CN116809363A - Piezoelectric MEMS ultrasonic transducer imitating Langmuir vibrator and preparation method thereof - Google Patents
Piezoelectric MEMS ultrasonic transducer imitating Langmuir vibrator and preparation method thereof Download PDFInfo
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
- B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
- B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
- B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
- B06B1/06—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction
- B06B1/0607—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using multiple elements
- B06B1/0622—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using multiple elements on one surface
- B06B1/0625—Annular array
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
- B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
- B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
- B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
- B06B1/06—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction
- B06B1/0607—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using multiple elements
- B06B1/0622—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using multiple elements on one surface
- B06B1/0629—Square array
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B06—GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS IN GENERAL
- B06B—METHODS OR APPARATUS FOR GENERATING OR TRANSMITTING MECHANICAL VIBRATIONS OF INFRASONIC, SONIC, OR ULTRASONIC FREQUENCY, e.g. FOR PERFORMING MECHANICAL WORK IN GENERAL
- B06B1/00—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency
- B06B1/02—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy
- B06B1/06—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction
- B06B1/0644—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using a single piezoelectric element
- B06B1/0662—Methods or apparatus for generating mechanical vibrations of infrasonic, sonic, or ultrasonic frequency making use of electrical energy operating with piezoelectric effect or with electrostriction using a single piezoelectric element with an electrode on the sensitive surface
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- Engineering & Computer Science (AREA)
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- Transducers For Ultrasonic Waves (AREA)
Abstract
The invention provides a piezoelectric MEMS ultrasonic transducer of a Langmuir-like vibrator and a preparation method thereof, wherein the piezoelectric MEMS ultrasonic transducer comprises a first silicon layer, a first electrode layer, a piezoelectric layer, a second electrode layer and a second silicon layer which are sequentially arranged from bottom to top; wherein: the first silicon layer is provided with a plurality of array units, the array units are separated by grooves, the grooves penetrate through the piezoelectric layer and the second electrode layer, and the second electrode layer is divided into a plurality of second electrode layer units by the grooves; the second silicon layer comprises a plurality of step-shaped protruding structures, and the protruding structures are respectively positioned on the second electrode layer units; the bump structure comprises an upper second silicon layer and a lower second silicon layer which are coaxially arranged, and the upper second silicon layer is far away from the second electrode layer unit; the area of the upper second silicon layer is smaller than that of the lower second silicon layer. The invention realizes d of Langmuir-like ten thousand vibrators 33 The piezoelectric MEMS ultrasonic transducer can be used for occasions with small size and high precision such as cardiovascular imaging, fingerprint identification and the like.
Description
Technical Field
The invention relates to the technical field of MEMS ultrasonic transducers, in particular to a piezoelectric MEMS ultrasonic transducer imitating Langmuir vibrator and a preparation method thereof.
Background
Ultrasound is increasingly used in industry and biomedical fields, such as non-destructive evaluation, ultrasound driving, medical imaging, therapeutic ultrasound, and particle and cell manipulation. Ultrasound can be excited by many different methods including piezoelectric, magnetostrictive, and photoacoustic effects. Among them, the piezoelectric effect is the most common and most commonly used. Conventional piezoelectric ultrasonic transducers (langevin ultrasonic transducers) typically have a layer of piezoelectric material with a thin, highly conductive electrode layer, such as Au or Pt, in between, and typically an adhesion layer, such as Cr or Ti, underneath, and connected to wires. Such conventional ultrasonic transducers employ a longitudinal vibration mode (d 33 Vibration mode). However, the Langmuir ultrasonic transducer is oversized and has a great limit in application in many occasions.
With the rapid development of micro-electro-mechanical system (MEMS) technology, micro-mechanical ultrasonic transducers based on capacitive (cMUT) and piezoelectric (pMUT) can significantly reduce the size of the device for various complex high-resolution applications, and the low power consumption and better acoustic impedance matching medium make it have wider application scenarios. In general, cmuts have very high electromechanical coupling coefficients, but they suffer from limited vertical deformation, nonlinear driving effects, and high dc bias voltages. With advances in piezoelectric material technology, pmuts are beginning to become increasingly alternatives to cmuts. The most widely used piezoelectric thin film materials at present are lead zirconium titanate (PZT) and aluminum nitride (AlN). PZT has better piezoelectric properties than AlN, so it is often used in applications where high performance devices are required.
