Multi-mode temperature and pressure ultrasonic sensor

Abstract

The utility model provides a multi-mode temperature and pressure ultrasonic sensor, and relates to the technical field of sensors, the multi-mode temperature and pressure ultrasonic sensor comprises a substrate, the substrate is provided with a cavity, an elastic lamination layer and a piezoelectric lamination layer are sequentially laminated at the position, covering the cavity, of the substrate, the elastic lamination layer is provided with a PN junction region, a piezoresistive sensor is formed in the PN junction region, and the piezoelectric lamination layer is provided with a piezoelectric layer. And an ultrasonic sensor and a temperature sensor are also formed outside the PN junction region. An ultrasonic sensor, a temperature sensor and a piezoresistive sensor are integrated into a whole through a micro-nano machining technology, meanwhile, the functions of measuring temperature and pressure and transmitting and receiving ultrasonic waves are achieved, two kinds of signals of current environment temperature and pressure can be detected without interference at the same time, and transmitting and receiving of the ultrasonic waves are achieved; the temperature and the pressure of the working medium of the ultrasonic sensor are accurately measured, and the precision of the ultrasonic flowmeter is improved.

Description

Technical Field

[0001] The present application relates to the field of sensor technology, and in particular to a multi-mode temperature and pressure ultrasonic sensor. Background Art

[0002] When the ultrasonic flow meter is measuring, the temperature of the working medium will affect the sound velocity, and thus affect the calculation of the flow measurement results. Therefore, a traditional ultrasonic flow meter is additionally equipped with a temperature sensor to monitor the temperature of the current working environment in real time. In addition, the pressure of the working medium of the ultrasonic flow meter will change the resonant frequency of the ultrasonic sensor, thereby affecting the frequency calibration of the ultrasonic sensor. Therefore, an additional pressure sensor is also configured to monitor the pressure of the current working environment in real time.

[0003] Due to some hardware installation problems, the temperature sensor and the ultrasonic sensor cannot be placed in the same position. Therefore, the temperature sensor cannot accurately monitor the temperature of the working medium in which the ultrasonic wave propagates, which leads to measurement errors. The pressure sensor cannot accurately measure the pressure exerted on the ultrasonic sensor, which will cause inaccurate frequency calibration results of the ultrasonic sensor, thus affecting the working efficiency of the ultrasonic sensor. Utility Model Content

[0004] The purpose of the embodiments of the present application is to provide a multi-mode temperature and pressure ultrasonic sensor that can integrate a temperature sensor, a piezoresistive sensor and an ultrasonic sensor to accurately monitor the temperature and pressure of the working medium of the ultrasonic sensor.

[0005] According to one aspect of an embodiment of the present application, a multi-mode temperature-pressure ultrasonic sensor is provided, comprising: a substrate having a cavity, an elastic stack and a piezoelectric stack stacked in sequence on the substrate covering the cavity, the elastic stack having a PN junction region, a piezoresistive sensor being formed in the PN junction region, and an ultrasonic sensor and a temperature sensor being formed outside the PN junction region.

[0006] Optionally, a projection of the PN junction region is located within the cavity, a layered structure above the cavity forms the ultrasonic sensor, and the temperature sensor is located outside the cavity.

[0007] Optionally, the area of ​​the piezoelectric stack occupies 70% to 80% of the area of ​​the cavity.

[0008] Optionally, the piezoresistive sensor is located 15 μm to 20 μm away from the edge of the substrate.

[0009] Optionally, it further includes a piezoresistive sensor pin, an ultrasonic sensor pin and a temperature sensor pin, the piezoresistive sensor pin is connected to the piezoresistive sensor, the ultrasonic sensor pin is connected to the ultrasonic sensor, and the temperature sensor pin is connected to the temperature sensor.

[0010] Optionally, the elastic stack includes a buried oxide layer, an elastic layer and a barrier layer stacked in sequence.

