Mg-doped gallium oxide photoconductive modulated microwave device and method of manufacturing the same

Abstract

The application discloses a kind of Mg-doped and hole-conducting unipolar gallium oxide photoconductive modulation microwave devices, mainly solve the problem of low voltage resistance, small output power, low output signal frequency in prior art.The device includes a semi-insulating substrate (1), a pair of ohmic electrodes (3), a pair of electrode thickening layers (4) and a trigger source (6), the semi-insulating substrate uses Mg-doped gallium oxide single crystal substrate, and two symmetrical grooves (2) are opened in the upper part, the pair of ohmic electrodes and the electrode thickening layer are located inside each groove from bottom to top;The region between the two grooves is provided with a high resistance layer (5) formed by high temperature annealing in an oxygen atmosphere.The application can only excite hole carriers to participate in conduction under the irradiation of the trigger source, improve the working time of the device under high voltage, and increase the dark state resistance and reduce the on-state resistance of the device through the high resistance layer, improve the voltage resistance of the device, increase the output frequency, and can be used to generate high-frequency and tunable microwave output signals.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of solid-state high-power microwave technology, and particularly relates to a Mg-doped gallium oxide photoconductive modulation microwave device, which can be used to generate high-frequency and tunable microwave output signals. BACKGROUND

[0002] With the advent of the new generation of 5G communication and the information age of equipment, higher requirements are put forward for high-power microwave technology. High-power microwave technology plays an important role in many fields because it can generate large current, high voltage and fast response speed. The main content of high-power microwave technology research usually includes three aspects of energy storage, pulse formation and switching technology. Among them, the switch is the core device of the high-power microwave system, which connects the power supply system, energy storage system and load system into an organic whole and realizes energy conversion. The photoconductive switch has become the international frontier and hotspot of current research because of its simple structure, small size, high voltage resistance, fast response speed and low jitter.

[0003] The photoconductive switch device is a new type of device that controls the conductivity of the material by using a fast laser pulse to generate a large number of photo-generated carriers in the semiconductor device body, thereby realizing the turn-on and turn-off of the device. Compared with traditional spark gap switches, turn-off thyristors and metal oxide semiconductor field effect transistors, the photoconductive switch has the advantages of fast closing time, small jitter time, high repetition frequency, and is not affected by electromagnetic interference, and is small in size. It can balance power capacity and repetition frequency. The semiconductor materials based on photoconductive switches usually have the first generation of semiconductors Si, the second generation of semiconductors GaAs, wide bandgap and super wide bandgap semiconductor materials, which are the basis for the rapid development of microwave devices in high performance and miniaturization in recent years, thereby becoming ideal materials for preparing photoconductive switches. The gallium oxide material has a higher bandgap, critical breakdown field strength and Johnson's value than other wide bandgap materials, making it a popular material in the field of high-frequency and high-power devices.

[0004] The patent document with the application number CN202110414332.4 discloses a gallium oxide-based high-power light-controlled microwave device, as shown in Figure 1 The structure of the device is to deposit metal cathodes and anodes on both sides of the gallium oxide single crystal substrate, and to realize microwave output by using a light-controlled gallium oxide photoconductive switch to improve the on-off ratio of the device photocurrent and dark current. Although the device power can reach the megawatt level and realize high-power light-controlled microwave output, the device is prone to alignment errors that affect device performance due to the use of a vertical structure to prepare the electrodes, and the preparation process is complex. Due to the characteristics of the vertical structure, it is difficult to produce high-frequency microwave signal output.

[0005] A Mg-doped gallium oxide photoconductive modulation microwave device and a preparation method thereof are provided to improve the high-voltage time of a photoconductive switch, and the device structure is simplified to facilitate the output of a high-frequency adjustable signal and the compact and integrated preparation. SUMMARY

[0006] The Mg-doped gallium oxide photoconductive modulation microwave device and the preparation method thereof are provided to improve the high-voltage time of a photoconductive switch, and the device structure is simplified to facilitate the output of a high-frequency adjustable signal and the compact and integrated preparation.

[0007] The technical idea for achieving the purpose of the present application is that a photoconductive switch device is prepared on a Mg-doped gallium oxide single crystal substrate through a planar groove electrode structure and combined with an oxygen annealing process. The device only excites holes to participate in conduction under illumination to generate a high-frequency microwave output signal. The Mg-doped gallium oxide material used in the device reduces the oxygen vacancy content on the surface of the device after oxygen annealing, increases the dark state resistance, improves the voltage resistance of the device, reduces the on-state resistance, increases the photocurrent, and thus improves the output power of the device.

[0008] According to the above idea, the technical scheme of the present application includes the following:

[0009] 1. A Mg-doped gallium oxide photoconductive modulation microwave device, comprising a semi-insulating substrate, a pair of ohmic electrodes, a pair of electrode thickening layers, and a trigger source, characterized in that:

[0010] The semi-insulating substrate is a Mg-doped gallium oxide single crystal substrate, so that only hole carriers are excited to participate in conduction under illumination of the trigger source; two symmetrical grooves are formed in the upper part of the substrate;

[0011] The pair of ohmic electrodes and the pair of electrode thickening layers are located inside each groove from bottom to top;

[0012] The region between the two grooves is provided with a high resistance layer to increase the dark state resistance and reduce the on-state resistance of the device;

[0013] As a preferred, the depth of each groove is less than the sum of each ohmic electrode and each electrode thickening layer to improve the photocurrent.

[0014] As a preferred, the pair of ohmic electrodes adopts a double-layer structure of titanium with a thickness of 15nm-25nm and gold with a thickness of 225nm-235nm.

[0015] As a preferred, the pair of electrode thickening layers adopts a double-layer structure of titanium with a thickness of 15nm-25nm and gold with a thickness of 395nm-405nm.

[0016] As a preferred, the length of each groove is 3mm-5mm, the width is 1mm-3mm, and the depth is 355nm-365nm, and the distance between the two grooves is 0.5mm-1.5mm.

[0017] As a preferred, the high resistance layer is formed by annealing in an oxygen atmosphere, and has a length of 3mm-5mm and a width of 0.5mm-1.5mm.

