A microwave diode with low noise and low operating voltage and a method for manufacturing the same

Abstract

The application discloses a low-noise and low-working-voltage microwave diode and a preparation method thereof, and the microwave diode is a vertical heterojunction structure composed of indium selenide (InSe) and black phosphorus (BP). The traditional material for preparing an impact ionization avalanche transit time (IMPATT) microwave diode is replaced by the two-dimensional material BP, and a ballistic avalanche mechanism unique to the BP, that is, a scattering-free quantum coherent transport avalanche mode, so that the IMPATT microwave diode in the application is obviously lower than a traditional avalanche device in terms of avalanche noise, and the avalanche threshold voltage is 2-3 orders of magnitude lower than that of the traditional device. In addition, the bipolarity of the BP makes it unnecessary to chemically dope the material when the IMPATT diode is prepared, thereby reducing the preparation difficulty of the device. Compared with the IMPATT diode prepared from the traditional material, the IMPATT diode in the application not only has lower avalanche noise and avalanche breakdown voltage, but also is simple to prepare, thereby greatly improving the working performance of the device.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of microwave diodes, and particularly relates to a microwave diode with low noise and low working voltage and a preparation method thereof. BACKGROUND

[0002] At present, as a power semiconductor device for high-frequency microwave electronic equipment, an IMPATT diode can produce the highest continuous wave power output in the millimeter wave frequency band (30 GHz to 300 GHz). Compared with low-frequency microwave or infrared systems, the millimeter wave system has the advantages of light weight, small size, wide frequency band, all-weather operation and high-resolution narrow beam width, so the IMPATT diode has many advantages in communication and radar system applications and is widely used in radio astronomy, air traffic control signals and weather radars.

[0003] In the face of such extensive application prospects, the preparation process of IMPATT diodes based on silicon (Si) and gallium nitride (GaN) has been mature and has been applied in practice, but a problem worth paying attention to in its application is that the noise caused by random fluctuations during avalanche multiplication is very high. The reason for high noise is that the acceleration process after collision ionization is random, so the number of carriers involved in the next collision process cannot be determined, and this uncertainty leads to a lot of noise, which may greatly reduce the performance of the device. In addition, in the traditional IMPATT diodes based on Si and GaN, in order to realize the avalanche function, the channel length is usually much larger than the mean free path of the channel material, and the longer channel length will lead to a large avalanche threshold voltage. Under such a large avalanche threshold voltage, the channel material thermal effect may be abnormally serious, eventually making the device unable to work normally.

[0004] In traditional avalanche devices, the main reason for the above problems is that the avalanche collision ionization region is too long. Therefore, the natural idea is to reduce the length of the collision ionization region to solve this problem. If we reduce the length of the channel to within the range of the mean free path of the material, the transport of carriers in the channel will become ballistic transport. Ballistic transport is a kind of quantum coherent transport without scattering. Therefore, the carriers will not lose energy during the acceleration process in the channel, and the avalanche threshold voltage of the device will also be reduced accordingly, and only a bias voltage of the order of the band gap is needed to realize the avalanche. In addition, the ballistic transport process does not involve phonons, so it will not introduce additional noise. Therefore, the combination of ballistic transport process and avalanche can perfectly solve the problems of high noise and large avalanche threshold voltage in traditional avalanche devices.

