Laminated piezoelectric MEMS structure

Abstract

The invention relates to the technical field of semiconductor technologies, in particular to a laminated piezoelectric MEMS structure and a preparation method thereof.The structure comprises a substrate, the substrate is provided with a front face and a back face which are opposite, a piezoelectric layer grows on the back face of the substrate, a substrate is bonded to the surface, away from the substrate, of the piezoelectric layer, and a back cavity penetrates through the substrate; the back cavity provides a vibration space for the vibrating diaphragm of the piezoelectric layer; the preparation method comprises the following steps: preparing a substrate having a front surface and a back surface opposite to each other, and growing a piezoelectric layer on the back surface of the substrate; preparing a substrate, and penetrating through the substrate to form a back cavity; the substrate is bonded to the surface, away from the substrate, of the piezoelectric layer, the back cavity is used for providing a vibration space for a vibrating diaphragm of the piezoelectric layer, the piezoelectric layer is grown through the glass substrate, the substrate serves as the substrate, the substrate can be directly and electrically connected with the first electrode and the second electrode respectively, additional packaging steps are not needed, and cost is saved.

Description

Technical Field

[0001] This specification relates to the field of MEMS semiconductor process technology, and in particular to a stacked piezoelectric MEMS structure and its fabrication method. Background Technology

[0002] MEMS chips are miniature systems that integrate mechanical components, sensors, actuators, and electronic circuits onto a single silicon substrate. Microelectromechanical systems (MEMS) are high-tech electromechanical devices developed based on microelectronics technology (semiconductor manufacturing technology), integrating techniques such as photolithography, etching, thin film processing, LIGA, silicon micromachining, non-silicon micromachining, and precision machining. MEMS are miniature devices or systems that integrate microsensors, microactuators, micromechanical structures, micropower supplies, signal processing and control circuits, high-performance integrated electronic devices, interfaces, and communication. MEMS is a revolutionary new technology widely used in high-tech industries and is a key technology related to national scientific and technological development, economic prosperity, and national defense security.

[0003] In existing technologies, MEMS chips mostly use SOI or silicon substrates as substrates. After growing piezoelectric structures on the substrate, the substrate is then etched to form a back cavity for the diaphragm. After forming the MEMS chip, it is necessary to use the substrate for external packaging and interconnection. The process is complicated and the production cost is high.

[0004] Based on the above reasons, this application proposes a stacked piezoelectric MEMS structure and fabrication method to solve the aforementioned problems. Summary of the Invention

[0005] This invention aims to solve the problems mentioned in the background art by proposing a stacked piezoelectric MEMS structure and its fabrication method. First, a piezoelectric layer is grown on a glass substrate. Then, the piezoelectric layer is bonded to a substrate after a back cavity is formed, with the substrate serving as the substrate. At the same time, the substrate can be directly electrically interconnected with the first electrode and the second electrode respectively, without the need for additional packaging steps, thus saving costs. In addition, the easy-to-clean feature of the glass substrate can make the MEMS structure waterproof and dustproof.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A stacked piezoelectric MEMS structure includes a substrate having a front side and a back side, a piezoelectric layer grown on the back side of the substrate, a substrate bonded to the surface of the piezoelectric layer away from the substrate, and a back cavity formed through the substrate, the back cavity providing space for the diaphragm of the piezoelectric layer to vibrate.

[0008] As a further embodiment of the present invention, the substrate is a glass substrate, a UTG glass substrate, or a PI substrate.

[0009] As a further aspect of the present application, the thickness of the substrate is 30-100 μm.

[0010] As a further aspect of the present application, the substrate is a BT substrate.

[0011] As a further aspect of the present application, the thickness of the substrate is 200-600 μm.

[0012] As a further aspect of the present application, the piezoelectric layer comprises a first electrode, a piezoelectric film and a second electrode, the first electrode is grown on the back surface of the substrate, the piezoelectric film is grown on the surface of the first electrode away from the substrate, and the second electrode is grown on the surface of the piezoelectric film away from the first electrode.

[0013] As a further aspect of the present application, the piezoelectric film is a PZT piezoelectric film.

[0014] As a further aspect of the present application, the first electrode is exposed by penetrating the second electrode and the piezoelectric film, and the substrate is bonded to the piezoelectric layer and is electrically interconnected with the first electrode and the second electrode respectively.

