An ultra-high temperature MEMS sensor packaging structure based on full high-temperature ceramic material and a preparation method thereof

Abstract

The application relates to the technical field of sensors and discloses an ultra-high-temperature MEMS sensor packaging structure based on a full high-temperature ceramic material and a preparation method thereof, wherein the packaging structure comprises a top cover, an adapter plate and a base; the top cover, the adapter plate and the base are all prepared from ceramic materials; the top cover and the base jointly form a ceramic packaging shell of a sensor chip; the top of the top cover is provided with a thread for realizing the installation of the packaged sensor in a test environment; the adapter plate is connected with the top cover and the base through threads; a first Al2O3 ceramic layer is arranged on the adapter plate, the sensor chip is fixed through the first Al2O3 ceramic layer, the electrodes of the sensor chip and the adapter plate are connected through wire bonding, and the electrical signal transmission of the sensor chip to a wire is realized. The application can realize the effective high-temperature-resistant packaging of the sensor chip and provide support for the normal work of the sensor under ultra-high temperature.

Description

Technical Field

[0001] This invention relates to the field of sensor technology, and in particular to an ultra-high temperature MEMS sensor packaging structure based on all high temperature ceramic materials and its fabrication method. Background Technology

[0002] With the rapid development of microelectronics technology, microelectromechanical systems (MEMS) sensors have been widely used in aerospace, automotive, industrial control, environmental monitoring, and other fields. However, the operational stability of MEMS sensors in harsh environments such as high temperatures still faces many challenges, especially in high-temperature packaging technology for chips. Without effective packaging, the sensor's internal precision structure may be directly exposed to the external environment, making it highly susceptible to factors such as high temperature, humidity, vibration, and chemical corrosion, leading to performance degradation, measurement inaccuracies, or even complete failure. Therefore, reliable high-temperature packaging technology for MEMS sensors is particularly important for harsh high-temperature environments. High-temperature packaging technology involves many factors, especially in high-temperature environments. The matching of the thermal expansion coefficient of the packaging material and the sensor material is crucial for the success of the packaging technology. Suitable packaging materials can ensure that the sensor maintains structural stability even under prolonged high-temperature operation, preventing packaging damage or internal component damage due to thermal expansion mismatch.

[0003] Currently, various high-temperature packaging solutions are available on the market, among which metal packaging and ceramic packaging are common. Metal packaging is a traditional and common high-temperature packaging method, typically using metal materials (such as stainless steel, aluminum alloy, etc.) as the package shell and connecting materials. Chip fixation and electrical connections are achieved through soldered leads or mechanical connections, offering excellent thermal conductivity and mechanical strength. However, due to the high coefficient of thermal expansion of metals, their compatibility with silicon chips is poor, easily generating thermal stress during high-temperature cycling, leading to chip breakage or connection failure. Furthermore, metal packaging usually requires a large package volume to accommodate soldered leads and ensure connection strength, which limits its miniaturization applications.

[0004] Ceramic packaging has become an ideal packaging method for high-temperature environments due to its excellent high-temperature stability, electrical insulation, and corrosion resistance. Commonly used ceramic materials include alumina (Al₂O₃), aluminum nitride (AlN), and silicon carbide (SiC), which have low coefficients of thermal expansion, close to those of silicon. Therefore, they can effectively reduce interfacial thermal stress and improve the reliability and long-term stability of the packaging under high-temperature conditions. However, there is currently no reliable solution for ceramic packaging, so it is not used alone. Instead, two or more materials (such as a ceramic substrate and a metal shell) are combined to optimize packaging performance. The surface of the ceramic substrate usually has metal lines to achieve electrical connections. The connection between these metal lines and the ceramic substrate is often accomplished through sputtering or electroplating techniques. Existing ceramic packaging solutions usually rely on the combination of metal materials and ceramic substrates, which to some extent solves the problems of matching thermal expansion coefficients and electrical connections. In summary, although ceramic packaging has many advantages, there is currently no all-ceramic high-temperature packaging form for MEMS sensors.

[0005] The existing technology CN119043565A proposes a packaging structure for a miniature high-temperature pressure sensor. The pressure-sensitive chip is fixed onto a ceramic fixing plate by ultrasonic welding to form a pressure-sensitive core, which realizes the transmission of electrical signals and chip fixation. The ceramic fixing plate is then installed into the mounting groove of a metal tube shell for fixation, and leads are welded. Finally, the pressure-sensitive core and the welding points are fixed and protected by metal sealant, thus realizing the packaging of the high-temperature pressure sensor.

