A BAW pressure sensor and its manufacturing method

Abstract

The present invention provides a BAW pressure sensor and a method for manufacturing the same, relating to the field of semiconductor technology. The sensor comprises a substrate, a bottom electrode, a piezoelectric layer, and a top electrode stacked in sequence, with a cavity provided between the substrate and the bottom electrode. The top surface of the top electrode is covered with a sensing layer that changes color under pressure. The sensing layer is used to generate a color-changing signal based on pressure changes, which is used to qualitatively analyze pressure changes. The BAW pressure sensor of the present invention solves the problem of the top electrode being affected by the environment, which affects the accuracy of measurement results, and the lack of qualitative pressure analysis in current BAW pressure sensors, thereby improving the accuracy of measurement results and enabling qualitative pressure analysis.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a BAW pressure sensor and a preparation method thereof. Background Art

[0002] BAW pressure sensors (piezoelectric) offer a wide measurement range and excellent dynamic response, adapting to a variety of complex environments and rapidly changing pressure conditions. Furthermore, their simple structure, compact size, and light weight facilitate installation and maintenance, enhancing measurement convenience and flexibility. These advantages make BAW pressure sensors promising for broad application in industrial automation, environmental monitoring, biomedicine, and other fields.

[0003] Compared with traditional pressure sensors (such as piezoresistive and capacitive pressure sensors), traditional pressure sensors often need to be used in conjunction with other equipment (such as filters, signal amplification equipment, analog-to-digital conversion equipment, etc.) to process the signal before outputting the pressure value. BAW pressure sensors only need to obtain the frequency of their piezoelectric effect to quantitatively analyze the pressure value, so their timeliness is much higher than traditional pressure sensors.

[0004] However, BAW pressure sensors are sensitive to changes in ambient temperature and humidity. The main reason is that oxygen and water vapor in the air can easily affect the top electrode, causing fluctuations in the performance of the BAW pressure sensor and affecting the accuracy of the measurement results.

[0005] In addition, compared with traditional pressure sensors, although BAW pressure sensors have higher timeliness in quantitative analysis of pressure, the acquisition of pressure values still depends on the processing of the piezoelectric effect frequency. Therefore, the pressure changes cannot be intuitively observed from the BAW pressure sensor. Therefore, the current BAW pressure sensors still lack qualitative analysis of pressure.

[0006] There is currently no effective technical solution to the above problems. Summary of the Invention

[0007] The purpose of the present invention is to provide a BAW pressure sensor and a preparation method thereof, which solves the problem that the top electrode is affected by the environment, thereby affecting the accuracy of the measurement results and the current BAW pressure sensor lacks qualitative analysis of pressure, thereby achieving the effect of improving the accuracy of the measurement results and realizing qualitative analysis of the pressure.

[0008] In a first aspect, the present invention provides a BAW pressure sensor comprising a substrate, a bottom electrode, a piezoelectric layer and a top electrode stacked in sequence, a cavity being provided between the substrate and the bottom electrode, the upper surface of the top electrode being covered with a sensing layer, the sensing layer being capable of changing color under pressure, and the sensing layer being used to form a color change signal according to the pressure change for performing qualitative analysis of the pressure change.

[0009] The BAW pressure sensor provided by the present invention protects the top electrode by covering the upper surface of the top electrode with a sensing layer, effectively reducing the impact of the external environment on the top electrode, thereby helping to improve the accuracy of the measurement results. At the same time, the sensing layer can also intuitively reflect pressure changes through color changes, which helps users to qualitatively analyze pressure changes through the BAW pressure sensor.

[0010] Furthermore, the sensing layer is made of a phthalimethylene malononitrile type compound material.

[0011] Furthermore, the chemical structural formula of the o-phthalimethylene malononitrile compound is:

[0012] ;

[0013] in, and All of them are nitrogen-containing aromatic rings or their derivatives.

[0014] Furthermore, the horizontal areas of the top electrode and the bottom electrode are both smaller than the horizontal area of the substrate.

[0015] Furthermore, the top electrode and the bottom electrode extend from the left and right sides of the piezoelectric layer respectively in opposite directions, and downward projections of the top electrode and the bottom electrode completely cover the cavity.

[0016] This structure ensures that the electrode does not simply cover the piezoelectric layer, but extends from the side, ensuring that when the horizontal area of the electrode is smaller than the horizontal area of the substrate, it can still provide sufficient electrode coverage for the piezoelectric layer above the cavity.

[0017] Furthermore, an inclination angle is set between the inner side wall of the cavity and the bottom surface of the cavity, and the inclination angle range is greater than or equal to 70° and less than 90°.

[0018] This angled design avoids the dead-angle effect that may be caused by vertical sidewalls, improves the efficiency and integrity of the sacrificial layer release, thereby reducing the risk of sacrificial layer residue and improving the performance and reliability of the BAW pressure sensor.

[0019] Furthermore, the top electrode and the bottom electrode are both made of at least one material selected from the group consisting of gold, copper, silver, aluminum, tungsten, platinum, molybdenum, rhodium, iridium, and titanium.

[0020] Furthermore, the piezoelectric layer is made of at least one polycrystalline or single crystal piezoelectric material selected from the group consisting of AlN, ZnO, PTZ, and LN.

