Miniature propeller and preparation method thereof

Abstract

The invention discloses a micro propeller and a preparation method thereof. The micro propeller comprises a silicon substrate provided with a heating chamber and a Laval nozzle, an outlet of the heating chamber is communicated with the Laval nozzle, and the heating chamber is used for containing ultrapure water; the heating electrode is arranged on the silicon substrate, at least part of the heating electrode is located on the heating chamber so as to make contact with the ultrapure water in the heating chamber, and the heating electrode is electrically connected with an external power source; and the glass substrate is arranged on the silicon substrate and the heating electrode. In the invention, the heating chamber and the Laval nozzle are directly integrated on the silicon substrate, and the heating electrode is arranged above the heating chamber for accommodating the ultrapure water, so that the controlled phase change evaporation of the ultrapure water is realized to generate corresponding thrust; therefore, the stable attitude control impulse can be provided on the premise that the volume mass of small satellites such as a cubesat or a nanosatellite platform is not obviously increased.

Description

Technical Field

[0001] This invention relates to the field of propulsion technology, and in particular to a micro-propulsion device and its manufacturing method. Background Technology

[0002] With the continuous miniaturization of electronic systems and sensor technologies, nanoscale and microsatellites (such as CubeSats) have emerged. These platforms possess extremely low mass and power consumption, enabling them to perform comparable or even more flexible missions at a significantly lower cost than traditional large spacecraft. Against the backdrop of rapid development in the aerospace industry, economics has become a core driving force for technological evolution, prompting the gradual replacement of traditional large, complex, and expensive systems with small, lightweight, low-cost, and reliable satellites. Since launch costs are closely related to the mass and volume of the payload, the economic advantages of small satellites are becoming increasingly prominent, enabling academic institutions, developing countries, startups, and even emerging user groups such as high schools to participate in space missions.

[0003] Currently, small satellites such as pico-satellites and nanosatellites are widely used in short-term surveillance, communication relay, orbit insertion, telemetry support in shadowed regions, and upper atmosphere mapping missions in low Earth orbit, lunar orbit, and planetary orbits, demonstrating significant advantages in cost-effectiveness and rapid deployment. However, these platforms still face prominent challenges in propulsion: existing propulsion technologies are often bulky and difficult to integrate, making it impossible to provide high-precision attitude control and orbital maneuvering capabilities for small satellites without excessively increasing system mass. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a micro-thruster and its manufacturing method, so as to solve the problems of large structural volume and difficulty in integration of existing micro-satellite propulsion technology.

[0005] In one aspect of the invention, a micro-thruster is provided. The micro-thruster includes: A silicon substrate is provided with a heating chamber and a Laval nozzle, the outlet of the heating chamber is connected to the Laval nozzle, and the heating chamber is used to contain ultrapure water; A heating electrode is disposed on the silicon substrate and at least partially located on the heating chamber to contact ultrapure water in the heating chamber, and the heating electrode is electrically connected to an external power source. A glass substrate is disposed on the silicon substrate and the heating electrode.

[0006] In some embodiments, the Laval nozzle includes, in sequence, a tapering section, a throat, and a expanding section in the extending direction. One end of the throat is connected to the tapering section, and the other end of the throat is connected to the expanding section. The width of the tapering section gradually decreases in the extending direction, and the width of the expanding section gradually increases in the extending direction.

[0007] In some embodiments, the micro-thruster further includes an elastic membrane and an induction electrode assembly. The glass substrate is disposed on the elastic membrane and has a perforated portion. The perforated portion and the elastic membrane form a liquid metal tank. The liquid metal tank is correspondingly disposed with the Laval nozzle and is used to hold liquid metal. The induction electrode assembly includes a first liquid metal induction electrode and a second liquid metal induction electrode. The first liquid metal induction electrode is disposed above the glass substrate, and the second liquid metal induction electrode is disposed below the silicon substrate and correspondingly disposed with the Laval nozzle.

[0008] In some embodiments, the liquid metal tank includes a storage tank and a descending channel tank that are in communication with each other, the descending channel tank being located below the storage tank.

[0009] In some embodiments, the micro-propulsion device further includes an adhesive layer through which the heating electrode is adhered to the bottom of the elastic membrane.

[0010] In some embodiments, the micro-thruster further includes a liquid metal pressurized water reservoir, which includes a liquid metal vertical pump. The liquid metal vertical pump has an ultrapure water storage area for storing ultrapure water, and the liquid metal vertical pump also has an outlet communicating with the ultrapure water storage area. The liquid metal pressurized water reservoir is used to supply ultrapure water to the inlet of the thruster through the outlet.

[0011] In some embodiments, the liquid metal vertical pump is further provided with a liquid metal storage area and an inert gas isolation layer. The liquid metal storage area is used to store liquid metal and is located at the bottom of the liquid metal vertical pump. The inert gas isolation layer contains inert gas and is located between the ultrapure water storage area and the liquid metal storage area.

[0012] In some embodiments, an electrical connection groove and an electrical connection hole are formed on the silicon substrate. The electrical connection groove and the electrical connection hole are arranged in a one-to-one correspondence and are connected to each other. The electrical connection groove is used to accommodate part of the heating electrode, and the electrical connection hole is used to connect the electrical connection mechanism.

[0013] In another aspect of the present invention, a method for fabricating a micro-thruster is provided, the method comprising the following steps: Electrical connection grooves, Laval nozzles, heating chambers, and liquid inlets are sequentially formed on a silicon wafer through photolithography and etching processes to form a wafer intermediate. Electrical connections are formed on the wafer intermediate by coating, photolithography and etching processes to obtain a silicon substrate; A glass wafer is obtained, and photolithography, coating and lift-off processes are performed on the glass wafer in sequence to form an adhesion layer and heating electrodes under the glass wafer, thereby obtaining a glass substrate with adhesion heating electrodes. The silicon substrate and the glass substrate with the adhesive heating electrode are bonded together and then cut. Liquid metal is then injected into the liquid metal tank of the glass substrate, and the first liquid metal induction electrode and the second liquid metal induction electrode are bonded to the upper and lower surfaces respectively to obtain a micro-propeller.

[0014] In another aspect of the present invention, a method for fabricating a micro-thruster is provided, the method comprising the following steps: On a silicon wafer, the throat region of the Laval nozzle is formed sequentially through photolithography and etching processes; Electrical connection grooves are formed on the silicon wafer through photolithography and etching processes in sequence; On the silicon wafer, a heating chamber and a nozzle inlet communicating with the heating chamber are formed sequentially through photolithography and etching processes; On the silicon wafer, a liquid inlet is formed sequentially through photolithography and etching processes; The silicon wafer is sequentially coated, photolithographically etched, and etched to form electrical connection holes and nozzle outlets that penetrate the silicon wafer, thereby obtaining a silicon substrate; On a glass wafer, photolithography, coating and lift-off processes are sequentially performed to form an adhesion layer and a heating electrode under the glass wafer, thereby obtaining a glass substrate with an adhesion heating electrode. The silicon substrate and the glass substrate with the adhesive heating electrode are bonded together and then cut. Liquid metal is then injected into the liquid metal tank of the glass substrate, and the first liquid metal induction electrode and the second liquid metal induction electrode are bonded to the upper and lower surfaces respectively to obtain a micro-propeller.

