Endoscope ultrasonic transducer probe based on barium calcium zirconium titanium material and preparation method thereof

Abstract

The application relates to an endoscope ultrasonic transducer probe based on a barium calcium zirconium titanium material and a preparation method thereof in the field of piezoelectric ultrasonic transducers, the endoscope ultrasonic transducer probe comprising a micromechanical ultrasonic transducer array, the micromechanical ultrasonic transducer array comprising a plurality of ultrasonic units; each ultrasonic unit comprising a substrate layer, a bottom electrode, a piezoelectric layer and a top electrode, the bottom electrode, the piezoelectric layer and the top electrode being sequentially covered on the surface of one side of the substrate layer, the surface of the other side of the substrate layer being formed with a back cavity, and the piezoelectric layer being a BCZT material. The application forms the ultrasonic unit based on the barium calcium zirconium titanium material by utilizing semiconductor technology, forms the micromechanical ultrasonic transducer array by array arrangement of the plurality of ultrasonic units, can realize the self-generation and self-reception functions of the endoscope ultrasonic transducer probe, can realize the high consistency, miniaturization and precise frequency control of the endoscope ultrasonic transducer probe, and makes the endoscope ultrasonic transducer probe have the piezoelectric performance with high resolution and high uniformity.

Description

Technical Field

[0001] This application relates to the field of piezoelectric ultrasonic transducers, and in particular to an endoscopic ultrasonic transducer probe based on barium calcium zirconium titanium material and its preparation method. Background Technology

[0002] Ultrasound imaging technology has been widely used in medicine and industry. Ultrasound probes based on volume piezoelectricity are now highly mature and commercialized. However, they have certain limitations in resolution and bandwidth flexibility, and their relatively large size makes miniaturization and integration difficult. This limits their application scenarios and increases application costs.

[0003] In recent years, piezoelectric micromechanical ultrasonic transducer (PMUT) probes based on lead zirconate titanate (PZT) thin films and MEMS technology have received widespread attention. These probes offer advantages such as smaller size and flexibility, flexible frequency and resolution design, compatibility with multi-frequency operation, high integration, compatibility with CMOS technology, and cost advantages. However, due to the toxicity and environmental risks of lead, the European Union has restricted the use of PZT materials. In recent years, there has been increasing interest in highly biocompatible piezoelectric thin films, and research into lead-free materials to replace PZT has focused on several promising materials, among which barium calcium zirconium titanium (BCZT) has attracted attention due to its piezoelectric properties comparable to PZT.

[0004] Currently, BCZT is mainly used in ceramic cutting, which results in poor process consistency. When used in medical imaging, it often leads to problems such as low signal-to-noise ratio, low resolution, and poor uniformity of piezoelectric properties. Summary of the Invention

[0005] The main objective of this invention is to provide an endoscopic ultrasonic transducer probe based on barium calcium zirconium titanium material and its preparation method, aiming to solve at least one of the above-mentioned technical problems.

[0006] To achieve the above objectives, this invention proposes an endoscopic ultrasonic transducer probe based on barium calcium zirconium titanium material, comprising a micromechanical ultrasonic transducer array, wherein the micromechanical ultrasonic transducer array includes multiple ultrasonic units; each ultrasonic unit includes a substrate layer, a bottom electrode, a piezoelectric layer and a top electrode, wherein the bottom electrode, the piezoelectric layer and the top electrode sequentially cover the surface of one side of the substrate layer, and a back cavity is formed on the surface of the other side of the substrate layer, wherein the piezoelectric layer is made of BCZT material.

[0007] In some embodiments of the present invention, a transition layer is provided between the bottom electrode and the piezoelectric layer.

[0008] In some embodiments of the present invention, the material of the transition layer is selected from LNO or SRO.

[0009] In some embodiments of the present invention, the top electrode has the same shape as the back cavity.

