A high-sensitivity MEMS acoustic device and method of fabrication

Abstract

This application relates to the field of acoustic transducers, and particularly to a high-sensitivity MEMS acoustic device and its fabrication method. The high-sensitivity MEMS acoustic device is composed of an upper electrode layer, a piezoelectric layer, a lower electrode layer, a passive layer, an insulating layer, and a substrate connected in sequence. The multilayer composite film is radially symmetrical on the passive layer. A slit through the center of radial symmetry divides the composite film into several partitions. The upper and lower electrode layers of each partition are respectively provided with pads for signal extraction. The voltage signals of the pads in each partition are extracted through series or parallel connection. This application increases the output voltage by dividing the piezoelectric sensitive composite film into multiple sensitive regions and combining the sensitive regions in series, antiphase superposition, or other forms, thereby improving the sensitivity of the piezoelectric MEMS device.

Description

Technical Field

[0001] This application relates to the field of acoustic transducers, specifically to a high-sensitivity MEMS acoustic device and its fabrication method. Background Technology

[0002] Piezoelectric thin film-based sensors have become a research hotspot in the field of MEMS sensors in recent years. Piezoelectric MEMS acoustic devices utilize the piezoelectric effect of piezoelectric thin films and the bending vibration of the composite structure formed by the piezoelectric thin film and the silicon substrate to realize the conversion of electrical energy into mechanical energy. Through the mechanical energy transfer with the surrounding fluid medium, they realize the transmission and reception of sound waves. They have the characteristics of small size, compact structure, adjustable shape, easy integration with circuits, suitable for 2D phase control and 3D imaging, no need for DC bias voltage, fast response speed, and immunity to electromagnetic interference.

[0003] The transmit and receive sensitivity of piezoelectric MEMS acoustic devices is limited by the volume of the piezoelectric material. How to improve the sensitivity of piezoelectric MEMS acoustic devices through structural optimization design under the constraint of limited volume is a technical challenge that urgently needs to be overcome. Summary of the Invention

[0004] In view of this, this application discloses a high-sensitivity MEMS acoustic device and its fabrication method to solve the problem of low sensitivity in existing piezoelectric MEMS, including:

[0005] A high-sensitivity MEMS acoustic device is composed of an upper electrode layer, a piezoelectric layer, a lower electrode layer, a passive layer, an insulating layer, and a substrate connected in sequence; the upper electrode layer, the piezoelectric layer, and the lower electrode layer together constitute a multilayer composite thin film;

[0006] The multilayer composite film is radially symmetrical on the passive layer. The composite film is divided into several partitions by a slit through the center of radial symmetry. Each partition has an upper electrode layer and a lower electrode layer respectively provided with pads for signal output. The voltage signals of each partition's pads are output through series or parallel connection. In the series connection, the upper electrodes and lower electrodes of different partitions are connected to each other. In the parallel connection, the upper electrodes of different partitions are connected to each other, and the lower electrodes are connected to each other.

[0007] A method for fabricating a high-sensitivity MEMS acoustic device, comprising:

[0008] S1. Obtain a silicon substrate and sequentially grow an insulating layer, a lower electrode layer, a piezoelectric layer, and an upper electrode layer on the silicon substrate; the lower electrode layer, the piezoelectric layer, and the upper electrode layer constitute a multilayer composite film;

[0009] S2. Pattern the multilayer composite film so that the pattern satisfies radiation symmetry;

[0010] S3. Growing a protective layer on a multilayer composite film;

[0011] S4. Pattern the protective layer using photolithography and etching to expose the reserved positions of the pads and grow the pads; use metal lines to lead out the pad voltage signals of each partition through series or parallel connection;

[0012] S5. A back cavity is fabricated on the back of a silicon substrate through photolithography and etching to form a suspended diaphragm structure that can vibrate.

