Electrothermal loudness resistance piston motion MEMS speaker and manufacturing method

Abstract

The application discloses an electrothermal loud resistance piston movement type MEMS loudspeaker and a manufacturing method, and belongs to the field of acoustic devices and acoustic-electric conversion. The MEMS loudspeaker adopts a hidden connection structure which is not coplanar with a diaphragm, and the displacement range of the diaphragm in the vertical direction is within the height range of the cavity formed by the support structure extending along the thickness direction of the base. The hidden connection structure can increase the front and back cavity sound resistance values of the piston movement type loudspeaker in the working state, and improve the output sound pressure level of the piston movement type loudspeaker. By optimizing the diaphragm structure, support structure and other components of the piston type loudspeaker with the hidden connection structure, the length, cross-sectional area of the air gap between the front and back cavities and the opening of the base can be adjusted, and the sound resistance and the output sound pressure level can be further improved. The manufacturing method adopts MEMS surface micro-processing technology and MEMS body micro-processing technology, and by using SOI and cavity-SOI with a cavity structure, the complexity of the processing technology is reduced, and the realizability of the device is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of acoustics devices, and relates to an electrothermal MEMS loudspeaker and a manufacturing method thereof, which can be applied to consumer electronics or medical electronics. BACKGROUND

[0002] The core index of a MEMS loudspeaker is an output sound pressure level (SPL). Since the output sound pressure of the loudspeaker is proportional to the square of the frequency and the first power of the diaphragm displacement, the SPL is usually small at low frequencies (20Hz-1kHz). It is very difficult to achieve a high SPL in the low frequency range by using a solidly mounted membrane loudspeaker under the condition that the device size is mm level or even um level. Therefore, a loudspeaker based on an open piston motion mode of a driving structure needs to be used.

[0003] The loudspeaker based on the open piston motion mode of the driving structure has a large motion displacement range, but has the problem of acoustic short circuit between the front and rear cavities. When the diaphragm vibrates, the front and rear cavities generate audio signals with opposite phases at the same time. If there is a large air gap between the front and rear cavities, the audio signals of the front and rear cavities will be superimposed through the air gap, which will weaken the audio signal generated by the loudspeaker, which corresponds to the acoustic resistance of the air gap between the front and rear cavities. Under the premise of not affecting the vibration of the rear cavity air spring, the smaller the air gap, the greater the acoustic resistance between the front and rear cavities, and the greater the conversion coefficient of the energy generated by the mechanical motion of the diaphragm into the energy of the sound radiated to the air in the front cavity, so that a greater SPL can be generated.

[0004] The driving mechanism of a commonly used MEMS loudspeaker mainly includes an electrostatic MEMS loudspeaker, an electrothermal MEMS loudspeaker, a piezoelectric MEMS loudspeaker, and an electromagnetic MEMS loudspeaker. Among them, the electrothermal MEMS loudspeaker has the advantages of low driving voltage, large motion displacement, and mature preparation process. Therefore, it is necessary to provide a large acoustic resistance piston motion type loudspeaker based on an electrothermal driving structure and a manufacturing method thereof, which can not only make the diaphragm produce large displacement motion, but also provide sufficient acoustic resistance, thereby improving the energy conversion efficiency and the output sound pressure level of the loudspeaker. SUMMARY

[0005] One of the main purposes of the present application is to provide an electrothermal large acoustic resistance piston movement type MEMS loudspeaker. Unlike the connecting structure coplanar with the diaphragm in the traditional piston loudspeaker, the electrothermal large acoustic resistance piston movement type MEMS loudspeaker disclosed in the present application adopts a hidden connecting structure coplanar with the diaphragm, and the displacement range of the diaphragm in the vertical direction is within the cavity height range formed by the support structure extending along the thickness direction of the base. On the basis of maintaining the large displacement advantage of the piston loudspeaker, the hidden connecting structure can significantly alleviate the problem of serious air leakage caused by structural design and process limitations, increase the front and back cavity acoustic resistance values of the piston movement type loudspeaker in the working state, and thus effectively improve the output sound pressure level of the piston movement type loudspeaker. In addition, by optimizing the diaphragm structure, support structure and other components of the piston loudspeaker with the above hidden connecting structure, the length, cross-sectional area of the air gap between the front and back cavities and the opening of the base can be adjusted to further improve the acoustic resistance and output sound pressure level.

[0006] In view of the technical problem that there is no manufacturable method for the electrothermal large acoustic resistance piston movement type MEMS loudspeaker, the second main purpose of the present application is a manufacturing method for an electrothermal large acoustic resistance piston movement type MEMS loudspeaker. The method adopts MEMS surface micro-machining technology and MEMS bulk micro-machining technology, reduces the requirement for etching accuracy in the processing technology by using SOI and cavity-SOI with a cavity structure, realizes the manufacturing of the electrothermal large acoustic resistance piston movement type MEMS loudspeaker, and can reduce the process steps.

[0007] One of the purposes of the present application is realized by the following technical solutions:

[0008] The electrothermal large acoustic resistance piston movement type MEMS loudspeaker disclosed in the present application comprises a base, a vibration cavity, an electrothermal driving assembly, a connecting assembly and a diaphragm. The base comprises a base and a support structure extending along the thickness direction of the base, and the support structure is surrounded on all sides to form a vibration cavity. The connecting assembly is not coplanar with the diaphragm, i.e. it is a hidden connecting structure. The electrothermal driving assembly is an electrothermal driving structure, i.e. the difference in thermal expansion coefficients between the driving assembly materials is used to introduce deformation, thereby driving the diaphragm to produce piston movement. The driving assembly and the connecting assembly are the same structure and are composed of one or more driving units. The diaphragm is located inside the cavity, the diaphragm is not coplanar with the connecting assembly, the diaphragm is above or below the connecting assembly, a hidden connecting structure is realized, the displacement range of the diaphragm in the vertical direction is within the cavity height range formed by the support structure extending along the thickness direction of the base, thereby achieving the purposes of reducing air leakage of the MEMS loudspeaker during the working process and improving the sound pressure level.