[0010] In some embodiments of the present invention, the ratio of the cross-sectional area of ​​the top electrode to that of the back cavity is 1:2.

[0011] In some embodiments of the present invention, the size of the ultrasonic unit is less than or equal to 200 μm.

[0012] In some embodiments of the present invention, the center frequency of the endoscope ultrasonic transducer probe based on barium calcium zirconium titanium material is ≥7.5MHz.

[0013] In some embodiments of the present invention, the fractional bandwidth of the endoscopic ultrasonic transducer probe based on barium calcium zirconium titanium material is greater than or equal to 85%.

[0014] In some embodiments of the present invention

[0015] To achieve the above objectives, this invention proposes a method for fabricating the aforementioned endoscope ultrasonic transducer probe based on barium calcium zirconium titanium material, comprising the following steps: preparing a substrate; growing a bottom electrode by physical vapor deposition on one side of the substrate; growing a BCZT thin film by physical vapor deposition on the bottom electrode; patterning the BCZT thin film and exposing the bottom electrode according to the design of the micromechanical ultrasonic transducer array; continuing to grow a top electrode by physical vapor deposition on the BCZT thin film through a photoresist mask according to the design of the micromechanical ultrasonic transducer array, and removing the photoresist mask by stripping; continuing to deposit metal wires and lead pads on the top electrode and the bottom electrode according to the design of the micromechanical ultrasonic transducer array; continuing to etch deep silicon on the other side of the substrate to release the back cavity according to the design of the micromechanical ultrasonic transducer array.

[0016] In some embodiments of the present invention, the patterning of the BCZT thin film is accomplished by wet etching and photoresist masking.

[0017] This application provides an endoscopic ultrasonic transducer probe based on barium-calcium-zirconium-titanium materials and its fabrication method. It utilizes semiconductor technology to form ultrasonic units based on barium-calcium-zirconium-titanium materials. Multiple ultrasonic units are arranged in an array to form a micromechanical ultrasonic transducer array, which can realize the self-transmission and self-reception function of the endoscopic ultrasonic transducer probe. It achieves high consistency, miniaturization and precise frequency control of the endoscopic ultrasonic transducer probe, and enables the endoscopic ultrasonic transducer probe to have high resolution and high uniformity piezoelectric properties. Attached Figure Description

[0018] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0019] Figure 1 This is a schematic diagram of the overall structure of the endoscopic ultrasonic transducer probe of the present invention.

[0020] Figure 2 This is a cross-sectional view of the ultrasonic unit of the present invention at the radial position;

[0021] Figures 3-10 Schematic diagrams of structures obtained by some steps in the preparation method provided by the present invention are given;

[0022] Figure 11 This invention relates to a PMUT array receiving voltage-frequency curve.

[0023] The labels in the attached diagram represent the following: 1. Ultrasonic unit; 2. Substrate layer; 3. Bottom electrode; 4. Piezoelectric layer; 5. Top electrode; 6. Back cavity; 7. Transition layer; 8. Printed circuit board; 9. Transducer area; 10. Pin area. Detailed Implementation

[0024] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0025] In the following description, when referring to the accompanying drawings, the same numbers in different drawings denote the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0026] In the description of this application, it should be understood that the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances. Furthermore, in the description of this application, unless otherwise stated, "multiple" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship.

[0027] This application discloses an endoscopic ultrasonic transducer probe based on barium-calcium-zirconium-titanium materials. For example... Figure 1 As shown, the endoscopic ultrasound transducer probe includes a micromechanical ultrasound transducer array, which includes multiple ultrasound units 1.

[0028] like Figure 2 As shown, each ultrasonic unit 1 includes a substrate layer 2, a bottom electrode 3, a piezoelectric layer 4, and a top electrode 5. The bottom electrode 3, the piezoelectric layer 4, and the top electrode 5 are sequentially covered on one side of the substrate layer 2, and a back cavity 6 is formed on the other side of the substrate layer 2. The piezoelectric layer 4 is made of BCZT material.

