A ceramic sensor and a preparation method thereof

Abstract

The present invention discloses a ceramic sensor and a preparation method thereof. The ceramic sensor includes a ceramic elastic thin sheet, a ceramic base, and a conductive channel formed as an integral structure. A cavity is formed between the ceramic elastic thin sheet and the ceramic base, and the thickness of the ceramic elastic thin sheet is less than that of the ceramic base. A common electrode is provided on the bottom surface of the ceramic elastic thin sheet, and a pressure sensing electrode and a reference electrode are provided in the central area of the top surface of the ceramic base. The conductive channel is provided on the ceramic base and is composed of a channel hole and a conductive electrode filling the channel hole, and includes a first conductive channel connected to the common electrode, a second conductive channel connected to the pressure sensing electrode, and a third conductive channel connected to the reference electrode. Each conductive electrode penetrates through the bottom of the ceramic base to have a lead-out end. The ceramic sensor of the present invention can effectively solve the problems of too low airtightness yield and poor reliability of the existing ceramic sensors.

Description

Technical Field

[0001] The present invention relates to the field of sensors, and particularly to a ceramic sensor and a preparation method thereof. Background Art

[0002] For existing ceramic sensors, such as ceramic capacitive pressure sensors, electrodes are respectively arranged on the opposite surfaces of a ceramic elastic sheet and a ceramic base, and the ceramic elastic sheet and the ceramic base are sealed by a sealing material (such as glass paste) to form a cavity structure between their opposite surfaces. In addition, through holes are reserved on the ceramic base, and internal electrodes are led out by inserting pins into the through holes. The current ceramic capacitive pressure sensors have problems such as poor sealing performance, and thus problems such as poor reliability. Summary of the Invention

[0003] In order to make up for the deficiencies of the above-mentioned prior art, the present invention provides a ceramic sensor and a preparation method thereof.

[0004] The technical problems of the present invention are solved by the following technical solutions:

[0005] A ceramic sensor includes a ceramic elastic sheet, a ceramic base, and a conductive channel; a cavity is formed between the middle region of the bottom surface of the ceramic elastic sheet and the middle region of the top surface of the ceramic base, and the thickness of the ceramic elastic sheet is less than the thickness of the ceramic base; a common electrode is provided on the bottom surface of the ceramic elastic sheet corresponding to the cavity, a pressure-sensitive electrode and a reference electrode are provided on the central region of the top surface of the ceramic base corresponding to the cavity, the reference electrode is annular, concentric with the pressure-sensitive electrode and surrounds the pressure-sensitive electrode with a gap therebetween; the projection of the common electrode on the top surface of the ceramic base corresponding to the cavity completely covers both the pressure-sensitive electrode and the reference electrode; the conductive channel is arranged on the ceramic base and consists of a channel hole and a conductive electrode filling the channel hole, and includes a first conductive channel connected to the common electrode, a second conductive channel connected to the pressure-sensitive electrode, and a third conductive channel connected to the reference electrode, and each conductive electrode penetrates out of the bottom of the ceramic base to have a lead-out end; the ceramic elastic sheet, the ceramic base, and the conductive channel are sintered to form an integral structure.

[0006] Preferably, a temperature-sensitive electrode is further included, the temperature-sensitive electrode is formed in the ceramic base, and the conductive channel further includes a fourth conductive channel and a fifth conductive channel connected to the temperature-sensitive electrode.

[0007] Preferably, a welding layer is respectively formed on the lead-out ends of each conductive electrode after electroplating treatment.

[0008] Preferably, the distance between the pressure-sensitive electrode and the reference electrode is 0.1 mm to 0.8 mm.

[0009] A method for preparing a ceramic sensor, comprising the following steps:

[0010] (1) Prepare a plurality of first green tapes, one second green tape, a plurality of third green tapes, and one fourth green tape, and form channel holes of the conductive channels by punching holes in each of the third green tapes;

[0011] Among them, the plurality of first green tapes and the plurality of third green tapes are both obtained by tape casting and drying of a first ceramic slurry, and the second green tape is obtained after printing the common electrode in the middle region of the surface of one of the first green tapes;

[0012] Among them, the formation of the fourth green tape includes the following steps:

[0013] A. Print the reference electrode and the pressure-sensitive electrode in the middle region of the surface of one of the third green tapes;

[0014] B. Print a second ceramic slurry on the surface of the green tape formed in step A where the reference electrode and the pressure-sensitive electrode are located, except for the channel holes and the middle region;

[0015] C. Print a slurry that can be decomposed at medium and low temperatures on the middle region of the green tape formed in step B to obtain the fourth green tape, wherein the printing thicknesses of step B and step C are the same;

[0016] (2) Fill each channel hole in each of the third green tapes and the fourth green tape with a conductive slurry and dry it;

[0017] (3) Stack the first green tape, the second green tape, the fourth green tape, and the third green tape in sequence to form a green body, wherein the side of the second green tape provided with the common electrode is closely adjacent to the side of the fourth green tape printed with the slurry that can be decomposed at medium and low temperatures, the first green tape and the second green tape are stacked to form the ceramic elastic thin sheet, and the third green tape and the fourth green tape are stacked to form the ceramic base;

[0018] (4) Perform isostatic pressing on the green body formed in step (3), and then perform cutting to form a sensor green body;

[0019] (5)Debind and sinter the green body of the sensor formed in step (4). During the debinding and sintering process, the slurry that can be decomposed at medium and low temperatures is first completely decomposed to form the cavity, and then after continuous sintering, the conductive slurry is formed into a conductive electrode filling the channel holes, and the conductive electrode has a lead-out end on the bottom surface of the ceramic base, and the ceramic elastic sheet, the ceramic base, and the conductive channel become an integrated structure.