[0009] On the basis of the electric heating type piston movement type MEMS loudspeaker with a hidden connection structure, the diaphragm structure and the support structure of the loudspeaker are further optimized, that is, the opening shape, size and number of the base in the direction parallel to the diaphragm are optimized and designed, the distance between the diaphragm and the support structure extending in the thickness direction of the base in the direction parallel to the diaphragm is minimized as much as possible, the overlapping distance between the diaphragm and the support structure extending in the thickness direction of the base in the direction perpendicular to the diaphragm is maximized as much as possible, and the shape of the support structure extending in the thickness direction of the base is optimized and designed, so as to control the air leakage phenomenon in the working process of the loudspeaker, further increase the acoustic resistance of the front and rear cavities and the output sound pressure level of the loudspeaker. The driving structure of the electric heating sensor and actuator is simple, the driving voltage is low, and the movement displacement is large, and the use of the electric heating type driving assembly can ensure a large displacement range of the diaphragm. The MEMS surface micro-processing technology and the MEMS body micro-processing technology are used, the cavity-SOI with a cavity structure is used, the requirement for etching accuracy in the processing technology is reduced, the complexity of the processing technology is reduced, the realizability of the device is improved, and the consistency of the device structure is improved, so that the distance between the diaphragm and the support structure extending in the thickness direction of the base in the direction parallel to the diaphragm can be more accurately reduced, the overlapping distance between the diaphragm and the support structure extending in the thickness direction of the base in the direction perpendicular to the diaphragm can be more accurately increased, and the predetermined shape of the support structure can be more accurately formed.

[0010] In order to reduce the device power consumption and improve the working efficiency of the electric heating type driving assembly, as a further improvement, a thermal isolation connection structure is added between the electric heating type driving assembly and the diaphragm assembly and between the electric heating type driving assembly and the support assembly, so as to prevent heat diffusion to the diaphragm and the support assembly.

[0011] The working method of the electric heating type large acoustic resistance piston movement type MEMS loudspeaker disclosed in the application is as follows: the multiple layers of the driving assembly have different thermal expansion coefficients, and under the excitation of an external electric signal, the multiple layers of the electric heating type driving assembly are deformed to different degrees to cause the driving assembly to warp in the direction perpendicular to the diaphragm, so as to drive the diaphragm to move and vibrate in the vertical direction in a piston type. The diaphragm moving and vibrating in the vertical direction drives the air in the vibration cavity to move, so as to generate a sound wave signal. Since the diaphragm is a suspended structure and is suspended in the vibration cavity, the diaphragm is not coplanar with the driving assembly, and the air gap width between the diaphragm edge and the base side wall is very small, and the length of the air gap between the diaphragm edge and the base side wall is very large. Therefore, the air leakage of the diaphragm in the process of moving in the vertical direction in a piston type is reduced, the acoustic resistance is increased, the sound pressure level loss is reduced, and the sound pressure level of the sound output is improved. The MEMS loudspeaker has the advantages of device miniaturization, low power consumption and easy integration, the endurance of the MEMS loudspeaker is improved, and the application range of the MEMS loudspeaker is widened.

[0012] The second object of the present application is achieved by the following technical solutions.

[0013] The manufacturing method of the electrothermal large acoustic resistance piston movement type MEMS loudspeaker disclosed in the present application is used for manufacturing the electrothermal large acoustic resistance piston movement type MEMS loudspeaker, and comprises the following steps.

[0014] Step one: a conventional SOI wafer is provided, the SOI wafer comprising a first silicon layer, a second silicon layer and a silicon oxide layer sandwiched between the first silicon layer and the second silicon layer.

[0015] Step two: a heat transfer layer material, a first layer of thermal expansion material and a second layer of thermal expansion material are deposited and patterned on the surface of the first silicon layer of the SOI wafer, so as to form an electrothermal driving assembly (i.e. a connecting assembly) and a diaphragm assembly with a specific shape on the surface of the first silicon layer. The electrothermal driving assembly is composed of three layers of materials, i.e. the heat transfer layer material, the first layer of thermal expansion material and the second layer of thermal expansion material, and is used for generating displacement. The diaphragm assembly is composed of a first silicon layer with a predetermined thickness or a first silicon layer with a predetermined thickness and a thermal expansion material layer. In the horizontal direction, the diaphragm assembly is located at the center position of the first silicon layer, and the electrothermal driving assembly (i.e. the connecting assembly) covers the first silicon layer and is uniformly distributed outside the diaphragm around the diaphragm. At this time, the electrothermal driving assembly covers the surface of the first silicon layer and cannot move freely, and does not have driving capability; the electrothermal driving assembly is the connecting assembly.

[0016] Step three: the first silicon layer in the SOI wafer is etched from the direction close to the first silicon layer outside the electrothermal driving assembly, and the etching is performed to the silicon oxide layer, so as to determine the size of the diaphragm;

[0017] Step four: the SOI wafer is subjected to deep reactive ion back cavity etching from the direction of the second silicon layer, and the etching is stopped at the silicon oxide layer, so as to form the vibration cavity, i.e. the region in which the diaphragm moves as a piston. By adjusting the rate of deep reactive ion etching, the vibration cavity with a predetermined shape category is formed. By setting the size of the mask layer deposited on the surface of the second silicon layer during the back cavity etching process, the size of the substrate is determined, and the substrate is formed;

[0018] Step five: the silicon oxide layer of the SOI wafer is etched from the direction close to the second silicon layer;

[0019] Step six: etching the first silicon layer from the direction of the SOI wafer towards the first silicon layer, between the position of the electrothermal driving component on the surface of the first silicon layer and the gap between the positions of the diaphragm, to etch part of the thickness of the silicon in the first silicon layer under the electrothermal driving component, thereby separating the electrothermal driving component from the first silicon layer, at this time the electrothermal driving component has driving capability. The first silicon layer under the electrothermal driving component uniformly distributed around the diaphragm assembly on the outside of the diaphragm assembly is not completely etched, and there is still a predetermined thickness of the first silicon layer under the partially etched first silicon layer, the thinner first silicon layer close to the outside and the thicker first silicon layer not etched at the central position form the diaphragm assembly. From the direction of the second silicon layer, the diaphragm assembly partially blocks the electrothermal driving component (connection component), that is, the hidden connection structure. After the first silicon layer is etched, the electrothermal driving component has driving capability, that is, the electrothermal large acoustic resistance piston movement type MEMS loudspeaker is prepared by releasing the device.

