Suspension embedded ceramic-based sensitive device and preparation method thereof

Abstract

The application discloses a kind of suspension embedded ceramic base sensitive device and preparation method thereof.The suspension embedded ceramic base sensitive device includes ceramic substrate and sensitive structure arranged in layers.The ceramic substrate includes frame, center block and cantilever, frame is arranged around center block, and cantilever is fixedly connected with frame and center block at both ends respectively.Sensitive material is arranged on the surface of center block, and electric heating structure is arranged in the inside of ceramic substrate, and the electric heating structure includes heating body, heating body is located in the inside of center block, and the end of heating circuit is exposed to surface at least.The suspension embedded ceramic base sensitive device provided by the application does not need to deposit heating structure in layers, and the deposition of thermal insulation layer is reduced, the process is simplified, the overall structure of device is simple, the cost is low, and the stress problem caused by existing multilayer lamination is avoided;Process is simple, forming rate is high, further reduce cost;The components, structure and process of ceramic powder and slurry can also be adjusted to meet the performance requirements of device, and the process is flexible.

Description

Technical Field

[0001] This invention relates to the field of sensitive device technology, and in particular to a suspended embedded ceramic-based sensitive device and its preparation method. Background Technology

[0002] Sensitive devices have wide applications in various fields. With the increasing integration of devices, the requirements for sensors are also becoming more demanding. Among them, micro-hotplate gas sensors based on MEMS technology have become a research hotspot in the field of low-power gas sensors due to their low power consumption, small size, and ease of integration. Most MEMS gas sensors use platinum wire as the heating structure and Au metal wire as the testing structure, with silicon nitride / silicon oxide as the insulating layer in between. The suspended thin-film structure of the micro-hotplate is realized using back-side bulk silicon processing technology. There are also reports of even lower power gas sensors that etch out silicon beam structures.

[0003] Currently, commonly used semiconductor gas sensors include silicon-based, glass-based, and ceramic-based gas sensors. The fabrication process of ceramic substrates typically involves mixing, casting, pre-firing, pressing, and sintering, which is complex. The high sintering temperature results in high density of the ceramic substrate, leading to easy heat loss and high heat dissipation. Furthermore, for beam-type structures, ceramic substrate sensors are difficult to process and have high manufacturing difficulty. Due to advancements in substrate technology, sensing devices typically form insulating layers, heating layers, and testing layers on the substrate, each requiring corresponding processing steps, which is cumbersome and increases costs.

[0004] The existing device structures still suffer from problems such as complex structure, high cost, and difficult fabrication. Developing a low-power gas sensor or other types of sensitive devices with simple fabrication process, good consistency, simple structure, and damage resistance has very broad application value in consumer electronics, white goods and other fields. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a suspended embedded ceramic-based sensing device and its fabrication method.

[0006] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0007] In a first aspect, the present invention provides a suspended embedded ceramic-based sensing device, which includes a ceramic substrate and a sensing structure stacked together.

[0008] The ceramic substrate includes a frame, a central block, and a cantilever. The frame is arranged around the central block and forms a gap between the frame and the central block. The cantilever is arranged in the gap, and the two ends of the cantilever are fixedly connected to the frame and the central block, respectively.

[0009] The sensitive material in the sensitive structure is disposed on the surface of the central block, and an electric heating structure is disposed inside the ceramic substrate. The ceramic substrate and the electric heating structure are integrally formed. The end of the heating circuit in the electric heating structure is exposed at least on the outer surface of the ceramic substrate.

[0010] Secondly, the present invention also provides a method for preparing the above-mentioned suspended embedded ceramic-based sensing device, comprising:

[0011] Provide ceramic materials and electric heating structures;

[0012] The ceramic material is embedded in the electric heating structure through injection molding or hot pressing, thereby making the ceramic material and the heating structure integrally formed, and the electric heating structure has multiple exposed ends to form a ceramic substrate;

[0013] A sensitive structure is coated on the surface of the ceramic substrate.

