Micromachined ultrasonic transducer array based on dissimilatory electrode configuration
By using a micromechanical ultrasonic transducer array with heterogeneous electrode configuration, combined with upper and lower electrode and coplanar electrode modes, the problem of pMUT arrays having difficulty in achieving both high transmission and reception performance is solved, realizing high transmission and reception performance of the device and improving detection distance and resolution.
Patent Information
- Application Number
- CN202511187283.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-22
- Publication Date
- 2025-11-07
AI Technical Summary
Existing pMUT arrays struggle to simultaneously achieve high transmit and receive performance, as the dielectric constant and piezoelectric coefficient of piezoelectric materials limit the device's transmit and receive capabilities.
A micromechanical ultrasonic transducer array with heterogeneous electrode configuration is used. By combining upper and lower electrode modes and coplanar electrode modes, the patterning of the upper electrode layer is designed to achieve high transmission performance in the upper and lower electrode working mode and high reception performance in the coplanar electrode working mode.
This significantly improves the transmission and reception performance of the pMUT array, enabling it to achieve higher detection distances and resolutions in applications.
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Figure CN120900927A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application relates to a micro-mechanical ultrasonic transducer array based on a hetero-electrode configuration, and belongs to the technical field of micro-electro-mechanical system (MEMS) devices. BACKGROUND
[0002] With the rapid development of micro-electro-mechanical system (MEMS) technology, micro-mechanical ultrasonic transducers (MUT) are widely used in intelligent medical treatment, industrial non-destructive testing, non-contact human-computer interaction, acoustic sensing and communication, and the like, due to their advantages of flexible design, low cost, high integration, and the like. Among them, piezoelectric micro-mechanical ultrasonic transducers (pMUT) are gradually replacing the market position of traditional ultrasonic transducers, due to their advantages of high frequency response, high sensitivity, high linearity, and no bias voltage, and the like.
[0003] Transmitting and receiving performance are core indexes for measuring the advantages and disadvantages of pMUT. Among them, the transmitting performance reflects the ability of pMUT to convert an electrical signal into mechanical vibration and radiate an ultrasonic wave under the excitation of an alternating current signal. The piezoelectric material with a high piezoelectric coefficient can effectively improve the transmitting performance of pMUT, such as lead zirconate titanate (PZT), lead magnesium niobate-lead titanate (PMN-PT), and the like. The receiving performance reflects the detection ability of pMUT to an external ultrasonic wave echo signal, and this performance is significantly related to the dielectric properties of the piezoelectric material. A lower dielectric constant can effectively reduce the noise floor of the device and improve the impedance matching characteristics, thereby significantly improving the receiving sensitivity of pMUT. Typical piezoelectric materials that meet this requirement currently include aluminum nitride (AlN) and scandium-doped aluminum nitride (AlScN), and the like. Single-crystal lithium niobate (LN) material has a suitable piezoelectric coefficient, a lower dielectric constant and dielectric loss, so that the LN pMUT device simultaneously exhibits high receiving sensitivity, detection limit and transmitting sensitivity, and is expected to simultaneously improve the transmitting and receiving performance of the device.
[0004] In addition to the performance of the piezoelectric material, the transmitting or receiving performance of pMUT can also be effectively improved by optimizing the electrode configuration and driving mode, and the like. For example, the pMUT device using a coplanar electrode, i.e., a transverse electrode excitation, can effectively reduce the equivalent capacitance of the device, thereby improving the receiving sensitivity of the device, but this scheme will reduce the transmitting performance of pMUT, and affect the detection distance of the device. SUMMARY
[0005] In order to solve the problem that the pMUT array in the prior art is difficult to have high transmission and reception performance, the application provides a micro-mechanical ultrasonic transducer array based on a differentiated electrode configuration.
[0006] The application adopts the following technical scheme:
[0007] According to the first aspect of the application, a micro-mechanical ultrasonic transducer array based on a differentiated electrode configuration is provided, comprising a plurality of upper and lower electrode mode pMUTs and a plurality of coplanar electrode mode pMUTs.
[0008] The upper and lower electrode mode pMUTs and the coplanar electrode mode pMUTs each comprise a diaphragm and a back cavity arranged in layers.
[0009] The diaphragm comprises an upper electrode layer, a piezoelectric layer, a lower electrode layer and a structural layer arranged in order from top to bottom.
[0010] In the upper and lower electrode mode pMUT, the upper electrode layer is a geometric conformal electrode consistent with the cross-sectional shape of the back cavity.
[0011] In the coplanar electrode mode pMUT, the upper electrode layer is an interdigital electrode.