[0011] Optionally, the piezoelectric stack includes a seed layer, a bottom electrode, a dielectric layer and a top electrode sequentially stacked on the barrier layer.

[0012] Optionally, the thickness of the bottom electrode and the top electrode are both less than 200 nm; the material of the seed layer and the dielectric layer includes scandium-doped aluminum oxide, and the material of the bottom electrode and the top electrode includes molybdenum.

[0013] Optionally, the piezoresistive sensor is formed by doping silicon into the PN junction.

[0014] Optionally, the temperature sensor comprises a gold trace.

[0015] The multi-mode temperature and pressure ultrasonic sensor provided in the embodiment of the present application integrates an ultrasonic sensor, a temperature sensor and a piezoresistive sensor into one through micro-nano processing technology; the ultrasonic sensor is located in the middle, and the piezoresistive sensors are arranged around the ultrasonic sensor, and the two share a diaphragm; the multi-mode temperature and pressure ultrasonic sensor is integrated into a sensor with the functions of measuring temperature and pressure and receiving and transmitting ultrasonic waves, and can simultaneously and without interference detect the current ambient temperature and pressure signals, and can realize the reception and transmission of ultrasonic waves; it can realize the accurate measurement of the temperature and pressure of the working medium of the ultrasonic sensor, greatly improving the accuracy of the ultrasonic flowmeter. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0017] Figure 1 This is one of the structural schematic diagrams of the multi-mode temperature and pressure ultrasonic sensor provided in this embodiment;

[0018] Figure 2 This is the second structural schematic diagram of the multi-mode temperature and pressure ultrasonic sensor provided in this embodiment;

[0019] Figure 3 to Figure 17 It is a process diagram of the preparation method of the multi-mode temperature and pressure ultrasonic sensor provided in this embodiment.

[0020] Icon: 1-temperature sensor; 1a-third metal layer; 2-piezoresistive sensor; 3-ultrasonic sensor; 4-temperature sensor pin; 5-piezoresistive sensor pin; 6-ultrasonic sensor pin; 10-substrate; 10a-cavity; 10b-protective layer; 10A-elastic stack; 11-buried oxide layer; 12-elastic layer; 12a-PN junction region; 13-barrier layer; 14-seed layer; 3a-bottom electrode; 15-dielectric layer; 3b-top electrode; 16-wire layer; 100-first photoresist layer; 101-second photoresist layer; 102-hard mask; 103-third photoresist layer. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application.

[0022] In the description of this application, it should be noted that the terms "inside", "outside", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the application is usually placed when in use, which is only for the convenience of describing this application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0023] It should also be noted that, unless otherwise clearly specified and limited, the terms "disposed" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0024] Please refer to Figure 1 , Figure 2 As shown, an embodiment of the present application provides a multi-mode temperature-pressure ultrasonic sensor, including a base layer, the base layer having a PN junction region 12a, a piezoresistive sensor 2 formed in the PN junction region 12a, and an ultrasonic sensor 3 and a temperature sensor 1 formed outside the PN junction region 12a.

[0025] The base layer includes a substrate 10, a buried oxide layer 11, an elastic layer 12 and a barrier layer 13 stacked in sequence. The buried oxide layer 11, the elastic layer 12 and the barrier layer 13 form an elastic stack 10A. Ions are implanted from the barrier layer 13 to the elastic layer 12 by ion implantation to form a PN junction region 12a in the elastic layer 12 to constitute a PN junction.

[0026] A piezoresistive sensor 2 is formed in the PN junction region 12a, and an ultrasonic sensor 3 and a temperature sensor 1 are also formed outside the PN junction region 12a, so as to integrate the piezoresistive sensor 2, the ultrasonic sensor 3 and the temperature sensor 1 into one. The multi-mode temperature and pressure ultrasonic sensor of the present application has the temperature measurement function of the traditional temperature sensor 1, the pressure measurement function of the traditional piezoresistive sensor 2, and the ultrasonic sensor 3's ultrasonic transmission and reception function. The three sensors are integrated into one sensor through micro-nano processing technology and used in the field of flow metering, which can accurately monitor the temperature and pressure of the working medium of the ultrasonic sensor 3; it not only reduces the number of sensors, but also makes the measurement of temperature and pressure more accurate and effective.