[0029] The endoscopic ultrasonic transducer probe of the present invention utilizes semiconductor technology to form an ultrasonic unit 1 based on barium calcium zirconium titanium material. Multiple ultrasonic units 1 are arranged in an array to form a micromechanical ultrasonic transducer array, which can realize the self-transmission and self-reception function of the endoscopic ultrasonic transducer probe. It achieves high consistency, miniaturization and precise frequency control of the endoscopic ultrasonic transducer probe, and enables the endoscopic ultrasonic transducer probe to have high resolution and high uniformity piezoelectric performance.

[0030] In some embodiments of the present invention, such as Figure 2 As shown, a transition layer 7 is provided between the bottom electrode 3 and the piezoelectric layer 4.

[0031] Furthermore, the materials of the transition layer 7 include, but are not limited to, LNO (lithium nickel oxide), SRO (silicon-rich oxide), etc.

[0032] In some embodiments of the present invention, the top electrode 5 and the back cavity 6 have the same shape.

[0033] Furthermore, the ratio of the cross-sectional area of ​​the top electrode 5 to that of the back cavity 6 is 1:2.

[0034] Furthermore, the shapes of the top electrode 5 and the back cavity 6 include, but are not limited to, circles or polygons of different sizes.

[0035] It should be noted that, in this invention, different frequency and bandwidth requirements can be achieved by designing the top electrode 5 and the back cavity 6 according to different sizes.

[0036] In some embodiments of the present invention, the size of the ultrasonic unit 1 is less than or equal to 200 μm.

[0037] In some embodiments of the present invention, the BCZT material composition includes, but is not limited to, BCZT85.

[0038] Furthermore, BCZT material doping includes, but is not limited to, undoped and CuO-doped materials.

[0039] In some embodiments of the present invention, the thickness of the piezoelectric layer 4 is 0.5-5 μm.

[0040] It should be understood that the thickness of the piezoelectric layer 4 can be designed as needed, and the piezoelectric layer 4 can be customized from 500 nanometers to 5 micrometers.

[0041] In some embodiments of the present invention, the substrate layer 2 material includes, but is not limited to, Si, SOI, mica, etc.; the bottom electrode 3 material includes, but is not limited to, Pt, etc.; and the top electrode 5 material includes, but is not limited to, Au, Al, etc.

[0042] In some embodiments of the present invention, such as Figure 2 As shown, the endoscopic ultrasound transducer probe also includes a printed circuit board 8 (PCB), which is bonded to the top electrode 5 on the side opposite to the piezoelectric layer 4.

[0043] Furthermore, the printed circuit board 8 includes, but is not limited to, rigid PCBs, flexible PCBs, or rigid-flex PCBs.

[0044] This embodiment also proposes a method for fabricating the above-mentioned endoscope ultrasonic transducer probe based on barium calcium zirconium titanium material, which includes the following steps:

[0045] 1) Prepare the substrate and clean it, such as... Figure 3 As shown.

[0046] 2) The bottom electrode is grown by physical vapor deposition (PVD) on one side of the substrate, such as... Figure 4 As shown.

[0047] 3) A transition layer is grown on the bottom electrode by physical vapor deposition, such as... Figure 5 As shown.

[0048] 4) BCZT thin films are grown by physical vapor deposition on the transition layer, such as... Figure 6 As shown.

[0049] Specifically, this invention utilizes sol-gel processing and thin-film deposition techniques, employing highly hydrophilic substrate surface treatment and uniformly dispersed nano-droplets to form BCZT thin films. This allows for precise control over the composition, thickness, and structural properties of the BCZT film, optimizing its piezoelectric properties, mechanical robustness, and adhesion to planar or complex curved MEMS substrates. This enhances its sensing, actuation, and energy harvesting capabilities. The invention can form BCZT films with a uniform thickness of 0.5-5 μm, achieving properties such as d33 ≥ 200 pC / N, dielectric loss tanδ < 0.02, and coupling coefficient k. 33 ≥0.5, Young's modulus is 120±20GPa.