[0021] In a second aspect, the present invention provides a method for preparing the above-mentioned BAW pressure sensor, comprising the following steps:

[0022] S1. After forming a groove on the substrate, a sacrificial layer is deposited into the groove;

[0023] S2. After sequentially forming the bottom electrode, the piezoelectric layer, and the top electrode on the substrate, a solution of a phthalimethylene malononitrile-type compound is added dropwise to the upper surface of the top electrode and the sensing layer is obtained by spin coating;

[0024] S3. Release the sacrificial layer to form a cavity between the substrate and the bottom electrode, thereby manufacturing the BAW pressure sensor.

[0025] Furthermore, the o-phthalimethylene malononitrile compound is obtained by the following steps:

[0026] A1. The phthalate compound is dissolved in pyridine and malononitrile is added to obtain a first mixture;

[0027] A2. heating the first mixture to reflux and continuing stirring for a specified period of time until the first mixture is completely reacted and then stopping heating;

[0028] A3. To the completely reacted first mixture was added a saturated NH4Cl solution to neutralize the reaction system to obtain a second mixture;

[0029] A4. The second mixture was extracted three times with dichloromethane to combine the organic phases to obtain a first solution;

[0030] A5. By adding anhydrous Na2SO4 to the first solution to adsorb water in the first solution, to obtain a third mixture;

[0031] A6. The third mixture is filtered to remove Na2SO4 to obtain a first filtrate;

[0032] A7. The first filtrate was dried using a rotary evaporator to obtain a first crude product;

[0033] A8. The first crude product is dissolved in a mixed solvent of dichloromethane and petroleum ether, and crystals are precipitated by first heating and dissolving the mixture and then slowly cooling the mixture. The crystals are the o-phthalimethylene malononitrile-type compound.

[0034] From the above, it can be seen that the BAW pressure sensor provided by the present invention covers the upper surface of the top electrode with a sensing layer. On the one hand, the sensing layer acts as a barrier to the top electrode, thereby preventing the top electrode from direct contact with the environment, reducing the impact of oxygen and water vapor on the top electrode, and thus weakening the performance fluctuation of the BAW pressure sensor, thereby improving the accuracy of the measurement results; on the other hand, the sensing layer will change color under pressure, so the user can intuitively observe the pressure change based on the color of the sensing layer, allowing the BAW pressure sensor to realize qualitative analysis of pressure. This dual mechanism (qualitative analysis + quantitative analysis) further significantly improves the timeliness, accuracy and reliability of the BAW pressure sensor.

[0035] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the embodiments of the present invention. The purposes and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 A schematic structural diagram of a BAW pressure sensor provided in an embodiment of the present invention.

[0037] Figure 2 A flow chart of the preparation method provided in an embodiment of the present invention.

[0038] Description of labels:

[0039] 100, substrate; 200, bottom electrode; 300, piezoelectric layer; 400, top electrode; 500, cavity; 600, sensing layer. DETAILED DESCRIPTION

[0040] The embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and are not to be construed as limiting the present invention.

[0041] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0042] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to mechanical connections, electrical connections, or mutual communication; they may refer to direct connections or indirect connections through an intermediate medium; they may refer to internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0043] In the present invention, unless otherwise expressly specified or limited, a first feature being "above" or "below" a second feature may include the first and second features being in direct contact, or may include the first and second features being in contact not directly but through another feature between them. Furthermore, a first feature being "above," "above," and "above" a second feature may include the first feature being directly above or obliquely above the second feature, or may simply mean that the first feature is higher in level than the second feature. A first feature being "below," "below," and "below" a second feature may include the first feature being directly below or obliquely below the second feature, or may simply mean that the first feature is lower in level than the second feature.

[0044] The disclosure below provides many different embodiments or examples for realizing different structures of the present invention. In order to simplify the disclosure of the present invention, the components and settings of specific examples are described below. Of course, they are merely examples and are not intended to limit the present invention. In addition, the present invention may repeat reference numbers and / or reference letters in different examples. Such repetition is for the purpose of simplicity and clarity and does not in itself indicate the relationship between the various embodiments and / or settings discussed. In addition, the present invention provides examples of various specific processes and materials, but those skilled in the art will recognize the application of other processes and / or the use of other materials.

[0045] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.

[0046] It should be noted that similar numbers and letters represent similar items in the following figures, so once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. In addition, the terms "first" and "second" are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, features defined as "first" and "second" may explicitly or implicitly include one or more of the said features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined. At the same time, in the description of the present invention, the terms "first", "second", etc. are only used to distinguish descriptions and are not to be understood as indicating or implying relative importance.

[0047] Reference Attachment Figure 1 The present invention provides a BAW pressure sensor, comprising a substrate 100, a bottom electrode 200, a piezoelectric layer 300 and a top electrode 400 stacked in sequence, a cavity 500 being provided between the substrate 100 and the bottom electrode 200, and a sensing layer 600 covering the upper surface of the top electrode 400. The sensing layer 600 can change color under pressure, and the sensing layer 600 is used to generate a color change signal according to the pressure change for performing qualitative analysis of the pressure change.

