A multi-layered high-voltage, high-thermal-conductivity photoconductive switch device and its fabrication method

Abstract

This invention discloses a multi-layered high-voltage, high-thermal-conductivity photoconductive switch device and its fabrication method, mainly solving the thermal failure problem of existing photoconductive switch devices. It includes several semi-insulating substrates (1), metal electrodes (2), connecting electrodes (3), and external connecting electrodes (4). The metal electrodes are distributed at the center of the upper and lower surfaces of each semi-insulating substrate; the connecting electrodes are connected to the metal electrodes and the external connecting electrodes respectively; boron nitride sheets (5) are disposed close to the upper and lower parts of each semi-insulating substrate, forming a multi-layered structure; each boron nitride sheet has a through-hole with the same shape and size as the connecting electrode at its center, and the connecting electrode passes through the through-hole of the boron nitride sheet to connect to the metal electrodes on two adjacent semi-insulating substrates. This invention solves the thermal failure problem in photoconductive switch devices, reduces the inter-stage capacitance of the device, and improves the withstand voltage and frequency response capability of the device, making it suitable for ultra-wideband electromagnetic pulse generators and solid-state compact pulse power supplies.

Description

Technical Field

[0001] This invention belongs to the field of microelectronics technology, and specifically relates to a photoconductive switching device that can be used in ultra-wideband electromagnetic pulse generators and solid-state compact pulse power supplies. Background Technology

[0002] Photoconductive switches are characterized by short jitter time, fast response, and adjustable frequency. They have broad application prospects in high-power pulse generation and high-power microwave generation. Compared with the traditional vacuum generator, which has a single frequency and large device size, photoconductive switches have the advantages of adjustable frequency and miniaturization. A photoconductive switch is a device that converts low-power energy accumulated over a long period of time into high-power energy in a short period of time and transmits high-power electromagnetic pulses to a load. With the continuous in-depth research on photoconductive switches, the requirements for their performance in terms of ultra-fast frequency, ultra-high power, and stability are also increasing. One of the unavoidable central problems encountered by photoconductive switches is their lifespan. The lifespan problem of photoconductive switches is related to the thermal failure of the device, which mainly comes from three aspects: 1) During the conduction of the photoconductive switch, the ultra-high density current filament formed within the current filament undergoes avalanche collisional ionization, generating Joule heating. 2) When the photoconductive switch is irradiated by a high-energy laser beam, a large amount of light energy is lost in the form of heat. At the same time, a single laser beam triggering the photoconductive switch generates a single high-density charge carrier filament. 3) The leakage current of the photoconductive switch in the dark state will also generate heat loss, and a large amount of heat accumulation will damage the switch.

[0003] In their paper "Design and Testing of High-Power Photoconductive Switch Silicon Microchannel Heat Sink," Zhao Yue et al. designed a microchannel heat sink for heat dissipation. Its basic structure consists of a heat sink body and a cover plate. The heat sink body has a distribution channel and a collection channel, which are connected by a microchannel array formed using MEMS technology. The cover plate uses semiconductor etching to create a through-hole structure. The heat sink body and cover plate are connected by bonding to form a closed fluid channel. Epoxy resin is used to bond the photoconductive switch to a diamond sheet, which is then bonded to the microchannel heat sink using thermally conductive silicone grease. The heat sink is fixed to a ceramic sheet with through-holes to increase its mechanical thickness. Fluid enters the distribution channel through the inlet, is evenly distributed into the microchannels, and carries away heat from the device through surface convection. The fluid is then collected in the collection channel and enters the outlet. However, due to the small geometric dimensions of this microchannel structure and the through-holes, it is easily affected by surface roughness. Surface roughness not only greatly affects the liquid flow characteristics but also creates microfluidic circulation within the microchannels, which is detrimental to heat dissipation.

[0004] Patent application CN201911368860.X discloses a GaAs photoconductive switch with a non-planar structure based on a graphene interface layer and its fabrication process. This method involves transferring high-quality graphene onto a target substrate and then depositing metal on the surface to form a substrate-graphene-metal composite structure. This homogenizes the electric field, preventing current concentration and reducing heat generation, which significantly extends the device's lifespan. However, fabricating a graphene film between the metal electrode and the substrate material can affect the adhesion between them, leading to electrode detachment. Furthermore, the thin-layer structure of graphene makes its processing and integration into other materials very difficult, requiring precise control. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of the above-mentioned technologies by providing a multi-layered high-voltage, high-thermal-conductivity photoconductive switch device and its fabrication method, so as to effectively improve the heat dissipation performance of the device, reduce the interstage capacitance of the device, and improve the voltage withstand capability of the device.