[0020] Preferably, it further includes the step of forming a temperature-sensing electrode: printing a temperature-sensing electrode on any one of the third green tapes or on the fourth green tape, and forming a conductive channel corresponding to the temperature-sensing electrode on the ceramic base.

[0021] Preferably, it further includes step (6): electroplating the lead-out ends of the conductive electrodes in step (5) respectively to form a welding layer.

[0022] Preferably, the slurry for printing the temperature-sensing electrode is a metal slurry with TCR > 2000 ppm / °C, sheet resistance > 20 mΩ / square, and sintering temperature > 1500 °C, and the printing thickness is 5 - 20 μm.

[0023] Preferably, the aperture of the channel hole is 50 - 1000 μm; the printing thicknesses of the common electrode, the reference electrode, and the pressure-sensing electrode are each independently 1 - 5 μm; in step B, the printing thickness of the second ceramic slurry is 20 - 100 μm; in step C, the printing thickness of the slurry that can be decomposed at medium and low temperatures is 20 - 100 μm.

[0024] Preferably, the first ceramic slurry includes the following components by mass fraction: main powder 45% - 60%, sintering aid 0.5% - 5%, organic solvent for tape casting 20% - 35%, dispersant 0.5% - 2%, and binder 5% - 15%; the second ceramic slurry includes the following components by mass fraction: main powder 55% - 75%, sintering aid 0.5% - 6%, organic solvent for printing 8% - 20%, surfactant 1% - 5%, and binder 5% - 15%; the slurry that can be decomposed at medium and low temperatures includes the following components by mass fraction: carbon powder 60% - 80%, organic solvent 8% - 20%, binder 5% - 15%, and surfactant 1% - 5%.

[0025] The beneficial effects of the present invention compared with the prior art include: The ceramic sensor of the present invention forms an integrated structure of a ceramic elastic sheet, a ceramic base, and a conductive channel, ensuring the sealed connection between the ceramic elastic sheet and the ceramic base, and also ensuring the good sealed connection between the conductive channel and each electrode. Subsequently, a plating welding layer can be further electroplated on the lead-out end of the conductive electrode in the conductive channel for effective welding with an external circuit in the future. Since the conductive channel is formed during the formation of the ceramic sensor and forms a direct contact connection with each electrode, there is no need to connect through pins subsequently, solving the problems of poor airtightness and poor reliability caused by poor sealing and pin insertion in the existing ceramic sensors, greatly improving the sealing and reliability of the ceramic sensor, and extending the service life of the sensor.

[0026] Furthermore, the temperature-sensing electrode is also integrated in the ceramic sensor, enabling the ceramic sensor to be used for both pressure and temperature detection without increasing the volume. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a cross-sectional schematic view of the ceramic capacitive pressure and temperature sensor in an embodiment of the present invention;

[0028] Figure 2 is a schematic view of the top surface of the ceramic base of the ceramic capacitive pressure and temperature sensor in an embodiment of the present invention;

[0029] Figure 3 is a schematic view of the bottom surface of the ceramic elastic sheet of the ceramic capacitive pressure and temperature sensor in an embodiment of the present invention;

[0030] Figure 4 is a schematic view of step (7) of the preparation method of the ceramic capacitive pressure and temperature sensor in an embodiment of the present invention;

[0031] Figure 5 is a graph showing the output relationship between the resistance R and the temperature T of the ceramic capacitive pressure and temperature sensor in an embodiment of the present invention;

[0032] Figure 6 is a graph showing the output relationship between the pressure and the capacitance of the ceramic capacitive pressure and temperature sensor in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] The present invention will be further described below with reference to the accompanying drawings and preferred embodiments. It should be noted that, without conflict, the embodiments and features in the present application can be combined with each other.

[0034] It should be noted that the orientation terms such as left, right, up, down, top, and bottom in this embodiment are only relative concepts to each other or are referenced based on the normal use state of the product, and should not be considered restrictive.