[0005] Therefore, in order to solve the problems of high noise and large avalanche threshold voltage in the traditional IMPATT, a vertical microwave diode structure based on two-dimensional materials indium selenide (InSe) and black phosphorus (BP) is designed, and the unique ballistic avalanche mechanism of two-dimensional material BP is used to replace the traditional avalanche mechanism. In fact, the idea of combining ballistic and avalanche to realize ballistic avalanche was proposed as early as the 1980s, but due to the limitations of technology and materials, it has not been realized in experiments. For materials with small mean free path, the threshold voltage of avalanche breakdown is generally large, and before the avalanche breakdown occurs, the material will be burned out under such a large voltage. Therefore, in order to realize avalanche breakdown, a material with high mobility is generally selected as the channel material, which can easily make the size of the channel below the mean free path. However, to realize avalanche, the existence of PN junction is also required. For traditional materials, it is quite difficult to realize a perfect PN heterojunction of tens of nanometers. Fortunately, BP is such a high-mobility material, and the band structure of BP and InSe matches well, which can form a good PN heterojunction. In addition, in the invention, the BP layer and the InSe layer are designed as a vertical heterojunction structure, mainly considering that the vertical heterojunction is easier to adjust the channel length, only by changing the thickness of the material. Therefore, under the action of the unique ballistic avalanche mechanism of two-dimensional material BP, the InSe / BP-based IMPATT diode has lower avalanche noise and avalanche threshold voltage, thereby improving the working performance of the device and enabling it to work normally. SUMMARY

[0006] TECHNICAL PROBLEMS SOLVED

[0007] In view of the deficiencies of the prior art, the present application solves the technical problems of high avalanche noise and large avalanche threshold voltage in the traditional IMPATT microwave diode, and provides a microwave diode with low noise and low working voltage and a preparation method thereof.

[0008] TECHNICAL SCHEME

[0009] To achieve the above-mentioned purpose, the present application is realized by the following technical scheme:

[0010] A microwave diode with low noise and low working voltage, the microwave diode with low noise and low working voltage is a vertical heterojunction structure composed of an InSe layer and a BP layer, the upper layer of the heterojunction structure is the InSe layer, and the lower layer is the BP layer, wherein the BP layer is divided into three regions from left to right as BP region a, BP region b and BP region c, the BP layer is provided with a SiO2 layer at the bottom, and the InSe layer is arranged directly above the BP region a; a Ti / Au double-layer metal electrode a is led out above the InSe layer; a Ti / Au double-layer metal electrode b is led out above the BP region c; and a Ti / Au double-layer metal electrode c is led out on the SiO2 layer below the BP region c.

[0011] Further, the InSe layer has a thickness of 10 nm; and the BP layer has a thickness of 10 nm.

[0012] Further, the InSe layer has the same width as the BP region a, both being 10 nm.

[0013] Further, the total width of the BP layer is 50 nm, wherein the width of the BP region a is 10 nm, the width of the BP region b is 30 nm, and the width of the BP region c is 10 nm.

[0014] A preparation method of a microwave diode with low noise and low working voltage, comprising the following steps:

[0015] First step: obtaining an InSe layer and a BP layer by mechanical exfoliation;

[0016] Second step: finding the BP region a under a microscope, which has a width range of 0-10 nm on the BP layer, and transferring the exfoliated InSe layer to the directly above the BP region a to form a vertical heterojunction structure composed of the InSe layer and the BP layer;

[0017] Third step: transferring the vertical heterojunction structure composed of the InSe layer and the BP layer to the SiO2 layer;

[0018] Fourth step: evaporating a Ti / Au double-layer metal electrode a and a Ti / Au double-layer metal electrode b above the InSe layer and the BP region c respectively, and then evaporating a Ti / Au double-layer metal electrode c below the SiO2 layer under the BP region c, thereby forming a microwave diode with low noise and low working voltage.

[0019] Further, a positive voltage is applied to the Ti / Au double-layer metal electrode a, a negative voltage is applied to the Ti / Au double-layer metal electrode b, and a negative voltage is applied to the Ti / Au double-layer metal electrode c in the fourth step, so that the entire microwave diode with low noise and low working voltage obtains a reverse bias and avalanche breakdown occurs; at the same time, the Ti / Au double-layer metal electrode c below the BP region c becomes a high-doped p region due to the application of a negative voltage.

[0020] Further, the InSe layer is transferred above the BP region a in the second step by using a PDMS-based dry transfer technology to avoid the influence of chemical reagents in the wet transfer technology on the performance and quality of the material.