[0018] As a preferred, the trigger source adopts a laser source with a wavelength of 500nm-564nm.

[0019] 2. A method for manufacturing a Mg-doped gallium oxide photoconductive modulation microwave device, comprising the following steps:

[0020] S1: cleaning the semi-insulating substrate;

[0021] S2: spin coating photoresist on the front surface of the cleaned semi-insulating substrate;

[0022] S3: exposing and developing the semi-insulating substrate with spin-coated photoresist by a photoetch machine loaded with a photoetch plate to form two rectangular groove regions;

[0023] S4: etching and cleaning the groove on the front surface of the semi-insulating substrate by an etching machine;

[0024] S5: spin coating photoresist on the front surface of the etched semi-insulating substrate;

[0025] S6: aligning, exposing and developing the semi-insulating substrate with spin-coated photoresist by a photoetch machine loaded with a photoetch plate to form two rectangular ohmic electrode regions;

[0026] S7: Oxygen plasma treatment is carried out on the front surface of the semi-insulating substrate, titanium and gold are sputtered through a sputtering station, and then stripping and cleaning are carried out, and annealing is carried out in a nitrogen atmosphere to form an ohmic electrode;

[0027] S8: Photoresist is spin-coated on the front surface of the semi-insulating substrate after annealing;

[0028] S9: The semi-insulating substrate spin-coated with photoresist is aligned, exposed and developed through a photoetching machine loaded with a photoetching plate to form two rectangular electrode thickening layer regions;

[0029] S10: Oxygen plasma treatment is carried out on the front surface of the semi-insulating substrate, titanium and gold are sputtered through a sputtering station, and then stripping and cleaning are carried out to form an electrode thickening layer;

[0030] S11: Annealing is carried out in an oxygen atmosphere to form a high-resistance layer, and device preparation is completed.

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

[0032] Firstly, the present application uses Mg-doped gallium oxide single crystal substrate, which can only excite one kind of hole carrier to participate in conduction under the irradiation of a trigger source, thereby realizing unipolar conduction to improve the withstand voltage performance, providing a new idea for solving the current difficulty in P-type doping of gallium oxide system; and gallium oxide is a direct bandgap material with higher quantum efficiency, and is easier to grow than other materials, and is easier to dope when a single crystal substrate is prepared by a pulling method, and the doping concentration meeting the design requirements is easier to control, and the preparation cost is low.

[0033] Secondly, the present application has two symmetrical planar grooves on the upper side of the substrate, which can not only continuously adjust the output signal of the P to L band, but also can reach more than 75% in the S band, realizing higher frequency tuning.

[0034] Thirdly, the present application deposits ohmic electrodes and electrode thickening layers from bottom to top in the grooves, and the depth of each groove is less than the sum of the ohmic electrodes and the electrode thickening layers, so that the area during conduction is increased, and the photocurrent is improved.

[0035] Fourthly, the present application reduces the oxygen vacancy content by annealing in an oxygen atmosphere, so that a high-resistance layer is formed in the region between the two grooves, the dark state resistance is increased, the withstand voltage level is improved, more carriers can be excited to participate in conduction under light, thereby increasing the light absorption efficiency and improving the photocurrent. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 is a structure diagram of the Mg-doped gallium oxide photoconductive modulation microwave device of the present application;

[0037] Figure 2is the Mg-doped gallium oxide energy level diagram in the device of the present application;

[0038] Figure 3 is the representation diagram of the surface oxygen vacancy content before and after forming the high resistance layer in the device of the present application;

[0039] Figure 4 is the implementation flow diagram for preparing the device of the present application. DETAILED DESCRIPTION

[0040] The present application is further described in detail below in conjunction with the accompanying drawings and examples.

[0041] Referring to Figure 1 The Mg-doped gallium oxide photoconductive modulation microwave device of the present application comprises a semi-insulating substrate 1, two grooves 2, two ohmic electrodes 3, two electrode thickening layers 4, a high resistance layer 5 and a trigger source 6, wherein:

[0042] The semi-insulating substrate 1 adopts a Mg-doped gallium oxide single crystal substrate; its shape is a square with a side length of 9mm-11mm and a thickness of 500μm-540μm, which is used to excite only hole carriers to participate in conduction under the irradiation of the trigger source 6, so as to realize unipolar conduction to improve the withstand voltage performance, and provide a new idea to solve the current problem of difficult P-type doping of gallium oxide system; and the gallium oxide has higher quantum efficiency as a direct band gap material, and is easier to grow single crystal substrate by doping when prepared by the pulling method, and the doping concentration meeting the design requirements is easier to control, and the preparation cost is low.

[0043] The two grooves 2 are located on the upper part of the semi-insulating substrate 1 and are parallel to each other, each groove has a length of 3mm-5mm, a width of 1mm-3mm and a depth of 355nm-365nm, and the distance between the two grooves is 0.5mm-1.5mm, the two grooves not only can continuously adjust the output signal of P to L band, but also can reach more than 75% modulation degree in S band, realizing higher frequency tuning and improving the output frequency of the device.

[0044] The two ohmic electrodes 3 are respectively located at the lower part of each groove 2, and the lower surface is tightly combined with the bottom of the groove, the length is 3mm-5mm, the width is 1mm-3mm, and the material is a composite metal layer composed of titanium and gold, wherein the thickness of titanium is 15nm-25nm, and the thickness of gold is 225nm-235nm, which is used to reduce the potential barrier between the metal electrode and the semi-insulating material.

[0045] The two electrode thickening layers 4 are located in the upper part of each groove 2, and the lower surface thereof is combined with the upper surface of the ohmic electrode 3, the length thereof is 3mm-5mm, the width thereof is 1mm-3mm, and the material thereof is a composite metal layer composed of titanium and gold, wherein the thickness of titanium is 15nm-25nm, and the thickness of gold is 395nm-405nm, which is used for connecting each ohmic electrode with external circuit.

