High-sensitivity PMUT and preparation method thereof

Abstract

The invention belongs to the field of sensors, and particularly relates to a high-sensitivity PMUT and a preparation method thereof.The preparation method comprises the steps that a vibrating diaphragm structure of a piezoelectric micromechanical ultrasonic transducer is prepared, and the vibrating diaphragm structure comprises a silicon substrate, a buried oxide layer, a passive layer, a lower electrode layer, a piezoelectric layer and an upper electrode layer from bottom to top; in a non-anchoring area and / or a central vibration area of a vibrating diaphragm structure of the piezoelectric micromechanical ultrasonic transducer, rigidity weakening is carried out on a piezoelectric layer and / or an upper electrode layer, and the high-sensitivity piezoelectric micromechanical ultrasonic transducer is obtained; according to the invention, the electromechanical coupling coefficient is improved, and the sound output capability when the transducer is used as an emitter and the sensitivity when the transducer is used as a receiver are also improved.

Description

Technical Field

[0001] This invention belongs to the field of sensors, specifically relating to a high-sensitivity PMUT and its preparation method. Background Technology

[0002] A piezoelectric micromachined ultrasonic transducer (PMUT) is a miniature ultrasonic transducer based on the piezoelectric effect, manufactured using microelectromechanical systems (MEMS) technology, enabling the transmission and reception of ultrasonic waves. As a next-generation ultrasonic transducer, PMUTs, with their advantages of miniaturization, low power consumption, and high integration, are opening up broad application prospects in the medical, industrial, and consumer electronics fields.

[0003] In the medical field, medical ultrasound imaging requires transducers with high penetration depth. However, traditional fixed-support piezoelectric micromechanical ultrasonic transducers (PMUTs) are limited by their low electromechanical coupling coefficient, resulting in insufficient electrical-to-mechanical energy conversion efficiency and low acoustic output energy, making it difficult to meet the needs of deep tissue imaging. PMUTs typically employ a multilayer thin-film structure, including a passive layer, a lower electrode, a piezoelectric layer, and a upper electrode. This structure has high stiffness, limiting vibration displacement and consequently leading to a low electromechanical coupling coefficient. Among existing optimization methods, material modification can improve performance to some extent, but the improvement effect is limited and the process is complex; while increasing the driving voltage to enhance the electromechanical coupling coefficient will accelerate device aging. Summary of the Invention

[0004] To address the problem of insufficient electromechanical coupling coefficient in fixed-support piezoelectric micromechanical ultrasonic transducers, which affects their penetration depth in medical ultrasound imaging, this invention provides a high-sensitivity PMUT and its fabrication method.

[0005] In a first aspect, the present invention provides a method for preparing a high-sensitivity PMUT, comprising the following steps:

[0006] S1. Fabrication of the diaphragm structure of a piezoelectric micromechanical ultrasonic transducer, comprising, from bottom to top, a silicon substrate, a buried oxide layer, a passive layer, a lower electrode layer, a piezoelectric layer, and an upper electrode layer;

[0007] S2. In the non-anchored region and / or central vibration region of the diaphragm structure of the piezoelectric micromechanical ultrasonic transducer, the stiffness of the piezoelectric layer and / or the upper electrode layer is weakened to obtain a high-sensitivity piezoelectric micromechanical ultrasonic transducer.

[0008] Furthermore, step S2, which weakens the stiffness of the piezoelectric layer and / or the upper electrode, includes:

[0009] Using MEMS etching technology, etching is performed on the non-anchored area and / or central vibration area corresponding to the piezoelectric layer and / or upper electrode layer according to the designed etching pattern, and the etching pattern is removed.

[0010] Furthermore, the passive layer is made of silicon, silicon dioxide, or composite materials.

[0011] Furthermore, the piezoelectric layer is made of lead zirconate titanate, aluminum nitride, or scandium aluminum nitride.

[0012] In a second aspect, the present invention provides a high-sensitivity PMUT, which is prepared using a high-sensitivity PMUT and its preparation method as described in the first aspect.

[0013] The beneficial effects of this invention are:

[0014] This invention reduces the stiffness of the multilayer structure of a fixed-support piezoelectric micromechanical ultrasonic transducer by introducing a carefully designed local stiffness-weakening region. This allows the transducer to generate greater vibration displacement under the same driving voltage or higher electrical signal output under the same sound pressure. This not only improves the electromechanical coupling coefficient but also enhances the transducer's acoustic output capability as a transmitter and its sensitivity as a receiver, thereby effectively improving its penetration depth and signal-to-noise ratio in applications such as medical ultrasound imaging and industrial non-destructive testing. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a traditional fixed-support PMUT structure;

[0016] Figure 2 This is a schematic diagram of the structure of a high-sensitivity PMUT according to the present invention;

[0017] Figure 3 This is a top view of the electrode structure of a high-sensitivity PMUT according to the present invention;

[0018] Figure 4 This is a schematic diagram comparing the vibration modes and vibration displacements of a traditional fixed-support PMUT and the high-sensitivity PMUT of this invention.

[0019] Among them, 1-silicon substrate, 2-buried oxide layer, 3-passive layer, 4-lower electrode layer, 5-piezoelectric layer, and 6-upper electrode layer. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Figure 1 This is a schematic diagram of a traditional fixed-support PMUT structure. This structure has high stiffness, which restricts vibration displacement and consequently leads to a low electromechanical coupling coefficient. To address this issue, this invention provides a method for fabricating a high-sensitivity PMUT, aiming to introduce local stiffness-weakening regions to structurally optimize the fixed-support PMUT diaphragm.