[0012] Optionally, the upper and lower electrode mode pMUT further comprises a via hole arranged through the piezoelectric layer.
[0013] Optionally, the upper and lower electrode mode pMUT and the coplanar electrode mode pMUT further comprise a support layer arranged on the side of the structural layer away from the piezoelectric layer.
[0014] The back cavity is a cavity opened on the support layer, and the cavity extends to the lower side end surface of the structural layer.
[0015] Optionally, in the upper and lower electrode mode pMUT, the size of the upper electrode is 20%-70% of the cross-sectional area of the back cavity.
[0016] Optionally, a plurality of the upper and lower electrode mode pMUTs form a transmission unit of the micro-mechanical ultrasonic transducer array for transmitting ultrasonic signals.
[0017] A plurality of the coplanar electrode mode pMUTs form a reception unit of the micro-mechanical ultrasonic transducer array for receiving ultrasonic signals.
[0018] Optionally, the piezoelectric layer is a single crystal material thin film.
[0019] Optionally, the thickness of the piezoelectric layer is 0.1-50 μm.
[0020] Optionally, the thickness of the structure layer is 0.1-100 μm.
[0021] Optionally, the thickness of the upper electrode layer is 0.01-2 μm; the thickness of the lower electrode layer is 0.01-2 μm.
[0022] Optionally, the depth of the back cavity is 5-50 μm.
[0023] The beneficial effects of the present application include:
[0024] The micro-mechanical ultrasonic transducer array based on the differentiated electrode configuration provided by the present application adopts two electrode configuration schemes of upper and lower electrodes and coplanar electrodes in structure, wherein the transmitting unit adopts the upper and lower electrode mode, which has a higher equivalent capacitance, can convert more electrical signals into mechanical vibration of the device, and promotes the emission of ultrasonic signals; and the receiving unit adopts the coplanar electrode mode, which has a smaller equivalent capacitance. Smaller capacitance usually means that the device has higher impedance, so that it has a higher voltage response to external ultrasonic signals, so that it can capture weak ultrasonic signals and improve the receiving sensitivity. Through the differentiated electrode configuration of the pMUT array, it is expected to significantly improve the transmitting and receiving performance of the pMUT array, so that the micro-mechanical ultrasonic transducer has the characteristics of high transmitting and receiving performance, so that it has higher detection distance and resolution in application, etc. BRIEF DESCRIPTION OF DRAWINGS
[0025] Figure 1 Fig. 1 is a structural schematic diagram of the micro-mechanical ultrasonic transducer array based on the differentiated electrode configuration of the present application;
[0026] Figure 2 Fig. 2 is a top view of the upper electrode of the micro-mechanical ultrasonic transducer array based on the differentiated electrode configuration of the present application in the coplanar electrode mode, wherein (a)-(c) are three different shapes of interdigital electrodes;
[0027] Figure 3 Fig. 3 is a top view of the upper electrode of the micro-mechanical ultrasonic transducer array based on the differentiated electrode configuration of the present application in the upper and lower electrode mode, wherein (a)-(c) are three different shapes of geometric conformal electrodes.
[0028] IDENTIFICATION OF DRAWINGS
[0029] 1, support layer; 2, back cavity; 3, structure layer; 4, lower electrode layer; 5, piezoelectric layer; 6, interdigital electrode; 7, geometric conformal electrode; 8, via hole. DETAILED DESCRIPTION
[0030] The present application will be described in detail below in conjunction with examples, but the present application is not limited to these examples.
[0031] The raw materials in the embodiments of the present application are all purchased through commercial channels unless otherwise specified.
[0032] The test methods are all conventional methods unless otherwise specified, and the instrument settings are all recommended settings of the manufacturers.
[0033] At present, the piezoelectric materials for pMUT devices are generally lead-based piezoelectric materials, aluminum nitride and its doped modified thin film materials in the academic and industrial circles. The lead-based piezoelectric ceramic is suitable for preparing an ultrasonic transducer with high emission performance, but its large dielectric constant and dielectric loss limit the receiving performance of the device. AlN is suitable for preparing an ultrasonic transducer with high receiving performance, but its low piezoelectric coefficient limits the emission performance of the device. In terms of device design, it is difficult for a pMUT array to have high emission and receiving performance at the same time without considering the material performance of the piezoelectric layer. In order to achieve high emission performance, the pMUT needs to have a large equivalent capacitance, which can make the transducer store more electric energy, so that the electric field excitation of the piezoelectric material is more effective, and stronger amplitude and acoustic energy are generated, thereby improving the emission performance of the transducer. However, in order to have high receiving sensitivity, the pMUT needs to have a low equivalent capacitance, which is contradictory. Therefore, the existing pMUT array is difficult to have high emission and receiving performance at the same time.