[0015] The beneficial effects of this invention are as follows: by directly integrating the heating chamber and Laval nozzle onto the silicon substrate, and placing a heating electrode above the heating chamber for containing ultrapure water, ultrapure water can be used as the propellant to generate reverse thrust on a highly miniaturized and integrated basis. In summary, the micro-thruster of this invention has a highly compact structure, low power requirements, and can provide stable attitude control impulse without significantly increasing the volume and mass of small satellites such as CubeSats or nanosatellite platforms. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the micro-thruster described in this invention from one perspective under one embodiment.

[0017] Figure 2 This is an exploded view of the micro-thruster described in one embodiment of the present invention from one perspective.

[0018] Figure 3 This is an exploded view of another structure of the micro-thruster described in one embodiment of the present invention, viewed from one perspective.

[0019] Figure 4 This is a schematic diagram of the propeller body in the micro-propeller of the present invention from one perspective in one embodiment.

[0020] Figure 5 This is a schematic diagram of the propeller body in the micro-propeller of the present invention from another perspective in one embodiment.

[0021] Figure 6 This is an exploded view of the main body of the micro-thruster in one embodiment of the present invention from one perspective.

[0022] Figure 7 This is an exploded view of the main body of the micro-thruster described in this invention, with some structural elements hidden.

[0023] Figure 8 This is a schematic diagram of the silicon substrate in the micro-thruster described in this invention.

[0024] Figure 9 for Figure 8 The diagram shows the structure at point A on the silicon substrate.

[0025] Figure 10 This is a top view of the propeller body in one embodiment of the micro-propeller described in this invention.

[0026] Figure 11 for Figure 10 The diagram shows a cross-sectional view of the silicon substrate.

[0027] Figure 12 This is a top view of the micro-thruster described in one embodiment of the present invention.

[0028] Figure 13 for Figure 12 The diagram shows a cross-sectional view of the micro-thruster.

[0029] Figure 14 This is an exploded view of the liquid metal vertical pump in the micro-thruster of the present invention from one perspective, according to one embodiment.

[0030] Label Explanation: 1. Thruster body; 2. Silicon substrate; 21. Liquid inlet; 22. Heating chamber; 23. Laval nozzle; 24. Tapered section; 25. Throat; 26. Diverging section; 27. Electrical connection groove; 28. Electrical connection hole; 3. Heating electrodes; 4. Adhesive layer; 5. Elastic membrane; 6. Glass substrate; 61. Liquid metal tank; 62. Storage tank; 63. Descent channel tank; 7. Induction electrode assembly; 71. First liquid metal induction electrode; 72. Second liquid metal induction electrode; 8. Liquid metal pressurized water tank; 81. Water tank body; 82. Liquid metal vertical pump; 83. Ultrapure water storage area; 84. Inert gas isolation layer; 85. Liquid metal storage area; 86. Graphite electrode; 87. Opening; 88. Filter screen; 89. Receiving cavity; 9. Top cover; 91. Slot; 92. Notch; 93. Bolt. Detailed Implementation

[0031] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0032] With the continuous miniaturization of electronic systems and sensor technologies, nanoscale and microsatellites (such as CubeSats) have emerged. These platforms possess extremely low mass and power consumption, enabling them to perform comparable or even more flexible tasks at a cost far lower than traditional large spacecraft. Against the backdrop of rapid development in the aerospace industry, economics has become a core driving force for technological evolution, prompting the gradual replacement of traditional large, complex, and expensive systems with small, lightweight, low-cost, and reliable satellites. Since launch costs are closely related to the mass and volume of the payload, the economic advantages of small satellites are becoming increasingly prominent, enabling academic institutions, developing countries, startups, and even emerging user groups such as high schools to participate in space missions. Currently, small satellites such as picosatellites and nanosatellites are widely used in short-term surveillance, communication relay, orbit insertion, shadowed region telemetry support, and upper atmosphere mapping missions in low Earth orbit, lunar orbit, and planetary orbits, demonstrating significant advantages in cost-effectiveness and rapid deployment.

[0033] However, some key bottlenecks remain in this field: there is currently a lack of a mature, compact, and efficient propulsion technology that can provide adjustable thrust and high-precision attitude control for such micro-platforms without excessively increasing system mass. Although traditional propulsion systems have attempted miniaturization improvements, and various novel propulsion schemes (such as cold gas propulsion, electrospray, and ionic liquid propulsion) are in the exploratory stage, they still have limitations in terms of specific impulse, power requirements, integration complexity, or operational lifespan.

[0034] On the other hand, in existing micro-thruster technologies, the nozzle geometry is typically fixed during the manufacturing stage, and the throat size, expansion ratio, and overall flow channel shape cannot be dynamically adjusted during operation. Therefore, the thrust and specific impulse of the thruster can only be indirectly adjusted by changing input power, heating temperature, or flow conditions. This not only limits the adjustment range but also often results in slow response speed, reduced efficiency, or increased energy consumption. Especially in microscale propulsion systems, fluid behavior is significantly affected by interfacial forces, phase change dynamics, and microchannel effects. Relying solely on power adjustment makes it difficult to achieve large-scale, rapid, and stable performance control, and it cannot meet the differentiated thrust and specific impulse requirements of different flight phases. Furthermore, the fixed nozzle structure limits the adaptability of micro-thrusters in complex mission environments. For example, when a mission requires high specific impulse to improve orbital maneuverability or high thrust to cope with instantaneous loads, traditional thrusters struggle to achieve both types of performance indicators within the same structure, leading to a decrease in the mission flexibility and overall efficiency of the propulsion system.

[0035] Please refer to Figure 1 , Figure 2 as well as Figure 3 This invention provides a micro-thruster, comprising a thruster body 1, which includes a silicon substrate 2, a heating electrode 3, and a glass substrate 6. The silicon substrate 2 has a heating chamber 22 and a Laval nozzle 23, the outlet of which communicates with the Laval nozzle 23. The heating chamber 22 is used to contain ultrapure water. The heating electrode 3 is disposed on the silicon substrate 2 and at least partially located on the heating chamber 22 to contact the ultrapure water in the heating chamber 22. The heating electrode 3 is electrically connected to an external power source. The glass substrate 6 is disposed on the silicon substrate 2 and the heating electrode 3.

