Dual-mode underwater acoustic sensor and method of making same

Abstract

The application discloses a dual-mode underwater acoustic sensor and a preparation method thereof. The sensor structure comprises an SOI substrate, a sensitive structure comprising a middle mass block, a rectangular beam and a frame supporting the mass block through the rectangular beam, a piezoresistive detection unit comprising a piezoresistive resistor arranged at the end of each rectangular beam and a metal lead and an electrode connected into a Wheatstone bridge, and a capacitive detection unit comprising movable comb-tooth capacitive plates arranged around the mass block except the side of the rectangular beam and fixed comb-tooth capacitive plates arranged on the frame and intersecting with the movable comb-tooth capacitive plates. When an underwater acoustic signal causes the mass block to be offset, the rectangular beam is bent to cause the piezoresistive resistor to change in resistance value, and the facing area of the comb-tooth capacitive plates is changed to cause the capacitance to change, so that piezoresistive and capacitive dual-mode signal detection is realized. The application integrates the advantages of high precision of piezoresistance and strong temperature drift resistance of capacitance through integrated design, the comb-tooth capacitive mode can calibrate the piezoresistive mode, and the measurement accuracy, stability and robustness in a complex marine environment are significantly improved.

Description

Technical Field

[0001] This invention relates to underwater acoustic sensing technology, and in particular to a dual-mode underwater acoustic sensor and its fabrication method. Background Technology

[0002] With the development of marine scientific research, environmental monitoring, and military reconnaissance, the demand for efficient and accurate underwater acoustic detection technology is increasing. Underwater acoustic sensors are the core components of underwater acoustic detection systems, and they are widely used in underwater communication, detection, monitoring, and many other fields. However, most existing underwater acoustic sensors rely on a single sensing mode, which limits their effectiveness in complex marine environments.

[0003] Piezoresistive sensors detect underwater signals by utilizing the stress change of a piezoresistive resistor caused by the acoustic pressure gradient, exhibiting high accuracy and stability. However, a significant drawback of piezoresistive sensors is their extreme sensitivity to temperature changes. Temperature variations directly affect the resistance of the material, leading to deviations in the sensor's output signal and impacting its detection accuracy. Particularly in marine environments, seawater experiences significant temperature variations across different areas, times, and depths; these drastic temperature fluctuations can cause piezoresistive sensors to fail to accurately reflect underwater acoustic signals. In contrast, comb-type capacitive sensors possess stronger resistance to temperature interference. Since capacitance changes are primarily related to the distance and area between capacitor plates and variations in the dielectric constant, which is generally less affected by temperature changes, comb-type capacitive sensors maintain relatively stable performance even in environments with significant temperature variations. However, existing single-mode underwater acoustic sensors face the challenge of simultaneously achieving high accuracy, resistance to temperature interference, and signal self-calibration capabilities in complex marine environments.

[0004] It should be noted that the information disclosed in the background section above is only for understanding the background of this application, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] The main objective of this invention is to overcome the defects existing in the above-mentioned background technology and provide a dual-mode underwater acoustic sensor and its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A dual-mode underwater acoustic sensor, comprising:

[0008] The SOI substrate has, from bottom to top, a bottom silicon layer, a buried oxide layer, and a top silicon layer, with a through-hole cavity on the back side of the bottom silicon layer.

[0009] The sensitive structure, formed by etching the top silicon layer, includes a mass block located in the middle, rectangular beams symmetrically connected to the left and right sides of the mass block, and a frame supporting the mass block through the rectangular beams.

[0010] The piezoresistive detection unit includes a piezoresistor disposed at the end of each of the rectangular beams, and metal leads and metal electrodes connecting the piezoresistors into a Wheatstone bridge.

[0011] The capacitance detection unit includes a movable comb-tooth capacitor plate disposed around the mass block except for the side where the rectangular beam is located, and a fixed comb-tooth capacitor plate disposed on the frame and intersecting with the movable comb-tooth capacitor plate. A variable capacitance is formed between the movable comb-tooth capacitor plate and the fixed comb-tooth capacitor plate.

