Focusing sound vortex MEMS (Micro Electro Mechanical System) transducer as well as design method and preparation method thereof

Abstract

The invention relates to the technical field of focused ultrasonic treatment, particle control and ultrasonic transducers, in particular to a design and preparation technology of a micro-electromechanical system (MEMS) device of a highly focused vortex sound field. A design part of the focused sound vortex sound field MEMS device comprises a binary holographic spiral metal electrode, a piezoelectric material and a watertight coupling layer material; the preparation process comprises a clean room photoetching method, a spin-coating sealing method and electrode lead welding. By designing the working frequency of the MEMS device, a focused vortex sound field with an expected focal length can be obtained. According to the design and preparation method of the focusing sound vortex MEMS transducer, accurate dynamic regulation and control of the focal length can be achieved, and a technical scheme which does not need a prism, is economical and effective and is easy to integrate is provided for the application field of a high-quality focusing vortex sound field.

Description

Technical Field

[0001] The present invention relates to the technical fields of focused ultrasound therapy, particle manipulation and ultrasonic transducer, and in particular to a focused acoustic vortex based micro-electromechanical system (MEMS) transducer and a design method and a preparation method thereof. Background Art

[0002] Focused acoustic fields are widely used in ultrasonic imaging, ultrasonic therapy, particle manipulation and other fields. Their focusing performance and preparation cost affect the practical application of focused ultrasonic transducers. Focused acoustic vortex is a special acoustic field with a zero pressure center and a spiral phase wavefront. It can exert acoustic radiation force and torque on particles, realize contactless capture, movement, rotation manipulation, and has good biocompatibility.

[0003] At present, the methods of constructing vortex acoustic fields are mainly divided into two categories: active and passive, but both methods have certain limitations. Specifically, although active phase-controlled technology performs well in flexibility and controllability, its complex circuit system not only hinders the miniaturization process of the equipment, but also limits the large-scale promotion and application of this technology due to its high cost. In contrast, passive structure control technology is highly favored because of its simple structure and easy implementation, but its focusing accuracy can usually only reach the micron level, which is difficult to meet application scenarios with strict requirements for high spatial resolution.

[0004] In view of this, it is particularly urgent to develop a method for constructing focused acoustic vortices that is efficient, economical, flexible and controllable, in order to further explore the huge potential of focused acoustic vortices in fields such as particle manipulation. In recent years, acoustic transducers based on microelectromechanical systems (MEMS) have been developed because they can improve the economic efficiency of devices through mass production, and the developed MEMS transducers have the characteristics of miniaturization and are easy to integrate with existing microscopic platforms, and have the potential to be used in a wide range of different application fields and scenarios. Therefore, the use of MEMS technology to develop acoustic transducers is expected to become an important way to achieve efficient, economical, flexible and controllable focused acoustic vortex construction. Summary of the invention

[0005] The present invention aims at the shortcomings of the prior art, such as insufficient focusing accuracy of the focused acoustic vortex sound field and high cost of the vortex sound field construction method based on the phased array, and provides a focused acoustic vortex MEMS transducer and a design method and a preparation method thereof. The ideal focused spherical sound field has good focusing performance, but a series of transducers need to be placed on the closed surface around the center of the focused vortex, and the completely closed structure greatly limits the practicality. By using a plane to intercept the ideal converging spherical vortex sound field, two sets of equal phase lines with opposite phases can be formed on the plane, so that a single-beam focused acoustic vortex sound field with a limited aperture can be designed based on the Fresnel principle. Using ultraviolet photolithography technology, two clusters of electrodes are engraved on the piezoelectric material. After power is turned on, the local vibration of the piezoelectric substrate caused by the inverse piezoelectric effect generates a spatial sound field, which is coupled and emitted into the liquid medium to form a focused vortex sound field.

[0006] The technical solution of the present invention is as follows:

[0007] On the one hand, the present invention provides a design method for a focused acoustic vortex MEMS transducer, which is characterized by comprising:

[0008] A1. Design a focused acoustic vortex sound field MEMS transducer structure comprising a binary holographic spiral metal electrode, a piezoelectric material and a watertight coupling layer material, wherein the binary holographic spiral metal electrode is divided into two groups of electrodes with opposite phases, which are used to generate a spatial sound field on the piezoelectric material based on the inverse piezoelectric effect after power is applied;

[0009] A2. Designing a photolithography mask for forming a pattern of the binary holographic spiral metal electrode on the piezoelectric material;

[0010] A3. Design the operating frequency of the MEMS device to obtain a focused vortex acoustic field with a desired focal length by adjusting the frequency.