[0006] The technical solution of this invention is implemented as follows:

[0007] 1. A multi-layered high-voltage, high-thermal-conductivity, photoconductive switching device, comprising several semi-insulating substrates, metal electrodes, connecting electrodes, and external connecting electrodes, wherein the metal electrodes are distributed at the center of the upper and lower surfaces of each semi-insulating substrate, and the connecting electrodes are respectively connected to the metal electrodes and the external connecting electrodes, characterized in that:

[0008] A boron nitride sheet is placed between each pair of adjacent semi-insulating substrates, forming a multi-layered structure;

[0009] Each boron nitride sheet has a through hole at its center that is the same size and shape as the connecting electrode. The connecting electrode passes through the through hole of the boron nitride sheet and connects to metal electrodes on two adjacent semi-insulating substrates.

[0010] Preferably, the boron nitride sheet is a cube with a thickness of 0.5 mm to 1 mm and a side length of 18 mm to 24 mm.

[0011] Preferably, each semi-insulating substrate is a cube with a side length of 6mm to 14mm and a thickness of 0.35mm to 1mm, and its material is one of silicon carbide, gallium nitride, gallium arsenide, gallium oxide, and diamond.

[0012] Preferably, the metal electrode and the semi-insulating substrate are in ohmic contact, and the material is one of Ni / Ti / Pt / Au composite metal layer, Ti / Pt / Au composite metal layer, W / Ti / Au composite metal layer, Ni / Ti / Au composite metal layer or Ni / Au composite metal layer.

[0013] Preferably, the shape and size of the connecting electrode are the same as those of the metal electrode, and the thickness is the same as that of the boron nitride sheet. The material used is copper.

[0014] Preferably, the external connecting electrode is made of copper, with a length greater than half the side length of the boron nitride sheet, a width of 2mm to 6mm, and a thickness of 0.05mm to 0.1mm.

[0015] 2. A method for fabricating a multi-layered high-voltage, high-thermal-conductivity, photoconductive switching device, characterized by comprising the following steps:

[0016] S1) Clean the semi-insulating substrate wafer and uniformly apply photoresist to its front side.

[0017] S2) Photolithography and development are performed on the front side of the semi-insulating substrate wafer coated with photoresist using a mask to form several metal electrode-shaped groove areas, and then a metal layer is formed by magnetron sputtering on the front side of the semi-insulating substrate wafer.

[0018] S3) Remove all metal outside the front electrode area of ​​the semi-insulating substrate wafer to form the front metal electrode.

[0019] S4) The back side of the semi-insulating substrate wafer with the front metal electrode is cleaned again, and photoresist is evenly applied to the cleaned back side.

[0020] S5) Photolithography and development are performed on the back side of a semi-insulating substrate wafer coated with photoresist using a mask to form several grooves in the shape of metal electrodes. Then, a back metal layer is formed by magnetron sputtering on the back side of the semi-insulating substrate.

[0021] S6) Remove all metal outside the metal electrode area on the back side of the semi-insulating substrate wafer to form the back metal electrode.

[0022] S7) The semi-insulating substrate wafer is attached to the blue film and then diced and split to prepare several individual photoconductive switches, and each photoconductive switch has a metal electrode on its upper and lower surfaces.

[0023] S8) Select several cubic boron nitride sheets and use laser cutting or plasma cutting to cut a through hole of the same size as the electrode in the center of each boron nitride sheet.

[0024] S9) Select several connecting electrodes and place them in the corresponding boron nitride sheet through holes. Then, arrange and stack them in the order of boron nitride sheet, photoconductive switch, boron nitride sheet, photoconductive switch, ..., boron nitride sheet from top to bottom to form a stacked structure. Align the connecting electrodes with the metal electrodes of the photoconductive switch and then use eutectic bonding to connect each connecting electrode in the stacked structure to the adjacent metal electrode.

[0025] S10) Two external connecting electrodes are selected and connected to the connecting electrodes in the first boron nitride sheet through hole and the last boron nitride sheet through hole in the stacked structure, respectively.

[0026] S11) Using a packaging mold, the prepared stacked structure is encapsulated with potting compound to completely cover several photoconductive switches, and the edges of each boron nitride sheet are exposed outside the packaging material, thus completing the device fabrication.

[0027] 3. A mold for encapsulating photoconductive switching devices, made of Teflon material, characterized in that it includes several boron nitride sheet grooves, several substrate grooves, and external connection electrode grooves;

[0028] The depth of each boron nitride groove is 0.75 to 1 times the side length of the boron nitride sheet;

[0029] The depth of each substrate groove is 0.5 to 1 times the side length of the boron nitride sheet;

[0030] The length and width of each external electrode groove are consistent with the width and thickness of the external electrode, respectively, and the depth is greater than the length of the external electrode.