[0012] The mass block shifts under the influence of the underwater acoustic signal, causing the rectangular beam to bend and thus changing the resistance of the piezoresistor. It also changes the capacitance by altering the facing area of ​​the movable comb-tooth capacitor plate and the fixed comb-tooth capacitor plate, thereby achieving dual-mode underwater acoustic signal detection using both piezoresistive and capacitive methods.

[0013] A method for fabricating a dual-mode underwater acoustic sensor, comprising the following steps:

[0014] Step 1: Set a first mask on the top silicon layer of the SOI substrate, and perform light boron ion implantation on the piezoresistive region to form a P-type piezoresistive structure;

[0015] Step 2: Set up a second mask and implant heavy boron ions into the heavily doped region to form a P-type heavily doped region;

[0016] Step 3: Deposit an oxide layer on the entire front surface;

[0017] Step 4: Set a third mask and etch the oxide layer to expose the top silicon layer of the ohmic contact region and the capacitor electrode region;

[0018] Step 5: Set up the fourth mask, and deposit chromium and gold sequentially to form metal lines and electrodes;

[0019] Step 6: Annealing treatment to create ohmic contact between the metal wires and the top silicon layer;

[0020] Step 7: Set the fifth mask, and etch the oxide layer and the top silicon layer in sequence to etch out the mass block, rectangular beam, movable comb-tooth capacitor plate, fixed comb-tooth capacitor plate and electrical isolation groove;

[0021] Step 8: Set the sixth mask and etch the bottom silicon and buried oxide layer sequentially from the back side to form the back cavity.

[0022] The present invention has the following beneficial effects:

[0023] This invention relates to a dual-mode underwater acoustic sensor and its fabrication method, effectively solving the problem that traditional underwater acoustic sensors, relying on a single sensing mode, struggle to achieve stable and accurate underwater acoustic signal measurement in complex aquatic environments. Through an integrated design that shares a mass block-rectangular beam-frame within the same sensitive structure, the piezoresistive effect and the comb-tooth capacitance effect are integrated into the same sensor structure, enabling high-precision measurement and stability in complex marine environments.

[0024] Specifically, while piezoresistive sensors offer high detection accuracy and stability, they are sensitive to temperature changes. Temperature fluctuations in different areas, depths, and times of day in the ocean can easily lead to output signal deviations. In contrast, comb-type capacitive sensors, whose capacitance value primarily depends on the electrode geometry and dielectric constant, are less affected by temperature and possess strong resistance to temperature interference. This invention integrates a mass block-rectangular beam-frame structure, simultaneously carrying a piezoresistive resistor and a comb-type capacitor plate, by etching a mass block onto the top silicon layer of the same SOI substrate. This fully combines the advantages and complementary characteristics of both. When an underwater acoustic signal acts on the mass block, the mass block's offset causes a change in the resistance of the piezoresistive resistor at the end of the rectangular beam and alters the facing area of ​​the movable and fixed comb-type capacitor plates, thereby simultaneously outputting signals in both piezoresistive and capacitive modes. This dual-mode design not only allows for calibration of the piezoresistive mode via the comb-type capacitive mode, significantly improving the accuracy and robustness of the measurement signal, but also provides a more comprehensive underwater acoustic signal detection capability, making it particularly suitable for deep-sea exploration or marine monitoring scenarios with drastic temperature changes and complex environments.

[0025] Experimental analysis results of this invention show that a significant stress distribution is generated on the rectangular beam when an acoustic pressure load is applied, and the output voltage of the piezoresistive detection unit changes regularly with the load, proving that the structure can effectively detect underwater acoustic signals through the piezoresistive effect. Simultaneously, the capacitance change of the comb-type capacitor unit also shows a clear correlation with the load, verifying the feasibility of detecting underwater acoustic signals using the comb-type capacitor mode. In summary, this invention overcomes many limitations of traditional underwater sensors while possessing enormous potential for engineering applications.