[0015] A preparation method for preparing the above-mentioned laminated piezoelectric MEMS structure, comprising the following steps:

[0016] S1, preparing a substrate, the substrate having opposite front and back surfaces, and a piezoelectric layer is grown on the back surface of the substrate;

[0017] S1-1, growing a first electrode on the back surface of the substrate;

[0018] S1-2, growing a piezoelectric film on the surface of the first electrode away from the substrate;

[0019] S1-3, growing a second electrode on the surface of the piezoelectric film away from the first electrode, thereby completing the growth of the piezoelectric layer;

[0020] In the second electrode 23 is a double electrode structure, the second electrode is divided into an inner electrode 231 and an outer electrode 232;

[0021] S2, preparing a substrate, and forming a back cavity through the substrate;

[0022] S3, bonding the substrate to the surface of the piezoelectric layer away from the substrate, and the back cavity is used to provide a vibration space for the diaphragm of the piezoelectric layer.

[0023] As a further aspect of the present application, the step S2 further comprises:

[0024] S1-4, a lead-through channel is formed by penetrating the second electrode and the piezoelectric film to expose part of the first electrode, and a metal solder is injected into the lead-through channel.

[0025] Advantages of the present application:

[0026] 1. The BT substrate is directly bonded to the surface of the piezoelectric layer away from the substrate, and can be directly electrically interconnected with the first electrode and the second electrode respectively, without the need for additional packaging interconnection steps, greatly reducing the packaging process steps and saving the corresponding process cost. The etching of the traditional SOI substrate is wafer-level etching, which requires high precision and has a high scrap rate. The present application uses a BT substrate, and the formation of the back cavity belongs to panel-level etching, which has a lower precision requirement than wafer-level etching, thereby reducing the scrap rate and the cost loss caused by scrap.

[0027] 2. The piezoelectric layer is grown on a glass substrate (or UTG glass substrate, PI substrate), which can provide good waterproof and dustproof effect for the piezoelectric layer during device use, avoiding direct contact of water or dust with the piezoelectric layer and reducing the influence of the external environment on the performance of the piezoelectric layer. At the same time, the surface of the glass substrate is smooth, so even if dust or water falls on its surface, it is easy to clean and maintain, which helps to prolong the service life of the device.

[0028] 3. The piezoelectric layer of the present application adopts the structure of the first electrode, the PZT piezoelectric film and the second electrode, the PZT piezoelectric film has good piezoelectric performance, which can ensure the stable and reliable performance of the MEMS structure in vibration response and other performances. The back cavity on the substrate provides sufficient vibration space for the diaphragm of the piezoelectric layer, ensuring that the diaphragm can vibrate normally, thereby ensuring that the functions of the device can be normally realized. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the one or more embodiments of the present application or the prior art, the drawings needed in the embodiment or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only one or more embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0030] Figure 1 A structure schematic diagram of the laminated piezoelectric MEMS structure proposed in the embodiment of the present application;

[0031] Figure 2 Another structure schematic diagram of the laminated piezoelectric MEMS structure proposed in the embodiment of the present application;

[0032] Figures 3-7 A flowchart of the preparation method proposed in the embodiment of the present application.

[0033] Figures 8-9 A flowchart of a method for preparing a metal soldering piece according to an embodiment of the present application is shown in the figure.

[0034] Figure 10 A structure diagram of a double electrode according to an embodiment of the present application is shown in the figure.

[0035] In the figure, 1 is a substrate, 2 is a piezoelectric layer, 21 is a first electrode, 22 is a piezoelectric film, 23 is a second electrode, 231 is an inner electrode, 232 is an outer electrode, 3 is a base, and 24 is a metal soldering piece. DETAILED DESCRIPTION

[0036] Embodiments of the present application are described in detail below with reference to the accompanying drawings, in which the same or similar symbols represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application and cannot be understood as a limitation of the present application.

[0037] The specific structure of a laminated piezoelectric MEMS structure according to an embodiment of the present application is described below according to Figure 1 and Figure 2

[0038] Embodiment 1

[0039] Referring to Figure 1 , the laminated piezoelectric MEMS structure according to an embodiment of the present application includes a base 3, and the base 3 has opposite front and back surfaces.

