Charge-enhanced MEMS (Micro Electro Mechanical System) hydrophone

Abstract

The invention belongs to the field of piezoelectric micro-mechanical sensors, and particularly relates to a charge-enhanced MEMS hydrophone, which comprises a silicon substrate layer; the silicon substrate layer is connected with a buried oxide layer; the silicon substrate layer is provided with a cylindrical cavity which is through up and down; the buried oxide layer is connected with a silicon device layer; the silicon device layer is connected with a seed layer; the seed layer is connected with a lower electrode; piezoelectric layers are arranged on the silicon device layer and the lower electrode; the piezoelectric layer is connected with an upper electrode; the upper electrode is connected with a protective layer; the hydrophone is provided with an annular groove penetrating through the protective layer, the upper electrode, the piezoelectric layer, the lower electrode and the seed layer. The problem of charge offset can be solved, effective superposition of inductive charges is realized, the charge output capability and the detection sensitivity of the hydrophone are remarkably improved, the technical bottleneck of a conventional structure is broken through, and the hydrophone is adaptive to high-precision underwater detection scenes such as marine resource exploration and underwater communication.

Description

Technical Field

[0001] This invention belongs to the field of piezoelectric micromechanical sensors, and in particular relates to a charge-enhanced MEMS hydrophone. Background Technology

[0002] MEMS hydrophones, as miniaturized and low-power acoustic detection devices, play a crucial role in marine resource exploration, underwater communication, anti-submarine warfare, and environmental monitoring. With the continuous expansion of underwater detection scenarios, higher demands are placed on the hydrophone's charge output capability, detection sensitivity, and signal recognition accuracy. Improving its performance directly affects the detection range and data accuracy of the detection system, thus possessing significant scientific research value and practical application significance.

[0003] Existing conventional MEMS hydrophones generally adopt a layered basic structure, specifically including a silicon substrate layer, a buried oxide layer, a silicon device layer, a lower electrode, a piezoelectric layer, and a upper electrode. This structure forms a complete acoustic-to-electrical signal conversion path through interlayer connections from top to bottom. During operation, it relies on the mechanical deformation of the piezoelectric layer under the pressure of sound waves, which induces charge generation through the piezoelectric effect. Finally, the upper and lower electrodes conduct the charge to achieve the conversion and detection of acoustic signals.

[0004] However, conventional MEMS hydrophones have inherent design flaws: the induced charges generated by the piezoelectric layer cancel each other out in their inner and outer regions, resulting in extremely low effective output charge density. This problem directly limits the improvement of hydrophone sensitivity, making it difficult for conventional structures to meet the requirements of high-precision, long-distance underwater detection in commonly used detection frequency bands in terms of sensitivity and charge output capability. Therefore, how to overcome the limitation of charge cancellation through structural optimization, enhance charge output efficiency, and improve detection sensitivity has become a core issue that urgently needs to be addressed in the current development of MEMS hydrophone technology. Summary of the Invention

[0005] To address the problems existing in the background art, the present invention provides a charge-enhanced MEMS hydrophone, comprising: a silicon substrate layer; a buried oxide layer connected to the silicon substrate layer; a cylindrical cavity extending vertically through the silicon substrate layer; a silicon device layer connected to the buried oxide layer; a seed layer connected to the silicon device layer; a lower electrode connected to the seed layer; a piezoelectric layer disposed on the silicon device layer and the lower electrode; an upper electrode connected to the piezoelectric layer; a protective layer connected to the upper electrode; and an annular groove penetrating the protective layer, the upper electrode, the piezoelectric layer, the lower electrode, and the seed layer in the hydrophone.

[0006] The present invention has at least the following beneficial effects

[0007] This invention designs a basic stacked structure consisting of a silicon substrate layer, a buried oxide layer, a silicon device layer, a seed layer, a lower electrode, a piezoelectric layer, an upper electrode, and a protective layer. Combined with a cylindrical cavity and an annular groove penetrating the protective layer, upper electrode, piezoelectric layer, and lower electrode, this effectively separates the inner and outer electrodes. This structurally solves the charge cancellation problem inherent in conventional structures, enabling effective superposition of induced charges. It ensures structural stability and acoustic-to-electrical signal conversion efficiency, ultimately significantly improving the hydrophone's charge output capability and detection sensitivity. This effectively overcomes the technical bottlenecks of conventional structures, making it better suited for high-precision underwater detection scenarios with high performance requirements for MEMS hydrophones, such as marine resource exploration, underwater communication, and anti-submarine warfare, thus meeting the high-performance needs of practical applications. Attached Figure Description

[0008] Figure 1 A schematic diagram of a traditional MEMS hydrophone structure;

[0009] Figure 2 This is a schematic diagram of the charge-enhanced MEMS hydrophone structure of the present invention;

[0010] Figure 3 This is a schematic diagram showing the charge distribution in the piezoelectric layer of the conventional structure and the present invention.