[0048] The sensing layer is located on the upper surface of the top electrode. The sensing layer material changes color under pressure. When pressure is applied to the BAW pressure sensor, the pressure is transmitted to the sensing layer. Under the influence of pressure, the sensing layer changes color. By observing the color change of the sensing layer, the pressure change can be intuitively determined. This color change intuitively reflects the pressure level, enabling qualitative pressure analysis. The sensing layer is a key technical feature that enables qualitative pressure analysis.

[0049] Specifically, because the sensing layer is made of a material that changes color under pressure, it changes color under the influence of pressure. The observer can directly observe the color change of the sensing layer with the naked eye and qualitatively judge the pressure change, such as an increase or decrease in pressure. The basic structure of the BAW pressure sensor, including the substrate, bottom electrode, piezoelectric layer, and top electrode, is used to sense pressure and convert it into an electrical signal for output. This provides the basic platform for pressure sensing in the sensing layer. The sensing layer, on this basis, realizes the intuitive display function of pressure changes.

[0050] In some embodiments, the sensing layer 600 is made of a phthalimethylene malononitrile type compound material.

[0051] A phthalimethylene malononitrile-based compound material changes color when exposed to pressure. The sensing layer is located on the upper surface of the top electrode. When pressure is applied to the BAW pressure sensor, the pressure is transmitted to the sensing layer. Because the sensing layer is made of phthalimethylene malononitrile-based compound material, it changes color under pressure. By observing the color change of the sensing layer, pressure changes can be qualitatively determined. Different pressure levels will cause the sensing layer to display different colors. This color change can be observed by the naked eye, enabling intuitive qualitative analysis of pressure changes.

[0052] Specifically, the phthalimethylenemalononitrile compound material in the sensing layer senses pressure, causing its molecular structure to change, which in turn causes changes in the material's optical properties, manifesting macroscopically as a color change. Observers can directly observe the color change of the sensing layer with the naked eye, such as a shift from light to dark. For example, in a state of no pressure or low pressure, the sensing layer may appear light or colorless. When pressure increases, the color of the sensing layer gradually deepens, such as to blue or purple, or changes from one color to another. This allows one to determine whether pressure has changed and the general trend of the change. The magnitude of the color change in the sensing layer corresponds to the amount of pressure; the greater the pressure, the more pronounced the color change may be.

[0053] In certain embodiments, the chemical formula of the o-phthalimethylene malononitrile-type compound is:

[0054] ;

[0055] in, and All of them can be nitrogen-containing aromatic rings such as carbazole, triphenylamine, diphenylamine, acridine, indole, or their derivatives.

[0056] In some embodiments, the horizontal area of the top electrode 400 and the bottom electrode 200 are both smaller than the horizontal area of the substrate 100 .

[0057] The substrate is used as the supporting structure of the BAW pressure sensor, providing mechanical strength and stability for the entire device. The top electrode and the bottom electrode are arranged on the substrate, and the horizontal area of both are designed to be smaller than the horizontal area of the substrate. Therefore, when external pressure is applied to the upper surface of the sensor, the pressure can be transmitted to the piezoelectric layer more concentratedly. The piezoelectric layer deforms under the action of pressure, generating a piezoelectric effect, which in turn causes the frequency of the BAW resonator to change. The magnitude of the frequency change is proportional to the magnitude of the pressure, and the pressure value can be quantitatively analyzed by detecting the frequency change. The concentrated pressure on the piezoelectric layer makes the piezoelectric effect more obvious, which improves the sensitivity and response speed of the sensor to pressure. As a supporting component, the substrate ensures that the entire device does not bend or deform excessively when subjected to pressure, maintaining the stability of the structure.

[0058] As a preferred embodiment, the horizontal area of the substrate can be at least twice the horizontal area of the top electrode or bottom electrode to ensure a more significant pressure concentration effect. Furthermore, the top and bottom electrodes can be designed to be circular, rectangular, or other regular or irregular shapes. Regardless of the shape, their horizontal areas must be smaller than the horizontal area of the substrate.

[0059] In certain embodiments, reference is made to the accompanying Figure 1 The top electrode 400 and the bottom electrode 200 extend from the left and right sides of the piezoelectric layer 300 in opposite directions, respectively, and the downward projections of the top electrode 400 and the bottom electrode 200 completely cover the cavity 500 .

[0060] The top electrode and the bottom electrode can be designed to extend horizontally from two opposite sides of the piezoelectric layer, like the two ends of a bridge overlapping in the middle. This structure allows the electrode to not simply cover the top of the piezoelectric layer, but to extend from the side, ensuring that when the horizontal area of the electrode is smaller than the horizontal area of the substrate, it can still provide sufficient electrode coverage for the piezoelectric layer above the cavity. Furthermore, the downward projections of the top electrode and the bottom electrode completely cover the cavity, which means that when viewed from the vertical direction, the coverage of the electrode completely includes the area of the cavity without omission. As a possible embodiment, the top electrode and the bottom electrode can have the same width, and the extension length is precisely designed to ensure that the projection completely covers the cavity.