[0040] Optionally, the base 3 is a glass base, a UTG base or a PI base. The thickness of the base 3 is 30-100 μm, which ensures a certain strength and stability of the structure, and also has good flexibility and lightness.

[0041] When the base 3 is a glass base, the surface flatness is high, which is conducive to the deposition and growth of the piezoelectric layer 2 and other structures, and can ensure the uniformity of the performance of the laminated piezoelectric MEMS structure.

[0042] The glass base serves as the growth base of the piezoelectric layer 2, and in the subsequent use process of the device, the waterproof and dustproof effect can be achieved, avoiding direct contact of water or dust with the piezoelectric layer 2, and water or dust falling on the surface of the glass base is easy to clean.

[0043] The UTG base has the characteristics of ultra-thin and bendable, so that the laminated piezoelectric MEMS structure can be applied to some scenes with requirements for bending performance, such as wearable devices.

[0044] ​The PI substrate has good insulation and flexibility, and can further expand the application range of the laminated piezoelectric MEMS structure, and is especially suitable for cases that need to be in contact with the human body or used in complex environments.

[0045] The back surface of the substrate 3 is grown with a piezoelectric layer 2, which includes a first electrode 21, a piezoelectric film 22, and a second electrode 23. The first electrode 21 is arranged on the back surface of the substrate 3, the piezoelectric film 22 is arranged on the surface of the first electrode 21 away from the substrate 3, and the second electrode 23 is arranged on the surface of the piezoelectric film 22 away from the first electrode 21.

[0046] The piezoelectric film 22 is the key part to realize piezoelectric conversion, which is usually made of materials with good piezoelectric properties, which can improve the sensitivity and performance of the laminated piezoelectric MEMS structure.

[0047] This structure design enables the piezoelectric layer 2 to realize piezoelectric effect under the action of an electric field. When a voltage is applied between the first electrode 21 and the second electrode 23, the piezoelectric film 22 will deform under the action of the electric field and generate stress.

[0048] Preferably, the piezoelectric film 22 is a PZT piezoelectric film, which has excellent piezoelectric properties, high piezoelectric constant, and can produce large deformation under the action of a small electric field, thereby significantly improving the sensitivity of the laminated piezoelectric MEMS structure. At the same time, the PZT piezoelectric film also has a good electromechanical coupling coefficient, which can realize efficient conversion between electrical energy and mechanical energy, making the structure perform well in energy harvesting, sensors and other applications.

[0049] The surface of the piezoelectric layer 2 away from the substrate 3 is bonded with a substrate 1, and the substrate 1 is provided with a back cavity to provide a space for the vibration of the diaphragm.

[0050] Optionally, the substrate 1 is a BT substrate, and the thickness of the substrate 1 is 200-600 μm. The use of the BT substrate can provide stable support and good electrical performance for the entire laminated piezoelectric MEMS structure.

[0051] The BT substrate has a low thermal expansion coefficient, which can effectively reduce the stress caused by temperature changes, thereby improving the stability and reliability of the structure.

[0052] In practical applications, the thickness range of 200-600 μm can ensure the structural strength while not excessively increasing the overall weight and volume. When the thickness approaches 200 μm, the structure is relatively thin, which is beneficial to miniaturization and integrated design, and is suitable for scenarios with high requirements for space and weight, such as sensors in wearable devices. When the thickness reaches 600 μm, the strength and stability of the structure are further enhanced, which can better withstand external impact and vibration, and is suitable for some harsh working environments, such as monitoring devices in industrial sites.

[0053] Optionally, as shown in Figure 2 The lead-through channel is formed through the second electrode 23 and the piezoelectric film 22, and the metal welding piece 24 is implanted. After the substrate 1 is bonded, it is electrically interconnected with the first electrode 21 and the second electrode 23 respectively, without the need for additional packaging interconnection, reducing the packaging process steps and saving costs.

[0054] Embodiment 2:

[0055] The preparation method proposed in the embodiment of the application is used for preparing the laminated piezoelectric MEMS structure proposed in Embodiment 1, as shown in Figures 3 to 7 The preparation method comprises the following steps:

[0056] S1, preparing a substrate 3, as shown in Figure 3 The substrate 3 has opposite front and back surfaces, and the piezoelectric layer 2 is grown on the back surface of the substrate 3.