[0026] Other beneficial effects of the embodiments of the present invention will be further described below. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of a dual-mode underwater acoustic sensor according to an embodiment of the present invention.

[0028] Figure 2 This is a top view of the structure of the dual-mode underwater acoustic sensor according to an embodiment of the present invention.

[0029] Figure 3 This is a schematic diagram of the Wheatstone bridge connection according to an embodiment of the present invention.

[0030] Figure 4 This is a schematic diagram of the lightly doped region mask according to an embodiment of the present invention.

[0031] Figure 5 This is a schematic diagram of the mask for the heavily doped region in an embodiment of the present invention.

[0032] Figure 6 This is a schematic diagram of the ohmic contact area mask according to an embodiment of the present invention.

[0033] Figure 7 This is a schematic diagram of the metal region mask according to an embodiment of the present invention.

[0034] Figure 8 This is a schematic diagram of the mask for the etched area of ​​the structure according to an embodiment of the present invention.

[0035] Figure 9 This is a schematic diagram of the mask for the back cavity etching area in an embodiment of the present invention.

[0036] Figure 10 This is a flowchart illustrating the fabrication process of the dual-mode underwater acoustic sensor according to an embodiment of the present invention.

[0037] Figure 11 This is a schematic diagram of stress distribution on a single rectangular beam according to an embodiment of the present invention.

[0038] Figure 12 This is a graph showing the change of output voltage with applied load according to an embodiment of the present invention.

[0039] Figure 13 This is a graph showing the change in capacitance as a function of applied load, according to an embodiment of the present invention. Detailed Implementation

[0040] The embodiments of the present invention will be described in detail below. It should be emphasized that the following description is merely exemplary and not intended to limit the scope and application of the present invention.

[0041] It should be noted that when a component is referred to as "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as "connected to" another component, it can be directly connected to or indirectly connected to that other component. Furthermore, a connection can be used for fixing, coupling, or communication.

[0042] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0043] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of the present invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0044] See Figure 1 and Figure 2 This invention provides a dual-mode underwater acoustic sensor, including an SOI substrate 10, a sensitive structure, a piezoresistive detection unit, and a capacitance detection unit.

[0045] The SOI substrate 10 has, from bottom to top, a bottom silicon layer 11, a buried oxide layer 12 and a top silicon layer 13. The bottom silicon layer 11 has a through-hole cavity 14 on its back side. By way of example only and not limitation, the top silicon layer 13 is N-type silicon with a resistivity of, for example, 0.01 Ω·cm.

[0046] The sensitive structure is formed by etching the top silicon layer 13 and includes a mass block 20 located in the middle, rectangular beams 30 symmetrically connected to the left and right sides of the mass block 20, and a frame 40 supporting the mass block 20 through the rectangular beams 30.

[0047] The piezoresistive detection unit includes varistors (R1, R2, R3, and R4) disposed at the ends of each of the rectangular beams 30, and metal leads 50 and metal electrodes connecting the varistors to form a Wheatstone bridge. The metal electrodes include a power supply electrode, an output electrode, and a ground electrode. Specifically, the left power supply electrode 51a, varistor R1, varistor R2, and left ground electrode 53a are connected in series, with the connection point of varistor R1 and R2 connected to the left output electrode 52a; the right power supply electrode 51b, varistor R4, varistor R3, and right ground electrode 53b are connected in series, with the connection point of varistor R4 and R3 connected to the right output electrode 52b; the left ground electrode 53a and right ground electrode 53b are connected through an external circuit, and the left power electrode 51a and right power electrode 51b are connected through an external circuit to form a Wheatstone bridge. The circuit structure of the Wheatstone bridge is as follows: Figure 3 As shown, the connections are as follows: R1 and R2 are connected in series to form one arm of the bridge, and R3 and R4 are connected in series to form the other arm of the bridge; the power supply electrode 51a on the left and the power supply electrode 51b on the right are connected between R1 and R4; the output electrode 52a on the left is connected between R1 and R2, and the output electrode 52b on the right is connected between R3 and R4; the ground electrode 53a on the left and the ground electrode 53b on the right are connected between R2 and R3.