[0035] The present invention provides a ceramic sensor, which includes a ceramic elastic sheet, a ceramic base, and a conductive channel; a cavity is formed between the middle region of the bottom surface of the ceramic elastic sheet and the middle region of the top surface of the ceramic base, and the thickness of the ceramic elastic sheet is less than the thickness of the ceramic base; a common electrode is provided on the bottom surface of the ceramic elastic sheet corresponding to the cavity, and a pressure sensing electrode and a reference electrode are provided on the central region of the top surface of the ceramic base corresponding to the cavity. The reference electrode is annular (an annular shape with an opening), is concentric with the pressure sensing electrode, surrounds the pressure sensing electrode on the outside, and is spaced apart from the pressure sensing electrode; the projection of the common electrode on the top surface of the ceramic base corresponding to the cavity completely covers both the pressure sensing electrode and the reference electrode; the conductive channel is provided on the ceramic base and is composed of a channel hole and a conductive electrode filling the channel hole, and includes a first conductive channel connected to the common electrode, a second conductive channel connected to the pressure sensing electrode, and a third conductive channel connected to the reference electrode. Each conductive electrode penetrates out of the bottom of the ceramic base and has a lead-out end; the ceramic elastic sheet, the ceramic base, and the conductive channel are sintered to form an integral structure.

[0036] The ceramic sensor formed by the above solution is used to detect pressure and is a ceramic capacitive pressure sensor. Among them, the common electrode and the pressure sensing electrode form a measurement capacitance Cp, and the common electrode and the reference electrode form a reference capacitance Cr. When the ceramic elastic sheet is deformed under pressure, the common electrode also deforms, resulting in a smaller gap in the cavity and a change in capacitance. By respectively converting the change amounts of Cp and Cr into DC voltage outputs, the magnitude of the applied pressure is measured through the difference signal of the two output voltages. The greater the pressure, the greater the capacitance change.

[0037] Ceramic capacitive pressure sensors are usually used in automotive and industrial systems. In these harsh working environments, there is a requirement for the sensors to have high reliability and long life. Most of the existing ceramic capacitive pressure sensors use glass paste as the sealing material between the ceramic elastic thin sheet and the ceramic base to form a cavity structure. In addition, through holes are reserved on the ceramic base, and the internal electrodes are led out by inserting pins into the through holes. The above existing solutions are prone to problems such as too low sealing yield of the sensor ceramic core due to the mismatch of different materials and poor pin insertion, and there are potential reliability problems such as open circuits under high and low temperature shocks in subsequent applications. In the present invention, the ceramic elastic thin sheet, the ceramic base and the conductive channel are formed into an integral structure, and the formed ceramic elastic thin sheet and the ceramic base are made of the same material, so there will be no problem of mismatch of different materials. At the same time, the sintering of the ceramic elastic thin sheet and the ceramic base into one body also ensures the sealed connection between the ceramic elastic thin sheet and the ceramic base. Moreover, the conductive channel is also sintered into an integral structure with the ceramic elastic thin sheet and the ceramic base, ensuring good sealed connection between the conductive channel and the electrodes on the ceramic base and the ceramic elastic thin sheet (the conductive electrodes in the conductive channel are directly in contact with the respective electrodes). Since the conductive channel is formed during the formation of the ceramic capacitive pressure sensor and is in direct contact connection with the respective electrodes, there is no need to connect through pins later, solving the problems of poor airtightness and poor reliability caused by poor sealing and pin insertion of the existing ceramic capacitive pressure sensors, greatly improving the airtightness and reliability of the ceramic capacitive pressure sensor and increasing the service life of the sensor.

[0038] In some preferred embodiments, it further includes a temperature sensing electrode formed inside the ceramic base. The conductive channel further includes a fourth conductive channel and a fifth conductive channel connected to the temperature sensing electrode. A more preferred way is that the temperature sensing electrode is also formed on the top surface of the ceramic base, on the same surface as the reference electrode and the pressure sensing electrode, but not inside the cavity. The temperature sensing electrode is an annular shape with an opening, surrounding the periphery of the reference electrode, and the fourth conductive channel and the fifth conductive channel are respectively arranged at both ends of the annular shape.

[0039] Ceramic capacitive pressure sensors are widely used in the pressure detection of water, gas, liquid and various media. In the corresponding application environments, it is often necessary to simultaneously measure the pressure and temperature values. Moreover, when calibrating the sensors, the synergistic effects of temperature and pressure need to be considered simultaneously to improve the output accuracy of the sensors. In existing solutions, corresponding temperature sensors and pressure sensors are separately selected for testing and calibration, or a temperature sensor is attached to the outside of the ceramic capacitive pressure sensor core body, and then they are riveted together as a whole, resulting in inherent defects such as bloated sensor volume, increased cost, or insufficient output accuracy. In the preferred solution of this application, the temperature-sensing electrodes are also integrated into the ceramic sensor, enabling the ceramic sensor to be used for measuring pressure and temperature simultaneously without increasing the volume. This ceramic sensor can be called a ceramic capacitive pressure and temperature sensor.

[0040] After adding the temperature measurement function, the accuracy of the sensor can be further optimized. Since the capacitance values of the sensor are slightly different at different temperatures (without pressure), if there is no temperature sensor, the capacitance difference will be misinterpreted as a pressure change, resulting in poor test accuracy of the sensor. By integrating the temperature and pressure sensors together, through the change of temperature and the change of capacitance value difference, the backend circuit chip can record the relationship between the temperature difference and the capacitance difference through calibration, and thus improve the accuracy of the sensor.

