ASIC and System State Key Lab, Department of Microelectronics, Fudan University, Shanghai 200433, PR China.
Ultrasonics. 2012 Jan;52(1):47-53. doi: 10.1016/j.ultras.2011.06.009. Epub 2011 Jun 26.
High-frequency ultrasonic transducer arrays are essential for high resolution imaging in clinical analysis and Non-Destructive Evaluation (NDE). However, the fabrication of conventional backing-layer structure, which requires a pitch (distance between the centers of two adjacent elements) of half wavelength in medium, is really a great challenge.
Here we present an alternative buffer-layer structure with a silicon lens for volumetric imaging. The requirement for the size of the pitch is less critical for this structure, making it possible to fabricate high-frequency (100MHz) ultrasonic linear array transducers. Using silicon substrate also makes it possible to integrate the arrays with IC (Integrated Circuit). To compare with the conventional backing-layer structure, a finite element tool, COMSOL, is employed to investigate the performances of acoustic beam focusing, the influence of pitch size for the buffer-layer configuration, and to calculate the electrical properties of the arrays, including crosstalk effect and electrical impedance.
For a 100MHz 10-element array of buffer-layer structure, the ultrasound beam in azimuth plane in water could be electronically focused to obtain a spatial resolution (a half-amplitude width) of 86μm at the focal depth. When decreasing from half wavelength in silicon (42μm) to half wavelength in water (7.5μm), the pitch sizes weakly affect the focal resolution. The lateral spatial resolution is increased by 4.65% when the pitch size decreases from 42μm to 7.5μm. The crosstalk between adjacent elements at the central frequency is, respectively, -95dB, -39.4dB, and -60.5dB for the 10-element buffer, 49-element buffer and 49-element backing arrays. Additionally, the electrical impedance magnitudes for each structure are, respectively, 4kΩ, 26.4kΩ, and 24.2kΩ, which is consistent with calculation results using Krimholtz, Leedom, and Matthaei (KLM) model.
These results show that the buffer-layer configuration is a promising alternative for the fabrication of high-frequency ultrasonic linear arrays dedicated to volumetric imaging.
高频超声换能器阵列对于临床分析和无损评估（NDE）中的高分辨率成像至关重要。然而，在中等介质中制造常规背衬层结构（其需要半波长的节距（两个相邻元件中心之间的距离））确实是一个巨大的挑战。
在这里，我们提出了一种具有硅透镜的替代缓冲层结构，用于体积成像。对于这种结构，对节距尺寸的要求不那么关键，因此可以制造高频（100MHz）超声线性阵列换能器。使用硅衬底还可以使阵列与集成电路（IC）集成。为了与常规背衬层结构进行比较，使用有限元工具 COMSOL 来研究声束聚焦性能、缓冲层结构的节距尺寸的影响，并计算阵列的电特性，包括串扰效应和阻抗。
对于缓冲层结构的 100MHz 10 元件阵列，在水中的方位平面中的超声束可以进行电子聚焦，以在焦点深度处获得 86μm 的空间分辨率（半幅度宽度）。当从硅中的半波长（42μm）减小到水中的半波长（7.5μm）时，节距尺寸对焦点分辨率的影响较弱。当节距尺寸从 42μm 减小到 7.5μm 时，横向空间分辨率提高了 4.65%。在中心频率处，相邻元件之间的串扰分别为 10 元件缓冲、49 元件缓冲和 49 元件背衬阵列的-95dB、-39.4dB 和-60.5dB。此外，每个结构的阻抗幅度分别为 4kΩ、26.4kΩ 和 24.2kΩ，与使用 Krimholtz、Leedom 和 Matthaei（KLM）模型的计算结果一致。
这些结果表明，缓冲层结构是制造用于体积成像的高频超声线性阵列的有前途的替代方案。