[0048] The capacitance detection unit includes a movable comb-tooth capacitor plate 60 disposed around the mass block 20, excluding the side where the rectangular beam 30 is located, and a fixed comb-tooth capacitor plate 70 disposed on the frame 40 and intersecting with the movable comb-tooth capacitor plate 60. A variable capacitor is formed between the movable comb-tooth capacitor plate 60 and the fixed comb-tooth capacitor plate 70. The movable comb-tooth capacitor plate 60 and the fixed comb-tooth capacitor plate 70 intersect each other with a gap width of 5μm, forming a comb-tooth capacitor. The capacitance detection unit also includes an electrical isolation groove 80 disposed on the frame 40. The isolation groove 80 electrically isolates the area where the movable comb-tooth capacitor plate 60 is located from the area where the fixed comb-tooth capacitor plate 70 is located. Capacitor electrodes are respectively provided in the two areas. The capacitor electrode in the area where the movable comb-tooth capacitor plate 60 is located is capacitor electrode 61, and the capacitor electrode in the area where the fixed comb-tooth capacitor plate 70 is located is capacitor electrode 71. The mass block 20 shifts under the action of the underwater acoustic signal, causing the rectangular beam 30 to bend and thus changing the resistance of the piezoresistor. It also changes the area of ​​the movable comb-tooth capacitor plate 60 and the fixed comb-tooth capacitor plate 70, thus changing the capacitance. This enables dual-mode underwater acoustic signal detection using both piezoresistive and capacitive methods.

[0049] Since the injected varistor is a P-type silicon, it forms a PN junction with the N-type top silicon 13 in the region where the movable comb-type capacitor plate 60 is located. During operation, the capacitor electrode 61 is connected to the power supply, and the voltage of the capacitor electrode 61 is higher than the voltage of the power supply electrode, so that the PN junction is in a reverse bias state. The depletion region formed by the PN junction electrically isolates the piezoresistive region from the comb-type capacitor region, avoiding crosstalk.

[0050] This invention integrates a piezoresistive detection unit and a comb-capacitive detection unit into a dual-mode underwater acoustic sensing scheme within a mass block-rectangular beam-frame sensitive structure on the same SOI substrate. This overcomes the limitations of single-mode underwater acoustic sensors in complex marine environments where high accuracy and resistance to temperature interference are difficult to achieve simultaneously. By utilizing the physical mechanism that the displacement of the mass block caused by the underwater acoustic signal simultaneously changes the resistance value of the piezoresistor at the end of the rectangular beam and the area of ​​the comb-capacitive plate, synchronous signal output of both piezoresistive and capacitive modes is achieved. This fully leverages the complementary advantages of the high accuracy of the piezoresistive effect and the strong resistance to temperature drift of the comb-capacitive plate. The piezoresistive mode can be calibrated through the comb-capacitive mode, significantly improving the accuracy, stability, and robustness of the measurement. It is particularly suitable for deep-sea exploration and marine monitoring scenarios with drastic temperature changes and complex environments.

[0051] By way of example only and not limitation, in some embodiments, the SOI substrate 10 has a top silicon layer 13 with a thickness of 40 μm, a buried oxide layer 12 with a thickness of 2 μm, and a bottom silicon layer 11 with a thickness of 400 μm; the mass block 20 has a side length of 1500 μm and a thickness of 40 μm; and the rectangular beam 30 has a length of 1000 μm, a width of 140 μm, and a thickness of 40 μm.