[0057] Optionally, the substrate 3 is a glass substrate, a UTG substrate or a PI substrate, and the thickness of the substrate 3 is 30-100 μm.

[0058] Preferably, when the piezoelectric layer 2 is grown on the back surface of the substrate 3, a magnetron sputtering process or the like can be used to ensure that the piezoelectric layer 2 is uniformly and tightly attached to the substrate 3.

[0059] The thickness of the substrate 3 is controlled in the range of 30-100 μm, which can ensure the structural stability while taking into account the overall flexibility and lightness.

[0060] Further, the piezoelectric layer 2 comprises a first electrode 21, a piezoelectric film 22 and a second electrode 23, and when the piezoelectric layer 2 is grown on the back surface of the substrate 3, the steps comprise:

[0061] As shown in Figure 4 S1-1, magnetron sputtering is used to grow the first electrode 21 on the back surface of the substrate 3.

[0062] As shown in Figure 5 S1-2, magnetron sputtering is used to grow the piezoelectric film 22 on the surface of the first electrode 21 away from the substrate 3.

[0063] Preferably, the piezoelectric film 22 is a PZT piezoelectric film.

[0064] like Figure 6 As shown in S1-3, a second electrode 23 is grown by magnetron sputtering on the surface of the piezoelectric thin film 22 away from the first electrode 21.

[0065] The stacked piezoelectric MEMS structure formed by the above process can have better performance.

[0066] Preferred, such as Figure 10 As shown, the second electrode 23 can be a dual-electrode structure. That is, after the second electrode 23 is deposited, it is patterned and divided into an inner electrode 231 and an outer electrode 232. The inner electrode 231 and the outer electrode 232 are electrically connected to the substrate, respectively. Simultaneously, excitation is applied to the inner electrode 231 and the outer electrode 232, generating positive stress and negative stress, respectively. The bidirectional stress changes the deformation of the piezoelectric film 22, thereby increasing the sound pressure level of the entire device by increasing the diaphragm displacement.

[0067] On the one hand, by sequentially growing the first electrode 21, the piezoelectric thin film 22, and the second electrode 23 through magnetron sputtering, the thickness and uniformity of each layer can be precisely controlled, making the electrical properties of the piezoelectric layer 2 more stable. The close bonding between the first electrode 21, the piezoelectric thin film 22, and the second electrode 23 can effectively reduce the interface resistance and improve the current transmission efficiency, thereby enhancing the piezoelectric conversion efficiency of the entire structure.

[0068] On the other hand, this growth process helps improve the mechanical stability of the stacked piezoelectric MEMS structure. The uniformly grown piezoelectric layer 2 is firmly bonded to the substrate 3, which can better withstand external mechanical stress and vibration, reducing the risk of damage or failure during use. In practical applications, this structure can operate more reliably under different environmental conditions, such as high temperature, high humidity, or environments with certain mechanical impacts, while still maintaining good performance.

[0069] Optional, such as Figure 8 As shown, it also includes the following steps:

[0070] S1-4, a lead wire channel is formed through the second electrode 23 and the piezoelectric film 22, and a metal welding piece 24 is implanted in the lead wire channel.

[0071] Through step S1-4, an effective electrical connection channel can be established for the laminated piezoelectric MEMS structure. The implantation of the metal welding piece 24 in the lead channel provides a stable and reliable bridge for the connection of the second electrode and the external circuit. In an actual electrical system, this connection mode can ensure that the current can be smoothly transmitted from the second electrode to the outside, avoiding the problem of signal loss or transmission interruption caused by unstable connection.

[0072] S2, prepare the substrate 1, and form a back cavity through the substrate 1.

[0073] The size and shape of the back cavity are accurately controlled according to specific application requirements and design requirements. Suitable back cavity size can adjust the acoustic performance, mechanical performance, etc. of the structure.

[0074] Optionally, the substrate 1 is a BT substrate, and the thickness of the substrate 1 is 200-600 μm.

[0075] Such a thickness range allows the substrate to ensure a certain mechanical strength while not increasing the overall weight and volume of the structure due to excessive thickness. The BT substrate has good heat resistance, chemical corrosion resistance and electrical insulation performance, and is very suitable for use in laminated piezoelectric MEMS structures. In a high temperature environment, it can maintain stable physical and chemical properties, ensuring that the performance of the structure is not affected by temperature changes.