[0006] The existing technology CN117842924A proposes a leadless packaged high-temperature pressure sensor. The sensor chip has a glass-silicon-glass three-layer structure with high strength. Therefore, the chip is directly packaged by paste sintering. It is bonded to the metal base by insulating high-temperature paste sintering. At the same time, the electrical signal is connected to the base pins by the conductive metal paste, thus realizing the packaging of the high-temperature pressure sensor.

[0007] Research revealed that the most common packaging method for MEMS sensors in high-temperature environments is a combination of a ceramic substrate and a metal casing. While the stable physical and chemical properties of both materials allow them to withstand high ambient temperatures, issues such as thermal expansion and lead wires still compromise the reliability and stability of the packaged sensor at high temperatures. On one hand, the coefficient of thermal expansion of ceramic materials is close to that of the chip (typically Si or SiC). A transitional connection between the chip, ceramic, and metal can alleviate thermal stress caused by the difference in thermal expansion coefficients to some extent. However, current connections between sensor components rely on methods such as paste bonding, metal welding, and mechanical fixing. Due to material differences, connection failures and poor contact are still prone to occur at high temperatures, thus affecting the sensor's performance and long-term stability. On the other hand, current lead wire methods mostly employ silver paste sintering or ultrasonic welding, but these methods have limitations in high-temperature packaging. Direct silver paste sintering typically requires a large contact area to ensure sufficient strength, thus only suitable for larger devices and not for miniaturized MEMS chips. Furthermore, the significant difference in thermal expansion coefficients between the silver paste and the chip can lead to thermal stress concentration, easily causing chip breakage or connection failure. Another common wire bonding technology is ultrasonic welding, which connects metal leads to the chip through mechanical vibration. However, due to the low reliability of solder joints at high temperatures, the solder joints may degrade, loosen, or fail due to temperature changes. In addition, some technologies currently employ adapter circuit boards and sputtering or electroplating on ceramic substrates, but these are also prone to detachment at high temperatures. Therefore, there is currently no reliable high-temperature packaging and wire bonding solution for MEMS sensors. Summary of the Invention

[0008] The purpose of this invention is to provide an ultra-high temperature MEMS sensor packaging structure based on all high temperature ceramic materials and its fabrication method. The circuit layout of the ceramic substrate is completed by using a precursor ceramic fabrication process, and then the chip is sintered and fixed on the ceramic substrate using ceramic paste. The electrical signal connection from the chip to the ceramic adapter board is realized by wire bonding. The wires of the base are led out and fixed by sintering silver paste and ceramic paste respectively. The various parts of the packaging shell are connected by threads to form a high temperature packaging structure made of all ceramic materials.

[0009] To achieve the above objectives, the following technical solution is adopted:

[0010] In a first aspect, the present invention provides an ultra-high temperature MEMS sensor packaging structure based on all high temperature ceramic materials, including a top cover, an adapter plate, and a base; the top cover, the adapter plate, and the base are all made of ceramic materials;

[0011] The top cover and the base together form a ceramic package shell for the sensor chip. The top of the top cover is provided with threads to enable the sensor to be installed in the test environment after packaging.

[0012] The adapter plate is connected to the top cover and the base by threads;

[0013] The adapter board is provided with a first Al2O3 ceramic layer, which is used to fix the sensor chip. The electrodes of the sensor chip and the adapter board are connected by wire bonding to realize the transmission of electrical signals from the sensor chip to the wires.

[0014] Furthermore, a shallow groove is formed on the upper surface of the adapter plate, and the sensor chip is fixed to the edge of the shallow groove by a ceramic slurry sintering process to form the Al2O3 ceramic layer.

[0015] Furthermore, a first through hole is provided on the adapter plate, and an adapter electrode is formed by injecting PSN silazane polymer into the through hole and then performing photocrosslinking and high-temperature pyrolysis.

[0016] Furthermore, a Ti / Ni / Au metal system is magnetron sputtered onto the upper surface of the adapter electrode to perform gold-to-gold wire bonding with the chip, thereby enabling the transmission of electrical signals from the sensor chip to the adapter electrode.

[0017] Furthermore, the side surface of the adapter plate is machined with threads, which are mechanically connected to the first mating thread of the top cover and the second mating thread of the base to realize the encapsulation of the sensor chip.

[0018] Furthermore, a third groove is formed on the upper surface of the base to cooperate with the adapter plate. A second through hole is formed on the base, through which the wire is connected to the adapter electrode. A second Al2O3 ceramic layer is disposed in the second through hole. The second Al2O3 ceramic layer is used to fix the wire. A conductive silver layer is disposed on the upper end of the second Al2O3 ceramic layer. The conductive silver layer is used to realize the electrical signal connection between the wire and the adapter electrode. The adapter electrode is connected to the sensor chip through gold wire leads.