[0011] Figure 4 This is a schematic diagram comparing the charge density and sensitivity of the conventional structure and the present invention at 1 kHz. Detailed Implementation

[0012] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0013] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures, and should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0014] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing 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, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0015] Please see Figure 1 , Figure 1 The structure is a conventional MEMS hydrophone, comprising: a silicon substrate layer; a buried oxide layer connected to the silicon substrate layer; a silicon device layer connected to the buried oxide layer; a lower electrode connected to the silicon device layer; a piezoelectric layer connected to the lower electrode; and an upper electrode connected to the piezoelectric layer.

[0016] In this embodiment, the bottom layer of a conventional MEMS hydrophone is a silicon substrate layer, which serves as the mechanical support carrier for the entire device and provides a stable mounting foundation for the upper structure. Above the silicon substrate layer is a buried oxide layer, which mainly plays an insulating role, avoiding unnecessary electrical signal interference between layers. Above the buried oxide layer is the silicon device layer, which provides structural support. Above the silicon device layer, a lower electrode, a piezoelectric layer, and a top electrode are stacked in sequence. The piezoelectric layer is the core acoustic-to-electrical signal conversion component, while the lower and upper electrodes are responsible for sensing and extracting the electrical signals generated by the piezoelectric layer. The working principle of this conventional structure is as follows: when underwater sound waves act on the device, the sound wave pressure causes mechanical deformation of the piezoelectric layer. Due to the piezoelectric effect, induced charges are generated on the upper and lower surfaces of the piezoelectric layer. These charges are captured by the lower and upper electrodes, respectively, thus forming a detectable electrical signal, realizing the conversion of acoustic signals to electrical signals. However, this structure has an inherent defect—the induced charges generated by the piezoelectric layer cancel each other out in its inner and outer regions, resulting in a low actual effective output charge density, which ultimately limits the detection sensitivity of the hydrophone and makes it difficult to meet the requirements of high-precision underwater detection.

[0017] Please see Figure 2 This invention provides a charge-enhanced MEMS hydrophone, comprising: a silicon substrate layer; a buried oxide layer connected to the silicon substrate layer; a cylindrical cavity extending vertically through the silicon substrate layer; a silicon device layer connected to the buried oxide layer; a seed layer connected to the silicon device layer; a lower electrode connected to the seed layer; a piezoelectric layer disposed on the silicon device layer and the lower electrode; an upper electrode connected to the piezoelectric layer; a protective layer connected to the upper electrode; and an annular groove penetrating the protective layer, the upper electrode, the piezoelectric layer, the lower electrode, and the seed layer in the hydrophone.

[0018] Preferably, the seed layer has a thickness of 20-100 nm, the protective layer has a thickness of 20 nm to 2 μm, and the silicon substrate has a thickness of 50 μm to 675 μm.

[0019] Preferably, the thickness of the piezoelectric layer is 500nm-3um.

[0020] Preferably, the thickness of the upper electrode and the lower electrode is 30 nm to 2 μm.

[0021] Preferably, the cylindrical cavity and the annular groove are vertically opposite each other and are on the same axis.

[0022] Preferably, a cylindrical back cavity structure that runs vertically through the buried oxygen layer is provided below the buried oxygen layer;

[0023] Preferably, the diameter of the cylindrical cavity is 50 μm to 2 mm; the diameter of the annular groove is 2 μm to 400 μm.

[0024] Preferably, the material of the buried oxide layer includes: SiO2, Si3N4, AlN, Al2O3 or silicon carbide.

[0025] Preferably, the seed layer has the same shape as the lower electrode and its material includes AlN, Al2O3 or silicon carbide; the protective layer has the same shape as the upper electrode and its material includes SiO2, Si3N4, SiON, AlN, Al2O3 or silicon carbide.

