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A Wearable Ultrasonic Neurostimulator—Part II: A 2D CMUT Phased Array System With a Flip-Chip Bonded ASIC | IEEE Journals & Magazine | IEEE Xplore

A Wearable Ultrasonic Neurostimulator—Part II: A 2D CMUT Phased Array System With a Flip-Chip Bonded ASIC


Abstract:

A 2D 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 ...Show More

Abstract:

A 2D 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 × 32 CMUT array flip-chip bonded to a pitch-matched pulser ASIC for ultrasonic neuromodulation. The ASIC consists of 32 × 32 unipolar high-voltage (HV) pulsers, each of which occupies an area of 250 \mum × 250 \mum. The phase of each pulser output is individually programmable with a resolution of 1/f_{\mathrm{C}}/16, where f_{\mathrm{C}} is less than 10 MHz. This enables the fine granular control of a focus. The ASIC was fabricated in the TSMC 0.18-\mum HV BCD process within an area of 9.8 mm × 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 × 32 array. A compact-form-factor wireless neural stimulator system—only requiring a connected 15-V DC power 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 (\mathrm{I_{SPPA}}) of 12.4 and 33.1 W/{\rm cm^{2}}; and a 3-dB focal volume of 0.2 and 0.05 {\rm mm^{3}}—at a depth of 5 mm—at 2 and 3.4 MHz...
Published in: IEEE Transactions on Biomedical Circuits and Systems ( Volume: 15, Issue: 4, August 2021)
Page(s): 705 - 718
Date of Publication: 16 August 2021

ISSN Information:

PubMed ID: 34398764

Funding Agency:


References

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