern. Then, sputter-deposit a metal thin film, anneal in an inert gas to form an ohmic contact, and then remove the excess metal and clean the sample to complete the electrode preparation and obtain the entire photoconductive microwave device.

6. According to the method for preparing a graphene multi-interlayer silicon carbide photoconductive microwave device as described in Claim 5, the cleaning of the silicon carbide semi-insulating material substrate in Step 2 includes the following steps: 2.

1. Ultrasonic cleaning of the substrate: Place the silicon carbide semi-insulating material substrate of the silicon ink layer into acetone (CH3COCH3) and isopropyl alcohol ((CH3)2CH(OH)) in sequence for ultrasonic cleaning for 5 minutes; 2.

2. Removal of organic contaminants with Piranha solution: Place it into a mixed solution of concentrated sulfuric acid (H2SO4): hydrogen peroxide (H2O2) = 4:1, and soak at 180 °C for 10 minutes; 2.

3. Removal of the oxide layer: Place it into hydrofluoric acid (HF) and soak at room temperature for 5 minutes; 2.

4. Removal of metal ions: Then place it into a mixed solution of deionized water (H2O): hydrogen peroxide (H2O2): hydrochloric acid (HCl) = 4:1:1, and soak at 80 °C for 10 minutes; 2.

5. Gentle removal of the oxide: Place it into a mixed solution of deionized water (H2O): hydrofluoric acid (HF) = 5:1, and soak at room temperature for 5 minutes; 2.

6. Rinse with deionized water and dry with a nitrogen gun: In the above cleaning process, rinse with deionized water for 5 minutes before and after each cleaning with the solution, and dry with a nitrogen gun. Finally, obtain the semi-insulating silicon carbide material substrate after cleaning is completed.

7. According to the method for preparing a graphene multi-intercalated silicon carbide photoconductive microwave device as described in claim 5, the hydrogen etching of the upper surface of the semi-insulating silicon carbide material substrate in step 3 includes the following steps: 3.

1. Place the substrate in the etching furnace, rapidly heat up and hold the temperature: Place the cleaned semi-insulating silicon carbide material substrate into the reaction chamber of the etching furnace, heat up from room temperature to 800 °C within 90 s, and hold the temperature for 90 s. 3.

2. Continue to heat up and hold the temperature again, and introduce hydrogen: Heat up the temperature in the reaction chamber from 800 °C to 1150 °C within 30 s and hold the temperature for 30 s. After the temperature holding is completed, introduce high-purity hydrogen with a pressure of 0.7 - 0.9 atmospheres. 3.

3. Heat up to the etching temperature and perform hydrogen etching: Heat up the temperature in the reaction chamber from 1150 °C to the etching temperature within 90 s. The etching temperature is usually 1450 °C to 1650 °C. After the heating process is completed, start hydrogen etching, and the duration is 10 min to 30 min. 3.

4. Naturally cool down under hydrogen protection: After etching is completed, to prevent oxidation, the entire cooling process is carried out under hydrogen protection. Due to the carbon felt insulation layer, it takes about 3 h to naturally cool down to room temperature. 3.

5. Take out the substrate after cooling to room temperature: After cooling is completed, take out the semi-insulating silicon carbide material substrate to obtain the semi-insulating silicon carbide material substrate after hydrogen etching.

8. According to the method for preparing a graphene multi-intercalated silicon carbide photoconductive microwave device as described in claim 5, the preparation of the graphene intercalation layer in step 4 includes the following steps: 4.

1. Place the substrate in the high-temperature furnace and heat up and hold the temperature for the first time: Place the semi-insulating silicon carbide material substrate into the high-temperature furnace, heat up from room temperature to 800 °C within 90 s, and hold the temperature for 90 s. 4.

2. Heat up and hold the temperature for the second time: Subsequently, heat up the temperature in the high-temperature furnace from 800 °C to 1150 °C within 90 s and hold the temperature for 90 s. After the temperature holding is completed, introduce argon with a pressure of 0.8 - 0.9 atmospheres. 4.

3. Heat up to the graphitization temperature: Under argon protection, heat up the temperature in the high-temperature furnace from 1150 °C to the graphitization temperature within 60 s. The temperature during the graphitization process is 1500 °C to 1650 °C. During this process, the Si-C bonds break, Si atoms sublimate, and C atoms are enriched and reconstructed to form epitaxial graphene. The duration is 10 min to 50 min. 4.

4. Cool down to room temperature: To prevent the graphene from being oxidized, the entire cooling process is carried out under argon protection for about 3 h. After naturally cooling down to room temperature, take it out to complete the preparation of the first silicon-carbon layer.

9. According to the method for preparing a graphene multi-intercalated silicon carbide photoconductive microwave device as described in claim 5, the epitaxial growth of silicon carbide in step 5 includes the following steps: 5.

1. Clean the reaction chamber and place the materials. Heat up to the growth temperature in a hydrogen atmosphere: Pass an inert gas such as argon into the reaction chamber for cleaning to ensure no contaminants. Place the materials into the reaction chamber and heat up the reaction chamber to the growth temperature of 1300 - 1600 °C in a hydrogen atmosphere, controlling the pressure at atmospheric pressure or low pressure of 100 - 500 Torr. 5.

2. Pass hydrogen for in-situ etching: Pass hydrogen to conduct in-situ etching on the graphene surface to remove residual contaminants. 5.

3. Pass silicon source and carbon source gases to start epitaxial growth: Pass the silicon source silane SiH4 or silicon tetrachloride SiCl4 and the carbon source propane C3H8 or methane CH4 gases to start the epitaxial growth of silicon carbide. 5.

4. Anneal in an inert gas after growth: After growth, anneal in an inert gas such as argon at 1400 - 1600 °C for 3 - 5 hours. 5.

5. Cool down to room temperature: After annealing, cool down the temperature in the reaction chamber to room temperature to complete the epitaxial growth of the silicon carbide semi-insulating material layer on the silicon ink layer.

10. According to the method for preparing a graphene multi-intercalated silicon carbide photoconductive microwave device as described in claim 5, the preparation of ohmic contact electrodes on the device substrate in step 7 includes the following steps: 7.

1. Clean the device substrate to remove contaminants: Use organic solvents such as acetone, isopropyl alcohol, and deionized water to clean the device substrate to remove surface contaminants. 7.

2. Make the surface flat by polishing or etching: Make the surface flat by chemical mechanical polishing (CMP) or dry etching such as reactive ion etching. 7.

3. Spin-coat photoresist and expose to define the electrode pattern: Spin-coat photoresist on the surface of the device substrate, use a lithography machine to expose through a mask to define a square electrode pattern, and use a developer to remove the photoresist in the exposed area to form the electrode pattern. 7.

4. Sputter-deposit a metal thin film: Deposit a metal thin film by sputtering methods using Ti / Pt / Au metal, Ni / Ti / Pt / Au metal, or Wu / Ti / Au metal. 7.

5. Anneal in an inert gas to form an ohmic contact: Anneal in an inert gas such as nitrogen or argon at 800 °C to 1000 °C for 1 to 5 minutes to promote the reaction between the metal and the silicon carbide semi-insulating material on the upper surface of the device substrate to form a low-resistance ohmic contact. 7.

6. Remove the excess metal: Immerse the device in a photoresist stripper such as acetone to remove the excess metal in the unexposed area. 7.

7. Clean the sample: Rinse the sample with deionized water to remove residual chemicals, complete the preparation of the device electrodes, and obtain the entire photoconductive microwave device.

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