Flexible graphene transformer vibration sensor packaging design method based on micro-cap structure

Abstract

The invention provides a flexible graphene transformer vibration sensor packaging design method based on a micro-cap structure, and belongs to the technical field of sensors. The method comprises the following steps: preparing an H-type graphene resonator layer on a flexible polyimide substrate; a porous PDMS structure layer containing graphene is constructed on the resonator layer through a salt template method; forming a graphene-containing microstructure layer on the surface of the porous layer by adopting an abrasive paper template method; preparing a micro-cap groove with a silicon dioxide / chromium / gold layer on the silicon-based insulator wafer; and the porous / microstructure layer assembly integrated with the H-shaped resonator and the micro-cap structure layer form a vacuum sealing cavity through gold-silicon eutectic bonding. The flexible graphene vibration sensor designed by the invention can accurately identify wide vibration characteristics in the operation of the transformer, effectively distinguish normal and abnormal working conditions, and can stably work in a complex electromagnetic environment and an oil contamination condition, thereby realizing long-term, accurate and reliable transformer vibration state monitoring.

Description

Technical Field

[0001] This invention relates to the field of flexible graphene vibration sensor technology, and in particular to a packaging design method for a flexible graphene transformer vibration sensor based on a microcap structure. Background Technology

[0002] With the rapid development of smart grids and IoT technologies, transformer vibration monitoring places higher demands on the sensitivity, range, and environmental adaptability of sensors. Currently, vibration sensing technology faces multiple technical bottlenecks in the field of power equipment condition monitoring. Traditional sensors, limited by material properties and structural design, struggle to achieve high-precision measurements under complex operating conditions. While piezoelectric devices offer fast response, their physical brittleness leads to insufficient overload resistance, making them prone to failure in the high-vibration environment of transformers. Capacitive sensors extend their range through flexible dielectric layers, but the hysteresis of microstructural deformation recovery causes significant signal drift, making it difficult to meet long-term stable monitoring requirements.

[0003] Furthermore, existing packaging technologies inherently present a trade-off between miniaturization and reliability. Conventional vacuum-sealed structures rely on large-area bonding interfaces to maintain airtightness, resulting in bulky devices that cannot meet the installation requirements of the confined space in transformer windings. Simultaneously, the difference in expansion coefficients between metal packaging materials and organic dielectrics can easily lead to interface delamination under temperature cycling conditions, causing sensors to be prone to dielectric permeation failure in oil-immersed environments. Summary of the Invention

[0004] In view of this, the present invention provides a packaging design method for a flexible graphene transformer vibration sensor based on a microcap structure, comprising the following steps:

[0005] (1) An H-type graphene resonator layer was prepared on a flexible polyimide substrate;

[0006] (2) A porous PDMS structure layer containing graphene was constructed on the resonator layer by means of a salt template method;

[0007] (3) A graphene-containing microstructure layer is formed on the surface of the porous layer using a template method, thus obtaining a porous / microstructure layer assembly for an integrated H-type resonator;

[0008] (4) Fabricate microcap grooves with silicon dioxide / chromium / gold layers on silicon-based insulator wafers;

[0009] (5) The porous / microstructure layer assembly of the integrated H-type resonator and the microcap structure layer are bonded together with gold-silicon eutectic bonding to form a vacuum-sealed cavity.

[0010] Further, the preparation method of the H-type graphene resonator layer in step (1) includes the following steps: forming an H-type photoresist pattern on the surface of a flexible polyimide substrate using photolithography, then removing the material in the exposed area by etching to form an H-type channel structure, and finally growing a single layer of graphene inside the channel structure by chemical vapor deposition to obtain the H-type graphene resonator layer.

[0011] Furthermore, the thickness of the flexible polyimide substrate is 100-150 μm, and the H-shaped channel structure is 400-450 μm long and 5-8 μm wide.

[0012] Further, the preparation method of the graphene-containing porous PDMS structure layer in step (2) includes the following steps: mixing PDMS prepolymer and curing agent in proportion to prepare PDMS matrix, slowly adding NaCl particles to PDMS matrix, mechanically stirring, then adding graphene, vacuum degassing, curing, and dissolving the salt template with deionized water to form a porous PDMS structure layer.

