The Parylene C as a Flexible Substrate and Passivation Layer: A Promising Candidate for a Piezoelectric, Piezoresistive, and Capacitive Pressure Sensor in Low-Pressure Range

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Parylene C is widely used as a passivation layer due to its excellent chemical inertness, electrical insulation, biocompatibility, and flexibility. But, it is a potential piezoelectric material that can be used as a flexible pressure sensor. Herein, the parylene C is synthesized via the chemical vapor deposition method. The flexible piezoelectric, piezoresistive, and capacitive pressure sensors based on parylene C are fabricated. The flexible piezoelectric pressure sensor is used for the first time. The sensing performance of these sensors is comparatively investigated, showing high sensitivities of 140 mV$\cdot $kPa$^{-{1}}$, 0.046 kPa$^{-{1}}$, and 0.080 kPa$^{-{1}}$in the low-pressure range (< 4 kPa), respectively. Furthermore, the response times (0.40, 0.37, and 0.48 s) and the relaxation times (0.21, 0.37, and 0.62 s) are achieved. This work demonstrates that parylene C, which is often used as a passivation layer, can also be used as a flexible piezoresistive and capacitive pressure sensor. It could also be a potential candidate for wearable healthcare monitoring, human–machine interfaces, and soft robotics in the low-pressure range.