[0041] In some preferred embodiments, after the lead-out ends of each conductive electrode are electroplated, a welding layer is respectively formed. Through the formed welding layer, effective welding can be carried out with the external circuit subsequently. Preferably, a nickel layer is first plated on the lead-out end, and then a tin layer is plated on the surface of the nickel layer to wrap the nickel layer. The preferred thickness of the nickel layer is 2 - 5 μm, and the thickness of the tin layer is 3 - 10 μm.

[0042] In some preferred embodiments, the interval between the pressure-sensing electrode and the reference electrode is 0.1 mm - 0.8 mm.

[0043] The present invention also provides a preparation method for the above-mentioned ceramic sensor, including the following steps:

[0044] (1) Prepare several first green tapes, one second green tape, several third green tapes and one fourth green tape, and open holes on each third green tape to form the channel holes of the conductive channels;

[0045] Among them, the several first green tapes and the several third green tapes are both obtained by casting and drying the first ceramic slurry, and the second green tape is obtained by printing the common electrode in the middle area on the surface of one of the first green tapes;

[0046] Among them, the formation of the fourth green tape includes the following steps:

[0047] A. Print the reference electrode and the pressure-sensitive electrode in the middle region on the surface of one of the third green tapes;

[0048] B. Print the second ceramic slurry at positions other than the channel holes and the middle region on the surface of the green tape formed in step A that has the reference electrode and the pressure-sensitive electrode;

[0049] C. Print the slurry that can be decomposed at medium and low temperatures on the middle region of the green tape formed in step B to obtain the fourth green tape, wherein the printing thicknesses in step B and step C are the same;

[0050] (2) Fill and completely fill each channel hole in the third green tape and the fourth green tape with the conductive slurry and then dry it;

[0051] (3) Stack and press the first green tape, the second green tape, the fourth green tape, and the third green tape in sequence to form a green body. Among them, the side of the second green tape with the common electrode is in close contact with the side of the fourth green tape printed with the slurry that can be decomposed at medium and low temperatures. After the first green tape and the second green tape are stacked and pressed, the ceramic elastic sheet is formed, and after the third green tape and the fourth green tape are stacked and pressed, the ceramic base is formed; the preferred lamination pressure is 20 - 40 t, and the lamination temperature is: 30 - 70 °C.

[0052] (4) Perform isostatic pressing on the green body formed in step (3), and then perform cutting to form a green body of the sensor; preferably, the isostatic pressing treatment is carried out at a water temperature of 60 - 70 °C and a pressure of 10 - 100 MPa.

[0053] (5) Debind and sinter the green body of the sensor formed in step (4). During the debinding and sintering process, the slurry that can be decomposed at medium and low temperatures is first completely decomposed to form the cavity, and then after continuous sintering, the conductive slurry forms a conductive electrode that fills the channel holes, and the conductive electrode has a lead-out end on the bottom surface of the ceramic base. The ceramic elastic sheet, the ceramic base, and the conductive channel become an integral structure. Preferably, the sintering temperature is: 1350 - 1600 °C, and it is carried out in air or a reducing atmosphere.

[0054] In some preferred embodiments, the preparation method further includes the step of forming a temperature-sensing electrode: printing a temperature-sensing electrode on any one of the third green tapes or on the fourth green tape, and forming a conductive channel corresponding to the temperature-sensing electrode on the ceramic base. A more preferred way is that the temperature-sensing electrode is formed on the same surface as the reference electrode and the pressure-sensing electrode on the fourth green tape, but not in the cavity. That is, when printing the reference electrode and the pressure-sensing electrode in the middle area of the surface of one of the third green tapes in step A, the temperature-sensing electrode is also printed. In step B, when printing the second ceramic paste, the second ceramic paste may cover the temperature-sensing electrode or may not cover the temperature-sensing electrode.

[0055] In some preferred embodiments, it further includes step (6): electroplating the lead-out ends of the respective conductive electrodes in step (5) to form welding layers respectively. Preferably, a nickel layer is first plated on the lead-out end, and then a tin layer is plated on the surface of the nickel layer to wrap the nickel layer. The preferred thickness of the nickel layer is 2 - 5 μm, and the thickness of the tin layer is 3 - 10 μm.

[0056] In some preferred embodiments, the aperture diameter of the channel hole is 50 - 1000 μm; the printing thicknesses of the common electrode, the reference electrode, and the pressure-sensing electrode are each independently 1 - 5 μm.

[0057] In some preferred embodiments, the paste for printing the temperature-sensing electrode is a metal paste with TCR > 2000 ppm / °C, sheet resistance > 20 mΩ / □, and sintering temperature > 1500 °C, and the printing thickness is 5 - 20 μm.

[0058] In some preferred embodiments, the pastes for printing the common electrode, the reference electrode, and the pressure-sensing electrode are each independently made of metal powders such as Pt, Ag-Pt, Pd, Ag-Pd, W, Ni alloy, etc. that can withstand high-temperature sintering. More preferably, the three select the same material and the same thickness.