[0019] Furthermore, the top cover has a first groove and a second groove. The second groove is used to realize the mating connection between the top cover and the adapter plate. The first groove is used to provide a margin for the gold wire. The head of the top cover is provided with an installation thread.

[0020] Secondly, the present invention provides a method for fabricating an ultra-high temperature MEMS sensor packaging structure based on all-high temperature ceramic materials as described above, the fabrication method comprising:

[0021] Take three Al2O3 ceramic substrates and, based on the determined structure of the top cover, the adapter plate, and the base, process the top cover, the adapter plate, and the base.

[0022] Weigh out PSN and photoinitiator, mix them, heat and stir until homogeneous to obtain PSN solution;

[0023] The PSN solution was injected into the first through-hole and cured in a UV environment to obtain a cured sample.

[0024] The solidified sample was pyrolyzed to obtain a pyrolyzed sample;

[0025] The pyrolysis sample was polished and then cleaned to obtain SiCN ceramic.

[0026] Three metal layers, Ti, Ni, and Au, are sequentially sputtered onto the upper surface of the SiCN ceramic to obtain the transfer electrode;

[0027] The adapter plate is connected to the base via a thread and a second mating thread. Wires are prepared and bonded to the adapter electrode using high-temperature silver paste. The wires are then placed at a first target temperature for initial curing and then at a second target temperature for complete curing, forming a dense conductive silver layer. Ceramic paste is injected onto the surface of the conductive silver layer and cured to form a second Al2O3 ceramic layer.

[0028] The sensor chip is bonded to the edge of the shallow trench using a ceramic slurry. After repeating the initial curing and sintering process of the Al2O3 ceramic slurry, the first Al2O3 ceramic layer is formed.

[0029] Gold wires are led from the chip electrodes to the adapter electrodes. During the bonding process, the length, curvature, and starting ball diameter of the gold wires are controlled to ensure the strength and stability of the wire bond, enabling the transmission of electrical signals from the chip to the adapter electrode.

[0030] The top cover is connected to the adapter plate via the first mating thread to achieve sealing of the sensor chip.

[0031] Further, the solidified sample is pyrolyzed to obtain a pyrolyzed sample, comprising:

[0032] The solidified sample is heated to a first temperature at a set heating rate under nitrogen protection, held at that temperature, and then cooled to a second temperature at a set cooling rate, followed by natural cooling to obtain a pyrolysis sample.

[0033] Further, three metal layers of Ti, Ni, and Au are sequentially sputtered onto the upper surface of the SiCN ceramic to obtain a transfer electrode, comprising:

[0034] In a vacuum environment, photoresist is used as a mask, and patterning is performed by exposure and development. Three metal layers of Ti, Ni and Au are sputtered sequentially on the upper surface of SiCN ceramic.

[0035] The beneficial effects of this invention are:

[0036] This invention utilizes a low-stress, high-temperature packaging technology for MEMS sensors based on all-ceramic materials. By employing ceramic materials with matched coefficients of thermal expansion (such as Al2O3 and SiCN) and precursor ceramic fabrication processes, it achieves an integrated design for chip fixation, circuit layout, and wire lead-out. The packaging structure is resistant to high temperatures and chemically stable, significantly reducing stress problems caused by thermal expansion mismatch. Furthermore, the combined sintering process of silver paste and ceramic paste improves the strength and reliability of wire connections. A modular threaded connection and integrated adapter board design, along with gold-to-gold wire bonding for microchip signal lead-out, reduces the packaging size and improves the sensor's stability and performance in high-temperature environments. The overall structure is suitable for testing conditions above 600°C, providing highly reliable and competitive technical support for high-temperature applications in aerospace, industrial equipment, and other fields.

[0037] Specifically, this is reflected in the following aspects:

[0038] (1) The sensor packaging structure adopts an all-ceramic material design. Through matching the thermal expansion coefficient and the high-temperature stability of the material, the stress effect under high temperature environment is significantly reduced, realizing a low-stress, high-reliability sensor packaging.

[0039] (2) The packaging structure consists of three parts: top cover, adapter plate and base. Each component is mechanically connected by threads. The adapter plate serves as an intermediate connecting part. The top cover head is designed with mounting threads so that the sensor can be installed in the test environment.