[0027] The base layer also has a cavity 10a, the projection of the PN junction region 12a is located in the cavity 10a, and a piezoelectric stack is stacked on the base layer, the piezoelectric stack includes a seed layer 14, a bottom electrode 3a, a dielectric layer 15 and a top electrode 3b; all the hierarchical structures above the cavity 10a form an ultrasonic sensor 3, and all the hierarchical structures above the cavity 10a are equivalent to a diaphragm to propagate vibration to the substrate 10 to generate an ultrasonic sensing function. The ultrasonic sensor 3 is located above the cavity 10a, and the temperature sensor 1 is located outside the cavity 10a.

[0028] The cavity 10a is formed in the substrate 10, and the projection of the PN junction region 12a is located in the cavity 10a; in addition, the piezoelectric stack occupies most of the area of ​​the cavity 10a, approximately between 70% and 80%; in a preferred embodiment, the ultrasonic sensor 3 is located at the center of the cavity 10a.

[0029] The temperature sensors 1 are located on both sides outside the cavity 10 a . Generally, the piezoresistive sensors 2 are located 15 μm to 20 μm away from the edge of the base layer (substrate 10 ).

[0030] The multi-mode temperature and pressure ultrasonic sensor of the present application can be applied to the field of liquid or gas flow, and the steps of use are as follows:

[0031] a. Connect the excitation signal to the temperature sensor pin 4 to excite the temperature sensor 1. You can choose to excite either one or both.

[0032] b. Connect the excitation signal to the piezoresistive sensor pin 5 to excite all the piezoresistive sensors 2;

[0033] c. Connect the excitation signal to the ultrasonic sensor pin 6 to excite the ultrasonic sensor 3;

[0034] d. The excitation, excitation order and excitation times of the three sensors can be freely combined;

[0035] e. In the above step d, the combination method may be to first excite the ultrasonic sensor 3 twice and then excite the temperature sensor 1 once, so as to calibrate the parameters affecting the temperature on the ultrasound;

[0036] f. In the above step d, the combination method may be to first stimulate the ultrasonic sensor 3 five times and then stimulate the piezoresistive sensor 2 twice, so as to calibrate the parameters of the influence of the fluid pressure on the ultrasound;

[0037] g. In the above step d, the combination method can be to first stimulate the temperature sensor 1 once, then stimulate the ultrasonic sensor 3 three times, and finally stimulate the piezoresistive sensor 2 once, so as to convert the working condition into the standard condition, so as to facilitate the unification of the measurement standard.

[0038] Figure 1 In the example, there are two temperature sensors 1, which are symmetrically distributed along the central axis of the ultrasonic sensor 3 and placed on both sides of the cavity 10a; there are four piezoresistive sensors 2, which are alternately and evenly arranged around the ultrasonic sensor 3 and placed in the area with maximum strain in the cavity 10a; the ultrasonic sensor 3 is placed in the exact center of the entire device.

[0039] There is no specific restriction on the shapes of the ultrasonic sensor 3, piezoelectric sensor, and temperature sensor 1 of the present application, and the present application can be implemented by being a circle, a regular polygon, etc.; there is no specific restriction on the number of ultrasonic sensors 3, piezoelectric sensors, and temperature sensors 1, and the present application can be implemented by at least being greater than or equal to one, and the greater the number, the more accurate the measurement effect; there is no specific restriction on the placement positions of the ultrasonic sensors 3, piezoelectric sensors, and temperature sensors 1, wherein the piezoresistive sensor 2 can be placed in the cavity 10a area to implement the present solution, and the measurement effect is best if it is evenly arranged in the area with the largest strain in the cavity 10a.

