CN118041279A - PMUT structure with mass block and electronic equipment comprising same - Google Patents

Abstract

The invention relates to a PMUT structure with a first void portion and an electronic device comprising the same. The PMUT structure includes: a substrate provided with at least one cavity; at least one PMUT corresponding to the at least one cavity, wherein the PMUT comprises a first electrode layer, a piezoelectric layer and a second electrode layer, and one side and the other side of the piezoelectric layer are respectively provided with the first electrode layer and the second electrode layer; and at least one mass corresponding to the at least one cavity, disposed above the PMUT and opposite the corresponding cavity location. The PMUT structure can adjust the frequency of the PMUT without changing the overall shape and the size of the PMUT and affecting the acoustic performance of the PMUT, thereby obtaining the PMUT array with large bandwidth and good acoustic performance.

Description

PMUT structure with mass block and electronic equipment comprising same

Technical Field

Embodiments of the present invention relate to the field of semiconductors, and more particularly, to a PMUT structure with a mass and an electronic device including the same.

Background

A piezoelectric micromachined ultrasonic transducer (Piezoelectric Micromachined Ultrasonic Transducer, PMUT) is a MEMS (Micro-Electro-MECHANICAL SYSTEM) device that uses the positive and negative piezoelectric effects of piezoelectric materials to vibrate a piezoelectric film, thereby transmitting or receiving ultrasonic signals. The PMUT can be used as an actuator to emit sound waves and can be used as a sensor to receive sound waves, and the cost of the PMUT is greatly reduced based on the mass production of MEMS standard processes and wafer level packaging, so that the PMUT is very suitable for large-scale commercial application. The PMUT has good application prospects in the aspects of ultrasonic ranging, ultrasonic imaging, ultrasonic nondestructive testing, ultrasonic fingerprint identification, ultrasonic flow detection, ultrasonic mechanical feedback and the like, and can be used in specific products and scenes such as an ultrasonic imager, an ultrasonic radar, a sonar detection, a sweeping robot, an ultrasonic smoke alarm, an ultrasonic flowmeter and the like. The above applications all relate to the transmission and reception of ultrasonic signals of PMUTs, so that the transmission and reception performance of PMUTs are key indexes thereof, and determine the advantages and disadvantages of products.

The bandwidth of PMUT is one of its core parameters, taking an ultrasound imager as an example, high frequency ultrasound is required for better resolution, on the basis of which a large ultrasound bandwidth is a necessary condition for obtaining high depth-direction resolution. In general, the higher the frequency is, the higher the requirement of the transducer on the large bandwidth is, taking the conventional 70% ultrasonic bandwidth index as an example, the frequency range of-6 dB bandwidth satisfying the transducer with the center resonance frequency of 1MHz is 700kHz (650 kHz-1350 kHz), the frequency range of the transducer with the center resonance frequency of 5MHz is increased to 3.5MHz (3.25 MHz-6.75 MHz), and the frequency range satisfying the 70% bandwidth is increased to 7MHz (6.5 MHz-13.5 MHz) for the PMUT with the center resonance frequency of 10 MHz. The higher the center resonant frequency, the wider the frequency response range of the device meeting bandwidth requirements, and the more difficult it is to achieve. However, the low bandwidth is one of the inherent characteristics of PMUTs, and in general, the higher the frequency, the lower the bandwidth, for example, the bandwidth of PMUTs with a central resonance frequency of 1MHz can exceed 100%, while when the central resonance frequency is raised to 10MHz, the bandwidth is very narrow, even as low as below 10%, which severely limits the resolution capability of PMUTs in the depth direction, and the requirements of practical application scenarios on performance indexes of PMUTs cannot be met. Increasing the bandwidth of PMUTs, especially high frequency PMUTs, is a major issue in achieving their application goals. Thus, there is also a real need to select different PMUTs in a PMUT array to have different or appropriate center resonant frequencies to meet the bandwidth of the PMUT.

For insufficient PMUT bandwidth, forming an array by integrating multiple frequency PMUTs is an effective means. It is well known that PMUT acoustic emission performance is positively correlated with a fill factor, the higher the fill factor, the greater the emitted sound pressure. One of the advantages of PMUTs is a large-scale two-dimensional array, three-dimensional high-resolution detection is realized, however, the deflectable angle of an ultrasonic phased array and the focusing degree of sound waves are related to the ratio of the center distances between two adjacent PMUT cells to the ultrasonic wavelength, and a PMUT array with smaller center distance sizes in all directions needs to be designed. There is therefore a need for a large bandwidth PMUT array development scheme that has small size limitations on the PMUT center-to-center spacing and small impact on its acoustic transmit and receive performance.

Disclosure of Invention

The present invention has been made to alleviate or solve at least one of the above-mentioned problems of the prior art.

According to an aspect of an embodiment of the present invention, there is provided a PMUT structure comprising:

a substrate provided with at least one cavity;

at least one PMUT corresponding to the at least one cavity, wherein the PMUT comprises a first electrode layer, a piezoelectric layer and a second electrode layer, and one side and the other side of the piezoelectric layer are respectively provided with the first electrode layer and the second electrode layer; and

At least one mass corresponding to the at least one cavity is disposed above the PMUT and opposite the corresponding cavity location.

Embodiments of the present invention also relate to an electronic device comprising the PMUT structure described above.

Drawings

These and other features and advantages of the various embodiments of the disclosed invention will be better understood from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate like parts throughout the several views, and wherein:

FIG. 1A is a schematic cross-sectional view of a known PMUT structure;

fig. 1B is a schematic cross-sectional view of a conventional PMUT array structure;

Fig. 2-5 are schematic cross-sectional views of PMUT structures according to various exemplary embodiments of the invention;

FIG. 6 is a schematic top view of the PMUT structure of FIG. 3, where the structure shown in FIG. 3 corresponds to section A-A' in FIG. 6;

FIG. 7A is a graph of displacement versus frequency for the PMUT structure of FIG. 1A;

FIG. 7B is a graph of displacement versus frequency for the PMUT structure of FIG. 1A after adding a first void portion;

fig. 7C and 7D are graphs of displacement versus frequency for the PMUT structure of fig. 3, wherein the masses corresponding to fig. 7C and 7D differ in mass;

Fig. 8A and 8B are graphs of displacement versus frequency of the PMUT structure of fig. 2 and 3, respectively;

Fig. 9A to 9D are similar to fig. 7A to 7D in description, but the first void portion arrangement range and the layer structure thickness corresponding to fig. 9A to 9D are different from those of fig. 7A to 7D.

Fig. 10 is a schematic cross-sectional view of a PMUT structure according to an example embodiment of the invention, wherein two PMUTs corresponding to two adjacent cavities are bonded to each other, and the masses corresponding to different cavities are the same in thickness and different in width;

Fig. 11 is a schematic cross-sectional view of a PMUT structure according to an example embodiment of the invention, wherein two PMUTs corresponding to two adjacent cavities are bonded to each other, and the widths and thicknesses of the masses corresponding to different cavities are the same;

Fig. 12 is a schematic cross-sectional view of a PMUT structure according to an example embodiment of the invention, wherein a spacer trench is provided between two PMUTs corresponding to two adjacent cavities;

fig. 13-16 are schematic cross-sectional views of PMUT structures according to various exemplary embodiments of the invention;

FIG. 17 is a schematic top view of the PMUT structure of FIG. 12;

Fig. 18-24 are top schematic views of PMUT structures including at least two array elements according to various exemplary embodiments of the invention.

