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

Abstract

The invention relates to an endoscope ultrasonic transducer probe based on a barium-calcium-zirconium-titanium material and a preparation method of the endoscope ultrasonic transducer probe in the field of piezoelectric ultrasonic transducers. The endoscope ultrasonic transducer probe comprises a micromechanical ultrasonic transducer array, and the micromechanical ultrasonic transducer array comprises a plurality of ultrasonic units; each ultrasonic unit comprises a substrate layer, a bottom electrode, a piezoelectric layer and a top electrode, the bottom electrode, the piezoelectric layer and the top electrode sequentially cover the surface of one side of the substrate layer, a back cavity is formed in the surface of the other side of the substrate layer, and the piezoelectric layer is made of a BCZT material. The ultrasonic units are formed on the basis of the barium calcium zirconium titanium material by utilizing a semiconductor technology, and a plurality of ultrasonic units are arranged in an array to form the micro-mechanical ultrasonic transducer array, so that the self-transmitting and self-receiving functions of the endoscope ultrasonic transducer probe can be realized, and high consistency, microminiature and precise frequency control of the endoscope ultrasonic transducer probe can be realized; therefore, the ultrasonic transducer probe of the endoscope has high-resolution and high-uniformity piezoelectric properties.

Description

Technical Field

[0001] The present 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 a preparation method thereof. Background Art

[0002] Ultrasonic imaging technology has been widely used in medicine and industry. Bulk piezoelectric-based ultrasound probes are now highly mature and commercialized. However, they have certain limitations in resolution and bandwidth flexibility, and are relatively large in size, making miniaturization and integration difficult. This limits their application scenarios and increases their application costs.

[0003] In recent years, piezoelectric micromachined ultrasonic transducer (PMUT) probes based on lead zirconate titanate (PZT) thin films and MEMS technology have received widespread attention. The probes have smaller size and flexibility, flexible frequency and resolution design, and are compatible with multi-frequency operation. They are highly integrated and compatible with CMOS technology, and have cost advantages. However, due to the toxicity and environmental risks of lead, the European Union restricts the use of PZT materials. In recent years, people have shown increasing interest in highly biocompatible piezoelectric films, and research on finding lead-free materials to replace PZT has focused on some 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 the form of ceramic cutting, and the process consistency is poor. When used in medical imaging, it often brings problems such as low signal-to-noise ratio, low resolution and poor uniformity of piezoelectric performance. Summary of the invention

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

[0006] To achieve the above-mentioned objectives, the present 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 comprises a plurality of ultrasonic units; each of the ultrasonic units comprises a substrate layer, a bottom electrode, a piezoelectric layer and a top electrode, wherein the bottom electrode, the piezoelectric layer and the top electrode are sequentially covered on the surface of one side of the substrate layer, a back cavity is formed on the surface of the other side of the substrate layer, and the piezoelectric layer is a 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 and the back cavity have the same shape.

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

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

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

[0013] In some embodiments of the present invention, the fractional bandwidth of the endoscopic ultrasound transducer probe based on the 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, the present invention proposes a method for preparing the above-mentioned endoscopic 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; according to the design of a micromechanical ultrasonic transducer array, graphing the BCZT thin film and exposing the bottom electrode; continuing to grow a top electrode by physical vapor deposition through a photoresist mask on the BCZT thin film according to the design of the micromechanical ultrasonic transducer array, and removing the photoresist mask by stripping; continuing to deposit metal wires and pin pads on the top electrode and the bottom electrode according to the design of the micromechanical ultrasonic transducer array; continuing to release the back cavity by deep silicon etching on the other side of the substrate according to the design of the micromechanical ultrasonic transducer array.

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

[0017] The embodiment of the present application provides an endoscopic ultrasonic transducer probe based on barium calcium zirconium titanium material and a preparation method thereof, which utilizes semiconductor technology to form an ultrasonic unit based on barium calcium zirconium titanium material, and an array of multiple ultrasonic units is arranged to form a micromechanical ultrasonic transducer array, which can realize the self-transmitting and self-receiving function of the endoscopic ultrasonic transducer probe, and realizes the high consistency, miniature size and precise frequency control of the endoscopic ultrasonic transducer probe, so that the endoscopic ultrasonic transducer probe has high resolution and high uniformity of piezoelectric performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Also, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

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

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

[0021] Figure 3-Figure 10 A schematic diagram of the structures obtained in some steps of the preparation method provided by the present invention is given;

[0022] Fig.11 The present invention discloses a PMUT array receiving voltage frequency curve.

