Low-cost monolithic processing of large-area ultrasound transducer arrays

Large-area flexible ultrasound arrays can offer new ultrasound modalities in multiple fields. The production of these arrays when using CMOS-type fabrication techniques faces scalability challenges and costs increase dramatically when upscaled to large dimensions. We investigate the monolithic production of large-area PPT (Printed Polymer Transducer) arrays directly on a flexible substrate. Here, a vibrating membrane is defined by a circular opening in a thick photoresist layer. Since the photoresist layer is processed on top of the P(VDF-TrFE), a thin barrier layer is used to prevent diffusion into the P(VDF-TrFE). An annealing procedure is developed to reduce the surface roughness of the P(VDF-TrFE) layer and make it compatible with thin film electrode deposition. We measure a remnant polarization of 7-8 μC/cm ² and a coercive field of around 50 MV/m. Laser scanning vibrometer measurements reveal a uniform peak displacement and fundamental resonance frequency (66 kHz) across the PPT array.