Through the search and discovery aiming at the prior art:
chao Wang, zheyao Wang et al, IEEE SENSORS JOURNAL written "A Micromachined Piezoelectric Ultrasonic Transducer Operating in d 33 Mode Using Square Interdigital Electrodes ", reports a working at d 33 In mode (pMUT), the top electrode is a square interdigital electrode, in-plane polarization and interdigital electricityPole pMUT working at d 33 In the mode, the PZT converts in-plane stress induced by ultrasonic pressure into in-plane direction charge; the square interdigital electrode fully utilizes the stress of the diaphragm to improve the sensitivity of the device and increase the capacitance of the device, and the pMUT is optimized by changing the size of the square interdigital electrode instead of the thickness of the PZT thin film. This operation is at d 33 The modal pMUT has a large ultrasound transmit/receive area, and is suitable for ultrasound applications requiring high directivity.
Yuri Kusano, itaru Ishii et al, IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL written "High-SPL Air-Coupled Piezoelectric Micromachined Ultrasonic Transducers Based on% scanin Thin-Film", and reported a pMUT of High performance 36% scandium-doped aluminum nitride (scanin) Film having a piezoelectric coefficient 2 times higher than AlN and a sound pressure level of 105dB at 10cm at an operating frequency of 100kHz, while the attenuation in the 2m range was only 30dB.
S Sadeghopour, M Kraft et al, journal ofMicromechanics and Microengineering written "Design and fabrication strategy for an efficient lead zirconate titanate based piezoelectric micromachined ultrasound transducer", introduced a design and fabrication method for pMUT based on PZT thin films to improve performance of pMUTs, and studied the effect of the optimum thickness, electrode radius and residual stress of piezoelectric ceramics on the resonant frequency of piezoelectric ceramics by using finite element simulation and analytical equations.
To sum up: the piezoelectric MEMS ultrasonic transducer reported at present mostly adopts d 31 Vibration mode, and thickness of the piezoelectric film is difficult to be increased due to process limitation, resulting in large sound pressure level and directivity limitation for d 33 The mode can only be realized by adopting an interdigital electrode method at present. The piezoelectric MEMS ultrasonic transducer which has the advantages of small size, thick film preparation, sound pressure output enhancement through a matching layer and the like is not reported at present.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a piezoelectric MEMS ultrasonic transducer of a Langmuir-like vibrator and a preparation method thereof.
According to one aspect of the invention, a piezoelectric MEMS ultrasonic transducer of a Langmuir-like resonator is provided, and the piezoelectric MEMS ultrasonic transducer comprises a first silicon layer, a first electrode layer, a piezoelectric layer, a second electrode layer and a second silicon layer which are sequentially arranged from bottom to top; wherein:
the first silicon layer is provided with a plurality of array units, the array units are separated by grooves, the grooves penetrate through the piezoelectric layer and the second electrode layer, and the second electrode layer is divided into a plurality of second electrode layer units by the grooves;
the second silicon layer comprises a plurality of step-shaped protruding structures, and the protruding structures are respectively positioned on the second electrode layer units;
the bump structure comprises an upper second silicon layer and a lower second silicon layer which are coaxially arranged, and the upper second silicon layer is far away from the second electrode layer unit; the area of the upper second silicon layer is smaller than that of the lower second silicon layer.
Further, the array units may be arranged in a rectangular array or a circular array.
Further, the thickness of the upper second silicon layer is equal to that of the lower second silicon layer, and the thicknesses of the upper second silicon layer and the lower second silicon layer are half of that of the second silicon layer.
Further, the piezoelectric MEMS ultrasonic transducer further includes a lead for leading out the first electrode layer and the second electrode layer of each array unit.