[0061] Specifically, when the BAW pressure sensor is working, pressure acts on the sensing layer and is transmitted to the piezoelectric layer through the top electrode. In order to ensure that the piezoelectric layer can effectively convert pressure into an electrical signal, the top electrode and the bottom electrode need to apply a uniform and sufficient electric field to the piezoelectric layer. If the electrode does not adequately cover the piezoelectric layer above the cavity, the piezoelectric effect will be weakened and the sensitivity of the sensor will be reduced. By extending the top electrode and the bottom electrode from the left and right sides of the piezoelectric layer respectively, and making the electrode projection completely cover the cavity, it can be ensured that the electrode is in full contact with the piezoelectric layer above the cavity, forming an effective electric field area. As a result, the deformation of the piezoelectric layer under pressure can be effectively converted into an electrical signal, thereby improving the performance of the sensor.

[0062] In certain embodiments, reference is made to the accompanying Figure 1 An inclination angle is set between the inner wall of the cavity 500 and the bottom surface of the cavity 500, and the inclination angle range is greater than or equal to 70° and less than 90°.

[0063] The technical solution of creating a tilt angle between the inner sidewall and the cavity floor (the tilt angle is the supplementary angle of the angle between the inner sidewall and the cavity floor) can be implemented in a variety of ways. For example, during the cavity-forming etching process, etching parameters such as etchant concentration, etching time, and etching temperature can be adjusted to control the shape of the cavity sidewall. Specifically, wet or dry etching techniques can be employed. In wet etching, controlling the anisotropy of the etchant can form sidewalls with a specific tilt angle. In dry etching, such as reactive ion etching, parameters such as process gas ratio, RF power, and bias voltage can be adjusted to precisely control the etching direction and rate, thereby achieving sidewalls with a specific tilt angle. As a preferred embodiment, a tilted-angle etching mask method can be employed. A mask pattern with tilted edges can be pre-designed. During the etching process, the tilted shape of the mask edge is transferred to the underlying material layer, thereby forming the cavity sidewalls with a specific tilt angle.

[0064] Specifically, setting the inclination angle is intended to solve the problem of incomplete release of the sacrificial layer that may be caused by the vertical cavity sidewalls in the preparation method. When the inner sidewalls of the cavity are vertical, the fluidity of the etching solution or the release liquid inside the cavity may be hindered, especially in a cavity structure with a large depth-to-width ratio. The vertical sidewalls are prone to form dead corners, resulting in the sacrificial layer material being unable to be completely contacted and removed by the etching solution. As a result, the residual sacrificial layer may affect the performance and reliability of the BAW pressure sensor. By setting the angle between the inner sidewall of the cavity and the bottom surface of the cavity to an inclination angle greater than or equal to 70° and less than 90°, the fluidity of the etching solution or the release liquid in the cavity can be improved. The inclined sidewalls reduce the resistance to the flow of the etching solution, making it easier for the etching solution to penetrate into every corner of the cavity and more fully contact the sacrificial layer material. This inclination design avoids the dead corner effect that may be caused by the vertical sidewalls, improves the efficiency and integrity of the sacrificial layer release, thereby reducing the risk of sacrificial layer residue and improving the performance and reliability of the BAW pressure sensor.

[0065] In some embodiments, the top electrode 400 and the bottom electrode 200 are both made of at least one material selected from the group consisting of gold, copper, silver, aluminum, tungsten, platinum, molybdenum, rhodium, iridium, and titanium.

[0066] In some embodiments, the piezoelectric layer 300 is made of at least one polycrystalline or single crystal piezoelectric material selected from the group consisting of AlN, ZnO, PTZ, and LN.

[0067] Reference Attachment Figure 2 The present invention provides a method for preparing the BAW pressure sensor in the above embodiment, comprising the following steps:

[0068] S1. After forming a groove on the substrate, a sacrificial layer is deposited into the groove;

[0069] S2. After sequentially forming a bottom electrode, a piezoelectric layer, and a top electrode on a substrate, a solution of a phthalimethylene malononitrile-type compound is added dropwise to the upper surface of the top electrode and a sensing layer is obtained by spin coating;

[0070] S3. Release the sacrificial layer to form a cavity between the substrate and the bottom electrode, thereby manufacturing a BAW pressure sensor.

[0071] Before executing step S1 , the substrate may be cleaned by an RCA cleaning process and then the grooves may be etched after drying.

[0072] In step S1, the groove can be formed by an etching process (e.g., a groove depth of 20 μm), such as dry etching or wet etching, to form a recessed region of a predetermined depth on the substrate surface. The sacrificial layer can be deposited using a variety of materials and methods, such as silicon dioxide or polysilicon, using chemical vapor deposition or physical vapor deposition. The sacrificial layer is used to subsequently form the cavity structure.

[0073] In step S2, the production of the bottom electrode, piezoelectric layer, and top electrode is a sequential thin film deposition and patterning process. Thin film deposition can be performed by sputtering, evaporation, or chemical vapor deposition, while patterning can be achieved through photolithography and etching processes to form an electrode layer and a piezoelectric layer with a specific pattern. After the top electrode is completed, a solution containing a phthalimethylene malononitrile-type compound is added dropwise to the upper surface of the top electrode, and a sensing layer is prepared by a spin coating process. The spin coating process controls the rotation speed and time so that the solution is evenly spread on the surface of the top electrode, and the solvent is evaporated, ultimately forming a uniform thin film sensing layer.

