Piezoresistive sensor ceramic device and preparation method thereof

Abstract

The invention discloses a piezoresistive sensor ceramic device and a preparation method thereof, and belongs to the technical field of functional ceramic diaphragm preparation. The device comprises a thick base and a central thin-wall pressure sensing diaphragm which are integrally sintered and formed, the base is provided with a blind hole, the diaphragm is arranged at the bottom of the blind hole, and an annular supporting convex point is arranged on the outer side of the diaphragm; the diaphragm is composed of alumina ceramics with the average grain size of 20-30 [mu] m, and zirconia nanoparticles are dispersed and distributed on the grain boundary. The relative density gt of the device; 99.5%, and the maximum porosity is 1t; 1 [mu] m. By cooperatively controlling the grain size, the grain boundary phase and the defects, the problems of low strength, poor consistency and difficult forming processing of the ultrathin ceramic pressure sensing diaphragm are solved at one stroke, and the obtained device has extremely high bursting strength, low pressure hysteresis and excellent reliability, and is particularly suitable for a high-performance piezoresistive pressure sensor.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of functional ceramic diaphragm preparation, and particularly relates to a piezoresistive sensor ceramic device and a preparation method. BACKGROUND

[0002] The piezoresistive pressure sensor is widely used in industrial control, automobile electronics, medical equipment, aerospace and other fields due to its high precision, high stability and good dynamic response characteristics. The core pressure sensing element of the piezoresistive pressure sensor is usually made of metal or ceramic material. Among them, alumina ceramic becomes an ideal material for high-performance sensor diaphragm due to its excellent insulation, hardness, corrosion resistance and long-term stability.

[0003] The traditional alumina ceramic pressure sensing diaphragm is usually prepared by a process of dry pressing and sintering. However, under the demand of higher range, smaller size and higher reliability, the sensor tends to use thinner ceramic pressure sensing diaphragm (for example, thickness ≤0.3mm) to improve the sensitivity. This trend brings serious technical challenges: 1) Strength and reliability problem of thin-walled diaphragm: when the diaphragm thickness is thinned to sub-millimeter level, its microstructure becomes particularly critical. The grain size of conventional alumina ceramic is usually 40-80μm. If a 0.2mm thick diaphragm is prepared with this grain size, only about 3-4 grains can be arranged in the thickness direction, forming a so-called oligocrystal or single crystal structure. In this structure, the defects, anisotropy or brittleness of the grain boundaries of the single grain will directly dominate the overall mechanical properties of the diaphragm, resulting in low burst strength, poor fatigue resistance, difficulty in bearing the pressure impact of three times the rated range required by the sensor, and a sharp drop in product yield and reliability.

[0004] 2) Microstructure uniformity and densification control problem: to obtain fine-grained ceramic with high strength and high reliability, it is necessary to achieve almost complete densification (relative density > 99.5%) and extremely small internal defect (pore) size (<1μm). This requires the starting powder to have high activity and excellent dispersibility, and to effectively inhibit the abnormal growth of grains during sintering. In the conventional process, problems such as powder agglomeration and uneven distribution of additives are prone to form micro-pores or weak grain boundaries after sintering, which become stress concentration sources and crack initiation points.

[0005] 3) Complex structure integrated forming and precision machining problem: in order to package pressure liquid, the ceramic part of the sensor is usually designed as an integrated structure with a blind hole. When the traditional dry-pressed blind hole part is formed, the density gradient or layer cracking defects are easily generated in the area of the hole bottom (i.e. the future pressure sensing diaphragm) due to uneven powder filling and poor exhaust. The subsequent precision grinding of the diaphragm plane also lacks effective protection, which easily leads to diaphragm over-thinning, uneven thickness or introduction of machining damage, seriously affecting the consistency of product performance.

[0006] Therefore, developing a piezoresistive sensor ceramic device capable of achieving ultra-thin thickness, ultra-high strength, and ultra-high uniformity, and its fabrication method through integrated precision manufacturing, has become a critical technological bottleneck that urgently needs to be overcome in this field. Existing technologies have not yet systematically solved the above problems, particularly the end-to-end coordinated control from powder source to final product, to achieve precise control of grain size, grain boundary phase, and defect size in the microstructure of the diaphragm. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by proposing a piezoresistive sensor ceramic device and its preparation method. In particular, it relates to a thin-walled ceramic diaphragm that, while ensuring high hardness and high purity, also possesses high burst strength and high reliability, and its preparation method.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A piezoresistive sensor ceramic device includes a thick base and a thin-walled pressure-sensitive diaphragm. A through hole is provided at the center of the side of the thick base. The thin-walled pressure-sensitive diaphragm is located at one end of the through hole and forms a blind hole structure with the inner wall of the through hole. A cap is provided at the other end of the through hole to form a sealed cavity. The sealed cavity is filled with pressurized liquid for applying pressure. The thick base and the thin-walled pressure-sensitive diaphragm are integrally sintered together. A pressure-resistance conversion circuit is provided on the outer side of the thin-walled pressure-sensitive diaphragm away from the pressurized liquid.

[0009] Preferably, the outer surface of the thick base is provided with a ring of support protrusions surrounding the thin-walled pressure-sensitive diaphragm, providing support points during grinding.