According to a second aspect of the present invention, there is provided a method for manufacturing the piezoelectric MEMS ultrasonic transducer of the langevin vibrator, the method comprising:
providing two double polished silicon wafers, wherein the thickness of the second silicon wafer is larger than that of the first silicon wafer;
forming a first metal layer on one side of the first silicon wafer and forming a second metal layer on one side of the second silicon wafer;
providing a piezoelectric material sheet, and respectively bonding two sides of the piezoelectric material sheet with the first metal layer and the second metal layer;
depositing an oxide layer or a metal layer on one side of the second silicon wafer far away from the piezoelectric material sheet, forming a pattern through photoetching, and then etching the oxide layer or the metal layer to serve as a first hard mask;
after the pattern is formed by photoetching, etching the second silicon wafer by deep silicon, and stopping etching when the second silicon wafer is etched to half of the thickness of the second silicon wafer;
after photoresist is washed away, etching the silicon layer left by the second silicon wafer by using the first hard mask deep silicon, and stopping etching after etching the second metal layer;
providing a second hard mask, bonding the second hard mask to the second metal layer, and etching the second metal layer by using the second hard mask;
etching the piezoelectric material layer to expose the first metal layer, and forming a plurality of array units on the first silicon wafer to obtain the piezoelectric MEMS ultrasonic transducer imitating the Langmuir oscillator.
Further, the thickness of the two double polished silicon wafers is determined according to the sound velocity of the material and the required resonance frequency.
Further, the deep silicon etches the second silicon wafer, wherein: the deep silicon etching pattern includes any one of a circle and a polygon.
Further, the second hard mask is formed by laser cutting, the material of the second hard mask is PI adhesive tape, and the pattern of the second hard mask is square.
Further, the etching away the piezoelectric material layer includes: the piezoelectric material layer is etched by ion beam etching or wet etching.
Further, the first metal layer is used as a first electrode layer of the ultrasonic transducer, the second metal layer is used as a second electrode layer of the ultrasonic transducer, and after the first metal layer is exposed, the method further comprises the steps of: the first electrode layer and the second electrode layer of each array unit are led out through a wire bonding machine so as to facilitate the excitation and collection of signals.
Compared with the prior art, the invention has at least one of the following beneficial effects:
the invention works at d through MEMS technology 33 The size of the ultrasonic transducer in the vibration mode is reduced to the micron level, the miniaturization of the traditional Langmuir ultrasonic transducer is realized, the performance of the piezoelectric MEMS ultrasonic transducer is greatly improved, and the ultrasonic transducer can be used for application scenes such as ultrasonic imaging, nondestructive detection, high-precision distance measurement and the like.
Drawings
Other features, objects and advantages of the present invention will become more apparent upon reading of the detailed description of non-limiting embodiments, given with reference to the accompanying drawings in which:
FIG. 1 is a schematic structural diagram of a piezoelectric MEMS ultrasonic transducer with a pseudo-Langmuir oscillator according to an embodiment of the present invention;
FIG. 2 is a schematic side view of a piezoelectric MEMS ultrasonic transducer with a pseudo-Langmuir oscillator according to an embodiment of the present invention;
FIG. 3 is a schematic top view of a piezoelectric MEMS ultrasonic transducer with a pseudo-Langmuir oscillator according to an embodiment of the present invention;
FIG. 4 is a flowchart of a method for manufacturing a piezoelectric MEMS ultrasonic transducer with a pseudo-Langmuir oscillator according to an embodiment of the present invention;
in the figure: 1 is a second silicon layer, 2 is a second electrode layer, 3 is a piezoelectric layer, 4 is a first electrode layer, and 5 is a first silicon layer.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the present invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications could be made by those skilled in the art without departing from the inventive concept. These are all within the scope of the present invention.
With the development of electronic devices, piezoelectric MEMS ultrasonic transducers with higher sound pressure levels and better directivity have become a necessary trend. For this reason, the embodiment of the invention provides a piezoelectric MEMS ultrasonic transducer of a langevin vibrator, referring to fig. 1-3, the piezoelectric MEMS ultrasonic transducer comprises a first silicon layer 5, a first electrode layer 4, a piezoelectric layer 3, a second electrode layer 2 and a second silicon layer 1 which are sequentially arranged from bottom to top; wherein: the first silicon layer 5 is provided with a plurality of array units, the array units are separated by grooves, the grooves penetrate through the piezoelectric layer 3 and the second electrode layer 2, and the second electrode layer 2 is divided into a plurality of second electrode layer units by the grooves; the second silicon layer 1 comprises a plurality of step-shaped protruding structures, the number of the protruding structures is equal to that of the array units, and the protruding structures are respectively positioned on the second electrode layer units; the bump structure comprises an upper second silicon layer and a lower second silicon layer which are coaxially arranged, and the upper second silicon layer is far away from the second electrode layer unit; the area of the upper second silicon layer is smaller than that of the lower second silicon layer, and the piezoelectric MEMS ultrasonic transducer with a unique horn structure is formed.