[0046] The high resistance layer 5 is located in the middle area of the two grooves 2, and is formed by reducing the oxygen vacancy content after annealing in oxygen atmosphere; the pure gallium oxide single crystal substrate is weak n-type due to background impurities and oxygen vacancy defects, the doped Mg element can be used as an acceptor to compensate for a small amount of background impurities and oxygen vacancy defects to form semi-insulation, and the oxygen vacancy defects can be filled by oxygen annealing to reduce the oxygen vacancy defect content, which reduces the reason for the gallium oxide single crystal substrate to form weak n-type, thereby increasing the insulation of the single crystal substrate, increasing the dark state resistance, and reducing the number of Mg impurity elements compensating for oxygen vacancy defects due to the reduction of oxygen vacancy defect content in the high resistance layer, which can generate more hole carriers to participate in conduction under the irradiation of the trigger source 6, thereby increasing the light absorption efficiency and improving the photocurrent; the length thereof is 3mm-5mm, the width thereof is 0.5mm-1.5mm, which is used for increasing the dark state resistance of the device, improving the withstand voltage level, and exciting more carriers to participate in conduction under light, thereby increasing the light absorption efficiency and improving the photocurrent.

[0047] The trigger source 6 is a laser source irradiated on the high resistance layer 5, the wavelength thereof is 500nm-564nm, and the repetition frequency thereof is 1GHz-8GHz, which is used for exciting the holes on the Mg energy level in the semi-insulating substrate 1 to the valence band to form carriers, so as to participate in conduction under the action of an external electric field.

[0048] Referring to Figure 4 , the present application provides three embodiments of Mg-doped gallium oxide photoconductive modulation microwave devices.

[0049] Embodiment 1: A Mg-doped gallium oxide single crystal substrate with a square edge length of 10mm and a thickness of 520μm is used to make a photoconductive modulation microwave device.

[0050] Step 1: Select a Mg-doped gallium oxide single crystal substrate, such as Figure 4 (a).

[0051] Referring to Figure 2Gallium oxide crystals contain some background impurities and oxygen vacancy defects. Si, as a shallow donor impurity, has an energy level located 30 meV below the conduction band bottom and can be excited to the conduction band bottom at room temperature. Ir, as a deep donor impurity, has an energy level located 2.3 eV below the conduction band bottom. Oxygen vacancy defects, as deep donor impurities, have energy levels located 1.3 eV to 2.7 eV below the conduction band bottom. The doped Mg, as an acceptor impurity, has an energy level located 1.2 eV above the valence band top. The band gap of gallium oxide material is 4.9 eV, and it exhibits a weak n-type structure due to the presence of background impurities and oxygen vacancy defects. In the dark state, the doped Mg impurity compensates for the background impurities and oxygen vacancy defects, forming a semi-insulator. Since the Mg energy level is 3.7 eV away from the conduction band bottom, a 532 nm laser is insufficient to excite electrons at this energy level to reach the conduction band, but it can excite holes at this energy level to reach the valence band, forming a unipolar device with only holes conducting electricity. Therefore, this step selects a Mg-doped gallium oxide single crystal substrate 1.

[0052] Step 2: Clean the Mg-doped gallium oxide semi-insulating substrate.

[0053] The Mg-doped gallium oxide semi-insulating substrate 1 was first placed in acetone and sonicated for 5 minutes; then placed in isopropanol and sonicated for 5 minutes; then rinsed in deionized water for 5 minutes.

[0054] Finally, the cleaned substrate was dried using nitrogen gas.

[0055] Step 3: Perform the first spin coating of photoresist on the front side of the cleaned substrate.

[0056] The substrate was baked using a temperature-controlled heating stage at 200°C for 5 minutes.

[0057] Select AZ6130 photoresist, fix the substrate on the coating stage, drop the photoresist onto the substrate, and spin coat at 4000r for 30 seconds;

[0058] A temperature-controlled heating stage was used to pre-bake the substrate with photoresist rotating at 100°C for 2 minutes to fix the photoresist onto the substrate.

[0059] Step 4: The photoresist fixed on the substrate undergoes its first exposure and development, such as... Figure 4 (b)

[0060] The substrate with the photoresist fixed was exposed for the first time for 12 seconds using a photolithography machine with a photomask.

[0061] The exposed substrate was immersed in developing solution for 80 seconds.

[0062] Rinse the developed substrate with deionized water for 3 minutes and then dry it with nitrogen.

[0063] The substrate after drying is hardened by a temperature-controlled heating table to remove water on the substrate, the temperature of the heating table is 100℃, and the hardening time is 1 minute.

[0064] Step 5, the substrate after removing water is etched in a groove, such as Figure 4 (c).

[0065] The substrate after removing water is etched in a groove 2 in a plasma etching machine, the gas atmosphere is a mixed gas of boron chloride, chlorine and argon, and the etching time is 15 minutes.

[0066] Step 6, the substrate after groove etching is cleaned.

[0067] The substrate after etching groove 2 is first placed in acetone for ultrasonic for 5 minutes; then soaked in stripping liquid heated to 60℃ for 15 minutes; then ultrasonic in acetone for 5 minutes; then ultrasonic in isopropyl alcohol for 5 minutes; then rinsed in deionized water for 3 minutes and then dried by nitrogen.

[0068] Step 7, the front surface of the substrate after cleaning and drying is spin-coated with photoresist for the second time.

[0069] The substrate after cleaning and drying is baked by a temperature-controlled heating table, the temperature is 200℃, and the time is 5 minutes;

[0070] The type of photoresist selected is SF6, the baked substrate is fixed on the coating table, and the photoresist is dropped on the substrate, and spin-coated at a speed of 2000r for 30 seconds;

[0071] The substrate after spin-coating SF6 photoresist is pre-baked by a temperature-controlled heating table, the temperature is 200℃, and the time is 5 minutes;

[0072] The type of photoresist selected is EPI621, the pre-baked substrate is fixed on the coating table, and the photoresist is dropped on the pre-baked substrate, and spin-coated at a speed of 5000r for 30 seconds;

[0073] The substrate after spin-coating EPI621 photoresist is pre-baked by a temperature-controlled heating table to fix the photoresist on the substrate, the temperature is 90℃, and the time is 1 minute.

[0074] Step 8, the photoresist fixed on the substrate is exposed and developed for the second time, such as Figure 4 (d).