[0013] This application divides the piezoelectric sensitive composite film into multiple sensitive regions and combines the output pads of each sensitive region in series, inverse superposition, and other forms. Series connection increases the output voltage, and parallel connection improves the signal-to-noise ratio. Under the condition of unchanged device size, it significantly increases the output voltage of a single PMUT (Piezoelectric Micromachined Ultrasonic Transducer), thereby greatly improving the sensitivity of piezoelectric MEMS. Attached Figure Description

[0014] Figure 1 This is a cross-sectional schematic diagram of the high-sensitivity MEMS acoustic device in Embodiment 1 of this application;

[0015] Figure 2 This is a schematic diagram of the high-sensitivity MEMS acoustic device in Embodiment 1 of this application;

[0016] Figure 3 This is a schematic diagram of the multilayer composite film pattern in Embodiment 2 of this application;

[0017] Figure 4 This is a schematic diagram showing the voltage signal output between the multilayer composite film and the pad in Embodiment 4 of this application;

[0018] Figure 5 This is a schematic cross-sectional view of different partitions before the growth pads in Embodiment 4 of this application;

[0019] Figure 6 This is a cross-sectional schematic diagram of the high-sensitivity MEMS acoustic device in Embodiment 4 of this application;

[0020] Reference numerals: 1-Multilayer composite film, 101-Upper electrode layer, 102-Piezoelectric layer, 103-Lower electrode layer, 2-Passive layer, 3-Insulating layer, 4-Substrate, 51-Section 1, 511-Upper electrode layer of Section 1, 512-Piezoelectric layer of Section 1, 513-Lower electrode layer of Section 1, 52-Section 2, 521-Upper electrode layer of Section 2, 522-Piezoelectric layer of Section 2, 523-Lower electrode layer of Section 2, 53-Section 3, 531-Upper electrode layer of Section 3, 532-Piezoelectric layer of Section 3, 533-Lower electrode layer of Section 2, 54-Section 4, 601-Upper electrode layer pad, 603-Lower electrode layer pad, 7-Cut seam. Detailed Implementation

[0021] To make the objectives, technical solutions, features, and advantages of this application clearer and to enable those skilled in the art to better understand the technical solutions of this application, the following detailed description of this application is provided in conjunction with the accompanying drawings and embodiments.

[0022] Example 1:

[0023] This embodiment includes a high-sensitivity MEMS acoustic device, as shown in the cross-sectional schematic diagram. Figure 1 As shown, it consists of an upper electrode layer 101, a piezoelectric layer 102, a lower electrode layer 103, a passive layer 2, an insulating layer 3, and a substrate 4 connected in sequence. A back cavity is provided on the substrate to realize the suspended diaphragm structure in MEMS acoustic devices.

[0024] The passive layer is used for structural support and stress buffering. The upper electrode layer 101, the piezoelectric layer 102, and the lower electrode layer 103 together constitute the multilayer composite film 1. The multilayer composite film 1 is radially symmetrical on the passive layer 2. The multilayer composite film 1 is divided into several partitions by the cut 7 through the center of radial symmetry. The upper electrode layer and the lower electrode layer of each partition are respectively provided with pads 601 and 603 for signal output. The voltage signals of the pads of each partition are output through series or parallel connection.

[0025] In the series connection, the upper and lower electrodes of different zones are interconnected; in the parallel connection, the upper electrodes of different zones are connected to each other, and the lower electrodes are connected to each other. Series connection increases the output voltage, while parallel connection improves the signal-to-noise ratio. Through this design, the high-sensitivity MEMS acoustic device of this application can reduce the noise introduced by the subsequent amplifier circuit when increasing signal strength.

[0026] The high-sensitivity MEMS acoustic device in this embodiment is such as Figure 2As shown, taking two adjacent partitions 51 and 52 as an example, a voltage signal output method for pads is introduced: the upper electrode pad of partition 52 is connected to the upper electrode pad and the lower electrode pad of partition 51, and the upper electrode pad of partition 52 is connected to the lower electrode pad of partition 51; the connection between the lower electrodes realizes the series connection of voltage signals to improve voltage output.

[0027] Example 2:

[0028] This embodiment includes a high-sensitivity MEMS acoustic device. The difference from Embodiment 1 is that this embodiment patterns a multilayer composite thin film as shown in the figure. Figure 3 The eight partitions shown form a graphic structure with an outer ring surrounding a fan-shaped inner layer. The multilayer composite film is divided into an outer partition and a central partition. Since the output voltage of the outer sensitive part and the central sensitive part is out of phase, when the pad voltage signal is extracted, the electrical signals of the outer partition and the central partition are extracted separately and superimposed in opposite phase to improve the voltage output.

