Evaluation of wafer bonded CMUTs with rectangular membranes featuring high fill factor.
Evaluation of wafer bonded CMUTs with rectangular membranes featuring high fill factor.
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DOI：
10.1109/tuffc.897
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发表时间：
2008-09
期刊：
影响因子：
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通讯作者：
Khuri-Yakub BT
中科院分区：
文献类型：
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作者：
Wong SH;Kupnik M;Zhuang X;Lin DS;Butts-Pauly K;Khuri-Yakub BT
增加填充系数是提高电容式微机械超声换能器（CMUTs）平均输出位移、输出压力和灵敏度的一种设计方法。对于矩形单元格，单元格之间的间距和纵横比决定填充因子。在本文中，我们探讨了这些参数对性能的影响，特别是相邻电池之间崩溃电压的不均匀性以及在空气或浸入式操作中存在的高阶模式。我们使用白光干涉仪来测量相邻细胞之间偏转的不均匀性。我们发现，减小电池间距会导致中心支撑柱弯曲，从而将相邻电池之间的崩溃电压不均匀性放大到18.4%。利用二维有限元模型（FEM），我们发现对于我们的设计，将支撑桩宽度增加到膜厚度的1.67倍可以缓解桩的弯曲问题。利用阻抗和干涉仪测量观察长宽比对高阶模态的影响，我们发现随着长宽比的增加，矩形的（1,3）模态频率接近于（1,1）模态频率。在空气工作中，在中心频率的连续波激励下，矩形单元表现为（1,1）模式。在浸没中，由于色散引导模式，当中心频率处的连续波信号激励时，这些细胞在高阶模式下工作。这导致了产出压力的丧失；因此，我们的矩形设计不适合浸没的连续波操作。
Increasing fill factor is one design approach used to increase average output displacement, output pressure, and sensitivity of capacitive micromachined ultrasonic transducers (CMUTs). For rectangular cells, the cell-to-cell spacing and the aspect ratio determine the fill factor. In this paper, we explore the effects of these parameters on performance, in particular the nonuniformity of collapse voltage between neighboring cells and presence of higher order modes in air or immersed operation. We used a white light interferometer to measure nonuniformity in deflection between neighboring cells. We found that reducing the cell-to-cell spacing could cause bending of the center support post, which amplifies nonuniformities in collapse voltage to 18.4% between neighboring cells. Using a 2-D finite element model (FEM), we found that for our designs, increasing the support post width to 1.67 times the membrane thickness alleviated the post bending problem. Using impedance and interferometer measurements to observe the effects of aspect ratio on higher order modes, we found that the (1,3) modal frequency approached the (1,1) modal frequency as the aspect ratio of the rectangles increased. In air operation, under continuous wave (CW) excitation at the center frequency, the rectangular cells behaved in the (1,1) mode. In immersion, because of dispersive guided modes, these cells operated in a higher order mode when excited with a CW signal at the center frequency. This contributed to a loss of output pressure; for this reason our rectangular design was unsuitable for CW operation in immersion.