[0075] The substrate with fixed photoresist is exposed for the second time by a photoetching machine loaded with a photoetching plate, and the exposure time is 19 seconds;

[0076] The substrate after exposure is post-baked by a temperature-controlled heating table, the temperature is 110℃, and the time is 1 minute;

[0077] The baked substrate is soaked in the developer for 50 seconds.

[0078] The developed substrate is rinsed in deionized water for 3 minutes and dried with nitrogen.

[0079] The dried substrate is subjected to ohmic electrode deposition.

[0080] The surface of the dried substrate is bombarded in an oxygen plasma for 5 minutes.

[0081] The substrate after oxygen plasma treatment is subjected to titanium metal deposition using a magnetron sputtering table, with a power of 75 W, a gas flow of 1.5 mTorr, a time of 400 seconds, and a thickness of 20 nm.

[0082] The titanium metal is subjected to gold metal deposition using a magnetron sputtering table, with a power of 25 W, a gas flow of 3 mTorr, a time of 2300 seconds, and a thickness of 230 nm, forming an ohmic electrode 3 composite layer composed of titanium and gold.

[0083] Step 10, the substrate after deposition of the ohmic electrode composite layer is subjected to the first stripping, such as Figure 4 (e).

[0084] The substrate after deposition of the ohmic electrode 3 composite layer is first soaked in acetone for 10 hours.

[0085] Then ultrasonic in acetone for 5 minutes, and use a plastic straw to blow for 5 minutes.

[0086] Then heated to 60℃ in the stripping solution, soaked for 30 minutes.

[0087] Then ultrasonic in acetone, isopropyl alcohol for 5 minutes respectively.

[0088] Then use deionized water to rinse for 5 minutes and dry with nitrogen.

[0089] Step 11, the dried substrate is subjected to ohmic annealing.

[0090] The dried substrate is subjected to high-temperature rapid annealing in a nitrogen atmosphere, with a temperature of 470℃ and an annealing time of 1 minute.

[0091] Step 12, the front surface of the annealed substrate is spin-coated with photoresist for the third time.

[0092] The annealed substrate is baked using a temperature-controlled heating table, with a temperature of 200℃ and a time of 5 minutes.

[0093] The annealed substrate is fixed on the coating table, and the photoresist is dropped onto the annealed substrate, and spin-coated at a speed of 2000r for 30 seconds.

[0094] The substrate after spin-coating SF6 photoresist is pre-baked on a temperature-controlled heating table at 200°C for 5 minutes.

[0095] The pre-baked substrate is fixed on a coating table, and the photoresist is dropped on the pre-baked substrate at a rotation speed of 5000r for 30 seconds.

[0096] The substrate after spin-coating EPI621 photoresist is pre-baked on a temperature-controlled heating table at 90°C for 1 minute to fix the photoresist on the substrate.

[0097] Step 13: The photoresist fixed on the substrate is exposed and developed for the third time, as Figure 4 (f).

[0098] The substrate after the third exposure is post-baked on a temperature-controlled heating table at 110°C for 1 minute.

[0099] The substrate after the third exposure is post-baked on a temperature-controlled heating table at 110°C for 1 minute.

[0100] The post-baked substrate is soaked and developed in a developing solution for 50 seconds.

[0101] The developed substrate is rinsed with deionized water for 3 minutes and dried with nitrogen.

[0102] Step 14: The dried substrate is subjected to electrode thickening layer deposition.

[0103] The surface of the dried substrate is bombarded in an oxygen plasma for 5 minutes.

[0104] Metallic titanium is deposited on the substrate after oxygen plasma treatment using a magnetron sputtering table at a power of 75W, a gas flow of 1.5mTorr, a time of 400 seconds, and a thickness of 20nm.

[0105] Metallic gold is deposited on the metallic titanium using a magnetron sputtering table at a power of 25W, a gas flow of 3mTorr, a time of 4000 seconds, and a thickness of 400nm, forming an electrode thickening 4 composite layer composed of titanium and gold.

[0106] Step 15: The substrate after deposition of the electrode thickening composite layer is subjected to the second stripping, as Figure 4 (g).

[0107] The substrate after deposition of the ohmic electrode 4 composite layer is first soaked in acetone for 10 hours.

[0108] Then it is ultrasonically treated in acetone for 5 minutes and blown with a plastic straw for 5 minutes.

[0109] Then heated to 60℃ in the stripping solution and soaked for 30 minutes;

[0110] Then sequentially ultrasonic in acetone, isopropanol for 5 minutes each;

[0111] Then rinsed with deionized water for 5 minutes and dried with nitrogen.

[0112] Step 16, the dried substrate is oxygen annealed to form a high resistance layer, such as Figure 4 (h).

[0113] The principle of forming the high resistance layer 5 by oxygen annealing is as follows:

[0114] The pure gallium oxide single crystal substrate is weak n-type due to background impurities and oxygen vacancy defects, and the oxygen vacancy defects are filled by oxygen annealing, which reduces the content of oxygen vacancy defects, reduces the reasons for the formation of weak n-type in gallium oxide single crystal substrate, improves the insulation of the single crystal substrate, increases the dark state resistance, and thus forms the high resistance layer 5.

[0115] In this example, the dried substrate is annealed in an oxygen atmosphere at a temperature of 470℃ for 30 minutes to form a high resistance layer 5, and the device is completed.

[0116] The high resistance layer 5 region in the middle of the two grooves 2 before and after oxygen annealing is characterized by X-ray photoelectron spectrometer, and the results are as follows Figure 3 . Among them Figure 3 (a) is the O1s fine spectrum obtained by X-ray photoelectron spectrometer and the peak fitting results after C1s calibration, Figure 3 (b) is the quantitative representation of the oxygen vacancy content after peak fitting.

[0117] From Figure 3 (a), it can be seen that the O1s fine spectrum of gallium oxide can be measured by X-ray photoelectron spectrometer, which is peak fitted after C1s calibration. The O1s fine spectrum can be decomposed into three different peaks: peak OI is derived from Ga-O bond, peak OII is attributed to oxygen deficiency region, and peak OIII corresponds to the presence of chemisorbed hydroxyl and carbonate substances. Among them, peak OII is caused by the existence of oxygen defects in gallium oxide, and the area ratio of peak OII to peak (OI+OII) can be used to qualitatively evaluate the relative proportion of oxygen vacancy in gallium oxide.