[0013] Furthermore, the NaCl particles have a particle size of 100-120 μm, the mass ratio of the PDMS prepolymer to NaCl is 1:2-1:3, the mass ratio of the PDMS prepolymer to the curing agent is 10:1-7:1, the graphene doping amount is 1.1-1.5 wt%, the porosity of the porous PDMS structure layer is 60-70%, the thickness of the porous PDMS structure layer is 300-350 μm, and the pore distribution exhibits a gradient characteristic, with the bottom layer pore diameter being 60-80 μm and the surface layer pore diameter being 20-30 μm.

[0014] Furthermore, the template method described in step (3) includes, but is not limited to, the sandpaper template method or the nanoimprint template method.

[0015] Further, the preparation method of the graphene-containing microstructure layer in step (3) includes the following steps: covering the surface of the porous PDMS structure layer with a sandpaper template, pouring the mixture of graphene-containing PDMS prepolymer and curing agent onto the sandpaper template, and after vacuum and curing treatment, peeling off the sandpaper template to form a graphene-containing microstructure layer.

[0016] Furthermore, the particle size of the sandpaper particles is 200-240 mesh, the graphene doping amount in the mixture is 0.5-1.0 wt%, the curing temperature is 75℃, the size of the graphene-containing microstructure layer is 50μm×50μm and the height is 20-25μm, and the surface of the graphene-containing microstructure layer has randomly distributed pyramid-shaped protrusions.

[0017] Furthermore, an encapsulation protective layer is covered on the surface of the microstructure layer. The encapsulation protective layer consists of 2-4 layers of hexagonal boron nitride film with a thickness of 5-10 nm. The encapsulation protective layer is covered by a transfer process, which includes, but is not limited to, mechanical peeling. The graphene doping amount of the porous PDMS structure layer is 0.3-0.5 wt% higher than that of the microstructure layer.

[0018] Further, the method for preparing the microcap groove in step (4) includes the following steps: etching a microcap groove on a silicon-based insulator wafer, and sequentially depositing a SiO2 insulating layer, a chromium adhesion layer, and a gold layer.

[0019] Furthermore, the etching process is a deep reactive ion etching process, the depth of the microcap groove is 40μm, the sidewall tilt angle is 85-88°, the thickness of the SiO2 insulating layer is 1μm, the thickness of the chromium adhesion layer is 50nm, and the thickness of the gold layer is 500nm.

[0020] Furthermore, the process parameters for gold-silicon eutectic bonding in step (5) include: bonding temperature 380-420℃, pressure 8-12MPa, and vacuum degree ≤1×10⁻⁶. -3 Pa, bonding time 30-45 minutes, the thickness of the bonded layer formed is 2-3 μm.

[0021] The residual gas pressure of the vacuum-sealed cavity is ≤0.1Pa, the distance between the resonator and the top of the cavity is 10μm, and the lateral gap is 5μm.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] This invention utilizes a hierarchical stress transfer mechanism involving microstructure layers and porous layers to accurately identify wide-amplitude vibration characteristics during transformer operation and effectively distinguish between normal and abnormal operating conditions.

[0024] This invention forms a vacuum-sealed cavity by bonding a porous / microstructure layer assembly of an integrated H-type resonator to a specific microcap structure layer via gold-silicon eutectic bonding. This cavity can operate stably in complex electromagnetic environments and oil-contaminated conditions, enabling long-term, accurate, and reliable monitoring of transformer vibration status. Attached Figure Description

[0025] Figure 1 This is a schematic diagram illustrating the fabrication of the porous / microstructure layer component of the present invention.

[0026] Figure 2 This is a schematic diagram of the packaging and bonding of the present invention.

[0027] Figure 3 This is a diagram of the microcap structure of the present invention.

[0028] Figure 4 This is a system flowchart of the present invention. Detailed Implementation

[0029] This invention provides a packaging design method for a flexible graphene transformer vibration sensor based on a microcap structure, comprising the following steps:

[0030] (1) An H-type graphene resonator layer was prepared on a flexible polyimide substrate;

[0031] (2) A porous PDMS structure layer containing graphene was constructed on the resonator layer by means of a salt template method;

[0032] (3) A graphene-containing microstructure layer is formed on the surface of the porous layer using a template method, thus obtaining a porous / microstructure layer assembly for an integrated H-type resonator;

[0033] (4) Fabricate microcap grooves with silicon dioxide / chromium / gold layers on silicon-based insulator wafers;

[0034] (5) The porous / microstructure layer assembly of the integrated H-type resonator and the microcap structure layer are bonded together with gold-silicon eutectic bonding to form a vacuum-sealed cavity.