[0014] Based on the above technical solution, compared with the prior art, the beneficial effects of the present invention include at least the following:

[0015] The suspended embedded ceramic substrate sensing device provided by this invention can form a ceramic substrate with a certain porosity by injection molding or pressing ceramic powder or slurry. The heating structure is set in the mold and integrally formed with the ceramic substrate, eliminating the need for a heating device stacking step. Since the heating element stacking process is not set on the substrate, the deposition step of the insulation layer is also reduced, simplifying the entire process, simplifying the overall device structure, reducing costs, and mitigating the stress problems caused by existing multi-layer stacking. Furthermore, compared with ceramic substrate sensing devices formed by conventional processes, which are not easy to form cantilever beam structures, ceramic powder or slurry can form cantilever beam structures in one step through injection molding or pressing, making the process simpler, with a higher molding rate, and further reducing costs. Moreover, the composition, structure, and process of the ceramic powder and slurry can be adjusted according to the device's heat dissipation requirements to meet the device's performance requirements, making the process flexible.

[0016] The above description is merely an overview of the technical solution of the present invention. In order to enable those skilled in the art to better understand the technical means of this application and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described below in conjunction with detailed drawings. Attached Figure Description

[0017] Figure 1 This is a side view of a suspended embedded ceramic-based sensing device provided in a typical embodiment of the present invention.

[0018] Figure 2This is a front view of a suspended embedded ceramic-based sensitive device provided in a typical embodiment of the present invention (the heating circuit is shown in dashed lines, which is a perspective view of the internal arrangement).

[0019] Figure 3 This is a schematic diagram of the overall fabrication process of a suspended embedded ceramic-based sensitive device provided in a typical embodiment of the present invention;

[0020] Figures 4a-4e This is a schematic diagram of the step-by-step fabrication process of a suspended embedded ceramic-based sensitive device provided in a typical embodiment of the present invention.

[0021] Explanation of reference numerals in the attached figures:

[0022] 101. Frame; 102. Cantilever; 103. Center block; 201. Heating circuit; 202. Heating element; 300. Insulating and thermally conductive layer; 401. Test circuit; 402. Sensitive material. Detailed Implementation

[0023] In view of the shortcomings of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. The following will further explain and illustrate this technical solution, its implementation process, and its principles.

[0024] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0025] Currently, commonly used silicon-based MEMS gas sensors mainly combine MEMS microfabrication technology, utilizing thin-film deposition processes to prepare insulating, barrier, and seed layers, followed by the deposition of metal heating and testing layers through wet or dry etching processes. Sensitive materials are then deposited using sputtering, spraying, or printing methods, and after aging tests, the overall structure of the MEMS gas sensor is completed. This type of MEMS gas sensor has two main problems: First, the deposition of multiple thin films on silicon, especially multilayer composites of metal films and silicon oxide or silicon nitride films, easily leads to high stress, causing device failure. Second, current MEMS gas sensors require operation at specific temperatures; the superposition of multiple materials can easily cause a mismatch in thermal expansion coefficients, resulting in device damage. Third, after etching the cavity on the back side, the printing of the sensitive material can also damage the suspended structure.

[0026] To overcome the shortcomings of existing low-power silicon-based suspended membrane or beam-type gas sensors, this invention proposes a cantilever beam structure based on ceramic raw materials, formed through injection molding or pressing processes. A corresponding heating structure is embedded within this ceramic structure. This not only makes the sensor's central structure primarily beam-type, creating a well-insulated fixed structure for heat loss, but also simplifies the structure, eliminating the need for insulation and thermal conductive layers. Furthermore, the manufacturing process is relatively simple, with lower costs, making it suitable for mass production.

[0027] To achieve the above objectives, see Figure 1 and Figure 2 This invention provides a suspended embedded ceramic-based sensitive device, comprising a stacked ceramic substrate and a sensitive structure. The ceramic substrate includes a frame 101, a central block 103, and a cantilever 102. The frame 101 surrounds the central block 103 and forms a space between them. The cantilever 102 is disposed in the space, and its two ends are fixedly connected to the frame 101 and the central block 103, respectively. The sensitive material 402 in the sensitive structure is disposed on the surface of the central block 103. An electric heating structure is disposed inside the ceramic substrate. The electric heating structure includes a heating element 202 and a plurality of heating circuits 201 electrically connected to the heating element 202. The heating element 202 is located inside the central block 103, and the ends of the heating circuits 201 are at least exposed on the surface of the ceramic substrate.