[0074] In step S3 , the sacrificial layer is released to form a cavity between the substrate and the bottom electrode, which is usually achieved by removing the sacrificial layer material through methods such as wet etching or dry etching.

[0075] Specifically, this embodiment first makes a groove on the substrate and deposits a sacrificial layer, laying the foundation for the subsequent formation of the cavity. The presence of the sacrificial layer allows thin film deposition and patterning to be performed on it in subsequent steps, and ultimately, by removing the sacrificial layer, a cavity can be formed between the substrate and the bottom electrode. Then, the bottom electrode, piezoelectric layer, and top electrode are fabricated on the substrate. These steps typically use micro-nano processing technologies such as thin film deposition and photolithography to ensure the quality and graphic accuracy of each layer of film. The core step is the preparation of the sensing layer, in which the o-phthalimethylene malononitrile-type compound material is evenly coated on the upper surface of the top electrode by spin coating. The spin coating method can accurately control the thickness and uniformity of the thin film to ensure the performance of the sensing layer. Finally, by releasing the sacrificial layer, the cavity structure of the BAW pressure sensor is formed, completing the preparation of the device.

[0076] In certain embodiments, the o-phthalimethylene malononitrile-type compound is obtained by the following steps:

[0077] A1. A phthalate compound (eg, bis(4'-(diphenylamino)-[1,1'-diphenyl])methanone or bis(4-(9H-carbazolyl)-phenyl)methanone) is dissolved in pyridine and malononitrile is added to obtain a first mixture;

[0078] A2. The first mixture is heated to reflux and stirred for a specified period of time until the first mixture is completely reacted and heating is stopped;

[0079] A3. To the completely reacted first mixture was added a saturated NH4Cl solution to neutralize the reaction system to obtain a second mixture;

[0080] A4. The second mixture was extracted three times with dichloromethane to combine the organic phases to obtain a first solution;

[0081] A5. By adding anhydrous Na2SO4 to the first solution to adsorb water in the first solution, to obtain a third mixture;

[0082] A6. The third mixture was filtered to remove Na2SO4 to obtain a first filtrate;

[0083] A7. The first filtrate was dried using a rotary evaporator to obtain a first crude product;

[0084] A8. The first crude product is dissolved in a mixed solvent of dichloromethane and petroleum ether, and the mixture is heated to dissolve and then slowly cooled to precipitate crystals. The crystals are phthalimethylene malononitrile-type compounds.

[0085] In this embodiment, for example, reactant A (chemical formula: ) can be obtained through chemical reaction to obtain product B (chemical structure: ) and product C (chemical structure: ). Wherein, product B and product C are both phthalate compounds.

[0086] It should be noted that the reactant A is an element, specifically one of F, Cl, Br or I.

[0087] Finally, product B and product C can be reacted to produce a phthalimethylene malononitrile compound (the chemical structure of this embodiment is: ).

[0088] It should be noted that the product B and the o-phthalimethylene malononitrile type compound and All of them can be nitrogen-containing aromatic rings such as carbazole, triphenylamine, diphenylamine, acridine, indole, or their derivatives.

[0089] Preferably, the phthalate compound is bis(4'-(diphenylamino)-[1,1'-diphenyl])methanone or bis(4-(9H-carbazolyl)-phenyl)methanone as an example, which will be described in detail below:

[0090] In step A1, a phthalone compound and malononitrile react in a pyridine solvent.

[0091] In step A2, heating under reflux and continuous stirring can promote a more complete chemical reaction of the phthalone compound to generate the target product, a phthalimethylene malononitrile-type compound; the reaction temperature is generally controlled at 120°C-150°C, and the reaction time is generally 36-48 hours.

[0092] In step A3, the addition of saturated ammonium chloride solution is used to neutralize the reaction system, the purpose of which is to terminate the reaction and to facilitate the preliminary separation of the reaction product.

[0093] In step A4, dichloromethane is used for extraction, which can transfer the target product from the aqueous phase to the organic phase, thereby achieving separation and purification of the product.

[0094] In step A5, by adding anhydrous sodium sulfate, the residual water in the organic phase can be effectively adsorbed to achieve the purpose of drying the organic solution.

[0095] In step A6, the suction filtration operation is used to remove the solid desiccant sodium sulfate to obtain a dry organic solution.

[0096] In step A7, the organic solvent is removed by a rotary evaporator, and the product can be concentrated to obtain a first crude product.

[0097] In step A8, by dissolving the first crude product in a mixed solvent of dichloromethane and petroleum ether, heating to dissolve and then slowly cooling, crystals can be precipitated. The recrystallization process can effectively purify the crude product to ultimately obtain high-purity phthalimethylene malononitrile-type compound crystals.

[0098] Specifically, the present embodiment provides a specific preparation method. The method realizes the preparation of o-phthalimethylene malononitrile type compound through a series of chemical synthesis and purification steps. First, by dissolving a specific o-phthalic ketone compound in pyridine and adding malononitrile, the necessary reactants and solvent environment are provided for the reaction. Subsequently, heating to reflux and stirring promote the progress of the chemical reaction, ensuring the generation of the target product. After the reaction is completed, the reaction product is separated and purified by steps such as neutralization, extraction, drying, filtering, rotary evaporation and recrystallization, and finally a high-purity o-phthalimethylene malononitrile type compound is obtained. Thus, the present embodiment ensures the availability and quality controllability of the sensing layer material, provides a material basis for the preparation of the sensing layer of the BAW pressure sensor, and thus solves the problem of the lack of qualitative analysis of pressure in the BAW pressure sensor in the background technology, so that the sensing layer prepared using the compound can effectively indicate pressure changes by color changes.