[0010] Preferably, the thickness of the thin-walled pressure-sensitive diaphragm is 0.2 mm to 1.1 mm, and its microstructure consists of alumina ceramic grains with an average grain size of 20 μm to 30 μm, with zirconia nanoparticles distributed in a dispersed phase at the alumina grain boundaries; the relative density of the ceramic device is greater than 99.5%, and the maximum internal pore size is less than 1 μm.

[0011] Furthermore, the alumina ceramic grains in the thin-walled pressure-sensitive diaphragm are alumina particles with a purity of not less than 99.5%.

[0012] This invention also proposes a method for fabricating the aforementioned piezoresistive sensor ceramic device, comprising the following steps: S1. Powder acid hydrolysis activation: High-purity α-Al₂O₃ powder (purity ≥99.5%) with an average particle size of 20-25 μm was dispersed in a 0.1-1.0 mol / L nitric acid aqueous solution, with a solid content controlled at 10-20 wt%. The mixture was stirred at a constant temperature of 60-80℃ for 2-4 hours. After the reaction, the powder was washed with deionized water by centrifugation until the pH of the supernatant was 6-7. The powder was then dried at 110℃ for 12 hours and calcined at 400-450℃ for 2 hours to obtain surface-activated alumina powder. S2, Composite Surface Modification and Molecular-Level Doping: Surface-activated alumina powder is dispersed in anhydrous ethanol, and a composite non-silicone coupling agent is added. The composite non-silicone coupling agent is composed of aluminate coupling agent and zirconate coupling agent in a mass ratio of (7-8):(2-3). The mixture was refluxed at 70°C for 8 hours. After the reaction was completed, it was washed three times by centrifugation with anhydrous ethanol and then vacuum dried at 80°C to obtain the surface-modified powder. S3, Granulation: The surface-modified powder is mixed with 1-1.5% polyvinyl butyral binder, 0.5-0.8% polyethylene glycol plasticizer and 0.2-0.3% stearic acid lubricant in anhydrous ethanol, and after being ball-milled evenly, it is spray-dried to obtain spherical granulated powder with good flowability. S4. Dry pressing: The granulated powder is dry-pressed using a mold to obtain a green body; S5. Debinding and Sintering: The green body is placed in an air atmosphere sintering furnace, heated to 350°C at 1°C / min and held for 60 minutes, then heated to 500°C at 1°C / min and held for 120 minutes to complete the debinding. After debinding, the temperature is increased to 1500-1600℃ at 5℃ / min and held for 2-2.5 hours, then cooled in the furnace to obtain dense ceramic parts rough material; S6, Precision Grinding: The upper and lower large planes of the sintered ceramic device are ground on both sides to obtain the finished ceramic device.

[0013] Preferably, the aluminate coupling agent in step S2 is distearyl isopropoxy aluminate, and the zirconate coupling agent is neodecanoate zirconium.

[0014] Preferably, the mass percentage of zirconium oxide in the final ceramic device is controlled to be 2-5% by the amount of zirconium ester coupling agent added in step S2.

[0015] Preferably, the mold of S4 has a venting channel with a diameter of 0.2 mm inside the lower punch core rod, and the upper punch end face is machined with the cavity of the annular support protrusion. During the dry pressing of S4, when demolding, external air enters the blind hole of the thick base through the venting channel of the lower punch core rod to balance the air pressure inside the hole. A two-way stepped pressurization method is adopted: first, pre-pressurize at 10 MPa and hold for 30 seconds, then slowly pressurize to 60 MPa at a rate of 1 MPa / s and hold for 60 seconds, and then slowly depressurize to obtain the green blank.

[0016] Preferably, the double-sided grinding of S6 includes the following steps: first, a light pressure of 0.1 MPa and a high speed of 60 rpm are used for initial grinding to remove the deformed layer; then, a heavy pressure of 0.3 MPa and a low speed of 30 rpm are used for fine grinding; the annular support protrusion is always in contact with the grinding disc during the grinding process to provide support for the thin-walled pressure-sensitive diaphragm until its height is flush with the diaphragm surface.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention precisely controls the average grain size of the ceramic diaphragm within the range of 20-30 μm. For ultrathin films ranging from 0.2 mm to 0.3 mm, 6-15 grains can be arranged along the thickness direction, forming a stable polycrystalline structure. This effectively avoids overall failure caused by defects in a single grain in an oligocrystalline structure, allowing stress to be uniformly transmitted and dispersed among multiple grains and grain boundaries. Simultaneously, the uniformly dispersed nano-zirconia particles at the grain boundaries further stabilize the grain boundaries and refine the grains through a pinning effect, and consume crack propagation energy through a potential phase transformation toughening mechanism, collectively increasing the diaphragm's fracture strength to over 400 MPa, far exceeding that of conventional ceramic diaphragms. This achieves high strength and high reliability for ultrathin ceramic diaphragms, meeting the stringent requirements of three times the range of sensor burst pressure.