[0035] In some embodiments of the present invention, the preparation method of the H-type graphene resonator layer in step (1) includes the following steps: forming an H-type photoresist pattern on the surface of a flexible polyimide substrate using photolithography, then removing the material in the exposed area by etching to form an H-type channel structure, and finally growing a single layer of graphene inside the channel structure by chemical vapor deposition to obtain the H-type graphene resonator layer.

[0036] The H-type resonator prepared by this invention amplifies the transformer vibration signal through a double cantilever beam structure and utilizes the central hollow area to promote the efficient transmission of stress waves in the porous layer.

[0037] In some embodiments of the present invention, the thickness of the flexible polyimide substrate is 100-150 μm, and the H-shaped channel structure is 400-450 μm long and 5-8 μm wide. Preferably, the thickness of the flexible polyimide substrate is 125 μm, and the H-shaped channel structure is 420 μm long and 6 μm wide.

[0038] In some embodiments of the present invention, the preparation method of the graphene-containing porous PDMS structure layer in step (2) includes the following steps: mixing PDMS prepolymer and curing agent in proportion to prepare PDMS matrix, slowly adding NaCl particles to PDMS matrix, mechanically stirring, then adding graphene, vacuum degassing, curing, and dissolving salt template with deionized water to form a porous PDMS structure layer.

[0039] The salt template method plays an irreplaceable core role in this invention. The interconnected pore network formed by the dissolution of sodium chloride crystals can realize the gradient stress transmission channel from the bottom layer to the surface of the porous layer. This is a structural feature that cannot be spontaneously formed by other template methods (such as foaming agent / microsphere templates).

[0040] In this invention, the porous PDMS structure layer serves as a stress transfer medium. The large pores at the bottom of the structure efficiently absorb the low-frequency, large-amplitude vibration energy of the transformer core, while the gradually narrowing pores on the surface form a mechanical interlock with the microstructure layer, transmitting the broadband vibration signal in stages to the H-type graphene resonator. At the same time, as a conductive network carrier, the gradient-dispersed graphene forms an asymmetric conductive path within the porous framework.

[0041] In some embodiments of the present invention, the NaCl particles have a particle size of 100-120 μm, the mass ratio of the PDMS prepolymer to NaCl is 1:2-1:3, the mass ratio of the PDMS prepolymer to the curing agent is 10:1-7:1, the graphene doping amount is 1.1-1.5 wt%, the porosity of the porous PDMS structure layer is 60-70%, the thickness of the porous PDMS structure layer is 300-350 μm, and the pore distribution exhibits a gradient characteristic, with the bottom layer pores having a diameter of 60- The NaCl particles have a diameter of 80 μm and a surface pore diameter of 20-30 μm. Preferably, the NaCl particles have a diameter of 100 μm, the mass ratio of the PDMS prepolymer to NaCl is 1:3, the mass ratio of the PDMS prepolymer to the curing agent is 10:1, the graphene doping amount is 1.5 wt%, the porosity of the porous PDMS structure layer is 64%, the thickness of the porous PDMS structure layer is 350 μm, the pore distribution exhibits a gradient characteristic, the bottom pore diameter is 80 μm, and the surface pore diameter is 30 μm.

[0042] In some embodiments of the present invention, the template method in step (3) includes, but is not limited to, the sandpaper template method or the nanoimprint template method.

[0043] In some embodiments of the present invention, the preparation method of the graphene-containing microstructure layer in step (3) includes the following steps: covering the surface of the porous PDMS structure layer with a sandpaper template, pouring the graphene-containing PDMS prepolymer and curing agent mixture onto the sandpaper template, and after vacuum and curing treatment, peeling off the sandpaper template to form a graphene-containing microstructure layer.

[0044] In some embodiments of the present invention, the particle size of the sandpaper particles is 200-240 mesh, the graphene doping amount in the mixture is 0.5-1.0 wt%, the curing temperature is 75°C, the size of the graphene-containing microstructure layer is 50 μm × 50 μm and the height is 20-25 μm, and the surface of the graphene-containing microstructure layer has randomly distributed pyramid-shaped protrusions. Preferably, the particle size of the sandpaper particles is 240 mesh, the graphene doping amount in the mixture is 1.0 wt%, the curing temperature is 75°C, the size of the graphene-containing microstructure layer is 50 μm × 50 μm and the height is 25 μm, and the surface of the graphene-containing microstructure layer has randomly distributed pyramid-shaped protrusions.