[0099] In some specific embodiments, the specific steps for preparing the o-phthalimethylene malononitrile compound may be: first, dissolving 1 gram of bis(4'-(diphenylamino)-[1,1'-diphenyl]-ketone in 20 milliliters of pyridine and adding 2 grams of malononitrile to obtain a first mixture; then, heating the first mixture to reflux temperature and continuously stirring for 12 hours to ensure that the reaction is fully carried out; after the reaction is completed, adding an appropriate amount of saturated ammonium chloride solution to the reaction system to neutralize the reaction system; then, using 50 milliliters of dichloromethane to extract the mixture three times, and combining the organic phases; then, adding sufficient anhydrous sodium sulfate to the organic phase for drying; then removing the sodium sulfate by suction filtration to obtain a filtrate; removing the solvent in the filtrate using a rotary evaporator to obtain a crude product; finally, dissolving the crude product in a small amount of a mixed solvent of dichloromethane and petroleum ether, heating to dissolve, and then slowly cooling, and the precipitated crystals are the target product o-phthalimethylene malononitrile compound. Through the above series of steps, high-purity o-phthalimethylene malononitrile-type compounds can be effectively prepared, providing key materials for preparing BAW pressure sensors with sensing layers.

[0100] In certain embodiments, bis(4'-(diphenylamino)-[1,1'-diphenyl]yl)methanone is obtained by the following steps:

[0101] B1. dissolving di(4-bromophenyl)methanone in oxygen-free THF / H2O and adding Pd[(Ph)3P]4, Na2CO3 and 4-triphenylamine boronic acid to obtain a fourth mixture;

[0102] B2. The fourth mixture is heated to reflux and stirred for a specified period of time until the fourth mixture is completely reacted and heating is stopped;

[0103] B3. To the completely reacted fourth mixture was added a saturated NH4Cl solution to neutralize the reaction system to obtain a fifth mixture;

[0104] B4. The fifth mixture was extracted three times with dichloromethane to combine the organic phases to obtain a second solution;

[0105] B5. By adding anhydrous Na2SO4 to the second solution to adsorb water from the second solution, to obtain a sixth mixture;

[0106] B6. The sixth mixture was filtered to remove Na2SO4 to obtain a second filtrate;

[0107] B7. The second filtrate was dried using a rotary evaporator to obtain a second crude product;

[0108] B8. The second crude product was separated by column chromatography to obtain bis(4'-(diphenylamino)-[1,1'-diphenyl]-1)methanone.

[0109] In step B1, di(4-bromophenyl)ketone (chemical structural formula: ) as the starting material was dissolved in a mixed solvent of oxygen-free tetrahydrofuran and water (i.e., THF / H2O). Subsequently, the catalyst Pd[(Ph)3P]4, sodium carbonate, and 4-triphenylamine boronic acid (chemical formula: ), thereby forming a fourth mixture.

[0110] In step B2, the fourth mixture is heated to reflux and stirred to promote the reaction until the reaction is complete (the chemical structure of the product obtained by the reaction is: The reaction temperature is generally controlled at 75°C-100°C, and the reaction time generally lasts for 8-24 hours.

[0111] In step B3, a saturated ammonium chloride solution is added to the reaction mixture to neutralize the reaction system.

[0112] In step B4, the reaction mixture is extracted with dichloromethane to transfer the organic product to the organic phase. The extraction operation is repeated three times to improve the product extraction efficiency. The combined organic phases constitute the second solution.

[0113] In step B5, anhydrous sodium sulfate is added to the second solution to absorb residual water in the solution.

[0114] In step B6, solid sodium sulfate is removed by suction filtration to obtain a second filtrate.

[0115] In step B7, the second filtrate is dried by rotary evaporation on a rotary evaporator to remove the solvent and obtain a second crude product.

[0116] In step B8, the second crude product is purified by column chromatography to obtain the target product, di(4'-(diphenylamino)-[1,1'-diphenyl]-1,1'-diphenyl)methanone (the chemical structure of this embodiment is: ).

[0117] Specifically, this embodiment is the step of preparing the raw material di(4'-(diphenylamino)-[1,1'-diphenyl])methanone in the above embodiment. Through the Suzuki coupling reaction of steps B1-B2, di(4-bromophenyl)methanone and 4-triphenylamine boric acid undergo a coupling reaction under the action of a catalyst and a base to construct the core structure of di(4'-(diphenylamino)-[1,1'-diphenyl]methanone. Subsequent steps B3-B8 are conventional operations for separating and purifying the reaction products, including neutralization, extraction, drying, filtration, concentration and chromatographic separation, to ultimately obtain a high-purity target product. This embodiment makes the raw material preparation method for preparing o-phthalimethylene malononitrile-type compounds more complete, ensuring the smooth preparation of a BAW pressure sensor with a pressure qualitative analysis function.