[0118] From Figure 3 (b), it can be seen that the oxygen vacancy content is reduced from 37.8% before oxygen annealing to 9.2%, which shows that the photoconductive switch prepared by Mg-doped gallium oxide single crystal substrate is annealed in an oxygen atmosphere. The oxygen vacancy content in the middle region of the two electrodes is less, which reduces the reasons for the formation of weak n-type in gallium oxide single crystal substrate, improves the insulation of the single crystal substrate, increases the dark state resistance, and thus forms the high resistance layer 5.

[0119] Example 2: A Mg-doped gallium oxide single crystal substrate with a square shape of 9 mm in side length and 500 μm in thickness is prepared; each groove has a length of 3 mm, a width of 1 mm, and a depth of 355 nm; each ohmic electrode has a length of 3 mm and a width of 1 mm; each electrode thickening layer has a length of 3 mm and a width of 1 mm; and each high resistance layer has a length of 3 mm and a width of 0.5 mm. The light guide modulated microwave device is prepared.

[0120] Step 1. A Mg-doped gallium oxide single crystal substrate is selected and cleaned, for example, as follows: Figure 4 (a).

[0121] This step is implemented in the same manner as steps 1 and 2 of Example 1.

[0122] Step 2. The front surface of the cleaned substrate is spin-coated with photoresist for the first time.

[0123] The front surface of the cleaned substrate is placed on a temperature-controlled hot plate, which is set to a temperature of 180°C, and baked for 6 minutes.

[0124] The AZ4620 photoresist is dropped onto the photoresist-coated table with the substrate loaded thereon, and spin-coated at a speed of 3000 r for 40 seconds.

[0125] The substrate with the spin-coated AZ4620 photoresist is placed on a temperature-controlled hot plate, which is set to a temperature of 140°C, and pre-baked for 1 minute to fix the first spin-coated photoresist on the substrate.

[0126] Step 3. After the first spin-coated photoresist is fixed on the substrate, the substrate is exposed to light and developed, for example, as follows: Figure 4 (b).

[0127] The substrate with the fixed first photoresist is placed on a photoetching machine with an etching plate loaded thereon, and exposed to light for 19 seconds. The exposed substrate is then immersed in a developing solution for 60 seconds.

[0128] The developed substrate is then placed in deionized water for 4 minutes and dried with nitrogen.

[0129] The dried substrate is placed on a temperature-controlled hot plate, which is set to a temperature of 90°C, and baked for 2 minutes to remove water from the substrate.

[0130] Step 4. The baked substrate is etched to form grooves, for example, as follows: Figure 4 (c).

[0131] The baked substrate is placed in a plasma etching machine, and etched to form grooves for 14 minutes in a mixed gas atmosphere of boron chloride, chlorine, and argon.

[0132] Step five. The etched substrate is cleaned according to the same procedure as step 6 of example 1.

[0133] Step six. The front side of the cleaned substrate is spin coated with photoresist for the second time.

[0134] The front side of the cleaned substrate is placed on a temperature controlled hot plate and baked at 180°C for 6 minutes. SF6 photoresist is then dropped onto the spin coater table with the substrate and spin coated onto the substrate at 2000 rpm for 30 seconds.

[0135] The substrate with the SF6 photoresist is placed on a temperature controlled hot plate and baked at 180°C for 6 minutes to fix the SF6 photoresist to the substrate.

[0136] 49CP photoresist is then dropped onto the substrate with the SF6 photoresist and spin coated onto the substrate at 4000 rpm for 40 seconds.

[0137] The substrate with the SF6 photoresist and the 49CP photoresist is placed on a temperature controlled hot plate and baked at 90°C for 1 minute to fix the 49CP photoresist to the SF6 photoresist to form a composite double layer of SF6 photoresist and 49CP photoresist.

[0138] Step seven. The composite double layer is exposed and developed, as Figure 4 (d).

[0139] The substrate with the fixed composite double layer is placed on a photoresist stepper and exposed for 21 seconds. The exposed substrate is then placed on a temperature controlled hot plate and baked at 100°C for 2 minutes.

[0140] The baked substrate is then placed in a developer bath and developed for 60 seconds. The developed substrate is then rinsed in deionized water for 4 minutes and dried with nitrogen.

[0141] Step eight. The dried substrate is subjected to Ohmic electrode deposition.

[0142] The dried substrate is placed in an oxygen plasma and bombarded for 4 minutes.

[0143] The bombarded substrate is then placed on a magnetron sputter table and subjected to a 15 nm thick titanium metal deposition at a power of 74 W, a gas flow of 1.0 mTorr and a time of 300 seconds.

[0144] The substrate on which the titanium metal is deposited is placed on a magnetron sputtering table to deposit a 225 nm thick gold metal under the process conditions of a power of 24 W, a gas flow of 2.5 mTorr, and a time of 2250 seconds to form an ohmic electrode 3 composite layer composed of titanium and gold.

[0145] Step nine. The substrate on which the ohmic electrode composite layer is deposited is stripped, as Figure 4 (e).

[0146] The substrate on which the ohmic electrode 3 composite layer is deposited is placed in acetone for 10.5 hours of immersion; the immersed substrate is then placed in acetone for 4 minutes of ultrasonic treatment and blown for 4 minutes using a plastic straw;

[0147] The dried substrate is placed in a stripping solution and heated to 55°C for 35 minutes of immersion;

[0148] The immersed substrate is then placed in acetone, isopropanol, and deionized water for 4 minutes of ultrasonic treatment each and dried using nitrogen.

[0149] Step ten. The dried substrate is placed in a nitrogen atmosphere and set to a temperature of 460°C for 65 seconds of rapid annealing.

[0150] Step eleven. The front side of the annealed substrate is spin-coated with photoresist for a third time.