[0036] It should be noted that the micro-thruster of the present invention uses ultrapure water as the propellant. The ultrapure water is precisely delivered to the heating chamber 22 through the inlet 21 and related microchannels located on the silicon substrate 2. Based on this, the working principle of the micro-thruster of the present invention is as follows: (1) A heating electrode 3 is integrated at the bottom of the heating chamber 22. The electrode is made of a metal material with specific resistance characteristics. When a current (a relatively large power input) is applied to the heating electrode 3 through an external power source, the heating electrode 3 generates heat rapidly due to the Joule effect (i.e., the temperature rises rapidly). Since the ultrapure water in the heating chamber 22 is in direct contact with the heating electrode 3, the heating electrode 3 can quickly conduct heat to the ultrapure water in direct contact with it. When the ultrapure water is heated and vaporized into water vapor, the water vapor expands in volume compared to the ultrapure water, causing the pressure in the heating chamber 22 to rise. Under the pressure difference, the high-pressure gas is ejected at high speed through the Laval nozzle 23. According to the principle of conservation of momentum, the micro-thruster can obtain thrust opposite to the direction of the jet. (2) In the initial non-working state, due to the surface tension of ultrapure water, the propellant will form a stable meniscus at the throat 25 of the Laval nozzle 23 at the micrometer scale. This meniscus is maintained by the balance between the liquid surface tension and the static pressure inside the cavity, thereby effectively preventing leakage of the propellant when there is no drive. When the heating electrode 3 is energized (small current), since the ultrapure water in the heating chamber 22 is in direct contact with the heating electrode 3, the heat generated by the heating electrode 3 is rapidly transferred to the ultrapure water in contact with it through direct heat conduction. As the local water temperature rises, the surface tension of the water decreases significantly (it should be noted that surface tension is very sensitive to temperature; the higher the temperature, the lower its value). When the surface tension drops to the point where it can no longer maintain the balance of the meniscus at the throat 25, the ultrapure water will break through the capillary constraint and flow into the diffuser section 26 of the Laval nozzle 23. At this time, since the micro-thruster is operating in a near-vacuum environment in space, the superheated water or saturated steam entering the diffuser section 26 of the Laval nozzle 23 undergoes violent vaporization (i.e., "vacuum boiling" or "flash vaporization") under extremely low environmental pressure. The volume expands rapidly and is transformed into a high-speed steam flow, which is then ejected through the Laval nozzle 23. The high-speed ejected steam generates a reaction force. According to the principle of conservation of momentum, the micro-thruster thus obtains thrust in the opposite direction.

[0037] As can be seen from the above description, the beneficial effects of the present invention are as follows: by directly integrating the heating chamber 22 and the Laval nozzle 23 onto the silicon substrate 2, and configuring the heating electrode 3 above the heating chamber 22 for containing ultrapure water, ultrapure water can be used as the propellant to generate reverse thrust based on high miniaturization and integration. In summary, the micro-thruster of the present invention has a highly compact structure, low power requirements, and can provide stable attitude control impulse without significantly increasing the volume and mass of small satellites such as CubeSats or nanosatellite platforms.

[0038] In some embodiments, such as Figure 9As shown, the Laval nozzle 23 sequentially includes a tapering section 24, a throat 25, and a expanding section 26 in the extending direction. One end of the throat 25 is connected to the tapering section 24, and the other end is connected to the expanding section 26. The width of the tapering section 24 gradually decreases in the extending direction, while the width of the expanding section 26 gradually increases in the extending direction. In practical applications, the throat 25 can have various configurations. For example, the width of the throat 25 in the extending direction can remain constant. Alternatively, the throat 25 can be divided into two connected segments: the first segment connects to the tapering section 24 and its width gradually decreases in the extending direction, while the second segment connects to the expanding section 26 and its width gradually increases in the extending direction. This is not limited here. It should be noted that the extending direction refers to the width direction of the rectangular silicon substrate 2, and it is the direction from the liquid inlet 21 towards the Laval nozzle 23.

[0039] As described above, by defining the converging-throat 25-expanding structure of the Laval nozzle 23, the converging section 24 accelerates the ultrapure water to the throat 25 to reach the speed of sound, the throat 25 serves as the key control section for flow rate and velocity, and the expanding section 26 further expands and accelerates the sonic flow to supersonic speed, maximizing the conversion of the internal energy of the working fluid into directional kinetic energy, thereby maximizing the jet speed and improving propulsion efficiency, enabling the propulsion device to obtain a higher specific impulse under microscale and limited working fluid and energy input.

[0040] In some embodiments, such as Figure 5 , Figure 6 as well as Figure 7 As shown, the micro-thruster also includes an elastic membrane 5 (such as a PDMS elastic membrane 5) and an induction electrode assembly 7. A glass substrate 6 is disposed on the elastic membrane 5 and has a perforated portion. The perforated portion and the elastic membrane 5 form a liquid metal tank 61. The liquid metal tank 61 is correspondingly disposed with the Laval nozzle 23 and is used to hold liquid metal. The induction electrode assembly 7 includes a first liquid metal induction electrode 71 and a second liquid metal induction electrode 72. The first liquid metal induction electrode 71 is disposed above the glass substrate 6, and the second liquid metal induction electrode 72 is disposed below the silicon substrate 2 and correspondingly disposed with the Laval nozzle 23. In practical applications, the liquid metal in the liquid metal tank can be directionally driven by energizing the first liquid metal induction electrode 71 and the second liquid metal induction electrode 72. When energized, the entire liquid metal can be induced to gather and move toward the second liquid metal induction electrode 72 (i.e. toward the nozzle throat) by controlling the polarity of the upper and lower induction electrodes (e.g., the second liquid metal induction electrode 72 is connected to positive voltage, grounded or negative voltage).

[0041] It should be noted that, according to the Navier-Stokes equations and related numerical simulation results, for a Laval nozzle with a converging section 24—throat 25—diverging section 26 structure, the cross-sectional area of ​​the throat 25 is a key parameter determining its flow rate, velocity, and expansion ratio, directly affecting the flow state at the nozzle exit and the overall performance of the propeller. Specifically, reducing the cross-sectional area of ​​the throat 25 will decrease the working fluid mass flow rate, allowing the fluid per unit mass to expand and accelerate more fully within the nozzle, thereby increasing the exit velocity and specific impulse. Simultaneously, due to the enhanced expansion, the proportion of fluid converting from internal energy to kinetic energy increases, and the exit temperature decreases. Conversely, increasing the cross-sectional area of ​​the throat 25 can increase the flow rate, but the exit velocity and specific impulse will decrease accordingly; this represents a typical trade-off between thrust and specific impulse.

[0042] Based on the above mechanism, this invention uses liquid metal as the actuating medium to achieve dynamic adjustment of the effective cross-sectional area of ​​the throat 25 of the Laval nozzle 23. The specific implementation is as follows: A liquid metal tank 61 is etched into a glass substrate 6, and liquid metal is injected into the tank 61. A PDMS elastic film 5 is bonded to the lower surface of the glass substrate 6, and a first liquid metal induction electrode 71 is provided on the upper surface, thereby sealing the liquid metal within the tank. Simultaneously, this invention also places a second liquid metal induction electrode 72 below the silicon substrate 2 and correspondingly positioned to the Laval nozzle 23. When a voltage is applied to the first liquid metal induction electrode 71 and the second liquid metal induction electrode 72, the generated electric field drives the liquid metal to move towards the lower second liquid metal induction electrode 72 (i.e., the silicon substrate 2). Due to the constraint of the PDMS elastic membrane 5, the liquid metal does not enter the nozzle flow channel. Instead, it drives the PDMS elastic membrane 5 to undergo controllable micro-scale deformation, such as localized micro-convex downward deformation under pressure, thereby changing the equivalent flow area of ​​the throat 25 of the corresponding Laval nozzle 23 below it. When the external electric field is removed, the driving force on the liquid metal disappears, and the PDMS elastic membrane 5 rebounds to its initial shape under its own elastic restoring force. The liquid metal then returns to its original position, and the cross-sectional area of ​​the nozzle throat 25 also returns to its original state. This structure enables rapid, reversible, and precise adjustment of the cross-sectional area of ​​the throat 25, thereby allowing the thruster to flexibly optimize thrust and specific impulse performance under different operating conditions.