[0045] In some embodiments of the present invention, an encapsulation protective layer is covered on the surface of the microstructure layer. The encapsulation protective layer consists of 2-4 layers of hexagonal boron nitride thin film with a thickness of 5-10 nm. The graphene doping amount of the porous PDMS structure layer is 0.3-0.5 wt% higher than that of the microstructure layer. Preferably, the encapsulation protective layer consists of 2 layers of hexagonal boron nitride thin film with a thickness of 5 nm. The encapsulation protective layer is covered by a transfer process, which includes, but is not limited to, mechanical peeling. The graphene doping amount of the porous PDMS structure layer is 0.3-0.5 wt% higher than that of the microstructure layer, forming an asymmetric conductive network structure.

[0046] The graphene-containing microstructure layer described in this invention forms a mechanical interlock with the porous PDMS layer through randomly distributed pyramid-like protrusions on its surface, effectively enhancing the efficiency of vibration stress transmission. At the same time, the three-dimensional conductive network constructed by the uniformly dispersed graphene in the microstructure layer efficiently converts mechanical vibration signals into electrical signals, and is protected by a boron nitride encapsulation layer to ensure long-term stable operation in oily environments.

[0047] The porous structure layer described in this invention employs a high graphene doping level design. By constructing a high-density conductive network at the bottom layer, it achieves sensitive capture of large-amplitude vibrations. At the same time, the constructed surface microstructure layer with lower doping optimizes the high-frequency signal response. This gradient concentration configuration not only avoids the signal aliasing problem caused by uniform doping, but also significantly improves the signal-to-noise ratio of the sensor in broadband vibration monitoring through the characteristics of the asymmetric conductive network. It effectively solves the technical problem that traditional sensors cannot achieve both low-frequency and high-frequency vibration detection accuracy.

[0048] In some embodiments of the present invention, the method for preparing the microcap groove in step (4) includes the following steps: etching a microcap groove on a silicon-based insulator wafer, and sequentially depositing a SiO2 insulating layer, a chromium adhesion layer, and a gold layer.

[0049] In some embodiments of the present invention, the etching process is a deep reactive ion etching process, the depth of the microcap groove is 40 μm, the sidewall tilt angle is 85-88°, the thickness of the SiO2 insulating layer is 1 μm, the thickness of the chromium adhesion layer is 50 nm, and the thickness of the gold layer is 500 nm.

[0050] The chromium adhesion layer has an irreplaceable dual function in this invention. Its oxide interface properties can form chemical covalent bonds with the silicon dioxide insulating layer during high-temperature bonding, and at the same time generate metallurgical diffusion bonding with the gold layer. In contrast, materials such as titanium and nickel will undergo interface delamination under oil immersion thermal cycling conditions.

[0051] In this invention, the microcap groove structure provides a stable vacuum working environment for the H-type resonator by precisely controlling the cavity depth and sidewall tilt angle. At the same time, its geometric configuration and porous / microstructure layer form mechanical constraints to ensure precise alignment of the vibration transmission path. The SiO2 insulating layer deposited sequentially on the groove surface effectively isolates complex electromagnetic interference. The chromium adhesion layer achieves a reliable transition between the gold layer and SiO2 through strong interfacial bonding force. The gold layer, as a eutectic bonding medium, forms a hermetically sealed interface with the silicon substrate under high temperature and pressure. The three elements work together to ensure the long-term stable monitoring of the sensor in oil immersion and strong electromagnetic environments.

[0052] In some embodiments of the present invention, the process parameters for gold-silicon eutectic bonding in step (5) include: bonding temperature 380-420℃, pressure 8-12MPa, and vacuum degree ≤1×10⁻⁶. -3 Pa, bonding time 30-45 minutes, the thickness of the bonded layer formed is 2-3 μm.

[0053] In some embodiments of the present invention, the residual gas pressure of the vacuum-sealed cavity is ≤0.1Pa, the distance between the resonator and the top of the cavity is 10μm, and the lateral gap is 5μm.