Detailed Description

The technical scheme of the invention is further specifically described below through examples and with reference to the accompanying drawings. In the specification, the same or similar reference numerals denote the same or similar components. The following description of embodiments of the present invention with reference to the accompanying drawings is intended to illustrate the general inventive concept and should not be taken as limiting the invention. Some, but not all embodiments of the invention. All other embodiments, which are derived by a person skilled in the art based on the embodiments of the invention, fall within the scope of protection of the invention.

Reference numerals in the present invention are explained as follows:

100: the substrate, see for example fig. 2 and 3, is a single crystal silicon, gallium nitride, gallium arsenide, sapphire, quartz, silicon carbide, diamond, etc. as an alternative material.

101: A cavity, see for example fig. 2 and 3, which is exemplarily provided at one side of the substrate and provides a space for bending vibrations of the PMUT, the shape of which is for example circular, elliptical, rectangular, square, etc.;

102: the spacer trenches, see fig. 12, the spacer trenches 102 also extend into the substrate 100 in the thickness direction of the PMUT;

190: array elements, see for example fig. 12 or 13, each array element comprising at least two cavities or at least two PMUTs.

200: A second electrode layer (corresponding to the bottom electrode in the figures), for example, referring to fig. 2 and 3, the material may be molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium, or a composite or alloy thereof, etc., which may be the same as or different from the material of the first electrode layer;

300: the piezoelectric layer, for example, referring to fig. 2 and 3, may be selected from polycrystalline aluminum nitride (AlN), polycrystalline zinc oxide, polycrystalline lead zirconate titanate (PZT), polycrystalline lithium niobate (LiNbO 3), polycrystalline lithium tantalate (LiTaO 3), polycrystalline potassium niobate (KNbO 3), etc., or single crystal aluminum nitride, single crystal gallium nitride, single crystal lithium niobate, single crystal lead zirconate titanate, single crystal potassium niobate, single crystal quartz thin film, or single crystal lithium tantalate, etc., where the single crystal or polycrystalline material may further include rare earth element doped material with a certain atomic ratio, such as scandium doped aluminum nitride (AlScN);

301: a first void portion, which is an edge void portion of the PMUT, for example, see fig. 2 and 3, penetrates at least the piezoelectric layer in the thickness direction of the PMUT (see description below), and overlaps the cavity 101 in the thickness direction of the PMUT, and an open end of the first void portion near the cavity communicates with the cavity for weakening or eliminating support or restraint of the PMUT by the substrate;

310: filling material layer as shown in fig. 13, filling material layer 310 is used to fill first void 301;

400: a first electrode layer (corresponding to the top electrode in the figures), for example, referring to fig. 2 and 3, the material may be molybdenum, ruthenium, gold, aluminum, magnesium, tungsten, copper, titanium, iridium, osmium, chromium, or a composite or alloy thereof, etc., which may be the same as or different from the material of the second electrode layer;

500: a barrier layer, see for example fig. 3, covering the open end face of the first void portion remote from the cavity, the optional material being silicon nitride, aluminum nitride, silicon, etc.;

600: a support layer, see for example fig. 2 and 3, for biasing the neutral layer of the PMUT away from the central axis of the piezoelectric layer to achieve flexural vibration of the PMUT, which may be disposed above or below the PMUT, optionally of silicon nitride, silicon dioxide, silicon, etc., or not;

601: a second void or edge gap, which is an edge void of the PMUT, see, e.g., fig. 14;

602: a thinned layer provided at an edge of the PMUT, for example, see fig. 15, which is obtained by thinning or removing an upper side of the support layer 600 in a thickness direction of the PMUT (see description below);

700-704: a mass, see for example fig. 2 and 3 or fig. 10, for adjusting the central resonant frequency of the PMUT, the shape, size and number of which are not limited;

900: the PMUT includes the first electrode layer, the piezoelectric layer, and the second electrode layer described above, and the first electrode layer and the second electrode layer are respectively located on both sides of the piezoelectric layer, which are used to transmit or receive acoustic waves.

In order to increase the bandwidth of the PMUT structure, it is desirable to propose a PMUT array that has small restrictions on the size of the PMUT and has little impact on its acoustic transmit and receive performance. The main idea of the invention is to arrange a mass block on the PMUT, and adjust the central resonance frequency of the PMUT through the mass block without changing the shape and the size of the PMUT, thereby increasing the bandwidth of the PMUT array. In addition, in the invention, the thinning part is also arranged at the edge of the PMUT, and the restraint of the substrate or the structure of the PMUT except the PMUT on the PMUT is reduced by using the thinning part, so that the acoustic performance of the PMUT can be improved, and the influence of the mass block on the acoustic performance can be counteracted or reduced. By combining the two aspects, the frequency of the PMUT can be adjusted under the condition that the overall shape and the size of the PMUT are not changed and the acoustic performance of the PMUT is not affected, so that the PMUT array with large bandwidth and good acoustic performance is obtained.

The PMUT structure in the embodiment of the invention is not limited in shape and size, and can obtain larger ultrasonic resolution in all directions.

Referring to the drawings, the present invention provides a PMUT structure comprising: a substrate provided with at least one cavity; at least one PMUT corresponding to the at least one cavity, wherein the PMUT comprises a first electrode layer, a piezoelectric layer and a second electrode layer, and one side and the other side of the piezoelectric layer are respectively provided with the first electrode layer and the second electrode layer; and at least one mass corresponding to the at least one cavity, disposed above the PMUT and opposite the corresponding cavity location.

Fig. 2 is a schematic cross-sectional view of a PMUT structure according to an example embodiment of the invention. As shown in fig. 2, the upper surface of the substrate 100 is provided with a cavity 101. The PMUT900 is disposed over the substrate 100. Inside the PMUT, there are, in order from bottom to top, a second electrode layer (or called bottom electrode layer) 200, a piezoelectric layer 300, and a first electrode layer (or called top electrode layer) 400. A support layer 600 (i.e., a deposition structure) is disposed over the first electrode layer 400. A mass 700 is disposed above the support layer 600. The mass 700 is positioned opposite the cavity 101.

In this embodiment, the equivalent mass of the PMUT900 can be adjusted by using the mass 700, so as to adjust the center resonance frequency of the PMUT 900.

As shown in fig. 10-24, the PMUT structure may be an array structure formed by PMUTs 900, such that with masses 700, the center resonant frequencies of different PMUTs may be adjusted by selecting different masses, thereby increasing the bandwidth of the PMUT array.

However, the mass 700 reduces the amplitude of the PMUT900, which adversely affects the acoustic performance of the PMUT (e.g., sound pressure when transmitting sound waves, sensitivity when receiving sound waves). In this regard, in further embodiments of the present invention, thinned portions, such as the spacer grooves 102, the first void portions 301, the second void portions 601, the thinned layer 602, etc., are introduced, with which to enhance the acoustic performance of the PMUT. This is explained below with reference to the drawings.