[0018] 2. This invention solves the molding and processing challenges of monolithic ceramic devices with blind pores through an acid-activated, composite coupling agent-based molecular-level doping powder treatment process, ensuring high product consistency and high yield. Acid activation creates uniform active sites on the surface of high-purity alumina powder, enabling the subsequent aluminum / zirconium composite coupling agent to achieve monolayer coating via chemical bonding. This not only significantly improves the powder's dispersibility and sintering activity but also ensures the uniform distribution of the zirconia precursor at the molecular scale. During sintering, zirconia is generated in situ as nanoparticles and precisely enriched at the alumina grain boundaries, rather than agglomerating in the grain triangles. Combined with an optimized sintering regime, a near-defect-free microstructure with a relative density greater than 99.5% and a maximum pore size of less than 1 μm is ultimately obtained, fundamentally eliminating large crack sources and reducing the pressure hysteresis error to below 0.05%FS.

[0019] 3. This invention also employs a unique mold design—a lower punch with an exhaust channel and an upper punch with annular support protrusions in the cavity—combined with a bidirectional stepped pressurization process, achieving uniform filling and densification of powder within the complex cavity of blind holes. The exhaust channel balances air pressure during demolding, preventing cracking of the green body; the stepped pressurization allows for thorough rearrangement of powder particles and smooth gas discharge, effectively avoiding layered defects at the bottom of blind holes and laying the foundation for obtaining a structurally complete green body. The pre-designed annular support protrusions play a crucial role in subsequent double-sided grinding. As a mechanical stop, it ensures that the grinding pressure is primarily borne by the thick base area, thus protecting the central thin-walled diaphragm from over-grinding. Combined with a two-step grinding process—initial grinding with light pressure and high speed to remove the damaged layer, and fine grinding with heavy pressure and low speed to fix the thickness—the process precisely controls the diaphragm thickness while minimizing residual surface stress and microcracks, resulting in a high-quality functional surface.

[0020] 4. This invention forms a complete, controllable, and mass-producible preparation process, from powder surface modification and molecular-level doping to defect-controlled molding, precision atmosphere sintering, and protective grinding. By controlling factors such as acid concentration, coupling agent ratio, pressure curve, sintering temperature, and grinding pressure / speed, a final film product with a fine-grained, dense, uniform, and complete microstructure is obtained. The process has good reproducibility and is suitable for industrial production. Attached Figure Description

[0021] Figure 1 This is an internal structure diagram of a piezoresistive sensor ceramic device proposed in this invention; Figure 2 This is a top view of the piezoresistive sensor ceramic device proposed in this invention; Figure 3 This is an electron microscope image of the green blank of the thin-walled pressure-sensitive diaphragm prepared by the method in Example 1 of the present invention after dry pressing; Figure 4 This is an electron microscope image of the thin-walled pressure-sensitive diaphragm obtained by the method in Example 1 of this invention after complete sintering; Figure 5 This is an electron microscope image of the thin-walled pressure-sensitive diaphragm green blank prepared by the method of Comparative Example 1 of the present invention after dry pressing.

[0022] In the diagram: 1-Thick base, 2-Thin-walled pressure-sensitive diaphragm, 3-Annular support protrusion. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0024] I. Product Structure Design: like Figures 1-2As shown, a piezoresistive sensor ceramic device includes a thick, integrally sintered base 1 and a thin-walled pressure-sensitive diaphragm 2 located at the center of the base. A blind hole is formed on the thick base 1, the bottom of which is formed by the thin-walled pressure-sensitive diaphragm 2. The blind hole is filled with a pressurized liquid for applying pressure. A pressure-resistance conversion circuit is provided on the side of the thin-walled pressure-sensitive diaphragm 2 away from the pressurized liquid. A ring of annular support protrusions 3 surrounds the thin-walled pressure-sensitive diaphragm 2 on the outer surface of the thick base 1, providing support points during grinding. The thickness of the thin-walled pressure-sensitive diaphragm 2 is 0.2 mm to 1.1 mm, and its microstructure consists of alumina ceramic grains with an average grain size of 20 μm to 30 μm, with zirconia nanoparticles distributed in a dispersed phase at the alumina grain boundaries. The relative density of the ceramic device is greater than 99.5%, and the maximum internal pore size is less than 1 μm. The alumina ceramic grains in the thin-walled pressure-sensitive diaphragm 2 are alumina particles with a purity of not less than 99.5%.

[0025] II. Product Process Design: Preliminary research indicates that typical ceramic grains are 40-80 μm in size, with an average of 60 μm. Therefore, a 0.2 mm thickness typically results in only 3-4 layers of grain breakage, making the film prone to rupture under pressure. This invention controls the grain size to 20-30 μm, ensuring that with a 0.2 mm thickness, grain breakage occurs in 6-10 layers, thus improving burst strength and achieving three times the required burst pressure range for this product. Controlling grain size requires precise management of material selection, grinding particle size, and sintering temperature.