[0031] Compared with the prior art, the present invention has the following advantages:

[0032] Firstly, because the present invention has a boron nitride sheet between the photoconductive switches, it can not only take advantage of the high thermal conductivity of boron nitride material to dissipate the heat during the operation of the photoconductive switches in a timely manner, reducing the thermal damage of the photoconductive switch devices; but also act as a field plate to homogenize the electric field distribution at the metal electrodes and improve the withstand voltage capability of the devices.

[0033] Secondly, by using the connecting electrodes in the through holes of the boron nitride sheet to connect multiple photoconductive switches to form a stacked structure, the present invention can increase the withstand voltage of the device, reduce the interstage capacitance of the device, and improve the cutoff frequency and response capability of the device.

[0034] Thirdly, by exposing the edge of the boron nitride sheet outside the packaging material during encapsulation, the high thermal conductivity of boron nitride material can effectively solve the problem of heat accumulation in the photoconductive switch during operation and extend the working life of the photoconductive switch device. Attached Figure Description

[0035] Figure 1 Device structure diagram of the present invention;

[0036] Figure 2 Preparation of this invention Figure 1 Flowchart of device implementation;

[0037] Figure 3 This invention encapsulation Figure 1 Diagram of the mold structure used in the device. Specific implementation methods

[0038] The following detailed description of specific examples of the present invention is provided in conjunction with the accompanying drawings.

[0039] Example 1: Structure of a multi-layered high-voltage, high-thermal-conductivity, photoconductive switching device

[0040] Reference Figure 1 This example is based on a multi-layered high-voltage, high-thermal-conductivity, and photoconductive switching device structure, including a semi-insulating substrate 1, a metal electrode 2, a connecting electrode 3, an external connecting electrode 4, and a boron nitride sheet 5, wherein:

[0041] The semi-insulating substrate 1 is configured in several parts, each with a side length of 6mm to 14mm and a thickness of 0.35mm to 1mm, and the material is one of silicon carbide, gallium nitride, gallium arsenide, gallium oxide, and diamond.

[0042] The metal electrode 2 is located at the center of the upper and lower surfaces of each semi-insulating substrate, and the material is one of Ni / Ti / Pt / Au composite metal layer, Ti / Pt / Au composite metal layer, W / Ti / Au composite metal layer, Ni / Ti / Au composite metal layer or Ni / Au composite metal layer.

[0043] The boron nitride 5 has a side length of 18mm to 24mm and a thickness of 0.5mm to 1mm. It has a through hole in the center that is the same shape and size as the metal electrode 2. It is located above and close to each adjacent semi-insulating substrate 1, forming a stacked structure with boron nitride sheets and semi-insulating substrates arranged alternately from top to bottom.

[0044] The connecting electrode 3 is located in the through hole of the boron nitride 5. It is connected to the metal electrode on the adjacent semi-insulating substrate 1. Its shape and size are the same as those of the metal electrode 2, and its height is the same as the thickness of the boron nitride sheet. It is made of copper.

[0045] The external connecting electrodes 4 are provided in two parts, each with a length of 15mm to 20mm, a width of 2mm to 6mm, and a thickness of 0.05mm to 0.1mm. Both are made of copper. They are located on the connecting electrodes of the top and bottom layers of the stacked structure, respectively. One of them is welded to the connecting electrode in the first boron nitride sheet through-hole in the stacked structure and is located on the left half of the connecting electrode; the other is welded to the connecting electrode in the last boron nitride sheet through-hole in the stacked structure and is located on the right half of the connecting electrode.

[0046] Reference Figure 2 This invention provides three embodiments for fabricating the above-mentioned device.

[0047] Example 2: A photoconductive switch device with a three-layer stacked structure consisting of a silicon carbide semi-insulating substrate with a side length of 8 mm and a thickness of 1 mm, and a boron nitride substrate with a side length of 18 mm and a thickness of 0.5 mm was fabricated.

[0048] Step 1: Clean the silicon carbide semi-insulating substrate and perform homogenization, as shown in 2a.

[0049] The silicon carbide semi-insulating substrate wafer was sequentially immersed in BOE solution, deionized water, acetone, isopropanol, and deionized water for ultrasonic cleaning for 120s, 180s, 600s, 180s, and 180s respectively, and then photoresist was uniformly coated on its front side.

[0050] Step 2: Prepare a metal layer on the front side of the cleaned silicon carbide semi-insulating wafer, as shown in 2b.

[0051] A mask with a 5mm diameter circular electrode pattern is used to perform photolithography and development on the front side of a silicon carbide semi-insulating substrate wafer coated with photoresist, forming several circular electrode-shaped groove areas.