[0022] like Figure 2 As shown, the specific solution includes the following steps:

[0023] S1. Fabrication of the diaphragm structure of a piezoelectric micromechanical ultrasonic transducer, comprising, from bottom to top, a silicon substrate 1, a buried oxide layer 2, a passive layer 3, a lower electrode layer 4, a piezoelectric layer 5, and an upper electrode layer 6.

[0024] Specifically, a cavity is formed by hollowing out the center of the silicon substrate.

[0025] Specifically, the passive layer is made of silicon, silicon dioxide, or composite materials.

[0026] Specifically, the lower electrode layer is made of a metallic material, preferably platinum or molybdenum.

[0027] Specifically, the piezoelectric layer uses one of the following materials: lead zirconate titanate (PZT), aluminum nitride (AlN), or scandium aluminum nitride (ScAlN).

[0028] Specifically, the upper electrode layer is made of one of the following materials: aluminum, titanium, etc.

[0029] Specifically, the diaphragm structure of the piezoelectric micromechanical ultrasonic transducer was fabricated using conventional MEMS technology.

[0030] S2. In the non-anchored region and / or central vibration region of the diaphragm structure of the piezoelectric micromechanical ultrasonic transducer, the stiffness of the piezoelectric layer and / or the upper electrode is weakened to obtain a high-sensitivity piezoelectric micromechanical ultrasonic transducer.

[0031] Specifically, the present invention selectively modifies the structure of local areas of the piezoelectric layer and / or the upper electrode layer by using micro-nano fabrication technology in the non-anchored region and / or the central vibration region of the diaphragm structure to form specific local stiffness weakening regions.

[0032] First, the etching pattern is designed based on performance requirements and structural characteristics. The etching pattern can be an array of circles, squares, or other regular shapes. The size and distribution of the etching area should be determined based on simulation and experimental results to ensure optimal results in reducing structural stiffness and increasing the effective vibration area.

[0033] MEMS etching processes, such as dry or wet etching, are used to etch the non-anchored regions and / or central vibration regions corresponding to the piezoelectric layer and / or upper electrode layer according to a pre-designed etching pattern. During the etching process, it is necessary to precisely control the etching depth and range to ensure that only a predetermined portion of the piezoelectric layer and upper electrode layer is etched away without damaging the lower electrode layer and passive layer.

[0034] For example, dry etching is performed using inductively coupled plasma etching (ICP). The wafer with the prepared diaphragm structure is placed in the etching equipment. Based on the material properties of the piezoelectric layer and the upper electrode layer, appropriate etching parameters are set, such as radio frequency power, gas flow rate, and etching time. The etching is performed according to the designed pattern until the preset etching effect is achieved.

[0035] Figure 3 This is a top view of the electrode structure of a high-sensitivity PMUT according to the present invention. From top to bottom, it consists of an upper electrode layer, a piezoelectric layer, and a lower electrode layer. Since a portion of both the upper electrode layer and the piezoelectric layer has been etched away, a step exists between each layer. Compared to the traditional fixed-branch PMUT structure, the lengths of the piezoelectric layer and the upper electrode are significantly reduced.

[0036] Figure 4 The left side shows a schematic cross-sectional view of the vibration modes of a traditional fixed-support PMUT at resonance. The middle side shows a schematic cross-sectional view of the vibration modes of the high-sensitivity PMUT structure proposed in this invention at resonance. The rightmost color gradient represents the magnitude of the vibration displacement amplitude; the darker the color, the larger the amplitude. Because this invention etches part of the piezoelectric layer, at the same color gradient, the etched part of the PMUT has a displacement of 0 (white part), but the vibration displacement of the diaphragm part is larger, thus achieving an improvement in sensitivity.

[0037] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "setting," "connection," "fixing," "rotation," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Unless otherwise explicitly limited, those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0038] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-sensitivity PMUT, characterized in that, Includes the following steps: S1. Fabrication of the diaphragm structure of a piezoelectric micromechanical ultrasonic transducer, comprising, from bottom to top, a silicon substrate, a buried oxide layer, a passive layer, a lower electrode layer, a piezoelectric layer, and an upper electrode layer; S2. In the non-anchored region and / or central vibration region of the diaphragm structure of the piezoelectric micromechanical ultrasonic transducer, the stiffness of the piezoelectric layer and / or the upper electrode layer is weakened to obtain a high-sensitivity piezoelectric micromechanical ultrasonic transducer.

2. The method for preparing a high-sensitivity PMUT according to claim 1, characterized in that, Step S2, which weakens the stiffness of the piezoelectric layer and / or the upper electrode layer, includes: Using MEMS etching technology, etching is performed on the non-anchored region and / or central vibration region corresponding to the piezoelectric layer and / or upper electrode layer according to the designed etching pattern.

3. The method for preparing a high-sensitivity PMUT according to claim 2, characterized in that, The etching pattern is designed based on performance requirements and structural characteristics.

4. The method for preparing a high-sensitivity PMUT according to claim 1, characterized in that, The passive layer is made of silicon, silicon dioxide, or composite materials.

5. The method for preparing a high-sensitivity PMUT according to claim 1, characterized in that, The piezoelectric layer is made of lead zirconate titanate, aluminum nitride, or scandium aluminum nitride.

6. A high-sensitivity PMUT, characterized in that, It is prepared using the preparation method of a high-sensitivity PMUT as described in any one of claims 1-5.

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