Fig. 1A is a known PMUT structure. As shown in fig. 1A, the PMUT structure includes a substrate 100, a second electrode layer 200, a piezoelectric layer 300, a first electrode layer 400, and a support layer 600. The second electrode layer 200, the piezoelectric layer 300, and the first electrode layer 400 constitute a PMUT900. The upper surface of the substrate 100 is provided with a cavity 101. The PMUT above the cavity 101 is in flexural vibration during operation, thereby transmitting and receiving ultrasonic waves. It can be seen that the PMUT in fig. 1A is fully supported or constrained by the substrate at the boundary of the cavity 101. Under the same condition, the size of the PMUT transmitting sound pressure and the sensitivity of the receiving sound pressure are related to the area and the amplitude of the PMUT, and the larger the area and the amplitude of the PMUT, the larger the transmitting sound pressure and the higher the sensitivity of the receiving sound pressure. For the PMUT structure of fig. 1A, the amplitude of the PMUT is also limited because the effective area of the PMUT is about one third of the cross-sectional area of the cavity 101, as the PMUT is fully supported or constrained by the substrate 100.

As shown in fig. 2, the edge of the PMUT is provided with a first void 301 penetrating the piezoelectric layer 300 and the second electrode layer 200 of the PMUT in the thickness direction (for example, vertical direction) of the PMUT. The first void 301 divides the PMUT structure into a centered PMUT and other structures at the edges. The first void 301 and the cavity 101 overlap in the thickness direction of the PMUT, and a region having a width a corresponds to the overlapping region in the cross section shown in fig. 2. The opening of the first void portion 301 near the cavity 101 communicates with the cavity 101. The first void portion 301 may release the PMUT from the substrate 100, so that the PMUT in the center is spaced a certain distance from the substrate 100, thereby weakening the support or constraint of the substrate 100 on the PMUT, improving the effective area and amplitude of the PMUT, and improving the acoustic performance of the PMUT.

In an alternative embodiment, although not shown, the portion outside the central PMUT may include only the piezoelectric layer without the first electrode layer and the second electrode layer, in which case the first void portion penetrates the piezoelectric layer only in the thickness direction of the PMUT.

As can be appreciated, the greater the edge first void portion width a, the weaker the constraint of the substrate 100 on the central PMUT, the greater the effective area of the PMUT, and the better the acoustic performance of the PMUT. However, there is a limit to the edge first void portion width a of the PMUT structure in fig. 2. The reason is that, for the PMUT structure in fig. 2, it is generally necessary to provide a protective structure (e.g., a support layer 600 and/or a protective layer, not shown, etc.) over the first void portion 301 to prevent the first void portion 301 from being affected by subsequent processes or external environments. The protective structure is typically formed by deposition (and thus may be referred to as a deposited structure). When the edge first void width a is small (e.g., less than 0.5 μm), referring to fig. 2, a deposition structure (i.e., support layer 600) may be directly deposited over the PMUT and the first void 301. But the smaller edge first void width a may limit the improvement of the acoustic performance of the PMUT structure. When the edge first void portion width a is large (for example, more than 1.0 μm), although not shown, deposition substances may enter the cavity through the first void portion and remain in the cavity and the first void portion when depositing the protection structure, reducing the cavity size and blocking the first void portion, which may have an unpredictable effect on the center resonance frequency of the PMUT, and also may decrease the ability of the first void portion to release the support or constraint, thereby resulting in reduced performance of the PMUT.

In an alternative embodiment, to address the above problems, a barrier layer 500 is provided over the PMUT, as shown in fig. 3. The barrier layer 500 covers the first void 301 from above. A support layer 600 (i.e., a deposition structure) is disposed over the barrier layer. During deposition of the support layer 600, the barrier layer 500 is capable of blocking deposition material from entering the first void portion 301 and the cavity 101. Whatever the magnitude of the edge first void width a, neither the first void 301 nor the cavity 101 is filled with deposited material, and the acoustic performance of the PMUT structure is not affected.

In alternative embodiments, the barrier layer 500 may be fabricated with a sacrificial material.

As before, the greater the value of the edge first void portion width a, the further the center PMUT is from the cavity 101 or substrate 100, the weaker the substrate 101 constrains the center PMUT, the greater the effective area of the PMUT, and the better the acoustic performance of the PMUT. In one example, the edge first void portion width a of the PMUT structure of fig. 3 may be greater than or equal to 1.0 μm, yet further, 1.5 μm, yet further, 2 μm, which enables better acoustic performance compared to the PMUT structure of fig. 2.

Alternatively, as shown in fig. 3, the barrier layer 500 includes a first portion provided in the same layer as the first electrode layer 400, a second portion higher than the first electrode layer 400 to cover the open end face of the first void 301 away from the cavity 101, and a third portion higher than the first electrode layer 400 and covering the first electrode layer 400, wherein the first portion covers a part of the side face of the first void 301.

In an alternative embodiment, although not shown, the barrier layer may cover only the open end face of the first void portion remote from the cavity, and not the side face of the cavity, for the first void portion.

Fig. 7A is a graph of displacement versus frequency for the PMUT structure of fig. 1A, and fig. 8A and 8B are graphs of displacement versus frequency for the PMUT structure of fig. 2 and 3, respectively, wherein the three PMUT structures have the same layer structure thickness.

As shown in fig. 7A, the PMUT structure has a central resonance frequency of 8MHz in an aqueous environment, and a central resonance shift of 0.45nm at an excitation voltage of 1V.

Fig. 8A is a graph of displacement versus frequency for the PMUT structure of fig. 2, where the first gap width is 0.5um, and the mass thickness is adjusted, which also corresponds to a case where the center resonance frequency in the aqueous environment is 5.4MHz, and the excitation voltage is 1V. It can be seen that the center resonance shift of the PMUT structure in fig. 2 is 0.65nm.

Fig. 8B is a graph of displacement versus frequency for the PMUT structure of fig. 3, where the first gap has a width of 2um, and the mass thickness is adjusted to correspond to a resonance frequency of 5.4MHz and an excitation voltage of 1V in an aqueous environment. It can be seen that the center resonance shift of the PMUT structure in fig. 3 is 0.8nm.

It can be seen that the center resonance displacement of the PMUT structure in fig. 2 is increased by 44% compared to the center resonance displacement of the PMUT structure in fig. 1A, and the center resonance displacement of the PMUT structure in fig. 3 is increased by 23% compared to the center resonance displacement of the PMUT structure in fig. 2, so that the resonance displacement of the PMUT structure in fig. 2 is significantly increased compared to the center resonance displacement of the PMUT structure in fig. 1A, thereby having better acoustic performance; the PMUT structure shown in fig. 3 has significantly increased resonant displacement compared to the PMUT structure shown in fig. 2, and thus has better acoustic performance.

The PMUT structure in other exemplary embodiments of the present invention also has a technical effect similar to the PMUT structure shown in fig. 2 or 3, that is, the center resonance displacement is significantly increased compared to the center resonance displacement of the PMUT structure shown in fig. 1A, so that better acoustic performance is provided, and will not be described here.