[0028] In the above structure, the ceramic substrate not only serves as a carrier to reduce heat loss through the cantilever 102, but also as an insulator and protective bearing for the heating structure. This eliminates the need for additional insulating materials between the heating and testing structures, as well as additional protective layers for the heating structure. The simplest implementation requires only two layers: the ceramic substrate and the sensitive structure, which greatly reduces the complexity of the device. In particular, it avoids the problems of interlayer stress and interlayer thermal mismatch, significantly improving the device's damage resistance.

[0029] In some embodiments, an insulating and thermally conductive layer 300 may be spaced between the ceramic substrate and the sensitive structure. The insulating and thermally conductive layer 300 may be made of ceramic materials such as alumina.

[0030] In some embodiments, the frame 101, the central block 103, and the cantilever 102 can be integrally formed; the thickness of the cantilever 102 is 30-80% of the thickness of the central block 103, and the width of the cantilever 102 is 20-80% of the width of the central block 103. This ratio of width to thickness ensures that the cross-sectional area of ​​the cantilever 102 is much smaller than that of the central block 103. While maintaining good support and preventing damage, this also reduces the amount of heat conducted through the cantilever 102, thus helping to reduce power consumption.

[0031] In a further preferred embodiment, the microstructure of the cantilever 102 may be different from that of the central block 103, at least making the thermal conductivity of the cantilever 102 significantly lower than that of the central block 103. For example, the porosity of the cantilever 102 may be higher than that of the central block 103, and the central block 103 tends to have a microstructure with smaller porosity. In this way, the heat generated can act on the sensitive structure more quickly and is less likely to be dissipated from the cantilever 102.

[0032] In a more preferred embodiment, the side of the central block 103 facing the sensitive structure is the aforementioned dense structure (with lower porosity), while the side facing away from the sensitive structure is a porous structure (with higher porosity). This ensures that heat is transferred on the front side while reducing heat loss on the back side.

[0033] The aforementioned different microstructures can be prepared by integrally pressing ceramic powders of the same material but different porosities into different corresponding positions.

[0034] In some embodiments, at least a portion of the heating circuit 201 is disposed inside the cantilever 102 and extends along the cantilever 102 in a direction away from the heating element 202, with the end of the heating circuit 201 exposed on the surface of the frame 101.

[0035] In some embodiments, the heating circuit 201 and the heating element 202 are integrally connected wire-type structures; the cross-sectional area of ​​the heating circuit 201 is larger than that of the heating element 202. This is a preferred form of heating structure. Due to its integral molding, the middle part is thinner, equivalent to a heating wire, and the heating position is exactly at the center block 103. The two ends are thicker, which plays a role in transmitting current. Of course, the structure of the heating element 202 is not limited to this. For example, it is also possible to use an electric heating element such as a heating resistor welded in the middle of the metal wires at both ends. The heating structure is made of metal wire, thermally conductive paste, etc., and the metal wire is embedded in the substrate in one molding process.

[0036] In some embodiments, multiple cantilever 102s are provided, and multiple heating circuits 201 are arranged along different cantilever 102s.

[0037] In some embodiments, the sensitive structure includes a plurality of test circuits 401 electrically connected to the sensitive material 402, the test circuits 401 extending along the surface of the cantilever 102 in a direction away from the sensitive material 402.

[0038] In some embodiments, multiple heating circuits 201 and test circuits 401 are arranged on different cantilever 102.

[0039] Therefore, the above circuit can be arranged using different cantilever 102, and as a specific example, such as Figure 2 As shown, there are a total of four cantilever arms 102. The heating circuit 201 is arranged inside the left and right cantilever arms 102 respectively, and is exposed from the bottom surface of the frame 101 (the side facing away from the sensitive structure) to form a PAD. The test circuit 401 is arranged on the front of the upper and lower cantilever arms 102 (the side facing the sensitive structure), and is also formed as a PAD on the front of the frame 101 for connection with external circuits. This arrangement allows the cantilever arms 102 to not only have a fixing function, but also to arrange wiring. The wiring layout is simple and clear, making it very convenient to connect with external circuits. Of course, it is also possible to use a method of wiring out from the side of the frame 101, and the corresponding circuit connection method can be adjusted accordingly.

[0040] Correspondingly, see the merger. Figure 3 The present invention also provides a method for fabricating a suspended embedded ceramic-based sensing device according to any of the above embodiments, which includes the following steps:

[0041] Provide ceramic powder or slurry and electric heating structure.