[0151] The front side of the annealed substrate is placed on a temperature-controlled heating table and baked at a temperature of 180°C for 6 minutes; SF6 photoresist is selected and dropped onto the photoresist-coated table with the substrate and spin-coated onto the substrate at a speed of 2000 r for 30 seconds; the substrate with the spin-coated SF6 photoresist is placed on the temperature-controlled heating table and baked at a temperature of 180°C for 6 minutes to fix the SF6 photoresist on the substrate;

[0152] 49CP photoresist is selected and dropped onto the substrate with the SF6 photoresist and placed on the photoresist-coated table and spin-coated at a speed of 4000 r for 40 seconds;

[0153] The substrate with the fixed SF6 photoresist and spin-coated 49CP photoresist is placed on the temperature-controlled heating table and baked at a temperature of 90°C for 1 minute to fix the 49CP photoresist on the SF6 photoresist to form a composite double-layer photoresist composed of SF6 photoresist and 49CP photoresist.

[0154] Step twelve. The composite double-layer photoresist formed in step eleven is exposed and developed, as Figure 4 (f).

[0155] The substrate with the third spin-coated composite double-layered resist is placed on a photoetching machine loaded with a photoetching plate for exposure for 21 seconds; and the exposed substrate is placed on a temperature-controlled heating table for pre-baking at 100°C for 2 minutes.

[0156] The pre-baked substrate is immersed in a developing solution for 60 seconds, and then the immersed substrate is rinsed in deionized water for 4 minutes and dried with nitrogen.

[0157] Step 13. The dried substrate is subjected to electrode thickening layer deposition.

[0158] The dried substrate is subjected to surface bombardment in an oxygen plasma for 4 minutes.

[0159] The bombarded substrate is placed on a magnetron sputtering table for deposition of a 15 nm thick metal titanium layer under the following process conditions: power of 74 W, gas flow of 1.0 mTorr, and time of 300 seconds.

[0160] The substrate with the deposited metal titanium is placed on a magnetron sputtering table for deposition of a 395 nm thick metal gold layer under the following process conditions: power of 24 W, gas flow of 2.5 mTorr, and time of 3950 seconds, thereby forming an electrode thickening 4 composite layer composed of titanium and gold.

[0161] Step 14. The substrate with the deposited electrode thickening composite layer is subjected to stripping, as described in Figure 4 (g).

[0162] The substrate with the deposited electrode thickening 4 composite layer in Step 13 is immersed in acetone for 10.5 hours; and the immersed substrate is ultrasonically treated in acetone for 4 minutes and then dried with a pipette.

[0163] The dried substrate is immersed in a stripping solution heated to 55°C for 35 minutes.

[0164] The immersed substrate is sequentially placed in acetone, isopropanol, and deionized water, each for 4 minutes of ultrasonic treatment, and then dried with nitrogen.

[0165] Step 15. The dried substrate is subjected to oxygen annealing to form a high-resistance layer, as described in Figure 4 (h).

[0166] This step is implemented in the same manner as Step 16 of Example 1.

[0167] Example 3: A Mg-doped gallium oxide single crystal substrate with a square shape of 11 mm in side length and a thickness of 540 μm is prepared; the length of each groove is 5 mm, the width is 3 mm, and the depth is 365 nm; the length of each ohmic electrode is 5 mm, and the width is 3 mm; the length of each electrode thickening layer is 5 mm, and the width is 3 mm; the length of each high resistance layer is 5 mm, and the width is 1.5 mm, to form a photoconductive modulated microwave device.

[0168] Step A. A Mg-doped gallium oxide single crystal substrate is selected and cleaned, as in Figure 4 (a).

[0169] This step is implemented in the same manner as steps 1 and 2 of Example 1.

[0170] Step B. The front surface of the cleaned substrate is spin-coated with photoresist for the first time.

[0171] B1) The front surface of the cleaned substrate is baked on a temperature-controlled baking table at a temperature of 220 °C for 4 minutes;

[0172] B2) Photoresist is dropped onto the baked substrate and spin-coated, using AZ1500 as the photoresist, at a spin-coating table speed of 4000 r and a spin-coating time of 20 seconds;

[0173] B3) The substrate with the spin-coated AZ1500 photoresist is placed on a temperature-controlled baking table for pre-baking, with the temperature set to 60 °C and the pre-baking time set to 3 minutes, to fix the first spin-coated AZ1500 photoresist on the substrate.

[0174] Step C. After the first spin-coated photoresist is fixed on the substrate, the substrate is exposed to light and developed, as in Figure 4 (b).

[0175] C1) The substrate with the fixed photoresist is placed on a photoetching machine with an etching plate to be exposed to light for 21 seconds;

[0176] C2) The exposed substrate is placed in a developing solution to be developed for 100 seconds;

[0177] C3) The developed substrate is rinsed in deionized water and dried with nitrogen;

[0178] C4) The dried substrate is placed on a temperature-controlled baking table to be hard-baked to remove moisture from the substrate, with the hard-baking temperature set to 110 °C and the time set to 0.5 minutes.

[0179] Step D. The hard-baked substrate is etched and cleaned to form grooves, as in Figure 4 (c).

[0180] D1) Put the substrate after hardening into the mixed gas consisting of boron chloride, chlorine and argon to etch the groove 2, and the etching time is 16 minutes;

[0181] D2) Clean the etched substrate according to the same operation as step 6 of example 1.

[0182] Step E. Spin the photoresist twice on the front side of the cleaned substrate.

[0183] E1) Bake the front side of the cleaned substrate on the temperature-controlled heating table, and the baking temperature is 220°C, and the time is 4 minutes;

[0184] E2) Drop and spin the photoresist on the baked substrate for the first time, and the photoresist selected is SF6 type, the rotation speed of the coating table is 2000r, and the spinning time is 30 seconds;

[0185] E3) Bake the substrate with SF6 photoresist on the temperature-controlled heating table to fix the SF6 photoresist on the substrate, and the baking temperature is 220°C, and the time is 4 minutes;

[0186] E4) Drop and spin the photoresist on the substrate with fixed SF6 photoresist for the second time, and the photoresist selected is 14CP type, the rotation speed of the coating table is 5000r, and the spinning time is 20 seconds;

[0187] E5) Pre-bake the substrate with fixed 14CP photoresist to fix the 14CP photoresist on the SF6 photoresist, forming a composite double-layered glue consisting of SF6 photoresist and 14CP photoresist, and the pre-baking temperature is 110°C, and the time is 0.5 minutes.