[0021] Further, the working principle of the above-mentioned microwave diode with low noise and low working voltage is that:

[0022] In the microwave diode, the ballistic avalanche phenomenon is very sensitive to the thickness of BP. Once the thickness of BP is greater than the mean free path of the carriers, the ballistic avalanche phenomenon disappears. Therefore, with the increase of the thickness of BP, the devices that can see the ballistic avalanche phenomenon will be less and less until they disappear. In this application, the thickness of the BP layer is set to 10 nm, the main reason is that the thin layer of BP can easily achieve less than the mean free path of the carriers in thickness. The BP region a is used as an avalanche region to generate carriers, and the BP region b is used as a drift region to provide drift time shift space. When the diode works, an external reverse bias is needed. When the reverse bias is higher than the voltage required for the reverse breakdown of the diode, a large number of carriers will be generated in the BP region a. The generated electrons will be collected by the InSe layer, and a large number of holes will pass through the BP region b to the right, and finally reach the heavily doped BP region c. Due to the existence of the BP region c, the holes generated in the BP region a can quickly pass through the drift region BP region b and be collected by the BP region c.

[0023] Further, in the IMPATT microwave diode, there are two important time delay effects, one is the avalanche multiplication delay of the carriers in the avalanche BP region a, and the other is the transit time delay of the carriers passing through the transit BP region b. Due to these two time delays, the IMPATT microwave diode can generate alternating current negative resistance at microwave frequency. Bias the diode at the breakdown voltage V B nearby, and then add a high-frequency small signal RF signal to both ends, the diode will have the following working process: in the positive half cycle of the RF voltage, the total voltage across the diode is higher than the breakdown voltage, and the avalanche BP region a will continue to generate electron-hole pairs through collision ionization. The concentration and current of the carriers in the diode will increase exponentially. In the negative half cycle of the RF, the total voltage across the diode will be lower than the breakdown voltage, and the generation rate and current of the carriers will decrease. The number of carriers generated through the avalanche multiplication process will reach a maximum at the end of the positive half cycle of the RF, i.e. when the RF voltage is equal to 0. Therefore, the avalanche multiplication process will make the current generated in the avalanche region have a phase delay of 90°. Then the current pulse generated by the avalanche BP region a will be injected into the transit BP region b. The carriers move at a saturated speed in the transit region, thereby generating an induced current J ind in the external circuit. The fundamental component of the generated external current also has a phase delay of more than 90° with respect to the applied RF voltage, thereby causing the diode to exhibit negative resistance.

[0024] In the application, the unique ballistic avalanche mechanism of the two-dimensional material BP is utilized, so that the prepared IMPATT diode has the advantages of low avalanche noise and small avalanche threshold voltage, thereby improving the working performance of the device; compared with the chaotic ionization process in the traditional avalanche effect, the channel length is much larger than the average free path of the carriers, in the ballistic avalanche mechanism, the length of the collision ionization region is smaller than the average free path of the carriers, the carriers are ballistically transported from the lower surface (B end) of the two-dimensional material BP to the upper surface (A end) of BP, and electron-hole pairs are generated by collision ionization; the holes stay at the A end, and the electrons are ballistically transported to the B end to generate electron-hole pairs again, and the electrons stay at the B end, and the holes return to continue the process; in the absence of external interference, the process will continue, and a large number of carriers will be generated instantaneously.

[0025] In addition, in the application, the bipolarity feature of the two-dimensional material BP is utilized, and the main carrier type of each region is changed by electric field driving, which is specifically embodied as follows: a negative voltage is applied to the Ti / Au double-layer metal electrode c, so that the BP region c becomes a high-doped p region; in addition, due to the intrinsic p-type characteristics of the two-dimensional material BP, the BP region a and the BP region b both exhibit low-doped p-type regions; therefore, in the application, any material does not need to be doped as n-type or p-type, which not only reduces the preparation difficulty of the material, but also saves the production cost.

