空气耦合式电容微超声换能器的设计与分析

Design and analysis of air-coupled capacitive micromachined ultrasonic transducers

传统的电容式微超声换能器(CMUT)采用密闭腔体,振膜两侧存在压力差不易起振,需要施加较大的偏置电压;同时狭小腔体对振膜振动产生阻碍,降低了机电耦合效率。针对这一问题,设计了带孔的振膜结构,消除了腔体密闭带来的不利影响;研究了振膜腐蚀孔的大小、位置对CMUT频率特性的影响;设计了基于表面硅牺牲层工艺的工艺流程,加工了64阵元CMUT阵列;对CMUT阵列中单个阵元进行了阻抗校准,测试了振膜的谐振特性,并进行了阵列中的阵元一致性扫查。实验结果表明:非密闭腔体带孔方膜CMUT满足设计需求,且各阵元之间一致性良好。

Traditional Capacitive Micromachined Ultrasonic Transducer （CMUT）adopts sealed cavity;there exists pressure difference across the vibrating membrane,which makes it difficult to vibrate and leads to require high DC bias voltage.Meanwhile,the narrow cavity hinders the membrane vibration,which reduces the electromechanical coupling efficiency.Aiming at this problem,a vented vibration membrane structure was designed,which eliminates the adverse effect caused by sealed cavity.The influence of the size and position of the etch holes on the frequency characteristics of CMUT was studied.The fabrication process based on surface silicon sacrificial technology was designed;a 64-element CMUT array was fabricated.The impedance calibration of single element in the CMUT array was conducted.Then the resonant characteristic of the vibration membrane was tested,and the consistency of the elements in the array was also tested.Analysis and experiment results demonstrate that the CMUT with vented vibrition membrane and non-sealed cavity can satisfy the design requirements,and the elements in the array have satisfactory consistency.