Ultrasound (US) is a promising modality for wirelessly powering implantable devices, requiring encapsulated receivers to ensure long-term stability. Traditional hermetic packaging often limits acoustic transmission, making polymer-based encapsulation a more suitable alternative. This study investigates how implant-grade polymers, thermoplastic polyurethane (TPU), parylene-C, and medical-grade silicones (MED-1000 and MED2-4213), affect the receive performance of piezoelectric micromachined ultrasonic transducers (PMUTs). Simulations and measurements between 1 and 7 MHz show that all tested materials exhibit transmission coefficients above 94% at nanometer- and micrometer-scale thicknesses, confirming their acoustic transparency. The results show that although coated PMUTs are acoustically well matched with the surrounding water medium, the added mechanical load of the coating can hinder membrane motion and reduce the energy transferred to the PMUTs. Modeling and experimental data demonstrate that stiffer coatings, such as parylene-C, lead to a reduced sensitivity when similar thicknesses are used. Likewise, residual stress in materials like MED-1000 can also degrade the performance. These effects are not evident from acoustic transmission measurements alone, underscoring the need to assess both acoustic and mechanical properties when selecting encapsulation materials. In general, softer materials offer excellent acoustic performance for PMUT encapsulation, while stiffer materials must be applied in thinner layers to avoid impairing PMUT function.

Ultrasound (US)-based neuromodulation has recently emerged as a spatially selective yet non-invasive alternative to conventional electrically-based neural interfaces. However, the fundamental mechanisms of US neuromodulation are not yet clarified. Thus, there is a need for in-vitro bimodal investigation tools that allow us to compare the effect of US versus electrically-induced neural activity in the vicinity of the transducing element. To this end, we propose a MicroElectrode-MicroTransducer Array (MEMTA), where a dense array of electrodes is co-fabricated on top of a similarly dense array of US transducers.In this paper, we test the proof of concept for such co-fabrication using a non-monolithic approach, where, at its most challenging scenario, desired topologies require electrodes to be formed directly on top of fragile piezoelectric micromachined ultrasound transducer (PMUTs) membranes. On top of the PMUTs, a thin-film microelectrode array was developed utilizing microfabrication processes, including metal sputtering, lithography, etching and soft encapsulation. The samples were analysed through focused ion beam–scanning electron microscopy (FIB-SEM), and the results have shown that damage to the membranes does not occur during any of the process steps. This paper proves that the non-monolithic development of a miniaturised bimodal neuroscientific investigation tool can be achieved, thus, opening up a series of possibilities for further understanding and investigation of the nervous system.