[0118] In some specific embodiments, 10 grams of di(4-bromophenyl)ketone is dissolved in a mixed solvent of 200 milliliters of oxygen-free tetrahydrofuran and 50 milliliters of water. Subsequently, 0.5 grams of Pd[(Ph)3P]4, 5 grams of sodium carbonate, and 8 grams of 4-triphenylamine boric acid are added to form a fourth mixture. The fourth mixture is stirred and reacted at reflux temperature for 12 hours until the reaction is complete. After the reaction is completed, 100 milliliters of saturated ammonium chloride solution is added for neutralization. The mixture is extracted three times with 200 milliliters of dichloromethane, and the organic phases are combined to obtain a second solution. 15 grams of anhydrous sodium sulfate is added to the second solution for drying. After filtering to remove the sodium sulfate, the filtrate is concentrated by rotary evaporator to obtain a crude product. The crude product is separated and purified by column chromatography to obtain pure di(4'-(diphenylamino)-[1,1'-diphenyl]-ketone. Through the above steps, di(4'-(diphenylamino)-[1,1'-diphenyl])methanone was effectively prepared, laying the foundation for the subsequent synthesis of o-phthalimethylene malononitrile-type compounds.

[0119] In certain embodiments, bis(4-(9H-carbazolyl)-phenyl)methanone is obtained by the following steps:

[0120] C1. Dissolving di(4-bromophenyl)methanone in anhydrous oxygen-free toluene and adding Pd[(t-Bu)3P]4, Na2CO3 and carbazole to obtain a seventh mixture;

[0121] C2. The seventh mixture is heated to reflux and stirred for a specified period of time until the seventh mixture is completely reacted and heating is stopped;

[0122] C3. To the complete reaction mixture was added a saturated NH4Cl solution to neutralize the reaction system to obtain an eighth mixture;

[0123] C4. The eighth mixture was extracted three times using chloroform to combine the organic phases to obtain a third solution;

[0124] C5. By adding anhydrous Na2SO4 to the third solution to adsorb water in the third solution, to obtain a ninth mixture;

[0125] C6. The ninth mixture was filtered to remove Na2SO4 to obtain a third filtrate;

[0126] C7. The third filtrate was dried using a rotary evaporator to obtain a third crude product;

[0127] C8. The third crude product was separated by column chromatography to obtain di(4-(9H-carbazolyl)-phenyl)methanone.

[0128] In step C1, di(4-bromophenyl)methanone is dissolved in anhydrous and oxygen-free toluene, followed by the addition of palladium catalyst Pd[(t-Bu)3P]4, sodium carbonate Na2CO3 and carbazole (chemical formula: ), thereby forming a seventh mixture, anhydrous and oxygen-free environment is crucial for preventing side reactions and ensuring the efficiency of the Suzuki coupling reaction;

[0129] In step C2, the seventh mixture is heated to reflux and stirred for a specific time to promote the reaction to proceed fully (the chemical structure of the product obtained by the reaction is: ), reflux provides the energy required for the reaction, stirring ensures that the reactants are fully mixed and the temperature is uniform, and the completion of the reaction is determined by monitoring methods such as thin layer chromatography or gas chromatography-mass spectrometry; the reaction temperature is generally controlled at 100°C-130°C, and the reaction time generally lasts 24-48 hours.

[0130] In step C3, after the reaction is completed, a saturated ammonium chloride solution NH4Cl is added to terminate the reaction and neutralize the reaction system;

[0131] In step C4, the eighth mixture is extracted with chloroform, and the organic phases are combined through three extractions to maximize the extraction of the organic product;

[0132] In step C5, anhydrous sodium sulfate Na2SO4 is added to the third solution to absorb moisture from the solution and ensure that the organic solution is dry;

[0133] In step C6, the solid sodium sulfate is removed by filtering the ninth mixture;

[0134] In step C7, the third filtrate is concentrated by a rotary evaporator to remove the chloroform solvent to obtain a third crude product;

[0135] In step C8, the third crude product is purified by column chromatography separation technology to finally obtain high-purity di(4-(9H-carbazolyl)-phenyl)methanone (the chemical structure of this embodiment is: ).

[0136] Specifically, this example describes the steps for preparing the raw material di(4-(9H-carbazolyl)-phenyl)methanone in the above example. The preparation process begins with a Suzuki coupling reaction between di(4-bromophenyl)methanone and carbazole. The reaction is carried out in an anhydrous, oxygen-free toluene solvent under reflux conditions in the presence of a palladium catalyst, Pd[(t-Bu)3P]4, and Na2CO3. The Suzuki coupling reaction forms a carbon-carbon bond, connecting the carbazole group to di(4-bromophenyl)methanone, thereby constructing the target molecular structure. After completion of the reaction, the mixture is quenched and neutralized with a saturated NH4Cl solution. Subsequently, the organic product is extracted with chloroform, dried over anhydrous Na2SO4, and filtered to remove the desiccant. The solvent is removed by rotary evaporation to obtain a crude product. Finally, the crude product is purified by column chromatography to obtain high-purity di(4-(9H-carbazolyl)-phenyl)methanone. Each step is crucial to the successful synthesis and purification of the target compound, ensuring a reliable supply of key intermediates required for the subsequent synthesis of pressure-sensitive materials.