[0026] Beneficial effects:

[0027] The application provides a microwave diode with low noise and low working voltage and a preparation method thereof, and has the following beneficial effects compared with the prior art:

[0028] 1. The unique ballistic avalanche mechanism of BP is creatively applied to the IMPATT diode to solve the problems of high avalanche noise and large working voltage in the traditional IMPATT diode, and a new idea is provided for the future research direction of the IMPATT diode.

[0029] 2. After experimental testing of the device, the avalanche noise power spectrum of the Si-based traditional IMPATT diode and the InSe / BP-based IMPATT diode under different reverse biases is measured. The experimental results show that the avalanche noise of the Si-based traditional IMPATT diode is the traditional white noise, and the power spectrum values are all above 10 -4 W / Hz; and in the InSe / BP-based IMPATT diode, due to the ballistic avalanche mechanism of the two-dimensional material BP, no additional noise is introduced in the ballistic transport process, so that the avalanche noise power spectrum value after the avalanche of the IMPATT diode is not only smaller than that of the Si-based traditional IMPATT diode, but also presents a perfect 1 / f shape, which is obviously different from the white noise in the traditional device.

[0030] 3. The avalanche threshold voltage of the InSe / BP-based IMPATT diode and the traditional GaN-based IMPATT diode is tested by an experimental method, and the experimental results show that the IMPATT diode prepared from the traditional material GaN occurs avalanche breakdown at about 190 V, and the avalanche threshold voltage of the IMPATT diode in the application is about -8 V. The lower avalanche threshold voltage is due to the fact that the carriers in the diode do not scatter under the action of the ballistic avalanche mechanism of the two-dimensional material BP, and the energy is not lost in the channel acceleration process, so that the avalanche threshold voltage of the device is reduced by 2 to 3 orders of magnitude compared with the traditional device.

[0031] 4. The bipolarity of the two-dimensional material BP makes it unnecessary to chemically dope the material during the preparation of the IMPATT diode, and only the driving of the electric field can change the main carrier type of each region. Compared with the traditional chemical doping, the electric field driving is a fast, dynamic and reversible effective method, and also provides a new idea and method for the future preparation process of the IMPATT diode.

[0032] 5. The vertical ballistic avalanche phenomenon in the InSe / BP-based IMPATT diode improves the stability of the device. Due to the influence of thermal carriers, the device in the avalanche breakdown region can only be repeated for several times. The diode prepared by the application has a long service life and is stable, and can still maintain good avalanche breakdown characteristics after hundreds of use cycles. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is a structure schematic diagram of a low-noise and low-working-voltage microwave diode of the application.

[0034] Figure 2 is a structure schematic diagram of a traditional IMPATT microwave diode.

[0035] Figure 3 is a preparation flowchart of a low-noise and low-working-voltage microwave diode of the application.

[0036] Figure 4 is a large-signal working of the microwave diode of the application, showing the end voltage, avalanche generation rate and end current diagram.

[0037] Figure 5 is a traditional avalanche effect schematic diagram.

[0038] Figure 6 is a ballistic avalanche mechanism schematic diagram.

[0039] Figure 7The IV characteristic curve of the GaN-based conventional IMPATT diode.

[0040] Figure 8 The IV characteristic curve of the InSe / BP heterojunction and InSe / BP-based IMPATT diode.

[0041] Figure 9 The avalanche noise curve of the Si-based conventional IMPATT diode.

[0042] Figure 10 The avalanche noise curve of the InSe / BP heterojunction and InSe / BP-based IMPATT diode.

[0043] Explanation of reference signs: 1, InSe layer, 2, BP region a, 3, BP region b, 4, BP region c, 5, BP layer, 6, SiO2 layer, 11, Ti / Au double-layer metal electrode a, 41, Ti / Au double-layer metal electrode b, 42, Ti / Au double-layer metal electrode c. DETAILED DESCRIPTION

[0044] The application will be further described in conjunction with examples, which are only used to illustrate the application and do not limit the scope of the claims. Other alternative means that can be thought of by those skilled in the art are within the scope of the claims of the application.