[0052] The silicon carbide semi-insulating substrate wafer with the grooved region is then placed in the magnetron sputtering vacuum chamber, with the front side facing the target, at a vacuum level of 1×10⁻⁶. -5 In an argon atmosphere at 1 Pa, the temperature was set to 200 degrees Celsius, the magnetron sputtering pressure to 1 Pa, and the sputtering power to 5 W / cm². 2 Under the specified process conditions, Ni, Ti, Pt, and Au targets were used sequentially to deposit metal layers with thicknesses of 300nm / 200nm / 200nm / 2000nm respectively, forming the front metal layer.

[0053] Step 3: Fabricate metal electrodes on the front side of the silicon carbide semi-insulating wafer, as shown in 2c.

[0054] The metal layer outside the groove area on the front side of the semi-insulating substrate wafer is completely removed by peeling off the blue film and using a stripper to form the Ni / Ti / Pt / Au front metal electrode.

[0055] Step 4: Clean the back side of the silicon carbide semi-insulating wafer, as shown in 2d.

[0056] The back side of the semi-insulating substrate wafer with the front metal electrode is cleaned again. BOE solution, deionized water, acetone, isopropanol, and deionized water are used in sequence for ultrasonic cleaning for 120s, 180s, 600s, 180s, and 180s, respectively. Then, photoresist is evenly applied to the back side.

[0057] Step 5: Prepare a metal layer on the back side of the silicon carbide semi-insulating wafer, as shown in 2e.

[0058] A mask with a 5mm diameter circular electrode pattern on the back side is used to perform photolithography and development on the back side of a silicon carbide semi-insulating substrate wafer coated with photoresist, forming several circular electrode-shaped groove areas.

[0059] The silicon carbide semi-insulating substrate wafer with the grooved area is then placed in the magnetron sputtering vacuum chamber with its back side facing the target. The process is carried out at a vacuum level of 1×10⁻⁶. -5 In an argon atmosphere at 1 Pa, the temperature was set to 200 degrees Celsius, the magnetron sputtering pressure to 1 Pa, and the sputtering power to 5 W / cm². 2 Under the specified process conditions, Ni, Ti, Pt, and Au targets were used sequentially to deposit metal layers with thicknesses of 300 nm, 200 nm, 200 nm, and 2000 nm, respectively.

[0060] Step 6: Prepare a metal electrode on the back side of the silicon carbide semi-insulating wafer, as shown in 2f.

[0061] The metal layer outside the groove area on the back of the semi-insulating substrate wafer is completely removed by peeling off the blue film and using a stripping machine to form the Ni / Ti / Pt / Au back metal electrode.

[0062] Step 7: Divide and cleave a silicon carbide wafer with metal electrodes to prepare a single photoconductive switch, as shown in 2g.

[0063] A blue film is attached to both sides of a silicon carbide semi-insulating substrate wafer. The silicon carbide wafer is first diced and then split to prepare several individual silicon carbide semi-insulating substrates with a side length of 8 mm and a thickness of 1 mm. Each silicon carbide semi-insulating substrate has a metal electrode at the center of its upper and lower surfaces.

[0064] Step 8: Prepare through holes on the boron nitride sheet, as shown in step 2h.

[0065] Four cubic boron nitride sheets with a side length of 18 mm and a thickness of 0.5 mm were selected, and a through hole of the same size as the electrode was cut in the center of each boron nitride sheet using laser cutting technology.

[0066] Step 9: Prepare a boron nitride and silicon carbide substrate stack structure, as shown in 2i.

[0067] Four cylindrical connecting electrodes with a diameter of 5 mm and a height of 0.5 mm are selected. They are first placed in the corresponding four boron nitride sheet through holes. Then, boron nitride is placed on the upper and lower surfaces of each silicon carbide semi-insulating substrate. The electrodes are arranged and stacked in the following order from top to bottom: boron nitride sheet, semi-insulating substrate, boron nitride sheet, semi-insulating substrate, boron nitride sheet, semi-insulating substrate, boron nitride sheet to form a three-layer stacked structure. The connecting electrodes are aligned with the metal electrodes on the semi-insulating substrate. Then, eutectic bonding is used to connect each connecting electrode in the stacked structure to the adjacent metal electrode.

[0068] Step 10: Weld external connecting electrodes onto the laminated structure, such as... Figure 2 As shown in j.

[0069] Two external connecting electrodes, each 14 mm long, 4 mm wide, and 0.05 mm thick, were selected. One electrode was soldered to the left half of the connecting electrode in the first boron nitride sheet through-hole of the stacked structure; the other electrode was soldered to the right half of the connecting electrode in the last boron nitride sheet through-hole of the stacked structure, thus completing the device fabrication.