In some embodiments, because the energy of a single array unit (array element) is insufficient, multiple array units can provide more energy or can realize functions such as phased array, so as to realize more applications, the array shape of the multiple array units is rectangular array or annular array, specifically, the annular array means that the multiple array units are firstly arranged into a first circular shape, then are arranged into the first circular shape in a progressive manner, form a concentric second circular shape by being arranged with a smaller radius, and are sequentially progressively arranged to the center of a circle, so as to form an array.
In some embodiments, the thickness of the upper second silicon layer and the lower second silicon layer are equal, which is half the thickness of the second silicon layer 1, and the equal thickness is beneficial to matching acoustic impedances.
In some implementations, the piezoelectric MEMS ultrasound transducer in the examples of the invention further includes leads for leading out the first electrode layer 4 and the second electrode layer 2 of each array unit.
Compared with the traditional piezoelectric MEMS ultrasonic transducer, the piezoelectric MEMS ultrasonic transducer of the pseudo-Langmuir vibrator has the advantage of small size and excellent ultrasonic performance.
The invention also provides a preparation method of the piezoelectric MEMS ultrasonic transducer of the Langmuir-like hundred thousand vibrators, which comprises the following steps:
s1, providing two double polished silicon wafers, wherein the thickness of a second silicon wafer is larger than that of a first silicon wafer;
s2, forming a first metal layer on one side of the first silicon wafer and forming a second metal layer on one side of the second silicon wafer;
s3, providing a piezoelectric material sheet as a piezoelectric material layer (piezoelectric layer), and respectively bonding two sides of the piezoelectric material sheet with the first metal layer and the second metal layer to form a piezoelectric wafer;
s4, depositing an oxide layer or a metal layer on one side of the second silicon wafer far away from the piezoelectric material sheet, forming a pattern through photoetching, and then etching the oxide layer or the metal layer to serve as a first hard mask;
s5, etching the second silicon wafer by deep silicon after the pattern is formed by photoetching, and stopping etching when the second silicon wafer is etched to half of the thickness of the second silicon wafer;
s6, after photoresist is washed away, etching the silicon layer left by the second silicon wafer by using the first hard mask deep silicon, and stopping etching after etching the second metal layer to form an array;
s7, providing a second hard mask, bonding the second hard mask to the second metal layer, and etching the second metal layer by using the second hard mask;
and S8, etching the piezoelectric material layer to expose the first metal layer so as to facilitate wiring, and forming a plurality of array units on the first silicon wafer to obtain the piezoelectric MEMS ultrasonic transducer imitating the Langmuir vibrator.
According to the embodiment of the invention, the size of the ultrasonic transducer working in the d33 vibration mode is reduced to the micron level through the MEMS process, the miniaturization of the traditional Langmuir ultrasonic transducer is realized, the performance of the piezoelectric MEMS ultrasonic transducer is greatly improved, and the piezoelectric MEMS ultrasonic transducer can be used for application scenes such as ultrasonic imaging, nondestructive detection, high-precision distance measurement and the like.
In some embodiments, in S1, the double polished silicon wafer is used as a substrate, and the thickness of the two double polished silicon wafers is determined according to the sound velocity of the material and the required resonance frequency. Preferably, two double polished silicon wafers with strictly controlled thicknesses are selected, wherein the thickness of one silicon wafer is twice that of the other silicon wafer; for example, the thickness of the two double polished silicon wafers is 200 μm and 400 μm respectively. In other embodiments, the two thicknesses may also be sized according to the speed of sound of the material and the desired resonant frequency, and are not limited to a relationship of twice the thickness. The substrate materials include, but are not limited to, si, siC, ITO glass, gallium arsenide, aluminum nitride ceramic plates and other rigid substrates and PDMS, PI and other flexible substrates, and when other materials are used, the substrates can be etched by adopting an ion beam etching mode.
In some embodiments, in S2, the metal sputtered by the first metal layer and the second metal layer is a metal material that is highly conductive and suitable for use as an electrode, including but not limited to Au, pt, cu, al, and the like.