[0050] Furthermore, the present invention employs a highly hydrophilic substrate surface treatment and uniformly dispersed nano-droplets, comprising the following steps:

[0051] 41) Pretreatment of planar or curved substrates. The surface energy of the substrate is reduced by simple flame or plasma treatment, thereby significantly improving the substrate wetting ability during droplet deposition.

[0052] 42) Electrostatically induced droplet nanoforming and uniform spraying. The required equipment mainly includes a slurry supply module, an atomization module, and a triaxial substrate receiving platform. Uniform deposition of thin films on various substrate materials and topological surfaces is achieved mainly by adjusting parameters such as voltage, deposition height, slurry flow rate, and the trajectory and speed of the motion platform.

[0053] The piezoelectric material slurry is formulated to a suitable range of physical properties, such as viscosity less than 1338 mPa·s and surface tension less than 50 mN·m. -1 Electrical conductivity greater than 10⁻¹¹ S·m -1 The piezoelectric paste was injected using a micro-injection pump at a rate of 5 × 10⁻⁶. -11 -9×10 - 9 m 3 The piezoelectric paste is pushed into the stainless steel nozzle through a silicone tube at a flow rate of / s. When a sufficiently large electrostatic field, such as 5-10Kv, is applied to the nozzle, the piezoelectric paste will be ejected from the nozzle and further atomized into nano-droplets.

[0054] This process is the result of the combined effects of droplet gravity, viscosity, surface tension, and electric field. The XYZ three-axis motion platform enables precise deposition of thin film materials under different motion trajectories and speeds. Throughout the process, the size of the stainless steel nozzle can be changed according to the size and shape requirements of the thin film, and the distance between the nozzle and the substrate can be adjusted between 0-40mm.

[0055] The XYZ three-axis motion platform has a linear displacement accuracy of 2.5μm and a repeatability accuracy of <2μm. By adjusting the physical properties of the piezoelectric paste and deposition process parameters, such as voltage, deposition height, paste flow rate, motion platform trajectory and speed, uniform deposition of nanodroplets on planar and complex curved surfaces can be achieved.

[0056] 43) Shaping and sintering of planar or curved BCZT thin films. The liquid film formed by nanodroplets on the substrate undergoes in-situ thermal curing and layer-by-layer pyrolysis at 200-350℃ to remove organic solvents and release residual stress. Finally, the film is subjected to high-temperature crystallization at 600-750℃ to obtain the desired crystal structure.

[0057] In this invention, electrostatically induced nanodroplet deposition is beneficial for improving the spraying precision and sintering quality of BCZT thin films: the electric field strength is the key factor determining the breakup of charged droplets in a high-voltage electric field; the forces acting on the droplets are mainly contractile forces pointing inwards and electric field forces pointing outwards. The charge q of the charged droplet is:

[0058]

[0059] In the formula: ε is the dielectric constant of the droplet; E is the electric field strength; r is the droplet radius; and f is the percentage of charge obtained.

[0060] If we assume the droplet is a sphere with a uniformly distributed charge, then the charge density ρ of the droplet is:

[0061]

[0062] The electric force per unit area on the surface of the droplet is:

[0063]

[0064] The contractile force P on the surface of the droplet is:

[0065]

[0066] When the electric force per unit area of ​​a charged droplet is greater than the contractile force, the charged droplet breaks up.