[0034] The present application provides a micro-mechanical ultrasonic transducer array based on a dissimilar electrode configuration, which aims to solve the foregoing technical problems. In the technical solution, the pMUT array with a dissimilar electrode configuration adopts a multi-patterned upper electrode layer, and the pattern of the upper electrode layer is designed differently according to the functions of the array units, including the interdigital electrode of the pMUT receiving unit and the geometric conformal electrode of the transmitting unit.
[0035] Through the multi-patterned upper electrode layer, the present application realizes the upper and lower electrode working mode with high emission performance and the coplanar electrode working mode with high receiving performance on the same pMUT array, and obtains a pMUT array with high receiving and transmitting performance.
[0036] According to an embodiment of the present application, the micro-mechanical ultrasonic transducer array based on a dissimilar electrode configuration comprises a plurality of upper and lower electrode mode pMUTs and a plurality of coplanar electrode mode pMUTs.
[0037] The upper and lower electrode mode pMUTs and the coplanar electrode mode pMUTs all comprise a diaphragm and a back cavity arranged in a stack;
[0038] The diaphragm comprises an upper electrode layer, a piezoelectric layer, a lower electrode layer and a structural layer arranged in sequence from top to bottom;
[0039] The upper electrode layer in the upper and lower electrode mode pMUT is a geometric conformal electrode consistent with the cross-sectional shape of the back cavity;
[0040] The upper electrode layer in the co-planar electrode mode pMUT is an interdigital electrode.
[0041] In one embodiment, the back cavity has a cross-sectional shape selected or designed as needed, such as a circular shape, a square shape, a hexagonal shape, or a polygonal shape.
[0042] In one embodiment, the upper-and-lower-electrode mode pMUT further comprises a via formed through the piezoelectric layer. The pMUT with an interdigital electrode as the upper electrode layer is configured in a co-planar electrode mode for receiving ultrasonic waves, and the lower electrode layer does not need to be led out during operation. The pMUT with a geometrically conformal electrode as the upper electrode layer is configured in an upper-and-lower-electrode mode for transmitting ultrasonic waves, and the lower electrode layer needs to be led out through the via during operation.
[0043] In one embodiment, the upper-and-lower-electrode mode pMUT and the co-planar electrode mode pMUT further comprise a support layer disposed on a side of the structural layer away from the piezoelectric layer.
[0044] The back cavity is a cavity formed on the support layer, and the cavity extends to the lower end surface of the structural layer.
[0045] The material of the support layer can be selected as needed, such as silicon. The formation of the cavity is not strictly limited, such as being formed by etching.
[0046] In one embodiment, the size of the upper electrode in the upper-and-lower-electrode mode pMUT is 20%-70% of the cross-sectional area of the back cavity. The ratio of the electrode area to the cavity diameter affects the electromechanical coupling efficiency and acoustic performance of the pMUT. A too large electrode area leads to excessive load on the piezoelectric layer, affecting the resonance frequency and vibration mode. Too many electrodes can cause the acoustic impedance of the device to rise, which is not conducive to acoustic impedance matching.
[0047] In one embodiment, a plurality of the upper-and-lower-electrode mode pMUTs form a transmitting unit of the micro-mechanical ultrasonic transducer device array for transmitting ultrasonic signals.
[0048] A plurality of the co-planar electrode mode pMUTs form a receiving unit of the micro-mechanical ultrasonic transducer device array for receiving ultrasonic signals.
[0049] The pMUT array in the upper-and-lower-electrode mode has a high equivalent capacitance, which can improve the energy conversion efficiency and promote the transmission of ultrasonic signals, so the pMUT array has high transmission performance. The pMUT array in the co-planar electrode mode has a small equivalent capacitance, which can produce a high voltage response to external ultrasonic signals and capture weak ultrasonic signals to improve the receiving sensitivity, so it has high receiving performance. Therefore, the pMUT array has both high transmission and detection performance.
[0050] In one embodiment, the piezoelectric layer is a thin film of single crystal material. The piezoelectric layer material is the core functional material of the pMUT, which functions to convert electrical energy and mechanical energy. Lead-based piezoelectric materials such as PZT or PMN-PT have a high piezoelectric coefficient, which can enable the pMUT to have high transmission performance, but the high dielectric constant of the material can limit the receiving performance of the pMUT; AlN and LN and other lead-free materials have a suitable dielectric constant and good receiving performance, but the low piezoelectric coefficient can affect the transmission performance. Therefore, the core of the present patent is to weaken the influence of the piezoelectric material performance on the transmission and receiving performance of the pMUT through the configuration of the dissimilar electrodes, and to simultaneously improve the transmission and receiving performance.