[0043] As described above, by forming a liquid metal tank 61 between the glass substrate 6 and the elastic membrane 5, and configuring upper and lower induction electrodes, the effective cross-sectional area of ​​the nozzle throat 25 is dynamically adjusted, thereby introducing a variable geometry structure based on electrostatic drive of liquid metal. Specifically, when an electric field is applied between the first and second liquid metal induction electrodes, the liquid metal moves towards the throat 25 under electrostatic driving force, compressing the elastic membrane 5 to undergo micro-deformation, thereby changing the flow area of ​​the nozzle throat 25 below it and reducing the cross-sectional area of ​​the throat 25; after power is cut off, the elastic membrane 5 rebounds and resets. This mechanism enables the micro-thruster to switch between high thrust (large cross-sectional area throat 25) and high specific impulse (small cross-sectional area throat 25) operating modes in real time at the same power consumption level, breaking through the limitations of fixed performance parameters of traditional micro-thrusters, and significantly improving the adaptability and mission flexibility of microsatellites in different mission phases such as orbital maneuvering and position holding.

[0044] In some embodiments, such as Figure 7 as well as Figure 11 As shown, the liquid metal tank 61 includes a storage tank 62 and a descending channel 63 that are connected to each other, and the descending channel 63 is located below the storage tank 62.

[0045] As described above, the liquid metal tank 61 adopts a double-layer connected structure of storage tank 62 and descending channel tank 63. The upper storage tank 62 with a larger volume provides sufficient liquid metal storage, while the lower narrow descending channel tank 63 precisely guides the positioning flow of liquid metal, ensuring that the liquid metal can accurately and controllably enter or exit the throat 25 influence area under the action of electrostatic drive.

[0046] In some embodiments, such as Figure 6 as well as Figure 7 As shown, the micro-thruster may also include an adhesion layer 4, through which the heating electrode 3 is adhered to the bottom of the elastic membrane 5.

[0047] As described above, by introducing the adhesion layer 4 (such as titanium or chromium), a strong mechanical connection and good electrical contact are achieved between the heating electrode 3 and the elastic film 5 (or glass substrate 6). The adhesion layer 4 (such as titanium or chromium) forms a strong chemical bond between the platinum or other precious metal electrode and the glass or polymer substrate, which greatly enhances the adhesion of the electrode under thermal cycling and mechanical vibration environments and prevents electrode peeling failure.

[0048] In some embodiments, such as Figure 3 as well as Figure 13As shown, the micro-thruster may further include a liquid metal pressurized water reservoir 8, which includes a liquid metal vertical pump 82. The liquid metal vertical pump 82 has an ultrapure water storage area 83 for storing ultrapure water, and also has an outlet communicating with the ultrapure water storage area 83. The liquid metal pressurized water reservoir 8 is used to supply ultrapure water to the inlet 21 of the thruster through the outlet. In practical applications, the ultrapure water is only injected into the inlet 21 and the heating chamber 22 through the liquid metal pressurized water reservoir 8 during operation; in a static state, the heating chamber 22 does not contain ultrapure water.

[0049] In practical applications, such as Figure 2 , Figure 3 as well as Figure 13 As shown, the liquid metal pressurized water reservoir 8 also includes a reservoir body 81, which has a receiving cavity 89 in which the liquid metal vertical pump 82 is located. Meanwhile, the micro-propeller may also include a top cover 9, which is locked to the reservoir body 81 by multiple bolts 93. The top cover 9 also has a slot 91 for securing the propeller body 1, facilitating quick and easy installation. At the bottom of the slot 91, there is a through hole connecting to the ultrapure water storage area 83 inside the liquid metal vertical pump 82, allowing the ultrapure water in the ultrapure water storage area 83 to enter the inlet 21 of the propeller body 1 and gradually reach the Laval nozzle 23.

[0050] As described above, a corresponding liquid metal pressurized water reservoir 8 is provided for the thruster body 1. The liquid metal pressurized water reservoir 8 can quickly and effectively deliver ultrapure water from the reservoir to the thruster inlet when needed, ensuring the effective operation of the thruster body 1. At the same time, the decoupled design of the liquid metal pressurized water reservoir 8 from the thruster body 1 can effectively improve the overall modularity and liquid supply flexibility of the system.

[0051] In some embodiments, such as Figure 2 , Figure 3 as well as Figure 13 As shown, the liquid metal pressurized water storage device 8 also includes two graphite electrodes 86, which are symmetrically arranged on both sides of the liquid metal vertical pump 82. The liquid metal vertical pump 82 is also provided with a liquid metal storage area 85 and an inert gas isolation layer 84. The liquid metal storage area 85 is used to store liquid metal and is located at the bottom of the liquid metal vertical pump 82. The inert gas isolation layer 84 contains inert gas and is located between the ultrapure water storage area 83 and the liquid metal storage area 85.

[0052] In practical applications, such as Figure 13 as well as Figure 14 As shown, the liquid metal vertical pump 82 has a cavity divided into three parts, from bottom to top: a liquid metal storage area 85, an inert gas isolation layer 84, and an ultrapure water storage area 83. The side wall of the liquid metal vertical pump 82 has two symmetrical openings 87 and two filters 88. Each filter 88 covers one opening 87 and has a through hole. The liquid metal storage area 85 communicates with the receiving cavity 89 through these through holes. It should be noted that the area of ​​the receiving cavity 89 not occupied by the liquid metal vertical pump 82 is an annular cavity containing electrolyte. Figure 13 As shown, the bottoms of the two graphite electrodes 86 pass through the water reservoir body 81 to be inserted into the receiving cavity 89, thereby coming into contact with the electrolyte.

[0053] Based on this, the working principle of the liquid metal pressurized water storage device 8 of the present invention is as follows: First, a power connection is made, connecting both graphite electrodes to the positive terminal of an external DC power supply, while simultaneously connecting one of the filter screens to the negative terminal of the power supply, thereby directly connecting the liquid metal (LM) droplet to the negative terminal and ensuring that it remains in an electrochemical reduction state. When a DC voltage is applied, a stable electric field is formed in the electrolyte environment (electrolysis occurs). This electric field acts on the interface between the liquid metal and the electrolyte, causing it to form a double-layer structure, and a surface tension gradient is generated due to the uneven potential distribution. This surface tension gradient triggers the Marangoni effect, that is, this surface tension gradient induces the liquid metal to produce directional flow along the direction of the electric field (such as inducing the liquid metal to flow upward), forming an electrowetting driven flow (also known as the Marangoni flow), thereby realizing the pumping effect on the working fluid. An inert gas isolation layer 84 is also provided between the liquid metal and the ultrapure water storage area 83. This structure effectively prevents direct contact between the liquid metal and its surrounding electrolyte environment and the ultrapure water, ensuring that the physicochemical properties of the two liquids do not affect each other, thereby maintaining the high purity and stability of the ultrapure water working medium. Driven by the Marangoni effect, the continuous upward movement of the liquid metal will exert pressure on the upper inert gas isolation layer 84 and the ultrapure water storage area 83. This pressure forces the ultrapure water to flow into the microchannel of the thruster through the outlet, thereby increasing the local pressure at the thruster inlet and achieving active regulation of its working performance.