[0067]

[0068] Therefore, the critical field strength E for the breakup of charged droplets is:

[0069]

[0070] The maximum charge limit of a droplet is primarily influenced by the surface tension of the liquid and the droplet size. As the solvent evaporates during deposition, the size of the charged droplets gradually decreases, while the charge density increases. This causes the droplets to break up, eventually forming extremely fine droplets or solid particles that are deposited onto the substrate. Charged droplets carry the same charge, thus repelling each other during atomization deposition, effectively preventing droplet aggregation and improving the uniformity of the deposited coating. When charged droplets are deposited on the substrate surface, their movement in the direction perpendicular to the substrate is restricted, and they begin to spread and deform in the direction tangential to the substrate. The former enhances the adhesion of the droplets to the substrate surface, while the latter helps improve the spreadability of the droplets on curved substrates. The induction of charged droplets generates opposite charges on the substrate surface, which improves the deposition efficiency and enhances the adsorption of droplets on the substrate surface.

[0071] Good deposition quality further affects the subsequent sintering quality of the film. The nanoparticles in the deposited liquid film act as nuclei during the high-temperature crystallization process, thus promoting grain formation and growth. The sol acts as a binder between the nanoparticles, allowing the film to crystallize into a dense structure at a lower temperature, thereby avoiding defects such as cracking and porosity during high-temperature crystallization. To further reduce residual stress generated during the spraying of multiple liquid films, a heating step can be introduced after each layer is formed to remove organic components from the structure, effectively ensuring the uniformity of the BCZT film. The surface roughness of the obtained BCZT film is less than 100 nm.

[0072] 5) Based on the design of the micromechanical ultrasonic transducer array, wet etching and photoresist masking were used to pattern the BCZT thin film and transition layer, exposing the bottom electrode, such as... Figure 7 and Figure 8 As shown.

[0073] In this invention, before the probe is fabricated, a multi-model approach can be used, such as combining finite element simulation with lumped parameter model simulation, to design an ultra-high working bandwidth and ultra-high sensitivity piezoelectric micro-ultrasonic transducer array. Through thin film design, the advantage of the bending mode ultrasonic transducer being easily matched with the low acoustic impedance of the human body can be taken advantage of.

[0074] 6) Continuing with the design of the micromechanical ultrasonic transducer array, the top electrode is grown on the BCZT thin film using physical vapor deposition with a photoresist mask, and the photoresist mask is removed by lift-off, as shown below. Figure 8 As shown.

[0075] 7) Continuing with the design of the micromechanical ultrasonic transducer array, deposit metal wires and pin pads on the top and bottom electrodes, such as... Figure 9 As shown.

[0076] Furthermore, such as Figure 1 As shown, multiple ultrasonic unit arrays are arranged to form a micromechanical ultrasonic transducer array. The micromechanical ultrasonic transducer array is set as transducer region 9. Pin regions 10 are provided at intervals on one side of transducer region 9. Electrodes connected to metal wires and pin pads are deposited in pin regions 10.

[0077] Furthermore, the electrode shape of the pin region 10 includes, but is not limited to, circles or polygons.

[0078] This invention relates to MEMS fabrication technology for piezoelectric micro-ultrasonic probes based on bending mode, which significantly reduces the difficulty of wire connection, improves the operating frequency and manufacturing yield, and realizes the development of endoscopic imaging arrays with high fill factor.

[0079] 8) Continuing with the design of the micromechanical ultrasonic transducer array, deep silicon etching is performed on the other side of the substrate to create a back cavity, such as... Figure 10 As shown.

[0080] 9) Bond the substrate with each layer structure, which has undergone back cavity processing in step 8), to the printed circuit board to finally obtain the following: Figure 1 and Figure 2 The endoscope ultrasonic transducer probe shown is based on barium calcium zirconium titanium material.

[0081] Furthermore, the bonding methods between the electrodes in the pin area and the printed circuit board include, but are not limited to, wire bonding, flip-chip bonding, or reflow soldering.

[0082] This invention utilizes standardized MEMS processes and layout design to achieve patterning and high-precision device fabrication based on BCZT thin film material stacks, enabling the fabrication of ultrasonic endoscopic probes with flexible frequencies and high resolution. This allows BCZT materials to be compatible with both CMOS and MEMS processes, reducing process costs and improving uniformity while possessing the potential for large-scale integration with CMOS processes. Compared to traditional ultrasonic probes that commonly use lead-containing PZT materials, this invention uses a process method based on lead-free piezoelectric materials, resulting in devices with higher biosafety and environmental friendliness.