[0029] Furthermore, other numbers can be used for the number of cuts.

[0030] Example 3:

[0031] This embodiment includes a method for fabricating a high-sensitivity MEMS acoustic device, used to fabricate the high-sensitivity MEMS acoustic device described in Example 1, comprising:

[0032] S1. Obtain a silicon substrate and grow an insulating layer, a lower electrode layer, a piezoelectric layer, and an upper electrode layer sequentially on the silicon substrate. The lower electrode layer, the piezoelectric layer, and the upper electrode layer constitute a multilayer composite film.

[0033] The silicon substrate is usually an SOI wafer or a high-resistivity silicon wafer with a thickness of 300~600μm; the insulating layer has a thickness of 100~300nm and can be AlN or SiO2; the lower electrode layer has a thickness of 200~400nm and can be molybdenum; the piezoelectric layer has a thickness of 1~3μm and can be made of piezoelectric materials such as AlN, PZT, AlScN, and KNN.

[0034] S2. Patterning of the multilayer composite thin film, wherein the pattern satisfies radiation symmetry; in this embodiment, the device obtained after patterning is as follows: Figure 2 As shown.

[0035] S3. A protective layer is grown on the multilayer composite film to protect the electrodes and piezoelectric layer. The protective layer material can be AlN, SiO2, etc., with a thickness of 100~300nm.

[0036] S4. The protective layer is patterned by photolithography and etching to expose the reserved positions of the pads and grow the pads; the voltage signals of the pads in each zone are led out by series or parallel using metal lines.

[0037] S5. A back cavity is fabricated on the back of a silicon substrate by photolithography and etching to form a suspended diaphragm structure that can vibrate, thus completing the fabrication of a high-sensitivity MEMS acoustic device.

[0038] Example 4:

[0039] A method for fabricating a high-sensitivity MEMS acoustic device, differing from Example 3 in that, in this example, the multilayer composite thin film is patterned as shown... Figure 4 The 16 partitions shown form a graphic structure where a ring-shaped outer layer surrounds a fan-shaped inner layer. For example... Figure 6 The diagram shown is a cross-sectional schematic of the high-sensitivity MEMS acoustic device in this embodiment. 53 and 54 represent the outer ring partitions corresponding to the sector partitions 51 and 52, respectively.

[0040] Figure 5 The diagram shows the cross-sectional view of partitions 51, 52, 53, and 54 before the growth pads. 511, 512, and 513 represent the upper electrode layer, piezoelectric layer, and lower electrode layer of 51, respectively. The reference numerals for partitions 52, 53, and 54 are similar.

[0041] Considering the out-of-phase output voltages of the outer and inner partitions, when the voltage signal is led out through the pads, the electrical signals of the two regions are led out separately and superimposed in opposite phases to further improve the voltage output.

[0042] In this embodiment, a schematic diagram of the pad voltage signal output is shown below. Figure 4 As shown, the lower electrode 543 of 54 is connected to the lower electrode 523 of 52, the upper electrode 521 of 52 is connected to the lower electrode 513 of 51, and the upper electrode 511 of 51 is connected to the lower electrode 533 of 53. This connection method achieves full series connection of voltages between different zones, effectively improving voltage sensitivity. When extracting signals from other zones, the above-mentioned pad connection method can be referenced, or the signals can be extracted based on the principle of series or parallel extraction of voltage signals from each zone's pads.

[0043] Furthermore, a back cavity is fabricated on the back side of the silicon substrate to form a suspended diaphragm structure that can vibrate, thus completing the fabrication of a high-sensitivity MEMS acoustic device.

[0044] Finally, it should be noted that the above description only depicts some embodiments of this application. For those skilled in the art, various changes, modifications, substitutions, and variations can be conceived of these embodiments without departing from the principles and spirit of this application. The scope of protection of this application is defined by the appended claims and their equivalents, and all the above-mentioned behaviors should be covered within the scope of protection of this application.