Fig. 4 is a schematic cross-sectional view of a PMUT structure according to an exemplary embodiment of the present invention, which is different from the PMUT structure in fig. 3 in that one mass 700 is disposed on the support layer 600 in fig. 3, and a plurality of (e.g., three) masses 700 are disposed on the support layer 600 in fig. 4. The shape, material, and size of the plurality of masses 700 may be the same or different.

Fig. 5 is a schematic cross-sectional view of a PMUT structure according to an exemplary embodiment of the invention, which differs from the PMUT structure of fig. 3 in that in fig. 3 a support layer 600 is provided on a barrier layer 500, a mass 700 is provided on the support layer 600, whereas in fig. 5 the support layer 600 is provided between the substrate 100 and the PMUT, the mass 700 is provided on the barrier layer 500. In addition, the first void portion 301 in fig. 5 also penetrates the support layer 600 in the vertical direction.

Fig. 6 is a schematic top view of the PMUT structure of fig. 3, wherein the structure of fig. 3 corresponds to section A-A' of fig. 6. In fig. 6, a broken line represents the first void portion 301, and a solid line represents the cavity 101. It is noted that in the top view of fig. 6, both the first void 301 and the cavity 101 are not visible. The dashed and solid lines in fig. 6 are only used to distinguish between different structures and do not represent the visibility of the corresponding structures.

Referring to fig. 6, the PMUT structure includes a plurality (e.g., four) of first void portions 301, adjacent two of the plurality of first void portions 301 being separated by a layer structure of the PMUT. Optionally, the plurality of first void portions 301 are uniformly arranged along the boundary of the cavity 101. The mass 700 is located above the PMUT structure.

In fig. 6, the cavity 101 is circular, and each of the first void portions 301 includes a portion located within the circular, that is, a portion corresponding to the overlapping portion of the cavity 101 and the first void portion 301 in the PMUT thickness direction. The overall shape of the plurality of first void portions 301 corresponds to the shape of the boundary of the cavity 101.

As shown in fig. 6, a part of the boundary of the cavity 101 is provided with the first void 301, and the other part is not provided with the first void 301. In an alternative embodiment, at least 45% of the portion on the boundary of the cavity 101 is correspondingly provided with the first void portion 301. In a further embodiment, at least 60% of the portion on the boundary of the cavity 101 is provided with the first void portion 301. It is easy to understand that, under the same conditions, the larger the range in which the first void portion 301 is provided on the boundary of the cavity 101, the smaller the restriction of the substrate to the PMUT, the larger the amplitude of the PMUT, and the better the acoustic performance thereof.

Fig. 7A is a graph of displacement versus frequency for the PMUT structure of fig. 1A. As shown in fig. 7A, the PMUT structure has a resonance frequency of 8MHz in an aqueous environment, and a resonance shift of 0.45nm at a center of an excitation voltage of 1V.

Fig. 7B is a graph of displacement versus frequency for the PMUT structure of fig. 1A with the addition of a first void. As shown in fig. 7B, after adding the first void portion, the central resonance frequency of the PMUT structure in the water environment decreases to 7.7MHz, and the resonance shift of the center at the excitation voltage of 1V increases to 0.6nm. It follows that by providing slits, the acoustic performance of the PMUT can be improved.

Fig. 7C and 7D are displacement versus frequency curves for the PMUT structure of fig. 3, which have the same stack structure and thickness as the PMUT structure of fig. 1A.

By adding a certain mass block, the central resonance frequency of the PMUT structure in fig. 3 is the same as that of the PMUT structure corresponding to fig. 7A, and the displacement-frequency curve of the PMUT structure is shown in fig. 7C. As can be seen from fig. 7C, the PMUT structure maintains the center resonance frequency at 8MHz in the aqueous environment, while the center resonance shift at an excitation voltage of 1V increases to 0.58nm. Thus, by providing the first void and the mass, the displacement or amplitude of the PMUT can be increased while maintaining the same frequency, and the acoustic performance of the PMUT structure can be improved.

By adding a mass to the PMUT structure of fig. 3 that covers the center PMUT entirely, a corresponding PMUT structure is obtained, whose displacement-frequency curve is shown in fig. 7D. As can be seen from fig. 7D, the central resonance frequency of the PMUT structure in an aqueous environment increases to 8.8MHz, while the central resonance shift at an excitation voltage of 1V remains at 0.45nm.

As can be seen from the examples corresponding to fig. 7A to 7D, by providing the first void portion and the mass, the acoustic performance of the PMUT can be improved, while the frequency of the PMUT can be adjusted. The combination of the PMUT structures with different mass blocks can improve the ultrasonic bandwidth of the PMUT array. The above example can utilize a mass to adjust the frequency of the PMUT structure from 7.7MHz to 8.8MHz, with a frequency adjustment space of 1.1 MHz.

Fig. 9A to 9D are similar to fig. 7A to 7D in description, but the first void portion arrangement range and the layer structure thickness (including the thickness of each layer structure separately and the total thickness of the whole) corresponding to fig. 9A to 9D are different from fig. 7A to 7D. The first void portion setting range (i.e., the proportion of the portion on the cavity boundary where the first void portion is provided, see the foregoing description) corresponding to fig. 7B to 7D is 45%, and the first void portion setting range corresponding to fig. 9B to 9D is 60%.

Fig. 9A is a graph of displacement versus frequency for the PMUT structure of fig. 1A, where the layer thickness of the PMUT structure is different from the layer thickness of the corresponding PMUT structure of fig. 7A. As shown in fig. 9A, the PMUT structure has a center resonance frequency of 5.4MHz in an aqueous environment, and a center resonance shift of 0.6nm at an excitation voltage of 1V.

Fig. 9B is a graph of displacement versus frequency after adding a first void portion to the PMUT structure corresponding to fig. 1A, where the first void portion of the PMUT structure is disposed within a range of 60%. As shown in fig. 9B, after adding the first void portion, the central resonance frequency of the PMUT structure in the water environment decreases to 4.7MHz, and the central resonance displacement at the excitation voltage of 1V increases to 1.3nm. The displacement is more than twice of the initial displacement (0.6 nm), and the acoustic performance of the PMUT structure is obviously improved.

By adding a certain mass block, the central resonance frequency of the PMUT structure in fig. 3 is the same as the central resonance frequency of the PMUT structure corresponding to fig. 9A (the thicknesses of the layers of the two layers are the same), and the displacement-frequency curve of the PMUT structure is shown in fig. 9C. As can be seen from fig. 9C, the central resonance frequency of the PMUT structure in an aqueous environment is maintained at 5.4MHz, while the central resonance shift at an excitation voltage of 1V is increased to 0.8nm. It can be seen that the frequency is the same as the initial frequency (5.4 MHz) and the displacement is 30% higher than the initial displacement (0.6 nm), so that the PMUT structure has better acoustic performance.