[0054] This invention involves transferring a single layer of graphene onto a flexible polyimide (PI) substrate via chemical vapor deposition, and defining an H-type resonator structure using photolithography and reactive ion etching. Next, using the H-type resonator as the bottom layer, a polydimethylsiloxane (PDMS) prepolymer is mixed with sodium chloride particles in a specific ratio using a salt template method. After curing, the salt template is dissolved to form a porous structure layer, in which graphene is uniformly dispersed. Subsequently, a graphene-containing PDMS prepolymer is cast onto the surface of the porous structure layer using a sandpaper template method. After curing and peeling, a microstructure layer is formed, resulting in a porous / microstructure layer assembly integrating the H-type resonator. Microcap grooves are fabricated on a silicon-based insulator wafer using an etching process, followed by the sequential deposition of a silicon dioxide layer, a chromium adhesion layer, and a gold layer. Finally, the porous / microstructure layer assembly integrating the H-type resonator is aligned with the microcap grooves, and gold-silicon eutectic bonding is achieved by applying pressure and high temperature to form a vacuum-sealed cavity, completing the encapsulation.

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0056] Unless otherwise specified, the test methods or experimental methods described in the following examples are all conventional methods; unless otherwise specified, the raw materials and additives are obtained from conventional commercial sources or prepared by conventional methods.

[0057] Example 1

[0058] A packaging design method for a flexible graphene transformer vibration sensor based on a microcap structure, comprising the following steps:

[0059] (1) A flexible polyimide film with a thickness of 125 μm was selected as the substrate, and an H-shaped pattern mask was formed by photolithography. The specific process of the photolithography was as follows: First, positive photoresist was spin-coated on the surface of the flexible polyimide substrate at a rotation speed of 3000 rpm and a thickness of 1.2 μm. Then, ultraviolet exposure (wavelength 365 nm, exposure dose 120 mJ / cm) was performed. 2 The H-shaped mask pattern is transferred to the photoresist layer. A 0.5% NaOH solution is used as the developer, and the development time is 60 seconds, ultimately forming an H-shaped photoresist mask. An H-shaped trench with a length of 420 μm and a width of 6 μm is prepared using reactive ion beam etching (RIE). The specific process of RIE is as follows: argon is used as the working gas (flow rate 50 sccm), the chamber pressure is maintained at 0.5 Pa, the RF power is set to 200 W, the bias voltage is -150 V, and the etching rate is controlled at 100 nm / min, ultimately forming an H-shaped trench structure. Monolayer graphene is grown within the trench using chemical vapor deposition (CVD). The specific process of CVD for growing monolayer graphene is as follows: methane is used as the carbon source (flow rate 20 sccm), hydrogen is used as the carrier gas (flow rate 50 sccm), the reaction chamber temperature is raised to 1000 °C, the substrate preheating time is 30 minutes, and the growth pressure is maintained at 20 mbar, forming a piezoresistive sensitive unit.

[0060] (2) PDMS matrix is ​​prepared by mixing PDMS prepolymer and curing agent in a certain proportion. The mass ratio of PDMS prepolymer to curing agent is 10:1. NaCl particles with a particle size of 100μm are slowly added to the PDMS matrix. The mass ratio of NaCl particles to PDMS prepolymer is 1:2.5. The mixture is mechanically stirred and then 1.5wt% graphene is added. After vacuum degassing and curing at 85℃ for 2 hours, the salt template is dissolved in deionized water to form a gradient porous PDMS structure layer with a porosity of 64% and a thickness of 350μm. The bottom layer pore diameter is 80μm and the surface pore diameter is reduced to 30μm to achieve stress gradient transfer function.

[0061] (3) Cover the surface of the gradient porous PDMS structure layer with a 240-mesh sandpaper template, pour the PDMS prepolymer containing 1.0wt% graphene and the curing agent mixture onto the sandpaper template, and peel off the template after vacuum penetration and curing at 75°C to form a microstructure layer with a substrate size of 50μm×50μm and a height of 25μm.

[0062] Two hexagonal boron nitride films were coated on the surface of the microstructure layer using a mechanical exfoliation method to form an encapsulation protective layer with a thickness of about 5 nm. By controlling the graphene concentration gradient between the porous layer (1.5 wt%) and the microstructure layer (1.0 wt%), an asymmetric conductive network was constructed to achieve differential response of broadband vibration signals.