[0045] Example 1:

[0046] See Figure 1 The low-noise and low-working-voltage microwave diode of the embodiment is a vertical heterojunction structure composed of an InSe layer 1 and a BP layer 5. The upper layer of the heterojunction structure is the InSe layer 1, and the lower layer is the BP layer 5. The BP layer 5 is divided into three regions from left to right, namely BP region a 2, BP region b 3 and BP region c 4. The BP layer 5 is provided with a SiO2 layer 6 at the bottom, and the InSe layer 1 is placed directly above the BP region a 2. A Ti / Au double-layer metal electrode a 11 is led out above the InSe layer 1. A Ti / Au double-layer metal electrode b 41 is led out above the BP region c 4. A Ti / Au double-layer metal electrode c 42 is led out on the SiO2 layer 6 below the BP region c 4.

[0047] The thickness of the InSe layer 1 is 10 nm; the thickness of the BP layer 5 is 10 nm; the width of the InSe layer 1 and the BP region a 2 is the same, both being 10 nm; and the total width of the BP layer 5 is 50 nm, of which the width of the BP region a 2 is 10 nm, the width of the BP region b 3 is 30 nm, and the width of the BP region c 4 is 10 nm.

[0048] A method for preparing a microwave diode with low noise and low operating voltage, comprising the steps of:

[0049] S1: obtaining an InSe layer 1 by mechanical exfoliation, as follows:

[0050] S11: cleaning the SiO2 / Si substrate with deionized water and ethanol, and blowing dry with nitrogen;

[0051] S12: sticking 0.5 g of InSe crystal on the adhesive tape, and peeling off the InSe with the adhesive tape for multiple times;

[0052] S13: sticking the single-layer InSe layer peeled off by the adhesive tape on the SiO2 / Si substrate, and slowly separating the adhesive tape from the substrate to obtain the single-layer InSe layer 1, the thickness of which is initially determined by an optical microscope and finally determined by an atomic force microscope, and a 10 nm long and high cube is obtained;

[0053] S2: obtaining a BP layer 5 by mechanical exfoliation, as follows:

[0054] S21: before using the BP sample, clamping 1 g of BP with a clean tweezers, and immersing it in a beaker containing acetone for five minutes, and then immersing it in a small beaker containing isopropyl alcohol solution for ten minutes, so as to remove impurities on the surface of the material;

[0055] S22: then, after thoroughly blowing the cleaned BP crystal with ultrapure nitrogen, sticking 0.5 g of the BP crystal on a clean adhesive tape, the adhesive tape should be ensured to be just torn off and placed on a clean and flat platform, then folding the adhesive tape and gently pressing it, so that the adhesive tape fully contacts the BP crystal, and the adhesive surface of the adhesive tape should not be touched by hand or other surfaces, so as to avoid contaminating the adhesive tape and the BP crystal, and sticking the adhesive tape to the BP crystal from both sides;

[0056] S23: then, quickly tearing open the adhesive tape, and the BP crystal will be torn from the layer by the adhesion of the adhesive tape. Repeating the action of folding and quickly tearing open the adhesive tape for five to ten times, and the BP material is spread on the adhesive tape, and the color becomes lighter;

[0057] S24: finally, the BP layer we need will appear on the adhesive tape; attention should be paid to not folding and tearing open the adhesive tape too many times, otherwise the material will be too messy to be spread, which will increase the difficulty of subsequent transfer work; the thickness of the BP layer is initially determined by an optical microscope and finally determined by an atomic force microscope, and a 50 nm long and 10 nm high cuboid is obtained;

[0058] S3: Find BP area a2 under microscope, which has a width range of 0-10 nm on BP layer 5, and transfer the exfoliated InSe layer 1 to the directly above BP area a2 to form a vertical heterojunction structure composed of InSe layer 1 and BP layer (5), see the following steps:

