Guldiken Rasim O, McLean Jeff, Degertekin F Levent
G. W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA.
IEEE Trans Ultrason Ferroelectr Freq Control. 2006 Feb;53(2):483-91. doi: 10.1109/tuffc.2006.1593388.
In this paper, we introduce capacitive micro-machined ultrasonic transducers (CMUTs) with electrically isolated multiple electrodes embedded in the same silicon nitride CMUT membrane. Some of the advantages of this structure are demonstrated using a dual-electrode CMUT with separate transmit and receive electrodes as an example. By locating the transmit electrodes near the edges of a rectangular CMUT membrane, the stable displacement range, hence the maximum pressure amplitude during transmit mode is increased without collapsing the membrane when operated within static collapse voltage range. In the receive mode, the center receive electrode is brought closer to the substrate by biasing the side electrodes, and a higher electromechanical transformer ratio is obtained at low direct current (DC) bias. Therefore, dual-electrode CMUT has an effectively larger gap as compared to conventional CMUT during transmit, and it has an effectively smaller gap during receive. Demonstrative experiments are performed on dual-electrode CMUTs with rectangular membranes with different side and center electrode sizes for transmit and receive measurements. By using the two 4-microm wide side electrodes and an 8-microm wide center electrode on a 20-microm wide membrane, a 6.8 dB increase in maximum output pressure is obtained with side electrode excitation as compared to conventional center electrode. Similarly, the receive performance improvement was demonstrated while reducing the DC bias requirements. Simple finite-element and equivalent circuit-based models were developed to successfully model the behavior of dual-electrode CMUTs. Simulations show that, with simple modifications, more than 10 dB overall sensitivity improvement is feasible with dual-electrode CMUTs with rectangular membranes.
在本文中，我们介绍了一种电容式微机械超声换能器（CMUT），其在同一氮化硅CMUT膜中嵌入了电隔离的多个电极。以具有单独发射和接收电极的双电极CMUT为例，展示了这种结构的一些优点。通过将发射电极放置在矩形CMUT膜的边缘附近，在静态崩溃电压范围内工作时，稳定位移范围增加，从而发射模式下的最大压力幅度增加，且膜不会塌陷。在接收模式下，通过对侧电极施加偏置，使中心接收电极更靠近基板，在低直流（DC）偏置下可获得更高的机电变压器比。因此，与传统CMUT相比，双电极CMUT在发射期间有效间隙更大，而在接收期间有效间隙更小。对具有不同侧边和中心电极尺寸的矩形膜双电极CMUT进行了演示实验，用于发射和接收测量。在20微米宽的膜上使用两个4微米宽的侧电极和一个8微米宽的中心电极，与传统中心电极相比，侧电极激励下最大输出压力提高了6.8分贝。同样，在降低直流偏置要求的同时展示了接收性能的提升。开发了简单的基于有限元和等效电路的模型，以成功模拟双电极CMUT的行为。仿真表明，通过简单修改，具有矩形膜的双电极CMUT总体灵敏度提高超过10分贝是可行的。