[0059] In some preferred embodiments, in step B, the printing thickness of the second ceramic paste is 20 - 100 μm; the printing thickness of the paste that can be decomposed at medium and low temperatures in step C is 20 - 100 μm, and the depth of the cavity formed after final sintering is 10 - 80 μm.

[0060] In some preferred embodiments, the first ceramic slurry comprises the following components by mass fraction: 45% - 60% of main powder, 0.5% - 5% of sintering aid, 20% - 35% of organic solvent for tape casting, 0.5% - 2% of dispersant, and 5% - 15% of binder; wherein, the main powder in the first ceramic slurry is one of Al2O3 powder, ZrO2 powder or a mixture of the two powders, the sintering aid is at least one of ZnO, CaO, MgO, SiO2, the organic solvent for tape casting is at least one of toluene, propyl acetate, isobutanol and ethanol, the brand of the dispersant is BYK - 110, and the binder is acrylic resin, butyral resin, etc.; the components of the first ceramic slurry are mixed in proportion, zirconia balls are added as the medium and ball milled continuously for 15h - 30h to form a tape-casting slurry.

[0061] In some preferred embodiments, the second ceramic slurry comprises the following components by mass fraction: 55% - 75% of main powder, 0.5% - 6% of sintering aid, 8% - 20% of organic solvent for printing, 1% - 5% of surfactant, and 5% - 15% of binder; wherein, the main powder in the second ceramic slurry is one of Al2O3 powder, ZrO2 powder or a mixture of the two powders, the sintering aid is at least one of ZnO, CaO, MgO, SiO2, the organic solvent for printing is at least one of terpineol, butyl carbitol and butyl carbitol acetate, the surfactant is at least one of lecithin and bis(3 - trimethoxysilylpropyl)amine (trade name KH170), and the binder is at least one of ethyl cellulose, acrylic resin and butyral resin; the components of the second ceramic slurry are mixed in proportion, zirconia balls are added as the medium and ball milled continuously for 15h - 30h to form a printing slurry. More preferably, the main powder of the first ceramic slurry and the main powder of the second ceramic slurry are selected from the same material.

[0062] In some preferred embodiments, the slurry decomposable at medium and low temperatures comprises the following components by mass fraction: 60% - 80% of carbon powder, 8% - 20% of organic solvent, 5% - 15% of binder, and 1% - 5% of surfactant; wherein, the organic solvent is at least one of terpineol, butyl carbitol and butyl carbitol acetate, the binder is at least one of ethyl cellulose, acrylic resin and butyral resin, and the surfactant is at least one of lecithin and bis(3 - trimethoxysilylpropyl)amine (trade name KH170); the components of the slurry decomposable at medium and low temperatures are mixed in proportion, zirconia balls are added as the medium and ball milled continuously for 15h - 30h to form a printing slurry.

[0063] The present invention is described in detail below through more specific examples.

[0064] As Figures 1-3As shown, this example is a ceramic capacitive pressure and temperature sensor, which includes a ceramic elastic sheet 1, a ceramic base 2, a conductive channel, and a welding layer 11. A cavity 12 is formed between the middle region of the bottom surface of the ceramic elastic sheet 1 and the middle region of the top surface of the ceramic base 2. The thickness of the ceramic elastic sheet 1 is less than that of the ceramic base 2. A common electrode 3 is provided on the bottom surface of the ceramic elastic sheet corresponding to the cavity 12. A pressure-sensing electrode 5 and a reference electrode 4 are provided on the central region of the top surface of the ceramic base 2 corresponding to the cavity 12. The reference electrode 4 is in the shape of a ring with an opening, concentric with the pressure-sensing electrode 5 and surrounding the pressure-sensing electrode 5 and spaced apart from the pressure-sensing electrode (in this example, the spacing is 0.6 mm). The projection of the common electrode 3 on the top surface of the ceramic base corresponding to the cavity completely covers both the pressure-sensing electrode 5 and the reference electrode 4. There is also a temperature-sensing electrode 6 on the periphery of the cavity on the top surface of the ceramic base 2. The temperature-sensing electrode 6 is also in the shape of a ring with an opening, surrounding the pressure-sensing electrode 5. The conductive channel is provided on the ceramic base 2 and is composed of channel holes 13, 14, 15, 16, and 17 and conductive electrodes filling the channel holes 13, 14, 15, 16, and 17. The conductive channel includes a first conductive channel 10 connected to the common electrode 3, a second conductive channel 8 connected to the pressure-sensing electrode 5, a third conductive channel 9 connected to the reference electrode 4, a fourth conductive channel 7-1 and a fifth conductive channel 7-2 connected to the temperature-sensing electrode. Each conductive electrode penetrates out of the bottom of the ceramic base and has a lead-out end. After electroplating treatment of each lead-out end, a welding layer 11 is respectively formed. The ceramic elastic sheet 1, the ceramic base 2, and each conductive channel are sintered to form an integral structure.

[0065] The preparation method steps of the ceramic capacitive pressure and temperature sensor are as follows:

[0066] (1) Prepare the first ceramic slurry (for tape casting slurry): The first ceramic slurry includes the following components in mass fractions: main powder (Al2O3 powder) 50%, sintering aid (ZnO) 5%, organic solvent (ethanol) 28%, dispersant (brand BYK-110) 2%, and binder (acrylic resin) 15%. Mix each component in proportion, add zirconia balls as the medium and continuously ball mill for 30 h to form a tape casting slurry.