[0040] (3) The circuit layout on the adapter board is achieved by using the precursor ceramic SiCN. Since it and the overall packaging material are both ceramic materials, they have similar coefficients of thermal expansion, which reduces the impact of thermal stress. The fabrication process adopts the liquid injection molding, photocrosslinking and high-temperature pyrolysis method of PSN to complete the fabrication.

[0041] (4) The sensor chip is fixed to the adapter board by the sintering process of ceramic slurry, and the coefficient of thermal expansion is close.

[0042] (5) The lead wire is divided into two parts: electrical connection and strength fixation. A solid conductive silver layer is formed by high-temperature silver paste sintering to realize the electrical connection between the lead wire and the transfer electrode. Ceramic paste is poured into its surface and sintered to form a dense Al2O3 ceramic layer to improve the connection strength and structural stability.

[0043] (6) The sintering process of high-temperature silver paste and ceramic paste is divided into two stages. The first stage is preliminary curing at a temperature of 100-150℃, at which point it does not have bonding strength. The second stage is further curing at a high temperature of 400-500℃, at which point a dense solid is formed. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 This is a three-dimensional schematic diagram of an ultra-high temperature MEMS sensor packaging structure based on all high temperature ceramic materials, provided in an embodiment of the present invention.

[0046] Figure 2 This is an exploded view of a component of an ultra-high temperature MEMS sensor packaging structure based on all high temperature ceramic materials, provided in an embodiment of the present invention.

[0047] Figure 3 This is a component cutaway diagram of an ultra-high temperature MEMS sensor packaging structure based on all-high temperature ceramic materials provided in an embodiment of the present invention;

[0048] Figure 4 This is a cross-sectional view of an ultra-high temperature MEMS sensor packaging structure based on all-high temperature ceramic materials, provided in an embodiment of the present invention.

[0049] Explanation of reference numerals in the attached figures:

[0050] 1-Top cover; 2-Adapter plate; 3-Base; 4-Mounting thread; 5-First groove; 6-Second groove; 7-First mating thread; 8-Shallow groove; 9-First through hole; 10-Thread; 11-Third groove; 12-Second mating thread; 13-Second through hole; 14-Sensor chip; 15-First Al2O3 ceramic layer; 16-Gold wire lead; 17-Adapter electrode; 18-Conductive silver layer; 19-Second Al2O3 ceramic layer; 20-Wire. Detailed Implementation

[0051] 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 also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.

[0052] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.

[0053] Example 1:

[0054] This invention provides an ultra-high temperature MEMS sensor packaging structure based on all-high temperature ceramic materials, such as... Figure 1 and Figure 2 As shown, the ultra-high temperature MEMS sensor packaging structure based on all high-temperature ceramic materials includes a top cover 1, an adapter plate 2, and a base 3. The top cover 1, adapter plate 2, and base 3 are all made of ceramic materials. The overall structure, from the packaging shell and adapter plate to the bonding materials, is formed of ceramic materials, which has high temperature stability. The coefficient of thermal expansion is close to that of the sensor chip material (Si, SiC, etc.). Furthermore, the circuit arrangement of the ceramic adapter plate is realized through the precursor ceramic process, avoiding the need to arrange the circuit on the ceramic substrate through magnetron sputtering or electroplating. This reduces the stress caused by the thermal expansion of different materials under the influence of high temperature environment, and enables effective high-temperature resistant packaging of the sensor chip, providing support for the normal operation of the sensor at ultra-high temperatures.

[0055] Specifically, such as Figure 2 The packaging structure consists of three parts: a top cover 1, an adapter plate 2, and a base 3. First, the top cover 1 and base 3 together form the ceramic package shell for the sensor chip. Second, the top cover 1 has threads on its top for easy installation of the sensor in the testing environment after packaging. The base 3 is responsible for leading out the sensor's wires, enabling signal transmission. The adapter plate 2 is the core component. Firstly, it acts as the hub of the packaging structure, connecting the top cover 1 and base 3 via threads. Secondly, it uses Al2O3 ceramic slurry to fix the sensor chip and connects the electrodes of the chip and the adapter plate via wire bonding, ultimately enabling electrical signal transmission from the chip to the wires. All components are made of ceramic material, resistant to high temperatures, and the entire system can achieve sensor packaging in high-temperature environments.