By adding a mass block to the PMUT structure in fig. 3, which covers the center PMUT entirely, a corresponding PMUT structure (the layer structure thickness of the PMUT structure is the same as that of the PMUT structure corresponding to fig. 9A) is obtained, and the displacement-frequency curve of the PMUT structure is shown in fig. 9D. As can be seen from fig. 9D, the central resonance frequency of the PMUT structure in an aqueous environment increases to 8.5MHz, while the central resonance displacement at an excitation voltage of 1V decreases to 0.36nm. The displacement is reduced compared to the initial displacement (0.6 nm), but the frequency is increased more than the initial frequency (5.4 MHz), so that the acoustic performance of the PMUT as a whole is still improved.

In the corresponding example of fig. 9A-9D, by providing the first void and mass such that the PMUT frequency is tuned in the range of 4.7MHz-8.5MHz, there is a 3.8MHz frequency tuning space that is greater than the tuning space in the previous example. Meanwhile, in the example, the center resonance displacement is larger, and the ultrasonic performance is better. Calculated as a center resonance frequency of 6.1MHz, the bandwidth in this example is at least greater than 60% of the center resonance frequency and the acoustic performance is uniform over the entire frequency range.

Fig. 10-24 are schematic cross-sectional and top views of PMUT structures including a plurality of PMUTs therein, and the plurality of PMUTs constituting a PMUT array, according to various exemplary embodiments of the invention.

Fig. 10 is a schematic cross-sectional view of a PMUT structure in accordance with an exemplary embodiment of the invention. Optionally, as shown in fig. 10, at least two (e.g., four) cavities are provided on the substrate 100, one PMUT is provided above each cavity, one mass (e.g., mass 701, mass 702, mass 703, or mass 704) is provided on each PMUT,

Alternatively, as shown in fig. 10, the piezoelectric layers 300 of two PMUTs corresponding to the adjacent two cavities 101 are connected to each other. Further, as shown in fig. 10, the support layers 500 of two PMUTs corresponding to the adjacent two cavities 101 are also connected to each other.

Alternatively, as shown in fig. 10, the thickness of the corresponding mass of different cavities 101 is the same, but the width is different. Assuming that the materials of the respective masses are the same, the masses of the respective masses corresponding to the different cavities 101 are different, so that the center resonance frequencies of PMUTs corresponding to the different cavities 101 are different.

The mass blocks with the same thickness and different widths can be prepared at one time based on the manufacturing steps of the same layer structure, and the manufacturing efficiency is improved.

Fig. 11 is a schematic cross-sectional view of a PMUT structure according to an exemplary embodiment of the present invention, which differs from the PMUT structure of fig. 10 in that the thicknesses of the masses corresponding to the different cavities 101 of fig. 10 are the same and the widths are different, and the widths of the masses corresponding to the different cavities of fig. 11 are the same and the thicknesses are different.

Fig. 12 is a schematic cross-sectional view of a PMUT structure according to an exemplary embodiment of the present invention, which differs from the PMUT structure in fig. 10 in that the piezoelectric layers 300 of two PMUTs corresponding to two adjacent cavities 101 in fig. 10 are connected to each other, and the layer structures of two PMUTs corresponding to two adjacent cavities 101 in fig. 12 are spaced apart from each other.

Optionally, as shown in fig. 12, a spacer trench 102 is disposed between two PMUTs corresponding to two adjacent cavities 101, and the spacer trench 102 further extends into the substrate 100 along the thickness direction of the PMUTs. Spacing the grooves 102, or the spacing between two PMUTs, can reduce the lateral consumption of acoustic waves and improve the ultrasonic performance of the PMUT structure.

Fig. 17 is a schematic top view of the PMUT structure of fig. 12. As shown in fig. 17, the respective cavities 101 on the substrate 100 have the same shape and size. Alternatively, as shown in fig. 17, a plurality of cavities 101 or a plurality of PMUTs are arranged in rows and columns, wherein the corresponding masses 700 of the cavities 101 of each row have the same shape and different sizes, and the corresponding masses of the cavities 101 of each column have the same shape and the same size.

Fig. 13-16 are schematic cross-sectional views of PMUT structures according to various exemplary embodiments of the invention.

As shown in fig. 13, the filling material layer 310 is used to fill the first void portion 301, and the stiffness, density or other characteristics of the material are different from those of the surrounding material of the first void portion 301, so that the resonant frequency, emission performance of the PMUT device can be changed, and the lateral consumption of sound waves can be reduced. It should be noted that the rigidity of the material filled in the first void portion 301 may be lower than that of the material around the first void portion 301 or higher than that of the material around the first void portion 301. The first void 301 may be filled with materials having different characteristics, or may be partially filled with materials, or may be partially not filled with materials (e.g., only the bottom electrode and the support layer 600 (to be described later) are etched, or only the gap of the support layer may be filled without filling the gap of the bottom electrode).

Although not shown, in other embodiments, the first void portion 301 may extend through only a certain membrane layer (e.g., only the piezoelectric layer is etched), or only a few membrane layers (e.g., only the bottom electrode and the piezoelectric layer are etched), or may extend through the entire membrane structure of the PMUT structure. When only a few film layers are penetrated, the etched film layers can be adjacent (such as a bottom electrode and a piezoelectric layer) or not adjacent (such as a bottom electrode and a supporting layer).

Referring to fig. 14, the second void portion 601 penetrates the support layer 600 in the thickness direction of the PMUT900 to terminate at the barrier layer 500. The second void portion 601 can reduce clamping constraint of the PMUT diaphragm, improve effective vibration area and amplitude of the PMUT, improve emission performance, and reduce lateral propagation and loss of sound waves. The second void portion 601 above the barrier layer 500 may be a plurality of concentric annular grooves adjacent to each other, or may be only one annular groove. The concentric ring grooves may be complete rings or incomplete rings with intermittent portions in the middle.

Referring to fig. 15, the thinner layer 602 is obtained by thinning or removing the upper side of the support layer 600 in the thickness direction of the PMUT 900. Specifically, the supporting layer material outside the edge of the supporting layer 600 of the PMUT is partially or entirely etched, so that the thickness of the supporting layer outside the effective vibrating portion of the diaphragm is reduced. The structure can reduce the edge rigidity of the vibrating diaphragm, so that the effective vibrating area and the vibration amplitude of the vibrating diaphragm can be improved, and the ultrasonic emission performance of the PMUT can be improved. The thinned region of the support layer 600, that is, the thinned layer 602, may be only a region other than the vibration region of the PMUT membrane structure, or may be a region including the outer edge portion of the vibration region of the diaphragm, that is, a region including the portion directly above the outer edge of the cavity 101 and all regions other than the vibration portion directly above the cavity.

The structures shown in fig. 13-15 may also be combined with the structures shown in fig. 2-5, and fig. 16 gives such an example. As shown in fig. 16, the second void 601 above the barrier layer 500 is provided simultaneously with the first void 301 below, and fig. 16 shows a schematic cross-sectional view of a PMUT array provided with a thinned portion including the first void 301 and the second void 601 in fig. 16. The structure shown in fig. 16 can more effectively adjust the resonant frequency and more effectively reduce the propagation and loss of the sound wave in the transverse direction. The second void 601 on the upper side of the barrier layer 500 may be a plurality of adjacent concentric circular grooves, or may be only one circular groove, and the concentric circular groove may be a complete circular ring or may be a non-complete circular ring having a discontinuous portion in the middle.