In some embodiments, in S3, the sheet of piezoelectric material is a piezoelectric material, including but not limited to PZT piezoceramics, znO, alN, PMN-PT, PVDF, or the like; the thickness of the piezoelectric material sheet is 100 mu m, and compared with the MEMS technology in the prior art, the method provided by the embodiment of the invention realizes the preparation of the thick film in the piezoelectric MEMS ultrasonic transducer, and the thickness of the piezoelectric material sheet can be adjusted according to the requirement of the practical application resonance frequency. And bonding the sputtered two silicon wafers and the piezoelectric material sheet through conductive silver paste.
In some embodiments, in S4, a hard mask is required to be made in advance because the second deep silicon etch cannot use photoresist as a mask. And depositing an oxide layer or a metal layer on the thicker side of the silicon wafer, namely the second silicon wafer by a Plasma Enhanced Chemical Vapor Deposition (PECVD) method, wherein the thickness of the oxide layer or the metal layer is mainly determined according to deep silicon etching, generally 200um Si is etched, about 3um silicon oxide is needed, if the silicon layer is not too thick, generally hundreds of nm, forming a pattern by photoetching, and then etching the oxide layer or the metal layer by reactive ion etching to serve as a first hard mask.
In some embodiments, in S5, etching is stopped when the second silicon wafer is half as thick, so as to make a horn-like shape to improve the transmission efficiency of sound, and the equal thickness is beneficial to matching of acoustic impedances. The deep silicon etching pattern includes any one of a circle and a polygon, such as a rectangle, a triangle, or other polygons, and of course, in other embodiments, other deep silicon etching patterns may be used to facilitate the arrangement, so long as the same functions as those in the embodiments of the present invention can be achieved.
The diameter or side length of the array units is related to the resonance frequency, the number of the array units is determined according to the specific application scenario and the size, in some embodiments, in S6, the array units are arranged as rectangular arrays, the number is 5*5, the diameter or side length of the array units in the array is 500 μm, in other embodiments, any suitable adjustment can be made on the number of the rectangular arrays, the diameter or side length of the array units in the array according to the required resonance frequency, and a ring array can be also adopted, so long as the same functions as those in the embodiments of the present invention can be achieved.
In some embodiments, in S7, the second hard mask is formed by laser cutting, the material of the second hard mask being a high temperature resistant material, such as PI tape; the pattern of the second hard mask is required to be able to etch the underlying first metal layer and piezoelectric material layer, preferably the pattern of the second hard mask is square.
In some embodiments, in S8, etching away the piezoelectric material layer includes: the piezoelectric material layer is etched by ion beam etching or wet etching.
The first metal layer serves as a first electrode layer of the ultrasonic transducer and the second metal layer serves as a second electrode layer of the ultrasonic transducer, and in some embodiments, after exposing the first metal layer, further comprises: the first electrode layer and the second electrode layer of each array unit are led out through a wire bonding machine so as to facilitate the excitation and collection of signals.
In the embodiment of the invention, a MEMS technology is adopted to prepare a top hard mask, namely a first hard mask, which is used as a mask for step etching; secondly, forming a horn shape of top silicon, namely a second silicon wafer, through two-step deep silicon etching, wherein the first-step deep silicon etching uses photoresist as a mask for patterning, the top electrode layer, namely a second metal layer, is etched, and the second-step deep silicon etching uses a top hard mask as a mask; finally, the patterned PI thick adhesive tape is cut by laser and used as a second hard mask, the top electrode layer is etched by ion beams, and the piezoelectric material layer is etched by wet etching or ion beams so as to expose the bottom electrode layer, namely the first metal layer. The embodiment of the invention imitates the Lang's Ten-thousand vibrator structure to finish the manufacture of a unique horn structure, realizes the preparation of a thick film in the piezoelectric MEMS ultrasonic transducer, and is different from the d31 vibration mode of the traditional piezoelectric MEMS ultrasonic transducer, the d31 mode is that a piezoelectric sheet takes two sides as anchor points to vibrate up and down. The piezoelectric MEMS ultrasonic transducer of the Langmuir-like vibrator can be used for occasions with small size, high precision and the like such as cardiovascular imaging, fingerprint identification and the like, and um-level devices can be made into single or multiple devices according to the application scene requirements, for example, in the cardiovascular imaging, the devices can be integrated on a cardiac catheter, so that the ultrasonic intracardiac imaging is realized; in fingerprint identification, because of the small-size characteristic of the device, the integration is possible, so that the device can be integrated on a smart phone or other intelligent equipment to realize ultrasonic fingerprint identification.