[0070] Step 11: Package the stacked structure to complete the device fabrication, such as... Figure 2 As shown in k.

[0071] The three-layer stacked structure with external connecting electrodes is placed in the packaging mold. First, epoxy resin is poured into the packaging mold. Then, the mold is placed in a vacuum chamber to evacuate the air inside the resin. After cooling and waiting for the epoxy resin to solidify, the device is removed from the mold, completing the device fabrication.

[0072] Example 3: A four-layer stacked photoconductive switch device with a gallium nitride semi-insulating substrate having a side length of 14 mm and a thickness of 0.35 mm, and a boron nitride substrate having a side length of 24 mm and a thickness of 0.35 mm was fabricated.

[0073] Step 1: Clean the gallium nitride semi-insulating substrate wafer and perform homogenization, as shown in 2a.

[0074] The specific implementation of this step is the same as step 1 in Example 1.

[0075] Step 2: Prepare a metal layer on the front side of the gallium nitride semi-insulating wafer after cleaning and homogenization, as shown in 2b.

[0076] 2.1) Using a mask with a pre-prepared circular electrode pattern of 8 mm diameter on the front side, the front side of a silicon carbide semi-insulating substrate wafer coated with photoresist is photolithographically etched and developed to form several circular electrode-shaped groove areas.

[0077] 2.2) Place the silicon carbide semi-insulating substrate wafer with the grooved region in the magnetron sputtering vacuum chamber, with the front side facing the target, at a vacuum level of 1×10⁻⁶. -5 In an argon atmosphere at 0.8 Pa, the temperature was set at 200 degrees Celsius, the magnetron sputtering pressure was 0.8 Pa, and the sputtering power was 5 W / cm². 2 Under the specified process conditions, Ni and Au targets were used sequentially to deposit metal layers with thicknesses of 300 nm and 3000 nm respectively, forming the front metal layer.

[0078] Step 3: Fabricate metal electrodes on the front side of the gallium nitride semi-insulating wafer, as shown in 2c.

[0079] The metal layer outside the groove area on the front side of the semi-insulating substrate wafer is completely removed by peeling off the blue film and using a stripper to form the Ni / Au front metal electrode.

[0080] Step 4: Clean the back side of the gallium nitride semi-insulating substrate, as shown in 2d.

[0081] The specific implementation of this step is the same as step 4 in Example 1.

[0082] Step 5: Prepare a metal layer on the back side of the gallium nitride wafer, as shown in 2e.

[0083] 5.1) Using a mask with a prepared circular electrode pattern of 8 mm diameter on the back side, photolithography and development are performed on the back side of a gallium nitride semi-insulating substrate wafer coated with photoresist to form several circular electrode-shaped groove areas.

[0084] 5.2) Place the gallium nitride semi-insulating substrate wafer with the grooved region in the magnetron sputtering vacuum chamber, with the back side facing the target, at a vacuum level of 1×10⁻⁶. -5 In an argon atmosphere at 200°C, with a magnetron sputtering pressure of 0.8 Pa and a sputtering power of 5 W / cm², the sputtering was performed at an argon atmosphere at 200°C. 2 Under the specified process conditions, Ni and Au metals with thicknesses of 300 nm and 3000 nm are deposited sequentially to form the back metal layer.

[0085] Step 6: Fabricate metal electrodes on the back side of the silicon carbide semi-insulating wafer, as shown in 2f.

[0086] The metal layer outside the groove area on the back of the semi-insulating substrate wafer is completely removed by peeling off the blue film and using a stripper to form the Ni / Au back metal electrode.

[0087] Step 7: Divide and cleave the gallium nitride wafer to prepare a single photoconductive switch, as shown in 2g.

[0088] Blue film is attached to both sides of a gallium nitride semi-insulating substrate wafer. The gallium nitride wafer is first diced and then split to prepare several individual gallium nitride semi-insulating substrates with a side length of 14 mm and a thickness of 0.35 mm. Each gallium nitride semi-insulating substrate has a metal electrode at the center of its upper and lower surfaces, forming a single photoconductive switch.

[0089] Step 8: Prepare through holes on the boron nitride sheet, as shown in step 2h.

[0090] Five cubic boron nitride sheets with a side length of 24 mm and a thickness of 0.35 mm were selected, and a through hole of the same size as the electrode was cut in the center of each boron nitride sheet using laser cutting technology.

[0091] Step 9: Prepare a boron nitride and gallium nitride substrate stack structure, as shown in 2i.