[0083] Compared to traditional volume ultrasound probes, the endoscopic ultrasound transducer probe of this invention uses a wafer-level process and, through finite element analysis, achieves the same frequency and over 80% fractional bandwidth design as the volume ultrasound probe. Specifically, it can achieve a center frequency of not less than 7.5MHz and a high operating bandwidth of not less than 85% for imaging requirements. This bandwidth is difficult to achieve with volume piezoelectric probes, and this performance improvement significantly enhances imaging resolution. Figure 11 The present invention demonstrates the receiving voltage-frequency curve of a PMUT array. This design achieves a center frequency of 7.74MHz and a working bandwidth of 92%, meeting the performance requirements of endoscopic ultrasound imaging. Endoscopic systems based on the probe of the present invention can have high signal-to-noise ratio and high frame rate, imaging resolution of not less than 225μm, ultrasound blood flow velocity detection range of 10-1000mm / s, and blood flow contrast with surrounding background signal greater than or equal to 30dB.

[0084] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An endoscopic ultrasonic transducer probe based on barium calcium zirconium titanium material, characterized in that, It includes a micromechanical ultrasonic transducer array, wherein the micromechanical ultrasonic transducer array comprises multiple ultrasonic units; Each of the ultrasonic units includes a substrate, a bottom electrode, a piezoelectric layer, and a top electrode. The bottom electrode, the piezoelectric layer, and the top electrode are sequentially covered on one side of the substrate. A back cavity is formed on the other side of the substrate. The piezoelectric layer is made of BCZT material and has a thickness of 0.5-5 μm. A transition layer is provided between the bottom electrode and the piezoelectric layer, and the material of the transition layer is selected from LNO or SRO. The center frequency of the endoscope ultrasonic transducer probe based on barium calcium zirconium titanium material is ≥7.5MHz, and the fractional bandwidth of the endoscope ultrasonic transducer probe based on barium calcium zirconium titanium material is greater than or equal to 85%.

2. The endoscopic ultrasonic transducer probe based on barium calcium zirconium titanium material according to claim 1, characterized in that, The top electrode has the same shape as the back cavity.

3. The endoscopic ultrasonic transducer probe based on barium calcium zirconium titanium material according to claim 2, characterized in that, The ratio of the cross-sectional area of ​​the top electrode to that of the back cavity is 1:

2.

4. The endoscopic ultrasonic transducer probe based on barium calcium zirconium titanium material according to claim 1, characterized in that, The size of the ultrasonic unit is less than or equal to 200 μm.

5. A method for fabricating an endoscopic ultrasonic transducer probe based on barium calcium zirconium titanium material as described in any one of claims 1-4, characterized in that, Includes the following steps: Prepare the substrate; A bottom electrode is grown by physical vapor deposition on one side of the substrate; A transition layer is grown on the bottom electrode by physical vapor deposition; a BCZT thin film is grown on the transition layer by physical vapor deposition. Based on the design of the micromechanical ultrasonic transducer array, the BCZT film and transition layer are patterned and the bottom electrode is exposed. Continuing with the design of the micromechanical ultrasonic transducer array, the top electrode is grown on the BCZT thin film by physical vapor deposition through a photoresist mask, and the photoresist mask is removed by stripping. Continuing with the design of the micromechanical ultrasonic transducer array, metal wires and pin pads are deposited on the top electrode and the bottom electrode; Continuing with the design of the micromechanical ultrasonic transducer array, a back cavity is created by deep silicon etching on the other side of the substrate.

6. The preparation method according to claim 5, characterized in that, The patterning of the BCZT thin film was accomplished using wet etching and photoresist masking.

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