[0056] In one exemplary embodiment, please refer to Figures 1 to 4As shown, in this ultra-high temperature MEMS sensor packaging structure based on all-high temperature ceramic materials, in terms of the overall structure, the adapter plate 2 serves as the fixing frame for the sensor chip 14. Since the fixing anchor points of the sensor chip are basically around the perimeter, and the central structure of the chip is mostly required to be suspended, a shallow groove 8 is formed on the upper surface. The sensor chip is fixed to the edge of the shallow groove 8 through a ceramic slurry sintering process, forming the first Al2O3 ceramic layer 15. This can minimize the occupation of the chip's bonding area and achieve the suspension of the chip's central structure, thus supporting and fixing the sensor chip as a whole. In addition, to avoid the mismatch between the thermal expansion coefficients of the metal circuit and the ceramic substrate in traditional circuit layouts, the electrode material of the adapter plate uses SiCN precursor ceramic. This type of ceramic can be prepared by liquid casting and photocrosslinking of PSN silazane polymer, and can withstand high temperature conditions. The process transforms the material into SiCN ceramic. Therefore, a first through-hole 9, serving as a mold, is arranged on the adapter plate. By injecting PSN silazane polymer, an adapter electrode 17 is formed through photocrosslinking and high-temperature pyrolysis. At this point, the sensor chip can be directly charged using silver paste. However, this requires a large contact area and a large chip size. Simply using silver paste cannot achieve the output of electrical signals from a small chip. Wire bonding is still required, typically gold-to-gold wire bonding. Therefore, a Ti / Ni / Au metal system is magnetron sputtered onto the surface of the adapter electrode 17 and gold-to-gold wire bonded to the chip, thereby enabling the transmission of electrical signals from the sensor chip to the adapter plate electrode. The side surface of the adapter plate 2 is machined with threads 10, which are mechanically connected to the first mating thread 7 of the top cover 1 and the second mating thread 12 of the base 3 to achieve the encapsulation of the sensor chip.

[0057] In an exemplary embodiment, a third groove 11 is formed on the upper surface of the base 3 to cooperate with the adapter plate 2, and a second through hole 13 is formed. The wire 20 is connected to the adapter electrode 17 by using high-temperature silver paste and ceramic paste. The conductive silver layer 18 can realize the electrical signal connection between the wire 20 and the adapter electrode 17, but its mechanical strength is low and it is easy to break in high temperature environment. Other methods are needed to strengthen the connection strength. After sintering, the ceramic paste forms a dense solid ceramic with high bonding strength. Therefore, a layer of ceramic paste is poured into the surface of the conductive silver layer 18. After sintering, a second Al2O3 ceramic layer 19 is formed, which can further improve the connection strength and stability.

[0058] In this embodiment, the adapter plate 2 serves as the main body supporting the sensor chip 14 and is fixed by the first Al2O3 ceramic layer 15. Electrical signals are transmitted from the chip to the adapter electrode 17 formed by the precursor ceramic through gold wire leads 16, then connected to the wire 20 through the conductive silver layer 18, and further fixed by the second Al2O3 ceramic layer 19, thus realizing the transmission of electrical signals from the chip to the outside world and ultimately completing the high-temperature encapsulation of the sensor.

[0059] In an exemplary embodiment, the top cover 1 has a first groove 5 and a second groove 6. The second groove 6 enables the top cover 1 to be connected to the adapter plate 2. The third groove 5 provides slack for the gold wire lead 16 of the chip. The head of the top cover 1 is provided with mounting threads 4 to enable the sensor to be installed and fixed with the test environment. Overall, the low-stress MEMS sensor high-temperature packaging with all-ceramic materials is achieved.

[0060] In one exemplary embodiment, the top cover 1, the adapter plate 2, and the base 3 are made of Al2O3 ceramic material with a coefficient of thermal expansion of 6.5 × 10⁻⁶. -6 ~8×10 -6 Between / ℃, the sensor chip 15 is typically made of Si, SiO2, or SiC, with thermal expansion coefficients of 10×10⁻⁶ respectively. -6 / ℃, 5×10 -6 / ℃ and 4×10 -6 The ceramic slurry used is Al2O3, and it is sintered at 400-500 degrees Celsius to form a dense ceramic. There is limited research on SiCN ceramics, making it impossible to determine their exact coefficient of thermal expansion. However, their physical properties are similar to those of SiC and Si3N4, with Si3N4 having a coefficient of thermal expansion of 2.35 × 10⁻⁶. -6 / ℃, the thermal expansion coefficient of SiCN ceramic is close to that of both, the overall packaging material can withstand high temperature, has stable chemical properties, and the thermal expansion coefficient is close, which minimizes the stress problems caused by high temperature environment.