In a specific embodiment, as shown in fig. 4, the operation flow of the preparation method of the piezoelectric MEMS ultrasonic transducer with the lang-hundred thousand oscillators can be subdivided into 6 steps, which is specifically described as follows:
first, as shown in fig. 4 (a), metal layers are sputtered on two silicon wafers with different thicknesses to serve as a top electrode layer, namely a second electrode layer, and a bottom electrode layer, namely a first electrode layer, respectively, and then the silicon wafers are bonded on two sides of the piezoelectric material piece through conductive silver paste, and the metal layers face the piezoelectric material piece.
As a preferred embodiment, the metal of the top electrode layer and the bottom electrode layer is Au, and the thickness is 300nm.
As a preferred embodiment, the piezoelectric material sheet is a PZT piezoelectric ceramic sheet having a thickness of 100 μm.
As a preferred embodiment, the thickness of the two silicon wafers is 400 μm and 200 μm respectively, wherein the 400 μm silicon wafer is the top silicon layer, i.e. the second silicon layer, and the 200 μm silicon wafer is the bottom silicon layer, i.e. the first silicon layer.
Second, as shown in fig. 4 (b), a metal layer or an oxide layer is deposited on the top silicon layer, then a photoresist is coated on the metal layer or the oxide layer for 5 μm, pre-baking is performed for 90s, exposure is performed for 45s, development is performed for 50s, deionized water is performed for 30s, nitrogen is used for drying, post-baking is performed for 12min, and the metal layer or the oxide layer is etched, and the remaining metal layer or oxide layer is used as a first hard mask for subsequent etching.
As a preferred embodiment, the metal layer or oxide layer is SiO 2 The method comprises the steps of carrying out a first treatment on the surface of the The thickness of the metal layer or oxide layer is 5 μm.
As a preferred embodiment, the metal layer or oxide layer is etched to form an array of 5*5, the array elements are circular with a diameter of 250 μm, and the array element pitch, i.e. the size of the trenches between the array elements, is 1000 μm.
And thirdly, as shown in (c) of fig. 4, coating photoresist on the top silicon layer for 5 mu m, pre-baking for 90s, exposing for 45s, developing for 50s, washing with deionized water for 30s, drying with nitrogen, post-baking for 12min, etching the top silicon layer with deep silicon, and stopping etching with deep silicon after the second metal layer on the second silicon layer is exposed.
As a preferred embodiment, the top silicon layer etches an array of arrays patterned 5*5, the array elements being circular with a diameter of 500 μm, the array element spacing being 1000 μm.
A fourth step of using SiO formed in the second step as shown in FIG. 4 (d) 2 And taking the layer as a first hard mask, performing deep silicon etching, and detecting the etching depth through a step instrument during etching.
As a preferred embodiment, the deep silicon etch has an etch depth of 200 μm.
And fifth, as shown in (e) of fig. 4, bonding the second hard mask cut by laser to the top silicon layer, and etching the second metal layer by ion beam etching to form a pattern of the top electrode.
As a preferred embodiment, the laser cut second hard mask material is a thick PI tape;
as a preferred embodiment, the pattern of the hard mask is 700 μm by 700 μm square in order to etch the underlying first metal layer and piezoelectric material layer through the second hard mask.
Sixth, as shown in fig. 4 (f), after the ion beam etching in the fifth step, wet etching the PZT piezoelectric layer to expose the bottom electrode layer for routing, immersing the wafer in the configured etching solution for etching, and stirring the etching solution by using a magnetic stirrer to improve the etching uniformity and speed; then placing the etched wafer into a prepared HNO3 solution for soaking for 3min; finally, the mixture is put into deionized water to be soaked for a few minutes so as to be cleaned to remove surface impurities. Drying with nitrogen and drying in vacuum.
As a preferred embodiment, the wet etched mask is still a PI thick tape hard mask of step five.
As a preferred embodiment, the top electrode and the bottom electrode of each array element are led out by a wire bonding machine after the preparation step is finished, so that the excitation and the acquisition of signals are facilitated;
as a preferred embodiment, a layer of biocompatible material Parylene-N film with the thickness of 2 mu m is deposited after the lead wire is finished, and the biocompatible material Parylene-N film has the effect of matching with the acoustic impedance of a specific material in a specific scene.