As shown in fig. 1B, in the existing PMUT structure array, PMUTs above all cavities 101 are the same, frequencies of all cells are the same, and overall bandwidths are low. As shown in fig. 12 and 17, PMUTs corresponding to the cavities 101 are mutually independent to form a plurality of PMUT vibrating elements, and PMUTs with multiple frequencies are contained on the whole surface and used for responding to ultrasonic signals with different frequencies, so that the PMUT structure can realize a two-dimensional PMUT array with small center distances of the vibrating elements in two-dimensional directions.

In addition, the shape and the size of each cavity 101 are consistent, the frequency adjustment is realized through the mass block 700 on the PMUT, the filling factor of the PMUT vibrating element and the center distance of the vibrating element are not influenced, and a PMUT array with large bandwidth, excellent ultrasonic transmitting and receiving performance and compact structure in the two-dimensional direction can be obtained.

In the invention, under the condition that the shapes and the sizes of the cavities corresponding to the PMUTs are consistent, the center-to-center distances between adjacent PMUTs or between vibrating elements in the formed PMUT array are the same in the two-dimensional direction, or even the differences are within the range of 5%. Compared with the prior art that PMUT with different cavity sizes is adopted for integrating to solve the problem of insufficient PMUT bandwidth, the technical scheme can effectively control the center distance between two adjacent PMUT units, avoid or reduce the deflection angle of an ultrasonic phased array and the change or the larger change of the focusing degree of sound waves along with the difference of the center distances of adjacent PMUTs in the two-dimensional direction, and therefore the PMUT array with small influence on acoustic emission and receiving performance and large bandwidth can be obtained. Furthermore, PMUT combinations for the same cavity size and shape help to obtain high fill factor PMUT arrays, resulting in large emitted sound pressures.

Fig. 18-24 are schematic top views of PMUT structures according to various exemplary embodiments of the invention.

Optionally, referring to fig. 17 to 24, a plurality of array units 190 are disposed on the substrate, each array unit 190 includes at least two cavities 101, and at least two masses 700 corresponding to the at least two cavities 101 included in each array unit 190 are different in mass. The mass of the at least two masses 700 is different, which means that the mass of at least one mass 700 is different from the mass of the other masses 700.

Alternatively, adjacent array elements 190 may be aligned with each other (see fig. 19) or may be offset (see fig. 18).

Alternatively, as shown in fig. 19, the masses 700 in each array unit 190 are each different from each other in mass. Or as shown in fig. 18 or 20, the masses 700 in each array unit 190 are equal in pairs.

Alternatively, as shown in fig. 18, at least two cavities 101 included in each array unit 190 are arranged in a linear array. The first electrode layer and the second electrode layer of each PMUT on each linear array are connected in parallel, so that each PMUT on each linear array works simultaneously. And combining the linear PMUTs to form a one-dimensional large-bandwidth PMUT array because the central resonant frequencies of the PMUTs on the same linear array are different.

Alternatively, as shown in fig. 19, at least two cavities 101 included in each array unit 190 are arranged in an area array. The first electrode layer and the second electrode layer of each PMUT on each area array are connected in parallel, so that each PMUT on each area array works simultaneously. And combining the planar PMUTs to form a two-dimensional large-bandwidth PMUT array in a two-dimensional direction because the central resonant frequencies of the PMUTs on the same planar array are different.

Alternatively, as shown in fig. 18 or 19, the plurality of masses 700 corresponding to different array units 190 are arranged in the same manner.

The cross-sectional shape of the mass 700 in embodiments of the present invention may include a variety of shapes, such as circular (see fig. 18), square (see fig. 19), oval (see fig. 22), and the like.

The shape of the boundary of the hollow cavity 101 in the embodiment of the present invention may include various shapes such as a circle (see fig. 21), a square (see fig. 23), an ellipse (see fig. 22), and the like.

In the embodiment shown in fig. 18-24, the shape and size of the plurality of cavities 101 on the same substrate are the same. In alternative embodiments, although not shown, the shape or size of the plurality of cavities 101 on the same substrate may be different.

Alternatively, as shown in fig. 21, one or more masses 700 may be disposed on a PMUT corresponding to the same cavity 101.

Alternatively, as shown in fig. 24, the mass 700 may be provided in the form of a mass removing portion such as a hole or a groove. Further, the mass removing portion may be provided in a functional layer such as a piezoelectric layer, a first electrode layer, a second electrode layer, a barrier layer, or a support layer. As can be appreciated, the more mass removed, the greater the PMUT frequency variation, and eventually the PMUTs of multiple frequencies can be combined to form a large bandwidth PMUT array.

In addition, in the embodiments shown in fig. 10-23, the masses on the PMUT cells are separate from each other, there is a single mass, or a combination of separate masses, but each mass is not interconnected with each other (i.e., independent of each other). But the present invention is not limited thereto. Referring to fig. 24, the mass blocks on each PMUT cell in fig. 24 are integrally connected (i.e., interconnected with each other), and as described above, the area of the mass block is implemented by removing a portion of the material, and the thickness removed may be a portion of the mass block, and the entire mass block may even include a portion of the supporting layer, the top electrode, the piezoelectric layer, the bottom electrode, and other functional layers. As more material is removed, the amount of frequency variation is greater, eventually the multiple frequency PMUT cells can be combined to form a large bandwidth. As can be appreciated, two or more interconnected masses may also be masses obtained by adding mass.

The embodiment of the invention also provides electronic equipment comprising the PMUT structure.

In an alternative embodiment, the electronic device includes at least one of the following: ultrasonic imaging instrument, ultrasonic range finder, ultrasonic fingerprint sensor, nondestructive inspection instrument, flowmeter, force sense feedback equipment and smoke alarm.

Based on the above, the invention provides the following technical scheme:

1. a PMUT structure, comprising:

a substrate provided with at least one cavity;

at least one PMUT corresponding to the at least one cavity, wherein the PMUT comprises a first electrode layer, a piezoelectric layer and a second electrode layer, and one side and the other side of the piezoelectric layer are respectively provided with the first electrode layer and the second electrode layer; and

At least one mass corresponding to the at least one cavity is disposed above the PMUT and opposite the corresponding cavity location.

2. The PMUT structure of 1, further comprising:

At least one thinned portion disposed along a perimeter of the PMUT for reducing a restriction of vibration of the PMUT by a membrane layer other than the PMUT of the PMUT structure.

3. The PMUT structure of claim 2, wherein:

The thinning part comprises at least one first gap part corresponding to the at least one cavity, the first gap part at least penetrates through the piezoelectric layer along the thickness direction of the PMUT and at least partially overlaps with the corresponding cavity along the thickness direction of the PMUT, and an opening of the first gap part, which is close to the corresponding cavity, is communicated with the corresponding cavity.

4. The PMUT structure of claim 3, wherein:

the first void portion is an air gap or at least a portion of the first void portion is filled with a layer of filler material that is a different material than the material surrounding the first void portion.

5. The PMUT structure of claim 3, further comprising:

And the blocking layer covers the opening end face of the first gap part, which is far away from the corresponding cavity, and the mass block is arranged above the blocking layer.