[0054] As described above, on the one hand, the inert gas layer (such as nitrogen or argon) forms a physical and chemical barrier between the liquid metal (and its electrolyte environment) and the ultrapure water storage area 83, which can effectively block the contact between the liquid metal and the ultrapure water, avoiding chemical reactions or contamination. On the other hand, by setting up corresponding graphite electrodes 86 to apply an electric field to the liquid metal (such as gallium indium tin alloy), the vertical movement of the liquid metal is driven by electrochemical principles, realizing pressure generation without mechanical moving parts.

[0055] In some embodiments, such as Figure 7 as well as Figure 8 As shown, the silicon substrate 2 has electrical connection grooves 27 and electrical connection holes 28. The electrical connection grooves 27 and electrical connection holes 28 are arranged in a one-to-one correspondence and are interconnected. The electrical connection grooves 27 are used to accommodate part of the heating electrode 3, and the electrical connection holes 28 are used to connect the electrical connection mechanism. In practical applications, the upper cover 9 can be provided with corresponding notches 92 at the positions corresponding to the electrical connection holes 28 to facilitate electrical connection.

[0056] As described above, the integration of electrical connection groove 27 and through electrical connection hole 28 on the silicon substrate 2 provides a standardized electrical interface for the heating electrode 3. The electrical connection groove 27 accommodates and positions the electrode leads, while the electrical connection hole 28 allows wires or conductive springs to be led out from the back side, achieving electrical isolation and convenient connection between the front flow channel structure and the back circuit, and simplifying the packaging process.

[0057] To fabricate the aforementioned micro-thrusters, this invention also provides corresponding fabrication methods for micro-thrusters. It should be noted that this invention provides two microfabrication methods for fabricating Laval nozzles on a silicon substrate 2. These two methods are essentially the same in terms of the overall process flow and the key process equipment used, such as photolithography, etching, and bonding. Their core difference lies in the different cross-sectional structures of the resulting Laval nozzle flow channels.

[0058] The first method aims to fabricate Laval nozzles with uniform groove depths, meaning that the taper section 24, throat 25, and divergence section 26 of the nozzle have the same etching depth over the entire flow channel length. This method specifically includes the following steps: S1, an electrical connection groove 27, a Laval nozzle 23, a heating chamber 22 and a liquid inlet are sequentially formed on a silicon wafer through photolithography and etching processes to form a wafer intermediate; S2, Perform coating, photolithography and etching processes on the wafer intermediate to form electrical connection ports to obtain silicon substrate 2; S3, obtain a glass wafer, and perform photolithography, coating and lift-off processes on the glass wafer in sequence to form an adhesion layer 4 and a heating electrode 3 under the glass wafer, thereby obtaining a glass substrate 6 with the heating electrode 3 attached. S4, the silicon substrate 2 and the glass substrate 6 of the adhesive heating electrode 3 are bonded together and cut. Then, liquid metal is injected into the liquid metal tank 61 of the glass substrate 6, and the first liquid metal induction electrode 71 and the second liquid metal induction electrode 72 are bonded to the upper and lower surfaces respectively to obtain a micro thruster.

[0059] For example, after preparing materials such as silicon wafers (e.g., 300 micrometers thick) and borosilicate glass wafers (e.g., 300 micrometers thick), the propeller of a Laval nozzle with consistent cross-sectional groove depth can be fabricated as follows. It should be noted that during photolithography and other operations, different types of photoresists, such as S1813 or 4620 photoresists, can be selected according to the actual situation. Of course, the conditions for pre-baking and other operations can be set according to the type of photoresist, and are not limited here.

[0060] First, the electrical connection groove 27 is formed. Wafer preparation and cleaning: Ultrapure water is used to remove surface dust from the silicon wafer, followed by the use of piranha solution (a mixture of concentrated sulfuric acid and hydrogen peroxide) to remove the surface oxide layer and organic contaminants, ensuring a clean etch substrate.

[0061] Photolithography: First, a photoresist film is prepared on the wafer surface using a dropper application method combined with a spin coater or direct spraying. Since the etching depth in this step is relatively shallow, the photoresist thickness should be controlled to be above 1 micrometer. Then, the spin-coated wafer is placed on a hot plate for pre-baking. In practical applications, when using S1813 photoresist, the pre-baking conditions can be 115°C for 60 seconds. After pre-baking, the wafer should be allowed to stand for at least 5 minutes to allow the photoresist to fully rehydrate, thus ensuring the accuracy and reliability of subsequent pattern transfer.

[0062] Development: By aligning and exposing the photoresist, specific areas are damaged, followed by post-baking. For example, if S1813 photoresist is used, the wafer can be heated at 110°C for 40 seconds after homogenization using a hot plate before being removed. Then, development is performed to remove unwanted photoresist.

[0063] Deep reactive ion etching (DRIE): After development, a short rinse with piranha solution is performed again to remove the native oxide layer in the exposed areas. Next, deep reactive ion etching is performed to a depth of 1-2 micrometers, forming shallow trenches. Finally, the photoresist on the wafer surface is completely removed.

[0064] Second, the nozzle and heating chamber 22 are formed. Repeat the cleaning process described above to thoroughly clean the silicon wafer.

[0065] Photolithography: First, a photomask is placed or a laser direct-write device is used to form a photoresist layer on the cleaned wafer surface for patterning. Since the etching depth is moderate, a thicker photoresist such as 4620 can be used, and a photoresist layer with a thickness of at least 5 micrometers is formed through a spin coating process. Then, the spin-coated wafer is placed on a hot plate for pre-baking (e.g., pre-baking at 115°C for 60 seconds). After pre-baking, the wafer is allowed to rest for at least 5 minutes to allow the photoresist to fully rehydrate.

[0066] Development: First, alignment and exposure are performed to induce a selective photochemical reaction in the photoresist corresponding to the patterned areas of the mask. After exposure, the wafer is placed on a hot plate and post-baked at 110°C for 40 seconds to stabilize the exposed pattern. Finally, the exposed photoresist areas are removed using a developer, resulting in the desired photoresist mask pattern on the wafer surface.

[0067] Deep reactive ion etching (DRIE): First, the wafer surface is cleaned using a piranha solution to thoroughly remove the oxide layer in the etchable area. After cleaning, deep reactive ion etching is performed, controlling the etching depth to 20 micrometers to form the desired three-dimensional microstructure. After etching, residual photoresist on the wafer surface is removed, completing the transfer of the pattern layer.

[0068] Third, inlet molding Clean the silicon wafer again.