[0061] Example 2:

[0062] This invention provides a method for fabricating an ultra-high temperature MEMS sensor packaging structure based on all-high temperature ceramic materials. The fabrication method of the ultra-high temperature MEMS sensor packaging structure based on all-high temperature ceramic materials provided in Example 1 can be implemented as follows:

[0063] The ceramic component processing includes top cover 1, adapter plate 2, and base 3. An Al2O3 ceramic substrate is prepared, and the encapsulation structure is processed using laser cutting, drilling, turning, and other mechanical processing methods. This mainly includes the processing of grooves, internal and external threads, and through holes. These steps complete the preparation of top cover 1, adapter plate 2, and base 3. PSN treatment involves weighing PSN and photoinitiator at a weight ratio of 95:5, mixing them, heating in an oil bath at 90°C, and magnetically stirring for 60 minutes. PSN photocuring is then performed using adapter plate 2 as a mold, slowly injecting the stirred PSN solution into the first through hole 9, avoiding the formation of air bubbles, and placing it at a power per unit area of ​​150mW / cm². 2Under ultraviolet light, the sample was continuously irradiated for 30 minutes until solidification, at which point a pale yellow solid was visible. High-temperature pyrolysis involved placing the PSN sample in a high-temperature furnace, activating nitrogen protection to ensure an oxidation-free environment, slowly raising the furnace temperature to 1000℃, holding for 3 hours, and then slowly cooling to room temperature. At this point, a black or dark gray ceramic-like SiCN was visible. Polishing involved using diamond polishing paste for rough and fine polishing of the SiCN ceramic surface, ultimately controlling the surface roughness to Ra ≤ 0.05 μm. After polishing, the surface was cleaned with anhydrous ethanol. Magnetron sputtering was performed in a vacuum environment using a lifter. In the Off process, three metal layers of Ti, Ni, and Au are sequentially sputtered onto the upper surface of the SiCN ceramic to prepare for subsequent wire bonding. The wire is led out and connected to the base 3 via threads, preparing a high-temperature wire 20. High-temperature silver paste is used to connect it to the adapter electrode 17, and it undergoes preliminary curing at 100°C for 20 minutes, followed by complete curing at 500°C for 30 minutes to form a conductive silver layer 18. Ceramic paste is then injected onto the surface, undergoing preliminary curing at 150°C for 20 minutes, followed by sintering at 500°C for 30 minutes to transform it into an Al2O3 ceramic layer 19, completing the high-temperature wire bonding process. The process involves several steps: chip bonding, wire bonding, and top cover assembly. The top cover 1 is connected to the adapter plate 2 via a first mating thread 7. The mounting thread 4 is used for sensor installation in the testing environment. This completes the low-stress, high-temperature packaging of the all-ceramic MEMS sensor. The sensor chip is bonded to the edge of the shallow trench 8 using ceramic slurry, followed by initial curing and sintering to form a dense first Al2O3 ceramic layer 15, thus securing the chip to the adapter plate while ensuring the chip's central structure remains suspended. Wire bonding is then performed using a gold wire bonding machine to draw gold wires from the chip electrodes to the adapter electrode 17, enabling the transmission of electrical signals from the chip to the adapter plate electrodes. Finally, the top cover 1 is assembled to the adapter plate 2 via a first mating thread 7, and a mounting thread 4 is used for sensor installation in the testing environment. This completes the low-stress, high-temperature packaging of the all-ceramic MEMS sensor.

[0064] It should be noted that for the fabrication steps of the ultra-high temperature MEMS sensor packaging structure based on all high temperature ceramic materials, three Al2O3 ceramic substrates need to be prepared during the fabrication process. These substrates are used to fabricate the top cover 1, the adapter plate 2, and the base 3, respectively. The ceramic slurry used for bonding and sintering is made of Al2O3 material. The conductive medium used for wire lead-out is high temperature silver paste. The adapter electrode 17 on the adapter plate 2 is a precursor ceramic SiCN, which can be fabricated using PSN. The selection of the above materials is not unique and can be modified accordingly based on the process and actual performance.

[0065] For ease of understanding, this preparation method can be implemented through the following steps:

[0066] Step 1: Ceramic component processing. After preparing the three required Al2O3 ceramic substrates, including the top cover 1, adapter plate 2, and base 3, the initial shape is first processed by laser cutting. Through-hole processing is then performed using a CNC drilling machine, including the first through-hole 9 and the second through-hole 13. Thread turning and groove milling are then performed using diamond tools on a CNC machine, including the mounting thread 4, the first mating thread 7, thread 10, the second mating thread 12, the first groove 5, the second groove 6, the shallow groove 8, and the third groove 11. Subsequently, key areas are polished, and processing residues are removed by ultrasonic cleaning.

