摘 要

超声换能器作为一种重要的声电转换器件，其在国防、航空航天、电子设备、汽车无人驾驶、医疗设备等领域有着很大的应用市场，并且随着IC制造工艺逐渐成熟，出现了较为高效的MEMS技术，综合MEMS技术，出现了更高性能的压电微机械超声换能器，其具有效应速度快，能耗低，高灵敏度等特点。现如今对于pMUT单元性能的改善基本上是从结构以及压电材料等方面进行考虑。

而本文从结构方面提出了一种基于AlN的压电微机械超声换能器的附加质量块的新型结构，并用COMSOL多物理场耦合的仿真软件对传统pMUT和附加质量块的新型pMUT的性能做了详细分析，并对其加工方法做了研究。

（1）针对传统结构pMUT进行了仿真分析研究，并对传统pMUT上电极尺寸做了一些优化，仿真结果显示当上电极尺寸与pMUT器件面积的比例约为0.7时，其性能可以达到最优。

（2）针对基于腔体SOI技术的附加质量块pMUT做了有关仿真分析研究，并将其结果与传统pMUT结果相互比较发现其在传输声压、振膜中心位移以及有效机电耦合系数等方面有着显著的改善效果。

（3）分别从质量块厚度、半径尺寸、以及所用材料等三个方面展开了相关研究，得到初步仿真结果：

a. 质量块厚度尺寸对pMUT有效机电耦合系数的影响可忽略，而pMUT振膜中心的振动位移和传输声压与厚度尺寸成正比，厚度尺寸越大，振膜中心振动位移和中心传输声压也就越大。

b. 质量块半径尺寸与pMUT有效机电耦合系数成反比，随着半径尺寸的增加，有效机电耦合系数逐渐减小；对pMUT振膜中心位移的影响可忽略；pMUT表面传输声压与半径尺寸成反比，即半径尺寸越大，振膜中心表面传输声压越小。

c. 当用Cu作质量块材料时，其振膜中心位移最大为0.27μm，较为明显，当Al作质量块材料时，其有效机电耦合系数最大为1.03％。

（4）根据所设计pMUT结构对pMUT加工工艺流程做了详细设计。

（5）针对超声传感器在无人驾驶中探知环境的功能提出了几种基本的测距方法和原理，以及在无人驾驶汽车中的超声测距系统结构。

关键词：压电微机械超声换能器；Mo质量块；有效机电耦合系数；表面传输声压；超声波测距

Abstract

As an important acoustoelectric conversion device, ultrasonic transducer has a large application market in the fields of national defense, aerospace, electronic equipment, automotive unmanned driving, medical equipment, etc., and as the IC manufacturing process gradually matures, it appears With more efficient MEMS technology and integrated MEMS technology, higher performance piezoelectric micromechanical ultrasonic transducers have appeared, which have the characteristics of fast effect speed, low energy consumption and high sensitivity. Nowadays, the improvement of pMUT cell performance is basically considered from the aspects of structure and piezoelectric materials.

In this paper, a new structure of additional mass of piezoelectric micromechanical ultrasonic transducer based on AlN is proposed in terms of structure, and the performance of the traditional pMUT and the new pMUT of additional mass is done with COMSOL multiphysics coupling simulation software. Detailed analysis and research on its processing methods.

(1) Carrying out simulation analysis and research on the traditional structure pMUT, and optimizing the size of the traditional pMUT upper electrode, the simulation results show that when the ratio of the upper electrode size to the pMUT device area is about 0.7, its performance can be optimized.

(2) The simulation analysis of the additional mass pMUT based on the cavity SOI technology is done, and the results are compared with the traditional pMUT results. It is found that it has some aspects in terms of transmission sound pressure, diaphragm center displacement, and effective electromechanical coupling coefficient. Significant improvement effect.