[0040] The multi-mode temperature-pressure ultrasonic sensor of the present application can be realized based on processes such as silicon on insulator (SOI) and buried cavity SOI (C-SOI).

[0041] Therefore, on the other hand, the embodiment of the present application also provides a method for preparing a multi-mode temperature and pressure ultrasonic sensor, comprising the following steps:

[0042] Step 200: forming a base layer.

[0043] For details, please see Figure 3 , step 200 - 1 : depositing a protection layer 10 b on the substrate 10 .

[0044] The substrate 10 is generally a bare silicon wafer, and the thickness of the bare silicon wafer is usually in the range of 400 μm to 725 μm. This range is selected to balance two considerations. Too thin silicon wafers are prone to breakage, especially during processing, while too thick silicon wafers will increase the difficulty of etching, resulting in reduced processing efficiency. Therefore, when selecting the thickness of the bare silicon wafer, it is necessary to consider the processing technology and the stability of the silicon wafer in order to obtain the best processing effect.

[0045] After obtaining the bare silicon wafer, a protective layer 10b with a thickness of about 0.5 μm is deposited on the bare silicon wafer by PECVD. It is generally a silicon dioxide film. The main purpose is to protect the front of the crystal surface when the crystal surface is flipped and the mark on the back of the crystal surface is etched. The protective layer 10b can protect the front of the crystal surface and reduce the wear on the front of the crystal surface. The role of the protective layer 10b is to provide a certain degree of protection to make the silicon wafer more stable in subsequent processes. At the same time, the protective layer 10b does not need to be too thick so as not to affect the subsequent processing steps. Therefore, choosing an appropriate thickness of the silicon dioxide film can protect the crystal surface without affecting the subsequent processing.

[0046] Step 200-1 After the protective layer 10b is deposited, Figure 4 As shown, the silicon wafer is turned over, and a first photoresist layer 100 is applied to the back of the substrate 10 and developed to engrave mark 0. Laser marking + BSA silicon etching are used to provide alignment for subsequent front SUSS (photolithography) exposure.

[0047] like Figure 5 , step 200 - 2 : etching the cavity 10 a in the protection layer 10 b so that the cavity 10 a extends to a portion of the substrate 10 .

[0048] After flipping the silicon wafer so that the front side faces upward, etching is performed to form a cavity 10a. The depth of the cavity 10a is usually controlled within the range of 15μm to 25μm, and this range is selected taking into account many factors. A cavity 10a that is too shallow may affect the up and down vibration of the diaphragm (multi-mode temperature and pressure ultrasonic sensor), while a cavity 10a that is too deep will increase the difficulty of etching.

[0049] The diameter of the cavity 10a will depend on the frequency of the device, and the size may vary from tens to hundreds of microns, and the specific size varies depending on the specific device. Therefore, during the preparation process, the depth and diameter of the cavity 10a need to be precisely controlled to ensure the performance and stability of the device.

[0050] like Figure 6 , step 200 - 3 : removing the protective layer 10 b , and forming an elastic stack 10A on the substrate 10 to cover the cavity 10 a .

[0051] The elastic stack 10A includes a buried oxide layer 11, an elastic layer 12, and a barrier layer 13 which are formed in sequence. The buried oxide layer 11, the elastic layer 12, and the barrier layer 13 are stacked to cover the cavity 10a.

[0052] The buried oxide layer 11 and the elastic layer 12 are generally formed by bonding. For example, silicon is used for bonding. During the bonding process, a certain thickness of top silicon (elastic layer 12, with a thickness of 1um to 10um) and silicon dioxide (buried oxide layer 11, with a thickness of 0.1um to 1um) need to be bonded. The role of silicon dioxide is to promote silicon-silicon bonding, while the top silicon is used as the elastic layer 12 of the device to adjust the frequency of the device.

