压电-静电混合驱动新型MEMS超声换能器机理与制备技术研究

In view of the drawbacks of contradiction in transmitting and receiving performances, high operating voltage, susceptible to parasitic capacitance for the applications of capacitive micromachined ultrasonic transducer (CMUT) in cutting-edge areas such as point of care ultrasound diagnostic and ultrasound gesture recognition, this project proposes a novel piezo-electrostatically hybrid-actuated MEMS ultrasonic transducer using AlN as the post material instead of the silicon dioxide in traditional CMUT. This novel MEMS transducer takes the advantages of the electrostriction of the piezoelectric post to adjust the height of the vacuum cavity to solve the contradiction in transmitting and receiving performances; utilizes the idea that the piezoelectric post can vibrate to produce effect energy conversion under voltage or incident sound wave to eliminate the parasitic capacitance of the post area between CMUT cells and reduce the needed operating voltage. The project will the investigate the multi-physics coupling theories of the two-stage vibration system composed of the piezoelectric post and membrane under piezo-electrostatically hybrid-actuation, and reveal the variation regulations of the main performances such as pull-in voltage, electromechanical coupling coefficient, transmitting acoustic pressure, and transmitting and receiving sensitivities; study the cross-talk mechanism between cells of CMUT array under the compound sound field produced by the two-stage vibration system, and establish the cell and array structure optimization design theories; investigate the effects of process parameters on the AlN-Si wafer-bonding, and develop the AlN-Si wafer-bonding based fabrication technology; finally to establish the theory and technology foundation for the design and fabrication of the novel MEMS transducer.

针对电容微超声换能器（CMUT）在即时超声诊断、超声姿态识别等前沿技术领域应用中存在的发射和接收性能相互制约、工作电压高、受寄生电容影响大的共性问题，项目采用氮化铝替代CMUT中二氧化硅等传统支柱材料，提出基于压电-静电混合驱动的新型MEMS超声换能器：利用压电支柱的电致伸缩特性来调节空腔高度以解决收发性能的相互制约问题，并基于压电支柱在电压或声场激励下可发生振动产生有效能量转化的思想来消除单元间支柱区域寄生电容，降低所需工作电压。拟探索混合驱动条件下由压电支柱和薄膜构成的二级振动系统的多场耦合机理，揭示塌陷电压、机电耦合系数、发射声压以及收发灵敏度等性能的变化规律；研究二级振动系统所产生的复合声场条件下单元间声场相互影响机理，建立单元及阵列结构优化设计理论；研究工艺参数对氮化铝-硅键合强度的影响规律，开发基于氮化铝-硅键合的制备技术等；为该类新型超声换能器的设计与制备提供理论与技术基础。

电容式微加工超声换能器（CMUTs）在超声成像与治疗、工业无损检测、超声生物特征识别、超声姿态识别以及非接触控制等领域具有重要工程应用价值。然而，现有CMUTs却存在工作电压大、发射和接收性能难以同时提高、基础设计理论研究不足等问题，限制其广泛应用。本项目：1）提出基于经典层合薄板理论、伽辽金法、局部泰勒级数展开以及能量等效法的机电耦合建模方法，建立了单层和多层圆形与方形薄膜CMUTs在不同材料参数（各项异性和同性）、残余应力、流体静压力等条件下的机电耦合模型，获得了CMUTs塌陷电压、机电耦合系数、薄膜变形以及谐振频率等主要性能参数理论计算公式，为CMUTs在不同薄膜形状、结构特征、残余应力、压力及静电力等复合外力作用下的高精度设计与优化提供了理论依据；2）引入寄生电容影响，探索了CMUTs机械参数与电参数之间的等效关系，建立了典型CMUTs结构高精度分析等效电路模型，为CMUTs驱动与信号检测电路的设计与优化提供了理论基础；3）提出基于压电-静电混合驱动的高机电耦合系数、收发一体化电容式MEMS超声换能器以及基于T型空腔凹槽的低功耗、收发一体化CMUTs，建立了其仿真分析模型，研究了相关结构参数对其工作电压、薄膜变形、机电耦合系数、收发性能的影响规律，验证了设计可行性及优化设计方法；4）设计了T型空腔CMUTs制备工艺及流程，开展了关键参数实验研究及工艺优化，完成了T型空腔CMUTs结构的首次工艺流片，确定了最优化工艺流程及工艺参数；5）利用已有CMUTs芯片开展了典型应用研究，包括设计并制备了超声发射与接收电路，实验验证了其可行性，开展了基于CMUTs的流体气泡检测实验研究，实现气泡的非侵入式检测，拓展了CMUTs应用领域。