6. The PMUT structure of claim 5, wherein:

the minimum distance between the inner side wall of the first void portion and the side wall of the cavity in the direction perpendicular to the thickness direction of the PMUT is greater than or equal to 1.0 μm, still further, 1.5 μm, still further, 2 μm.

7. The PMUT structure of claim 5, wherein:

the first electrode layer and the barrier layer are positioned on the same side of the piezoelectric layer, and the barrier layer comprises a first part which is arranged on the same layer with the first electrode layer and a second part which is higher than the first electrode layer and covers the opening end face of the first gap part far away from the cavity, wherein the first part covers a part of the side face of the first gap part; or alternatively

The first electrode layer and the barrier layer are located on the same side of the piezoelectric layer, and for the first void portion, the barrier layer covers only an opening end face of the first void portion, which is far from the cavity.

8. The PMUT structure of claim 5, wherein:

the device further comprises a deposition structure, wherein the deposition structure covers one side of the barrier layer away from the first gap part;

the mass is disposed on the deposition structure.

9. The PMUT structure of claim 3, wherein:

one of the at least one cavity corresponds to at least two first void portions, adjacent two of the at least two first void portions being separated by a layer structure of the PMUT.

10. The PMUT structure of claim 9, wherein:

The at least two first void portions are uniformly arranged along the boundary of the cavity.

11. The PMUT structure of claim 3, wherein:

At least 45% of the boundary of the cavity is correspondingly provided with the first gap part; or alternatively

At least 60% of the boundary of the cavity is correspondingly provided with the first gap part.

12. The PMUT structure of claim 2, wherein:

the PMUT structure further comprises a blocking layer, the mass block is arranged above the blocking layer, and the PMUT is arranged on the lower side of the blocking layer;

The thinned portion includes a portion disposed on an upper side of the barrier layer.

13. The PMUT structure of claim 12, wherein:

the PMUT structure further comprises a supporting layer arranged on the upper side of the blocking layer;

the thinned portion includes an air gap formed through the support layer or removing a portion of the support layer, or includes a thinned layer formed after thinning the support layer.

14. The PMUT structure of claim 13, wherein:

the air gap comprises a plurality of concentric circular grooves or an annular groove, and the concentric circular grooves and the annular groove are in complete annular shapes or intermittent annular shapes.

15. The PMUT structure of claim 12, wherein:

The thinning part further comprises at least one first gap part corresponding to the at least one cavity, the first gap part at least penetrates through the piezoelectric layer along the thickness direction of the PMUT and at least partially overlaps with the corresponding cavity along the thickness direction of the PMUT, and an opening of the first gap part, which is close to the corresponding cavity, is communicated with the corresponding cavity.

16. The PMUT structure of claim 15, wherein:

at least a portion of the first void portion is filled with a layer of filler material that is a different material than a material surrounding the first void portion.

17. The PMUT structure of claim 2, wherein:

the thinned portion includes a void layer disposed in one or more membrane layers of the PMUT structure, the void layers disposed in the plurality of membrane layers being adjacent or spaced apart in a thickness direction of the PMUT structure.

18. The PMUT structure of claim 17, wherein:

at least a portion of the void layer is filled with a layer of filler material that is a material different from a material surrounding the void layer.

19. The PMUT structure of any one of claims 1-18, wherein:

The mass is provided as a mass removal portion.

20. The PMUT structure of claim 19, wherein:

The mass removal portion includes a hole or a slot.

21. The PMUT structure of any one of claims 1-18, wherein:

The shape of the cross section of the mass comprises a circle, an ellipse or a square.

22. The PMUT structure of any one of claims 1-18, wherein:

the at least one mass comprises at least two masses independent of each other; or alternatively

The at least one mass comprises at least two masses interconnected to each other.

23. The PMUT structure of any one of claims 1-18, wherein:

The at least one cavity comprises at least two cavities, each cavity in the at least two cavities corresponds to one PMUT, and piezoelectric layers of two PMUTs corresponding to two adjacent cavities are connected with each other; or alternatively

The at least one cavity comprises at least two cavities, each cavity in the at least two cavities corresponds to one PMUT, and the layer structures of two PMUTs corresponding to two adjacent cavities are spaced from each other.

24. The PMUT structure of claim 23, wherein:

the layer structures of two PMUTs corresponding to two adjacent cavities are spaced apart from each other, and a spacing groove is arranged between the two PMUTs corresponding to the two adjacent cavities, and extends into the substrate from the upper side of the PMUT structure along the thickness direction of the PMUT.

25. The PMUT structure of claim 24, wherein:

The spacing grooves comprise a plurality of concentric circular spacing grooves or a circular spacing groove, and the concentric circular spacing grooves and the circular spacing groove are in complete annular or discontinuous annular shapes.

26. The PMUT structure of claim 23, wherein:

the mass of at least two masses corresponding to the at least two cavities is different.

27. The PMUT structure of claim 26, wherein:

The masses of the at least two masses are each different from each other; and/or

The at least two masses have different thicknesses and/or different widths.

28. The PMUT structure of claim 23, wherein:

The at least two cavities are identical in shape and size.

29. The PMUT structure of claim 23, wherein:

The at least two cavities comprise at least four cavities, the at least four cavities are divided into at least two array units, each array unit comprises at least two cavities, and the mass of at least two mass blocks corresponding to the at least two cavities included in each array unit is different.

30. The PMUT structure of claim 29, wherein:

At least two cavities included in each array unit are arranged into a linear array; or alternatively

At least two cavities included in each array unit are arranged into an area array.

31. The PMUT structure of claim 29, wherein:

At least two PMUTs corresponding to at least two cavities included in each array unit are connected in parallel.

32. The PMUT structure of claim 29, wherein:

the arrangement modes of at least two mass blocks corresponding to different array units are the same.

33. The PMUT structure of either 1 or 2, wherein:

the at least one cavity comprises at least two cavities, the at least two cavities being identical in shape and size.

34. The PMUT structure of claim 33, wherein:

The at least one cavity comprises at least three cavities, and the at least one PMUT comprises at least three PMUTs; and is also provided with

The center-to-center spacing between adjacent PMUTs is the same or different from each other but within a range of 5%.

35. An electronic device comprising the PMUT structure of any one of claims 1-34.

36. The electronic device of claim 35, wherein:

The electronic device includes at least one of: ultrasonic imaging instrument, ultrasonic range finder, ultrasonic fingerprint sensor, nondestructive inspection instrument, flowmeter, force sense feedback equipment and smoke alarm.

Although embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.

Claims (36)

1. A PMUT structure, comprising:

a substrate provided with at least one cavity;

at least one PMUT corresponding to the at least one cavity, wherein the PMUT comprises a first electrode layer, a piezoelectric layer and a second electrode layer, and one side and the other side of the piezoelectric layer are respectively provided with the first electrode layer and the second electrode layer; and

At least one mass corresponding to the at least one cavity is disposed above the PMUT and opposite the corresponding cavity location.

2. The PMUT structure of claim 1, further comprising:

At least one thinned portion disposed along a perimeter of the PMUT for reducing a restriction of vibration of the PMUT by a membrane layer other than the PMUT of the PMUT structure.