[0067] (2) Prepare the second ceramic slurry (for printing slurry): The second ceramic slurry includes the following components in mass fractions: main powder (Al2O3 powder) 75%, sintering aid (ZnO) 5%, organic solvent (terpineol) 8%, surfactant (KH170) 2%, and binder (ethyl cellulose) 10%. Mix each component in proportion, add zirconia balls as the medium and continuously ball mill for 30 h to form a printing slurry.

[0068] (3) Prepare a paste that can be decomposed at medium and low temperatures (for printing): "Medium and low temperatures" in the paste that can be decomposed at medium and low temperatures refers to 200 - 1000 °C, and it includes the following components with mass fractions: 75% carbon powder, 12% organic solvent (terpineol), 10% binder (ethyl cellulose), and 3% surfactant (KH170); mix each component in proportion, add zirconia balls as the medium and continuously ball mill for 30 h to form a printing paste.

[0069] (3) Casting: Cast and dry the first ceramic paste prepared in step (1). The thickness of the dried casting is 50 μm. Make several green tapes through multiple productions. Some of the green tapes are used as the first green tapes for subsequent production of ceramic elastic sheets, and some of the green tapes are used as the third green tapes for subsequent production of ceramic bases.

[0070] (4) Punching holes: Adopt mechanical or laser punching methods to punch holes in each of the above-mentioned third green tapes at the electrode lead-out positions to form channel holes 13, 14, 15, 16, and 17. The preferred punching hole diameter is: 50 - 1000 μm. In this example, the punching hole diameter is 500 μm.

[0071] (5) Printing: Print the common electrode 3 in the middle area on the surface of one of the first green tapes to obtain a second green tape. The paste for printing the common electrode 3 is Pt paste, and the printing thickness is 4 μm.

[0072] (6) Printing: Print the reference electrode 4 and the pressure-sensitive electrode 5 in the middle area on the surface of one of the third green tapes. The reference electrode 4 is in the shape of a ring with an opening, concentric with the pressure-sensitive electrode 5 and surrounding the pressure-sensitive electrode 5 on the outside and spaced apart from the pressure-sensitive electrode by a distance of 0.6 mm; and continue to print the temperature-sensitive electrode 6 around the pressure-sensitive electrode 5. Among them, the pastes for printing the reference electrode 4 and the pressure-sensitive electrode 5 are both Pt paste, and the printing thicknesses are both 4 μm. In other examples, the materials of the common electrode 3, the reference electrode 4, and the pressure-sensitive electrode 5 can also be different, preferably the same; the paste for printing the temperature-sensitive electrode 6 is a metal paste with a temperature coefficient of resistance (TCR) > 2000 ppm / °C, sheet resistance (resistivity of the paste) > 20 mΩ / □, and sintering temperature > 1500 °C (Ag-Pd paste is selected in this example), and the printing thickness is 15 μm. As the temperature outside the sensor changes, the resistance value of the temperature-sensitive electrode also changes linearly. (In other examples, the temperature-sensitive electrode 6 can also be printed separately on another third green tape, not on the same layer as the reference electrode 4 and the pressure-sensitive electrode 5).

[0073] (7) Printing: On the green tape obtained in step (6), use the second ceramic paste prepared in step (2) according to Figure 4Print on the indicated position area 18 (the area filled with dots) (i.e., print the second ceramic slurry on the surface with the reference electrode, pressure-sensitive electrode, and temperature-sensitive electrode, and except for the channel holes and the middle area (i.e., Figure 4 the central blank area except for the channel hole positions in Figure 4 . The middle area is the area where the reference electrode and the pressure-sensitive electrode are provided, and this middle area is subsequently used to form a cavity)), that is, when printing, avoid the middle area and the channel holes that need to form a cavity subsequently, and the printing thickness is 25 μm.

[0074] (8) Printing: Use the slurry that can be decomposed at medium and low temperatures in step (3) to continue printing on the green tape formed in step (7). The printing area is the middle area not covered by the second ceramic slurry in step (7). The printing thickness is the same as that in step (7), which is 25 μm. After the processing of steps (6) to (8), the fourth green tape is obtained;

[0075] (9) Printing: For the third green tape and the fourth green tape with channel holes, print the conductive slurry into the corresponding channel holes and fill the channel holes, and then dry. Among them, after the conductive slurry filled in the channel holes 13 and 14 is sintered to form the fourth conductive channel 7-1 and the fifth conductive channel 7-2, it correspondingly connects the two ends of the temperature-sensitive electrode 6. After the conductive slurry filled in the channel hole 15 is sintered into the second conductive channel 8, it correspondingly connects the pressure-sensitive electrode 5. After the conductive slurry filled in the channel hole 16 is sintered into the third conductive channel 9, it correspondingly connects the reference electrode 4. After the conductive slurry filled in the channel hole 17 is sintered into the conductive channel 10, it correspondingly connects the common electrode 3; The conductive slurry is preferably but not limited to a conductive silver paste made of metal powders such as Pt, Ag-Pt, Pd, Ag-Pd, W, Ni alloy, etc. that can withstand high-temperature sintering. In this example, the conductive silver paste is Pt paste.