[0059] S31: Transfer the InSe layer 1 film to PDMS by using adhesive tape; since PDMS itself has certain viscoelasticity, the InSe sample is easier to stick to PDMS;

[0060] S32: After finding the InSe layer 1 under the optical microscope, stick the PDMS to the glass plate;

[0061] S33: Transfer the InSe layer 1 to the directly above target BP area a2 substrate by using a fixed-point transfer platform, and the width range of BP area a2 on BP layer 5 is 0-10 nm; after heating at 90°C, the two materials are more closely attached, the glass plate is removed, and a vertical heterojunction composed of InSe / BP is formed;

[0062] S4: Transfer the vertical heterojunction structure composed of InSe layer 1 and BP layer 5 to SiO2 layer 6;

[0063] S5: Evaporate Ti / Au double-layer metal electrode a11 and Ti / Au double-layer metal electrode b41 above InSe layer 1 and BP area c4, respectively, and the width range of BP area c4 on BP layer 5 is 40-50 nm;

[0064] S6: Evaporate Ti / Au double-layer metal electrode c42 on SiO2 layer 6 below BP area c4, and the width range of BP area c4 on BP layer 5 is 40-50 nm, thereby forming a low-noise and low-working-voltage microwave diode.

[0065] When preparing the IMPATT diode, it is also necessary to note that the IMPATT diode is a microwave power semiconductor device, and its working frequency is also particularly important for device performance; in the preparation process, the working frequency is further improved by changing the structure, geometry and material of the device; but in the high frequency band, with the increase of working frequency, the efficiency of IMPATT diode will be significantly reduced, which is also caused by the difficulties in device fabrication and circuit optimization, so when preparing the IMPATT diode in the present application, multiple factors should be considered to ensure that it works at a normal working frequency.

[0066] In this embodiment, the dry transfer technology is used to form a low-noise and low-working-voltage microwave diode composed of InSe layer 1, BP area a2, BP area b3 and BP area c4, see Figure 3 Preparation flowchart.

[0067] In this application, the avalanche threshold voltage of the InSe / BP-based IMPATT diode, the InSe / BP heterojunction and the conventional GaN-based IMPATT diode is tested by experimental method, and the experimental results are shown in Figure 7 and 8 It can be seen from the two figures that the IMPATT diode prepared by the conventional material GaN occurs avalanche breakdown at about 190 V, and the avalanche threshold voltage of the IMPATT diode composed of two-dimensional materials InSe and BP is about -8 V. In the case of forward bias, the device shows a normal on state, and in the case of reverse bias, the device is in the off state, and avalanche breakdown occurs at about -8 V. In addition, it can be seen that the IV characteristics of the InSe / BP heterojunction are similar to the InSe / BP-based IMPATT diode in this application, but the avalanche threshold voltage is lower than that of the IMPATT diode in this application. The main reason is that there is a longer transition zone in the InSe / BP-based IMPATT diode, and a higher avalanche threshold voltage is required for avalanche in the IMPATT diode. By testing the avalanche threshold voltage of the three different devices, it can be seen that the avalanche threshold voltage of the IMPATT diode composed of two-dimensional materials InSe and BP in this application is reduced by 2 orders of magnitude compared with the conventional GaN-based IMPATT diode, which greatly improves the working performance of the device.

[0068] In addition to testing the avalanche threshold voltage of the three different devices, the avalanche noise of the three devices is also tested, and the avalanche noise schematic diagram of each device is shown in Figure 9 and Figure 10 In Figure 10 , the avalanche noise data of the device is divided into two parts, the noise before avalanche of the InSe / BP heterojunction and the InSe / BP-based IMPATT diode corresponds to the two curves above the 1 / f noise, and the noise after avalanche corresponds to the two curves below the 1 / f noise. By comparing with the avalanche noise data of the conventional Si-based IMPATT diode in Figure 9 , the InSe / BP-based IMPATT diode and the InSe / BP heterojunction both show 1 / f noise type, and the avalanche noise of the InSe / BP-based IMPATT diode in this application is higher than that of the InSe / BP heterojunction. The 1 / f noise type shown in the two devices is caused by the ballistic transport characteristics, and the 1 / f noise type makes the ballistic avalanche device have smaller noise in the high frequency region, even lower than the theoretical noise limit of the conventional avalanche device.

