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

Interest in utilizing ultrasound (US) transducers for non-invasive neuromodulation treatment, including for low intensity transcranial focused ultrasound stimulation (tFUS), has grown rapidly. The most widely demonstrated US transducers for tFUS are either bulk piezoelectric transducers or capacitive micromachine transducers (CMUT) which require high voltage excitation to operate. In order to advance the development of the US transducers towards small, portable devices for safe tFUS at large scale, a low voltage array of US transducers with beam focusing and steering capability is of interest. This work presents the design methodology, fabrication, and characterization of 32-element phased array piezoelectric micromachined ultrasound transducers (PMUT) using 1.5 μm thick Pb(Zr0.52 Ti0.48)O3 films doped with 2 mol% Nb. The electrode/piezoelectric/electrode stack was deposited on a silicon on insulator (SOI) wafer with a 2 μm silicon device layer that serves as the passive elastic layer for bending-mode vibration. The fabricated 32-element PMUT has a central frequency at 1.4 MHz. Ultrasound beam focusing and steering (through beamforming) was demonstrated where the array was driven with 14.6 V square unipolar pulses. The PMUT generated a maximum peak-to-peak focused acoustic pressure output of 0.44 MPa at a focal distance of 20 mm with a 9.2 mm and 1 mm axial and lateral resolution, respectively. The maximum pressure is equivalent to a spatial-peak pulse-average intensity of 1.29 W/cm2, which is suitable for tFUS application.

利用超声（US）换能器进行非侵入性神经调节治疗，包括低强度经颅聚焦超声刺激（tFUS）的兴趣迅速增长。用于tFUS的最广泛展示的超声换能器要么是块状压电换能器，要么是电容式微机械换能器（CMUT），它们需要高压激励才能工作。为了推动超声换能器朝着小型、便携式设备发展，以便大规模安全地进行tFUS，具有波束聚焦和转向能力的低压超声换能器阵列备受关注。这项工作介绍了使用掺杂2摩尔%铌的1.5μm厚的Pb(Zr0.52Ti0.48)O3薄膜的32单元相控阵压电微加工超声换能器（PMUT）的设计方法、制造和特性。电极/压电/电极堆叠沉积在绝缘体上硅（SOI）晶片上，该晶片具有2μm的硅器件层，用作弯曲模式振动的被动弹性层。制造的32单元PMUT中心频率为1.4 MHz。展示了超声束聚焦和转向（通过波束形成），其中阵列由14.6 V方形单极脉冲驱动。PMUT在20 mm的焦距处产生了0.44 MPa的最大峰 - 峰聚焦声压输出，轴向和横向分辨率分别为9.2 mm和1 mm。最大压力相当于1.29 W/cm²的空间峰值脉冲平均强度，适用于tFUS应用。