阅读说明：本技术 具有亥姆霍兹谐振腔的mems压电超声换能器 (MEMS piezoelectric ultrasonic transducer with Helmholtz resonant cavity ) 是由 孙成亮 朱伟 吴志鹏 王磊 胡博豪 林炳辉 周禹 于 2019-09-10 设计创作，主要内容包括：一种MEMS压电超声换能器,压电式超声换能器(11)形成在衬底层(1)上,该衬底层(1)内形成有亥姆霍兹谐振腔(16),亥姆霍兹谐振腔(16)的谐振频率与压电式超声换能器(11)的谐振频率一致,亥姆霍兹谐振腔(16)包括高度大于压电式超声换能器(11)最大振幅的第一空腔(6),第一空腔(6)的中部下沉形成第二空腔(9),第一空腔(6)通过压电式超声换能器(11)上的通孔(7)与外部连通。本公开明显减小了亥姆霍兹谐振腔的容积,提高了亥姆霍兹谐振腔的谐振频率。将换能器的谐振频率与亥姆霍兹谐振腔匹配可以最终提高MEMS压电超声换能器的谐振频率。(The utility model provides a MEMS piezoelectric ultrasonic transducer, piezoelectric ultrasonic transducer (11) are formed on substrate layer (1), helmholtz resonant cavity (16) is formed in this substrate layer (1), the resonant frequency of helmholtz resonant cavity (16) is unanimous with piezoelectric ultrasonic transducer (11)'s resonant frequency, helmholtz resonant cavity (16) include highly be greater than first cavity (6) of piezoelectric ultrasonic transducer (11) maximum amplitude, the middle part of first cavity (6) sinks and forms second cavity (9), through-hole (7) and outside intercommunication on first cavity (6) through piezoelectric ultrasonic transducer (11). This is disclosed and has obviously reduced the volume of helmholtz resonant cavity, has improved the resonant frequency of helmholtz resonant cavity. Matching the resonant frequency of the transducer to the helmholtz resonator may ultimately increase the resonant frequency of the MEMS piezoelectric ultrasonic transducer.)

1. An MEMS piezoelectric ultrasonic transducer is characterized in that a piezoelectric ultrasonic transducer (11) is formed on a substrate layer (1), a Helmholtz resonant cavity (16) is formed in the substrate layer (1), and the resonant frequency of the Helmholtz resonant cavity (16) is consistent with the resonant frequency of the piezoelectric ultrasonic transducer (11); the Helmholtz resonant cavity (16) comprises a first cavity (6) with the height larger than the maximum amplitude of the piezoelectric ultrasonic transducer (11), a second cavity (9) formed by sinking the middle part of the first cavity (6), and a through hole (7) on the piezoelectric transducer (11); the first cavity (6) is communicated with the outside through a through hole (7).

2. The MEMS piezoelectric ultrasonic transducer according to claim 1, wherein the piezoelectric ultrasonic transducer (11) comprises a piezoelectric stack (12) or a piezoelectric bimorph (10) disposed on the substrate layer (1) to enclose the first cavity (6), and the through hole (7) is communicated with the first cavity (6) after penetrating through the piezoelectric stack (12) and the piezoelectric bimorph (10).

3. The MEMS piezoelectric ultrasonic transducer according to claim 2, wherein the piezoelectric stack (12) comprises an upper electrode (5), a piezoelectric layer (4), a lower electrode (3) and a substrate arranged in this order from top to bottom.

4. MEMS piezoelectric ultrasonic transducer according to any of claims 1 to 3, wherein the first cavity (6) is cylindrical, or cubical, or cuboid shaped.

5. A MEMS piezoelectric ultrasonic transducer according to any one of claims 1 to 3, wherein the second cavity (9) is cylindrical.

6. MEMS piezoelectric ultrasonic transducer according to any of claims 1 to 3, wherein the through-hole (7) is cylindrical, cubic or cuboid shaped.

Technical Field

The utility model belongs to the technical field of ultrasonic transducer, a MEMS piezoelectric ultrasonic transducer who relates to having helmholtz resonant cavity.