[0020] To realize a loudspeaker structure with large acoustic resistance characteristics, as a further improvement, the SOI in step one includes a traditional three-layer SOI and a cavity-SOI with a cavity structure. The cavity-SOI is used to increase the overlapping distance of the diaphragm and the support structure extending in the thickness direction of the base in the electrothermal large acoustic resistance piston movement type MEMS loudspeaker in the direction perpendicular to the diaphragm, or to reduce the distance between the diaphragm and the support structure extending in the thickness direction of the base in the direction parallel to the diaphragm.

[0021] In order to simplify the process steps, as a further improvement, the cavity structure of the cavity-SOI in step one is located in the device layer or the handle layer.

[0022] In order to improve the stability of the device, as a further improvement, the thickness of the cavity structure in the device layer of the cavity-SOI in step one is not more than 50% of the thickness of the device layer.

[0023] In order to improve the working efficiency of the electrothermal driving component, as a further improvement, the heat transfer layer material in step two is located between the first layer of thermal expansion material and the second layer of thermal expansion material.

[0024] In order to improve the success rate of device preparation, as a further improvement, the etching of the first silicon layer in step six uses gas to perform isotropic etching.

[0025] Advantages:

[0026] 1. The electrothermal large acoustic resistance piston motion type MEMS loudspeaker and manufacturing method disclosed by the application has a hidden connection structure, can increase the acoustic resistance between the front and rear cavities during the operation of the piston type loudspeaker, and improves the output sound pressure level of the loudspeaker. The MEMS loudspeaker has the advantages of miniaturization, low power consumption and easy integration, improves the endurance of the MEMS loudspeaker, and widens the application range of the MEMS loudspeaker. The manufacturing method of the MEMS loudspeaker has the characteristics of wafer level preparation, high standardization degree of the preparation process, and strong consistency of the device. The electrothermal driving assembly has low driving voltage, large motion displacement, and simple and easily available consumables, can provide large range displacement for the diaphragm of the loudspeaker, and thus a higher output sound pressure level is obtained.

[0027] 2. The electrothermal large acoustic resistance piston motion type MEMS loudspeaker and manufacturing method disclosed by the application, since the diaphragm and the connection assembly are not coplanar, the displacement range of the diaphragm is within the height range of the vibration cavity, the cross-sectional area of the air gap between the front and rear cavities during the piston motion of the diaphragm in the vertical direction is reduced, and air leakage is alleviated. In addition, based on the principle of increasing the length of the air gap between the front and rear cavities and reducing the cross-sectional area of the air gap between the front and rear cavities, the diaphragm and the support structure of the piston motion type loudspeaker with the hidden connection structure are optimized, and the target of increasing the acoustic resistance between the front and rear cavities and improving the sound pressure level of the sound output is achieved.

[0028] 3. The electrothermal large acoustic resistance piston motion type MEMS loudspeaker and manufacturing method disclosed by the application, since the diaphragm is connected with the support structure through the connection assembly, compared with the diaphragm with the edge fixed support, the displacement amount that the diaphragm can reach during the vibration process is not limited by the support structure, the vibration amplitude of the diaphragm is improved, and thus the output sound pressure level of the loudspeaker is improved.

[0029] 4. In view of the technical problem that there is no manufacturable manufacturing method for the electrothermal large acoustic resistance piston motion type MEMS loudspeaker, the electrothermal large acoustic resistance piston motion type MEMS loudspeaker manufacturing method disclosed by the application adopts the MEMS surface microprocessing technology and the MEMS body microprocessing technology, reduces the requirement for etching accuracy in the processing technology by using SOI and cavity-SOI with a cavity structure, realizes the manufacturing of the electrothermal large acoustic resistance piston motion type MEMS loudspeaker, and is convenient for the manufacturing of electrothermal large acoustic resistance piston motion type MEMS loudspeakers with different structures. By using consumables with a predetermined structure, the process steps are simplified, the device wafer level mass production is realized, the consistency of the device is improved, and the design and preparation of the MEMS loudspeaker are facilitated. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a structure schematic diagram of the electrothermal large acoustic resistance piston motion type MEMS loudspeaker provided by the first embodiment of the application.

[0031] Figure 2 is a cross-sectional view of the electrothermal large acoustic resistance piston movement type MEMS loudspeaker provided in Embodiment One of the present application;

[0032] Figure 3 is a process flow chart for preparing the electrothermal large acoustic resistance piston movement type MEMS loudspeaker provided in Embodiment One of the present application;

[0033] Wherein: 100 - large acoustic resistance piston movement type loudspeaker, 110 - base, 111 - pedestal, 112 - support structure, 120 - drive assembly, 130 - diaphragm, 140 - connecting assembly, 150 - cavity.

[0034] Figure 4 is a structural schematic view of the electrothermal large acoustic resistance piston movement type MEMS loudspeaker provided in Embodiment Two of the present application;

[0035] Figure 5 is a cross-sectional view of the electrothermal large acoustic resistance piston movement type MEMS loudspeaker provided in Embodiment Two of the present application;

[0036] Figure 6 is a process flow chart for preparing the electrothermal large acoustic resistance piston movement type MEMS loudspeaker provided in Embodiment Three of the present application;

[0037] Wherein: 200 - large acoustic resistance piston movement type loudspeaker, 210 - base, 211 - pedestal, 212 - support structure, 220 - drive assembly, 230 - diaphragm, 240 - connecting assembly, 250 - cavity.