[0042] The electric heating structure is set in the mold, and the electric heating structure is embedded in the mold through injection molding or hot pressing to form an integral ceramic substrate and heating structure; so that the electric heating structure has multiple exposed ends to form a ceramic substrate.

[0043] A sensitive structure is coated on the surface of the ceramic substrate.

[0044] In some embodiments, the preparation method may specifically include the following steps:

[0045] A cantilevered ceramic substrate structure is formed in one step using injection molding or pressing processes, or a metal layer is deposited on the surface of the ceramic substrate and then etched; ultimately, multiple test circuits 401 extending from the central block 103 of the ceramic substrate in a direction away from the central block 103 are formed.

[0046] On the surface of the central block 103, a sensitive material 402 is applied between the ends of the plurality of test circuits 401. The sensitive material 402 is electrically connected to the plurality of test circuits 401 respectively, so that the sensitive material 402 and the test circuits 401 constitute the sensitive structure.

[0047] Corresponding to the above-mentioned preferred microstructure distribution pattern, two different ceramic powders are provided during preparation: the first ceramic powder is a high-porosity powder, such as hollow microspheres or porous ceramic materials, and the second ceramic powder is a low-porosity powder (which can be flexibly selected according to the device performance). The first ceramic powder is filled at least in the mold at the corresponding position of the cantilever 102, and the second ceramic powder is filled at least in the corresponding position of the central block 103. After pressing and molding, the cantilever 102 and the central block 103 can have different thermal conductivity.

[0048] Furthermore, when filling the central block 103, the lower layer is filled with the first ceramic powder and the upper layer is filled with the second ceramic powder. In this way, after pressing and molding, the upper and lower surfaces of the central block 103 have different thermal conductivity characteristics.

[0049] As a typical application example of the above technical solution, a low-power ceramic gas sensor is used as an example. The sensor is based on ceramic, with a ceramic central block 103 in the middle. Test electrodes are formed sequentially on the central block 103, and the center of the test electrode is a sensitive material 402. The surrounding area is supported by cantilever beams and connected to the frame 101. The heating wire is embedded in the ceramic substrate, and the heating position is in the central block 103.

[0050] The fabrication method of the low-power ceramic gas sensor mainly uses ceramic powder as a substrate, and forms the substrate structure of the cantilever beam by injection molding or hot pressing, and then prints, plates or coats it to form the sensitive structure.

[0051] Ideally, an insulating and thermally conductive layer 300 with a thickness of 100nm-5000nm, such as an alumina layer, should be spaced between the ceramic substrate and the sensitive structure. The presence of this layer can serve as an intermediate medium to further reduce the degree of thermal mismatch and provide good adhesion for the sensitive structure. The test circuit 401 used is, for example, a metal such as Au, Ag, Cu, or Ni. The heating structure used is, for example, a wire made of metals such as Pt, Au, Ag, or Cu, with a round equivalent wire diameter of, for example, 100nm-5000nm.

[0052] The technical solution of the present invention will be further described in detail below through several embodiments and in conjunction with the accompanying drawings. However, the selected embodiments are only for illustrating the present invention and do not limit the scope of the present invention.

[0053] Example 1

[0054] This embodiment illustrates the fabrication process of a low-power ceramic gas sensor, as follows: Figures 4a-4e And as shown below:

[0055] Prepare alumina ceramic powder and press it with a heating wire to form a ceramic substrate. The ceramic substrate has a square central block 103 with a thickness of 300 μm and a side length of 400 μm. The central block 103 is surrounded by a square frame 101 with a side length of 1500 μm, a width of 300 μm, and a thickness of 500 μm. The frame 101 and the central block 103 are connected by a cantilever 102 with a width of 300 μm and a thickness of 200 μm. The central heating element 202 of the heating wire is located inside the central block 103. The heating circuit 201 is led out to the frame 101 through the two cantilever 102 on the left and right sides and continues to extend downward until it is exposed on the bottom surface of the frame 101 so that it can be connected to the external circuit during assembly, such as the corresponding external circuit on the PCB board.

[0056] Metallic gold is deposited and etched on the front side of the ceramic substrate to form a test circuit 401. The test circuit 401 extends from the surface of the central block 103 along the surfaces of the upper and lower cantilever 102 to the frame 101, and has a terminal block. Sensitive material 402 is coated between the ends of the two test circuits 401 on the surface of the central block 103 to form a gas sensitive structure.