[0053] The thickness of the top silicon needs to be moderate. Too thin will increase the process difficulty and easily cause cracks, while too thick will increase the stiffness of the diaphragm and affect the vibration performance. Therefore, it is very important to choose the appropriate top silicon thickness to ensure the stability and performance of the device. At the same time, the presence of silicon dioxide helps the formation of silicon-silicon bonding, improves the bonding quality, and facilitates subsequent processes.

[0054] Figure 7 In the embodiment, a buried oxide layer 11 and an elastic layer 12 are bonded on a substrate 10, and a barrier layer 13 is deposited on the elastic layer 12. The barrier layer 13 may also be silicon dioxide.

[0055] Considering that the top silicon (elastic layer 12) is thin and easily broken, it is of great significance to deposit a layer of silicon dioxide (barrier layer 13) by PECVD process. This layer of silicon dioxide (barrier layer 13) not only helps to prevent the top silicon (elastic layer 12) from breaking, but also serves as a part of the elastic stack 10A for controlling the frequency.

[0056] Most importantly, as a barrier layer 13, when etching the bottom metal (Mo, bottom electrode 3a), avoid over-etching onto the top silicon (elastic layer 12) to avoid device leakage and performance degradation.

[0057] The introduction of this step can significantly improve the yield of the device and ensure the reliability and stable performance of the device. It should be noted that when depositing this layer of silicon dioxide (barrier layer 13), excessive exposure to a long-term hot oxygen environment should be avoided to avoid affecting the performance of the device.

[0058] Step 201: forming a PN junction region 12a on a base layer, and forming a piezoresistive sensor 2 in each of the PN junction regions 12a.

[0059] Figure 8 As shown, step 201 - 1 : ion implanting a first metal into the elastic layer 12 from the barrier layer 13 to form a PN junction region 12 a in the elastic layer 12 , wherein the projection of the PN junction region 12 a along the stacking direction is located in the cavity 10 a .

[0060] The PN junction region 12a is constructed by forming a P-type region and an N-type region through ion implantation. Ion implantation and construction of a PN junction are the core of forming the piezoresistive sensor 2. In this process, ion implantation usually introduces a specific type of impurity into the semiconductor material through an ion implantation device, thereby changing its electrical properties. Constructing a PN junction involves forming a P-type (impurity-enriched) and N-type (impurity-doped) region in the semiconductor material, thereby forming a structure with positive and negative charge separation.

[0061] These steps are crucial for the piezoresistive sensor 2 because they can control the conductivity of the material and the distribution of electron-hole pairs, which in turn affects the resistance characteristics of the device. In the piezoresistive sensor 2, due to the effect of the external force or pressure, the concentration of electrons and holes in the PN junction region 12a will change, resulting in a change in resistance. Therefore, ion implantation and the construction of the PN junction directly affect the sensitivity and stability of the piezoresistive sensor 2.

[0062] Fig. 9 In step 201 - 2 , a second photoresist layer 101 is coated on the barrier layer 13 , and a doping groove is formed on the second photoresist layer 101 corresponding to the PN junction region 12 a.

[0063] Step 201-3: Continue to ion-implant more first metal into the PN junction region 12a through the doping groove, generally doping silicon, to form piezoresistive sensors 2 in the PN junction region 12a. Of course, the same metal as in step 201-1 can be selected for ion implantation to increase the amount of metal implanted; different metals can also be selected, depending on the needs.

[0064] Step 201 - 4 : removing the second photoresist layer 101 .

[0065] In order to improve the sensitivity of the piezoresistive sensor 2, the piezoresistive strip should be made in the maximum stress concentration area of ​​the sensitive diaphragm (multi-mode temperature and pressure ultrasonic sensor). By performing a stress simulation on the diaphragm of the piezoresistive sensor 2, it can be determined that the area with the maximum stress of the piezoresistive sensor 2 is 15μm to 20μm away from the edge of the sensitive diaphragm.