[0051] In one embodiment, the material of the piezoelectric layer is selected from at least one of lithium niobate (LN), aluminum nitride (AlN), scandium-doped aluminum nitride (AlScN), lead zirconate titanate (PZT), and lead magnesium niobate-lead titanate (PMN-PT).
[0052] The pMUT structure uses the upper and lower electrode mode of this high-capacitance design. The design logic is to use the high-capacitance properties of the material to exhibit high energy storage effects in the circuit, thereby generating a large driving current, and ultimately exhibiting strong sound pressure output of the device, thereby improving the transmission performance of the pMUT. The low-capacitance design of the coplanar electrode mode uses the low noise of the material in the low-capacitance mode to exhibit high input impedance in the circuit, thereby ensuring high-fidelity detection of weak signals and improving the receiving performance of the pMUT. Due to the different piezoelectric layer materials and pMUT design structures, the equivalent capacitances of different devices are different. For example, the equivalent capacitance of a pMUT with an AlN thin film material as the piezoelectric layer and an upper and lower electrode structure is about 80-150 pF, and the equivalent capacitance of a pMUT with a coplanar electrode structure is about 15-30 pF.
[0053] In one embodiment, the thickness of the piezoelectric layer is 0.1-50 μm. The thickness of the piezoelectric layer and the diameter of the cavity are important factors in determining the resonance frequency of the pMUT. When the diameter of the cavity is constant, changes in the thickness of the piezoelectric layer can cause a large change in the resonance frequency of the pMUT. For example, the resonance frequency of a 10 μm PZT diaphragm is 3 MHz, and when the diaphragm is 5 μm, the resonance frequency increases to 12 MHz. In the application field of pMUT, a piezoelectric layer thickness of 0.1-50 μm can meet most design requirements.
[0054] In one embodiment, the thickness of the structural layer is 0.1-100 μm. The thickness of the structural layer is generally 1-2 times the thickness of the piezoelectric layer. The core of the thickness design is to coordinate with the thickness of the piezoelectric layer to adjust the overall resonance frequency and vibration mode of the pMUT, etc. The material of the structural layer can be selected as needed, for example, it can be silicon dioxide, and the preparation method of the structural layer is not strictly limited, for example, it can be prepared by deposition.
[0055] In one embodiment, the thickness of the upper electrode layer is 0.01-2 μm; the thickness of the lower electrode layer is 0.01-2 μm. The thickness of the electrode layer is controlled between 0.01-2 μm to ensure the electrical conductivity and avoid device breakdown. Too thick electrode thickness will cause device resistance to increase, generate parasitic capacitance, increase mechanical load, and increase acoustic impedance, etc.
[0056] In one embodiment, the depth of the back cavity is 5-50 μm. The cavity depth can be less than the thickness of the support layer, or can penetrate through the support layer. The cavity depth needs to be optimized in coordination with the diameter of the diaphragm (diameter / depth ratio of 3:1-10:1), the thickness of the piezoelectric layer, and the like, which are related to the resonant frequency, vibration mode, and acoustic impedance matching of the pMUT, for example, increasing the cavity depth will cause the stiffness of the diaphragm to decrease, thereby reducing the overall resonant frequency of the device.
[0057] Example 1
[0058] The micro-mechanical ultrasonic transducer array based on the hetero-electrode configuration includes a plurality of upper and lower electrode mode pMUTs and a plurality of coplanar electrode mode pMUTs;
[0059] As shown in Figure 1 , the upper and lower electrode mode pMUTs and the coplanar electrode mode pMUTs each include a diaphragm and a back cavity;
[0060] The diaphragm includes an upper electrode layer, a piezoelectric layer 5, a lower electrode layer 4, a structural layer 3, and a support layer 1 arranged in order from top to bottom;
[0061] The support layer 1 is provided with a cavity as the back cavity 2, and the cavity extends to the lower side end surface of the structural layer 3;
[0062] In the coplanar electrode mode pMUT, the upper electrode layer is an interdigital electrode 6 selected from any one shape of the interdigital electrode 6 in (a) to (c) as shown in Figure 2 ;
[0063] In the upper and lower electrode mode pMUT, the upper electrode layer is a geometric conformal electrode 7 selected from any one shape of the geometric conformal electrode 7 in (a) to (c) as shown in Figure 3 ;
[0064] The material of the upper electrode layer is gold, and the thickness is 0.5 μm;
[0065] The piezoelectric layer 5 is a lithium niobate single crystal thin film, and the thickness is 5 μm;
[0066] The material of the lower electrode layer 4 is gold, and the thickness is 0.5 μm;
[0067] The material of the structural layer 3 is silicon dioxide, and the thickness is 5 μm;
[0068] The material of the support layer 1 is silicon, and the thickness is 100 μm;
[0069] The depth of the back cavity 2 is 20 μm;
[0070] The area of the geometric conformal electrode in the up-down electrode mode pMUT is 70% of the cross-sectional area of the back cavity 2.