[0188] Step F. Expose and develop the composite double-layered glue formed in step E, such as Figure 4 (d).

[0189] F1) Place the substrate with fixed composite double-layered glue on the photoetching machine loaded with photoetching plate to expose, and the exposure time is 21 seconds;

[0190] F2) Place the exposed substrate on the temperature-controlled heating table for post-baking, and the post-baking temperature is 100°C, and the time is 2 minutes;

[0191] F3) Place the post-baked substrate in the developing solution for development, and the developing time is 100 seconds;

[0192] F4) Place the developed substrate in deionized water for rinsing and dry with nitrogen.

[0193] Step G. Deposit the ohmic electrode on the substrate after step F.

[0194] G1) The dried substrate is placed in an oxygen plasma for surface bombardment for 6 minutes;

[0195] G2) The bombarded substrate is placed on a magnetron sputtering station for deposition of metal titanium, then for deposition of metal titanium, to form an ohmic electrode 3 composite layer composed of titanium and gold, wherein:

[0196] The process conditions for deposition of metal titanium are set as follows: power 76 W, gas flow 2.0 mTorr, deposition time 500 seconds, thickness of metal titanium 25 nm;

[0197] The process conditions for deposition of metal gold are set as follows: power 26 W, gas flow 3.5 mTorr, deposition time 2350 seconds, thickness of metal gold 235 nm.

[0198] Step H. The substrate on which the ohmic electrode composite layer has been deposited is stripped, for example by: Figure 4 (e).

[0199] H1) The substrate on which the ohmic electrode 3 composite layer has been deposited is immersed in acetone for 11 hours;

[0200] H2) The immersed substrate is subjected to ultrasonic treatment in acetone for 6 minutes, and is dried using a suction tube;

[0201] H3) The dried substrate is immersed in a stripping solution heated to 65°C for 25 minutes;

[0202] H4) The immersed substrate is subjected to ultrasonic treatment in acetone, isopropyl alcohol and deionized water in turn for 6 minutes, and is dried using nitrogen.

[0203] Step I. The dried substrate from step H is subjected to rapid annealing under a nitrogen atmosphere at a temperature of 480°C for 55 seconds.

[0204] Step J. The front surface of the annealed substrate is spin-coated with photoresist twice.

[0205] J1) The front surface of the annealed substrate is baked on a temperature-controlled baking station at a temperature of 220°C for 4 minutes;

[0206] J2) Photoresist is dropped onto the baked substrate for the first time and is spin-coated, the photoresist used being of type SF6, the spin-coating station being set to a speed of 2000 r, and the spin-coating time being 30 seconds;

[0207] J3) The substrate on which the SF6 photoresist has been spin-coated is baked on a temperature-controlled baking station to fix the SF6 photoresist to the substrate, the baking temperature being 220°C and the baking time being 4 minutes;

[0208] J4) on the substrate with the fixed SF6 photoresist, secondly dropping photoresist and performing spin coating, the photoresist is selected from 14CP model, the rotation speed of the coating table is 5000r, and the spin coating time is 20 seconds;

[0209] J5) on the temperature-controlled heating table, performing pre-baking on the substrate with the fixed spin-coated 14CP photoresist, so as to fix the 14CP photoresist on the SF6 photoresist, and form a composite double-layer photoresist composed of the SF6 photoresist and the 14CP photoresist, the pre-baking temperature is 110°C, and the pre-baking time is 0.5 minutes.

[0210] Step K. performing exposure and development on the composite double-layer photoresist formed in step J, such as Figure 4 (f).

[0211] K1) placing the substrate with the fixed composite double-layer photoresist on the photoetching machine loaded with a photoetching plate to perform exposure, and the exposure time is 21 seconds;

[0212] K2) placing the exposed substrate on the temperature-controlled heating table to perform post-baking, the post-baking temperature is 100°C, and the post-baking time is 2 minutes;

[0213] K3) placing the post-baked substrate in a developing solution to perform development, and the development time is 100 seconds;

[0214] K4) placing the developed substrate in deionized water to perform rinsing, and then blowing dry with nitrogen.

[0215] Step L. performing electrode thickening layer deposition on the substrate blown dry in step K.

[0216] L1) placing the substrate blown dry in an oxygen plasma to perform surface bombardment, and the bombardment time is 6 minutes;

[0217] L2) placing the bombarded substrate on a magnetron sputtering table to perform deposition of metal titanium first, and then performing deposition of metal titanium, so as to form an electrode thickening 4 composite layer composed of titanium and gold, wherein:

[0218] The process condition for depositing metal titanium is set as follows: the power is 76W, the gas flow is 2.0mTorr, the deposition time is 500 seconds, and the thickness of the metal titanium is 25nm;

[0219] The process condition for depositing metal gold is set as follows: the power is 26W, the gas flow is 3.5mTorr, the deposition time is 4050 seconds, and the thickness of the metal gold is 405nm.

[0220] Step M. performing stripping on the substrate with the deposited electrode thickening composite layer, such as ​ (g).

[0221] M1) immersing the substrate with the deposited electrode thickening 4 composite layer in acetone, and the immersion time is 11 hours;

[0222] M2) ultrasonic treatment of the soaked substrate in acetone for 6 minutes, and dried by a suction tube;

[0223] M3) soaking of the dried substrate in a stripping solution heated to 65°C for 25 minutes;

[0224] M4) ultrasonic treatment of the soaked substrate in acetone, isopropanol, and deionized water for 6 minutes, and dried by nitrogen.

[0225] Step N. Oxygen annealing of the dried substrate to form a high resistance layer, as in ​ (h).

[0226] This step is implemented in the same way as step 16 of Example 1.