[0052] In some embodiments, there are four varistors, located at the two ends of the left and right rectangular beams 30, respectively. Each varistor is 100 μm long and 20 μm wide. Each varistor has a square heavily doped region 90 with a side length of 20 μm at both ends. The metal lead 50 connects each varistor through the heavily doped region 90. The metal electrode includes a power electrode, an output electrode, and a ground electrode. The four varistors and the metal lead 50 form a Wheatstone bridge.

[0053] In some embodiments, the movable comb-tooth capacitor plate 60 and the fixed comb-tooth capacitor plate 70 are both 900μm long, 10μm wide, and 40μm thick, with a comb tooth spacing of 20μm and an intersecting gap of 5μm. The capacitance detection unit also includes an electrical isolation groove 80 disposed on the frame 40. The isolation groove 80 is 20μm wide and electrically isolates the area where the movable comb-tooth capacitor plate 60 is located from the area where the fixed comb-tooth capacitor plate 70 is located. Capacitor electrodes are respectively provided in the two areas.

[0054] In some embodiments, the metal electrodes (including power supply electrodes, output electrodes, and ground electrodes) of the piezoresistive detection unit and the capacitor electrodes of the capacitance detection unit are both squares with a side length of 200 μm.

[0055] See Figures 4 to 10 A method for fabricating a dual-mode underwater acoustic sensor, used to fabricate the dual-mode underwater acoustic sensor described in any of the above embodiments, includes the following steps:

[0056] Step 1: Set a first mask (corresponding to the lightly doped region, such as...) on the top silicon layer 13 of the SOI substrate 10. Figure 4 As shown in the figure, light boron ions were implanted into the piezoresistive region to form a P-type piezoresistive structure; the light boron ion implantation energy was 40 keV, and the implantation dose was 2 × 10⁻⁶. 14 cm -2 .

[0057] Step 2: Set a second mask (for the heavily doped region, such as...) Figure 5 As shown in the figure, heavy boron ion implantation was performed on the heavily doped region 90 to form a P-type heavily doped region; the heavy boron ion implantation energy was 80 keV and the implantation dose was 3 × 10⁻⁶. 15 cm -2 .

[0058] Step 3: Deposit an oxide layer on the entire front side; deposit a 2μm thick oxide layer to prevent the metal from contacting the top silicon 13 and forming an electrical connection.

[0059] Step 4: Set the third mask (corresponding to the ohmic contact area, such as...) Figure 6 As shown in the figure, the oxide layer is etched to expose the top silicon 13 of the ohmic contact area and the capacitor electrode area; the oxide layer is etched to 2 μm.

[0060] Step 5: Set the fourth mask (corresponding to the metal area, such as...) Figure 7 As shown, chromium and gold are deposited sequentially to form metal leads 50 and metal electrodes (including power supply electrode, output electrode, ground electrode) and capacitor electrodes; 20 nm of chromium and 300 nm of gold are deposited sequentially, and the metal in the heavily doped region 90 and the capacitor electrode region are in contact with the top silicon 13.

[0061] Step 6: Annealing treatment to form an ohmic contact between the metal lead 50 and the top silicon 13; annealing time 30 min, annealing temperature 350℃, the metal lead 50 of the heavily doped region 90 forms an ohmic contact with the top silicon 13, and the capacitor electrode forms an ohmic contact with the top silicon 13.

[0062] Step 7: Set the fifth mask (corresponding to the structure etching area, such as...) Figure 8As shown), the oxide layer and the top silicon layer 13 are etched sequentially to form the mass block 20, the rectangular beam 30, the movable comb-tooth capacitor plate 60, the fixed comb-tooth capacitor plate 70, and the electrical isolation trench 80; wherein, the oxide layer can be etched using reactive ion etching (RIE), and the top silicon layer can be etched using deep reactive ion etching (DRIE), and the etching of the oxide layer and the top silicon layer uses the same mask pattern ( Figure 8 Furthermore, the photoresist coating protects the formed metal structure from being affected; the oxide layer is etched to 2μm, and the top silicon layer is etched to 40μm.