[0038] Figure 7 is a structural schematic view of the electrothermal large acoustic resistance piston movement type MEMS loudspeaker provided in Embodiment Three of the present application;

[0039] Figure 8 is a cross-sectional view of the electrothermal large acoustic resistance piston movement type MEMS loudspeaker provided in Embodiment Three of the present application;

[0040] Figure 9 is a process flow chart for preparing the electrothermal large acoustic resistance piston movement type MEMS loudspeaker provided in Embodiment Three of the present application;

[0041] Wherein: 300 - large acoustic resistance piston movement type loudspeaker, 310 - base, 311 - pedestal, 312 - support structure, 320 - drive assembly, 330 - diaphragm, 340 - connecting assembly, 350 - cavity.

[0042] Figure 10 is a structural schematic view of the electrothermal large acoustic resistance piston movement type MEMS loudspeaker provided in Embodiment Four of the present application;

[0043] Figure 11is a cross-sectional schematic view of an electrothermal large acoustic resistance piston movement type MEMS loudspeaker provided in Embodiment Four of the present application;

[0044] Figure 12 is a preparation process flow chart of the electrothermal large acoustic resistance piston movement type MEMS loudspeaker provided in Embodiment Four of the present application;

[0045] 400 - large acoustic resistance piston movement type loudspeaker, 410 - base, 411 - pedestal, 412 - support structure, 420 - driving assembly, 430 - diaphragm, 440 - connecting assembly, 450 - cavity. DETAILED DESCRIPTION

[0046] For better illustrating the purposes and advantages of the present application, the following further illustrates the content of the present application in combination with the drawings and examples.

[0047] It should be noted that all directionality indications (such as up, down, left, right, front, back, in, out, top, bottom, etc.) in the embodiments of the present application are only used to explain the relative positional relationship between components and the like in a certain specific posture (as shown in the drawings), and if the specific posture changes, the directionality indications also change accordingly.

[0048] Embodiment One

[0049] Please refer to Figure 1 According to Embodiment One of the present application, an electrothermal large acoustic resistance piston movement type MEMS loudspeaker 100 is provided, which comprises a base 110, an electrothermal driving assembly 120, a diaphragm 130, a connecting assembly 140, and a cavity 150. The diaphragm 130 is square, and the cross section of the cavity 150 is square, matching the shape of the diaphragm 130. The electrothermal driving assembly 120 and the connecting assembly 140 are the same structure, and the electrothermal driving assembly 120 comprises four groups of driving units. The base 110 comprises a pedestal 111 and a support structure 112 extending in the thickness direction. The connecting assembly 140 comprises four groups of connecting units for connecting the support structure 112 and the diaphragm 130. The support structure 112 surrounds to form the cavity 150.

[0050] Please refer to the cross-sectional schematic view Figure 2, based on the structure design principle that the distance between the diaphragm and the support structure in the direction parallel to the diaphragm is as small as possible. The electrothermal large acoustic resistance piston movement type MEMS loudspeaker 100 provided by the first embodiment of the present application is not coplanar with the connecting assembly 140 and the diaphragm 130. The connecting assembly 140 and the diaphragm 130 overlap in the projection area on the horizontal plane, which is a hidden driving structure. The gap width of the diaphragm 130 and the support structure 112 in the horizontal direction is smaller than the width of the connecting assembly 140, effectively reducing the cross-sectional area of the air gap between the front cavity and the rear cavity. In the working state of the loudspeaker, the displacement range of the diaphragm 130 is within the height range of the cavity 150, ensuring that the cross-sectional area of the air gap between the front cavity and the rear cavity is maintained at a small value during the entire working process, achieving the purpose of increasing the acoustic resistance of the front cavity and the rear cavity.

[0051] Please refer to the cross-sectional schematic view Figure 2 , based on the structure design principle of adjusting the opening shape, size and number of the base in the direction parallel to the diaphragm. The electrothermal large acoustic resistance piston movement type MEMS loudspeaker 100 provided by the first embodiment of the present application is not coplanar with the connecting assembly 140 and the diaphragm 130. The connecting assembly 140 and the diaphragm 130 overlap in the projection area on the horizontal plane, which is a hidden driving structure. The gap width of the diaphragm 130 and the support structure 112 in the horizontal direction is smaller than the width of the connecting assembly 140, effectively reducing the cross-sectional area of the air gap between the front cavity and the rear cavity. In the working state of the loudspeaker, the displacement range of the diaphragm 130 is within the height range of the cavity 150, ensuring that the cross-sectional area of the air gap between the front cavity and the rear cavity is maintained at a small value during the entire working process, achieving the purpose of increasing the acoustic resistance of the front cavity and the rear cavity.

[0052] Please refer to Figure 3 , the present application also provides a manufacturing method S100 of the electrothermal large acoustic resistance piston movement type MEMS loudspeaker 100, comprising:

[0053] Step S101, please refer to Figure 3 (a), providing an SOI wafer, the SOI wafer comprising a first silicon layer 111, a second silicon layer 112 and a silicon oxide layer 121 sandwiched between the first silicon layer and the second silicon layer;

[0054] Step S102, please refer to Figure 3 (b), depositing and patterning a silicon oxide layer 122 on the first silicon layer 111 of the SOI wafer;

[0055] Step S103, please refer to Figure 3 (c), depositing and patterning a metal layer 131, which is the first layer of the electrothermal driving assembly;

[0056] Step S104, please refer to Figure 3 (d), depositing and patterning a metal layer 141, which is the second layer of the electrothermal driving assembly;

[0057] Step S105, please refer to Figure 3(e), deposit and pattern the silicon oxide layer 123, which is the third layer of the electrothermal driving component. At this time, the electrothermal driving component and the diaphragm component are preliminarily formed. In the horizontal direction, the diaphragm component is located at the center of the first silicon layer, and the electrothermal driving component (i.e., the connecting component) covers the first silicon layer and is uniformly distributed outside the diaphragm component. At this time, the electrothermal driving component covers the surface of the first silicon layer and cannot move freely, and does not have driving capability;

[0058] Step S106, refer to Figure 3 (f), deposit and pattern the silicon oxide layer 124 on the second silicon layer 112 of the SOI wafer, to provide a mask for subsequent back cavity etching of the second silicon layer;