3. The PMUT structure of claim 2, wherein:

The thinning part comprises at least one first gap part corresponding to the at least one cavity, the first gap part at least penetrates through the piezoelectric layer along the thickness direction of the PMUT and at least partially overlaps with the corresponding cavity along the thickness direction of the PMUT, and an opening of the first gap part, which is close to the corresponding cavity, is communicated with the corresponding cavity.

4. The PMUT structure of claim 3, wherein:

the first void portion is an air gap or at least a portion of the first void portion is filled with a layer of filler material that is a different material than the material surrounding the first void portion.

5. The PMUT structure of claim 3, further comprising:

And the blocking layer covers the opening end face of the first gap part, which is far away from the corresponding cavity, and the mass block is arranged above the blocking layer.

6. The PMUT structure of claim 5, wherein:

the minimum distance between the inner side wall of the first void portion and the side wall of the cavity in the direction perpendicular to the thickness direction of the PMUT is greater than or equal to 1.0 μm, still further, 1.5 μm, still further, 2 μm.

7. The PMUT structure of claim 5, wherein:

the first electrode layer and the barrier layer are positioned on the same side of the piezoelectric layer, and the barrier layer comprises a first part which is arranged on the same layer with the first electrode layer and a second part which is higher than the first electrode layer and covers the opening end face of the first gap part far away from the cavity, wherein the first part covers a part of the side face of the first gap part; or alternatively

The first electrode layer and the barrier layer are located on the same side of the piezoelectric layer, and for the first void portion, the barrier layer covers only an opening end face of the first void portion, which is far from the cavity.

8. The PMUT structure of claim 5, wherein:

the device further comprises a deposition structure, wherein the deposition structure covers one side of the barrier layer away from the first gap part;

the mass is disposed on the deposition structure.

9. The PMUT structure of claim 3, wherein:

one of the at least one cavity corresponds to at least two first void portions, adjacent two of the at least two first void portions being separated by a layer structure of the PMUT.

10. The PMUT structure of claim 9, wherein:

The at least two first void portions are uniformly arranged along the boundary of the cavity.

11. The PMUT structure of claim 3, wherein:

At least 45% of the boundary of the cavity is correspondingly provided with the first gap part; or alternatively

At least 60% of the boundary of the cavity is correspondingly provided with the first gap part.

12. The PMUT structure of claim 2, wherein:

the PMUT structure further comprises a blocking layer, the mass block is arranged above the blocking layer, and the PMUT is arranged on the lower side of the blocking layer;

The thinned portion includes a portion disposed on an upper side of the barrier layer.

13. The PMUT structure of claim 12, wherein:

the PMUT structure further comprises a supporting layer arranged on the upper side of the blocking layer;

the thinned portion includes an air gap formed through the support layer or removing a portion of the support layer, or includes a thinned layer formed after thinning the support layer.

14. The PMUT structure of claim 13, wherein:

the air gap comprises a plurality of concentric circular grooves or an annular groove, and the concentric circular grooves and the annular groove are in complete annular shapes or intermittent annular shapes.

15. The PMUT structure of claim 12, wherein:

The thinning part further comprises at least one first gap part corresponding to the at least one cavity, the first gap part at least penetrates through the piezoelectric layer along the thickness direction of the PMUT and at least partially overlaps with the corresponding cavity along the thickness direction of the PMUT, and an opening of the first gap part, which is close to the corresponding cavity, is communicated with the corresponding cavity.

16. The PMUT structure of claim 15, wherein:

at least a portion of the first void portion is filled with a layer of filler material that is a different material than a material surrounding the first void portion.

17. The PMUT structure of claim 2, wherein:

the thinned portion includes a void layer disposed in one or more membrane layers of the PMUT structure, the void layers disposed in the plurality of membrane layers being adjacent or spaced apart in a thickness direction of the PMUT structure.

18. The PMUT structure of claim 17, wherein:

at least a portion of the void layer is filled with a layer of filler material that is a material different from a material surrounding the void layer.

19. The PMUT structure of any one of claims 1-18, wherein:

The mass is provided as a mass removal portion.

20. The PMUT structure of claim 19, wherein:

The mass removal portion includes a hole or a slot.

21. The PMUT structure of any one of claims 1-18, wherein:

The shape of the cross section of the mass comprises a circle, an ellipse or a square.

22. The PMUT structure of any one of claims 1-18, wherein:

the at least one mass comprises at least two masses independent of each other; or alternatively

The at least one mass comprises at least two masses interconnected to each other.

23. The PMUT structure of any one of claims 1-18, wherein:

The at least one cavity comprises at least two cavities, each cavity in the at least two cavities corresponds to one PMUT, and piezoelectric layers of two PMUTs corresponding to two adjacent cavities are connected with each other; or alternatively

The at least one cavity comprises at least two cavities, each cavity in the at least two cavities corresponds to one PMUT, and the layer structures of two PMUTs corresponding to two adjacent cavities are spaced from each other.

24. The PMUT structure of claim 23, wherein:

the layer structures of two PMUTs corresponding to two adjacent cavities are spaced apart from each other, and a spacing groove is arranged between the two PMUTs corresponding to the two adjacent cavities, and extends into the substrate from the upper side of the PMUT structure along the thickness direction of the PMUT.

25. The PMUT structure of claim 24, wherein:

The spacing grooves comprise a plurality of concentric circular spacing grooves or a circular spacing groove, and the concentric circular spacing grooves and the circular spacing groove are in complete annular or discontinuous annular shapes.

26. The PMUT structure of claim 23, wherein:

the mass of at least two masses corresponding to the at least two cavities is different.

27. The PMUT structure of claim 26, wherein:

The masses of the at least two masses are each different from each other; and/or

The at least two masses have different thicknesses and/or different widths.

28. The PMUT structure of claim 23, wherein:

The at least two cavities are identical in shape and size.

29. The PMUT structure of claim 23, wherein:

The at least two cavities comprise at least four cavities, the at least four cavities are divided into at least two array units, each array unit comprises at least two cavities, and the mass of at least two mass blocks corresponding to the at least two cavities included in each array unit is different.

30. The PMUT structure of claim 29, wherein:

At least two cavities included in each array unit are arranged into a linear array; or alternatively

At least two cavities included in each array unit are arranged into an area array.

31. The PMUT structure of claim 29, wherein:

At least two PMUTs corresponding to at least two cavities included in each array unit are connected in parallel.

32. The PMUT structure of claim 29, wherein:

the arrangement modes of at least two mass blocks corresponding to different array units are the same.

33. The PMUT structure of claim 1 or 2, wherein:

the at least one cavity comprises at least two cavities, the at least two cavities being identical in shape and size.

34. The PMUT structure of claim 33, wherein:

The at least one cavity comprises at least three cavities, and the at least one PMUT comprises at least three PMUTs; and is also provided with

The center-to-center spacing between adjacent PMUTs is the same or different from each other but within a range of 5%.

35. An electronic device comprising the PMUT structure of any one of claims 1-34.

36. The electronic device of claim 35, wherein:

The electronic device includes at least one of: ultrasonic imaging instrument, ultrasonic range finder, ultrasonic fingerprint sensor, nondestructive inspection instrument, flowmeter, force sense feedback equipment and smoke alarm.