[0026] Preferably, the materials of the upper and lower electrodes include: metals, metal conductive compounds, and composite films of insulating dielectric materials and metals or metal conductive compounds. The materials used for the upper and lower electrodes can be the same or different, including but not limited to metallic materials. These can be single-layer metals or composite films containing metals. Materials include, but are not limited to, metals such as gold, tungsten, molybdenum, platinum, ruthenium, iridium, titanium-tungsten, aluminum, copper, chromium, and titanium, or metal-like conductive compounds such as titanium nitride, tantalum nitride, aluminum-silicon-copper, titanium silicide, cobalt silicide, and titanium silicide. Composite films include, but are not limited to, composite films of insulating dielectric materials such as AlN, Si3N4, SiO2, SiON, and silicon carbide with the aforementioned metals or metal conductive compounds.

[0027] Preferably, the seed layer, piezoelectric layer, and protective layer are made of piezoelectric materials. The piezoelectric layer material can be AlN, doped AlN, ZnO, LiNbO3, LiTaO3, quartz, lead zirconate titanate (PZT), HfO2, etc., wherein the doped AlN contains one or more rare earth elements, such as Sc, Y, lanthanides, actinides, etc.

[0028] In this embodiment, the bottom layer of the charge-enhanced MEMS hydrophone proposed in this invention is a silicon substrate layer, which provides mechanical support for the entire device. Above the silicon substrate layer is a buried oxide layer, which serves as an interlayer isolation and etching barrier layer. Above the buried oxide layer is a silicon device layer, which acts as a mounting carrier for the upper functional structure. Above the silicon device layer is a seed layer, which is used for the crystal orientation of the piezoelectric thin film crystal. Below the buried oxide layer is a cavity structure. The bottom surface of the seed layer is directly connected to the silicon device layer. The top surface of the seed layer is directly connected to the lower electrode. The top surface of the lower electrode is connected to the piezoelectric layer, and the top of the piezoelectric layer covers the upper electrode and the protective layer, forming a complete electrode-piezoelectric layer signal conversion unit. The device has an annular groove that penetrates the protective layer, the upper electrode, the piezoelectric layer, and the lower electrode, which is the core design to solve the charge cancellation problem. Working principle: When underwater sound waves act on the hydrophone, the sound pressure is sequentially transmitted to the protective layer, upper electrode, piezoelectric layer, lower electrode, seed layer, silicon device layer, buried oxygen layer, and back cavity structure, driving the piezoelectric material to undergo synchronous mechanical deformation. The induced charge generated by the deformation of the piezoelectric layer is constrained by the annular groove structure. The charges inside and outside the annular groove are opposite in polarity, so the generated charges do not cancel each other out. As the core layer for signal conversion that directly interacts with the electrodes, the induced charge generated by the deformation of the piezoelectric layer is isolated by the annular groove, completely avoiding the problem of charge cancellation between the inner and outer regions in conventional structures. The induced charge superimposed between the inner and outer regions is discharged through the upper and lower electrodes to form a stronger electrical signal, realizing efficient conversion of acoustic signals to electrical signals and fundamentally solving the problem of weak charge output in conventional structures.

[0029] Experimental simulation:

[0030] Please see Figure 3 , Figure 3 Comparing the charge distribution characteristics of conventional MEMS hydrophones with this solution, conventional structures are affected by the uniformity of stress distribution within the layers. The induced charges generated in the "inner region" and "outer region" of the piezoelectric layer have opposite polarities, resulting in significant internal and external charge cancellation. This cancellation leads to extremely low effective output charge density, directly causing weak subsequent electrical signal strength and severely suppressing sensitivity enhancement. In this solution, the piezoelectric layer (core signal conversion layer) avoids charge polarity cancellation between the inner and outer regions due to the "zoning isolation effect" of the annular groove, achieving effective superposition of inner and outer charges.

[0031] Please see Figure 4 , Figure 4 This chart contains two sub-graphs, corresponding to the core performance indicators of hydrophones—induced charge magnitude and sensitivity. Both are plotted on the x-axis (frequency in kHz), covering a test frequency range of 0-140kHz, with a focus on performance differences at 1kHz. In the conventional structure, due to charge cancellation issues in the internal and external regions, the induced charge output is extremely low at 1kHz (document data shows a charge value of around 10). -17The output is on the order of C, and its fluctuation with frequency is small, resulting in weak overall output capability. This solution significantly improves the induced charge output in the 1kHz band (charge value jumps to 10). -14 (On the order of C), and with higher charge output stability across the entire frequency band. The core reason is that the charge superposition effect increases the total effective charge captured by the electrodes, directly breaking through the charge output bottleneck of conventional structures. Conventional structures have a sensitivity of approximately -256.1 dB in the 1 kHz frequency band; this design achieves a sensitivity of -202.5 dB in the 1 kHz frequency band, an improvement of 53.6 dB compared to conventional structures. This enables the hydrophone to accurately detect weak sound waves, meeting the technical requirements of scenarios such as marine exploration and underwater communication.