[0026] Based on this research, the present invention includes the following embodiments and comparative examples: Example 1. A method for fabricating a piezoresistive sensor ceramic device, comprising the following steps: S1. Powder acid hydrolysis activation: High-purity α-Al₂O₃ powder (purity 99.6%) with an average particle size of 22 μm was dispersed in a 0.5 mol / L nitric acid aqueous solution, with the solid content controlled at 15 wt%. The mixture was stirred at 70 °C for 3 hours. After the reaction, the powder was washed with deionized water by centrifugation until the pH of the supernatant was 6-7. The supernatant was then dried at 110 °C for 12 hours and calcined at 420 °C for 2 hours to obtain surface-activated alumina powder. S2, Composite Surface Modification and Molecular-Level Doping: Surface-activated alumina powder is dispersed in anhydrous ethanol, and a composite non-silicone coupling agent is added. The composite non-silicone coupling agent is composed of an aluminate coupling agent and a zirconate coupling agent in a mass ratio of 7.5:2.5. The aluminate coupling agent in step S2 is distearyl isopropoxy aluminate, and the zirconate coupling agent is neodecanoate zirconium.

[0027] The amount of zirconate coupling agent added in step S2 is used to control the mass percentage of zirconium oxide in the final ceramic device to be 3.5%.

[0028] The mixture was refluxed at 70°C for 8 hours. After the reaction was completed, it was washed three times by centrifugation with anhydrous ethanol and then vacuum dried at 80°C to obtain the surface-modified powder. S3, Granulation: The surface-modified powder was mixed with 1.2% polyvinyl butyral binder, 0.6% polyethylene glycol plasticizer and 0.25% stearic acid lubricant by mass in anhydrous ethanol, and after being ball-milled evenly, it was spray-dried to obtain spherical granulated powder with good flowability. S4. Dry pressing: The granulated powder is dry-pressed using a mold to obtain a green body. The mold has a 0.2mm diameter venting channel inside the lower punch, and the upper punch end face is machined with the cavity of the annular support protrusion 3. During the dry pressing process in S4, external air enters the blind hole of the thick base 1 through the venting channel of the lower punch during demolding, balancing the air pressure inside the hole. A bidirectional stepped pressurization method is used: first, a pre-pressurization of 10MPa is applied and held for 30 seconds; then, the pressure is slowly increased to 60MPa at a rate of 1MPa / s and held for 60 seconds; finally, the pressure is slowly released to obtain the green body. The microstructure of the green body is as follows: Figure 3 As shown.

[0029] S5. Debinding and Sintering: The green body is placed in an air atmosphere sintering furnace, heated to 350°C at 1°C / min and held for 60 minutes, then heated to 500°C at 1°C / min and held for 120 minutes to complete the debinding. After debinding, the temperature was increased to 1550℃ at a rate of 5℃ / min and held for 2.2 hours, followed by furnace cooling to obtain dense ceramic component rough material; the microstructure of the rough material is as follows: Figure 4 As shown.

[0030] S6, Precision Grinding: The upper and lower large planes of the sintered ceramic device are subjected to double-sided grinding: First, a light pressure of 0.1 MPa and a high speed of 60 rpm are used for initial grinding to remove the deformed layer; then, a heavy pressure of 0.3 MPa and a low speed of 30 rpm are used for fine grinding. The annular support protrusion 3 remains in contact with the grinding disc throughout the grinding process, providing support for the thin-walled pressure-sensitive diaphragm 2, until its height is flush with the diaphragm surface. Diaphragm thickness: 0.3 mm.

[0031] Example 2. A method for fabricating a piezoresistive ceramic sensor, comprising the following steps: S1. Powder acid hydrolysis activation: High-purity α-Al₂O₃ powder (purity 99.5%) with an average particle size of 20 μm was dispersed in a 0.1 mol / L nitric acid aqueous solution, with the solid content controlled at 10 wt%. The mixture was stirred at 80 °C for 2 hours. After the reaction, the powder was washed with deionized water by centrifugation until the pH of the supernatant was 6-7. The powder was then dried at 110 °C for 12 hours and calcined at 450 °C for 2 hours to obtain surface-activated alumina powder. S2, Composite Surface Modification and Molecular-Level Doping: Surface-activated alumina powder is dispersed in anhydrous ethanol, and a composite non-silicone coupling agent is added. The composite non-silicone coupling agent is composed of an aluminate coupling agent and a zirconate coupling agent in a mass ratio of 7:3. The aluminate coupling agent in step S2 is distearyl isopropoxy aluminate, and the zirconate coupling agent is neodecanoate zirconium.

[0032] The amount of zirconate coupling agent added in step S2 is used to control the mass percentage of zirconium oxide in the final ceramic device to be 5%.

[0033] The mixture was refluxed at 70°C for 8 hours. After the reaction was completed, it was washed three times by centrifugation with anhydrous ethanol and then vacuum dried at 80°C to obtain the surface-modified powder. S3, Granulation: The surface-modified powder was mixed with 1.5% polyvinyl butyral binder, 0.5% polyethylene glycol plasticizer and 0.3% stearic acid lubricant by weight of the surface-modified powder in anhydrous ethanol. After being ball-milled evenly, the mixture was spray-dried to obtain spherical granulated powder with good flowability. S4. Dry pressing: The granulated powder is dry-pressed using a mold to obtain a green body. The mold has a 0.2mm diameter venting channel inside the lower punch core rod, and the upper punch end face is machined with the cavity of the annular support protrusion 3. During the dry pressing process in S4, external air enters the blind hole of the thick base 1 through the venting channel of the lower punch core rod during demolding, balancing the air pressure inside the hole. A two-way stepped pressurization method is adopted: first, a pre-pressurization of 10MPa is applied and held for 30 seconds, then the pressure is slowly increased to 60MPa at a rate of 1MPa / s and held for 60 seconds, followed by slow depressurization to obtain the green body.