[0069] The above-described specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application, and it should be understood that the above-described specific embodiments are merely examples of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A low noise and low operating voltage microwave diode characterized by: The low-noise and low operating voltage microwave diode is a collision ionization avalanche transit time diode, specifically a vertical heterojunction structure composed of an InSe layer (1) and a BP layer (5), wherein the upper layer of the heterojunction structure is the InSe layer (1), and the lower layer is the BP layer (5), wherein the BP layer (5) is divided into three regions from left to right as BP region a (2), BP region b (3), and BP region c (4), the bottom of the BP layer (5) is provided with a SiO2 layer (6), and the InSe layer (1) is arranged directly above the BP region a (2); a Ti / Au double-layer metal electrode a (11) is led out above the InSe layer (1); a Ti / Au double-layer metal electrode b (41) is led out above the BP region c (4); and a Ti / Au double-layer metal electrode c (42) is led out on the SiO2 layer (6) below the BP region c (4). The thickness of the InSe layer (1) is 10 nm, and the thickness of the BP layer (5) is 10 nm.

2. A low noise and low operating voltage microwave diode according to claim 1, characterized in that: The InSe layer (1) and the BP region a (2) have the same width, both being 10 nm.

3. A low noise and low operating voltage microwave diode as claimed in claim 1, characterized in that: The total width of the BP layer (5) is 50 nm, wherein the width of the BP region a (2) is 10 nm, the width of the BP region b (3) is 30 nm, and the width of the BP region c (4) is 10 nm.

4. A method of producing a low-noise and low operating voltage microwave diode as claimed in any one of claims 1 to 3, characterized in that: The method comprises the following steps: Step 1: obtaining the InSe layer (1) and the BP layer (5) by mechanical exfoliation; Step 2: finding the BP region a (2) under a microscope, the width of the BP region a (2) on the BP layer (5) ranges from 0 to 10 nm, and transferring the exfoliated InSe layer (1) to the upper side of the BP region a (2) to form a vertical heterojunction structure composed of the InSe layer (1) and the BP layer (5); Step 3: transferring the vertical heterojunction structure composed of the InSe layer (1) and the BP layer (5) to the SiO2 layer (6); Step 4: evaporating the Ti / Au double-layer metal electrode a (11) and the Ti / Au double-layer metal electrode b (41) on the InSe layer (1) and the BP region c (4) respectively, and then evaporating the Ti / Au double-layer metal electrode c (42) on the SiO2 layer (6) below the BP region c (4), thereby forming a low-noise and low operating voltage microwave diode.

5. The method of claim 4, wherein the microwave diode is fabricated by the steps of: forming a first electrode on a substrate; forming a second electrode on the substrate; and forming a dielectric layer between the first and second electrodes. In the fourth step, a positive voltage is applied to the Ti / Au double-layer metal electrode a (11), a negative voltage is applied to the Ti / Au double-layer metal electrode b (41), and a negative voltage is applied to the Ti / Au double-layer metal electrode c (42), so that the entire low-noise and low operating voltage microwave diode is reversely biased to cause avalanche breakdown; at the same time, the Ti / Au double-layer metal electrode c (42) below the BP region c (4) is applied with a negative voltage, so that the BP region c (4) becomes a high-doped p region.

6. The method for fabricating a low-noise and low-operating-voltage microwave diode according to claim 4, characterized in that: In the second step, the InSe layer (1) is transferred to the upper side of the BP region a (2) by using a PDMS-based dry transfer technology, so as to avoid the influence of chemical reagents in the wet transfer technology on the performance and quality of the material.

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