[0071] The core of the pMUT array in the application considering high transmitting and receiving performance is that the transmitting unit in the pMUT array adopts the up-down electrode mode, which has a higher equivalent capacitance, can convert more electrical signals into mechanical vibration of the device, and promote the emission of ultrasonic signals; and the receiving unit in the pMUT array adopts the coplanar electrode mode, which has a smaller equivalent capacitance. Smaller capacitance usually means that the device has higher impedance, so it has higher voltage response to external ultrasonic signals, so that it can capture weak ultrasonic signals and improve receiving sensitivity. In addition, low capacitance helps to reduce signal attenuation of the pMUT due to capacitive effect, so that the received signal can be better captured and processed.
[0072] The above is only a few embodiments of the application, and does not limit the application in any form. Although the application discloses the above preferred embodiments, it does not limit the application. Any skilled person in the art can make some changes or modifications to the above disclosed technical content without departing from the scope of the technical solution of the application, which is equivalent to the equivalent implementation examples, and belongs to the scope of the technical solution.
Claims
1. A micromachined ultrasonic transducer array based on a heterogenization electrode configuration, characterized by, The pMUTs include a plurality of top-and-bottom electrode mode pMUTs and a plurality of coplanar electrode mode pMUTs; The top-and-bottom electrode mode pMUTs and the coplanar electrode mode pMUTs each include a diaphragm and a back cavity arranged in a stack; The diaphragm includes, from top to bottom, an upper electrode layer, a piezoelectric layer, a lower electrode layer, and a structural layer; In the top-and-bottom electrode mode pMUT, the upper electrode layer is a geometric conformal electrode consistent with the cross-sectional shape of the back cavity; In the coplanar electrode mode pMUT, the upper electrode layer is an interdigital electrode.
2. The micro-machined ultrasonic transducer array based on a hetero- electrode configuration of claim 1, wherein, The top-and-bottom electrode mode pMUT further includes a via hole arranged through the piezoelectric layer.
3. The micro-machined ultrasonic transducer array based on a hetero- electrode configuration of claim 1, wherein, The top-and-bottom electrode mode pMUT and the coplanar electrode mode pMUT further include a support layer arranged on a side of the structural layer away from the piezoelectric layer; The back cavity is a cavity opened on the support layer, and the cavity extends to a lower side end surface of the structural layer.
4. The micro-machined ultrasonic transducer array based on a hetero- electrode configuration of claim 3, wherein, In the top-and-bottom electrode mode pMUT, the size of the upper electrode is 20%-70% of the cross-sectional area of the back cavity.
5. The micro-machined ultrasonic transducer array based on a hetero-electrode configuration according to claim 1, wherein A plurality of the top-and-bottom electrode mode pMUTs form a transmitting unit of the micro-machined ultrasonic transducer array for transmitting an ultrasonic signal. A plurality of the coplanar electrode mode pMUTs form a receiving unit of the micro-machined ultrasonic transducer array for receiving an ultrasonic signal.
6. The micro-machined ultrasonic transducer array based on a hetero- electrode configuration of claim 1, wherein, The piezoelectric layer is a single-crystal material thin film.
7. The micro-machined ultrasonic transducer array based on a hetero- electrode configuration of claim 1, wherein, The thickness of the piezoelectric layer is 0.1-50 μm.
8. The micro-machined ultrasonic transducer array based on a hetero- electrode configuration of claim 1, wherein, The thickness of the structural layer is 0.1-100 μm.
9. The micro-machined ultrasonic transducer array based on a hetero- electrode configuration of claim 3, wherein, The thickness of the upper electrode layer is 0.01-2 μm, and the thickness of the lower electrode layer is 0.01-2 μm.
10. The micro-machined ultrasonic transducer array based on a hetero- electrode configuration of claim 1, wherein, The depth of the back cavity is 5-50 μm.