[0034] S5. Debinding and Sintering: The green body is placed in an air atmosphere sintering furnace, heated to 350°C at 1°C / min and held for 60 minutes, then heated to 500°C at 1°C / min and held for 120 minutes to complete the debinding. After debinding, the temperature is increased to 1600℃ at 5℃ / min and held for 2 hours, and then cooled in the furnace to obtain dense ceramic parts rough material; S6, Precision Grinding: The upper and lower large planes of the sintered ceramic device are subjected to double-sided grinding: First, a light pressure of 0.1 MPa and a high speed of 60 rpm are used for initial grinding to remove the deformed layer; then, a heavy pressure of 0.3 MPa and a low speed of 30 rpm are used for fine grinding. The annular support protrusion 3 remains in contact with the grinding disc throughout the grinding process, providing support for the thin-walled pressure-sensitive diaphragm 2, until its height is flush with the diaphragm surface. Diaphragm thickness: 0.2 mm.

[0035] Example 3. A method for fabricating a piezoresistive sensor ceramic device, comprising the following steps: S1. Powder acid hydrolysis activation: High-purity α-Al₂O₃ powder (purity 99.7%) with an average particle size of 25 μm was dispersed in a 1.0 mol / L nitric acid aqueous solution, with the solid content controlled at 20 wt%. The mixture was stirred at 60 °C for 4 hours. After the reaction, the powder was washed with deionized water by centrifugation until the pH of the supernatant was 6-7. The supernatant was then dried at 110 °C for 12 hours and calcined at 400 °C for 2 hours to obtain surface-activated alumina powder. S2, Composite Surface Modification and Molecular-Level Doping: Surface-activated alumina powder is dispersed in anhydrous ethanol, and a composite non-silicone coupling agent is added. The composite non-silicone coupling agent is composed of an aluminate coupling agent and a zirconate coupling agent in a mass ratio of 8:2. The aluminate coupling agent in step S2 is distearyl isopropoxy aluminate, and the zirconate coupling agent is neodecanoate zirconium.

[0036] The amount of zirconate coupling agent added in step S2 is used to control the mass percentage of zirconium oxide in the final ceramic device to be 2%.

[0037] The mixture was refluxed at 70°C for 8 hours. After the reaction was completed, it was washed three times by centrifugation with anhydrous ethanol and then vacuum dried at 80°C to obtain the surface-modified powder. S3, Granulation: The surface-modified powder was mixed with 1% polyvinyl butyral binder, 0.8% polyethylene glycol plasticizer and 0.2% stearic acid lubricant by mass of the surface-modified powder in anhydrous ethanol, and after being ball-milled evenly, it was spray-dried to obtain spherical granulated powder with good flowability. S4. Dry pressing: The granulated powder is dry-pressed using a mold to obtain a green body. The mold has a 0.2mm diameter venting channel inside the lower punch core rod, and the upper punch end face is machined with the cavity of the annular support protrusion 3. During the dry pressing process in S4, external air enters the blind hole of the thick base 1 through the venting channel of the lower punch core rod during demolding, balancing the air pressure inside the hole. A two-way stepped pressurization method is adopted: first, a pre-pressurization of 10MPa is applied and held for 30 seconds, then the pressure is slowly increased to 60MPa at a rate of 1MPa / s and held for 60 seconds, followed by slow depressurization to obtain the green body.

[0038] S5. Debinding and Sintering: The green body is placed in an air atmosphere sintering furnace, heated to 350°C at 1°C / min and held for 60 minutes, then heated to 500°C at 1°C / min and held for 120 minutes to complete the debinding. After debinding, the temperature is increased to 1500℃ at 5℃ / min and held for 2 hours, and then cooled in the furnace to obtain dense ceramic parts rough material; S6, Precision Grinding: The upper and lower large planes of the sintered ceramic device are subjected to double-sided grinding: first, a light pressure of 0.1 MPa and a high speed of 60 rpm are used for initial grinding to remove the deformed layer; then, a heavy pressure of 0.3 MPa and a low speed of 30 rpm are used for fine grinding. The annular support protrusion 3 remains in contact with the grinding disc throughout the grinding process, providing support for the thin-walled pressure-sensitive diaphragm 2, until its height is flush with the diaphragm surface. Diaphragm thickness: 1.1 mm.

[0039] Comparative Example 1 (coarse particle size powder: 45 micrometers): Based on Example 1, the parameters were changed as follows: Powder: average particle size 45 μm, purity 99.6% α-Al2O3; other steps were exactly the same as in Example 1. The resulting film blank was as follows: Figure 5 As shown.

[0040] Comparative Example 2 (Fine-particle size powder: 1 micrometer): Based on Example 1, the parameters were changed as follows: Powder: average particle size 1 μm, purity 99.6% α-Al2O3, and other steps were exactly the same as in Example 1.