[0059] Step S107, refer to Figure 3 (g), etch the SOI first silicon layer 111 to the silicon oxide layer of the SOI wafer from the front side to determine the position of the speaker diaphragm;

[0060] Step S108, refer to Figure 3 (h), etch the SOI second silicon layer 112 from the back side to the silicon oxide layer to form the vibration cavity, i.e., the area in which the diaphragm moves as a piston;

[0061] Step S109, refer to Figure 3 (i), etch the SOI silicon oxide layer 121;

[0062] Step S110, refer to Figure 3 (j), etch the SOI first silicon layer from the front side to separate the driving structure and the diaphragm structure, and etch part of the thickness of the first silicon layer below the electrothermal driving component. At this time, the electrothermal driving component has driving capability. The first silicon layer below the electrothermal driving component that is uniformly distributed outside the diaphragm component is not completely etched, and a predetermined thickness of the first silicon layer is retained below the partially etched first silicon layer. The thinner first silicon layer retained near the outside and the thicker first silicon layer not etched at the center form the diaphragm component;

[0063] Step S111, refer to Figure 3 (k), deposit a barrier material 151 on the silicon oxide layer 124 below the SOI wafer;

[0064] Step S112, refer to Figure 4 (l), pattern the barrier material 151 to complete the electrothermal loud resistance piston movement type MEMS speaker with a through-hole structure and a hidden connection structure.

[0065] Example Two

[0066] Please refer to Figure 5, according to the second embodiment of the present application, there is provided an electrothermal large acoustic resistance piston motion type MEMS loudspeaker 200, comprising a substrate 210, an electrothermal driving assembly 220, a diaphragm 230, a connecting assembly 240, and a cavity 250. The diaphragm 230 is square, and the cross section of the cavity 250 is square and matches the shape of the diaphragm 230. The electrothermal driving assembly 220 and the connecting assembly 240 are of the same structure, and the electrothermal driving assembly 220 comprises four groups of driving units. The substrate 210 comprises a base 211 and a support structure 212 extending in the thickness direction. The connecting assembly 240 comprises four groups of connecting units for connecting the support structure 212 and the diaphragm 230. The support structure 212 surrounds the cavity 250.

[0067] Please refer to the cross-sectional schematic view Figure 5 , based on the structural design principle that the spacing between the diaphragm and the support structure in the direction parallel to the diaphragm is as small as possible. According to the second embodiment of the present application, the electrothermal large acoustic resistance piston motion type MEMS loudspeaker 200, the connecting assembly 240 and the diaphragm 230 are not coplanar. There is an overlapping part between the projection area of the connecting assembly 240 and the diaphragm 230 in the horizontal plane, which is a hidden driving structure. The gap width of the diaphragm 230 and the support structure 212 in the horizontal direction is smaller than the width of the connecting assembly 240, effectively reducing the cross-sectional area of the air gap between the front and rear cavities. In the working state of the loudspeaker, the displacement range of the diaphragm 230 is within the height range of the cavity 250, ensuring that the cross-sectional area of the air gap between the front and rear cavities is maintained at a small value throughout the working process, achieving the purpose of increasing the acoustic resistance of the front and rear cavities.

[0068] Please refer to the cross-sectional schematic view Figure 6 , based on the structural design principle that the spacing between the diaphragm and the support structure in the direction parallel to the diaphragm is as small as possible, the support structure is discontinuous in the thickness direction and is segmented perpendicularly to the diaphragm. According to the second embodiment of the present application, the electrothermal large acoustic resistance piston motion type MEMS loudspeaker 200, the support structure 212 is in the shape of an inverted "convex" character. To meet the process requirements, the upper side of the cavity 250 has a larger size. After the device is released, in the working state, the displacement range of the diaphragm 230 is within the range of the smaller size of the lower side of the cavity 250, to a certain extent, solving the problem of large spacing between the diaphragm and the support structure in the direction parallel to the diaphragm due to process limitations, ensuring that the cross-sectional area of the air gap between the front and rear cavities is maintained at a small value, achieving the purpose of increasing the acoustic resistance of the front and rear cavities.

[0069] Please refer to the cross-sectional schematic view Figure 6 , the second embodiment of the present application also provides a manufacturing method S200 for the electrothermal large acoustic resistance piston motion type MEMS loudspeaker 200, comprising:

[0070] Step S201, please refer to Figure 6(a), providing an SOI wafer, which comprises a first silicon layer 211, a second silicon layer 212 and a silicon oxide layer 221 sandwiched between the first silicon layer and the second silicon layer, the second silicon layer 212 comprising a cavity structure with a certain thickness;

[0071] Step S202, referring to Figure 6 (b), depositing and patterning a silicon oxide layer 222 on the first silicon layer 211 of the SOI wafer;

[0072] Step S203, referring to Figure 6 (c), depositing and patterning a metal layer 231, i.e. the first layer of the electrothermal driving assembly;

[0073] Step S204, referring to Figure 6 (d), depositing and patterning a metal layer 241, i.e. the second layer of the electrothermal driving assembly;

[0074] Step S205, referring to Figure 6 (e), depositing and patterning a silicon oxide layer 223, i.e. the third layer of the electrothermal driving assembly. At this time, the electrothermal driving assembly and the diaphragm assembly are preliminarily formed. In the horizontal direction, the diaphragm assembly is located at the center of the first silicon layer, and the electrothermal driving assembly (i.e. the connecting assembly) covers the first silicon layer and is uniformly distributed outside the diaphragm. At this time, the electrothermal driving assembly covers the surface of the first layer of silicon and cannot move freely, and does not have driving capability;

[0075] Step S206, referring to Figure 6 (f), depositing and patterning a silicon oxide layer 224 on the second silicon layer 212 of the SOI wafer, to provide a mask for subsequent back cavity etching of the second silicon layer;

[0076] Step S207, referring to Figure 6 (g), etching the SOI first silicon layer 211 to the silicon oxide layer of the SOI wafer from the front side to determine the position of the speaker diaphragm;