[0066] At the same time, the ultrasonic sensor 3 can be an ultrasonic micro piezoelectric transducer (PMUT). In order to achieve the largest possible amplitude of the ultrasonic sensor 3, its electrode area can only occupy 70% to 80% of the area of ​​the cavity 10a. Therefore, the edge of the diaphragm of the ultrasonic sensor 3 has just enough space to place the piezoresistive sensor 2.

[0067] Such design considerations fully utilize the space at the edge of the diaphragm of the ultrasonic sensor 3 and place the piezoresistive strips in the maximum stress concentration area of ​​the diaphragm of the piezoresistive sensor 2, thereby ensuring high-sensitivity detection of pressure changes. By combining the stress distribution of the piezoresistive sensor 2 film and the structural characteristics of the ultrasonic sensor 3, the design of the piezoresistive sensor 2 can be effectively optimized to improve its performance and stability.

[0068] Step 202: depositing a piezoelectric stack on the base layer and patterning the piezoelectric stack to form the ultrasonic sensor 3, so as to expose the PN junction region 12a. The piezoelectric stack includes a seed layer 14, a bottom electrode 3a, a dielectric layer 15 and a top electrode 3b.

[0069] Fig.10As shown, step 202 - 1 : depositing a seed layer 14 , a bottom electrode 3 a , a dielectric layer 15 and a top electrode 3 b in sequence on the barrier layer 13 .

[0070] Step 202 - 2 : patterning the top electrode 3 b , the dielectric layer 15 , the bottom electrode 3 a and the seed layer 14 in sequence to expose the PN junction region 12 a .

[0071] In the process of depositing the piezoelectric stack, 10% scandium-doped ALN (aluminum nitride) is selected as the seed layer 14 in order to optimize the deposition conditions of the electrode, and the electrode is made of Mo (molybdenum) material. Scandium-doped ALN material is easier to obtain directional crystal growth on Mo due to the small lattice mismatch (-1.0%) and similar thermal expansion coefficient. In addition, Mo has the advantages of low acoustic attenuation, low resistivity and sputtering temperature, so Mo is selected as the electrode. Among the scandium-doped ALN materials, selecting 20% ​​scandium-doped ALN can provide a higher piezoelectric response, so 20% scandium-doped ALN can also be selected as the dielectric layer 15.

[0072] The thickness of the seed layer 14 needs to be adjusted according to the frequency, generally in the range of 10nm to 1.5um, and the preferred thickness of scandium-doped ALN as the seed layer 14 is generally 0.8um to 1.5um. In the present application, the thickness of the seed layer 14 is significantly smaller than that of the dielectric layer 15.

[0073] The thickness of the bottom Mo as the bottom electrode 3a is generally not more than 200nm, and the thickness of the top Mo as the top electrode 3b is generally not more than 200nm. Such a design can ensure the stability and excellent performance of the piezoelectric stack while ensuring the piezoelectric response. By optimizing the deposition conditions and selecting suitable materials, the performance and stability of the piezoelectric stack can be improved to meet the needs of different application fields.

[0074] Fig.10 First pattern the top electrode 3b, then refer to Fig.11 Deposit silicon dioxide as a hard mask 102, pattern the dielectric layer 15, remove the hard mask 102; then press Fig.12 The bottom electrode 3a and the seed layer 14 are shown patterned.

[0075] The seed layer 14, the bottom electrode 3a, the dielectric layer 15 and the top electrode 3b form a piezoelectric stack, which is used to subsequently form the ultrasonic sensor 3. Therefore, the patterning of the piezoelectric stack material is crucial to achieving the maximum performance of the ultrasonic sensor 3. In order to fully utilize the performance of the piezoelectric stack material, the piezoelectric stack should occupy most of the area of ​​the cavity 10a, roughly between 70% and 80%, and preferably be centered in the center of the cavity 10a. Such a design can ensure that when an electric field is applied, the piezoelectric stack material can produce the maximum vibration effect, thereby achieving higher acoustic emission and reception performance of the ultrasonic sensor 3.