Background

An ultrasonic transducer is a transducer device that can convert electrical energy into acoustic energy and vice versa, and thus the ultrasonic transducer can be used for both transmitting and receiving ultrasonic waves. The ultrasonic transducer which is most widely applied at present is based on a piezoelectric transducer, the piezoelectric transducer mainly utilizes the vibration of piezoelectric ceramics, and because the resonant frequency is only related to the thickness of the piezoelectric ceramics, the ultrasonic transducers with different resonant frequencies are difficult to manufacture on the same plane. In addition, the thickness of the piezoelectric ceramic of such transducers is difficult to control to submicron precision, and is therefore unsuitable for high frequencies. The MEMS ultrasonic transducer is provided with a vibrating membrane with small thickness and low rigidity, has small acoustic impedance and can be better coupled with gas or liquid. In addition, the resonant frequency of the MEMS ultrasonic transducer is mainly determined by the plane size, so that the requirement on the processing precision is low. MEMS ultrasonic transducers are gaining more and more attention due to their advantages of high performance and low cost.

MEMS ultrasonic transducers can be classified into capacitive ultrasonic transducers (cMUT) and piezoelectric ultrasonic transducers (pMUT). Compared to cMUT, pmuts do not need to provide a bias voltage and are relatively simple to process and are currently widely used.

With regard to pmuts, extensive research has been conducted to seek improved approaches. Overall, improvements to the various layers, such as electrode shape, mass loading, have been primarily focused, but this has not contributed much to improving the energy conversion efficiency of pmuts.

Helmholtz resonators are a passive acoustic device that can be used for amplification, sound amplification, and sound absorption. By utilizing the characteristics, the sound pressure of sound waves emitted by the pMUT device can be increased when the pMUT device is used, so that the energy conversion efficiency is improved. This type of transducer is called a PSRC (piezoelectric-sound-resonance cavity). When the PSRC emits sound waves, the vibration of the pMUT causes a change in the volume of the helmholtz resonator, causing air to flow at the orifice, creating a flow velocity. When the resonance frequencies of the pMUT and the Helmholtz resonant cavity are consistent, the two structures resonate, a large pressure difference is generated between the Helmholtz resonant cavity and the outside, so that the air flow rate at the orifice is maximized, the air at the orifice flows to impact the orifice, sound waves are radiated outwards according to the vortex sound conversion principle, and the sound pressure of the sound waves is greatly enhanced; when the PSRC receives the acoustic wave, the intensity of the output signal increases due to the amplification of the helmholtz resonator.

In summary, the amplification effect is best when the resonance frequencies of the pMUT and helmholtz resonators are the same. But generally the resonance frequency of a helmholtz resonator is low, which when matched to the pMUT resonance frequency results in a low PSRC resonance frequency, while the size of the device is large. If the Helmholtz resonant cavity is applied to the MEMS piezoelectric ultrasonic transducer, the structure of the PSRC needs to be improved, and the resonant frequency of the Helmholtz resonant cavity is improved.

Disclosure of Invention

In order to be applied to MEMS piezoelectric ultrasonic transducer with the PSRC structure, improve the conversion efficiency of transducer, resonant frequency when improving pMUT and Helmholtz resonant cavity matching simultaneously, this disclosure provides MEMS piezoelectric ultrasonic transducer with Helmholtz resonant cavity.

According to an aspect of the embodiments of the present disclosure, there is provided a MEMS piezoelectric ultrasonic transducer, where the piezoelectric ultrasonic transducer is formed on a substrate layer, a helmholtz resonant cavity is formed in the substrate layer, a resonant frequency of the helmholtz resonant cavity is consistent with a resonant frequency of the piezoelectric ultrasonic transducer, the helmholtz resonant cavity includes a first cavity having a height greater than a maximum amplitude of the piezoelectric ultrasonic transducer, a middle portion of the first cavity is sunk to form a second cavity, and the first cavity is communicated with an outside through a through hole in the piezoelectric ultrasonic transducer.

In the above MEMS piezoelectric ultrasonic transducer, the piezoelectric ultrasonic transducer includes a piezoelectric stack or a piezoelectric bimorph disposed on the substrate layer to seal the first cavity, and the through hole penetrates through the piezoelectric stack and the piezoelectric bimorph and then communicates with the first cavity.