[0069] Photolithography: In the photolithography step, a photoresist film for patterning is first formed on the wafer surface by placing a mask or using a laser direct-write device. Due to the moderate etching depth, a relatively thick photoresist (such as model 4620) is selected, and a photoresist layer with a thickness of not less than 5 micrometers is formed through a spin coating process. A pre-baking process is then performed, where the spin-coated wafer is placed on a hot plate and heated at 115°C for 60 seconds before being removed. Afterward, the wafer is allowed to rest for at least 5 minutes to ensure that the photoresist is fully rehydrated.

[0070] Development: By aligning and exposing, the photoresist area corresponding to the mask pattern undergoes a photochemical reaction. Then, it is placed on a hot plate for post-baking (e.g., post-baking at 110°C for 40 seconds) to stabilize the pattern. Finally, a developer is used to remove the photoresist from the exposed areas, thereby forming the desired photoresist mask pattern on the wafer surface.

[0071] Deep reactive ion etching (DRIE): The wafer surface is cleaned using a piranha solution to remove the oxide layer in the areas to be etched. Then, a deep reactive ion etching process is used to precisely etch to the target depth of 100 micrometers. After etching, the photoresist on the wafer surface is completely removed. Fourth, electrical connection port molding. First, clean the silicon wafer and apply a coating, such as a chromium (Cr) or aluminum (Al) thin film, with a recommended thickness of not less than 200 nanometers.

[0072] Next, photolithography is performed. Specifically, first, photoresist is spin-coated onto the wafer surface using a photomask or laser direct writing. Since this step only requires shallow etching, the photoresist thickness can be controlled to approximately 1 micrometer. Then, pre-baking is performed, for example, by placing the wafer on a 115°C hot plate for 60 seconds, followed by resting for at least 5 minutes to allow the photoresist to fully hydrate.

[0073] Development: Alignment and exposure are performed to alter the properties of the photoresist in the corresponding areas of the mask pattern. After exposure, the wafer can be post-baked to stabilize the pattern (e.g., post-baking at 110°C for 40 seconds). Finally, the wafer is treated with a developer to remove the photoresist from the exposed (or unexposed, depending on the type of photoresist) areas, thus obtaining the photoresist pattern of the metal mask.

[0074] Deep reactive ion etching (DRIE): First, the surface is cleaned with a piranha solution to remove the oxide layer. Then, using the photoresist pattern as a mask, DIE is performed, first etching the exposed metal layer (such as Cr or Al), and then continuing to etch the silicon material until a through-hole structure with a depth of 300 micrometers is formed, penetrating the silicon wafer. After etching, the remaining metal mask layer and photoresist are removed.

[0075] Fifth, the heating electrode 3 is formed. In the fabrication of the 6-electrode on the glass substrate, the glass wafer is first cleaned to remove surface dust. Then, photolithography patterning is performed: a layer of adhesive is spin-coated, followed by photoresist, forming a layer with a total thickness of approximately 1 micrometer. After exposure via a mask or laser direct writing, pre-baking (e.g., pre-baking at 115°C for 60 seconds) is performed, followed by a 5-minute resting period to allow the photoresist to rehydrate. Next, development is performed: specific areas of the photoresist are disrupted through alignment and exposure, and the wafer after homogenization is heated using a hot plate (e.g., heating the wafer after homogenization at 110°C for 40 seconds), then removed and developed to form the electrode pattern. Subsequently, a titanium adhesive layer 4 approximately 2 nanometers thick and a platinum electrode layer approximately 18 nanometers thick are sequentially deposited using magnetron sputtering or electron beam evaporation. Finally, excess metal is removed through a stripping process: the wafer is heated in an NMP solution in a water bath for more than 1 hour, then immersed in acetone for more than 1 hour, rinsed with deionized water, and dried to obtain the desired patterned titanium / platinum thin film electrode.

[0076] Sixth, bonding packaging and slicing Anodic bonding: The prepared silicon substrate 2 and the glass substrate 6 with electrodes are precisely aligned using optical alignment marks, so that the microfluidic cavity on the silicon substrate 2 is sealed and bonded to the glass substrate 6. Anodic bonding is performed under appropriate temperature and voltage conditions to form strong chemical bonds at the silicon-glass interface, thereby encapsulating and forming a closed microfluidic system.

[0077] Slicing: After bonding is completed, the entire wafer is cut along the preset cutting path using a grinding wheel dicing machine. Then, liquid metal is injected into the liquid metal tank 61 of the glass substrate 6, and the first liquid metal induction electrode 71 and the second liquid metal induction electrode 72 are bonded to the upper and lower surfaces respectively to obtain a micro-propeller.

[0078] As described above, the fabrication of the thin-film evaporation micro-propeller can be completed through the above steps. This method has a clear process, is compatible with standard MEMS production lines, and is conducive to achieving efficient and consistent device manufacturing.

[0079] The second method aims to fabricate a Laval nozzle with variable groove depth. In this structure, the converging section 24, throat 25, and diverging section 26 of the nozzle are designed with different etching depths. For example, the depth of the throat 25 region can be intentionally made shallower to form a critical flow control section; while the depth of the diverging section 26 can be increased or even penetrate the substrate to facilitate sufficient expansion and acceleration of the working fluid. This variable depth design, through precise control of the three-dimensional geometry of the flow channel, can further optimize the expansion process and flow characteristics of the working fluid at the microscale, thereby potentially improving the performance parameters of the propulsion unit, such as specific impulse or thrust adjustment range. Specifically, the second fabrication method described above includes the following steps: S1, on a silicon wafer, the throat 25 region of the Laval nozzle 23 is formed sequentially through photolithography and etching processes; S2, Electrical connection grooves 27 are formed on the silicon wafer by photolithography and etching processes in sequence; S3, on the silicon wafer, a heating chamber 22 and a nozzle inlet communicating with the heating chamber 22 are formed sequentially by photolithography and etching processes; S4, On the silicon wafer, a liquid inlet is formed sequentially through photolithography and etching processes; S5, coating, photolithography and etching processes are sequentially performed on the silicon wafer to form an electrical connection hole 28 penetrating the silicon wafer and a nozzle outlet to obtain a silicon substrate 2; S6, on the glass wafer, photolithography, coating and lift-off processes are sequentially performed to form an adhesion layer 4 and a heating electrode 3 under the glass wafer, thereby obtaining a glass substrate 6 with the heating electrode 3 adhered to it; S7, the silicon substrate 2 and the glass substrate 6 of the adhesive heating electrode 3 are bonded together and cut, then liquid metal is injected into the liquid metal tank 61 of the glass substrate 6, and the first liquid metal induction electrode 71 and the second liquid metal induction electrode 72 are bonded to the upper and lower surfaces respectively, thereby obtaining a micro-propeller.