[0011] Furthermore, the focused acoustic vortex sound field is designed based on the Fresnel principle by intercepting two groups of equal phase lines with opposite phases on a certain plane of an ideal converging spherical vortex sound field.

[0012] Furthermore, the two groups of electrodes with opposite phases are composed of binary equal-phase spiral electrodes and connecting electrodes, and each cluster of spiral electrodes has the same initial phase.

[0013] In a second aspect, the present invention provides a method for preparing a focused acoustic vortex MEMS transducer, which is characterized in that it comprises the following steps:

[0014] S1. Designing a binary holographic spiral metal electrode and a photolithography mask according to any one of claims 1 to 3;

[0015] S2. Using ultraviolet lithography technology in a clean room, a binary holographic spiral metal electrode is prepared on a piezoelectric material substrate through a photolithography mask;

[0016] S3. Perform water sealing treatment on the electrode, and form a watertight coupling layer on the electrode by adding a watertight coupling layer material to ensure that the electrode works in a liquid environment;

[0017] S4. Welding electrode leads to connect the electrodes to the power amplifier;

[0018] S5. Given an input signal frequency, an electrical signal is provided to the MEMS device through a power amplifier, thereby generating a focused vortex acoustic field in the liquid medium.

[0019] Furthermore, the ultraviolet photolithography technique includes the steps of adding photoresist, exposure operation and adding developer.

[0020] Furthermore, the water sealing treatment is achieved by spin coating using SU8 spin coating glue, or by gluing a cover glass.

[0021] Furthermore, the electrode lead welding is performed by soldering.

[0022] Preferably, the photolithography mask in step S1 can be designed as a focused acoustic vortex transducer mask with different parameters such as aperture and excitation frequency, so as to improve the utilization rate and economy of the mask and piezoelectric materials.

[0023] Preferably, the piezoelectric material in step S2 can be lithium niobate material, which has high electromechanical coupling coefficient, good temperature stability, wide operating frequency, optical transparency, and is easy to use to prepare focused acoustic fields of different frequencies and high integration of optical microscopy systems. According to the photolithography mask provided in S1, a positive or negative resist can be selected according to the preparation process.

[0024] Preferably, the coupling layer material in step S3 can be SU-8 photoresist. SU-8 photoresist is an epoxy-type, near-ultraviolet negative photoresist, and the thickness of the coupling layer can be controlled by adjusting the rotation speed during the spin coating process, and it can be used as a watertight layer after drying and curing.

[0025] Preferably, the coupling layer material in step S3 can be a cover glass, and the thickness of the cover glass is selected according to the operating frequency of the transducer. The cover glass is mounted on the electrode surface by an adhesive as a watertight layer.

[0026] Preferably, in step S4, one end of the electrode lead is connected to the electrode, and then a sealant is added to make it watertight, so that this end of the lead can be immersed in a liquid environment such as water. The other end of the lead has a matching connector, which can be connected to a power amplifier.

[0027] Preferably, the sound fields of different frequencies emitted in step S5 can be controlled by a programmable signal generator.

[0028] Third, the present invention also provides a focused acoustic vortex MEMS transducer, which is prepared by the above-mentioned preparation method, comprising:

[0029] Piezoelectric material substrate;

[0030] A binary holographic spiral metal electrode is arranged on the piezoelectric material substrate, wherein the electrode is divided into two groups of electrodes with opposite phases; and

[0031] The watertight coupling layer material covering the electrode is used to couple the generated acoustic field into the liquid medium.

[0032] Compared with the prior art, the present invention has the following advantages:

[0033] (1) By designing a binary holographic spiral metal electrode, complex acoustic field distribution control can be achieved on the piezoelectric material, which can generate sound waves with specific phase and amplitude distribution, thereby forming the expected focused vortex acoustic field in space. It can achieve efficient acoustic field focusing and vortex generation using a limited aperture.