[0063] Step 8: Set the sixth mask (corresponding to the back cavity etching area, such as...) Figure 9 As shown), the bottom silicon 11 and the buried oxide layer 12 are etched sequentially from the back side to form a back cavity 14. The bottom silicon can be etched using deep reactive ion etching (DRIE), with the buried oxide layer 12 as a self-stopping layer. Due to the high selectivity of silicon and silicon oxide, and the need to etch the buried oxide layer later, appropriate over-etching is allowed. The buried oxide layer can be etched using HF gas, which has high perpendicularity to ensure complete etching. Double-sided alignment can be achieved using a double-sided etching machine with a CCD lens, using the front and back layout marks for alignment. The bottom silicon is etched to a thickness of 400 μm, and the buried oxide layer is etched to a thickness of 2 μm.

[0064] In some embodiments, in step one, the light boron ion implantation energy is 40 keV and the implantation dose is 2 × 10⁻⁶. 14 cm -2 In step two, the boron ion implantation energy is 80 keV, and the implantation dose is 3 × 10⁻⁶. 15 cm -2 .

[0065] In some embodiments, the oxide layer thickness deposited in step three is 2 μm; in step five, chromium 20 nm and gold 300 nm are deposited sequentially; and in step six, the annealing time is 30 min and the annealing temperature is 350 °C.

[0066] In some embodiments, in step seven, the oxide layer is etched to 2 μm and the top silicon layer is etched to 40 μm; in step eight, the bottom silicon layer is etched to 400 μm and the buried oxide layer is etched to 2 μm.

[0067] In some embodiments, the first to sixth masks sequentially correspond to a lightly doped region, a heavily doped region, an ohmic contact region, a metal region, a structural etching region, and a back cavity etching region, respectively as shown in the figures below. Figures 4 to 9 As shown.

[0068] The overall process flow is as follows: Figure 10 As shown.

[0069] A piezoresistive underwater acoustic sensor and a comb-type capacitive underwater acoustic sensor are integrated into a dual-mode underwater acoustic sensor. When the underwater acoustic sensor receives an underwater acoustic signal, the central mass block will shift under the influence of the sound pressure gradient on both sides.

[0070] The displacement of the central mass block will cause the rectangular beam to bend. Stress analysis of the structure reveals that the stress on the rectangular beam is:

[0071]

[0072] in, F The force generated to receive underwater acoustic signals l It is the length of the beam. b It is the width of the beam. t It refers to the thickness of the beam.

[0073] The stress change in the varistor region on the rectangular beam causes a change in the resistance of the four varistors. The output voltage of the Wheatstone bridge composed of varistors and metal leads is:

[0074]

[0075] in, U out It is the output voltage. π l It is the piezoresistive coefficient. σ l It is the stress in the piezoresistive region. V in It is the output voltage of the Wheatstone bridge.

[0076] In other words, the underwater acoustic signal will cause the resistance value of the varistor of the Wheatstone bridge to change, and the output voltage signal will be amplified and filtered by the amplification and filtering circuit.

[0077] The displacement of the mass block will cause a change in the facing area between the comb-shaped capacitor plates, which means the change in capacitance of the comb-shaped capacitor composed of the comb-shaped capacitor plates is:

[0078]

[0079] in, N This refers to the number of comb-tooth capacitor plates. ε r It is the dielectric constant between the comb-shaped capacitor plates. h It is the length of the overlap of the comb-shaped capacitor plates. d It is the gap between the comb-shaped capacitor plates, Δ t It is the distance that changes up and down on the capacitor plate.

[0080] In other words, the underwater acoustic signal causes a change in the capacitance value of the comb capacitor, and the change in capacitance is converted into a voltage signal by a CV conversion circuit. The comb capacitor and Wheatstone bridge enable dual-mode underwater acoustic signal detection in this invention. It is worth noting that this sensing structure primarily responds to vertical underwater acoustic signals; horizontal underwater acoustic signals can be suppressed through encapsulation methods (such as using sound-insulating materials) to ensure that the comb capacitor only reflects the change in the facing area caused by vertical displacement, avoiding interference from gap changes in detection.