[0080] For example, after preparing materials such as silicon wafers (e.g., with a thickness of 300 micrometers) and glass wafers (e.g., with a thickness of 300 micrometers), the propeller fabrication method for the variable depth Laval nozzle 23 is as follows: First, the nozzle throat is shaped at 25mm. First, the silicon wafer undergoes two cleaning processes: first, ultrapure water is used to remove surface dust, and then piranha solution is used to remove the oxide layer and organic matter. Next, photolithography is performed: a mask is placed or laser direct writing is used to spin-coat photoresist onto the wafer surface. Due to the small 25-inch linewidth and shallow etching depth (1-2 micrometers) in the throat area, a thin layer of photoresist is required to ensure pattern accuracy, with the photoresist thickness controlled at approximately 1 micrometer (corresponding to a spin coater speed of 3000-4000 rpm). Afterward, pre-baking (e.g., 115°C, 60 seconds) is performed, followed by a 5-minute resting period to allow the photoresist to hydrate. Then, alignment exposure, post-baking (e.g., 110°C, 40 seconds), and development are completed. Finally, the etched area is cleaned with piranha solution, deep reactive ion etching is performed to a depth of 1-2 micrometers, and the photoresist is removed.

[0081] Second, the electrical connection groove 27 is formed. The silicon wafer is cleaned again. Photolithography is performed to form the electrical connection trench 27 pattern: spin-coating photoresist to a thickness of 1 micrometer or more (corresponding to a spin coater speed of 2000-3000 rpm, to simultaneously protect the formed throat 25), followed by pre-baking (e.g., 115°C, 60 seconds) and resting for 5 minutes. Then, exposure, post-baking (e.g., 110°C, 40 seconds) and development are completed. Afterward, the wafer is cleaned with piranha solution, and deep reactive ion etching is performed to a depth of 1-2 micrometers to form shallow trenches before removing the photoresist.

[0082] Third, the heating chamber 22 and the nozzle inlet are formed. Clean the silicon wafer. Perform photolithography to define the heating chamber 22 and the nozzle inlet pattern: using a thicker photoresist (e.g., model 4620, thickness ≥ 5 micrometers), pre-baking (e.g., 115°C, 60 seconds), resting for 5 minutes, exposure, post-baking (e.g., 110°C, 40 seconds), and development. Subsequently, clean with piranha solution and perform deep reactive ion etching to a depth of 20 micrometers to form the heating chamber and nozzle inlet flow channel. After completion, remove the photoresist.

[0083] Fourth, inlet molding. Clean the silicon wafer. Perform photolithography to define the liquid inlet pattern: using thick photoresist (≥5 micrometers thick), sequentially perform pre-baking (e.g., 115°C, 60 seconds), resting, exposure, post-baking (e.g., 110°C, 40 seconds), and development. Subsequently, clean with piranha solution, perform deep reactive ion etching to a depth of 100 micrometers to form the liquid inlet channel, and then remove the photoresist.

[0084] Fifth, the electrical connection hole 28 is formed with the nozzle outlet. Clean the silicon wafer. First, deposit a layer of chromium (preferably) or aluminum as a metal hard mask on the surface, with a thickness of not less than 200 nanometers (250 nanometers recommended). Then, perform photolithography to pattern the metal mask: spin-coat a photoresist of about 1 micrometer thickness, followed by pre-baking (e.g., 115°C, 60 seconds), resting, exposure, post-baking (e.g., 110°C, 40 seconds), and development. Then, clean with piranha solution and perform deep reactive ion etching: first etch away the exposed metal layer, then continue etching the silicon material until a depth of 300 micrometers is reached and penetrates the wafer, forming electrical connection vias and nozzle exits. Finally, remove the remaining metal mask layer.

[0085] Sixth, electrode forming Clean the surface of the glass wafer. Perform photolithography to define the pattern of the heating electrode 3: first spin-coat the adhesive and pre-bake as required, then spin-coat the photoresist, with a total thickness of approximately 1 micrometer; followed by pre-baking (e.g., 115°C, 60 seconds), resting, exposure, post-baking (e.g., 110°C, 40 seconds), and development. Next, use magnetron sputtering or electron beam evaporation to sequentially deposit a titanium adhesive layer 4 approximately 2 nanometers thick and a platinum electrode layer approximately 18 nanometers thick. Finally, form the electrodes through a lift-off process: place the wafer in an NMP solution and heat in a water bath for more than 1 hour, then immerse it in acetone for more than 1 hour, rinse with deionized water, and dry.

[0086] Seventh, bonding and slicing The silicon substrate 2, after processing, is precisely aligned with the glass substrate 6 containing electrodes using alignment marks, and then firmly bonded together using an anodic bonding process. After bonding, a dicing machine is used to cut along a preset dicing path to separate individual micro-assist chip pieces.

[0087] Eighth, assembly Liquid metal (such as gallium indium tin alloy) is injected into a specific storage and transport tank on the glass substrate 6 using a micro-syringe. Subsequently, the corresponding induction electrodes are installed on the upper and lower designated surfaces of the chip, and electrical connections are completed by selecting appropriate bonding or fixing processes (such as using conductive adhesive) according to the electrode materials, ultimately resulting in a fully functional thruster unit.

[0088] As described above, by using multiple independent etching processes to process structures of different depths, first etching the shallow groove in the throat 25, then etching the heating chamber 22, and finally forming the outlet through the silicon wafer, the depth gradient of each section of the variable-depth Laval nozzle 23 can be precisely controlled, meeting the structural manufacturing requirements of wide-range thrust / specific impulse adjustment.

[0089] In an optional embodiment, since the micro-thruster may also include components such as a liquid metal pressurized water reservoir 8 and an upper cover 9, while preparing the above-mentioned thruster body 1, the liquid metal pressurized water reservoir 8 and the upper cover 9 may also be prepared by corresponding molds and other equipment. After the thruster body 1 is prepared, it can be directly embedded into the slot 91 of the upper cover 9 to obtain the micro-thruster of the present invention.

[0090] It should be noted that the structural parameters of the thruster body 1 of the micro-thruster obtained based on the above two preparation methods can be as follows.

[0091] The silicon substrate 2 is fabricated from pure silicon wafers, and the dimensions and other parameters of the various structures fabricated on it are as follows: (1) Liquid inlet: depth of 100 micrometers to 150 micrometers, width of 2000 micrometers to 4000 micrometers. (2) Heating chamber 22: rectangular, length of 3000 micrometers to 5000 micrometers, width of 1000 micrometers to 3000 micrometers. Its inlet is connected to the liquid inlet, and its outlet is connected to the Laval nozzle 23. (3) Laval nozzle 23: an array-arranged contraction-expansion structure. The inlet width is 10 micrometers to 40 micrometers, the throat width is 1 micrometer to 10 micrometers, the outlet width is 5 micrometers to 15 micrometers, and the depth is 20 micrometers. In the second fabrication method described above, the depth of the Laval nozzle 23 structure is adjustable: the inlet depth is the same as the depth of the heating chamber 22, the throat depth can vary from 1 micrometer to 20 micrometers, and the outlet depth is 20 micrometers or penetrates the entire thickness of the silicon substrate 2. (4) Electrical connection groove 27: with a depth of 0.5 micrometers to 2 micrometers, used to accommodate part of the heating electrode 3 and prevent the working fluid from overflowing. (5) Electrical connection hole 28: penetrating the silicon substrate 2, used to connect external wires, conductive springs and other electrical connection structures.