[0063] (4) A microcap groove with a depth of 40 μm and a sidewall tilt angle of 87° is prepared on a silicon-based insulator wafer using a deep reactive ion etching process. The specific process of preparing the microcap groove using the deep reactive ion etching process is as follows: the Bosch process is used to alternately etch (SF6 gas, flow rate 100 sccm, etching cycle 5s) and passivate (C4F8 gas, flow rate 80 sccm, passivation cycle 3s), with a radio frequency power of 180W, a chamber pressure of 1.2Pa, and an etching rate of 3μm / min. The etching depth is monitored in real time by an infrared interferometer, and finally a microcap groove structure is formed. A 1μm thick SiO2 insulating layer, a 50nm chromium adhesion layer and a 500nm gold layer are deposited sequentially.

[0064] (5) Align the porous / microstructure layer assembly of the integrated H-type resonator with the microcap structure layer, apply a pressure of 10 MPa and heat to 400 °C, and maintain a vacuum of 5 × 10⁻⁶. -4 The gold-silicon eutectic bonding process is carried out for 30 minutes to form a vacuum-sealed cavity with a bonding layer thickness of 2.5 μm. The residual gas pressure of the vacuum-sealed cavity is ≤0.1 Pa. The distance between the resonator and the top of the cavity is 10 μm, and the lateral gap is 5 μm, which meets the long-term stable monitoring requirements of transformers under complex operating conditions.

[0065] This invention verifies the stability and long-term reliability of the flexible graphene transformer vibration sensor based on the microcap structure prepared in Example 1 under complex environments through systematic experiments. In simulated transformer oil immersion conditions (500 cycles of hot oil at 120℃), the residual gas pressure in the vacuum-sealed cavity remains ≤0.1Pa, and the resonator frequency drift is <±0.5%. Under strong electromagnetic interference, the H-type resonator signal-to-noise ratio remains >60dB, and the gradient graphene network of the microstructure layer ensures that the sensor's sensitivity consistency error is <3% in a wide frequency range of 0.1-5kHz. During the experiment, no cracks appeared at the gold-silicon eutectic bonding interface, meeting the requirements for full life cycle monitoring of transformers.

[0066] Example 2:

[0067] A packaging design method for a flexible graphene transformer vibration sensor based on a microcap structure, comprising the following steps:

[0068] (1) A flexible polyimide film with a thickness of 100 μm is selected as the substrate, and an H-shaped pattern mask is formed by photolithography. The specific process of the photolithography is as follows: First, positive photoresist is spin-coated on the surface of the flexible polyimide substrate at a rotation speed of 3000 rpm and a thickness of 1.2 μm. Then, it is exposed to ultraviolet light (wavelength 365 nm, exposure dose 120 mJ / cm). 2 The H-shaped mask pattern is transferred to the photoresist layer. A 0.5% NaOH solution is used as the developer, and the development time is 60 seconds, ultimately forming an H-shaped photoresist mask. An H-shaped trench with a length of 400 μm and a width of 5 μm is prepared using reactive ion beam etching (RIE). The specific process of RIE is as follows: argon is used as the working gas (flow rate 50 sccm), the chamber pressure is maintained at 0.5 Pa, the RF power is set to 200 W, the bias voltage is -150 V, and the etching rate is controlled at 100 nm / min, ultimately forming an H-shaped trench structure. Monolayer graphene is grown within the trench using chemical vapor deposition (CVD). The specific process of CVD for growing monolayer graphene is as follows: methane is used as the carbon source (flow rate 15 sccm), hydrogen is used as the carrier gas (flow rate 40 sccm), the reaction chamber temperature is raised to 1000 °C, the substrate preheating time is 30 minutes, and the growth pressure is maintained at 20 mbar, forming a piezoresistive sensitive unit.

[0069] (2) PDMS matrix is ​​prepared by mixing PDMS prepolymer and curing agent in a certain proportion. The mass ratio of PDMS prepolymer to curing agent is 10:1. NaCl particles with a particle size of 120μm are slowly added to the PDMS matrix. The mass ratio of NaCl particles to PDMS prepolymer is 2:1. The mixture is mechanically stirred, and then 1.1wt% graphene is added. The mixture is degassed under vacuum and cured at 85℃ for 2 hours. The salt template is dissolved in deionized water to form a gradient porous PDMS structure layer with a porosity of 70% and a thickness of 300μm. The bottom layer pore diameter is 60μm and the surface pore diameter is reduced to 20μm to achieve the stress gradient transfer function.

[0070] (3) Cover the surface of the gradient porous PDMS structure layer with a 200-mesh sandpaper template, pour the PDMS prepolymer containing 0.5wt% graphene and the curing agent mixture onto the sandpaper template, and peel off the template after vacuum penetration and curing at 75°C to form a microstructure layer with a substrate size of 50μm×50μm and a height of 20μm.