[0227] The above description is only a few specific examples of the present application and does not constitute any limitation on the present application. It is obvious that after understanding the content and principles of the present application, those skilled in the art can make various modifications and changes in form and details without departing from the principles and structures of the present application. For example, various parameters of the device can be enlarged or reduced on the basis of the above-mentioned parameter range, but these modifications and changes based on the idea of the present application are still within the protection scope of the claims of the present application.

Claims

1. A Mg-doped gallium oxide photoconductive modulation microwave device, comprising a semi-insulating substrate (1), a pair of ohmic electrodes (3), a pair of electrode thickening layers (4), and a trigger source (6), characterized in that: The semi-insulating substrate (1) is a Mg-doped gallium oxide single crystal substrate, so that only hole carriers are excited to participate in conduction under the irradiation of the trigger source (6); the upper part of the substrate has two symmetrical grooves (2); The pair of ohmic electrodes (3) and the pair of electrode thickening layers (4) are located inside each groove (2) from bottom to top; A high-resistivity layer (5) is provided in the area between the two grooves (2) to increase the dark-state resistance of the device and reduce the on-state resistance.

2. The device according to claim 1, characterized in that, The depth of each groove (2) is less than the sum of the depth of each ohmic electrode (3) and each electrode thickening layer (4) to enhance photocurrent.

3. The device according to claim 1, characterized in that, Each ohmic electrode (3) is constructed of a double-layer structure consisting of titanium with a thickness of 15nm to 25nm and gold with a thickness of 225nm to 235nm.

4. The device according to claim 1, characterized in that, Each electrode thickening layer (4) is a double-layer structure consisting of titanium with a thickness of 15nm to 25nm and gold with a thickness of 395nm to 405nm.

5. The device according to claim 1, characterized in that, Each groove (2) has a length of 3mm to 5mm, a width of 1mm to 3mm, a depth of 355nm to 365nm, and a distance of 0.5mm to 1.5mm between two grooves.

6. The device according to claim 1, characterized in that, The high-resistivity layer (5) is formed by annealing in an oxygen atmosphere, and has a length of 3 mm to 5 mm and a width of 0.5 mm to 1.5 mm.

7. The device according to claim 1, characterized in that, The triggering source (6) is a laser source with a wavelength of 500nm to 564nm.

8. A method for fabricating a Mg-doped gallium oxide photoconductive modulation microwave device, characterized in that, Includes the following steps: S1: Clean the semi-insulating substrate (1); S2: Spin-coat photoresist on the front side of the cleaned semi-insulating substrate (1); S3: The semi-insulating substrate (1) coated with photoresist is exposed and developed by a photolithography machine carrying a photomask to form two rectangular groove (2) areas; S4: The groove (2) is etched and cleaned on the front side of the semi-insulating substrate (1) using an etching machine; S5: Spin-coat photoresist on the front side of the etched semi-insulating substrate (1); S6: The semi-insulating substrate coated with photoresist is overlaid, exposed, and developed by a photolithography machine carrying a photomask to form two rectangular ohmic electrode (3) regions; S7: The front side of the semi-insulating substrate (1) is treated with oxygen plasma and sputtered with titanium and gold by a sputtering station. After being stripped and cleaned, it is annealed in a nitrogen atmosphere to form an ohmic electrode (3). S8: Spin-coat photoresist on the front side of the annealed semi-insulating substrate (1); S9: The semi-insulating substrate (1) coated with photoresist is overlaid, exposed, and developed by a photolithography machine carrying a photomask to form two rectangular electrode thickening layer (4) regions; S10: The front side of the semi-insulating substrate (1) is treated with oxygen plasma and titanium and gold are sputtered by a sputtering station, and then cleaned after being stripped to form an electrode thickening layer (4). S11: Annealing in an oxygen atmosphere to form a high-resistivity layer (5) to complete device fabrication.

9. The method according to claim 8, characterized in that: The cleaning of the semi-insulating substrate (1) in steps S1), S4), S7) and S10) is to sonicate in acetone, isopropanol and deionized water for 4 to 6 minutes each, and then dry it in a nitrogen atmosphere. In steps S2), S5), and S8), photoresist is spin-coated onto the front side of the cleaned semi-insulating substrate. First, the substrate is baked on a temperature-controlled heating stage at 180℃ to 220℃ for 4 to 6 minutes. Then, the photoresist is spin-coated at 2000 to 5000 rpm for 20 to 40 seconds. Finally, the substrate is pre-baked on a temperature-controlled heating stage at 60℃ to 140℃ for 1 to 3 minutes. In steps S3), S6), and S9), the semi-insulating substrate coated with photoresist is exposed and developed using a photolithography machine with a photomask. The exposure time is 8 to 32 seconds, the development time is 60 to 100 seconds, and the substrate is rinsed with deionized water for 2 to 4 minutes, dried with nitrogen, and then hardened at a temperature of 90°C to 110°C for 0.5 to 2.0 minutes using a temperature-controlled heating stage.

10. The method according to claim 8, characterized in that: In step S4), the spin-coated semi-insulating substrate is etched with grooves using an etching machine. The etching gas atmosphere consisted of boron chloride, chlorine, and argon, and the etching time was 14 to 16 minutes. In steps S7) and S10), oxygen plasma treatment is performed on the front side of the semi-insulating substrate, followed by sputtering of titanium and gold using a sputtering stage and subsequent stripping; the parameter settings are as follows: The oxygen plasma treatment time is 4 to 6 minutes; The sputtering power for titanium is 74W to 76W, the gas flow rate is 1.0mTorr to 2.0mTorr, and the time is 300 seconds to 500 seconds; the sputtering power for gold is 24W to 26W, and the gas flow rate is 2.5mTorr to 3.5mTorr. The stripping process involves first soaking in acetone for 10-11 hours, then sonicating for 4-6 minutes to blow off the metal in the non-electrode areas, followed by filtration. Then, the stripping solution is soaked in a stripping solution at 55-65°C for 25-35 minutes, and finally sonicated in isopropanol for 4-6 minutes. In step S7), annealing is performed under a nitrogen atmosphere at a temperature of 460°C to 480°C for 55 to 65 seconds. In step S11), annealing is performed in an oxygen atmosphere at a temperature of 460°C to 480°C for 25 to 35 minutes.

Images