A 2D Ultrasonic Transmit Phased Array Based on a 32x32 CMUT Array Flip-Chip Bonded to an ASIC for Neural Stimulation

In this paper, we present a 2D ultrasonic transmit beamformer based on a 32x32 CMUT array flip-chip bonded to a pitch-matched pulser ASIC. The target application of the presented beamformer is a wearable ultrasonic brain stimulator that requires a small form factor with the capability of electronically steering beams in a three-dimensional (3D) space. The aperture size of the array is 8 mm x 8 mm and the natural focus is around 2 cm. The transducer array was driven with 2-MHz-which is the center frequency of the CMUT-continuous square waves generated by the ASIC. We achieved a peak-to-peak pressure of 574 kPa and a 3-dB focal volume of 0.2 mm³ at a depth of 5 mm. We also demonstrated the beam focusing and steering capability of the array in a 3D space.