[0071] Two hexagonal boron nitride films were coated on the surface of the microstructure layer using a mechanical exfoliation method to form an encapsulation protective layer with a thickness of about 5 nm. By controlling the graphene concentration gradient between the porous layer (1.5 wt%) and the microstructure layer (1.0 wt%), an asymmetric conductive network was constructed to achieve differential response of broadband vibration signals.

[0072] (4) A microcap groove with a depth of 40 μm and a sidewall tilt angle of 87° is prepared on a silicon-based insulator wafer using a deep reactive ion etching process. The specific process of preparing the microcap groove using the deep reactive ion etching process is as follows: the Bosch process is used to alternately etch (SF6 gas, flow rate 100 sccm, etching cycle 5s) and passivate (C4F8 gas, flow rate 80 sccm, passivation cycle 3s), with a radio frequency power of 180W, a chamber pressure of 1.2Pa, and an etching rate of 3μm / min. The etching depth is monitored in real time by an infrared interferometer, and finally a microcap groove structure is formed. A 1μm thick SiO2 insulating layer, a 50nm chromium adhesion layer and a 500nm gold layer are deposited sequentially.

[0073] (5) Align the porous / microstructure layer assembly of the integrated H-type resonator with the microcap structure layer, apply a pressure of 12 MPa and heat to 380 °C, and maintain a vacuum of 5 × 10⁻⁶. -4 The gold-silicon eutectic bonding process is carried out for 30 minutes to form a vacuum-sealed cavity with a bonding layer thickness of 2 μm. The residual gas pressure of the vacuum-sealed cavity is ≤0.1 Pa. The distance between the resonator and the top of the cavity is 10 μm, and the lateral gap is 5 μm, which meets the long-term stable monitoring requirements of transformers under complex operating conditions.

[0074] This invention verified the stability and long-term reliability of the flexible graphene transformer vibration sensor based on the microcap structure prepared in Example 2 under complex environments through systematic experiments. In simulated transformer oil immersion conditions (500 cycles of hot oil at 120℃), the residual gas pressure in the vacuum-sealed cavity remained ≤0.1 Pa, and the resonator frequency drift was <±0.5%. Under strong electromagnetic interference, the H-type resonator signal-to-noise ratio remained >60 dB, and the gradient graphene network of the microstructure layer ensured that the sensor's sensitivity consistency error was <3% over a wide frequency range of 0.1-5 kHz. During the experiment, no cracks appeared at the gold-silicon eutectic bonding interface, meeting the requirements for full-lifecycle transformer monitoring. The thin substrate prepared in Example 2 improved the resonator sensitivity by 12% compared to Example 1.

[0075] Comparative Example 1

[0076] The difference from Example 1 is that step (2) is different from that in Example 1.

[0077] The detailed operation process of step (2) of Comparative Example 1 is as follows:

[0078] A PDMS matrix was prepared by mixing PDMS prepolymer and curing agent at a mass ratio of 10:1. 1.5 wt% graphene was then directly added, and the mixture was mechanically stirred for 30 minutes until homogeneous. Following this, vacuum degassing was performed for 30 minutes (vacuum degree ≤ 1 × 10⁻³ Pa). The mixture was then poured into a custom mold and cured at 85°C for 2 hours to form a non-porous, dense PDMS structural layer with a thickness controlled at 350 μm. This structural layer exhibits a gradient-free pore design and is an overall uniform and dense PDMS-graphene composite material.

[0079] This step did not employ the salt template method and did not introduce any porous structure. Instead, a dense layer was formed through direct curing. In contrast to the gradient porous structure of Example 1, the stress transmission path is singular, making it unable to efficiently absorb and transmit low-frequency vibration energy, resulting in a significant decrease in sensitivity in the low-frequency range. The sensor prepared in Comparative Example 1 has 42% lower sensitivity in the 0.1-100Hz low-frequency range than that of Example 1, and cannot capture the vibration characteristics of the transformer core.