[0067] Step 2: PSN treatment. Weigh out PSN and photoinitiator by mass ratio of 95:5, mix them in a beaker, place the beaker on a magnetic stirrer, set the oil bath heating temperature to 90℃, and stir while heating for 1 hour to ensure uniform mixing.

[0068] Step 3: PSN light curing. Using adapter plate 2 as a mold, slowly inject the stirred PSN solution into the first through hole 9, avoiding the formation of air bubbles, and place it at a power per unit area of ​​150mW / cm². 2 Under a UV lamp, the distance between the UV lamp and the sample is 10cm to 15cm. The sample is continuously irradiated for 30 minutes until it solidifies, at which point a pale yellow solid can be seen.

[0069] Step 4: High-temperature pyrolysis. Place the UV-cured crosslinked sample on a high-temperature support and put it in a high-temperature furnace. Use nitrogen protection to ensure an oxidizing environment inside the furnace. Slowly raise the furnace temperature to 1000℃ at a rate of 1℃ / min and hold for 3 hours. Then slowly lower the temperature to 300℃ at a rate of 3℃ / min. Then turn off the heating device and stop the supply of protective gas. Allow the furnace to cool naturally to room temperature. Take out the pyrolyzed sample. At this time, black or dark gray ceramic-state SiCN can be seen.

[0070] Step 5: Polishing. The SiCN ceramic surface is rough and fine polished using diamond polishing paste, and the surface roughness is finally controlled to Ra≤0.05μm. After polishing, it is cleaned with anhydrous ethanol.

[0071] Step 6: Magnetron sputtering. In a vacuum environment, using the lift-off process, photoresist is used as a mask. Patterning is performed through exposure and development. Three metal layers of Ti, Ni, and Au are sequentially sputtered on the upper surface of the SiCN ceramic to prepare for subsequent gold wire bonding.

[0072] Step 7: Lead-out of wires. Connect the adapter plate 2 to the base 3 via thread 10 and the second mating thread 12. Prepare the wire 20 and bond it to the adapter electrode 17 using high-temperature silver paste. Place it at 100°C for 20 minutes to complete the initial curing. At this point, it has a certain strength but is in powder form. Then place it at 500°C for 30 minutes to completely cure it, forming a dense conductive silver layer 18. Inject ceramic paste onto the surface of the silver layer and place it at 150°C for 20 minutes to complete the initial curing. At this point, it is in powder form. Then place it at 500°C for 30 minutes to sinter it into a high-strength second Al2O3 ceramic layer 19. This step completes the lead-out and fixation of the high-temperature wire.

[0073] Step 8: Chip Fixing. The sensor chip is bonded to the edge of the shallow trench 8 using a ceramic slurry. After repeating the initial curing process of Al2O3 ceramic slurry at 150°C for 20 minutes and sintering at 500°C for 30 minutes, the first Al2O3 ceramic layer 15 is formed. At this time, a tight connection is formed between the chip and the adapter board, while ensuring the suspension of the chip's central structure.

[0074] Step 9: Wire Bonding. Using a gold wire bonding machine, gold wire 16 is led from the chip electrode to the adapter electrode 17. During the bonding process, the length, curvature, and starting ball diameter of the gold wire are strictly controlled to ensure the strength and stability of the wire bond, enabling the transmission of chip electrical signals to the adapter electrode.

[0075] Step 10: Top cover assembly. Connect the top cover 1 to the adapter plate 2 via the mating thread 7 to seal the sensor chip. Install the thread 4 to allow the sensor to be installed in the test environment.

[0076] The above achieves low-stress, high-temperature packaging of MEMS sensors using all-ceramic materials.

[0077] The above embodiments are only used to illustrate the present invention and are not intended to limit the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions also fall within the scope of the present invention, and the patent protection scope of the present invention should be defined by the claims.

Claims

1. A packaging structure for an ultra-high temperature MEMS sensor based entirely on high-temperature ceramic materials, characterized in that, It includes a top cover, an adapter plate, and a base; the top cover, adapter plate, and base are all made of ceramic material. The top cover and the base together form a ceramic package shell for the sensor chip. The top of the top cover is provided with threads to enable the sensor to be installed in the test environment after packaging. The adapter plate is connected to the top cover and the base by threads; The adapter board is provided with a first Al2O3 ceramic layer, which is used to fix the sensor chip. The electrodes of the sensor chip and the adapter board are connected by wire bonding to realize the transmission of electrical signals from the sensor chip to the wires.