In the above MEMS piezoelectric ultrasonic transducer, the piezoelectric stack includes an upper electrode, a piezoelectric layer, a lower electrode, and a substrate, which are sequentially disposed from top to bottom.

In the above MEMS piezoelectric ultrasonic transducer, the first cavity has a cylindrical shape, a cubic shape, or a rectangular parallelepiped shape.

In the above MEMS piezoelectric ultrasonic transducer, the second cavity is columnar.

In the above MEMS piezoelectric ultrasonic transducer, the through hole has a cylindrical shape, a cubic shape, or a rectangular parallelepiped shape.

The present disclosure combines a MEMS piezoelectric ultrasonic transducer with a helmholtz resonator. The MEMS piezoelectric ultrasonic transducer drives the Helmholtz resonant cavity to produce sound and can be used for transmitting and receiving ultrasonic waves. When the MEMS piezoelectric ultrasonic transducer is used for transmitting ultrasonic waves, the MEMS piezoelectric ultrasonic transducer is used for driving the Helmholtz resonant cavity to produce sound, and when the resonance frequency of the MEMS piezoelectric ultrasonic transducer is consistent with that of the Helmholtz resonant cavity, the amplitude of the sound waves transmitted by the ultrasonic transducer is greatly increased through the Helmholtz resonant cavity, so that the electroacoustic energy conversion efficiency of the ultrasonic transducer is improved; when it is used to receive ultrasonic waves, the output electrical signal may be enhanced by amplification of the Helmholtz cavity.

The height of the first cavity is only slightly larger than the maximum amplitude of the MEMS piezoelectric ultrasonic transducer, but due to the existence of the second cavity on the silicon substrate, the whole structure still meets the forming condition of a Helmholtz resonant cavity. That is, this disclosure has obviously reduced the volume of helmholtz resonator, has improved the resonant frequency of helmholtz resonator. Matching the resonant frequency of the transducer to the helmholtz resonator may ultimately increase the resonant frequency of the MEMS piezoelectric ultrasonic transducer.

Drawings

The present disclosure is described in further detail below with reference to the attached drawings and the detailed description.

Fig. 1 shows a cross-sectional view of a MEMS piezoelectric ultrasonic transducer having a helmholtz resonator according to a first embodiment of the present disclosure.

Fig. 2 shows a top view of the MEMS piezoelectric ultrasonic transducer shown in fig. 1.

Fig. 3 shows a cross-sectional view of a MEMS piezoelectric ultrasonic transducer having a helmholtz resonator according to a second embodiment of the present disclosure.

Fig. 4 shows a top view of the MEMS piezoelectric ultrasonic transducer shown in fig. 3.

Fig. 5 shows a cross-sectional view of a MEMS piezoelectric ultrasonic transducer having a helmholtz resonator according to a third embodiment of the present disclosure.

Fig. 6 shows a top view of the MEMS piezoelectric ultrasonic transducer shown in fig. 5.

FIGS. 7-12 show cross-sectional views of the MEMS piezoelectric ultrasonic transducer shown in FIG. 3 at various stages of processing.

Description of the attached label:

1-substrate layer, 2-sacrificial layer material, 3-lower electrode, 4-piezoelectric layer, 5-upper electrode, 6-first cavity, 7-through hole, 8-neutral plane, 9-second cavity, 10-piezoelectric bimorph, 11-pMUT, 12-piezoelectric lamination, 13-bulk silicon, 14-cylindrical hole, 15-cavity structure and 16-Helmholtz resonant cavity.

In addition, the MEMS piezoelectric ultrasonic transducer is generally called a piezoelectric micro-machined ultrasonic transducer, which is abbreviated as: pMUT. The MEMS capacitive ultrasonic transducer is called a capacitive piezoelectric ultrasonic transducer for short: cMUT.

Detailed Description

As shown in fig. 1 and 2, the MEMS piezoelectric ultrasonic transducer includes pMUT11 and a helmholtz resonator 16 formed on a substrate layer 1 made of silicon material, a resonance frequency of the helmholtz resonator 16 coincides with a resonance frequency of pMUT11, and an amplification of the helmholtz resonator 16 greatly enhances a sound pressure of a sound wave emitted from the ultrasonic transducer, thereby improving an energy conversion efficiency of the ultrasonic transducer.