[0080] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A packaging design method for a flexible graphene transformer vibration sensor based on a microcap structure, characterized in that, Includes the following steps: (1) An H-type graphene resonator layer was prepared on a flexible polyimide substrate; (2) A porous PDMS structure layer containing graphene was constructed on the resonator layer by means of a salt template method; (3) A graphene-containing microstructure layer is formed on the surface of the porous layer using a template method, thus obtaining a porous / microstructure layer assembly for an integrated H-type resonator; (4) Fabricate microcap grooves with silicon dioxide / chromium / gold layers on silicon-based insulator wafers; (5) The porous / microstructure layer assembly of the integrated H-type resonator and the microcap structure layer are bonded together with gold-silicon eutectic bonding to form a vacuum-sealed cavity.

2. The packaging design method for a flexible graphene transformer vibration sensor based on a microcap structure according to claim 1, characterized in that, The preparation method of the H-type graphene resonator layer in step (1) includes the following steps: forming an H-type photoresist pattern on the surface of a flexible polyimide substrate using photolithography, then removing the material in the exposed area by etching to form an H-type channel structure, and finally growing a single layer of graphene inside the channel structure by chemical vapor deposition to obtain the H-type graphene resonator layer.

3. The packaging design method for a flexible graphene transformer vibration sensor based on a microcap structure according to claim 2, characterized in that, The thickness of the flexible polyimide substrate is 100-150 μm, and the H-shaped channel structure is 400-450 μm long and 5-8 μm wide.

4. The packaging design method for a flexible graphene transformer vibration sensor based on a microcap structure according to claim 1, characterized in that, The preparation method of the graphene-containing porous PDMS structure layer in step (2) includes the following steps: mixing PDMS prepolymer and curing agent in proportion to prepare PDMS matrix, slowly adding NaCl particles to PDMS matrix, mechanically stirring, then adding graphene, vacuum degassing, curing, and dissolving salt template with deionized water to form a porous PDMS structure layer.

5. The packaging design method for a flexible graphene transformer vibration sensor based on a microcap structure according to claim 4, characterized in that, The NaCl particles have a particle size of 100-120 μm, the mass ratio of the PDMS prepolymer to NaCl is 1:2-1:3, the mass ratio of the PDMS prepolymer to the curing agent is 10:1-7:1, the graphene doping amount is 1.1-1.5 wt%, the porosity of the porous PDMS structure layer is 60-70%, the thickness of the porous PDMS structure layer is 300-350 μm, and the pore distribution exhibits a gradient characteristic, with the bottom layer pore diameter being 60-80 μm and the surface layer pore diameter being 20-30 μm.

6. The packaging design method for a flexible graphene transformer vibration sensor based on a microcap structure according to claim 1, characterized in that, The preparation method of the graphene-containing microstructure layer in step (3) includes the following steps: covering the surface of the porous PDMS structure layer with a sandpaper template, pouring the mixture of graphene-containing PDMS prepolymer and curing agent onto the sandpaper template, and after vacuum and curing treatment, peeling off the sandpaper template to form a graphene-containing microstructure layer.

7. The packaging design method for a flexible graphene transformer vibration sensor based on a microcap structure according to claim 6, characterized in that, The particle size of the sandpaper particles is 200-240 mesh, the graphene doping amount in the mixture is 0.5-1.0 wt%, the curing temperature is 75℃, the size of the graphene-containing microstructure layer is 50μm×50μm and the height is 20-25μm, and the surface of the graphene-containing microstructure layer has randomly distributed pyramid-shaped protrusions.

8. The packaging design method for a flexible graphene transformer vibration sensor based on a microcap structure according to claim 6, characterized in that, An encapsulation protective layer is covered on the surface of the microstructure layer. The encapsulation protective layer consists of 2-4 layers of hexagonal boron nitride film with a thickness of 5-10 nm. The graphene doping amount of the porous PDMS structure layer is 0.3-0.5 wt% higher than that of the microstructure layer.

9. The packaging design method for a flexible graphene transformer vibration sensor based on a microcap structure according to claim 1, characterized in that, The method for preparing the microcap groove in step (4) includes the following steps: etching a microcap groove on a silicon-based insulator wafer and depositing a SiO2 insulating layer, a chromium adhesion layer and a gold layer in sequence.

10. The packaging design method for a flexible graphene transformer vibration sensor based on a microcap structure according to claim 1, characterized in that, The process parameters for gold-silicon eutectic bonding in step (5) include: bonding temperature 380-420℃, pressure 8-12MPa, and vacuum degree ≤1×10 -3 Pa, bonding time 30-45 minutes, the thickness of the bonded layer formed is 2-3 μm.

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