[0081] Piezoresistive mode output signal U out Change in output capacitance in comb-type capacitor mode ΔC The calibrated output signal U cal for:

[0082]

[0083] in, k These are calibration coefficients, obtained through experimental calibration. When changes in ambient temperature cause piezoresistive signal drift, the comb capacitance signal changes relatively little; the piezoresistive output can be compensated in real time using the aforementioned relationship. The calibration can be achieved through analog circuits or digital signal processing.

[0084] A finite element method (FEM) simulation was used to model and simulate an underwater acoustic sensor, analyzing its output under the influence of underwater acoustic signals. The simulation environment was an aquatic environment, with fixed boundary conditions set for the bounded area. Acoustic pressure loads were applied to the structure, with the load unit being Pa. The stress on a single beam was calculated as follows: Figure 11 As shown. The relationship between output voltage and applied load is as follows. Figure 12 As shown, this demonstrates that underwater acoustic sensors can detect underwater acoustic signals through the piezoresistive effect. The relationship between capacitance change and applied acoustic pressure load is as follows: Figure 13 As shown, this demonstrates that the underwater acoustic sensor can detect underwater acoustic signals through the comb-tooth capacitance.

[0085] In summary, this invention addresses the shortcomings of traditional underwater acoustic sensors that rely on a single sensing mode and struggle to achieve both high accuracy and resistance to temperature interference in complex marine environments. It proposes a dual-mode underwater acoustic sensor based on piezoresistive effect and comb-cancerous capacitance, along with its integrated fabrication method. A sensitive structure consisting of a mass block, rectangular beams, and a frame is formed by etching on the top silicon layer of an SOI substrate. A piezoresistor is integrated at the end of the rectangular beam, and movable and fixed comb-cancerous capacitor plates are arranged around the mass block and on the frame, respectively. When the underwater acoustic signal causes the mass block to shift, the piezoresistor resistance is altered by bending the rectangular beam, and the facing area of ​​the comb-cancerous capacitor plates is changed, thus simultaneously outputting detection signals in both piezoresistive and capacitive modes. This dual-mode design not only allows for calibration of the piezoresistive mode using the comb-cancerous capacitance mode, significantly improving measurement accuracy, stability, and robustness, but also achieves integrated sensor fabrication through back-side etching of the cavity and a fabrication process involving six masking operations. Experimental analysis results further verified that the structure exhibits a regular response to changes in both output voltage and capacitance under acoustic pressure load, indicating that it possesses reliable dual-mode underwater acoustic signal detection capabilities, making it particularly suitable for deep-sea exploration and marine monitoring scenarios with drastic temperature changes and complex environments.

[0086] The above description provides a further detailed explanation of the present invention in conjunction with specific / preferred embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various substitutions or modifications can be made to these described embodiments without departing from the concept of the present invention, and all such substitutions or modifications should be considered within the scope of protection of the present invention. In the description of this specification, the reference to terms such as "an embodiment," "some embodiments," "preferred embodiment," "example," "specific example," or "some examples," etc., indicates that the specific features, structures, materials, or characteristics described in connection with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples. Without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and modifications can be made herein without departing from the scope of protection of the patent application.