[0023] The reference numerals in the accompanying drawings 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 DESCRIPTION

[0024] It should be clear that the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0025] When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. Instead, they are only examples of devices and methods consistent with some aspects of the present application as detailed in the attached claims.

[0026] In the description of the present application, it should be understood that the terms "first", "second", etc. are used for descriptive purposes only and should not be understood as indicating or implying relative importance. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances. In addition, in the description of the present application, unless otherwise specified, "multiple" refers to two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. The character " / " generally indicates that the objects associated before and after are in an "or" relationship.

[0027] The present application discloses an endoscopic ultrasonic transducer probe based on a barium calcium zirconium titanium material. Figure 1 As shown, the endoscopic ultrasonic transducer probe includes a micromachined ultrasonic transducer array, and the micromachined ultrasonic transducer array includes a plurality of ultrasonic 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 the surface of one side of the substrate layer 2. A back cavity 6 is formed on the surface of 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. A plurality of ultrasonic units 1 are arranged in an array to form a micromechanical ultrasonic transducer array, which can realize the self-transmitting and self-receiving function of the endoscopic ultrasonic transducer probe, and realize the high consistency, miniature size and precise frequency control of the endoscopic ultrasonic transducer probe, so that the endoscopic ultrasonic transducer probe has high resolution and high uniformity of piezoelectric performance.

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

[0031] Furthermore, the material of the transition layer 7 includes but is not limited to LNO (lithium nickel oxide), SRO (silicon rich oxide) and the like.

[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 the present 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 ultrasound unit 1 is less than or equal to 200 μm.

[0037] In some embodiments of the present invention, the BCZT material components include but are not limited to BCZT85 and the like.

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

[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 present invention can design the thickness of the piezoelectric layer 4 as required, thereby achieving customized processing of the piezoelectric layer 4 from a thickness of 500 nanometers to a thickness of 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.; the top electrode 5 material includes but is not limited to Au, Al, etc.

[0042] In some embodiments of the present invention, Figure 2 As shown, the endoscopic ultrasound transducer probe further includes a printed circuit board 8 (PCB), and the printed circuit board 8 is bonded to a side of the top electrode 5 facing away from the piezoelectric layer 4 .

[0043] Furthermore, the printed circuit board 8 includes but is not limited to a hard PCB, a flexible PCB or a hard-soft combination board.

[0044] This embodiment also proposes a method for preparing the above-mentioned endoscopic ultrasonic transducer probe based on the barium calcium zirconium titanium material, and the preparation method comprises the following steps:

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

[0046] 2) Physical vapor deposition (PVD) is used to grow the bottom electrode on one side of the substrate, such as Figure 4 shown.

[0047] 3) Physical vapor deposition growth transition layer on the bottom electrode, such as Figure 5 shown.

[0048] 4) Physical vapor deposition growth of BCZT thin film on the transition layer, such as Figure 6 shown.

[0049] The present invention can specifically form a BCZT film through sol-gel processing and thin film deposition technology, using highly hydrophilic substrate surface treatment and uniformly dispersed nano-droplets, to achieve precise control of the composition, thickness and structural characteristics of the BCZT film, optimize the piezoelectric properties, mechanical robustness and adhesion of the BCZT film to a flat or complex curved MEMS substrate, and improve its sensing, driving and energy collection capabilities. It can form a BCZT film with a uniform thickness of 0.5-5μm, and the BCZT film can achieve performance d33≥200pC / N, dielectric loss tanδ<0.02, and coupling coefficient k 33 ≥0.5, Young's modulus is 120±20GPa.

[0050] Furthermore, the present invention uses highly hydrophilic substrate surface treatment and uniformly dispersed nanosized droplets, including the following steps:

[0051] 41) Pretreatment of flat or curved substrates: Reduce the surface energy of the substrate by simple flame treatment or plasma treatment, thereby greatly improving the substrate wetting ability during droplet deposition.

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

[0053] The piezoelectric material slurry is prepared within the appropriate physical parameter range, such as viscosity less than 1338mPa·s and surface tension less than 50mN·m -1 , conductivity greater than 10-11S·m -1 The piezoelectric slurry was injected into the microinjection pump at a rate of 5×10 -11 -9×10 - 9 m 3 / s flow rate is pushed into the stainless steel spray needle through the silicone hose. When there is a sufficiently large electrostatic field, such as 5-10Kv, acting on the spray needle, the piezoelectric slurry will be ejected from the spray needle orifice 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 undertakes the substrate material to achieve precise deposition of thin film materials under different motion trajectories and speeds. During the whole process, the size of the stainless steel spray needle can be changed according to the film size and morphology requirements, and the distance between the spray needle and the substrate can be adjusted between 0-40mm.