(3) Relevant research was carried out from three aspects of mass thickness, radius, and materials used, and preliminary simulation results were obtained:

a. The influence of the thickness of the mass on the effective electromechanical coupling coefficient of pMUT is negligible, and the vibration displacement and transmission sound pressure of the center of the pMUT diaphragm are proportional to the thickness dimension. The larger the thickness, the vibration displacement and the center transmission sound pressure of the diaphragm center The bigger it is.

b. The mass radius size is inversely proportional to the pMUT effective electromechanical coupling coefficient. As the radius size increases, the effective electromechanical coupling coefficient gradually decreases; the effect on the center displacement of the pMUT diaphragm is negligible; the pMUT surface transmission sound pressure is proportional to the radius size Inversely, that is, the larger the radius, the smaller the sound pressure transmitted on the center surface of the diaphragm.

c. When Cu is used as the mass material, the maximum displacement of the diaphragm center is 0.27μm, which is more obvious. When Al is used as the mass material, the effective electromechanical coupling coefficient is at most 1.03%.

(4) According to the designed pMUT structure, the detailed design of the pMUT processing process is made.

(5) Several basic ranging methods and principles are proposed for the function of ultrasonic sensors to detect the environment in unmanned driving, and the structure of ultrasonic ranging systems in unmanned vehicles.

Key Words: Piezoelectric micromachined ultrasonic transducer; Mo mass; Effective electromechanical coupling coefficient; Surface transmitted sound pressure; Ultrasonic distance measurement

目录

第1章 绪论 1

1.1 MEMS技术简介 1

1.2 超声换能器概述 1

1.2.1电容式超声换能器 1

1.2.2压电式超声换能器 2

1.3 研究背景及意义 3

1.4国内外研究现状分析 4

1.5 论文结构安排 7

第2章 压电超声换能器理论基础 9

2.1 压电理论基础 9

2.1.1 压电效应和压电方程 9

2.1.2 常用压电材料概述 11

2.2 声学理论基础 12

2.2.1声场与声压级 12

2.2.2声阻抗、声阻抗率与媒质特性阻抗 12

2.2.3超声波的概念和波形 13

2.3 压电超声换能器工作原理 13

2.4压电振子的振动模式概述 14

2.5 pMUT理论分析 15

2.5.1力学分析 15

2.5.2电学分析 17

第3章 压电超声换能器设计与加工 20

3.1压电材料选择 20

3.2 pMUT结构尺寸设计与仿真 21

3.2.3新型pMUT理论分析 21

3.2.1新型pMUT结构尺寸设计 22

3.2.2传统pMUT仿真及分析 23

3.2.4新型pMUT仿真及分析 30

3.2.5新型pMUT结构改进及相关仿真分析 34

3.2.6两种pMUT仿真参数比较 36

3.2.7 附加质量块pMUT各参数对性能的影响研究 37

3.2.8新型pMUT加工工艺 43

第4章 pMUT的实际应用 46

4.1超声波测距方法和原理 46

4.2无人驾驶汽车中的超声测距结构 47

第5章 总结与展望 48

5.1总结 48

5.2未来工作展望 49

参考文献 50

致 谢 52

第1章 绪论

1.1 MEMS技术简介

由于半导体器件制造技术的不断革新，MEMS技术（微机械系统技术）开始逐步发展起来，并成为微米纳米制造领域的一个重要发展方向，它是一种集微传感器、微执行器、微机械结构、微能源、信号处理和控制电路、高性能电子集成器件、接口、通信等于一体的微器件或系统^[1,2]。由于自身的尺寸特点该技术拥有可集成化、功耗低、成本低、性能稳定等优势，MEMS是一种革命性的技术，在高新技术领域拥有极大的应用前景，随着MEMS技术的不断成熟，MEMS已经从实验研究阶段过渡到大范围实际应用阶段，现今已融入到航空航天，医疗诊断，自动控制，消费电子以及国防兵器等多个重要领域。

1.2 超声换能器概述