[0076] After patterning the piezoelectric stack, the PN junction region 12a is exposed.

[0077] like Fig.13 As shown, step 203: depositing a wire layer 16 on the piezoelectric stack, and opening holes at positions of the wire layer 16 corresponding to the P-type region, the N-type region and the piezoelectric stack to serve as wire reserved grooves.

[0078] Step 203 - 1 : Open a hole from the conductive line layer 16 to the PN junction region 12 a to penetrate the doping groove of the PN junction region 12 a to expose the piezoresistive sensor 2 .

[0079] Silicon dioxide is generally selected for deposition to form the wiring layer 16 .

[0080] Step 203 - 2 : Open holes from the wiring layer 16 to the bottom electrode 3 a and the top electrode 3 b to expose the opening areas of the bottom electrode 3 a and the top electrode 3 b.

[0081] Step 203-3: Sputter a second metal in the opening area and pattern it to lead out the wires of the piezoresistive sensor 2 and the ultrasonic sensor 3, as shown in FIG. Fig.14 shown.

[0082] Al Cu is used as the second metal, and Al Cu is sputtered and patterned in the opening area, in order to lead out the wires of the piezoresistive sensor 2 and the ultrasonic sensor 3 to form the piezoresistive sensor pin 5 and the ultrasonic sensor pin 6.

[0083] Step 204 : forming gold traces on the wire layer 16 to prepare the temperature sensor 1 .

[0084] like Fig.15 Step 204-1: Coat the third photoresist layer 103 on the wire layer 16 and pattern the third photoresist layer 103 to reserve positions for gold traces, so that the reserved positions for gold traces are located on both sides of the cavity 10a. The purpose of this step is to coat and develop the patterned gold traces.

[0085] Step 204 - 2 : depositing a third metal layer 1 a on the third photoresist layer 103 , and filling the reserved gold trace positions with the third metal layer 1 a .

[0086] Step 204 - 3 : Sputtering gold traces on the third metal layer 1 a .

[0087] The third metal layer 1a is Ti, and the gold trace is generally Au; when sputtering the gold trace, a layer of Ti can be deposited first in order to optimize the deposition conditions of Au, see Fig.16 .

[0088] like Fig.17 , step 204-4: remove the third photoresist layer 103, form the temperature sensor 1 at the location of the gold trace, and form the temperature sensor pin 4.

[0089] Temperature is an important parameter in many applications, and the gold trace has a simple structure and can be easily placed next to the cavity 10a. Therefore, by adding a few extra steps to the original process flow, the integration of temperature parameters can be easily achieved without changing the original process flow. This integration method is very convenient and efficient.

[0090] The gold trace is a resistance temperature sensor 1, and the temperature can be determined by measuring its resistance value. By placing the gold trace next to the cavity 10a, real-time monitoring of the temperature near the cavity 10a can be achieved.

[0091] At this point, all the hierarchical structures above the cavity 10a form the ultrasonic sensor 3. In the design of the ultrasonic sensor 3, adding the gold trace temperature sensor 1 can provide the device with more comprehensive performance monitoring and temperature compensation functions, thereby improving the stability and reliability of the ultrasonic sensor 3.

[0092] Therefore, by integrating the gold trace temperature sensor 1 into the design of the ultrasonic sensor 3, the temperature parameter monitoring function can be added to the equipment without changing the original process flow, thereby improving the overall performance and reliability; this integration method is simple and effective and is a very practical method.