[0076] (10) Laminating: According to the structural design sequence, sequentially laminate the first green tape, the second green tape, the fourth green tape, and the third green tape obtained above into a blank. The lamination pressure is 35 t, and the pressing temperature is: 60 °C. Among them, the side of the second green tape with the common electrode is closely attached face to face with the side of the fourth green tape printed with the slurry that can be decomposed at medium and low temperatures. After the first green tape and the second green tape are laminated, they are used to form a ceramic elastic sheet, and after the third green tape and the fourth green tape are laminated, they are used to form a ceramic base.

[0077] (11) Warm isostatic pressing: Clamp the upper and lower surfaces of the blank in step (10) with flat steel plates, place it on a sealed bag for vacuuming, and perform isostatic pressing at a water temperature of 70 °C and a pressure of 60 MPa.

[0078] (12) Cutting: According to the product size design, the green body processed in step (11) is cut to form independent sensor green blanks. Among them, the ceramic elastic thin sheet and the ceramic base can be one of square, circular or oval.

[0079] (13) Debinding and sintering: The green blanks obtained in step (12) are debound. After debinding, sintering is carried out in air or reducing atmosphere, and the sintering temperature is 1450 °C. After sintering, the ceramic elastic thin sheet, the ceramic base and the conductive channels form an integral structure. The reference electrode, the pressure-sensitive electrode, the common electrode and the temperature-sensitive electrode form good direct contact with the conductive electrodes in the corresponding conductive channels, and there is no need to insert needles to lead out the electrodes during subsequent use.

[0080] (14) Electroplating: The sintered ceramic body in step (13) is loaded into a basket with media such as electroplating balls. First, nickel is electroplated on the lead-out ends of each conductive electrode, and then tin is electroplated on the surface of nickel to wrap nickel. The thickness of the nickel layer is 3 μm, and the thickness of the tin layer is 6 μm, forming a welding layer 11 for effective welding with the external circuit subsequently.

[0081] In the finally formed ceramic capacitive pressure and temperature sensor, the thickness of the ceramic elastic thin sheet is between 0.3 mm and 1.2 mm, and the thickness of the ceramic base is greater than that of the ceramic elastic thin sheet, about 4 - 5 mm. In the ceramic capacitive pressure and temperature sensor prepared in this example, the thickness of the ceramic elastic thin sheet is 0.5 mm, and the thickness of the ceramic base is 3 mm.

[0082] As Figures 5-6 shown, Figure 5 is the output relationship diagram of the resistance R and temperature T of the ceramic capacitive pressure and temperature sensor in this example, where the solid line represents the measured value and the dashed line represents the fitted linear curve. This diagram shows that the temperature and the output resistance are linearly related, and the corresponding temperature can be determined by the output resistance; Figure 6 is the output relationship diagram of the pressure and capacitance of the ceramic capacitive pressure and temperature sensor in this example. It can be seen that as the pressure changes, the capacitance also changes linearly.

[0083] The following table shows the sealing test results of the ceramic capacitive pressure sensor made by the existing process (using glass paste as the sealing material between the ceramic elastic thin sheet and the ceramic base and realizing the lead-out of internal electrodes by inserting needles) (shown as a comparative example in the table) and the ceramic capacitive pressure and temperature sensor made by the method of this application (shown as an example in the table). It can be seen from this that the sealing performance of the ceramic capacitive pressure and temperature sensor of this application has been greatly improved, laying a good foundation for the reliability of subsequent sensors.

[0084]

[0085] The preparation method of the present invention obtains a green tape by using the casting method, perforates the green tape by mechanical or laser means, forms each electrode and cavity by using the screen printing process, laminates, sinters, electroplates, etc. It can integrate the temperature and pressure test functions inside the ceramic core at the same time, and can also effectively solve the problems of too low airtightness yield and poor reliability of existing ceramic sensors.

[0086] The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those skilled in the technical field to which the present invention belongs, without departing from the concept of the present invention, several equivalent substitutions or obvious modifications can be made, and if the performance or use is the same, they should all be regarded as belonging to the protection scope of the present invention.

Claims

1. A ceramic sensor, characterized in that, It includes a ceramic elastic sheet, a ceramic base, and a conductive channel; A cavity is formed between the middle region of the bottom surface of the ceramic elastic sheet and the middle region of the top surface of the ceramic base, and the thickness of the ceramic elastic sheet is less than that of the ceramic base; A common electrode is provided on the bottom surface of the ceramic elastic sheet corresponding to the cavity, and a pressure-sensitive electrode and a reference electrode are provided on the central region of the top surface of the ceramic base corresponding to the cavity. The reference electrode is annular, concentric with the pressure-sensitive electrode and surrounds the pressure-sensitive electrode with a gap therebetween; the projection of the common electrode on the top surface of the ceramic base corresponding to the cavity completely covers both the pressure-sensitive electrode and the reference electrode; The conductive channel is provided on the ceramic base and is composed of a channel hole and a conductive electrode filling the channel hole, and includes a first conductive channel connected to the common electrode, a second conductive channel connected to the pressure-sensitive electrode, and a third conductive channel connected to the reference electrode. Each conductive electrode penetrates through the bottom of the ceramic base to have a lead-out end; The ceramic elastic sheet, the ceramic base, and the conductive channel are sintered to form an integral structure; The cavity is formed by the complete decomposition of the slurry that can be decomposed at medium and low temperatures during the debinding and sintering process of the sensor green body.