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

[0056] 43) Flat or curved BCZT film shaping and sintering. The liquid film formed by the nano-droplets on the substrate is subjected to in-situ thermal curing and layer-by-layer pyrolysis treatment at a heat treatment temperature of 200-350°C to remove the organic solvent in the film and release the residual stress. Finally, the film is subjected to high-temperature crystallization treatment at a temperature of 600-750°C to obtain the desired crystal structure.

[0057] In the present invention, the electrostatic field-induced nanodroplet deposition is beneficial to improving the BCZT thin film spraying accuracy and sintering quality: the electric field strength is the key factor that determines the splitting and fragmentation of the charged droplets in the high-voltage electric field. The forces on the droplets are mainly the contraction force pointing to the inside of the droplets and the electric field force pointing to the outside of the droplets. The charge q of the charged droplets is:

[0058]

[0059] Where: ε is the dielectric constant of the droplet; E is the electric field strength; r is the radius of the droplet; f is the thousandth of the acquired charge.

[0060] If the droplet is assumed to be a spherical shape with uniform charge distribution, the charge density ρ of the droplet is:

[0061]

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

[0063]

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

[0065]

[0066] When the electric field force per unit area of ​​the charged droplet is greater than the contraction force, the charged droplet breaks:

[0067]

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

[0069]

[0070] That is, the limit value of the droplet charge is mainly affected by the surface tension of the liquid and the droplet size. As the solvent evaporates continuously during the deposition process, the particle size of the charged droplets gradually decreases, the charge density gradually increases, and the droplets will continue to break, and finally form extremely fine droplets or solid particles that are deposited on the substrate. The charged droplets carry the same charge, so they will repel each other during the atomization deposition process, which can effectively prevent the droplets from agglomerating and improve the uniformity of the deposited coating. When the charged droplets are deposited on the surface of the substrate, 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 can enhance the adhesion of the droplets on the substrate surface, and the latter helps to improve the spreadability of the droplets on the curved substrate. The induction of the charged droplets will cause the substrate surface to produce opposite charges, which can improve the deposition efficiency of the droplets and enhance the adsorption of the substrate surface to the droplets.

[0071] Good deposition quality also further affects the subsequent sintering quality of the film. The nanoparticles in the deposited liquid film will act as crystal nuclei during the high-temperature crystallization process of the film, thereby facilitating the formation and growth of grains, while the sol can act as a bond between the nanopowders, allowing the film to crystallize into a dense structure at a lower temperature, thereby avoiding cracking, porosity and other defects during the high-temperature crystallization process. In order to further reduce the residual stress generated during the spraying of multiple layers of liquid film, a heating step can be introduced after each layer is sprayed to remove the organic components in the structure, effectively ensuring the uniformity of the BCZT film, and the surface roughness of the obtained BCZT film is less than 100nm.

[0072] 5) According to the design of the micro-mechanical ultrasonic transducer array, the BCZT film and the transition layer are patterned by wet etching and photoresist mask to expose the bottom electrode, such as Figure 7 and Figure 8 shown.

[0073] In the present invention, before starting to prepare the probe, a multi-model combination method can be used, such as combining finite element simulation with lumped parameter model simulation, to design a piezoelectric micro ultrasonic transducer array with ultra-high working bandwidth and ultra-high sensitivity. Through thin film design, the advantage of the bending mode ultrasonic transducer that is easy to match with the low acoustic impedance of the human body can be brought into play.

[0074] 6) Continue to grow the top electrode on the BCZT film by physical vapor deposition through a photoresist mask according to the design of the micromechanical ultrasonic transducer array, and remove the photoresist mask by stripping, as shown in Figure 8 shown.

[0075] 7) Continue to deposit metal wires and pin pads on the top electrode and the bottom electrode according to the design of the micromechanical ultrasonic transducer array, such as Fig. 9 shown.

[0076] Furthermore, if Figure 1 As shown, multiple ultrasonic unit arrays are arranged to form a micromechanical ultrasonic transducer array, and the micromechanical ultrasonic transducer array is set as a transducer area 9. A pin area 10 is arranged at intervals on one side of the transducer area 9, and electrodes connected to metal wires and pin pads are deposited in the pin area 10.

[0077] Furthermore, the shape of the electrodes in the pin area 10 includes but is not limited to a circle or a polygon.

[0078] The MEMS processing and manufacturing technology of the piezoelectric micro-ultrasonic probe based on the bending mode of the present invention greatly reduces the difficulty of lead wires, improves the operating frequency and manufacturing yield, and realizes the development of an endoscopic imaging array with a high filling factor.