[0092] 9.1) Select five cylindrical connecting electrodes with a diameter of 8 mm and a height of 0.35 mm, and place them in the corresponding five boron nitride sheet through holes;

[0093] 9.2) Place boron nitride on the upper and lower surfaces of each gallium nitride semi-insulating substrate, and stack them in the following order from top to bottom: boron nitride sheet, semi-insulating substrate, boron nitride sheet, semi-insulating substrate, boron nitride sheet, semi-insulating substrate, boron nitride sheet, semi-insulating substrate, boron nitride sheet, boron nitride sheet, and so on, to form a four-layer stacked structure, and align the connecting electrodes with the metal electrodes on the semi-insulating substrate.

[0094] 9.3) Eutectic bonding is used to connect each connecting electrode in the stacked structure to the adjacent metal electrode.

[0095] Step 10: Weld external connecting electrodes onto the laminated structure, such as... Figure 2 As shown in j.

[0096] Two external connecting electrodes, each 20 mm long, 6 mm wide, and 0.05 mm thick, were selected. One electrode was soldered to the left half of the connecting electrode in the first boron nitride sheet through-hole of the stacked structure; the other electrode was soldered to the right half of the connecting electrode in the last boron nitride sheet through-hole of the stacked structure, thus completing the device fabrication.

[0097] Step eleven: Package the stacked structure to complete the device fabrication, such as... Figure 2 As shown in k.

[0098] The four-layer stacked structure with external connecting electrodes is placed in the packaging mold. First, epoxy resin is poured into the packaging mold. Then, the mold is placed in a vacuum chamber to evacuate the air in the resin. After cooling and waiting for the epoxy resin to solidify, the device is removed from the mold, completing the device fabrication.

[0099] Example 4: A photoconductive switch device with a two-layer stacked structure was fabricated, consisting of a gallium arsenide semi-insulating substrate with a side length of 10 mm and a thickness of 0.5 mm, and a boron nitride substrate with a side length of 20 mm and a thickness of 0.5 mm.

[0100] Step A: Clean the gallium arsenide semi-insulating substrate and perform homogenization, as shown in 2a.

[0101] The specific implementation of this step is the same as step 1 in Example 1.

[0102] Step B: Prepare a metal layer on the front side of the gallium arsenide wafer, as shown in 2b.

[0103] B1 uses a mask with a pre-prepared circular electrode pattern of 7mm diameter on the front side to perform photolithography and development on the front side of a gallium arsenide semi-insulating substrate wafer coated with photoresist, forming several circular electrode-shaped groove areas.

[0104] B2 places a gallium arsenide semi-insulating substrate wafer with grooved regions into a magnetron sputtering vacuum chamber, with the front side facing the target, at a vacuum level of 1×10⁻⁶. -5 In an argon atmosphere at 200°C, the magnetron sputtering pressure was set to 1.2 Pa, and the sputtering power to 5 W / cm². 2 Under the specified process conditions, Ni, Ti, and Au targets were used sequentially to deposit metal layers with thicknesses of 300nm / 500nm / 3000nm, respectively, to form the front metal layer.

[0105] Step C: Fabricate a metal electrode on the front side of the gallium arsenide semi-insulating wafer, as shown in 2c.

[0106] The metal layer outside the front electrode area of ​​the gallium arsenide semi-insulating substrate wafer is completely removed by peeling off the blue film and using a stripping machine to form the Ni / Ti / Au front metal electrode.

[0107] Step D involves cleaning the back side of the gallium arsenide semi-insulating wafer, as shown in 2d.

[0108] The specific implementation of this step is the same as step 4 in Example 1.

[0109] Step E: Prepare a metal layer on the back side of the gallium arsenide wafer, as shown in 2e.

[0110] E1) Using a mask with a prepared circular electrode pattern on the back side of a gallium arsenide semi-insulating substrate wafer coated with photoresist, photolithography and development are performed to form several circular electrode-shaped groove areas.

[0111] E2) A gallium arsenide semi-insulating substrate wafer with grooved regions is placed in a magnetron sputtering vacuum chamber with its back side facing the target. The sputtering is performed at a vacuum level of 1×10⁻⁶. -5 The argon atmosphere was maintained at 200°C, the magnetron sputtering pressure was 1.2 Pa, and the sputtering power was 5 W / cm². 2 Under the specified process conditions, Ni, Ti, and Au targets are used sequentially to deposit metal layers with thicknesses of 300nm / 500nm / 3000nm respectively, forming the back metal layer.

[0112] Step F: Prepare a metal electrode on the back side of the gallium arsenide wafer, as shown in 2f.

[0113] The metal layer outside the back electrode area of ​​the gallium arsenide semi-insulating substrate wafer is completely removed by peeling off the blue film and using a stripping machine to form the Ni / Ti / Au back metal electrode.