[0041] Comparative Example 3 (without acid hydrolysis activation): Based on Example 1, the parameters were changed: the S1 acid hydrolysis activation step was skipped, and the S2 surface modification was performed directly. The reduction in surface activity may cause local agglomeration of zirconia, which forms micron-sized clusters, thereby reducing performance.

[0042] Comparative Example 4 (without zirconate coupling agent): Based on Example 1, the parameters were changed: only aluminate coupling agents were used as the composite coupling agent.

[0043] Comparative Example 5 (Conventional uniaxial pressure molding): Based on Example 1, the parameters were changed: Molding: uniaxial pressure up to 60MPa (no stepped pressure, no exhaust channel).

[0044] Comparative Example 6 (Grinding without annular support bumps): Based on Example 1, the parameters were changed: the mold has no annular support protrusion cavity, and the diaphragm directly contacts the grinding disc during S6 grinding.

[0045] Comparative Example 7 (High-speed heavy-pressure grinding): Based on Example 1, the parameters were changed: S6 grinding process with a pressure of 0.3MPa and a speed of 60rpm throughout.

[0046] The product structure information and performance tests of Examples 1-3 and Comparative Examples 1-7 are summarized, mainly focusing on the dimensions of microstructure (grain size, zirconium oxide distribution, porosity), mechanical properties (fracture strength, density), and functional performance (pressure hysteresis error), as detailed in Tables 1 and 2 below: Table 1. Effect of alumina particle size on the performance of ceramic diaphragms

[0047] Table 2. Influence of process parameters on the performance of ceramic diaphragms

[0048] It should be noted that in Tables 1 and 2, the estimated number of grain layers = film thickness (mm) / average grain size (mm), rounded up to the nearest integer.

[0049] Data Analysis: 1. Controlling the grain size to 20-30 μm is to ensure a sufficient number of grain layers (6-10 layers) in ultrathin (e.g., 0.2 mm) films, avoiding structural inhomogeneity and the risk of breakage due to insufficient grain size (3-4 layers). This set of data perfectly verifies and deepens this theory: Reference Figures 3-4 Examples 1 (12-13 layers) and 2 (9-10 layers): The grain size (22-24 μm) was precisely controlled within the target range. Even for a 0.2 mm ultrathin film (Example 2), the number of grain layers reached 9-10, forming a polycrystalline structure that effectively dispersed stress, thus achieving extremely high fracture strength (420-450 MPa) and extremely low hysteresis error (0.04-0.05%FS). This confirms that fine grains and a multilayer structure are key to high-strength, high-precision thin-walled films.

[0050] Comparative Example 1 (5-6 layers): Using 45μm coarse powder, the grains abnormally grew to 52μm after sintering. At a thickness of 0.3mm, the number of grain layers was only about 5-6, approaching the danger zone indicated by layer thickness warnings. The result was extremely uneven structure, where defects or oversized pores (15μm) in any grain easily triggered through-cracks. Consequently, its strength plummeted to 260MPa, and the hysteresis error reached 0.40%FS, making its performance completely unacceptable. This conversely demonstrates the necessity of controlling the initial powder particle size to prevent final grain coarsening.

[0051] Comparative Example 2 (37-38 layers): Using 1μm fine powder, the sintered grain size was 8μm, resulting in a high number of layers, but the performance was inferior to the example. This indicates that simply pursuing a high number of layers is insufficient. The fundamental reason is that the high specific surface area of ​​the fine powder leads to severe agglomeration, causing the zirconium oxide distribution to fail (network agglomeration) and introducing more defects (1.5μm porosity). Its strength (360MPa) is acceptable, but the hysteresis error (0.12%FS) is poor, indicating that material uniformity and grain boundary strengthening are more important than simply the number of layers.

[0052] Conclusion: The 20-30μm grain target is a comprehensive optimal solution: it can ensure that there are enough grain layers (≥6 layers) in the thin wall to avoid the fragility of single-layer / sparse-layer grains, and it can also match the subsequent zirconia dispersion strengthening process to avoid the process problems caused by excessively fine or coarse powder.

[0053] 2. Failure analysis of key process steps: Comparative Example 3, without acid-based activation, resulted in the lowest relative density (98.9%), largest porosity (5 μm), largest grain size (31 μm), and one of the worst strengths (280 MPa). The purpose of acid-based activation in Example 1 was not only cleaning, but also to achieve… + The zirconia reacts with the Al₂O₃ surface to form a uniform hydroxylated surface. This provides uniform and highly active anchoring sites for subsequent chemical bonding of coupling agents (especially zirconate esters). Skipping this step results in uneven modification of the coupling agent, poor adhesion of the zirconia precursor to the powder surface, leading to localized agglomeration (micron-sized clusters) during sintering and an inability to suppress grain boundary migration (grain coarsening). Large zirconia agglomerates and accompanying large pores become the main crack initiation sites, severely impairing strength and reliability.