[0034] (2) The selection of piezoelectric materials enables the device to stimulate mechanical vibrations through electrical signals, thereby generating sound waves. The watertight coupling layer material ensures that the sound waves can be efficiently transmitted to the liquid medium, while maintaining the sealing of the device to prevent liquid leakage from damaging the device. At the same time, through the inverse piezoelectric effect, the piezoelectric material can convert electrical signals into mechanical vibrations, thereby generating sound waves. This efficient energy conversion and transmission mechanism makes the device highly efficient in energy utilization. Lithium niobate piezoelectric material has optical transparency and can be integrated with optical microscope systems. The transducer device is a planar structure with a flat surface, which is compatible with devices such as cover glasses and microchannels.

[0035] (3) By using a plane to intercept the ideal converging spherical vortex sound field, two sets of equal phase lines with opposite phases can be formed on the plane, thereby designing a single-beam focused acoustic vortex sound field with a limited aperture. This method not only simplifies the structure of the device, but also improves its practicality. Near the design frequency of the transducer, the focal length varies linearly with the excitation frequency. Therefore, the focal length of the focused vortex sound field can be accurately changed by adjusting the signal input frequency.

[0036] (4) Compared with the traditional phased array focused acoustic vortex transducer, there is no need for complex circuits and array element control systems. The transducer with high focusing function is designed based on physical principles and can be directly connected to the positive and negative electrodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of a binary holographic spiral electrode in a focused acoustic vortex MEMS transducer of the present invention;

[0038] Figure 2 Schematic diagram of binary isophase spiral electrode connection

[0039] Figure 3 It is a flow chart of photolithography preparation of focused acoustic vortex acoustic field MEMS device;

[0040] Figure 4 The 40MHz sound field distribution diagram is calculated based on the angular spectrum method, (a) amplitude, (b) phase; DETAILED DESCRIPTION

[0041] The technical solution of the present invention will be described in detail below in conjunction with embodiments and drawings, but this should not limit the protection scope of the present invention.

[0042] This embodiment provides a design and preparation method of a focused acoustic vortex MEMS transducer, which is mainly composed of a piezoelectric material with a metal electrode and a watertight coupling layer. The transducer can generate a highly focused vortex acoustic field in a liquid environment.

[0043] A binary isophase spiral electrode and a connecting electrode are designed for preparing a photolithography mask, including:

[0044] The ideal converging spherical vortex acoustic field is intercepted by a finite plane. Complex sound pressure of an ideal converging spherical vortex sound field with the center at the origin O The expression formula is as follows:

[0045]

[0046] Among them, p0 is the incident wave amplitude, k=ωc is the wave number, ω is the circular frequency, c is the speed of sound, t represents time, and i is the imaginary unit.

[0047] After the MEMS device is connected to the positive and negative electrodes, the two clusters of spiral electrodes excite the piezoelectric material to vibrate, forming an initial sound field with an anti-phase characteristic (phase difference π).

[0048] The expression formula for a set of equal-phase spiral electrodes (connected to the positive electrode) is as follows:

[0049]

[0050] The expression formula of another set of inverse-phase equal-phase spiral electrodes (connected to the negative electrode) is as follows:

[0051]

[0052] Where C2 is a constant, and each integer n corresponds to a set of anti-phase electrode pairs. The value of the integer n determines the aperture R of the transducer. A size.

[0053] The relationship between focal length and frequency is obtained by derivation:

[0054]

[0055] Where h0 is the design focal length, k0 is the wave number corresponding to the design frequency, k is the wave number corresponding to any driving frequency, and C is a constant.

[0056] Near the design frequency, the focal length varies with frequency, and the approximate expression is as follows:

[0057]

[0058] It shows that near the design frequency, the focal length changes linearly with the frequency, and the focal length can be accurately and dynamically controlled by adjusting the driving frequency.

[0059] Two clusters of anti-phase spiral cluster electrodes are connected by adding connecting electrodes to ensure that each cluster of spiral electrodes has the same initial phase, such as Figure 2 shown.

[0060] According to the binary isophase spiral electrode and the interconnecting electrode, a photolithography mask is prepared for preparing MEMS devices in a clean room. That is, in a clean room, ultraviolet photolithography technology is used to print the metal electrode pattern of the MEMS transducer on the piezoelectric material substrate through the steps of adding photoresist, exposure operation and adding developer. Figure 3 As shown. Depending on the positive and negative properties of the developer, different processes can be used to print metal electrodes, all of which can achieve the purpose of accurately printing technical electrode patterns.