The foregoing describes specific embodiments of the present invention. It is to be understood that the invention is not limited to the particular embodiments described above, and that various changes and modifications may be made by one skilled in the art within the scope of the claims without affecting the spirit of the invention. The above-described preferred features may be used in any combination without collision.
Claims (10)
1. The piezoelectric MEMS ultrasonic transducer of the Langmuir-like vibrator is characterized by comprising a first silicon layer, a first electrode layer, a piezoelectric layer, a second electrode layer and a second silicon layer which are sequentially arranged from bottom to top; wherein:
the first silicon layer is provided with a plurality of array units, the array units are separated by grooves, the grooves penetrate through the piezoelectric layer and the second electrode layer, and the second electrode layer is divided into a plurality of second electrode layer units by the grooves;
the second silicon layer comprises a plurality of step-shaped protruding structures, and the protruding structures are respectively positioned on the second electrode layer units;
the bump structure comprises an upper second silicon layer and a lower second silicon layer which are coaxially arranged, and the upper second silicon layer is far away from the second electrode layer unit; the area of the upper second silicon layer is smaller than that of the lower second silicon layer.
2. The piezoelectric MEMS ultrasonic transducer of a pseudo-langevin transducer of claim 1, wherein the array elements are arranged in a rectangular array or a circular array.
3. The piezoelectric MEMS ultrasonic transducer of a langevin transducer of claim 1, wherein the upper second silicon layer and the lower second silicon layer are equal in thickness and are each half the thickness of the second silicon layer.
4. The piezoelectric MEMS ultrasonic transducer of a pseudo-langevin transducer of claim 1, further comprising leads for extracting the first electrode layer and the second electrode layer of each array element.
5. A method of manufacturing a piezoelectric MEMS ultrasonic transducer of a langevin vibrator as claimed in any one of claims 1 to 4, comprising:
providing two double polished silicon wafers, wherein the thickness of the second silicon wafer is larger than that of the first silicon wafer;
forming a first metal layer on one side of the first silicon wafer and forming a second metal layer on one side of the second silicon wafer;
providing a piezoelectric material sheet, and respectively bonding two sides of the piezoelectric material sheet with the first metal layer and the second metal layer;
depositing an oxide layer or a metal layer on one side of the second silicon wafer far away from the piezoelectric material sheet, forming a pattern through photoetching, and then etching the oxide layer or the metal layer to serve as a first hard mask;
after the pattern is formed by photoetching, etching the second silicon wafer by deep silicon, and stopping etching when the second silicon wafer is etched to half of the thickness of the second silicon wafer;
after photoresist is washed away, etching the silicon layer left by the second silicon wafer by using the first hard mask deep silicon, and stopping etching after etching the second metal layer;
providing a second hard mask, bonding the second hard mask to the second metal layer, and etching the second metal layer by using the second hard mask;
etching the piezoelectric material layer to expose the first metal layer, and forming a plurality of array units on the first silicon wafer to obtain the piezoelectric MEMS ultrasonic transducer imitating the Langmuir oscillator.
6. The method of manufacturing a piezoelectric MEMS ultrasonic transducer of a langevin vibrator according to claim 5, wherein the thickness of the two pieces of the double polished silicon wafer is determined according to the sound velocity of the material and the required resonance frequency.
7. The method of fabricating a piezoelectric MEMS ultrasonic transducer of a langevin vibrator of claim 5, wherein the deep silicon etches the second silicon wafer, wherein: the deep silicon etching pattern includes any one of a circle and a polygon.
8. The method for manufacturing a piezoelectric MEMS ultrasonic transducer of a langevin vibrator according to claim 5, wherein the second hard mask is formed by laser cutting, the material of the second hard mask is PI tape, and the pattern of the second hard mask is square.
9. The method of manufacturing a piezoelectric MEMS ultrasonic transducer of a langevin vibrator according to claim 5, wherein the etching away the piezoelectric material layer comprises: the piezoelectric material layer is etched by ion beam etching or wet etching.
10. The method for manufacturing a piezoelectric MEMS ultrasonic transducer of a langevin vibrator according to claim 5, wherein the first metal layer is used as a first electrode layer of the ultrasonic transducer, the second metal layer is used as a second electrode layer of the ultrasonic transducer, and after exposing the first metal layer, the method further comprises: the first electrode layer and the second electrode layer of each array unit are led out through a wire bonding machine so as to facilitate the excitation and collection of signals.
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