[0045] Furthermore, in the above description of the embodiments, unless otherwise explicitly specified and limited, if the terms "upper," "lower," "horizontal," "inner," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the invention is usually placed during use, they are only for the convenience of describing this application and simplifying the description, and do not limit or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application; if the terms "first," "second," etc., appear, they are only used to distinguish the description and should not be construed as indicating or implying relative importance. The components shown and described in the accompanying drawings and embodiments can be arranged and designed in various different configurations. The term "horizontal" does not imply that the component must be absolutely horizontal, but rather that it can be slightly tilted. "Horizontal" simply means that its direction is more horizontal than "vertical," not that the structure must be completely horizontal, but rather that it can be slightly tilted. The terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can be mechanical connections or electrical connections; they can be direct connections or indirect connections through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

Claims

1. A high-sensitivity MEMS acoustic device, comprising an upper electrode layer, a piezoelectric layer, a lower electrode layer, a passive layer, an insulating layer, and a substrate connected in sequence; characterized in that, The upper electrode layer, piezoelectric layer, and lower electrode layer together constitute a multilayer composite film. The multilayer composite film is radially symmetrical on the passive layer. The composite film is divided into several partitions by a slit through the center of radial symmetry. The upper electrode layer and lower electrode layer of each partition are also provided with pads for signal output. The voltage signals of the pads of each partition are output through series or parallel connection.

2. The high-sensitivity MEMS acoustic device according to claim 1, characterized in that, In the series connection, the upper and lower electrodes of different zones are connected to each other; in the parallel connection, the upper electrodes of different zones are connected to each other, and the lower electrodes are connected to each other.

3. The high-sensitivity MEMS acoustic device according to claim 1, characterized in that, The multilayer composite film is radially symmetrical on the passive layer, forming a pattern structure in which an outer ring surrounds a fan-shaped inner layer. The multilayer composite film is divided into an outer partition and a central partition.

4. The high-sensitivity MEMS acoustic device according to claim 3, characterized in that, When extracting the pad voltage signal, the electrical signals of the outer partition and the center partition are extracted separately and superimposed in opposite phase.

5. A method for fabricating a high-sensitivity MEMS acoustic device, characterized in that, For fabricating the high-sensitivity MEMS acoustic device as described in any one of claims 1 to 4, comprising: S1. Obtain a silicon substrate and sequentially grow an insulating layer, a lower electrode layer, a piezoelectric layer, and an upper electrode layer on the silicon substrate; the lower electrode layer, the piezoelectric layer, and the upper electrode layer constitute a multilayer composite film; S2. Pattern the multilayer composite film so that the pattern satisfies radiation symmetry; S3. Growing a protective layer on a multilayer composite film; S4. Pattern the protective layer using photolithography and etching to expose the reserved positions of the pads and grow the pads; use metal lines to lead out the pad voltage signals of each partition through series or parallel connection; S5. A back cavity is fabricated on the back of a silicon substrate by photolithography and etching to form a suspended diaphragm structure that can vibrate, thus completing the fabrication of a high-sensitivity MEMS acoustic device.

6. The method for fabricating a high-sensitivity MEMS acoustic device according to claim 5, characterized in that, The thickness of the silicon substrate is 300~600μm.

7. The method for fabricating a high-sensitivity MEMS acoustic device according to claim 5, characterized in that, The thickness of the insulating layer is 100~300nm.

8. The method for fabricating a high-sensitivity MEMS acoustic device according to claim 5, characterized in that, The thickness of the lower electrode layer is 200~400nm, and the thickness of the piezoelectric layer is 1~3μm.

9. The method for fabricating a high-sensitivity MEMS acoustic device according to claim 5, characterized in that, When patterning multilayer composite films, a pattern structure is formed in which an outer ring surrounds a fan-shaped inner layer.

10. The method for fabricating a high-sensitivity MEMS acoustic device according to claim 9, characterized in that, When the voltage signal is brought out through the pads, the electrical signals of the two regions are brought out separately and superimposed in opposite phases.

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