[0114] Step G involves dicing and splitting gallium arsenide wafers to fabricate individual photoconductive switches, as shown in 2g.

[0115] A blue film is attached to both sides of a gallium arsenide semi-insulating substrate wafer. The gallium arsenide wafer is first diced and then split to prepare several individual gallium arsenide semi-insulating substrates with a side length of 10 mm and a thickness of 0.5 mm. Each gallium arsenide semi-insulating substrate has a metal electrode at the center of its upper and lower surfaces, forming a single photoconductive switch.

[0116] Step H: Prepare through holes on the boron nitride sheet, as shown in step 2h.

[0117] Three cubic boron nitride sheets with a side length of 20 mm and a thickness of 0.5 mm were selected, and a through hole of the same size as the electrode was cut in the center of each boron nitride sheet using laser cutting technology.

[0118] Step I: Prepare a boron nitride and gallium arsenide semi-insulating substrate stack structure, as shown in 2i.

[0119] I1) Select three cylindrical connecting electrodes with a diameter of 7 mm and a height of 0.5 mm, and place them in the corresponding three boron nitride sheet through holes;

[0120] I2) Place boron nitride on the upper and lower surfaces of each gallium arsenide semi-insulating substrate, and then arrange and stack them in the order of boron nitride sheet, gallium arsenide semi-insulating substrate, boron nitride sheet, gallium arsenide semi-insulating substrate, and boron nitride sheet from top to bottom to form a two-layer stacked structure. Align the connecting electrode with the metal electrode of the photoconductive switch.

[0121] I3) Eutectic bonding is used to connect each connecting electrode in the stacked structure to the adjacent metal electrode.

[0122] Step J: Weld external connecting electrodes onto the laminated structure, such as... Figure 2 As shown in k.

[0123] Two external connecting electrodes with a length of 15 mm, a width of 6 mm, and a thickness of 0.05 mm are selected. One of them is welded to the left half of the electrode in the first boron nitride sheet through hole in the stacked structure; the other is welded to the right half of the electrode in the last boron nitride sheet through hole in the stacked structure.

[0124] Step K involves encapsulating the stacked structure to complete the device fabrication, such as... Figure 2 As shown in k.

[0125] The two-layer stacked structure with external connecting electrodes is placed in the packaging mold. First, epoxy resin is poured into the packaging mold. Then, the mold is placed in a vacuum chamber to evacuate the air in the resin. After cooling and waiting for the epoxy resin to solidify, the device is removed from the mold, and the device fabrication is completed.

[0126] Example 5: Packaging mold structure for multi-layer high-voltage, high-thermal-conductivity, and photoconductive switching devices

[0127] Reference Figure 3 This example is a mold for encapsulating multi-layered high-voltage, high-thermal-conductivity, and photoconductive switching devices. It is made of Teflon material and includes several deep grooves I, several shallow grooves II, and a metal electrode groove III, wherein:

[0128] The aforementioned deep grooves I are identical in shape and size. The depth of each groove is set to 0.75 to 1 times the side length of the boron nitride sheet, and the length and width are consistent with the side length and thickness of the boron nitride sheet, respectively.

[0129] The aforementioned shallow grooves II are identical in shape and size. The depth of each groove is set to 1.4 to 2 times the side length of the semi-insulating substrate, the length is 1.2 to 1.8 times the side length of the semi-insulating substrate, and the width is consistent with the thickness of the semi-insulating substrate. The shallow grooves are located on the upper and lower sides of each deep groove, arranged in the order of shallow groove, deep groove, shallow groove, deep groove, ..., shallow groove, forming a stacked structure.

[0130] The external connection electrode groove Ⅲ is located in the middle of the bottom of the top shallow groove in the stacked structure. Its length and width are consistent with the width and thickness of the external connection electrode, respectively, and its depth is greater than the length of the external connection electrode.

[0131] The deep groove I, shallow groove II, and metal electrode groove III of the packaging mold can all be adjusted according to the actual size of the stacked structure to be packaged.

[0132] The above descriptions are merely a few specific examples of the present invention and do not constitute any limitation on the present invention. Obviously, those skilled in the art, after understanding the content and principles of the present invention, may make various modifications and changes in form and details without departing from the principles and structure of the present invention. However, these modifications and changes based on the ideas of the present invention are still within the scope of protection of the claims of the present invention.