[0054] Comparative Example 4, without the introduction of zirconium oxide, showed a comprehensive decline in all material properties: while strength (320 MPa) and density (99.3%) remained acceptable, hysteresis error (0.15%FS) significantly worsened. This indicates that grain boundaries are a relatively weak point in high-purity alumina ceramics. The introduction of nano-zirconia particles in Example 1 inhibited grain growth and refined the grains through a pinning effect; more importantly, it may undergo phase transformation toughening (t-ZrO2→m-ZrO2) under stress, absorbing crack energy and significantly improving fracture toughness. The material in Comparative Example 4 lacked this mechanism, resulting in insufficient grain boundary strength. Under cyclic pressure loading, it was more prone to microplastic deformation and microcracks, manifesting as increased hysteresis error and poor long-term stability.

[0055] Comparative Example 5 used conventional uniaxial pressurization without venting, preventing the gas inside the green blank from escaping and resulting in macroscopic lamination defects (8μm pores) after sintering. Although the grain and zirconium oxide distribution were acceptable, this fatal defect made its strength (300MPa) and hysteresis performance (0.30%FS) among the worst. The venting channels and bidirectional stepped pressurization of the mold in Example 1 were specifically designed for blind-hole structures. The venting channels balance the gas pressure during demolding, preventing the green blank from springing back and cracking; the stepped pressurization allows for sufficient rearrangement of powder particles, and gas is slowly expelled. The process in Comparative Example 5 forms an air cushion at the bottom of the blind hole. After pressing, this area has low density, and after sintering, lamination cracks parallel to the diaphragm form, greatly reducing the effective load-bearing thickness and strength of the diaphragm.

[0056] Comparative Example 6 lacks support bumps and mechanical stops, causing the diaphragm area to bear all the pressure during grinding, resulting in over-grinding to approximately 0.15 mm. This not only drastically reduced the number of grain layers to a dangerous level but also directly damaged the diaphragm strength (250 MPa) due to the concentrated grinding stress. The excessively thin and damaged diaphragm caused a sharp increase in its deformation nonlinearity, leading to a hysteresis error as high as 0.50% FS, resulting in complete product failure.

[0057] Comparative Example 7 involved rough grinding with improper grinding parameters. Although the thickness was controllable, the high-speed, heavy-pressure grinding resulted in high residual tensile stress and microcracks on the surface. These surface defects become crack initiation points during pressure loading. While their impact on static strength (400 MPa) was relatively small, they significantly deteriorated signal stability under cyclic loading, manifested as an increase in hysteresis error to 0.20%FS. This highlights the scientific validity of the two-step method of light-pressure, high-speed de-damage layer removal followed by heavy-pressure, low-speed, fixed-thickness fine-tuning.

[0058] 3. Analysis of the process adjustments in the example: Compared to Example 1, Example 2 used a finer initial powder (20 μm) and a higher zirconium oxide content (5%), and was sintered at a higher temperature (1600 °C). This resulted in finer grains (22 μm) and higher density (99.8%), achieving the highest strength (450 MPa) and best precision (0.04% FS). This demonstrates that, provided the powder has sufficient activity (20 μm) and good dispersion (acid hydrolysis + coupling), increasing the zirconium oxide content can further strengthen grain boundaries and optimize performance.

[0059] Compared to Example 1, Example 3 used coarser initial powder (25 μm) and a lower zirconium oxide content (2%), and was sintered at a lower temperature (1500 °C). The grain size (27 μm) was close to the upper limit of the range, the density was slightly lower (99.6%), and the zirconium oxide strengthening effect was weaker. Although the absolute strength was acceptable (380 MPa) due to its thicker film (1.1 mm), its strength efficiency and precision per unit thickness (0.07%FS) were lower than those of Examples 1 and 2. This indicates that while this process still has advantages for non-polar thin films, it is not the optimal configuration.

[0060] 4. Conclusion: Example 1 represents a complete set of optimized technical solutions: selection of powders with specific particle sizes, acid lysis activation and molecular-level doping, proprietary molding technology, ring-shaped support bumps, and a two-step grinding method. By precisely controlling the grain size to 20-30 μm, sufficient grain layers (≥6 layers) are ensured in the thickness direction of the ultrathin pressure-sensitive diaphragm, laying a solid foundation for high reliability from a geometrical perspective. Through acid lysis activation and the application of aluminum / zirconium composite coupling agents, uniform and dispersed distribution of nano-zirconium oxide at the alumina grain boundaries is achieved, chemically strengthening the grain boundaries and realizing fine-grain strengthening and phase transformation toughening. The unique molding and grinding process effectively avoids macroscopic defects (delamination) and processing damage (over-grinding, high residual stress), ensuring the integrity of the diaphragm structure and a good surface condition. Only by fully adhering to Embodiment 1 of this invention can a relative density of >99.5%, a pore size of <1μm, and a grain size of 20-30μm be simultaneously achieved, ultimately translating into excellent fracture strength (>420MPa) and extremely high measurement accuracy (hysteresis error <0.05%FS), meeting the stringent requirements of high-end piezoresistive sensors for their core ceramic components. The absence or deviation of any single link will lead to a break in the performance chain, preventing the product from achieving its design goals.