3-6, to reduce the volume of the Helmholtz cavity 16 and increase the resonant frequency of the Helmholtz cavity 16, the present disclosure sets the height of the first cavity 6 of the Helmholtz cavity 16 to be greater than the maximum amplitude of the MEMS piezoelectric ultrasonic transducer, and sinks the middle of the first cavity 6 to form the second cavity 9. Furthermore, pMUT11 has a through hole 7 communicating with first cavity 6. That is, the cavities 6, 9 and the through-hole 7 together constitute a helmholtz resonator 16 of significantly reduced volume. The first cavity 6 may be cylindrical, or cubic, or rectangular parallelepiped, or other geometric shape. The second cavity 9 may be cylindrical, prismatic or otherwise shaped and the through-hole 7 may be cylindrical, prismatic or otherwise shaped.

As shown in fig. 3 and 4, the piezoelectric stack 12 of pMUT11 is disposed on a substrate layer 1 of silicon material to enclose the first cavity 6. The piezoelectric stack 12 includes a substrate (which may be a silicon layer), a lower electrode 3, a piezoelectric layer 4, and an upper electrode 5, which are sequentially disposed from bottom to top. The piezoelectric stack 12 is used for vibration to generate sound waves or for receiving sound wave vibration to generate electrical signals, wherein the neutral plane 8, also called neutral layer, is located below the piezoelectric layer 4, and in the cross-section shown in the figure, the length of the piezoelectric stack 12 does not change as it bends. The lower electrode 3 is a bulk metal electrode, and metals such as Mo and Al can be selected as electrode materials. The upper electrode 5 is a metal electrode, and metals such as Mo and Al can be selected as electrode materials. The upper electrode 5 is patterned by an etching process, and the shape of the pattern is not limited, and may be, for example, a ring shape. As shown in fig. 5 and 6, piezoelectric bimorph 10 may be used instead of piezoelectric stack 12. The through hole 7 penetrates through the piezoelectric bimorph 10 and the piezoelectric stack 12 and then communicates with the first cavity.

When the MEMS piezoelectric ultrasonic transducer emits ultrasonic waves, the pMUT11 drives the helmholtz resonant cavity 16 to vibrate and produce sound, and when the resonance frequencies of the pMUT11 and the helmholtz resonant cavity 16 are consistent, the sound pressure of the sound waves emitted by the ultrasonic transducer is greatly enhanced through the amplification of the helmholtz resonant cavity 16, so that the energy conversion efficiency of the ultrasonic transducer is improved; when the MEMS piezoelectric ultrasonic transducer receives ultrasonic waves, the output electrical signal can be enhanced by amplification of the helmholtz resonator 16.

This is disclosed for improving the resonant frequency of helmholtz resonator 16, and the means of taking is for reducing helmholtz resonator 16 cavity volume. As the cavity volume decreases, the resonance frequency of the helmholtz resonator 16 increases, according to the following equation. The resonance frequency of the helmholtz resonator 16 is:

wherein c is the sound velocity in the medium, S is the bottom area of the through hole 7, t is the height of the through hole 7, d is the diameter of the through hole 7, and V is the sum of the volumes of the cavity cavities 6 and 9.

The processing method of the MEMS piezoelectric ultrasonic transducer comprises the following steps. As shown in fig. 7, a cylindrical hole 14 is etched in bulk silicon 13. As shown in fig. 8, bulk silicon 13 is further etched to form a cavity structure 15. As shown in fig. 9, the cavity structure 15 is filled with a sacrificial layer material 2 and ground flat. As shown in fig. 10, silicon, a lower electrode 3, a piezoelectric layer 4, and an upper electrode 5 are deposited in this order to form a piezoelectric stack 12. As shown in fig. 11, a pattern is etched on the upper electrode 5 by a photolithography process. As shown in fig. 12, a via 7 is etched in the piezoelectric stack 12, and then the sacrificial layer material 2 is removed.