[0079] 8) According to the design of the micro-machined ultrasonic transducer array, deep silicon etching is performed on the other side of the substrate to release the back cavity, such as Fig.10 shown.

[0080] 9) Bonding the substrate with each layer structure processed by the back cavity in step 8) to a printed circuit board, finally obtaining Figure 1 and Figure 2 An endoscopic ultrasound transducer probe based on barium calcium zirconium titanium material is shown.

[0081] Furthermore, the bonding method between the electrode in the pin area and the printed circuit board includes but is not limited to wire bonding, flip-chip soldering or reflow soldering.

[0082] The present invention realizes the graphicization and high-precision deviceization based on the stacking of BCZT thin film materials through MEMS standardized process and layout design, and prepares an ultrasonic endoscopy probe with flexible frequency and high resolution, so that the BCZT material is compatible with the CMOS process and the MEMS process, and has the potential for large-scale integration with the CMOS process while reducing the process cost and improving the uniformity. Compared with the traditional ultrasonic probe generally using the lead-containing material PZT, the present invention is based on the process method of lead-free piezoelectric material, so that the prepared device has higher biosafety and environmental friendliness.

[0083] Compared with the conventional bulk ultrasound probe, the endoscopic ultrasound transducer probe of the present invention has a probe chip based on wafer-level technology. Through finite element analysis, the probe has achieved the same frequency and more than 80% fractional bandwidth design as the bulk ultrasound probe. Specifically, the central frequency of not less than 7.5 MHz and the high working bandwidth imaging requirement of not less than 85% can be achieved. This bandwidth is difficult to achieve with bulk piezoelectric probes. This performance improvement greatly improves the imaging resolution. Fig.11 The present invention shows a PMUT array receiving voltage frequency curve. The design achieves a center frequency of 7.74 MHz and a working bandwidth of 92%, meeting the performance requirements of endoscopic ultrasound imaging. The endoscope system based on the probe of the present invention can have a high signal-to-noise ratio and a high frame rate, an imaging resolution of not less than 225 μm, an ultrasonic blood flow velocity detection range of 10-1000 mm / s, and a contrast ratio between blood flow and surrounding background signals greater than or equal to 30 dB.

[0084] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. An endoscopic ultrasonic transducer probe based on barium calcium zirconium titanium material, characterized in that: The micromechanical ultrasonic transducer array includes a plurality of ultrasonic units; Each of the ultrasonic units includes a substrate layer, a bottom electrode, a piezoelectric layer and a top electrode. The bottom electrode, the piezoelectric layer and the top electrode are sequentially covered on the surface of one side of the substrate layer. A back cavity is formed on the surface of the other side of the substrate layer. The piezoelectric layer is made of BCZT material.

2. The endoscopic ultrasonic transducer probe based on barium calcium zirconium titanium material according to claim 1, characterized in that: A transition layer is provided between the bottom electrode and the piezoelectric layer.

3. The endoscopic ultrasonic transducer probe based on barium calcium zirconium titanium material according to claim 2, characterized in that: The material of the transition layer is selected from LNO or SRO.

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

5. The endoscopic ultrasonic transducer probe based on barium calcium zirconium titanium material according to claim 4, characterized in that: The ratio of the cross-sectional area of ​​the top electrode to that of the back cavity is 1:

2.

6. 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.

7. The endoscopic ultrasonic transducer probe based on barium calcium zirconium titanium material according to claim 1, characterized in that: The central frequency of the endoscopic ultrasonic transducer probe based on barium calcium zirconium titanium material is ≥7.5 MHz.

8. The endoscopic ultrasonic transducer probe based on barium calcium zirconium titanium material according to claim 7, characterized in that: The fractional bandwidth of the endoscopic ultrasonic transducer probe based on the barium calcium zirconium titanium material is greater than or equal to 85%.

9. A method for preparing an endoscopic ultrasonic transducer probe based on a barium calcium zirconium titanium material according to any one of claims 1 to 8, characterized in that: The following steps are involved: 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; According to the design of the micromechanical ultrasonic transducer array, the BCZT film is patterned to expose the bottom electrode; Continuing to grow a top electrode on the BCZT film by physical vapor deposition 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 pin pads on the top electrode and the bottom electrode according to the design of the micromechanical ultrasonic transducer array; According to the design of the micromachined ultrasonic transducer array, deep silicon etching is performed on the other side of the substrate to release the back cavity.

10. The preparation method according to claim 9, characterized in that: The patterning of the BCZT film is completed by wet etching and photoresist mask.

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