[0077] Step S208, referring to Figure 6 (h), etching the SOI second silicon layer 212 from the back side to stop at the silicon oxide layer to form the vibration cavity, i.e. the area where the diaphragm moves as a piston;

[0078] Step S209, referring to Figure 6 (i), etching the SOI silicon oxide layer 221;

[0079] Step S210, referring to Figure 7(j), the first silicon layer under the electrothermal driving assembly is etched to separate the driving structure and the diaphragm structure, and the silicon in the first silicon layer under the electrothermal driving assembly is etched to a partial thickness, at this time, the electrothermal driving assembly has a driving capability. The first silicon layer under the electrothermal driving assembly which is uniformly distributed around the diaphragm assembly outside the diaphragm assembly is not completely etched, and a predetermined thickness of the first silicon layer is reserved under the partially etched first silicon layer, and the thinner first silicon layer reserved near the outside and the thicker first silicon layer not etched at the central position form the diaphragm assembly, and the electrothermal loud-sound-resistance piston movement type MEMS loudspeaker with a segmented cavity structure and a hidden connection structure is prepared.

[0080] Embodiment three

[0081] Please refer to Figure 8 According to the electrothermal loud-sound-resistance piston movement type MEMS loudspeaker 300 provided in the embodiment three of the present application, the diaphragm 330 is square, and the cross section of the cavity 350 is square, matching the shape of the diaphragm 330. The electrothermal driving assembly 320 and the connection assembly 340 are the same structure, and the electrothermal driving assembly 320 includes four groups of driving units. The base 310 includes a base 311 and a support structure 312 extending in the thickness direction. The connection assembly 340 includes four groups of connection units for connecting the support structure 312 and the diaphragm 330. The support structure 312 surrounds to form the cavity 350.

[0082] Please refer to the cross-sectional schematic view Figure 8 Based on the structural design principle that the spacing between the diaphragm and the support structure in the direction parallel to the diaphragm is as small as possible, the electrothermal loud-sound-resistance piston movement type MEMS loudspeaker 300 provided in the embodiment three of the present application is not coplanar with the diaphragm 330. There is an overlapping part between the projection area of the connection assembly 340 and the diaphragm 330 in the horizontal plane, which is a hidden driving structure. The gap width between the diaphragm 330 and the support structure 312 in the horizontal direction is smaller than the width of the connection assembly 340, effectively reducing the cross-sectional area of the air gap between the front and rear cavities. In the working state of the loudspeaker, the displacement range of the diaphragm 330 is within the height range of the cavity 350, which ensures that the cross-sectional area of the air gap between the front and rear cavities is maintained at a small value during the entire working process, achieving the purpose of increasing the sound resistance of the front and rear cavities.

[0083] Please refer to the cross-sectional schematic view Figure 9, based on the design principle that the distance between the diaphragm and the support structure in the direction parallel to the diaphragm is as small as possible, the support structure is continuous in the thickness direction but is not perpendicular to the diaphragm, and the support structure is at an inclined angle with the diaphragm. The electrothermal large acoustic resistance piston movement type MEMS loudspeaker 300 provided in the third embodiment of the present application has an inverted isosceles trapezoidal cross-sectional profile of the support structure 312. In order to meet the process requirements, the size of the cavity 350 gradually increases from the base 311 to the diaphragm 230. Compared with the loudspeaker structure in which the cavity side wall is perpendicular to the diaphragm, the cross-sectional area of the air gap between the front cavity and the rear cavity is significantly reduced when the diaphragm 230 moves to the position close to the base 311 in the working state. To some extent, the problem that the distance between the diaphragm and the support structure in the direction parallel to the diaphragm is large due to the process limit is solved, and the purpose of increasing the acoustic resistance of the front cavity and the rear cavity is achieved.

[0084] Referring to Figure 9 The third embodiment of the present application further provides a manufacturing method S300 of the electrothermal large acoustic resistance piston movement type MEMS loudspeaker 300, comprising the following steps.

[0085] In step S301, referring to Figure 9 (a), an SOI wafer is provided, which comprises a first silicon layer 311, a second silicon layer 312, and a silicon oxide layer 321 arranged between the first silicon layer and the second silicon layer;

[0086] In step S302, referring to Figure 9 (b), a silicon oxide layer 322 is deposited and patterned on the first silicon layer 311 of the SOI wafer;

[0087] In step S303, referring to Figure 9 (c), a metal layer 331, i.e., the first layer of the electrothermal driving assembly, is deposited and patterned;

[0088] In step S304, referring to Figure 9 (d), a metal layer 341, i.e., the second layer of the electrothermal driving assembly, is deposited and patterned;

[0089] In step S305, referring to Figure 9 (e), a silicon oxide layer 323, i.e., the third layer of the electrothermal driving assembly, is deposited and patterned. At this time, the electrothermal driving assembly and the diaphragm assembly are preliminarily formed. In the horizontal direction, the diaphragm assembly is located at the center position of the first silicon layer, and the electrothermal driving assembly (i.e., the connecting assembly) covers the first silicon layer and is uniformly distributed outside the diaphragm. At this time, the electrothermal driving assembly covers the surface of the first silicon layer and cannot move freely, and does not have driving capability;

[0090] In step S306, referring to Figure 9(f) depositing and patterning a silicon oxide layer 324 on the second silicon layer 312 of the SOI wafer, to provide a mask for subsequent back cavity etching of the second silicon layer;

[0091] Step S307, refer to Figure 9 (g) etching the SOI first silicon layer 311 from the front side to the silicon oxide layer of the SOI wafer, to determine the position of the speaker diaphragm;

[0092] Step S308, refer to 9(h), etching the SOI second silicon layer 312 from the back side, etching to the silicon oxide layer to stop, forming the vibration cavity, i.e. the area where the diaphragm moves as a piston;

[0093] Step S309, refer to Figure 9 (i) etching the SOI silicon oxide layer 321;

[0094] Step S310, refer to Figure 10 (j) etching the SOI first silicon layer from the front side to separate the driving structure and the diaphragm structure, etching part of the thickness of the first silicon layer below the electrothermal driving assembly, at this time the electrothermal driving assembly has driving capability. The first silicon layer below the electrothermal driving assembly uniformly distributed around the diaphragm assembly outside the diaphragm assembly is not completely etched, there is still a predetermined thickness of the first silicon layer below the partially etched first silicon layer, the thinner first silicon layer reserved near the outside and the thicker first silicon layer not etched at the center position form the diaphragm assembly, and the electrothermal large acoustic resistance piston movement type MEMS speaker with inclined cavity and hidden connection structure is prepared.