[0061] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A piezoresistive sensor ceramic device, characterized in that, It includes a thick base (1) and a thin-walled pressure-sensitive diaphragm (2). The thick base (1) has a through hole at the center of its side. The thin-walled pressure-sensitive diaphragm (2) is located at one end of the through hole and forms a blind hole structure with the inner wall of the through hole. The other end of the through hole is provided with a cap to form a sealed cavity. The sealed cavity is filled with pressurized liquid for applying pressure. The thick base (1) and the thin-walled pressure-sensitive diaphragm (2) are integrally sintered. The outer side of the thin-walled pressure-sensitive diaphragm (2) away from the pressurized liquid is provided with a pressure resistance conversion circuit. The thickness of the thin-walled pressure-sensitive diaphragm (2) is 0.2 mm to 1.1 mm, and its microstructure is composed of alumina ceramic grains with an average grain size of 20 μm to 30 μm, and zirconia nanoparticles are distributed in the form of a dispersed phase at the alumina grain boundaries; the relative density of the ceramic device is greater than 99.5%, and the maximum internal pore size is less than 1 μm.

2. The piezoresistive sensor ceramic device according to claim 1, characterized in that, The outer surface of the thick base (1) is provided with a ring of support protrusions (3) surrounding the thin-walled pressure-sensitive diaphragm (2), which provides support points during grinding.

3. The piezoresistive sensor ceramic device according to claim 1, characterized in that, The alumina ceramic grains in the thin-walled pressure-sensitive diaphragm (2) are alumina particles with a purity of not less than 99.5%.

4. A method for fabricating a piezoresistive sensor ceramic device as described in any one of claims 1-3, characterized in that, Includes the following steps: S1. Powder acid hydrolysis activation: High-purity α-Al₂O₃ powder (purity ≥99.5%) with an average particle size of 20-25 μm was dispersed in a 0.1-1.0 mol / L nitric acid aqueous solution, with a solid content controlled at 10-20 wt%. The mixture was stirred at a constant temperature of 60-80℃ for 2-4 hours. After the reaction, the powder was washed with deionized water by centrifugation until the pH of the supernatant was 6-7. The powder was then dried at 110℃ for 12 hours and calcined at 400-450℃ for 2 hours to obtain surface-activated alumina powder. S2, Composite Surface Modification and Molecular-Level Doping: Surface-activated alumina powder is dispersed in anhydrous ethanol, and a composite non-silicone coupling agent is added. The composite non-silicone coupling agent is composed of aluminate coupling agent and zirconate coupling agent in a mass ratio of (7-8):(2-3). The mixture was refluxed at 70°C for 8 hours. After the reaction was completed, it was washed three times by centrifugation with anhydrous ethanol and then vacuum dried at 80°C to obtain the surface-modified powder. S3, Granulation: The surface-modified powder is mixed with 1-1.5% polyvinyl butyral binder, 0.5-0.8% polyethylene glycol plasticizer and 0.2-0.3% stearic acid lubricant in anhydrous ethanol, and after being ball-milled evenly, it is spray-dried to obtain spherical granulated powder with good flowability. S4, Dry pressing: The granulated powder is dry-pressed using a mold to obtain a green body; S5. Debinding and Sintering: The green body is placed in an air atmosphere sintering furnace, heated to 350°C at 1°C / min and held for 60 minutes, then heated to 500°C at 1°C / min and held for 120 minutes to complete the debinding. After debinding, the temperature is increased to 1500-1600℃ at 5℃ / min and held for 2-2.5 hours, then cooled in the furnace to obtain dense ceramic parts rough material; S6, Precision Grinding: The upper and lower large planes of the sintered ceramic device are ground on both sides to obtain the finished ceramic device.

5. The method for fabricating a piezoresistive sensor ceramic device according to claim 4, characterized in that, The aluminate coupling agent in step S2 is distearyl isopropoxy aluminate, and the zirconate coupling agent is neodecanoate zirconium.

6. The method for fabricating a piezoresistive sensor ceramic device according to claim 4, characterized in that, The amount of zirconate coupling agent added in S2 is used to control the mass percentage of zirconium oxide in the final ceramic device to be 2-5%.

7. The method for fabricating a piezoresistive sensor ceramic device according to claim 4, characterized in that, The mold of S4 has an exhaust channel with a diameter of 0.2 mm inside the lower punch core rod, and the upper punch end face is machined with a cavity of annular support protrusion (3). In the dry pressing of S4, when demolding, external air enters the blind hole of the thick base (1) through the exhaust channel of the lower punch core rod to balance the air pressure in the hole. The two-way step pressurization is adopted: first, the pressure is pre-pressurized at 10 MPa and held for 30 seconds, then the pressure is slowly increased to 60 MPa at a rate of 1 MPa / s and held for 60 seconds, and then the pressure is slowly released to obtain the green blank.

8. The method for fabricating a piezoresistive sensor ceramic device according to claim 4, characterized in that, The double-sided grinding of S6 includes the following steps: First, a light pressure of 0.1MPa and a high speed of 60rpm are used for initial grinding to remove the deformed layer; then, a heavy pressure of 0.3MPa and a low speed of 30rpm are used for fine grinding; the annular support protrusion (3) is always in contact with the grinding disc during the grinding process to provide support for the thin-walled pressure-sensitive diaphragm (2) until its height is flush with the surface of the diaphragm.

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