[0076] S3, bonding the substrate 1 to the surface of the piezoelectric layer 2 away from the substrate 3, realizing the close connection between the substrate 1 and the piezoelectric layer 2, and obtaining a MEMS structure as shown in Figure 7 or Figure 9 .

[0077] The bonding process needs to strictly control process parameters such as temperature, pressure and time. Suitable bonding temperature can make the bonding material achieve the best fluidity and adhesion, ensuring that the substrate 1 and the piezoelectric layer 2 form a firm bond.

[0078] In the present application, a glass substrate is used as the growth substrate of the piezoelectric layer 2. In the subsequent device use process, the glass substrate can achieve the effect of waterproof and dustproof, avoiding direct contact of water or dust with the piezoelectric layer 2, and water or dust falling on the surface of the glass substrate is easy to clean. The back cavity of the BT substrate provides a vibration space for the diaphragm of the piezoelectric layer 2, replacing the traditional SOI substrate as the growth substrate 3, and etching the SOI substrate to form the back cavity. The etching of the SOI substrate is wafer-level etching, which has higher precision requirement and higher waste rate compared to the plate-level etching of the BT substrate. At the same time, the BT substrate is directly electrically interconnected with the first electrode 21 and the second electrode 23, without the need for additional packaging interconnection, reducing the packaging process and saving production cost.

[0079] The above merely describes preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art, according to the technical solution and inventive concept of the present application, makes equivalent replacement or change within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A stacked piezoelectric MEMS structure, characterized by, The application relates to a piezoelectric layer bonded to a substrate, and a back cavity formed through the substrate to provide a vibrating space for a diaphragm of the piezoelectric layer. The piezoelectric layer is bonded to a substrate away from the surface of the substrate, and a back cavity is formed through the substrate to provide a vibrating space for a diaphragm of the piezoelectric layer.

2. The laminated piezoelectric MEMS structure of claim 1, wherein, The substrate is a glass substrate, a UTG glass substrate or a PI substrate.

3. The laminated piezoelectric MEMS structure of claim 2, wherein, The thickness of the substrate is 30-100 microns.

4. The laminated piezoelectric MEMS structure of claim 1, wherein, The substrate is a BT substrate.

5. The laminated piezoelectric MEMS structure of claim 4, wherein, The thickness of the substrate is 200-600 microns.

6. The laminated piezoelectric MEMS structure according to claim 1, wherein The piezoelectric layer comprises a first electrode, a piezoelectric film and a second electrode; The first electrode is grown on the back surface of the substrate, the piezoelectric film is grown on the surface of the first electrode away from the substrate, and the second electrode is grown on the surface of the piezoelectric film away from the substrate.

7. The laminated piezoelectric MEMS structure of claim 6, wherein, The piezoelectric film is a PZT piezoelectric film.

8. The laminated piezoelectric MEMS structure of claim 7, wherein, The second electrode and the piezoelectric film are penetrated to expose part of the first electrode, and the substrate is bonded to the piezoelectric layer and is electrically interconnected with the first electrode and the second electrode respectively.

9. A method of manufacture for manufacturing the laminated piezoelectric MEMS structure according to any one of the preceding claims 1 to 8, characterized in that, The method comprises the following steps: S1, a substrate is prepared, the substrate has opposite front and back surfaces, and a piezoelectric layer is grown on the back surface of the substrate; S1-1, a first electrode is grown on the back surface of the substrate; S1-2, a piezoelectric film is grown on the surface of the first electrode away from the substrate; S1-3, a second electrode is grown on the surface of the piezoelectric film away from the first electrode, and the growth of the piezoelectric layer is completed; The second electrode 23 is a double-electrode structure, and the second electrode is divided into an inner electrode 231 and an outer electrode 232; S2, a substrate is prepared, and a back cavity is formed through the substrate; S3, the substrate is bonded to the surface of the piezoelectric layer away from the substrate, and the back cavity is used to provide a vibrating space for a diaphragm of the piezoelectric layer.

10. The method of claim 9, wherein, The step S2 further comprises: S1-4, a lead channel is formed by penetrating the second electrode and the piezoelectric film to expose part of the first electrode, and a metal welding member is injected into the lead channel.

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