多振膜结构电容式微超声传感器关键技术研究

发布时间：2018-02-24 01:46

本文关键词： 电容式微超声传感器形变特性频率特性声场特性　出处：《天津大学》2016年博士论文　论文类型：学位论文

【摘要】：超声技术是声学发展中最活跃的技术领域之一,在国防、生物、医学及航空航天等众多领域得到了广泛应用,而超声传感器是实现力电声多场耦合与能量转换的关键部件。随着集成电路制造技术与微加工技术的不断发展,超声传感器的制造与加工技术也在不断进步。基于MEMS工艺的电容式微超声传感器(CMUT)具有声阻抗低、体积小、灵敏度高、频带宽、易于集成等特点,在无损检测、超声驱动、医学成像、超声理疗、细胞控制等高精尖领域具有潜在的优势,受到国内外研究工作者的关注。本文以CMUT超声成像系统为应用对象,开展了多振膜结构CMUT关键技术研究,主要包括形变特性、频率特性、声场特性、加工与性能测试等。(1)针对带有真空密闭腔体的全电极覆盖圆膜CMUT,建立了机械场均匀载荷挠度模型及机电耦合非线性载荷吸附模型。该模型不但可量化电极结构参数、密闭腔体内真空度与CMUT挠度、吸附特性之间的关系,而且与开放空间内的单层薄板CMUT模型相比,可为不同载荷条件下的CMUT提供精确预测。(2)针对CMUT多层振膜结构,建立了静态挠度和动态响应频率的数学模型,并对真实器件残余应力进行补偿。该模型将多层结构对CMUT特性的影响进行直观表述,与仿真结果及实验数据之间一致性良好,且与传统单层薄板CMUT模型相比,显著地提高了理论模型的准确度。(3)为提高CMUT的面积效率,增强其作为成像系统元件的成像分辨率,本文提出了一种椭圆形振膜CMUT结构。建立了椭圆形CMUT阵元的频率模型,与相同可动面积下的常规形貌CMUT阵元的特性对比表明,椭圆形振膜CMUT具有较高的一阶工作频率,由其组成的阵列具有较小的主瓣宽度和旁瓣幅值。(4)为适应待测环境内较大的压强变化,设计了带孔振膜CMUT结构。与传统平膜CMUT相比,相同直流偏置电压下带孔振膜CMUT平均形变量减小,吸附电压降低,工作压强耐受范围扩大。同时,带孔振膜CMUT可通过参数调整,实现CMUT工作频率的灵活设计。(5)建立了不同振膜结构CMUT的声场模型,研究了指向性函数的特性,详细分析了阵列设计参数对声场指向性的影响。针对指向性图中出现的旁瓣现象,研究了多种旁瓣抑制优化算法,分别在一维线性阵列和二维平面阵列上有效地降低了旁瓣幅值。(6)针对CMUT振膜特殊结构进行了工艺设计与关键工艺讨论,对器件进行加工制作与后续处理。进行了CMUT形貌测试与残余应力测试,同时,搭建实验测试系统,进行了CMUT力学、电学和声学性能测试,得到不同振膜形貌CMUT的挠度、频率及部分声学特性,并进行了CMUT单元的一致性检验。实验结果验证了本文设计理论与设计思想的正确性。
[Abstract]:Ultrasonic technology is one of the most active fields in the development of acoustics. It has been widely used in many fields, such as national defense, biology, medicine, aerospace and so on. Ultrasonic sensor is the key component to realize electroacoustic coupling and energy conversion. With the development of integrated circuit manufacturing technology and micromachining technology, The fabrication and processing technology of ultrasonic sensor is also improving. The capacitive ultrasonic sensor based on MEMS process has the characteristics of low acoustic impedance, small volume, high sensitivity, frequency bandwidth, easy integration, etc., in nondestructive testing, ultrasonic drive, etc. Medical imaging, ultrasound physiotherapy and cell control have potential advantages and have attracted the attention of researchers at home and abroad. In this paper, the key technology of multivibrator membrane structure (CMUT) is studied based on CMUT ultrasonic imaging system. Mainly including deformation characteristics, frequency characteristics, sound field characteristics, Machining and performance testing. (1) aiming at the full electrode covered circular membrane CMUTs with a vacuum closed cavity, a mechanical field uniform load deflection model and a mechanical coupling nonlinear load adsorption model are established. The model can not only quantify the electrode structure parameters, but also can quantify the electrode structure. The relationship between vacuum degree and CMUT deflection, adsorption characteristics, and compared with the CMUT model of single layer thin plate in open space, it can provide accurate prediction for CMUT under different loading conditions. The mathematical model of static deflection and dynamic response frequency is established, and the residual stress of real device is compensated. The model intuitively describes the effect of multilayer structure on CMUT characteristics, which is in good agreement with the simulation results and experimental data. Compared with the traditional single-layer thin plate CMUT model, the accuracy of the theoretical model is significantly improved. In order to improve the area efficiency of the CMUT and enhance its imaging resolution as an imaging system element, the accuracy of the theoretical model is greatly improved. In this paper, an elliptical membrane CMUT structure is proposed, and the frequency model of elliptical CMUT elements is established. The comparison of the characteristics of the elliptical CMUT elements with the conventional topography CMUT elements under the same movable area shows that the elliptical membrane CMUT has a higher first order working frequency. The array consists of a small main lobe width and a side lobe amplitude. 4) in order to adapt to the larger pressure variation in the environment to be measured, a diaphragm CMUT structure with holes is designed. Compared with the conventional flat film CMUT, the structure of the diaphragm is designed. At the same DC bias voltage, the average shape variable of CMUT decreases, the adsorption voltage decreases, and the working pressure tolerance range is enlarged. At the same time, the CMUT with holes can be adjusted by the parameters. In this paper, the sound field model of CMUT with different vibration membrane structure is established, the characteristic of directivity function is studied, and the influence of array design parameters on the directivity of sound field is analyzed in detail. A variety of sidelobe suppression optimization algorithms are studied. The sidelobe amplitudes are effectively reduced on one dimensional linear array and two dimensional planar array respectively. The process design and key process discussion for the special structure of CMUT diaphragm are carried out. The CMUT morphology and residual stress were measured. At the same time, the CMUT mechanical, electrical and acoustic properties were tested, and the deflection of CMUT was obtained. The frequency and some acoustic characteristics are tested and the consistency of the CMUT element is verified. The experimental results verify the correctness of the design theory and the design idea in this paper.
【学位授予单位】：天津大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TP212

【相似文献】