2. The ceramic sensor according to claim 1, wherein: It further includes a temperature-sensitive electrode, the temperature-sensitive electrode is formed in the ceramic base, and the conductive channel further includes a fourth conductive channel and a fifth conductive channel connected to the temperature-sensitive electrode.

3. The ceramic sensor according to claim 1 or 2, characterized in that: A welding layer is respectively formed on the lead-out ends of each conductive electrode after electroplating treatment.

4. The ceramic sensor according to claim 1, characterized in that: The gap between the pressure-sensitive electrode and the reference electrode is 0.1 mm to 0.8 mm.

5. A method for preparing the ceramic sensor according to claim 1, characterized in that, It includes the following steps: (1) Prepare a plurality of first green tapes, one second green tape, a plurality of third green tapes, and one fourth green tape, and open holes in each third green tape to form the channel holes of the conductive channel; Among them, the plurality of first green tapes and the plurality of third green tapes are both obtained by casting and drying the first ceramic slurry, and the second green tape is obtained by printing the common electrode on the middle region of the surface of one of the first green tapes; Among them, the formation of the fourth green tape includes the following steps: A. Print the reference electrode and the pressure-sensitive electrode on the middle region of the surface of one of the third green tapes; B. Print the second ceramic slurry on the surface of the green tape formed in step A with the reference electrode and the pressure-sensitive electrode, except for the channel holes and the middle region; C. Print the slurry that can be decomposed at medium and low temperatures on the middle region of the green tape formed in step B to obtain the fourth green tape, where the printing thicknesses of step B and step C are the same; (2) Fill the conductive slurry into each channel hole in each of the third green tape and the fourth green tape and dry it; (3) Stack and press the first green tape, the second green tape, the fourth green tape, and the third green tape in sequence to form a green body. Among them, the side of the second green tape with the common electrode is in close contact with the side of the fourth green tape printed with the paste that can be decomposed at medium and low temperatures. After the first green tape and the second green tape are stacked and pressed, the ceramic elastic sheet is formed. After the third green tape and the fourth green tape are stacked and pressed, the ceramic base is formed; (4) Perform isostatic pressing on the green body formed in step (3), and then perform cutting to form a green body of the sensor; (5) Debind and sinter the green body of the sensor formed in step (4). During the debinding and sintering process, the paste that can be decomposed at medium and low temperatures is first completely decomposed to form the cavity. Then, after continuous sintering, the conductive paste forms a conductive electrode filling the channel holes, and the conductive electrode has an extraction end on the bottom surface of the ceramic base. The ceramic elastic sheet, the ceramic base, and the conductive channel become an integrated structure.

6. The preparation method according to claim 5, characterized in that, It further includes the step of forming a temperature-sensing electrode: print a temperature-sensing electrode on any one of the third green tapes or on the fourth green tape, and form a conductive channel corresponding to the temperature-sensing electrode on the ceramic base.

7. The preparation method according to claim 5 or 6, characterized in that, It further includes step (6): electroplate the extraction ends of the conductive electrodes in step (5) respectively to form a welding layer.

8. The preparation method according to claim 6, characterized in that, The paste for printing the temperature-sensing electrode is a metal paste with TCR > 2000 ppm / °C, sheet resistance > 20 mΩ / square, and sintering temperature > 1500 °C, and the printing thickness is 5 - 20 μm.

9. The preparation method according to claim 5, characterized in that, The aperture of the channel hole is 50 - 1000 μm; the printing thicknesses of the common electrode, the reference electrode, and the pressure-sensing electrode are each independently 1 - 5 μm; in step B, the printing thickness of the second ceramic paste is 20 - 100 μm; in step C, the printing thickness of the paste that can be decomposed at medium and low temperatures is 20 - 100 μm.

10. The preparation method according to claim 5, wherein The first ceramic paste includes the following components in mass fractions: main powder 45% - 60%, sintering aid 0.5% - 5%, organic solvent for tape casting 20% - 35%, dispersant 0.5% - 2%, and binder 5% - 15%; The second ceramic paste includes the following components in mass fractions: main powder 55% - 75%, sintering aid 0.5% - 6%, organic solvent for printing 8% - 20%, surfactant 1% - 5%, and binder 5% - 15%; The paste that can be decomposed at medium and low temperatures includes the following components in mass fractions: carbon powder 60% - 80%, organic solvent 8% - 20%, binder 5% - 15%, and surfactant 1% - 5%.

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