2. The ultra-high temperature MEMS sensor packaging structure based on all high temperature ceramic materials as described in claim 1, characterized in that, The upper surface of the adapter plate has a shallow groove. The sensor chip is fixed to the edge of the shallow groove by a ceramic slurry sintering process to form the Al2O3 ceramic layer.

3. The ultra-high temperature MEMS sensor packaging structure based on all high temperature ceramic materials as described in claim 1, characterized in that, The adapter plate is provided with a first through hole, and the adapter electrode is formed by injecting PSN silazane polymer into the through hole and then performing photocrosslinking and high-temperature pyrolysis.

4. The ultra-high temperature MEMS sensor packaging structure based on all high temperature ceramic materials as described in claim 3, characterized in that, Ti / Ni / Au metal system is magnetron sputtered on the upper surface of the adapter electrode to form gold-to-gold wire bonding with the chip, thereby realizing the transmission of electrical signals from the sensor chip to the adapter electrode.

5. The ultra-high temperature MEMS sensor packaging structure based on all high temperature ceramic materials as described in claim 1, characterized in that, The side surface of the adapter plate is machined with threads, which are mechanically connected to the first mating thread of the top cover and the second mating thread of the base to realize the encapsulation of the sensor chip.

6. The ultra-high temperature MEMS sensor packaging structure based on all high temperature ceramic materials as described in claim 3, characterized in that, The upper surface of the base has a third groove that mates with the adapter plate. The base has a second through hole through which a wire is connected to the adapter electrode. A second Al2O3 ceramic layer is disposed within the second through hole to fix the wire. A conductive silver layer is disposed at the upper end of the second Al2O3 ceramic layer to enable electrical signal connection between the wire and the adapter electrode. The adapter electrode is connected to the sensor chip via a gold wire lead.

7. The ultra-high temperature MEMS sensor packaging structure based on all high temperature ceramic materials as described in claim 6, characterized in that, The top cover has a first groove and a second groove. The second groove is used to realize the mating connection between the top cover and the adapter plate. The first groove is used to provide a margin for the gold wire. The head of the top cover is provided with an installation thread.

8. The method for fabricating an ultra-high temperature MEMS sensor packaging structure based on all-high temperature ceramic materials as described in any one of claims 1 to 7, characterized in that, The preparation method includes: Take three Al2O3 ceramic substrates and, based on the determined structure of the top cover, the adapter plate, and the base, process the top cover, the adapter plate, and the base. Weigh out PSN and photoinitiator, mix them, heat and stir until homogeneous to obtain PSN solution; The PSN solution was injected into the first through-hole and cured in a UV environment to obtain a cured sample. The solidified sample was pyrolyzed to obtain a pyrolyzed sample; The pyrolysis sample was polished and then cleaned to obtain SiCN ceramic. Three metal layers, Ti, Ni, and Au, are sequentially sputtered onto the upper surface of the SiCN ceramic to obtain the transfer electrode; The adapter plate is connected to the base via a thread and a second mating thread. Wires are prepared and bonded to the adapter electrode using high-temperature silver paste. The wires are then placed at a first target temperature for initial curing and then at a second target temperature for complete curing, forming a dense conductive silver layer. Ceramic paste is injected onto the surface of the conductive silver layer and cured to form a second Al2O3 ceramic layer. The sensor chip is bonded to the edge of the shallow trench using a ceramic slurry. After repeating the initial curing and sintering process of the Al2O3 ceramic slurry, the first Al2O3 ceramic layer is formed. Gold wires are led from the chip electrodes to the adapter electrodes. During the bonding process, the length, curvature, and starting ball diameter of the gold wires are controlled to ensure the strength and stability of the wire bond, enabling the transmission of electrical signals from the chip to the adapter electrode. The top cover is connected to the adapter plate via the first mating thread to achieve sealing of the sensor chip.

9. The preparation method according to claim 8, characterized in that, The solidified sample is pyrolyzed to obtain a pyrolyzed sample, comprising: The solidified sample is heated to a first temperature at a set heating rate under nitrogen protection, held at that temperature, and then cooled to a second temperature at a set cooling rate, followed by natural cooling to obtain a pyrolysis sample.

10. The preparation method according to claim 8, characterized in that, A transfer electrode is obtained by sequentially sputtering three metal layers of Ti, Ni, and Au onto the upper surface of the SiCN ceramic, comprising: In a vacuum environment, photoresist is used as a mask, and patterning is performed by exposure and development. Three metal layers of Ti, Ni and Au are sputtered sequentially on the upper surface of SiCN ceramic.

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