[0061] This embodiment uses spin coating to make the metal electrode watertight. The spin coating glue can be SU8. The thickness of the photoresist can be adjusted by adjusting the rotation speed. After drying and hardening, the watertight effect can be achieved. It can also be protected by gluing a cover glass of preferred thickness to protect its working performance in a liquid environment.

[0062] In order to improve economy and yield, multiple focused acoustic vortex MEMS devices with the same or different frequencies can be designed and manufactured on a circular wafer.

[0063] The invention adopts soldering to connect the two metal electrode ends to the wires for inputting signals and energy to the power amplifier.

[0064] The following is an embodiment of a method for designing and preparing a focused acoustic vortex MEMS transducer.

[0065] The design frequency of the MEMS device is 40MHz, the number of electrode circles n=26, the design focal length is 40mm, and the maximum radius of the electrode is R A =70mm, surrounded by water medium.

[0066] When the excitation frequency is the design frequency f0 = 40MHz, the sound field exhibits good focusing characteristics. The spatial sound field is simulated and calculated by the angular spectrum method, such as Figure 4 As shown, the amplitude and phase distribution of the focused acoustic vortex sound field are given.

[0067] The above description is only an implementation mode of the present invention, and does not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A design method for a focused acoustic vortex MEMS transducer, characterized in that: include: A1. Design a focused acoustic vortex sound field MEMS transducer structure comprising a binary holographic spiral metal electrode, a piezoelectric material and a watertight coupling layer material, wherein the binary holographic spiral metal electrode is divided into two groups of electrodes with opposite phases, which are used to generate a spatial sound field on the piezoelectric material based on the inverse piezoelectric effect after power is applied; A2. Designing a photolithography mask for forming a pattern of the binary holographic spiral metal electrode on the piezoelectric material; A3. Design the operating frequency of the MEMS device to obtain a focused vortex acoustic field with a desired focal length by adjusting the frequency.

2. The design method of the focused acoustic vortex MEMS transducer according to claim 1, characterized in that: The focused acoustic vortex sound field is designed based on the Fresnel principle by intercepting two groups of equal phase lines with opposite phases on a certain plane of an ideal converging spherical vortex sound field.

3. The design method of the focused acoustic vortex MEMS transducer according to claim 1, characterized in that: The two groups of electrodes with opposite phases are composed of binary equal-phase spiral electrodes and connecting electrodes, and each cluster of spiral electrodes has the same initial phase.

4. A method for preparing a focused acoustic vortex MEMS transducer, characterized in that: The following steps are involved: S1. Designing a binary holographic spiral metal electrode and a photolithography mask according to any one of claims 1 to 3; S2. Using ultraviolet lithography technology in a clean room, a binary holographic spiral metal electrode is prepared on a piezoelectric material substrate through a photolithography mask; S3. Perform water sealing treatment on the electrode, and form a watertight coupling layer on the electrode by adding a watertight coupling layer material to ensure that the electrode works in a liquid environment; S4. Welding electrode leads to connect the electrodes to the power amplifier; S5. Given an input signal frequency, an electrical signal is provided to the MEMS device through a power amplifier, thereby generating a focused vortex acoustic field in the liquid medium.

5. The method for preparing a focused acoustic vortex MEMS transducer according to claim 4, characterized in that: The ultraviolet photolithography technology includes the steps of adding photoresist, exposure operation and adding developer.

6. The method for preparing a focused acoustic vortex MEMS transducer according to claim 4, characterized in that: The water sealing treatment is achieved by spin coating using SU8 spin coating glue, or by gluing a cover glass.

7. The method for preparing a focused acoustic vortex MEMS transducer according to claim 4, characterized in that: The electrode lead welding adopts tin soldering.

8. A focused acoustic vortex MEMS transducer, characterized in that: The invention is prepared by the preparation method according to any one of claims 4 to 7.

9. The focused acoustic vortex MEMS transducer according to claim 8, characterized in that: include: Piezoelectric material substrate; A binary holographic spiral metal electrode is arranged on the piezoelectric material substrate, wherein the electrode is divided into two groups of electrodes with opposite phases; as well as The watertight coupling layer material covering the electrode is used to couple the generated acoustic field into the liquid medium.

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