Claims

1. A dual-mode underwater acoustic sensor, characterized in that, include: The SOI substrate has, from bottom to top, a bottom silicon layer, a buried oxide layer, and a top silicon layer, with a through-hole cavity on the back side of the bottom silicon layer. The sensitive structure, formed by etching the top silicon layer, includes a mass block located in the middle, rectangular beams symmetrically connected to the left and right sides of the mass block, and a frame supporting the mass block through the rectangular beams. The piezoresistive detection unit includes a piezoresistor disposed at the end of each of the rectangular beams, and metal leads and metal electrodes connecting the piezoresistors into a Wheatstone bridge. The capacitance detection unit includes a movable comb-tooth capacitor plate disposed around the mass block except for the side where the rectangular beam is located, and a fixed comb-tooth capacitor plate disposed on the frame and intersecting with the movable comb-tooth capacitor plate. A variable capacitance is formed between the movable comb-tooth capacitor plate and the fixed comb-tooth capacitor plate. The mass block shifts under the influence of the underwater acoustic signal, causing the rectangular beam to bend and thus changing the resistance of the piezoresistor. It also changes the capacitance by altering the facing area of ​​the movable comb-tooth capacitor plate and the fixed comb-tooth capacitor plate, thereby achieving dual-mode underwater acoustic signal detection using both piezoresistive and capacitive methods.

2. The dual-mode underwater acoustic sensor according to claim 1, characterized in that, In the SOI substrate, the top silicon layer is N-type silicon.

3. The dual-mode underwater acoustic sensor according to claim 1, characterized in that, There are four varistors, located at the two ends of the left and right rectangular beams respectively; each varistor has a heavily doped region at both ends, and the metal leads are connected to each varistor through the heavily doped region; the metal electrode includes a power electrode, an output electrode and a ground electrode, and the four varistors and the metal leads form a Wheatstone bridge.

4. The dual-mode underwater acoustic sensor according to claim 1, characterized in that, The movable comb-tooth capacitor plate and the fixed comb-tooth capacitor plate intersect each other and have gaps; the capacitor detection unit also includes an electrical isolation groove disposed on the frame, the isolation groove electrically isolates the movable comb-tooth capacitor plate area from the fixed comb-tooth capacitor plate area, and the two areas are respectively provided with capacitor electrodes.

5. The dual-mode underwater acoustic sensor according to claim 1, characterized in that, The metal electrodes of the piezoresistive detection unit and the capacitor electrodes of the capacitance detection unit are both square.

6. A method for fabricating a dual-mode underwater acoustic sensor, used to fabricate the dual-mode underwater acoustic sensor as described in any one of claims 1 to 5, characterized in that, Includes the following steps: Step 1: Set a first mask on the top silicon layer of the SOI substrate, and perform light boron ion implantation on the piezoresistive region to form a P-type piezoresistive structure; Step 2: Set up a second mask and implant heavy boron ions into the heavily doped region to form a P-type heavily doped region; Step 3: Deposit an oxide layer on the entire front surface; Step 4: Set a third mask and etch the oxide layer to expose the top silicon layer of the ohmic contact region and the capacitor electrode region; Step 5: Set up the fourth mask, and deposit chromium and gold sequentially to form metal lines and electrodes; Step 6: Annealing treatment to create ohmic contact between the metal wires and the top silicon layer; Step 7: Set the fifth mask, and etch the oxide layer and the top silicon layer in sequence to etch out the mass block, rectangular beam, movable comb-tooth capacitor plate, fixed comb-tooth capacitor plate and electrical isolation groove; Step 8: Set the sixth mask and etch the bottom silicon and buried oxide layer sequentially from the back side to form the back cavity.

7. The preparation method according to claim 6, characterized in that, In step seven, reactive ion etching is used to etch the oxide layer, and deep reactive ion etching is used to etch the top silicon layer. The same mask pattern is used for etching the oxide layer and the top silicon layer.

8. The preparation method according to claim 6, characterized in that, In step eight, the bottom silicon is etched using deep reactive ion etching, with the buried oxide layer as a self-stopping layer; the buried oxide layer is etched using HF gas.

9. The preparation method according to claim 6, characterized in that, In step eight, double-sided alignment is achieved using a double-sided etching machine with a CCD lens, and alignment is performed using the front and back pattern marks.

10. The preparation method according to any one of claims 6 to 9, characterized in that, The first to sixth masks correspond to the lightly doped region, the heavily doped region, the ohmic contact region, the metal region, the structure etching region, and the back cavity etching region, respectively.

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