[0095] Example Four

[0096] Please refer to Figure 11 According to the fourth embodiment of the present application, an electrothermal large acoustic resistance piston movement type MEMS speaker 400 is provided, which comprises a substrate 410, an electrothermal driving assembly 420, a diaphragm 430, a connecting assembly 440, and a cavity 450. The diaphragm 430 is square, and the cross section of the cavity 450 is square, matching the shape of the diaphragm 430. The electrothermal driving assembly 420 and the connecting assembly 440 are the same structure, and the electrothermal driving assembly 420 comprises four groups of driving units. The substrate 410 comprises a base 411 and a support structure 412 extending in the thickness direction. The connecting assembly 440 comprises four groups of connecting units for connecting the support structure 412 and the diaphragm 430. The support structure 412 surrounds the cavity 450.

[0097] Please refer to the cross-sectional schematic diagram Figure 11, based on the structural design principle that the distance between the diaphragm and the support structure in the direction parallel to the diaphragm is as small as possible. In the electrothermal large acoustic resistance piston motion type MEMS speaker 400 provided in the fourth embodiment of the present invention, the connection component 440 and the diaphragm 430 are not coplanar. There is an overlapping part in the projection area of the connection component 440 and the diaphragm 430 on the horizontal plane, which is a hidden drive structure. The gap width between the diaphragm 430 and the support structure 412 in the horizontal direction is less than the width of the connection component 440, effectively reducing the cross-sectional area of the air gap between the front and rear cavities. In the working state of the speaker, the displacement range of the diaphragm 430 is within the height range of the cavity 450, ensuring that the cross-sectional area of the air gap between the front and rear cavities remains small throughout the working process, achieving the purpose of increasing the acoustic resistance between the front and rear cavities.

[0098] Please refer to the cross-sectional schematic diagram Figure 12 , based on the structural design principle that the overlapping distance between the diaphragm and the support structure in the direction perpendicular to the diaphragm is as large as possible. In the electrothermal large acoustic resistance piston motion type MEMS speaker 400 provided in the fourth embodiment of the present invention, the cross-sectional view of the diaphragm 430 is in the shape of "冖". Compared with the diaphragm structure with a rectangular cross-sectional view, on the basis of controlling the mass of the diaphragm, the overlapping area between the diaphragm 430 and the support structure 412 in the direction perpendicular to the diaphragm 430 is increased, effectively increasing the length of the air gap between the front and rear cavities, achieving the purpose of increasing the acoustic resistance between the front and rear cavities.

[0099] Refer to Figure 12 , the fourth embodiment of the present invention also provides a manufacturing method S400 for an electrothermal large acoustic resistance piston motion type MEMS speaker 400, including:

[0100] Step S401, refer to Figure 12 (a), Provide a SOI wafer, the SOI wafer includes a first silicon layer 411, a second silicon layer 412, and a silicon oxide layer 421 sandwiched between the first silicon layer and the second silicon layer, and the first silicon layer 411 contains a cavity structure with a certain thickness;

[0101] Step S402, refer to Figure 12 (b), Deposit and pattern the silicon oxide layer of 422 on the first silicon layer 411 of the SOI wafer;

[0102] Step S403, refer to Figure 12 (c), Deposit and pattern the metal layer 431, which is the first layer of the electrothermal drive component; <o000271>

[0103] Step S404, refer to Figure 12 (d), Deposit and pattern the metal layer 441, which is the second layer of the electrothermal drive component; <00002x75>Step S40s, refer toFigure 12 (e), deposit and patternize the silicon oxide layer 423, which is the third layer of the electrothermal driving component. At this time, the electrothermal driving component and the diaphragm component are preliminarily formed. In the horizontal direction, the diaphragm component is located at the center of the first silicon layer, and the electrothermal driving component (i.e., the connecting component) covers the first silicon layer and is uniformly distributed outside the diaphragm component. At this time, the electrothermal driving component covers the surface of the first silicon layer and cannot move freely, and does not have driving capability;

[0105] Step S406, refer to Figure 12 (f), deposit and patternize the silicon oxide layer 424 on the second silicon layer 412 of the SOI wafer, to provide a mask for subsequent back cavity etching of the second silicon layer;

[0106] Step S407, refer to Figure 12 (g), etch the SOI first silicon layer 411 from the front side to the silicon oxide layer of the SOI wafer, to determine the position of the speaker diaphragm;

[0107] Step S408, refer to Figure 12 (h), etch the SOI second silicon layer 412 from the back side, and stop etching at the silicon oxide layer to form the vibration cavity, i.e., the region in which the diaphragm moves as a piston;

[0108] Step S409, refer to Figure 12 (i), etch the SOI silicon oxide layer 421;

[0109] Step S410, refer to ​ (j), etch the SOI first silicon layer from the front side to separate the driving structure and the diaphragm structure, and etch part of the thickness of the first silicon layer below the electrothermal driving component. At this time, the electrothermal driving component has driving capability. The first silicon layer below the electrothermal driving component, which is uniformly distributed outside the diaphragm component, is not completely etched, and a predetermined thickness of the first silicon layer is retained below the partially etched first silicon layer. The thinner first silicon layer retained near the outside and the thicker first silicon layer not etched at the center form the diaphragm component, and the electrothermal loud-piston movement MEMS speaker with a "ㄗ" shaped diaphragm structure and a hidden connecting structure is prepared.

[0110] The above detailed description further describes the purpose, technical solution and beneficial effects of the application. It should be understood that the above description is only a specific embodiment of the application and is not used to limit the protection scope of the application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the application should be included in the protection scope of the application.