[0032] Figure 3 and Figure 4 The simulation results form a closed-loop verification from mechanism (charge distribution) to indicators (charge, sensitivity): This scheme completely solves the charge cancellation problem of conventional MEMS hydrophones through the design of annular groove structure, realizes charge superposition, and finally achieves a breakthrough in charge density increase of 405 times and sensitivity increase of 53.6dB in the 1kHz key frequency band, providing structural technical support for high-precision underwater detection.

[0033] In summary, this invention, through the design of a basic stacked structure of silicon substrate layer-buried oxide layer-silicon device layer-seed layer-lower electrode-piezoelectric layer-upper electrode-protective layer, combined with a cylindrical cavity and an annular groove penetrating the protective layer, upper electrode, piezoelectric layer, and lower electrode, effectively separates the inner and outer electrodes. This structurally solves the charge cancellation problem of conventional structures, achieving effective superposition of induced charges. It ensures structural stability and acoustic-to-electrical signal conversion efficiency, ultimately significantly improving the charge output capability and detection sensitivity of the hydrophone. This effectively overcomes the technical bottlenecks of conventional structures and is better suited for high-precision underwater detection scenarios with high performance requirements for MEMS hydrophones, such as marine resource exploration, underwater communication, and anti-submarine warfare, meeting the high-performance needs of practical applications.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A charge-enhanced MEMS hydrophone, characterized in that, include: Silicon substrate; A buried oxide layer is connected to the silicon substrate layer; a cylindrical cavity running vertically through the silicon substrate layer is provided on the silicon substrate layer; a silicon device layer is connected to the buried oxide layer; a seed layer is connected to the silicon device layer; a lower electrode is connected to the seed layer; a piezoelectric layer is provided on the silicon device layer and the lower electrode; an upper electrode is connected to the piezoelectric layer; a protective layer is connected to the upper electrode; and an annular groove penetrating the protective layer, the upper electrode, the piezoelectric layer, the lower electrode, and the seed layer is formed on the hydrophone.

2. The charge-enhanced MEMS hydrophone according to claim 1, characterized in that, The thickness of the piezoelectric layer is 500nm-3um.

3. The charge-enhanced MEMS hydrophone according to claim 1, characterized in that, The thickness of the upper and lower electrodes is 30 nm to 2 μm.

4. The charge-enhanced MEMS hydrophone according to claim 1, characterized in that, The seed layer has a thickness of 20-100 nm, the protective layer has a thickness of 20 nm to 2 μm, and the silicon substrate has a thickness of 50 μm to 675 μm.

5. A charge-enhanced MEMS hydrophone according to claims 1-4, characterized in that, The cylindrical cavity and the annular groove are vertically opposite each other and are on the same axis.

6. A charge-enhanced MEMS hydrophone according to claims 1-4, characterized in that, The diameter of the cylindrical cavity is 50µm to 2mm; the diameter of the annular groove is 2µm to 400µm.

7. A charge-enhanced MEMS hydrophone according to claims 1-4, characterized in that, The materials of the buried oxide layer include: SiO2, Si3N4, AlN, Al2O3 or silicon carbide.

8. A charge-enhanced MEMS hydrophone according to claims 1-4, characterized in that, The materials of the upper and lower electrodes include: metals, metal conductive compounds, and composite films of insulating dielectric materials and metals or metal conductive compounds.

9. A charge-enhanced MEMS hydrophone according to claims 1-4, characterized in that, The piezoelectric layer is made of piezoelectric material.

10. A charge-enhanced MEMS hydrophone according to claims 1-4, characterized in that, The seed layer has the same shape as the lower electrode and its material includes AlN, Al2O3 or silicon carbide; the protective layer has the same shape as the upper electrode and its material includes SiO2, Si3N4, SiON, AlN, Al2O3 or silicon carbide.

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