[0137] In some specific embodiments, in step C1, 10 mmoles of di(4-bromophenyl)methanone are dissolved in 50 ml of anhydrous, oxygen-free toluene. Subsequently, 0.5 mmoles of Pd[(t-Bu)3P]4, 20 mmoles of Na2CO3, and 20 mmoles of carbazole are added. The mixture is heated to reflux and stirred for 24 hours under a nitrogen atmosphere. After cooling to room temperature, 50 ml of a saturated NH4Cl solution is added. The mixture is extracted three times with 50 ml of chloroform. The combined organic phases are dried over anhydrous Na2SO4, filtered, and concentrated by rotary evaporation. The crude product is purified by column chromatography to obtain pure di(4-(9H-carbazolyl)-phenyl)methanone.

[0138] By using the Suzuki coupling reaction, efficient carbon-carbon bond formation was achieved, which is essential for constructing the complex molecular structure of bis(4-(9H-carbazolyl)-phenyl)methanone. The use of anhydrous and oxygen-free conditions, as well as specific catalysts and bases, ensured high reaction efficiency and selectivity, thereby reducing the production of by-products. Subsequent purification steps, including extraction, drying, and column chromatography, are all standard techniques that can effectively remove impurities and obtain high-purity products. High purity is crucial for the subsequent synthesis of pressure-sensitive materials and the performance of BAW pressure sensors. The detailed steps make the preparation method clear and reproducible, solving the previously identified deficiency of the lack of a method to prepare this key intermediate.

[0139] In this document, relational terms such as first and second, etc. are used merely to distinguish one entity or operation from another entity or operation, but do not necessarily require or imply any actual relationship or order between these entities or operations.

[0140] Descriptions with reference to the terms "one embodiment," "certain embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" mean that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, illustrative uses of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0141] The foregoing description is merely an embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A BAW pressure sensor, comprising a substrate (100), a bottom electrode (200), a piezoelectric layer (300), and a top electrode (400) stacked in sequence, wherein a cavity (500) is provided between the substrate (100) and the bottom electrode (200), and characterized in that: The upper surface of the top electrode (400) is covered with a sensing layer (600), the sensing layer (600) being capable of changing color under pressure, and the sensing layer (600) being used to generate a color change signal for performing a qualitative analysis of the pressure change according to the pressure change; the sensing layer (600) is made of a phthalimethylene malononitrile type compound material; The chemical structural formula of the o-phthalimethylene malononitrile type compound is: ； in, and All of them are nitrogen-containing aromatic rings or their derivatives.

2. The BAW pressure sensor according to claim 1, characterized in that The horizontal areas of the top electrode (400) and the bottom electrode (200) are both smaller than the horizontal area of the substrate (100).

3. The BAW pressure sensor according to claim 2, characterized in that The top electrode (400) and the bottom electrode (200) extend in opposite directions from the left and right sides of the piezoelectric layer (300), respectively, and downward projections of the top electrode (400) and the bottom electrode (200) completely cover the cavity (500).

4. The BAW pressure sensor according to claim 1, wherein: An inclination angle is provided between the inner side wall of the cavity (500) and the bottom surface of the cavity (500), and the inclination angle ranges from greater than or equal to 70° to less than 90°.

5. The BAW pressure sensor according to claim 1, characterized in that The top electrode (400) and the bottom electrode (200) are both made of at least one material selected from the group consisting of gold, copper, silver, aluminum, tungsten, platinum, molybdenum, rhodium, iridium, and titanium.

6. The BAW pressure sensor according to claim 1, characterized in that The piezoelectric layer (300) is made of at least one polycrystalline or single crystal piezoelectric material selected from the group consisting of AlN, ZnO, PTZ, and LN.

7. A method for preparing a BAW pressure sensor according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. After forming a groove on the substrate, a sacrificial layer is deposited into the groove; S2. After sequentially forming the bottom electrode, the piezoelectric layer, and the top electrode on the substrate, a solution of a phthalimethylene malononitrile-type compound is added dropwise to the upper surface of the top electrode and the sensing layer is obtained by spin coating; S3. Release the sacrificial layer to form a cavity between the substrate and the bottom electrode, thereby manufacturing the BAW pressure sensor.

8. The preparation method according to claim 7, characterized in that The o-phthalimethylene malononitrile type compound is obtained by the following steps: A1. The phthalate compound is dissolved in pyridine and malononitrile is added to obtain a first mixture; A2. heating the first mixture to reflux and continuing stirring for a specified period of time until the first mixture is completely reacted and then stopping heating; A3. To the completely reacted first mixture was added a saturated NH4Cl solution to neutralize the reaction system to obtain a second mixture; A4. The second mixture was extracted three times with dichloromethane to combine the organic phases to obtain a first solution; A5. By adding anhydrous Na2SO4 to the first solution to adsorb water in the first solution, to obtain a third mixture; A6. The third mixture is filtered to remove Na2SO4 to obtain a first filtrate; A7. The first filtrate was dried using a rotary evaporator to obtain a first crude product; A8. The first crude product is dissolved in a mixed solvent of dichloromethane and petroleum ether, and crystals are precipitated by first heating and dissolving the mixture and then slowly cooling the mixture. The crystals are the o-phthalimethylene malononitrile-type compound.

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