新型电容式微机械超声波换能器(CMUT)设计及仿真分析

Design and Simulation Analysis of Novel Capacitive Micromechanical Ultrasonic Transducers

针对传统CMUT的上电极加工在振动薄膜的上表面,振动薄膜的厚度会增加上、下极板之间的有效距离,影响CMUT的发射性能和接收性能的问题,提出了一种将上电极加工在振动薄膜的底部以减小上、下极板之间有效距离的新型结构CMUT。首先从理论上分析了上、下极板之间有效距离对发射和接收性能的影响。然后设计了新型结构CMUT的加工工艺流程。最后对新型结构CMUT进行了仿真分析。吸合仿真结果表明振动薄膜与下电极发生吸合时振动薄膜中心点位移为腔高的36.52%,与理论值三分之一接近。仿真结果与Comsol Multiphysics案例中的结果一致,证明了建立的仿真模型具有很高的准确性。有预应力模态分析和有预应力频域分析得到一阶固有频率约为6.1 MHz。时域分析结果表明,新型结构CMUT发射和接收性能相对传统结构分别提高了11.9倍和12.2倍。

Considering that the upper electrode of traditional CMUT is designed on the upper surface of the vibrating membrane,the thickness of the vibrating membrane will increase the effective distance between the upper and lower plates,which will affect the transmitting and receiving performances of CMUT.A novel structure of CMUT is proposed,in which the upper electrode is designed at the bottom of the vibrating membrane to reduce the effective distance between the upper and lower plates.First,the influence of the distance between the upper and lower plates on the transmitting performance is analyzed.Then the process flow of the novel structure CMUT is designed.Last,the CMUT of the novel structure is simulated and analyzed.Pull-in simulation results show that the displacement of the center point of the vibrating film is 36.52%of the cavity height when the vibrating film is attracted to the lower electrode,which is close to the theoretical value one third.The simulation results are consistent with the results of COMSOL Multiphysics case,which proves that the simulation model established in this paper holds high accuracy.Results of modal analysis and frequency domain analysis show that the first natural frequency is about 6.1 MHz.The results of time domain analysis show that the transmitting and receiving performances of the novel CMUT structure are improved by 11.9 times and 12.2 times respectively compared with the traditional structure.