[0093] Therefore, the preparation method of the multi-mode temperature and pressure ultrasonic sensor provided in the embodiment of the present application integrates the ultrasonic sensor 3, the temperature sensor 1 and the piezoresistive sensor 2 into one by micro-nano processing technology; the ultrasonic sensor 3 is located in the middle and above the cavity 10a, and the piezoresistive sensor 2 is arranged around the ultrasonic sensor 3, and the two share a diaphragm; wherein the ultrasonic sensor 3 is a piezoelectric stack that drives the elastic stack 10A on the cavity 10a to vibrate and generate ultrasound, so the membranes on the cavity 10a are all ultrasonic sensors 3. The multi-mode temperature and pressure ultrasonic sensor is integrated into a sensor that has the functions of measuring temperature and pressure and transmitting and receiving ultrasonic waves at the same time, and can simultaneously detect the current ambient temperature and pressure signals without interference, and can realize the transmission and reception of ultrasonic waves; it can realize the accurate measurement of the temperature and pressure of the working medium of the ultrasonic sensor 3, greatly improving the accuracy of the ultrasonic flowmeter.

[0094] The method for preparing the multi-mode temperature and pressure ultrasonic sensor has the same structure and beneficial effects as the multi-mode temperature and pressure ultrasonic sensor in the aforementioned embodiment. The structure and beneficial effects of the multi-mode temperature and pressure ultrasonic sensor have been described in detail in the aforementioned embodiment and will not be repeated here.

[0095] The above description is only an embodiment of the present application and is not intended to limit the protection scope of the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A multi-mode temperature and pressure ultrasonic sensor, characterized in that: The invention comprises a substrate having a cavity, an elastic stack and a piezoelectric stack are sequentially stacked on the substrate covering the cavity, the elastic stack has a PN junction region, a piezoresistive sensor is formed in the PN junction region, and an ultrasonic sensor and a temperature sensor are formed outside the PN junction region.

2. The multi-mode temperature and pressure ultrasonic sensor according to claim 1, characterized in that: The projection of the PN junction region is located in the cavity, the layered structure above the cavity forms the ultrasonic sensor, and the temperature sensor is located outside the cavity.

3. The multi-mode temperature and pressure ultrasonic sensor according to claim 1, characterized in that: The area of ​​the piezoelectric stack occupies 70% to 80% of the area of ​​the cavity.

4. The multi-mode temperature and pressure ultrasonic sensor according to claim 1, characterized in that: The piezoresistive sensor is located 15 μm to 20 μm away from the edge of the substrate.

5. The multi-mode temperature and pressure ultrasonic sensor according to any one of claims 1 to 4, characterized in that: It also includes a piezoresistive sensor pin, an ultrasonic sensor pin and a temperature sensor pin. The piezoresistive sensor pin is connected to the piezoresistive sensor, the ultrasonic sensor pin is connected to the ultrasonic sensor, and the temperature sensor pin is connected to the temperature sensor.

6. The multi-mode temperature and pressure ultrasonic sensor according to any one of claims 2 to 4, characterized in that: The elastic stack comprises an oxide-buried layer, an elastic layer and a barrier layer which are stacked in sequence.

7. The multi-mode temperature and pressure ultrasonic sensor according to claim 6, characterized in that: The piezoelectric stack includes a seed layer, a bottom electrode, a dielectric layer, and a top electrode sequentially stacked on the barrier layer.

8. The multi-mode temperature and pressure ultrasonic sensor according to claim 7, characterized in that: The thickness of the bottom electrode and the top electrode are both less than 200 nm; the material of the seed layer and the dielectric layer includes scandium-doped aluminum oxide, and the material of the bottom electrode and the top electrode includes molybdenum.

9. The multi-mode temperature and pressure ultrasonic sensor according to any one of claims 1 to 4, characterized in that: The piezoresistive sensor is formed by doping silicon into the PN junction region.

10. The multi-mode temperature and pressure ultrasonic sensor according to any one of claims 1 to 4, characterized in that: The temperature sensor includes a gold trace.

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