[0057] Example 2

[0058] The fabrication process of the low-power ceramic gas sensor in Example 1 of this embodiment is largely the same as that in Example 1, with the main difference being:

[0059] During pressing, solid alumina ceramic powder is used to fill the central block 103 in the mold, and hollow alumina ceramic microspheres are used to fill the cantilever 102. Finally, the corresponding gas sensor is obtained through the same size and process.

[0060] The gas sensor prepared in this embodiment consumes 5% less power than that in Embodiment 1.

[0061] Example 3

[0062] During pressing, hollow alumina ceramic microspheres are first filled halfway in the central block 103 of the mold. After laying the heating wire, solid alumina ceramic powder is then used to fill the other half. Hollow alumina ceramic microspheres are used to fill the cantilever 102. Finally, the corresponding gas sensor is obtained through the same size and process.

[0063] The gas sensor prepared in this embodiment consumes 7% less power than that in Embodiment 1.

[0064] Based on the above embodiments, it is clear that the suspended embedded ceramic substrate sensing device provided by the present invention avoids the disadvantages of traditional multi-layer stacked device structures by setting the heating structure in the ceramic substrate and combining it with the suspended structure of the central block 103 of the ceramic substrate. It reduces the layer structure and processes, and the overall structure of the device is simple, consistent, and not easily damaged. It can also simplify the manufacturing process and reduce production costs.

[0065] It should be understood that the above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A suspended embedded ceramic-based sensing device, characterized in that, This includes a stacked ceramic substrate and a sensitive structure; The ceramic substrate includes a frame, a central block, and a cantilever. The frame is arranged around the central block and forms a gap between the frame and the central block. The cantilever is arranged in the gap, and the two ends of the cantilever are fixedly connected to the frame and the central block, respectively. The sensitive material in the sensitive structure is disposed on the surface of the central block, and an electric heating structure is disposed inside the ceramic substrate, with the ceramic substrate and the electric heating structure integrally formed. The end of the heating circuit in the electric heating structure is exposed at least on the outer surface of the ceramic substrate; The electric heating structure includes a heating element and multiple heating circuits electrically connected to the heating element. The heating element is located inside the central block. The porosity of the cantilever is higher than that of the central block. The central block has a multi-layer structure, including a first layer and a second layer stacked together. The first layer is far away from the sensitive structure, and the second layer is close to the sensitive structure. The porosity of the second layer is higher than that of the first layer.

2. The suspended embedded ceramic-based sensing device according to claim 1, characterized in that, The porosity of the ceramic substrate is 10-60%.

3. The suspended embedded ceramic-based sensing device according to claim 2, characterized in that, The frame, center block, and cantilever are integrated into one unit.

4. The suspended embedded ceramic-based sensing device according to claim 3, characterized in that, At least a portion of the heating circuit is disposed inside the cantilever and extends along the cantilever in a direction away from the heating element, with the end of the heating circuit exposed on the surface of the frame; The cantilever is provided in multiple ways, and the multiple heating circuits are arranged along different cantilevers.

5. The suspended embedded ceramic-based sensing device according to claim 4, characterized in that, The sensitive structure includes a plurality of test circuits electrically connected to the sensitive material, the test circuits extending along the surface of the cantilever in a direction away from the sensitive material; The multiple heating circuits and test circuits are arranged on different cantilever arms.

6. The method for fabricating the suspended embedded ceramic-based sensitive device according to any one of claims 1-5, characterized in that, include: Provide ceramic powder or slurry, and electric heating structure; The ceramic material is embedded in the electric heating structure through injection molding or pressing processes, thereby making the ceramic material and the heating structure integrally formed, and the electric heating structure has multiple exposed ends to form a ceramic substrate; A sensitive structure is coated on the surface of the ceramic substrate.

7. The preparation method according to claim 6, characterized in that, Specifically, it includes: A cantilevered ceramic substrate structure formed in one step using injection molding or pressing processes; A metal layer is deposited on the surface of the ceramic substrate and the metal layer is etched to form multiple test circuits extending from the center block of the ceramic substrate in a direction away from the center block; A sensitive material is applied between the ends of the plurality of test circuits on the surface of the central block. The sensitive material is electrically connected to the plurality of test circuits, so that the sensitive material and the test circuits constitute the sensitive structure.

Images