[0092] The glass substrate 6 is made of BF33 borosilicate glass and is used for anodic bonding with the silicon substrate 2. The following structures are prepared on it: (1) Adhesion layer 4: made of titanium or chromium, with a thickness of 2 to 10 nanometers, used to enhance the adhesion between the heating electrode 3 and the glass substrate 6. (2) Heating electrode 3: made of platinum (Pt), with a thickness of 18 to 30 nanometers, constituting the heating electrode 3. (3) Liquid metal tank 61: divided into upper and lower layers. The upper layer is a liquid metal storage tank 62, which is rectangular in shape, with a width of 500 to 2000 micrometers, a length of 2000 to 3000 micrometers, and a depth of 150 to 200 micrometers. The lower layer is a liquid metal descending channel tank 63, which is rectangular in shape, with a width of 5 to 20 micrometers, a length similar to that of the upper tank, and a depth of 100 to 150 micrometers.

[0093] The aforementioned liquid metal pressurized water reservoir 8 is connected to the propulsion unit and includes a liquid metal vertical pump 82 and a graphite electrode 86. The graphite electrode 86 is rod-shaped and has a length of 30 mm to 50 mm. The liquid metal vertical pump 82 includes an electrolyte (such as sodium hydroxide solution), liquid metal (such as gallium indium tin alloy), a filter (such as an aluminum filter), and an inert gas isolation layer 84. The inert gas isolation layer 84 is located between the liquid metal and ultrapure water to isolate them. The ultrapure water layer stores the propellant. The aforementioned top cover 9, fastening screws, and O-rings are used for overall encapsulation and sealing. The fastening screws can be M3 or M4, and the O-rings can have a cross-sectional diameter of 1 mm or 2 mm and an outer diameter of 10 mm to 30 mm.

[0094] In summary, the present invention provides a micro-thruster and its fabrication method: This invention discloses a radio-frequency heated liquid evaporation micro-thruster, aiming to achieve miniaturization, easy integration, and high specific impulse at low power by utilizing microscale thermal management and phase change principles, thus overcoming the current limitations of CubeSats in terms of maneuverability and mission flexibility. Furthermore, by introducing a liquid metal actuation method, this invention enables the micro-thruster to adjust the cross-sectional area of ​​the throat of the Laval nozzle 23 in real time during operation. This allows the thruster to achieve wide-range controllable adjustment of key performance parameters such as thrust and specific impulse without significantly altering power consumption, providing a technical foundation for multi-mode, high-efficiency operation of micro-thrusters.

[0095] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention's specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A miniature thruster, characterized in that, include: A silicon substrate is provided with a heating chamber and a Laval nozzle, the outlet of the heating chamber is connected to the Laval nozzle, and the heating chamber is used to contain ultrapure water; A heating electrode is disposed on the silicon substrate and at least partially located on the heating chamber to contact ultrapure water in the heating chamber, and the heating electrode is electrically connected to an external power source. A glass substrate is disposed on the silicon substrate and the heating electrode.

2. The micro-thruster according to claim 1, characterized in that, The Laval nozzle includes, in sequence, a tapering section, a throat, and a expanding section in the extending direction. One end of the throat is connected to the tapering section, and the other end of the throat is connected to the expanding section. The width of the tapering section gradually decreases in the extending direction, and the width of the expanding section gradually increases in the extending direction.

3. The micro-thruster according to claim 1, characterized in that, It also includes an elastic membrane and an induction electrode assembly. The glass substrate is disposed on the elastic membrane and has a perforated portion. The perforated portion and the elastic membrane form a liquid metal tank. The liquid metal tank is correspondingly disposed with the Laval nozzle and is used to hold liquid metal. The induction electrode assembly includes a first liquid metal induction electrode and a second liquid metal induction electrode. The first liquid metal induction electrode is disposed above the glass substrate, and the second liquid metal induction electrode is disposed below the silicon substrate and is correspondingly disposed with the Laval nozzle.

4. The micro-thruster according to claim 3, characterized in that, The liquid metal tank includes a storage tank and a descending channel tank that are connected to each other, the descending channel tank being located below the storage tank.

5. The micro-thruster according to claim 3, characterized in that, It also includes an adhesive layer, through which the heating electrode is adhered to the bottom of the elastic membrane.

6. The micro-thruster according to claim 1, characterized in that, It also includes a liquid metal pressurized water storage device, which includes a liquid metal vertical pump. The liquid metal vertical pump has an ultrapure water storage area for storing ultrapure water, and the liquid metal vertical pump also has an outlet connected to the ultrapure water storage area. The liquid metal pressurized water storage device is used to supply ultrapure water to the inlet of the propeller through the outlet.

7. The micro-thruster according to claim 6, characterized in that, The liquid metal vertical pump is further provided with a liquid metal storage area and an inert gas isolation layer. The liquid metal storage area is used to store liquid metal and is located at the bottom of the liquid metal vertical pump. The inert gas isolation layer contains inert gas and is located between the ultrapure water storage area and the liquid metal storage area.

8. The micro-thruster according to claim 1, characterized in that, The silicon substrate has electrical connection grooves and electrical connection holes. The electrical connection grooves and electrical connection holes are arranged in a one-to-one correspondence and are connected to each other. The electrical connection grooves are used to accommodate part of the heating electrodes, and the electrical connection holes are used to connect the electrical connection mechanism.

9. A method for preparing a micro-thruster, characterized in that, Includes the following steps: Electrical connection grooves, Laval nozzles, heating chambers, and liquid inlets are sequentially formed on a silicon wafer through photolithography and etching processes to form a wafer intermediate. Electrical connections are formed on the wafer intermediate by coating, photolithography and etching processes to obtain a silicon substrate; A glass wafer is obtained, and photolithography, coating and lift-off processes are performed on the glass wafer in sequence to form an adhesion layer and heating electrodes under the glass wafer, thereby obtaining a glass substrate with adhesion heating electrodes. The silicon substrate and the glass substrate with the adhesive heating electrode are bonded together and then cut. Liquid metal is then injected into the liquid metal tank of the glass substrate, and the first liquid metal induction electrode and the second liquid metal induction electrode are bonded to the upper and lower surfaces respectively to obtain a micro-propeller.

10. A method for fabricating a micro-thruster, characterized in that, Includes the following steps: On a silicon wafer, the throat region of the Laval nozzle is formed sequentially through photolithography and etching processes; Electrical connection grooves are formed on the silicon wafer through photolithography and etching processes in sequence; On the silicon wafer, a heating chamber and a nozzle inlet communicating with the heating chamber are formed sequentially through photolithography and etching processes; On the silicon wafer, a liquid inlet is formed sequentially through photolithography and etching processes; The silicon wafer is sequentially coated, photolithographically etched, and etched to form electrical connection holes and nozzle outlets that penetrate the silicon wafer, thereby obtaining a silicon substrate; On a glass wafer, photolithography, coating and lift-off processes are sequentially performed to form an adhesion layer and a heating electrode under the glass wafer, thereby obtaining a glass substrate with an adhesion heating electrode. The silicon substrate and the glass substrate with the adhesive heating electrode are bonded together and then cut. Liquid metal is then injected into the liquid metal tank of the glass substrate, and the first liquid metal induction electrode and the second liquid metal induction electrode are bonded to the upper and lower surfaces respectively to obtain a micro-propeller.

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