32 Element Piezoelectric Micromachined Ultrasound Transducer (PMUT) Phased Array for Neuromodulation

Area of Science:

• Biomedical Engineering
• Materials Science
• Acoustics

Background:

• Interest in ultrasound (US) for non-invasive neuromodulation, particularly low-intensity transcranial focused ultrasound stimulation (tFUS), is increasing.
• Current US transducers for tFUS often require high voltage, limiting the development of small, portable devices.
• A low-voltage transducer array with beam focusing and steering is needed for large-scale, safe tFUS applications.

Purpose of the Study:

• To design, fabricate, and characterize a 32-element phased array piezoelectric micromachined ultrasound transducer (PMUT) for low-voltage operation.
• To demonstrate beam focusing and steering capabilities for tFUS applications.
• To evaluate the acoustic output and resolution of the fabricated PMUT array.

Main Methods:

• Fabrication of a 32-element PMUT array using 1.5 μm thick Nb-doped Pb(Zr0.52Ti0.48)O3 films on a silicon-on-insulator (SOI) wafer.
• Utilizing a 2 μm silicon device layer as a passive elastic layer for bending-mode vibration.
• Driving the array with 14.6 V square unipolar pulses to achieve beamforming for focusing and steering.

Main Results:

• The fabricated PMUT array operates at a central frequency of 1.4 MHz.
• Demonstrated ultrasound beam focusing and steering via beamforming.
• Achieved a maximum peak-to-peak focused acoustic pressure of 0.44 MPa at 20 mm focal distance.
• Obtained axial and lateral resolutions of 9.2 mm and 1 mm, respectively.
• Maximum spatial-peak pulse-average intensity reached 1.29 W/cm², suitable for tFUS.

Conclusions:

• The developed 32-element PMUT array operates at low voltage (14.6 V) and demonstrates effective beam focusing and steering.
• The array's acoustic output and resolution are suitable for transcranial focused ultrasound stimulation (tFUS).
• This technology advances the development of small, portable devices for non-invasive neuromodulation using ultrasound transducers.