A Wearable Ultrasonic Neurostimulator-Part II: A 2D CMUT Phased Array System With a Flip-Chip Bonded ASIC
A Wearable Ultrasonic Neurostimulator-Part II: A 2D CMUT Phased Array System With a Flip-Chip Bonded ASIC
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DOI：
10.1109/tbcas.2021.3105064
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发表时间：
2021-08-01
影响因子：
5.1
通讯作者：
Oralkan, Omer
中科院分区：
文献类型：
--
作者：
Seok, Chunkyun;Adelegan, Oluwafemi Joel;Oralkan, Omer
二维超声阵列是聚焦超声系统的最终形式，它能够在三维空间中电子聚焦波束。2D阵列也是用于各种应用的通用工具，例如3D成像、高强度聚焦超声、粒子操纵和图案生成。然而，构建2D系统涉及复杂的技术：制造2D换能器阵列，开发间距匹配的ASIC，以及将换能器和ASIC互连。以前，我们成功地证明了二维电容式微机械超声换能器（CMUT）阵列使用各种制造技术。在本文中，我们提出了一个二维超声发射相控阵列的基础上，32 × 32 CMUT阵列倒装芯片键合到一个间距匹配的脉冲发生器ASIC的超声神经调制。该ASIC由32 x32单极高压（HV）脉冲发生器，其中每一个占据了250 μ m × 250 μ m的面积。每个脉冲发生器输出的相位可单独编程，分辨率为1/f（C）/16，其中f（C）小于10 MHz。这使得能够对焦点进行细粒度控制。该ASIC采用台积电0.18 μ m HV BCD工艺在9.8 mm x 9.8 mm的面积内制造，然后进行晶圆级焊料凸点工艺。在将ASIC和CMUT阵列进行倒装芯片键合后，我们使用ASIC中的内置测试功能识别CMUT阵列中的短路元件，扫描整个32 x 32阵列大约需要9分钟。还开发了一种紧凑型无线神经刺激器系统，只需要连接15伏直流电源，集成了电源管理单元、时钟发生器和蓝牙低功耗微控制器。该系统在3D空间中的聚焦和转向能力得到了证明，同时在2和3.4 MHz下分别实现了12.4和33.1 W/cm（2）的空间峰值脉冲平均强度（ISPPA）以及0.2和0.05 mm（3）的3 dB焦量（深度为5 mm）。我们还描述了超声通过小鼠颅骨的传输，并通过使用ASIC中的可编程相位延迟功能补偿了由于颅骨引起的相位失真，实现了10%的压力改善和更紧密的聚焦。最后，我们演示了在5 mm x 5 mm平面上5 mm深度处的超声任意图案生成。
A2D ultrasonic array is the ultimate form of a focused ultrasonic system, which enables electronically focusing beams in a 3D space. A 2D array is also a versatile tool for various applications such as 3D imaging, high-intensity focused ultrasound, particle manipulation, and pattern generation. However, building a 2D system involves complicated technologies: fabricating a 2D transducer array, developing a pitch-matched ASIC, and interconnecting the transducer and the ASIC. Previously, we successfully demonstrated 2D capacitive micromachined ultrasonic transducer (CMUT) arrays using various fabrication technologies. In this paper, we present a 2D ultrasonic transmit phased array based on a 32 x 32 CMUT array flip-chip bonded to a pitch-matched pulser ASIC for ultrasonic neuromodulation. The ASIC consists of 32x32 unipolar high-voltage (HV) pulsers, each of which occupies an area of 250 mu m x 250 mu m. The phase of each pulser output is individually programmable with a resolution of 1/f(C)/16, where f(C) is less than 10 MHz. This enables the fine granular control of a focus. The ASIC was fabricated in the TSMC 0.18-mu m HV BCD process within an area of 9.8 mm x 9.8 mm, followed by a wafer-level solder bumping process. After flip-chip bonding an ASIC and a CMUT array, we identified shorted elements in the CMUT array using the built-in test function in the ASIC, which took approximately 9 minutes to scan the entire 32 x 32 array. A compact-form-factor wireless neural stimulator system-only requiring a connected 15-VDCpower supply-was also developed, integrating a power management unit, a clock generator, and a Bluetooth Low-Energy enabled microcontroller. The focusing and steering capability of the system in a 3D space is demonstrated, while achieving a spatial-peak pulse-average intensity (ISPPA) of 12.4 and 33.1 W/cm(2); and a 3-dB focal volume of 0.2 and 0.05 mm(3)-at a depth of 5 mm-at 2 and 3.4 MHz, respectively. We also characterized transmission of ultrasound through a mouse skull and compensated the phase distortion due to the skull by using the programmable phase-delay function in the ASIC, achieving 10% improvement in pressure and a tighter focus. Finally, we demonstrated a ultrasonic arbitrary pattern generation on a 5 mm x 5 mm plane at a depth of 5 mm.