Claims

1. A method for fabricating a multi-layered high-voltage, high-thermal-conductivity, photoconductive switching device, characterized in that, Includes the following steps: S1) Clean the semi-insulating substrate wafer and uniformly apply photoresist to its front side; S2) Photolithography and development are performed on the front side of a semi-insulating substrate wafer coated with photoresist using a mask to form several metal electrode-shaped groove areas, and then a metal layer is formed by magnetron sputtering on the front side of the semi-insulating substrate wafer. S3) Remove all metal outside the front electrode area of ​​the semi-insulating substrate wafer to form the front metal electrode; S4) Clean the back side of the semi-insulating substrate wafer with the front metal electrode again, and apply photoresist evenly to the cleaned back side. S5) Photolithography and development are performed on the back side of a semi-insulating substrate wafer coated with photoresist using a mask to form several grooves in the shape of metal electrodes, and then a back metal layer is formed by magnetron sputtering on the back side of the semi-insulating substrate. S6) Remove all metal outside the metal electrode area on the back side of the semi-insulating substrate wafer to form the back metal electrode; S7) The semi-insulating substrate wafer is attached to the blue film and then diced and split to prepare several individual photoconductive switches, and each photoconductive switch has a metal electrode on its upper and lower surfaces. S8) Select several cubic boron nitride sheets and use laser cutting or plasma cutting to cut a through hole of the same size as the electrode in the center of each boron nitride sheet; S9) Select several connecting electrodes, first place them in the corresponding boron nitride sheet through holes, and then arrange and stack them in the order of boron nitride sheet, photoconductive switch, boron nitride sheet, photoconductive switch, and boron nitride sheet from top to bottom to form a stacked structure. Align the connecting electrodes with the metal electrodes of the photoconductive switch, and then use eutectic bonding to connect each connecting electrode in the stacked structure to the adjacent metal electrode. S10) Two external connecting electrodes are selected and connected to the connecting electrode in the first boron nitride sheet through hole and the connecting electrode in the last boron nitride sheet through hole in the stacked structure, respectively. S11) Using a packaging mold, the prepared stacked structure is encapsulated with potting compound to completely cover several photoconductive switches, and the edges of each boron nitride sheet are exposed outside the packaging material, thus completing the device fabrication.

2. The method according to claim 1, characterized in that, The cleaning of the semi-insulating substrate wafer involves sequentially immersing the semi-insulating substrate wafer in BOE solution, deionized water, acetone, isopropanol, and deionized water for ultrasonic cleaning for 120s, 180s, 600s, 180s, and 180s, respectively.

3. The method according to claim 1, characterized in that, The aforementioned magnetron sputtering of the semi-insulating substrate involves placing the semi-insulating substrate wafer in a vacuum filled with argon gas, with a vacuum level better than 5× In an environment with a pressure of 0.5 Pa to 1.5 Pa, the magnetron sputtering gas pressure is set at 5 W / m². The Ni / Ti / Pt / Au target materials were sputtered sequentially.

4. A device fabricated according to the method of claim 1, comprising a plurality of semi-insulating substrates (1), metal electrodes (2), connecting electrodes (3), and external connecting electrodes (4), wherein the metal electrodes (2) are distributed at the center of the upper and lower surfaces of each semi-insulating substrate (1), and the connecting electrodes (3) are respectively connected to the metal electrodes (2) and the external connecting electrodes (4), characterized in that: A boron nitride sheet (5) is disposed between each pair of adjacent semi-insulating substrates, forming a multi-layer structure; Each boron nitride sheet (5) has a through hole at its center that is the same shape and size as the connecting electrode (3). The connecting electrode passes through the through hole of the boron nitride sheet and connects to the metal electrodes (2) on two adjacent semi-insulating substrates.

5. The device according to claim 4, characterized in that, The boron nitride sheet (5) is a cube with a thickness of 0.5 mm to 1 mm and a side length of 18 mm to 24 mm.

6. The device according to claim 4, characterized in that, Each of the semi-insulating substrates (1) is a cube with a side length of 6mm to 14mm and a thickness of 0.35mm to 1mm, and its material is one of silicon carbide, gallium nitride, gallium arsenide, gallium oxide, and diamond.

7. The device according to claim 4, characterized in that, The metal electrode (2) is in ohmic contact with the semi-insulating substrate, and the material is one of Ni / Ti / Pt / Au composite metal layer, Ti / Pt / Au composite metal layer, W / Ti / Au composite metal layer, Ni / Ti / Au composite metal layer or Ni / Au composite metal layer.

8. The device according to claim 4, characterized in that, The shape and size of the connecting electrode (3) are the same as those of the metal electrode, and the thickness is the same as that of the boron nitride sheet. The material is copper metal.

9. The device according to claim 4, characterized in that, The external connecting electrode (4) is made of copper, and its length is greater than half the side length of the boron nitride sheet (5), its width is 2mm to 6mm, and its thickness is 0.05mm to 0.1mm.

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