A critical component in a three-dimensional (3D) ultrasound imaging system is a two-dimensional (2D) transducer array. A 2D transducer array is also essential for the implementation of a compact form factor focused ultrasound system for therapeutic applications. Considering the difficulty associated with developing 2D transducer arrays using piezoelectric technology, capacitive micromachined ultrasonic transducer (CMUT) technology with the inherent advantages has emerged as a candidate to develop these devices. Previously, we demonstrated that 2D CMUT arrays can be fabricated with through-glass-via interconnects on borosilicate substrates using anodic bonding. In this paper, we present a fabrication process for implementing $16\times 16$ -element 2D CMUT arrays on an alkali-free glass substrate using the sacrificial release method. The vacuum-sealed $16\times 16$ -element 2D CMUT array is built on an SGW3 glass substrate with copper through-glass interconnects. The fabrication process developed for the 2D CMUT array is described in detail. Across the 256 elements of the 2D CMUT array, the mean resonant frequency is measured as 4.76 MHz with a standard deviation of 46.6 kHz. Also, the mean device capacitance across the array is measured as 1.17 pF with a standard deviation of 0.12 pF, and these results agree with the finite-element analysis. This study shows an alternative method to fabricate 2D CMUT arrays on glass substrates with metal interconnects, especially when the substrate is not suitable for anodic bonding. In addition to improved reliability and reduction in parasitic interconnect capacitance and resistance, this fabrication method benefits from the flexibility of developing 2D CMUT arrays on any type of insulating substrate, and still attain optimum uniformity in both yield and functionality of the fabricated devices. [2019-0246]

中文翻译：

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使用牺牲释放工艺在具有贯穿晶圆互连的绝缘基板上制造 2D 电容微机械超声换能器 (CMUT) 阵列

三维 (3D) 超声成像系统中的关键组件是二维 (2D) 换能器阵列。2D 换能器阵列对于实现用于治疗应用的紧凑型聚焦超声系统也是必不可少的。考虑到与使用压电技术开发二维换能器阵列相关的困难，具有固有优势的电容微机械超声换能器 (CMUT) 技术已成为开发这些设备的候选技术。之前，我们证明了 2D CMUT 阵列可以使用阳极键合在硼硅酸盐基板上通过玻璃通孔互连制造。在本文中，我们提出了一种使用牺牲释放方法在无碱玻璃基板上实现 $16\times 16$ -element 2D CMUT 阵列的制造工艺。真空密封的 16 美元\乘以 16 美元的元件 2D CMUT 阵列构建在具有铜穿玻璃互连的 SGW3 玻璃基板上。详细描述了为 2D CMUT 阵列开发的制造过程。在 2D CMUT 阵列的 256 个元件中，平均谐振频率测量为 4.76 MHz，标准偏差为 46.6 kHz。此外，阵列上的平均器件电容测量为 1.17 pF，标准偏差为 0.12 pF，这些结果与有限元分析一致。这项研究展示了一种在具有金属互连的玻璃基板上制造 2D CMUT 阵列的替代方法，特别是当基板不适合阳极键合时。除了提高可靠性并减少寄生互连电容和电阻之外，这种制造方法受益于在任何类型的绝缘基板上开发 2D CMUT 阵列的灵活性，并且仍然在制造的设备的产量和功能方面实现最佳均匀性。[2019-0246]