Claims

1. An electro-thermal loud resistance piston-motion MEMS loudspeaker, characterized by: The application relates to a piezoelectric transducer, which comprises a base, a vibration cavity, an electrothermal driving assembly, a connecting assembly and a diaphragm; the base comprises a base seat and a support structure extending along the thickness direction of the base seat, and the support structure is surrounded to form the vibration cavity; the connecting assembly is not coplanar with the diaphragm, that is, the connecting assembly is a hidden connecting structure; the electrothermal driving assembly is an electrothermal driving structure, that is, the driving assembly is driven to produce a piston movement by utilizing the difference between the thermal expansion coefficients of the materials of the driving assembly; the driving assembly and the connecting assembly are the same structure and are composed of one or more driving units; the diaphragm is located in the cavity, the diaphragm is not coplanar with the connecting assembly, the diaphragm is above or below the connecting assembly, the hidden connecting structure is realized, and the displacement range of the diaphragm in the vertical direction is within the height range of the cavity formed by the support structure extending along the thickness direction of the base seat.

2. The electro-thermal loud resistance piston-motion MEMS loudspeaker of claim 1, wherein: The MEMS surface micro-processing technology and the MEMS body micro-processing technology are adopted, and SOI is used for processing.

3. The electro-thermal loud resistance piston-motion MEMS loudspeaker of claim 2, wherein: A thermal isolation connecting structure is arranged between the electrothermal driving assembly and the diaphragm assembly and between the electrothermal driving assembly and the support assembly, so that heat diffusion to the diaphragm and the support assembly is prevented.

4. A method of manufacturing an electrothermal large acoustic resistance piston motion MEMS speaker for manufacturing an electrothermal large acoustic resistance piston motion MEMS speaker as claimed in claim 1, 2 or 3, characterized in that: The application further relates to a piezoelectric transducer manufacturing method, which comprises the following steps, Step one: an SOI wafer is adopted, the SOI wafer comprising a first silicon layer, a second silicon layer and a silicon oxide layer arranged between the first silicon layer and the second silicon layer; Step two: a heat transfer layer material, a first layer of thermal expansion material and a second layer of thermal expansion material are deposited and patterned on the surface of the first silicon layer of the SOI wafer, so as to form an electrothermal driving assembly and a diaphragm assembly with a specific shape on the surface of the first silicon layer; the electrothermal driving assembly is composed of three layers of materials, that is, the heat transfer layer material, the first layer of thermal expansion material and the second layer of thermal expansion material, and is used for producing displacement; the diaphragm assembly is composed of a first silicon layer with a predetermined thickness or a first silicon layer with a predetermined thickness and a thermal expansion material layer; in the horizontal direction, the diaphragm assembly is located at the center position of the first silicon layer, the electrothermal driving assembly covers the first silicon layer and is uniformly distributed outside the diaphragm around the diaphragm assembly; at this time, the electrothermal driving assembly covers the surface of the first silicon layer and cannot freely move, and does not have driving capacity; the electrothermal driving assembly is a connecting assembly; Step three: the first silicon layer in the SOI wafer is etched from the direction close to the first silicon layer and outside the electrothermal driving assembly, and the etching is stopped at the silicon oxide layer, so as to determine the size of the diaphragm; Step four: deep reactive ion back cavity etching is performed on the SOI wafer from the direction of the second silicon layer, and the etching is stopped at the silicon oxide layer, so as to form a vibration cavity, that is, the region in which the diaphragm moves as a piston; By adjusting the etching rate of the deep reactive ion etching and selecting different types of SOI, the vibration cavity with a predetermined shape category is formed; by setting the size of the mask layer deposited on the surface of the second silicon layer in the back cavity etching process, the size of the base is determined, and the base is formed; Step five: the silicon oxide layer of the SOI wafer is etched from the direction close to the second silicon layer. Step six: etching the first silicon layer from the direction of the SOI wafer to the first silicon layer, between the position of the electrothermal driving component on the surface of the first silicon layer and the gap between the positions of the diaphragm, to separate the electrothermal driving component from the first silicon layer, and the electrothermal driving component has driving ability at this time; The first silicon layer under the electrothermal driving component uniformly distributed around the diaphragm assembly is not completely etched, and a first silicon layer with a predetermined thickness is retained under the partially etched first silicon layer, and the thinner first silicon layer retained near the outside and the thicker first silicon layer not etched at the central position form the diaphragm assembly; from the direction of the second silicon layer, the diaphragm assembly partially blocks the electrothermal driving component, i.e. the hidden connection structure; the first silicon layer is etched, and the electrothermal driving component has driving ability, i.e. the electrothermal large acoustic resistance piston motion MEMS loudspeaker is prepared by releasing the device.

5. The electro-thermal loud resistance piston motion type MEMS speaker manufacturing method according to claim 4, characterized by: The SOI of step one adopts a cavity-SOI with a cavity structure.

6. The electro-thermal loud resistance piston motion type MEMS speaker manufacturing method according to claim 5, characterized by: The cavity structure of the cavity-SOI of step one is located in the device layer or the support layer.

7. The method of claim 6, wherein the method further comprises: The thickness of the cavity structure in the cavity-SOI of step one located in the device layer is not more than 50% of the thickness of the device layer.

8. The electro-thermal loud resistance-piston-motion MEMS speaker manufacturing method of claim 4, wherein: The heat transfer layer material of step two is located between the first layer of thermal expansion material and the second layer of thermal expansion material.

9. The electro-thermal loud resistance-piston-motion MEMS speaker manufacturing method of claim 4, wherein: The first silicon layer etching of step six adopts gas for isotropic etching.

10. The electrothermal loud resistance piston motion MEMS speaker of any of claims 1, 2 or 3, wherein: The multi-layer material of the driving component has different thermal expansion coefficients, and under the excitation of an external electric signal, the multi-layer structure of the electrothermal driving component deforms to different degrees, causing the driving component to warp perpendicular to the diaphragm direction, driving the diaphragm to move vertically as a piston; the diaphragm moving vertically as a piston drives the air inside the vibration cavity to move, thereby generating a sound signal.

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